bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Optics of Organic and Polymer Materials
Authors: Garito Anthony , Fang Shi Rui , Wu Marvin
Published: January 2008

Over the past decade the study of nonlinear optical processes in organic and polymer systems has enjoyed rapid and sustained growth. One indication of that growth is the increase in the number of articles published inrefereed society journals. The four-year period 1980–83 saw the publication of 124 such articles. For the four-year period a decade later the production of articles in the field had grown to 736—nearly a sixfold increase. In part, the rapid growth of the field can be attributed to the technological promise and interesting physical properties of these materials. Because of their large optical nonlinearities and mechanical, chemical, thermal and optical stability, organic nonlinear optical materials are the leading practical materials for fabricating optoelectronic devices. They also have proven to be excellent subjects in which to study many-body electron correlation effects and exotic states like polarons, excitons and even coherently propagating multiexciton strings.
Recollections of Lev Davidovich Landau
Authors: Akhiezer Alexander I.
Published: January 2008

The older I get, the more I am afflicted by fits of nostalgia. Even when they recall the best days of my youth, they nonetheless weigh heavy, because it's impossible to go back. I think the best way to deal with these memories is to convey them to paper. So I'd like to share some of my recollections of a great man, my unforgettable teacher Lev Davidovich Landau, to whom I was close for several decades until his tragic death in 1968. (See also the articles by I. M. Khalatnikov and Vitaly Ginzburg in PHYSICS TODAY, May 1989.)
Public Support of Science: Searching for Harmony
Authors: Schmitt Roland W.
Published: January 2008

My subject is the rationale for public support of science in the post cold-war era. The first question is, Whose rationale? Congressman George Brown's or Senator Barbara Mikulski's or President Bill Clinton's or Phil Anderson's or Leon Lederman's? Everyone seems to be singing different tunes, and it is hard to hear any harmony in their voices. And yet with the profound changes in the forces that have driven our Federal science and technology policies, it is now more important than ever to find that harmony.
Blue-Green Diode Lasers
Authors: Neumark Gertrude F. , Park Robert M. , Depuydt James M.
Published: January 2008

The development of compact, reliable and inexpensive short-wavelength lasers is certain to have profound effects on virtually any technology that uses coherent visible light. Although the impact of such devices will be far-reaching, the primary driving force behind efforts to develop blue-green diode lasers is without question optical recording. The demand for increased data storage capabilities is continually forcing the recording industry to increase storage densities.
X Rays From the Rest of the Universe
Authors: Helfand David J.
Published: January 2008

Just as x rays from a cathode-ray tube in Wilhelm Röntgen's laboratory revealed the bones in his wife's hand, x rays from space have revealed new objects and physical processes hidden from the view of optical telescopes. X rays from beyond Earth's atmosphere were first detected in 1949 in a 5-minute V-2 rocket observation of the Sun. Thirteen years later, the first nocturnal rocket flight quite unexpectedly discovered the existence of a diffuse isotropic glow of 10-kilo-electron-volt x rays across the celestial sphere, as well as the first discrete source of x-ray emission from beyond the Solar System. By 1965 the number of known sources of celestial x rays totaled 10; at this writing the number exceeds 105.
The Physics of Cerebral Aneurysms
Authors: Hademenos George J.
Published: January 2008

According to the most recent statistics, cerebrovascular disease is the third leading cause of death in the United States, ranking behind heart attack and all forms of cancer. One form of cerebrovascular disease is the cerebral aneuiysm, which manifests itself as a dilatation, or pouching, of the arterial wall. The dilatation develops at a diseased site along the wall into a distended sac of stressed arterial tissue. Fully developed cerebral aneurysms are typically from 5 to 10 millimeters in diameter. Aneurysms can and do occur at any point within the cardiac and peripheral vasculaturc. However, cerebral aneurysms tend to assume a simple spherical form that makes them well suited to a biophysical analysis. They also pose the greatest risks to the patient. Left untreated, an aneurysm continues to expand until it raptures, causing hemorrhage, severe neurological complications and possibly death. It is for these reasons that this article concentrates on cerebral aneurysms. Many aspects of the treatment given here will be applicable to other types of aneurysms.
Electronic Pairing in Exotic Superconductors
Authors: Cox Daniel L. , Maple M. Brian
Published: January 2008

Investigations of rare earth, Aactinide, organic and oxide compounds have yielded several new classes of exotic superconductors. These include magnetically ordered superconductors, A15 superconductors, buckyball superconductors, heavy-electron superconductors, organic superconductors and high-Tc oxide superconductors. These materials have properties significantly different from those of conventional superconductors such as Al and Zn, which are described well by the Bardeen-Cooper-Schrieffer model of superconductivity. We carefully distinguish between the BCS model and the more general BCS theory. In the BCS theory superconductivity arises, loosely speaking, from electron pairs that behave essentially as bosons and undergo macroscopic condensation to the lowest energy state at the critical temperature Tc The BCS model, presented in 1957, further specifies that the pairing is mediated by exchange of quantized lattice vibrations (phonons) between the electrons, yielding pairs with zero spin S (spin singlet) and zero angular momentum L (s wave). This model is but one example of the BCS pairing theory; another describes the superfluid state of 3He, where the fermionic 3He atoms form p-wave (L = 1) spin-triplet (S = 1) pairs held together by the exchange of magnetic excitations of the surrounding atomic sea.
How Would a Physicist Design a Tennis Racket?
Authors: Brody Howard
Published: January 2008

