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Circuit Idea/Series Voltage Summer

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Deriving a Series Voltage Summer from Kirchhoff's Voltage Law

Circuit idea: Connect voltage sources in series to sum their voltages according to Kirchhoff's Voltage Law.

Deriving a series voltage summer from KVL

Ohm's law has given us an idea how to create the most elementary voltage-to-current and current-to-voltage converters. Now, Kirchhoff's Voltage Law (KVL) will help us to make the simplest voltage summer.

According to the famous law, we have just to connect in series (Fig. 2) the input voltage sources and the load (let's for concreteness assume that we have three sources). The output voltage across the load is the sum of the input voltages:

VOUT = VIN1 + VIN2 + VIN3

Only, what is actually the summer here? Where is it? The input voltage sources and the load are external components; so, the rest (a bare loop or just a piece of wire) serves as a summer!

The simplest voltage summer is just a loop.

It is just wonderful! The series voltage summer is an ideal "device" because there is not actually a device:)!

The input voltage sources in the circuit on Fig. 2 are connected in the same direction; so, their voltages are summed. If we reverse some source, its voltage will be subtracted from the whole sum.

Floating sources

The summing circuit on Fig. 2 is "flying"; there is no connection with the common reference point referred to as ground. Usually, the input voltage sources and the load are preliminarily connected to the ground (they can be electronic devices connected to the common power supply). So, we have to choose a point from our summing circuit that to connect to the ground. Only, what point of the circuit do we connect to the ground? Let's try some connections.

First, we can ground the common point between the input source VIN1 and the load. Only, the sources VIN2 and VIN3 become floating.

Note that in this arrangement, all the input voltages are positive regarding to ground.

Floating source and load

Then, we can ground the common point between the input sources VIN1 and VIN2. Only, now the source VIN3 and the load become flying. Obviously, the series voltage summer has a problem with the common ground.

Travelling the loop in clockwise direction we can note that all the input voltages have the same polarity direction (- +, -  +, -  +). Only, regarding to the ground, the input voltage VIN1 is negative while the others are positive.

Floating load
Fortunately, there is a very successful combination - two grounded input sources and a differential load. It is widely used in op-amp circuit design because, as a rule, the operational amplifiers have differential inputs. Almost all the series summer applications are based on this arrangement (see the examples below).

Applications
The series voltage summer exists in many analog circuits considered in electronics books; only, authors do not discern and do not pay attention to it. As a result, it is presented rather implicitly than manifestly. In this section, we will do our best to show its presence in various electronic circuits. This famous circuit deserves our attention.

Series battery configuration
Is there a more suitable example of using a series voltage summer than a series battery configuration? It is invented by Volta in 1799 by placing many galvanic cells in series. From the classical viewpoint, such a battery consists only of cells; from our viewpoint, it contains cells and a series voltage summer (it sounds quite strange, doesn't it?):

Series battery = cells + series voltage summer

Wheatstone bridge

We may think of this legendary circuit as a system of two voltage dividers (Fig. 4). Their output voltages are connected in series with opposite polarities (- VR2 +, + VR4 -) so that they are subtracted (regarding to the ground, the voltages have the same polarities). In this way, the output voltage of this series voltage summer represents the difference between the voltages.

If the bridge is balanced, the result is zero

VOUT = VR2 - VR4 = 0

and no current flows through the load (no matter how much low-resistive it is). This phenomenon is referred to as bootstrapping; Baron Munchhausen put it in practice for the first time (the legend says that he was using his own boot straps to pull himself out of the sea:).

Note that in this arrangement, the two input voltage sources are grounded while the load (usually the so called zero indicator or galvanometer) is flying.

Circuits with series negative feedback

Circuits with negative feedback are the great mass of devices in analog electronics. Let's, for example, consider the most elementary of them - the voltage follower. It consists of three components (Fig. 5): a source of energy E (power source), a regulating element R and a voltage subtractor. The regulating element produces an output voltage VOUT (by controlling the energy of the power source) and continuously compares it with the input voltage VIN by the voltage subtractor, in order to keep zero difference between them. As a result, the output "copy" voltage is equal to the input "original" one.

Depending on the nature of the voltage subtractor (series or parallel), there are two kinds of circuits: with series negative feedback and with parallel negative feedback. Circuits with series negative feedback are based on a series voltage summer acting as a subtractor.

Transistor NFB circuits

Emitter follower is the most elementary transistor circuit with series negative feedback that we can build. For this purpose, we connect the output part of the transistor (collector-emitter) in series to the power supply and the load (Fig. 6). It acts as a regulating element that doses the voltage of the power supply by changing its present resistance.

Then, to make the transistor compare the output voltage VOUT with the input voltage VIN, we connect the two voltages in series and apply their difference dV = VIN - VOUT to the input part of the transistor (the base-emitter junction). As a result, the transistor produces an output voltage that is almost equal to the input one:

VOUT ≈ VIN (we have written "≈" instead "=" because of the troublesome voltage VBE0).

According to the classical viewpoint, the emitter follower consists only of a transistor. From our viewpoint, the emitter follower contains a power supply, a transistor and a series voltage summer:

Emitter follower = power supply + transistor + series voltage summer

Op-amp NFB circuits

Similarly, an op-amp voltage follower is the most elementary op-amp circuit with series negative feedback that we can build. For this purpose, we supply properly the op-amp and connect the op-amp output to the load (Fig. 7). Now, the op-amp acts as a regulating element that doses the voltage of the power supply by changing the present resistance of its output transistors.

Then, in order to make the op-amp compare the output voltage VOUT with the input voltage VIN, we connect as above the two voltages in series and apply their difference dV = VIN - VOUT to the op-amp input (the input voltage - to the non-inverting op-amp input and the output voltage - to the inverting op-amp input). As a result, the op-amp produces an output voltage that is almost exactly equal to the input one: VOUT = VIN.

From the classical viewpoint, the op-amp voltage follover consists only of an operational amplifier. From our viewpoint, the op-amp follower consists of a power supply, an op-amp and a series voltage summer (a bare loop):

Op-amp voltage follower = power supply + op-amp + series voltage summer

Series versus parallel summer
We can do a few remarks about the circuit of a series voltage summer comparing it with the parallel one.

• The output voltage of the series summer is a sum of the whole input voltages; if we want to sum voltages with weighting coefficients, we have to attenuate them by voltage dividers. The circuit of the parallel voltage summer is more appropriate for this case.

• The output voltage of the series summer can exceed any of the input voltages; the output voltage of the parallel voltage summer is less than the highest input voltage.

• There are not any losses in the series summer; the resistors of the parallel voltage summer dissipate power.

• The series voltage summer has a problem with the common ground; the parallel voltage summer has not such a problem.

• An interesting feature of the series voltage summer is that the current flowing through the input voltage sources and the load is the same.

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title: Circuit Idea/Series Voltage Summer


text:
Basic Algebra/Radical Expressions and Equations/Chapter Test

Please post your test problems this way:
 * Problem:(answer,level of difficulty(easy, medium, hard))
 * Example 2x=6: (x=3,easy)

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


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User talk:91.109.115.30

Welcome to Wikibooks. We invite everyone to contribute constructively to our collection. Take a look at the welcome page if you would like to learn more about contributing. However, unconstructive edits are considered vandalism, and if you continue in this manner you may be blocked from editing without further warning. Please stop, and consider improving rather than damaging the hard work of others. Thanks. – Mike.lifeguard  | talk 18:16, 5 September 2007 (UTC)

title: User talk:91.109.115.30


text:
User talk:65.220.97.130

You have been blocked from editing Wikibooks  as a result of your .  Please note that page blanking, addition of random text or spam, deliberate misinformation, privacy violations, personal attacks; and repeated, blatant violations of our neutral point of view policy are considered vandalism. If you wish to make useful contributions, you are welcome to come back after the block expires. – Mike.lifeguard  | talk 18:18, 5 September 2007 (UTC)

title: User talk:65.220.97.130


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The Geology of Indonesia/Earthquake

Earthquakes are frequent in Indonesia, part of the seismically active Pacific "Ring of Fire".

