bluuebunny/crossref_metadata_2025 huggingface dataset:
Laboratory Antarctica: Research Contributions to Global Problems
Authors: Weller Gunter , Bentley Charles R. , Elliot David H. , Lanzerotti Louis J. , Webber Patrick J.
Published: October 2006

Research in Antarctica is becoming increasingly important in the large interdisciplinary studies of connections within the earth's geosphere-biosphere system. Four examples of broad research areas are discussed. Upper atmosphere research explores the sun-earth interactions, which are most intense in the polar regions. The mass balance and dynamics of the large Antarctic ice sheet, and its paleoclimatic records recovered from deep ice cores, are important indicators of past and present global changes. Antarctica and sediment cores from the Southern Ocean contain the history of inception and growth of the ice masses and their subsequent fluctuations, and the long-term history of paleoclimate. The remarkable adaptations of Antarctic biota to extreme cold and drought may allow, through biotic monitoring, the detection of changes in the ocean and climate of Antarctica.
Direct Observation of Dissociated Dislocations in Garnet
Authors: Allen F. M. , Smith B. K. , Buseck P. R.
Published: October 2006

Dislocation core structures in garnet [grossularite (Ca
2.9
Fe
II
0.1
)(Al
1.9
Fe
III
0.1
)Si
3.0
O
12
] have been examined with near atomic resolution transmission electron microscopy. Dissociated dislocations have been observed as parallel
a
/4〈111〉 partial dislocations that are separated by stacking faults. The partial dislocations have narrow cores (∼3 burgers vectors), and the stacking fault zone between the narrow partial dislocations is apparently a low-energy configuration that results from the occupancy of previously unfilled dodecahedral and tetrahedral sites. Previous studies of garnet dislocations suggested that dissociation involves departures from garnet stoichiometry (that is, trace amounts of impurities), but evidence of detectable amounts of impurities has not been found even in the highest resolution images. These results have implications for mantle mineral rheology and transformations as well as for ceramics of material science interest.
Growth of Thin Chemically Bonded Diamondlike Films by Ion Beam Deposition
Authors: Rabalais J. Wayne , Kasi Srinandan
Published: October 2006

Carbon films with a diamondlike structure that are chemically bonded to surfaces have been deposited by means of low-energy C
+
ion beams. When mass-selected C
+
beams at energies in the range from 20 to 200 electron volts impinge on atomically clean surfaces, the first carbon monolayer grows as a carbide structure that is chemically bonded to the surface. As deposition continues, the structure evolves over the next several atomic layers into a diamondlike structure. These pure carbon films are strongly adhered to the surface through the carbide bonds, which also provide for an intimate interface. There are significant applications for such films, particularly as insulators and doped semiconductors.
IRAS 14348-1447, an Ultraluminous Pair of Colliding, Gas-Rich Galaxies: The Birth of a Quasar?
Authors: Sanders D. B. , Scoville N. Z. , Soifer B. T.
Published: October 2006

Ground-based observations of the object IRAS 14348-1447, which was discovered with the Infrared Astronomical Satellite, show that it is an extremely luminous colliding galaxy system that emits more than 95 percent of its energy at far-infrared wavelengths. IRAS 14348-1447, which is receding from the sun at 8 percent of the speed of light, has a bolometric luminosity more than 100 times larger than that of our galaxy, and is therefore as luminous as optical quasars. New optical, infrared, and spectroscopic measurements suggest that the dominant luminosity source is a dust-enshrouded quasar. The fuel for the intense activity is an enormous supply of molecular gas. Carbon monoxide emission has been detected at a wavelength of 2.6 millimeters by means of a new, more sensitive receiver recently installed on the 12-meter telescope of the National Radio Astronomy Observatory. IRAS 14348-1447 is the most distant and luminous source of carbon monoxide line emission yet detected. The derived mass of interstellar molecular hydrogen is 6 × 10
10
solar masses. This value is approximately 20 times that of the molecular gas content of the Milky Way and is similar to the largest masses of atomic hydrogen found in galaxies. A large mass of molecular gas may be a prerequisite for the formation of quasars during strong galactic collisions.
The Magnon Pairing Mechanism of Superconductivity in Cuprate Ceramics
Authors: Chen Guanhua , Goddard William A.
Published: October 2006

The magnon pairing mechanism is derived to explain the high-temperature superconductivity of both the La

2-
x

Sr

x

Cu
1
O
4
and Y
1
Ba
2
Cu
3
O
7
systems. Critical features include (i) a one- or two-dimensional lattice of linear Cu-O-Cu bonds that contribute to large antiferromagnetic (superexchange) coupling of the Cu
II
(
d
9
) orbitals; (ii) holes in the oxygen
p
π bands [rather than Cu
III
(
d
8
)] leading to high mobility hole conduction; and (iii) strong ferromagnetic coupling between oxygen
p
π holes and adjacent Cu
II
(
d
9
) electrons. The ferromagnetic coupling of the conduction electrons with copper
d
spins induces the attractive interaction responsible for the superconductivity, leading to triplet-coupled pairs called "tripgems." The disordered Heisenberg lattice of antiferromagnetically coupled copper
d
spins serves a role analogous to the phonons in a conventional system. This leads to a maximum transition temperature of about 200 K. For La
1.85
Sr
0.15
Cu
1
O
4
, the energy gap is in excellent agreement with experiment. For Y
1
Ba
2
Cu
3
O
7
, we find that both the CuO sheets and the CuO chains can contribute to the supercurrent.
The Motion of Untwisted Untorted Scroll Waves in Belousov-Zhabotinsky Reagent
Authors: Keener James P. , Tyson John J.
Published: October 2006

