bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion trap for mass-selective production of nanoclusters
Authors: Kanayama Toshihiko , Murakami Hirohiko
Published: July 2002

To form nanoclusters with a specified atomic structure, an electrical trapping technique of charged particles was developed that allows us to confine, grow, and mass selectively eject cluster ions. Theoretical calculations and experiments using inert gas ions indicate that the developed ion trap can confine ions with a wide range of mass values using the external field of an ac quadrupole, and send out the ions mass selectively through the internal region of the quadrupole. To demonstrate performance, Si6H12+ clusters were selectively grown using SiH4 as a starting material. In the trap, confined SiHx+ ions were allowed to react with neutral SiH4 molecules or SiHy radicals, and SinHx+ clusters were grown, from which Si6H12+ clusters were automatically ejected by tuning trapping parameters.
200 eV–10 keV boron implantation and rapid thermal annealing: Secondary ion mass spectroscopy and transmission electron microscopy study
Authors: Current M. I. , Lopes D. , Foad M. A. , England J. G. , Jones C. , Su D.
Published: July 2002

Atomic profiles (secondary ion mass spectroscopy) and cross-section transmission electron microscopy (TEM) images of selectively etched, annealed profiles were studied for boron energies from 200 eV to 10 keV and rapid thermal processing anneals at 900, 975, and 1050 °C. Consistent variations of dopant depth were obtained over this process range. TEM images showed evidence of lateral dopant variation near the edges of poly-Si gate structures, perhaps an effect of lateral straggling and reflection of ions from the polymask.
Two-dimensional pn-junction delineation and individual dopant identification using scanning tunneling microscopy/spectroscopy
Authors: Chao Kuo-Jen , Smith Arthur R. , McDonald Andrew J. , Kwong Dim-Lee , Streetman Ben G. , Shih Chih-Kang
Published: July 2002

We have used scanning tunneling microscopy and spectroscopy (STM/S) to study multiple pn junctions on cross-sectional surfaces of both Si and GaAs devices. The spectroscopy results indicate that pn junctions can be resolved at the nanometer scale by using the two-dimensional STS technique. STM is also used to identify Zn dopants on GaAs(110) surfaces. A detail dopant location identification method is presented.
Investigation of Ce-doped silicates for low voltage field emission displays
Authors: Lee R. Y. , Zhang F. L. , Penczek J. , Wagner B. K. , Yocom P. N. , Summers C. J.
Published: July 2002

The feasibility of using Ce-doped silicates as an alternative to the P22 blue phosphor (ZnS:Ag) was investigated for low voltage field emission displays (FEDs). Silicates of various composition were evaluated based on their chromaticity, intrinsic efficiency, and brightness saturation behavior. The influence of silicate composition and particle morphology on the cathodoluminescence properties was also assessed. Saturation measurements indicated that the high saturation resistance of the Ce-doped samples can yield better performance than ZnS:Ag when operating at low voltages. The silicates are also attractive for their stability in a FED environment.
In situ temperature control of molecular beam epitaxy growth using band-edge thermometry
Authors: Johnson Shane , Kuo Chau-Hong , Boonzaayer Martin , Braun Wolfgang , Koelle Ulrich , Zhang Yong-Hang , Roth John
Published: July 2002

Band-edge thermometry is becoming an established noncontact method for determining substrate temperature during molecular beam epitaxy. However, with this technique thin-film interference and/or absorption in the growing epilayer can cause shape distortions of the spectrum that may be interpreted erroneously as real temperature shifts of the substrate. An algorithm is presented that uses the width of the spectrum to correct for apparent temperature errors caused by interference and absorption in the epilayer. This correction procedure is tested on substrate temperature data taken during the growth of a λ=930 nm resonant cavity, where the apparent substrate temperature oscillates ±5 °C during the growth of the mirror stacks. These oscillations are reduced to ±3 °C using the correction algorithm. A recently developed model for the substrate temperature dynamics in molecular beam epitaxy shows that roughly ±1 °C of the remaining ±3 °C temperature oscillations are real. Band-edge thermometry is also used to control the substrate temperature to within ±2 °C during the growth of near-lattice-matched InGaAs on InP, whereas the same growth under constant thermocouple temperature would result in a 50 °C rise in the actual substrate temperature.
Luminescence of GaN/GaAs(111)B grown by molecular beam epitaxy with hydrazine
Authors: Nikishin S. A. , Antipov V. G. , Guriev A. I. , Elyukhin V. A. , Faleev N. N. , Kudriavtsev Yu. A. , Lebedev A. B. , Shubina T. V. , Zubrilov A. S. , Temkin H.
Published: July 2002

Hexagonal GaN layers were grown on (111)B GaAs substrates by gas-source molecular beam epitaxy using hydrazine as a source of nitrogen. A smooth and abrupt AlN/GaAs interface was prepared by nitridation of an AlAs buffer layer grown on clean GaAs(111)B surface. This buffer layer is stable at growth temperatures above 700 °C. The AlN layer prepared on this buffer exhibits two-dimensional growth. The subsequent GaN and GaInN layers show a quasi-two-dimensional growth. The photo-and cathodoluminescence spectra of these samples show a narrow (∼160 meV) band-edge emission and the absence of the “yellow” defect band. Further narrowing (∼20 meV) of the edge emission in unintentionally In-doped GaN is ascribed to the presence of confined domains of Ga1−xInxN.
Changes in morphology using atomic hydrogen during Si/Si1−xGex molecular beam epitaxy growth on Si (100)
Authors: Silvestre C. , Jernigan G. G. , Twigg M. E. , Thompson P. E.
Published: July 2002

