bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear Decay Techniques in Ion Chemistry
Authors: Cacace Fulvio
Published: October 2006

The spontaneous decay of chemically bound radioactive atoms affords a route to ions of well-defined structure and charge location, free of counterions. The nuclear nature of the ionization process makes it insensitive to environmental effects, so that exactly the same charged species can be generated, and its reactivity investigated, in widely varying media, from low-pressure gases to liquids and solids. Techniques based on nuclear decay are used in studies of the production of otherwise inaccessible species, the structural characterization of free ions, and the comparative evaluation of their reactivity in different environments, in particular, gas phase and solution.
Subsurface Energy Storage and Transport for Solar-Powered Geysers on Triton
Authors: Kirk Randolph L. , Brown Robert H. , Soderblom Laurence A.
Published: October 2006

The location of active geyser-like eruptions and related features close to the current subsolar latitude on Triton suggests a solar energy source for these phenomena. Solid-state greenhouse calculations have shown that sunlight can generate substantially elevated subsurface temperatures. A variety of models for the storage of solar energy in a sub-greenhouse layer and for the supply of gas and energy to a geyser are examined. "Leaky greenhouse" models with only vertical gas transport are inconsistent with the observed upper limit on geyser radius of ∼1.5 kilometers. However, lateral transport of energy by gas flow in a porous N
2
layer with a block size on the order of a meter can supply the required amount of gas to a source region ∼1 kilometer in radius. The decline of gas output to steady state may occur over a period comparable with the inferred active geyser lifetime of five Earth years. The required subsurface permeability may be maintained by thermal fracturing of the residual N
2
polar cap. A lower limit on geyser source radius of ∼50 to 100 meters predicted by a theory of negatively buoyant jets is not readily attained.
Molecular Chaperones: The Plant Connection
Authors: Ellis R. John
Published: October 2006

Molecular chaperones are a family of unrelated proteins found in all types of cell. They mediate the correct assembly of other polypeptides, but are not components of the mature assembled structures. Chaperones function by binding specifically to interactive protein surfaces that are exposed transiently during many cellular processes and so prevent them from undergoing incorrect interactions that might produce nonfunctional structures. The concept of molecular chaperones originated largely from studies of the chloroplast enzyme rubisco, which fixes carbon dioxide in plant photosynthesis; the function of chaperones forces a rethinking of the principle of protein self-assembly.
Evolution of a Balanced Sex Ratio by Frequency-Dependent Selection in a Fish
Authors: Conover David O. , Van Voorhees David A.
Published: October 2006

Balanced (1 to 1) sex ratios are thought to evolve by a process known as frequency- dependent selection of the minority sex. Five populations of a fish with genetically based variation in temperature-dependent sex determination were maintained for 5 to 6 years in artificial constant-temperature environments that initially caused the sex ratio to be highly skewed. Increases in the proportion of the minority sex occurred in subsequent generations until a balanced sex ratio was established, thus confirming a central premise underlying the theory of sex-ratio evolution.
Preferential Heterodimer Formation by Isolated Leucine Zippers from Fos and Jun
Authors: O'Shea Erin K. , Rutkowski Rheba , Stafford Walter F. , Kim Peter S.
Published: October 2006

The products of the nuclear oncogenes
fos
and
jun
are known to form heterodimers that bind to DNA and modulate transcription. Both proteins contain a leucine zipper that is important for heterodimer formation. Peptides corresponding to these leucine zippers were synthesized. When mixed, these peptides preferentially form heterodimers over homodimers by at least 1000-fold. Both homodimers and the heterodimer are parallel α helices. The leucine zipper regions from Fos and Jun therefore correspond to autonomous helical dimerization sites that are likely to be short coiled coils, and these regions are sufficient to determine the specificity of interaction between Fos and Jun. The Fos leucine zipper forms a relatively unstable homodimer. Instability of homodimers provides a thermodynamic driving force for preferential heterodimer formation.
Ocular Responses to Linear Motion Are Inversely Proportional to Viewing Distance
Authors: Schwarz U. , Busettini C. , Miles F. A.
Published: October 2006

Eye movements exist to improve vision, in part by preventing excessive retinal image slip. A major threat to the stability of the retinal image comes from the observer's own movement, and there are visual and vestibular reflexes that operate to meet this challenge by generating compensatory eye movements. The ocular responses to translational disturbances of the observer and of the scene were recorded from monkeys. The associated vestibular and visual responses were both linearly dependent on the inverse of the viewing distance. Such dependence on proximity is appropriate for the vestibular reflex, which must transform signals from Cartesian to polar coordinates, but not for the visual reflex, which operates entirely in polar coordinates. However, such shared proximity effects in the visual reflex could compensate for known intrinsic limitations that would otherwise compromise performance at near viewing.
Detection of CN Emission from (2060) Chiron
Authors: Bus Schelte J. , A'Hearn Michael F. , Schleicher David G. , Bowell Edward
Published: October 2006

In the past decade there has been a gradual, but substantial change in our understanding of the physical nature of (2060) Chiron. Once thought to be the first known member of a population of asteroids orbiting between Saturn and Uranus, Chiron is now generally regarded as the largest known comet. The detection of CN emission in the spectrum of Chiron is reported. Not only do these observations underscore the cometary nature of Chiron, but, at a heliocentric distance exceeding 11 astronomical units, represent the most distant detection yet of a neutral gas species common in comets. These results are consistent with the outgassing from Chiron being primarily driven by isolated outbursts of CO
2
from a very small fraction of Chiron's surface. These may be indicative of primordial inhomogeneities.
A
-Axis—Oriented YBa
2
Cu
3
O
7
/PrBa
2
Cu
3
O
7
Superlattices
Authors: Eom C. B. , Marshall A. F. , Triscone J.-M. , Wilkens B. , Laderman S. S. , Geballe T. H.
Published: October 2006