Rotating waves of activity are seen in various biological phenomena and in chemical mixtures. In thin layers of these media, the waves often appear as spirals spinning around a pivot point, but actually they are scroll-shaped waves rotating around a curved filament in three-space. The filament about which the scroll rotates is not stationary, but rather moves through space until it achieves a stable configuration or disappears altogether. Some features of the temporal evolution of a planar scroll wave filament can be understood in terms of the simple equation
N
=
D
κ, where
N
is the velocity of the filament in the direction of its principal normal, κ is the curvature of the filament, and
D
is the diffusion coefficient of the active chemical species. This equation of motion implies that a scroll ring shrinks in size and collapses in finite time, that an elongated spiral evolves into a symmetric spiral, and that an elongated target pattern becomes more symmetrical and vanishes in finite time. Characteristic times for these processes are estimated. In each case, good quantitative agreement is found between implications of the model and observations of scroll-wave evolution in shallow layers of the Belousov-Zhabotinsky reagent.
Parallel Supercomputers for Lattice Gauge Theory
Authors: Brown Frank R. , Christ Norman H.
Published: October 2006

During the past 10 years, particle physicists have increasingly employed numerical simulation to answer fundamental theoretical questions about the properties of quarks and gluons. The enormous computer resources required by quantum chromodynamic calculations have inspired the design and construction of very powerful, highly parallel, dedicated computers optimized for this work. This article gives a brief description of the numerical structure and current status of these large-scale lattice gauge theory calculations, with emphasis on the computational demands they make. The architecture, present state, and potential of these special-purpose supercomputers is described. It is argued that a numerical solution of low energy quantum chromodynamics may well be achieved by these machines.
Short-Lived s-Process Gamma-Ray Lines in Type II Supernovae
Authors: Harris M. J.
Published: October 2006

The nuclear abundances in the helium-burning shells of presupernova stellar models are calculated. For stars of over 20 solar masses the
22
Ne(α,n)
25
Mg reaction produces enough neutrons on a sufficiently short time scale for the s-process to produce
59
Fe (half-life = 45 days) and
60
Co (half-life = 5.3 years). These isotopes are expected to survive the passage of the shock, and gamma rays from their decays should be detectable from most galactic type II supernovae with the NASA Gamma Ray Observatory. Because of its great distance and low metallicity, these lines are not expected to be observable from supernova 1987A.
Secondary Structure is the Major Determinant for Interaction of HIV
rev
Protein with RNA
Authors: Olsen Henrik S. , Nelbock Peter , Cochrane Alan W. , Rosen Craig A.
Published: October 2006

A region in the human immunodeficiency virus (HIV)
env
message, with the potential to form a complex secondary structure (designated RRE), interacts with the rev protein (Rev). This interaction is believed to mediate export of HIV structural messenger RNAs from the nucleus to the cytoplasm. In this report the regions essential for Rev interaction with the RRE are further characterized and the functional significance of Rev-RRE interaction in vivo is examined. A single hairpin loop structure within the RRE was found to be a primary determinant for Rev binding in vitro and Rev response in vivo. Maintenance of secondary structure, rather than primary nucleotide sequence alone, appeared to be necessary for Rev-RNA interaction, which distinguishes it from the mechanism for cis-acting elements in DNA. Limited changes within the 200 nucleotides, which preserved the proper RRE conformational structure, were well tolerated for Rev binding and function. Thus, variation among the RRE elements present in the diverse HIV isolates would have little, if any, effect on Rev responsiveness.
Turning Down the Heat on Thin Films
Authors: Pool Robert
Published: October 2006

Superconducting thin films will be essential to any practical application of superconductivity to microelectronics. Scientists have now succeeded in putting these thin films onto silicon, which is the base element in most integrated circuits.
Estimate of Electromagnetic Quantities in Space from Ground Magnetic Records
Authors: Kamide Y.
Published: October 2006

Magnetic field records at the earth's surface contain the effects of a variety of different source currents flowing in outer space. During the last decade, several computational techniques for the use of magnetometer data have been proposed to obtain the global pattern of the electric fields and currents and Joule heating in the ionosphere. The numerical algorithm has now been enormously improved, such that simultaneous more direct or in situ measurements by satellites and radars can be incorporated into the scheme. In particular, owing to recent progress in satellite-viewed auroral images, it is possible to estimate "instantaneous" patterns of the ionospheric electrodynamic quantities over the entire polar region with a time resolution of several minutes. This report demonstrates that, contrary to our conventional views, large ionospheric currents can flow in regions of low auroral activity.
Antigenic Variation and Resistance to Neutralization in Poliovirus Type 1
Authors: Diamond David C. , Jameson Bradford A. , Bonin Jutta , Kohara Michinori , Abe Shinobu , Itoh Heihachi , Komatsu Toshihiko , Arita Mineo , Kuge Shusuke , Nomoto Akio , Osterhaus A. D. M. E. , Crainic Radu , Wimmer Eckard
Published: October 2006

