bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional studies of human intestinal alkaline sphingomyelinase by deglycosylation and mutagenesis
Authors: WU Jun , HANSEN Gert H. , NILSSON Åke , DUAN Rui-Dong
Published: February 2005

Intestinal alk-SMase (alkaline sphingomyelinase) is an ectoenzyme related to the NPP (nucleotide phosphodiesterase) family. It has five potential N-glycosylation sites and predicated transmembrane domains at both the N- and C-termini. The amino acid residues forming the two metal-binding sites in NPP are conserved, and those of the active core are modified. We examined the functional changes of the enzyme induced by deglycosylation and mutagenesis. Treating alk-SMase cDNA-transfected COS-7 cells with tunicamycin rendered the expressed enzyme completely inactive. Mutations of the five potential N-glycosylation sites individually and in combination showed that these sites were all glycosylated and deficient glycosylation decreased the enzyme activity. Immunogold labelling showed that the wild-type enzyme was mainly located in the plasma membrane, whereas the C-terminal domain-truncated enzyme was released into the medium. Deglycosylation blocked the release of the enzyme that accumulated in endosome-like structures. The enzyme activity was also decreased by mutations of the residues forming the putative metal-binding sites and the active core. Substitution of the active core sequence with that of NPP or mutation of T75 in the core abolished the enzyme activity against sphingomyelin but failed to render the enzyme NPP active. Our results indicate that alk-SMase activity is severely affected by defective N-glycosylation and structural alterations of the putative metal-binding sites and the predicted active core.
Linking Smads and transcriptional activation
Authors: INMAN Gareth J.
Published: February 2005

TGF-β1 (transforming growth factor-β1) is the prototypical member of a large family of pleiotropic cytokines that regulate diverse biological processes during development and adult tissue homoeostasis. TGF-β signals via membrane bound serine/threonine kinase receptors which transmit their signals via the intracellular signalling molecules Smad2, Smad3 and Smad4. These Smads contain conserved MH1 and MH2 domains separated by a flexible linker domain. Smad2 and Smad3 act as kinase substrates for the receptors, and, following phosphorylation, they form complexes with Smad4 and translocate to the nucleus. These Smad complexes regulate gene expression and ultimately determine the biological response to TGF-β. In this issue of the Biochemical Journal, Wang et al. have shown that, like Smad4, the linker domain of Smad3 contains a Smad transcriptional activation domain. This is capable of recruiting the p300 transcriptional co-activator and is required for Smad3-dependent transcriptional activation. This study raises interesting questions about the nature and regulation of Smad-regulated gene activation and elevates the status of the linker domain to rival that of the much-lauded MH1 and MH2 domains.
Critical Themes in Electronic Commerce Research: A Meta-Analysis
Authors: Wareham Jonathan , Zheng Jack G , Straub Detmar
Published: February 2005

This paper profiles the eCommerce research of the past 7 years. Drawing on a sample of 582 articles in both academic and professional journals, we highlight the major domains and explore the most salient themes in each area. Our analysis finds that the interdisciplinary nature of eCommerce research has led to great diversity in the topics explored. Moreover, eCommerce researchers have been diverse in their use of both research approaches and methods. Our analysis delineates several areas that remain underserved, highlighting a number of research opportunities for the IS community as eCommerce continues to evolve.
Protonated clathrate cages enclosing neutral water molecules: H+(H2O)21 and H+(H2O)28
Authors: Wu Chih-Che , Lin Chih-Kai , Chang Huan-Cheng , Jiang Jyh-Chiang , Kuo Jer-Lai , Klein Michael L.
Published: February 2005

This paper describes a systematic study on the clathrate structure of H+(H2O)21 using tandem mass spectrometry, vibrational predissociation spectroscopy, Monte Carlo simulations, and density functional theory calculations. We produced H+(H2O)n from a continuous corona-discharged supersonic expansion and observed three anomalies simultaneously at the cluster temperature near 150K, including (1) the peak at n=21 is more intense than its neighboring ions in the mass spectrum, (2) the size-dependent dissociation fractions show a distinct drop for the 21-mer, and (3) the infrared spectrum of H+(H2O)21 exhibits only a single feature at 3699cm−1, corresponding to the free-OH stretching of three-coordinated water molecules. Interestingly, the anomalies appear or disappear together with cluster temperature, indicating close correlation of these three observations. The observations, together with Monte Carlo simulations and density functional theory calculations, corroborate the notion for the formation of a distorted pentagonal dodecahedral (512) cage with a H2O molecule in the cage and a H3O+ ion on the surface for this “magic number” water cluster ion. The dodecahedral cage melts at higher temperatures, as evidenced by the emergence of a free-OH stretching feature at 3717cm−1 for the two-coordinated water in H+(H2O)21 produced in a warmer molecular beam. Extension of this study to larger clusters strongly suggests that the experimentally observed isomer of H+(H2O)28 is most likely to consist of a distorted protonated pentakaidecahedral (51263) cage enclosing two neutral water molecules.
Phase separation of the Widom–Rowlinson mixture in confined geometry
Authors: Góźdź W. T.
Published: February 2005

The behavior of binary Widom–Rowlinson [J. Chem. Phys. 52, 1670 (1970)] mixture in confined geometry is investigated. The influence of confinement on phase separation is examined. Coexistence curves for the mixture in slitlike pores and pores of complex geometry are calculated in Monte Carlo simulations. Finite size scaling analysis is used to determine precisely the location of critical point for the bulk mixture.
Dopant site selectivity in BaCe0.85M0.15O3-δ by extended x-ray absorption fine structure
Authors: Wu J. , Webb S. M. , Brennan S. , Haile S. M.
Published: February 2005

