bluuebunny/crossref_metadata_2025 huggingface dataset:
Physics, physicists, and security
Authors: Phelps John B. , Pollard Ernest C.
Published: January 2009

For the last fifteen years, a great part of physical research in the United States and a high proportion of the working hours of US physicists have been related, in one way or another, to national security. During World War II the objectives of physicists and their research programs were more or less clearly defined. The overriding task then was to produce the better weapons and countermeasures which could, and did, speed the day of victory. The impressive wartime successes in applied research helped to establish physics and the other sciences as indispensable to progress in the “hardware” of war. In a broader sense, the military man, the statesman, the average citizen—and the scientist—all came, quite understandably, to associate scientific progress with greater security for our country. And in this broad association of science with security physics has probably occupied the most prominent position, whether this prominence be measured by respect, money, publicity, or security restrictions.
Anticipations… a continental view of physics and its future
Authors: Casimir H. B. G.
Published: January 2009

Though I greatly value the invitation to speak at this memorable occasion, yet when the day approached I felt more and more worried about what I should say. You may think that that is the usual predicament of a fairly busy man who is in the bad habit of putting off things to the very last moment. I think that the reason for my uneasiness is this time more fundamental. The fact is that, while I tried to ponder the European outlook on the future of physics and physicists, I came to realize that at a similar gathering in Europe I would almost certainly have been asked to speak on just one more aspect of the development of physics during the past twenty-five years, a task which I would have performed with greater ease and at the end of which I might have ventured some hesitating and nebulous remarks about future developments. So let me begin by congratulating the American Institute of Physics, not for its share in the phenomenal development and spectacular successes of American physics during the past 25 years, but rather for the fact that even on a day like this it declines to rest on its laurels and wants to use a few moments of quiet reflection for looking ahead. Is it our tendency to cling to the past which has bereft European physics of some of its impetus? However this may be, I cannot forsake my European background and the only way in which I feel that I can contribute at all to a discussion of the future is to interpret in my personal way some of the predominant trends of the development of recent years.
…of time and the Sun
Authors: Sutton Richard M.
Published: January 2009

On the floor of my office at Haverford College there is painted in several colors a precision sun dial which, after the manner of Topsy, “just growed”. It all started in a casual way, but as it has developed for more than two years, it has become increasingly interesting. From it, my students and I have learned much about the equation of time and the need for the mean solar second. The inappropriateness of the sun as a primary time keeper, despite our constant dependence on its regularity, is clearly disclosed. The method of approach has been that of the natural philosopher who seeks a more complete understanding of the sun's slightly irregular apparent motions. The tools employed are mostly those that have been available through the centuries. With the exception of a pocket watch or an electric clock frequently checked against time signals from the Bureau of Standards' Station WWV, the tools are like those available to the ancient Egyptians or Mayas, and they compete in accuracy with those used by Tycho Brahe.
Mt. Wrangell expedition
Authors: Beiser Arthur
Published: January 2009

The summit of a dormant volcano nearly three miles high and located in the wilds of central Alaska—this is the unlikely site of a cosmic-ray laboratory that was put into operation during the past summer. Established by an expedition under the joint sponsorship of New York University and the University of Alaska, and with the substantial assistance of the Army, Navy, and Air Force, the Mount Wrangell Observatory can now be added to the roster of the world's high altitude stations.
The role of physics in engineering education
Authors: Seeger R. J.
Published: January 2009

Since the organization of the American Society for Engineering Education in 1893, there have been many studies of engineering curricula, such as the Mann Report (Carnegie Bulletin No. 11), the Wickenden Report of 1923 (said to be “monumental”), the “Aims and Scope of Engineering Curricula” (1940), “Engineering Education after the War” (1944), and Jackson's “Present Status and Trends of Engineering Education in the United States” (1939, essentially a “supplement to the Wickenden Report”).
International and national aspects of science
Authors: von Muralt Alexander
Published: January 2009

When I started studying physics and medicine after the first World War, the word “science” had but one meaning for us: To search for truth, to understand the experimental world by means of logical deduction, and to mould an inductive conception of this world. “Experimental world” meant everything on this planet and everything available by optical and mathematical methods in the universe. The thought that scientific method might be influenced by any other aspects did not come to the mind of a Swiss student at that time.
Philosophy for science students
Authors: FitzGerald John J.
Published: January 2009

Einstein's resolution of the apparent incompatability between the Newtonian principle of relativity and the law of the constancy of the velocity of light in vacuo by a reflective analysis of the physical conceptions of time and space disclosed, in theoretical physics, the unsuspected operation of an epistemological factor which had already been discerned in experimental physics by Duhem, Poincaré, and others. The analysis and interpretation of this factor have originated a variety of philosophies of science which are relevant here only as they offer unmistakable witness to the bearing of philosophy and its characteristic procedures upon physical science; a bearing in the ignorance of which one might achieve distinction in science without, however, understanding one's claim to distinction. On the assumption that this bearing presents the only available, solid, practical ground upon which scientist and philosopher can meet, each without benefit of the highly specialized and sustained training demanded for competence in these areas today, we, at Notre Dame, are in the process of constructing and presenting a course in philosophy for majors in physics and mathematics. The purpose of this paper is to sketch, for any helpful comment which it might evoke, the origins, content, spirit, and aims of this course.
Nuclear research in Norway
Authors: McReynolds A. W.
Published: January 2009