Mutations have been identified in variants of poliovirus, type 1 (Mahoney) on the basis of their resistance to neutralization by individual monoclonal antibodies. The phenotypes of these variants were defined in terms of antibody binding; the pattern of epitopes expressed or able to be exploited for neutralization were complex. Single amino acid changes can have distant (in terms of linear sequence) and generalized effects on the antigenic structure of poliovirus and similarly constituted virions.
Sequence of the Immunodominant Epitope for the Surface Protein on Sporozoites of
Plasmodium vivax
Authors: McCutchan Thomas F. , Lal Altaf A. , de la Cruz Vidal F. , Miller Louis H. , Maloy W. Lee , Charoenvit Yupin , Beaudoin Richard L. , Guerry Patricia , Wistar Richard , Hoffman Stephen L. , Hockmeyer Wayne T. , Collins William E. , Wirth Dyann
Published: October 2006

Plasmodium vivax
is one of the four malaria parasites that cause disease in humans. The structure of the immunodominant repeating peptide of the circumsporozoite (CS) protein of
P. vivax
was determined. A fragment of
P. vivax
DNA that encodes this tandemly repeating epitope was isolated by use of an oligonucleotide probe whose sequence is thought to be conserved in CS protein genes. DNA sequence analysis of the
P. vivax
clone indicates that the CS repeat is nine amino acids in length (Gly-Asp-Arg-Ala-Asp-Gly-Gln-Pro-Ala). The structure of the repeating region was confirmed with synthetic peptides and monoclonal antibodies directed against
P. vivax
sporozoites. This information should allow synthesis of a vaccine for
P. vivax
that is similar to the one being tested for
P. falciparum
.
Arctic Ocean Ventilation Studied with a Suite of Anthropogenic Halocarbon Tracers
Authors: Krysell M. , Wallace D. W. R.
Published: October 2006

The chlorofluoromethanes (CFMs: CCl
2
F
2
and CCl
3
F), methyl chloroform (CH
3
CCl
3
), and carbon tetrachloride (CCl
4
) have been measured in deep waters of the Arctic Ocean. Oceanic and atmospheric inventories of these compounds result from known anthropogenic releases; because the CFMs and CCl
4
are also chemically nonreactive, they can be used as transient tracers of ocean circulation. The input history of CCl
4
is longer than that of any other transient tracer identified to date (∼70 years). This long input history, together with an
e
-folding time scale of increase (τ) of ∼28 years, makes CCl
4
potentially the most useful tracer for calibrating models of the oceanic uptake of the fossil-fuel CO
2
transient (τ ≈ 25 years). The bottom water of the Nansen Basin, Arctic Ocean, has detectable CCl
4
but undetectable CFM
s
and CH
3
CCl
3
, which suggests either that the bottom water is ∼50 years old, or that there is a small, nonanthropogenic component of atmospheric CCl
4
(<6 parts per trillion by volume).
Observations of Nuclear Reactors on Satellites with a Balloon-Borne Gamma-Ray Telescope
Authors: O'Neill Terrence J. , Kerrick Alan D. , Ait-Ouamer Farid , Tumer O. Tumay , Zych Allen D. , White R. Stephen
Published: October 2006

Gamma rays at energies of 0.3 to 8 megaelectron volts (MeV) were detected on 15 April 1988 from four nuclear-powered satellites including Cosmos 1900 and Cosmos 1932 as they flew over a double Compton gamma-ray telescope. The observations occurred as the telescope, flown from a balloon at an altitude of 35 kilometers from Alice Springs, Australia, searched for celestial gamma-ray sources. The four transient signals were detected in 30 hours of data. Their time profiles show maxima with durations of (21 ± 1) and (27 ± 1) seconds (half-width at half maximum) for the lower two satellites and (85 ± 5) and (113 ± 7) seconds for the remaining two. Their durations place the origin of the two shorter signals at orbital radii of 260
+40
-60
and 260 ± 60 km above the earth and the two longer at 800
+100
-300
and 800
+250
-300
kilometers. Their luminosities for energies >0.3 MeV are then (6.1 ± 1.5) × 10
15
, (3.9 ± 1.0) × 10
15
, (1.10 ± 0.28) × 10
16
, and (1.30 ± 0.32) × 10
16
photons per second. The imaging of the strongest signal indicates a southeastern direction passing nearly overhead. The energy spectrum can be fit to an exponential with index 2.4 ± 1.4. These transient events add to the already large backgrounds for celestial gamma ray sources.
Scandinavian, Siberian, and Arctic Ocean Glaciation: Effect of Holocene Atmospheric CO
2
Variations
Authors: Lindstrom D. R. , MacAyeal D. R.
Published: October 2006

A computer model of coupled ice sheet-ice shelf behavior was used to evaluate whether observed changes in atmospheric CO
2
concentration could have caused the advance and retreat of Pleistocene ice sheets in the Eurasian Arctic. For CO
2
concentrations below a threshold of approximately 250 parts per million, an extensive marine-based ice sheet covering Scandinavia, the Barents, Kara, and East Siberian seas, and parts of the Arctic Ocean developed in the model simulations. In the simulations, climatic warming associated with the Holocene rise of atmospheric CO
2
was sufficient to collapse this widespread glaciation and restore present-day ice conditions.
Foregut Fermentation in the Hoatzin, a Neotropical Leaf-Eating Bird
Authors: Grajal Alejandro , Strahl Stuart D. , Parra Rodrigo , Dominguez Maria Gloria , Neher Alfredo
Published: October 2006

