bluuebunny/crossref_metadata_2025 huggingface dataset:
Expression of High-affinity Binding of Human Immunoglobulin E by Transfected Cells
Authors: Miller Larry , Blank Ulrich , Metzger Henry , Kinet Jean-Pierre
Published: October 2006

The receptor with high affinity for immunoglobulin E (IgE) on mast cells and basophils is critical in initiating allergic reactions. It is composed of an IgE-binding α subunit, a β subunit, and two γ subunits. The human α subunit was expressed on transfected cells in the presence of rat β and γ subunits or in the presence of the γ subunit alone. The IgE binding properties of the expressed human α were characteristic of receptors on normal human cells. These results now permit a systematic analysis of human IgE binding and a search for therapeutically useful inhibitors of that binding.
Inhibitors of Angiotensin-Converting Enzyme Prevent Myointimal Proliferation After Vascular Injury
Authors: Powell Jerry S. , Clozel Jean-Paul , Müller Rita K. M. , Kuhn Herbert , Hefti Fridolin , Hosang Markus , Baumgartner Hans R.
Published: October 2006

The role of a local angiotensin system in the vascular response to arterial injury was investigated by administering the angiotensin-converting enzyme (CE) inhibitor cilazapril to normotensive rats in which the left carotid artery was subjected to endothelial denudation and injury by balloon catheterization. In control animals, by 14 days after balloon injury, the processes of smooth muscle cell (SMC) proliferation, migration of SMCs from the media to the intima, and synthesis of extracellular matrix produced marked thickening of the intima, with reduction of the cross-sectional area of the lumen. However, in animals that received continuous treatment with the CE inhibitor, neointima formation was decreased (by about 80 percent), and lumen integrity was preserved. Thus, the angiotensin-converting enzyme may participate in modulating the proliferative response of the vascular wall after arterial injury, and inhibition of this enzyme may have therapeutic applications to prevent the proliferative lesions that occur after coronary angioplasty and vascular surgery.
Statistical Data Analysis in the Computer Age
Authors: Efron Bradley , Tibshirani Robert
Published: October 2006

Most of our familiar statistical methods, such as hypothesis testing, linear regression, analysis of variance, and maximum likelihood estimation, were designed to be implemented on mechanical calculators. Modern electronic computation has encouraged a host of new statistical methods that require fewer distributional assumptions than their predecessors and can be applied to more complicated statistical estimators. These methods allow the scientist to explore and describe data and draw valid statistical inferences without the usual concerns for mathematical tractability. This is possible because traditional methods of mathematical analysis are replaced by specially constructed computer algorithms. Mathematics has not disappeared from statistical theory. It is the main method for deciding which algorithms are correct and efficient tools for automating statistical inference.
Commensurability and Mobility in Two-Dimensional Molecular Patterns on Graphite
Authors: Rabe Jürgen P. , Buchholz Stefan
Published: October 2006

Two-dimensional molecular patterns were obtained by the adsorption of long-chain alkanes, alcohols, fatty acids, and a dialkylbenzene from organic solutions onto the basal plane of graphite. In situ scanning tunneling microscopy (STM) studies revealed that these molecules organize in lamellae with the extended alkyl chains oriented parallel to a lattice axis within the basal plane of graphite. The planes of the carbon skeletons, however, can be oriented either predominantly perpendicular to or predominantly parallel with the substrate surface, causing the lamellar lattice to be either in or near registry with the substrate (alkanes and alcohols) or not in registry (fatty acids and dialkylbenzenes). In the case of the alcohols and the dialkylbenzene the molecular axes are tilted by +30° or -30° with respect to an axis normal to the lamella boundaries, giving rise to molecularly well-defined domain boundaries. Fast STM image recording allowed the spontaneous switch between the two tilt angles to be observed in the alcohol monolayers on a time scale of a few milliseconds.
Order and Disorder in C
60
and K

x

C
60
Multilayers: Direct Imaging with Scanning Tunneling Microscopy
Authors: Li Y. Z. , Chander M. , Patrin J. C. , Weaver J. H. , Chibante L. P. F. , Smalley R. E.
Published: October 2006

Monolayer and multilayer structures of C
60
, a high temperature van der Waals solid, have been studied with scanning tunneling microscopy. Structures grown on GaAs(110) at 300 kelvin and at elevated temperatures show significantly different morphologies because of balances between thermodynamics and kinetics. Condensation onto stepped surfaces demonstrates preferred bonding and nucleation at step edges. Detailed studies of potassium incorporation in crystalline C
60
show highly ordered structures in the K
3
C
60
metallic state but disordered non-metallic structures for high potassium concentrations.
The Economics of Pesticide Use and Regulation
Authors: Zilberman David , Schmitz Andrew , Casterline Gary , Lichtenberg Erik , Siebert Jerome B.
Published: October 2006

Pesticides enhance agricultural productivity, but the environmental and health side effects of their use justify government regulation, a subject of continuing societal debate. Bans on pesticide use are the principal regulatory device used in the United States. The economic impacts of such bans depend on the availability of substitutes, supply and trade conditions, and research and development. Without substitutes, pesticide bans result in reduced production levels and higher prices, a substantial loss of discretionary income to consumers, and a redistribution of income among agricultural producers. Most food safety concerns can be addressed by establishing standards and markets for pesticide-differentiated products, but worker safety and clean water concerns will require direct controls. Pesticide-use fees are shown to be more efficient than outright pesticide bans as a mechanism to obtain environmental goals.
Quantification of Primary Versus Secondary C-H Bond Cleavage in Alkane Activation: Propane on Pt
Authors: Weinberg W. Henry , Sun Yong-Kui
Published: October 2006