Recent Earthquakes

 * 16 August 2007 - A 6.2 magnitude earthquake hit 145 miles southeast of Ambon, the capital of Maluku province
 * 9 August 2007 - A powerful undersea earthquake off Indonesia's main island of Java (100 km east of Jakarta). The magnitude 7.5 quake hit at 0005 on Thursday (1705 GMT Wednesday) at a depth of 289km (180 miles). No casualties or damage, only created panic among Jakarta's highrise residential. The earthquake on the relatively quiet region in Indonesia give another concern of the safety of nuclear power plant that planned nearby.
 * March 6, 2007: A magnitude-6.3 earthquake strikes Sumatra island, leaving at least 52 people dead and some 250 injured. Two hours later, a 6.1 aftershock rattles the region.
 * Jan. 21, 2007: A magnitude-7.3 earthquake in a regional capital on Sulawesi island in northeastern Indonesia leaves four people dead and four injured.
 * July 17, 2006: A magnitude-6.1 earthquake triggers a tsunami off of Java island's southern coast, killing at least 600 people.
 * May 27, 2006: A magnitude-6.2 quake flattens homes and hotels near the ancient central city of Yogyakarta, killing more than 3,000 and injuring thousands.
 * March 28, 2005: A magnitude-8.7 quake strikes Nias and Simeulue islands off the western coast of Sumatra, killing about 900 people and flattening thousands of houses and bridges.
 * Dec. 26, 2004: A magnitude-9 earthquake ruptures the sea floor off Sumatra island, triggering a tsunami that hits a dozen countries, including Indonesia, where at least 131,029 are killed and tens of thousands remain missing.
 * Nov. 26, 2004: A magnitude-6.4 earthquake rocks Indonesia's West Papua, near Nabire, killing about 30 people and causing dozens of buildings and homes to collapse.
 * Nov. 12, 2004: A magnitude-6 quake strikes off the eastern coast of Alor island, about 1,600 kilometers (1,000 miles) east of Jakarta. At least 27 people are killed and hundreds of buildings are damaged.
 * Feb. 6-7, 2004: A magnitude-6.9 quake on Feb. 6 and a magnitude-7.1 aftershock the following day kill 34 and devastate Nabire in remote Papua province.
 * Nov. 2, 2002: A magnitude-7.7 earthquake rocks Indonesia's Sumatra island, killing two people and injuring at least 40.
 * June 4, 2000: A magnitude-7.9 quake hits Bengkulu province, killing at least 117 people and injuring about 1,900.
 * May 4, 2000: A magnitude-7.5 earthquake shakes Sulawesi province, killing at least 35 people and injuring at least 148.

title: The Geology of Indonesia/Earthquake


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User talk:70.72.164.13

Realpedia
I notice that you removed a tag from this book. Can I ask what the book is going to be? As well, if you're going to be editing Wikibooks a lot, I suggest registering an account with us.

 – Mike.lifeguard  | talk 18:35, 5 September 2007 (UTC)

title: User talk:70.72.164.13


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User talk:67.142.130.28

I've replied to your query here.  – Mike.lifeguard  | talk 18:46, 5 September 2007 (UTC)

title: User talk:67.142.130.28


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The Geology of Indonesia/Plate Tectonic

Indonesia is a meeting point of several tectonic plates. Indo-Australian Plate is moving northward, Eurasia Plate moves southeast direction. Both Filipino and Pacific plate move westward. The Indo-Australian plate was moved northward and partly subducted under the Eurasian plate. The subduction zone can be traced from northern tip of Sumatra until the Lesser Islands, that creates deep submarine trench. Most of the earthquake also concentrate in this subduction zone. This subduction also triggers the formation of volcanic range from Sumatra, Java to Lesser Islands.

The center part of Indonesia also experienced another subduction of Pacific plate that move southwesterly under the Eurasian plate. This subduction create the formation of volcanoes in the North Sulawesi, Sangihe and Halmahera.

The Australian and Pacific plate collides in the eastern part of Indonesia and formed the mountain range in central Papua, with Puncak Jaya / Carstenz Pyramide as the highest peak.

Below is a regional cross section of Indonesia from west to east showing the relationship of the tectonic components of Indonesia, their depth, and structural features.

title: The Geology of Indonesia/Plate Tectonic


text:
User talk:205.202.50.248

Thanks for experimenting with Wikibooks. Your test worked, and has now been removed. Please use Sandbox for any other tests you want to do, since testing material in modules will normally be removed quickly. Please see the welcome page if you would like to learn more about contributing to our project. Thanks. – Mike.lifeguard  | talk 19:05, 5 September 2007 (UTC)

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text:
User talk:128.84.45.6

 – Mike.lifeguard  | talk 19:07, 5 September 2007 (UTC)

title: User talk:128.84.45.6


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The Geology of Indonesia/Tsunami

The largest and deadly tsunami in Indonesia occurred in the Aceh region, in the northern tip of Sumatra Island. Ten thousands of people died due to this deadly tsunami. The tsunami with wave up to 30 m was triggered by submarine earthquake and possible submarine landslide.

title: The Geology of Indonesia/Tsunami


text:
Contemporary Educational Psychology/Chapter 13: The Reflective Practitioner/Resources for Professional Development

Types of Resources for Professional Development and Learning
At some level reflection on practice is something you must do for yourself, since only you have had your particular teaching experiences, and only you can choose how to interpret and make use of them. But this rather individual activity also benefits from the stimulus and challenge offered by fellow professionals. Others’ ideas may differ from your own, and they can therefore help in working out your own thoughts and in alerting you to ideas that you may otherwise take for granted. These benefits to reflection can happen in any number of ways, but most fall into one of four general categories:

In the next sections we explore what each of these activities has to offer.
 * talking and collaborating with colleagues,
 * participating in professional associations,
 * attending professional development workshops and conferences, and
 * reading professional literature.

Colleagues as a Resource
Perhaps the simplest way to stimulate reflections about your own teaching is to engage fellow teachers or other colleagues in dialogue (or thoughtful conversation) about teaching and learning: What do you think of this kind of experience? Have you ever had one like it yourself, and what did you make of it? Note that to be helpful in stimulating reflection, these conversations need to be largely about educational matters, not about personal ones (“What movie did you see last night?”). Dialogues with individual colleagues have certain advantages to more complex or formal professional experiences. Talking with an individual generally allows more participation for both of you, since only two people may need to express their views. It also can provide a measure of safety or confidentiality if your conversation partner is a trusted colleague; sometimes, therefore, you can share ideas of which you are not sure, or that may be controversial.

A somewhat more complex way of stimulating reflection is group study. Several teachers at a school gather regularly to bring themselves up to date on a new curriculum, for example, or to plan activities or policies related to a schoolwide theme (e.g. “the environment”). Group meetings often result in considerable dialogue among the members about the best ways to teach and to manage classrooms, as well as stories about students’ behavior and learning experiences. For a beginning teacher, group study can be a particularly good way to learn from experienced, veteran teachers.

Sharing of ideas becomes even more intense if teachers collaborate with each other about their work on an extended basis. Collaboration can take many forms; in one form it might be “team teaching” by two or more teachers working with one group of students, and in another form it might be two or more teachers consulting regularly to coordinate the content of their courses. Collaborations work best when each member of the team brings responsibilities and expertise that are unique, but also related to the other members’ responsibilities. Imagine, for example, a collaboration between Sharon, who is a middle-years classroom teacher, and Pat, who is a resource teacher—one whose job is to assist classroom teachers in working with students with educational disabilities or special needs. If Pat spends time in Sharon’s classroom, then not only will the students benefit, but they both may learn from each other’s presence. Potentially, Pat can learn the details of the middle-years curriculum and learn more about the full range of students’skills—not just those of students having difficulties. Sharon can get ideas about how to help individuals who, in a classroom context, seem especially difficult to help. Achieving these benefits, of course, comes at a cost: the two teachers may need to take time not only for the students, but also for talking with each other. Sometimes the time-cost can be reduced somewhat if their school administrators can arrange for a bit of extra planning and sharing time. But even if this does not happen, the benefits of collaboration will be very real, and often make the investment of time worthwhile.

Professional Associations and Professional Development Activities
Another way to stimulate reflection about teaching is by joining and participating in professional associations—organizations focused on supporting the work of teachers and on upholding high standards of teaching practice. Table 13-1 lists several major professional associations related to education and their Internet addresses. Most of them are composed of local branches or chapters serving the needs of a particular city, state, or region.

To achieve their purposes, a professional association provides a mixture of publications, meetings, and conferences intended for the professional development of educators, including classroom teachers. Typically the publications include either a relatively frequent newsletter or a less frequent journal focused on issues of practice or research. Very large associations often publish more than one newsletter or journal, each of which is focused on a particular topic or type of news (for example, the National Education Association in the United States publishes eight separate periodicals). Some also publish online journals (there are several listed as part of Table 13-2) or online versions of print journals. Whatever format they take, professionally sponsored publications stimulate thinking by discussing issues and dilemmas faced by professional educators, and sometimes also by presenting recent educational research and the recommendations for teaching that flow from that research. We discuss ways of using these publications further in the next section of this chapter.

