bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic force microscope study of amorphous silicon and polysilicon low-pressure chemical-vapor-deposited implanted layers
Authors: Edrei R. , Shauly E. N. , Hoffman A.
Published: July 2002

The roughness of the poly/interpoly oxide interface plays a most important role in the performance of devices; it is expected that for a smoother interface, the double-polysilicon structure will present better electrical properties, such as higher breakdown voltage, and will be more reliable. To obtain the best electrical properties of the oxide layer, it is, therefore, essential to control the polysilicon morphological properties. The overall performances will be affected by the postdeposition process: implantation (dose, energy, and ion), oxidation (temperature, time, ambient), and preoxidation cleaning procedures. In this study, polysilicon and amorphous silicon films were produced under different controlled process conditions and were analyzed using atomic force microscopy (AFM). Significant differences in morphology between polysilicon and amorphous silicon films were obtained. Polysilicon roughness is an order of magnitude higher than amorphous silicon. Roughness of amorphous silicon films increased after rapid thermal annealing treatment performed after deposition. Phosphorus implantations at doses of 3×1015 cm−2 and energy of 40 keV affect the grain size. Implantation doses between 0.8×1015 and 2×1015 cm−2 and implantation energies between 40 and 100 keV do not affect the topography. The roughness of the amorphous silicon film increased as a result of the cleaning process, which involves growing an oxide layer and stripping it with hydrofluoric acid. Poor morphology information was gained from high resolution scanning electron microscopy imaging of these films. We conclude that AFM scanning can obtain quantitative and qualitative morphology information of amorphous and polysilicon layers deposited on silicon wafers.
Substrate transfer process for InP-based heterostructure barrier varactor devices
Authors: Arscott S. , Mounaix P. , Lippens D.
Published: July 2002

We report on transferred-substrate InP-based heterostructure barrier varactor (HBV) devices. Individual HBV devices having active device diameters ranging from 10 to 40 μm have been fabricated on a SiO2 glass host substrate following a novel epitaxial layer transfer technique. This process utilizes the negative photoresist SU-8 as a photopatternable intermediate bonding layer and could be extended to other InP-based devices. The transferred HBV device characteristics have been measured and compared to devices which have been fabricated on InP. The transferred devices exhibited highly symmetrical electrical characteristics due to the preservation of the high quality molecular beam epitaxy layers during the transfer process. A leakage current of 4.5 A/cm2 at 10 V together with an associated conductance value of 40 nS/μm2 were observed. The rf measurements revealed a zero bias capacitance of 1 fF/μm2 and a capacitance ratio of 5:1.
Real-time composition control using spectral ellipsometry in growth of Hg1−xCdxTe by molecular beam epitaxy
Authors: Aqariden F. , Shih H. D. , Liao P. K. , Duncan W. M. , Dat R.
Published: July 2002

Real-time composition control using spectral (or spectroscopic) ellipsometry (SE) in the growth of long-wavelength infrared (LWIR) Hg1−xCdxTe (x∼0.225) on Cd0.96Zn0.04Te(211) B by molecular beam epitaxy (MBE) was investigated. Excellent compositional reproducibility among the 10 LWIR Hg1−xCdxTe growth runs was demonstrated with the aid of SE, with the average composition being x=0.225 and the standard deviation in x being 0.000 42, the lowest figure that has ever been reported. The ability of MBE to switch from one composition to another on demand and with first pass success using SE is also demonstrated.
Characterization of in situ etched and molecular beam epitaxy regrown GaAs interfaces using capacitance–voltage measurements, far infrared spectroscopy, and magnetotransport measurements
Authors: Klein C. , Kramp S. , Beyer S. , Heyn Ch. , Hansen W. , Heitmann D.
Published: July 2002

In this study, we characterize GaAs interfaces processed by ion beam etching (IBE), chemical assisted ion beam etching (CAIBE), and chemical gas etching (CGE). The etched interfaces are overgrown with GaAs or AlGaAs using molecular beam epitaxy. Interfaces in Si-doped GaAs are characterized with capacitance–voltage (C–V) profiling. Furthermore, we use a two-dimensional electron gas (2DEG), located directly at the etched interface in modulation doped AlGaAs/GaAs heterostructures, to probe the interface quality with far infrared (FIR) transmission spectroscopy and magnetotransport measurements. Applying a CGE process with suitable parameters we can remove more than 100 nm GaAs and generate clean surfaces with 2DEGs similar to those of nonetched reference samples. In addition we can reduce the interface state density of an IBE or CAIBE etched surface significantly applying a subsequent CGE process, which removes the ion damaged layer. However the two-dimensional electron systems at such interfaces show characteristic FIR absorption of dot-like potentials, which is a clear sign of a contaminated or disturbed surface.
Super-flat interfaces in pseudomorphic In0.72Ga0.28As/In0.52Al0.48As quantum wells grown on (411)A InP substrates by molecular beam epitaxy
Authors: Aoki Toyohiro , Kitada Takahiro , Shimomura Satoshi , Hiyamizu Satoshi
Published: July 2002