A modulated structure has been fabricated from high transition temperature superconductors where the individual CuO
2
planes are composed of alternating superconducting and insulating strips. This structure is made by growing
a
-axis—oriented YBa
2
Cu
3
O
7
/PrBa
2
Cu
3
O
7
superlattices by 90° off-axis sputtering on (100)SrTiO
3
and (100)LaAlO
3
substrates. Superlattice modulation is observed to a modulation wavelength of 24 angstroms (12 angstroms—YBa
2
Cu
3
O
7
/12 angstroms—PrBa
2
Cu
3
O
7
), both by x-ray diffraction and by cross-sectional transmission electron microscopy. Rutherford backscattering spectroscopy indicates a high degree of crystalline perfection with a channeling minimum yield of 3 percent. Quasi—one-dimensional conductivity should be obtainable in these structures.
Electronic States of K

x

C
60
: Insulating, Metallic, and Superconducting Character
Authors: Benning P. J. , Martins José Luís , Weaver J. H. , Chibante L. P. F. , Smalley R. E.
Published: October 2006

The recent report of electrical conductivity in the alkali metal fullerides and the discovery of superconductivity at 18 K for K

x

C
60
has raised fundamental questions about the electronic states on either side of the Fermi level, their occupancy with K intercalation, and the mechanism of superconductivity. Direct photoemission evidence is presented of filling of bands derived from the lowest unoccupied molecular orbital as a function of K incorporation for the metallic and insulating phases. This filling is not rigid band-like, and it reflects disorder in the K sites. Theoretical analysis indicates that K

x

C
60
is a strong coupling superconductor, and we suggest that the enhanced electron-phonon interaction is related to the unique hybridization of the C
sp
-derived states.
Evolution of Pollen Morphology
Authors: Dajoz Isabelle , Till-Bottraud Irène , Gouyon Pierre-Henri
Published: October 2006

Over evolutionary time, the morphology of angiosperm pollen has evolved toward an increasing number of apertures, among other things. From a neo-Darwinian point of view, this means that (i) some polymorphism for aperture number must exist and (ii) there must be some fitness increase associated with increasing the aperture number. Pollen types with different aperture numbers often occur in the same species. Such is the case in
Viola diversifolia
. Comparison of pollen with three and four apertures in this species showed that four-apertured grains germinated faster than three-apertured ones but that the four-apertured ones experienced other disadvantages. These results obtained on the gametophyte can be interpreted in terms of strategies of the sporophyte.
Enols and Other Reactive Species
Authors: Chiang Yvonne , Kresge A. Jerry
Published: October 2006

Rapid advances in the chemistry of enols and other reactive species have been made possible recently by the development of methods for generating these short-lived substances in solution under conditions where they can be observed directly and their reactions can be monitored accurately. New laboratory techniques are described and a sample of the new chemistry they have made available is provided; special attention is given to ynols and ynamines and the remarkable effects that the carbon-carbon triple bonds of these substances have on their acid-base properties.
Molecular Recognition at Crystal Interfaces
Authors: Weissbuch I. , Addadi L. , Lahav M. , Leiserowitz L.
Published: October 2006

Nucleation, growth, and dissolution of crystals have been studied by stereochemical approach involving molecular recognition at interfaces. A methodology is described for using ''tailor-made'' additives designed to interact stereospecifically with crystal surfaces during growth and dissolution. This procedure was instrumental in controlling crystal morphology and in revising the concept of the structure and symmetry of solid solutions. Consequently, it was applied to the transformation of centrosymmetric single crystals into solid solutions with polar arrangement displaying second-harmonic generation and to the performance of asymmetric synthesis of guest molecules inside centrosymmetric host crystals. The method has led to a discovery of a new ''relay'' mechanism explaining the effect of solvent on crystal growth. Finally, it allowed for the design of auxiliary molecules that act as promoters or inhibitors of crystal nucleation that can be used to resolve enantiomers and crystallize desired polymorphs.
13
C NMR Spectroscopy of K

x

C
60
: Phase Separation, Molecular Dynamics, and Metallic Properties
Authors: Tycko R. , Dabbagh G. , Rosseinsky M. J. , Murphy D. W. , Fleming R. M. , Ramirez A. P. , Tully J. C.
Published: October 2006

The results of
13
C nuclear magnetic resonance (NMR) measurements on alkali fullerides K

x

C
60
are reported. The NMR spectra demonstrate that material with 0 <
x
< 3 is in fact a two-phase system at equilibrium, with
x
= 0 and
x
= 3. NMR lineshapes indicate that C
3–
60
ions rotate rapidly in the K
3
C
60
phase at 300 K, while C
6–
60
ions in the insulating K
6
C
60
phase are static on the time scale of the lineshape measurement. The temperature dependence of the
13
C spin-lattice relaxation rate in the normal state of K
3
C
60
is found to be characteristic of a metal, indicating the important role of the C
3–
60
ions in the conductivity. From the relaxation measurements, an estimate of the density of electronic states at the Fermi level is derived.
Climatic Change in Tasmania Inferred from a 1089-Year Tree-Ring Chronology of Huon Pine
Authors: Cook Edward , Bird Trevor , Peterson Mike , Barbetti Mike , Buckley Brendan , D'Arrigo Rosanne , Francey Roger , Tans Pieter
Published: October 2006

