bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic Programming
Authors: Bellman Richard 
Published: October 2006

Little has been done in the study of these intriguing questions, and I do not wish to give the impression that any extensive set of ideas exists that could be called a "theory." What is quite surprising, as far as the histories of science and philosophy are concerned, is that the major impetus for the fantastic growth of interest in brain processes, both psychological and physiological, has come from a device, a machine, the digital computer. In dealing with a human being and a human society, we enjoy the luxury of being irrational, illogical, inconsistent, and incomplete, and yet of coping. In operating a computer, we must meet the rigorous requirements for detailed instructions and absolute precision. If we understood the ability of the human mind to make effective decisions when confronted by complexity, uncertainty, and irrationality, then we could use computers a million times more effectively than we do. Recognition of this fact has been a motivation for the spurt of research in the field of neurophysiology.
The more we study the information-processing aspects of the mind, the more perplexed and impressed we become. It will be a very long time before we understand these processes sufficiently to reproduce them.
In any case, the mathematician sees hundreds and thousands of formidable new problems in dozens of blossoming areas, puzzles galore, and challenges to his heart's content. He may never resolve some of these, but he will never be bored. What more can he ask?
Chemotaxis in Bacteria
Authors: Adler Julius 
Published: October 2006

Motile
Escherichia coli
placed at one end of a capillary tube containing an energy source and oxygen migrate out into the tube in one or two bands, which are clearly visible to the naked eye and can also be demonstrated by photography, microscopy, and densitometry and by assaying for bacteria throughout the tube. The formation of two bands is not due to heterogeneity among the bacteria, since the bacteria in each band, when reused, will form two more bands.

If an anaerobically utilizable energy source such as galactose is present in excess over the oxygen, the first band consumes all the oxygen and a part of the sugar and the second band uses the residual sugar anaerobically. On the other hand, if oxygen is present in excess over the sugar, the first band oxidizes all the sugar and leaves behind unused oxygen, and the second band uses up the residual oxygen to oxidize an endogenous energy source.

The essence of the matter is that the bacteria create a gradient of oxygen or of an energy source, and then they move preferentially in the direction of the higher concentration of the chemical. As a consequence, bands of bacteria (or rings of bacteria in the case of agar plates) form and move out. These results show that
E. coli
is chemotactic toward oxygen and energy sources such as galactose, glucose, aspartic acid, threonine, or serine. The full repertoire of chemotactic responses by
E. coli
is no doubt greater than this, and a more complete list remains to be compiled.

The studies reported here demonstrate that chemotaxis allows bacteria to find that environment which provides them with the greatest supply of energy. It is clearly an advantage for bacteria to be able to carry out chemotaxis, since by this means they can avoid unfavorable conditions and seek optimum surroundings.
Finally, it is necessary to acknowledge the pioneering work of Englemann, Pfeffer, and the other late-19th-century biologists who discovered chemotaxis in bacteria, and to point out that the studies reported here fully confirm the earlier reports of Beijerinck and Sherris and his collaborators on a band of bacteria chemotactic toward oxygen. By using a chemically defined medium instead of a complex broth, it has been possible to study this band more closely and to demonstrate in addition the occurrence of a second band of bacteria chemotactic toward an energy source. Beijerinck did, in fact, sometimes observe a second band, but he did not offer an explanation for it.
Visual and Nonvisual Auditory Systems in Mammals
Authors: Harrison J. M. , Irving R. 
Published: October 2006

Examination of the structural organization of the auditory system of the brain stem shows that the system is composed of a number of separate ascending pathways. This suggests that there may be at least two auditory systems, analogous to the rod and cone pathways in vision. We examined this possibility by investigating the variation in relative size of the medial and lateral superior olivary nuclei in a number of different mammalian species.
The lateral superior olive is present in the hedgehog (an insectivore), cat (a carnivore), and squirrel monkey (a primate), but the medial superior olive is absent in the hedgehog. In a group of animals of the same taxonomic order (rodents) the lateral superior olive was present in all species examined, but the medial superior olive was almost wholly absent in the mouse and very prominent in the chinchilla and guinea pig. The absence of the medial superior olive in some animals is surprising because recent anatomical and physiological work has implicated the nucleus in auditory localization. Because of this implication, the medial and lateral olivary nuclei were examined in three species of bat and one dolphin, all echolocating animals. The medial superior olive was absent in these animals, and the lateral superior olive was prominent.
These observations support the idea that the medial and lateral superior olives are nuclei on two different ascending auditory systems. It was also noted that the medial superior olive was always well developed in animals with well-developed eyes, and this suggested that the nucleus is in some way related to the visual system. We examined this idea by studying the relation between the numbers of cells in the medial superior olive and in the nucleus of the 6th cranial nerve (one of the motor nuclei concerned with eye movement) in a number of mammalian species. An approximately linear function was found between the sizes of the 6th nucleus and of the medial superior olive in three primates with cone-cell retinas (squirrel monkey, man, and macaque) and four rodents with rod-cell retinas (mouse, rat, guinea pig, and chinchilla). The cell numbers for the ground squirrel (a rodent with cone-cell retina) fitted an extension of the primate curve, and the cell numbers for the cat (in whose retina rods predominate) fitted an extension of the rodent curve. Thus, it is clear that the medial superior olive is related to the visual system, and that it is present in animals with cone-cell fovea and retina (diurnal animals) and animals with rod-cell retina (that is, nocturnal animals) having good vision. In nonvisual nocturnal animals the nucleus is small or absent. The medial superior olive is probably not concerned with auditory localization in the psychophysical sense but is probably concerned with the movement of head and eyes in the direction of a sound in space. Localization in the psychophysical sense and fine auditory discrimination probably depend upon the ascending pathway which includes the lateral superior olive.
Pattern Classification by Adaptive Machines
Authors: Rosen Charles A. 
Published: October 2006

