bluuebunny/crossref_metadata_2025 huggingface dataset:
Photothermal cantilever actuation for fast single-molecule force spectroscopy
Authors: Stahl Stefan W. , Puchner Elias M. , Gaub Hermann E.
Published: July 2009

Photothermal cantilever excitation provides a fast and easy to implement means to control the deflection of standard atomic force microscopy cantilevers. Minute heat pulses yield deflections on the order of several tens of nanometers or when the deflection is kept constant, forces of several hundreds of piconewton can be applied. In our case these pulses resulted in less than 1 K temperature changes at the sample position. Here we present and characterize the implementation of photothermal actuation for single-molecule force-spectroscopy experiments. When molecules are stretched under force-clamp conditions, fast control cycles that re-establish the pulling force after the rupture of molecular domains are essential for detecting the complete unfolding pattern with high precision. By combining the fast response of photothermal cantilever excitation with a conventional piezoactuator, a fast force-clamp with high accuracy and large working distances is reached. Simple feedback mechanisms and standard cantilever geometries lead to step response times of less than 90 μs, which is more than one order of magnitude faster than those of conventional force-clamp systems that are based only on piezo feedback. We demonstrate the fast and accurate performance of the setup by unfolding a protein construct consisting of one green fluorescent protein and eight surrounding immunoglobulin domains at constant force.
A criterion for grain-size limit of polycrystalline materials
Authors: Qin W. , Szpunar J. A. , Umakoshi Y.
Published: July 2009

The transformation from the crystalline to the amorphous state was frequently found in some polycrystalline materials when grain refinement reaches a certain degree. Grain-size reduction induced lattice distortion and its effects on crystal structural instability were analyzed based on our recent work [Qin et al., Philos. Mag. Lett. 88, 169 (2008); Qin et al., J. Appl. Phys. 102, 124303 (2007); Qin et al., J. Phys.: Condens. Matter 19, 236217 (2007)] and Koike’s model [Phys. Rev. B 47, 7700 (1993)]. A criterion for determining the possible grain-size limit below which the amorphization occurs was proposed. Theoretical results may well account for experimental observations.
Observation of local dipole moment of Si atoms on Si(100) surfaces using noncontact scanning nonlinear dielectric microscopy
Authors: Kin Nobuhiro , Osa Yuhei , Cho Yasuo
Published: July 2009

To confirm the performance of noncontact scanning nonlinear dielectric microscopy (NC-SNDM), we attempted to determine the local dipole moment of Si atoms on a cleaned Si (100) surface under UHV conditions. From the topography images, atomically flat terraces, step structures, and defects were clearly recognized, and paired bright spots with a 2×1 symmetry were observed with clear contrast. In addition, we observed the local electric dipole moment distribution of Si atoms on a 2×1 structure. This revealed that the surface is naturally biased with an offset potential of −0.2V, and the direction of the local dipole moment is upward at dimer sites for bias values above −0.2V.
Optical discrimination of deep trap contribution to carrier recombination in semi-insulating crystals
Authors: Kadys A. , Jarašiūnas K. , Verstraeten D.
Published: July 2009

We demonstrate a novel application of light-induced transient grating technique for discrimination of deep trap contribution to carrier recombination in compensated semiconductors. This application is based on photoexcitation of deep impurity levels by light interference pattern and subsequent optical monitoring of the recharged state dynamics. The spatially modulated deep trap occupation leads to changes in a probe beam absorption and formation of a transient diffraction grating. Employment of light diffraction on a short-period reflection grating allowed to realize conditions when the absorption modulation in deep traps dominates over the coexisting refractive index modulation. Selectivity of a transient reflection grating configuration solely to processes in deep traps was proven experimentally and confirmed by numerical modeling. In this way, we discriminated the deep vanadium impurity governed carrier recombination rate from the other coexisting recombination channels in as-grown and annealed semi-insulating CdTe:V crystals.
Electronic transport and Schottky barrier heights of Pt/n-type GaN Schottky diodes in the extrinsic region
Authors: Lin Yow-Jon
Published: July 2009

The current-voltage characteristics of n-type GaN Schottky diodes have been measured in the extrinsic region (that is, the temperature range of 100–300 K). The effective density of states in the conduction band decreases with decreasing temperature and is close to the electron concentration at 100 K, leading to a reduction in the energy difference between the conduction band minimum and Fermi level and an increase in the probability of tunneling. Therefore, changes in the effective density of states in the conduction band and the probability of tunneling at low temperature are responsible for the decrease of the barrier height and increase in the ideality factor on the basis of the thermionic emission model. The mechanism of forward current flow has been clearly established in this study, leading to the thermionic emission (thermionic field emission) interpretation of the I-V characteristics at 300 K (100 K).
Shock-induced spall in solid and liquid Cu at extreme strain rates
Authors: Luo Sheng-Nian , An Qi , Germann Timothy C. , Han Li-Bo
Published: July 2009