Rare earth doped BaCeO3 has been widely investigated as a proton conducting material. Trivalent dopants are generally assumed to fully occupy the Ce4+-site, and thereby introduce oxygen vacancies into the perovskite structure. Recent studies indicate the possibility of partial dopant incorporation onto the Ba2+-site concomitant with BaO evaporation, reducing the oxygen vacancy content. Because proton incorporation requires, as a first step, the generation of oxygen vacancies such dopant partitioning is detrimental to protonic conductivity. A quantitative Extended X-ray Absorption Fine Structure (EXAFS) study of BaCe0.85M0.15O3-δ(M=Yb,Gd) is presented here along with complementary x-ray powder diffraction and electron probe chemical analyses. The EXAFS results demonstrate that as much as 4.6% of the ytterbium and 7.2% of the gadolinium intended for incorporation onto the Ce site, in fact, resides on the Ba site. The results are in qualitative agreement with the diffraction and chemical analyses, which additionally show an even greater extent of Nd incorporation on the Ba site.
Dissipative quantum phase space dynamics on dynamically adapting grids
Authors: Hughes Keith H.
Published: February 2005

A moving grid approach to a dynamical study of dissipative systems is described. The dynamics are studied in phase space for the Caldeira–Leggett master equation. The grid movement is based on the principle of equidistribution and, by using a grid smoothing technique, the grid points trace a path that continuously adapts to reflect the dynamics of a phase-space distribution function. The technique is robust and allows accurate computations to be obtained for long propagation times. The effects of dissipation on the dynamics are studied and results are presented for systems subject to both periodic and nonperiodic multiminimum potential functions.
The structure of hyperspherical fluids in various dimensions
Authors: Bishop Marvin , Whitlock Paula A. , Klein Dino
Published: February 2005

The structure of hard, hyperspherical fluids in dimension one, two, three, four, and five has been examined by calculating the pair correlation function using a Monte Carlo simulation. The pair correlation functions match known results in one, two, and three dimensions. The contact value of the pair correlation functions in all the different dimensions agrees well with the theory of Song, Mason, and Stratt [J. Phys. Chem. 93, 6916 (1989)]. The decrease in ordering as the dimension is increased is readily apparent in the structure of the pair correlation function.
Euclidean quantum mechanics in the momentum representation
Authors: Privault Nicolas , Zambrini Jean-Claude
Published: February 2005

A time reversible probabilistic representation of solutions of the (Euclidean) Schrödinger equation in momentum representation is constructed using Lévy processes and bridges. Each diffusion in the position representation is associated with a jump diffusion in the momentum space. Our method can be looked upon as a rigorous version of Feynman’s path integral approach. Several examples are studied.
Excited states dynamics of DNA and RNA bases: Characterization of a stepwise deactivation pathway in the gas phase
Authors: Canuel Clélia , Mons Michel , Piuzzi François , Tardivel Benjamin , Dimicoli Iliana , Elhanine Mohamed
Published: February 2005

Radiationless deactivation pathways of excited gas phase nucleobases were investigated using mass-selected femtosecond resolved pump-probe resonant ionization. By comparison between nucleobases and methylated species, in which tautomerism cannot occur, we can access intrinsic mechanisms at a time resolution never reported so far (80fs). At this time resolution, and using appropriate substitution, real nuclear motion corresponding to active vibrational modes along deactivation coordinates can actually be probed. We provide evidence for the existence of a two-step decay mechanism, following a 267nm excitation of the nucleobases. The time resolution achieved together with a careful zero time-delay calibration between lasers allow us to show that the first step does correspond to intrinsic dynamics rather than to a laser cross correlation. For adenine and 9-methyladenine a first decay component of about 100fs has been measured. This first step is radically increased to 200fs when the amino group hydrogen atoms of adenine are substituted by methyl groups. Our results could be rationalized according to the effect of the highly localized nature of the excitation combined to the presence of efficient deactivation pathway along both pyrimidine ring and amino group out-of-plane vibrational modes. These nuclear motions play a key role in the vibronic coupling between the initially excited ππ* and the dark nπ* states. This seems to be the common mechanism that opens up the earlier phase of the internal conversion pathway which then, in consideration of the rather fast relaxation times observed, would probably proceed via conical intersection between the nπ* relay state and high vibrational levels of the ground state.
Gallium oxide and dioxide: Investigation of the ground and low-lying electronic states via anion photoelectron spectroscopy
Authors: Meloni Giovanni , Sheehan Sean M. , Neumark Daniel M.
Published: February 2005

The GaO and GaO2 molecules were investigated using negative ion photoelectron spectroscopy. All the photoelectron spectra showed vibrationally resolved progressions. With the aid of electronic structure calculations and Franck–Condon spectral simulations, different molecular parameters and energetics of GaO−∕GaO and GaO2−∕GaO2 were determined, including the electron affinity of GaO, the vibrational frequency of GaO−, and the term energy, spin-orbit splitting, and vibrational frequency for the first excited AΠΩ2 state of GaO. The GaO2− photoelectron spectra comprised three bands assigned as transitions from the linear XΣg+1 ground state of GaO2− to three linear neutral states: the AΠg2, BΠu2, and CΣu+2 states. The symmetric stretch frequencies of the anion and three neutral states as well as the spin-orbit splitting of the neutral Π2 states were determined. Electronic structure calculations found the neutral lowest energy linear structure to be only 63meV higher than the neutral bent geometry.
Polarization response of water and methanol investigated by a polarizable force field and density functional theory calculations: Implications for charge transfer
Authors: Chelli Riccardo , Pagliai Marco , Procacci Piero , Cardini Gianni , Schettino Vincenzo
Published: February 2005