Man's intelligent behavior is due in part to his ability to select, classify, and abstract significant information reaching him from his environment by way of his senses. This function, pattern recognition, has become a major focus of research by scientists working in the field of artificial intelligence.
At the lowest level, pattern recognition reduces to pattern classification, which consists of the separation, into desired classes, of groups of objects, sounds, odors, events, properties, and the like; the separations are based on sets of measurements made on the entities being classified. The pattern classifier is composed of a data filter and a categorizer. The data filter selects the distinguishing features and represents them as sets of real numbers; each set is termed a pattern. The categorizer assigns each pattern to one of several desired classes.

Patterns can be represented geometrically as points in an
n
-dimensional space; the
n
coordinates of each point are the numerical values of the features selected to represent the pattern. A pattern classification system separates an
n
-dimensional space into regions, each of which ideally contains points of only one class. One method to effect this separation is by means of "trainable" categorizers—major components of adaptive machines. They consist of networks whose internal parameters are varied according to a set of fixed rules during a training cycle. A statistically large sample of known patterns are presented, one at a time, to the networks; internal corrections are made each time a pattern is erroneously classified. Classification performance tends to improve as the set of known patterns is cycled repetitively through the machine. Finally, the adequacy of adaptation is tested by a separate set of similar patterns which have not been used in the training process.

A number of different machine organizations and training rules have been developed and are being applied successfully to numerous classification problems. More difficult recognition problems requiring the aid of logical tests and analysis, search and association, use the digital computer programmed to supplement the functions of the adaptive classifier.
Shock Effects in Certain Rock-Forming Minerals
Authors: Chao E. C. T. 
Published: October 2006

Shock effects in quartz, plagioclase, biotite, amphibole, and some accessory minerals have been observed in rocks subjected to various degrees of metamorphism by meteoritic impact. The shock features described are unique; they are never observed in rocks from normal geologic environments. Such features are described:
1) Multiple sets of closely spaced planar microstructures occur in quartz, plagioclase, and other rock-forming minerals. Those characteristic of shock consist of alternating platelets, with a range of reduced mean index of refraction and birefringence; they consist of platelets that have been partially or completely transformed to an amorphous phase.
2) Quartz and plagioclase are selectively and completely transformed to silica glass and plagioclase glass in the solid state, whereas the associated mafic minerals remained crystalline. There is no reaction between adjacent minerals.
3) High-pressure polymorphs occur, such as coesite or stishovite. Coesite occurs exclusively within silica glass; it has not been observed as a reaction or breakdown product.
4) Nickel-iron spherules occur in the fused glass or impactites.
5) The occurrence of droplets of ilmenite, rutile, pseudobrookite, and baddaleyite in impactites indicates a temperature of formation exceeding 1500°C.
6) Dense glass occurs, similar in composition to bulk rock, in which iron oxide, such as fine particles of magnetite, is completely dissolved.
All these features are characteristic of a process involving the rapid rise and fall of extremely high pressures and temperatures. Minerals and mineral assemblages experiencing such high strain rates and sudden changes of pressures and temperatures react and change independently to the bulk chemical composition, under nonequilibrium conditions.
Many aspects of shock features require careful study. Kink bands in biotite and deformation lamellae in quartz occur in tectonically deformed rocks. These features should be studied with great care in order to determine whether reduction in mean index of refraction and total birefringence along the planar structures have resulted from vitrification or phase transition; their presence is additional evidence in favor of a shock mechanism.
Vitreous phases or glasses formed by shock also have many unique properties; they have not been studied by such methods as thermoluminescence, electron spin resonance, low-angle x-ray diffraction, or infrared spectroscopy. Shock-fused glass of high density needs to be studied in detail in carefully controlled laboratory conditions.
Experimental shock-wave studies of the equation-of-state of single minerals and mineral assemblages, under carefully controlled conditions, must precede estimates of peak pressures and peak and residual temperatures of shocked natural mineral assemblages. Detailed petrographic and mineralogic studies, however, have provided useful and definitive criteria for characterization of impact events. Such data should be of paramount importance in the study of samples brought back from Moon.
Teaching Effectiveness and Government Awards
Authors: Bresler Jack B. 
Published: October 2006