The trapping-mediated dissociative chemisorption of three isotopes of propane (C
3
H
8
, CH
3
,CD
2
CH
3
, and C
3
D
8
) has been investigated on the Pt(110)-(1 × 2) surface, and both the apparent activation energies and the preexponential factors of the surface reaction rate coefficients have been measured. In addition, the probabilities of primary and secondary C-H bond cleavage for alkane activation on a surface were evaluated. The activation energy for primary C-H bond cleavage was 425 calories per mole greater than that of secondary C-H bond cleavage, and the two true activation energies that embody the single measured activation energy were determined for each of the three isotopes. Secondary C-H bond cleavage is also preferred on entropic grounds, and the magnitude of the effect was quantified.
Modified Phases of Diamond Formed Under Shock Compression and Rapid Quenching
Authors: Hirai Hisako , Kondo Ken-Ichi
Published: October 2006

Two modified forms of carbon were quenched by a rapid-cooling technique from graphite sheets shock-compressed to 65 gigapascals and 3700 K. One form, "n-diamond," which was obtained from the most rapidly cooled part, has a crystal structure close to that of cubic diamond. The other form, found in the relatively slow-cooled part, was comparable to an i-carbon prepared by an ion-beam technique. The n-diamond is interpreted as a metastable form, the same as hexagonal diamond, converted from graphite through a martensitic transition, for which either the region or the path may be different from that of hexagonal diamond. The second form was found to be produced through reconstruction.
Laser Manipulation of Atoms and Particles
Authors: Chu Steven
Published: October 2006

A variety of powerful techniques to control the position and velocity of neutral particles has been developed. As examples of this new ability, lasers have been used to construct a variety of traps, to cool atoms to temperatures below 3 × 10-6kelvin, and to create atomic fountains that may give us a hundredfold increase in the accuracy of atomic clocks. Bacteria can be held with laser traps while they are being viewed in an optical microscope, and organelles within a cell can be manipulated without puncturing the cell wall. Single molecules of DNA can now be stretched out and pinned down in a water solution with optical traps. These new capabilities may soon be applied to a wide variety of scientific questions as diverse as precision measurements of fundamental symmetries in physics and the study of biochemistry on a single molecule basis.
Global Text Matching for Information Retrieval
Authors: Salton Gerard , Buckley Chris
Published: October 2006

An approach is outlined for the retrieval of natural language texts in response to available search requests and for the recognition of content similarities between text excerpts. The proposed retrieval process is based on flexible text matching procedures carried out in a number of different text environments and is applicable to large text collections covering unrestricted subject matter. For unrestricted text environments this system appears to outperform other currently available methods.
Chemistry With A Thousand Faces
Authors: Amato Ivan
Published: October 2006

Like a species that has moved into open niches, evolved, and diversified, chemistry can no longer be seen as a discrete scientific field. Its methods, concepts, and practitioners are penetrating virtually every nook and cranny of science and technology. That message came through clearly 2 weeks ago in New York City at the Fourth Chemical Congress of North America—a week-long conference organized by the American Chemical Society, the Chemical Institute of Canada, and the Chemical Society of Mexico and attended by some 10,000 scientists, engineers, and entrepreneurs. In roughly 4200 papers, participants explored such topics as borrowing from nature to improve industrial processes and electronic devices, and controlling the molecular architecture of clays and polymers.
Structural Control of Flank Volcanism in Continental Rifts
Authors: Ellis Michael , King Geoffrey
Published: October 2006

Many volcanoes emerge from the flank (footwall) of normal faults in continental rift zones. Because such locations are commonly topographically high and exhibit minor compressional structures, the association is enigmatic. A simple flexing plate model shows that deformation of a flexurally supported upper crust during normal faulting generates a dilational strain field in the footwall at the base of the crust. This strain field allows cracking and tapping of preexisting melt.
Electronic Correlation Effects and Superconductivity in Doped Fullerenes
Authors: Chakravarty Sudip , Gelfand Martin P. , Kivelson Steven
Published: October 2006

A theory of the electronic properties of doped fullerenes is proposed in which electronic correlation effects within single fullerene molecules play a central role, and qualitative predictions are made which, if verified, would support this hypothesis. Depending on the effective intrafulllerene electron-electron repulsion and the interfullerene hopping amplitudes (which should depend on the dopant species, among other things), the calculations indicate the possibilities of singlet superconductivity and ferromagnetism.
Viviparous Leaves Produced by Somatic Activation of an Inactive Cytokinin-Synthesizing Gene
Authors: Estruch Juan Josè , Prinsen Els , Van Onckelen Harry , Schell Jeff , Spena Angelo
Published: October 2006

Tobacco plants that are somatic mosaics for expression of a cytokinin-synthesizing gene have viviparous leaves. Such a formation of shoots in an abnormal position represents a significant deviation from the usual organization of the plant body where a central axis produces shoots only in the axils of lateral leaf appendages and according to a precise phyllotactic pattern. This report links vivipary to the expression of a gene whose product is involved in the synthesis of the phytohormone cytokinin.
Regulation of Lymphokine Messenger RNA Stability by a Surface-Mediated T Cell Activation Pathway
Authors: Lindstein Tullia , June Carl H. , Ledbetter Jeffrey A. , Stella Gregory , Thompson Craig B.
Published: October 2006

