bluuebunny/crossref_metadata_2025 huggingface dataset:
The soft x-ray instrument for materials studies at the linac coherent light source x-ray free-electron laser
Authors: Schlotter W. F. , Turner J. J. , Rowen M. , Heimann P. , Holmes M. , Krupin O. , Messerschmidt M. , Moeller S. , Krzywinski J. , Soufli R. , Fernández-Perea M. , Kelez N. , Lee S. , Coffee R. , Hays G. , Beye M. , Gerken N. , Sorgenfrei F. , Hau-Riege S. , Juha L. , Chalupsky J. , Hajkova V. , Mancuso A. P. , Singer A. , Yefanov O. , Vartanyants I. A. , Cadenazzi G. , Abbey B. , Nugent K. A. , Sinn H. , Lüning J. , Schaffert S. , Eisebitt S. , Lee W.-S. , Scherz A. , Nilsson A. R. , Wurth W.
Published: April 2012

The soft x-ray materials science instrument is the second operational beamline at the linac coherent light source x-ray free electron laser. The instrument operates with a photon energy range of 480–2000 eV and features a grating monochromator as well as bendable refocusing mirrors. A broad range of experimental stations may be installed to study diverse scientific topics such as: ultrafast chemistry, surface science, highly correlated electron systems, matter under extreme conditions, and laboratory astrophysics. Preliminary commissioning results are presented including the first soft x-ray single-shot energy spectrum from a free electron laser.
Dielectric resonance and magnetic properties of Fe-3% doped BaSnO3 thin films grown by pulsed laser deposition
Authors: Balamurugan K. , Senthil Kumar E. , Ramachandran B. , Venkatesh S. , Harish Kumar N. , Ramachandra Rao M. S. , Santhosh P. N.
Published: April 2012

Fe-3% doped BaSnO3 thin films of good crystalline quality with lattice constant a = 4.053 Å were grown on (2 0 0) n-type Si substrates by pulsed laser deposition. Micro Raman spectra of the thin films showed the presence of strain-induced Raman modes with reference to that of the bulk polycrystalline Fe-3% doped BaSnO3. The films exhibited dielectric resonance in the frequency range 20 – 60 MHz and it is explained qualitatively based on the phenomenon of electromechanical piezoelectric resonance. The measured values of the resonant frequency and the surface resistivity showed a strong dependence on the thickness and the crystalline-character of the thin films. Magnetic measurements were performed selectively for the two films having (2 0 0) preferred orientation. It was found that both of them possess ferromagnetic ordering at 300 K and 1.8 K. At 300 K, the inherent diamagnetism of the undoped BaSnO3 was found to be dominating for higher applied magnetic field.
Freezing of parallel hard cubes with rounded edges
Authors: Marechal Matthieu , Zimmermann Urs , Löwen Hartmut
Published: April 2012

The freezing transition in a classical three-dimensional system of rounded hard cubes with fixed, equal orientations is studied by computer simulation and fundamental-measure density functional theory. By switching the rounding parameter s from zero to one, one can smoothly interpolate between cubes with sharp edges and hard spheres. The equilibrium phase diagram of rounded parallel hard cubes is computed as a function of their volume fraction and the rounding parameter s. The second order freezing transition known for oriented cubes at s = 0 is found to be persistent up to s = 0.65. The fluid freezes into a simple-cubic crystal which exhibits a large vacancy concentration. Upon a further increase of s, the continuous freezing is replaced by a first-order transition into either a sheared simple cubic lattice or a deformed face-centered cubic lattice with two possible unit cells: body-centered orthorhombic or base-centered monoclinic. In principle, a system of parallel cubes could be realized in experiments on colloids using advanced synthesis techniques and a combination of external fields.
Field-free particle focusing in microfluidic plugs
Authors: Kurup G. K. , Basu Amar S.
Published: April 2012