The meetings and conferences sponsored by a professional association also take a variety of forms. Depending on the size of the association and on the importance of the topic, a meeting could be as short as a one half-day workshop or as long as a full week with many sessions occurring simultaneously. Sometimes, too, an association might sponsor a more extended course—a series of meetings focused on one topic or problem of concern to teachers, such as classroom management or curriculum planning. In some cases, the course might carry university credit, though not always.

As you might expect, the size of a professional association makes a difference in kinds of professional development experiences it can provide. In general, the smaller the association, the more exclusively it focuses on local news and educational needs, both in its publications and in its meetings or other activities. At a professional development workshop sponsored by a local teachers’ association, for example, you are relatively likely to see colleagues and acquaintances not only from your own school, but from other neighboring schools. Locally sponsored events are also more likely to focus on local issues, such as implementing a new system for assessing students’ learning within the local schools. In general, too, local events tend to cost less to attend, in both time and money.

By the same token, the larger the association, the more its professional development opportunities are likely to focus on large-scale trends in education, such as the impact of the No Child Left Behind legislation we discussed in Chapter 1 or the latest trends in using computer technology for teaching. Conferences or other professional development events are more likely to span several days and to be located outside the immediate town or region whether you live and work. You may therefore see fewer of your everyday colleagues and acquaintances, but you may also have a greater incentive to make new acquaintances whose interests or concerns are similar to your own. The event is also more likely to feature educators who are well-known nationally or internationally, and to call attention to educational trends or issues that are new or unfamiliar.

Whether large or small, the activities of professional associations can stimulate thinking and reflecting about teaching. By meeting and talking with others at a meeting of an association, teachers learn new ideas for teaching, become aware of emerging trends and issues about education, and confront assumptions that they may have made about their own practices with students. Professional meetings, conferences, and workshops can provide these benefits because they draw on the expertise and experience of a wide range of professionals—usually wider than is possible within a single school building. But compared simply to talking with your immediate colleagues, they have a distinct disadvantage: they take effort and a bit of money to attend, and sometimes they are available at convenient times. Well-balanced professional development should therefore also include activities that are available frequently, but that also draw on a wide range of expertise. Fortunately, an activity with these features is often easily at hand: the reading of professional publications about educational research and practice.

(back to Chapter 13...)


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Contemporary Educational Psychology/Chapter 13: The Reflective Practitioner/Understanding Professional Articles

Reading and Understanding Professional Articles
Although publications about educational issues and research can take many forms, they tend to serve three major purposes in some sort of combination. A publication could either: Benefiting from a professional publication depends partly on understanding which of these purposes a particular article or book is emphasizing.
 * 1) provide a framework for understanding teaching and learning,
 * 2) offer advice about how to teach, or
 * 3) advocate particular ideas or practices about education.

Three Purposes of Educational Publications
Consider the first purpose, to provide a framework for understanding teaching and learning (Hittleman and Simon, 2005). A "framework" in this context means a perspective or general viewpoint for understanding specific events and actions. They are much like the theories described earlier in this book, though not always as formal or broad. A published article might propose, for example, a way of understanding why certain students are disrespectful in spite of teachers’ efforts to prevent such behaviour (perhaps they are reinforced by peers for being disrespectful). It might offer evidence supporting this perspective. In doing so, the author provides a sort of “theory of disrespectful behavior,” though he or she may not call it a theory explicitly.

A second purpose is to offer advice about appropriate teaching practices. An article intended for this purpose, for example, might suggest how to introduce reading instruction to first-graders, or how to use fiction to teach high school history, or how to organize a class to include a student with a disability. Often giving such advice overlaps with the first purpose, providing a framework for understanding, since thinking about an educational issue in a particular way may imply certain ways of dealing with it in practice.

A third purpose of a published article is to advocate ideas and persuade others to take actions benefiting students and society. It might take a position about important issues in education: Is it a good idea or not to retain (or hold back) a student in grade level for another year if the student fails the curriculum the first time? Should schools teach about sexuality? Should girls learn science in classrooms separate from boys? In advocating for ideas or policies about such matters, the article may express concern about what is good, ethical or desirable in education, not just about what is factually true or practical. The author may seek explicitly to persuade readers of the author’s point of view. These features do not mean, however, that you need to give up thinking for yourself. On the contrary, when reading an advocacy-oriented article, reflection may be especially important.

Whatever its purpose—understanding, advice, or advocacy—an article or book about a professional issue can stimulate thinking about what you know and believe about teaching and learning. It should therefore create, rather than undermine, your individuality as a teacher. Think of professional reading as a dialogue or conversation about education: some of the comments in the conversation will probably be more helpful than others, but each participant contributes somehow, even if none can give a final answer or everlasting truth. It is the same with publications; some may be more helpful than others, but none will be so perfect that you can afford to cease further reading or further thinking. If you are about to begin a teaching career, for example, you may be especially interested in anything published about classroom management, but less interested in the problems of administering schools or in the political issues that usually accompany educational systems. Yet some publications may discuss these latter issues anyway, and eventually you may find yourself more concerned about them than at the start of a career. Your job, as a reflective teacher, will be sort out the currently useful articles (or parts of articles) from ones you cannot use immediately.

To experience educational publications in this way, however, you must think of the authors as your collaborators as well as general authorities. As a reader, you need to assume that you are entitled to consider an author’s ideas, but not obligated to accept it without question. There are several strategies for developing this attitude, but to keep the discussion focused, we will look at just two. We have already discussed the first strategy, which is to understand the purposes of any particular piece of research which you encounter, in order to assess its current usefulness to your daily work and your long-term professional goals. We have already indicated several general purposes of educational research publications, but we will go into more detail about this in the next section. The second strategy for relating to authors as collaborators is to think about how you yourself might contribute to professional knowledge by engaging in research of your own, even as a classroom teacher—an activity often called action research (Mills, 2006; Stringer, 2007). At the end of this chapter we discuss what action research involves, and how you might consider using it.

Authors’ Assumptions about Readers
Authors of professional articles and books also make assumptions about their readers, and it helps to be aware of these while you read. The assumptions affect the style, content, and significance of the author’s ideas in ways that are both obvious and subtle.

One assumption is about the response which an author expects from you, the reader: does he or she expect you actually to do something new, or simply to consider doing something new? Or does the author just want you to be aware of a new idea? Consider, for example, an article reviewing best practices about inclusion of students with special needs. The author may imply, or even urge you to take a moral position: you should include these students, the author may seem to say. But in a different article—one recommending particular teaching practices—the author may merely ask you to think about alternatives to your normal ways of teaching. Certain strategies worked under certain teaching conditions, the author says, so simply consider whether they might work for you as well.

A second, less obvious difference among professional publications is in their unstated assumptions about prior experiences and attitudes of readers. This assumption may be either helpful or frustrating, depending on you actual prior background. A piece intended as a “framework for understanding” may assume, for example, that you are familiar with basic theories of learning already. If you have read and understood what we outlined in Chapter 2, about basic learning theories, the article may turn out to be relatively accessible or understandable to you even if you have relatively little experience in actual classroom teaching, and even if you have never studied learning theories in detail. The article might seem more accessible than expect because, for example, it focuses primarily on how teacher's praise affects students' learning, an idea with which you may be somewhat familiar already.

On the other hand, a professional publication may assume that you have taught school for a number of years already, or that you are at least familiar with classroom life from the point of view not of students, but of a teacher. An author writing about "withitness" (discussed in Chapter 7), for example, may make this assumption, since the concept originated by observing teachers managing large group classroom activities. If you yourself are experienced at actual teaching, reading about withitness may trigger a lot of questions about just how withit teachers are able to be in practice, and about whether in fact they always need to be withit. You can also ask yourself these questions even if you have not yet been a teacher yourself, of course, but they may seem less immediate or urgent.

A professional article intended to advocate for a particular educational policy or practice may make very different assumptions about you as a reader. It may assume, for example, that you do in fact enjoy persuading others of your point of view, even when others initially disagree or react indifferently. This sort of assumption may show up as much in what the writing omits, as in what it includes: if the term cooperative learning activity is used without explanation, for example, the researcher may be assuming not only that you are the sort of person—perhaps a teacher—who knows what that term means already, but also that you already believe in the value of cooperative learning and are motivated to explain its value to others.

