bluuebunny/crossref_metadata_2025 huggingface dataset:
Hole-Burning Spectroscopy and Relaxation Dynamics of Amorphous Solids at Low Temperatures
Authors: Jankowiak R. , Small G. J.
Published: October 2006

The magnitude and temperature dependence of most of the properties of amorphous solids are anomalous at very low temperatures (≲ 1 Kelvin). Phonon-assisted tunneling of a distribution of glassy bistable configurations, or two-level systems, can account for these anomalies. A unified understanding of the low-temperature properties is required for an understanding of the glassy state. Persistent nonphotochemical hole burning of impurity optical transitions allows a glass state to be produced that is thermally inaccessible to the preburn state, and that allows the probing of tunneling dynamics on time scales that range between picoseconds and days. These data combined with recently obtained distribution functions for the two-level systems offer new insights into the tunneling dynamics.
Age and Diet of Fossil California Condors in Grand Canyon, Arizona
Authors: Emslie Steven D.
Published: October 2006

A dozen new radiocarbon dates, together with a thorough review of its fossil distribution, shed new light on the time and probable cause of extinction of the California condor,
Gymnogyps californianus
, in Grand Canyon, Arizona. The radiocarbon data indicate that this species became extinct in Grand Canyon, and other parts of the inland West, more than 10,000 years ago in coincidence with the extinction of megafauna (proboscidians, edentates, perissodactyls). That condors relied on the megafauna for food is suggested by the recovery of food bones from a late Pleistocene nest cave in Grand Canyon. These fossil data have relevance to proposed release and recovery programs of the present endangered population of California condors.
Evidence for Highly Reflecting Materials on the Surface and Subsurface of Venus
Authors: Jurgens R. F. , Slade M. A. , Saunders R. S.
Published: October 2006

Radar images at a 12.5-centimeter wavelength made with the Goldstone radar interferometer in 1980 and 1986, together with lunar radar images and recent Venera 15 and 16 data, indicate that material on the surface and subsurface of Venus has a Fresnel reflectivity in excess of 50 percent. Such high reflectivities have been reported on the surface in mountainous regions. Material of high reflectivity may also underlie lower reflectivity surficial materials of the plains regions, where it has been excavated by impact cratering in some areas.
An Assessment of the Performance and Requirements for "Adiabatic" Engines
Authors: Zucchetto James , Myers Phillip , Johnson John , Miller Dennis
Published: October 2006

A review of research on low heat rejection engines, on cooperative efforts in the United States and abroad to incorporate ceramics in intermittent combustion engines, and on the use of ceramics in these engines is presented. The reduction of heat loss from the combustion chamber of diesel engines improves fuel efficiency only 3 or 4 percent. Some other gains may be possible from a smaller cooling system, recovery of exhaust energy, and improvements in aerodynamics. It is judged that designs of low heat rejection engines will have the greatest initial impact on armored combat vehicles. Organization, coordination, planning, and cooperation on R&D for the use of ceramics in intermittent combustion engines appear to be greater abroad than in the United States.
Design of a Monomeric Arsinogallane and Chemical Conversion to Gallium Arsenide
Authors: Byrne Erin K. , Parkanyi Laszlo , Theopold Klaus H.
Published: October 2006

A monomeric arsinogallane containing a covalent gallium-arsenic bond has been prepared, and its molecular structure has been determined by x-ray crystallography. The compound reacted with
tert
-butanol at ambient temperature to yield the III-V semiconductor gallium arsenide as a finely divided amorphous solid. During the initial stages of the reaction small clusters of gallium arsenide were apparently present in solution. The band gaps of these particles, as observed by their absorption spectra, were larger than that of the bulk material. This work is a step toward the development of new molecular precursors for technologically important materials and the study of quantum size effects in small semiconductor particles.
Enhancement of Symbiotic Dinitrogen Fixation by a Toxin-Releasing Plant Pathogen
Authors: Knight Thomas J. , Langston-Unkefer Pat J.
Published: October 2006

An approximate doubling in plant growth, total plant nitrogen, nodulation, and overall dinitrogen fixation of alfalfa are the consequences of the action of a toxin delivered by a
Pseudomonas
infesting the alfalfa rhizosphere. The toxin, tabtoxinine-β-lactam, inactivates selectively one form of glutamine synthetase in the nodules. Thus, normal glutamine synthetase-catalyzed ammonia assimilation is significantly impaired; yet these plants assimilated about twice the normal amount of nitrogen. How plants regulate dinitrogen fixing symbiotic associations is an important and unresolved question; the current results imply that the glutamine synthetase-catalyzed step in ammonia assimilation, a plant function, strongly influences overall dinitrogen fixation in legumes.
Brain "Identifier Sequence" Is Not Restricted to Brain: Similar Abundance in Nuclear RNA of Other Organs
Authors: Owens Gregory P. , Chaudhari Nirupa , Hahn William E.
Published: October 2006

A repeated 82 base pair sequence in genomic DNA of the rat was previously proposed as being a control element governing brain (neuron) specific genetic expression. This intronic sequence, termed the brain "identifier" (ID), is complementary to small RNA species localized in brain cytoplasm, and it was thought to be represented specifically in RNA produced by brain nuclei in vitro. The RNA blot analyses of total nuclear and polyadenylated heterogeneous nuclear RNA described in the present report show that this ID sequence is also present in the liver and kidney in abundances similar to those in the brain. This repeated sequence is not, therefore, restricted to transcripts produced in the brain as suggested from previous transcriptional "runoff" experiments. Measurements on rat and mouse nuclear RNA indicate that the abundance of ID sequence transcript is roughly proportional to the number of copies of this repeat in the respective genomes. This suggests a rather random genomic location and transcription of this sequence. From these results it seems improbable that the ID sequence functions as a transcriptional-level control element in genes expressed specifically in the brain.
Laser-Selective Demagnetization: A New Technique in Paleomagnetism and Rock Magnetism
Authors: Renne Paul R. , Onstott Tullis C.
Published: October 2006