Electronic polarization response in hydrogen-bond clusters and liquid configurations of water and methanol has been studied by density functional theory (DFT) and by a polarizable force field based on the chemical potential equalization (CPE) principle. It has been shown that an accurate CPE parametrization based on isolated molecular properties is not completely transferable to strongly interacting hydrogen-bond clusters with discrepancies between CPE and DFT overall dipole moments as large as 15%. This is due to the lack of intermolecular charge transfer in the standard CPE implementation. A CPE scheme for evaluating the amount of transferred charge has been developed. The charge transfer parameters are determined with the aid of accurate DFT calculations using only hydrogen-bond dimer configurations. The amount of transferred charge is found to be of the order of few hundredths of electrons, as already found in recent studies on hydrogen-bond systems. The parameters of the model are then used, without further adjustment, to different hydrogen-bond clustered forms of water and methanol (oligomer and liquid configurations). In agreement with different approaches proposed in literature for studying charge transfer effects, the transferred charge in hydrogen-bond dimers is found to decrease exponentially with the hydrogen-bond distance. When allowance is made for charge transfer according to the proposed scheme, the CPE dipole moments are found to reproduce satisfactorily the DFT data.
Triplet recombination at Pb centers and its implications for capture cross sections
Authors: Friedrich Felice , Boehme Christoph , Lips Klaus
Published: February 2005

Pulsed electrically detected magnetic resonance measurements are presented showing that Pb centers at the crystalline silicon (c-Si) (111) to silicon dioxide (SiO2) interface can cause recombination of strongly coupled spin pairs in singlet and triplet configurations. The implication of these findings is that two different electron capture cross sections can exist at a single defect. This shows that the previously observed two capture cross sections at the c-Si∕SiO2 interface do not necessarily imply the existence of additional non-Pb-like centers such as oxygen-backbonded silicon dangling bonds.
Electrically induced pattern formation in thin leaky dielectric films
Authors: Craster R. V. , Matar O. K.
Published: February 2005

The stability of the interface between two thin leaky dielectric liquid layers bounded between two flat electrodes is considered. A coupled system of evolution equations is derived for the interfacial location and charge density using lubrication theory. This system is parametrized by the dielectric constants of the two fluids in addition to ratios of their conductivities, viscosities, and thicknesses. A linear stability analysis is conducted and the behavior of the system in the nonlinear regime is also examined. The system is destabilized by electrical stresses that are resisted by capillarity and modified by viscous dissipation. Our results suggest that decreasing the thickness ratio is destabilizing, giving rise to periodic structures of decreasing wavelength. Decreasing the viscosity ratio was also found to lead to the formation of sharp-edged structures whose vertical extent is virtually equal to the gap width between the electrodes. Similar structures were also determined upon increasing the ratio of the dielectric constants and electric conductivities.
Commutator errors in the filtering approach to large-eddy simulation
Authors: van der Bos Fedderik , Geurts Bernard J.
Published: February 2005

We analyze the large-eddy equations that are obtained from the application of a spatially nonuniform filter to the Navier–Stokes equations. Next to the well-known turbulent stress tensor a second group of subgrid terms arises; the so-called commutator errors. These additional subgrid terms emerge in the large-eddy equations solely as a consequence of the nonuniformity of the filter. We compare the magnitude of the divergence of the turbulent stress tensor with that of the commutator errors and pay attention to the role of the explicit filter that is adopted. It is shown that the turbulent stress contributions and the commutator errors display the same scaling behavior on the filter width and its derivative. Correspondingly, the use of higher-order filters is shown not only to decrease the commutator errors but likewise the turbulent stresses are uniformly reduced with increasing filter order. In addition, we establish that skewness of the spatial filter has a strong influence on the magnitude of the commutator errors while leaving the turbulent stress contributions roughly unaltered. The analysis of the order of magnitude of the various terms provides an impression of the flow conditions and filter width nonuniformities which necessitate explicit commutator-error modeling next to the more traditional turbulent stress subgrid modeling. Some explicit models for the commutator errors are put forward and an a priori assessment of these commutator-error models in turbulent mixing layers is obtained. Generalized similarity models appear promising in this respect and display high correlation with the exact commutator errors.
Local environment of ferromagnetically ordered Mn in epitaxial InMnAs
Authors: Chiu P. T. , Wessels B. W. , Keavney D. J. , Freeland J. W.
Published: February 2005

The magnetic properties of the ferromagnetic semiconductor In0.98Mn0.02As were characterized by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. The Mn exhibits an atomic-like L2,3 absorption spectrum that indicates that the 3d states are highly localized. In addition, a large dichroism at the Mn L2,3 edge was observed from 5 to 300 K at an applied field of 2T. A calculated spectrum assuming atomic Mn2+ yields the best agreement with the experimental InMnAs spectrum. A comparison of the dichroism spectra of MnAs and InMnAs shows clear differences suggesting that the ferromagnetism observed in InMnAs is not due to hexagonal MnAs clusters. The temperature dependence of the dichroism indicates the presence of two ferromagnetic species, one with a transition temperature of 30 K and another with a transition temperature in excess of 300 K. The dichroism spectra are consistent with the assignment of the low temperature species to random substitutional Mn and the high temperature species to Mn near-neighbor pairs.
Micro-Raman-scattering study of stress distribution in GaN films grown on patterned Si(111) by metal-organic chemical-vapor deposition
Authors: Wang D. , Jia S. , Chen K. J. , Lau K. M. , Dikme Y. , van Gemmern P. , Lin Y. C. , Kalisch H. , Jansen R. H. , Heuken M.
Published: February 2005