Tennis players dream of finding Lhe perfect racket that will immediately transform them into champions. While that may be wishful thinking, it is generally agreed that today's rackets are much better than those of 20 years ago. Though they may not turn you into an instant Wimbledon winner (after all, your opponent has one too), they will clearly improve your game. There is still hope among inventors, racket manufacturers and players that a perfect racket will come along someday. If and when such a racket is developed, what will its properties be and how will it affect the game of tennis?
Spectroscopy and Imaging with Diffusing Light
Authors: Yodh Arjun , Chance Britton
Published: January 2008

Visually opaque media are ubiquitous in nature. While some materials are opaque because they strongly absorb visible light, others, such as loam, white paint, biological tissue and milk, are opaque because photons traveling within them are predominantly scattered rather than absorbed. A vanishingly small number of photons travel straight through such substances. Instead, light is transported through these materials in a process similar to heat diffusion (figure 1).
Micromagnetic Microscopy and Modeling
Authors: Dahlberg E. Dan , Zhu Jian-Gang
Published: January 2008

With the miniaturization of magnetic technologies, the need to understand magnetization on length scales below a micron is becoming increasingly important. This booming interest in micro magnetics has fueled a renaissance in both micro-magnetic modeling and measurement techniques. Conversely, the codevelop-ment of modeling and imaging has made possible recent advances in this critical area of magnetism. On the modeling side, the rapid development of high-speed computing has had a tremendous impact on micromagnetics simulations. On the measurement side, a number of microscopies have been developed for imaging on a length scale of tens of nanometers. Figure 1 shows an image of rows of bits in a magneto-optical medium. The bits were both written and imaged using a magnetic force microscope. Results on this length scale provide information that can be used in models and also challenge models’ predictive capabilities. The image on the cover of this issue shows naturally occurring domain patterns in a single-crystal ferrite, a system that exhibits extremely complex magnetic stmctures.
Research on Silicon and Germanium in World War II
Authors: Seitz Frederick
Published: January 2008

A relatively large and well-funded group of investigators did intense research on the electrical properties of silicon and germanium during World War II. Their work completely transformed attitudes toward the physical properties of the pure crystalline forms of the semiconductors: No longer regarded merely as exotic materials, these elements became components of flexibly useful circuit elements that could be manipulated to show various properties by the addition of small amounts of other elements. In this sense, the wartime research laid the groundwork for the invention of the transistor shortly after the war and ultimately the development of the integrated circuit. The work opened up a now age of electronics.
Strategic Curiosity: Semiconductor Physics in the 1950s
Authors: Ehrenreich Henry
Published: January 2008

When I arrived at the General Electric Research Laboratory at the beginning of 1955, fresh from a PhD at Cornell, I was greeted by my supervisor, Leroy Apker, who looked after the semiconductor section of the general physics department. I asked him to suggest some research topics that might be germane to the interests of the section. He said that what I did was entirely up to me. After recovering from my surprise, I asked, “Well, how are you going to judge my performance at the end of the year?” He replied, “Oh, I'll just call up the people at Bell and ask them how they think you are doing.” Viewed from today's environment, what is particularly hard to understand about this conversation is how an industrial laboratory, responsible to the operating units of the company and to the stockholders, could afford to take such a relaxed view.
Julian Schwinger: Prodigy, Problem Solver, Pioneering Physicist
Authors: Martin Paul C. , Glashow Sheldon L.
Published: January 2008

Most theoretical physicists rely on interactions with others to stay abreast of theoretical and experimental advances. In classrooms and seminars, on blackboards and napkins, they exchange and clarify ideas with colleagues and students. Rare is the theoretical physicist who makes repeated and varied contributions apart from the throng; rarer still is one who not only contributes but also sets standards and priorities singlehandedly. Julian Seymour Schwinger, who died 16 July 1994 at the age of 76, was such an individual. Gentle but steadfastly independent, quiet but dramatically eloquent, self-taught and self-propelled, brilliant and prolific, Schwinger remained active and productive until his death. His ideas, discoveries and techniques pervade all areas of theoretical physics.
Special Issue: X Rays 100 Years Later
Authors: Benka Stephen G. , Lubkin Gloria B.
Published: January 2008

One century ago this month, highenergy electromagnetic radiation—the “X” or “unknown” ray—was discovered by Wilhelm Conrad Rontgen in his basement laboratory. Few other scientific discoveries were as immediately sensational. From hospitals to airports, in physics and biology labs, in the fabrication of nanostructures for electronics and machinery, x rays have come to permeate the modern world. In this special issue we cannot look at the full history and extent of research using x rays. Rather, we have chosen to take a few snapshots of research then and now.
Recent Applications of X Rays in Condensed Matter Physics
Authors: Als-Nielsen Jens , Materlik Gerhard
Published: January 2008