During a year spent in Norway as a Fulbright research scholar, I attended two scientific conferences which, between them, perhaps cover the scope of physics there. One, the annual meeting of Norsk Fysisk Selskap (the Norwegian Physical Society), was national in character and rather like an American Physical Society meeting minus some of the congestion and simultaneous sessions. The other, the first international conference on nuclear reactors, represents a step toward future scientific cooperation in that field. It was attended by delegates from nineteen different nations, and was arranged by JENER, the Norwegian-Dutch “Joint Establishment for Nuclear Energy Research”. This account of physics in Norway (and some observations about Sweden) is as viewed through the eyes of a guest for the year at the JENER nuclear reactor laboratory—but first perhaps we should start back at the Fysisk Selskap meeting and visit some of the institutions whose work was reported.
Acoustics conference in Moscow
Authors: Beyer Robert T.
Published: January 2009

In the spring of this year, a number of American acousticians, the author included, received invitations from the Planning Commission of the Fourth All-Union Conference on Acoustics to attend a May meeting in Moscow and deliver a paper on an appropriate topic. The opportunity of seeing Soviet science at first hand was too good to be missed, and, having made all the usual arrangements, I left New York on May 23, flying via Copenhagen and Stockholm.
A further report on physics teaching in Java
Authors: Hanau Richard
Published: January 2009

Sprawling 2900 miles along the equator, Indonesia is a big country, rich in natural resources, overpopulated in Java, and struggling to take its place among the nations of the world. East to west it covers more than one tenth the circumference of the earth; from north to south, slightly less than one tenth the distance from pole to pole. An archipelago republic, it consists of four large islands—Sumatra, Java, Kalimantan, and Sulawesi—and 3000 small ones, many uninhabited. In between in size are the well-known islands of the former Dutch East Indies: Bali, Timor, and the other smaller Spice Islands.
Theoretical Physics at Boulder
Authors: Brittin Wesley E.
Published: January 2009

The past summer.
Society of Rheology 1957 Annual Meeting: Bingham Medal Address
Authors: Zener Clarence M.
Published: January 2009

The Society of Rheology held its 1957 Annual Meeting, November 7–9 in Princeton, New Jersey, on which occasion the Bingham Medal of the Society was presented to Clarence M. Zener, Director of the Research Laboratories of the Westinghouse Electric Corporation. Dr. Zener's response is printed below.
Canadian high-altitude station at Sulphur Mountain
Authors: Korff Serge A.
Published: January 2009

A recent and a most welcome addition to the roster of high-altitude research facilities is the new Canadian station on Sulphur Mountain near Banff, Alberta, in the Canadian Rockies. This station is of particular importance because, in addition to being well supplied and equipped, it is also the only high-altitude research facility in this area, and therefore is of so much importance in completing the world network of stations. The importance of the location was underscored at the 1954 Rome meeting of the Special Committee for the International Geophysical Year (CSAGI), by the Geographical Coordination Committee of which the present author was fortunate to be a member. This Committee considered what should be the optimum distribution of stations all over the world in order best to intercept cosmic-ray impact zones and favorably to locate many other important IGY research activities such as auroral studies and ionospheric physics. The establishment of a station in the Rockies was recommended at that meeting.
Low temperature conference
Authors: Wilks J.
Published: January 2009

The department of physics at the University of Wisconsin, Madison, Wisconsin, was host to the Fifth International Conference on Low-Temperature Physics and Chemistry from August 26 to 31, 1957. The National Science Foundation, Office of Naval Research, Atomic Energy Commission, International Union of Pure and Applied Physics, and the Wisconsin Alumni Research Foundation joined with the University of Wisconsin in sponsoring this conference. 440 scientists attended with 353 coming from the United States, 24 from Canada, and a total of 63 from the following 11 countries: Australia, Belgium, Finland, France, Germany, Great Britain, Holland, Italy, Japan, Norway, and Switzerland.
Nuclear orientation and nuclear cooling
Authors: Kurti Nicholas
Published: January 2009

In this talk I propose to give a general survey of experiments with oriented nuclear systems produced by cryogenic methods. In order to give a reasonably comprehensive picture I shall not restrict myself to work with which I personally was associated but shall also refer to work by others both in the Clarendon Laboratory and elsewhere.
AIP annual report 1957
Authors: Hutchisson Elmer
Published: January 2009

The year 1957 was a full one for the American Institute of Physics. The conversion of the building at 335 East Forty-Fifth Street mentioned in last year's annual report began on January 2. On June 8, the Institute staff moved into the new AIP headquarters. The building was completely modernized and provides the space so badly needed for present operations, and also considerable space for future expansion. Through the generosity of Mr. Alfred P. Sloan, Jr., a handsomely furnished board room, named in honor of Karl Taylor Compton, is available for meetings of the Institute Governing Board, other professional council meetings, and appropriate committee meetings.
Advice to young physicists
Authors: Bothe W.
Published: January 2009