We investigate spallation in solid and liquid Cu at high strain rates induced by planar shock loading with classical molecular dynamics. Shock simulations are performed at different initial temperatures and shock stresses but similar strain rates (ε̇∼1010–1011s−1). The anisotropy in spall strength (σsp) is explored for five crystallographic orientations, ⟨100⟩, ⟨110⟩, ⟨111⟩, ⟨114⟩, and ⟨123⟩. For liquid, we examine shock- and release-induced melts as well as premelted Cu. The acoustic method for deducing σsp and ε̇ is a reasonable first-order approximation. The anisotropy in σsp is pronounced for weak shocks and decreases for stronger shocks. Voids are nucleated at defective sites in a solid. For weak solid shocks, spallation occurs without tensile melting; for stronger shocks or if the temperature right before spallation (Tsp) is sufficiently high, spallation may be accompanied or preceded by partial melting. Tsp appears to have a dominant effect on spallation for the narrow range of ε̇ studied here. σsp decreases with increasing Tsp for both solids and liquids, and σsp(Tsp) follows an inverse power law for liquids. The simulated σsp for solid Cu at low Tsp is consistent with the prediction of the power-law relation σsp(ε̇) based on low strain rate experiments.
Cryogenic vacuum tribology of diamond and diamond-like carbon films
Authors: Aggleton M. , Burton J. C. , Taborek P.
Published: July 2009

Friction measurements have been performed on microcrystalline, ultrananocrystalline, and diamond-like carbon (DLC) films with natural diamond counterfaces in the temperature range of 8 K to room temperature. All films exhibit low friction (μ≤0.1) in air at room temperature. In ultrahigh vacuum, microcrystalline diamond quickly wears into a high friction state (μ≈0.6), which is independent of temperature. DLC has low friction even at the lowest temperatures. In contrast, friction in ultrananocrystalline films has a significant temperature dependence, with a broad transition from a low to a high friction state between 120 and 220 K observed on both heating and cooling. The role of hydrogen transport in determining the temperature dependence of friction is discussed.
Molecular dynamics simulations of concentrated polymer solutions in thin film geometry. I. Equilibrium properties near the glass transition
Authors: Peter S. , Meyer H. , Baschnagel J.
Published: July 2009

We report on results of molecular dynamics simulations for supported polymer films with explicit solvent. The simulation represents the polymers by bead-spring chains and the solvent particles by monomers. The interaction between polymer and solvent favors mixing. We find that the solvent acts as a plasticizer. The glass transition temperature Tg is reduced relative to the pure polymer film. Near Tg we explore equilibrium properties as a function of temperature and solvent concentration. We find that the structure and dynamics of the films are spatially heterogeneous. The solvent density is enriched at the supporting wall and at the free surface where the film is in equilibrium with solvent vapor. At both interfaces the solvent dynamics is fast, but smoothly crosses over to bulk dynamics when moving from the interfaces toward the center of the film. A smooth gradient from enhanced dynamics at the interfaces to bulk behavior in the film center is also found for the monomers. We show that the same formula used to parametrize the spatial gradient of the dynamics in the pure polymer film may also be applied here. Furthermore, we determine the concentration dependence of the relaxation time of the solvent in the center of film and compare this dependence to models proposed in literature.
Hill’s equation with random forcing parameters: The limit of delta function barriers
Authors: Adams Fred C. , Bloch Anthony M.
Published: July 2009

This paper considers random Hill’s equations in the limit where the periodic forcing function becomes a Dirac delta function. For this class of equations, the forcing strength qk, the oscillation frequency λk, and the period (Δτ)k are allowed to vary from cycle to cycle. Such equations arise in astrophysical orbital problems in extended mass distributions, in the reheating problem for inflationary cosmologies, and in periodic Schrödinger equations. The growth rates for solutions to the periodic differential equation can be described by a matrix transformation, where the matrix elements vary from cycle to cycle. Working in the delta function limit, this paper addresses several coupled issues. We find the growth rates for the 2×2 matrices that describe the solutions. This analysis is carried out in the limiting regimes of both large qk⪢1 and small qk⪡1 forcing strength parameters. For the latter case, we present an alternate treatment of the dynamics in terms of the Fokker–Planck equation, which allows for a comparison of the two approaches. Finally, we elucidate the relationship between the fundamental parameters (λk,qk) appearing in the stochastic differential equation and the matrix elements that specify the corresponding discrete map. This work provides analytic—and accurate—expressions for the growth rates of these stochastic differential equations in both the qk⪢1 and the qk⪡1 limits.
Bi-Hamiltonian structures for integrable systems on regular time scales
Authors: Szablikowski Błażej M. , Błaszak Maciej , Silindir Burcu
Published: July 2009

A construction of the bi-Hamiltonian structures for integrable systems on regular time scales is presented. The trace functional on an algebra of δ-pseudodifferential operators, valid on an arbitrary regular time scale, is introduced. The linear Poisson tensors and the related Hamiltonians are derived. The quadratic Poisson tensors are given by the use of the recursion operators of the Lax hierarchies. The theory is illustrated by Δ-differential counterparts of Ablowitz–Kaup–Newell–Segur and Kaup–Broer hierarchies.
Retention in nonvolatile silicon transistors with an organic ferroelectric gate
Authors: Gysel Roman , Stolichnov Igor , Tagantsev Alexander K. , Riester Sebastian W. E. , Setter Nava , Salvatore Giovanni A. , Bouvet Didier , Ionescu Adrian M.
Published: July 2009

