bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic imaging of the monolayer nucleation and unpinning of a compound semiconductor surface during atomic layer deposition
Authors: Clemens Jonathon B. , Chagarov Evgueni A. , Holland Martin , Droopad Ravi , Shen Jian , Kummel Andrew C.
Published: October 2010

The reaction of trimethyl aluminum on the group III rich reconstructions of InAs(0 0 1) and In0.53Ga0.47As(0 0 1) is observed with scanning tunneling microscopy/spectroscopy. At high coverage, a self-terminated ordered overlayer is observed that provides the monolayer nucleation density required for subnanometer thick transistor gate oxide scaling and removes the surface Fermi level pinning that is present on the clean InGaAs surface. Density functional theory simulations confirm that an adsorbate-induced reconstruction is the basis of the monolayer nucleation density and passivation.
Impact-induced friction ignition of an explosive: Infrared observations and modeling
Authors: Perry W. Lee , Gunderson Jake A. , Balkey Matthew M. , Dickson Peter M.
Published: October 2010

A contaminant (grit) trapped between an explosive and an impacted surface can significantly reduce the impact energy required to initiate a secondary high explosive. Several severe accidents have occurred when an explosive charge was dropped from a height insufficient to cause ignition by heating due only to plastic deformation; the frictional heating from embedded grit has been implicated. Here, we describe an idealization of this situation where a small sample of a polymer-bonded cyclotetramethylenetetranitramine explosive (HMX-PBX 9501), with a 400 μm diameter sphere of silica embedded in the surface, was impacted between instrumented transparent anvils and infrared images were recorded. The instrumentation provided temperature and the work done by the friction between the grit and the anvil surface for the impact process, up to ignition. All experiments were conducted under impact conditions insufficient to cause ignition without grit. Ignition occurred at approximately 500 μs, a grit temperature of 1000 K, and an impact load of 12 kN. A high-fidelity numerical heat transport model, using four-step reversible decomposition kinetics for HMX, clarified the physical mechanism of ignition in the experiment. The model suggested that only a very small part of the silica sphere was heated by the friction process and residual heat in the impacted surface behind the moving grit caused ignition. The model agreed well with the experiment in terms of time and temperature, and we have good confidence in the mechanistic picture provided by the model.
Scintillating screens sensitivity and resolution studies for low energy, low intensity beam diagnostics
Authors: Harasimowicz Janusz , Cosentino Luigi , Finocchiaro Paolo , Pappalardo Alfio , Welsch Carsten P.
Published: October 2010

In order to investigate the limits of scintillating screens for beam profile monitoring in the ultra-low energy, ultra-low intensity regime, CsI:Tl, YAG:Ce, and a Tb glass-based scintillating fiber optic plate (SFOP) were tested. The screens response to 200 and 50 keV proton beams with intensities ranging from a few picoampere down to the subfemtoampere region was examined. In the following paper, the sensitivity and resolution studies are presented in detail for CsI:Tl and the SFOP, the two most sensitive screens. In addition, a possible use of scintillators for ultra-low energy antiproton beam monitoring is discussed.
Pressure-dependent electronic structures in multiferroic DyMnO3: A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study
Authors: Chen J. M. , Lee J. M. , Chou T. L. , Chen S. A. , Huang S. W. , Jeng H. T. , Lu K. T. , Chen T. H. , Liang Y. C. , Chen S. W. , Chuang W. T. , Sheu H.-S. , Hiraoka N. , Ishii H. , Tsuei K. D. , Huang Eugene , Lin C. M. , Yang T. J.
Published: October 2010

Variations in the electronic structure and structural distortion in multiferroic DyMnO3 were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn–Teller distortion of Mn sites within MnO6 octahedra in DyMnO3 on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO3 progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO3 shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn–Teller distortion of MnO6 octahedra in compressed DyMnO3. A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra.
A one-electron model for the aqueous electron that includes many-body electron-water polarization: Bulk equilibrium structure, vertical electron binding energy, and optical absorption spectrum
Authors: Jacobson Leif D. , Herbert John M.
Published: October 2010

Previously, we reported an electron-water pseudopotential designed to be used in conjunction with a polarizable water model, in order to describe the hydrated electron [L. D. Jacobson et al., J. Chem. Phys. 130, 124115 (2009)]. Subsequently, we found this model to be inadequate for the aqueous electron in bulk water, and here we report a reparametrization of the model. Unlike the previous model, the current version is not fit directly to any observables; rather, we use an ab initio exchange-correlation potential, along with a repulsive potential that is fit to reproduce the density maximum of the excess electron’s wave function within the static-exchange approximation. The new parametrization performs at least as well as the previous model, as compared to ab initio benchmarks for (H2O)n− clusters, and also predicts reasonable values for the diffusion coefficient, radius of gyration, and absorption maximum of the bulk species. The new model predicts a vertical electron binding energy of 3.7 eV in bulk water, which is 1.4 eV smaller than the value obtained using nonpolarizable models; the difference represents the solvent’s electronic reorganization energy following electron detachment. We find that the electron’s first solvation shell is quite loose, which may be responsible for the electron’s large, positive entropy of hydration. Many-body polarization alters the electronic absorption line shape in a qualitative way, giving rise to a high-energy tail that is observed experimentally but is absent in previous simulations. In our model, this feature arises from spatially diffuse excited states that are bound only by electronic reorganization (i.e., solvent polarization) following electronic excitation.
Dielectric and Raman scattering studies of phase transitions in the (100−x)Na0.5Bi0.5TiO3–xSrTiO3 system
Authors: Rout Dibyaranjan , Moon Kyoung-Seok , Kang Suk-Joong L. , Kim I. W.
Published: October 2010

