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Radius of gyration

Radius of gyration or gyradius of a body about the axis of rotation is defined as the radial distance to a point which would have a moment of inertia the same as the body's actual distribution of mass, if the total mass of the body were concentrated there. The radius of gyration has dimensions of distance [L] or [M0LT0] and the SI unit is the metre (m).

Formulation
Mathematically the radius of gyration is the root mean square distance of the object's parts from either its center of mass or a given axis, depending on the relevant application. It is actually the perpendicular distance from point mass to the axis of rotation. One can represent a trajectory of a moving point as a body. Then radius of gyration can be used to characterize the typical distance travelled by this point. Suppose a body consists of $$n$$ particles each of mass $$m$$. Let $$r_1, r_2, r_3, \dots, r_n$$ be their perpendicular distances from the axis of rotation. Then, the moment of inertia $$I$$ of the body about the axis of rotation is If all the masses are the same ($$m$$), then the moment of inertia is $$I=m(r_1^2+r_2^2+\cdots+r_n^2)$$. Since $$m = M/n$$ ($$M$$ being the total mass of the body),
 * $$I = m_1 r_1^2 + m_2 r_2^2 + \cdots + m_n r_n^2$$
 * $$I=M(r_1^2+r_2^2+\cdots+r_n^2)/n$$

From the above equations, we have
 * $$MR_g^2=M(r_1^2+r_2^2+\cdots+r_n^2)/n$$

Radius of gyration is the root mean square distance of particles from axis formula
 * $$R_g^2=(r_1^2+r_2^2+\cdots+r_n^2)/n$$

Therefore, the radius of gyration of a body about a given axis may also be defined as the root mean square distance of the various particles of the body from the axis of rotation. It is also known as a measure of the way in which the mass of a rotating rigid body is distributed about its axis of rotation.

Applications in structural engineering
In structural engineering, the two-dimensional radius of gyration is used to describe the distribution of cross sectional area in a column around its centroidal axis with the mass of the body. The radius of gyration is given by the following formula:

 * $$R_{\mathrm{g}} = \sqrt{ \frac {I} {A} }$$

Where $$I$$ is the second moment of area and $$A$$ is the total cross-sectional area.

The gyration radius is useful in estimating the stiffness of a column. If the principal moments of the two-dimensional gyration tensor are not equal, the column will tend to buckle around the axis with the smaller principal moment. For example, a column with an elliptical cross-section will tend to buckle in the direction of the smaller semiaxis.

In engineering, where continuous bodies of matter are generally the objects of study, the radius of gyration is usually calculated as an integral.

Applications in mechanics
The radius of gyration about a given axis ($$r_{\mathrm{g}\text{ axis}}$$) can be calculated in terms of the mass moment of inertia $$I_\text{axis}$$ around that axis, and the total mass m;

 * $$r_{\mathrm{g}\text{ axis}} = \sqrt{ \frac{I_\text{axis}}{m}}$$

$$I_\text{axis}$$ is a scalar, and is not the moment of inertia tensor.

Molecular applications

In polymer physics, the radius of gyration is used to describe the dimensions of a polymer chain. The radius of gyration of an individual homopolymer with degree of polymerization N at a given time is defined as:

R_\mathrm{g}^2 \ \stackrel{\mathrm{def}}{=}\ \frac{1}{N} \sum_{k=1}^{N} \left|\mathbf{r}_k - \mathbf{r}_\mathrm{mean} \right|^2 $$

where $$\mathbf{r}_\mathrm{mean}$$ is the mean position of the monomers. As detailed below, the radius of gyration is also proportional to the root mean square distance between the monomers:

R_\mathrm{g}^2 \ \stackrel{\mathrm{def}}{=}\ \frac{1}{2N^2} \sum_{i\ne j} \left| \mathbf{r}_i - \mathbf{r}_j \right|^2 $$

As a third method, the radius of gyration can also be computed by summing the principal moments of the gyration tensor.

Since the chain conformations of a polymer sample are quasi infinite in number and constantly change over time, the "radius of gyration" discussed in polymer physics must usually be understood as a mean over all polymer molecules of the sample and over time. That is, the radius of gyration which is measured as an average over time or ensemble:

R_{\mathrm{g}}^2 \ \stackrel{\mathrm{def}}{=}\ \frac{1}{N} \left\langle \sum_{k=1}^{N} \left| \mathbf{r}_k - \mathbf{r}_\mathrm{mean} \right|^2 \right\rangle $$

where the angular brackets $$\langle \ldots \rangle$$ denote the ensemble average.

An entropically governed polymer chain (i.e. in so called theta conditions) follows a random walk in three dimensions. The radius of gyration for this case is given by

 * $$R_\mathrm{g} = \frac{1}{\sqrt{6}\ } \ \sqrt{N}\ a$$

Note that although $$aN$$ represents the contour length of the polymer, $$a$$ is strongly dependent of polymer stiffness and can vary over orders of magnitude. $$N$$ is reduced accordingly.

One reason that the radius of gyration is an interesting property is that it can be determined experimentally with static light scattering as well as with small angle neutron- and x-ray scattering. This allows theoretical polymer physicists to check their models against reality. The hydrodynamic radius is numerically similar, and can be measured with Dynamic Light Scattering (DLS).

Derivation of identity
To show that the two definitions of $$R_{\mathrm{g}}^{2}$$ are identical, we first multiply out the summand in the first definition:

R_{\mathrm{g}}^{2} \ \stackrel{\mathrm{def}}{=}\ \frac{1}{N} \sum_{k=1}^{N} \left( \mathbf{r}_{k} - \mathbf{r}_{\mathrm{mean}} \right)^{2} = \frac{1}{N} \sum_{k=1}^{N} \left[ \mathbf{r}_{k} \cdot \mathbf{r}_{k} + \mathbf{r}_{\mathrm{mean}} \cdot \mathbf{r}_{\mathrm{mean}} - 2 \mathbf{r}_{k} \cdot \mathbf{r}_{\mathrm{mean}} \right] $$

Carrying out the summation over the last two terms and using the definition of $$\mathbf{r}_{\mathrm{mean}}$$ gives the formula

R_{\mathrm{g}}^{2} \ \stackrel{\mathrm{def}}{=}\ -\mathbf{r}_{\mathrm{mean}} \cdot \mathbf{r}_{\mathrm{mean}} + \frac{1}{N} \sum_{k=1}^{N} \left( \mathbf{r}_{k} \cdot \mathbf{r}_{k} \right) $$

On the other hand, the second definition can be calculated in the same way as follows.

\begin{align} R_{\mathrm{g}}^{2} \ &\stackrel{\mathrm{def}}{=}\ \frac{1}{2N^2} \sum_{i,j} \left| \mathbf{r}_i - \mathbf{r}_j \right|^2 \\ &= \frac{1}{2N^2} \sum_{i,j} \left( \mathbf{r}_{i} \cdot \mathbf{r}_{i} - 2 \mathbf{r}_{i} \cdot \mathbf{r}_{j} + \mathbf{r}_{j} \cdot \mathbf{r}_{j} \right) \\ &= \frac{1}{2N^2} \left[ N \sum_{i} \left(\mathbf{r}_{i} \cdot \mathbf{r}_{I} \right) - 2 \sum_{i,j} \left(\mathbf{r}_{i} \cdot \mathbf{r}_{j} \right) + N \sum_{j} \left( \mathbf{r}_{j} \cdot \mathbf{r}_{j}\right) \right] \\ &= \frac{1}{N} \sum_{k}^{N} \left( \mathbf{r}_{k} \cdot \mathbf{r}_{k} \right)- \frac{1}{N^2} \sum_{i,j} \left(\mathbf{r}_{i} \cdot \mathbf{r}_{j} \right) \\ &= \frac{1}{N} \sum_{k}^{N} \left(\mathbf{r}_{k} \cdot \mathbf{r}_{k} \right)- \mathbf{r}_{\mathrm{mean}} \cdot \mathbf{r}_{\mathrm{mean}} \end{align} $$ Thus, the two definitions are the same.

The last transformation uses the relationship

\begin{align} \frac{1}{N^2}\sum_{i,j} \left(\mathbf{r}_{i} \cdot \mathbf{r}_{j} \right) &= \frac{1}{N^2} \sum_{i} \mathbf{r}_{i} \cdot \left( \sum_{j} \mathbf{r}_{j} \right) \\ &= \frac{1}{N} \sum_{i} \mathbf{r}_{i}\cdot \mathbf{r}_{\mathrm{mean}} \\ &= \mathbf{r}_{\mathrm{mean}} \cdot \mathbf{r}_{\mathrm{mean}}. \end{align} $$

Applications in geographical data analysis
In data analysis, the radius of gyration is used to calculate many different statistics including the spread of geographical locations. These locations have recently been collected from social media users to investigate the typical mentions of a user. This can be useful for understanding how a certain group of users on social media use the platform.

R_{\mathrm{g}} = \sqrt{\frac{\sum_{i=1}^{N}m_i(r_i-r_{C})^2}{\sum_{i=1}^{N}m_i}} $$

title: Radius of gyration


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Portland, Maine

Portland is the most populous city in the U.S. state of Maine and the seat of Cumberland County. Portland's population was 68,408 in April 2020. The Greater Portland metropolitan area has a population of approximately 550,000 people. Historically tied to commercial shipping, the marine economy, and light industry, Portland's economy in the 21st century relies mostly on the service sector. The Port of Portland is the second-largest tonnage seaport in the New England area as of 2019.

The city seal depicts a phoenix rising from ashes, a reference to Portland's recovery from four devastating fires. Portland was named after the English Isle of Portland. In turn, the city of Portland, Oregon, was named after Portland, Maine. The word Portland is derived from the Old English word Portlanda, which means "land surrounding a harbor". The Greater Portland area has emerged as an important center for the creative economy, which is also bringing gentrification.

History

The original Algonquin-speaking Eastern Abenaki residents called the Portland peninsula Machigonne ("great neck"). It is also called Məkíhkanək (“at the fish hook”) in Penobscot.

The first European settler was Christopher Levett, an English naval captain granted 6000 acre in 1623 to found a settlement in Casco Bay. A member of the Council for New England and agent for Ferdinando Gorges, Levett built a stone house where he left a company of ten men, then returned to England to write a book about his voyage to bolster support for the settlement. Ultimately, the settlement was a failure and the fate of Levett's colonists is unknown. The explorer sailed from England to the Massachusetts Bay Colony to meet John Winthrop in 1630, but never returned to Maine. Fort Levett in the harbor is named for him.

The peninsula was settled in 1632 as a fishing and trading village named Casco. When the Massachusetts Bay Colony took over Casco Bay in 1658, the town's name changed again to Falmouth. In 1676, the village was destroyed by the Abenaki during King Philip's War. It was rebuilt. During King William's War, a raiding party of French and their native allies attacked and largely destroyed it again in the Battle of Fort Loyal (1690).