A silicone-based one-transistor nonvolatile memory cell has been implemented by integration of a ferroelectric polymer gate on a standard n-type metal oxide semiconductor field effect transistor. The polarization reversal in the gate results in a stable and reproducible memory effect changing the source-drain current by a factor 102–103, with the retention exceeding 2–3 days. Analysis of the drain current relaxation and time-resolved study of the spontaneous polarization via piezoforce scanning probe microscopy indicates that the retention loss is controlled by the interface-adjacent charge injection rather than the polarization instability. A semiquantitative model describes the time-dependent retention loss characterized by an exponential decay of the open state current of the transistor. The unique combination of properties of the ferroelectric copolymer of vinylidene fluoride and trifluoroethylene, including an adequate spontaneous polarization and low dielectric constant as well as rather benign processing demands, makes this material a promising candidate for memories fully compatible with silicon technology.
Large-scale correlated study of excited state absorptions in naphthalene and anthracene
Authors: Sony Priya , Shukla Alok
Published: July 2009

In this paper, we report theoretical calculations of the photoinduced absorption (PA) spectrum of naphthalene and anthracene, with the aim of understanding those excited states, which are invisible in the linear optical absorption. The excited state absorption spectra are computed from the 1B2u+ and the 1B3u+ states and a detailed analysis of the many-body character of the states contributing to various peaks in the spectra is presented. The calculations are performed using the Pariser–Parr–Pople (PPP) Hamiltonian, along with the full configuration interaction technique. The role of Coulomb parameters used in the PPP Hamiltonian is examined by considering standard Ohno parameters, as well as a screened set of parameters. The results of our calculations are extensively compared with the experimental data where available and very good agreement has been obtained. Moreover, our calculations predict the presence of high intensity features which, to the best of our knowledge, have not been explored earlier. We also present concrete predictions on the polarization properties of the PA spectrum, which can be verified in experiments performed on oriented samples.
Theoretical study of dc-biased single-surface multipactors
Authors: Jeon Seok-Gy , Kim Jung-Il , Han Seong-Tae , Jung Sun-Shin , Kim Jong Uk
Published: July 2009

The physical characteristics of a dc-biased single-surface multipactor are investigated, and a novel scheme of the multipactor that uses a photonic crystal cavity resonator maximizing insulation gap distance is introduced. With a restriction of no premature impact, a resonant rf phase minimizing rf electric field is analytically obtained, which is universal for any surface material. The surface material properties bring about a restriction of secondary electron energy by which some backscattered, high energy electrons may have no fixed resonant phases. With an assumption of zero initial velocity, analytical derivations and a parametric map for the phase locking are presented. In the map, without possibility of premature impact, a bifurcation of a stable resonant phase into two stable resonant phases appears when the ratio of rf to dc electric field is over a critical value. This distinctive phenomenon is demonstrated by a three-dimensional particle-in-cell simulation.
Investigation into polymer electrolyte membrane fuel cell characteristics using four-layer electrode catalyst
Authors: Ide Masahiro , Ikeda Hironosuke
Published: July 2009

The use of auxiliary power and the cost of using main power decrease when the reactive gas is applied at low humidity for the operation of polymer electrolyte membrane fuel cells. The electrolyte membrane and the three-phase boundary of the electrode need to be improved to maintain this low humidity. We carried out a study of the electrode catalyst at low humidity in order to improve the cathode catalyst. Carbon support with a catalyst and fluorocarbon resin were mixed and then were treated at the melting temperature of fluorocarbon resin to fabricate the cathode-electrode catalyst layer. The transmission electron microscopy images of this electrode catalyst revealed that the surfaces of the catalyst particle and the carbon support were partly coated with a thin film of melted fluorocarbon resin. Ionomer electrolyte material was added to this electrode catalyst, and an electrode catalyst with a four-layer structure was fabricated. The durability of this four-layer electrode catalyst being operated at low humidity (42% relative humidity on the anode and the cathode) was evaluated by using a cell that contained the catalyst. The results demonstrated that the rate of deterioration was smaller than that of a conventional three-layer electrode catalyst. In addition, the load change test to assess the durability of the cell (current range between 75 and 600 mA cm−2) produced good results.
Self-assembled bioinspired quantum dots: Optical properties
Authors: Amdursky N. , Molotskii M. , Gazit E. , Rosenman G.
Published: July 2009

Until now, the wide research field of quantum dots (QDs) focused on inorganic structures. In the present study, we report on quantum confinement phenomena found in peptide nanocrystalline regions formed within self-assembly peptide nanospheres. These bioinspired nanostructures exhibit the optical absorption characteristics of QDs with pronounced luminescence of excitons whose origin is at the UV region. Theoretical estimations based on experimental data show that the radius of the self assembled peptide QDs is 1.3 nm.
Single InAs quantum dot arrays and directed self-organization on patterned GaAs (311)B substrates
Authors: Selçuk E. , Silov A. Yu. , Nötzel R.
Published: July 2009