Laser-selective demagnetization (LSD) enables the determination of the magnetic moment associated with individual mineral grains in thin sections of rock. Small volumes can be demagnetized with laser pulses directed through the optics of a microscope, permitting resolution of remanence components in individual mineral grains. LSD of mafic granulite samples revealed two paleomagnetic directional components of opposite polarity: one resided in coarse magnetite, the other in ilmenohematite-hemoilmenite exsolution intergrowths and fine magnetite inclusions in clinopyroxene. These directions are consistent with those inferred from bulk demagnetization techniques, but LSD permits direct identification of the remanence carriers. The ability to discriminate magnetization components in different generations of a single mineral and to define intergrain magnetic moment distributions are significant advantages of LSD.
Structure, Antigenic Determinants of Some Clinically Important Insect Allergens: Chironomid Hemoglobins
Authors: Baur Xaver , Aschauer Heinz , Mazur Gertraud , Dewair Mahmoud , Prelicz Hugo , Steigemann Wolfgang
Published: October 2006

Determination of the molecular structure and properties of allergens that elicit severe immediate-type hypersensitivity diseases in humans and a knowledge of the structure of their antibody-binding sites should provide new insight into the pathogenetic mechanisms of allergic diseases. Monomeric and homodimeric hemoglobins (CTT I to X) have been identified as potent allergenic components of Chironomidae, a family of Diptera. Immunologic investigations of peptides of three of these hemoglobins (CTT IV, CTT VI, and CTT VIII) showed that human antibodies of the E and G classes recognize at least two different sites within each molecule. Individual hemoglobin peptides were aligned with homologous regions of chironomid hemoglobin CTT III, whose tertiary structure has been determined by x-ray analysis at a resolution of 1.4 angstroms. The antigenic site CTT IV(91 to 101) showed the following characteristics: (i) seven polar or hydroxylated amino acids, from a total of eleven, occupying predominantly superficial regions; (ii) the property of linkage to other molecules by hydrogen bonds or solvent clusters; and (iii) high thermal mobility factors. In contrast, peptide CTT IV(102 to 108), which does not bind human antibodies, contained no polar amino acids and had low thermal mobility factors. These results support the idea that the antigenicity of clinically relevant proteins is related to regions with a predominance of polar amino acids and with low energy barriers between different conformations, which allow high flexibility, including site-specific adaptation in antibody binding.
Nonlinear Mixing of Electromagnetic Waves in Plasmas
Authors: Stefan V. , Cohen B. I. , Joshi C.
Published: October 2006

Recently, a strong research effort has been focused on applications of beat waves in plasma interactions. This research has important implications for various aspects of plasma physics and plasma technology. This article reviews the present status of the field and comments on plasma probing, heating of magnetically confined and laser plasmas, ionospheric plasma modification, beat-wave particle acceleration, beat-wave current drive in toroidal devices, beat wave—driven free-electron lasers, and phase conjugation with beat waves.
Research Toward Malaria Vaccines
Authors: Miller Louis H. , Howard Russell J. , Carter Richard , Good Michael F. , Nussenzweig Victor , Nussenzweig Ruth S.
Published: October 2006

Malaria exacts a toll of disease to people in the Tropics that seems incomprehensible to those only familiar with medicine and human health in the developed world. The methods of molecular biology, immunology, and cell biology are now being used to develop an antimalarial vaccine. The
Plasmodium
parasites that cause malaria have many stages in their life cycle. Each stage is antigenically distinct and potentially could be interrupted by different vaccines. However, achieving complete protection by vaccination may require a better understanding of the complexities of B- and T-cell priming in natural infections and the development of an appropriate adjuvant for use in humans.
Construction of Synthetic Immunogen: Use of New T-Helper Epitope on Malaria Circumsporozoite Protein
Authors: Good Michael F. , Maloy W. Lee , Lunde Milford N. , Margalit Hanah , Cornette James L. , Smith Geoffrey L. , Moss Bernard , Miller Louis H. , Berzofsky Jay A.
Published: October 2006

The circumsporozoite (CS) protein of
Plasmodium falciparum
is the focus of intense efforts to develop an antisporozoite malaria vaccine. Localization of sites for T-cell recognition on this molecule is critical for vaccine design. By using an algorithm designed to predict T-cell sites and a large panel of H-2 congenic mice, a major nonrepetitive T-cell site was located. When a synthetic peptide corresponding to this site was covalently linked to the major B-cell site on the molecule, an immunogen capable of eliciting a high-titer antibody response was formed. This peptide sequence could prime helper T cells for a secondary response to the intact CS protein. The new helper T-cell site is located outside the repetitive region of the CS protein and appears to be the immunodominant T site on the molecule. This approach should be useful in the rational design and construction of vaccines.
Tissue Distribution and Developmental Expression of the Messenger RNA Encoding Angiogenin
Authors: Weiner Henry L. , Weiner Lynne H. , Swain Judith L.
Published: October 2006