Si and Si1−xGex molecular beam epitaxial growths have been conducted with and without 10−3 Pa atomic hydrogen (AH) overpressure to observe the effect of AH on surface morphology. Si1−xGex (x=0.1 and 0.2) layers 3 nm thick grown at 710 °C without AH showed flat epitaxy by transmission electron microscopy but identical layers grown in the presence of AH showed interface stress undulations. Stress undulations were also observed for a 20% Ge alloy grown with AH at 600 °C. For 30% Ge alloy layers grown at 710 °C, undulations were seen both with and without AH with a ≈250 nm period, however the amplitudes of the undulations were greater with AH. Low energy electron diffraction investigation of Si homoepitaxy revealed, at growth temperatures between 600 and 800 °C, improved epitaxy with 100 s of 10−3 Pa AH. In combination, these results are evidence that AH has increased the adatom mobility.
Hopping conduction and localized states in p-Si wires formed by focused ion beam implantations
Authors: Iwano Hirotaka , Zaima Shigeaki , Yasuda Yukio
Published: July 2002

Localized states in p-Si wires formed in n-Si(100) substrates by selective ion implantation using a focused Ga+ ion beam have been investigated. The electrical conductance has the temperature dependence of one-dimensional (1D) variable-range-hopping conduction in the temperature range below 50 K, σ=σ0 exp[−(T0/T)1/2]. The magnetoresistance R(H) of p-Si wires at 4.2 K shows the negative and positive magnetoresistances at weak and strong magnetic fields, which have the relation that R(H)/R0 ∝exp(−βH) and R(H)/R0 ∝exp(αH2), respectively, where R0 is the resistance without the magnetic field H. These characteristics can be explained by the 1D hopping conduction mechanism under the magnetic field. By expanding a three-dimensional model, we derive an equation of positive magnetoresistance in 1D hopping conduction. From the temperature dependence of conductance and positive magnetoresistance, the localization length, hopping distance, and density of localized states are estimated to be about 2 nm, 8–9 nm and about 109 cm−1 eV−1, respectively. This result indicates that the carrier transport is confined with the region of a few tens of nanometers.
Application of dual-functional MoO3/WO3 bilayer resists to focused ion beam nanolithography
Authors: Hashimoto Masahiro , Koreeda Toshishige , Koshida Nobuyoshi , Komuro Masanori , Atoda Nobufumi
Published: July 2002

Ultrafine patterning and metallization technologies have been studied using a combination of refractory metal oxide (MoO3 and WO3) resists and Ga+ focused ion beam lithography. It is demonstrated that, depending on the preparation condition of the films, these thin oxide films act as either a negative or a positive resist with high-contrast capability. As a novel application of this dual-functional behavior, a bilayer resist system using negative (MoO3) and the positive-type (WO3) resists is presented here in order to enhance the high-resolution capability. Based on this technique, nanometer-width MoO3/WO3 line patterns can be delineated onto Si substrates. The delineated line patterns were directly reduced to fine Mo/W wires by heat treatment in a dry H2 gas atmosphere. The electrical properties of the Mo/W lines were evaluated in terms of sheet resistance and their temperature dependence. By introduction of the bilayer resist, the sheet resistance of reduced nanowires was significantly decreased in comparison to that of the monolayer case. The usefulness of oxide resists as refractory metal nanowiring has been further increased by employing the bilayer resist system.
Reduction of oxygen contamination in InGaP and AlGaInP films grown by solid source molecular beam epitaxy
Authors: Hoke W. E. , Lemonias P. J. , Torabi A.
Published: July 2002

Oxygen contamination has been observed in In0.5Ga0.5P and (Al0.23Ga0.77)0.5In0.5P films grown by solid source molecular beam epitaxy with elemental phosphorus. Using a conventional P4 cracking zone temperature of 950 °C, spike contamination levels as high as 1×1019 cm−3 were observed at growth interrupted interfaces with the resultant deactivation of silicon doping pulses. By reducing the phosphorus cracking temperature to 700 °C, the oxygen level in InGaP was reduced to below the secondary ion mass spectrometry background level of 3×1016 cm−3. No measurable accumulation of oxygen was observed at growth interrupted interfaces and efficient silicon pulse doping was obtained. InGaP films grown at the lower cracking temperature exhibited improved mobilities and enhanced photoluminescence intensities. An oxygen level in (Al0.23Ga0.77)0.5In0.5P of less than 1.5×1017 cm−3 was obtained with good mobilities and luminescence. Efficient silicon pulse doping in AlGaInP was demonstrated. The oxygen contamination is in the phosphorus flux and is likely a volatile phosphorus oxide such as P4O6.
Low-energy electron-beam lithography using calixarene
Authors: Tilke A. , Vogel M. , Simmel F. , Kriele A. , Blick R. H. , Lorenz H. , Wharam D. A. , Kotthaus J. P.
Published: July 2002

Low-energy electron-beam lithography using calixarene as a negative electron resist has been investigated in the energy range between 0.5 and 20 keV. The suitability of electron energies down to 2 keV with a writing resolution of about 10 nm is clearly demonstrated. At low electron energies the required electron dose is drastically reduced. Moreover, irradiation damage during the exposure of a high-mobility two-dimensional electron gas using calixarene plays no significant role in the low-energy regime.
Characteristics of chemically vapor deposited TiN films prepared using tetrakis-ethylmethyl-amido-titanium
Authors: Kim Do-Heyoung , Lim Gyeong Taek , Kim Su-Kyung , Park Jin Won , Lee Jae-Gab
Published: July 2002