Quiescent T cells can be induced to express many genes by mitogen or antigen stimulation. The messenger RNAs of some of these genes undergo relatively rapid degradation compared to messenger RNAs from constitutively expressed genes. A T cell activation pathway that specifically regulates the stability of messenger RNAs for the lymphokines interleukin-2, interferon-γ, tumor necrosis factor-α, and granulocyte-macrophage colony-stimulating factor is induced by stimulation of the CD28 surface molecule. This pathway does not directly affect the steady-state messenger RNA level, transcription, or messenger RNA half-life of other T cell activation genes, including c-
myc
, c-
fos
, IL-2 receptor, and the 4F2HC surface antigen. These data show that stimuli received at the cell surface can alter gene expression by inducing specific changes in messenger RNA degradation.
Identification by ENDOR of Trp
191
as the Free-Radical Site in Cytochrome c Peroxidase Compound ES
Authors: Sivaraja Mohanram , Goodin David B. , Smith Michael , Hoffman Brian M.
Published: October 2006

The chemical identity of the amino acid free-radical site that represents one of the two oxidizing equivalents stored in the H
2
O
2
-oxidized intermediate (compound ES) of the mitochondrial heme enzyme, cytochrome c peroxidase (CcP) has been sought for almost a quarter of a century. Site-directed mutagenesis alone cannot yield this answer. Low-temperature 35-gigahertz (Q-band) electron nuclear double resonance (ENDOR) spectroscopy was used to examine compound ES prepared from proteins containing specifically deuterated methionine or tryptophan, as well as the amino acid replacement Trp
51
→ Phe. The results definitely identify the site of the radical in compound ES as tryptophan, most likely Trp
191
.
Large Quasi-Circular Features Beneath Frost on Triton
Authors: Helfenstein Paul , Veverka Joseph , McCarthy Derek , Lee Pascal , Hillier John
Published: October 2006

Specially processed Voyager 2 images of Neptune's largest moon, Triton, reveal three large quasi-circular features ranging in diameter from 280 to 935 kilometers within Triton's equatorial region. The largest of these features contains a central, irregularly shaped area of comparatively low albedo about 380 kilometers in diameter, surrounded by crudely concentric annuli of higher albedo materials. None of the features exhibit significant topographic expression, and all appear to be primarily albedo markings. The features are located within a broad equatorial band of anomalously transparent frost that renders them nearly invisible at the large phase angles (α > 90°) at which Voyager obtained its highest resolution coverage of Triton. The features can be discerned at smaller phase angles (α = 66°) at which the frost only partially masks underlying albedo contrasts. The origin of the features is uncertain but may have involved regional cryovolcanic activity.
Ti
8
C
12
+
-Metallo-Carbohedrenes: A New Class of Molecular Clusters?
Authors: Guo B. C. , Kerns K. P. , Castleman A. W.
Published: October 2006

During the course of studying the dehydrogenation reactions of hydrocarbons by titanium atoms, ions, and clusters, an exceptionally stable and abundant cluster which contains 8 titaniums and 12 carbons was discovered. "Titration" reactions with ND
3
reveal the uptake of eight molecules, pointing to the fact that the titanium atoms are at exposed positions of similar coordination. A dodecahedral structure of

T
h

point group symmetry is proposed to account for the unusual stability of this molecular cluster. The Ti
8
C
12
+
dodecahedron has 12 pentagonal rings and each of the rings is formed by two titanium and three carbon atoms, where each titanium is bound to three carbons. Based on the model, it is expected that neutral Ti
8
C
12
would be a stable metallo-carbododecahedral molecule and may comprise one member of a new class of molecules, namely metallo-carbohedrenes.
A Mass Transfer Explanation of Metabolic Scaling Relations in Some Aquatic Invertebrates and Algae
Authors: Patterson Mark R.
Published: October 2006

Chemical engineering theory can be used in accounting for the broad range of metabolic scaling exponents found in some aquatic invertebrates and algae. Delivery of metabolically important compounds to these organisms occurs by diffusion through a boundary layer. Dimensionless relations (Sherwood-Reynolds number functions) demonstrate the degree to which water motion and organism size affect mass transfer, and ultimately, metabolic rate. Derivation of mass exponents in the range 0.31 to 1.00 for simple geometries such as plates, spheres, and cylinders directly follows from knowledge of the Sherwood-Reynolds number relations. The range of exponents predicted is that found by allometric studies of metabolic rate in these organisms.
The Breakup of a Meteorite Parent Body and the Delivery of Meteorites to Earth
Authors: Benoit Paul H. , Sears D. W. G.
Published: October 2006

Whether many of the 10,000 meteorites collected in the Antarctic are unlike those failing elsewhere is contentious. The Antarctic H chondrites, one of the major classes of stony meteorites, include a number of individuals with higher induced thermoluminescence peak temperatures than observed among non-Antarctic H chondrites. The proportion of such individuals decreases with the mean terrestrial age of the meteorites at the various ice fields. These H chondrites have cosmic-ray exposure ages of about 8 million years, experienced little cosmic-ray shielding, and suffered rapid postmetamorphic cooling. Breakup of the H chondrite parent body, 8 million years ago, may have produced two types of material with different size distributions and thermal histories. The smaller objects reached Earth more rapidly through more rapid orbital evolution.
Response of Regional Seismicity to the Static Stress Change Produced by the Loma Prieta Earthquake
Authors: Reasenberg Paul A. , Simpson Robert W.
Published: October 2006