Many a person has had a single fruitful idea at the right time and has built his scientific life's work upon it. As a rule, however, things are somewhat different. Of a hundred ideas that one carries around with him, ninety prove on closer scrutiny to be incapable of realization, inopportune, trivial, false, or something of the sort. Of the remaining ten, there is always one that is most promising, most practical, and easiest to execute. It takes time to find this one; instinct and intuition often play a decisive role here. Once you have found this idea, use all your energies to put it into practice, lest it be anticipated by others.
Generalized conformal realizations of Kac–Moody algebras
Authors: Palmkvist Jakob
Published: January 2009

We present a construction which associates an infinite sequence of Kac–Moody algebras, labeled by a positive integer n, to one single Jordan algebra. For n=1, this reduces to the well known Kantor–Koecher–Tits construction. Our generalization utilizes a new relation between different generalized Jordan triple systems, together with their known connections to Jordan and Lie algebras. Applied to the Jordan algebra of Hermitian 3×3 matrices over the division algebras R, C, H, O, the construction gives the exceptional Lie algebras f4, e6, e7, e8 for n=2. Moreover, we obtain their infinite-dimensional extensions for n≥3. In the case of 2×2 matrices, the resulting Lie algebras are of the form so(p+n,q+n) and the concomitant nonlinear realization generalizes the conformal transformations in a spacetime of signature (p,q).
Scale interactions and scaling laws in rotating flows at moderate Rossby numbers and large Reynolds numbers
Authors: Mininni P. D. , Alexakis A. , Pouquet A.
Published: January 2009

The effect of rotation is considered to become important when the Rossby number is sufficiently small, as is the case in many geophysical and astrophysical flows. Here we present direct numerical simulations to study the effect of rotation in flows with moderate Rossby numbers (down to Ro≈0.03) but at Reynolds numbers large enough to observe the beginning of a turbulent scaling at scales smaller than the energy injection scale. We use coherent forcing at intermediate scales, leaving enough room in the spectral space for an inverse cascade of energy to also develop. We analyze the spectral behavior of the simulations, the shell-to-shell energy transfer, scaling laws and intermittency, as well as the geometry and the anisotropy of the structures in the flow. At late times, the direct transfer of energy at small scales is mediated by interactions with the largest scale in the system, the energy containing eddies with k⊥≈1, where ⊥ refers to wavevectors perpendicular the axis of rotation. The transfer between modes with wavevector parallel to the rotation is strongly quenched. The inverse cascade of energy at scales larger than the energy injection scale is nonlocal, and energy is transferred directly from small scales to the largest available scale. We observe both a direct and inverse cascade of energy at high rotation rate, indicative that these cascades can take place simultaneously. Also, as time evolves and the energy piles up at the large scales, the intermittency of the direct cascade of energy is preserved while corrections due to intermittency are found to be the same (within error bars) as in homogeneous nonrotating turbulence.
Dichroism in Ag nanoparticle composites with bimodal size distribution
Authors: Magruder R. H. , Robinson S. J. , Smith C. , Meldrum A. , Halabica A. , Haglund R. F.
Published: January 2009

We measured the reflectivity of nanoparticle thin films with bimodal size distributions clearly separated by depth and found distinctive spectral differences depending on the direction of illumination. In contrast with previous experiments that implied such differences, the samples in this experiment are prepared by ion implantation at sufficiently high energy to achieve the necessary spatial separation between larger and smaller nanoparticles. We demonstrate that the difference between scattering and absorption probabilities as a function of nanoparticle size is responsible for the differences in maximum reflectivities as the direction of illumination is reversed. This conjecture is supported by a Mie scattering calculation.
Light scattering in glass ceramic x-ray storage phosphors
Authors: Winch N. , Edgar A.
Published: January 2009

We have performed numerical simulations to determine the modulation transfer function for glass ceramic x-ray imaging plates where the image readout is by a scanned laser beam. We focus, in particular, on the role of the effective scattering length in determining the width of the modulation transfer function, covering a range of scattering lengths describing very opaque to very transparent glass ceramics. We find that the shape of the modulation transfer function is, in general, bimodal, with a broad contribution from the laser beam width, and superimposed a narrow one from scattering. The overall width of the modulation transfer function reaches a minimum when the scattering length is comparable with the beam width, and so scattering lengths either much greater or less than the beam width, corresponding to either strongly scattering or highly transparent glass ceramics, give the best expected spatial resolution. However, for a practical range of scattering parameters, transparent glass ceramics are predicted to have a superior resolution compared to very opaque ones. Simulations are included which also demonstrate the effect of particle size, optical absorption, and readout laser power. Stronger optical absorption at the wavelength of the stimulating beam in comparison with that at the wavelength of the emitted light has a markedly beneficial effect on the spatial resolution at the expense of sensitivity. Simulation results are confronted with experimental results for a commercial BaFBr:Eu2+ powder-based imaging plate and a europium-doped fluorozirconate glass ceramic, and good agreement is obtained.
Everyday radiation
Authors: Cowan Frederick P.
Published: January 2009

