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Nanotechnology/Nanomanipulation

=Nanomanipulation=
 * Wikipedia Nanorobotics
 * Nanorobotics introduction
 * Video clips of Nanomanipulation on YouTube
 * Pick and Place of NW in SEM on YouTube
 * Video of the manipulation of a nanowire for TEM observation on YouTube

=AFM manipulation= With AFM nanostructures such as nanotubes and nanowires lying on surfaces can be manipulated to make electrical circuits and measure their mechanical properties and the forces involved in manipulating them.

=STM manipulation= Using an STM individual atoms can be manipulated on surface this was first demonstrated by Eigler et al. Here Xe atoms were manipulated on Ni to spell out IBM. This was then extended by Crommie et al., where Fe atoms were moved to create quantum corals. Here the electron standing waves created inside the corral are imaged by the STM tip. The probably demonstrates the highest resolution nanomanipulation.

=In-situ SEM manipulation=

To monitor a three-dimensional nanomanipulation process, in-situ SEM or TEM manipulation seems preferable. AFM (or STM) does have the resolution to image nanoscale objects, even down to the sub-atomic scale, but the imaging frame rate is usually slow compared to SEM or TEM and the structures will normally have to be planar. SEM offers the possibility of high frame rates; almost nanometer resolution imaging of three-dimensional objects; imaging over a large range of working distances; and ample surrounding volume in the sample chamber for the manipulation setup. TEM has a much more limited space available for the sample and manipulation systems but can on the other hand provide atomic resolution. For detailed studies of the nanowires' structure, TEM is a useful tool, but for the assembly of nanoscale components of a well defined structure, such as batch fabricated nanowires and nanotubes, the SEM resolution should be sufficient to complete the assembly task.

As the STM and AFM techniques opened up completely new fields of science by allowing the investigator to interact with the sample rather than just observe, development of nanomanipulation tools for SEM and TEM could probably have a similar effect for three-dimensional manipulation. Recently, commercial systems for such tasks have become available such as the F100 Nanomanipulator System from Zyvex in October 2003. Several research groups have also pursued developing such systems.

To date the tools used for in-situ SEM nanomanipulation have almost exclusively been individual tips (AFM cantilever tips or etched tungsten tips), sometimes tips used together with electron beam deposition have been used to create nanowire devices. Despite the availability of commercial microfabricated grippers in the last couple of years, little has been reported on the use of such devices for handling nanostructures. Some electrical measurements and manipulation tasks have been performed in ambient conditions with carbon nanotube nanotweezers.

Companies selling hardware

 * Omniprobe
 * Zyvex
 * Imina Technologies

The Optimal SEM Image for Nanomanipulation
As the typical SEM image is created from the secondary electrons collected from the sample, compromises must always be made to obtain the optimal imaging conditions regarding resolution and contrast. The contrast in a SEM SE image depends on the variations in SE yield from the different surface regions in the image and the signal to noise level. The resolution depends on the beam diameter and is at least some nm larger due to the SE range.

The optimal solution is always to use as good an emitter as possible (high ß_{e} in Eq. ). This means using FEG sources. Working at short r_{wd} gives a narrow beam (Eq. ), but will usually shield the standard ET detectors from attracting sufficient secondary electrons. Nanomanipulation often requires working with high resolution between two large manipulator units which further limits the efficiency of signal detection.

The manipulation equipment must be designed to make the end-effector and samples meet at short r_{wd}, and without obstructing the electron path towards the detector. A short r_{wd} also gives a short depth of focus, which can be a help during nanomanipulation because it makes it possible to judge the working distance to various objects by focussing on them. The operator can use this to get an impression of the height of the objects in the setup. Generally, for nanomanipulation, the above considerations indicate an inlens detector often can be advantageous.

Reducing the beam current to narrow the electron beam necessarily limits the number of detected electrons and make the signal-to-noise ratio low, unless one makes very slow scans to increase the number of counts

The signal to noise ratio S/N for Poisson distributed count measurements n is S/N=vn and high counts are necessary to reduce noise in the images. .

When used for in-situ nanomanipulation one needs a fast scan rate to follow the moving tools (preferably at rates approaching live video) and this requires high beam currents. The acceleration voltage is also important, and too high PE energy can make the sample transparent (such as the carbon coating in Fig. b) while low energy usually make the image susceptible to drift due to charging and similar effects.

=In-situ TEM manipulation= TEM offers atomic 3D resolution but the extreme requirements on stability combined with very limited sample space makes the construction of in-situ TEM manipulation equipment quite a task. With such systems, people have observed freely suspended wires of individual atoms between a gold tip and a gold surface; carbon nanotubes working as nanoscale pipettes for metals and a wealth of other exotic phenomena.

Companies selling hardware
 * Nanofactory

=References=

See also notes on editing this book about how to add references Nanotechnology/About.

title: Nanotechnology/Nanomanipulation


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Nanotechnology/Biosensors

=Biosensors= Biological sensor functionalisation, receptors and signals
 * Assays for measuring the biochemical properties, such as immunesystem responses, specific proteins etc.
 * DNA binding protein
 * Functional group
 * Receptor biochemistry
 * Neuron
 * The Biotin -  Streptavidin binding is the strongest biochemical bond and often used when you need to demonstrate a sensor or bind different biomolecules together.
 * Biofouling - by using certain polymers such as PEG or PLL-PEG, cell adhesion to surface can be drastically reduced.

DNA Biosensors
In the future, DNA will find use as a versatile material from which scientists can craft biosensors. DNA biosensors can theoretically be used for medical diagnostics, forensic science, agriculture, or even environmental clean-up efforts. No external monitoring is needed for DNA-based sensing devices. This is a significant advantage. DNA biosensors are complicated mini-machines—consisting of sensing elements, micro lasers, and a signal generator. At the heart of DNA biosensor function is the fact that two strands of DNA stick to each other by virtue of chemical attractive forces. On such a sensor, only an exact fit—that is, two strands that match up at every nucleotide position—gives rise to a fluorescent signal (a glow) that is then transmitted to a signal generator.

=Resources= . *Performance limits of nanobiosensors App. Phys. Lett. 88, 233120, 2006.

=References= "The Chemistry of Health." The Chemistry of Health (2006): 42-43. National Institutes of Health and National Institute of General Medical Sciences. Web

See also notes on editing this book about how to add references Nanotechnology/About.

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

title: Nanotechnology/Biosensors


text:
Nanotechnology/Health effects of nanoparticles

=Nanotoxicology: Health effects of nanotechnology=

The environmental impacts of nanotechnology have become an increasingly active area of research.

Until recently the potential negative impacts of nanomaterials on human health and the environment have been rather speculative and unsubstantiated.

However, within the past number of years several studies have indicated that exposure to specific nanomaterials, e.g. nanoparticles, can lead to a gamut of adverse effects in humans and animals, , .

This has made some people very concerned drawing specific parallels to past negative experiences with small particles ,.

Some types of nanoparticles are expected to be benign and are FDA approved and used for making paints and sunscreen lotion etc. However, there are also dangerous nanosized particles and chemicals that are known to accumulate in the food chain and have been known for many years:
 * Asbestos
 * Diesel particulate matter
 * ultra fine particles
 * DDT
 * lead

The problem is that it is difficult to extrapolate experience with bulk materials to nanoparticles because their chemical properties can be quite different. For instance, anti-bacterial silver nanoparticles dissolve in acids that would not dissolve bulk silver, which indicates their increased reactivity.

An overview of some exposure cases for humans and the environment shown in the table. For an overview of nanoproducts see the section Nanotech Products in this book.

The peer-reviewed journal Nanotoxicology is dedicated to Research relating to the potential for human and environmental exposure, hazard and risk associated with the use and development of nano-structured materials. Other journals also report on the research, for see the full Nano-journal list in this book.

Nanoecotoxicology
In response to the above concerns a new field of research has emergence termed “nano(eco-)toxiciolgoy” defined as the “science of engineered nanodevices and nanostructures that deals with their effects in living organisms” .