The only known case of an avian digestive system with active foregut fermentation is reported for the hoatzin (
Opisthocomus hoazin
), one of the world's few obligate folivorous (leaf-eating) birds. Hoatzins are one of the smallest endotherms with this form of digestion. Foregut fermentation in a flying bird may be explained by increased digestive efficiency by selection of highly fermentable and extremely patchy resources, coupled with microbial nutritional products and secondary compound detoxification. This unexpected digestive system gives a new perspective to the understanding of size limitations of vertebrate herbivores and to the evolution of foregut fermentation.
Stimulation of RNA and Protein Synthesis by Intracellular Insulin
Authors: Miller David S.
Published: October 2006

Like insulin-sensitive somatic cells, stage IV oocytes from
Xenopus laevis
increase their synthesis of RNA, protein, and glycogen in response to extracellular insulin. Synthesis of RNA and protein are also increased when oocytes are maintained under paraffin oil and insulin is microinjected into the cytoplasm. The effects of external and intracellular insulin are additive, suggesting separate mechanisms of action. Experiments with nuclei isolated under oil show that RNA synthesis can be stimulated by applying insulin to the nucleus directly. Thus, the nucleus appears to be one intracellular site of hormone action.
Changing the Acceptor Identity of a Transfer RNA by Altering Nucleotides in a "Variable Pocket"
Authors: McClain William H. , Foss K.
Published: October 2006

The specificity of tRNA
Arg
(arginine transfer RNA) for aminoacylation (its acceptor identity) were first identified by computer analysis and then examined with amber suppressor tRNAs in
Escherichia coli
. On replacing two nucleotides in tRNA
Phe
(phenylalanine transfer RNA) with the corresponding nucleotides from tRNA
Arg
, the acceptor identity of the resulting tRNA was changed to that of tRNA
Arg
. The nucleotides used in the identity transformation occupy a "variable pocket" structure on the surface of the tRNA molecule where two single-stranded loop segments interact. The middle nucleotide in the anticodon also probably contributes to the interaction, since an amber suppressor of tRNA
Arg
had an acceptor identity for lysine as well as arginine.
Dynamic Pore-Pressure Fluctuations in Rapidly Shearing Granular Materials
Authors: Iverson Richard M. , LaHusen Richard G.
Published: October 2006

Results from two types of experiments show that intergranular pore pressures fluctuated dynamically during rapid, steady shear deformation of water-saturated granular materials. During some fluctuations, the pore water locally supported all normal and shear stresses, while grain-contact stresses transiently fell to zero. Fluctuations also propagated outward from the shear zone; this process modifies grain-contact stresses in adjacent areas and potentially instigates shear-zone growth.
Innovation on Trial: Punitive Damages Versus New Products
Authors: Mahoney Richard J. , Littlejohn Stephen E.
Published: October 2006

Innovation, scientific discovery transformed into valuable products, is a powerful asset for the United States in today's global economy, but it is being put on trial by the U.S. product liability system. Strict liability and huge jury awards, bloated by the uncontrolled imposition of punitive damages, have led to a proliferation of lawsuits, which in turn has created immense legal uncertainty for innovators who want to create new products. Because a high level of legal uncertainty and scientific innovation cannot coexist, new, safe products may be kept off the market and the scope of research and development restricted. Punitive damages constitute the driving force behind this problem, and both judges and legislators should aim at bringing them under control with legal reforms.
Geophysics from Triton to the Deep Blue Sea
Authors: Kerr Richard A.
Published: October 2006

Geophysics is closing out the 1980s with a bang. October's Loma Prieta earthquake grabbed the spotlight at this month's American Geophysical Union's annual fall meeting in, of all places, San Francisco; the quake also closed down one of the official hotels, depriving hundreds of the 4500 attendees of rooms. Other hot topics of the late 1980s—Voyager's tour of the outer solar system and the greenhouse effect—got their share of attention as well.
Specific Block of Calcium Channel Expression by a Fragment of Dihydropyridine Receptor cDNA
Authors: Lotan Ilana , Goelet Philip , Gigi Ariela , Dascal Nathan
Published: October 2006

Although the structure of rabbit skeletal muscle dihydropyridine (DHP) receptor, deduced from cDNA sequence, indicates that this protein is the channel-forming subunit of voltage-dependent calcium channel (VDCC), no functional proof for this prediction has been presented. Two DNA oligonucleotides complementary to DHP-receptor RNA sequences coding for putative membrane-spanning regions of the DHP receptor specifically suppress the expression of the DHP-sensitive VDCC from rabbit and rat heart in
Xenopus
oocytes. However, these oligonucleotides do not suppress the expression of the DHP-insensitive VDCC and of voltage-dependent sodium and potassium channels. Thus, the gene for DHP receptor of rabbit skeletal muscle is closely related, or identical to, a gene expressed in heart that encodes a component of the DHP-sensitive VDCC. The DHP-sensitive and DHP-insensitive VDCCs are distinct molecular entities.
Superconductivity and the Quantization of Energy
Authors: McDonald D. G.
Published: October 2006

Ideas about quantized energy levels originated in atomic physics, but research in superconductivity has led to unparalleled precision in the measurement of energy levels. A comparison of levels produced by two Josephson junctions shows that they differ by no more than 3 parts in 10
19
at an energy of 0.0003 electron volt. The fact that the myriad of interactions of 10
12
particles in a macroscopic body, a Josephson junction, can produce sharply defined energy levels suggests a dynamical state effectively divorced from the complexities of its environment. The existence of this state, the macroscopic quantum state of superconductors, is well established, but its isolation from intrinsic perturbations has recently been shown to be extraordinary. These new results, with an improved precision of about ten orders of magnitude, are discussed in the context of highly accurate results from quantum electrodynamics, atomic spectroscopy, and the standards of metrology. Further refinements in precision may be achievable at higher energy levels, about 12 electron volts, as they become available from a new series array of 18,992 Josephson junctions.
All-Optical Nonlinearities in Organics
Authors: Greene B. I. , Orenstein J. , Schmitt-Rink S.
Published: October 2006