Temperature-driven and composition-driven phase transformations in a mixed A-site Pb-free solid solution series of (100−x)Na0.5Bi0.5TiO3–xSrTiO3 (0≤x≤40) were investigated by means of x-ray diffraction, dielectric, and Raman scattering techniques over a temperature range of 20–550 °C. The phonon anomalies observed in the room temperature Raman spectra with increasing Sr concentration revealed a morphotropic phase boundary (MPB) at x∼20. The distinct and discontinuous changes in dielectric properties at x∼20 confirmed the existence of MPB. On heating, the Raman spectral features for different compositions displayed substantial changes at temperatures almost identical to the critical temperatures determined by dielectric measurement, such as ferroelectric–antiferroelectric (Td), rhombohedral–tetragonal (TR-T), and antiferroelectric–paraelectric (Tm) phase transition temperature. However, the two phonon anomalies observed at higher temperatures (∼400 and 500 °C for x=10) suggested the coexistence of rhombohedral–tetragonal and tetragonal–cubic phases, respectively. The transition temperatures determined by the Raman and dielectric measurements gradually decreased as Sr concentration increased. The system showed strong relaxor behavior at x≥20 and the dielectric constant (ε) at room temperature was enhanced significantly from ∼500 (x=0) to ∼3800 (x=40) at 1 kHz.
Higher-order corrections to dust ion-acoustic soliton in a quantum dusty plasma
Authors: Chatterjee Prasanta , Das Brindaban , Mondal Ganesh , Muniandy S. V. , Wong C. S.
Published: October 2010

Dust ion-acoustic soliton is studied in an electron-dust-ion plasma by employing a two-fluid quantum hydrodynamic model. Ions and electrons are assumed to follow quantum mechanical behaviors in dust background. The Korteweg–de Vries (KdV) equation and higher order contribution to KdV equations are derived using reductive perturbation technique. The higher order contribution is obtained as a higher order inhomogeneous differential equation. The nonsecular solution of the higher order contribution is obtained by using the renormalization method and the particular solution of the inhomogeneous equation is determined using a truncated series solution method. The effects of dust concentration, quantum parameter for ions and electrons, and soliton velocity on the amplitude and width of the dressed soliton are discussed.
Parallel shear flow instabilities in strongly coupled Yukawa liquids: A comparison of generalized hydrodynamic model and molecular dynamics results
Authors: J. Ashwin , Ganesh R.
Published: October 2010

Using a generalized hydrodynamic (GH) model, the growth rate spectra of Kelvin–Helmholtz (KH) instability has been obtained analytically for a step shear profile in strongly coupled Yukawa liquids. The class of shear flows studied is assumed to be incompressible in nature. The growth rate spectra calculated exhibit viscous damping at high mode numbers, destabilization at stronger coupling, and in the limit τm (viscoelastic relaxation time)→0, reduce to the regular Navier–Stokes growth rate spectra. A direct comparison is made with previous molecular dynamics (MD) simulations [Ashwin J. and R. Ganesh, Phys. Rev. Lett. 104, 215003 (2010)] of KH instability. We find that for a given value of Reynolds number R and coupling parameter 1<Γ<100, the GH and MD growth rates are in a qualitative agreement. The inclusion of the effect of shear heating as an effective coupling parameter Γe appears to improve the quantitative comparison as well.
On universality of bulk local regime of the Hermitian sample covariance matrices
Authors: Shcherbina Tatyana
Published: October 2010

We consider the Hermitian sample covariance matrices Hn=m−1Σn1/2Am,nAm,n∗Σn1/2 in which Σn is a positive definite Hermitian matrix (possibly random) and Am,n is a n×m complex Gaussian random matrix (independent of Σn), and m→∞, n→∞, such that mn−1→c>1. Assuming that the normalized counting measure of Σn converges weakly (in probability) to a nonrandom measure N(0) with a bounded support, we prove the universality of the local eigenvalue statistics in the bulk of the limiting spectrum of Hn.
Energy splitting of resonant photonic states in nonlinear nanophotonic double waveguides
Authors: Cox Joel D. , Singh Mahi R.
Published: October 2010

We have studied the energy splitting of bound photonic states in Kerr-nonlinear double photonic waveguides. The structure is formed by embedding two Kerr-nonlinear photonic crystals in a linear photonic crystal. When an intense external laser field is applied to the system, two coupled waveguides are induced. These waveguides may also be induced by applying a stress field to the system. Due to the coupling between waveguides, bound states split into symmetric and antisymmetric pairs. Using the transfer matrix method we obtained expressions for these split bound states and their energy separation. We have shown that the energy splitting depends on the separation of the waveguides and the intensity of the applied laser. The energy splitting predicted by our expressions agrees well with the splitting of resonant states in simulated transmission spectra. Our findings agree qualitatively with existing experimental observations of coupled photonic wells fabricated from photonic crystals. We found that the bound state energy levels can be tuned using the laser and stress fields, and that the system can be switched between zero to one or more pairs of resonant states. The results described here can be used to develop all-optical switches, tunable filters and nonlinear coupled waveguides.
Note: A helical velocity selector for continuous molecular beams
Authors: Szewc Carola , Collier James D. , Ulbricht Hendrik
Published: October 2010