Three bodies of available data at Tufts University were used in determining whether there are meaningful relationships between teaching effectiveness, publication, and the receipt of government support. A search of the literature showed that virtually all comments in the popular literature and most references in professional journals suggest that publication and receipt of support for research somehow detract from teaching performance in the classroom.
The empirical data of the Tufts study do not support these previous conclusions. The students rated as their best instructors those faculty members who had published articles and who had received or were receiving government support for research.
The Status and Problems of High-Energy Physics Today
Authors:   High Energy Physics Advisory Panel of the Atomic Energy Commission
Published: October 2006

In January 1967 the Atomic Energy Commission established a Panel on High Energy Physics, for the purpose of providing advice and guidance to the commission in this area of physical science research. The panel reports to the Division of Research of the Atomic Energy Commission. It was established to consider important matters relating to this area of research and advise the commission concerning the best course of action to be taken in the interest of a vigorous and productive national high-energy-physics program. The panel is composed of 11 physical scientists; at present the membership list is as follows: Rodney L. Cool, Brookhaven National Laboratory; Earle C. Fowler, Duke University; Leon Ledermann, Columbia University; Edward J. Lofgren, Lawrence Radiation Laboratory; George E. Pake, Washington University; W. K. H. Panofsky, Stanford University; Robert Sachs, Argonne National Laboratory; Keith R. Symon, University of Wisconsin; Robert L. Walker, California Institute of Technology; C. N. Yang, State University of New York, Stony Brook; V. F. Weisskopf (chairman), Massachusetts Institute of Technology. When the following report was written, R. R. Wilson, of Cornell University, was also a member. He resigned because of the pressures of his new duties as director of the 200-Bev National Accelerator Laboratory.
One of the first tasks which the panel has set itself is a review of the present status and problems of high-energy physics in the United States and, in particular, the impact of the recent budget restrictions on these activities. The panel has issued a status report on this subject, pointing out the difficulties arising from the large discrepancy between the long-range budget forecasts made in a policy statement of the AEC which was submitted to Congress by the President in 1965 and the financial support actually provided high-energy physics. The report analyzes the serious consequences for the future of this fundamental field in which the United States has invested much effort and money.
The report was submitted to the Atomic Energy Commission and was subsequently transmitted to the Joint Committee for Atomic Energy of the Congress. It is presented here with minor changes for a wider audience.
Magnetism and Local Molecular Field
Authors: Néel Louis 
Published: October 2006

Despite its somewhat naive simplicity, the method of the local molecular field has had undeniable success in satisfactorily explaining a large number of previously known facts and in opening the way for the discovery of new facts. Let us note, however, that all the structures that have been discussed above are collinear structures: on the average (in time) all the atomic magnets pointing in one or the opposite direction are parallel to a single direction. However, the local molecular field method can also be extended to noncollinear structures such as that of helimagnetism, which Yoshimori and Villain discovered independently in an absolutely unexpected manner; one can thus interpret phenomena in a remarkably simple and concrete manner.
Nevertheless, the method can hardly be recommended for more complex structures such as the umbrella structure, which requires the decomposition of the principal crystal lattice into a large number of sublattices. Indeed, under these conditions an atom belonging to a given sublattice has only a very small number of neighbors (one or two) in each of the other sublattices, and the molecular field method, which consists in replacing the instantaneous action of an atom by that of an average atom, will be more likely to yield a correct result, the larger the number of atoms to which it is applied. Its correctness probably also increases as the atomic spin becomes larger. Independently of this problem, the method applied to a large number of sublattices completely loses its chief advantage, simplicity. The method also involves more insidious traps. If a judicious choice of parameters is made, the method can lead one to calculate curves and thermal variations of the spontaneous magnetization or paramagnetic susceptibility that coincide remarkably well with the experimental results, for example, to within a few thousandths. Under these conditions, one could expect that the elementary interaction energies deduced from these parameters would correspond to the actual values with the same accuracy. This is not so; errors of 10 to 20 percent and even greater are frequently made in this manner. A certain amount of caution thus becomes imperative.
On the other hand, recourse to the local molecular field seems indispensable since more rigorous methods lead to insurmountable complications. Consider for example that the rigorous solution is not yet known for the simplest case, that of a simple cubic lattice with identical atoms of spin 1/2, and interactions reduced to those present between nearest-neighbor atoms. How then should one treat the case of garnets with 160 atoms in the unit cell, spins up to 5/2, and at least six different coupling constants? One must therefore be lenient toward the imperfections of the molecular field methods, considering the simplicity with which the successes recalled in the first few lines of these conclusions were obtained.
Gene Selection in Hemoglobin and in Antibody-Synthesizing Cells
Authors: Kabat David 
Published: October 2006