A climatically sensitive huon pine tree-ring chronology from western Tasmania allows inferences about Austral summer temperature change since A.D. 900. Since 1965, huon pine growth has been unusually rapid for trees that are in many cases over 700 years old. This growth increase correlates well with recent anomalous warming in Tasmania on the basis of instrumental records and supports claims that a climatic change, perhaps influenced by greenhouse gases, is in progress. Although this temperature increase exceeds any that are inferred to have occurred during the past 1089 years at this location, it has not yet clearly emerged from the natural background variability of climate in this part of the Southern Hemisphere.
Images from Galileo of the Venus Cloud Deck
Authors: Belton Michael J. S. , Gierasch Peter J. , Smith Michael D. , Helfenstein Paul , Schinder Paul J. , Pollack James B. , Rages Kathy A. , Ingersoll Andrew P. , Klaasen Kenneth P. , Veverka Joseph , Anger Clifford D. , Carr Michael H. , Chapman Clark R. , Davies Merton E. , Fanale Fraser P. , Greeley Ronald , Greenberg Richard , Head James W. , Morrison David , Neukum Gerhard , Pilcher Carl B.
Published: October 2006

Images of Venus taken at 418 (violet) and 986 [near-infrared (NIR)] nanometers show that the morphology and motions of large-scale features change with depth in the cloud deck. Poleward meridional velocities, seen in both spectral regions, are much reduced in the NIR. In the south polar region the markings in the two wavelength bands are strongly anticorrelated. The images follow the changing state of the upper cloud layer downwind of the subsolar point, and the zonal flow field shows a longitudinal periodicity that may be coupled to the formation of large-scale planetary waves. No optical lightning was detected.
Quantum Mechanical Calculations to Chemical Accuracy
Authors: Bauschlicher Charles W. , Langhoff Stephen R.
Published: October 2006

Full configuration-interaction (FCI) calculations have given an unambiguous standard by which the accuracy of theoretical approaches of incorporating electron correlation into molecular structure calculations can be judged. In addition, improvements in vectorization of programs, computer technology, and algorithms now permit a systematic study of the convergence of the atomic orbital (or so-called one-particle) basis set. These advances are discussed and some examples of the solution of chemical problems by quantum mechanical calculations are given to illustrate the accuracy of current techniques.
Changes in the West Antarctic Ice Sheet
Authors: Alley R. B. , Whillans I. M.
Published: October 2006

The portion of the West Antarctic ice sheet that flows into the Ross Sea is thinning in some places and thickening in others. These changes are not caused by any current climatic change, but by the combination of a delayed response to the end of the last global glacial cycle and an internal instability. The near-future impact of the ice sheet on global sea level is largely due to processes internal to the movement of the ice sheet, and not so much to the threat of a possible greenhouse warming. Thus the near-term future of the ice sheet is already determined. However, too little of the ice sheet has been surveyed to predict its overall future behavior.
Atomic and Molecular Manipulation with the Scanning Tunneling Microscope
Authors: Stroscio Joseph A. , Eigler D. M.
Published: October 2006

The prospect of manipulating matter on the atomic scale has fascinated scientists for decades. This fascination may be motivated by scientific and technological opportunities, or from a curiosity about the consequences of being able to place atoms in a particular location. Advances in scanning tunneling microscopy have made this prospect a reality; single atoms can be placed at selected positions and structures can be built to a particular design atom-by-atom. Atoms and molecules may be manipulated in a variety of ways by using the interactions present in the tunnel junction of a scanning tunneling microscope. Some of these recent developments and some of the possible uses of atomic and molecular manipulation as a tool for science are discussed.
Role of Na
+
/H
+
Exchange by Interferon-γ in Enhanced Expression of JE and I-A
β
Genes
Authors: Prpic Veronica , Yu Sheau-Fung , Figueiredo Figueiredo , Hollenbach Paul W. , Gawdi Gowind , Herman Brian , Uhing Ronald J. , Adams Dolph O.
Published: October 2006

The rapid transductional sequences initiated by interferon-γ (IFN-γ) on binding to its receptor regulate functional and genomic responses in many cells but are not well defined. Induction of macrophage activation is an example of such functional and genomic changes in response to IFN-γ. Addition of IFN-γ to murine macrophages, at activating concentrations, produced rapid (within 60 seconds) alkalinization of the cytosol and a concomitant, rapid influx of
22
Na
+
. Amiloride inhibited the ion fluxes and the accumulation of specific messenger RNA for two genes induced by IFN-γ (the early gene JE and the β chain of the class II major histocompatibility complex gene I-A). The data indicate that IFN-γ initiates rapid exchange of Na
+
and H
+
by means of the Na
+
/H
+
antiporter and that these amiloride-sensitive ion fluxes are important to some of the genomic effects of IFN-γ.
AP1/
jun
Function Is Differentially Induced in Promotion-Sensitive and Resistant JB6 Cells
Authors: Bernstein Lori R. , Colburn Nancy H.
Published: October 2006