Since their discovery by Wilhelm Conard Röntgen, X rays have played a significant role in our lives: they make the unseen in our bodies visible; they enhance our security in air travel; they make possible nondestructive testing of a wide variety of materials. And through x-ray diffraction and spectroscopy they make it possible to probe the order of matter at the atomic level.
The Physics of Baseball
Authors: Adair Robert K.
Published: January 2008

The illumination of the ordinary—of why the sky is blue or why the stars shine—is not the least important role of physics and physicists. Then can't we add to the list of deeper queries some of the questions that seemed so important to me in my youth: How can Babe Ruth hit so many home runs? What makes Carl Hubble's curveball and screwball swerve in their trips to the plate? And if baseball plays no known role in the fundamental structure of the universe (see The Iowa Baseball Confederacy by W. P. Kinsella for a contrary position), it is not of trivial importance in the perception and appreciation of that universe by some of its inhabitants. Although not quite so important now, in the period between the Civil War and World War II baseball was a significant part of what defined the United States. Forty years ago, Jacques Barzun, a preeminent student of American culture and a native of France, said, “Whoever wants to know… America had better learn baseball.” But, even as the game itself is subtle and complex, I have found subtleties and complexities in my attempts to know the physical bases of this American game.
Stellar Optical Interferometry in the 1990s
Authors: Thomas Armstrong J. , Hutter Donald J. , Johnston Kenneth J. , Mozurkewich David
Published: January 2008

The unaided eye has an angular resolution of about 1 arcminute. From the invention of the telescope in the 17th century to the middle of the 1970s, astronomers improved on this resolution by two orders of magnitude by building bigger telescopes and putting them at good sites. Even at good sites, however, atmospheric turbulence limits the resolution at visible and infrared wavelengths to 1 arcsec or a little better. In the past 20 years, a further factor-of-ten improvement has come with two developments that deal with the atmosphere: “speckle interferometry,” in which the blurred image is frozen in a short exposure and the image is reconstructed from many exposures, and adaptive optics, in which the effects of the atmosphere are sensed, then corrected with a defbrmable mirror, before the image is recorded. (See Laird A. Thompson's article in PHYSICS TODAY, December 1994, page 24.)
Agreement Between Theory and Experiment
Authors: Aharoni Amikam
Published: January 2008

A theory is usually expected to explain existing experimental results and to predict new results, while an experiment is usually expected to check the validity of existing theories and to gather data for modifying them. This approach is normally presented to students as foolproof as if it were one of the basic laws of “good” science. In practice these goals are achieved in some cases, but sometimes the comparison between a theory and an experiment can be very misleading. Here I am going to discuss these unusual cases, to warn against the possible pitfalls. They may or may not be rare, but in any event it is important to bear in mind that they do exist.
Thermoacoustic Engines and Refrigerators
Authors: Swift Gregory W.
Published: January 2008

We ordinarily think of a sound wave in a gas as consisting of coupled pressure and displacement oscillations. However, temperature oscillations always accompany the pressure changes. The combination of all these oscillations, and their interaction with solid boundaries, produces a rich variety of “thermoacoustic” effects. Although these effects as they occur in everyday life are too small to be noticed, one can harness extremely loud sound waves in acoustically sealed chambers to produce powerful heat engines, heat pumps and refrigerators. Whereas typical engines and refrigerators have crankshaft-coupled pistons or rotating turbines, thermoacoustic engines and refrigerators have at most a single flexing moving part (as in a loudspeaker) with no sliding seals. Thermoacoustic devices may be of practical use where simplicity, reliability or low cost is more important than the highest efficiency (although one cannot say much more about their cost-competitiveness at this early stage).
The Discovery of Superfluidity
Authors: Donnelly Russell J.
Published: January 2008

Two of the greatest physics discoveries in the first half of the 20th century were superconductivity and superfluidity. Superconductivity involves the frictionless conduction of electricity in wires, and superfluidity the frictionless flow of superfluid liquid helium through channels. Both discoveries led to the arcane phenomenon of macroscopic quantization: the manifestation of the laws of quantum mechanics not just on atomic dimensions but also on the scale of common laboratory apparatus. Both discoveries required the liquefaction of helium, which was first done in 1908.
Acoustic Wavefronts in Crystalline Solids
Authors: Wolfe James P.
Published: January 2008

Drop a pebble into a pond and the result is quite predictable: A circular wave expands out from the disturbance. Similarly, sound waves in the atmosphere radiate spherically from a point source. Vibrational waves in a solid medium, however, exhibit a much more intriguing behavior.
Scanning Force Microscopy in Biology
Authors: Bustamante Carlos , Keller David
Published: January 2008