The 1989 Loma Prieta, California, earthquake perturbed the static stress field over a large area of central California. The pattern of stress changes on major faults in the region predicted by models of the earthquake's dislocation agrees closely with changes in the regional seismicity rate after the earthquake. The agreement is best for models with low values of the coefficient of friction (0.1 ≤ μ ≤ 0.3) on Bay Area faults. Both the stress models and measurements suggest that stresses were increased on the San Andreas fault north of the Loma Prieta rupture, but decreased slightly on the Hayward fault. This relaxation does not warrant lower probability estimates for large earthquakes on the Hayward fault in the next 30 years, however.
DNA Topoisomerase I—Targeted Chemotherapy of Human Colon Cancer in Xenografts
Authors: Giovanella Beppino C. , Stehlin John S. , Wall Monroe E. , Wani Mansukh C. , Nicholas Allan W. , Liu Leroy F. , Silber Robert , Potmesil Milan
Published: October 2006

Drug development is needed to improve chemotherapy of patients with locally advanced or metastatic colon carcinoma, who otherwise have an unfavorable prognosis. DNA topoisomerase I, a nuclear enzyme important for solving topological problems arising during DNA replication and for other cellular functions, has been identified as a principal target of a plant alkaloid 20(
S
)-camptothecin. Significantly increased concentrations of this enzyme, compared to that in normal colonic mucosa, were found in advanced stages of human colon adenocarcinoma and in xenografts of colon cancer carried by immunodeficient mice. Several synthetic analogs of camptothecin, selected by tests with the purified enzyme and tissue-culture screens, were evaluated in the xenograft model. Unlike other anticancer drugs tested, 20(
RS
)-9-amino-camptothecin (9-AC) induced disease-free remissions. The overall drug toxicity was low and allowed for repeated courses of treatment.
Molecular Cloning of the Thyrotropin Receptor
Authors: Parmentier Marc , Libert Frederick , Maenhaut Carine , Lefort Anne , Gérard Catherine , Perret Jason , Van Sande Jacqueline , Dumont Jacques E. , Vassart Gilbert
Published: October 2006

The pituitary hormone thyrotropin, or thyroid-stimulating hormone (TSH), is the main physiological agent that regulates the thyroid gland. The thyrotropin receptor (TSHR) was cloned by selective amplification with the polymerase chain reaction of DNA segments presenting sequence similarity with genes for G protein-coupled receptors. Out of 11 new putative receptor clones obtained from genomic DNA, one had sequence characteristics different from all the others. Although this clone did not hybridize to thyroid transcripts, screening of a dog thyroid complementary DNA (cDNA) library at moderate stringency identified a cDNA encoding a 4.9-kilobase thyroid-specific transcript. The polypeptide encoded by this thyroid-specific transcript consisted of a 398-amino acid residue amino-terminal segment, constituting a putative extracellular domain, connected to a 346-residue carboxyl-terminal domain that contained seven putative transmembrane segments. Expression of the cDNA conferred TSH responsiveness to
Xenopus
oocytes and Y1 cells and a TSH binding phenotype to COS cells. The TSHR and the receptor for luteinizing hormone-choriogonadotropin constitute a subfamily of G protein-coupled receptors with distinct sequence characteristics.
Oceanic Uptake of Fossil Fuel CO
2
: Carbon-13 Evidence
Authors: Quay P. D. , Tilbrook B. , Wong C. S.
Published: October 2006

The δ
13
C value of the dissolved inorganic carbon in the surface waters of the Pacific Ocean has decreased by about 0.4 per mil between 1970 and 1990. This decrease has resulted from the uptake of atmospheric CO
2
derived from fossil fuel combustion and deforestation. The net amounts of CO
2
taken up by the oceans and released from the biosphere between 1970 and 1990 have been determined from the changes in three measured values: the concentration of atmospheric CO
2
, the δ
13
C of atmospheric CO
2
and the δ
13
C value of dissolved inorganic carbon in the ocean. The calculated average net oceanic CO
2
uptake is 2.1 gigatons of carbon per year. This amount implies that the ocean is the dominant net sink for anthropogenically produced CO
2
and that there has been no significant net CO
2
released from the biosphere during the last 20 years.
An SCF Solvation Model for the Hydrophobic Effect and Absolute Free Energies of Aqueous Solvation
Authors: Cramer Christopher J. , Truhlar Donald G.
Published: October 2006

A model for absolute free energies of solvation of organic, small inorganic, and biological molecules in aqueous solution is described. This model has the following features: (i) the solute charge distribution is described by distributed monopoles, and solute screening of dielectric polarization is treated with no restrictions on solute shape; (ii) the energetic effects of cavity formation, dispersion interactions, and solute-induced restructuring of water are included by a semiempirical cavity surface tension; and (iii) both of these effects are included in the solute Hamiltonian operator for self-consistent field (SCF) calculations to allow solvent-induced electronic and geometric distortion of the solute. The model is parameterized for solutes composed of H, C, N, O, F, P, S, Cl, Br, and I against experimental data for 150 neutral solutes and 28 ions, with mean absolute errors of 0.7 and 2.6 kilocalories per mole, respectively.
Geothermal Evidence from Canada for a Cold Period Before Recent Climatic Warming
Authors: Wang Kelin , Lewis Trevor J.
Published: October 2006