We investigated flatness of heterointerfaces in pseudomorphic In0.72Ga0.28As/In0.52Al0.48As quantum wells (QWs) with well widths Lw of 1.3, 1.7, and 3.4 nm grown on (411)A InP substrates by molecular beam epitaxy (MBE). Full width at half maximum of a photoluminescence (12 K) peak from the (411)A QW with Lw=1.3 nm was as narrow as 20.7 meV, which is 28% smaller than that (28.9 meV) of the corresponding QW grown on a conventional (100) InP substrate. This result indicates that effectively atomically flat interfaces [(411)A super-flat interfaces] were successfully formed, for the first time, in pseudomorphic In0.72Ga0.28As/In0.52Al0.48As QWs grown on the (411)A InP substrate by MBE.
Molecular beam epitaxial growth of monolithic 1.55 μm vertical cavity surface emitting lasers with AlGaAsSb/AlAsSb Bragg mirrors
Authors: Almuneau G. , Hall E. , Nakagawa S. , Kim J. K. , Lofgreen D. , Sjölund O. , Luo C. , Clarke D. R. , English J. H. , Coldren L. A.
Published: July 2002

The molecular beam epitaxy and the characterization of single-step grown long wavelength vertical cavity surface emitting lasers (LW–VCSEL) are reported. The devices were fabricated using highly reflective AlGaAsSb/AlAsSb distributed Bragg reflectors (DBRs), and an AlGaInAs-based active region embedding a tunnel (or Esaki) junction. The VCSELs operate at 1.55 μm at room temperature with a threshold current density of 1.4 kA/cm2. Characterization of the VCSELs and DBRs’ thermal and electrical properties is presented. Major improvement on the voltage drop in an InGaAs capped DBR is demonstrated, resulting in a value as low as 40 mV/pair.
Modulation-doped ZnSe/(Zn,Cd,Mn)Se quantum wells and superlattices
Authors: Berry J. J. , Knobel R. , Ray O. , Peoples W. , Samarth N.
Published: July 2002

The fabrication of “magnetic” two-dimensional electron gases in modulation-doped ZnSe/Zn1−x−yCdxMnySe quantum wells and superlattices is described, with a focus on correlating growth conditions with low temperature transport, atomic force microscopy, and photoluminescence. Optimization of the growth parameters results in a two-fold increase in 0.3 K mobility (∼23 000 cm2/V s) for the host ZnCdSe two-dimensional electron gasses (2DEGs) and a similar relative increase for magnetic 2DEGs. The improved sample growth is applied to the fabrication of modulation doped, strained-layer magnetic superlattices containing up to 25 periods of moderately strained quantum wells, without significant reduction in mobility.
Phase stability during molecular beam epitaxial growth of CdTe on InSb(111) substrates
Authors: Huerta J. , López M. , Zelaya-Angel O.
Published: July 2002

A study of CdTe layers grown by molecular beam epitaxy on InSb(111)A (In terminated), and (111)B (Sb terminated) substrates is reported. The growth of CdTe on InSb(111) substrates was studied in situ by reflection high-energy electron diffraction, and characterized by atomic force microscopy, Raman spectroscopy, x-ray diffraction, and photoreflectance. We observed a markedly different CdTe growth behavior on InSb(111)A and B surfaces. CdTe grows nearly two dimensionally on the (111)B surface, whereas on the A surface a three-dimensional growth is obtained, resulting in polycrystalline regions with zinc-blende and wurtzite phases. Our results indicate that In–Te compounds are formed at the CdTe/InSb interface. The amount of these compounds is larger on the (111)A face, thus hindering the smooth CdTe growth on this face.
Beryllium-10 from the Sun
Authors: Nishiizumi K. , Caffee M. W.
Published: July 2002

Beryllium-10 (
10
Be) in excess of that expected from in situ cosmic ray spallation reactions is present in lunar surface soil 78481; its presence was revealed with a sequential leaching technique. This excess
10
Be, representing only 0.7 to 1.1% of the total
10
Be inventory, is associated with surface layers (<1 micrometer) of the mineral grains composing 78481. This excess
10
Be and its association with surficial layers corresponds to (1.9 ± 0.8) × 10
8
atoms per square centimeter, requiring a
10
Be implantation rate of (2.9 ± 1.2) × 10
−6
atoms per square centimeter per second on the surface of the Moon. The most likely site for the production of this excess
10
Be is the Sun's atmosphere. The
10
Be is entrained into the solar wind and transported to the lunar surface.
Imprinting and the Epigenetic Asymmetry Between Parental Genomes
Authors: Ferguson-Smith Anne C. , Surani M. Azim
Published: July 2002

Genomic imprinting confers a developmental asymmetry on the parental genomes, through epigenetic modifications in the germ line and embryo. These heritable modifications regulate the monoallelic activity of parental alleles resulting in their functional differences during development. Specific
cis
-acting regulatory elements associated with imprinted genes carry modifications involving chromatin structural changes and DNA methylation. Some of these modifications are initiated in the germ line. Comparative genomic analysis at imprinted domains is emerging as a powerful tool for the identification of conserved elements amenable to more detailed functional analysis, and for providing insight into the emergence of imprinting during the evolution of mammalian species. Genomic imprinting therefore provides a model system for the analysis of the epigenetic control of genome function.
Correction of Sickle Cell Disease in Transgenic Mouse Models by Gene Therapy
Authors: Pawliuk Robert , Westerman Karen A. , Fabry Mary E. , Payen Emmanuel , Tighe Robert , Bouhassira Eric E. , Acharya Seetharama A. , Ellis James , London Irving M. , Eaves Connie J. , Humphries R. Keith , Beuzard Yves , Nagel Ronald L. , Leboulch Philippe
Published: July 2002