Tumor promoters may bring about events that lead to neoplastic transformation by inducing specific promotion-relevant effector genes. Functional activation of the transacting transcription factor AP-1 by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) may play an essential role in this process. Clonal genetic variants of mouse epidermal JB6 cells that are genetically susceptible (P
+
) or resistant (P
-
) to promotion of transformation by TPA were transfected with 3XTRE-CAT, a construct that has AP-1 cis-enhancer sequences attached to a reporter gene encoding chloramphenicol acetyltransferase (CAT). Transfected JB6 P
+
, but not P
-
variants, showed TPA-inducible CAT synthesis. Epidermal growth factor, another transformation promoter in JB6 cells, also caused P
+
specific induction of CAT gene expression. These results demonstrate an association between induced AP-1 function and sensitivity to promotion of neoplastic transformation.
Cloning of Breakpoints of a Chromosome Translocation Identifies the AN2 Locus
Authors: Gessler Manfred , Simola Kalle O. J. , Bruns Gail A. P.
Published: October 2006

Chromosome translocations involving 11p13 have been associated with familial aniridia in two kindreds highlighting the chromosomal localization of the AN2 locus. This locus is also part of the WAGR complex (Wilms tumor, aniridia, genitourinary abnormalities, and mental retardation). In one kindred, the translocation is associated with a deletion, and probes for this region were used to identify and clone the breakpoints of the translocation in the second kindred. Comparison of phage restriction maps exclude the presence of any sizable deletion in this case. Sequences at the chromosome 11 breakpoint are conserved in multiple species, suggesting that the translocation falls within the AN2 gene.
Behavioral Neurochemistry: Neuroregulators and Behavioral States
Authors: Barchas Jack D. , Akil Huda , Elliott Glen R. , Holman R. Bruce , Watson Stanley J.
Published: October 2006

There is compelling evidence that behavioral events alter neurochemical function and that altered neurochemical function can change behavior. Such processes have been related both to neurotransmitters and to neuromodulators, together termed neuroregulators. Available research tools and theoretical constructs have begun to permit studies of certain types of behavior, primarily those related to emotional states and drives. This work is changing long-held concepts about severe mental disorders and the treatment of them.
Fermi Surfaces, Fermi Liquids, and High-Temperature Superconductors
Authors: Pickett W. E. , Singh D. J. , Krakauer H. , Cohen R. E.
Published: October 2006

Recent experimental results are beginning to limit seriously the theories that can be considered to explain high-temperature superconductivity. The unmistakable observations of a Fermi surface, by several groups and methods, make it the focus of realistic theories of the metallic phases. Data from angle-resolved photoemission, positron annihilation, and de Haas-van Alphen experiments are in agreement with band theory predictions, implying that the metallic phases cannot be pictured as doped insulators. The character of the low energy excitations ("quasiparticles"), which interact strongly with atomic motions, with magnetic fluctuations, and possibly with charge fluctuations, must be sorted out before the superconducting pairing mechanism can be given a microscopic basis.
Measured Trends in Stratospheric Ozone
Authors: Stolarski Richard , Bojkov Rumen , Bishop Lane , Zerefos Christos , Staehelin Johannes , Zawodny Joseph
Published: October 2006

Recent findings, based on both ground-based and satellite measurements, have established that there has been an apparent downward trend in the total column amount of ozone over mid-latitude areas of the Northern Hemisphere in all seasons. Measurements of the altitude profile of the change in the ozone concentration have established that decreases are taking place in the lower stratosphere in the region of highest ozone concentration. Analysis of updated ozone records, through March of 1991, including 29 stations in the former Soviet Union, and analysis of independently calibrated satellite data records from the Total Ozone Mapping Spectrometer and Stratospheric Aerosol and Gas Experiment instruments confirm many of the findings originally derived from the Dobson record concerning northern midlatitude changes in ozone. The data from many instruments now provide a fairly consistent picture of the change that has occurred in stratospheric ozone levels.
Nucleoid Condensation in
Escherichia coli
That Express a Chlamydial Histone Homolog
Authors: Barry Clifton E. , Hayes Stanley F. , Hackstadt Ted
Published: October 2006

Chlamydial cell types are adapted for either extracellular survival or intracellular growth. In the transcriptionally inert elementary bodies, the chromosome is densely compacted; in metabolically active reticulate bodies, the chromatin is loosely organized. Condensation of the chlamydial nucleoid occurs concomitant with expression of proteins homologous to eukaryotic histone H1. When the
Chlamydia trachomatis
18-kilodalton histone homolog Hc1 is expressed in
Escherichia coli
, a condensed nucleoid structure similar to that of chlamydiae is observed with both light and electron microscopy. These results support a role for Hc1 in condensation of the chlamydial nucleoid.
Reproducible Imaging and Dissection of Plasmid DNA Under Liquid with the Atomic Force Microscope
Authors: Hansma H. G. , Vesenka J. , Siegerist C. , Kelderman G. , Morrett H. , Sinsheimer R. L. , Elings V. , Bustamante C. , Hansma P. K.
Published: October 2006

Reproducible images of uncoated DNA in the atomic force microscope (AFM) have been obtained by imaging plasmid DNA on mica in
n
-propanol. Specially sharpened AFM tips give images with reproducible features several nanometers in size along the DNA. Plasmids can be dissected in propanol by increasing the force applied by the AFM tip at selected locations.
Tyrosine Phosphorylation of the
vav
Proto-Oncogene Product in Activated B Cells
Authors: Bustelo Xosέ R. , Barbacid Mariano
Published: October 2006