Three deep boreholes in a small area in Quebec, each having two high-accuracy temperature logs separated by 22 years, allow reliable determination of the ground surface temperature history during the past few centuries. The temperature logs show that the recent climatic warming was preceded by a cold period near the end of the 19th century in this area. The presence of such a cold period is also suggested by borehole temperature data from other areas in Canada.
Order and Low Dimensionality in the Organic Superconductor (BEDT-TTF)
2
Cu(NCS)
2
Revealed by STM
Authors: Fainchtein R. , D'Arcangelis S. T. , Yang S. S. , Cowan D. O.
Published: October 2006

Single-crystal samples of [(BEDT-TTF)
2
]
+
[Cu(NCS)
2
]
-
were synthesized and studied with a scanning tunneling microscope (STM). Real-space images of the anion and cation surfaces with molecular resolution were obtained. The images show no evidence of structural disorder or stacking faults previously suggested. The presence of an additional modulation commensurate with the lattice provides evidence of a lattice distortion. The cause of this modulation is unknown. The presence of a charge density wave in the material would have implications on the dimensionality of the material that may explain the peculiar temperature dependence of the electrical conductivity. This interpretation is consistent with the calculated Fermi surface, which allows nesting of the wave vector.
The Oxidizing Capacity of the Earth's Atmosphere: Probable Past and Future Changes
Authors: Thompson Anne M.
Published: October 2006

The principal oxidants in the lower atmosphere are ozone (O
3
) and two by-products of O
3
photodissociation, the hydroxyl radical (OH) and hydrogen peroxide (H
2
O
2
). A number of critical atmospheric chemical problems depend on the earth's "oxidizing capacity," which is essentially the global burden of these oxidants. There is limited direct evidence for changes in the earth's oxidizing capacity since recent preindustrial times when, because of industrial and population growth, increasing amounts of O
3
precursor trace gases (carbon monoxide, nitrogen oxides, and hydrocarbons) have been released into the atmosphere. The concentrations of O
3
and possibly H
2
O
2
have increased over large regions. Models predict that tropospheric O
3
will increase ∼0.3 to 1% per year over the next 50 years with both positive and negative trends possible for OH and H
2
O
2
. Models and the observational network for oxidants are improving, but validation of global models is still at an early stage.
Scandium Clusters in Fullerene Cages
Authors: Yannoni Costantino S. , Hoinkis Mark , de Vries Mattanjah S. , Bethune Donald S. , Salem Jesse R. , Crowder Mark S. , Johnson Robert D.
Published: October 2006

The production and spectroscopic characterization of fullerene-encapsulated metal-atom clusters is reported. In particular, both solution and solid-state electron paramagnetic resonance (EPR) spectra of Sc
3
C
82
have been obtained. ScC
82
also gives an EPR spectrum, but Sc
2
C

n

species—the most abundant metallofullerenes in the mass spectrum—are EPR-silent even though Sc
2
is EPR-active in a rare-gas matrix at 4.2 K. The results suggest that the three scandium atoms in Sc
3
C
82
form an equilateral triangle—as was previously suggested for Sc
3
molecules isolated in a cryogenic rare-gas matrix. The spectrum of ScC
82
has features similar to those found earlier for LaC
82
and YC
82
, suggesting that it can also be described as a +3 metal cation within a -3 fullerene radical anion. An implication of this work is that production of macroscopic quantities of cluster-containing fullerenes may make possible the fabrication of exotic new structures with regular arrays of metal-atom clusters isolated in fullerene molecules, resulting in a new type of host/guest nanostructured material.
The Discovery of Quarks
Authors: Riordan Michael
Published: October 2006

Quarks are widely recognized today as being among the elementary particles of which matter is composed. The key evidence for their existence came from a series of inelastic electron-nucleon scattering experiments conducted between 1967 and 1973 at the Stanford Linear Accelerator Center. Other theoretical and experimental advances of the 1970s confirmed this discovery, leading to the present standard model of elementary particle physics.
Melting in Semiconductor Nanocrystals
Authors: Goldstein A. N. , Echer C. M. , Alivisatos A. P.
Published: October 2006

New physics occurs in semiconductors when one or more dimensions of the crystal are reduced to a size comparable to bulk electron delocalization lengths (tens to hundreds of angstroms). The properties of "quantum dots" or semiconductor nanocrystals are now being studied, as techniques to fabricate the crystallites are developed. Temperature-dependent electron diffraction studies on nanocrystals of CdS show a large depression in the melting temperature with decreasing size, as a larger fraction of the total number of atoms is on the surface. Thermal stability may play a role in determining the uses of semiconductor nanocrystals.
Observation of Transition-State Vibrational Thresholds in the Rate of Dissociation of Ketene
Authors: Lovejoy Edward R. , Kim Sang Kyu , Moore C. Bradley
Published: October 2006

Rate constants for the dissociation of highly vibrationally excited ketene (CH
2
CO) have been measured at the threshold for the production of CH
2
(
3
B
1
) and CO(
1
σ
+
). The rate constant increases in a stepwise manner with increasing energy, consistent with the long-standing premise that the rate of a unimolecular reaction is controlled by flux through quantized transition-state thresholds. The data give the energies of the torsional and C-C-O bending vibrations of the transition state.
The Tropical Timber Trade and Sustainable Development
Authors: Vincent Jeffrey R.
Published: October 2006