In the following we will first try to explain why some people are concerned about nanomaterials and especially nanoparticles. This will lead to a general presentation of what is known about the hazardous properties of nanoparticles in the field of the environment and nanoecotoxicology. This includes a discussion of the main areas of uncertainty and gaps of knowledge.

Human or ecotoxicology
The focus of this chapter is on the ecotoxicological - and environmental effects of nanomaterials, however references will be made to studies on human toxicology where it is assumed that such analogies are warranted or if studies have provided new insights that are relevant to the field of nanoecotoxicology as well. As further investigations are made, more knowledge will be gained about human toxicology of nanoparticles.

=Production and applications of nanotechnology=

At present the global production of nanomaterials is hard to estimate for three main reasons:
 * Firstly, the definition of when something is “nanotechnology” is not clear-cut.
 * Secondly, nanomaterials are used in a great diversity of products and industries and
 * Thirdly, there is a general lack of information about what and how much is being produced and by whom.

In 2001 the future global annual production of carbon-based nanomaterials was estimated to be several hundred tons, but already in 2003 the global production of nanotubes alone was estimated to be around 900 tons distributed between 16 manufacturers .

The Japanese company, Frontier Carbon Corp, plan to start an annual production of 40 tons of C60 .

It is estimated that the global annual production of nanotubes and fiber was 65 tons equal to €144 million worth and it is expected to surpass €3 billion by 2010 representing an annual growth rate of well over 60% .

Even though the information about the production of carbon-based nanomaterials is scarce, the annual production volumes of for instance quantum dots, nano-metals, and materials with nanostructured surfaces are completely unknown.

The development of nanotechnology is still in its infancy, and the current production and use of nanomaterials is most likely not representative for the future use and production. Some estimates for the future manufacturing of nanomaterials have been made. For instance the Royal Society and the Royal Academy of Engineering estimated that nanomaterials used in relation to environmental technology alone will increase from 10 tons per year in 2004 to between 1000-10.000 tons per year before 2020. However, the basis of many of these estimations is often highly unclear and the future production will depend on a number of things such as for instance:

 * 1) Whether the use of nanomaterials indeed entails the promised benefits in the long run;
 * 2) which and how many different applications and products will eventually be developed and implemented;
 * 3) And on how nanotechnology is perceived and embraced by the public?

With that said, the expectations are enormous. It is estimated that the global market value of nano-related products will be U.S. $1 trillion in 2015 and that potentially 7 million jobs will be created globally ,

=Exposure of environment and humans= Exposure of nanomaterials to workers, consumers, and the environment seems inevitable with the increasing production volumes and the increasing number of commercially available products containing nanomaterials or based on nanotechnology .

Exposure is a key element in risk assessment of nanomaterials since it is a precondition for the potential toxicological and ecotoxicological effects to take place. If there is no exposure – there is no risk. Nanoparticles are already being used in various products and the exposure can happen through multiple routes.

Human routes of exposure are:
 * dermal (for instance through the use of cosmetics containing nanoparticles);
 * inhalation (of nanoparticles for instance in the workplace);
 * ingestion (of for instance food products containing nanoparticles);
 * and injection (of for instance medicine based on nanotechnology).

Although there are many different kinds of nanomaterials, concerns have mainly been raised about free nanoparticles ,.

Free nanoparticles could either get into the environment through direct outlet to the environment or through the degradation of nanomaterials (such as surface bound nanoparticles or nanosized coatings).

Environmental routes of exposure are multiple.

One route is via the wastewater system. At the moment research laboratories and manufacturing companies must be assumed to be the main contributor of carbon-based nanoparticles to the wastewater outlet.

For other kinds of nanoparticles for instance titanium dioxide and silver, consumer products such as cosmetics, crèmes and detergents, is a key source already and discharges must be assumed to increase with the development of nanotechnology.

However, as development and applications of these materials increases this exposure pattern must be assumed to change dramatically. Traces of drugs and medicine based on nanoparticles can also be disposed of through the wastewater system into the environment.

Drugs are often coated, and studies have show that these coatings can be degraded through either metabolism inside the human body or transformation in environment due to UV-light . Which only emphasises the need to studying the many possible process that will alter the properties of nanoparticles once they are released in nature.

Another route of exposure to the into the environment is from wastewater overflow or if there is an outlet from the wastewater treatment plant where nanoparticles are not effectively held back or degraded.

Additional routes of environmental exposure are spills from production, transport, and disposal of nanomaterials or products .

While many of the potential routes of exposure are uncertain scenarios, which need confirmation, the direct application of nanoparticles, such as for instance nano zero valent iron for remediation of polluted areas or groundwater, is one route of exposure that will certainly lead to environmental exposure. Although, remediation with the help of free nanoparticles is one of the most promising environmental nanotechnologies, it might also be one the one raising the most concerns. The Royal Society and The Royal Academy of Engineering actually recommend that the use of free nanoparticles in environmental applications such as remediation should be prohibited until it has been shown that the benefits outweigh the risks.

The presence of manufactured nanomaterials in the environment is not widespread yet, it is important to remember that the concentration of xenobiotic organic chemicals in the environment in the past has increased proportionally with the application of these – meaning that it is only a question of time before we will find nanomaterials such as nanoparticles in the environment – if we have the means to detect them.

The size of nanoparticles and our current lack of metrological methods to detect them is a huge potential problem in relation to identification and remediation both in relation to their fate in the human body and in the environment.

Once there is a widespread environmental exposure human exposure through the environment seems almost inevitable since water- and sediment living organisms can take up nanoparticles from water or by ingestion of nanoparticles sorbed to the vegetation or sediment and thereby making transport of nanoparticles up through the food chain possible .

=Nanoecotoxicology= Despite the widespread development of nanotechnology and nanomaterials through the last 10-20 years, it is only recently that focus has been turned onto the potential toxicological effects on humans, animals, and the environment through the exposure of manufactured nanomaterials .

With that being said, it is a new development that potential negative health and environmental impacts of a technology or a material is given attention at the developing stage and not after years of application .

The term “nano(eco-)toxicology” has been developed on the request of a number of scientists and is now seen as a separate scientific discipline with the purpose of generating data and knowledge about nanomaterials effects on humans and the environment , . Toxicological information and data on nanomaterials is limited and ecotoxicological data is even more limited. Some toxicological studies have been done on biological systems with nanoparticles in the form of metals, metal oxides, selenium and carbon , however the majority of toxicological studies have been done with carbon fullerenes . Only a very limited number of ecotoxicological studies have been performed on the effects of nanoparticles on environmentally relevant species, and, as for the toxicological studies, most of the studies have been done on fullerenes. However, according to the European Scientific Committee on Emerging and Newly Identified Health Risks results from human toxicological studies on the cellular level can be assumed to be applicable for organisms in the environment, even though this of cause needs further verification. In the following a summary of the early findings from studies done on bacteria, crustaceans, fish, and plants will be given and discussed.

Bacteria
The effect of nanoparticles on bacteria is very important since bacteria constitute the lowest level and hence the entrance to the food chain in many ecosystems .

The effects of C60 aggregates on two common soil bacteria E. coli (gram negative) and B. subtilis (gram positive) was investigated by Fortner et al. on rich and minimal media, respectively, under aerobe and anaerobe conditions. At concentrations above 0.4 mg/L growth was completely inhibited in both cultures exposed with and without oxygen and light. No inhibition was observed on rich media in concentration up to 2.5 mg/L, which could be due to that C60 precipitates or gets coated by proteins in the media. The importance of surface chemistry is highlighted by the observation that hydroxylated C60 did not give any response, which is in agreement with the results obtained by Sayes et al. who investigated the toxicity on human dermal- and liver cells. The antibacterial effects of C60 has furthermore been observed by Oberdorster , who observed remarkably clearer water during experiments with fish in the aquarium with 0.5 mg/L compared to control.