Formation of laterally ordered single InAs quantum dot (QD) arrays by self-organized anisotropic strain engineering of InGaAs/GaAs superlattice templates on GaAs (311)B by molecular beam epitaxy is achieved through optimization of growth temperature, InAs amount, and annealing. Directed self-organization of these QD arrays is accomplished by coarse substrate patterns providing absolute QD position control over large areas. Due to the absence of one-to-one pattern definition the site-controlled QD arrays exhibit excellent optical properties revealed by resolution limited (80 μeV) linewidth of the low-temperature photoluminescence from individual QDs.
Characterization of blue-green m-plane InGaN light emitting diodes
Authors: Lin You-Da , Chakraborty Arpan , Brinkley Stuart , Kuo Hsun Chih , Melo Thiago , Fujito Kenji , Speck James S. , DenBaars Steven P. , Nakamura Shuji
Published: July 2009

High indium content blue-green (460–520 nm) m-plane InGaN light emitting diodes (LEDs) were grown on low defect-density m-plane GaN substrates. Systematic studies were performed on packaged blue-green LED lamps by using a range of well and barrier thicknesses. Photoluminance and electroluminance peak wavelengths increased while the well width was increased from 2 to 4 nm. The highest output power was achieved for well width of 2.5 nm. The output power improved significantly with the increase in barrier thickness. Nearly blueshift-free emission was observed in all LEDs from 1–400 A/cm2 current density under pulsed operation.
Surface intercalation of gold underneath a graphene monolayer on SiC(0001) studied by scanning tunneling microscopy and spectroscopy
Authors: Premlal B. , Cranney M. , Vonau F. , Aubel D. , Casterman D. , De Souza M. M. , Simon L.
Published: July 2009

The effects of gold deposition on monolayer graphene (MG) epitaxied on SiC (0001) substrate are examined via scanning tunneling microscopy and scanning tunneling spectroscopy (STS). Two types of surfaces with distinctive topography are demonstrated: (i) intercalated gold clusters having no interaction with graphene and (ii) 13×13-G reconstruction attributed to a Moiré pattern arising from the intercalation of 1 ML of gold between a MG and the underlying SiC substrate. This surface also displays a 23×23R30-Au (111) surface reconstruction interpreted as surface corrugation. The STS curve shows a possible hole-doping effect in the latter case.
Transient charge trapping and detrapping properties of a thick SiO2/Al2O3 stack studied by short single pulse Id-Vg
Authors: Chang Man , Jo Minseok , Jung Seungjae , Lee Joonmyoung , Jeon Sanghun , Hwang Hyunsang
Published: July 2009

The transient charge trapping and detrapping of a thick SiO2/Al2O3 gate oxide device has been evaluated by single pulse Id-Vg (PIV). During the period of a single pulse, we observed fast electron detrapping. This occurred through the gate electrode, causing a counterclockwise PIV hysteresis despite electron injections from the channel region. The hysteresis direction transitioned from counterclockwise to clockwise as a function of pulse base level and peak level. The trap energy level of Al2O3, extracted by PIV at various temperatures, was found to be in the range of 1.14–1.39 eV, indicating the Frenkel–Poole defect band.
The effect of dielectric constant on device mobilities of high-performance, flexible organic field effect transistors
Authors: Tan H. S. , Mathews N. , Cahyadi T. , Zhu F. R. , Mhaisalkar S. G.
Published: July 2009

High-performance pentacene (μsat=6.3 cm2/V s) and poly(3-hexylthiophene) (μsat=0.43 cm2/V s) field effect transistors have been realized on flexible substrate with low operating voltage (<−5 V), utilizing a trilayer sol-gel silica gate dielectric. Furthermore, the permittivity of the dielectric was tuned from ∼7 to ∼10 by varying plasma treatments, allowing the study of charge carrier mobility variation with k. A 65% reduction in the saturation mobility of the devices was observed when k increases, suggesting that the energetic disorder at the interface between the active layer and the dielectric can be modulated by the high polarizability of the bulk dielectric.
Seeing structures and measuring properties with transmission electron microscopy images: A simple combination to study size effects in nanoparticle systems
Authors: Donnadieu Patricia , Lazar Sorin , Botton Gianluigi A. , Pignot-Paintrand Isabelle , Reynolds Michael , Perez Serge
Published: July 2009

We report on a method to measure the mean inner potential (V0) using transmission electron microscopy. It is based on phase retrieval from a focus series and has allowed to measure V0 as a function of the size for a system of gold nanoparticles. It comes out that V0 increases for particles below 2 nm. The focus series being carried out in conditions close to the high-resolution ones, structural information can be directly obtained. The high-resolution images have revealed that significant structural change occurs below the 2 nm size, which should be related to the V0 increase.
Nd-doped silicon nanowires with room temperature ferromagnetism and infrared photoemission
Authors: Lee Wei-Fan , Lee Chung-Yang , Ho Mei-Lin , Huang Chi-Te , Lai Chen-Ho , Hsieh Ho-Yen , Chou Pi-Tai , Chen Lih-Juann
Published: July 2009