Particle concentration is a key unit operation in biochemical assays. Although there are many techniques for particle concentration in continuous-phase microfluidics, relatively few are available in multiphase (plug-based) microfluidics. Existing approaches generally require external electric or magnetic fields together with charged or magnetized particles. This paper reports a passive technique for particle concentration in water-in-oil plugs which relies on the interaction between particle sedimentation and the recirculating vortices inherent to plug flow in a cylindrical capillary. This interaction can be quantified using the Shields parameter (θ), a dimensionless ratio of a particle’s drag force to its gravitational force, which scales with plug velocity. Three regimes of particle behavior are identified. When θ is less than the movement threshold (region I), particles sediment to the bottom of the plug where the internal vortices subsequently concentrate the particles at the rear of the plug. We demonstrate highly efficient concentration (∼100%) of 38 μm glass beads in 500 μm diameter plugs traveling at velocities up to 5 mm/s. As θ is increased beyond the movement threshold (region II), particles are suspended in well-defined circulation zones which begin at the rear of the plug. The length of the zone scales linearly with plug velocity, and at sufficiently large θ, it spans the length of the plug (region III). A second effect, attributed to the co-rotating vortices at the rear cap, causes particle aggregation in the cap, regardless of flow velocity. Region I is useful for concentrating/collecting particles, while the latter two are useful for mixing the beads with the solution. Therefore, the two key steps of a bead-based assay, concentration and resuspension, can be achieved simply by changing the plug velocity. By exploiting an interaction of sedimentation and recirculation unique to multiphase flow, this simple technique achieves particle concentration without on-chip components, and could therefore be applied to a range of heterogeneous screening assays in discrete nl plugs.
Proton trajectories and electric fields in a laser-accelerated focused proton beam
Authors: Foord M. E. , Bartal T. , Bellei C. , Key M. , Flippo K. , Stephens R. B. , Patel P. K. , McLean H. S. , Jarrott L. C. , Wei M. S. , Beg F. N.
Published: April 2012

The focusing properties of a laser generated proton beam have been investigated using hemispherical targets in both freestanding and enclosed cone-shaped geometries. The proton trajectories and focusing were strongly affected by the electric fields in the beam, bending the trajectories near the axis. In the cone targets, a sheath field effectively channels the proton beam through the open cone tip, substantially improving the beam focusing from ≈90 μm to ≈55 μm diameter for protons with energies >3 MeV. The proton generation and focusing were modeled using 2D hybrid particle-in-cell simulations, which compared well with the experimental results. Simulations predict further improvement in focusing with more uniform target illumination. These results are of significant interest to proton fast ignition and other high energy density physics applications.
Incorporating a completely renormalized coupled cluster approach into a composite method for thermodynamic properties and reaction paths
Authors: Nedd Sean A. , DeYonker Nathan J. , Wilson Angela K. , Piecuch Piotr , Gordon Mark S.
Published: April 2012

The correlation consistent composite approach (ccCA), using the S4 complete basis set two-point extrapolation scheme (ccCA-S4), has been modified to incorporate the left-eigenstate completely renormalized coupled cluster method, including singles, doubles, and non-iterative triples (CR-CC(2,3)) as the highest level component. The new ccCA-CC(2,3) method predicts thermodynamic properties with an accuracy that is similar to that of the original ccCA-S4 method. At the same time, the inclusion of the single-reference CR-CC(2,3) approach provides a ccCA scheme that can correctly treat reaction pathways that contain certain classes of multi-reference species such as diradicals, which would normally need to be treated by more computationally demanding multi-reference methods. The new ccCA-CC(2,3) method produces a mean absolute deviation of 1.7 kcal/mol for predicted heats of formation at 298 K, based on calibration with the G2/97 set of 148 molecules, which is comparable to that of 1.0 kcal/mol obtained using the ccCA-S4 method, while significantly improving the performance of the ccCA-S4 approach in calculations involving more demanding radical and diradical species. Both the ccCA-CC(2,3) and ccCA-S4 composite methods are used to characterize the conrotatory and disrotatory isomerization pathways of bicyclo[1.1.0]butane to trans-1,3-butadiene, for which conventional coupled cluster methods, such as the CCSD(T) approach used in the ccCA-S4 model and, in consequence, the ccCA-S4 method itself might fail by incorrectly placing the disrotatory pathway below the conrotatory one. The ccCA-CC(2,3) scheme provides correct pathway ordering while providing an accurate description of the activation and reaction energies characterizing the lowest-energy conrotatory pathway. The ccCA-CC(2,3) method is thus a viable method for the analyses of reaction mechanisms that have significant multi-reference character, and presents a generally less computationally intensive alternative to true multi-reference methods, with computer costs and ease of use that are similar to those that characterize the more established, CCSD(T)-based, ccCA-S4 methodology.
Handheld magnetic sensor for measurement of tension
Authors: Singal K. , Rajamani R.
Published: April 2012