Lyon et al. explored the influence of four different preparation methods of C60 (stirred C60, THF-C60, toluene-C60, and PVP-C60) on Bacillus subtilis and found that all four suspensions exhibited relatively strong antibacterial activity ranging from 0.09 ± 0.01 mg/L- 0.7 ± 0.3 mg/L, and although fractions containing smaller aggregates had greater antibacterial activity, the increase in toxicity was disproportionately higher than the associated increase in surface area.

Silver nanoparticles are increasingly used as antibacterial agent

Crustacean
A number of studies have been performed with the freshwater crustacean Daphnia magna, which is an important ecological important species that furthermore is the most commonly used organisms in regulatory testing of chemicals.

The organism can filter up to 16 ml an hour, which entails contact with large amounts of water in its surroundings. Nanoparticles can be taken up via the filtration and hence could lead to potential toxic effects . Lovern and Klaper , observed some mortality after 48 hours of exposure to 35 mg/L C60 (produced by stirring and also known as “nanoC60” or “nC60”), however 50% mortality was not achieved, and hence an LC50 could not be determined . A considerable higher toxicity of LC50 = 0.8 mg/L is obtained when using nC60 put into solution via the solvent tetrahydrofuran (THF) – which might indicate that residues of THF is bound to or within the C60-aggreggates, however whether this is the case in unclear at the moment. The solubility of C60 using sonication has also been found to increase toxicity , whereas unfiltered C60 dissolved by sonication has been found to cause less toxicity (LC50 = 8 mg/L). This is attributed to the formation of aggregates, which causes a variation of the bioavailability to the different concentrations. Besides mortality, deviating behavior was observed in the exposed Daphnia magna in the form of repeated collisions with the glass beakers and swimming in circles at the surface of the water . Changes in the number of hops, heart rate, and appendage movement after subtoxic levels of exposure to C60 and other C60-derivatives . However, Titanium dioxide (TiO2) dissolved via THF has been observed to cause increased mortality in Daphania magna within 48 hours (LC50= 5.5 mg/L), but to a lesser extent than fullerenes, while unfiltered TiO2 dissolved by sonication did not results in a increasing dose-response relationship, but rather a variation response . Lovern and Klaper have furthermore investigated whether THF contributed to the toxicity by comparing TiO2 manufactured with and without THF and found no difference in toxicity and hence concluded that THF did not contribute to neither the toxicity of TiO2 or fullerenes.

Experiments with the marine species Acartia tonsa exposed to 22.5 mg/L stirred nC60 have been found to cause up to 23% mortality after 96 hours, however mortality was not significantly different from control25. And exposure of Hyella azteca by 7 mg/L stirred nC60 in 96 hours did not lead to any visible toxic effects – not even by administration of C60 through the feed .

Only a limited number of studies have investigated long-term exposure of nanoparticles to crustaceans. Chronic exposure of Daphnia magna with 2.5 mg/L stirred nC60 was observed to cause 40% mortality besides causing sub-lethal effects in the form of reduced reproducibility (fewer offspring) and delayed shift of shield . Templeton et al. observed an average cumulative life-cycle mortality of 13 ± 4% in an Estuarine Meiobenthic Copepod Amphiascus tenuiremis after being exposed to SWCNT, while mean life-cycle mortalities of 12 ± 3, 19 ± 2, 21 ± 3, and 36 ± 11 % were observed for 0.58, 0.97, 1.6, and 10 mg/L.

Exposure to 10 mg/L showed: Templeton also observed that exposure to 1.6 mg/L caused a significantly increase in development rate of 1 day faster, whereas a 6 day significant delay was seen for 10 mg/L.
 * 1) significantly increased mortalities for the naupliar stage and cumulative life-cycle;
 * 2) a dramatically reduced development success to 51% for the nauplius to copepodite window, 89% for the copepodite to adult window, and 34% overall for the nauplius to adult period;
 * 3) a significantly depressed fertilization rate averaging only 64 ± 13%.

Fish
A limited number of studies have been done with fish as test species. In a highly cited study Oberdorster found that 0.5 mg/L C60 dissolved in THF caused increased lipid peroxidation in the brain of largemouth bass (Mikropterus salmoides). Lipid peroxidation was found to be decreased in the gills and the liver, which was attributed to reparation enzymes. No protein oxidation was observed in any of the mentioned tissue, however a discharge of the antioxidant glutathione occurred in the liver possibility due to large amount of reactive oxygen molecules stemming from oxidative stress caused by C60 .

For Pimephales promelas exposured to 1 mg/L THF-dissolved C60, 100 % mortality was obtained within 18 hours, whereas 1 mg/L C60 stirred in water did not lead to any mortality within 96 hours. However, at this concentration inhibition of a gene which regulates fat metabolism was observed. No effect was observed in the species Oryzia latipes at 1 mg/L stirred C60, which indicates different inter-species sensitivity toward C60 ,.

Smith et al. observed a dose-dependent rise in ventilation rate, gill pathologies (oedema, altered mucocytes, hyperplasia), and mucus secretion with SWCNT precipitation on the gill mucus in juvenile rainbow trout.

Smith et al. also observed:
 * dose-dependent changes in brain and gill Zn or Cu, partly attributed to the solvent;
 * a significant increases in Na+K+ATPase activity in the gills and intestine;
 * a significant dose-dependent decreases in TBARS especially in the gill, brain and liver;
 * and a significant increases in the total glutathione levels in the gills (28 %) and livers (18 %), compared to the solvent control (15 mg/l SDS).
 * Finally, they observed increasing aggressive behavior; possible aneurisms or swellings on the ventral surface of the cerebellum in the brain and apoptotic bodies and cells in abnormal nuclear division in liver cells.

Recently Kashiwada 29 reported observing 35.6% lethal effect in embryos of the medaka Oryzias latipes (ST II strain) exposed to 39.4 nm polystyrene nanoparticles at 30 mg/L, but no mortality was observed during the exposure and postexposure to hatch periods at exposure to 1 mg/L. The lethal effect was observed to increase proportionally with the salinity, and 100% complete lethality occurred at 5 time higher concentrated embryo rearing medium. Kashwada also found that 474 nm particles showed the highest bioavailability to eggs, and 39.4 nm particles were confirmed to shift into the yolk and gallbladder along with embryonic development. High levels of particles were found in the gills and intestine for adult medaka exposed to 39.4 nm nanoparticles at 10 mg/L, and it is hypothesized that particles pass through the membranes of the gills and/or intestine and enter the circulation.

Plants
To our knowledge only one study has been performed on phytotoxicity, and it indicates that aluminum nanoparticles become less toxic when coated with phenatrene, which again underlines the importance to surface treatments in relation to the toxicity of nanoparticles .

=Identification of key hazard properties= Size is the general reason why nanoparticles have become a matter of discussion and concern.

The very small dimensions of nanoparticles increases the specific surface area in relation to mass, which again means that even small amounts of nanoparticles have a great surface area on which reactions could happen.

If a reaction with chemical or biological components of an organism leads to a toxic response, this response would be enhanced for nanoparticles. This enhancement of the inherent toxicity is seen as the main reason why smaller particles are generally more biologically active and toxic that larger particles of the same material .

Size can cause specific toxic response if for instance nanoparticles will bind to proteins and thereby change their form and activity, leading to inhibition or change in one or more specific reactions in the body .

Besides the increased reactivity, the small size of the nanoparticles also means that they can easier be taken up by cells and that they are taken up and distributed faster in organism compared to their larger counterparts ,.

Due to physical and chemical surface properties all nanoparticles are expected to absorb to larger molecules after uptake in an organism via a given route of uptake .

Some nanoparticles such as fullerene derivates are developed specifically with the intention of pharmacological applications because of their ability of being taken up and distributed fast in the human body, even in areas which are normally hard to reach – such as the brain tissue . Fast uptake and distribution can also be interpreted as a warning about possible toxicity, however this need not always be the case . Some nanoparticles are developed with the intension of being toxic for instance with the purpose of killing bacteria or cancer cells , and in such cases toxicity can unintentionally lead to adverse effects on humans or the environment.