Nd-doped silicon nanowires have been synthesized by a vapor transport and condensation method. The incorporation of neodymium within silicon nanowires was achieved by using NdCl3⋅6H2O powder as the doping source. Ferromagnetism and infrared photoluminescence at room temperature were discovered. The significant variation and versatility of the properties exhibited by the Nd-doped silicon nanowires are promising for exploitation for the advanced silicon-based devices.
Size effects in submicron exchange bias square elements
Authors: Vallejo-Fernandez G. , Chapmam J. N.
Published: July 2009

The behavior of submicron exchange bias square elements has been investigated for systems containing metallic polycrystalline layers. Numerical simulations using a simple theoretical model show that the exchange bias for such elements can increase and/or decrease depending on the microstructure of the antiferromagnetic layer and, in particular, its grain size distribution. The predictions are based on a granular model of exchange bias that accounts for grain cutting at the edges of the nanoelements that takes place during ion milling/etching. This leads to distributions of exchange bias fields that can be quite broad, especially in sub-250 nm elements.
Atomic layer deposition of ZrO2/La2O3 high-k dielectrics on germanium reaching 0.5 nm equivalent oxide thickness
Authors: Abermann S. , Bethge O. , Henkel C. , Bertagnolli E.
Published: July 2009

We investigate ultrathin ZrO2/La2O3 high-k dielectric stacks on germanium grown by atomic layer deposition. La2O3 is deposited from tris(N,N′-diisopropylformamidinate)-lanthanum and oxygen. Interfacial layer-free oxide stacks with a relative dielectric constant of 21 and equivalent oxide thickness values as low as 0.5 nm are obtained. Metal oxide semiconductor capacitors with platinum as the gate electrode exhibit well-behaved capacitance-voltage characteristics, gate leakage current densities in the range of 0.01–1 A/cm2, and interface trap densities in the range of ∼3×1012 eV−1 cm−2.
Probing negative differential resistance on Si(111)-3×3-Ag surface with scanning tunneling microscopy
Authors: Wang Weihua , Zhao Aidi , Wang Bing , Hou J. G.
Published: July 2009

We present our study on the Si(111)-3×3-Ag surface using scanning tunneling microscopy/spectroscopy. The results reveal that the well defined localized surface-state bands S2/S3 in the surface with lightly doped Si substrate play an important role in electron transport. The relative wide space charge layer beneath the surface interplays with the localized surface states, thus leading to the effect of the negative differential resistance.
Assessing the relevance of node features for network structure
Authors: Bianconi Ginestra , Pin Paolo , Marsili Matteo
Published: July 2009

Networks describe a variety of interacting complex systems in social science, biology, and information technology. Usually the nodes of real networks are identified not only by their connections but also by some other characteristics. Examples of characteristics of nodes can be age, gender, or nationality of a person in a social network, the abundance of proteins in the cell taking part in protein-interaction networks, or the geographical position of airports that are connected by directed flights. Integrating the information on the connections of each node with the information about its characteristics is crucial to discriminating between the essential and negligible characteristics of nodes for the structure of the network. In this paper we propose a general indicator Θ, based on entropy measures, to quantify the dependence of a network's structure on a given set of features. We apply this method to social networks of friendships in U.S. schools, to the protein-interaction network of
Saccharomyces cerevisiae
and to the U.S. airport network, showing that the proposed measure provides information that complements other known measures.
Imaging rapid redistribution of sensory-evoked depolarization through existing cortical pathways after targeted stroke in mice
Authors: Sigler Albrecht , Mohajerani Majid H. , Murphy Timothy H.
Published: July 2009

Evidence suggests that recovery from stroke damage results from the production of new synaptic pathways within surviving brain regions over weeks. To address whether brain function might redistribute more rapidly through preexisting pathways, we examined patterns of sensory-evoked depolarization in mouse somatosensory cortex within hours after targeted stroke to a subset of the forelimb sensory map. Brain activity was mapped with voltage-sensitive dye imaging allowing millisecond time resolution over 9 mm
2
of brain. Before targeted stroke, we report rapid activation of the forelimb area within 10 ms of contralateral forelimb stimulation and more delayed activation of related areas of cortex such as the hindlimb sensory and motor cortices. After stroke to a subset of the forelimb somatosensory cortex map, function was lost in ischemic areas within the forelimb map center, but maintained in regions 200–500 μm from blood flow deficits indicating the size of a perfused, but nonfunctional, penumbra. In many cases, stroke led to only partial loss of the forelimb map, indicating that a subset of a somatosensory domain can function on its own. Within the forelimb map spared by stroke, forelimb-stimulated responses became delayed in kinetics, and their center of activity shifted into adjacent hindlimb and posterior-lateral sensory areas. We conclude that the focus of forelimb-specific somatosensory cortex activity can be rapidly redistributed after ischemic damage. Given that redistribution occurs within an hour, the effect is likely to involve surviving accessory pathways and could potentially contribute to rapid behavioral compensation or direct future circuit rewiring.
A molecular brake, not a clutch, stops the
Rhodobacter sphaeroides
flagellar motor
Authors: Pilizota Teuta , Brown Mostyn T. , Leake Mark C. , Branch Richard W. , Berry Richard M. , Armitage Judith P.
Published: July 2009