Sickle cell disease (SCD) is caused by a single point mutation in the human β
A
globin gene that results in the formation of an abnormal hemoglobin [HbS (α
2
β
S
2
)]. We designed a β
A
globin gene variant that prevents HbS polymerization and introduced it into a lentiviral vector we optimized for transfer to hematopoietic stem cells and gene expression in the adult red blood cell lineage. Long-term expression (up to 10 months) was achieved, without preselection, in all transplanted mice with erythroid-specific accumulation of the antisickling protein in up to 52% of total hemoglobin and 99% of circulating red blood cells. In two mouse SCD models, Berkeley and SAD, inhibition of red blood cell dehydration and sickling was achieved with correction of hematological parameters, splenomegaly, and prevention of the characteristic urine concentration defect.
Role of the Hrp Pilus in Type III Protein Secretion in
Pseudomonas syringae
Authors: Jin Qiaoling , He Sheng-Yang
Published: July 2002

Bacterial surface appendages called pili and needle-like filaments are associated with protein and/or DNA transfer to recipient plant, human, or bacterial cells during pathogenesis or conjugation. Although it has long been suspected that pili function as a conduit for protein or DNA transfer, direct evidence has been lacking. The Hrp pilus of
Pseudomonas syringae
is assembled by the type III secretion system. We used an in situ immunogold labeling procedure to visualize the extrusion of an effector protein, AvrPto, from the tip of the Hrp pilus, providing direct evidence that a bacterial pilus can function as a conduit for protein delivery.
Conserved Structure for Single-Stranded Telomeric DNA Recognition
Authors: Mitton-Fry Rachel M. , Anderson Emily M. , Hughes Timothy R. , Lundblad Victoria , Wuttke Deborah S.
Published: July 2002

The essential Cdc13 protein in the yeast
Saccharomyces cerevisiae
is a single-stranded telomeric DNA binding protein required for chromosome end protection and telomere replication. Here we report the solution structure of the Cdc13 DNA binding domain in complex with telomeric DNA. The structure reveals the use of a single OB (oligonucleotide/oligosaccharide binding) fold augmented by an unusually large loop for DNA recognition. This OB fold is structurally similar to OB folds found in the ciliated protozoan telomere end-binding protein, although no sequence similarity is apparent between them. The common usage of an OB fold for telomeric DNA interaction demonstrates conservation of end-protection mechanisms among eukaryotes.
Merging Genomes with Geochemistry in Hydrothermal Ecosystems
Authors: Reysenbach Anna-Louise , Shock Everett
Published: July 2002

Thermophilic microbial inhabitants of active seafloor and continental hot springs populate the deepest branches of the universal phylogenetic tree, making hydrothermal ecosystems the most ancient continuously inhabited ecosystems on Earth. Geochemical consequences of hot water-rock interactions render these environments habitable and supply a diverse array of energy sources. Clues to the strategies for how life thrives in these dynamic ecosystems are beginning to be elucidated through a confluence of biogeochemistry, microbiology, ecology, molecular biology, and genomics. These efforts have the potential to reveal how ecosystems originate, the extent of the subsurface biosphere, and the driving forces of evolution.
Hunting for Animal Alternatives
Authors: Roush Wade
Published: July 2002

Scientists in product testing and research are trying to reduce the number of animal experiments performed, such as the Draize rabbit eye irritation test, but they face roadblocks ranging from regulatory sluggishness to the scientific value of a whole-animal response. Still, in recent years the number of animals used in research has dropped substantially, with a 35% drop in the United States in the past decade, and even more dramatic reductions in Europe.
Kap104p: A Karyopherin Involved in the Nuclear Transport of Messenger RNA Binding Proteins
Authors: Aitchison John D. , Blobel Günter , Rout Michael P.
Published: July 2002

A cytosolic yeast karyopherin, Kap104p, was isolated and shown to function in the nuclear import of a specific class of proteins. The protein bound directly to repeat-containing nucleoporins and to a cytosolic pool of two nuclear messenger RNA (mRNA) binding proteins, Nab2p and Nab4p. Depletion of Kap104p resulted in a rapid shift of Nab2p from the nucleus to the cytoplasm without affecting the localization of other nuclear proteins tested. This finding suggests that the major function of Kap104p lies in returning mRNA binding proteins to the nucleus after mRNA export.
Requirement of the
Manx
Gene for Expression of Chordate Features in a Tailless Ascidian Larva
Authors: Swalla Billie J. , Jeffery William R.
Published: July 2002

An evolutionary change in development was studied in two closely related ascidian species, one exhibiting a conventional tadpole larva and the other a modified tailless larva. Interspecific hybridization restores chordate features to the tailless larva. The zinc finger gene
Manx
is expressed in cells that generate chordate features in the tailed species but is down-regulated in the tailless species.
Manx
expression is restored in hybrid embryos. Antisense oligodeoxynucleotide treatment inhibited
Manx
expression and chordate features in hybrid embryos, which suggests that
Manx
is required for development of the chordate larval phenotype in ascidians.
Positive Selection of T Cells Induced by Viral Delivery of Neopeptides to the Thymus
Authors: Nakano Naoko , Rooke Ronald , Benoist Christophe , Mathis Diane
Published: July 2002

The relation between an antigenic peptide that can stimulate a mature T cell and the natural peptide that promoted selection of this cell in the thymus is still unknown. An experimental system was devised to address this issue in vivo—mice expressing neopeptides in thymic stromal cells after adenovirus-mediated delivery of invariant chain-peptide fusion proteins. In this system, selection of T cells capable of responding to a given antigenic peptide could be promoted by the peptide itself, by closely related analogs lacking agonist and antagonist activity, or by ostensibly unrelated peptides. However, the precise repertoire of T cells selected was dictated by the particular neopeptide expressed.
Controlling Cell Death
Authors: Golstein Pierre
Published: July 2002