On October 18, 1775, Falmouth was burned in the Revolution by the Royal Navy under command of Captain Henry Mowat. Following the war, a section of Falmouth called The Neck developed as a commercial port and began to grow rapidly as a shipping center. In 1786, the citizens of Falmouth formed a separate town in Falmouth Neck and named it Portland, after the isle off the coast of Dorset, England. Portland's economy was greatly stressed by the Embargo Act of 1807 (prohibition of trade with the British), which ended in 1809, and the War of 1812, which ended in 1815.

In 1820, Maine was established as a state with Portland as its capital. In 1832, the capital was moved north and east to Augusta. In 1851, Maine led the nation by passing the first state law prohibiting the sale of alcohol except for "medicinal, mechanical or manufacturing purposes." The law subsequently became known as the Maine Law, as eighteen other states quickly followed. The Portland Rum Riot occurred on June 2, 1855.

In 1853, upon completion of the Grand Trunk Railway to Montreal, Portland became the primary ice-free winter seaport for Canadian exports. The Portland Company, located on Fore Street, manufactured more than six hundred 19th-century steam locomotives, as well as engines for trains and boats, fire engines and other railroad transportation equipment. The Portland Company was, for a time, the city's largest employer and many of its employees were immigrants from Canada, Ireland and Italy. Portland became a 20th-century rail hub as five additional rail lines merged into Portland Terminal Company in 1911. These rail lines also facilitated movement of returning Canadian troops from the First World War in 1919. Following nationalization of the Grand Trunk system in 1923, Canadian export traffic was diverted from Portland to Halifax, resulting in marked local economic decline. Icebreakers later enabled ships to reach Montreal in winter, drastically reducing Portland's role as a winter port for Canada.

On June 26, 1863, a Confederate raiding party led by Captain Charles Read entered the harbor at Portland leading to the Battle of Portland Harbor, one of the northernmost battles of the Civil War. The 1866 Great Fire of Portland, Maine, on July 4, 1866, ignited during the Independence Day celebration, destroyed most of the commercial buildings in the city, half the churches and hundreds of homes. More than 10,000 people were left homeless.

By act of the Maine Legislature in 1899, Portland annexed the city of Deering, despite a vote by Deering residents rejecting the motion, thereby greatly increasing the size of the city and opening areas for development beyond the peninsula.

In 1967, the city began the controversial razing of Franklin Street to construct a limited-access highway to improve access in and out of the city for non-residents. The reconstruction of the street demolished 130 homes and businesses and caused an unknown number of families to be relocated or displaced. The construction of The Maine Mall, an indoor shopping center established in South Portland in 1971, economically depressed downtown Portland. The trend reversed when tourists and new businesses started revitalizing the old seaport, a part of which is known locally as the Old Port.

Since the 1990s, the historically industrial Bayside neighborhood has seen rapid development, including attracting a Whole Foods Market and Trader Joe's grocery stores, as well as Baxter Academy for Technology and Science, a charter school. Other developing neighborhoods include the India Street neighborhood, near the Ocean Gateway, and Munjoy Hill, where many modern condominiums have been built. The Maine College of Art has been a revitalizing force downtown, attracting students from around the country. The historic Porteous Building on Congress Street was restored by the college. Universities operating in the city are expanding. The University of Southern Maine is improving its Portland campus with a 580-bed dormitory, student center, and an arts center. The University of New England intends to move its medical school from its Biddeford campus to its Portland campus. Northeastern University's Roux Institute plans to build on the former B&M Baked Beans factory campus in East Deering.

Portland is known as a walkable city, offering many opportunities for walking tours which feature its maritime and architectural history.

Geography

According to the United States Census Bureau, the city has a total area of 69.44 sqmi, of which 21.31 sqmi is land and 48.13 sqmi is water. Portland is situated on a peninsula in Casco Bay on the Gulf of Maine and the Atlantic Ocean.

Portland borders South Portland, Westbrook and Falmouth.

Climate
Portland has a humid continental climate (Köppen: Dfb, closely bordering on Dfa), with cold, snowy, and often prolonged winters, and warm to hot, yet relatively short summers. The monthly average high temperature ranges from roughly 30 °F in January to around 80 °F in July. Daily high temperatures reach or exceed 90 °F on only four days per year on average, while cold-season lows of 0 °F or below are reached on 10 nights per year on average. The area can be affected by severe nor'easters during winter, with high winds and snowfall totals often measuring over a foot. Annual liquid precipitation (rain) averages 47.2 in and is plentiful year-round, but with a slightly drier summer. Annual frozen precipitation (snow) averages 69 in in the city. However, this number can fluctuate seasonally from as little as 30 inches to as much as 150 inches, depending on a multitude of factors. In Southern Maine, snowstorms can be intense from November through early April, while warm-season thunderstorms are somewhat less frequent than in the Midwestern, Mid-Atlantic, and Southeastern U.S. (although their frequency has increased in recent years). Direct strikes by hurricanes or tropical storms are rare, partially due to the normally cooler Atlantic waters off the Maine coast (which usually weaken tropical systems), but primarily because most tropical systems approaching or reaching 40 degrees North latitude recurve (due to the Coriolis force) and track east out to sea well south of the Portland area. Extreme temperatures range from −39 °F on February 16, 1943, to 103 °F on July 4, 1911, and August 2, 1975. The hardiness zones are 5b and 6a.

Sea-level rise
Portland is becoming increasingly affected by global warming and the rise of sea levels. The coast is one of the fastest-warming saltwater bodies, and is predicted to see an increase to about 10–17 inches by 2030, in comparison to the levels in 2000. This is a major threat to the residents and ocean life around the area. In 2022, the National Oceanic and Atmospheric Administration issued a report that showed sea level in Portland could rise by six inches by 2050, two feet by 2060 and two to six feet by 2100.

In January 2024, Portland experienced a record-high tide of 14.57 ft. Combined with heavy rainfall and strong winds, it caused severe flooding.

Neighborhoods

Portland is organized into neighborhoods generally recognized by residents, but they have no legal or political authority. In many cases, city signs identify neighborhoods or intersections (which are often called corners). Most city neighborhoods have a local association which usually maintains ongoing relations of varying degrees with the city government on issues affecting the neighborhood.

On March 8, 1899, Portland annexed the neighboring city of Deering. Deering neighborhoods now comprise the northern and eastern sections of the city before the merger. Portland's Deering High School was formerly the public high school for Deering.

Portland's neighborhoods include the Arts District, Bayside, Bradley's Corner, Cliff Island, Cushing's Island, Deering Center, Deering Highlands, Downtown, East Deering, East Bayside, East End, Eastern Cemetery, Great Diamond Island, Highlands, Kennedy Park, Libbytown, Little Diamond Island, Lunt's Corner, Morrill's Corner, Munjoy Hill, Nason's Corner, North Deering, Oakdale, the Old Port, Parkside, Peaks Island, Riverton Park, Rosemont, Stroudwater, West End, and Woodfords Corner.

From the early 2000s onward, many of Portland's neighborhoods have faced gentrification, causing many local residents to be "priced out" of their neighborhoods. In 2015, the Portland Press Herald published a series of articles documenting the "super-tight apartment market" and the trauma caused by evictions and steep jumps in monthly rent. Also in that year, city landlords raised rents by an average of 17.4%, which was the second-largest jump in the country.

2010 census
As of the census of 2010, there were 66,194 people, 30,725 households, and 13,324 families residing in the city. The population density was 3106.2 PD/sqmi. There were 33,836 housing units at an average density of 1587.8 /sqmi. The racial makeup of the city was 85.0% White (83.6% non-Hispanic White alone), down from 96.6% in 1990, 7.1% African American, 0.5% Native American, 3.5% Asian, 1.2% from other races, and 2.7% from two or more races. Hispanic or Latino of any race were 3.0% of the population. 40.7% of the population had a bachelor's degree or higher.

There were 30,725 households, of which 20.7% had children under the age of 18 living with them, 29.7% were married couples living together, 10.1% had a female householder with no husband present, 3.6% had a male householder with no wife present, and 56.6% were non-families. 40.5% of all households were made up of individuals, and 11.4% had someone living alone who was 65 years of age or older. The average household size was 2.07 and the average family size was 2.88.

The median age in the city was 36.7 years. 17.1% of residents were under the age of 18; 11.4% were between the ages of 18 and 24; 33.1% were from 25 to 44; 25.9% were from 45 to 64; and 12.6% were 65 years of age or older. The gender makeup of the city was 48.8% male and 51.2% female.

2000 census
As of the census of 2000, there were 64,250 people, 29,714 households, and 13,549 families residing in the city. The population density was 3,029.2 PD/sqmi. There were 31,862 housing units at an average density of 1,502.2 /sqmi.

According to the U.S. Census Bureau, Portland's immediate metropolitan area ranked 147th in the nation in 2000 with a population of 243,537, while the Portland/South Portland/Biddeford metropolitan area included 487,568 total inhabitants. This has increased to an estimated 513,102 inhabitants (and the largest metro area in Northern New England). Much of this increase in population has been due to growth in the city's southern and western suburbs.

The racial makeup of the city was 91.27% White, 2.59% African American, 0.47% Native American, 3.08% Asian, 0.06% Pacific Islander, 0.67% from other races, and 1.86% from two or more races. Hispanic or Latino of any race were 1.52% of the population.

The largest ancestries include: British (including Scottish, Welsh, and English) (21.2%), Irish (19.2%), French (10.8%), Italian (10.5%), and German (6.9%).

There were 29,714 households, out of which 21.4% had children under the age of 18 living with them, 32.1% were married couples living together, 10.5% had a female householder with no husband present, and 54.4% were non-families. 40.1% of all households were made up of individuals, and 11.5% had someone living alone who was 65 years of age or older. The average household size was 2.08 and the average family size was 2.89.

In the city, the population was spread out, with 18.8% under the age of 18, 10.7% from 18 to 24, 36.1% from 25 to 44, 20.6% from 45 to 64, and 13.9% who were 65 years of age or older. The median age was 36 years. For every 100 females, there were 91.8 males. For every 100 females age 18 and over, there were 89.0 males.

The median income for a household in the city was $35,650, and the median income for a family was $48,763. Males had a median income of $31,828 versus $27,173 for females. The per capita income for the city was $22,698. About 9.7% of families and 14.1% of the population were below the poverty line, including 12.5% of those under age 18 and 11.9% of those age 65 or over.

