Казанский (приволжский) федеральный университет институт языка Кафедра английского языка

НазваниеКазанский (приволжский) федеральный университет институт языка Кафедра английского языка
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ТипМетодические указания
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partial analysis.

In some instances, indirect effects may not be too important and it will make sense for economists to devote their efforts to very detailed analyses of particular industries or activities. In other circumstances, the indirect effects are too important to be swept under the carpet and an alternative simplification must be found.

Macroeconomics emphasizes the interactions in the economy as a whole. It deliberately simplifies the individual building blocks of the analysis in order to retain a manageable analysis of the complete interaction of the economy.

For example, macroeconomists typically do not worry about the breakdown of consumer goods into cars, bicycles, televisions, and calculators. They prefer to treat them all as a single bundle called 'consumer goods' because they are more interested in studying the interaction between households' purchases of consumer goods and firms' decisions about purchases of machinery and buildings.

Because these macroeconomic concepts are intended to refer to the economy as a whole, they tend to receive more coverage on television and in the newspapers than microeconomic concepts, which are chiefly of interest to those who belong to the specific group in question. To give an idea of the building blocks of macroeconomics, we introduce three concepts which you have probably read about in the newspapers or seen discussed on television.

Gross domestic product (GDP) is the value of all goods and services produced in the economy in a given period such as a year.

GDP is the basic measure of the total output of goods and services in the economy.

The aggregate price level is a measure of the average level of prices of goods and services in the economy, relative to their prices at some fixed date in the past.

There is no reason why the prices of different goods should always move in line with one another. The aggregate price level tells us what is happening to prices on average. When the price level is rising, we say that the economy is experiencing inflation.

The unemployment rate is the percentage of the labour force without a job.

By the labour force we mean those people of working age who in principle would like to work if a suitable job were available. Some of the landed gentry are of working age but have no intention of looking for work. They are not in the labour force and should not be counted as unemployed.

Already we can see two themes of modern macroeconomic analysis. Society reveals, both through statements by individuals and by the policy pronouncements of politicians who must submit themselves for re-election by the people, that it does not like inflation and unemployment. Yet for most of the 1970s economic interactions within and between national economies led to substantial inflation rates. In the 1980s, most Western economies faced sharp rises in the aggregate unemployment rate. Macroeconomists wish to understand how interactions within the economy can lead to these outcomes and whether government policy can make any difference.

Embryology and growth of fishes

Segmentation of the Egg. - The egg of the fish develops only after fertilization (amphimixis). This process is the union of its nuclear substance with that of the sperm-cell from the male, each cell carrying its equal share in the function of heredity. When this process takes place the egg is ready to begin its segmentation. The eggs of all fishes are single cells containing more or less food-yolk. The presence of this food-yolk affects the manner of segmentation in general, those eggs having the least amount of food-yolk developing most typically. The simplest of all fish-like vertebrates, the lancelet (Branchiostoma) has very small eggs, and in their early development it passes through stages that are typical for all many-celled animals. The first stage in development is the simple splitting of the egg into two halves. These two daughter cells next divide so that there are four cells; each of these divides, and this division is repeated until a great number of cells is produced. The phenomenon of repeated division of the germ-cell is called cleavage, and this cleavage is the first stage of development in the case of all many-celled animals. Instead of forming a solid mass the cells arrange themselves in such a way as to form a hollow ball, the wall being a layer one cell thick. The included cavity is called the segmentation cavity, and the whole structure is known as a blastula. This stage also is common to all the many-celled animals. The next stage is the conversion of the blastula into a double-walled cup, known as a gastrula by the pushing in of one side. All the cells of the blastula are very small, but those on one side are somewhat larger than those of the other, and here the wall first flattens and then bends in until finally the larger cells come into contact with the smaller and the segmentation cavity is entirely obliterated. There is now an inner layer of cells and an outer layer, the inner layer being known as the endoblast and the outer as the ectoblast. The cavity of the cup thus formed is the archenteron and gives rise primarily to the alimentary canal. This third well-marked stage is called the gastrula stage, and it is thought to occur either typically or in some modified form in the development of all metazoa, or many-celled animals. In the lampreys, the Ganoids, and the Dipnoans the eggs contain a much greater quantity of yolk than those of the lancelet, but the segmenta­tion resembles that of the lancelet in that it is complete; that is, the whole mass of the egg divides into cells. There is a great difference, however, in the size of the cells, those at the upper pole being much smaller than those at the lower. In Petromyzon and the Dipnoans blastula and gastrula stages result, which, though differing in some particulars from the corresponding stages of the lancelet, may yet readily be compared with them. In the hagfishes, sharks, rays, chimaeras, and most bony fishes there is a large quantity of yolk, and the protoplasm, instead of being distributed evenly throughout the egg, is for the most part accumulated upon one side, the nucleus being within this mass of protoplasm. When the food substance or yolk is consumed and the little fish is able to shift for itself, it leaves the egg-envelopes and is said to be hatched.