Recognition that organic solids possess some of the largest all-optical nonlinearities of all known materials has resulted in an interdisciplinary effort directed at both the basic understanding and exploitation of these effects. Parallel efforts on inorganic semiconductors have already reached a mature stage whereby the origin of the effects, together with the prospects for device applications, are well known and appreciated. In this article, a unified picture of nonlinear optical phenomena in both classes of materials is presented. The specific implications for organic-based optical devices are discussed.
Stable Carbon Isotopic Evidence for Carbon Limitation in Hydrothermal Vent Vestimentiferans
Authors: Fisher C. R. , Kennicutt M. C. , Brooks J. M.
Published: October 2006

Stable carbon isotope composition (δ
13
C values) can be used to evaluate an animal's source of nutritional carbon. Most animals with chemoautotrophic endosymbionts have quite negative tissue δ
13
C values due to discrimination against
13
C associated with chemoautotrophic assimilation of inorganic carbon. However, the δ
13
C values of hydrothermal vent (HTV) vestimentiferans are significantly higher than the values reported for non-HTV vestimentiferans or other invertebrates with chemoautotrophic endosymbionts. Tissue δ
13
C values of two species of HTV vestimentiferans increase with increasing size of the animals. This relation supports the hypothesis that the relatively high δ
13
C values are the result of inorganic carbon limitation during carbon fixation. A more favorable relation between gas exchange and carbon fixation in the smaller individuals is expected, due to differences in the geometric scaling of gas-exchange surfaces and trophosome volume.
Murine MHC Polymorphism and T Cell Specificities
Authors: Roy Syamal , Scherer Mark T. , Briner Thomas J. , Smith John A. , Gefter Malcolm L.
Published: October 2006

The major histocompatibility complex (MHC) genes are polymorphic in mouse and man. The products of these genes are receptors for peptides, which while bound, are displayed to T lymphocytes. When bound peptides from antigens are recognized by T lymphocytes, an immune response is initiated against the antigens. This study assessed the relation of the polymorphic MHC molecules to their peptide specificity. The results indicate that although an individual of the species has a limited ability to recognize antigens, the species as a whole has broad reactivity. This rationalizes the extreme polymorphism observed.
The RNA Processing Enzyme RNase MRP Is Identical to the Th RNP and Related to RNase P
Authors: Gold Heidi A. , Topper James N. , Clayton David A. , Craft Joe
Published: October 2006

Sera from patients with autoimmune diseases often contain antibodies that bind ribonucleoproteins (RNPs). Sera from 30 such patients were found to immunoprecipitate ribonuclease P (RNase P), an RNP enzyme required to process the 5′ termini of transfer RNA transcripts in nuclei and mitochondria of eukaryotic cells. All 30 sera also immunoprecipitated the nucleolar Th RNP, indicating that the two RNPs are structurally related. Nucleotide sequence analysis of the Th RNP revealed it was identical to the RNA component of the mitochondrial RNA processing enzyme known as RNase MRP. Antibodies that immunoprecipitated the Th RNP selectively depleted murine and human cell extracts of RNase MRP activity, indicating that the Th and RNase MRP RNPs are identical. Since RNase P and RNase MRP are not associated with each other during biochemical purification, we suggest that these two RNA processing enzymes share a common autoantigenic polypeptide.
Sequence-Specific Isotope Effects on the Cleavage of DNA by Bleomycin
Authors: Kozarich John W. , Worth Leroy , Frank Bruce L. , Christner Donna F. , Vanderwall Dana E. , Stubbe JoAnne
Published: October 2006

Bleomycin is a metal- and oxygen-dependent DNA cleaver. The chemistry of DNA damage has been proposed to involve rate-limiting abstraction of the 4′-hydrogen. A DNA fragment has been prepared that contains [4′-
2
H]thymidine residues of high isotopic content. Primary kinetic isotope effects have been directly observed at individual thymidine residues with DNA sequencing technology.
Electro-Optical Evidence for the Chelate Effect at Semiconductor Surfaces
Authors: Lisensky George C. , Penn Rona L. , Murphy Catherine J. , Ellis Arthur B.
Published: October 2006

Monoamines and diamines dissolved in cyclohexane solution reversibly enhance the band-edge photoluminescence (PL) intensity of immersed n-type cadmium sulfide (n-CdS) and n-type cadmium selenide (n-CdSe) substrates through adsorption. The magnitude of the PL increase is used to estimate amine-induced contractions in the semiconductor's depletion width, and the dependence of the PL intensity on amine concentration provides an estimate of the adduct formation constant. Two diamines, ethylenediamine and
o
-phenylenediamine, exhibit unusually low reductions in depletion width and substantially larger adduct equilibrium constants relative to the other amines studied, consistent with chelation to surface Cd
2+
ions. These studies demonstrate that PL can be used as a contactless, in situ technique for characterizing the steric and electronic landscape of semiconductor surfaces and for correlating molecular and surface chemistry.
Allometric Engineering: An Experimental Test of the Causes of Interpopulational Differences in Performance
Authors: Sinervo Barry , Huey Raymond B.
Published: October 2006