Race/ethnicity composition

Economy

Portland has become Maine's economic capital because the city has Maine's largest port, largest population, and is close to Boston (105 miles to the southwest). Over the years, the local economy has shifted from fishing, manufacturing, and agriculture towards a more service-based economy. Most national bank institutions and other related financial organizations, such as Bank of America and Key Bank, base their Maine operations in Portland. UnumProvident, Covetrus, TruChoice Federal Credit Union, People's United Bank, ImmuCell Corp, and Pioneer Telephone have headquarters here, and Portland's neighboring cities of South Portland, Westbrook and Scarborough, provide homes for other corporations including IDEXX and WEX Inc. Between 1867 and 2021, Burnham & Morrill Company, maker of B&M Baked Beans, had its main plant in Portland (the B&M Baked Beans factory).

The city's port is also undergoing a revival, and the first-ever container train departed from the new International Marine Terminal with fifteen containers of locally produced bottled tap water in early 2016.

In January 2020, Portland was announced to be the location of a new research institute that will focus on the application of artificial intelligence and machine learning. Northeastern University was selected by technology entrepreneur David Roux to lead the institute that will include programs that will allow graduate student research.

Portland also has a large subsidized housing industry, with several large real estate companies in the business. The city is described as one of the "best places to live" in the United States.

Arts and culture
Portland has a long history of prominence in the arts, peaking the first time in the early 19th century, when the city was "a rival, and not a satellite of either Boston or New York." In that period, Henry Wadsworth Longfellow got his start as a poet and John Neal held a central position in leading American literature toward its great renaissance, having founded Maine's first literary periodical, The Yankee, in 1828. Other notable literary or artistic figures who were contemporaries include Grenville Mellen, Nathaniel Parker Willis, Seba Smith, Elizabeth Oakes Smith, Benjamin Paul Akers, Charles Codman, Franklin Simmons, John Rollin Tilton, and Harrison Bird Brown. Since 2000, Portland has hosted a monthly First Friday Art Walk event which attracts more than 3,000 visitors.

Sites of interest
The Arts District, centered on Congress Street, is home to the Portland Museum of Art, Portland Stage Company, Maine Historical Society & Museum, Portland Public Library, Maine College of Art, SPACE Gallery, Children's Museum of Maine, Merrill Auditorium, the Kotzschmar Memorial Organ, and Portland Symphony Orchestra, as well as many smaller art galleries and studios.

Baxter Boulevard around Back Cove, Deering Oaks Park, the Eastern Promenade, Western Promenade, Lincoln Park and Riverton Park are all historical parks within the city. Other parks and natural spaces include Payson Park, Post Office Park, Baxter Woods, Evergreen Cemetery, Western Cemetery and the Fore River Sanctuary.

Thompson's Point, in the Libbytown neighborhood, has been a focus of renovation and redevelopment since the 2010s. The location hosts a concert venue, ice rink, hotels, restaurants, wineries, and breweries.

Notable buildings

The spire of the Cathedral of the Immaculate Conception has been a notable feature of the Portland skyline since its completion in 1854. In 1859, Ammi B. Young designed the Marine Hospital, the first of three local works by Supervising Architects of the U.S. Treasury Department. Although the city lost to redevelopment its 1867 Greek Revival post office, which was designed by Alfred B. Mullett of white Vermont marble and featured a Corinthian portico, Portland retains his 1868 United States Custom House on Fore Street.

Franklin Towers is a 16-story residential tower. Between 1969 and 2023, at 175 ft, it was Maine's tallest residential building. It was surpassed by 201 Federal Street, which is 29.5 ft taller.

During the building boom of the 1980s, several new buildings rose on the peninsula, including the 1983 Charles Shipman Payson Building by Henry N. Cobb of Pei, Cobb, Freed & Partners at the Portland Museum of Art complex (a component of which is the 1801 McLellan-Sweat Mansion), and the Back Bay Tower, a fifteen-story residential building completed in 1990.

477 Congress Street (known locally as the Time and Temperature Building) is situated near Monument Square in the Arts District and is a major landmark: the 14-story building features a large electronic sign on its roof that flashes time and temperature data, as well as parking-ban information in the winter. The building is home to several radio stations. The Press Herald Building, at 390 Congress Street, is strategically located across Congress Street from Portland City Hall and was built in 1923. It was expanded in 1948 for use as the newspaper's headquarters.

The Westin Portland Harborview, completed in 1927, is a prominent hotel located downtown on High Street. Photographer Todd Webb lived in Portland during his later years and took many pictures of the city. Some of Webb's pictures can be found at the Evans Gallery.

Media
The city is home to one daily newspaper, The Portland Press Herald/Maine Sunday Telegram, founded in 1862. The Press Herald is published Monday through Saturday and The Maine Sunday Telegram is published on Sundays. Both are published by MaineToday Media Inc., which also operates an entertainment website, MaineToday.com and owns papers in Augusta, Waterville, and Bath.

Portland had an alternative weekly newspaper, The Portland Phoenix, published by the Phoenix Media/Communications Group, which also produced a New England-wide news, arts, and entertainment website, thephoenix.com, and a twice-annual LGBT issues magazine, Out in Maine.

Other publications include The Portland Forecaster, a weekly newspaper; The Bollard, a monthly alternative magazine formerly known as Mainer; The West End News, The Munjoy Hill Observer, The Baysider, The Waterfront, Portland Magazine, and The Companion. Portland is also the home office of The Exception Magazine, an online newspaper which covers Maine.

The Portland broadcast media market is the largest one in Maine for both radio and television. Radio stations located in Portland include WFNK (Classic Hits), WJJB (Sports), WTHT (Country), WBQW (Classical), WHXR (Rock), WHOM (Adult Contemporary), WJBQ (Top 40), WCLZ (Adult Album Alternative), WBLM (Classic Rock), WYNZ (1960s–1970s Hits), and WCYY (Modern Rock). WMPG is a local non-commercial radio station run by community members and the University of Southern Maine. The Maine Public Broadcasting Network's (MPBN) radio news operations are based in Portland.

Television stations include WCSH 6 (NBC), WMTW 8 (ABC), WGME 13 (CBS), WPFO 23 (Fox), WIPL 35 (ION), and WPXT 51 (The CW; MyNetworkTV on DT3). There is no PBS affiliate licensed to the city of Portland, but the market is served by MPBN outlets WCBB Channel 10 in Augusta and WMEA-TV Channel 26 Biddeford.

Historical newspapers
Newspapers formerly published in Portland include the Eastern Argus, Evening Express, The Pleasure Boat and The Portland Daily Sun.

Number of restaurants
Downtown Portland, including the Arts District and the Old Port, has a high concentration of eating and drinking establishments, with many more to be found throughout the rest of the peninsula, outlying neighborhoods, and neighboring communities. The city is also home to numerous food trucks and food carts, which park on the city streets and at festivals, events and breweries. Most operate in the summer; a few operate year-round.

Notable restaurants include Fore Street, Duckfat, Becky's Diner, and The Great Lost Bear.

Food recognition
Portland has developed a national reputation for the quality of its restaurants, eateries, and food culture. The city has been visited by many food shows, including Rachael Ray's Food Network show $40 a Day, the Travel Channel's Man v. Food, and Anthony Bourdain: No Reservations. Bon Appetit named Portland the Restaurant City of the Year in 2018.

Beverages
Portland is home to numerous juice bars, coffee shops, coffee roasteries, tea houses, distilleries, microbreweries and brewpubs.

Brewers include the D. L. Geary Brewing Company, Gritty McDuff's Brewing Company, Shipyard Brewing Company, and Allagash Brewing Company. Portland's spirits industry has also grown in recent years.

The city is known for its pure tap water. The water comes from Sebago Lake. It is piped to Portland by the Portland Water District. Sebago Lake is one of fifty surface-water supplies among 13,000 in the country that the Environmental Protection Agency says do not need filtration.

Farmers markets
The Portland Farmers' Market takes place Wednesdays in Monument Square, Saturdays in Deering Oaks Park (from early May to the end of November), and Saturdays at The Maine Girls Academy (from early December to the end of April).

Vegetarian food
The city has the state's most vegan and vegetarian restaurants. Vegetarian-friendly restaurants number more than 200 in 2020, according to the Maine Sunday Telegram. Celebrity chef Toni Fiore first filmed the PBS cooking show Totally Vegetarian in 2002 at the cable access station in Portland. The Portland Press Herald has featured a vegan column by Avery Yale Kamila in its Food & Dining section since 2009. In 2011, the Portland Public Schools added a daily vegetarian cold lunch to its school menu choices. In 2019, the district changed to a daily hot vegan school meal option.

Food festivals
Portland hosts a number of food and beverage festivals, including:
 * Festival of Nations, takes place in July in Deering Oaks Park and organized by group of local organizations
 * Greek Festival, three-day event in June at Holy Trinity Greek Orthodox Church
 * Harvest on the Harbor, multi-day event takes place in October
 * Italian Street Festival & Bazaar, three-day event in August outside St. Peter's Parish commemorates the Feast of the Assumption of the Blessed Virgin Mary and the Feast of Saint Rocco
 * Maine Brewers Festival, held multiple times a year by the Maine Brewers' Guild
 * Maine VegFest, takes place in October and organized by Maine Animal Coalition since 2005; the event features all vegan food and was originally called Maine Vegetarian Food Festival
 * Taste of the Nation, fundraiser for food insecurity that stopped after 2015 but happened again in 2019
 * Maine Restaurant Week, takes place over twelve days in March
 * Maine Seaweed Week, takes place in the spring

Food history
Since 1768, the Portland Farmers Market has been in operation. It was first established in the Town Hall that "served 136 families on the peninsula."

Portland is where national Prohibition started. Portland mayor and temperance leader Neal Dow led Maine to ban alcohol sales in 1851. The law led to the Portland Rum Riot in 1855. In 1845, The Pleasure Boat was the earliest vegetarian publication in Maine.

Canned corn was developed in Portland by the N. Winslow company. By 1852 the Winslow's Patent Hermetically Sealed Green Corn was a commercial success and the company became a world leader in the canning industry. An historic B&M Baked Beans canning plant built in 1913 operated on the waterfront until 2021 when it closed and production moved to the midwest. By late 2022, B&M customers were reporting that the baked beans were undercooked, crunchy, and tasted different. Customers speculated that the beans were no longer being baked. Some customers were hoarding B&M bean cans produced at the Portland plant.

In the early 20th century, a Little Italy neighborhood developed around India Street. The city's Amato's Italian delicatessen on India Street is reported to be the birthplace of the Italian sandwich, called "an Italian" by locals, which Amato's first served in 1902. The Village Restaurant, an Italian restaurant in the city's East End, was in operation for 71 years, from 1936 to 2007. In 1949, Miccuci's Grocery Co. opened on India Street and remains in business.