The tropical timber trade appears to have promoted neither sustained forest management nor sustained forest-based industrialization. The boom-and-bust export pattern is often blamed on demand by developed countries, high import barriers, and low international wood prices. In fact, it is rooted in tropical countries' own policies related to timber concessions and wood-processing industries. These policies suppress timber scarcity signals and must be revised if the trade is to promote sustained economic growth. Even if this is done, the trade may not promote sustained-yield forestry in individual countries.
Scanning Tunneling Spectroscopic Evidence for Granular Metallic Conductivity in Conducting Polymeric Polyaniline
Authors: Jeon D. , Kim J. , Gallagher M. C. , Willis R. F.
Published: October 2006

Scanning tunneling microscopy (STM) and point-probe electrical conductivity measurements of electrochemically protonated films of the emeraldine-base form of the conducting polymer, polyaniline are reported. The conductivity varies spatially, dependent on the size (
L
M
≈ 200 to 300 angstroms) of granular metallic regions which relate directly to the inhomogeneous micromorphology of the electrodeposited films. The normalized conductivity at zero bias is observed to increase with doping, indicating an increase in states at the Fermi level. The STM electronic measurements also show regions of negative differential resistance. Negative differential resistance is observed for all samples, although more frequently on less oxidized samples.
Triple Helix-Specific Ligands
Authors: Mergny J. L. , Duval-Valentin G. , Nguyen C. H. , Perrouault L. , Faucon B. , Rougée M. , Montenay-Garestier T. , Bisagni E. , Hélène C.
Published: October 2006

A triple helix is formed upon binding of an oligodeoxynucleotide to the major groove of duplex DNA. A benzo[
e
]pyridoindole derivative (BePI) strongly stabilized this structure and showed preferential binding to a triplex rather than to a duplex. Energy transfer experiments suggest that BePI intercalates within the triple helix. Sequence-specific inhibition of transcription initiation of a specific gene by
Escherichia coli
RNA polymerase by a triplex-forming oligodeoxynucleotide is strongly enhanced when the triplex is stabilized by BePI. Upon irradiation with ultraviolet light, BePI induces covalent modifications of the target within the triple helix structure.
Picosecond Optical Switching Based on Biphotonic Excitation of an Electron Donor-Acceptor-Donor Molecule
Authors: O'Neil Michael P. , Niemczyk Mark P. , Svec Walter A. , Gosztola David , Gaines George L. , Wasielewski Michael R.
Published: October 2006

An electron donor-acceptor-donor molecule consisting of two porphyrin donors rigidly attached to the two-electron acceptor
N,N
′-diphenyl-3,4,9,10-perylenebis(dicarboximide) acts as a light intensity—dependent molecular switch on a picosecond time scale. Excitation of the porphyrins within this molecule with subpicosecond laser pulses results in single or double reduction of the acceptor depending on the light intensity. The singly and doubly reduced electron acceptors absorb light strongly at 713 and 546 nanometers, respectively. Because these absorption changes are produced solely by electron transfers, this molecular switch effectively has no moving parts and switches significantly faster than photochromic molecules that must undergo changes in molecular structure.
Matrix-Mediated Synthesis of Nanocrystalline γ-Fe2O3: A New Optically Transparent Magnetic Material
Authors: Ziolo Ronald F. , Giannelis Emmanuel P. , Weinstein Bernard A. , O'Horo Michael P. , Ganguly Bishwanath N. , Mehrotra Vivek , Russell Michael W. , Huffman Donald R.
Published: October 2006

A new magnetic material with appreciable optical transmission in the visible region at room temperature has been isolated as a γ-Fe2O3/polymer nanocomposite. The synthesis is carried out in an ion-exchange resin at 60°C. Magnetization and susceptibility data demonstrate loading-dependent saturation moments as high as 46 electromagnetic units per gram and superparamagnetism for lower loadings where particle sizes are less than 100 angstroms. Optical absorption studies show that the small-particle form of γ-Fe2O3is considerably more transparent to visible light than the single-crystal form. The difference in absorption ranges from nearly an order of magnitude in the "red" spectral region to a factor of 3 at 5400 angstroms. The magnetization of the nanocomposite is greater by more than an order of magnitude than those of the strongest room-temperature transparent magnets, FeBO3and FeF3.
Phototaxis of Spiral Waves
Authors: Markus Mario , Nagy-Ungvarai Zsuzsanna , Hess Benno
Published: October 2006

The drift of spiral waves toward regions of higher light intensity was observed experimentally in the ruthenium-catalyzed Belousov-Zhabotinsky reaction. A light gradient can thus be used to manipulate optical information in new computational systems based on photochemical media. The drift of a gradient that is rotationally invariant in space is three to four times as fast as that of a translationally invariant gradient. Simulations based on the use of a cellular automaton, which is made isotropic by a semirandom distribution of cells, are in agreement with the experimental results.
High-Pressure Brillouin Studies and Elastic Properties of Single-Crystal H
2
S Grown in a Diamond Cell
Authors: Shimizu H. , Sasaki S.
Published: October 2006