Activation of B lymphocytes by engagement of their immunoglobulin M antigen receptors results in phosphorylation of a number of proteins on tyrosine residues. One such protein is p95

vav

, the product of the
vav
proto-oncogene. Tyrosine phosphorylation of p95

vav

occurred within seconds of immunoglobulin M cross-linking and was independent of other events induced during stimulation of B cells, such as protein kinase C activation, guanosine triphosphate-binding protein signaling, and calcium mobilization. Moreover, engagement of antigen receptors induced the rapid (∼5 seconds) and transient (∼60 seconds) association of p95

vav

with a 70-kilodalton tyrosine-phosphorylated protein, Vap-1, an interaction mediated by the Src homology 2 domain of p95

vav

. These results suggest that the
vav
proto-oncogene participates in the signaling processes that mediate the antigen-induced activation of B lymphocytes.
Identification of Heregulin, a Specific Activator of p185
erbB2
Authors: Holmes William E. , Sliwkowski Mark X. , Akita Robert W. , Henzel William J. , Lee James , Park John W. , Yansura Daniel , Abadi Nasrin , Raab Helga , Lewis Gail D. , Shepard H. Michael , Kuang Wun-Jing , Wood William l. , Goeddel David V. , Vandlen Richard L.
Published: October 2006

The proto-oncogene designated
erb
B2 or HER2 encodes a 185-kilodalton transmembrane tyrosine kinase (p185

erb
B2

), whose overexpression has been correlated with a poor prognosis in several human malignancies. A 45-kilodalton protein heregulin-α (HRG-α) that specifically induced phosphorylation of p185

erb
B2

was purified from the conditioned medium of a human breast tumor cell line. Several complementary DNA clones encoding related HRGs were identified, all of which are similar to proteins in the epidermal growth factor family. Scatchard analysis of the binding of recombinant HRG to a breast tumor cell line expressing p185

erb
B2

showed a single high affinity binding site [dissociation constant (
K
d
) = 105 ± 15 picomolar]. Heregulin transcripts were identified in several normal tissues and cancer cell lines. The HRGs may represent the natural ligands for p185

erb
B2

.
Hydrogen Exchange Measurement of the Free Energy of Structural and Allosteric Change in Hemoglobin
Authors: Englander S. Walter , Englander Joan J. , McKinnie Russell E. , Ackers Gary K. , Turner George J. , Westrick Judy A. , Gill Stanley J.
Published: October 2006

The inability to localize and measure the free energy of protein structure and structure change severely limits protein structure-function investigations. The local unfolding model for protein hydrogen exchange quantitatively relates the free energy of local structural stability with the hydrogen exchange rate of concerted sets of structurally related protons. In tests with a number of modified hemoglobin forms, the loss in structural free energy obtained locally from hydrogen exchange results matches the loss in allosteric free energy measured globally by oxygen-binding and subunit dissociation experiments.
Myoglobin in a Cyanobacterium
Authors: Potts Malcolm , Angeloni Stephen V. , Ebel Richard E. , Bassam Deeni
Published: October 2006

Myoglobin was found in the nitrogen-fixing cyanobacterium
Nostoc commune
. This cyanobacterial myoglobin, referred to as cyanoglobin, was shown to be a soluble hemoprotein of 12.5 kilodaltons with an amino acid sequence that is related to that of myoglobins from two lower eukaryotes, the ciliated protozoa
Paramecium caudatum
and
Tetrahymena pyriformis
. Cyanoglobin is encoded by the
glbN
gene, which is positioned between
nifU
and
nifH
—two genes essential for nitrogen fixation—in the genome of
Nostoc
. Cyanoglobin was detected in
Nostoc
cells only when they were starved for nitrogen and incubated microaerobically.
The Motor Cortex and the Coding of Force
Authors: Georgopoulos Apostolos P. , Ashe James , Smyrnis Nikolaos , Taira Masato
Published: October 2006

The relation of cellular activity in the motor cortex to the direction of two-dimensional isometric force was investigated under dynamic conditions in monkeys. A task was designed so that three force variables were dissociated: the force exerted by the subject, the net force, and the change in force. Recordings of neuronal activity in the motor cortex revealed that the activity of single cells was directionally tuned and that this tuning was invariant across different directions of a bias force. Cell activity was not related to the direction of force exerted by the subject, which changed drastically as the bias force changed. In contrast, the direction of net force, the direction of force change, and the visually instructed direction all remained quite invariant and congruent and could be the directional variables, alone or in combination, to which cell activity might relate.
Chemiluminescence of Anodized and Etched Silicon: Evidence for a Luminescent Siloxene-Like Layer on Porous Silicon
Authors: McCord Paul , Yau Shueh-Lin , Bard Allen J.
Published: October 2006

Treatment of anodized or chemically etched silicon ("porous silicon") with dilute nitric acid or persulfate solution results in weak chemiluminescence in the visible region. Concentrated nitric acid reacts violently with porous Si produced by anodization with a bright flash of light. The fact that similar reactions occur with siloxene (Si
6
H
6
O
3
) prepared from CaSi
2
suggests that the visible emission seen with porous Si can be attributed to this substance.
Transfer of Biologically Derived Nanometer-Scale Patterns to Smooth Substrates
Authors: Douglas Kenneth , Devaud Genevieve , Clark Noel A.
Published: October 2006

Atomic force microscopy has been used to measure the surface profile of a periodic array of 10-nanometer (nm)-diameter holes fabricated by fast-atom beam milling of a smooth graphite surface in which a 3.5-nm-thick titanium oxide screen was used as a mask. The nanostructured titanium oxide mask was itself derived from a protein crystal template. Pattern transfer from the biological crystal to the metal oxide film and finally to the graphite substrate was accomplished entirely by parallel processing.
The Crisis in Antibiotic Resistance
Authors: Neu Harold C.
Published: October 2006