GaN films were grown by metal-organic chemical-vapor deposition on Si(111) substrates patterned with arrays of squares and rectangular stripes with a 3.5-μm height and various lateral dimensions. Spatial distributions of tensile stress in the GaN pattern units were mapped out using micro-Raman spectroscopy. At the center of a square GaN film, the tensile stress is the largest and relaxes symmetrically towards the square edges where stress-release free facets are available. The largest crack-free square size for a 1-μm-thick GaN film is in the order of ∼100×100μm2, which is much larger than a theoretically predicted value (∼14μm).
Breakup and capture of two sedimenting drops in a vertical temperature gradient
Authors: Rother Michael A. , Davis Robert H.
Published: February 2005

A curvatureless three-dimensional boundary-integral algorithm has been developed for tangential Marangoni stresses and used to study breakup and capture of two deformable drops for arbitrary drop-to-medium viscosity and thermal conductivity ratios in parallel and antiparallel arrangements of gravity and an applied vertical temperature gradient. When the driving forces are opposed, the previously observed inhibition of breakup by a weak thermocapillary effect for drops with equal viscosity and thermal conductivity ratios is shown to be almost exclusively the result of changing interfacial tension, with Marangoni stresses having virtually no influence. Alignment of gravity and the temperature gradient in the same direction enhances breakup more than opposing driving forces reduce it, with the limitation that the drops are moving toward a region of zero interfacial tension. The thermal conductivity ratio has negligible impact on these interactions. For bubbles, the effect of a temperature gradient on gravitational results is much less pronounced than for drops. Under certain conditions, parallel orientation of the driving forces weakly inhibits the capture interaction for bubbles, while antiparallel orientation enhances the phenomenon.
Magnetization reversal in individual micrometer-sized polycrystalline Permalloy rings
Authors: Moore T. A. , Hayward T. J. , Tse D. H. Y. , Bland J. A. C. , Castaño F. J. , Ross C. A.
Published: February 2005

The magnetization reversal of individual 2 μm and 5 μm diameter polycrystalline Permalloy rings, with respective widths 0.75 μm and 1 μm, thickness 45 nm, has been investigated by focused magneto-optic Kerr effect (MOKE) magnetometry. Micromagnetic simulation of the reversal in the 2 μm diameter ring reveals that the onion-to-vortex state switching occurs by nucleation and subsequent annihilation of vortex walls that span the width of the ring, and that the vortex-to-reverse-onion state switching occurs by expansion of a reverse domain. The hysteresis loop shows good agreement with the experimental MOKE loop. Measurements of the switching through one-half of a 5 μm diameter ring enable the determination of the circulation of the vortex states accessed during one applied field cycle. The rings switch via one vortex state (either clockwise or anticlockwise) on both downward and upward applied field sweeps. The number of applied field cycles spent switching via one vortex state before changing to switch via the opposite vortex state is random, likely to be due to the history of the spin configuration and thermal fluctuations.
On the crystalline structure, stoichiometry and band gap of InN thin films
Authors: Yu K. M. , Liliental-Weber Z. , Walukiewicz W. , Shan W. , Ager J. W. , Li S. X. , Jones R. E. , Haller E. E. , Lu Hai , Schaff William J.
Published: February 2005

Detailed transmission electron microscopy, x-ray diffraction (XRD), and optical characterization of a variety of InN thin films grown by molecular-beam epitaxy under both optimized and nonoptimized conditions is reported. Optical characterization by absorption and photoluminescence confirms that the bandgap of single-crystalline and polycrystalline wurtzite InN is 0.70±0.05eV. Films grown under optimized conditions with an AlN nucleation layer and a GaN buffer layer are stoichiometric, single-crystalline wurtzite structure with dislocation densities not exceeding mid-1010cm−2. Nonoptimal films can be polycrystalline and display an XRD diffraction feature at 2θ≈33°; this feature has been attributed by others to the presence of metallic In clusters. Careful indexing of wide-angle XRD scans and selected area diffraction patterns shows that this peak is in fact due to the presence of polycrystalline InN grains; no evidence of metallic In clusters was found in any of the studied samples.
Copper nanopattern on SiO2 from sputter etching a Cu∕SiO2 interface
Authors: Stepanova M. , Dew S. K. , Soshnikov I. P.
Published: February 2005

We have observed a Cu nanostructure self-assembled on a SiO2 substrate during ion beam etching the Cu∕SiO2 interface. We have deposited a thin Cu layer on a glass substrate and etched the deposited layer by a neutralized argon ion beam. At the stage when almost all metal is removed by etching, we have observed an ∼20-nm-sized Cu pattern on the substrate. By atomistic Monte Carlo simulations we have demonstrated that during sputter etching, a morphology self-organizes on the surface of the Cu layer whose size and shape matches the observed Cu nanostructure. We conclude that the observed Cu nanopattern on the substrate results from the surface morphology developed by sputter instability during etching of the deposited layer.
1
∕
f
noise in gold nanoparticle chemosensors
Authors: Kurdak C. , Kim J. , Kuo A. , Lucido J. J. , Farina L. A. , Bai X. , Rowe M. P. , Matzger A. J.
Published: February 2005