In the 1970s and 1980s, The Hollow Reed was a notable vegetarian restaurant on Fore Street cited for its influence on the city's restaurant culture. In 1979, The Great Lost Bear opened on Forest Avenue and was recognized for its large selection of draft craft beers. In 1982 DiMillo's on the Water opened in a former car ferry docked at Portland's Long Wharf. In 1988, the Gritty McDuff's brewpub was founded on Fore Street and is considered the first brewpub to open in Maine since Prohibition ended. In 1989, Marcy's Diner opened on Free Street, and in 2015 it made international headlines following a spat between the then-cook-owner and a patron over the latter's screaming child.

In 1991, Becky's Diner opened on Commercial Street, after it got an exception to the city's zoning laws prohibiting non-fishery businesses on the waterfront, and has attracted famous patrons including Taylor Swift and president Bill Clinton. In 2007, the Green Elephant opened on Congress Street and received critical attention for the vegetarian menu.

In 2024, ZU Bakery located in the West End won the James Beard award for Outstanding Bakery, and Atsuko Fujimoto, owner of Norimoto Bakery, in Deering Center, won the James Beard award for Outstanding Pastry Chef or Baker.

Sports
The city is also home to Portland Rugby Football Club, the oldest continually active sports team in the city, founded in 1969. The team competes in Division II of the New England Rugby Football Union.

Other pro and semi-pro sports teams in the city include the Portland Lumberjacks, a bowling team competing in the PBA League, and Portland Rising, a women's ultimate team competing in the Premier Ultimate League.

Previously, Portland was home of several minor league ice hockey teams: the Maine Nordiques (NAHL) from 1973 to 1977, the Maine Mariners (AHL) from 1977 to 1992, and the Portland Pirates (AHL) from 1993 to 2016. The Mariners were three-time Calder Cup winners, winning it in 1978, 1979 and 1984, while the Pirates would win the Calder Cup in 1995.

GPS Portland Phoenix soccer teams played in USL League Two from 2009 until 2020.

The Maine Mammoths of the National Arena League played in 2018 and were the first indoor football team to call Portland home. The team suspended operations after one season while it negotiated with local ownership groups, but was ultimately dissolved.

The city was previously home to an Australian rules football team, the Maine Cats. The team played in the United States Australian Football League from 2018 until it merged with the Boston Demons in 2023.

The Portland Sports Complex, located off of Park and Brighton Avenues near I-295 and Deering Oaks park, houses several of the city's stadiums and arenas, including:
 * Hadlock Field – baseball (Capacity 7,368)
 * Fitzpatrick Stadium – football, soccer, lacrosse, field hockey, and outdoor track (Capacity 6,000+ seated)
 * Portland Exposition Building – basketball, indoor track, concerts and trade shows (Capacity 3,000)
 * Portland Ice Arena – hockey and figure skating (Capacity 400)

Cross Insurance Arena has 6,733 permanent seats following renovation in 2014.

The Portland area has eleven professional golf courses, 124 tennis courts, and 95 playgrounds. There are also over 100 mi of nature trails.

Portland hosts the Maine Marathon each October.

Bayside Bowl was expanded in 2017 to 20 lanes, including a rooftop deck. It hosted the 2017 PBA League and Elias Cup.

Memorial Stadium is the home of the Deering High School sports teams and is located behind the school.

Parks and recreation
The city of Portland includes more than 700 acres of open space and public parks. The city and surrounding communities are linked by 70 miles of trails, both urban and wooded, maintained by the nonprofit Portland Trails. The Portland Parks Conservancy, which was established in 2019, is a nonprofit organization that raises money to support Portland's park system. In 2021, the Portland Parks Conservancy funded the establishment of the Portland Youth Corp. The Portland Youth Corp performs work in Portland's parks and residents between the ages of 14 and 16 can apply to participate in the paid program.

The city requires organic land care techniques be used on both public and private property. In 2018, the Portland City Council banned the use of synthetic pesticides. In 2020, the city received a $10,000 grant from Hannaford, Stonyfield Farm, and Osborn Organics to pay for soil tests and other start up costs of transitioning the heavily used Fox Field in Kennedy Park to an organic maintenance plan.

Well-known and historic parks include: Parks with splash pads and pools:
 * Deering Oaks Park
 * Eastern Promenade
 * Western Promenade
 * Baxter Boulevard
 * Lincoln Park
 * Congress Square Park
 * Payson Park
 * East End Beach
 * East End Trail
 * Bayside Trail
 * Kennedy Park
 * Riverside Municipal Golf Course
 * Fort Sumner Park
 * Baxter Woods
 * Fore River Sanctuary
 * Quarry Run Dog Park
 * Riverton Trolley Park

 * Deering Oaks Ravine
 * Kiwanis Pool
 * Peppermint Park
 * Payson Park
 * Stone Street Playground

Government

The city has adopted a council-manager style government that is detailed in the city charter. The citizens of Portland are represented by a nine-member city council which makes policy, passes ordinances, approves appropriations, appoints the city manager and oversees the municipal government. The city council of nine members is elected by the citizens of Portland. The city has five voting districts, with each district electing a city councilor to represent their neighborhood interests for a three-year term. There are also four members of the city council who are elected at-large. The four at-large members are elected through Proportional ranked-choice voting.

From 1923 until 2011, city councilors chose one of themselves each year to serve as Mayor of Portland, a primarily ceremonial position. On November 2, 2010, Portland voters narrowly approved a measure that allowed them to elect the mayor. On November 8, 2011, former State Senator and candidate for U.S. Congress Michael F. Brennan was elected as mayor. On December 5, 2011, he was sworn in as the first citizen-elected mayor in 88 years (see Portland, Maine mayoral election, 2011). The office of mayor is a four-year position that earns a salary of 150% of the city's median income. The current mayor is Mark Dion, who narrowly defeated city councilor Andrew Zarro after 5 ranked choice rounds in the November 2023 election.

A city manager is appointed by the city council. The city manager oversees the daily operations of the city government, appoints the heads of city departments, and prepares annual budgets. The city manager directs all city agencies and departments, and is responsible for the executing laws and policies passed by the city council. The current city manager is Danielle West.

Aside from the main city council, there is also an elected school board for the Portland Public School system. The school board is made up in the same manner of the city council, with five district members, four at-large members and one chairman. There are also three students from the local high schools elected to serve on the board. There are many other boards and committees such as the Planning Committee, Board of Appeals, and Harbor Commission, etc. These committees and boards have limited power in their respective areas of expertise. Members of boards and committees are appointed by city council members.

On November 5, 2013, Portland voters overwhelmingly approved an ordinance to legalize the possession and private use of cannabis for adults, making the city the first municipality in the Eastern United States to do so.

James E. Craig was chief of the Portland Police Department from 2009 to 2011. He would later go on to become the chief of the Cincinnati Police Department and Detroit Police Department.

In the U.S. House of Representatives, Portland is included in Maine's 1st congressional district and is currently represented by Democrat Chellie M. Pingree.

Voter registration

High schools

 * Baxter Academy for Technology and Science (charter)
 * Casco Bay High School (public-expeditionary)
 * Cheverus High School (private)
 * Deering High School (public)
 * Portland Arts & Technology High School (public-vocational)
 * Portland High School (public)
 * Waynflete School (private)

Colleges and universities
College expansions underway in 2022 at the University of Southern Maine to add a 580-bed dorm, at the University of New England to move the medical school from Biddeford into a new $93 million building on the Portland campus, and at the Northeastern University Roux Institute to build a campus on the site of the former B&M Baked Beans factory have the potential, within two decades, to bring the total college and university students in the city to 15,000, which would be similar to the percentage of students in Boston.
 * Institute for Doctoral Studies in the Visual Arts
 * Maine College of Art
 * Roux Institute
 * University of Maine School of Law
 * University of New England
 * University of Southern Maine

Fire department
The Portland Fire Department (PFD) provides fire protection and emergency medical services to the city of Portland 24/7, 365. Established on March 29, 1768, the PFD is made up of over 230 paid, professional firefighters and operates out of seven fire stations, located throughout the city, in addition to those staffed by "on-call" firefighters on Peaks Island, Great Diamond Island, Cushing Island and Cliff Island. The Portland Fire Department also operates an Airport Division Station at 1001 Westbrook St., at the Portland International Jetport, and a Marine Division Station, located at 54 Commercial St.

Police
The Portland Police Department is the largest municipal police department in the state of Maine.

Hospitals

Maine Medical Center is the state's only Level I trauma center and is the largest hospital in Maine.

Mercy Hospital, a faith-based institution, is the fourth largest in the state. It completed the first phase of its new campus along the Fore River in 2008.

The formerly-independent Brighton Medical Center (once known as the Osteopathic Hospital) is now owned by Maine Medical Center and is operated as a minor care center under the names Brighton First Care and New England Rehab. In 2010, Maine Medical Center's Hannaford Center for Safety, Innovation, and Simulation opened at the Brighton campus. The former Portland General Hospital is now home to the Barron Center nursing facility.

Wastewater management
One wastewater management project is named the Bedford Street Sewer Separation, with its goal to "improve the water quality and health of Back Cove by reducing the amount of combined sewer overflows (CSO) that over flow during heavy rain events through the use of sewer separation and water treatment devices."

Roads
Portland is accessible from I-95 (the Maine Turnpike), I-295, and US 1. U.S. Route 302, a major travel route and scenic highway between Maine and Vermont, has its eastern terminus in Portland. State Routes include SR 9, SR 22, SR 25, SR 26, SR 77, and SR 100. SR 25 Business goes through southwestern Portland.

Intercity buses and trains
Amtrak's Downeaster service offers five daily trains connecting the city's station with eight towns and cities to the south, ending at Boston's North Station. Trains also go north to Freeport and Brunswick.

Concord Coach Lines bus service connects Portland to 14 other communities in Maine as well as to Boston's South Station and Logan Airport. Both the Downeaster and the Concord Coach Lines can be found at the Portland Transportation Center on Thompsons Point Road, in the Libbytown neighborhood.

Local bus service
Local bus transit is provided by Greater Portland Metro with connections to South Portland Bus Service and Biddeford Saco Old Orchard Beach Transit.

Airports
Commercial air service is available at the Portland International Jetport (PWM), located in Stroudwater, west of the city's downtown district. American, Southwest, JetBlue, Breeze Airways, Sun Country, Delta, and United Airlines service the airport. Direct flights are available to Atlanta, Baltimore, Charlotte, Chicago, Detroit, Denver, Minneapolis, Orlando, Philadelphia, New York, Newark, Raleigh-Durham, Sarasota, and Washington, D.C.