Cells can die in two ways: in a disorderly, destructive process called necrosis or by programmed cell death (or apoptosis), an orderly series of biochemical events that neatly eliminate the cell. Four reports in this week's issue by Chinnaiyan (
1122
), Wu (
1126
), Yang (p. 1129), and Kluck (p. 1132) elucidate two critical steps in the biochemical cascade of programmed cell death. In his Perspective, Golstein describes how these demonstrations—that the
Caenorhabditis elegans
protein CED-4 directly contacts CED-3 and CED-9 and that Bcl-2 causes release of cytochrome c from mitochondria—advance our understanding of programmed cell death.
Topographically Induced Mixing Around a Shallow Seamount
Authors: Lueck Rolf G. , Mudge Todd D.
Published: July 2002

Measurements of the rate of dissipation of kinetic energy around a shallow seamount in the eastern North Pacific show that mixing there is 100 to 10,000 times as large as that far away from the seamount. If such values are typical of other seamounts, mixing across density surfaces in the ocean occurs mainly at their boundaries, and topographically induced mixing may help to explain the discrepancy between the observed intensity of mixing in the interior of the oceans and that required to satisfy models of ocean circulation.
Free-Marketing Science
Authors: Owens Larry
Published: July 2002

The Economic Laws of Scientific Research.
TERENCE KEALEY. St. Martin's, New York, 1997. xii, 382 pp. $75, ISBN 0-312-12847-9; paper, $19.95, ISBN 0-312-17306-7. Published in the UK by Macmillan. £47.50, ISBN 0-333-56045-0; paper, £16.99, ISBN 0-333-65755-1.
Contrasting Genetic Influence of
CCR2
and
CCR5
Variants on HIV-1 Infection and Disease Progression
Authors: Smith Michael W. , Dean Michael , Carrington Mary , Winkler Cheryl , Huttley Gavin A. , Lomb Deborah A. , Goedert James J. , O'Brien Thomas R. , Jacobson Lisa P. , Kaslow Richard , Buchbinder Susan , Vittinghoff Eric , Vlahov David , Hoots Keith , Hilgartner Margaret W. ,   Hemophilia Growth and Development Study (HGDS), Study Multicenter AIDS Cohort Study (MACS), Multicenter Hemophilia , O'Brien Stephen J.
Published: July 2002

The critical role of chemokine receptors (CCR5 and CXCR4) in human immunodeficiency virus–type 1 (HIV-1) infection and pathogenesis prompted a search for polymorphisms in other chemokine receptor genes that mediate HIV-1 disease progression. A mutation (
CCR2-64I
) within the first transmembrane region of the
CCR2
chemokine and HIV-1 receptor gene is described that occurred at an allele frequency of 10 to 15 percent among Caucasians and African Americans. Genetic association analysis of five acquired immunodeficiency syndrome (AIDS) cohorts (3003 patients) revealed that although
CCR2-64I
exerts no influence on the incidence of HIV-1 infection, HIV-1–infected individuals carrying the
CCR2
-
64I
allele progressed to AIDS 2 to 4 years later than individuals homozygous for the common allele. Because
CCR2-64I
occurs invariably on a
CCR5-+
–bearing chromosomal haplotype, the independent effects of
CCR5-Δ32
(which also delays AIDS onset) and
CCR2-64I
were determined. An estimated 38 to 45 percent of AIDS patients whose disease progresses rapidly (less than 3 years until onset of AIDS symptoms after HIV-1 exposure) can be attributed to their
CCR2-+/+
or
CCR5-+/+
genotype, whereas the survival of 28 to 29 percent of long-term survivors, who avoid AIDS for 16 years or more, can be explained by a mutant genotype for
CCR2
or
CCR5.
A Macrophage Invasion Mechanism of Pathogenic Mycobacteria
Authors: Schorey Jeffrey S. , Carroll Michael C. , Brown Eric J.
Published: July 2002

Tuberculosis is the leading cause of death due to an infectious organism, killing an estimated 3 million people annually.
Mycobacterium tuberculosis
, the causative agent of tuberculosis, and other pathogenic mycobacteria require entry into host macrophages to initiate infection. An invasion mechanism was defined that was shared among pathogenic mycobacteria including
M. tuberculosis
,
M. leprae
, and
M. avium
but not by nonpathogenic mycobacteria or nonmycobacterial intramacrophage pathogens. This pathway required the association of the complement cleavage product C2a with mycobacteria resulting in the formation of a C3 convertase. The mycobacteria-associated C2a cleaved C3, resulting in C3b opsonization of the mycobacteria and recognition by macrophages.
Inner Core Rotation Rate from Small-Scale Heterogeneity and Time-Varying Travel Times
Authors: Creager Kenneth C.
Published: July 2002

The time it takes seismic waves to propagate from South Atlantic earthquakes through the inner core to station COL in Alaska has decreased systematically over the past 30 years. Travel times from three earthquakes in 1991 to an array of 37 seismometers in Alaska suggest that lateral gradients in seismic wavespeeds are steep in this part of the inner core. This combination of observations can be explained by postulating that the inner core is rotating 0.2° to 0.3° per year faster than the mantle.
Spatial Pattern Formation in an Insect Host-Parasitoid System
Authors: Maron John L. , Harrison Susan
Published: July 2002

Spatial models in ecology predict that populations may form patchy distributions within continuous habitats, through strong predator-prey or host-parasitoid interactions combined with limited dispersal. Empirical support of these models is provided. Parasitoids emanating from a population outbreak of tussock moths (
Orgyia vetusta
) suppressed the growth of nearby experimental populations of the moth, while experimental populations farther away were able to grow. This result explains the observed localized nature of tussock moth outbreaks and illustrates how population distributions can be regulated by dynamic spatial processes.
Role of Cue1p in Ubiquitination and Degradation at the ER Surface
Authors: Biederer Thomas , Volkwein Corinna , Sommer Thomas
Published: July 2002