Microscopes have played a fundamental role in the development of biology as an experimental science. It was Robert Hooke who, when using a compound microscope in 1655, noticed that thin slices of cork were made up of identical and small self-contained units, which he called “cells.” The generalization of this observation and its acceptance, though, had to wait until the late 1830s, when German microscopists Matthias Schleiden and Thcodor Schwann—working independently—introduced the “cell theory” of complex organisms. By the second half of the 19th century Magnus Retzius, Santiago Ramón y Cajal and Camillo Golgi were busy completing the microscopic anatomical description of the cell.
Symmetry in Physics: Wigner's Legacy
Authors: Gross David J.
Published: January 2008

Until the twentieth century, principles of symmetry played little explicit role in theoretical physics. Conservation laws, especially those of energy and momentum, were considered to be of fundamental importance. But these were regarded as consequences of the dynamical laws of nature, rather than as consequences of the symmetries that underlay these laws. Maxwell's equations, formulated in 1865, embodied both Lorentz invariance and gauge invariance. But these symmetries of electrodynamics were not fully appreciated for 40 years or more.
X Rays in Molecular Biophysics
Authors: Hendrickson Wayne A.
Published: January 2008

X rays have had a profound impact in advancing the field of biology, and the pace of fundamental discovery is still accelerating. Through the awesome powers of recombinant DNA technology and synchrotron radiation, as combined in modern-day x-ray crystallography, ever-more-complicated molecules and assemblages are being worked out in atomic detail. The insights into biological processes derived from these studies are transforming cell and molecular biology.
The Discovery of Radioactivity
Authors: Badash Lawrence
Published: January 2008

One hundred years ago, several remarkable discoveries were crowded into the short space of ten years: x rays in 1895, radioactivity the next year, the electron in 1897, quantum theory in 1900 and special relativity in 1905. Individually, each had enormous significance. Collectively, they heralded what we now know as “modern physics.” Practitioners of the old “classical physics” had no anticipation of the momentous change about to grip their science. Indeed, a few even claimed that all the great discoveries had already been made and that their profession would be reduced merely to measurements of greater and greater accuracy. No doubt some discoveries lay in the next decimal place, as illustrated by the 1894 revelation of the rare gas argon during very accurate measurements of the constituents of air. But a career centered only on making increasingly precise measurements would not have appealed to most physicists.
Beyond Brownian Motion
Authors: Klafter Joseph , Shlesinger Michael F. , Zumofen Gert
Published: January 2008

Newtonian physics began with an attempt to make precise predictions about natural phenomena, predictions that could be accurately checked by observation and experiment. The goal was to understand nature as a deterministic, “clockwork” universe. The application of probability distributions to physics developed much more slowly. Early uses of probability arguments focused on distributions with well-defined means and variances. The prime example was the Gaussian law of errors, in which the mean traditionally represented the most probable value from a series of repeated measurements of a fixed quantity, and the variance was related to the uncertainty of those measurements.
Probing Cosmic Mysteries by Supercomputer
Authors: Norman Michael L.
Published: January 2008

Astrophysicists have had a love affair with big computers since the dawn of the digital era. Although it is unlikely that the 1946 ENIAC (Electronic Numerical Integrator and Computer) was ever used for astrophysical calculations, Princeton University astronomer Martin Schwarzschild made extensive use of the follow-on MANIAC computer at the Los Alamos laboratory for his pioneering calculations of stellar evolution. Since World War II, simulating the inner workings of nuclear weapons has been one of the key applications driving the development of supercomputer technology. Because many of the same physical processes operate in stars and nebulae as in hydrogen bombs, supercomputers designed with defense needs in mind have been ideally suited to computational astrophysics research. Until the mid-1980s, however, access to supercomputers was limited to a small cadre of researchers at defense laboratories or at a few specialized academic institutions.
Data Acquisition and Analysis in Extremely High Data Rate Experiments
Authors: Butler Joel N. , Quarrie David R.
Published: January 2008

The goal of elementary particle physics is to unravel the properties of matter at the deepest level—that is, to answer questions such as. What are the basic constituents of matter and how do they interact with each other? The search for the answers to such questions has led us to probe the structure of matter at ever-smaller length scales—from atomic to nuclear and now subnuclear scales. Investigating very small distance scales (below 10−13 cm) has required very high-energy particles and, consequently, the development of gigantic particle accelerators for producing such particles. (See the box on page 55.) Although these high energy accelerators are marvels of technical and scientific ingenuity, the massive amount of data they produce could not be collected, analyzed and reduced to physics results without another marvel of modern technology: the digital computer!
Special Issue: 50 Years of Computers and Physicists
Authors: Lubkin Gloria B.
Published: January 2008

Fifty years ago, a physics graduate student burning the midnight oil might labor for several years with a lab notebook, Marchant desk calculator and graph paper. Today the time it takes to receive the PhD might be even longer, but today's tools were probably never dreamt of by that struggling student of the past.
Researchers Glance at Magnetic Surfaces with Synchrotron X Rays
Authors: Ladbury Ray
Published: January 2008