Water transportation
The Port of Portland is the second-largest cruise and passenger destination in the state (next to Bar Harbor) and is served by the Ocean Gateway International Marine Passenger Terminal. Ferry service is available year-round to many destinations in Casco Bay. From 2006 to 2009, Bay Ferries operated a high speed ferry called The Cat featuring a five-hour trip to Yarmouth, Nova Scotia, for summer passengers and cars. In years past the Scotia Prince Cruises trip took eleven hours. A proposal to replace the defunct Nova Scotia ferry service was rejected in 2013 by the province. From May 15, 2014, until October 2015, the cruise ship ferry Nova Star made daily trips to Yarmouth, Nova Scotia. Due to poor passenger numbers and financial problems, Nova Scotia selected Bay Ferries, the prior operator of The Cat, to operate the service starting in 2016, citing the company's experience and industry relationships. Nova Star officials pledged a smooth transition to the new operator. The Nova Star was later ordered seized by federal marshals for nonpayment of bills.

Bay Ferries announced on March 24, 2016, the charter of the former Hawaii Superferry boat HST-2 from the US Navy for the Portland-Yarmouth service for two years. Bay Ferries signed a ten-year deal with Nova Scotia to run the ferry route, which will take about five and a half hours each way. They stated that the boat would be renamed The Cat and that service would begin around June 15, after refitting in South Carolina. There is still a dispute as to whether the ferry will be permitted to carry trucks, desired by Nova Scotia businesses but opposed by the City of Portland.

The Casco Bay Lines operate several passenger ferries with dozens of trips every day year-round to the major populated islands of Casco Bay. The service to Peaks Island also provides an auto ferry for most of its schedule.

Sister cities
Portland's sister cities are:
 * 🇷🇺 Arkhangelsk, Russia
 * 🇭🇹 Cap-Haïtien, Haiti
 * 🇰🇪 Garissa Township, Kenya
 * 🇬🇷 Mytilene, Greece
 * 🇯🇵 Shinagawa (Tokyo), Japan

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Portland, Maine


text:
Rib

In vertebrate anatomy, ribs (costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the thoracic cavity. They serve to protect the lungs, heart, and other vital organs of the thorax. In some animals, especially snakes, ribs may provide support and protection for the entire body.

Rib details
Human ribs are flat bones that form part of the rib cage to help protect internal organs. Humans usually have 24 ribs, in 12 pairs. 1 in 500 people have an extra rib known as a cervical rib. People may have a cervical rib on the right, left or both sides. All are attached at the back to the thoracic vertebrae and are numbered from 1 to 12 according to the vertebrae to which they attach. The first rib is attached to thoracic vertebra 1 (T1). At the front of the body, most of the ribs are joined by costal cartilage to the sternum. Ribs connect to vertebrae at the costovertebral joints.

The parts of a rib includes the head, neck, body (or shaft), tubercle, and angle.

The head of the rib lies next to a vertebra. The ribs connect to the vertebrae with two costovertebral joints, one on the head and one on the neck. The head of the rib has a superior and an inferior articulating region, separated by a crest. These articulate with the superior and inferior costal facets on the connecting vertebrae. The crest gives attachment to the intra-articulate ligament that joins the rib to the vertebra of the same number, at the intervertebral disc. Another ligament, the radiate ligament joins the head of the rib to both the body of the upper vertebra and to the body of the lower vertebra. The smaller middle part of the ligament connects to the intervertebral disc. This plane joint is known as the articulation of the head of the rib.

The other costovertebral joint is that between the tubercle on the neck and the transverse process of the joining thoracic vertebra of the same rib number, and this is known as the costotransverse joint. The superior costotransverse ligament attaches from the non-articular facet of the tubercle to the transverse process of the vertebra.

The neck of the rib is a flattened part that extends laterally from the head. The neck is about 3 cm long. Its anterior surface is flat and smooth, whilst its posterior is perforated by numerous foramina and its surface rough, to give attachment to the ligament of the neck. Its upper border presents a rough crest (crista colli costae) for the attachment of the anterior costotransverse ligament; its lower border is rounded.

A tubercle of rib on the posterior surface of the neck of the rib, has two facets (surfaces) one articulating and one non-articulating. The articular facet, is small and oval and is the lower and more medial of the two, and connects to the transverse costal facet on the thoracic vertebra of the same rib number. The transverse costal facet is on the end of the transverse process of the lower of the two vertebrae to which the head is connected. The non-articular portion is a rough elevation and affords attachment to the ligament of the tubercle. The tubercle is much more prominent in the upper ribs than in the lower ribs.

Rib cage
The first seven sets of ribs, known as "true ribs", are attached to the sternum by the costal cartilages. The first rib is unique and easier to distinguish than other ribs. It is a short, flat, C-shaped bone, and attaches to the manubrium. The vertebral attachment can be found just below the neck at the first thoracic vertebra, and the majority of this bone can be found above the level of the clavicle. Ribs 2 through 7 then become longer and less curved as they progress downwards. The following five sets are known as "false ribs", three of these sharing a common cartilaginous connection to the sternum, while the last two (eleventh and twelfth ribs) are termed floating ribs. They are attached to the vertebrae only, and not to the sternum or cartilage coming off of the sternum.

In general, human ribs increase in length from ribs 1 through 7 and decrease in length again through rib 12. Along with this change in size, the ribs become progressively oblique (slanted) from ribs 1 through 9, then less slanted through rib 12.

The rib cage is separated from the lower abdomen by the thoracic diaphragm which controls breathing. When the diaphragm contracts, the thoracic cavity is expanded, reducing intra-thoracic pressure and drawing air into the lungs. This happens through one of two actions (or a mix of the two): when the lower ribs the diaphragm connects to are stabilized by muscles and the central tendon is mobile, when the muscle contracts the central tendon is drawn down, compressing the cavity underneath and expanding the thoracic cavity downward. When the central tendon is stabilized and the lower ribs are mobile, a contraction of the diaphragm elevates the ribs, which works in conjunction with other muscles to expand the thoracic indent upward.

Development
Early in the developing embryo, somites form and soon subdivide into three mesodermal components – the myotome, dermatome, and the sclerotome. The vertebrae and ribs develop from the sclerotomes.

During the fourth week (fertilization age) costal processes have formed on the vertebral bodies. These processes are small, lateral protrusions of mesenchyme that develop in association with the vertebral arches. During the fifth week the costal processes on the thoracic vertebrae become longer to form the ribs. In the sixth week, the costovertebral joints begin to develop and separate the ribs from the vertebrae. The first seven pairs of ribs, the true ribs join at the front to the sternal bars. By the fetal stage the sternal bars have completely fused.

The ribs begin as cartilage that later ossifies – a process called endochondral ossification. Primary ossification centers are located near the angle of each rib, and ossification continues in the direction away from the head and neck. During adolescence secondary ossification centers are formed in the tubercles and heads of the ribs.

Other animals
In jawed fish, there are often two sets of ribs attached to the vertebral column. One set, the dorsal ribs, are found in the dividing septum between the upper and lower parts of the main muscle segments, projecting roughly sideways from the vertebral column. The second set, the ventral ribs arise from the vertebral column just below the dorsal ribs, and enclose the lower body, often joining at the tips. Not all species possess both types of rib, with the dorsal ribs being most commonly absent. Sharks, for example, have no ventral ribs, and only very short dorsal ribs. In some teleosts, there may be additional rib-like bones within the muscle mass.

Tetrapods, however, only ever have a single set of ribs which are probably homologous with the dorsal ribs of fishes. In the earlier choanates, every vertebra bore a pair of ribs, although those on the thoracic vertebrae are typically the longest. The sacral ribs were stout and short, since they formed part of the pelvis, connecting the backbone to the hip bones.

In most true tetrapods, many of these early ribs have been lost, and in living amphibians and reptiles, there is great variation in rib structure and number. For example, turtles have only eight pairs of ribs, which are developed into a bony or cartilaginous carapace and plastron, while snakes have numerous ribs running along the full length of their trunk. Frogs typically have no ribs, aside from a sacral pair, which form part of the pelvis.

In birds, ribs are present as distinct bones only on the thoracic region, although small fused ribs are present on the cervical vertebrae. The thoracic ribs of birds possess a wide projection to the rear; this uncinate process is an attachment for the shoulder muscles. Usually dogs have 26 ribs. Mammals usually also only have distinct ribs on the thoracic vertebra, although fixed cervical ribs are also present in monotremes. In therian mammals, the cervical and lumbar ribs are found only as tiny remnants fused to the vertebrae, where they are referred to as transverse processes. In general, the structure and number of the true ribs in humans is similar to that in other mammals. Unlike reptiles, caudal ribs are never found in mammals.

Ribs as food
Ribs as food are widely used from many animals. The ribs are the less meaty part of the meat chop and they are often cooked as part of a slab; five or more is known as a rack, as in a rack of lamb. Short ribs are ribs of beef either served singly or several as a plate. A rib steak from beef is a popular choice used in many cuisines. Pork ribs, including spare ribs are popular in European and Asian cuisine.

title: Rib


text:
Sea butterfly

The Thecosomata (collective/plural: thecosomes, meaning "case/shell-body"), or sea butterflies, are a taxonomic suborder of small, pelagic, free-swimming sea snails known as holoplanktonic opisthobranch gastropod mollusks, in the order Pteropoda (also included within the informal group Opisthobranchia). Most pteropods have some form of calcified shell, although it is often very light, even translucent.

The sea butterflies include some of the world's most abundant gastropod species; as their large numbers are an essential part of the ocean food chain, they are a significant contributor to the oceanic carbon cycle.

Morphology
Unlike other sea snails, or even land snails, sea butterflies float and swim freely through the ocean, traveling along with the currents. This has led to a number of evolutionary adaptations in their bodies, including complete or near-complete loss of the shell and the gill in several families. Their gastropodal foot has also taken the form of two wing-like lobes, or parapodia, which propel the animal through the sea by slow flapping movements.

Most thecosomes have some form of calcified shell, although often very light. They are rather difficult to see, since their shell, if present, is mostly transparent, fragile, and usually tiny (less than 1 cm in length). Although their shell may be so fine as to be transparent, it is nevertheless calcareous, and an important part of the oceanic calcium cycle. Their shells are bilaterally symmetric and can vary widely in shape, ranging from coiled or needle-like to triangular or globular.

The shell is present in all life cycle stages of the Cavolinioidea (euthecosomata). In the Cymbulioidea (pseudothecosomata), adult Peraclididae also bear shells; the Cymbuliidae shed their larval shells and develop a cartilaginous pseudoconch in adulthood. Only the Desmopteridae lack any rigid covering when mature.

Swimming kinematics
Molluscan pteropods develop their feet into a pair of wing-like parapodia in the growing phase. These 'wings' are highly flexible, as the orientation of the muscles is different, and they have a hydrostatic skeleton filled with a pressurized fluid. Thus, the high bending-angle supports the parapodia to diminish the drag forces generated by the classic "clap-and-fling" maneuver; additionally, it aids in carrying the extra weight of a shell and ascending the water column for the diel vertical migration.