Hatchling lizards (
Sceloporus occidentalis
) from a southern population are large and have high locomotor performance (speed and stamina) relative to hatchlings from northern populations. In order to determine whether differences in performance are an allometric consequence of interpopulation differences in size, yolk was removed from southern eggs, thereby producing miniaturized hatchlings equivalent in size to northern hatchlings. Miniaturized southern hatchlings no longer had higher speed than northern hatchlings, but maintained higher stamina. Interpopulation differences in speed but not in stamina are thus an allometric consequence of differences in egg size. Size manipulation adds an experimental dimension to aliometric analyses.
Experiments with Separated Oscillatory Fields and Hydrogen Masers
Authors: Ramsey Norman F.
Published: October 2006

Descriptions are given of the methods of separated and successive oscillatory fields and of the atomic hydrogen maser. Their applications to the precision spectroscopy of atoms and molecules are discussed along with specific examples of fundamental measurements best made with such devices. The applications of these methods to atomic clocks are discussed. Cesium-separated oscillatory fields atomic beam clocks are accurate to 10
-13
, and hydrogen masers are stable for several hours to 10
-15
. A discussion is given of fundamental experiments that require highly stable clocks, such as long-base-line radio astronomy, precise measurement of pulsar frequencies and stabilities, tests of relativity theories, and accurate navigation both on the earth and in outer space.
Bicarbonate Ion Transport: A Mechanism for the Acidification of Urine in the Turtle
Authors: Schilb Theodore P.
Published: October 2006

The uricotelic turtle
Pseudemys scripta
acidifies the urine to a
p
H as low as 4 in the urinary bladder. Data in this report show that the mechanism of acidification in this bladder is the transport of bicarbonate ion from lumen to serosa, and that the temperature to which the turtles are adapted prior to the in vitro experiment largely determines the direction of the transmural carbon dioxide gradient observed. This temperature effect also serves to reconcile apparently disparate data that were previously reported. A new technique for the direct determination of the partial pressure of carbon dioxide was employed.
A Novel Topological Compression Mechanism in a Covalent Liquid
Authors: Stixrude Lars , Bukowinski M. S. T.
Published: October 2006

Monte Carlo simulations of tetrahedrally bonded SiO
2
liquid show that pressure induces large changes in the topology of its four-coordinated framework structure but leaves the average properties of local coordination environments virtually unchanged. Ring statistics are used to describe the liquid's topology; the observed changes paradoxically indicate that the liquid compresses primarily by increasing the size of its rings. A theory for the effects of ring formation on density, which also explains the density of crystalline tectosilicates, accounts for the compression of the liquid.
Genetic Control of Flower Development by Homeotic Genes in
Antirrhinum majus
Authors: Schwarz-Sommer Zsuzsanna , Huijser Peter , Nacken Wolfgang , Saedler Heinz , Sommer Hans
Published: October 2006

Homeotic mutants have been useful for the study of animal development. Such mutants are also known in plants. The isolation and molecular analysis of several homeotic genes in
Antirrhinum majus
provide insights into the underlying molecular regulatory mechanisms of flower development. A model is presented of how the characteristic sequential pattern of developing organs, comprising the flower, is established in the process of morphogenesis.
Simulations of the Folding of a Globular Protein
Authors: Skolnick Jeffrey , Kolinski Andrzej
Published: October 2006

Dynamic Monte Carlo simulations of the folding of a globular protein, apoplastocyanin, have been undertaken in the context of a new lattice model of proteins that includes both side chains and α-carbon backbone atoms and that can approximate native conformations at the level of 2 angstroms (root mean square) or better. Starting from random-coil unfolded states, the model apoplastocyanin was folded to a native conformation that is topologically similar to the real protein. The present simulations used a marginal propensity for local secondary structure consistent with but by no means enforcing the native conformation and a full hydrophobicity scale in which any nonbonded pair of side chains could interact. These molecules folded through a punctuated on-site mechanism of assembly where folding initiated at or near one of the turns ultimately found in the native conformation. Thus these simulations represent a partial solution to the globular-protein folding problem.
Mesoscopic Conductors and Correlations in Laser Speckle Patterns
Authors: Feng Shechao , Lee Patrick A.
Published: October 2006

Submicrometer disordered metallic systems at low temperatures display interesting conductance fluctuation effects, owing to the interference of coherent electron wave transmission through the system. This quantum interference phenomenon also gives rise to the striking experimental observation that the 1/
f
noise power (where
f
is frequency) in disordered conductors increases as the temperature is decreased, contrary to common intuition. The theoretical techniques developed for this problem can be applied to the transmission of light through a random medium, and this yields novel predictions for the correlations in the laser speckle patterns and the possibility of studying the positions and motions of scatterers in a medium which multiply scatter the probing light.
High Winds of Neptune: A Possible Mechanism
Authors: Suomi V. E. , Limaye S. S. , Johnson D. R.
Published: October 2006

Neptune receives only 1/900th of the earth's solar energy, but has wind speeds of nearly 600 meters per second. How the near-supersonic winds can be maintained has been a puzzle. A plausible mechanism, based on principles of angular momentum and energy conservation in conjunction with deep convection, leads to a regime of uniform angular momentum at low latitudes. In this model, the rapid retrograde winds observed are a manifestation of deep convection, and the high efficiency of the planet's heat engine is intrinsic from the room allowed at low latitudes for reversible processes, the high temperatures at which heat is added to the atmosphere, and the low temperatures at which heat is extracted.
The Quark-Hadron Transition in Cosmology and Astrophysics
Authors: Olive K. A.
Published: October 2006