Due to the lack of knowledge and lack of studies, the toxicity of nanoparticles is often discussed on the basis of ultra fine particles (UFPs), asbestos, and quartz, which due to their size could in theory fall under the definition of nanotechnology ,.

An estimation of the toxicity of nanoparticles could also be made on the basis of the chemical composition, which is done for instance in the USA, where safety data sheets for the most nanomaterials report the properties and precautions related to the bulk material .

Within such an approach lies the assumption that it is either the chemical composition or the size that is determining for the toxicity. However, many scientific experts agree that that the toxicity of nanoparticles cannot and should not be predicted on the basis of the toxicity of the bulk material alone ,.

The increased surface area-to-mass ratio means that nanoparticles could potentially be more toxic per mass than larger particles (assuming that we are talking about bulk material and not suspensions), which means that the dose-response relationship will be different for nanoparticles compared to their larger counterparts for the same material. This aspect is especially problematic in connection with toxicological and ecotoxicological experiments, since conventional toxicology correlates effects with the given mass of a substance ,.

Inhalation studies on rodents have found that ultrafine particles of titanium dioxide causes larger lung damage in rodents compared to larger fine particles for the same amount of the substance. However, it turned out that ultra fine- and fine particles cause the same response, if the dose was estimated as surface area instead of as mass .

This indicates that surface area might be a better parameter for estimating toxicity than concentration, when comparing different sizes of nanoparticles with the same chemical composition5. Besides surface area, the number of particles has been pointed out as a key parameter that should be used instead of concentration . Although comparison of ultrafine particles, fine particles, and even nanoparticles of the same substance in a laboratory setting might be relevant, it is questionable whether or not general analogies can be made between the toxicity of ultrafine particles from anthropogenic sources (such as cooking, combustion, wood-burning stoves, etc.) and nanoparticles, since the chemical composition and structure of ultrafine particles is very heterogeneous when compared to nanoparticles which will often consists of specific homogeneous particles . From a chemical viewpoint nanoparticles can consist of transition metals, metal oxides, carbon structures and in principle any other material, and hence the toxicity is bound to vary as a results of that, which again makes in impossible to classify nanoparticles according to their toxicity based on size alone .

Finally, the structure of nanoparticles has been shown to have a profound influence on the toxicity of nanoparticles. In a study comparing the cytotoxicity of different kinds of carbon-based nanomaterials concluded that single walled carbon nanotubes was more toxic that multi walled carbon nanotubes which again was more toxic than C60 .

=Hazard identification=

In order to complete a hazard identification of nanomaterials, the following is ideally required
 * ecotoxicological studies
 * data about toxic effects
 * information on physical-chemical properties
 * Solubility
 * Sorption
 * biodegradability
 * accumulation
 * and all likely depending on the specific size and detailed composition of the nanoparticles

In addition to the physical-chemical properties normally considered in relation to chemical substances, the physical-chemical properties of nanomaterials is dependent on a number of additional factors such as size, structure, shape, and surface area. Opinions on, which of these factors are important differ among scientists, and the identification of key properties is a key gap of our current knowledge ,, . There is little doubt that the physical-chemical properties normally required when doing a hazard identification of chemical substances are not representative for nanomaterials, however there is at current no alternative methods. In the following key issues in regards to determining the destiny and distribution of nanoparticles in the environment will be discussed, however the focus will primarily be on fullerenes such as C60.

Solubility
Solubility in water is a key factor in the estimation of the environmental effects of a given substance since it is often via contact with water that effects-, or transformation, and distribution processes occur such as for instance bioaccumulation.

Solubility of a given substance can be estimated from its structure and reactive groups. For instance, Fullerenes consist of carbon atoms, which results in a very hydrophobic molecule, which cannot easily be dissolved in water. Fortner et al. have estimated the solubility of individual C60 in polar solvents such as water to be 10-9 mg/L. When C60 gets in contact with water, aggregates are formed in the size range between 5-500 nm with a greater solubility of up to 100 mg/L, which is 11 orders of magnitude greater than the estimated molecular solubility. This can, however, only be obtained by fast and long-term stirring in up to two months. Aggregates of C60 can be formed at pH between 3.75 and 10.25 and hence also by pH-values relevant to the environment . As mentioned the solubility is affected by the formation of C60 aggregates, which can lead to changes in toxicity .

Aggregates form reactive free radicals, which can cause harm to cell membranes, while free C60 kept from aggregation by coatings do not form free radical . Gharbi et al. point to the accessibility of double bonds in the C60 molecule as an important precondition for its interactions with other biological molecules.

The solubility of C60 is less in salt water, and according to Zhu et al. only 22.5 mg/L can be dissolved in 35 ‰ sea water. Fortner et al. have found that aggregate precipitates from the solution in both salt water and groundwater with an ionic strength above 0.1 I, but aggregates would be stable in surface- and groundwater, which typically have an ionic strength below 0.5 I. The solubility of C60 can be increased to about 13,000-100,000 mg/L by chemically modifying the C60–molecule with polar functional groups such as hydroxyl . The solubility can furthermore be increased by the use of sonication or the use of none-polar solvents.

C60 will neither behave as molecules nor as colloids in aqueous systems, but rather as a mixture of the two ,.

The chemical properties of individual C60 such as the log octanol-water partitioning coefficient (log Kow) and solubility are not appropriate in regard to estimating the behavior of aggregates of C60. Instead properties such as size and surface chemistry should be applied a key parameters 18.

Just as the number of nanomaterials and the number of nanoparticles differ greatly so does the solubility of the nanoparticles. For instance carbon nanotubes have been reported to completely insoluble in water . It should be underlined that which method is used to solute nanoparticles is vital when performing and interpreting environmental and toxicological tests.

Evaporation
Information about evaporation of C60 from aqueous suspensions has so far not been reported in the literature and since the same goes for vapor pressure and Henry’s constant, evaporation cannot be estimated for the time being. Fullerenes are not considered to evaporate – neither from aqueous suspension or solvents – since the suspension of C60 using solvents still entails C60 after evaporation of the solvent ,.

Sorption
According to Oberdorster et al. nanoparticles will have a tendency to sorb to sediments and soil particles and hence be immobile because of the great surface area when compared to mass. Size alone will furthermore have the effect that the transport of nanoparticles will be dominated by diffusion rather than van der Waal forces and London forces, which increases transport to surfaces, but it is not always that collision with surfaces will lead to sorption . For C60 and carbon nanotubes the chemical structure will furthermore result in great sorption to organic matter and hence little mobility since these substances consists of carbon. However, a study by Lecoanet et al. 45 found that both C60 and carbon nanotubes are able to migrate through porous medium analogous to a sandy groundwater aquifer and that C60 in general is transported with lower velocity when compared to single walled carbon nanotubes, fullerol, and surface modified C60. The study further illustrates that modification of C60 on the way to - or after - the outlet into the environment can profoundly influence mobility. Reactions with naturally occurring enzymes , electrolytes or humid acid can for instance bind to the surface and make thereby increase mobility , just as degradation by UV-light or microorganisms could potentially results in modified C60 with increased mobility 45.

Degradability
Most nanomaterials are likely to be inert , which could be due to the applications of nanomaterials and products, which is often manufactured with the purpose of being durable and hard-wearing. Investigations made so far have however showed that fullerene might be biological degradable whereas carbon nanotubes are consider biologically non-degradable , . According to the structure of fullerenes, which consists of carbon only, it is possible that microorganisms can use carbon as an energy source, such as it happens for instance with other carbonaceous substances.

Fullerenes have been found to inhibit the growth of commonly occurring soil- and water bacteria ,, which indicates that toxicity can hinder degradability. It is, however, possible that biodegradation can be performed by microorganisms other than the tested microorganisms, or that the microorganism adapt after long-term exposure. Besides that C60 can be degraded by UV-light and O. UV-radiation of C60 dissolved in hexane, lead to a partly or complete split-up of the fullerene structure depending on concentration .