The proliferation in recent years of the number of techniques for studying surface magnetism is partly attributable to the increasing importance of surface magnetism in the multibillion-dollar recording industry—in the design of ultrahigh-density storage devices and possible applications of giant and colossal magneto resistance in metallic thin film multilayers, for example. To many physicists, however, surface magnetism has a more fundamental importance: Bulk magnetism is the quintessential example of long-range ordering, and crystalline symmetry—on which theories of bulk magnetism depend—is broken at the surface. As such, surface magnetism provides physicists with an opportunity to investigate the mechanisms of magnetic ordering between the well-understood limits of atomic and bulk-matter magnetism.
The Pool-Table Analogy with Axion Physics
Authors: Sikivie Pierre
Published: January 2008

Elementary particle physicists enjoy talking about particles for which there is no experimental evidence, and of these particles the axion seems one of the strangest and least accessible. The mass of the axion is expected to be roughly 10−5 eV, a factor of a million below current limits on the neutrino mass, and the axion's couplings are suppressed by a factor of 10−12 relative to those of pions and other familiar particles. Yet there are serious claims that axions make up most of the mass of the universe and equally serious experiments to demonstrate the presence of these tenuous particles. Why should one believe in the axion? I attempt to answer this question by drawing an analogy with the physics of a pool table.
The Introductory Calculus-Based Physics Textbook
Authors: Amato Joseph
Published: January 2008

Each year, more than 150 000 college students across the US enroll in calculus-based introductory physics courses. Most of these courses are taught in the traditional mode, with students sitting passively through two or more lectures per week and reporting once or twice a week to recitation classes and laboratory sessions. Students often plow through as many as 500 pages of equation-laden text each semester and complete one or two written assignments per week. And faculty members expend considerable effort conducting the whole enterprise.
Ontogeny of metabolic effects on embryonic development in lactating and weaned primiparous sows
Authors: Vinsky M. D. , Paradis F. , Dixon W. T. , Dyck M. K. , Foxcroft G. R.
Published: January 2008

Using an established experimental paradigm, feed restriction during the last week of lactation in primiparous sows reduces embryonic growth and development and produces female-specific embryonic mortality by Day 30 of gestation. Because this gender-specific loss of embryos at Day 30 was associated with changes in the variation of markers of epigenetic imprinting, the present study sought to establish the ontogeny of such epigenetic affects. Leucocyte DNA of restrict-fed sows exhibited decreased global methylation during the last week of lactation and during the return to oestrus (P < 0.05), but no associated changes in plasma folate and vitamin B12. Furthermore, no changes in methylation of blastocyst DNA, embryonic sex ratios or development were evident at Day 6 of gestation that would characterise the underlying defects that reduced female embryo survival by Day 30. However, regardless of treatment, embryo recovery rates and synchrony in embryonic development were associated with the stage of development of the recovered embryos (r = 0.68; P < 0.001). The subset of sows classified as bearing litters with superior embryonic development had lower net energy balance over lactation (P < 0.01) and higher ovulation rates (P < 0.005) compared with sows classified as having poorer embryonic development. Collectively, these data suggest that a subset of litters within restrict-fed sows will be most sensitive to the latent epigenetic mechanisms that ultimately trigger gender-specific loss of embryos by Day 30 of gestation, but that these selective mechanisms are not evident by Day 6 of gestation.
Generation of sex ratio biases in the red-tailed phascogale (Phascogale calura)
Authors: Foster W. K. , Taggart D. A.
Published: January 2008

Male semelparous dasyurid species are annual breeders that use a promiscuous mating system. These species have shown biases in litter sex ratios and, with females producing more young than they have available teats, this provides an opportunity for the manipulation of the sex ratio at birth. The sex ratio of embryos and pouch young, and the degree of embryonic overproduction, in red-tailed phascogales (Phascogale calura) was investigated to gain an understanding of the mechanism by which sex biases may be generated. The sex ratio of embryos did not differ from parity, but a male bias was observed in young attaching to teats. Females produced an average of 15.1 ± 1.9 corpora lutea and 10.5 ± 3.5 viable embryos, with no difference in fecundity observed with female age or weight. Because females only have eight teats, the overproduction of young, and male-biased attachment, was sufficient to explain the observed male bias in pouch young. No relationship was observed between maternal weight and sex ratio, but heavier females did tend to produce more ova. Meta-analysis of studies providing information on litter sex ratios in male semelparous dasyurid species did not show any consistent trend.
Effect of plasmin, plasminogen activators and a plasmin inhibitor on bovine in vitro embryo production
Authors: Papanikolaou Thomas , Amiridis Georgios S. , Dimitriadis Ioannis , Vainas Emmanuel , Rekkas Constantinos A.
Published: January 2008