Low pressure chemical vapor deposition of TiN was studied with tetrakis-ethylmethyl-amido titanium (TEMAT) in a cold-wall-type vertical flow reactor with helium or ammonia. Thermal decomposition of the precursor under helium atmosphere yielded TiN films at substrate temperatures of 250 °C. On the contrary, the reaction of TEMAT with ammonia occurred even at 100 °C. The film growth rate increased with increasing deposition temperature and precursor mole fraction. However, deposition rate was greatly reduced in the system of ammonia/TEMAT compared to thermal decomposition probably due to a vigorous gas phase reaction in the latter case. For the case of thermal decomposition, the growth rate levels off at 325 °C and this behavior has been interpreted as a transition from surface reaction to gas phase mass transfer control. The resistivity of the films deposited under similar conditions decreased with increasing thickness. It was found that higher deposition temperature and ammonia addition produced films of lower resistivity. Air exposure of the films caused an increase in resistivity, probably by oxidation of the films. Surface morphology of the TiN films in an ammonia-free system was smoother than that in the ammonia system. Conformality of the films strongly depended on the deposition temperature, ammonia usage, and ammonia flow rate. Lowering the deposition temperature and ammonia flow rate improved the conformality. Barrier performance of the TiN films deposited under helium atmosphere to copper diffusion in the Cu/TiN/Si structure showed an evidence of copper diffusion even after annealing at 550 °C for 1 h.
Selective plasma etching for contact holes using a fluorine-based chemistry with addition of N2
Authors: Meijer Peter M. , Roelofs Michel E. F. , Manders Bart S.
Published: July 2002

The effects the addition of nitrogen to a CHF3/CF4/Ar-gas mixture on the selectivity of SiO2 to TiSi2 and Si are reported for a magnetically enhanced reactive ion etch system. The selectivity to TiSi2 is more than doubled by adding 10% of nitrogen to the gas mixture, whereas the same addition lowers the selectivity to Si by more than half. The selectivity to TiSi2 is lowered by a factor of 2 by changing the wafer temperature from 70 to 100 °C. The selectivity to Si is not influenced by this change in wafer temperature. This contrasting behavior suggests different etch selectivity mechanisms for SiO2/TiSi2 and SiO2/Si. This is confirmed by x-ray photoemission spectroscopy measurements of the TiSi2 and Si surfaces.
Growth and modification of Ag islands on hydrogen terminated Si(100) surfaces
Authors: Butcher M. J. , Jones F. H. , Beton P. H.
Published: July 2002

The interaction of Ag with the Si(100)-2×1:H surface has been studied using a scanning tunneling microscope (STM). By comparing surfaces with various dangling bond defect densities, it is shown that such sites nucleate the growth of Ag islands. The critical Ag coverage above which coalescence of islands occurs, together with the mean height and width of islands are all determined by the initial dangling bond density on the Si(100)-2×1:H surface. We have also observed that the surface may be modified by scanning with a STM resulting in the transfer of Ag from the sample to the tip.
Comparison of two-dimensional carrier profiles in metal–oxide– semiconductor field-effect transistor structures obtained with scanning spreading resistance microscopy and inverse modeling
Authors: De Wolf P. , Vandervorst W. , Smith H. , Khalil N.
Published: July 2002

Scanning spreading resistance microscopy (SSRM) is used to determine the complete two-dimensional carrier profile of fully processed 0.29 μm p- and n-type metal–oxide–semiconductor field-effect transistors with various source/drain implants. A comparison is made between the quantified profiles determined using SSRM and the profiles extracted from the electrical device characteristics using an inverse modeling technique. This comparison includes source/drain and well implants, epilayers, and field implants. The data are compared in terms of depth precision and carrier-concentration accuracy and show a good agreement. This article also addresses the limitations and possible artifacts of both methods.
Ar addition effect on mechanism of fluorocarbon ion formation in CF4/Ar inductively coupled plasma
Authors: Choi Chang Ju , Kwon O Sung , Seol Yeo Song , Kim Yil Wook , Choi Il Hyun
Published: July 2002

Using a Langmuir probe and an energy-resolved ion mass spectrometer, gas-phase kinetics of fluorocarbon ions has been investigated as a function of the Ar percentage in a mixed CF4/Ar plasma. Spatially resolved electron energy distribution function, plasma potential, and ion density are measured in an inductively coupled plasma. As the Ar percentage increases, the average electron energy decreases while the electron density remains flat. The ion density also stays constant at low Ar percentages but increases over the Ar percentage larger than 63% mainly due to the increase of the Ar+ density. The plasma potential decreases as a result of the increase of Ar partial pressure, and this is confirmed by measuring the ion energy distributions of argon and fluorocarbon ions using the ion mass spectrometry. With the mass spectrometry, it is found that the most prominent ions, CF3+ and CF+, are formed predominantly by a process of dissociative ionization or radical ionization while CF2+ ions are formed dominantly by a process of charge transfer. As a practical application of this study for SiO2 etching, the densities of the fluorocarbon ions and radicals are correlated with the SiO2 etch rate and its selectivity to photoresist. Microtrench profile is also investigated as a function of Ar percentage and it is observed that the microtrench tends to be suppressed with the increase of the Ar percentage. This tendency is correlated with changes in the plasma chemistry as the Ar percentage increases.
Growth of high density self-organized (In,Ga)As quantum dots with ultranarrow photoluminescence linewidths using buried In(Ga,Al)As stressor dots
Authors: Krishna Sanjay , Sabarinathan Jayshri , Linder Kojo , Bhattacharya Pallab , Lita B. , Goldman R. S.
Published: July 2002

High density InAs and In0.4Ga0.6As dots were grown by molecular beam epitaxy on buried In0.4Al0.6As and In0.4Ga0.3Al0.3As stressor dots, respectively. Selective radiative recombination was achieved by engineering the band gap of the dots. Structural and luminescence measurements reveal increased size uniformity in the active region dots along with an increase in the dot density. A narrow photoluminescence linewidth of 19 meV was measured at T=17 K.
Universality and Scaling in the Disordering of a Smectic Liquid Crystal
Authors: Bellini Tommaso , Radzihovsky Leo , Toner John , Clark Noel A.
Published: July 2002