We present a systematic study of low-frequency noise in Au nanoparticle chemosensors. All the sensors we have studied exhibit 1∕f-type noise at low frequencies. The magnitude of the 1∕f noise was smaller in devices with a larger device area, indicating that the 1∕f noise is caused by intrinsic processes. The noise amplitude was found to be strongly temperature dependent between 40–300K, with a local peak at around 100K, and weakly dependent below 40K. The noise data could not be fit by a single activated process indicating that multiple noise processes must be present in our sensors.
High extinction ratio antiresonant reflecting optical waveguide-type polarizers with large core diameter
Authors: Lin J. Y. , Chu A. K.
Published: February 2005

An optical polarizer based on antiresonant reflecting optical waveguide (ARROW) structure is presented. The advantage over conventional ARROW devices is the fact that high extinction ratio of the proposed polarizer can be obtained even with a large core diameter. This comes into effect because loss discrimination against TM modes is dramatically enhanced due to birefringence of the polyimide core. In addition, the loss discrimination can be further increased by reducing the thickness of the core at the first antiresonant condition. The measured extinction ratio and insertion loss of a 2-cm-long polyimide∕Ta2O5∕SiO2 ARROW polarizer are 40dB and 2.2dB, respectively.
Dielectric breakdown and Poole–Frenkel field saturation in silicon oxynitride thin films
Authors: Habermehl S. , Apodaca R. T.
Published: February 2005

Dielectric breakdown is studied in silicon oxynitride thin films varying in composition from SiN1.33 to SiO0.60N0.93. The films are observed to exhibit Poole–Frenkel emission as the dominant charge transport mechanism, with a compositionally dependent ionization potential ranging from 1.22 to 1.51 eV. The barrier lowering energy at the point of dielectric breakdown is independently determined to be likewise compositionally dependent, with the energies correlated to within ∼2kT of the ionization potential. Field saturation-induced trap ionization is discussed as a means to negate carrier scattering from bulk traps as an impediment to impact ionization and dielectric breakdown.
Structural influence on atomic hopping and electronic states of Pd-based bulk metallic glasses
Authors: Tang X.-P. , Löffler Jörg F. , Schwarz R. B. , Johnson William L. , Wu Yue
Published: February 2005

Atomic motion and electronic structures of Pd–Ni–Cu–P bulk metallic glasses were investigated using P31 nuclear magnetic resonance. The hopping rate of P atoms was determined by the stimulated echo technique. Significant hopping was observed in all alloys well below the glass transition temperature. Increasing the Cu content to above 25at.% increases P hopping significantly, consistent with the previous finding that the openness of the structure increases with Cu content. In contrast, P hopping is not influenced by changes of local electronic states at P sites, induced by the substitution of Ni by Cu.
Planck blackbody emissive power in particulate media
Authors: Prasher Ravi
Published: February 2005

Modifications of the Planck blackbody intensity and emissive power are proposed due to the modifications of the photon energy transport velocity and the density of states in particulate media. These modifications result from the multiple scattering of photons. These modifications affect the heat flux and temperature predictions in particulate media. Results show that current methods of predicting heat flux and temperature can lead to erroneous conclusions in a multiple-scattering radiative system.
Transformation-induced plasticity and cascading structural changes in hexagonal boron nitride under high pressure and shear
Authors: Levitas Valery I. , Ma Yanzhang , Hashemi Javad
Published: February 2005

In situ x-ray diffraction study and modeling of the degree of disorder, s, and phase transformation (PT) in hexagonal hBN were performed. It was proven that changes in s are strain-induced and that s can be used to quantify plastic strain. During the strain-induced hBN→wurtzitic wBN PT, the transformation-induced plasticity (TRIP) was exposed and quantified. TRIP exceeds conventional plasticity by a factor of 20. Cascading structural changes were revealed. Strain-induced disorder explains why PT under hydrostatic and nonhydrostatic conditions started at the same pressure ∼10GPa. For the same disorder, plastic shear reduces PT pressure by a factor of 3–4.
p
H
sensors based on hydrogenated diamond surfaces
Authors: Garrido Jose A. , Härtl Andreas , Kuch Stefan , Stutzmann Martin , Williams Oliver A. , Jackmann R. B.
Published: February 2005

We report on the operation of ungated surface conductive diamond devices in electrolytic solutions. The effect of electrolyte pH on the channel conductivity is studied in detail. It is shown that fully hydrogen terminated diamond surfaces are not pH sensitive. However, a pronounced pH sensitivity arises after a mild surface oxidation by ozone. We propose that charged ions from the electrolyte adsorbed on the oxidized surface regions induce a lateral electrostatic modulation of the conductive hole accumulation layer on the surface. In contrast, charged ions are not expected to be adsorbed on the hydrogen terminated surface, either due to the screening induced by a dense layer of strongly adsorbed counter-ions or by the absence of the proper reactive surface groups. Therefore, the modulation of the surface conductivity is generated by the oxidized regions, which are described as microscopic chemical in-plane gates. The pH sensitivity mechanism proposed here differs qualitatively from the one used to explain the behavior of conventional ion sensitive field effect transistors, resulting in a pH sensitivity higher than the Nernstian limit.
High efficiency visible electroluminescence from silicon nanocrystals embedded in silicon nitride using a transparent doping layer
Authors: Cho Kwan Sik , Park Nae-Man , Kim Tae-Youb , Kim Kyung-Hyun , Sung Gun Yong , Shin Jung H.
Published: February 2005