In making these distinctions among published articles, keep in mind a point we made at the outset: that an individual article usually serves more than one purpose at a time and makes more than one assumption about your prior knowledge and about how you are supposed to respond to the article. The differences are only about emphasis. To illustrate these ideas about the purposes and effects of research, look in the next section at three examples of actual published articles relevant to education. The studies are not a full cross-section of educational research or publications, but they do suggest some the variety possible (and necessary) among them. Each example serves a mixture of purposes, but also emphasizes one purpose in particular (perspective-taking, teaching recommendations, or advocacy) described earlier. The authors of each example also particular assumptions about you, the reader—about the intellectual work which the authors expect you to do and about the motivations which they assume you have or hope that you will acquire. For each example, we describe the reactions of one of us (Kelvin Seifert) as he read the article.

(back to Chapter 13...)


text:
User talk:65.94.240.144

Thanks for experimenting with Wikibooks. Your test worked, and has now been removed. Please use Sandbox for any other tests you want to do, since testing material in modules will normally be removed quickly. Please see the welcome page if you would like to learn more about contributing to our project. Thanks. – Mike.lifeguard  | talk 20:11, 5 September 2007 (UTC)

title: User talk:65.94.240.144


text:
Contemporary Educational Psychology/Chapter 13: The Reflective Practitioner/Examples of Professional Articles

As stated in the previous section, the authors of each of the following examples make particular assumptions about you, the reader. They expect you to have particular background knowledge, to have particular goals, and to do particular intellectual work in reading their material.

Example #1: How Do Children Acquire Moral Commitments?
In 1997, Herbert Saltzstein and several colleagues published a research-oriented article about how children acquire moral beliefs (Saltzstein, et al., 1997). The group of researchers were all graduate students and professors of psychology, working mostly at the City University of New York. When one of the contributors to this Wikibook, KelvinLeeSeifert, read of their affiliation with psychology, he suspected that they would talk about moral beliefs in general, and not necessarily about moral issues in classrooms, such as cheating or treating classmates with care and respect. Still, the article interested Kelvin as a former and current teacher, because he had long been concerned with fostering qualities like integrity, honesty, cooperation, and loyalty in students. If Kelvin could find out about the mechanism or process by which children acquire mature moral beliefs, he reasoned, maybe he could modify his teaching to take advantage of that knowledge.

So Kelvin began reading the article. He discovered some parts were challenging and required careful reflection, whereas others were easier to read. One of the most challenging passages came almost immediately, in the second and third paragraphs; these paragraphs, it seemed, required a bit of prior knowledge about theories of moral development. But Kelvin was willing to concentrate more fully on these paragraphs, because he expected that they might clarify the rest of the study. Here are the paragraphs (in italics), followed by some of Kelvin’s thoughts as he read them:

 * We began by re-examining the phenomenon of heteronomy, Piaget's assertion (1932/1965) following Kant (1785/1959) that young children equate moral obligation with deference to authority when justifying their moral judgments. The concept is important because it is central to the organismic account of moral development as a series of differentiations and integrations....[p. 37]

 * This was one of the difficult paragraphs, perhaps especially because Kelvin had never read the specific book by Piaget or by the philosopher Kant. But Kelvin did recall reading, at various times over the years, about Piaget's views on moral development. Piaget believed that at first, children define morality in terms of what adults think:  an action is "good" if and only if adults (e.g. parents) consider it good, and "bad" if and only if adults consider it bad.  This is the idea of "heteronomy" that Saltzstein is referring to. Children, in this view, take quite awhile to develop or "grow" into truly autonomous moral beliefs. Autonomous beliefs form slowly out of earlier beliefs, in the way that a young plant or animal might grow.  This is the "organismic account of moral development" that Saltzstein is talking about.

 * ...This account has been challenged by Turiel's "domain theory" (Turiel, 1983). According to Turiel and his colleagues, even young children intuitively distinguish moral from conventional rules. [p. 37]

 * Here was an idea that was intriguing! Saltzstein and his colleagues were pointing to research (by the person cited, named Turiel) that suggests that even preschoolers know the difference between truly moral rules and merely conventional rules. Apparently they believe, for example, that it would be wrong to steal toys or to hit someone, even if adults gave you permission to do so.  But apparently they also know that it would be OK for traffic lights to use different colors--for red to mean "go" and green to mean "stop"—provided that everyone agreed on changing the rule.  That is what the researcher named Turiel apparently meant by distinguishing convention from morality.

The introduction continued in this academically challenging style for about two pages, requiring Kelvin to read slowly and carefully in order to understand its points. Kelvin was not discouraged from continuing, though, because he wanted to find out more about how, in general, children acquire moral beliefs. Did moral beliefs take time to develop—did they "grow" on children slowly after initially being borrowed from parents or other adults? In this case, then maybe Kelvin owed it to his students to adopt and express desirable moral attitudes myself, so as to provide a good model for their developing beliefs. Or were students’ key moral beliefs already in place when they entered school—almost as if "hard wired" in their minds, or at least already learned during infancy and the preschool years? In this second case, it might still be desirable for Kelvin to adopt positive moral attitudes, but not for the purpose of modeling them for students. Students already “hard wired” for key moral beliefs might not need a model so much as an enforcer of desirable moral behaviors. Concerning the issue of cheating, for example, the students might already understand the undesirable nature and implications of this behavior. As a result they might not need demonstrations of honest integrity from their teacher as much as affirmations from the teacher of the importance of honesty and integrity, along with consistent enforcement of appropriate sanctions against cheating when it did occur.

For Kelvin, therefore, the outcomes of research on moral development—including Saltzstein's that he was currently reading—posed issues of classroom management, both in university classrooms and in public school classrooms. So Kelvin read on. Saltzstein proposed resolving the issues about the origins of moral development by distinguishing between moral conflicts and moral dilemmas:

 * Moral conflicts are conflicts between moral duty or right and a non-moral desire. An example might be the conflict between whether to return a wallet to its rightful owner or keep the coveted wallet with its extra cash.  In contrast, moral dilemmas are conflicts involving two moral rights or duties.  For example, [a person might feel a dilemma between] whether to steal a drug to save a spouse's life. [p. 38]

 * The distinction between conflicts and dilemmas looked promising to Kelvin. Moral conflicts looked fairly simple in cognitive terms, even if they were sometimes difficult emotionally.  The "right" action was obvious.  Moral dilemmas were more complex cognitively as well as emotionally, because two "goods" were being weighed against each other.  The moral alternatives might both be right and wrong at the same time, and their relative "rightness" might not be immediately obvious.

Saltzstein and his colleagues proposed that when young children show awareness of moral rules, they may be doing so in the simpler context of moral conflicts. A young child might believe that you should return a dollar to its owner, even if the child has trouble in practice overcoming a selfish impulse to keep the dollar. The same child might have trouble deciding, however, whether it is "right" to inform his teacher if a best friend has cheated on a test. In that case two moral principles compete for attention—honesty and loyalty to a friend. To sort out the implications of choosing between these principles, a young child might need to rely on older, wiser minds, such as parents or other adults. And the minute that he or she does so, the child is showing the moral heteronomy that Piaget used to write about and that Saltzstein referred to early in the article.

Understanding these ideas took effort, but once Kelvin began figuring them out, the rest of the article was easier to follow. In reading the remaining pages, he noted in passing that the researchers used several techniques common in educational research. For example, they interviewed participants, a common way of gathering systematic information about individuals' thinking. They also imposed controls on their procedures and on the selection of participants. Procedures were controlled, for example, by posing the same three moral dilemmas and to all participants, so that individuals' responses could be compared meaningfully. The selection of participants was controlled by selecting two age groups for deliberate comparison with each other—one that was seven years old and the other that was eleven. Since the researchers wanted to generalize about moral development as much as possible, but obviously could not interview every child in the world, they also sampled participants: they selected a manageable number (sixty-five, to be exact) from the larger student population of one particular school. In a second part of the investigation, they also selected a comparable number of children of the same two ages (7 and 11) from the city of Recife, located in Brazil. The Brazilian group's responses were compared deliberately with the American group's, in order to allow for the impact of cultural beliefs on moral development in general.

Kelvin recognized this research strategy as an example of using control groups. In research terms, the Brazilian group "controlled for" the impact of American culture on children's moral beliefs. And vice versa: the American group controlled for the impact of Brazilian culture on children's moral beliefs. Altogether, these techniques helped insure that the interviews of children's moral beliefs really illustrated what they were supposed to illustrate—that they were reliable and valid, in the senses that we discussed in Chapter 11. As Kelvin noticed Saltzstein's attention to good research techniques, he gained confidence in Saltzstein’s observations and in the interpretations that the authors made from them.