We present experimental and theoretical studies of the effects of quenched disorder on one-dimensional crystal ordering in three dimensions. This fragile smectic liquid crystal layering, the material with the simplest positional order, is also the most easily deformed periodic structure and is, therefore, profoundly affected by disorder, introduced here by confinement in silica aerogel. Theory and experiment combine to characterize this system to an extraordinary degree, their close accord producing a coherent picture: crystal ordering is lost, giving way to extended short-range correlations that exhibit universal structure and scaling, anomalous layer elasticity, and glassy dynamics.
Human Chromosome 19 and Related Regions in Mouse: Conservative and Lineage-Specific Evolution
Authors: Dehal Paramvir , Predki Paul , Olsen Anne S. , Kobayashi Art , Folta Peg , Lucas Susan , Land Miriam , Terry Astrid , Ecale Zhou Carol L. , Rash Sam , Zhang Qing , Gordon Laurie , Kim Joomyeong , Elkin Christopher , Pollard Martin J. , Richardson Paul , Rokhsar Dan , Uberbacher Ed , Hawkins Trevor , Branscomb Elbert , Stubbs Lisa
Published: July 2002

To illuminate the function and evolutionary history of both genomes, we sequenced mouse DNA related to human chromosome 19. Comparative sequence alignments yielded confirmatory evidence for hypothetical genes and identified exons, regulatory elements, and candidate genes that were missed by other predictive methods. Chromosome-wide comparisons revealed a difference between single-copy HSA19 genes, which are overwhelmingly conserved in mouse, and genes residing in tandem familial clusters, which differ extensively in number, coding capacity, and organization between the two species. Finally, we sequenced breakpoints of all 15 evolutionary rearrangements, providing a view of the forces that drive chromosome evolution in mammals.
Synthesis Beyond the Molecule
Authors: Reinhoudt D. N. , Crego-Calama M.
Published: July 2002

Weak, noncovalent interactions between molecules control many biological functions. In chemistry, noncovalent interactions are now exploited for the synthesis in solution of large supramolecular aggregates. The aim of these syntheses is not only the creation of a particular structure, but also the introduction of specific chemical functions in these supramolecules.
Mixed Self-Assembled Monolayers in Chemical Separations
Authors: Wirth Mary J. , Fairbank R. W. Peter , Fatunmbi Hafeez O.
Published: July 2002

Chemical separations of many biomolecules and pharmaceuticals are limited by their electrostatic interaction with the surfaces of the separation medium. Mixed self-assembled monolayers of octadecyl and methyl chains organize into a dense, two-dimensionally cross-linked network over the chromatographic silica surface to reduce acid dissociation of the surface silanols. Molecular models predict that two-dimensional cross-linking is sterically possible for pure methylsiloxane monolayers, silicon-29 nuclear magnetic resonance measurements show that cross-linking predominates for mixed monolayers of primarily methylsiloxane, and chromatographic measurements confirm that electrostatic interactions are reduced when the monolayer is primarily methylsiloxane. Chromatographic separation of genetic variants of a highly charged protein, cytochrome c, demonstrates the promise of self-assembled monolayers in separations of biomolecules.
Continuous in Vitro Evolution of Catalytic Function
Authors: Wright Martin C. , Joyce Gerald F.
Published: July 2002

A population of RNA molecules that catalyze the template-directed ligation of RNA substrates was made to evolve in a continuous manner in the test tube. A simple serial transfer procedure was used to achieve approximately 300 successive rounds of catalysis and selective amplification in 52 hours. During this time, the population size was maintained against an overall dilution of 3 × 10
298
. Both the catalytic rate and amplification rate of the RNAs improved substantially as a consequence of mutations that accumulated during the evolution process. Continuous in vitro evolution makes it possible to maintain laboratory “cultures” of catalytic molecules that can be perpetuated indefinitely.
s-Process Zirconium in Presolar Silicon Carbide Grains
Authors: Nicolussi Günther K. , Davis Andrew M. , Pellin Michael J. , Lewis Roy S. , Clayton Robert N. , Amari Sachiko
Published: July 2002

The isotopic composition of zirconium in silicon carbide grains from the Murchison meteorite was measured by resonant ionization mass spectrometry of laser-ablated neutral atoms. These grains are condensates from the atmospheres of red giant stars that existed before the formation of our sun and solar system, and they contain records of nucleosynthesis in these stars. The r-process–dominated isotope zirconium-96 was depleted by more than a factor of 2 compared with the s-process–dominated isotopes zirconium-90, zirconium-91, zirconium-92, and zirconium-94, in agreement with expectations for neutron capture nucleosynthesis in asymptotic giant branch stars.
Ecological Accountancy
Authors: Pearce David
Published: July 2002

Nature's Services.
Societal Dependence on Natural Ecosystems. GRETCHEN C. DAILY, Ed. Island Press, Washington, DC, 1997. xx, 392 pp., illus. $49.95, ISBN 1-55963-475-8; paper, $24.95, ISBN 1-55963-476-6.
Targeting of HIV- and SIV-Infected Cells by CD4-Chemokine Receptor Pseudotypes
Authors: Endres Michael J. , Jaffer Salman , Haggarty Beth , Turner Julie D. , Doranz Benjamin J. , O'Brien Peter J. , Kolson Dennis L. , Hoxie James A.
Published: July 2002

Retroviral vectors containing CD4 and an appropriate chemokine receptor were evaluated for the ability to transduce cells infected with human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV). These CD4–chemokine receptor pseudotypes were able to target HIV- and SIV-infected cell lines and monocyte-derived macrophages in a manner that corresponded to the specificity of the viral envelope glycoprotein for its CD4–chemokine receptor complex. This approach could offer a way to deliver antiviral genes directly to HIV-infected cells in vivo and could provide an additional treatment strategy in conjunction with existing antiviral therapies.
Interaction of Short-Range Repressors with
Drosophila
CtBP in the Embryo
Authors: Nibu Yutaka , Zhang Hailan , Levine Michael
Published: July 2002