We report on a modern realization of the classic helical velocity selector for gas phase particle beams. The device operates stably under high vacuum conditions at rotational frequencies limited only by commercial dc motor capabilities. Tuning the rotational frequency allows selective scanning over a broad velocity band. The width of the selected velocity distributions at full-width-half-maximum is as narrow as a few percent of the selected mean velocity and independent of the rotational speed of the selector. The selector generates low vibrational noise amplitudes comparable to mechanically damped state-of-the-art turbo-molecular pumps and is therefore compatible with vibration sensitive experiments like molecule interferometry.
Selenium adsorbed single wall carbon nanotubes as a potential candidate for nanoscale interconnects
Authors: Krishnan Sridevi , Yilmaz Hulusi , Vadapoo Rajasekarakumar , Marin Carlos
Published: October 2010

Using ab initio calculations, we show that atomic selenium (Se) strongly adsorbs to the outer surface of single wall carbon nanotubes (SWCNTs), converting the semiconductor nanotubes to metallic and enhancing the conductance of the metallic and semimetallic ones. Considering the ease of vaporizing and depositing selenium, due to its volatile nature and low melting point, this system could be potentially viable. Thus, selenium adsorption offers a single process for enhancing the conductance of SWCNTs regardless of their chirality making them a promising candidate for nanoscale interconnects applications.
Communication: Constrained search formulation of the ground state energy as a functional of an idempotent one-matrix
Authors: Taube Andrew G.
Published: October 2010

Despite the fact that idempotent one-particle reduced density matrices are pervasive in quantum chemistry, the understanding of a general energy functional of such idempotent density matrices for the ground state energy has been lacking. By a constrained search, we show the structure of the general functional, illuminating the contributions from various terms. For the examples of the “best idempotent density matrix” and Kohn–Sham idempotent density matrices, we contrast the functional forms and suggest how the best idempotent density matrix approach may be a good starting point for further development.
Variational transcorrelated method
Authors: Luo Hongjun
Published: October 2010

We propose a new approach to the use of Jastrow ansatz in the calculation of electron correlations, based on a modification of the transcorrelated method of Boys and Handy [Proc. R. Soc. London, Ser. A 309, 209 (1969)]. In this new method, the original transcorrelated orbital equation is replaced with a general variational equation for the reference wave function, whereas the equation for the correlation factor remains the same. The method can be applied to a single determinant Jastrow ansatz as well as to a multideterminant one. For the single determinant ansatz, we obtain a Hartree–Fock type self-consistent equation for the optimization of orbitals, and for the multideterminant ansatz we have tested a CI type equation. We apply the new method in calculations of the C2 molecule and compare the results with those of variational quantum Monte Carlo calculations.
Influence of organic ions on DNA damage induced by 1 eV to 60 keV electrons
Authors: Zheng Yi , Sanche Léon
Published: October 2010

We report the results of a study on the influence of organic salts on the induction of single strand breaks (SSBs) and double strand breaks (DSBs) in DNA by electrons of 1 eV to 60 keV. Plasmid DNA films are prepared with two different concentrations of organic salts, by varying the amount of the TE buffer (Tris-HCl and EDTA) in the films with ratio of 1:1 and 6:1 Tris ions to DNA nucleotide. The films are bombarded with electrons of 1, 10, 100, and 60 000 eV under vacuum. The damage to the 3197 base-pair plasmid is analyzed ex vacuo by agarose gel electrophoresis. The highest yields are reached at 100 eV and the lowest ones at 60 keV. The ratios of SSB to DSB are surprisingly low at 10 eV (∼4.3) at both salt concentrations, and comparable to the ratios measured with 100 eV electrons. At all characteristic electron energies, the yields of SSB and DSB are found to be higher for the DNA having the lowest salt concentration. However, the organic salts are more efficient at protecting DNA against the damage induced by 1 and 10 eV electrons. DNA damage and protection by organic ions are discussed in terms of mechanisms operative at each electron energy. It is suggested that these ions create additional electric fields within the groove of DNA, which modify the resonance parameter of 1 and 10 eV electrons, namely, by reducing the electron capture cross-section of basic DNA units and the lifetime of corresponding transient anions. An interstrand electron transfer mechanism is proposed to explain the low ratios for the yields of SSB to those of DSB produced by 10 eV electrons.
Absolute cross sections for electronic excitations of cytosine by low energy electron impact
Authors: Bazin M. , Michaud M. , Sanche L.
Published: October 2010