Bioaccumulation
Carbon based nanoparticles are lipophilic which means that they can react with and penetrate different kinds of cell membranes . Nanomaterials with low solubility (such as C60) could potentially accumulate in biological organisms , however to the best of our knowledge no studies have been performed investigating this in the environment. Biokinetic studies with C60 in rats result in very little excretion which indicates an accumulation in the organisms . Fortner et al. estimates that it is likely that nanoparticles can move up through the food chain via sediment consuming organisms, which is confirmed by unpublished studies performed at Rice University, U.S. Uptake in bacteria, which form the basis for many ecosystems, is also seen as a potential entrance to whole food chains .

=Surface chemistry and coatings= In addition to the physical and chemical composition of the nanoparticles, it is important to consider any coatings or modifications of a given nanoparticles .

A study by Sayes et al. found that the cytotoxicity of different kinds of C60-derivatives varied by seven orders of magnitude, and that the toxicity decreased with increasing number of hydroxyl- and carbonyl groups attached to the surface. According to Gharbi et al. , it is in contradiction to previous studies, which is supported by Bottini et al. who found an increased toxicity of oxidized carbon nanotubes in immune cells when compared to pristine carbon nanotubes.

The chemical composition of the surface of a given nanoparticle influences both the bioavailability and the surface charge of the particle, both of which are important factors for toxicology and ecotoxicology. The negative charge on the surface of C60 is suspected to be able to explain these particles ability to induce oxidative stress in cells .

The chemical composition also influences properties such as lipophilicity, which is important in relation to uptake through cells membranes in addition to distribution and transport to tissue and organs in the organisms5. Coatings can furthermore be designed so that they are transported to specific organs or cells, which has great importance for toxicity .

It is unknown, however, for how long nanoparticles stay coated especially inside the human body and/or in the environment, since the surface can be affected by for instance light if they get into the environment. Experiments with non-toxic coated nanoparticles, turned out to be very cell toxic after 30 min. exposure to UV-light or oxygen in air .

=Interactions in the Environment= Nanoparticles can be used to enhance the bioavailability of other chemical substances so that they are easily degradable or harmful substances can be transported to vulnerable ecosystems .

Besides the toxicity of the nanoparticles itself, it is furthermore unclear whether nanoparticles increases the bioavailability or toxicity of other xenobiotics in the environment or other substances in the human body. Nanoparticles such as C60 have many potential uses in for instance in medicine because of their ability to transport drugs to parts of the body which are normally hard to reach. However, this property is exactly what also may be the source to adverse toxic effects . Furthermore research is being done into the application of nanoparticles for spreading of contaminants already in the environment. This is being pursued in order to increase the bioavailability for degradation of microorganisms 54, however it may also lead to increase uptake and increased toxicity of contaminants in plants and animals, but to the best of our knowledge, no scientific information is available that supports this ,.

=Conclusion= It is still too early to determine whether nanomaterials or nanoparticles are harmful or not, however the effects observed lately have made many public and governmental institutions aware of , .
 * 1) the lack of knowledge concerning the properties of nanoparticles
 * 2) the urgent need for a systematic evaluation of the potential adverse effect of Nanotechnology

Furthermore, some guidance is needed as to which precautionary measures are warranted in order to encourage the development of “green nanotechnologies” and other future innovative technologies, while at the same time minimizing the potential for negative surprises in the form of adverse effects on human health and/or the environment.

It is important to understand that there are many different nanomaterials and that the risk they pose will differ substantially depending on their properties. At the moment it is not possible to identify which properties or combination of properties make some nanomaterials harmful and which make them harmless, and properly it will depend on the nanomaterial is question. This makes it is extremely difficult to do risk assessments and life-cycle assessment of nanomaterials because, in theory, you would have to do a risk assessment for each of the specific variation of nanomaterial – a daunting task!

=Contributors to this page= This material is based on notes by
 * Steffen Foss Hansen, Rikke Friis Rasmussen, Sara Nørgaard Sørensen, Anders Baun. Institute of Environment & Resources, Building 113, NanoDTU Environment, Technical University of Denmark
 * Stig Irving Olsen, Institute of Manufacturing Engineering and Management, Building 424, NanoDTU Environment, Technical University of Denmark
 * Kristian Mølhave, Dept. of Micro and Nanotechnology - DTU - www.mic.dtu.dk

=References=

See also notes on editing this book about how to add references Nanotechnology/About.


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Control Systems/Licensing

License
The text of this wikibook is released under the terms of the GNU Free Documentation License version 1.2. The particular version of that license that is being used can be found at:

 * http://en.wikibooks.org/wiki/Wikibooks:GNU_Free_Documentation_License

The text of that license will also be appended to the end of the printable version of this wikibook.

Images used in this document may not be released under the GFDL, and the licenses used with each image in this book will be listed in a table below. Some contributors may cross-license their contributions under the GFDL and another compatible license. Some contributions have been released into the public domain.

Images
The individual images used in this wikibook are released under a variety of different licenses, including the GFDL, and Creative-Commons licenses. Some images have been released into the public domain. The following table will list the images used in this book, along with the license under which the image is released, and any additional information about the images that is needed under the terms of the applicable licenses.

Authors
The authors of this text can list themselves below. Authors should be listed in alphabetical order by first name (if a real name is used), or by username. This is not a canonical list.

 * Andrew Whitworth (Whiteknight)

The usernames of additional contributors, as well as the size and scope of the contributions made by the authors listed above can be found in the history records of the individual pages on the Wikibooks website. Those history pages satisfy the attribution requirement of the GFDL, and any lists of authors that appear here or anywhere else do not count as legal attribution under the terms of that license.

Child Versions
The Control Systems wikibook is offered with a number of child versions, which represent subsets of the material available in the parent book. Because certain chapters are omitted from the child versions, some of the images listed above may not be present, and some of the authors listed above may not have made any contributions to some printed and distributed versions of this text.

title: Control Systems/Licensing


text:
Java Programming/Basic Synchronization

In a multi-threaded environment, when more than one thread can access and modify a resource, the outcome could be unpredictable. For example, let's have a counter variable that is incremented by more than one thread.

Beware! Synchronization is an ambiguous term. It doesn't consist of making all threads executing the same code section at the same time. It is the opposite. It prevents any two threads from executing the same code section at the same time. It synchronizes the end of one processing with the beginning of a second processing.

The above code is built up by the following sub-operations: Let's say that two threads need to execute that code, and if the initial value of the  variable is zero, we expect after the operations the value to be 2.
 * Read ; read variable
 * Add ; add 1 to the value
 * Save ; save the new value to variable

In the above case Thread 1 operation is lost, because Thread 2 overwrites its value. We'd like Thread 2 to wait until Thread 1 finishes the operation. See below:

 * Critical Section : In the above example the code  must be executed by one and only one thread at any given time. That is called critical section. During programming, in a multi-threading environment we have to identify all those pieces of code that belongs to a critical section, and make sure that only one thread can execute those codes at any given time. That is called synchronization.

 * Synchronizing threads : The thread access to a critical section code must be synchronized among the threads, that is to make sure that only one thread can execute it at any given time.

 * Object monitor : Each object has an Object monitor. Basically it is a semaphore, indicating if a critical section code is being executed by a thread or not. Before a critical section can be executed, the thread must obtain an Object monitor. Only one thread at a time can own that object's monitor.

 * A thread becomes the owner of the object's monitor in one of three ways :
 * By executing a synchronized instance method of that object. See keyword.
 * By executing the body of a synchronized statement that synchronizes on the object. See keyword.
 * For objects of type Class, by executing a synchronized static method of that class.