Human CtBP attenuates transcriptional activation and tumorigenesis mediated by the adenovirus E1A protein. The E1A sequence motif that interacts with CtBP, Pro-X-Asp-Leu-Ser-X-Lys (P-DLS-K), is present in the repression domains of two unrelated short-range repressors in
Drosophila
, Knirps and Snail, and is essential for the interaction of these proteins with
Drosophila
CtBP (dCtBP). A P-element–induced mutation in dCtBP exhibits gene-dosage interactions with a null mutation in
knirps
, which is consistent with the occurrence of Knirps-dCtBP interactions in vivo. These observations suggest that CtBP and dCtBP are engaged in an evolutionarily conserved mechanism of transcriptional repression, which is used in both
Drosophila
and mammals.
Stabilization of Interleukin-2 mRNA by the c-Jun NH
2
-Terminal Kinase Pathway
Authors: Chen Ching-Yi , Del Gatto–Konczak Fabienne , Wu Zhenguo , Karin Michael
Published: July 2002

Signaling pathways that stabilize interleukin-2 (IL-2) messenger RNA (mRNA) in activated T cells were examined. IL-2 mRNA contains at least two cis elements that mediated its stabilization in response to different signals, including activation of c-Jun amino-terminal kinase (JNK). This response was mediated through a cis element encompassing the 5′ untranslated region (UTR) and the beginning of the coding region. IL-2 transcripts lacking this 5′ element no longer responded to JNK activation but were still responsive to other signals generated during T cell activation, which were probably sensed through the 3′ UTR. Thus, multiple elements within IL-2 mRNA modulate its stability in a combinatorial manner, and the JNK pathway controls turnover as well as synthesis of IL-2 mRNA.
C
1
Transfer Enzymes and Coenzymes Linking Methylotrophic Bacteria and Methanogenic Archaea
Authors: Chistoserdova Ludmila , Vorholt Julia A. , Thauer Rudolf K. , Lidstrom Mary E.
Published: July 2002

Methanogenic and sulfate-reducing Archaea are considered to have an energy metabolism involving C
1
transfer coenzymes and enzymes unique for this group of strictly anaerobic microorganisms. An aerobic methylotrophic bacterium,
Methylobacterium extorquens
AM1, was found to contain a cluster of genes that are predicted to encode some of these enzymes and was shown to contain two of the enzyme activities and one of the methanogenic coenzymes. Insertion mutants were all unable to grow on C
1
compounds, suggesting that the archaeal enzymes function in aerobic C
1
metabolism. Thus, methylotrophy and methanogenesis involve common genes that cross the bacterial/archaeal boundaries.
p53-Independent Role of MDM2 in TGF-β1 Resistance
Authors: Sun Peiqing , Dong Ping , Dai Kang , Hannon Gregory J. , Beach David
Published: July 2002

Transforming growth factor–β (TGF-β) inhibits cell proliferation, and acquisition of TGF-β resistance has been linked to tumorigenesis. A genetic screen was performed to identify complementary DNAs that abrogated TGF-β sensitivity in mink lung epithelial cells. Ectopic expression of murine double minute 2 rescued TGF-β–induced growth arrest in a p53-independent manner by interference with retinoblastoma susceptibility gene product (Rb)/E2F function. In human breast tumor cells, increased MDM2 expression levels correlated with TGF-β resistance. Thus, MDM2 may confer TGF-β resistance in a subset of tumors and may promote tumorigenesis by interference with two independent tumor suppressors, p53 and Rb.
Enhancement of Cation Diffusion Rates Across the 410-Kilometer Discontinuity in Earth's Mantle
Authors: Chakraborty S. , Knoche R. , Schulze H. , Rubie D. C. , Dobson D. , Ross N. L. , Angel R. J.
Published: July 2002

Rates of cation diffusion (magnesium, iron, and nickel) have been determined in olivine and its high-pressure polymorph, wadsleyite, at 9 to 15 gigapascals and 1100° to 1400°C for compositions that are relevant to Earth's mantle. Diffusion in olivine becomes strongly dependent on composition at high pressure. In wadsleyite, diffusion is one to two orders of magnitude faster than in olivine, depending on temperature. Homogenization of mantle heterogeneities (chemical mixing) and mineral transformations involving a magnesium-iron exchange will therefore occur considerably faster in the transition zone than at depths of less than 410 kilometers.
Inheritance of Resistance to
Bacillus thuringiensis
Toxin (Dipel ES) in the European Corn Borer
Authors: Huang F. , L. L. , Buschman  , A. R. , Higgins  , McGaughey W. H.
Published: July 2002

Resistance in the European corn borer,
Ostrinia nubilalis
(Hübner), to a commercial formulation of
Bacillus thuringiensis
(
Bt
) Berliner toxin, Dipel ES, appears to be inherited as an incompletely dominant autosomal gene. This contrasts with the inheritance of resistance to
Bt
in other insects, where it has usually been characterized as a recessive trait. The proposed high-dose/refuge strategy for resistance management in
Bt
maize depends on resistance being recessive or partially recessive. If field resistance turns out to be similar to this laboratory resistance, the usefulness of the high-dose/refuge strategy for resistance management in
Bt
maize may be diminished.
Recruitment of the Auditory Cortex in Congenitally Deaf Cats by Long-Term Cochlear Electrostimulation
Authors: Klinke Rainer , Kral Andrej , Heid Silvia , Tillein Jochen , Hartmann Rainer
Published: July 2002