Post-embryonic Development. - In all the fishes the development of the embryo goes on within the egg long after the gastrula stage is passed, and until the embryo becomes a complex body, composed of many differing tissues and organs. Almost all the development may take place within the egg, so that when the young animal hatches there is necessary little more than a rapid growth and increase of size to make it a fully developed mature animal. This is the case with most fishes: a little fish just hatched has most of the tissues and organs of a full-grown fish, and is simply a small fish. But in the case of some fishes the young hatches from the egg before it has reached such an advanced state of development, and the young looks very different from its parent. It must yet undergo considerable change before it reaches the structural condition of a fully developed and fully grown fish. Thus the development of most fishes is almost wholly embryonic development—that is, development within the egg or in the body of the mother—while the development of some of them is to a considerable degree post-embryonic or larval development. There is no important difference between embryonic and post-embryonic development. The de­velopment is continuous from egg-cell to mature animal and, whether inside or outside of an egg, it goes on with a degree of regularity. While certain fishes are subject to a sort of metamorphosis, the nature of this change is in no way to be compared with the change in insects which undergo a complete metamorphosis. In the insects all the organs of the body are broken down and rebuilt in the process of change. In all fishes a structure once formed maintains a more nearly continuous integrity although often considerably altered in form.

Why are some animals so smart?

Carel Van Schaik

The unusual behavior of orangutans in a Sumatran swamp suggests a surprising answer.

Even though we humans write the textbooks and may justifiably be suspected of bias, few doubt that we are the smartest creatures on the planet. Many animals have special cognitive abilities that allow them to excel in their particular habitats, but they do not often solve novel problems. Some of course do, and we call them intelligent, but none are as quick-witted as we are.

What favored the evolution of such distinctive brainpower in humans or, more precisely, in our hominid ancestors? One approach to answering this question is to examine the factors that might have shaped other creatures that show high intelligence and to see whether the same forces might have operated in our forebears. Several birds and nonhuman mammals, for instance, are much better problem solvers than others: elephants, dolphins, parrots, crows. But research into our close relatives, the great apes, is surely likely to be illuminating.

Scholars have proposed many explanations for the evolution of intelligence in primates, the lineage to which humans and apes belong (along with monkeys, lemurs and lorises). Over the past 13 years, though, my group's studies of orangutans have unexpectedly turned up a new explanation that we think goes quite far in answering the question.

Incomplete Theories

One influential attempt at explaining primate intelligence credits the complexity of social life with spurring the development of strong cognitive abilities. This Machiavellian intelligence hypothesis suggests that success in social life relies on cultivating the most profitable relationships and on rapidly reading the social situation—for instance, when deciding whether to come to the aid of an ally attacked by another animal. Hence, the demands of society foster intelligence because the most intelligent beings would be most successful at making self-protective choices and thus would survive to pass their genes to the next generation. Machiavellian traits may not be equally beneficial to other lineages, however, or even to all primates, and so this notion alone is unsatisfying.

One can easily envisage many other forces that would promote the evolution of intelligence, such as the need to work hard for one's food. In that situation, the ability to figure out how to skillfully extract hidden nourishment or the capacity to remember the perennially shifting locations of critical food items would be advantageous, and so such cleverness would be rewarded by passing more genes to the next generation.