This letter develops an analytical formulation for measurement of tension in a string using a handheld sensor. By gently pushing the sensor against the string, the tension in the string can be obtained. An experimental sensor prototype is constructed to verify the analytical formulation. The centimeter-sized prototype utilizes three moving pistons and magnetic field based measurements of their positions. Experimental data show that the sensor can accurately measure tension on a bench top rig. The developed sensor could be useful in a variety of orthopedic surgical procedures, including knee replacement, hip replacement, ligament repair, shoulder stabilization, and tendon repair.
Localization transition of instantaneous normal modes and liquid diffusion
Authors: Clapa Vasile Iulian , Kottos Tsampikos , Starr Francis W.
Published: April 2012

We analyze the structure of instantaneous normal modes (INM) associated with the Hessian matrix of a liquid. Utilizing a scaling theory developed in the framework of Anderson localization studies, we unambiguously identify the crossover point in the INM spectrum between extended and localized modes. We establish a relation between the unstable, delocalized INMs and the liquid diffusion coefficient that appears valid over a large temperature range, covering both Arrhenius and non-Arrhenius regimes of temperature dependence. These results suggest a possible route to theoretically relate dynamics to thermodynamical properties of the liquid via the tomography of the INMs.
Core level (S 2p) excitation and fragmentation of the dimethyl sulfide and dimethyldisulfide molecules
Authors: Bernini R. B. , da Silva L. B. G. , Rodrigues F. N. , Coutinho L. H. , Rocha A. B. , de Souza G. G. B.
Published: April 2012

Electronic excitation and ionic dissociation of dimethylsulfide (DMS) and dimethyldisulfide (DMDS) have been studied around the S 2p edge using synchrotron radiation and time-of-flight mass spectrometry techniques. Mass spectra were obtained for both molecules, below, on and above the well defined resonances observed in the S 2p photoabsorption spectrum and centered at approximately 166 eV photon energy. Ab initio IS-CASSCF calculations were performed for a better understanding of the photoabsorption spectra. Similar calculations were also performed for the H2S molecule, in order to establish a bench mark. For both molecules, a higher fragmentation degree is observed with increasing photon energy. In the DMDS case, selective fragmentation was observed in the formation of the [CHnS]+ ions at the first S 2p resonance (corresponding to excitation to a σ*SS state) and in the formation of the [S2]+ and [S]+ ions at the third S 2p resonance (corresponding to excitation to a σ*CS state). Previously unreported doubly charged ([S]2+, [CH3]2+) are observed for DMS and DMDS.
Reversible wettability of electron-beam deposited indium-tin-oxide driven by ns-UV irradiation
Authors: Persano Luana , Del Carro Pompilio , Pisignano Dario
Published: April 2012

Indium tin oxide (ITO) is one of the most widely used semiconductor oxides in the field of organic optoelectronics, especially for the realization of anode contacts. Here the authors report on the control of the wettability properties of ITO films deposited by reactive electron beam deposition and irradiated by means of nanosecond-pulsed UV irradiation. The enhancement of the surface water wettability, with a reduction of the water contact angle larger than 50°, is achieved by few tens of seconds of irradiation. The analyzed photo-induced wettability change is fully reversible in agreement with a surface-defect model, and it can be exploited to realize optically transparent, conductive surfaces with controllable wetting properties for sensors and microfluidic circuits.
Dependence of diffusivity on density and solute diameter in liquid phase: A molecular dynamics study of Lennard-Jones system
Authors: Varanasi Srinivasa R. , Kumar Parveen , Yashonath S.
Published: April 2012

Investigations into the variation of self-diffusivity with solute radius, density, and degree of disorder of the host medium is explored. The system consists of a binary mixture of a relatively smaller sized solute, whose size is varied and a larger sized solvent interacting via Lennard-Jones potential. Calculations have been performed at three different reduced densities of 0.7, 0.8, and 0.933. These simulations show that diffusivity exhibits a maximum for some intermediate size of the solute when the solute diameter is varied. The maximum is found at the same size of the solute at all densities which is at variance with the prediction of the levitation effect. In order to understand this anomaly, additional simulations were carried out in which the degree of disorder has been varied while keeping the density constant. The results show that the diffusivity maximum gradually disappears with increase in disorder. Disorder has been characterized by means of the minimal spanning tree. Simulations have also been carried out in which the degree of disorder is constant and only the density is altered. The results from these simulations show that the maximum in diffusivity now shifts to larger distances with decrease in density. This is in agreement with the changes in void and neck distribution with density of the host medium. These results are in excellent agreement with the predictions of the levitation effect. They suggest that the effect of disorder is to shift the maximum in diffusivity towards smaller solute radius while that of the decrease in density is to shift it towards larger solute radius. Thus, in real systems where the degree of disorder is lower at higher density and vice versa, the effect due to density and disorder have opposing influences. These are confirmed by the changes seen in the velocity autocorrelation function, self part of the intermediate scattering function and activation energy.
An unnoticed property of the cylindrical relativistic Brillouin flow
Authors: Simon D. H. , Lau Y. Y. , Luginsland J. W. , Gilgenbach R. M.
Published: April 2012