In congenitally deaf cats, the central auditory system is deprived of acoustic input because of degeneration of the organ of Corti before the onset of hearing. Primary auditory afferents survive and can be stimulated electrically. By means of an intracochlear implant and an accompanying sound processor, congenitally deaf kittens were exposed to sounds and conditioned to respond to tones. After months of exposure to meaningful stimuli, the cortical activity in chronically implanted cats produced field potentials of higher amplitudes, expanded in area, developed long latency responses indicative of intracortical information processing, and showed more synaptic efficacy than in naı̈ve, unstimulated deaf cats. The activity established by auditory experience resembles activity in hearing animals.
Room-Temperature Magnetic Bistability in Organic Radical Crystals
Authors: Fujita Wataru , Awaga and Kunio
Published: July 2002

A large first-order magnetic phase transition in an organic radical, 1,3,5-trithia-2,4,6-triazapentalenyl, is described. The transition occurs with a wide thermal hysteresis loop over the temperature range 230 to 305 kelvin. The high-temperature phase is paramagnetic, and its structure consists of a uniform one-dimensional stacking of the radical. The low-temperature phase is diamagnetic because of strong dimerization along the stacking direction. The results may have applications in thermal sensors, switching units, and information storage media based on organic radical crystals.
Induction of Metaphase Arrest in Cleaving
Xenopus
Embryos by the Protein Kinase p90
Rsk
Authors: Gross Stefan D. , Schwab Markus S. , Lewellyn Andrea L. , Maller James L.
Published: July 2002

Before fertilization, vertebrate eggs are arrested in metaphase of meiosis II by cytostatic factor (CSF), an activity that requires activation of the mitogen-activated protein kinase (MAPK) pathway. To investigate whether CSF arrest is mediated by the protein kinase p90
Rsk
, which is phosphorylated and activated by MAPK, a constitutively activated (CA) form of Rsk was expressed in
Xenopus
embryos. Expression of CA Rsk resulted in cleavage arrest, and cytological analysis showed that arrested blastomeres were in M phase with prominent spindles characteristic of meiotic metaphase. Thus, Rsk appears to be the mediator of MAPK-dependent CSF arrest in vertebrate unfertilized eggs.
Requirement of the Prolyl Isomerase Pin1 for the Replication Checkpoint
Authors: Winkler Katharine E. , Swenson Katherine I. , Kornbluth Sally , Means Anthony R.
Published: July 2002

The peptidyl-prolyl isomerase Pin1 has been implicated in regulating cell cycle progression. Pin1 was found to be required for the DNA replication checkpoint in
Xenopus laevis
. Egg extracts depleted of Pin1 inappropriately transited from the G
2
to the M phase of the cell cycle in the presence of the DNA replication inhibitor aphidicolin. This defect in replication checkpoint function was reversed after the addition of recombinant wild-type Pin1, but not an isomerase-inactive mutant, to the depleted extract. Premature mitotic entry in the absence of Pin1 was accompanied by hyperphosphorylation of Cdc25, activation of Cdc2/cyclin B, and generation of epitopes recognized by the mitotic phosphoprotein antibody, MPM-2. Therefore, Pin1 appears to be required for the checkpoint delaying the onset of mitosis in response to incomplete replication.
Genetic Suppression of Polyglutamine Toxicity in
Drosophila
Authors: Kazemi-Esfarjani Parsa , Benzer Seymour
Published: July 2002

A
Drosophila
model for Huntington's and other polyglutamine diseases was used to screen for genetic factors modifying the degeneration caused by expression of polyglutamine in the eye. Among 7000 P-element insertions, several suppressor strains were isolated, two of which led to the discovery of the suppressor genes described here. The predicted product of one, dHDJ1, is homologous to human heat shock protein 40/HDJ1. That of the second, dTPR2, is homologous to the human tetratricopeptide repeat protein 2. Each of these molecules contains a chaperone-related J domain. Their suppression of polyglutamine toxicity was verified in transgenic flies.
Isolating the Spectroscopic Signature of a Hydration Shell With the Use of Clusters: Superoxide Tetrahydrate
Authors: Weber J. Mathias , Kelley Jude A. , Nielsen Steen B. , Ayotte Patrick , Johnson Mark A.
Published: July 2002

Cluster spectroscopy, aided by ab initio theory, was used to determine the detailed structure of a complete hydration shell around an anion. Infrared spectra of size-selected O
2
−
· (H
2
O)

n

(
n
= 1 to 4) cluster ions were obtained by photoevaporation of an argon nanomatrix. Four water molecules are required to complete the coordination shell. The simple spectrum of the tetrahydrate reveals a structure in which each water molecule is engaged in a single hydrogen bond to one of the four lobes of the π* orbital of the superoxide, whereas the water molecules bind together in pairs. This illustrates how water networks deform upon accommodating a solute ion to create a distinct supramolecular species.
Suppressing Wall Turbulence by Means of a Transverse Traveling Wave
Authors: Du Yiqing , Karniadakis George Em
Published: July 2002

Direct numerical simulations of wall-bounded flow reveal that turbulence production can be suppressed by a transverse traveling wave. Flow visualizations show that the near-wall streaks are eliminated, in contrast to other turbulence-control techniques, leading to a large shear stress reduction. The traveling wave can be induced by a spanwise force that is confined within the viscous sublayer; it has its maximum at the wall and decays exponentially away from it. We demonstrate the application of this approach in salt water, using arrays of electromagnetic tiles that produce the required traveling wave excitation at a high efficiency.
Propagation of Seismic Ground Motion in the Kanto Basin, Japan
Authors: Koketsu Kazuki , Kikuchi Masayuki
Published: July 2002