Endoplasmic reticulum (ER) degradation of aberrant proteins is mediated by the ubiquitin-proteasome pathway. Here, a membrane-bound component of the ubiquitin system, Cue1p, was identified. It was shown to recruit the soluble ubiquitin-conjugating enzyme Ubc7p to the ER membrane. In the absence of Cue1p, unassembled and thus cytosolically mislocalized Ubc7p was unable to participate in ER degradation or in the turnover of soluble non-ER proteins. Moreover, ubiquitination by Cue1p-assembled Ubc7p and Ubc6p was a prerequisite for retrograde transport of lumenal substrates out of the ER, which suggests that ubiquitination is mechanistically integrated into the ER degradation process.
Immune Versus Natural Selection: Antibody Aldolases with Enzymic Rates But Broader Scope
Authors: Barbas Carlos F. , Heine Andreas , Zhong Guofu , Hoffmann Torsten , Gramatikova Svetlana , Björnestedt Robert , List Benjamin , Anderson James , Stura Enrico A. , Wilson Ian A. , Lerner Richard A.
Published: July 2002

Structural and mechanistic studies show that when the selection criteria of the immune system are changed, catalytic antibodies that have the efficiency of natural enzymes evolve, but the catalytic antibodies are much more accepting of a wide range of substrates. The catalytic antibodies were prepared by reactive immunization, a process whereby the selection criteria of the immune system are changed from simple binding to chemical reactivity. This process yielded aldolase catalytic antibodies that approximated the rate acceleration of the natural enzyme used in glycolysis. Unlike the natural enzyme, however, the antibody aldolases catalyzed a variety of aldol reactions and decarboxylations. The crystal structure of one of these antibodies identified the reactive lysine residue that was selected in the immunization process. This lysine is deeply buried in a hydrophobic pocket at the base of the binding site, thereby accounting for its perturbed p
K
a
.
Coupling of Ras and Rac Guanosine Triphosphatases Through the Ras Exchanger Sos
Authors: Nimnual Anjaruwee S. , Yatsula Bogdan A. , Bar-Sagi Dafna
Published: July 2002

The Son of Sevenless (Sos) proteins control receptor-mediated activation of Ras by catalyzing the exchange of guanosine diphosphate for guanosine triphosphate on Ras. The NH
2
-terminal region of Sos contains a Dbl homology (DH) domain in tandem with a pleckstrin homology (PH) domain. In COS-1 cells, the DH domain of Sos stimulated guanine nucleotide exchange on Rac but not Cdc42 in vitro and in vivo. The tandem DH-PH domain of Sos (DH-PH-Sos) was defective in Rac activation but regained Rac stimulating activity when it was coexpressed with activated Ras. Ras-mediated activation of DH-PH-Sos did not require activation of mitogen-activated protein kinase but it was dependent on activation of phosphoinositide 3-kinase. These results reveal a potential mechanism for coupling of Ras and Rac signaling pathways.
Capture of Interplanetary and Interstellar Dust by the Jovian Magnetosphere
Authors: Colwell Joshua E. , Horányi Mihály , Grün Eberhard
Published: July 2002

Interplanetary and interstellar dust grains entering Jupiter's magnetosphere form a detectable diffuse faint ring of exogenic material. This ring is composed of particles in the size range of 0.5 to 1.5 micrometers on retrograde and prograde orbits in a 4:1 ratio, with semimajor axes 3 <
a
< 20 jovian radii, eccentricities 0.1 <
e
< 0.3, and inclinations
i
≲ 20 degrees or
i
≳ 160 degrees. The size range and the orbital characteristics are consistent with in situ detections of micrometer-sized grains by the Galileo dust detector, and the measured rates match the number densities predicted from numerical trajectory integrations.
NMR Structure of a Classical Pseudoknot: Interplay of Single- and Double-Stranded RNA
Authors: Kolk Michaël H. , van der Graaf Marinette , Wijmenga Sybren S. , Pleij Cornelis W. A. , Heus Hans A. , Hilbers Cornelis W.
Published: July 2002

Pseudoknot formation folds the 3′ ends of many plant viral genomic RNAs into structures that resemble transfer RNA in global folding and in their reactivity to transfer RNA–specific proteins. The solution structure of the pseudoknotted T arm and acceptor arm of the transfer RNA–like structure of turnip yellow mosaic virus (TYMV) was determined by nuclear magnetic resonance (NMR) spectroscopy. The molecule is stabilized by the hairpin formed by the 5′ end of the RNA, and by the intricate interactions related to the loops of the pseudoknot. Loop 1 spans the major groove of the helix with only two of its four nucleotides. Loop 2, which crosses the minor groove, interacts closely with its opposing helix, in particular through hydrogen bonds with a highly conserved adenine. The structure resulting from this interaction between the minor groove and single-stranded RNA at helical junctions displays internal mobility, which may be a general feature of RNA pseudoknots that regulates their interaction with proteins or other RNA molecules.
Transition from Moderate to Excessive Drug Intake: Change in Hedonic Set Point
Authors: Ahmed S. H. , Koob G. F.
Published: July 2002