My own explanation, which is not incompatible with these other forces, puts the emphasis on social learning. In humans, intelligence develops over time. A child learns primarily from the guidance of patient adults. Without strong social—that is, cultural—inputs, even a potential wunderkind will end up a bungling bumpkin as an adult. We now have evidence that this process of social learning also applies to great apes, and I will argue that, by and large, the animals that are intelligent are the ones that are cultural: they learn from one another innovative solutions to ecological or social problems. In short, I suggest that culture promotes intelligence.

I came to this proposition circuitously, by way of the swamps on the western coast of the Indonesian island of Sumatra, where my colleagues and I were observing orangutans. The orangutan is Asia's only great ape, confined to the islands of Borneo and Sumatra and known to be something of a loner. Compared with its more familiar relative, Africa's chimpanzee, the red ape is serene rather than hyperactive and reserved socially rather than convivial. Yet we discovered in them the conditions that allow culture to flourish.

Technology in the Swamp

We were initially attracted to the swamp because it sheltered disproportionately high numbers of orangutans— unlike the islands' dryland forests, the moist swamp habitat supplies abundant food for the apes year -round and can thus support a large population. We worked in an area near Suaq Balimbing in the Kluet swamp, which may have been paradise for orangutans but, with its sticky mud, profusion of biting insects, and oppressive heat and humidity, was hell for researchers.

One of our first finds in this unlikely setting astonished us: the Suaq orangutans created and wielded a variety of tools. Although captive red apes are avid tool users, the most striking feature of tool use among the wild orangutans observed until then was its absence. The animals at Suaq ply their tools for two major purposes. First, they hunt for ants, termites and, especially, honey (mainly that of sting-less bees)—more so than all their fellow orangutans elsewhere. They often cast discerning glances at tree trunks, looking for air traffic in and out of small holes. Once discovered, the holes become the focus of visual and then manual inspection by a poking and picking finger. Usually the finger is not long enough, and the orangutan prepares a stick tool. After carefully inserting the tool, the ape delicately moves it back and forth, and then withdraws it, licks it off and sticks it back in. Most of this "manipulation" is done with the tool clenched between the teeth; only the largest tools, used primarily to hammer chunks off termite nests, are handled.

The second context in which the Suaq apes employ tools involves the fruit of the Neesia. This tree produces woody, five-angled capsules up to 10 inches long and four inches wide. The capsules are filled with brown seeds the size of lima beans, which, because they contain nearly 50 percent fat, are highly nutritious—a rare and sought-after treat in a natural habitat without fast food. The tree protects its seeds by growing a very tough husk. When the seeds are ripe, however, the husk begins to split open; the cracks gradually widen, exposing neat rows of seeds, which have grown nice red attachments (arils) that contain some 80 percent fat. To discourage seed predators further, a mass of razor-sharp needles fills the husk. The orangutans at Suaq strip the bark off short, straight twigs, which they then hold in their mouths and insert into the cracks. By moving the tool up and down inside the crack, the animal detaches the seeds from their stalks. After this maneuver, it can drop the seeds straight into its mouth. Late in the season, the orangutans eat only the red arils, deploying the same technique to get at them without injury.

Both these methods of fashioning sticks for foraging are ubiquitous at Suaq. In general, "fishing" in tree holes is occasional and lasts only a few minutes, but when Neesia fruits ripen, the apes devote most of their waking hours to ferreting out the seeds or arils, and we see them grow fatter and sleeker day by day.

Conceptual Models for Binding

Molecular binding interactions are fundamental properties of all matter. Though this statement is trivial at first sight and does not deserve special mention, it sets a bold limit to all attempts in the design of specific interactions towards the construction of selective molecular host compounds. The most promising approach towards this goal relies on idealized models that reflect just one prominent aspect of the entire interaction, making it illustrative and as such easily comprehensible. However, owing to the persuasive power of pictorial arguments, the premises of the models may be overlooked and their applicability is then stretched too far. Notorious in this respect is the famous metaphor of the lock-and-key fit in host-guest binding, coined by Emil Fischer more than a century ago to cite geometrical complementarity as the origin for substrate discrimination between various sugars and glycosidases. Beyond question, geometrical complementarity is an important feature to ascertain the mutual stickiness of specific binding partners, because it maximizes the help from the attractive van der Waals interactions which, in combination with the repulsive interactions of orbital overlap (Pauli principle), serve to sort out and reject less well-fitting competitors. The requirement of geometrical fit emerges from the steep distance dependence of the interacting surfaces which, in the case of the van der Waals attraction, follows an inverse sixth power law (van der Waals attractive interaction ~r 6; r = distance), whilst the repulsive interaction stemming from the Pauli constraint adheres to an even more extreme inverse 12th power law (repulsive energy ~r 12). The overlay of both distance dependencies gives an energetic well featuring an optimal separation, the van der Waals contact distance. In conjunction with the accumulative and monotonously attractive character of the pairwise interaction between distinct positions in host and guest, these features constitute the driving urge to form extended interface areas of minimal separation in order to maximize binding.