What did Saltzstein and his colleagues find out—or more to the point, what did Kelvin Seifert learn from what Saltzstein and his colleagues wrote about? There were three ideas that occurred to Kelvin. One was that in everyday life, children probably deal with moral beliefs of all levels of cognitive complexity, and not just "simple" moral conflicts and "complex" moral dilemmas. Saltzstein found that children's solutions to moral dilemmas depended a lot on the content of the dilemma. Children advocated strongly for truthfulness in some situations (for example, in deciding whether to tell the teacher about a friend's cheating), but not in other situations (like in deciding whether to back up a friend who is being teased and who has lied in an effort to stop the teasing). But it was rare for all children to support any one moral principle completely; they usually supported a mix.

Another idea that Kelvin learned from Saltzstein's research was about how children expressed moral heteronomy versus moral autonomy. Age, it seemed, did not affect the beliefs that children stated; younger and older children took similar positions on all dilemmas initially. But age did affect how steadfastly children held to initial beliefs. Younger children were more easily influenced to switch opinions when an adult "cross-examined" with probing questions; older children were more likely to keep to their initial position. Moral heteronomy was revealed not by a child's views as such, but by the kind of dialogue a child has with adults.

A third idea that Kelvin learned was about children's perceptions of adults' moral beliefs. Saltzstein found that even though older children (the 11-year-olds) showed more moral autonomy (were more steadfast) than younger children, they tended to believe that adults thought about moral issues in ways similar to children who were younger. In the "teasing" dilemma mentioned above, for example, the 11-year-olds opted much more often than 7-year-olds for remaining loyal to a friend, even though doing so meant further untruthfulness with peers. Yet the 11-year-olds also more often stated a belief that adults would resolve the same dilemma in a way characteristic of 7-year-olds—that is, by telling the truth to peers and thus betraying loyalty to a friend. This finding puzzled Kelvin. Why should older, and presumably more insightful, children think that adults are more like younger children than like themselves? Saltzstein suggested an interpretation, however, that helped him make sense of the apparent inconsistency:
 * ...Consistent with our past research, children attributed the kinds of moral choices made by younger children to adults. In our view, this finding tends to support a constructivist rather than a [social modeling] view of morality, which would predict that the child's judgments mirror (or develop toward) their representation of adult judgments. [p. 41]

 * In other words, thought Kelvin, if children learned moral beliefs by imitating (or modeling themselves after) parents or other adults, then they ought to see themselves as resembling adults more and more as they get older. Instead, they see themselves as resembling adults less, at least during middle childhood.  This would happen only if they were preoccupied with "constructing" their own beliefs on the basis of their experiences, and therefore failed to notice that adults might also have constructed beliefs similar to their own.

Relevance: A Framework for Understanding Moral Development
The article by Saltzstein offered a way to understand how children develop moral beliefs, and especially to understand the change from moral heteronomy to moral autonomy. By imposing controls on the procedures (uniform interviews) and on the selection of participants (particular ages, particular societies or cultures), the researchers eliminated certain sources of ambiguity or variability in children's responses. By framing their project in terms of previous theories of moral development (Piaget’s, Turiel’s), furthermore, they made it easier to interpret their new results in the general terms of these theories as well. In these ways the investigation aspired to provide a general perspective about children's moral development. Providing a framework for understanding, you recall, is one of the major purposes of many professional publications.

But note that the authors paid a price for emphasizing this purpose. By organizing their work around existing general theory and research, they had to assume that readers already had some knowledge of that theory and research. This is not an unreasonable assumption if the readers are expected to be fellow researchers; after all, many of them make a living by "knowing the literature" of psychology. But assuming such knowledge can be an obstacle if the authors intend to communicate with non-psychologists: in that case, either the authors must make more of an effort to explain the relevant background research, or readers must educate themselves about the research. The latter activity is not necessarily difficult (the background knowledge for Saltzstein's work, for example, took me only a few paragraphs to explain in writing), but it must be done to make full sense of research that tries to provide a universal framework of psychological knowledge.

The Reader's Role: Interested Observer of Children
In conducting and reporting their research, Saltzstein and his colleagues were not presenting themselves as school teachers, nor were they expecting readers necessarily to respond as teachers. As they put it in the first paragraph of the article, they sought to offer "a more contextualized perspective for understanding the development of moral judgments" [p. 37]. Unlike most teachers, they seemed indifferent to recommending how children's moral judgments ought to be fostered. Observation of children was their purpose, not intervention. The meaning of the term "contextualized perspective" was not obvious to Kelvin when he first read it, but eventually it became clearer: they were talking about the importance of distinguishing among types of moral decisions and moral beliefs. They did sometimes note information relevant to teaching—for example, they pointed out that for cultural reasons, teachers in Brazil do not command high respect and therefore compared to American children, Brazilian children may feel less compelled to tell the truth to their teachers. But this comment was not the primary focus of their research, nor did the authors discuss what (if anything) it might imply about teaching in the United States.

Yet the non-teaching perspective of the article did not keep Kelvin, a long-time school teacher and current university teacher, from reflecting on the article in terms of its educational relevance. As we mentioned already, Kelvin was attracted to the article because of his own concerns about character development in students—how do they acquire moral beliefs and commitments, and how should he help them in doing so? Kelvin did not really expect to find an answer to the second of these questions, given the "observation" orientation of the authors. He did hope to find an answer to the first, although even here he also expected that to make allowances for the fact that research interviews are not usually identical to classroom situations. Children might respond differently when interviewed individually by a researcher, compared to how they might respond to a teacher in class. Or perhaps not. So in reflecting on the article, Kelvin had to note the context and purposes of Saltzstein's study, and to remind himself that once a teacher went beyond simply observing children to intervening on their behalf, the teacher might be led to different conclusions about children’s moral development. But in spite of these cautions—or maybe because of them—Kelvin found much food for thought in the article related to teaching.

Example #2: Learning Disability as a Misleading Label
In 2006, Ray McDermott, Shelley Goldman, and Hervé Varenne published an article that discussed the use of disability categories in education. The article attracted Kelvin’s attention because he had been concerned for a long time about the ambiguities of disability categories (see Chapter 5 of this book) as well as about their potential for stigmatizing individuals. He expected the article to document additional problems with labeling when a student is from a non-White ethnic group. Kelvin’s expectation was fulfilled partially, but he was surprised also to encounter an additional and tougher message in the article. Here is how the study began (again, printed in italics):

 * Since about 1850…classifying human beings by mental ability, accurately or not, has been a politically rewarded activity. Those with power have placed others, usually the downtrodden, into ability and disposition groups that they cannot escape… People who live together in a culture must struggle constantly with the constraints…of systems of classification and interpretation used in the culture.

 * Kelvin had a mixed reaction to this opening. In one way it seemed to say something familiar—that classification systems (such as categories for disabilities) may create problems for individuals. But the tone of the paragraph sounded more severely critical than Kelvin had expected: it was saying that power governed all classifications, implying that misclassifications may be widespread or even universal.

Kelvin’s initial hunch was therefore that the article would express a radically critical view of disability classifications—particularly as they affect the “downtrodden,” which presumably included children from minority ethnic groups. His expectation proved correct as the authors explained their point of view, which they called a cultural approach to understanding disability. Using learning disabilities (LD) as an example, here is how they explained their position:

 * We are not as interested in LD behavior as in the preoccupations—as seen from the level of classroom organization—of all those adults who are professionally poised to discover LD behavior. We are less interested in the characteristics of LD children than in the cultural arrangements that make an LD label relevant.

 * At this point Kelvin was not sure if he wanted to continue reading the article because it seemed like it might not be relevant to classroom life specifically. It also implied a severe criticism of professional educators—implied that they are too eager to find examples of LD and for this reason may misclassify students. On the other hand, Kelvin was already aware that LD are an especially ambiguous category of disability; maybe the article would help to show why. So he kept reading.

The authors continued by outlining the history of LD as a category of disability, describing this category as an outgrowth of the general intelligence testing movement during the twentieth century. By the 1970s, they argued, the concept of LD offered a way to classify children with academic difficulties without having to call the children mentally disabled. Because of this fact, the LD category was needed—literally—by well-off parents who did not want their children treated or educated as children with mental disabilities. LD as a concept and category came to be applied primarily to children from the White middle-class, and mental disability became, by default, the equivalent category for the non-White and poor.