It is shown that the vector potential and the scalar potential satisfy a Buneman-Hartree like (BHL) condition and a Hull-cutoff like (HCL) condition everywhere within the Brillouin flow of a cylindrical, relativistic magnetron, when the phase velocity in the Buneman-Hartree condition is replaced by the laminar, local flow velocity of the Brillouin flow. The vector potential and the scalar potentials include the Brillouin flow’s self magnetic field and the self electric fields. The HCL condition reduces to the conventional Hull cutoff condition derived from single particle orbit theory when the Brillouin hub extends to the anode. However, the BHL condition reduces to the conventional Buneman-Hartree condition only in the planar magnetron limit but may be substantially different for a cylindrical magnetron, as demonstrated recently [Lau et al., Phys. Plasmas 17, 033102 (2010)]. These conclusions apply also to the inverted magnetron configuration. The effects of ions are discussed.
Neuronal avalanches of a self-organized neural network with active-neuron-dominant structure
Authors: Li Xiumin , Small Michael
Published: April 2012

Neuronal avalanche is a spontaneous neuronal activity which obeys a power-law distribution of population event sizes with an exponent of –3/2. It has been observed in the superficial layers of cortex both invivo and invitro. In this paper, we analyze the information transmission of a novel self-organized neural network with active-neuron-dominant structure. Neuronal avalanches can be observed in this network with appropriate input intensity. We find that the process of network learning via spike-timing dependent plasticity dramatically increases the complexity of network structure, which is finally self-organized to be active-neuron-dominant connectivity. Both the entropy of activity patterns and the complexity of their resulting post-synaptic inputs are maximized when the network dynamics are propagated as neuronal avalanches. This emergent topology is beneficial for information transmission with high efficiency and also could be responsible for the large information capacity of this network compared with alternative archetypal networks with different neural connectivity.
Experimental evidence of synchronization of time-varying dynamical network
Authors: Bhowmick Sourav K. , Amritkar R. E. , Dana Syamal K.
Published: April 2012

We investigate synchronization of time varying networks and stability conditions. We derive interesting relations between the critical coupling constants for synchronization and switching times for time-varying and time average networks. The relations are based on the additive property of Lyapunov exponents and are verified experimentally in electronic circuit.
Nonlinear saturation amplitudes in classical Rayleigh-Taylor instability at arbitrary Atwood numbers
Authors: Liu W. H. , Wang L. F. , Ye W. H. , He X. T.
Published: April 2012

In this research, nonlinear saturation amplitudes (NSAs) of the first two harmonics in Rayleigh-Taylor instability (RTI) for irrotational, incompressible, and inviscid fluids, with a discontinuous profile at arbitrary Atwood numbers, are investigated analytically, by considering nonlinear corrections up to the tenth-order. The NSA of the fundamental mode is defined as the linear (purely exponential) growth amplitude of the fundamental mode at the saturation time when the growth of the fundamental mode (first harmonic) is reduced by 10% in comparison to its corresponding linear growth. The NSA of the second harmonic can be obtained in the same way. The analytic results indicate that the effects of the higher-order correction (HOC) and the Atwood number (A) play an important role in the NSA of the RTI. It is found that the NSA of the fundamental mode decreases with increasing A. And when the HOC effects are considered, the NSA of the fundamental mode is significantly larger than the prediction of previous literatures within the framework of third-order perturbation theory [J. W. Jacobs and I. Catton, J. Fluid Mech. 187, 329 (1988); S. W. Haan, Phys. Fluids B 3, 2349 (1991)]. We find that the NSA of the second harmonic first decreases quickly with increasing A, reaching a minimum, and then increases slowly. Furthermore, the NSAs of the first two harmonics demonstrate the trend of convergence as the order of corrections increases. Thus, it should be included in applications where the NSAs play a role, such as inertial confinement fusion ignition target design.
Experimental and theoretical analysis of the temperature dependence of the two-dimensional electron mobility in a strained Si quantum well
Authors: Tanaka Takahisa , Tsuchiya Go , Hoshi Yusuke , Sawano Kentarou , Shiraki Yasuhiro , Itoh Kohei M.
Published: April 2012