The rapid development of applied nuclear physics during the past decade has focused the attention of many people on radiation and radioactive materials. The fact that both are common constituents of our environment was realized by scientists working in the field soon after the discovery of radioactivity a half century ago. Many other scientists and the general public realize only vaguely or not at all that they are continually exposed to penetrating radiation of natural origin and that radioactive materials are found in small amounts in almost all substances including air, soil, building materials, and the human body.
Institute Doings
Authors: Barton H. A.
Published: January 2009

AS A RESULT of successful efforts to increase outside income, the American Institute of Physics will be able to send Physics Today to all members beginning with the January 1953 issue.
An Invited Communication
Authors: Meyerhoff Howard A.
Published: January 2009

Physicists and the AAAS
Earnings of physicists, 1951
Authors: Sharp Laure M. , Wood Helen
Published: January 2009

In physics, as in professional occupations in general, there has been up to the present time very little information as to the incomes which members of the profession can expect to earn during their working lives, and the influence on their earnings of such factors as educational background, experience, and type of employment.
UNESCO… and international cooperation in the physical sciences
Authors: Frazer Ronald
Published: January 2009

Whether in the written or the spoken word, I have long chosen to follow the example of Edmund Spenser in his preface to the Faerie Queene, when he elects to “thrust into the middest” of his subject with the first line of the first canto.
Optics in the Windy City
Authors: Ballard Stanley S.
Published: January 2009

OSA's Thirty-Sixth Annual Meeting
Gaseous Electronics
Authors: Malter L.
Published: January 2009

Annual Conference of Electron Physics
A new consequence of electron diffraction
Authors: Davisson C. J.
Published: January 2009

When we have heard of a person for years, physicist or other, we want to know more about him. In our human way, we want to know about his personal qualities as well as his public accomplishments. How are most of us to find out? By reading, of course.
The scientist's code of ethics
Authors: Leys Wayne A. R.
Published: January 2009

Few echoes of the controversy over the nature of science will be found in this article. An earlier generation agonized over the question: “Does scientific inquiry tell us anything about values and moral obligations?” and reached a very skeptical conclusion. Fifteen years ago studies of the language and logic of science appeared to many scientists and philosophers to have settled the question: you could not logically leap from assertions about what is and what is possible to assertions about what ought to be. Then came war and the Manhattan project, and many who had accepted the divorce of science and ethics were frightened into reconsidering the matter. If science had nothing to say about values and duties, so much the worse for science. There ought to be a connection between science and ethics. Whatever the semantic difficulties, something needed to be done to prevent a suicidal use of scientific knowledge. Since 1945 there have been many conferences, many symposia, reconsidering the relation of fact to value, the relation of science to ethics. Despite the ingenuity of these discussions, I find them, on the whole, inconclusive and disappointing.
Natural Radioactivity
Authors: Korff Serge A.
Published: January 2009

It may seem astonishing that after radioactive substances have been known for over half a century there should still remain important unsolved problems in the domain of natural radioactivity. This field was the first of the great subdivisions of nuclear physics to be explored, and yet much remains to be done here. The reason for this situation becomes evident when we recall that radium is expensive, and that until comparatively recently radioactive substances were not available in any large amounts. The second contributing factor is the great improvement in recent years in instrumentation, an improvement which has rendered many of the classical techniques obsolete.
The nucleus
Authors: Fermi Enrico
Published: January 2009

In the twenty–year period since the founding of the American Institute of Physics, nuclear physics has been advancing perhaps as rapidly as any other branch of our science. Twenty years ago the neutron had not yet been discovered, and a favored hypothesis as to the structure of the atomic nucleus was that it consisted of protons and electrons. This very fact may give some idea of the exponential rate of our progress.
What price scientific books?
Authors: Benjamin Curtis G.
Published: January 2009

Whenever two publishers of scientific books get together for more than a few minutes they always find themselves speaking gravely and shaking their heads dolefully. They compare notes on what is happening to the book industry in general and to them in particular. The burden of their complaint, of course, is the steadily rising spiral of costs and prices. They have no trouble in agreeing that its rate of ascent is leading the whole industry rapidly to ruin—upward in this case, not downward.
Universities or project centers?
Authors: Morse Philip M.
Published: January 2009

I was brought up to believe that the chief purpose of science departments in universities is to train more scientists. Since coming of age I have learned of two other jobs they are supposed to do. The other departments, and the university alumni, expect them to impart a modicum of scientific vocabulary to non-science undergraduates, a task not easy and not trivial. In addition the science faculty, and their professional colleagues, consider basic scientific research to be an essential part of their assignment.
Some thoughts on science in the federal government…
Authors: Condon E. U.
Published: January 2009

As my nearly six years of service as Director of the National Bureau of Standards draw to a close, it seems that an important final part of that service would be to set down some over-all views concerning the scientific work of the Federal Government growing out of that experience. Our governmental institutions are so close to us that I had some experience with them before entering Federal service full-time, especially during World War II, and likewise I expect to have association with such matters in the future while in private employment.
The flow of solids
Authors: Gross B.
Published: January 2009