New blood vessel growth occurs during normal fetal development and in diseases such as cancer and diabetes. The polypeptide angiogenin induces new blood vessel growth in two biological assays and may play a role in the vascular development of the fetus and in the neovascularization that accompanies diseases and wound healing. A complementary DNA probe for human angiogenin was used to examine the tissue distribution of angiogenin messenger RNA (mRNA) in the developing rat and in selected transformed cell lines. Angiogenin mRNA was detected predominantly in adult liver but was also detectable at low levels in other tissues. The expression of the angiogenin gene in rat liver was found to be developmentally regulated; mRNA levels were low in the developing fetus, increased in the neonate, and maximal in the adult. The amount of angiogenin mRNA in human HT-29 colon carcinoma and SK-HEP hepatoma cells was not greater than that in normal rat liver. These results demonstrate that angiogenin is predominantly expressed in adult liver, that the pattern of angiogenin gene expression is not temporally related to vascular development in the rat, and that the transformed cells studied do not contain more angiogenin mRNA than does normal liver. If angiogenin activity is controlled at the transcriptional level, the results of this study suggest that the primary function of angiogenin in vivo may be in processes other than the regulation of vascular growth.
A Near-Optimum Parallel Planarization Algorithm
Authors: Takefuji Yoshiyasu , Lee Kuo-Chun
Published: October 2006

A near-optimum parallel planarization algorithm is presented. The planarization algorithm, which is designed to embed a graph on a plane, uses a large number of simple processing elements called neurons. The proposed system, composed of an
N
×
N
neural network array (where
N
is the number of vertices), not only generates a near-maximal planar subgraph from a nonplanar graph or a planar graph but also embeds the subgraph on a single plane within 0(1) time. The algorithm can be used in multiple-layer problems such as designing printed circuit boards and routing very-large-scale integration circuits.
Shear Forces in Molecularly Thin Films
Authors: Schoen Martin , Rhykerd Charles L. , Diestler Dennis J. , Cushman John H.
Published: October 2006

Monte Carlo and molecular dynamics methods have been used to study the shearing behavior of an atomic fluid between two plane-parallel solid surfaces having the face-centered cubic (100) structure. A distorted, face-centered cubic solid can form epitaxially between surfaces that are separated by distances of one to five atomic diameters. Under these conditions a critical stress must be overcome to initiate sliding of the surfaces over one another at fixed separation, temperature, and chemical potential. As sliding begins, a layer of solid exits the space between the surfaces and the remaining layers become fluid.
Analysis of the Published Calorimetric Evidence for Electrochemical Fusion of Deuterium in Palladium
Authors: Miskelly Gordon M. , Heben Michael J. , Kumar Amit , Penner Reginald M. , Sailor Michael J. , Lewis Nathan S.
Published: October 2006

Estimates are given of the raw data that are the basis for the claims of excess power production by the electrochemical charging of palladium in deuterium oxide (D
2
O). Calorimetric results are also presented that show no anomalous power production in either 0.1
M
LiOD/D
2
O or 0.1
M
LiOH/H
2
O (LiOH is lithium hydroxide). Several possible sources of error in open-system calorimetry are discussed that can confound interpretation of temperature changes in terms of anomalous power production.
Demethylated CD8 Gene in CD4
+
T Cells Suggests that CD4
+
Cells Develop from CD8
+
Precursors
Authors: Carbone Amy M. , Marrack Philippa , Kappler John W.
Published: October 2006

Mature T cells and medullary thymocytes bear either the CD4 or CD8 differentiation antigen. Precursor cells in the thymus express neither CD4 nor CD8 (CD4
-
8
-
), but most cortical thymocytes are CD4
+
8
+
. Whether CD4
+
and CD8
+
mature T cells arise directly from CD4
-
8
-
precursors or from a CD4
+
8
+
intermediate remains unresolved. In this study, methylation of the CD8 gene in murine T cells and thymocytes was examined. There was progressive demethylation of the CD8 gene in the thymus during the transition from CD4
-
8
-
to CD4
+
8
+
. A similar pattern of demethylation of the CD8 gene was seen in CD4
+
mature T cells, suggesting previous expression of CD8 in the CD4
+
lineage.
Growth Factors Regulate Transin Gene Expression by c-
fos
-Dependent and c-
fos
-Independent Pathways
Authors: Kerr Lawrence D. , Holt Jeffrey T. , Matrisian Lynn M.
Published: October 2006

The rapid induction of the proto-oncogene c-
fos
by growth factors and other bioactive agents, and the recent evidence that the c-
fos
protein (Fos) is associated with transcriptional complexes, suggests that Fos may represent an integral part of an intracellular messenger pathway that triggers changes in gene expression and ultimately phenotypic alterations. This report examines the role of c-
fos
in growth factor stimulation of transin, a matrix-degrading secreted metalloproteinase. Platelet-derived growth factor (PDGF) stimulation of transin RNA was blocked by a selective reduction in Fos synthesis with antisense c-
fos
mRNA, whereas epidermal growth factor (EGF) stimulation of transin occurred despite an equivalent inhibition of Fos levels. The stimulatory effect of both PDGF and EGF on transin transcription involved factors recognizing the sequence TGAGTCA, which is found in the transin promoter and is reported to be a binding site for the transcriptional factor Jun/AP-1 and for associated Fos and Fos-related complexes. Thus both Fos-dependent and Fos-independent pathways exist for growth factor regulation of gene expression, and both effects may be mediated through the same cis-acting transcription element.
What the Longest Exposures from the Hubble Space Telescope Will Reveal
Authors: Bahcall John N. , Guhathakurta Puragra , Schneider Donald P.
Published: October 2006