The absolute cross sections (CSs) for electronic excitations of cytosine by electron impact between 5 and 18 eV were measured by electron-energy-loss (EEL) spectroscopy of the molecule deposited at low coverage on an inert Ar substrate. The lowest EEL features found at 3.55 and 4.02 eV are ascribed to transitions from the ground state to the two lowest triplet 1 A3′(π→π∗) and 2 A3′(π→π∗) valence states of the molecule. Their energy dependent CSs exhibit essentially a common maximum at about 6 eV with a value of 1.84×10−17 cm2 for the former and 4.94×10−17 cm2 for the latter. In contrast, the CS for the next EEL feature at 4.65 eV, which is ascribed to the optically allowed transition to the 2 A1′(π→π∗) valence state, shows only a steep rise to about 1.04×10−16 cm2 followed by a monotonous decrease with the incident electron energy. The higher EEL features at 5.39, 6.18, 6.83, and 7.55 eV are assigned to the excitations of the 3 A3,1′(π→π∗), 4 A1′(π→π∗), 5 A1′(π→π∗), and 6 A1′(π→π∗) valence states, respectively. The CSs for the 3 A3,1′ and 4 A1′ states exhibit a common enhancement at about 10 eV superimposed on a more or less a steep rise, reaching, respectively, a maximum of 1.27 and 1.79×10−16 cm2, followed by a monotonous decrease. This latter enhancement and the maximum seen at about 6 eV in the lowest triplet states correspond to the core-excited electron resonances that have been found by dissociative electron attachment experiments with cytosine in the gas phase. The weak EEL feature found at 5.01 eV with a maximum CS of 3.8×10−18 cm2 near its excitation threshold is attributed to transitions from the ground state to the 1 A3,1″(n→π∗) states. The monotonous rise of the EEL signal above 8 eV is attributed to the ionization of the molecule. It is partitioned into four excitation energy regions at about 8.55, 9.21, 9.83, and 11.53 eV, which correspond closely to the ionization energies of the four highest occupied molecular orbitals of cytosine. The sum of the ionization CS for these four excitation regions reaches a maximum of 8.1×10−16 cm2 at the incident energy of 13 eV.
What is Driving the Increasing Presence of Citizen Participation Initiatives?
Authors: Yetano Ana , Royo Sonia , Acerete Basilio
Published: October 2010

Nowadays there is an imperative for governments to be more responsive to community needs, and public sector modernisation programmes are introducing opportunities for citizen participation. We look at citizen participation initiatives through the lenses of institutional and stakeholder theories. Using survey data and exogenous variables we analyse experiences in thirty OECD and MERCOSUR local governments. We find that the possible gains in legitimacy and trust explain the efforts made towards citizen participation. In addition, the different levels of commitment towards meaningful citizen participation suggest that factors such as power and urgency can be complementary to legitimacy when analysing citizen participation.
Cornering the Market: Restriction of Retail Supermarket Locations
Authors: Cameron Nairne , Amrhein Carl G , Smoyer-Tomic Karen E , Raine Kim D , Chong Lee Yen
Published: October 2010

A major source of healthy foods, North American supermarkets have become larger in recent years, with new stores opening and older stores closing. Upon closure, there is evidence of some supermarket sites being placed under restrictive covenants, a practice that restricts future use of the site. The purpose is usually to limit food sales at the location, thus minimizing competition for a chain's nearby stores. In Edmonton, Alberta eighteen covenants have been documented on former supermarket sites. At six of these sites, termed food desolated, there is no operating supermarket within walking distance (800 m) of the former stores. The covenants disproportionately affect senior citizens as neighbourhoods with covenants have a significantly higher percentage of seniors than those neighbourhoods without covenants. Results of a group interview with community leaders from a neighbourhood that lost a supermarket and historical case study also point to the restrictive covenants resulting in difficulties for seniors accessing healthy food.
Meta-Analyses of Labour-Market Impacts of Immigration: Key Conclusions and Policy Implications
Authors: Longhi Simonetta , Nijkamp Peter , Poot Jacques
Published: October 2010

The number of immigrants across the world has doubled since 1980. The estimates of the impact of immigration on wages and employment in host countries are quantitatively small but vary widely. We summarize previous meta-analyses of the empirical literature and consider the implications for policy. We conclude that, on average, the impact on employment of the native born is smaller than on wages, while impacts are generally smaller in the US than in other countries studied to date. The variation in the estimates is related to the definition of the labour market, the extent of substitutability of foreign and native workers, and controls for endogeneity of immigrant settlement in statistical modelling. Policies enhancing labour-market flexibility, while at the same time improving immigrant economic integration, are likely to be effective in reducing transitory negative impacts.
A comparison of the effectiveness of camera trapping and live trapping for sampling terrestrial small-mammal communities
Authors: De Bondi Natasha , White John G. , Stevens Mike , Cooke Raylene
Published: October 2010

Context. There is an increasing reliance on the use of camera-trap technologies for surveys of medium to large terrestrial mammals. Camera trapping may, however, also have significant applications for broad-scale surveys of small mammals.
Aims. The present study aims to compare results from camera-trapping surveys to those of the more traditional live-trapping techniques. Specifically, it aims to test the effectiveness of the techniques for detecting species, and the cost effectiveness of both approaches.
Methods. Surveys were conducted across 36 sites in the Grampians National Park, Victoria, Australia, between April and July 2009. At each site, independent surveys were conducted for small mammals by using a combination of Elliot and cage trapping, then camera trapping. Results for the two different approaches were compared for both their ability to generate small-mammal presence data and their cost effectiveness.
Key results. Camera-trapping surveys of 36 sites in the Grampians National Park compared favourably with those of live-trapping surveys. Similar species were detected across the sites, and camera trapping was a considerably more cost effective than live trapping.
Conclusions. Camera-trapping surveys of small terrestrial mammals may provide a new and cost-effective technique for surveying terrestrial small mammals. This is particularly the case when presence data are the main requirement of the survey, with no requirement to capture and tag animals.
Implications. Given the cost-effective nature of camera trapping, there is potential to use this approach to increase the level of replication and spatial coverage of small-mammal surveys. Improving the replication and spatial coverage of studies has the potential to significantly increase the scope of research questions that can be asked, thus providing the potential to improve wildlife management.
LKB1 inhibits lung cancer progression through lysyl oxidase and extracellular matrix remodeling
Authors: Gao Yijun , Xiao Qian , Ma HuiMin , Li Li , Liu Jun , Feng Yan , Fang Zhaoyuan , Wu Jing , Han Xiangkun , Zhang Junhua , Sun Yihua , Wu Gongwei , Padera Robert , Chen Haiquan , Wong Kwok-kin , Ge Gaoxiang , Ji Hongbin
Published: October 2010