A transition from normal hadronic matter (such as protons and neutrons) to quark-gluon matter is expected at both high temperatures and densities. In physical situations, this transition may occur in heavy ion collisions, the early universe, and in the cores of neutron stars. Astrophysics and cosmology can be greatly affected by such a phase transition. With regard to the early universe, big bang nucleosynthesis, the theory describing the primordial origin of the light elements, can be affected by inhomogeneities produced during the transition. A transition to quark matter in the interior by neutron stars further enhances our uncertainties regarding the equation of state of dense nuclear matter and neutron star properties such as the maximum mass and rotation frequencies.
The Shapes and Sizes of Closed, Pressurized Random Walks
Authors: Rudnick Joseph , Gaspari George
Published: October 2006

Two-dimensional cell-like membranes acted on by osmotic pressure differentials are represented by closed, unrestricted random walks. The treatment omits excluded-volume effects, and the pressure that is imposed thus favors an oriented area, so that the shriveled configuration of a vesicle with excess external pressure is inaccessible in this model. Nevertheless, the approach has the decided advantage of yielding analytic expressions in a complete statistical analysis. Results are presented for the average square of the radius of gyration, the asphericity, and the probability distribution of the principal components of the radius of gyration tensor. The analysis is done in both the constant-pressure and constant-area ensembles.
Geometry, Topology, and Universality of Random Surfaces
Authors: Banavar Jayanath R. , Maritan Amos , Stella Attilio
Published: October 2006

Previous simulations of a self-avoiding, closed random surface with restricted topology (without handles) on a three-dimensional lattice have shown that its behavior on long length scales is consistent with that of a branched-polymer. It is shown analytically that such a surface with an unrestricted number of handles has a qualitatively different geometry and therefore is in a different universality class. The effect of a net external pressure is to suppress the handles and collapse the surface into a branched polymer-like configuration. Topology is thus shown to be a key factor in determining the universality class of the system.
Ex Situ Conservation of Plant Genetic Resources: Global Development and Environmental Concerns
Authors: Cohen Joel I. , Williams J. Trevor , Plucknett Donald L. , Shands Henry
Published: October 2006

Conservation of plant genetic resources is achieved by protection of populations in nature (in situ) or by preservation of samples in gene banks (ex situ). The latter are essential for users of germplasm who need ready access. Ex situ conservation also acts as a back-up for certain segments of diversity that might otherwise be lost in nature and in human-dominated ecosystems. The two methods are complementary, yet better understanding of this interrelation and the role of ex situ conservation in global environmental considerations is needed. Inclusion of ex situ conservation efforts within current environmental policies conserving global diversity would focus greater international attention on the safeguarding of these efforts.
Magnetic Field Studies of the Solar Wind Interaction with Venus from the Galileo Flyby
Authors: Kivelson M. G. , Kennel C. F. , McPherron R. L. , Russell C. T. , Southwood D. J. , Walker R. J. , Hammond C. M. , Khurana K. K. , Strangeway R. J. , Coleman P. J.
Published: October 2006

During the 10 February 1990 flyby of Venus, the Galileo spacecraft skimmed the downstream flank of the planetary bow shock. This provided an opportunity to examine both the global and the local structure of the shock in an interval during which conditions in the solar wind plasma were quite steady. The data show that the cross section of the shock in planes transverse to the flow is smaller in directions aligned with the projection of the interplanetary magnetic field than in directions not so aligned. Ultralow-frequency waves were present in the unshocked solar wind, and their amplitude peaked when the spacecraft was downstream of the foreshock. At large distances down the tail, the Mach number of the flow normal to the shock is low, thus providing the opportunity to study repeated crossings of the collisionless shock in an interesting parameter regime. Some of the shock crossings reveal structure that comes close to the theoretically predicted form of intermediate shocks, whose existence in collisionless plasmas has not been confirmed.
Mutations in a Protein Kinase C Homolog Confer Phorbol Ester Resistance on
Caenorhabditis elegans
Authors: Tabuse Yo , Nishiwaki Kiyoji , Miwa Johji
Published: October 2006

The
tpa-1
gene mediates the action of tumor-promoting phorbol esters in the nematode
Caenorhabditis elegans
. A genomic fragment that constitutes a portion of the
tpa-1
gene was cloned by Tc
1
transposon tagging and was used as a probe to screen a nematode complementary DNA library. One of the isolated complementary DNA clones had a nucleotide sequence that predicts a polypeptide of 526 amino acids. The predicted amino acid sequence revealed that the predicted
tpa-1
protein sequence is highly similar to protein kinase C molecules from various animals, including man.
Autonomic Regulation of a Chloride Current in Heart
Authors: Harvey Robert D. , Hume Joseph R.
Published: October 2006

In isolated heart cells, β-adrenergic receptor stimulation induced a background current that was suppressed by simultaneous muscarinic receptor stimulation. Direct activation of adenylate cyclase with forskolin also elicited this current, suggesting regulation by adenosine 3′,5′-monophosphate (cAMP). This current could be recorded when sodium, calcium, and potassium currents were eliminated by channel antagonists or by ion substitution. Alteration of the chloride equilibrium potential produced changes in the reversal potential expected for a chloride current. Activation of this chloride current modulated action potential duration and altered the resting membrane potential in a chloride gradient-dependent manner.
Recognition of Thymine Adenine Base Pairs by Guanine in a Pyrimidine Triple Helix Motif
Authors: Griffin Linda C. , Dervan Peter B.
Published: October 2006