In the present study, four experiments were conducted to investigate the possible effects of plasminogen activators (urokinase-type plasminogen activator (u-PA) and tissue-type plasminogen activator (t-PA)), plasmin, and a plasmin inhibitor (epsilon-aminocaproic acid (ϵ-ACA)) on different stages of bovine in vitro embryo production (IVP). The concentrations of these modifiers in IVP media were conditioned according to the plasminogen activator activity of bovine preovulatory follicular fluid. Media were modified in a single phase of IVP with an 18 h or 24 h incubation for in vitro maturation (IVM) and a 24 h or 48 h incubation for the IVF or in vitro culture (IVC), respectively. After IVM the oocytes were either fixed and stained or underwent IVF and IVC. The main findings were: (1) plasmin added to the 18 h IVM medium increased maturation rate without affecting fertilisation or embryo development rates; (2) t-PA added to the IVF medium significantly increased cleavage; (3) u-PA added to the IVC medium significantly increased embryo development rates; (4) the efficiency of all phases of IVP was reduced after the addition of ϵ-ACA; and (5) plasminogen addition had no effect in any IVP phase tested. We conclude that the members of the plasminogen activator–plasmin system contribute in different ways to bovine IVM, IVF and IVC.
Expression and localisation of breast cancer resistance protein (BCRP) in human fetal membranes and decidua and the influence of labour at term
Authors: Yeboah D. , Kalabis G. M. , Sun M. , Ou R. C. , Matthews S. G. , Gibb W.
Published: January 2008

Breast cancer resistance protein (BCRP) is a multidrug resistant ABC transport protein (ABCG-2). It extrudes a wide range of substrates, including many chemotherapy drugs, steroids and folate. It is present in many cancers, as well as normal tissues, in particular barrier tissues such as the blood–brain barrier, the intestine, blood vessels and the human placenta. Human fetal membranes (amnion and chorion laeve) provide the barrier between the maternal uterine environment and the fetus. In the present study, we defined the expression and localisation of BCRP mRNA and protein in human fetal membranes (amnion and chorion) and attached decidua obtained before and following labour at term. BCRP protein and mRNA was expressed in all tissues examined and the levels of expression were not altered by labour. BCRP was localised to the amnion epithelial cells, chorion trophoblast cells and decidua stromal cells, as well as the endothelial cells of maternal blood vessels in the decidua, but was absent from mesenchymal cells. In the amnion epithelium, BCRP protein was localised to the apical surface, cytoplasm and membrane between cells. In the chorion trophoblast and decidua stromal cells, BCRP protein was localised to the plasma membrane. However, in the chorion trophoblast, BCRP protein was also highly expressed in the nucleus. The level of BCRP protein in the membranes was comparable to that in the placenta. These high levels raise the possibility that this transporter plays an important role in the physiological function of the tissues.
Identification of genes regulated by an interaction between v3 integrin and vitronectin in murine decidua
Authors: Mangale S. S. , Modi D. N. , Reddy K. V. R.
Published: January 2008

The delicate balance between embryo invasion and suppression of maternal immune rejection requires a fully functional decidua in species with haemochorial placenta. Our understanding of the decidual function is very limited due to the molecular and cellular complexity involved in decidualisation. The cell adhesion molecule αvβ3 integrin and its ligand vitronectin are upregulated in the mouse decidua during mid-pregnancy. The implications of interactions between αvβ3 and vitronectin in regulating decidual function are not known. In the present study, interactions between αvβ3 and vitronectin in the decidual cells of the mouse were blocked in vitro and effects on cell fate were evaluated by studying the differentially regulated genes by cDNA array and real-time polymerase chain reaction (PCR). The results indicate that expression of various genes involved in apoptotic and cell cycle pathways, as well as cytokine receptors, was deranged. Signalling through αvβ3 seems to be important to maintain a balance between cell proliferation and apoptosis, along with the modulation of inflammatory responses of decidual cells.
Acrosome stability in the spermatozoa of dasyurid marsupials
Authors: Czarny N. A. , Mate K. E. , Rodger J. C.
Published: January 2008

The spermatozoa of most marsupials lack nuclear stabilising disulfide-bonded protamines found in eutherian mammals. However, disulfide stabilisation has been observed in the acrosome of macropodid (Macropus eugenii) and phalangerid (Trichosurus vulpecula) marsupials. As a result this organelle, which is normally fragile in eutherian mammals, is robust and able to withstand physical and chemical challenge in these marsupials. The present study examined acrosomal characteristics of the spermatozoa of three dasyurid marsupials; the fat-tailed dunnart (Sminthopsis crassicaudata), eastern quoll (Dasyurus viverrinus) and northern quoll (Dasyurus hallucatus). In all species examined Bryan’s staining demonstrated that significant acrosomal loss occurred following physical challenge with osmotic stress, cryopreservation without cryoprotectant and exposure to detergent (Triton-X). Bromobimane staining indicated that the acrosomes of dasyurids lacked stabilising disulfide bonds. As reported for the wallaby and possum, calcium ionophore (A23187) did not induce the acrosome reaction-like exocytosis in dasyurid spermatozoa but treatment with diacylglycerol (DiC8) caused significant acrosome loss at concentrations similar to those effective for other marsupials. The present study found that the spermatozoa of dasyurids are more sensitive to physical challenge than the previously-studied marsupials and we suggest that this is due to the absence of acrosomal stabilising disulfide bonds.
Action-blindsight in healthy subjects after transcranial magnetic stimulation
Authors: Christensen Mark Schram , Kristiansen Lasse , Rowe James B. , Nielsen Jens Bo
Published: January 2008