LKB1
loss-of-function mutations, observed in ∼30% of human lung adenocarcinomas, contribute significantly to lung cancer malignancy progression. We show that lysyl oxidase (LOX), negatively regulated by LKB1 through mTOR-HIF-1α signaling axis, mediates lung cancer progression. Inhibition of LOX activity dramatically alleviates lung cancer malignancy progression. Up-regulated LOX expression triggers excess collagen deposition in
Lkb1
-deficient lung tumors, and thereafter results in enhanced cancer cell proliferation and invasiveness through activation of β1 integrin signaling. High LOX level and activity correlate with poor prognosis and metastasis. Our findings provide evidence of how LKB1 loss of function promotes lung cancer malignancy through remodeling of extracellular matrix microenvironment, and identify LOX as a potential target for disease treatment in lung cancer patients.
Autophagy protein microtubule-associated protein 1 light chain-3B (LC3B) activates extrinsic apoptosis during cigarette smoke-induced emphysema
Authors: Chen Zhi-Hua , Lam Hilaire C. , Jin Yang , Kim Hong-Pyo , Cao Jiaofei , Lee Seon-Jin , Ifedigbo Emeka , Parameswaran Harikrishnan , Ryter Stefan W. , Choi Augustine M. K.
Published: October 2010

Chronic obstructive pulmonary disease (COPD) is a debilitating disease caused by chronic exposure to cigarette smoke (CS), which involves airway obstruction and alveolar loss (i.e., emphysema). The mechanisms of COPD pathogenesis remain unclear. Our previous studies demonstrated elevated autophagy in human COPD lung, and as a cellular and tissue response to CS exposure in an experimental model of emphysema in vivo. We identified the autophagic protein microtubule-associated protein 1 light chain-3B (LC3B) as a positive regulator of CS-induced lung epithelial cell death. We now extend these initial observations to explore the mechanism by which LC3B mediates CS-induced apoptosis and emphysema development in vivo. Here, we observed that
LC3B
−/−
mice had significantly decreased levels of apoptosis in the lungs after CS exposure, and displayed resistance to CS-induced airspace enlargement, relative to WT littermate mice. We found that LC3B associated with the extrinsic apoptotic factor Fas in lipid rafts in an interaction mediated by caveolin-1 (Cav-1). The siRNA-dependent knockdown of Cav-1 sensitized epithelial cells to CS-induced apoptosis, as evidenced by enhanced death-inducing signaling complex formation and caspase activation. Furthermore,
Cav-1
−/−
mice exhibited higher levels of autophagy and apoptosis in the lung in response to chronic CS exposure in vivo. In conclusion, we demonstrate a pivotal role for the autophagic protein LC3B in CS-induced apoptosis and emphysema, suggestive of novel therapeutic targets for COPD treatment. This study also introduces a mechanism by which LC3B, through interactions with Cav-1 and Fas, can regulate apoptosis.
Attractive noncovalent interactions in asymmetric catalysis: Links between enzymes and small molecule catalysts
Authors: Knowles Robert R. , Jacobsen Eric N.
Published: October 2010

Catalysis by neutral, organic, small molecules capable of binding and activating substrates solely via noncovalent interactions—particularly H-bonding—has emerged as an important approach in organocatalysis. The mechanisms by which such small molecule catalysts induce high enantioselectivity may be quite different from those used by catalysts that rely on covalent interactions with substrates. Attractive noncovalent interactions are weaker, less distance dependent, less directional, and more affected by entropy than covalent interactions. However, the conformational constraint required for high stereoinduction may be achieved, in principle, if multiple noncovalent attractive interactions are operating in concert. This perspective will outline some recent efforts to elucidate the cooperative mechanisms responsible for stereoinduction in highly enantioselective reactions promoted by noncovalent catalysts.
Neurophysiological origin of human brain asymmetry for speech and language
Authors: Morillon Benjamin , Lehongre Katia , Frackowiak Richard S. J. , Ducorps Antoine , Kleinschmidt Andreas , Poeppel David , Giraud Anne-Lise
Published: October 2010