The power-stroke for L. helicina starts with a sharp rotation of it is body accompanied by an increase in swimming speed; it then rotates its shell in the opposite direction to initiate the recovery-stroke and swims upward, with a speed less than the power phase. There is a drop in overall speed between power and recovery strokes, which develop a sawtooth trajectory in the sagittal plane. The hyper-pitch of the round shell of L. helicina diminishes the rotational drag and the moment of inertia; the extreme shell rotation also assists in raising the wingtips at the end of each stroke to create a figure-eight pattern, common for flying insects. In contrast, flying insects and shell-less pteropods encounter higher resistance forces that limit the body rotation.

Sea butterflies range from the tropics to the poles. They are "holoplanktonic"—they spend all their lives floating amongst plankton, rather than remaining planktonic during their larval stage. Thus, thecosomans are most common in the top 25 m of the ocean—in terms of diversity, species richness, and abundance—and become scarcer with increased depth.

Occasionally, thecosomans swarm in large numbers, and can sometimes be found washed ashore in flotsam, especially along the coastline of eastern Australia.

Diurnal vertical migration
Thecosomata beat their wing-like parapodia to "fly" through the water. When descending to deeper water, they hold their wings up.

They migrate vertically from day to night, so the community structure changes on a 24 hour cycle; during the day many organisms take refuge at water depths in excess of 100 m.

Feeding
Little is documented of the dietary habits or behaviour of sea butterflies, yet they are known to have a peculiar way of feeding. Being generally herbivorous, and mostly passive plankton-feeders, they live their lives according to the currents and find food by floating ventral-side up; some may more actively forage, at times. They ensnare planktonic food by entangling it in a mucous web measuring up to 5 cm wide—many times larger than their own bodies. If disturbed, they simply abandon the web and flap slowly away.

Each day, they embark on a regular diel vertical migration through the water column in their pursuit of planktonic prey. At night, they forage at the surface and return to deeper waters by the morning.

Fossil record
Geologically-speaking, Thecosomata is a rather young group, being known from the Late Paleocene of the Cenozoic Era.

The group is known within the fossil record from shells of those groups within the clade that mineralized. These carbonate shells are a major contributor to the oceanic carbon cycle, making up as much as 12% of global carbonate flux. However, the low stability of their aragonitic shells means that few end up being preserved within sediments as viable fossils; rather, they are mostly deposited in shallow, tropical seas.

Importance in the food chain
These creatures, which range from lentil- to orange-sized, are eaten by various marine species, including a wide variety of fish that are, in turn, consumed by penguins and polar bears. The sea butterflies form the sole food source of their relatives, the Gymnosomata. They are also consumed by sea birds, whales, and commercially important fish. However, if sea butterflies are consumed in large quantities fish can get "black gut", which makes them unsellable.

Taxonomy
Along with its sister group, the sea angels (Gymnosomata), the sea butterflies (Thecosomata) are included in the order Pteropoda. The validity of the pteropod order is not universally accepted; it fell out of favour for a number of years, but recent molecular evidence suggests that the taxon should be revived. Although most Thecosomata have some form of calcified shell, mature Gymnosomata have none.

Ponder & Lindberg
Order Thecosomata de Blainville, 1824
 * Infraorder Euthecosomata
 * Superfamily Limacinoidea
 * Family Limacinidae de Blainville, 1823
 * Superfamily Cavolinioidea
 * Family Cavoliniidae H. and A. Adams, 1854
 * Family Cliidae
 * Family Creseidae
 * Family Cuvierinidae
 * Family Praecuvierinidae
 * Infraorder Pseudothecosomata
 * Superfamily Peraclidoidea
 * Family Peraclidae Tesch, 1913
 * Superfamily Cymbulioidea
 * Family Cymbuliidae Gray, 1840
 * Family Desmopteridae Dall, 1921

Bouchet & Rocroi
In the new taxonomy of Bouchet & Rocroi (2005) Thecosomata is treated differently :

Clade Thecosomata :
 * Superfamily Cavolinioidea Gray, 1850 ( = Euthecosomata)
 * Family Cavoliniidae Gray, 1850 (1815)
 * Subfamily Cavoliinae Gray, 1850 (1815) (formerly Hyalaeidae Rafinesque, 1815 )
 * Subfamily Clioinae Jeffreys, 1869 (formerly Cleodoridae Gray, 1840 - nomen oblitum)
 * Subfamily Cuvierininae van der Spoel, 1967 (formerly : Cuvieriidae Gray, 1840 (nom. inv.); Tripteridae Gray, 1850 )
 * Subfamily Creseinae Curry, 1982
 * Family Limacinidae Gray, 1840 (formerly : Spirialidae Chenu, 1859 ; Spiratellidae Dall, 1921 )
 * † Family Sphaerocinidae A. Janssen & Maxwell, 1995
 * Superfamily Cymbulioidea Gray, 1840 ( = Pseudothecosomata)
 * Family Cymbuliidae Gray, 1840
 * Subfamily Cymbuliinae Gray, 1840
 * Subfamily Glebinae van der Spoel, 1976
 * Family Desmopteridae Chun, 1889
 * Family Peraclidae Tesch, 1913 (formerly Procymbuliidae Tesch, 1913

Bouchet & Rocroi (2005) move the family Limacinidae into the superfamily Cavolinioidea, making redundant the superfamily Limacinoidea erected for it in Ponder & Lindberg's taxonomy. The families Creseidae and Cuvierinidae are demoted to subfamilies of Cavoliniidae (Creseinae and Cuvierininae). The infraorder Pseudothecosomata becomes the superfamily Cymbulioidea. The family Peraclididae is included in the superfamily Cymbulioidea as the family Peraclidae, making the superfamily Peraclidoidea redundant.

title: Sea butterfly


text:
Positronium

Positronium (Ps) is a system consisting of an electron and its anti-particle, a positron, bound together into an exotic atom, specifically an onium. Unlike hydrogen, the system has no protons. The system is unstable: the two particles annihilate each other to predominantly produce two or three gamma-rays, depending on the relative spin states. The energy levels of the two particles are similar to that of the hydrogen atom (which is a bound state of a proton and an electron). However, because of the reduced mass, the frequencies of the spectral lines are less than half of those for the corresponding hydrogen lines.

States
The mass of positronium is 1.022 MeV, which is twice the electron mass minus the binding energy of a few eV. The lowest energy orbital state of positronium is 1S, and like with hydrogen, it has a hyperfine structure arising from the relative orientations of the spins of the electron and the positron.

The singlet state,, with antiparallel spins (S = 0, Ms = 0) is known as para-positronium (p-Ps). It has a mean lifetime of $0.12 ns$ and decays preferentially into two gamma rays with energy of $511 keV$ each (in the center-of-mass frame). Para-positronium can decay into any even number of photons (2, 4, 6, ...), but the probability quickly decreases with the number: the branching ratio for decay into 4 photons is $1.439$.

Para-positronium lifetime in vacuum is approximately $$t_0 = \frac{2 \hbar}{m_\mathrm{e} c^2 \alpha^5} = 0.1244 ~\mathrm{ns}.$$

The triplet states, 3S1, with parallel spins (S = 1, Ms = −1, 0, 1) are known as ortho-positronium (o-Ps), and have an energy that is approximately 0.001 eV higher than the singlet. These states have a mean lifetime of $142.05 ns$, and the leading decay is three gammas. Other modes of decay are negligible; for instance, the five-photons mode has branching ratio of ≈$$.

Ortho-positronium lifetime in vacuum can be calculated approximately as: $$t_1 = \frac{\frac{1}{2} 9 h}{2 m_\mathrm{e} c^2 \alpha^6 (\pi^2 - 9)} = 138.6 ~\mathrm{ns}.$$

However more accurate calculations with corrections to O(α2) yield a value of $7.04 us$−1 for the decay rate, corresponding to a lifetime of $142 ns$.

Positronium in the 2S state is metastable having a lifetime of $1,100 ns$ against annihilation. The positronium created in such an excited state will quickly cascade down to the ground state, where annihilation will occur more quickly.

Measurements
Measurements of these lifetimes and energy levels have been used in precision tests of quantum electrodynamics, confirming quantum electrodynamics (QED) predictions to high precision.

Annihilation can proceed via a number of channels, each producing gamma rays with total energy of $1,022 keV$ (sum of the electron and positron mass-energy), usually 2 or 3, with up to 5 gamma ray photons recorded from a single annihilation.

The annihilation into a neutrino–antineutrino pair is also possible, but the probability is predicted to be negligible. The branching ratio for o-Ps decay for this channel is $6.2$ (electron neutrino–antineutrino pair) and $9.5$ (for other flavour) in predictions based on the Standard Model, but it can be increased by non-standard neutrino properties, like relatively high magnetic moment. The experimental upper limits on branching ratio for this decay (as well as for a decay into any "invisible" particles) are <$4.3$ for p-Ps and <$4.2$ for o-Ps.

Energy levels
While precise calculation of positronium energy levels uses the Bethe–Salpeter equation or the Breit equation, the similarity between positronium and hydrogen allows a rough estimate. In this approximation, the energy levels are different because of a different effective mass, μ, in the energy equation (see electron energy levels for a derivation): $$E_n = -\frac{\mu q_\mathrm{e}^4}{8 h^2 \varepsilon_0^2} \frac{1}{n^2},$$ where:

 * $q_{e}$ is the charge magnitude of the electron (same as the positron),
 * $h$ is the Planck constant,
 * $ε_{0}$ is the electric constant (otherwise known as the permittivity of free space),
 * $μ$ is the reduced mass: $$\mu = \frac{m_\mathrm{e} m_\mathrm{p}}{m_\mathrm{e} + m_\mathrm{p}} = \frac{m_\mathrm{e}^2}{2m_\mathrm{e}} = \frac{m_\mathrm{e}}{2},$$ where $m_{e}$ and $m_{p}$ are, respectively, the mass of the electron and the positron (which are the same by definition as antiparticles).

Thus, for positronium, its reduced mass only differs from the electron by a factor of 2. This causes the energy levels to also roughly be half of what they are for the hydrogen atom.