Detailed simulations are presented of the longest exposures on representative fields that will be obtained with the Hubble Space Telescope, as well as predictions for the numbers and types of objects that will be recorded with exposures of different durations. The Hubble Space Telescope will reveal the shapes, sizes, and content of faint, distant galaxies and could discover a new population of Galactic stars.
The Formation of Sunlike Stars
Authors: Lada Charles J. , Shu Frank H.
Published: October 2006

Understanding how stars like the sun formed constitutes one of the principal challenges confronting modern astrophysics. In recent years, advances in observational technology, particularly at infrared and millimeter wavelengths, have produced an avalanche of critical data and unexpected discoveries about the process of star formation, which is blocked from external view at optical and shorter wavelengths by an obscuring blanket of interstellar dust. Fueled by this new knowledge, a comprehensive empirical picture of stellar genesis is beginning to emerge, laying the foundations for a coherent theory of the birth of sunlike stars.
Gamma-Ray Measurements of a Soviet Cruise-Missile Warhead
Authors: Fetter Steve , Cochran Thomas B. , Grodzins Lee , Lynch Harvey L. , Zucker Martin S.
Published: October 2006

A portable germanium detector was used to detect gamma-ray emissions from a nuclear warhead aboard the Soviet cruiser
Slava
. Measurements taken on the missile launch tube indicated the presence of uranium-235 and plutonium-239—the essential ingredients of nuclear weapons. With the use of this equipment, these isotopes probably could have been identified at a distance of 4 meters from the warhead. Such inspections do not reveal detailed information about the design of the warhead.
Conserved Repetitive Epitope Recognized by CD4
+
Clones From a Malaria-Immunized Volunteer
Authors: Nardin Elizabeth H. , Herrington Deirdre A. , Davis Jonathan , Levine Myron , Stuber Dietrich , Takacs Bela , Caspers Patrick , Barr Philip , Altszuler Rita , Clavijo Pedro , Nussenzweig Ruth S.
Published: October 2006

T cell clones obtained from a human volunteer immunized with
Plasmodium falciparum
sporozoites specifically recognized the native circumsporozoite (CS) antigen expressed on
P. falciparum
sporozoites, as well as bacteria- and yeast-derived recombinant falciparum CS proteins. The response of these CD4
+
CD8
-
cells was species-specific, since the clones did not proliferate or secrete gamma interferon when challenged with sporozoites or recombinant CS proteins of other human, simian, or rodent malarias. The epitope recognized by the sporozoite-specific human T cell clones mapped to the 5′ repeat region of the CS protein and was contained in the NANPNVDPNANP sequence.
The Takeover Wave of the 1980s
Authors: Shleifer Andrei , Vishny Robert W.
Published: October 2006

The takeover wave of the 1980s moved large enterprises toward specialization and away from the diversification of the 1960s. The easy availability of funds made acquisitions affordable, while the hands-off antitrust policy allowed mergers between two firms in the same industry. Hostile takeovers and leveraged buyouts fostered the break up of conglomerates and the sell-off of divisions to buyers in the same industry; they helped speed the economy-wide move toward specialization. The poor performance of conglomerates indicates that this trend toward specialization is likely to make U.S. industry more competitive. Current state antitakeover laws are probably the result of intense lobbying by managers trying to entrench themselves; these laws do not promote competitiveness of U.S. industry. In contrast, the current accommodating federal antitrust stance encourages specialization.
State- and Bond-Selected Unimolecular Reactions
Authors: Crim F. Fleming
Published: October 2006

Unimolecular reactions are crucial chemical events that have been the focus of increasingly sophisticated investigation in the past decade. Unraveling their details is one fundamental goal of experimental and theoretical studies of chemical dynamics. New techniques are revealing the possibilities, and challenges, of eigenstate- and bond-specific unimolecular reactions. These experiments clearly demonstrate the intimate connection between intramolecular processes and unimolecular reaction dynamics and suggest means of exploiting molecular properties to study and control reactions at the level of individual quantum states.
The Study of Solid/Liquid Interfaces with X-ray Standing Waves
Authors: Abruña H. D. , Bommarito G. M. , Acevedo D.
Published: October 2006

The principles and applications of the x-ray standing wave technique are described. Emphasis is placed on its utility for the study of structure, composition, and distribution of interfacial species especially at solid/liquid interfaces.
Activation of Salivary Secretion: Coupling of Cell Volume and [Ca
2+
]
i
in Single Cells
Authors: Foskett J. Kevin , Melvin James E.
Published: October 2006

High-resolution differential interference contrast microscopy and digital imaging of the fluorescent calcium indicator dye fura-2 were performed simultaneously in single rat salivary gland acinar cells to examine the effects of muscarinic stimulation on cell volume and cytoplasmic calcium concentration ([Ca
2+
]
i
). Agonist stimulation of fluid secretion is initially associated with a rapid tenfold increase in [Ca
2+
]
i
as well as a substantial cell shrinkage. Subsequent changes of cell volume in the continued presence of agonist are tightly coupled to dynamic levels of [Ca
2+
]
i
, even during [Ca
2+
]
i
oscillations. Experiments with Ca
2+
chelators and ionophores showed that physiological elevations of [Ca
2+
]
i
are necessary and sufficient to cause changes in cell volume. The relation between [Ca
2+
]
i
and cell volume suggests that the latter reflects the secretory state of the acinar cell. Agonist-induced changes in [Ca
2+
]
i
, by modulating specific ion permeabilities, result in solute movement into or out of the cell. The resultant cell volume changes may be important in modulating salivary secretion.
The Greenhouse Effect in Central North America: If Not Now, When?
Authors: Karl Thomas R. , Heim Richard R. , Quayle Robert G.
Published: October 2006