High-pressure Brillouin spectra of crystalline hydrogen sulfide (H
2
S) have been measured at up to 7 gigapascals at room temperature. The best fit of the angular dependence of Brillouin acoustic velocities between experimental values and calculations based on Every's expression for elastic waves of an arbitrary direction yielded the orientation of an H
2
S cubic crystal grown in the diamond-anvil high-pressure cell. In situ determinations of sound velocities, as a function of pressure, could be made for any direction, the refractive index, the density, and the elastic constants. This method provides a means for the systematic study of elastic properties and phase transitions of condensed gases under ultrahigh pressures.
Chaos, Symmetry, and Self-Similarity: Exploiting Order and Disorder in Mixing Processes
Authors: Ottino J. M. , Muzzio F. J. , Tjahjadi M. , Franjione J. G. , Jana S. C. , Kusch H. A.
Published: October 2006

Fluid mixing is a successful application of chaos. Theory anticipates the coexistence of order and disorder—symmetry and chaos—as well as self-similarity and multifractality arising from repeated stretching and folding. Experiments and computations, in turn, provide a point of confluence and a visual analog for chaotic behavior, multiplicative processes, and scaling behavior. All these concepts have conceptual engineering counterparts: examples arise in the context of flow classification, design of mixing devices, enhancement of transport processes, and controlled structure formation in two-phase systems.
Manipulation of the Wettability of Surfaces on the 0.1- to 1 -Micrometer Scale Through Micromachining and Molecular Self-Assembly
Authors: Abbott Nicholas L. , Folkers John P. , Whitesides George M.
Published: October 2006

Micromachining allows the formation of micrometer-sized regions of bare gold on the surface of a gold film supporting a self-assembled monolayer (SAM) of alkanethiolate. A second SAM forms on the micromachined surfaces when the entire system—the remaining undisturbed gold-supported SAM and the micromachined features of bare gold—is exposed to a solution of dialkyl disulfide. By preparing an initial hydrophilic SAM from HS(CH
2
)
15
COOH, micromachining features into this SAM, and covering these features with a hydrophobic SAM formed from [CH
3
(CH
2
)
11
S]
2
, it is possible to construct micrometer-scale hydrophobic lines in a hydrophilic surface. These lines provide new structures with which to manipulate the shapes of liquid drops.
Hubble Space Telescope Imaging of the North Polar Aurora on Jupiter
Authors: Caldwell J. , Turgeon B. , Hua X. -M.
Published: October 2006

The first direct images of the Jovian aurora at ultraviolet wavelengths were obtained by the Hubble Space Telescope Faint Object Camera near the time of the Ulysses spacecraft encounter with Jupiter on 8 February 1992. The auroral oval is not uniformly luminous. It exhibits a brightness minimum in the vicinity of longitude 180°. In the few images available, the brightest part of the oval occurs in late afternoon Jovian time. The observed oval is not concentric with calculated ovals in the O
6
model of Connerney. The size of the oval is consistent with auroral particles on field lines with magnetic
L
parameter >8, indicating significant migration from Io, its torus, or both, if these are their origins.
Ring Currents in Icosahedral C
60
Authors: Pasquarello Alfredo , Schlüter Michael , Haddon R. C.
Published: October 2006

A new formulation of the current within the London approximation allows the calculation of ring currents in topologically complex molecules. Application of this theory to C
60
demonstrates the existence of remarkable π electron ring currents. Paramagnetic currents, in size comparable to the ones in benzene, flow within the pentagons, whereas weaker diamagnetic currents flow all around the C.
60
molecule. The overall vanishing ring-current magnetic susceptibility results from a cancellation of diamagnetic and paramagnetic contributions. The presence of ring currents significantly affects chemical shifts as measured in nuclear magnetic resonance experiments. In contrast to the magnetic susceptibility, which is a property of the molecule as a whole, chemical shifts are sensitive to the local magnetic field and the effect of ring currents does not vanish.
Sensitivity of Glaciers and Small Ice Caps to Greenhouse Warming
Authors: Oerlemans J. , Fortuin J. P. F.
Published: October 2006

Recent field programs on glaciers have supplied information that makes simulation of glacier mass balance with meteorological models meaningful. An estimate of world-wide glacier sensitivity based on a modeling study of 12 selected glaciers situated in widely differing climatic regimes shows that for a uniform 1 K warming the area-weighted glacier mass balance will decrease by 0.40 meter per year. This corresponds to a sea-level rise of 0.58 millimeter per year, a value significantly less than earlier estimates.
The Seismic Attenuation Structure of a Fast-Spreading Mid-Ocean Ridge
Authors: Wilcock William S. D. , Solomon Sean C. , Purdy G. M. , Toomey Douglas R.
Published: October 2006

The two-dimensional P-wave attenuation structure of the axial crust of the East Pacific Rise was obtained from an inversion of waveform spectra collected during an active-source seismic tomography experiment. The structure shows that attenuation near the surface is high everywhere but decreases markedly within 1 to 3 kilometers of the rise axis. The near-axis variation is attributed to the thickening of the surface basalt layer and possibly to in situ changes in porosity related to hydrothermal circulation. High attenuation is also observed beneath the rise axis at depths ranging from about 2 kilometers (less than 1 kilometer beneath the axial magma lens) to the base of the crust. The levels of attenuation in this deeper region require at most only a small fraction of partial melt.
Open Framework Structures Based on Se

x

2–
Fragments: Synthesis of (Ph
4
P)[M(Se
6
)
2
] (M = Ga, In, TI) in Molten (Ph
4
P)
2
Se