To support this assertion, the authors reported a classroom observation of three non-White boys—Hector, Ricardo, and Boomer—while they worked together to design an imaginary research station in Antarctica. Citing actual transcripts of conversation while the boys worked, the authors concluded that all three boys showed intelligence and insight about the assignment, but that the teacher was only aware of the contributions of one of the boys. Hector systematically hid his knowledge from the teacher’s view by getting Boomer to speak for their group; Ricardo participated well in the group work but was rarely acknowledged by the other two boys. Boomer received considerable praise from the teacher, thanks to his speaking for the group. Yet the teacher was never aware of these subtleties. The authors blamed her oversight not on the teacher herself, but on an educational and cultural system that leads educators to classify or typify students too quickly or easily. Here is how they put it:

 * The American classroom is well organized for the production of display of failure, one child at a time if possible, but group by group if necessary…Even if the teacher manages to treat every child as capable, the children can hammer each other into negative status; and even if both…resist dropping everyone into predefined categories, the children’s parents can take over, demanding more and more boxes with which to specify kinds of kids doing better than other kinds of kids. In such a classroom, if there were no LD categories, someone would have to invent them.

 * When Kelvin read this conclusion, he did not really disagree, but he did feel that it was beside the point for most teachers. Maybe children do get classified too easily, he thought, but a teacher’s job is not just to lament this possibility, as the authors seemed to be doing. Instead their job is to help the real, live children for whom they have daily responsibility. What teachers need are therefore suggestions to avoid misclassifying students by overlooking key information about them. Kelvin wished, at the end, that the authors had made some of these suggestions.

Relevance: A Critical Framework
In this study the authors offered a sort of backhanded framework of thinking about categories of disability; or more precisely they offered a framework for understanding what the categories are not. In essence they said that disability categories describe qualities “in” students only in the sense that educators and others happen to think of disability categories in this way. An equally reasonable way to think about disabilities, they argued, is that modern society is organized so that its citizens have to be classified for many different reasons. Educators are simply helping to implement this society-wide expectation. A frequent result in classrooms is that teachers classify students too easily and that key evidence of students’ capacity is overlooked.

In making this argument, the authors implied an indirect recommendation about how to teach, though the recommendation actually focused on what teachers should not do. Instead of (mis)identifying children with learning difficulties, the authors implied, teachers and other educators should stop concerning themselves with classifying children, and seek to reorganize classrooms and schools so that classification is less important. “Change the school,” they wrote, “and LD becomes less relevant.” This conclusion may be an important reminder, but it is not especially helpful as a recommendation to practicing teachers, who usually need to know about more than what to avoid.

The Readers’ Role: Concerned Advocate for Social Justice
It is not surprising that the article lacked concrete recommendations for teaching, given that the authors seemed to speak to readers not as classroom teachers, but as general critics of society who are concerned about fairness or social justice. Their comments made two assumptions: first, that readers will want to minimize unfair stereotypes of students, and second, that readers will seek greater fairness in how teachers treat students. For readers who happen to be teachers themselves, the first of these assumptions is a reasonable one; most of us would indeed like to minimize unfair stereotyping of students. The second is also reasonable, but perhaps not in a way that the authors intended. Teachers probably do try their best to treat students fairly and respectfully. Their responsibilities usually mean, however, that they can only do this conveniently with their own students; the time available to work toward general social justice is often limited. (As you might suspect, Kelvin was not fully satisfied after he finished reading this article!)

Example #3: The Impact of Bilingualism on Reading
In 1995, three education professors—Robert Jiménez, Georgia García, and David Pearson—published a study about the impact of bilingualism on children's ability to read English (1995). The three specialized in curriculum studies, literacy acquisition, and bilingual language development, and were therefore motivated by a concern for the academic success of bilingual children and especially by concern for identifying why bilingual children sometimes have difficulty learning to read English. Too much research on bilingualism, they argued, was based on what they called a "deficit" framework: it focused on what bilingual children lacked compared to monolinguals. They sought an alternative framework, one focused on bilingual students' competence, and especially on their competence to read a second language.

To search for this alternative, the researchers mounted a large research program, and the article published in 1995 was one of the studies resulting from this research. It caught Kelvin’s interest not only because of its topic, but because of its approach. Instead of surveying dozens of students with a questionnaire, as researchers sometimes do, these investigators relied on just three students studied intensively. Each student became a case study and included detailed, lengthy observations and interviews of that particular student. Each student was chosen deliberately for a particular purpose. One was a highly proficient reader who was also bilingual (Spanish and English); a second was a marginally proficient reader who was bilingual (Spanish and English); and a third was a highly proficient reader who was monolingual in English. To qualify for the study, furthermore, each student had to be comfortable reflecting on and talking about their own reading processes, so that the authors could interview them at length on this topic. The researchers asked each student to read six one-page passages in English and (where relevant) in Spanish. They invited all three to think aloud about their reading as they went along, commenting on how they figured out particular words or passages. The oral readings and think-aloud commentaries were taped and transcribed, and became the information on which the authors based their conclusions and recommendations.

Using these procedures, Jiménez, García, and Pearson discovered important differences among the three girls. The proficient bilingual, Pamela, used her growing knowledge of each language to help in learning vocabulary from the other language. When she encountered the English word species, for example, she guessed correctly that it meant the same as the similar Spanish word especies; and when she encountered the Spanish liquído, she guessed correctly that it meant the English liquid. Her focus on learning vocabulary was stronger than for the proficient monolingual, Michelle, who commented less on specific words than how the overall reading passages related to her prior general knowledge. The difference presumably stemmed from Michelle's greater familiarity with English vocabulary—so much greater, in fact, that Michelle did not need to think about individual words deliberately. Both Michelle and Pamela differed, however, from the less-proficient bilingual reader, Christine. Like Pamela, Christine focused on vocabulary, but she did not think of her native Spanish as a resource for this task. When reading a Spanish word, she was sometimes reminded of English equivalents ("cognates," as language teachers call them), but she did not use her much greater knowledge of Spanish to assist with her more limited English. But she did not search for equivalent words deliberately, as Pamela did.

Relevance: Recommendations for Teaching English as an Additional Language
The authors of this article focused more directly on particular learning behaviors than did the authors of the two articles described earlier. Jimenez and his colleagues emphasized the importance of regarding a child's native language as a strength in the process, not a liability, and they then pointed out the importance of facilitating vocabulary development. But they did not claim this recommendation to be appropriate for all children or for all forms of bilingualism. They only focused on a particular pair of languages (Spanish and English in the USA), and on three combinations of skill level in these two languages. These are common bilingual experiences in the United States, but they are not the only ones, either in the United States or elsewhere in the world.

For other bilingual situations, their conclusions might not hold true. For some students (e.g. Chinese-Americans), the native language and the second language are much more different in vocabulary, pronunciation, and grammar than Spanish is to English, and therefore may provide less of a resource to a child learning to read. And in some settings, relationships between languages are more equal than in the United States. In Canada, for example, both the numbers and the overall social status of English speakers and French speakers are more equal than in the United States. In both of these situations, if a child fails to learn to read the second language, it may not be for the reasons suggested by Robert Jiménez, but for other reasons, ranging from difficulties with reading per se to cultural differences in how a child expects to be taught (Johnson, 2004).

The Reader's Role: Both Teacher and Researcher
In the published article describing their research, Jiménez, García, and Pearson assumed that readers have some familiarity with bilingual students and with issues related to teaching reading. They began their article by describing previous research studies in these areas—more than a dozen of them, in fact. In the middle they described numerous responses of the three bilingual students to the passages they were asked to read. At the end of the article they made specific suggestions for teaching, such as "focus more on vocabulary development." When Kelvin read these various sections, he found that his prior knowledge of and reflections about teaching helped to make sense of them. But he also found that did not need to be an expert in bilingualism order to understand the authors' messages—he had never, in fact, taught English as a Second Language, nor had he ever conducted research on reading or bilingual language development.

(back to Chapter 13...)


text:
Talk:Contemporary Educational Psychology/Chapter 13: The Reflective Practitioner/Examples of Professional Articles

This section is a bit long. Possibly it should be divided into three sections--one for each major example. The trouble is that the lengthy discussions seem necessary in order to make the key points about being a truly "reflective" practitioner.

KelvinLeeSeifert 20:38, 5 September 2007 (UTC)


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Talk:Contemporary Educational Psychology/Chapter 13: The Reflective Practitioner

Portions of this chapter were originally published in an earlier version as part of a book called Constructing a Psychology of Teaching and Learning, published by Houghton Mifflin in 1999 and authored by KelvinLeeSeifert. Houghton Mifflin returned the copyrights to Kelvin in 2003, and he is now relinquishing the rights so that this material can appear here as part of this Wikibook.