The physiological basis of human cerebral asymmetry for language remains mysterious. We have used simultaneous physiological and anatomical measurements to investigate the issue. Concentrating on neural oscillatory activity in speech-specific frequency bands and exploring interactions between gestural (motor) and auditory-evoked activity, we find, in the absence of language-related processing, that left auditory, somatosensory, articulatory motor, and inferior parietal cortices show specific, lateralized, speech-related physiological properties. With the addition of ecologically valid audiovisual stimulation, activity in auditory cortex synchronizes with left-dominant input from the motor cortex at frequencies corresponding to syllabic, but not phonemic, speech rhythms. Our results support theories of language lateralization that posit a major role for intrinsic, hardwired perceptuomotor processing in syllabic parsing and are compatible both with the evolutionary view that speech arose from a combination of syllable-sized vocalizations and meaningful hand gestures and with developmental observations suggesting phonemic analysis is a developmentally acquired process.
Quaking I controls a unique cytoplasmic pathway that regulates alternative splicing of myelin-associated glycoprotein
Authors: Zhao Lixia , Mandler Mariana D. , Yi Hong , Feng Yue
Published: October 2010

Precise control of alternative splicing governs oligodendrocyte (OL) differentiation and myelination in the central nervous system (CNS). A well-known example is the developmentally regulated expression of splice variants encoding myelin-associated glycoprotein (MAG), which generates two protein isoforms that associate with distinct cellular components crucial for axon-glial recognition during myelinogenesis and axon-myelin stability. In the quakingviable (qkv) hypomyelination mutant mouse, diminished expression of isoforms of the selective RNA-binding protein quaking I (QKI) leads to severe dysregulation of MAG splicing. The nuclear isoform QKI-5 was previously shown to bind an intronic element of MAG and modulate alternative exon inclusion from a MAG minigene reporter. Thus, QKI-5 deficiency was thought to underlie the defects of MAG splicing in the qkvmutant. Surprisingly, we found that transgenic expression of the cytoplasmic isoform QKI-6 in the qkvOLs completely rescues the dysregulation of MAG splicing without increasing expression or nuclear abundance of QKI-5. In addition, cytoplasmic QKI-6 selectively associates with the mRNA that encodes heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), a well-characterized splicing factor. Furthermore, QKI deficiency in the qkvmutant results in abnormally enhanced hnRNPA1 translation and overproduction of the hnRNPA1 protein but not hnRNPA1 mRNA, which can be successfully rescued by the QKI-6 transgene. Finally, we show that hnRNPA1 binds MAG pre-mRNA and modulates alternative inclusion of MAG exons. Together, these results reveal a unique cytoplasmic pathway in which QKI-6 controls translation of the splicing factor hnRNPA1 to govern alternative splicing in CNS myelination.
SHEP1 partners with CasL to promote marginal zone B-cell maturation
Authors: Browne Cecille D. , Hoefer Melanie M. , Chintalapati Suresh K. , Cato Matthew H. , Wallez Yann , Ostertag Derek V. , Pasquale Elena B. , Rickert Robert C.
Published: October 2010

The marginal zone is a cellular niche bordering the marginal sinus of the spleen that contains specialized B-cell and macrophage subsets poised to capture bloodborne antigens. Marginal zone B cells are retained in this niche by integrin-mediated signaling induced by G protein-coupled receptors (GPCRs) and, likely, the B-cell receptor (BCR). Sphingosine-1-phosphate (S1P) signaling via the S1P family of GPCRs is known to be essential for B-cell localization in the marginal zone, but little is known about the downstream signaling events involved. Here, we demonstrate that the adaptor protein SHEP1 is required for marginal zone B-cell maturation. SHEP1 functions in concert with the scaffolding protein CasL, because we show that SHEP1 and CasL are constitutively associated in B cells. SHEP1 association is required for the BCR or S1P receptor(s) to induce the conversion of CasL into its serine/threonine hyperphosphorylated form, which is important for lymphocyte adhesion and motility. Thus, SHEP1 orchestrates marginal zone B-cell movement and retention as a key downstream effector of the BCR and S1P receptors.
Chronology of the Grotte du Renne (France) and implications for the context of ornaments and human remains within the Châtelperronian
Authors: Higham Thomas , Jacobi Roger , Julien Michèle , David Francine , Basell Laura , Wood Rachel , Davies William , Ramsey Christopher Bronk
Published: October 2010

There is extensive debate concerning the cognitive and behavioral adaptation of Neanderthals, especially in the period when the earliest anatomically modern humans dispersed into Western Europe, around 35,000–40,000 B.P. The site of the Grotte du Renne (at Arcy-sur-Cure) is of great importance because it provides the most persuasive evidence for behavioral complexity among Neanderthals. A range of ornaments and tools usually associated with modern human industries, such as the Aurignacian, were excavated from three of the Châtelperronian levels at the site, along with Neanderthal fossil remains (mainly teeth). This extremely rare occurrence has been taken to suggest that Neanderthals were the creators of these items. Whether Neanderthals independently achieved this level of behavioral complexity and whether this was culturally transmitted or mimicked via incoming modern humans has been contentious. At the heart of this discussion lies an assumption regarding the integrity of the excavated remains. One means of testing this is by radiocarbon dating; however, until recently, our ability to generate both accurate and precise results for this period has been compromised. A series of 31 accelerator mass spectrometry ultrafiltered dates on bones, antlers, artifacts, and teeth from six key archaeological levels shows an unexpected degree of variation. This suggests that some mixing of material may have occurred, which implies a more complex depositional history at the site and makes it difficult to be confident about the association of artifacts with human remains in the Châtelperronian levels.
Endothelial histamine H1receptor signaling reduces blood–brain barrier permeability and susceptibility to autoimmune encephalomyelitis
Authors: Lu Changming , Diehl Sean A. , Noubade Rajkumar , Ledoux Jonathan , Nelson Mark T. , Spach Karen , Zachary James F. , Blankenhorn Elizabeth P. , Teuscher Cory
Published: October 2010