Climate models with enhanced greenhouse gas concentrations have projected temperature increases of 2° to 4°C, winter precipitation increases of up to 15 percent, and summer precipitation decreases of 5 to 10 percent in the central United States by the year 2030. An analysis of the climate record over the past 95 years for this region was undertaken in order to evaluate these projections. Results indicate that temperature has increased and precipitation decreased both during winter and summer, and that the ratio of winter-to-summer precipitation has decreased. The signs of some trends are consistent with the projections whereas others are not, but none of the changes is statistically significant except for maximum and minimum temperatures, which were not among the parameters predicted by the models. Statistical models indicate that the greenhouse winter and summer precipitation signal could have been masked by natural climate variability, whereas the increase in the ratio of winter-to-summer precipitation and the higher rates of temperature change probably should have already been detected. If the models are correct it will likely take at least another 40 years before statistically significant precipitation changes are detected and another decade or two to detect the projected changes of temperature.
Core Formation During Early Accretion of the Earth
Authors: Newsom Horton E. , Sims Kenneth W. W.
Published: October 2006

Recent studies are leading to a better understanding of the formation of the earth's metal core. This new information includes: better knowledge of the physics of metal segregation, improved geochemical data on the abundance of siderophile and chalcophile elements in the silicate part of the earth, and experimental data on the partitioning behavior of siderophile and chalcophile elements. Extensive melting of the earth as a result of giant impacts, accretion, or the presence of a dense blanketing atmosphere is thought to have led to the formation of the core. Collision between a planet-sized body and the earth may have also produced the moon. Near the end of accretion, core formation evidently ceased as upper mantle conditions became oxidizing. The accumulation of the oceans is a consequence of the change to oxidizing conditions.
Identification of Widespread Pollution in the Southern Hemisphere Deduced from Satellite Analyses
Authors: Fishman J. , Fakhruzzaman K. , Cros B. , Nganga D.
Published: October 2006

Vertical profiles of ozone obtained from ozonesondes in Brazzaville, Congo (4°S, 15°E), and Ascension Island (8°S, 15°W) show that large quantities of tropospheric ozone are present over southern Africa and the adjacent eastern tropical South Atlantic Ocean. The origin of this pollution is widespread biomass burning in Africa. These measurements support satellite-derived tropospheric ozone data that demonstrate that ozone originating from this region is transported throughout most of the Southern Hemisphere. Seasonally high levels of carbon monoxide and methane observed at middle- and high-latitude stations in Africa, Australia, and Antarctica likely reflect the effects of this distant biomass burning. These data suggest that even the most remote regions on this planet may be significantly more polluted than previously believed.
Advances in Helioseismology
Authors: Libbrecht K. G. , Woodard M. F.
Published: October 2006

Globally coherent oscillation modes were discovered in the sun about a decade ago, providing a unique seismological probe of the solar interior. Current observations detect modes that are phase-coherent for up to 1 year, with surface velocity amplitudes as low as 2 millimeters per second, and thousands of mode frequencies have been measured to accuracies as high as 1 part in 10
5
. This article discusses the properties of these oscillation modes and the ways in which they are adding to our understanding of the structure and dynamics of the sun.
Contact Adhesion of Thin Gold Films on Elastomeric Supports: Cold Welding Under Ambient Conditions
Authors: Ferguson Gregory S. , Chaudhury Manoj K. , Sigal George B. , Whitesides George M.
Published: October 2006

Thin gold films placed in contact on compliant elastomeric poly(dimethylsiloxane) supports weld together. This "cold welding" is remarkable both for the low loads required and for the fact that it occurs under ambient laboratory conditions, conditions in which the gold surfaces are covered with films of weakly adsorbed organic impurities. These impurities are probably displaced laterally during the welding. Welding can be prevented by the presence of a self-assembled gold(I) alkylthiolate monolayer on the gold surfaces. The welded contacts have low electrical resistivity and can be made thin enough to transmit light. This system is a promising one with which to study interaction between interfaces.
Identification of a tHyroid Hormone Receptor That Is Pituitary-Specific
Authors: Hodin Richard A. , Lazar Mitchell A. , Wintman Bruce I. , Darling Douglas S. , Koenig Ronald J. , Larsen P. Reed , Moore David D. , Chin William W.
Published: October 2006

Three cellular homologs of the v-
erbA
oncogene were previously identified in the rat; two of them encode high affinity receptors for the thyroid hormone triiodothyronine (T
3
). A rat complementary DNA clone encoding a T
3
receptor form of the ErbA protein, called r-ErbAβ-2, was isolated. The r-ErbAβ-2 protein differs at its amino terminus from the previously described rat protein encoded by c-
erbA
β and referred to as r-ErbAβ-1. Unlike the other members of the c-
erbA
proto-oncogene family, which have a wide tissue distribution, r-
erbA
β-2 appears to be expressed only in the anterior pituitary gland. In addition, thyroid hormone downregulates r-
erbA
β-2 messenger RNA but not r-
erbA
β-1 messenger RNA in a pituitary tumor-derived cell line. The presence of a pituitary-specific form of the thyroid hormone receptor that may be selectively regulated by thyroid hormone could be important for the differential regulation of gene expression by T
3
in the pituitary gland.
Genetic Mosaics in Strangler Fig Trees: Implications for Tropical Conservation
Authors: Thomson James D. , Herre E. A. , Hamrick J. L. , Stone J. L.
Published: October 2006