KelvinLeeSeifert 20:41, 5 September 2007 (UTC)


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User:Zazk

Enrique Juan de Dios

title: User:Zazk


text:
User talk:68.196.94.191

Please stop adding nonsense to Wikibooks. It is considered vandalism. If you would like to experiment, use the sandbox. Thank you. – Mike.lifeguard  | talk 21:04, 5 September 2007 (UTC)

title: User talk:68.196.94.191


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User:Klseifert

A bit about me:

Since 1974, I have been a professor of educational psychology at the University of Manitoba, located in Winnipeg, Manitoba, Canada. I have written other textbooks, primarily for Houghton Mifflin Company located in Boston, Massachusetts, USA, and primarily on topics related to developmental psychology, not educational psychology. I've also published a lot of other articles, chapters, and reviews, as part of my career as an academic.

You can learn more about me at [my home page], which also leads to a fairly complete, and only slightly out-of-date [curriculum vita].

My experiences with open-source material consists primarily of material contributed to the Wikibook called Contemporary Educational Psychology.

KelvinLeeSeifert 21:19, 5 September 2007 (UTC)

title: User:Klseifert


text:
User talk:68.173.145.66

Please stop posting the "Who is Slughorn?" question on Deathly Hallows chapter 6. It's a pointless question, and has been answered in depth in the previous book. Chazz (talk) 22:03, 5 September 2007 (UTC)

title: User talk:68.173.145.66


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Control Systems/Estimators and Observers

Estimators and Observers
A problem arises in which the internal states of many systems cannot be directly observed, and therefore state feedback is not possible. What we can do is try to design a separate system, known as an observer or an estimator that attempts to duplicate the values of the state vector of the plant, except in a way that is observable for use in state feedback. Some literature calls these components "observers", although they do not strictly observe the state directly. Instead, these devices use mathematical relations to try and determine an estimate of the state. Therefore, we will use the term "estimator", although the terms may be used interchangeably.

Creating an Estimator
There are several observer structures including Kalman's, sliding mode, high gain, Tau's, extended, cubic and linear observers. To illustrate the basics of observer design, consider a linear observer used to estimate the state of a linear system. Notice that we know the A, B, C, and D matrices of our plant, so we can use these exact values in our estimator. We know the input to the system, we know the output of the system, and we have the system matrices of the system. What we do not know, necessarily, are the initial conditions of the plant. What the estimator tries to do is make the estimated state vector approach the actual state vector quickly, and then mirror the actual state vector. We do this using the following system for an observer:

 * $$\hat{x}' = A\hat{x} + Bu + L(y - \hat{y})$$
 * $$\hat{y} = C\hat{x} + Du$$

L is a matrix that we define that will help drive the error to zero, and therefore drive the estimate to the actual value of the state. We do this by taking the difference between the plant output and the estimator output.

In order to make the estimator state approach the plant state, we need to define a new additional state vector called state error signal $$e_x(t)$$. We define this error signal as:

 * $$e_x(t) = x - \hat{x}$$

and its derivative:

 * $$e_x'(t) = x' - \hat{x}'$$

We can show that the error signal will satisfy the following relationship:

 * $$e_x'(t) = Ax + Bu - (A\hat{x} + Bu + L(y - \hat{y}))$$
 * $$e_x'(t) = A(x- \hat{x}) - L(Cx - C\hat{x})$$
 * $$e_x'(t) = (A - LC)e_x(t)$$

We know that if the eigenvalues of the matrix (A - LC) all have negative real parts that:

 * $$e_x(t) = e^{(A - LC)(t-t_0)}e_x(t_0) \to 0 $$ when $$ t \to \infty$$.

This $$e_x(\infty) = 0$$ means that the difference between the state of the plant $$x(t)$$ and the estimated state of the observer $$\hat{x}(t)$$ tends to fade as time approaches infinity.

Separation Principle
We have two equations:

 * $$e_x[k + 1] = (A - LC)e_x[k]$$
 * $$x[k + 1] = (A - BK)x[k] + BK \cdot e_x[k]$$

We can combine them into a single system of equations to represent the entire system:

 * $$\begin{bmatrix}e_x[k + 1] \\ x[k + 1]\end{bmatrix} = \begin{bmatrix}A - LC & 0 \\ +BK & A - BK\end{bmatrix} \begin{bmatrix}e_x[k] \\ x[k]\end{bmatrix}$$

We can find the characteristic equation easily using the separation principle. We take the Z-Transform of this digital system, and take the determinant of the coefficient matrix to find the characteristic equation. The characteristic equation of the whole system is: (remember the well known $$(zI-A)^{-1}$$)

 * $$\begin{vmatrix}zI - A + LC & 0 \\ -BK & zI - A + BK\end{vmatrix} = |zI - A + LC| |zI - A + BK|$$

Notice that the determinant of the large matrix can be broken down into the product of two smaller determinants. The first determinant is clearly the characteristic equation of the estimator, and the second is clearly the characteristic equation of the plant. Notice also that we can design the L and K matrices independently of one another.

It is worth mentioning that if the order of the system is n, this characteristic equation (full-order state observer plus original system) becomes of order 2n and so has twice the number of roots of the original system.

The L Matrix
You should select the L matrix in such a way that the error signal is driven towards zero as quickly as possible. The transient response of the estimator, that is the amount of time it takes the error to approximately reach zero, should be significantly shorter than the transient response of the plant. The poles of the estimator should be, by rule of thumb, at least 2-6 times faster then the poles of your plant. As we know from our study of classical controls, to make a pole faster we need to:

 * S-Domain:Move them further away from the imaginary axis (in the Left Half Plane!).
 * Z-Domain:Move them closer to the origin.

Notice that in these situations, the faster poles of the estimator will have less effect on the system, and we say that the plant poles dominate the response of the system. The estimator gain L can be computed using the dual of Ackerman's formula for selecting the gain K of the state feedback controller:

 * $$L = \alpha_e(z)Q\begin{bmatrix}0\\0\\ \vdots \\1\end{bmatrix}$$

Where Q is the observability matrix of the plant, and αe is the characteristic equation of your estimator.

This can be computed in MATLAB with the following command:

L=acker(A', C', K)';

where L is the estimator gain and K is the poles for the estimator.

Composite System
Once we have our L and K matrices, we can put these together into a single composite system equation for the case of state-feedback and zero input:

 * $$\begin{bmatrix}x[n + 1]\\ \bar{x}[n+1]\end{bmatrix} = \begin{bmatrix} A & -BK \\ LH & A - BK - LH\end{bmatrix} \begin{bmatrix}x[n] \\ \bar{x}[n]\end{bmatrix}$$
 * $$u[n] = -K \bar{x}[n]$$

Taking the Z-Transform of this discrete system and solving for an input-output relation gives us:

 * $$\frac{U(z)}{Y(z)} = -K[zI - A + BK +L C]^{-1}L$$

Notice that this is not the same as the transfer function, because the input is on top of the fraction and the output is on bottom. To get the transfer function from this equation we need to take the inverse of both sides. The determinant of this inverse will then be the characteristic equation of the composite system.

Notice that this equation gives us the ability to derive the system input that created the particular output. This will be valuable later.

Reduced-Order Observers
In many systems, at least one state variable can be either measured directly, or calculated easily from the output. This can happen in the case where the C matrix has only a single non-zero entry per system output.

If one or more state variables can be measured or observed directly, the system only requires a reduced-order observer, that is an observer that has a lower order than the plant. The reduced order observer can estimate the unmeasurable states, and a direct feedback path can be used to obtain the measured state values.


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Control Systems/Adaptive Control

Adaptive Controllers
What we've been studying up till this point are fixed systems, that is systems that do not change over time. However, real-world applications and experience tells us that the environment can change over time: New noise can be added to a signal, the signal quality can be degraded, or the specifications of the signals can be changed at the source.

There is a distinct need then for controllers which can modify themselves to produce the same output regardless of changes to the input. Herein lies the problem of adaptive control. We will introduce some of the concepts in this chapter, and discuss them in greater detail in future chapters.

title: Control Systems/Adaptive Control


text: Category:Book:Kdenlive

title: Category:Book:Kdenlive


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Australian History/1920s

Introduction
After World War I was announced to be over, Australia as a nation was eager to leave the hardships of war behind them. Several introductions to the domestic household that was meant to improve the quality of life such as the automobile and the wireless (radios) were changing the way people lived and shaped the industry around it. This was still the era of traditional social family structure, where man was viewed as the sole bread winner. However, women started to gain independence to a certain extent, although racial tension between natives and settlers remained high. The Great Depression in 1929 changed the way Australia operated due to the crash in the global stock markets. This lead to a reaction of events which eventually ended with the unemployment rate higher then ever before, and with Australians turning to sporting legends like Don Bradman for inspiration.