Differential access to cocaine self-administration produced two patterns of drug intake in rats. With 1 hour of access per session, drug intake remained low and stable. In contrast, with 6 hours of access, drug intake gradually escalated over days. After escalation, drug consumption was characterized by an increased early drug loading and an upward shift in the cocaine dose-response function, suggesting an increase in hedonic set point. After 1 month of abstinence, escalation of cocaine intake was reinstated to a higher level than before. These findings may provide an animal model for studying the development of excessive drug intake and the basis of addiction.
Caenorhabditis elegans
Is a Nematode
Authors: Blaxter Mark
Published: July 2002

Caenorhabditis elegans
is a rhabditid nematode. What relevance does this have for the interpretation of the complete genome sequence, and how will it affect the exploitation of the sequence for scientific and social ends? Nematodes are only distantly related to humans and other animal groups; will this limit the universality of the
C. elegans
story? Many nematodes are parasites; can knowledge of the
C. elegans
sequence aid in the prevention and treatment of disease?
Processing of the Notch Ligand Delta by the Metalloprotease Kuzbanian
Authors: Qi Huilin , D. Rand Matthew , Wu Xiaohui , Sestan Nenad , Wang Weiyi , Rakic Pasko , Xu Tian , Artavanis-Tsakonas Spyros
Published: July 2002

Signaling by the Notch surface receptor controls cell fate determination in a broad spectrum of tissues. This signaling is triggered by the interaction of the Notch protein with what, so far, have been thought to be transmembrane ligands expressed on adjacent cells. Here biochemical and genetic analyses show that the ligand Delta is cleaved on the surface, releasing an extracellular fragment capable of binding to Notch and acting as an agonist of Notch activity. The ADAM disintegrin metalloprotease Kuzbanian is required for this processing event. These observations raise the possibility that Notch signaling in vivo is modulated by soluble forms of the Notch ligands.
The Effect of Trematode Infection on Amphibian Limb Development and Survivorship
Authors: Johnson Pieter T. J. , Lunde Kevin B. , Ritchie Euan G. , Launer Alan E.
Published: July 2002

The causes of amphibian deformities and their role in widespread amphibian declines remain conjectural. Severe limb abnormalities were induced at high frequencies in Pacific treefrogs (
Hyla regilla
) exposed to cercariae of a trematode parasite (
Ribeiroia
sp.). The abnormalities closely matched those observed at field sites, and an increase in parasite density caused an increase in abnormality frequency and a decline in tadpole survivorship. These findings call for further investigation of parasite infection as a cause of amphibian deformities in other sites and species.
Contribution of Gular Pumping to Lung Ventilation in Monitor Lizards
Authors: Owerkowicz Tomasz , Farmer Colleen G. , Hicks James W. , Brainerd Elizabeth L.
Published: July 2002

A controversial hypothesis has proposed that lizards are subject to a speed-dependent axial constraint that prevents effective lung ventilation during moderate- and high-speed locomotion. This hypothesis has been challenged by results demonstrating that monitor lizards (genus
Varanus
) experience no axial constraint. Evidence presented here shows that, during locomotion, varanids use a positive pressure gular pump to assist lung ventilation. Disabling the gular pump reveals that the axial constraint is present in varanids but it is masked by gular pumping under normal conditions. These findings support the prediction that the axial constraint may be found in other tetrapods that breathe by costal aspiration and locomote with a lateral undulatory gait.
Atomic-Scale Quasi-Particle Scattering Resonances in Bi
2
Sr
2
CaCu
2
O
8+δ
Authors: Hudson E. W. , Pan S. H. , Gupta A. K. , Ng K.-W. , Davis J. C.
Published: July 2002

Low-temperature scanning tunneling spectroscopy of the high transition temperature (high-
T
c
) cuprate Bi
2
Sr
2
CaCu
2
O
8+δ
reveals the existence of large numbers of identical regions with diameters of about 3 nanometers that have a relatively high density of low-energy quasi-particle states. Their spatial and spectroscopic characteristics are consistent with theories of strong quasi-particle scattering from atomic-scale impurities in a
d
-wave superconductor. These characteristics include breaking of local particle-hole symmetry, a diameter near twice the superconducting coherence length, and an inverse square dependence of their local density-of-states on distance from the scattering center. In addition to the validation of
d
-wave quasi-particle scattering theories, these observations identify a source for the anomalously high levels of low-energy quasi-particles in Bi
2
Sr
2
CaCu
2
O
8+δ
at low temperatures.
Phosphorylation and Sequestration of Serotonin Transporters Differentially Modulated by Psychostimulants
Authors: Ramamoorthy Sammanda , Blakely Randy D.
Published: July 2002

Many psychotropic drugs interfere with the reuptake of dopamine, norepinephrine, and serotonin. Transport capacity is regulated by kinase-linked pathways, particularly those involving protein kinase C (PKC), resulting in transporter phosphorylation and sequestration. Phosphorylation and sequestration of the serotonin transporter (SERT) were substantially impacted by ligand occupancy. Ligands that can permeate the transporter, such as serotonin or the amphetamines, prevented PKC-dependent SERT phosphorylation. Nontransported SERT antagonists such as cocaine and antidepressants were permissive for SERT phosphorylation but blocked serotonin effects. PKC-dependent SERT sequestration was also blocked by serotonin. These findings reveal activity-dependent modulation of neurotransmitter reuptake and identify previously unknown consequences of amphetamine, cocaine, and antidepressant action.
A Mutation in the
C. elegans
EXP-2 Potassium Channel That Alters Feeding Behavior
Authors: Davis M. Wayne , Fleischhauer Richard , Dent Joseph A. , Joho Rolf H. , Avery Leon
Published: July 2002