The synthesis of large numbers of antibiotics over the past three decades has caused complacency about the threat of bacterial resistance. Bacteria have become resistant to antimicrobial agents as a result of chromosomal changes or the exchange of genetic material via plasmids and transposons.
Streptococcus pneumoniae, Streptococcus pyogenes
, and staphylococci, organisms that cause respiratory and cutaneous infections, and members of the
Enterobacteriaceae
and
Pseudomonas families
, organisms that cause diarrhea, urinary infection, and sepsis, are now resistant to virtually all of the older antibiotics. The extensive use of antibiotics in the community and hospitals has fueled this crisis. Mechanisms such as antibiotic control programs, better hygiene, and synthesis of agents with improved antimicrobial activity need to be adopted in order to limit bacterial resistance.
Transactivation by AP-1 Is a Molecular Target of T Cell Clonal Anergy
Authors: Kang Sang-Mo , Beverly Bart , Tran Annie-Chen , Brorson Kurt , Schwartz Ronald H. , Lenardot Michael J.
Published: October 2006

Anergy is a mechanism of T lymphocyte tolerance induced by antigen receptor stimulation in the absence of co-stimulation. Anergic T cells were shown to have a defect in antigen-induced transcription of the interleukin-2 gene. Analysis of the promoter indicated that the transcription factor AP-1 and its corresponding cis element were specifically down-regulated. Exposure of anergic T cells to interleukin-2 restored both antigen responsiveness and activity of the AP-1 element.
Fault Zone Connectivity: Slip Rates on Faults in the San Francisco Bay Area, California
Authors: Bilham Roger , Bodin Paul
Published: October 2006

The slip rate of a fault segment is related to the length of the fault zone of which it is part. In turn, the slip rate of a fault zone is related to its connectivity with adjoining or contiguous fault zones. The observed variation in slip rate on fault segments in the San Francisco Bay area in California is consistent with connectivity between the Hayward, Calaveras, and San Andreas fault zones. Slip rates on the southern Hayward fault taper northward from a maximum of more than 10 millimeters per year and are sensitive to the active length of the Maacama fault.
Relation Between Long-Term Trends of Oxygen-18 Isotope Composition of Precipitation and Climate
Authors: Rozanski Kazimierz , Araguás-Araguás Luis , Gonfiantini Roberto
Published: October 2006

Stable isotope ratios of oxygen (
18
O/
16
O) and hydrogen (D/H) in water have long been considered powerful indicators of paleoclimate. However, quantitative interpretation of isotope variations in terms of climate changes is hampered by a limited understanding of physical processes controlling the global isotope behavior. Analysis was conducted of time series of
18
O content (δ
18
O) of monthly precipitation and surface air temperature available through the International Atomic Energy Agency-World Meteorological Organization global network, "Isotopes in Precipitation." This study indicates that long-term changes of isotopic composition of precipitation over mid- and high-latitude regions during the past three decades closely followed long-term changes of surface air temperature with the average 8180-temperature coefficient around 0.6 per mil per degree Celsius.
Viscoelastic Dynamics of Confined Polymer Melts
Authors: Hu Hsuan-Wei , Granick Steve
Published: October 2006

The frequency-dependent shear response of an ultrathin polymer melt (polyphenylmethylsiloxane) confined between adsorbing surfaces (parallel plates of mica) is described. The sinusoidal deformations were sufficiently small to give linear response, implying that measurement did not perturb the film structure. A remarkable transition was observed with decreasing thickness. When the film thickness was less than five to six times the unperturbed radius of gyration, there emerged a strong rubber-like elasticity that was not characteristic of the bulk samples. This result indicates enhanced entanglement interactions in thin polymer films and offers a mechanism to explain the slow mobility of polymers at surfaces.
Electrical Resistivity and Stoichiometry of Ca

x

C
60
and Sr

x

C
60
Films
Authors: Haddon R. C. , Kochanski G. P. , Hebard A. F. , Fiory A. T. , Morris R. C.
Published: October 2006

The temperature- and concentration-dependent resistivities of annealed Ca

x

C
60
and Sr

x

C
60
films were measured near room temperature. Resistivity minima were observed at
x
= 2 and 5. The resistivities of these films were ρ
min
∼1 ohm-centimeter for
x
= 2 and ρ
min
∼10
–2
ohm-centimeter for
x
= 5. This latter value is comparable to the resistivities found in similar experiments on K
3
C
60
films. There is a maximum in the resistivity between
x
= 2 and 3, and another at
x
∼7. The conductivity is activated over the whole range of compositions, and the activation energy scales with the logarithm of the resistivity. The results suggest that the conductivity and superconductivity observed in Ca
5
C
60
are associated with the population of bands derived from the
t
1g
level of C
6O
.
A Homoeotic Mutant of
Arabidopsis thaliana
with Leafy Cotyledons
Authors: Meinke David W.
Published: October 2006

Cotyledons are specialized leaves produced during plant embryogenesis. Cotyledons and leaves typically differ in morphology, ultrastructure, and patterns of gene expression. The
leafy cotyledon
(
lec
) mutant of
Arabidopsis thaliana
fails to maintain this distinction between embryonic and vegetative patterns of plant development. Mutant embryos are phenotypically abnormal, occasionally viviparous, and intolerant of desiccation. Mutant cotyledons produce trichomes characteristic of leaves, lack embryo-specific protein bodies, and exhibit a vascular pattern intermediate between that of leaves and cotyledons. These results suggest that
lec
cotyledons are partially transformed into leaves and that the wild-type gene (
LEC
) functions to activate a wide range of embryo-specific pathways in higher plants.
Single-Crystal Epitaxial Thin Films of the Isotropic Metallic Oxides Sr