Single trees of six species of strangler figs (
Ficus
spp., Moraceae) in Panama were found to be made up of multiple genotypes, presumably formed by the fusion of different individuals. The phenomenon is frequent enough that strangler fig populations will contain considerably more genetic variation than would be expected from the number of trees. How this cryptic variation affects populations depends on the flowering phenology of composite trees. If the genetically different portions of trees flower asynchronously, populations of pollinating wasps may be more resistant to low host population sizes than previously thought. If different portions flower synchronously, attempts to infer mating-system parameters from the parentage of fruit crops will be misleading. The fruiting of figs, which are considered a keystone species in tropical forests, is important for maintaining biodiversity but is also particularly susceptible to failure at small population sizes. It is therefore important to know both the number of trees and the number of genotypes in a population.
Human Diabetes Associated with a Deletion of the Tyrosine Kinase Domain of the Insulin Receptor
Authors: Taira Masato , Taira Masanori , Hashimoto Naotake , Shimada Fumio , Suzuki Yoshifumi , Kanatsuka Azuma , Nakamura Fumiko , Ebina Yousuke , Tatibana Masamiti , Makino Hideichi , Yoshida Sho
Published: October 2006

The insulin receptor has an intrinsic tyrosine kinase activity that is essential for signal transduction. A mutant insulin receptor gene lacking almost the entire kinase domain has been identified in an individual with type A insulin resistance and acanthosis nigricans. Insulin binding to the erythrocytes or cultured fibroblasts from this individual was normal. However receptor autophosphorylation and tyrosine kinase activity toward an exogenous substrate were reduced in partially purified insulin receptors from the proband's lymphocytes that had been transformed by Epstein-Barr virus. The insulin resistance associated with this mutated gene was inherited by the proband from her mother as an apparently autosomal dominant trait. Thus a deletion in one allele of the insulin receptor gene may be at least partly responsible for some instances of insulin-resistant diabetes.
Gas-Phase Rates of Alkane C-H Oxidative Addition to a Transient CpRh(CO) Complex
Authors: Wasserman Eric P. , Moore C. Bradley , Bergman Robert G.
Published: October 2006

The gas-phase irradiation of CpRh(CO)
2
(Cp = η
5
-C
5
H
5
) was examined in order to study the rates of reaction of the 16-electron intermediates presumed to be involved in the C-H oxidative addition of alkanes. "Naked" (unsolvated) CpRh(CO) was detected, and direct measurements of the rates of reaction of this very short-lived complex with alkane C-H bonds were made. Activation of C-H bonds occurs on almost every collision for alkanes of moderate size, and intermediates in which the alkanes are bound to the metal centers, without their C-H bonds being fully broken, are implicated as intermediates in the overall reaction.
Optically Transparent, Electrically Conductive Composite Medium
Authors: Jin S. , Tiefel T. H. , Wolfe R. , Sherwood R. C. , Mottine J. J.
Published: October 2006

The development of an optically transparent yet electrically conductive material made with a composite structure having preferentially arranged conductive paths is described. The medium contains many vertically aligned but laterally isolated chains of ferromagnetic spheres dispersed in a sheet of transparent polymer. The sheet material transmits more than 90 percent of the incident light and is highly conductive only in the thickness direction. When suitably modified, the material exhibits on-off electrical switchability at a certain threshold pressure. These characteristics confer potential usefulness for visual communication devices such as write pads or touch-sensitive screens.
Antiferromagnetism in Pressure-Amorphized Fe
2
SiO
4
Authors: Kruger M. B. , Jeanloz R. , Pasternak M. P. , Taylor R. D. , Snyder B. S. , Stacy A. M. , Bohlen S. R.
Published: October 2006

Amorphous Fe
2
SiO
4
synthesized at elevated pressures exhibits a Néel transition at a temperature identical to that observed in the crystalline form,
T
N
= 65 (±2) kelvin at zero pressure. This behavior contrasts sharply with observations on other disordered systems, such as spin glasses, which characteristically exhibit strong "frustration" of the spins and consequent marked suppression of the Néel transition.
Extraction and STM Imaging of Spherical Giant Fullerenes
Authors: Lamb Lowell D. , Huffman Donald R. , Workman Richard K. , Howells Sam , Chen Ting , Sarid Dror , Ziolo Ronald F.
Published: October 2006

High-temperature, high-pressure extracts of soot produced by the Krätschmer-Huffman technique (KH carbon) were characterized by mass spectrometry and imaging with scanning tunneling microscopes (STMs). The mass spectra of these samples are similar to those of ambient-pressure, high-boiling-point solvent extractions, supporting the idea that solvent temperature and possibly pressure are key parameters in extraction of the giant fullerenes. The STM images show that the giant fullerenes in these samples are roughly spherical in shape and range in diameter from approximately 1 to 2 nanometers, corresponding to fullerenes containing 60 to 330 atoms. No evidence of bucky tubes was found.
Synthesis and Single-Crystal X-ray Structure of a Highly Symmetrical C
60
Derivative, C
60
Br
24
Authors: Tebbe Fred N. , Harlow Richard L. , Chase D. Bruce , Thorn David L. , Campbell G. Creston , Calabrese Joseph C. , Herron Norman , Young Robert J. , Wasserman E.
Published: October 2006