The nematode pharynx has a potassium channel with unusual properties, which allows the muscles to repolarize quickly and with the proper delay. Here, the
Caenorhabditis elegans exp-2
gene is shown to encode this channel. EXP-2 is a Kv-type (voltage-activated) potassium channel that has inward-rectifying properties resembling those of the structurally dissimilar human
ether-à-go-go
–related gene (HERG) channel. Null and gain-of-function mutations affect pharyngeal muscle excitability in ways that are consistent with the electrophysiological behavior of the channel, and thereby demonstrate a direct link between the kinetics of this unusual channel and behavior.
Information Storage and Retrieval Through Quantum Phase
Authors: Ahn J. , Weinacht T. C. , Bucksbaum P. H.
Published: July 2002

Information was stored as quantum phase in an
N
-state Rydberg atom data register. One or more flipped states stored in an eight-state atomic wave packet could be retrieved in a single operation, in agreement with a recent proposal by Grover.
Regulation of Protein Secretion Through Controlled Aggregation in the Endoplasmic Reticulum
Authors: Rivera Victor M. , Wang Xiurong , Wardwell Scott , Courage Nancy L. , Volchuk Allen , Keenan Terence , Holt Dennis A. , Gilman Michael , Orci Lelio , Cerasoli Frank , Rothman James E. , Clackson Tim
Published: July 2002

A system for direct pharmacologic control of protein secretion was developed to allow rapid and pulsatile delivery of therapeutic proteins. A protein was engineered so that it accumulated as aggregates in the endoplasmic reticulum. Secretion was then stimulated by a synthetic small-molecule drug that induces protein disaggregation. Rapid and transient secretion of growth hormone and insulin was achieved in vitro and in vivo. A regulated pulse of insulin secretion resulted in a transient correction of serum glucose concentrations in a mouse model of hyperglycemia. This approach may make gene therapy a viable method for delivery of polypeptides that require rapid and regulated delivery.
Requirement for DARPP-32 in Progesterone-Facilitated Sexual Receptivity in Female Rats and Mice
Authors: Mani S. K. , Fienberg A. A. , O'Callaghan J. P. , Snyder G. L. , Allen P. B. , Dash P. K. , Moore A. N. , Mitchell A. J. , Bibb J. , Greengard P. , O'Malley B. W.
Published: July 2002

DARPP-32, a dopamine- and adenosine 3′,5′-monophosphate (cAMP)–regulated phosphoprotein (32 kilodaltons in size), is an obligate intermediate in progesterone (P)–facilitated sexual receptivity in female rats and mice. The facilitative effect of P on sexual receptivity in female rats was blocked by antisense oligonucleotides to DARPP-32. Homozygous mice carrying a null mutation for the DARPP-32 gene exhibited minimal levels of P-facilitated sexual receptivity when compared to their wild-type littermates. P significantly increased hypothalamic cAMP levels and cAMP-dependent protein kinase activity. These increases were not inhibited by a D
1
subclass dopamine receptor antagonist. P also enhanced phosphorylation of DARPP-32 on threonine 34 in the hypothalamus of mice. DARPP-32 activation is thus an obligatory step in progestin receptor regulation of sexual receptivity in rats and mice.
The Eye Injury of King Philip II and the Skeletal Evidence from the Royal Tomb II at Vergina
Authors: Bartsiokas Antonis
Published: July 2002

The Royal Tomb II was discovered in Vergina, Greece, in 1977. It contained a male skeleton and a rich array of grave goods. Evidence of trauma supposedly in the orbital bones of the skull has been thought to correspond to an eye injury that King Philip II is historically known to have suffered. However, reexamination of the orbital morphology showed no evidence of such pathology. Therefore, the skeleton does not belong to Philip II. New skeletal evidence shows that the skeleton belongs to King Philip III Arrhidaeus. In this case, the tomb may well contain some of the paraphernalia of Alexander the Great.
Earliest Pleistocene Hominid Cranial Remains from Dmanisi, Republic of Georgia: Taxonomy, Geological Setting, and Age
Authors: Gabunia Leo , Vekua Abesalom , Lordkipanidze David , Swisher Carl C. , Ferring Reid , Justus Antje , Nioradze Medea , Tvalchrelidze Merab , Antón Susan C. , Bosinski Gerhard , Jöris Olaf , Lumley Marie-A.-de , Majsuradze Givi , Mouskhelishvili Aleksander
Published: July 2002

Archaeological excavations at the site of Dmanisi in the Republic of Georgia have uncovered two partial early Pleistocene hominid crania. The new fossils consist of a relatively complete cranium and a second relatively complete calvaria from the same site and stratigraphic unit that yielded a hominid mandible in 1991. In contrast with the uncertain taxonomic affinity of the mandible, the new fossils are comparable in size and morphology with
Homo ergaster
from Koobi Fora, Kenya. Paleontological, archaeological, geochronological, and paleomagnetic data from Dmanisi all indicate an earliest Pleistocene age of about 1.7 million years ago, supporting correlation of the new specimens with the Koobi Fora fossils. The Dmanisi fossils, in contrast with Pleistocene hominids from Western Europe and Eastern Asia, show clear African affinity and may represent the species that first migrated out of Africa.
Rapid Evolution of Reproductive Isolation in the Wild: Evidence from Introduced Salmon
Authors: Hendry Andrew P. , Wenburg John K. , Bentzen Paul , Volk Eric C. , Quinn Thomas P.
Published: July 2002