The pattern of ground motion for a magnitude 5.7 earthquake near Tokyo was captured by 384 strong ground motion instruments across the Kanto sedimentary basin and its surroundings. The records allow the visualization of the propagation of long-period ground motion in the basin and show the refraction of surface waves at the basin edge. The refracted wave does not travel directly from the earthquake epicenter, but traverses the basin obliquely to the edge. The surface wave inside the basin propagates more slowly than that outside such that the wavefronts separate from each other, and the refracted wave heals the discrepancy in the speed of advance of the wavefronts inside and outside the basin. The refracted arrival is dominant near the edge of the Kanto basin.
Hierarchical Self-Assembly of F-Actin and Cationic Lipid Complexes: Stacked Three-Layer Tubule Networks
Authors: Wong Gerard C. L. , Tang Jay X. , Lin Alison , Li Youli , Janmey Paul A. , Safinya Cyrus R.
Published: July 2002

We describe a distinct type of spontaneous hierarchical self-assembly of cytoskeletal filamentous actin (F-actin), a highly charged polyelectrolyte, and cationic lipid membranes. On the mesoscopic length scale, confocal microscopy reveals ribbonlike tubule structures that connect to form a network of tubules on the macroscopic scale (more than 100 micrometers). Within the tubules, on the 0.5- to 50-nanometer length scale, x-ray diffraction reveals an unusual structure consisting of osmotically swollen stacks of composite membranes with no direct analog in simple amphiphilic systems. The composite membrane is composed of three layers, a lipid bilayer sandwiched between two layers of actin, and is reminiscent of multilayered bacterial cell walls that exist far from equilibrium. Electron microscopy reveals that the actin layer consists of laterally locked F-actin filaments forming an anisotropic two-dimensional tethered crystal that appears to be the origin of the tubule formation.
Molecular Identification of a Taste Receptor Gene for Trehalose in
Drosophila
Authors: Ishimoto Hiroshi , Matsumoto Akira , Tanimura Teiichi
Published: July 2002

The molecular nature of sweet taste receptors has not been fully explored. Employing a differential screening strategy, we identified a taste receptor gene,
Tre1
, that controls the taste sensitivity to trehalose in
Drosophila melanogaster
. The
Tre1
gene encodes a novel protein with similarity to G protein–coupled seven-transmembrane receptors. Disruption of the
Tre1
gene lowered the taste sensitivity to trehalose, whereas sensitivities to other sugars were unaltered. Overexpression of the
Tre1
gene restored the taste sensitivity to trehalose in the
Tre1
deletion mutant. The
Tre1
gene is expressed in taste sensory cells. These results provide direct evidence that
Tre1
encodes a putative taste receptor for trehalose in
Drosophila
.
Living at Extremes
Authors: Campbell Kathleen A.
Published: July 2002

The Ecology of Deep-Sea Hydrothermal Vents
. Cindy Lee Van Dover. Princeton University Press, Princeton, NJ, 2000. 444 pp. $85, £53.50. ISBN 0-691-05780-X. Paper, $39.50, £24.95. ISBN 0-691-04929-7.

Targeting her fairly comprehensive overview at a broad audience, van Dover explores biological, chemical, geological, and evolutionary aspects of a luxuriant ecosystem based on geochemical energy rather than sunlight.
Sterility of
Drosophila
with Mutations in the Bloom Syndrome Gene--Complementation by
Ku70
Authors: Kusano Kohji , Johnson-Schlitz Dena M. , Engels William R.
Published: July 2002

The
Drosophila Dmblm
locus is a homolog of the human Bloom syndrome gene, which encodes a helicase of the RECQ family. We show that
Dmblm
is identical to
mus309
, a locus originally identified in a mutagen-sensitivity screen. One
mus309
allele, which carries a stop codon between two of the helicase motifs, causes partial male sterility and complete female sterility. Mutant males produce an excess of XY sperm and nullo sperm, consistent with a high frequency of nondisjunction and/or chromosome loss. These phenotypes of
mus309
suggest that
Dmblm
functions in DNA double-strand break repair. The mutant
Dmblm
phenotypes were partially rescued by an extra copy of the DNA repair gene
Ku70
, indicating that the two genes functionally interact in vivo.
Excretion of β-Lactam Antibiotics in Sweat—a Neglected Mechanism for Development of Antibiotic Resistance?
Authors: Høiby Niels , Pers Charlotte , Johansen Helle Krogh , Hansen Hanne ,   The Copenhagen Study Group on Antibiotics in Sweat
Published: July 2002

The concentrations of β-lactam antibiotics after standard doses were measured in blood and apocrine (axilla) and eccrine (forearm) sweat from six adult healthy persons. All persons had ceftazidime (axilla, 28.4 μg/ml; forearm, 11 μg/ml) and ceftriaxone (axilla, 8.9 μg/ml; forearm, 2.5 μg/ml) in sweat, and one person had cefuroxime in sweat (axilla, 7.8 μg/ml) (all data are mean peaks). Three persons had benzylpenicillin (axilla, 2.6 to 0.1 μg/ml) and one had phenoxymethylpenicillin (axilla, 0.4 μg/ml) in sweat. Excretion of β-lactam antibiotics in the sweat may explain why staphylococci so rapidly become resistant to these drugs.
Intracellular Penetration and Activity of Gemifloxacin in Human Polymorphonuclear Leukocytes
Authors: García Isabel , Pascual Alvaro , Ballesta Sofía , Joyanes Providencia , Perea Evelio J.
Published: July 2002

The intracellular penetration and activity of gemifloxacin in human polymorphonuclear leukocytes (PMN) were evaluated. Gemifloxacin reached intracellular concentrations eight times higher than extracellular concentrations. The uptake was rapid, reversible, and nonsaturable and was affected by environmental temperature, cell viability, and membrane stimuli. At therapeutic extracellular concentrations, gemifloxacin showed intracellular activity againstStaphylococcus aureus.
Efficacy of Telithromycin (HMR 3647) against Enterococci in a Mouse Peritonitis Model
Authors: Singh Kavindra V. , Zscheck Karen K. , Murray Barbara E.
Published: July 2002