The present widespread use of polymer plastics has made necessary the study of the mechanical properties of these substances and thus has focussed the interest of the engineer and the physicist once again upon the general problem of the flow properties of solid materials. This is a classical problem; over a period of nearly 100 years it has repeatedly made headlines in physics. The empirical foundations were laid by men whose names mark the development of classical physics—Maxwell, Hopkinson, Kohlrausch. Boltzmann and Wiechert developed a phenomenological, e.g. descriptive, theory which is still unsurpassed. The great Italian mathematician V. Volterra recognized the mathematical implications of this theory and therefrom established the theory of the integral equation that carries his name. The applied physicists and engineers joined forces, bringing with them the tools of modern technology and extending the field of experimental research to a point undreamed of some years ago. And now the theorists of modern physics begin to see a way in which the observed macroscopical behavior of matter may be explained in detail by a satisfactory molecular theory. But in spite of all this combined effort the problem is far from being completely solved.
College and university research in physics
Authors: Mattill John I.
Published: January 2009

The impact of the current national defense effort on scientific education has been the subject of wide concern in colleges and universities. An important part of this problem—and one which especially concerns physicists—is the colleges' growing participation in research.
A Letter to the Editor
Authors: Franzen Carl G. F.
Published: January 2009

I have read the article on “The Role of the Secondary School in the Teaching of Science” by Dr. George R. Harrison (Physics Today, June 1952) and find that it presents a point of view which I can endorse completely. It is indeed encouraging to find men of science who have taken the time to become so well aware of the problems of public school education as has Dr. Harrison, and even more encouraging when they will express themselves so brilliantly on problems of education in a publication such as Physics Today, which reaches not only physicists but scientists and engineers in general.
Theoretical study of enhanced Raman scattering for stratified concentric silicon-silver nanocylinders
Authors: Wu Y. B. , Wang Y. F. , Cao X. W.
Published: January 2009

This paper presents calculations of Raman enhancement for stratified concentric silicon-silver nanocylinders. The Raman enhancement factors of double-layer and triple-layer structures have been determined. Calculations have been performed for the following two-layer cylinders: Ag/Si(core), hollow silicon tube, and Si/Ag(core), and the following three-layer cylinders: Ag/Si/Ag(core), Si/Ag/Si(core), Si/vacuum/Ag(core), Si/vacuum/Si(core), and Si/Ag/vacuum(core). The results indicate that strong Raman enhancements can be obtained in stratified concentric silicon-silver nanocylinders in suitable conditions. These enhancements are sensitive to the excitation wavelength, the radius of the central material, the layer number, and the thickness of each layer of the stratified concentric silicon-silver nanocylinders. They are mainly attributed to the resonant excitations of the silicon cylinder, the resonant excitations of the silicon shell, the localized surface plasmon resonant excitations of silver, and the mirror effect of silver or silicon. The strongest Raman enhancement is about 1013 in two-layer and 1020 in three-layer concentric silicon-silver nanocylinders. The results indicate that the large Raman enhancement appears when the thin silicon layer is close to the silver.
Determining strain in amorphous alloys: Uncertainties with analyzing structural changes during deformation
Authors: Mendelev M. I. , Ott R. T. , Kramer M. J. , Sordelet D. J.
Published: January 2009

Molecular dynamics simulations were utilized to test the reliability of strain values obtained from diffraction data for noncrystalline alloys. We found that in the case of a one-component system, the strain value obtained from the pair correlation functions underestimates the actual value because of a small degree of atomic relaxations, which minimize the effects of the applied deformation. In the case of multicomponent systems, the different pairs are affected by applied deformation to different extents; moreover, this implies that the strain value determined from diffraction data should depend on the type of scattering.
Patterned medium for heat assisted magnetic recording
Authors: Şendur Kürşat , Challener William
Published: January 2009

Heat assisted magnetic recording (HAMR) is a potential solution to extend the limits of conventional magnetic recording. In HAMR, the heating of the recording medium is achieved with a near-field optical transducer. Although the literature suggests novel transducers, there is little consideration of the optical and thermal aspects of the magnetic medium. In this letter we suggest a recording medium that provides a significant enhancement in optical absorption and localized heating. The thermal profiles of the proposed medium and the conventional medium are compared using finite element method solutions of Maxwell’s and the heat transfer equations.
Probing magnetic configurations in Co/Cu multilayered nanowires
Authors: Wong Jared , Greene Peter , Dumas Randy K. , Liu Kai
Published: January 2009

Magnetic configurations in heterostructures are often difficult to probe when the magnetic entities are buried inside. In this study we have captured magnetic and magnetoresistance “fingerprints” of Co nanodisks embedded in Co/Cu multilayered nanowires using a first-order reversal curve method. In 200 nm diameter nanowires, the magnetic configurations can be tuned by adjusting the Co nanodisk aspect ratio. Nanowires with the thinnest Co nanodisks exhibit single domain behavior, while those with thicker Co reverse via a vortex state. A superposition of giant and anisotropic magnetoresistance is observed, which corresponds to the different magnetic configurations of the Co nanodisks.
An essential role for Radar (Gdf6a) in inducing dorsal fate in the zebrafish retina
Authors: Gosse Nathan J. , Baier Herwig
Published: January 2009