1–
x

Ca

x

RuO
3
(0 ≤ × ≤ 1)
Authors: Eom C. B. , Cava R. J. , Fleming R. M. , Phillips Julia M. , vanDover R. B. , Marshall J. H. , Hsu J. W. P. , Krajewski J. J. , Peck W. F.
Published: October 2006

Single-crystal epitaxial thin films of the isotropic metallic oxides Sr

1–
x

Ca

x
RuO

3
(0 ≤ x ≤ 1) were grown on miscut SrTiO
3
(100) substrates in situ by 90° off-axis sputtering. These thin films exhibit low isotropic resistivities, excellent chemical and thermal stability, good surface smoothness, and high crystalline quality. Furthermore, the lattice parameters and magnetic properties can be varied by simply changing the strontium/calcium ratio. These epitaxial thin films, and their multilayer structures with other oxide materials, can be used for the fabrication of superconducting, ferroelectric, magneto-optic, and electro-optic devices.
Structural and Electronic Properties of La@C
82
Authors: Laasonen Kari , Andreoni Wanda , Parrinello Michele
Published: October 2006

The structural and electronic properties of the La@C
82
fullerene have been investigated by means of the Car-Parrinello method, which is based on the local density approximation of the density functional theory. The topological arrangement of the C
82
cage was assumed to be a C
3v
symmetry isomer. Three configurations were considered, one with the lanthanum atom at the center of the cluster, one with it along the threefold axis, and one with it at a low-symmetry, highly coordinated site. The structure was fully relaxed and it was found that the last of these configurations is energetically preferred. In this position, the lanthanum atom is nearly in a La
3+
state and the unpaired electron is somewhat delocalized on the cage, in agreement with available experimental data. This arrangement suggests that the chemical shifts of the 5
s
and 5
p
lanthanum states can be used as a structural probe and as a way of further validating this picture. It is argued that this conclusion is not affected by the assumed fullerene structure.
Allometric Engineering: A Causal Analysis of Natural Selection on Offspring Size
Authors: Sinervo Barry , Zamudio Kelly , Doughty Paul , Huey Raymond B.
Published: October 2006

Techniques of offspring size manipulation, "allometric engineering," were used in combination with studies of natural selection to elucidate the causal relation between egg size and offspring survival of lizards. The results experimentally validate premises underlying theories of optimal egg size: fecundity selection favoring the production of large clutches of small eggs was balanced by survival selection favoring large offspring. However, large hatchlings did not always have the highest survival, contrary to most theoretical expectations. Optimizing selection on offspring size per se was the most common pattern. Moreover, matches between average and optimal egg size were qualitative, not quantitative, perhaps reflecting known functional constraints on the production of large eggs.
Comparative Compressibilities of Silicate Spinels: Anomalous Behavior of (Mg,Fe)
2
SiO
4
Authors: Hazen Robert M.
Published: October 2006

Compressibilities of five silicate spinels, including γ-Mg
2
SiO
4
, γ-Fe
2
SiO
4
, Ni
2
SiO
4
, and two ferromagnesian compositions, were determined on crystals positioned in the same high-pressure mount. Subjection of all crystals simultaneously to the same pressure revealed differences in compressibility that resulted from compositional differences. Ferromagnesian silicate spinels showed an anomalous 13 percent increase in bulk modulus with increasing iron content, from Mg
2
SiO
4
(184 gigapascals) to Fe
2
SiO
4
(207 gigapascals). This result suggests that ferrous iron and magnesium, which behave similarly under crustal conditions, are chemically more distinct at high pressures characteristic of the transition zone and lower mantle.
Beyond Nature's Chiral Pool: Enantioselective Catalysis in Industry
Authors: Nugent William A. , RajanBabu T. V. , Burk Mark J.
Published: October 2006

Enantioselective catalysts produce organic compounds in enantiomerically enriched form. They are highly efficient tools for the synthesis of biologically active materials, such as pharmaceuticals and crop-protection chemicals, in which enantiomeric purity can be critical. The design of chiral ligands is the key to developing new enantioselective catalysts. Three unusual families of ligands have been used to develop practical technology for enantioselective hydrocyanation of olefins, ring-opening of epoxides, and hydrogenation of various compounds.
Three-Dimensional Instabilities of Mantle Convection with Multiple Phase Transitions
Authors: Honda S. , Yuen D. A. , Balachandar S. , Reuteler D.
Published: October 2006

The effects of multiple phase transitions on mantle convection are investigated by numerical simulations that are based on three-dimensional models. These simulations show that cold sheets of mantle material collide at junctions, merge, and form a strong downflow that is stopped temporarily by the transition zone. The accumulated cold material gives rise to a strong gravitational instability that causes the cold mass to sink rapidly into the lower mantle. This process promotes a massive exchange between the lower and upper mantles and triggers a global instability in the adjacent plume system. This mechanism may be cyclic in nature and may be linked to the generation of superplumes.
The Mechanical Response of Gold Substrates Passivated by Self-Assembling Monolayer Films
Authors: Thomas Ross C. , Houston J. E. , Michalske Terry A. , Crooks Richard M.
Published: October 2006