Fashion
With the new age rapidly approaching, a new age in fashion was also taking flight. When Orville and Wilbur Wright first flew their bi-plane in 1903, little did they know what a world wide phenomenon it would be. Aviation was in, and corsets were out. People not only went to air shows, but also wore aviation equipment wherever they went. Pilots were regarded as heroes, and their planes were seen as a symbol of the perfect modern age. Aviation is still popular, even today. People flock to air shows to watch the latest planes and aircraft in action. The aviation fashion has not continued though. Unfortunately people don’t wear flying suits around town any more, or wear the over sized goggles.

The Ford Model T was by far the most popular automobile of the 1920s. People flocked to buy them, and Henry Ford’s revolutionary factories could produce them in less than 1 hour. When you went out driving with your family you usually dressed in full driving attire including the goggles. Not only did people think that the goggles meant that they were exclusive in this modern age, but they provided protection for the eyes, as many of the motorcars did not have roofs.

Suits were also very popular. The businessman wore a suit wherever he went, even if he was going off to play a soccer game, or slide down a slippery dip. It was incredibly fashionable to have fair skin. Women would go to extreme measures to keep their skin nice and pale. Parasols and hats were popular fashion accessories and often complemented the long flowing dresses the women wore.

As the years progressed the fashions began to change. Men no longer wore suits everywhere they went, but donned more relaxed styles of clothing like t-shirts and shorts. Women wore shorter dresses and usually cut their hair in short practical styles.

Music
The 1920s the host of musical styles was jazz to soul. Louis Armstrong, perhaps one of the most famous Jazz players of all time, rose to fame in the nightclubs of the 1920s. People eager to forget their sorrow and leave their pasts behind them would not only dance to their favorite tunes, but also with the revolutionary gramophone, listen to their favorite tracks in the comfort of their living rooms.

Movies that incorporated music were now also being released. Ben Hur, the most noted film of the 1920’s, incorporated nearly two whole hours of music in the film, which was met with open arms. The audience could now tell what the film was going to be about, just by listening to the music, due to the emotions that could be invoked with instruments. The Charleston also became rather famous.

Entertainment
During the 1920s and 1930s people were coming up with new and exciting ways to keep themselves entertained. Newsreels gave way to cinema with 95% of all movies in Australia coming from Hollywood. This was one of the first signs of the upcoming dominance of America. Although not many people in our modern day society go for joyrides in their cars, in the 1920s and 1930s going for a ride in your new Model-T or Model-A motorcar was the one of the best family outings there was. People would often seek out cheap forms of entertainment. Sports games were affordable and a very exciting way to spend your Saturday afternoon or evening. Soccer, cricket and Australian Rules football were by far the most popular sporting codes and could draw crowds of 20,000 plus. The wireless had justnbeen introduced as well. People could sit down for hours at a time and listen to their set. Beaches like Bondi were also growing in popularity. People would flock from all across the country to sit on those golden beaches and take a dip in the cool water. This new “beach rush” saw a change in fashion as well. Designers were designing short and practical swim suits for women to swim in. Some other things like dancing was a type of entertainment that Australians will do in parties at home, or out in the public. It was a good way of moving around, and getting exercise. Jazz was popular, but some other dance types like country was popular too.

Transport
Transport was changing. From wooden carts drawn by horses, to the beautifully designed and crafted model T by Ford, cars were quickly revolutionising the way people were living. They could now go and visit relatives or friends any time they pleased. If they needed to go shopping, they didn’t walk for an hour to get to the shops, simply took a quick drive in their motorcar . Henry Ford’s factories could produce thousands of cars every day. The factories were actually giant moving assembly lines. Henry Ford invented the moving assembly line as a way of hiring unskilled workers to produce cars. The moving assembly line was in essence a line that moved. The special thing was that every meter or so, someone would do a little job on the bit of car that was going past. Whether it was screwing in a bolt or putting on a door handle, every job was small and very easy to accomplish. This enabled Ford to avoid paying for skilled workers and pay low wages to the working class.

By 1921, Australia already has its first Airline, Qantas. These new flying machines could fly across the world in days, not weeks. What used to be a trip on the high seas turned into a pleasant and smooth flight flying as the hawk flew from destination A to B.

Electric trams were also fast revolutionising the way people traveled. The first trams could only travel a few kilometres an hour, but by 1920, they were reaching speeds of up to 30km/h.

Technology
New advances in the field of technology were taking the world by storm. In Australia the radio or wireless as it was known back then had just hit the airwaves. In 1923 Australia’s first radio station, 2SB, began transmitting. At first users needed to pay a small fee to the government, but this soon changed to lifelong membership. In 1925 60,000 people had subscribed to the radio in Australia. By 1929 over 300,000 people had a radio license.

The gramophone was also gaining popularity. A gramophone is a fancy piece of equipment that plays vinyl records. People liked to sit down much as we do today, and listen to their music pumping through their speakers. The radio was probably the most noted piece of technology in the period. It boomed growing from the first station to over 200 stations today. Unlike the past however, we can listen free unlike when people who lived back in the 1920s who paid a small fee to the government.

As electricity became more widely used, things like washing machines and hot water started creeping into people’s houses. All of these advances were contributing to a general feeling that society couldn’t really get any better, and people started to buy goods. It was this idea of a perfect society that provided the building block for Henry Ford’s Company. He employed unskilled workers, paid them good salaries and built cars. However, he developed a system to allow unskilled workers to build cars through a moving assembly line. The moving assembly line was his most genius creation. He pulled apart every little job there was in the creation of a car, and then gave that job to someone to do over and over. This enabled him produce thousands of cars everyday and sell them cheaply to the population.

The Sydney Harbour Bridge was built, during the Great Depression. It was an attempt to get the economy flowing again. The bridge, was maybe one of the greatest industrial achievements of the century. It measured over 1 km long and is the longest arch bridge in the world.

Sport
Sport in the 1920’s was just as prominent as it is now. Australia’s population not only followed professional sport, but played lots of sport themselves. Australians believed everyone should get a fair go, and this simple but just motto, still applies even today. Cricket, soccer and AFL were Australia’s favourite sports. Cricket, was one of the sports we were really good at. Australians flocked to pitches to see the likes of Gordon Coventry and Sir Donald Bradman. Sir Donald Bradman was a crowd favourite. His quick eye, good coordination, and perfect footwork gave him a freakish ability to score lots of runs, without getting out. It was Heroes like Don who attracted massive crowds to the sporting arenas. Sport however was sometimes used to promote bad intentions, Hitler used the 1936 Olympics as a way to promote Aryan supremacy over the world. Unfortunately for him, Athletes like Jesse Owens upset his plan by winning nearly everything they went in. The wireless radio had a massive impact on the sporting field. People could now follow their favourite individuals or teams, without actually being at the sporting ground. In 1924 people from all over Australia listened to Andrew Charlton win the 1500m swimming finals in Paris.

Aboriginal People
The 1920s and 1930s were scarred by racism towards the Aboriginal People. The Aboriginal Protection Board was meant to ease the tensions and fix Aboriginal problems. What they did was take away children from their parents and place them in white training institutions called missions. The belief was, if they took the children away, the Aboriginal problems would breed out. The generation has now become known as the Stolen Generation. Many of the Stolen Generation have struggled with depression, and some have even taken their own lives. Recently a case was settled for the government to pay compensation for a man who was taken from his parents. This money however is too little and too late. The Australian government also repossessed sacred Aboriginal land for soldier settlement schemes. Aboriginal soldiers who had served Australia in both World Wars lay forgotten or returned back to racism and hatred that they had faced before the war. Aboriginals were also subject to horrid working conditions. They often worked for 16 hours a day, and only received a fraction of what the equivalent white man would receive. It was these racial tensions that in 1928, lead to the murder of 31 Aboriginal men, women and children, in supposed self-defence as a team of investigators researched the death of a Dingo Hunter. On Australia Day 1938 The Aboriginals commemorated 150 years of white settlement not with a day of celebration but with a day of mourning.

Trade Unions
A Trade Union is an organisation which people of a certain skill are part of. Australian worker by the late 19th Century had developed strong Trade Unions. This enabled skilled workers to gain good wages for themselves and feed their hungry families. During World War 1, Trade Unions organised strikes. These strikes were to protest frozen wages that the tradesmen were submitted to. When the Labor party was torn apart by the conscription issue, Trade Unions received little to no support from the conservative parties and their powers were diminished.

Summary
As you can see, the 1920s and the 1930s were a time of great change. People forgot the old and embraced the new in an attempt to leave the hardship and struggles of the war behind them. New Technology was being created like toasters and cars. The fashion world was seeing great change in the latest fashions. Aboriginals still faced the racial tension from nearly the whole of Australia.

title: Australian History/1920s