So finally, the energy levels of positronium are given by $$ E_n = -\frac{1}{2} \frac{m_\mathrm{e} q_\mathrm{e}^4}{8 h^2 \varepsilon_0^2} \frac{1}{n^2} = \frac{-6.8~\mathrm{eV}}{n^2}.$$

The lowest energy level of positronium ($n = 1$) is $-6.8 eV$. The next level is $-1.7 eV$. The negative sign is a convention that implies a bound state. Positronium can also be considered by a particular form of the two-body Dirac equation; Two particles with a Coulomb interaction can be exactly separated in the (relativistic) center-of-momentum frame and the resulting ground-state energy has been obtained very accurately using finite element methods of Janine Shertzer. Their results lead to the discovery of anomalous states. The Dirac equation whose Hamiltonian comprises two Dirac particles and a static Coulomb potential is not relativistically invariant. But if one adds the $1⁄c^{2n}$ (or $α^{2n}$, where $α$ is the fine-structure constant) terms, where $n = 1,2...$, then the result is relativistically invariant. Only the leading term is included. The $α^{2}$ contribution is the Breit term; workers rarely go to $α^{4}$ because at $α^{3}$ one has the Lamb shift, which requires quantum electrodynamics.

Formation and decay in materials
After a radioactive atom in a material undergoes a β+ decay (positron emission), the resulting high-energy positron slows down by colliding with atoms, and eventually annihilates with one of the many electrons in the material. It may however first form positronium before the annihilation event. The understanding of this process is of some importance in positron emission tomography. Approximately:
 * ~60% of positrons will directly annihilate with an electron without forming positronium. The annihilation usually results in two gamma rays. In most cases this direct annihilation occurs only after the positron has lost its excess kinetic energy and has thermalized with the material.
 * ~10% of positrons form para-positronium, which then promptly (in ~0.12 ns) decays, usually into two gamma rays.
 * ~30% of positrons form ortho-positronium but then annihilate within a few nanoseconds by 'picking off' another nearby electron with opposing spin. This usually produces two gamma rays. During this time, the very lightweight positronium atom exhibits a strong zero-point motion, that exerts a pressure and is able to push out a tiny nanometer-sized bubble in the medium.
 * Only ~0.5% of positrons form ortho-positronium that self-decays (usually into three gamma rays). This natural decay rate of ortho-positronium is relatively slow (~140 ns decay lifetime), compared to the aforementioned pick-off process, which is why the three-gamma decay rarely occurs.

History

The Croatian physicist Stjepan Mohorovičić predicted the existence of positronium in a 1934 article published in Astronomische Nachrichten, in which he called it the "electrum". Other sources incorrectly credit Carl Anderson as having predicted its existence in 1932 while at Caltech. It was experimentally discovered by Martin Deutsch at MIT in 1951 and became known as positronium. Many subsequent experiments have precisely measured its properties and verified predictions of quantum electrodynamics.

A discrepancy known as the ortho-positronium lifetime puzzle persisted for some time, but was resolved with further calculations and measurements. Measurements were in error because of the lifetime measurement of unthermalised positronium, which was produced at only a small rate. This had yielded lifetimes that were too long. Also calculations using relativistic quantum electrodynamics are difficult, so they had been done to only the first order. Corrections that involved higher orders were then calculated in a non-relativistic quantum electrodynamics.

In 2024, the AEgIS collaboration at CERN was the first to cool positronium by laser light, leaving it available for experimental use. The substance was brought to -100 C using laser cooling.

Exotic compounds
Molecular bonding was predicted for positronium. Molecules of positronium hydride (PsH) can be made. Positronium can also form a cyanide and can form bonds with halogens or lithium.

The first observation of di-positronium (Ps2) molecules—molecules consisting of two positronium atoms—was reported on 12 September 2007 by David Cassidy and Allen Mills from University of California, Riverside.

Unlike muonium, positronium does not have a nucleus analogue, because the electron and the positron have equal masses. Consequently, while muonium tends to behave like a light isotope of hydrogen, positronium shows large differences in size, polarisability, and binding energy from hydrogen.

Natural occurrence
The events in the early universe leading to baryon asymmetry predate the formation of atoms (including exotic varieties such as positronium) by around a third of a million years, so no positronium atoms occurred then.

Likewise, the naturally occurring positrons in the present day result from high-energy interactions such as in cosmic ray–atmosphere interactions, and so are too hot (thermally energetic) to form electrical bonds before annihilation.

title: Positronium


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National parks of Scotland

The national parks of Scotland (Pàirc Nàiseanta) are managed areas of outstanding landscape where some forms of development are restricted to preserve the landscape and natural environment. At present, Scotland has two national parks: Loch Lomond and The Trossachs National Park, created in 2002, and the Cairngorms National Park, created in 2003.

Unlike the national parks of many other countries, the national parks of Scotland are not areas of uninhabited land owned by the state. The majority of the land is in the ownership of private landowners (including conservation bodies such as the National Trust for Scotland), and people continue to live and work in the parks. Although the landscapes often appear "wild" in character, the land is not wilderness, as it has been worked by humans for thousands of years. Like their English and Welsh counterparts the national parks of Scotland are effectively "managed landscapes", and are classified as IUCN Category V Protected Landscapes because of this. National parks are only one of a number of designations used to protect and conserve the landscape and natural environment of Scotland. Public access to all land in Scotland is governed by the Land Reform (Scotland) Act 2003, which grants the public the freedom to roam on most land (and water) for activities such as walking, camping, cycling, canoeing, swimming and climbing; this right applies to land regardless of ownership or whether or not it is in a national park, providing it is exercised responsibly (as defined by the Scottish Outdoor Access Code).

History
The concept of national parks was first proposed in the United States in the 1860s, where national parks were established to protect wilderness areas such as Yosemite. Scottish-born John Muir was early advocate for the preservation of wilderness in the United States, and is acknowledged as a leading figure in the formation of national parks in the US, as well as the conservation movement at large. Many other countries have since gone on to form national parks on the basis of setting aside areas of wilderness. Scotland however, lacks any such areas, as thousands of years of human activity have altered the landscape. Human settlement and activity, including agriculture, historical deforestation, overgrazing by sheep and deer, and extensive 20th century afforestation with introduced tree species (particularly conifers) have resulted in landscapes which are semi-natural.

Nonetheless, the idea that areas of wild or remote character should be designated to protect the environment and encourage public access grew in popularity throughout the nineteenth and early twentieth centuries. In 1931 a commission headed by Christopher Addison proposed the creation of a national park in the Cairngorms, alongside proposals for parks in England and Wales. Following the Second World War, the Labour government passed the National Parks and Access to the Countryside Act 1949, which led to the creation of 10 national parks in England and Wales between 1951 and 1957. No parks were created in Scotland, however a committee, chaired by Sir Douglas Ramsay, was established to consider the issue of national parks in Scotland. The report, published in 1945, proposed national parks in five areas: Loch Lomond & the Trossachs, the Cairngorms, Glen Coe-Ben Nevis-Black Mount, Wester Ross and Glen Strathfarrar-Glen Affric-Glen Cannich. The government designated these areas as "National Park Direction Areas", giving powers for planning decisions taken by local authorities to be reviewed by central government, however the areas were not given full national park status. In 1981 the direction areas were replaced by national scenic areas, of which there are now 40. Although the national scenic area designation provided a degree of additional protection via the planning process, there are no bodies equivalent to a national park authority, and whilst local authorities can produce a management strategy for each one, only the three national scenic areas within Dumfries and Galloway have current management strategies.

A 1974 report by the Countryside Commission for Scotland (CCS) entitled A Park System for Scotland did not explicitly recommend that national parks be established in Scotland, noting only that the issue would “no doubt continue to be debated”. A further CCS report into protection of the landscape of Scotland, The Mountain Areas of Scotland - Conservation and Management, was published in 1990. It recommended that four areas were under such pressure that they ought to be designated as national parks, each with an independent planning board, in order to retain their heritage value. The four areas identified were similar to those proposed by the Ramsay Committee: Loch Lomond & the Trossachs, the Cairngorms, Glen Coe-Ben Nevis-Black Mount and Wester Ross, although Wester Ross was not considered to require a dedicated planning body.

Despite this long history of recommendations that national parks be established in Scotland, no action was taken until the establishment of the Scottish Parliament in 1999. The two current parks were designated as such under the National Parks (Scotland) Act 2000, which was one of the first pieces of legislation to be passed by the Parliament. Since the original creation of the first two national parks, no further parks have been created, although the Cairngorms National Park was extended in 2010 to include the highland portion of Perthshire.

Proposals for additional parks
In June 2005, the Scottish Executive announced their intention to create Scotland's first coastal and marine national park. Five possible locations for this were considered, however no marine park has been established as of 2023.
 * Solway Firth
 * Argyll Islands and Coast
 * Ardnamurchan, Small Isles and South Skye Coast
 * North Skye Coast and Wester Ross
 * North Uist, Sound of Harris, Harris and South Lewis

In 2011 the Scottish Government rejected a proposal to create a national park on the Isle of Harris. In 2013 the Scottish Campaign for National Parks proposed the seven areas listed below as suitable for national park status, however no further parks were subsequently designated.

 * Harris
 * Wester Ross
 * Glen Affric
 * Mull and the Small Isles – to be a marine park
 * Ben Nevis, Glen Coe and the Black Mount
 * Galloway
 * Cheviot Hills

The power sharing arrangement agreed between the Scottish National Party and the Scottish Greens following the 2021 Scottish Parliament election committed the government to designate at least one additional national park by 2026. Areas that wish to be consider for national park status have been invited to submit applications between October 2023 and February 2024. As of October 2023, councils and local groups from the following areas are considering applications:

 * Galloway
 * Scottish Borders
 * Tay Forest
 * Ben Nevis and Lochaber
 * Eilean a' Cheo (Skye and Raasay)
 * Affric to Alladale
 * Glen Affric
 * Lammermuir Hills
 * Largo Bay
 * Loch Awe

Organisation
Each national park in Scotland is administered by a national park authority. Under the National Parks (Scotland) Act 2000, national parks in Scotland have four aims:
 * 1) To conserve and enhance the natural and cultural heritage of the area
 * 2) To promote sustainable use of the natural resources of the area
 * 3) To promote understanding and enjoyment (including enjoyment in the form of recreation) of the special qualities of the area by the public
 * 4) To promote sustainable economic and social development of the area's communities

The first two of these aims are identical to those included in the National Parks and Access to the Countryside Act 1949 legislation that governs national parks in England and Wales, however the Scottish national parks have two additional aims (3 and 4 above). The general purpose of the national park authority, as defined in the National Parks (Scotland) Act 2000, is to ensure that these aims are "collectively achieved ...in a coordinated way". Although the four aims have equal status, in accordance with the Sandford Principle, the first aim (conservation and enhancement of the natural and cultural heritage) is to be given greater weight when it appears to the park authority that there is irreconcilable conflict with the other aims.

A key function of the authority relates to planning permission: in this respect the two current Scottish parks differ. The Loch Lomond and The Trossachs National Park is a full planning authority, exercising powers that would otherwise be exercised by the local authority, whilst the Cairngorms National Park has the power to "call in" planning decisions from the local authority where they are considered to conflict with the aims of the park. National park authorities are also required to take the responsibility for managing access to the countryside that elsewhere falls to local authorities.