In quantitative terms the complementary fit model of host and guest binding refers to the energetic difference at constant temperature and pressure ∆ Hassoc (also called the exothermicity) of just two states: one mole each of host and guest molecules totally separated as opposed to the associated complex of the same components in its most favourable configuration. The model has been expanded in various directions to include other types of interaction, notably the participation of functional groups which supplemented the model with Coulomb-, dipolar/multipolar and hydrogen bonding terms, as well as contributions from the intrinsic distortions, bending and deformations affecting the distributions of electron density within the individual host and guest molecules. Though considerable improvements on the original idea were implemented over the years, and even gained in finesse by the inclusion of scaling factors to account for environmental influences (e.g. distance-dependent dielectric permittivity), the fundamental concept of enthalpy-based two-partner two-state binding remained unchanged and still dominates most attempts aimed at understanding molecular host-guest relations today.

In the description and explanation of real experimentally testable situations, the lock-and-key model claims a success story; however, in many cases - and among them are the majority of the more interesting biological examples -it fails to explain host-guest binding affinity and selectivity with reasonably ambitious satisfaction. For instance, anion binding in water very frequently shows endothermic rather than exothermic enthalpies of association, an observation that is incompatible with the naive complementarity model.

The reasons for the mediocre predictive power of simple models are fundamental and obvious: above all they suffer from the blunt comparison of binding enthalpies that emerge from the model treatment with free energies of binding ∆Gassoc that derive from the readily accessible affinities by straightforward recalculation (∆Gassoc = - RT 1n Kassoc). Such relations are equivalent to the neglect of the entropic contributions to binding that is justified only in the rare case if the interest in associations is restricted to the temperature regime near zero Kelvin (furnishing T∆S~ O) or the entropy of association (as TSassoc) is very small to render the enthalpy the dominating component. In reality this situation is considerably less frequent than commonly assumed, and in addition also depends dramatically on the polarity of the environment. Entropic factors tend to be of greater importance in intermolecular binding in the protic solvents typically required to generate anionic species as free entities in solution. For the calculation of anion binding in polar solvents around ambient temperature it is mandatory to employ free energies ∆Gassoc, although they are less accessible than plain enthalpies and eventually require the more sophisticated and lengthy calculation methods of molecular dynamics.

A second cause for the weakness of the complementarity model arises from the misconception that the binding process of host and guest is essentially the same whether it occurs in vacuum or in a condensed phase. For the latter this idea leads to the frequently voiced opinion that there is no physical contact between the host-guest partners in solution (they stay separated) if the binding free energy is zero. It follows from simple inspection of the relation ∆G°=-RT 1n Kassoc that at ∆G° =0 the association constant Kassoc equals 1, i.e. for non-zero concentrations of host and guest there is also a finite concentration of the 1:1 associate complex present. Is this binding? The case has been investigated in the context of protein denaturation by low molecular weight additives and has recently been lucidly unfolded by Schellman and Timasheff. The interaction between host and guest molecules, to the extent that the occupation of a binding site on the host matches the concentration of the guest in bulk solution, corresponds to the case of random collision and invokes the replacement of solvent from this site. Unlike the binding scenario in vacuo, the host-guest interaction in liquids is a genuine exchange process with solvent molecules that may favour or disfavour the uptake of the guest. Thus, the measurable free energy of binding ∆G°assoc is negative, and only ordinary binding isotherms are found if the interaction of the site with the incoming guest is more exergonic than the interaction of the same substructure with solvent (∆G°solv; ∆G°assoc=∆G°guestt-∆G° solv). An exergonic interaction of host and guest in the absolute sense is insufficient to bring about binding.

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