C
60
and liquid bromine react to form C
60
Br
24
, a crystalline compound isolated as a bromine solvate, C
60
Br
24
(Br
2
)
x
, The x-ray crystal structure defines a new pattern of addition to the carbon skeleton that imparts a rare high symmetry. The parent C
60
framework is recognizable in C
60
Br
24
, but
sp
3
carbons at sites of bromination distort the surface, affecting conformations of all of the hexagonal and pentagonal rings. Twenty-four bromine atoms envelop the carbon core, shielding the 18 remaining double bonds from addition. At 150° to 200°C there is effectively quantitative reversion of C
60
Br
24
to C
60
and Br
2
.
Role of CD8
+
T Cells in Murine Experimental Allergic Encephalomyelitis
Authors: Jiang Hong , Zhang Sheng-le , Pernis Benvenuto
Published: October 2006

The course of experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis, is affected by immunoregulatory T lymphocytes. When animals are immunized with encephalitogenic peptide of myelin basic protein and recover from the first episode of EAE, they become resistant to a second induction of this disease. Animals depleted of CD8
+
T cells by antibody-mediated clearance were used to examine the role of CD8
+
T cells in EAE. These cells were found to be major participants in the resistance to a second induction of EAE but were not essential for spontaneous recovery from the first episode of the disease.
The Mouse Pink-Eyed Dilution Gene: Association with Human Prader-Willi and Angelman Syndromes
Authors: Gardner John M. , Nakatsu Yoshimichi , Gondo Yoichi , Lee Susan , Lyon Mary F. , King Richard A. , Brilliant Murray H.
Published: October 2006

Complementary DNA clones from the pink-eyed dilution (
p
) locus of mouse chromosome 7 were isolated from murine melanoma and melanocyte libraries. The transcript from this gene is missing or altered in six independent mutant alleles of the
p
locus, suggesting that disruption of this gene results in the hypopigmentation phenotype that defines mutant
p
alleles. Characterization of the human homolog revealed that it is localized to human chromosome 15 at q11.2-q12, a region associated with Prader-Willi and Angelman syndromes, suggesting that altered expression of this gene may be responsible for the hypopigmentation phenotype exhibited by certain individuals with these disorders.
Induction of Hepatitis B Virus Core Gene in Human Cells by Cytosine Demethylation in the Promoter
Authors: Korba Brent E. , Wilson Vincent L. , Yoakum George H.
Published: October 2006

A recombinant human cell line constructed by transfection of epithelial cells with a plasmid containing the hepatitis B virus core gene (
HBc
) was used to study the regulation of
HBc
gene expression. Methylation of a single Hpa II site 280 base pairs upstream from the structural gene was found to regulate the expression of the core gene. Expression increased in cells treated with 5′-azacytidine as a result of cytosine demethylation at this site, and there was a fivefold increase in the number of
HBc
gene transcripts in total cellular messenger RNA. The varied life cycle of hepatitis B virus in diseases such as viral hepatitis and liver cancer may therefore be attributable to the site-specific regulation of the gene involved in replication of the viral DNA and to the cytopathic effects elicited by this gene in human cells.
Impurity-Driven Cone Formation During Laser Sputtering of Graphite
Authors: Krajnovich Douglas J. , Vázquez José E. , Savoy Richard J.
Published: October 2006

Sputtering of highly oriented pyrolytic graphite (HOPG) by 248-nanometer laser radiation was studied. Neutral carbon atoms and small clusters were ejected with significantly higher translational energies than were expected from a simple model of thermal vaporization in the absence of a potential barrier. The HOPG also developed a remarkable surface morphology that consists of regular cones and domes. Cone formation appears to be initiated by trace metal impurities that serve as heat shunts in this highly anisotropic material.
Disintegration Phenomena Expected During Collision of Comet Shoemaker-Levy 9 with Jupiter
Authors: Sekanina Zdenek
Published: October 2006

In July 1994, periodic comet Shoemaker-Levy 9 is expected to collide with Jupiter. The largest fragments of the comet's original nucleus will be tidally disrupted shortly before they enter the Jovian atmosphere, and all fragments, from large rocks to small grains, will suffer ablation and disintegration as a result of interaction with the atmosphere. Even if atmospheric entry takes place on the planet's far side, secondary phenomena triggered by the terminal explosions of kilometer-sized fragments are likely to be observable from the Earth.
Crystal Structure of the Polymer Electrolyte Poly(ethylene oxide)
3
:LiCF
3
SO
3
Authors: Lightfoot P. , Mehta M. A. , Bruce P. G.
Published: October 2006

Ionically conducting polymers (polymer electrolytes) are under intensive investigation because they form the basis of all solid-state lithium batteries, fuel cells, and electrochromic display devices, as well as being highly novel electrolytes. Little is known about the structures of the many crystalline complexes that form between poly(ethylene oxide) and a wide range of salts. The crystal structure is reported of the archetypal polymer electrolyte poly(ethylene oxide)
3
:LiCF
3
SO
3
, which has been determined from powder x-ray diffraction data. The poly(ethylene oxide) (PEO) chain adopts a helical conformation parallel to the crystallographic
b
axis. The Li
+
cation is coordinated by five oxygen atoms—three ether oxygens and one from each of two adjacent CF
3
SO
3
-
groups. Each CF
3
SO
3
-
in turn bridges two Li
+
ions to form chains running parallel to and intertwined with the PEO chain. There are no interchain links between PEO chains, and the electrolyte can be regarded as an infinite columnar coordination complex.
Uncertainties in Carbon Dioxide Radiative Forcing in Atmospheric General Circulation Models
Authors: Cess R. D. , Zhang M.-H. , Potter G. L. , Barker H. W. , Colman R. A. , Dazlich D. A. , Del Genio A. D. , Esch M. , Fraser J. R. , Galin V. , Gates W. L. , Hack J. J. , Ingram W. J. , Kiehl J. T. , Lacis A. A. , Le Treut H. , Li Z.-X. , Liang X.-Z. , Mahfouf J.-F. , McAvaney B. J. , Meleshko V. P. , Morcrette J.-J. , Randall D. A. , Roeckner E. , Royer J.-F. , Sokolov A. P. , Sporyshev P. V. , Taylor K. E. , Wang W.-C. , Wetherald R. T.
Published: October 2006