Many bacterial species swim by employing ion-driven molecular motors that power the rotation of helical filaments. Signals are transmitted to the motor from the external environment via the chemotaxis pathway. In bidirectional motors, the binding of phosphorylated CheY (CheY-P) to the motor is presumed to instigate conformational changes that result in a different rotor-stator interface, resulting in rotation in the alternative direction. Controlling when this switch occurs enables bacteria to accumulate in areas favorable for their survival. Unlike most species that swim with bidirectional motors,
Rhodobacter sphaeroides
employs a single stop-start flagellar motor. Here, we asked, how does the binding of CheY-P stop the motor in
R. sphaeroides
—using a clutch or a brake? By applying external force with viscous flow or optical tweezers, we show that the
R. sphaeroides
motor is stopped using a brake. The motor stops at 27–28 discrete angles, locked in place by a relatively high torque, approximately 2–3 times its stall torque.
Heat transfer from nanoparticles: A corresponding state analysis
Authors: Merabia Samy , Shenogin Sergei , Joly Laurent , Keblinski Pawel , Barrat Jean-Louis
Published: July 2009

In this contribution, we study situations in which nanoparticles in a fluid are strongly heated, generating high heat fluxes. This situation is relevant to experiments in which a fluid is locally heated by using selective absorption of radiation by solid particles. We first study this situation for different types of molecular interactions, using models for gold particles suspended in octane and in water. As already reported in experiments, very high heat fluxes and temperature elevations (leading eventually to particle destruction) can be observed in such situations. We show that a very simple modeling based on Lennard–Jones (LJ) interactions captures the essential features of such experiments and that the results for various liquids can be mapped onto the LJ case, provided a physically justified (corresponding state) choice of parameters is made. Physically, the possibility of sustaining very high heat fluxes is related to the strong curvature of the interface that inhibits the formation of an insulating vapor film.
A tethering mechanism for length control in a processive carbohydrate polymerization
Authors: May John F. , Splain Rebecca A. , Brotschi Christine , Kiessling Laura L.
Published: July 2009

Carbohydrate polymers are the most abundant organic substances on earth. Their degrees of polymerization range from tens to thousands of units, yet polymerases generate the relevant lengths without the aid of a template. To gain insight into template-independent length control, we investigated how the mycobacterial galactofuranosyltransferase GlfT2 mediates formation of the galactan, a polymer of galactofuranose residues that is an integral part of the cell wall. We show that isolated recombinant GlfT2 can catalyze the synthesis of polymers with degrees of polymerization that are commensurate with values observed in mycobacteria, indicating that length control by GlfT2 is intrinsic. Investigations using synthetic substrates reveal that GlfT2 is processive. The data indicate that GlfT2 controls length by using a substrate tether, which is distal from the site of elongation. The strength of interaction of that tether with the polymerase influences the length of the resultant polymer. Thus, our data identify a mechanism for length control by a template-independent polymerase.
Recovering time-varying networks of dependencies in social and biological studies
Authors: Ahmed Amr , Xing Eric P.
Published: July 2009

A plausible representation of the relational information among entities in dynamic systems such as a living cell or a social community is a stochastic network that is topologically rewiring and semantically evolving over time. Although there is a rich literature in modeling static or temporally invariant networks, little has been done toward recovering the network structure when the networks are not observable in a dynamic context. In this article, we present a machine learning method called TESLA, which builds on a temporally smoothedl1-regularized logistic regression formalism that can be cast as a standard convex-optimization problem and solved efficiently by using generic solvers scalable to large networks. We report promising results on recovering simulated time-varying networks and on reverse engineering the latent sequence of temporally rewiring political and academic social networks from longitudinal data, and the evolving gene networks over >4,000 genes during the life cycle ofDrosophila melanogasterfrom a microarray time course at a resolution limited only by sample frequency.
Distribution history and climatic controls of the Late Miocene Pikermian chronofauna
Authors: Eronen Jussi T. , Ataabadi Majid Mirzaie , Micheels Arne , Karme Aleksis , Bernor Raymond L. , Fortelius Mikael
Published: July 2009

The Late Miocene development of faunas and environments in western Eurasia is well known, but the climatic and environmental processes that controlled its details are incompletely understood. Here we map the rise and fall of the classic Pikermian fossil mammal chronofauna between 12 and 4.2 Ma, using genus-level faunal similarity between localities. To directly relate land mammal community evolution to environmental change, we use the hypsodonty paleoprecipitation proxy and paleoclimate modeling. The geographic distribution of faunal similarity and paleoprecipitation in successive timeslices shows the development of the open biome that favored the evolution and spread of the open-habitat adapted large mammal lineages. In the climate model run, this corresponds to a decrease in precipitation over its core area south of the Paratethys Sea. The process began in the latest Middle Miocene and climaxed in the medial Late Miocene, about 7–8 million years ago. The geographic range of the Pikermian chronofauna contracted in the latest Miocene, a time of increasing summer drought and regional differentiation of habitats in Eastern Europe and Southwestern Asia. Its demise at the Miocene-Pliocene boundary coincides with an environmental reversal toward increased humidity and forestation, changes inevitably detrimental to open-adapted, wide-ranging large mammals.
Structure of the vesicular stomatitis virus nucleocapsid in complex with the nucleocapsid-binding domain of the small polymerase cofactor, P
Authors: Green Todd J. , Luo Ming
Published: July 2009