Retinal ganglion cells form orderly topographic connections with the tectum, establishing a continuous neural representation of visual space. Mapping along the dorsal–ventral axis requires interactions between EphB and ephrin-B cell-surface molecules expressed as countergradients in both retina and tectum. We have discovered that the diffusible TGFß-related factor Radar (Gdf6a) is necessary and sufficient for activation of dorsal markers, such as Bmp4, Tbx5, Tbx2b, and Ephrin-B2, and suppression of the ventral marker Vax2 in the zebrafish retina. Radar mutant axons innervate only the dorsal half of the tectum, where they form a compressed retinotectal map. Wild-type cells transplanted into the dorsal retina are able to rescue the dorsal identity of nearby mutant cells. Moreover, Radar overexpression “dorsalizes” retinal ganglion cell identity in the ventral retina. We conclude that Radar is near the top of a signaling cascade that establishes dorsal–ventral positional information in the retina and controls the formation of the retinotectal map.
FK506-binding protein (FKBP) partitions a modified HIV protease inhibitor into blood cells and prolongs its lifetime in vivo
Authors: Marinec Paul S. , Chen Lei , Barr Kenneth J. , Mutz Mitchell W. , Crabtree Gerald R. , Gestwicki Jason E.
Published: January 2009

HIV protease inhibitors are a key component of anti-retroviral therapy, but their susceptibility to cytochrome P
450
metabolism reduces their systemic availability and necessitates repetitive dosing. Importantly, failure to maintain adequate inhibitor levels is believed to provide an opportunity for resistance to emerge; thus, new strategies to prolong the lifetime of these drugs are needed. Toward this goal, numerous prodrug approaches have been developed, but these methods involve creating inactive precursors that require enzymatic processing. Using an alternative strategy inspired by the natural product FK506, we have synthetically modified an HIV protease inhibitor such that it acquires high affinity for the abundant, cytoplasmic chaperone, FK506-binding protein (FKBP). This modified protease inhibitor maintains activity against HIV-1 protease (IC
50
= 19 nM) and, additionally, it is partitioned into the cellular component of whole blood via binding to FKBP. Interestingly, redistribution into this protected niche reduces metabolism and improves its half-life in mice by almost 20-fold compared with the unmodified compound. Based on these findings, we propose that addition of FKBP-binding groups might partially overcome the poor pharmacokinetic properties of existing HIV protease inhibitors and, potentially, other drug classes.
Prey choice and habitat use drive sea otter pathogen exposure in a resource-limited coastal system
Authors: Johnson Christine K. , Tinker Martin T. , Estes James A. , Conrad Patricia A. , Staedler Michelle , Miller Melissa A. , Jessup David A. , Mazet Jonna A. K.
Published: January 2009

The processes promoting disease in wild animal populations are highly complex, yet identifying these processes is critically important for conservation when disease is limiting a population. By combining field studies with epidemiologic tools, we evaluated the relationship between key factors impeding southern sea otter (
Enhydra lutris nereis
) population growth: disease and resource limitation. This threatened population has struggled to recover despite protection, so we followed radio-tagged sea otters and evaluated infection with 2 disease-causing protozoal pathogens,
Toxoplasma gondii
and
Sarcocystis neurona
, to reveal risks that increased the likelihood of pathogen exposure. We identified patterns of pathogen infection that are linked to individual animal behavior, prey choice, and habitat use. We detected a high-risk spatial cluster of
S. neurona
infections in otters with home ranges in southern Monterey Bay and a coastal segment near San Simeon and Cambria where otters had high levels of infection with
T. gondii
. We found that otters feeding on abalone, which is the preferred prey in a resource-abundant marine ecosystem, had a very low risk of infection with either pathogen, whereas otters consuming small marine snails were more likely to be infected with
T. gondii
. Individual dietary specialization in sea otters is an adaptive mechanism for coping with limited food resources along central coastal California. High levels of infection with protozoal pathogens may be an adverse consequence of dietary specialization in this threatened species, with both depleted resources and disease working synergistically to limit recovery.
The influence of oceanographic fronts and early-life-history traits on connectivity among littoral fish species
Authors: Galarza Juan A. , Carreras-Carbonell Josep , Macpherson Enrique , Pascual Marta , Roques Severine , Turner George F. , Rico Ciro
Published: January 2009