 * The Object Monitor takes care of the synchronization, so why do we need the "wait and notify methods"? : For synchronization we don't really need them, however for certain situations it is nice to use them. A nice and considerate thread will use them. It can happen that during executing a critical section, the thread is stuck, cannot continue. It can be because it's waiting for an IO and other resources. In any case, the thread may need to wait a relatively long time. It would be selfish for the thread to hold on to the object monitor and blocking other threads to do their work. So the thread goes to a 'wait' state, by calling the  method on the object. It has to be the same object the thread obtained its object monitor from.
 * On the other hand though, a thread should call the  method only if there is at least one other thread out there who will call the   method when the resource is available, otherwise the thread will wait for ever, unless a time interval is specified as parameter.

 * Let's have an analogy. You go in a shop to buy some items. You line up at the counter, you obtain the attention of the sales-clerk - you get her "object-monitor". You ask for the item you want. One item needs to be brought in from a warehouse. It'll take more than five minutes, so you release the sales-clerk (give her back her "object-monitor") so she can serve other customers. You go into a wait state.  Let's say there are five other customers already waiting. There is another sales-clerk, who brings in the items from the warehouse. As she does that, she gets the attention of the first sales-clerk, getting her object-monitor and notifies one or all waiting customer(s), so the waited customer(s) wake up and line up again to get the attention of the first sales-clerk.

 * Note the synchronization between the waiting customer and the sales-clerk who brings in the items. This is kind of producer-consumer synchronization.
 * Also note that there is only one object-monitor, belonging to the first sales-clerk. That object-monitor/the attention of clerk needs to be obtained first before a wait and a notify can happen.

 * method : The current thread must own this object's monitor. The thread releases ownership of this monitor and waits until another thread notifies the threads waiting on this object's monitor to wake up either through a call to the notify method or to the  method. The thread then waits until it can re-obtain ownership of the monitor and resume execution.

 * : The same as wait, but the thread wakes after the specified duration of time passes, regardless of whether there was a notification or not.

 * : This method should only be called by a thread that is the owner of this object's monitor. Wakes up a single thread that is waiting on this object's monitor. If many threads are waiting on this object's monitor, one of them is chosen to be awakened. The choice is arbitrary and occurs at the discretion of the implementation. A thread waits on an object's monitor by calling one of the wait methods.
 * The awakened thread will not be able to proceed until the current thread relinquishes the lock on this object. The awakened thread will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened thread enjoys no reliable privilege or disadvantage in being the next thread to lock this object.

 * : Same as, but it wakes up all threads that are waiting on this object's monitor.

 * What are the differences between the sleep and wait methods? :

 * : This is a static method of the Thread class. Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds. The thread does not lose ownership of any monitors. It means that if the thread has an object-monitor, all other threads that need that monitor are blocked. This method can be called regardless whether the thread has any monitor or not.

 * : This method is inherited from the class.  The thread must have obtained the object-monitor of that object first before calling the wait method.  The object monitor is released by the wait method, so it does not block other waiting threads wanting this object-monitor.

title: Java Programming/Basic Synchronization


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User talk:74.67.9.184

It might not have been your intention, but you recently removed content from A Wikimanual of Gardening/Strawberry. Please be careful not to remove content from Wikibooks without a valid reason, which you should specify in the edit summary or on the article's talk page. Thank you.--Az1568 23:47, 27 September 2006 (UTC)

title: User talk:74.67.9.184


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Neuroscience/Cellular Neurobiology/Action Potentials

Characteristics of Action Potentials
There are a few components to the action potential. On a graph, plotting membrane potential vs. time, the slope become steep and the potential goes over 0 mV in the overshoot phase. After it comes back down, the potential undershoots, and the resting potential returns.

Experimental Generation
Action potentials are generated at the axon hillock. Their frequency can vary but usually not the amplitude. If a recording electrode is placed close to the cell, it allows recording the action potentials across the membrane. Charge may be injected via the electrode, which causes a depolarization that, when the membrane potential reaches the threshold, causes a spike. In regular firing neurons, the cell continues to generate action potentials as long as the membrane potential stays above threshold. Also, if the depolarization is increased to a more positive potential, these cells fire at a faster rate. Other neurons cease firing action potentials during prolonged depolarization, and are therefore termed "bursters". Their firing mode is a very simple form of adaptation.

Action Potential Current
A current clamp can be used to monitor current. The injection electrode will trigger an action potential by injecting a suprathreshold voltage, but the potential across the membrane is held steady. The negative deflection represents the influx of a positive charge and the positive deflection represents the efflux of positive charge. Huxley used TTX(terodotoxin) to block voltage gated Na channels. They found that that blocked the inward component of the action potential. Using TEA(tetraethylammonium, an antagonist for K channels) they suppressed the outward component of the action potential, and they could look at the current vs. time graph of an action potential and extrapolate the current v. time graphs for K and Na individually. When suprathreshold potential is applied, Na channels open and then close even though membrane is depolarized. K v-channels do not close as long as depolarization is sustained. Na v-channel current is a 'non-inactivating'/'trangent' current and the K v-channel current a 'sustained' and 'inactivating' current.

Positive Na+/Negative K+ Feedback
If both Na and K channels are open, there is flow in both directions but the permeability is different. During the depolarization, Na rapidly depolarizes the membrane and then stops. It would gradually leak back to equilibrium. K flow repolarizes the membrane but is slower to flow. When enough Na channels let in enough Na that the efflux of K can't balance the depolarization, the depolarization continues and action potential occurs. Subthreshold, K channels open to increase the K+ current. At threshold depolarization, the negative feedback cycle doesn't stop, but is simply overwhelmed. If there were no Na flooding in, K wouldn't move across the membrane very quickly.

Current Clamp Technique
A capillary pipet can be fired on the end to melt the tip to a micrometer size opening to give a useful capillary and then filled with a salt solution. The pipet tip is put toward a membrane, and using negative pressure, it can pull in a area of the membrane. An impermeable seal is created, prevented ions from entering or leaving. Enables the measurement of the current of a single channel. Graphed, the current is a square shape. Positive or negative current indicates direct of current flow and can identify which ion is flowing. Depending on the type of channel, one can use voltage or neurotransmitter to control the opening and closing of a particular channel. Channels are either open or closed. The more the channel is open, the longer charge flows across the membrane.

Voltage Clamp Technique
The rapid, large change in potential is the result of the activities of ion channels. The purpose of the voltage clamp technique allows the recording of membrane current (as opposed to potential. Uses two electrodes: one to inject voltage and one to monitor membrane potential. Connecting these two electrodes is a error-correcting amplifier. This amplifier injects a set voltage into the cell and uses the monitor electrode to detect changes and compensate at the injection electrode. The purpose to electrically force the membrane to stay at one potential and then monitor the feedback to see what currents pass through the membrane.

Voltage-Gated Channels
They have a voltage sensor in their protein structure. They contain charged amino acids that react to a change in membrane voltage. When there is a more positive charge on the membrane, positively amino acids within the protein are repelled creating a force internal to the protein that will cause a change in conformation. When membrane is at -10mV, the channel is open 10-15% of the time. When at -10mV 80%, at 20mV 95%.

Whole-Cell Currents
A sum of all the single-channel currents. If recording a single Na channel, depolarization increases the occurrence of an open channel. Add two more channels to the sum, and the larger possible total current increases. As the number goes up, the curve represents the whole cell current curve of the Na portion of the total curve. Three graphs showing the current of K, the current of Na and the total current during one action potential; the graph lines up action potential curve with graph of current of Na and K channels independently so one can see which portion of the action potential is caused by a particular ion channel. After AP leak channels return resting potential. When the peak depolarization is reached, the Na channels have closed and the K channels have opened, quickly falling from the peak. Influx of Na causes rising part of action potential and the efflux of K brings the membrane potential back down

K and Na Channel Differences
Na Channel Has a quick onset and quickly turns off: inactivating channel. K is the opposite with slow onset and slow turn off: noninactivating channel. This difference is caused by differences in the two proteins. The Na channel has two gates: the activation gate and the inactivation gate. The activation gate is sensitive to the potential. When the activation gate is closed the inactivation gate is closed. When the inside of the cell is depolarized, the activation gate quickly opens. The inactivation gate, composed of negative proteins, slowly is repelled by the positive change in the intracellular environment, so it closes the channel by find its way into the pore of the channel.