Aside from the planning and access function, national parks authorities have considerable flexibility as to how the four aims are achieved. They can, for example, acquire land, make byelaws and management agreements, provide grants, offer advice, and undertake or commission research.

The national park authority is run by a board, consisting of members elected by the community living with the park, members from the local authorities with areas in the park, and members appointed by the Scottish government. The Cairngorms National Park board has 19 members, whilst the Loch Lomond and The Trossachs National Park board has 17 members (see below).

title: National parks of Scotland


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Chalcedony

Chalcedony (, or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic. Chalcedony's standard chemical structure (based on the chemical structure of quartz) is SiO2 (silicon dioxide).

Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a wide range of colors, but those most commonly seen are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black. The color of chalcedony sold commercially is often enhanced by dyeing or heating.

The name chalcedony comes from the Latin (alternatively spelled calchedonius) and is probably derived from the town of Chalcedon in Turkey. The name appears in Pliny the Elder's Naturalis Historia as a term for a translucent kind of jaspis. Another reference to a gem by the name of khalkedón is found in the Book of Revelation (21:19); however, it is a hapax legomenon, found nowhere else in the Bible, so it is hard to tell whether the precious gem mentioned in Revelation is the same as the mineral known by this name today. The term plasma is sometimes used to refer to green translucent chalcedony.

Varieties
Chalcedony occurs in a wide range of varieties. Many semi-precious gemstones are in fact forms of chalcedony. The more notable varieties of chalcedony are as follows:

Agate
Agate is a variety of chalcedony characterized by either transparency or color patterns, such as multi-colored curved or angular banding. Opaque varieties are sometimes referred to as jasper. Fire agate shows iridescent phenomena on a brown background; iris agate shows exceptional iridescence when light (especially pinpointed light) is shone through the stone. Landscape agate is chalcedony with a number of different mineral impurities making the stone resemble landscapes.

Carnelian
Carnelian (also spelled cornelian) is a clear-to-translucent reddish-brown variety of chalcedony. Its hue may vary from a pale orange to an intense almost-black coloration. Similar to carnelian is sard, which is brown rather than red.

Chrysoprase
Chrysoprase (also spelled chrysophrase) is a green variety of chalcedony, which has been colored by nickel oxide. (The darker varieties of chrysoprase are also referred to as prase. However, the term prase is also used to describe green quartz and to a certain extent is a color-descriptor, rather than a rigorously defined mineral variety.)

Blue-colored chalcedony is sometimes referred to as "blue chrysoprase" if the color is sufficiently rich, though it derives its color from the presence of copper and is largely unrelated to nickel-bearing chrysoprase.

Fire agate

Fire agate is a variety of chalcedony with inclusions of goethite or limonite causing an iridescent effect. It can display a wide range of iridescent colors including red, orange, yellow, green, blue, and purple.

Heliotrope
Heliotrope is a green variety of chalcedony, containing red inclusions of iron oxide that resemble drops of blood, giving heliotrope its alternative name of bloodstone. In a similar variety, the spots are yellow instead, known as plasma.

Moss agate
Moss agate contains green filament-like inclusions, giving it the superficial appearance of moss or blue cheese. There is also tree agate which is similar to moss agate except it is solid white with green filaments whereas moss agate usually has a transparent background, so the "moss" appears in 3D. It is not a true form of agate, as it lacks agate's defining feature of concentric banding.

Chrome chalcedony
Chrome chalcedony is a green variety of chalcedony, which is colored by chromium compounds. It is also known as "mtorolite" when found in Zimbabwe and "chiquitanita" when found in Bolivia.

Onyx
Onyx is a variant of agate with black and white banding. Similarly, agate with brown, orange, red and white banding is known as sardonyx.

Chalcedony ice-blue
In Greenland, white to greyish chalcedony is known from volcanic strata of the Paleocene, in the Disko-Nuussuaq area (West Greenland) and from the Scoresby Sound area (East Greenland). A light blue variety of chalcedony is known from Illorsuit, formed in the volcanic rocks along the southern coast of the island. Because of its bluish, ice-like colour, it has the local name chalcedony "ice-blue".

History
Chalcedony was used in tool making as early as 32,000 BP in Central Australia where archaeological studies at sites in the Cleland Hills uncovered flakes from stone brought in from quarries many kilometres away. Pre-contact uses described in the twentieth century included ceremonial stone knives.

Chalcedony was used for green and yellow color in prehistoric cave paintings, for example at the Bhimbetka rock shelters. The chalcedony was ground to powder form then mixed with water and animal fat or tree resin or gum.

In the Bronze Age chalcedony was in use in the Mediterranean region; for example, on Minoan Crete at the Palace of Knossos, chalcedony seals have been recovered dating to circa 1800 BC. People living along the Central Asian trade routes used various forms of chalcedony, including carnelian, to carve intaglios, ring bezels (the upper faceted portion of a gem projecting from the ring setting), and beads that show strong Greco-Roman influence.

Fine examples of first century objects made from chalcedony, possibly Kushan, were found in recent years at Tillya-tepe in north-western Afghanistan. Hot wax would not stick to it so it was often used to make seal impressions. The term chalcedony is derived from the name of the ancient Greek town Chalkedon in Asia Minor, in modern English usually spelled Chalcedon, today the Kadıköy district of Istanbul.

According to tradition, at least three varieties of chalcedony were used in the Jewish High Priest's Breastplate. (Jewish tradition states that Moses' brother Aaron wore the Breastplate, with inscribed gems representing the twelve tribes of Israel.) The Breastplate supposedly included jasper, chrysoprase and sardonyx, and there is some debate as to whether other agates were also used.

In the 19th century, Idar-Oberstein, Germany, became the world's largest chalcedony processing center, working mostly on agates. Most of these agates were from Latin America, in particular Brazil. Originally the agate carving industry around Idar and Oberstein was driven by local deposits that were mined in the 15th century. Several factors contributed to the re-emergence of Idar-Oberstein as agate center of the world: ships brought agate nodules back as ballast, thus providing extremely cheap transport. In addition, cheap labor and a superior knowledge of chemistry allowed them to dye the agates in any color with processes that were kept secret. Each mill in Idar-Oberstein had four or five grindstones. These were of red sandstone, obtained from Zweibrücken; and two men ordinarily worked together at the same stone.

Structure
Chalcedony was once thought to be a fibrous variety of cryptocrystalline quartz. More recently however, it has been shown to also contain a monoclinic polymorph of quartz, known as moganite. The fraction, by mass, of moganite within a typical chalcedony sample may vary from less than 5% to over 20%. The existence of moganite was once regarded as dubious, but it is now officially recognised by the International Mineralogical Association.

Solubility
Chalcedony is more soluble than quartz under low-temperature conditions, despite the two minerals being chemically identical. Possible reasons include the existence of the moganite component, defects caused by Brazil twinning, and small crystal size.

Solubility of quartz and chalcedony in pure water
This table gives equilibrium concentrations of total dissolved silicon as calculated by PHREEQC (PH REdox EQuilibrium (in C language, USGS)) using the llnl.dat database.

title: Chalcedony


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Carnelian

Carnelian (also spelled cornelian) is a brownish-red mineral commonly used as a semiprecious stone. Similar to carnelian is sard, which is generally harder and darker; the difference is not rigidly defined, and the two names are often used interchangeably. Both carnelian and sard are varieties of the silica mineral chalcedony colored by impurities of iron oxide. The color can vary greatly, ranging from pale orange to an intense almost-black coloration. Significant localities include Yanacodo (Peru); Ratnapura (Sri Lanka); and Thailand. It has been found in Indonesia, Brazil, India, Russia (Siberia), and Germany. In the United States, the official State Gem of Maryland is also a variety of carnelian called Patuxent River stone.

History

The red variety of chalcedony has been known to be used as beads since the Early Neolithic in Bulgaria. The first faceted (with constant 16+16=32 facets on each side of the bead) carnelian beads are described from the Varna Chalcolithic necropolis (middle of the 5th millennium BC). The bow drill was used to drill holes into carnelian in Mehrgarh in the 4th–5th millennium BC. Carnelian was recovered from Bronze Age Minoan layers at Knossos on Crete in a form that demonstrated its use in decorative arts; this use dates to approximately 1800 BC. Carnelian was used widely during Roman times to make engraved gems for signet or seal rings for imprinting a seal with wax on correspondence or other important documents, as hot wax does not stick to carnelian. Sard was used for Assyrian cylinder seals, Egyptian and Phoenician scarabs, and early Greek and Etruscan gems. The Hebrew odem (also translated as sardius), was mounted on both shoulder's of the High Priest's robe, also it was the first stone in the High Priest's breastplate, was a red stone, probably sard but perhaps red jasper. In Revelation 4:3, the One seated on the heavenly throne seen in the vision of John the apostle is said to "look like jasper and σαρδίῳ (sardius transliterated)." And likewise it is in Revelation 21:20 as one of the precious stones in the foundations of the wall of the heavenly city.

There is a Neo-Assyrian seal made of carnelian in the Western Asiatic Seals collection of the British Museum that shows Ishtar-Gula as a star goddess. She is holding a ring of royal authority and is seated on a throne. She is shown with the spade of Marduk (his symbol), Sibbiti (seven) gods, the stylus of Nabu and a worshiper. An 8th century BC carnelian seal from the collection of the Ashmolean Museum shows Ishtar-Gula with her dog facing the spade of Marduk and his red dragon.

Etymology
Although now the more common term, "carnelian" is a 16th-century corruption of the 14th-century word "cornelian" (and its associated orthographies corneline and cornalyn). Cornelian, cognate with similar words in several Romance languages, comes from the Mediaeval Latin corneolus, itself derived from the Latin word cornum, the cornel cherry, whose translucent red fruits resemble the stone. The Oxford English Dictionary calls "carnelian" a perversion of "cornelian," by subsequent analogy with the Latin word caro, carnis ("flesh"). According to Pliny the Elder, sard derived its name from the city of Sardis in Lydia from which it came, and according to others, may ultimately be related to the Persian word سرد (sered, "yellowish-red"). Another possible derivation is from the Greek σάρξ (sarx, "flesh"); compare the surer etymology of onyx, which comes from Greek ὄνυξ (onyx, "claw, fingernail"), presumably because onyx with flesh-colored and white bands can resemble a fingernail.

Distinction between carnelian and sard
The names carnelian and sard are often used interchangeably, but they can also be used to describe distinct subvarieties. The general differences are as follows: All of these properties vary across a continuum, so the boundary between carnelian and sard is inherently blurry.

title: Carnelian