Interfacial force microscopy has been used to show that a single layer of self-assembling molecules adsorbed on a gold substrate can prevent adhesion between gold and a tungsten probe. The passivated gold is able to elastically support large repulsive loads, with plots of load versus deformation closely following the Hertzian model. The gold shear-stress threshold for plastic deformation is determined to be ∼1 gigapascal, which is in agreement with the theoretical value for the intrinsic gold-lattice stability.
Near-Field Investigations of the Landers Earthquake Sequence, April to July 1992
Authors: Sieh Kerry , Jones Lucile , Hauksson Egill , Hudnut Kenneth , Eberhart-Phillips Donna , Heaton Thomas , Hough Susan , Hutton Kate , Kanamori Hiroo , Lilje Anne , Lindvall Scott , McGill Sally F. , Mori James , Rubin Charles , Spotila James A. , Stock Joann , Thio Hong Kie , Treiman Jerome , Wernicke Brian , Zachariasen Judith
Published: October 2006

The Landers earthquake, which had a moment magnitude (
M
w
) of 7.3, was the largest earthquake to strike the contiguous United States in 40 years. This earthquake resulted from the rupture of five major and many minor right-lateral faults near the southern end of the eastern California shear zone, just north of the San Andreas fault. Its
M
w
6.1 preshock and
M
w
6.2 aftershock had their own aftershocks and foreshocks. Surficial geological observations are consistent with local and far-field seismologic observations of the earthquake. Large surficial offsets (as great as 6 meters) and a relatively short rupture length (85 kilometers) are consistent with seismological calculations of a high stress drop (200 bars), which is in turn consistent with an apparently long recurrence interval for these faults.
Preparation of Amorphous Boron Nitride and Its Conversion to a Turbostratic, Tubular Form
Authors: Hamilton Ewan J. M. , Dolan Shawn E. , Mann Charles M. , Colijn Hendrik O. , McDonald Clare A. , Shore Sheldon G.
Published: October 2006

Amorphous boron nitride, BN, is obtained from the reaction of
B
-trichloroborazine, (BCINH)
3
, with cesium metal. The amorphous product is converted to a turbostratic form upon heating to 1100°C. Scanning electron microscopy reveals a previously unreported morphology composed of hollow tubular structures. The largest of these appear to be approximately 3 micrometers in external diameter and 50 to 100 micrometers in length. Transmission electron microscopy and selected-area electron diffraction also indicate the tube walls to be turbostratic in nature. The mechanism by which the tubes form is not known, although apparent sites of incipient tube growth have been observed.
Experimental Evidence for a New Iron Phase and Implications for Earth's Core
Authors: Saxena S. K. , Shen G. , Lazor P.
Published: October 2006

Iron is known to occur in four different crystal structural forms. One of these, the densest form (ε phase, hexagonal close-packed) is considered to have formed Earth's core. Theoretical arguments based on available high-temperature and high-pressure iron data indicate the possibility of a fifth less dense iron phase forming the core. Study of iron phase transition conducted between pressures of 20 to 100 gigapascals and 1000 to 2200 Kelvin provides an experimental confirmation of the existence of this new phase. The ε iron phase transforms to this lower density phase before melting. The new phase may form a large part of Earth's core.
Gas-Phase Ion Chromatography: Transition Metal State Selection and Carbon Cluster Formation
Authors: Bowers Michael T. , Kemper Paul R. , von Helden Gert , van Koppen Petra A. M.
Published: October 2006

Gas-phase ion chromatography can separate ions that have the same mass but differ in isomeric structure or electronic configuration. The main features of this technique are briefly outlined, and applications to a series of problems in transition metal chemistry and carbon cluster chemistry are described. Examples in transition metal chemistry include state-selective reactivity, excited state deactivation, and state-selective ligand binding energies. For clusters, ion chromatography was used to determine the structure of pure carbon cluster ions as a function of size from C
4
to C
84
. The results indicate that carbon grows first in linear chains, transforms to monocyclic planar rings at about C
10
, and forms new families of planar bi-, tri-, and tetracyclic rings at C
20
, C
30
, and C
40
, respectively. Fullerenes, which mysteriously appear at C
30
and dominate by C
50
, are generated by heating the planar ring systems above an isomerization barrier rather than by growth of graphite precursors.
Direct Imaging of the Diacetylene Solid-State Monomer-Polymer Phase Transformation
Authors: Liao Jun , Martin David C.
Published: October 2006

The solid-state phase transformation from 1,6-di(
N
-carbazolyl)-2-4-hexadiyne (DCHD) diacetylene monomer to polymer has been studied dynamically by low-dose selected area electron diffraction and high-resolution electron microscopy. The total exposure required to induce polymerization is five orders of magnitude smaller than the critical dose for electron beam damage. The phase transformation is quasi-homogeneous, with the lattice parameters changing continuously as a function of beam dose. Characteristic streaking that develops in the selected area electron diffraction patterns in the [200] reciprocal directions during the intermediate stages of the transformation provides information about the defect-mediated mechanisms of this reaction.
Relation Between Bond-Length Alternation and Second Electronic Hyperpolarizability of Conjugated Organic Molecules
Authors: Marder Seth R. , Gorman Christopher B. , Tiemann Bruce G. , Perry Joseph W. , Bourhill Grant , Mansour Kamjou
Published: October 2006

The solvent dependence of the second hyperpolarizability, γ, of a variety of unsaturated organic compounds has been measured by third harmonic generation at 1907 nanometers. It is seen that the measured γ is a function of solvent polarity. These solvent-dependent hyperpolarizabilities are associated with changes in molecular geometry from a highly bond-length alternated, polyene-like structure for a formyl-substituted compound in non-polar solvents, to a cyanine-like structure, with little bond-length alternation, for a dicyanovinyl-substituted compound in polar solvents. By tuning bond-length alternation, γ can be optimized in either a positive or negative sense for polymethine dyes of a given conjugation length.