K Channel. Has a single gate activated by the membrane potential, so it will stay open all the time the membrane has a certain potential. Na and K Conductances Na's conductance is characterized by a rapid onset and a rapid offset. K's conductance is characterized by a slow onset and a slow offset. Membrane potential line up temporally with a graph of conductance of K and Na on different lines. The upward rise of the AP is corresponds to the Na conductance change and the downward fall of the AP corresponds to the K conductance. K's slow offset creates an undershoot. This sets up a refractory period during which another AP cannot be generated because an action potential during the undershoot requires a much greater Na influx than during resting potential. Also, if the ball on the Na channel hasn't been released, the Na channel cannot conduct current creating a absolute refractory period during which no action potential can be generated, regardless of membrane potential. After the protein complex blocking the Na channel has been released is the relative refractory period where is more difficult.

Other types of Voltage-Gated Channels
Ca ion can keep the peak for a relatively long time before K brings the potential back. Ca can activate Ca-activated Na channels that help generate action potential waveforms.


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Wikijunior:Big Cats/Raising young

Cats can have anywhere from one to eight cubs or kittens in a litter, but most of them only have about two or three. Some of the smaller cats may have more, from four to seven. Cub is usually what you call young big cats, and kitten what you call young small cats. Cubs or kittens born in the same litter are called siblings.

Because most cats live in tropical locations, it doesn’t matter what time of the year they have their young, because food will usually be plentiful. However, for cats that live in places that get cold in the winter, they will usually have their young in the spring.

The father almost never has any part in raising the young. Male lions take the job of protecting the pride instead of taking care of the young, but most fathers will leave completely. This may sound selfish, but it is not. In the animal world, often the responsibility for finding food and for the young rests upon the female. As carnivores, most would be too noisy hunting in pairs, so they would have less of a chance to catch their prey.

When the young are born, they are blind and keep their eyes closed. They will open their eyes in about 10 days to 14 days after birth. Most young also have different markings from their parents when they are born. Lion and puma cubs have spots or splotches that disappear as they get older. Clouded leopard cubs have dark spots that eventually change into the shape of the adult spots. Cheetahs are one kind of cat in which the cubs have the same spots as the adults.

It can be very dangerous for the young of many big cats. Many cheetah cubs are killed by a lack of food or their natural enemies (lions and hyenas). Lion cubs may be killed if a new male lion takes over a pride.

The young are not able to eat meat right away; they usually must drink their mother’s milk anywhere from one to two months for the smaller cats and up to seven months in bigger cats. When they reach an age of about two to three months, the mother can start taking the young out and teaching them how to hunt.

At a few months of age, cubs and kittens become very playful. They chase one another and pounce on anything that moves. This play teaches them basic hunting techniques, which helps them to become successful hunters as adults.

Most cats will leave their mother after one or two years. Smaller types of cats may leave earlier, as soon as four or five months in the case of the wild cat. Sometimes the mother will chase her cubs or kittens away so that they can become independent. Often, the siblings will usually stay together for a few more months or years and work together before completely splitting up. Rogue lions and male cheetahs are especially known for staying together after leaving the mothers. Next Topic: Fossil History

title: Wikijunior:Big Cats/Raising young


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Wikijunior:Solar System/Puzzles

Crypto Quiz
Try to fill in the correct answer for each of the questions below. A letter should go on each blank line. The numbers underneath the lines match the entries in the secret message. What does it say?

Photo Word Scramble
Each of the names of the pictures below have been scrambled. Can you unscramble the letters to find the correct names?

Word Find
Each of the words except one in the list to the right can be found along a row, column, or diagonal somewhere inside the box below. See if you can find which one is missing by finding all the others.

title: Wikijunior:Solar System/Puzzles


text:
User:Brass shadow

Greetings, my name is Sean.

I enjoy reading random information and exploring random places. I might find myself hovering around wiki content for, photography, hiking (national and other parks), computers, and programming.

title: User:Brass shadow


text:
Microeconomics/Opportunity Cost

Every day everyone makes a myriad of decisions, choosing between two or ten or even hundreds of different possibilities. Action tends to be the best indicator of preference, of what people actually want, but in doing so people deny themselves all other options. This is the essence of scarcity: everyone can't have everything all at once.

With every expressed preference there exists a next-best option: something you would have done if the first option wasn't available. This is called the opportunity cost. Because you do one thing, you've lost the opportunity to do something else. Opportunity costs can be thought of as a sort of regret, pain people bear as they imagine what they could be enjoying even if they are enjoying what they are doing right now more. Another way to think about opportunity costs is money value; profit you would have made if you did something else, such as a business venture.

Understanding Opportunity Cost and Benefit
Opportunity Cost can be understood by looking at the first four of Mankiw's Principles of Economics

 * People face tradeoffs.
 * The cost of something is what you give up to get it.
 * Rational people think at the margin.
 * People respond to incentives.

To exemplify these four principles we will use the following example: It is a Friday night and you have the following options of things to do, in order of how much you want to do them (most enthusiasm to least enthusiasm):  1.)See a movie with a partner. 2.)See a movie with your buddies. 3.)Buy new jumper cables. 4.)Play chess against yourself. 5.)Study.

By putting the partner first, you have already faced the tradeoff of friends vs more-than-friends. How was this tradeoff made? By weighing costs and benefits. Your benefit in this tradeoff is that you may be entering into a romantic relationship, rather than simply keeping the platonic ones you already have. But what about the costs?

Each of the above options has the cost of time. You only have one Friday night until next week, so, for now, you only have time to do one thing. Both of your top two options have the added cost of spending money at the cinema. However,  the benefits of these options (namely being social and having fun with others) outweigh the costs so you have placed them above the others.

As stated before, for each of your top two options your opportunity costs include Time and Money. How do we know this? Because The Cost of Something is What You Give Up to Get It. Another way to remember this is with the adage "There Is No Such Thing As A Free Lunch," which means that there is some built-in cost for everything so nothing is truly free of charge. For each of the above options, you are spending your time and your money which could have been used on a multitude of different things. If you choose option one, you miss out on the next best option. That is, by choosing option one, you are giving up the opportunity of option two and it is therefore an opportunity cost. If you choose any option, you are giving up the other options to "get" your option.

The next thing to think about before making your final decision on what to do this fateful Friday would be does the opportunity benefit of option one outweigh the opportunity cost of option two? This is called thinking at the margin and is how rational decisions are made. In this example, if you choose option one, your friends might look down on you and say that you abandoned them to see your partner. Inversely, if you choose option two, you risk losing your partner to have fun with your buddies. For argument's sake, we will assume that although your friend's will hassle you for ditching them, they won't leave you and if you abandon you partner instead, he/she will leave you or be very angry with you. Therefore, seeing your buddies has a much greater opportunity cost than seeing your acquaintance does, so seeing your partner would be the rational decision - the decision made at the margin.

However, what if we throw in a twist to this example? What if option two has an incentive that makes option two a more rational decision than option one? This incentive could be that your friends want your partner to come with you if you decide to go with them? And they'll pay for your movie tickets? And give you a new car? These are incentives, and people respond to incentives.

Production possibility curve
Opportunity cost is the substance of production possibility curves, the opportunity cost of choices in current resource deployment on current production and future production capability.

The production possibility curve is a quarter curve 12pm-3pm, on a graph of two competing possibilities of production, with each product's quantity being the X and Y axes respectively.

Anything within the region left and under the curve, is the production possibilities, and represents what can be produced given the available resources.

Production is fully efficient on points lying on the curve, as resources are fully allocated, including employment.

If X is the horizontal axis quantity, then the right most, lowest point of the curve, shows maximum production of X, and no production of Y. Conversely, the left most, highest point, shows maximum production of Y, and no production of X.

The curve can grow outward, if relevant technology increases, or resources increase, the former representing increased maximum efficiency achievable.