We have fabricated light-emitting diodes with a transparent doping layer on silicon nanocrystals (nc-Si) embeded in silicon nitride matrix formed by plasma-enhanced chemical vapor deposition. Under forward biased condition, orange electroluminescence (EL) with its peak wavelength at about 600 nm was observed at room temperature. The peak position of the EL is very similar to that of the photoluminescence (PL) and the emitted EL intensity is proportional to the current density passing through the device. We suggest that the observed EL is originated from electron-hole pair recombination in nc-Si. By using indium tin oxide and n-type SiC layer combination as a transparent doping layer, we obtained high external quantum efficiency greater than 1.6%.
Photoconductivity decay in metamorphic InAsP∕InGaAs double heterostructures grown on InAsyP1−y compositionally step-graded buffers
Authors: Lin Y. , Hudait M. K. , Johnston S. W. , Ahrenkiel R. K. , Ringel S. A.
Published: February 2005

Lattice-mismatched InAs0.32P0.68∕In0.68Ga0.32As∕InAs0.32P0.68 double heterostructures (DH) were grown on compositionally graded InAsyP1−y∕InP substrates by solid-source molecular-beam epitaxy (MBE) out to a misfit of ∼1%. The kinetics of carrier recombination were investigated in the nearly totally relaxed MBE-grown DH structures using photoconductivity decay (PCD) measurements. High minority carrier lifetimes of 4–5μs close to the radiation limit were measured, indicating the ability of MBE-grown InAsyP1−y buffers in achieving high-electronic-quality, low-band-gap mismatched InGaAs layers. Analysis suggests that very low interface recombination velocities are achieved. A photogenerated carrier diffusion model is presented to explain the initial nonlinear decays observed in PCD data for these heterostructures.
Effects of capping on the Ga1−xMnxAs magnetic depth profile
Authors: Kirby B. J. , Borchers J. A. , Rhyne J. J. , O’Donovan K. V. , Wojtowicz T. , Liu X. , Ge Z. , Shen S. , Furdyna J. K.
Published: February 2005

Annealing can increase the Curie temperature and net magnetization in uncapped Ga1−xMnxAs films, effects that are suppressed when the films are capped with GaAs. Previous polarized neutron reflectometry (PNR) studies of uncapped Ga1−xMnxAs revealed a pronounced magnetization gradient that was reduced after annealing. We have extended this study to Ga1−xMnxAs capped with GaAs. We observe no increase in Curie temperature or net magnetization upon annealing. Furthermore, PNR measurements indicate that annealing produces minimal differences in the depth-dependent magnetization, as both as-grown and annealed films feature a significant magnetization gradient. These results suggest that the GaAs cap inhibits redistribution of interstitial Mn impurities during annealing.
AlGaAs emitter∕GaAs barrier terahertz detector with a 2.3 THz threshold
Authors: Rinzan M. B. M. , Perera A. G. U. , Matsik S. G. , Liu H. C. , Wasilewski Z. R. , Buchanan M.
Published: February 2005

A heterojunction interfacial work function internal photoemission (HEIWIP) detector with a threshold frequency (f0) of 2.3 THz (λ0=128μm) is demonstrated. The threshold limit of ∼3.3THz (92 μm) due to the Al fraction being limited to ∼0.005, in order to avoid control and transition from alloy to isoelectronic doping behavior, was surpassed using AlGaAs emitters and GaAs barriers. The peak values of responsivity, quantum efficiency, and the specific detectivity at 9.6 THz and 4.8 K for a bias field of 2.0kV∕cm are 7.3A∕W, 29%, 5.3×1011 Jones, respectively. The background-limited infrared photodetector temperature of 20 K with a 60° field of view was observed for a bias field of 0.15kV∕cm. The f0 could be further reduced toward ∼1THz regime (∼300μm) by adjusting the Al fraction to offset the effect of residual doping, and/or lowering the residual doping in the barrier, effectively lowering the band bending.
The emergence of grammar: Systematic structure in a new language
Authors: Sandler Wendy , Meir Irit , Padden Carol , Aronoff Mark
Published: February 2005

This report contains a linguistic description of a language created spontaneously without any apparent external influence in a stable existing community. We describe the syntactic structure of Al-Sayyid Bedouin Sign Language, a language that has arisen in the last 70 years in an isolated endogamous community with a high incidence of nonsyndromic, genetically recessive, profound prelingual neurosensory deafness. In the space of one generation from its inception, systematic grammatical structure has emerged in the language. Going beyond a conventionalized list of words for actions, objects, people, characteristics, and so on, a systematic way of marking the grammatical relations among those elements has appeared in the form of highly regular word order. These systematic structures cannot be attributed to influence from other languages, because the particular word orders that appear in Al-Sayyid Bedouin Sign Language differ from those found both in the ambient spoken languages in the community and in the other sign language found predominantly in the surrounding area. Therefore, the emerging grammatical structures should be regarded as an independent development within the language.
Identification of pathway-selective estrogen receptor ligands that inhibit NF-κB transcriptional activity
Authors: Chadwick Christopher C. , Chippari Susan , Matelan Edward , Borges-Marcucci Lisa , Eckert Amy M. , Keith James C. , Albert Leo M. , Leathurby Yelena , Harris Heather A. , Bhat Ramesh A. , Ashwell Mark , Trybulski Eugene , Winneker Richard C. , Adelman Steven J. , Steffan Robert J. , Harnish Douglas C.
Published: February 2005