Disruption of the blood–brain barrier (BBB) underlies the development of experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis. Environmental factors, such asBordetella pertussis, are thought to sensitize central endothelium to biogenic amines like histamine, thereby leading to increased BBB permeability.B. pertussis-induced histamine sensitization (Bphs) is a monogenic intermediate phenotype of EAE controlled by histamine H1receptor (Hrh1/H1R). Here, we transgenically overexpressed H1R in endothelial cells ofHrh1-KO (H1RKO) mice to test the role of endothelial H1R directly in Bphs and EAE. Unexpectedly, transgenic H1RKO mice expressing endothelial H1R under control of the von Willebrand factor promoter (H1RKO-vWFH1RTg) were Bphs-resistant. Moreover, H1RKO-vWFH1RTg mice exhibited decreased BBB permeability and enhanced protection from EAE compared with H1RKO mice. Thus, contrary to prevailing assumptions, our results show that endothelial H1R expression reduces BBB permeability, suggesting that endothelial H1R signaling may be important in the maintenance of cerebrovascular integrity.
Bacillus anthracis
produces membrane-derived vesicles containing biologically active toxins
Authors: Rivera Johanna , Cordero Radames J. B. , Nakouzi Antonio S. , Frases Susana , Nicola André , Casadevall Arturo
Published: October 2010

Extracellular vesicle production is a ubiquitous process in Gram-negative bacteria, but little is known about such process in Gram-positive bacteria. We report the isolation of extracellular vesicles from the supernatants of
Bacillus anthracis,
a Gram-positive bacillus that is a powerful agent for biological warfare.
B. anthracis
vesicles formed at the outer layer of the bacterial cell had double-membrane spheres and ranged from 50 to 150 nm in diameter. Immunoelectron microscopy with mAbs to protective antigen, lethal factor, edema toxin, and anthrolysin revealed toxin components and anthrolysin in vesicles, with some vesicles containing more than one toxin component. Toxin-containing vesicles were also visualized inside
B. anthracis
-infected macrophages. ELISA and immunoblot analysis of vesicle preparations confirmed the presence of
B. anthracis
toxin components. A mAb to protective antigen protected macrophages against vesicles from an anthrolysin-deficient strain, but not against vesicles from Sterne 34F2 and Sterne δT strains, consistent with the notion that vesicles delivered both toxin and anthrolysin to host cells. Vesicles were immunogenic in BALB/c mice, which produced a robust IgM response to toxin components. Furthermore, vesicle-immunized mice lived significantly longer than controls after
B. anthracis
challenge. Our results indicate that toxin secretion in
B. anthracis
is, at least, partially vesicle-associated, thus allowing concentrated delivery of toxin components to target host cells, a mechanism that may increase toxin potency. Our observations may have important implications for the design of vaccines, for passive antibody strategies, and provide a previously unexplored system for studying secretory pathways in Gram-positive bacteria.
White matter maturation reshapes structural connectivity in the late developing human brain
Authors: Hagmann P. , Sporns O. , Madan N. , Cammoun L. , Pienaar R. , Wedeen V. J. , Meuli R. , Thiran J.-P. , Grant P. E.
Published: October 2010

From toddler to late teenager, the macroscopic pattern of axonal projections in the human brain remains largely unchanged while undergoing dramatic functional modifications that lead to network refinement. These functional modifications are mediated by increasing myelination and changes in axonal diameter and synaptic density, as well as changes in neurochemical mediators. Here we explore the contribution of white matter maturation to the development of connectivity between ages 2 and 18 y using high b-value diffusion MRI tractography and connectivity analysis. We measured changes in connection efficacy as the inverse of the average diffusivity along a fiber tract. We observed significant refinement in specific metrics of network topology, including a significant increase in node strength and efficiency along with a decrease in clustering. Major structural modules and hubs were in place by 2 y of age, and they continued to strengthen their profile during subsequent development. Recording resting-state functional MRI from a subset of subjects, we confirmed a positive correlation between structural and functional connectivity, and in addition observed that this relationship strengthened with age. Continuously increasing integration and decreasing segregation of structural connectivity with age suggests that network refinement mediated by white matter maturation promotes increased global efficiency. In addition, the strengthening of the correlation between structural and functional connectivity with age suggests that white matter connectivity in combination with other factors, such as differential modulation of axonal diameter and myelin thickness, that are partially captured by inverse average diffusivity, play an increasingly important role in creating brain-wide coherence and synchrony.
Arginine methylation mediated by the
Arabidopsis
homolog of PRMT5 is essential for proper pre-mRNA splicing
Authors: Deng Xian , Gu Lianfeng , Liu Chunyan , Lu Tiancong , Lu Falong , Lu Zhike , Cui Peng , Pei Yanxi , Wang Baichen , Hu Songnian , Cao Xiaofeng
Published: October 2010