The spatial distribution of neutral genetic diversity is mainly influenced by barriers to dispersal. The nature of such barriers varies according to the dispersal means and capabilities of the organisms concerned. Although these barriers are often obvious on land, in the ocean they can be more difficult to identify. Determining the relative influence of physical and biotic factors on genetic connectivity remains a major challenge for marine ecologists. Here, we compare gene flow patterns of 7 littoral fish species from 6 families with a range of early-life-history traits sampled at the same geographic locations across common environmental discontinuities in the form of oceanic fronts in the Western Mediterranean. We show that these fronts represent major barriers to gene flow and have a strong influence on the population genetic structure of some fish species. We also found no significant relation between the early-life-history traits most commonly investigated (egg type, pelagic larval duration, and inshore-offshore spawning) and gene flow patterns, suggesting that other life-history factors should deserve attention. The fronts analyzed and the underlying physical mechanisms are not site-specific but common among the oceans, suggesting the generality of our findings.
Recurrent genomic alterations characterize medulloblastoma arising from DNA double-strand break repair deficiency
Authors: Frappart Pierre-Olivier , Lee Youngsoo , Russell Helen R. , Chalhoub Nader , Wang Yong-Dong , Orii Kenji E. , Zhao Jingfeng , Kondo Naomi , Baker Suzanne J. , McKinnon Peter J.
Published: January 2009

Inactivation of homologous recombination (HR) or nonhomologous end-joining (NHEJ) predisposes to a spectrum of tumor types. Here, we inactivated DNA double-strand break repair (DSBR) proteins, DNA Ligase IV (Lig4), Xrcc2, and Brca2, or combined Lig4/Xrcc2 during neural development using Nestin-cre. In all cases, inactivation of these repair factors, together with p53 loss, led to rapid medulloblastoma formation. Genomic analysis of these tumors showed recurring chromosome 13 alterations via chromosomal loss or translocations involving regions containing
Ptch1
. Sequence analysis of the remaining
Ptch1
allele showed a variety of inactivating mutations in all tumors analyzed, highlighting the critical tumor suppressor function of this hedgehog-signaling regulator. We also observed genomic amplification or up-regulation of either
N-Myc
or
cyclin D2
in all medulloblastomas. Additionally, chromosome 19, which contains Pten, was also selectively deleted in medulloblastoma arising after disruption of HR. Thus, our data highlight the preeminence of Ptch1 as a tumor suppressor in cerebellar granule cells and reveal other genomic events central to the genesis of medulloblastoma.
HIV-1 Rev protein assembles on viral RNA one molecule at a time
Authors: Pond Stephanie J. K. , Ridgeway William K. , Robertson Rae , Wang Jun , Millar David P.
Published: January 2009

Oligomerization of the HIV-1 protein Rev on the Rev Response Element (RRE) regulates nuclear export of genomic viral RNA and partially spliced viral mRNAs encoding for structural proteins. Single-molecule fluorescence spectroscopy has been used to dissect the multistep assembly pathway of this essential ribonucleoprotein, revealing dynamic intermediates and the mechanism of assembly. Assembly is initiated by binding of Rev to a high-affinity site in stem-loop IIB of the RRE and proceeds rapidly by addition of single Rev monomers, facilitated by cooperative Rev-Rev interactions on the RRE. Dwell-time analysis of fluorescence trajectories recorded during individual Rev-RRE assembly reactions has revealed the microscopic rate constants for several of the Rev monomer binding and dissociation steps. The high-affinity binding of multiple Rev monomers to the RRE is achieved on a much faster timescale than reported in previous bulk kinetic studies of Rev-RRE association, indicating that oligomerization is an early step in complex assembly.
A matrix convexity approach to some celebrated quantum inequalities
Authors: Effros Edward G.
Published: January 2009

Some of the important inequalities associated with quantum entropy are immediate algebraic consequences of the Hansen–Pedersen–Jensen inequalities. A general argument is given using matrix perspectives of operator convex functions. A matrix analogue of Maréchal's extended perspectives provides additional inequalities, including a
p
+
q
≤ 1 result of Lieb.
Sum rules and determination of exciton coupling using absorption and circular dichroism spectra of biological polymers
Authors: Burin Alexander L. , Armbruster Michael E. , Hariharan Mahesh , Lewis Frederick D.
Published: January 2009

Optical spectra of biological polymers contain important information about their structure and function in living organisms. This information can be accessed by extracting an optical interaction of monomers, i.e., their exciton coupling, from experimental data. This coupling is sensitive to molecular structure, geometry, and conformation and can be used to characterize them. However, the accurate determination of exciton coupling in important biological molecules is difficult because inhomogeneous broadening smears out the monomer interaction. We suggest a way to overcome this problem by applying exact sum rules. These sum rules are derived by establishing a straightforward relationship between integral characteristics of absorption and circular dicroism spectra, and exciton coupling. Exciton coupling between AT pairs in native DNA conformation is estimated by applying these sum rules to DNA hairpin optical spectra as
V
0
∼ 0.035 eV in agreement with the earlier numerical calculations.
Nesprin 4 is an outer nuclear membrane protein that can induce kinesin-mediated cell polarization
Authors: Roux Kyle J. , Crisp Melissa L. , Liu Qian , Kim Daein , Kozlov Serguei , Stewart Colin L. , Burke Brian
Published: January 2009