Inflammation is now recognized as a key component in a number of diseases such as atherosclerosis, rheumatoid arthritis, and inflammatory bowel disease. The transcription factor NF-κB has been shown to be involved in both the early and late stages of the inflammatory-proliferative process. In this report, we describe the identification of the pathway-selective estrogen receptor (ER) ligand, WAY-169916, that inhibits NF-κB transcriptional activity but is devoid of conventional estrogenic activity. This pathway-selective ligand does not promote the classic actions of estrogens such as stimulation of uterine proliferation or ER-mediated gene expression, but is a potent antiinflammatory agent, as demonstrated in the HLA-B27 transgenic rat model of inflammatory bowel disease. Our results indicate the potential utility of pathway-selective ER ligands such as WAY-169916 in the treatment of chronic inflammatory diseases.
Bacterial swimming and oxygen transport near contact lines
Authors: Tuval Idan , Cisneros Luis , Dombrowski Christopher , Wolgemuth Charles W. , Kessler John O. , Goldstein Raymond E.
Published: February 2005

Aerobic bacteria often live in thin fluid layers near solid–air–water contact lines, in which the biology of chemotaxis, metabolism, and cell–cell signaling is intimately connected to the physics of buoyancy, diffusion, and mixing. Using the geometry of a sessile drop, we demonstrate in suspensions of
Bacillus subtilis
the self-organized generation of a persistent hydrodynamic vortex that traps cells near the contact line. Arising from upward oxygentaxis and downward gravitational forcing, these dynamics are related to the Boycott effect in sedimentation and are explained quantitatively by a mathematical model consisting of oxygen diffusion and consumption, chemotaxis, and viscous fluid dynamics. The vortex is shown to advectively enhance uptake of oxygen into the suspension, and the wedge geometry leads to a singularity in the chemotactic dynamics near the contact line.
Dynamics of unbinding of cell adhesion molecules: Transition from catch to slip bonds
Authors: Barsegov V. , Thirumalai D.
Published: February 2005

The unbinding dynamics of complexes involving cell-adhesion molecules depends on the specific ligands. Atomic force microscopy measurements have shown that for the specific P-selectin–P-selectin glycoprotein ligand (sPSGL-1) the average bond lifetime 〈
t
〉 initially increases (catch bonds) at low (≤10 pN) constant force,
f
, and decreases when
f
> 10 pN (slip bonds). In contrast, for the complex with G1 anti-P-selectin monoclonal antibody 〈
t
〉 monotonically decreases with
f
. To quantitatively map the energy landscape of such complexes we use a model that considers the possibility of redistribution of population from one force-free state to another force-stabilized bound state. The excellent agreement between theory and experiments allows us to extract energy landscape parameters by fitting the calculated curves to the lifetime measurements for both sPSGL-1 and G1. Surprisingly, the unbinding transition state for P-selectin–G1 complex is close (0.32 nm) to the bound state, implying that the interaction is brittle, i.e., once deformed, the complex fractures. In contrast, the unbinding transition state of the P-selectin–sPSGL-1 complex is far (≈ 1.5 nm) from the bound state, indicative of a compliant structure. Constant
f
energy landscape parameters are used to compute the distributions of unbinding times and unbinding forces as a function of the loading rate,

r
f

. For a given

r
f

, unbinding of sPSGL-1 occurs over a broader range of
f
with the most probable
f
being an order of magnitude less than for G1. The theory for cell adhesion complexes can be used to predict the outcomes of unbinding of other protein–protein complexes.
Transcriptional coactivator PGC-1α regulates chondrogenesis via association with Sox9
Authors: Kawakami Yasuhiko , Tsuda Masanao , Takahashi Shigeru , Taniguchi Noboru , Esteban Concepción Rodríguez , Zemmyo Michihisa , Furumatsu Takayuki , Lotz Martin , Belmonte Juan Carlos Izpisúa , Asahara Hiroshi
Published: February 2005

Chondrogenesis is a multistep pathway in which multipotential mesenchymal stem cells (MSC) differentiate into chondrocytes. The transcription factor Sox9 (SRY-related high mobility group-Box gene 9) regulates chondrocyte differentiation and cartilage-specific expression of genes, such as
Col2a1
(collagen type II α1). However,
Sox9
expression is detected not only in chondrogenic tissue but also in nonchondrogenic tissues, suggesting the existence of a molecular partner(s) required for Sox9 to control chondrogenesis and chondrogenic gene expression. Here, we report identification of peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) as a coactivator for Sox9 during chondrogenesis. Expression of
PGC-1
α is induced at chondrogenesis sites during mouse embryonic limb development and during chondrogenesis in human MSC cultures. PGC-1α directly interacts with Sox9 and promotes Sox9-dependent transcriptional activity, suggesting that PGC-1α acts as a transcriptional coactivator for Sox9. Consistent with this finding, PGC-1α disruption in MSC by small interfering RNA inhibits
Col2a1
expression during chondrogenesis. Furthermore, overexpression of both
PGC-1
α and
Sox9
induced expression of chondrogenic genes, including
Col2a1
, followed by chondrogenesis in the MSC and developing chick limb. Together, our results suggest a transcriptional mechanism for chondrogenesis that is coordinated by PGC-1α.
Proline suppresses apoptosis in the fungal pathogen
Colletotrichum trifolii
Authors: Chen Changbin , Dickman Martin B.
Published: February 2005