Close linkage of mutually exclusive genes occurs in the non-α chain hemoglobin genes and in the immunoglobulin genes of man and other mammals. The expression of one gene in the cluster precludes the expression of any other linked gene. A simple, testable theory of gene selection called "looping-out excision" which was designed only to explain this mutual exclusivity in the hemoglobin system is described. The theory is closely concordant with a wide range of previously unexplained findings concerning hematopoiesis—including the developmental changes of hemoglobins, the increases in immature or fetal forms of hemoglobin that accompany anemia, and with the distribution of adult and fetal hemoglobins among erythrocytes during normal embryogenesis and in various pathological conditions. One corollary of this theory is that erythroid tissue in the normal adult bone marrow is constantly recapitulating the developmental stages of its embryogenesis. Another corollary is that the selection from among the linked globin genes occurs independently on the two chromosomes of the diploid organism. Both of these corollaries are supported by the available data.
The same theory of gene selection is also remarkably consistent with known data for immunoglobulin synthesis; it could explain not only the mutually exclusive activation of linked variable genes but also the splicing which occurs between genetically linked variable and constant region genes for the immunoglobulin polypeptide chains. The agreement between these two different tissues is considered to be strong evidence that the proposed mechanism is correct at least in broad outline. Evidence from the genetics of maize and of drosophila also supports this theory of somatic tissue variegation. On the basis of these comparisons, I suggest that looping-out excision probably occurs also in other tissues and may be one means of gene selection and activation in differentiating cells.
The Apollo 16 Lunar Samples: Petrographic and Chemical Description
Authors:   Apollo 16 Preliminary Examination Team
Published: October 2006

The preliminary characterization of the rocks and soils returned from the Apollo 16 site has substantiated the inference that the lunar terra are commonly underlain by plagioclase-rich or anorthositic rocks. No evidence has been found for volcanic rocks underlying the regolith in the Apollo 16 region. In their place, we have found anorthositic rocks that are thoroughly modified by crushing and partial melting. The textural and chemical variations in these rocks provide some evidence for the existence of anorthositic complexes that have differentiated on a scale of tens to hundreds of meters.
The occurrence of deep-seated or plutonic rocks in place of volcanic or pyroclastic materials at this site suggests that the inference from physiographic evidence that the latter materials are widespread in terra regions may be incorrect.
Several additional, more specific conclusions derived from this preliminary examination are:
1) The combination of data from the Descartes region with data from the orbital x-ray fluorescence experiment indicates that some backside, highland regions are underlain by materials that consist of more than 80 percent plagioclase.
2) The soil or upper regolith between North Ray and South Ray has not been completely homogenized since the time of formation of these craters.
3) The chemistry of the soil indicates that rocks rich in potassium, uranium, and thorium, similar to those that prevail at the Fra Mauro site, are relatively abundant (10 to 20 percent) in the Descartes region.
4) The K/U ratio of the lunar crust is similar to that of the KREEP basalts.
5) The carbon content of the premare lunar crust is even lower than that of the mare volcanic rocks.
Membrane Structure: Some General Principles
Authors: Bretscher Mark S. 
Published: October 2006

The arrangement of lipids and some proteins in the erythrocyte membrane has been discussed. The conclusions from this are listed here as a set of general guidelines for the structure of membranes of higher organisms: some of these rules may be wrong. But at this stage it seems useful to sharpen our thoughts in this way and thereby focus attention on various specific points.
1) The basis of a membrane is a lipid bilayer with (i) choline phospholipids and glycolipids in the external half and (ii) amino (and possibly some choline) phospholipids in the cytoplasmic half. There is effectively no lipid exchange across the bilayer (unless enzymatically catalyzed).
2) Some proteins extend across the bilayer. Where this is so, they will in general have carbohydrate on their surface remote from the cytoplasm. This carbohydrate may prevent the protein diffusing out of the membrane into the cytoplasm; it acts as a lock on the protein.
3) Just as lipids do not flip-flop, proteins do not rotate across the membrane. Lateral motion or rotation of lipids and proteins in the plane of the bilayer may be expected.
4) Most membrane protein is associated with the inner, cytoplasmic, surface of the membrane. Proteins are not usually associated exclusively with the outer half of the lipid bilayer.
5) Membrane proteins are a special class of cytoplasmic proteins, not of secreted proteins.