Nucleocytoplasmic coupling is mediated by outer nuclear membrane (ONM) nesprin proteins and inner nuclear membrane Sun proteins. Interactions spanning the perinuclear space create nesprin–Sun complexes connecting the cytoskeleton to nuclear components. A search for proteins displaying a conserved C-terminal sequence present in nesprins 1–3 identified nesprin 4 (Nesp4), a new member of this family. Nesp4 is a kinesin-1-binding protein that displays Sun-dependent localization to the ONM. Expression of Nesp4 is associated with dramatic changes in cellular organization involving relocation of the centrosome and Golgi apparatus relative to the nucleus. These effects can be accounted for entirely by Nesp4's kinesin-binding function. The implication is that Nesp4 may contribute to microtubule-dependent nuclear positioning.
RNA-directed DNA methylation induces transcriptional activation in plants
Authors: Shibuya Kenichi , Fukushima Setsuko , Takatsuji Hiroshi
Published: January 2009

A class-C floral homeotic gene of
Petunia
,
pMADS3
, is specifically expressed in the stamen and carpels of developing flowers. We had previously reported the ect-
pMADS3
phenomenon in which introduction of a part of the
pMADS3
genomic sequence, including intron 2, induces ectopic expression of endogenous
pMADS3
. Unlike transcriptional or posttranscriptional gene silencing triggered by the introduction of homologous sequences, this observation is unique in that the gene expression is up-regulated. In this study, we demonstrated that the ect-
pMADS3
phenomenon is due to transcriptional activation based on RNA-directed DNA methylation (RdDM) occurring in a particular CG in a putative
cis
-element in
pMADS3
intron 2. The CG methylation was maintained over generations, along with
pMADS3
ectopic expression, even in the absence of RNA triggers. These results demonstrate a previously undescribed transcriptional regulatory mechanism that could lead to the generation of a transcriptionally active epiallele, thereby contributing to plant evolution. Our results also reveal a putative negative
cis
-element for organ-specific transcriptional regulation of class-C floral homeotic genes, which could be difficult to identify by other approaches.
The fifth class of Gα proteins
Authors: Oka Yuichiro , Saraiva Luis R. , Kwan Yen Yen , Korsching Sigrun I.
Published: January 2009

All α-subunits of vertebrate heterotrimeric G proteins have been classified into 4 major classes, Gs, Gi, Gq, and G12, which possess orthologs already in sponges, one of the earliest animal phyla to evolve. Here we report the discovery of the fifth class of Gα protein, Gv, ancient like the other 4 classes, with members already in sponges, and encoded by 1–2
gnav
genes per species. Gv is conserved across the animal kingdom including vertebrates, arthropods, mollusks, and annelids, but has been lost in many lineages such as nematodes, fruit fly, jawless fish, and tetrapods, concordant with a birth-and-death mode of evolution. All Gv proteins contain 5 G-box motifs characteristic of GTP-binding proteins and the expected acylation consensus sites in the N-terminal region. Sixty amino acid residues are conserved only among Gv, suggesting that they may constitute interaction sites for Gv-specific partner molecules. Overall Gv homology is high, on average 70% amino acid identity among vertebrate family members. The
d
N
/
d
S
analysis of teleost
gnav
genes reveals evolution under stringent negative selection. Genomic structure of vertebrate
gnav
genes is well conserved and different from those of the other 4 classes. The predicted full ORF of zebrafish
gnav1
was confirmed by isolation from cDNA. RT-PCR analysis showed broad expression of
gnav1
in adult zebrafish and in situ hybridization demonstrated a more restricted expression in larval tissues including the developing inner ear. The discovery of this fifth class of Gα proteins changes our understanding of G protein evolution.
Characterization of the thymic IL-7 niche in vivo
Authors: Alves Nuno L. , Goff Odile Richard-Le , Huntington Nicholas D. , Sousa Ana Patricia , Ribeiro Vera S. G. , Bordack Allison , Vives Francina Langa , Peduto Lucie , Chidgey Ann , Cumano Ana , Boyd Richard , Eberl Gerard , Di Santo James P.
Published: January 2009

The thymus represents the “cradle” for T cell development, with thymic stroma providing multiple soluble and membrane cues to developing thymocytes. Although IL-7 is recognized as an essential factor for thymopoiesis, the “environmental niche” of thymic IL-7 activity remains poorly characterized in vivo. Using bacterial artificial chromosome transgenic mice in which YFP is under control of IL-7 promoter, we identify a subset of thymic epithelial cells (TECs) that co-express YFP and high levels ofIl7transcripts (IL-7hicells). IL-7hiTECs arise during early fetal development, persist throughout life, and co-express homeostatic chemokines (Ccl19,Ccl25,Cxcl12) and cytokines (Il15) that are critical for normal thymopoiesis. In the adult thymus, IL-7hicells localize to the cortico-medullary junction and display traits of both cortical and medullary TECs. Interestingly, the frequency of IL-7hicells decreases with age, suggesting a mechanism for the age-related thymic involution that is associated with declining IL-7 levels. Our temporal-spatial analysis of IL-7-producing cells in the thymus in vivo suggests that thymic IL-7 levels are dynamically regulated under distinct physiological conditions. This IL-7 reporter mouse provides a valuable tool to further dissect the mechanisms that govern thymic IL-7 expression in vivo.