Clinical cases of blindsight have shown that visually guided movements can be accomplished without conscious visual perception. Here, we show that blindsight can be induced in healthy subjects by using transcranial magnetic stimulation over the visual cortex. Transcranial magnetic stimulation blocked the conscious perception of a visual stimulus, but subjects still corrected an ongoing reaching movement in response to the stimulus. The data show that correction of reaching movements does not require conscious perception of a visual target stimulus, even in healthy people. Our results support previous results suggesting that an efference copy is involved in movement correction, and this mechanism seems to be consistent even for movement correction without perception.
A regular pattern of Ig super-motifs defines segmental flexibility as the elastic mechanism of the titin chain
Authors: von Castelmur Eleonore , Marino Marco , Svergun Dmitri I. , Kreplak Laurent , Ucurum-Fotiadis Zöhre , Konarev Petr V. , Urzhumtsev Alexandre , Labeit Dietmar , Labeit Siegfried , Mayans Olga
Published: January 2008

Myofibril elasticity, critical to muscle function, is dictated by the intrasarcomeric filament titin, which acts as a molecular spring. To date, the molecular events underlying the mechanics of the folded titin chain remain largely unknown. We have elucidated the crystal structure of the 6-Ig fragment I65–I70 from the elastic I-band fraction of titin and validated its conformation in solution using small angle x-ray scattering. The long-range properties of the chain have been visualized by electron microscopy on a 19-Ig fragment and modeled for the full skeletal tandem. Results show that conserved Ig–Ig transition motifs generate high-order in the structure of the filament, where conformationally stiff segments interspersed with pliant hinges form a regular pattern of dynamic super-motifs leading to segmental flexibility in the chain. Pliant hinges support molecular shape rearrangements that dominate chain behavior at moderate stretch, whereas stiffer segments predictably oppose high stretch forces upon full chain extension. There, librational entropy can be expected to act as an energy barrier to prevent Ig unfolding while, instead, triggering the unraveling of flanking springs formed by proline, glutamate, valine, and lysine (PEVK) sequences. We propose a mechanistic model based on freely jointed rigid segments that rationalizes the response to stretch of titin Ig-tandems according to molecular features.
Spreading of sexually transmitted diseases in heterosexual populations
Authors: Gómez-Gardeñes Jesús , Latora Vito , Moreno Yamir , Profumo Elio
Published: January 2008

The spread of sexually transmitted diseases (e.g., chlamydia, syphilis, gonorrhea, HIV, etc.) across populations is a major concern for scientists and health agencies. In this context, both the data collection on sexual contact networks and the modeling of disease spreading are intensive contributions to the search for effective immunization policies. Here, the spreading of sexually transmitted diseases on bipartite scale-free graphs, representing heterosexual contact networks, is considered. We analytically derive the expression for the epidemic threshold and its dependence with the system size in finite populations. We show that the epidemic outbreak in bipartite populations, with number of sexual partners distributed as in empirical observations from national sex surveys, takes place for larger spreading rates than for the case in which the bipartite nature of the network is not taken into account. Numerical simulations confirm the validity of the theoretical results. Our findings indicate that the restriction to crossed infections between the two classes of individuals (males and females) has to be taken into account in the design of efficient immunization strategies for sexually transmitted diseases.
Whole-genome expression profiling of the marine diatom
Thalassiosira pseudonana
identifies genes involved in silicon bioprocesses
Authors: Mock Thomas , Samanta Manoj Pratim , Iverson Vaughn , Berthiaume Chris , Robison Matthew , Holtermann Karie , Durkin Colleen , BonDurant Sandra Splinter , Richmond Kathryn , Rodesch Matthew , Kallas Toivo , Huttlin Edward L. , Cerrina Francesco , Sussman Michael R. , Armbrust E. Virginia
Published: January 2008

Formation of complex inorganic structures is widespread in nature. Diatoms create intricately patterned cell walls of inorganic silicon that are a biomimetic model for design and generation of three-dimensional silica nanostructures. To date, only relatively simple silica structures can be generated
in vitro
through manipulation of known diatom phosphoproteins (silaffins) and long-chain polyamines. Here, we report the use of genome-wide transcriptome analyses of the marine diatom
Thalassiosira pseudonana
to identify additional candidate gene products involved in the biological manipulation of silicon. Whole-genome oligonucleotide tiling arrays and tandem mass spectrometry identified transcripts for >8,000 genes, ≈3,000 of which were not previously described and included noncoding and antisense RNAs. Gene-specific expression profiles detected a set of 75 genes induced only under low concentrations of silicon but not under low concentrations of nitrogen or iron, alkaline pH, or low temperatures. Most of these induced gene products were predicted to contain secretory signals and/or transmembrane domains but displayed no homology to known proteins. Over half of these genes were newly discovered, identified only through the use of tiling arrays. Unexpectedly, a common set of 84 genes were induced by both silicon and iron limitations, suggesting that biological manipulation of silicon may share pathways in common with iron or, alternatively, that iron may serve as a required cofactor for silicon processes. These results provide insights into the transcriptional and translational basis for the biological generation of elaborate silicon nanostructures by these ecologically important microbes.
Generation of biologically contained Ebola viruses
Authors: Halfmann Peter , Kim Jin Hyun , Ebihara Hideki , Noda Takeshi , Neumann Gabriele , Feldmann Heinz , Kawaoka Yoshihiro
Published: January 2008