An illustrative example might be X is the production of cars, and Y is the production of mobile consumer items. Assuming that enlarging the production possibility curve is good, what is the optimal current production of X and Y, that will increase the production possibility curve of X and Y in the future?

Another way of framing the example, X is the production of cars and mobile electronic consumer items, Y is education, completed research papers, public-owned solar panel production companies, and public, independent labor legislation (to increase productivity by reducing health-damaging effects of work commitments).

title: Microeconomics/Opportunity Cost


text: User:LanguageGame

title: User:LanguageGame


text:
A-level Applied Science/Synthesising Organic Compounds

About this Unit
From the AQA Specification:

 In this unit you will learn about:

 * the wide range and number of organic compounds formed by carbon;
 * how to describe organic compounds;
 * how to recognise a range of aliphatic compounds, their functional groups, structural formula and shape;
 * recognising examples of a range of chemical reactions and writing balanced equations;
 * how to make and purify organic compounds;
 * how to determine theoretical and actual percentage yield.

How you will be assessed
This unit is assessed through the work you complete for your portfolio.

The marking criteria are found in the AQA specification.

References & notes

Organic chemistry: wikibook


text:
Orthopaedic Surgery/Bone

Bone
Bone is the tissue that makes us vertebrates. The stiffness and rigidity of our body is due to the presence of bone. Bone provides our body structural form and gives us the shape that we so often refer to as the human body. It is the internal scaffolding on which the rest of the body is built. Due to its ability to absorb force, bony structures also protect vital organs in the body. Bone is the unit that makes up the skeleton in vertebrates. Several bones join together in specialised areas, termed joints, to form the skeleton. Alongwith the muscle tissue, tendons and ligaments bones are able to move on one another at the joints and produce movement of various parts of the body. This also permits the movement of the human body from one location to another - locomotion.

Bones are a storehouse for two important minerals in our body - calcium and phosphorus. Matabolic activity in the bones is intimately related to the balance of these two minerals. Any alteration in the levels of calcium or phosphorus, as they do occur in many disease processes, is reflected  on the human skeleton. Bones are also the site for production of red blood cells, haematopoiesis.

In this chapter we try to understand important biological processes involving the bones. Understanding the basic anatomical tissue will provide us a sound ground for comprehending the pathological states they may be involved in.

 * Histology of Bone
 * Blood Supply of Long Bones
 * Bone Injury and Repair
 * Bone Mineralisation
 * Bone Viability

title: Orthopaedic Surgery/Bone


text:
User talk:Sunil.abraham

Welcome
Hello and welcome to Wikibooks!

Here are some tips to help you get started:
 * You can sign your name on Talk and vote pages using four tildes, like this: ~~~~.
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You will find more resources in Community Portal. If you want to ask a question, visit the Study help desk, the Staff lounge, IRC channel or ask me personally on my talk page.

Good luck! --Derbeth talk 09:59, 28 September 2006 (UTC)

title: User talk:Sunil.abraham


text:
Horticulture/Digitaria

Digitaria is a genus of about 300 species of grass (family ../Poaceae/) native to tropical and warm temperate regions. Common names include crabgrass, finger-grass, and fonio. They are slender monocotyledonous annual and perennial lawn, pasture, and forage plants; some are often considered lawn pests. Digitus is the Latin word for "finger", and they are distinguished by the long, finger-like inflorescences they produce.

Description
All crabgrasses have similar growth habits and flowering structures, but species are separated by minor differences in the flower structures and leaf pubescence. They typically have spreading stems with wide flat leaf blades that lay on the ground with the tips ascending. The inflorescence is a panicle in which the spike-like branches are arranged in digitate fashion. The spikelets are arranged in two rows on an angled or winged rachis. Each spikelet has two florets, only one of which is fertile. The first bracts at the base of the spikelets are either very minute or absent.

Ecology
Crabgrass seed has a long germination period; if conditions are right, it can germinate throughout the growing season. Crabgrasses occur in tropical, subtropical, and temperate regions of both hemispheres.

The most prevalent species of Digitaria in North America are Large Crabgrass (D. sanguinalis) and Smooth Crabgrass (D. ischaemum), which often become problem weeds in lawn and gardens. They are annual plants, and one plant is capable of producing 150,000 seeds per season. The seeds germinate in the late spring and early summer and outcompete the domesticated lawn grasses and expand outward in a circle up to 12 inches in diameter. In the fall when the plants die they leave large voids in the lawn. The voids then become prime areas for the crabgrass seeds to germinate the following season. Crabgrasses also have a different texture and color that often interrupts the uniformity of a lawn. In vegetable gardens, crabgrass can quickly out-compete desirable plants, causing yield reductions.

Uses
Despite their weediness, crabgrasses do have a few redeeming qualities. The seeds, most notably those of fonio, can be toasted and ground into a flour, which can be used to make porridge or fermented to make beer. Fonio has been widely used as a staple crop in parts of Africa. It also has decent nutrient qualities as a forage for cattle.

title: Horticulture/Digitaria


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Talk:Horticulture/Digitaria

Transwiki notes
Copied from Digitaria 10:29, 28 September 2006 (UTC) using this version.

title: Talk:Horticulture/Digitaria


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Horticulture/Flame Weeders

A flame weeder is a propane torch used for weed control, primarily in organic gardens and farms. They come in various sizes for different sorts of applications, from hand-held models to backpack versions to tractor-towed agricultural types.

Flame weeding has both advantages and disadvantages over other methods.

 * Pops seeds
 * Safe in lawns: lawn grasses are adapted to fire
 * Collateral damage
 * Expense: Propane costs can be prohibitive

/Tools

title: Horticulture/Flame Weeders


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User:Nicolas Lardot

fr:Utilisateur:Nicolas Lardot it:Utente:Nicolas Lardot

title: User:Nicolas Lardot


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Future Teachers Meet Wiki/How will you use Wiki as a teacher?

=Denise Wilson=

As a teacher I would use Wikibooks to excite my students. I know that I would use it in any of my high school English classes;however, middle school is another thing. I want to make sure that my students are mature enough to handle the work that will go into making a book together. I'm observing in a 7th grade English class right now and I don't know if they would want to do it. They groan about having to read novels that are no more than 180 pages so I can all image what that will say about having to post their work somewhere else.

Now in my high school classes I'll require for the students to analyze a short story or poem and write a paper. After grading the papers I'll give them a chance to correct them and fix them up before requiring them to post in Wikibooks. That way anyone else who maybe writing a paper or researching on a specific poem or short story can use the information they have written to support something that they want to put into their own paper.

Denise Wilson


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User talk:Vuara

Hello and welcome to Wikibooks!

Here are some tips to help you get started:
 * You can sign your name on Talk and vote pages using four tildes, like this: ~~~~.
 * Remember to conduct any editing experiments in the sandbox.
 * Check out our help page if you need additional help.
 * Eventually, you might want to read the Manual of Style and Policies and Guidelines.
 * Take a look at Naming policy
 * See list of templates which can save your time
 * Remember to maintain a Neutral point of view.
 * Explore, be bold in editing pages, and have fun!

You will find more resources in Community Portal. If you want to ask a question, visit the Study help desk, the Staff lounge, IRC channel or ask me personally on my talk page.

Good luck!

--DavidCary 12:06, 28 September 2006 (UTC)

I enjoyed the list of interesting documents on User:Vuara.

Did you know that many of those documents are available on Wikisource?

For example,

HOW THE ALPHABET WAS MADE is a copy of How_the_First_Letter_Was_Written How_the_Alphabet_Was_Made.

--DavidCary 12:06, 28 September 2006 (UTC)

Appleton's Cyclopedia of American Biography
Hi, while creating a Wikisource book Appleton's Cyclopedia of American Biography, I noticed your page User:Vuara/Appleton's Cyclopedia of American Biography. As a result I have copied your list of fictitious articles, and started concentrating on those. Thank you. John Vandenberg 22:49, 19 November 2007 (UTC)

title: User talk:Vuara