Colonization of new environments should promote rapid speciation as a by-product of adaptation to divergent selective regimes. Although this process of ecological speciation is known to have occurred over millennia or centuries, nothing is known about how quickly reproductive isolation actually evolves when new environments are first colonized. Using DNA microsatellites, population-specific natural tags, and phenotypic variation, we tested for reproductive isolation between two adjacent salmon populations of a common ancestry that colonized divergent reproductive environments (a river and a lake beach). We found evidence for the evolution of reproductive isolation after fewer than 13 generations.
Early Development of Ocular Dominance Columns
Authors: Crowley Justin C. , Katz Lawrence C.
Published: July 2002

The segregation of lateral geniculate nucleus (LGN) axons into ocular dominance columns is believed to involve a prolonged, activity-dependent sorting process. However, visualization of early postnatal ferret LGN axons by direct LGN tracer injections revealed segregated ocular dominance columns <7 days after innervation of layer 4. These early columns were unaffected by experimentally induced imbalances in retinal activity, implying that different mechanisms govern initial column formation and their modification during the subsequent critical period. Instead of activity-dependent plasticity, we propose that ocular dominance column formation relies on the targeting of distinct axonal populations to defined locales in cortical layer 4.
A β
2
Adrenergic Receptor Signaling Complex Assembled with the Ca
2+
Channel Ca
v
1.2
Authors: Davare Monika A. , Avdonin Vladimir , Hall Duane D. , Peden Erik M. , Burette Alain , Weinberg Richard J. , Horne Mary C. , Hoshi Toshinori , Hell Johannes W.
Published: July 2002

The existence of a large number of receptors coupled to heterotrimeric guanine nucleotide binding proteins (G proteins) raises the question of how a particular receptor selectively regulates specific targets. We provide insight into this question by identifying a prototypical macromolecular signaling complex. The β
2
adrenergic receptor was found to be directly associated with one of its ultimate effectors, the class C L-type calcium channel Ca
v
1.2. This complex also contained a G protein, an adenylyl cyclase, cyclic adenosine monophosphate–dependent protein kinase, and the counterbalancing phosphatase PP2A. Our electrophysiological recordings from hippocampal neurons demonstrate highly localized signal transduction from the receptor to the channel. The assembly of this signaling complex provides a mechanism that ensures specific and rapid signaling by a G protein–coupled receptor.
Benchmarking the In Vitro Activities of Moxifloxacin and Comparator Agents against Recent Respiratory Isolates from 377 Medical Centers throughout the United States
Authors: Jones Mark E. , Staples Angela M. , Critchley Ian , Thornsberry Clyde , Heinze Paul , Engler Howard D. , Sahm Daniel F.
Published: July 2002

To benchmark the activity of moxifloxacin (a newer fluoroquinolone), a U.S. study comprising 16,141 contemporary isolates of
Streptococcus pneumoniae
(5,640),
Haemophilus influenzae
(6,583), and
Moraxella catarrhalis
(3,648) referred from 377 institutions during 1998 is described. For
S. pneumoniae
the modal MIC and MIC at which 90% of the isolates were inhibited (MIC
90
) for moxifloxacin were 0.12 and 0.25 μg/ml, respectively, independent of susceptibility to other drug classes, geography, or site of infection. Eleven isolates were intermediate or resistant to levofloxacin and grepafloxacin; of these isolates, 1 remained susceptible to sparfloxacin, 2 remained susceptible to moxifloxacin, and 4 remained susceptible to trovafloxacin. All 11 isolates possessed classic mutations in
gyrA
and/or
parC
known to confer reduced susceptibility to fluoroquinolones. Four isolates (originating from four separate states) belonging to a multidrug-resistant, fluoroquinolone-resistant clone were identified by pulsed-field gel electrophoresis. For moxifloxacin and trovafloxacin, at least 87% of isolates demonstrated MICs ≥3 twofold concentrations below the susceptibility breakpoints, in contrast to no more than 15% for levofloxacin, grepafloxacin, and sparfloxacin. Of the isolates that were multidrug resistant (7.4%), >98% remained susceptible to moxifloxacin. The modal MIC and MIC
90
for
M. catarrhalis
(both 0.06 μg/ml) and for
H. influenzae
(both 0.03 μg/ml) were independent of β-lactamase production. These data demonstrate the in vitro activity of moxifloxacin and establish a baseline for future studies.
Structural and Topological Differences between a Glycopeptide-Intermediate Clinical Strain and Glycopeptide-Susceptible Strains of
Staphylococcus aureus
Revealed by Atomic Force Microscopy
Authors: Boyle-Vavra Susan , Hahm Jongin , Sibener S. J. , Daum Robert S.
Published: July 2002

Novel cell surface topography was revealed on cocci from a glycopeptide-intermediate
Staphylococcus aureus
(GISA) clinical strain by using atomic force microscopy. The GISA isolate and its revertant had two parallel circumferential surface rings. One equatorial surface ring was observed in control strains. In vancomycin-susceptible strains, additional rings were formed in the presence of vancomycin. Ring depth measurements also revealed striking differences between the GISA strain and susceptible strains grown with or without vancomycin.
Use of Molecular Beacons To Detect an Antifolate Resistance-Associated Mutation in
Plasmodium falciparum
Authors: Durand Rémy , Eslahpazire Jobin , Jafari Sayeh , Delabre Jean-François , Marmorat-Khuong Anne , di Piazza Jean-Philippe , Le Bras Jacques
Published: July 2002

A PCR-based technique using new fluorescent probes, called molecular beacons, was developed to detect the antifolate resistance-associated S108N point mutation in
Plasmodium falciparum
. One hundred African clinical isolates were tested by the new method in comparison with the PCR-restriction fragment length polymorphism method. This new molecular technique appears to be a promising tool for epidemiological studies.