Ebola virus (EBOV), a public health concern in Africa and a potential biological weapon, is classified as a biosafety level-4 agent because of its high mortality rate and the lack of approved vaccines and antivirals. Basic research into the mechanisms of EBOV pathogenicity and the development of effective countermeasures are restricted by the current biosafety classification of EBOVs. We therefore developed biologically contained EBOV that express a reporter gene instead of the VP30 gene, which encodes an essential transcription factor. A Vero cell line that stably expresses VP30 provides this essential protein
in trans
and biologically confines the virus to its complete replication cycle in this cell line. This complementation approach is highly efficient because biologically contained EBOVs lacking the VP30 gene grow to titers similar to those obtained with wild-type virus. Moreover, EBOVs lacking the VP30 gene are indistinguishable in their morphology from wild-type virus and are genetically stable, as determined by sequence analysis after seven serial passages in VP30-expressing Vero cells. We propose that this system provides a safe means to handle EBOV outside a biosafety level-4 facility and will stimulate critical studies on the EBOV life cycle as well as large-scale screening efforts for compounds with activity against this lethal virus.
Context- and scale-dependent effects of floral CO
2
on nectar foraging by
Manduca sexta
Authors: Goyret Joaquín , Markwell Poppy M. , Raguso Robert A.
Published: January 2008

Typically, animal pollinators are attracted to flowers by sensory stimuli in the form of pigments, volatiles, and cuticular substances (hairs, waxes) derived from plant secondary metabolism. Few studies have addressed the extent to which primary plant metabolites, such as respiratory carbon dioxide (CO
2
), may function as pollinator attractants. Night-blooming flowers of
Datura wrightii
show transient emissions of up to 200 ppm above-ambient CO
2
at anthesis, when nectar rewards are richest. Their main hawkmoth pollinator,
Manduca sexta
, can perceive minute variation (0.5 ppm) in CO
2
concentration through labial pit organs whose receptor neurons project afferents to the antennal lobe. We explored the behavioral responses of
M. sexta
to artificial flowers with different combinations of CO
2
, visual, and olfactory stimuli using a laminar flow wind tunnel. Responses in no-choice assays were scale-dependent; CO
2
functioned as an olfactory distance-attractant redundant to floral scent, as each stimulus elicited upwind tracking flights. However, CO
2
played no role in probing behavior at the flower. Male moths showed significant bias in first-approach and probing choice of scented flowers with above-ambient CO
2
over those with ambient CO
2
, whereas females showed similar bias only in the presence of host plant (tomato) leaf volatiles. Nevertheless, all males and females probed both flowers regardless of their first choice. While floral CO
2
unequivocally affects male appetitive responses, the context-dependence of female responses suggests that they may use floral CO
2
as a distance indicator of host plant quality during mixed feeding-oviposition bouts on
Datura
and
Nicotiana
plants.
Seed odor mediates an obligate ant–plant mutualism in Amazonian rainforests
Authors: Youngsteadt Elsa , Nojima Satoshi , Häberlein Christopher , Schulz Stefan , Schal Coby
Published: January 2008

Seed dispersal mutualisms are essential for the survival of diverse plant species and communities worldwide. Among invertebrates, only ants have a major role in seed dispersal, and thousands of plant species produce seeds specialized for ant dispersal in “diffuse” multispecies interactions. An outstanding but poorly understood ant–seed mutualism occurs in the Amazonian rainforest, where arboreal ants collect seeds of several epiphyte species and cultivate them in nutrient-rich nests, forming abundant and conspicuous hanging gardens known as ant-gardens (AGs). AG ants and plants are dominant members of lowland Amazonian ecosystems, and their interaction is both specific and obligate, but the means by which ants locate, recognize, and accept their mutualist seeds while rejecting other seeds is unknown. Here we address the chemical and behavioral basis of the AG interaction. We show that workers of the AG ant
Camponotus femoratus
are attracted to odorants emanating from seeds of the AG plant
Peperomia macrostachya
, and that chemical cues also elicit seed-carrying behavior. We identify five compounds from
P. macrostachya
seeds that, as a blend, attract
C. femoratus
workers. This report of attractive odorants from ant-dispersed seeds illustrates the intimacy and complexity of the AG mutualism and begins to illuminate the chemical basis of this important and enigmatic interaction.