x
Authors: Dhingra Sandeep , Kanatzidis Mercouri G.
Published: October 2006

Polychalcogenide compounds with open polymeric frameworks are rare, and they represent a class of compounds in which microporosity might be achieved. Microporous frameworks that are not oxide-based are now attracting interest because of the combination of catalytic and electronic properties they may simultaneously possess. Three new compounds that may be forerunners to such materials have been discovered and are reported here. The reaction of gallium (Ga), indium (In), and thallium (TI) metal with (Ph
4
P)
2
Se
5
(Ph, phenyl) and an excess of elemental selenium (Se) in a sealed, evacuated Pyrex tube at 200°C yielded small red crystals of (Ph
4
P)[Ga(Se
6
)
2
] (I), (Ph
4
P)[In(Se
6
)
2
] (II), and (Ph
4
P)[TI(Se
6
)
2
] (III), respectively. The [M(Se
6
)
2
]
–
(M = Ga, In, TI) ions form a two-dimensional, open framework filled with Ph
4
P
+
ions. The [M(Se
6
)
2
]

n

n
–

structure consists of tetrahedral M
3+
centers and bridging Se
6
2–
ligands, leading to an extended structure in two dimensions. These layers stack perfectly one on top of the other giving rise to one-dimensional channels running down the
c
axis that are filled with Ph
4
P
+
cations. These cations are situated in the layers, as opposed to between the layers, and the whole structure can be viewed as a template. Compound II shows remarkable thermal stability and melts congruently at 242°C. Upon cooling to room temperature it gives a glassy phase that recrystallizes upon subsequent heating to 160°C.
Expression of the Chlamydial Genus-Specific Lipopolysaccharide Epitope in
Escherichia coli
Authors: Nano Francis E. , Caldwell Harlan D.
Published: October 2006

The obligate intracellular prokaryote
Chlamydia trachomatis
is the etiological agent of trachoma and is a primary causative pathogen of sexually transmitted genital tract disease; both diseases affect millions of people each year. The cloning of genes encoding the enzyme or enzymes producing the genus-specific lipopolysaccharide antigen of
Chlamydia
into
Escherichia coli
is reported here. The cloned chlamydial lipopolysaccharide antigen appears to be a hybrid lipopolysaccharide molecule composed of both
Chlamydia
and
Escherichia coli
components. The chlamydial lipopolysaccharide antigen is expressed on the surfaces of the viable
Escherichia coli
recombinants. These findings may have a significant impact on defining the role of this highly conserved antigen in the pathogenesis and diagnosis of chlamydial infections.
Failure of T Cell Receptor V
β
Negative Selection in an Athymic Environment
Authors: Hodes Richard J. , Sharrow Susan O. , Solomon Adam
Published: October 2006

The mature T cell receptor (TCR) repertoire is the result of selection events during T cell development. Previous assessment of TCR β-chain selection with serologic and molecular probes demonstrated both positive and negative selection. Although this work suggested a critical role for the thymus, no direct assessment has been made of the requirement for a thymus in TCR V
β
selection. A comparison of TCR V
β
expression in four different congenic pairs of normal and nu/nu (athymic) mice indicated that the normal V
β
deletions associated with tolerance to self minor lymphocyte stimulating (Mls
c
) antigens or to self major histocompatibility complex (MHC)-encoded E
α
E
β
products did not occur in most athymic mice. Thus, the thymus has a critical role in mediating self tolerance by negative selection.
Atmospheric Lifetimes of Long-Lived Halogenated Species
Authors: Ravishankara A. R. , Solomon S. , Turnipseed A. A. , Warren R. F.
Published: October 2006

The atmospheric lifetimes of the fluorinated gases CF
4
, C
2
F
6
, c-C
4
F
8
, (CF
3
)
2
c-C
4
F
6
, C
5
F
12
, C
6
F
14
, C
2
F
5
Cl, C
2
F
4
Cl
2
, CF
3
Cl, and SF
6
are of concern because of the effects that these long-lived compounds acting as greenhouse gases can have on global climate. The possible atmospheric loss processes of these gases were assessed by determining the rate coefficients for the reactions of these gases with O(
1
D
), H, and OH and the absorption cross sections at 121.6 nanometers in the laboratory and using these data as input to a two-dimensional atmospheric model. The lifetimes of all the studied perfluoro compounds are >2000 years, and those of CF
3
Cl, CF
3
CF
2
Cl, and CF
2
ClCF
2
Cl are >300 years. If released into the atmosphere, these molecules will accumulate and their effects will persist for centuries or millennia.
Domain Structures in Langmuir-Blodgett Films Investigated by Atomic Force Microscopy
Authors: Chi L. F. , Anders M. , Fuchs H. , Johnston R. R. , Ringsdorf H.
Published: October 2006

Investigations of phase-separated Langmuir-Blodgett films by atomic force microscopy reveal that on a scale of 30 to 200 micrometers, these images resemble those observed by fluorescence microscopy. Fine structures (less than 1 micrometer) within the stearic acid domains were observed, which cannot be seen by conventional optical microscopic techniques. By applying the force modulation technique, it was found that the elastic properties of the domains in the liquid condensed phase and grains observed within the liquid expanded phase were comparable. Small soft residues in the domains could also be detected. The influence of trace amounts of a fluorescence dye on the micromorphology of monolayers could be detected on transferred films.