The role of reactive oxygen species (ROS) in cell communication, control of gene expression, and oxygen sensing is well established. Inappropriate regulation of ROS levels can damage cells, resulting in a diseased state. In
Colletotrichum trifolii
, a fungal pathogen of alfalfa, the mutationally activated oncogenic fungal Ras (DARas) elevates levels of ROS, causing abnormal fungal growth and development and eventual apoptotic-like cell death but only when grown under nutrient-limiting conditions. Remarkably, restoration to the wild-type phenotype requires only proline. Here, we describe a generally unrecognized function of proline: its ability to function as a potent antioxidant and inhibitor of programmed cell death. Addition of proline to DARas mutant cells effectively quenched ROS levels and prevented cell death. Treating cells with inhibitors of ROS production yielded similar results. In addition, proline protected wild-type
C. trifolii
cells against various lethal stresses, including UV light, salt, heat, and hydrogen peroxide. These observations appear to be general because proline also protected yeast cells from lethal levels of the ROS-generating herbicide methyl viologen (paraquat), suggesting a common protective role for proline in response to oxidative stress. The ability of proline to scavenge intracellular ROS and inhibit ROS-mediated apoptosis may be an important and broad-based function of this amino acid in responding to cellular stress, in addition to its well established role as an osmolyte.
Polyproline and the “spectroscopic ruler” revisited with single-molecule fluorescence
Authors: Schuler Benjamin , Lipman Everett A. , Steinbach Peter J. , Kumke Michael , Eaton William A.
Published: February 2005

To determine whether Förster resonance energy transfer (FRET) measurements can provide quantitative distance information in single-molecule fluorescence experiments on polypeptides, we measured FRET efficiency distributions for donor and acceptor dyes attached to the ends of freely diffusing polyproline molecules of various lengths. The observed mean FRET efficiencies agree with those determined from ensemble lifetime measurements but differ considerably from the values expected from Förster theory, with polyproline treated as a rigid rod. At donor–acceptor distances much less than the Förster radius
R
0
, the observed efficiencies are lower than predicted, whereas at distances comparable to and greater than
R
0
, they are much higher. Two possible contributions to the former are incomplete orientational averaging during the donor lifetime and, because of the large size of the dyes, breakdown of the point-dipole approximation assumed in Förster theory. End-to-end distance distributions and correlation times obtained from Langevin molecular dynamics simulations suggest that the differences for the longer polyproline peptides can be explained by chain bending, which considerably shortens the donor–acceptor distances.
Muscle regeneration in the prolonged absence of myostatin
Authors: Wagner Kathryn R. , Liu Xiaosong , Chang Xiaoli , Allen Ronald E.
Published: February 2005

Myostatin is an endogenous inhibitor of muscle conserved across diverse species. In the absence of myostatin, there is massive muscle growth in mice, cattle, and humans. Previous studies in the
mdx
mouse model of muscular dystrophy demonstrate that inhibiting myostatin attenuates several features of dystrophic muscle. These findings have encouraged the development of human therapies to block myostatin. However, little is known of the long-term effects on muscle of myostatin blockade. To evaluate potential sequelae from the prolonged absence of myostatin, senescent myostatin null (
mstn
-/-
) mice were studied. Senescent
mstn
-/-
mice continue to have normal muscle with increased mass and strength relative to controls. Muscles of senescent
mstn
-/-
mice regenerate robustly from both chronic and acute injury. Early markers of regeneration are enhanced in the absence of myostatin, suggesting a mechanism for the attenuation of dystrophic features found in
mdx
mice lacking myostatin.
A baculovirus-encoded protein tyrosine phosphatase gene induces enhanced locomotory activity in a lepidopteran host
Authors: Kamita Shizuo G. , Nagasaka Koukichi , Chua Josie W. , Shimada Toru , Mita Kazuei , Kobayashi Masahiko , Maeda Susumu , Hammock Bruce D.
Published: February 2005

Enhanced locomotory activity (ELA), such as wandering, is a normal behavior that occurs at the end of the larval stage in lepidopteran (butterflies and moths) insects. Baculovirus infection can also induce ELA in lepidopteran larvae. The belief is that the virus induces this behavior to increase its transmission [Goulson, D. (1997)Oecologia109, 219–228]. Here we show that a baculovirus-encoded protein tyrosine phosphatase (PTP) gene (ptp) induces ELA that is activated by light. ELA was induced in silkwormBombyx moriinfected with the baculovirusB.morinucleopolyhedrovirus (BmNPV) beginning at ≈3.75 days postinfection (p.i.) and continued until 4.75 days p.i. The intensity of the ELA was dramatically reduced immediately before death at 5.25 days p.i. Light activated the intensity of the ELA by ≈3-fold, and larvae with ELA showed positive phototropism. ELA was not induced in larvae ofB.moriinfected with a BmNPVptpknockout mutant (BmPTPD). However, when a silkworm-derivedptpgene (Bmptp-h) was inserted into BmPTPD, ELA was partially recovered.Bmptp-hwas identified from silkworms at 2 days after the start of the natural wandering stage. The deduced amino acid sequence ofBmptp-hshowed 48.2% identify (80.7% similarity) to the deduced amino acid sequence of BmNPVptp. On the basis of the high homology and larval stage at whichBmptp-hwas isolated, we postulate that the modern baculovirus may have acquired itsptpgene from an ancestral host and that this gene was selectively maintained because it increases virus transmission.