We used a mouse peritonitis model to evaluate the in vivo efficacy of telithromycin (HMR 3647) (TEL) and erythromycin (ERY) against four strains of
Enterococcus faecalis
and three strains of
Enterococcus faecium
with differing susceptibilities to TEL. TEL was highly active in vivo against Ery-susceptible (Ery
s
) and -intermediate (Ery
i
) strains (MIC of TEL = 0.015 to 0.062 μg/ml) and showed less efficacy against Ery-resistant (Ery
r
) isolates (MIC of TEL = 4 to 16 μg/ml), although this was overcome in part by a second subcutaneous dose. Quinupristin-dalfopristin was also noted to have less efficacy against Ery
r
versus Ery
s
or Ery
i
E. faecium
strains, but this difference was reduced by intravenous administration. In conclusion, TEL was more potent in vivo against enterococci than was ERY; its activity was lowered by the presence of
erm
(B)-mediated Ery
r
.
Genotypic and Phenotypic Resistance Patterns of Human Immunodeficiency Virus Type 1 Variants with Insertions or Deletions in the Reverse Transcriptase (RT): Multicenter Study of Patients Treated with RT Inhibitors
Authors: Masquelier Bernard , Race Esther , Tamalet Catherine , Descamps Diane , Izopet Jacques , Buffet-Janvresse Claudine , Ruffault Annick , Mohammed Ali Si , Cottalorda Jacqueline , Schmuck Anne , Calvez Vincent , Dam Elisabeth , Fleury Hervé , Brun-Vézinet Françoise ,   the ANRS AC11 Resistance Study Group
Published: July 2002

Genomic rearrangements in the 5′ part of the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) have been involved in multidrug resistance to nucleoside RT inhibitors (NRTI). We carried out a retrospective, multicenter study to investigate the prevalence, variability, and phenotypic consequences of such rearrangements. Data concerning the HIV-1 RT genotype and the biological and clinical characteristics of NRTI-treated patients were collected from 10 virology laboratories. Sensitivities of the different HIV-1 variants to RT inhibitors were analyzed in a single-cycle recombinant virus assay. Fifty-two of 2,152 (2.4%) RT sequences had a rearrangement in the 5′ part of the RT, with an extensive molecular variation. The number of codons inserted between positions 68 and 69 ranged from 1 (3 samples) or 2 (41 samples) to 5 and 11 in one case each. In four cases, codon 67 was deleted. High levels of phenotypic resistance to zidovudine (AZT), lamivudine (3TC), stavudine (d4T), abacavir (ABC), and didanosine (ddI) were found in 95, 92, 72, 62, and 15% of the 40 samples analyzed, respectively. Resistance to AZT, d4T, and ABC could be found in the absence of the T215Y/F mutations. Resistance to 3TC could develop in the absence of specific mutations. Low-level resistance to ddI was noticed in 40% of the patients. The deletions of codon 67 seemed to have little effect on NRTI sensitivity. Most of the rearrangements were shown to contribute to cross-resistance to NRTI. The results regarding susceptibility to ddI raise the question of the interpretation of the phenotypic data concerning this drug.
In Vitro Antibiotic Susceptibilities of
Burkholderia mallei
(Causative Agent of Glanders) Determined by Broth Microdilution and E-Test
Authors: Heine Henry S. , England Marilyn J. , Waag David M. , Byrne W. Russell
Published: July 2002

In vitro susceptibilities to 28 antibiotics were determined for 11 strains of
Burkholderia mallei
by the broth microdilution method. The
B. mallei
strains demonstrated susceptibility to aminoglycosides, macrolides, quinolones, doxycycline, piperacillin, ceftazidime, and imipenem. For comparison and evaluation, 17 antibiotic susceptibilities were also determined by the E-test. E-test values were always lower than the broth dilution values. Establishing and comparing antibiotic susceptibilities of specific
B. mallei
strains will provide reference information for assessing new antibiotic agents.
Identification and Minisequencing-Based Discrimination of SHV β-Lactamases in Nosocomial Infection-AssociatedKlebsiella pneumoniaein Brisbane, Australia
Authors: Howard Christopher , van Daal Angela , Kelly Gregory , Schooneveldt Jacqueline , Nimmo Graeme , Giffard Philip M.
Published: July 2002

Extended-spectrum β-lactamases (ESBLs) are active against oxyimino cephalosporins and monobactams. Twenty-oneKlebsiella pneumoniaeisolates obtained between 1991 and 1995 at the Princess Alexandra Hospital in Brisbane, Australia, were subject to amplification and sequencing of the SHV β-lactamase-encoding genes. Thirteen strains were phenotypically ESBL positive. Of these, six strains carried theblaSHV-2agene and seven strains carried theblaSHV-12gene. Eight strains were phenotypically ESBL negative. Of these, seven strains carried the non-ESBLblaSHV-11gene and one strain carried the non-ESBLblaSHV-1gene. There was complete correspondence between the ESBL phenotype and the presence or absence of an ESBL-encoding gene(s). In addition, it was determined that of the 13 ESBL-positive strains, at least 4 carried copies of a non-ESBL-encoding gene in addition to theblaSHV-2aorblaSHV12gene. A minisequencing-based assay was developed to discriminate the different SHV classes. This technique, termed “first-nucleotide change,” involves the identification of the base added to a primer in a single-nucleotide extension reaction. The assay targeted polymorphisms at the first bases of codons 238 and 240 and reliably discriminated ESBL-positive strains from ESBL-negative strains and also distinguished strains carryingblaSHV-2afrom strains carryingblaSHV-12. In addition, this method was used to demonstrate an association between the relative copy numbers ofblaSHVgenes in individual strains and the levels of antibiotic resistance.