Protein arginine methylation, one of the most abundant and important posttranslational modifications, is involved in a multitude of biological processes in eukaryotes, such as transcriptional regulation and RNA processing. Symmetric arginine dimethylation is required for snRNP biogenesis and is assumed to be essential for pre-mRNA splicing; however, except for in vitro evidence, whether it affects splicing in vivo remains elusive. Mutation in an
Arabidopsis
symmetric arginine dimethyltransferase, AtPRMT5, causes pleiotropic developmental defects, including late flowering, but the underlying molecular mechanism is largely unknown. Here we show that AtPRMT5 methylates a wide spectrum of substrates, including some RNA binding or processing factors and U snRNP AtSmD1, D3, and AtLSm4 proteins, which are involved in RNA metabolism. RNA-seq analyses reveal that AtPRMT5 deficiency causes splicing defects in hundreds of genes involved in multiple biological processes. The splicing defects are identified in transcripts of several RNA processing factors involved in regulating flowering time. In particular, splicing defects at the flowering regulator
FLOWERING LOCUS KH DOMAIN
(
FLK
) in
atprmt5
mutants reduce its functional transcript and protein levels, resulting in the up-regulation of a flowering repressor
FLOWERING LOCUS C
(
FLC
) and consequently late flowering. Taken together, our findings uncover an essential role for arginine methylation in proper pre-mRNA splicing that impacts diverse developmental processes.
Neutralization of West Nile virus by cross-linking of its surface proteins with Fab fragments of the human monoclonal antibody CR4354
Authors: Kaufmann Bärbel , Vogt Matthew R. , Goudsmit Jaap , Holdaway Heather A. , Aksyuk Anastasia A. , Chipman Paul R. , Kuhn Richard J. , Diamond Michael S. , Rossmann Michael G.
Published: October 2010

Many flaviviruses are significant human pathogens, with the humoral immune response playing an essential role in restricting infection and disease. CR4354, a human monoclonal antibody isolated from a patient, neutralizes West Nile virus (WNV) infection at a postattachment stage in the viral life-cycle. Here, we determined the structure of WNV complexed with Fab fragments of CR4354 using cryoelectron microscopy. The outer glycoprotein shell of a mature WNV particle is formed by 30 rafts of three homodimers of the viral surface protein E. CR4354 binds to a discontinuous epitope formed by protein segments from two neighboring E molecules, but does not cause any detectable structural disturbance on the viral surface. The epitope occurs at two independent positions within an icosahedral asymmetric unit, resulting in 120 binding sites on the viral surface. The cross-linking of the six E monomers within one raft by four CR4354 Fab fragments suggests that the antibody neutralizes WNV by blocking the pH-induced rearrangement of the E protein required for virus fusion with the endosomal membrane.
Crystal and solution structures of an odorant-binding protein from the southern house mosquito complexed with an oviposition pheromone
Authors: Mao Yang , Xu Xianzhong , Xu Wei , Ishida Yuko , Leal Walter S. , Ames James B. , Clardy Jon
Published: October 2010

Culex
mosquitoes introduce the pathogens responsible for filariasis, West Nile virus, St. Louis encephalitis, and other diseases into humans. Currently, traps baited with oviposition semiochemicals play an important role in detection efforts and could provide an environmentally friendly approach to controlling their populations. The odorant binding proteins (OBPs) in the female's antenna play a crucial, if yet imperfectly understood, role in sensing oviposition cues. Here, we report the X-ray crystallography and NMR 3D structures of OBP1 for
Culex quinquefasciatus
(CquiOBP1) bound to an oviposition pheromone (
5R,6S
)-6-acetoxy-5-hexadecanolide (MOP). In both studies, CquiOBP1 had the same overall six-helix structure seen in other insect OBPs, but a detailed analysis revealed an important previously undescribed feature. There are two models for OBP-mediated signal transduction: (
i
) direct release of the pheromone from an internal binding pocket in a pH-dependent fashion and (
ii
) detection of a pheromone-induced conformational change in the OBP·pheromone complex. Although CquiOBP1 binds MOP in a pH-dependent fashion, it lacks the C terminus required for the pH-dependent release model. This study shows that CquiOBP binds MOP in an unprecedented fashion using both a small central cavity for the lactone head group and a long hydrophobic channel for its tail.
Neuronal Abelson helper integration site-1 (Ahi1) deficiency in mice alters TrkB signaling with a depressive phenotype
Authors: Xu Xingshun , Yang Hao , Lin Yung-Feng , Li Xiang , Cape Austin , Ressler Kerry J. , Li Shihua , Li Xiao-Jiang
Published: October 2010

Recent studies suggest that the human Abelson helper integration site-1 (
AHI1
) gene on chromosome 6 is associated with susceptibility to schizophrenia and autism, two common neuropsychological disorders with depression symptoms. Mouse Ahi1 protein is abundant in the hypothalamus and amygdala, which are important brain regions for controlling emotion. However, the neuronal function of Ahi1 remains unclear. With the Cre–loxP system, we created a mouse model that selectively reduces Ahi1 expression in neuronal cells. Mice with neuronal Ahi1 deficiency show reduced TrkB level in the brain and depressive phenotypes, which can be alleviated by antidepressant drugs or by overexpression of TrkB in the amygdala. Ahi1 deficiency promotes the degradation of endocytic TrkB and reduces TrkB signaling in neuronal cells. Our findings suggest that impaired endocytic sorting and increased degradation of TrkB can induce depression and that this impaired pathway may serve as a previously uncharacterized therapeutic target for depression.