Global warming, caused by an increase in the concentrations of greenhouse gases, is the direct result of greenhouse gas—induced radiative forcing. When a doubling of atmospheric carbon dioxide is considered, this forcing differed substantially among 15 atmospheric general circulation models. Although there are several potential causes, the largest contributor was the carbon dioxide radiation parameterizations of the models.
The Bitter Pill
Authors: Djerassi Carl
Published: October 2006

Fundamentally new approaches to birth control—for example, a male pill, a once-a-month menses inducer, and an antifertility vaccine—cannot be realized before the next century, and then only if the virtual withdrawal of the pharmaceutical industry from this field can be reversed. Major changes in product liability would be the most significant incentive.
Localization of the Globin Gene in the Template Active Fraction of Chromatin of Friend Leukemia Cells
Authors: Wallace R. Bruce , Dube Shyam K. , Bonner James
Published: October 2006

Friend leukemia cell chromatin has been fractionated into template active and inactive components. The globin gene sequence is associated with the template active component both prior to and after the cells are induced with dimethyl sulfoxide to synthesize hemoglobin and therefore appears to be in an active configuration in uninduced as well as in induced Friend leukemia cells. In cells which have lost the ability to produce hemoglobin, the globin gene sequence is not associated with the template active fraction of chromatin. These results demonstrate the success of the fractionation procedure.
A Direct Repeat Is a Hotspot for Large-Scale Deletion of Human Mitochondrial DNA
Authors: Schon Eric A. , Rizzuto Rosario , Moraes Carlos T. , Nakase Hirofumi , Zeviani Massimo , DiMauro Salvatore
Published: October 2006

Kearns-Sayre syndrome (KSS) and progressive external ophthalmoplegia (PEO) are related neuromuscular disorders characterized by ocular myopathy and ophthalmoplegia. Almost all patients with KSS and about half with PEO harbor large deletions in their mitochondrial genomes. The deletions differ in both size and location, except for one, 5 kilobases long, that is found in more than one-third of all patients examined. This common deletion was found to be flanked by a perfect 13-base pair direct repeat in the normal mitochondrial genome. This result suggests that homologous recombination deleting large regions of intervening mitochondrial DNA, which previously had been observed only in lower eukaryotes and plants, operates in mammalian mitochondrial genomes as well, and is at least one cause of the deletions found in these two related mitochondrial myopathies.
Neonatal Thymectomy Results in a Repertoire Enriched in T Cells Deleted in Adult Thymus
Authors: Smith Hedy , Chen I.-Ming , Kubo Ralph , Tung Kenneth S. K.
Published: October 2006

In B6AF1 mice, T lymphocytes that use the V
β
11-positive (and not V
β
6-positive or V
β
8-positive) segment in their receptor for antigen are greatly reduced in the thymus and peripheral lymphoid tissues, most likely as a result of clonal deletion. The relative number of V
β
11-positive cells in adult lymph nodes was ten times as high in B6AF1 mice thymectomized 1 to 4 days after birth as in normal mice. Moreover, for the first 10 days of life of B6AF1 mice, mature V
β
11-positive T cells were readily detected in the thymus and spleen. Thus neonatal thymectomy results in the maintenance of the receptor repertoire of early postnatal life, and this correlates with the subsequent development of organ-specific autoimmune diseases.
Detection of Cell-Affecting Agents with a Silicon Biosensor
Authors: Parce J. Wallace , Owicki John C. , Kercso Karen M. , Sigal George B. , Wada H. G. , Muir Victoria C. , Bousse Luc J. , Ross Kevin L. , Sikic Branimir I. , McConnell Harden M.
Published: October 2006

Cellular metabolism is affected by many factors in a cell's environment. Given a sufficiently sensitive method for measuring cellular metabolic rates, it should be possible to detect a wide variety of chemical and physical stimuli. A biosensor has been constructed in which living cells are confined to a flow chamber in which a potentiometric sensor continually measures the rate of production of acidic metabolites. Exploratory studies demonstrate several applications of the device in basic science and technology.
Probing the Mechanisms of Macromolecular Recognition: the Cytochrome b
5
-Cytochrome C Complex
Authors: Rodgers Karla K. , Pochapsky Thomas C. , Sligar Stephen G.
Published: October 2006

The specificity of complex formation between cytochrome b
5
(cyt b
5
) and cytochrome c (cyt c) is believed to involve the formation of salt linkages between specific carboxylic acid residues of cyt b
5
with lysine residues on cyt c. Site-directed mutagenesis was used to alter the specified acidic residues of cyt b
5
to the corresponding amide analogues, which resulted in a lower affinity for complex formation with cyt c. The dissociation of the complex under high pressure resulted in specific volume changes, the magnitude of which reflected the degree of solvation of the acidic residues in the proposed protein-protein interface.