The negative-strand RNA viruses (NSRVs) are unique because their nucleocapsid, not the naked RNA, is the active template for transcription and replication. The viral polymerase of nonsegmented NSRVs contains a large polymerase catalytic subunit (L) and a nonenzymatic cofactor, the phosphoprotein (P). Insight into how P delivers the polymerase complex to the nucleocapsid has long been pursued by reverse genetics and biochemical approaches. Here, we present the X-ray crystal structure of the C-terminal domain of P of vesicular stomatitis virus, a prototypic nonsegmented NSRV, bound to nucleocapsid-like particles. P binds primarily to the C-terminal lobe of 2 adjacent N proteins within the nucleocapsid. This binding mode is exclusive to the nucleocapsid, not the nucleocapsid (N) protein in other existing forms. Localization of phosphorylation sites within P and their proximity to the RNA cavity give insight into how the L protein might be oriented to access the RNA template.
The spread of modern humans in Europe
Authors: Hoffecker John F.
Published: July 2009

The earliest credible evidence of
Homo sapiens
in Europe is an archaeological proxy in the form of several artifact assemblages (Bohunician) found in South-Central and possibly Eastern Europe, dating to ≤48,000 calibrated radiocarbon years before present (cal BP). They are similar to assemblages probably made by modern humans in the Levant (Emiran) at an earlier date and apparently represent a population movement into the Balkans during a warm climate interval [Greenland Interstadial 12 (GI 12)]. A second population movement may be represented by a diverse set of artifact assemblages (sometimes termed Proto-Aurignacian) found in the Balkans, parts of Southwest Europe, and probably in Eastern Europe, and dating to several brief interstadials (GI 11–GI 9) that preceded the beginning of cold Heinrich Event 4 (HE4) (≈40,000 cal BP). They are similar to contemporaneous assemblages made by modern humans in the Levant (Ahmarian). The earliest known human skeletal remains in Europe that may be unequivocally assigned to
H. sapiens
(Peçstera cu Oase, Romania) date to this time period (≈42,000 cal BP) but are not associated with artifacts. After the Campanian Ignimbrite volcanic eruption (40,000 cal BP) and the beginning of HE4, artifact assemblages assigned to the classic Aurignacian, an industry associated with modern human skeletal remains that seems to have developed in Europe, spread throughout the continent.
The role of transposable elements in the regulation of IFN-λ1 gene expression
Authors: Thomson Scott J. P. , Goh Fui G. , Banks Helen , Krausgruber Thomas , Kotenko Sergei V. , Foxwell Brian M. J. , Udalova Irina A.
Published: July 2009

IFNs λ1, λ2, and λ3, or type III IFNs, are recently identified cytokines distantly related to type I IFNs. Despite an early evolutionary divergence, the 2 types of IFNs display similar antiviral activities, and both are produced primarily in dendritic cells. Although virus induction of the type I IFN-β gene had served as a paradigm of gene regulation, relatively little is known about the regulation of IFN-λ gene expression. Studies of virus induction of IFN-λ1 identified an essential role of IFN regulatory factors (IRF) 3 and 7, which bind to a regulatory DNA sequence near the start site of transcription. Here, we report that the proximal promoter region of the IFN-λ1 regulatory region is not sufficient for maximal gene induction in response to bacterial LPS, and we identify an essential cluster of homotypic NF-κB binding sites. Remarkably, these sites, which bind efficiently to NF-κB and function independently of the IRF3/7 binding sites, originate as transposable elements of the Alu and LTR families. We also show that depletion of the NF-κB RelA protein significantly reduces the level of the IFN-λ1 gene expression. We conclude that IFN-λ1 gene expression requires NF-κB, and we propose a model for IFN-λ1 gene regulation, in which IRF and NF-κB activate gene expression independently via spatially separated promoter elements. These observations provide insights into the independent evolution of the IFN-λ1 and IFN-β promoters and directly implicate transposable elements in the regulation of the IFN-λ1 gene by NF-κB.
The proapoptotic function of SAP provides a clue to the clinical picture of X-linked lymphoproliferative disease
Authors: Nagy Noémi , Matskova Liudmila , Kis Loránd L. , Hellman Ulf , Klein George , Klein Eva
Published: July 2009