Oligonucleotide recognition offers a powerful chemical approach for the sequence-specific binding of double-helical DNA. In the pyrimidine-Hoogsteen model, a binding size of >15 homopurine base pairs affords >30 discrete sequence-specific hydrogen bonds to duplex DNA. Because pyrimidine oligonucleotides limit triple helix formation to homopurine tracts, it is desirable to determine whether oligonucleotides can be used to bind all four base pairs of DNA. A general solution would allow targeting of oligonucleotides (or their analogs) to any given sequence in the human genome. A study of 20 base triplets reveals that the triple helix can be extended from homopurine to mixed sequences. Guanine contained within a pyrimidine oligonucleotide specifically recognizes thymine⋅adenine base pairs in duplex DNA. Such specificity allows binding at mixed sites in DNA from simian virus 40 and human immunodeficiency virus.
Iraq and the Future of Nuclear Nonproliferation: The Roles of Inspections and Treaties
Authors: Pilat Joseph F.
Published: October 2006

In the aftermath of the Gulf War, revelations about Iraq's extensive program to develop nuclear weapons challenge the future of the international nuclear nonproliferation regime. Until inspections sanctioned by the U.N. Security Council began, Iraq's violations of its obligations under the Treaty on the Nonproliferation of Nuclear Weapons and its related safeguards agreement with the International Atomic Energy Agency went undetected. The ultimate impact of Iraq's behavior on the regime cannot yet be determined, but there is now an opportunity to improve safeguards and other aspects of the regime, including strengthening export controls and proliferation intelligence collection and sharing and the development of appropriate response capabilities.
State-to-State Rates for the D + H
2
(
v
= 1,
j
= 1) → HD(
v
',
j
') + H Reaction: Predictions and Measurements
Authors: Neuhauser Daniel , Judson Richard S. , Kouri Donald J. , Adelman David E. , Shafer Neil E. , Kliner Dahv A. V. , Zare Richard N.
Published: October 2006

A fully quantal wavepacket approach to reactive scattering in which the best available H
3
potential energy surface was used enabled a comparison with experimentally determined rates for the D + H
2
(
v
= 1,
j
= 1) → HD(
v
′ = 0, 1, 2;
j
′) + H reaction at significantly higher total energies (1.4 to 2.25 electron volts) than previously possible. The theoretical results are obtained over a sufficient range of conditions that a detailed simulation of the experiment was possible, thus making this a definitive comparison of experiment and theory. Good to excellent agreement is found for the vibrational branching ratios and for the rotational distributions within each product vibrational level. However, the calculated rotational distributions are slightly hotter than the experimentally measured ones. This small discrepancy is more marked for products for which a larger fraction of the total energy appears in translation. The most likely explanation for this behavior is that refinements are needed in the potential energy surface.
Mount Pinatubo Aerosols, Chlorofluorocarbons, and Ozone Depletion
Authors: Brasseur Guy , Granier Claire
Published: October 2006

The injection into the stratosphere of large quantities of sulfur during the June 1991 eruption of Mount Pinatubo (Philippines) and the subsequent formation of sulfate aerosol particles have generated a number of perturbations in the atmosphere with potential effects on the Earth's climate. Changes in the solar and infrared radiation budget caused by the eruption should produce a cooling of the troposphere and a warming of the lower stratosphere. These changes could affect atmospheric circulation. In addition, heterogeneous chemical reactions on the surface of sulfate aerosol particles render the ozone molecules more vulnerable to atmospheric chlorine and hence to man-made chlorofluorocarbons.
Imaging Observations of Jupiter's Sodium Magneto-Nebula During the Ulysses Encounter
Authors: Mendillo Michael , Flynn Brian , Baumgardner Jeffrey
Published: October 2006

Jupiter's great sodium nebula represents the largest visible structure traversed by the Ulysses spacecraft during its encounter with the planet in February 1992. Ground-based imaging conducted on Mount Haleakala, Hawaii, revealed a nebula that extended to at least ±300 Jovian radii (spanning ∼50 million kilometers); it was somewhat smaller in scale and less bright than previously observed. Analysis of observations and results of modeling studies suggest reduced volcanic activity on the moon Io, higher ion temperatures in the plasma torus, lower total plasma content in the torus, and fast neutral atomic clouds along the Ulysses inbound trajectory through the magnetosphere. Far fewer neutrals were encountered by the spacecraft along its postencounter, out-of-ecliptic trajectory.
Exsolution of Hornblende and the Solubility Limits of Calcium in Orthoamphibole
Authors: Smelik Eugene A. , Veblen David R.
Published: October 2006

Exsolution between orthorhombic and monoclinic amphibole has been postulated for many years on the basis of crystal-chemical and structural differences. Transmission and analytical electron microscope examination of calium-rich gedrite specimens from southwestern New Hampshire has now revealed evidence for exsolution of calcic clinoamphibole (hornblende) from ferromagnesian orthoamphibole. Analytical electron microscopy data suggests that calcium has a low solubility limit in the orthoamphibole structure. The hornblende lamellae range from only a few unit cells in thickness to about 80 nanometers. The formation of the calcic amphibole lamellae resulted from heterogeneous nucleation and growth along pre-existing (100) stacking faults. Thus, the deformation processes producing the stacking faults played a key role in preparing the sites for exsolution.