Deletion or mutation of the SAP gene is associated with the X-linked lymphoproliferative disease (XLP) that is characterized by extreme sensitivity to Epstein-Barr virus (EBV). Primary infection of the affected individuals leads to serious, sometimes fatal infectious mononucleosis (IM) and proneness to lymphoma. Our present results revealed a proapoptotic function of SAP by which it contributes to the maintenance of T-cell homeostasis and to the elimination of potentially dangerous DNA-damaged cells. Therefore, the loss of this function could be responsible for the uncontrolled T-cell proliferation in fatal IM and for the generation of lymphomas. We show now the role of SAP in apoptosis in T and B lymphocyte-derived lines. Among the clones of T-ALL line, the ones with higher SAP levels succumbed more promptly to activation induced cell death (AICD). Importantly, introduction of SAP expression into lymphoblastoid cell lines (LCL) established from XLP patients led to elevated apoptotic response to DNA damage. Similar results were obtained in the osteosarcoma line, Saos-2. We have shown that the anti-apoptotic protein VCP (valosin-containing protein) binds to SAP, suggesting that it could be instrumental in the enhanced apoptotic response modulated by SAP.
Language policy mechanisms and social practices in multilingual Luxembourg
Authors: Horner Kristine
Published: July 2009

Taking fluctuations in Luxembourgish language policy as a springboard for discussion, this paper is informed by two interrelated theoretical points that have been flagged in recent language policy scholarship. The first is the move to view language policy as encompassing much more than documents declaring “official” and “national” languages, which is connected to the assertion that language policy is never absent and that it is necessary for scholars to grapple with both explicit and implicit dimensions of policy. Second, a case is made for exploring the dynamics of language policy in a wide range of settings, considering both “top-down” implementations and acts “from below” ranging from compliance to resistance. A close look at the interrelationship between language policy mechanisms and social practices shows that events unfolding at the global and local levels need to be taken into account in addition to those at the level of the state.
Constructing lusobourgish ethnicities
Authors: Weber Jean-Jacques
Published: July 2009

This paper takes a language ideological approach to describe the ongoing processes of the construction and negotiation of emergent romano- or lusobourgish ethnicities and identities within Luxembourgish society. The first two sections discuss the main theoretical assumptions of the language ideological approach and provide an overview of the language situation in Luxembourg. The following two sections present the results of an ethnographic study of language use, language ideologies and identity construction among luso-descendant adolescents attending a number of youth centres in Luxembourg city. The final section considers the implications of these results for language-in-education policy and, more particularly, the importance of creating “literacy bridges” for transnational students, rather than some form of mother-tongue education, as a first step towards the elusive goal of educational equity.
Explicit and implicit dimensions of language policy in multilingual banks in Luxembourg
Authors: Kingsley Leilarna
Published: July 2009

For decades the primary focus of language policy research has been activities by states and their agencies, while policy activities in workplaces have attracted little attention. Addressing this gap, this paper investigates language management policies in financial institutions in the multilingual context of Luxembourg. Shohamy’s (2006) theoretical framework, largely based on the context of the state, is adopted and extended to financial institutions. Financial institutions operate in the globalised context of international banking and represent an interesting focal point for examining language policy in the globalising world. Explicit and implicit dimensions of policy are investigated by exploring the discrepancy between explicit language management policies on the working language of financial institutions and reported language use practices. Two international banks are discussed in this paper to provide insight into the complex nature of language policy and the importance of both top-down and bottom-up pressures on language practices.
EMPLOYERS' DEMAND FOR QUALIFICATIONS AND SKILLS
Authors: Dörfler Laura , van de Werfhorst Herman G.
Published: July 2009

The paper attempts to empirically test skill demand on the Austrian labour market between 1985 and 2005 by making use of job advertisements. We analyze job advertisements covering a time span of 20 years. This allows us to examine whether there is a trend towards increased merit selection. Our empirical research is based on a content analysis of 975 newspaper job advertisements. We expand on the operationalization of education by looking at both educational level and field of study. Results indicate that jobs described in advertisements increasingly demanded various types of skill. Besides educational merits, other types of skills are also relevant in modern-day economies: social and personal skills. It is demonstrated that the driving force in changing demands is not only compositional change (with the expansion of high-skill demanding jobs), but also changes within occupational groups.
Elimination of the enhanced Simon effect for older adults in a three-choice situation: Ageing and the Simon effect in a go/no-go Simon task
Authors: Kubo-Kawai Namiko , Kawai Nobuyuki
Published: July 2009

In a Simon task, participants show better performance when the irrelevant stimulus location corresponds with the response location than when it does not, and this effect is typically greater for older adults than for younger adults. To study the effect of cognitive ageing in the Simon task, we compared young and old adults using two versions of the Simon task: (a) a standard visual Simon task, for which participants respond with left and right key-presses to the red and green colours of stimuli presented in left and right locations; (b) a go/no-go version of the Simon task, which was basically the same, except that the shape of the stimulus in one third of the trials indicates that no response is to be made. In both tasks, both age groups showed the Simon effect. The magnitude of the effect for the standard Simon task was greater for the older adults than for the younger adults. Nevertheless, the two groups showed an equivalent Simon effect in the go/no-go version of the Simon task. Reaction time distribution analyses revealed basically similar functions for both age groups: a decreasing pattern of the Simon effect in the standard task and an increasing pattern of the effect in the go/no-go version of the task. The results suggest that older adults find it more difficult to suppress an automatic activation of the corresponding response, though this automatic activation was reduced in situations where the response was frequently inhibited.