The temperature dependence of the mobility of the two-dimensional electron gas (2DEG) in a silicon quantum well strained by Si0.7Ge0.3 relaxed buffer layer is determined precisely by a mobility spectrum analysis. The 2DEG mobility is 2780 cm2/V s at room temperature and, upon cooling, increases continuously to reach μ2DEG=7.4×104cm2/Vs at 7 K. A back gate installed on the sample changes the 2DEG concentration n successfully to establish μ2DEG∝n1.4 at the constant temperature T=10K, implying that the scattering at such low temperature is limited solely by the remote ionized impurity scattering. Based on this finding, theoretical analysis of the temperature dependence of μ2DEG is performed based on the relaxation time approximation using 2DEG wavefunctions and subband structures determined self-consistently and including three major scatterings; by intravalley acoustic phonons, intervalley g-processes of longitudinal optical (LO) phonons, and remote ionized impurities. The calculation included only three fitting parameters, the shear deformation potential (Ξu=9.5eV), LO phonon deformation potential for g-process scattering (D0=9.0×108eV/cm), and sheet density of remote ionized impurities that have been determined by quantitative comparison with our experimental results. The temperature dependence of μ2DEG calculated theoretically show excellent agreement with experimentally determined μ2DEG.
Tensegrity and motor-driven effective interactions in a model cytoskeleton
Authors: Wang Shenshen , Wolynes Peter G.
Published: April 2012

Actomyosin networks are major structural components of the cell. They provide mechanical integrity and allow dynamic remodeling of eukaryotic cells, self-organizing into the diverse patterns essential for development. We provide a theoretical framework to investigate the intricate interplay between local force generation, network connectivity, and collective action of molecular motors. This framework is capable of accommodating both regular and heterogeneous pattern formation, arrested coarsening and macroscopic contraction in a unified manner. We model the actomyosin system as a motorized cat's cradle consisting of a crosslinked network of nonlinear elastic filaments subjected to spatially anti-correlated motor kicks acting on motorized (fibril) crosslinks. The phase diagram suggests there can be arrested phase separation which provides a natural explanation for the aggregation and coalescence of actomyosin condensates. Simulation studies confirm the theoretical picture that a nonequilibrium many-body system driven by correlated motor kicks can behave as if it were at an effective equilibrium, but with modified interactions that account for the correlation of the motor driven motions of the actively bonded nodes. Regular aster patterns are observed both in Brownian dynamics simulations at effective equilibrium and in the complete stochastic simulations. The results show that large-scale contraction requires correlated kicking.
Elastic and inelastic cross sections for low-energy electron collisions with pyrimidine
Authors: Mašín Zdeněk , Gorfinkiel Jimena D. , Jones Darryl B. , Bellm Susan M. , Brunger Michael J.
Published: April 2012

We present theoretical elastic and electronic excitation cross sections and experimental electronic excitation cross sections for electron collisions with pyrimidine. We use the R-matrix method to determine elastic integral and differential cross sections and integral inelastic cross sections for energies up to 15 eV. The experimental inelastic cross sections have been determined in the 15–50 eV impact energy range. Typically, there is quite reasonable agreement between the theoretical and experimental integral inelastic cross sections. Calculated elastic cross sections agree very well with prior results.
Large optical polarization anisotropy due to anisotropic in-plane strain in m-plane GaInN quantum well structures grown on m-plane 6H-SiC
Authors: Jönen H. , Bremers H. , Langer T. , Rossow U. , Hangleiter A.
Published: April 2012

We investigated the optical polarization anisotropy of m-plane GaInN/GaN quantum well structures on m-plane SiC and bulk GaN substrates. On bulk GaN, the degree of polarization increases with increasing indium content according to the larger strain-induced separation of the topmost valence bands. On m-plane SiC, however, we observe constantly large polarization ratios of around 90% and more. From an x-ray strain state analysis and calculations of the valence band energies, we find that an anisotropic strain of the GaN buffer layer leads to a very strong separation of the topmost valence bands resulting in a large degree of polarization.
Low temperature cathodoluminecence and electron beam induced current studies of single GaN nanowires
Authors: Oh Eunsoon , Woo Lee Byoung , Shim So-Jeong , Choi Heon-Jin , Hee Son Byoung , Hwan Ahn Yeong , Dang Le Si
Published: April 2012

Single crystalline GaN nanowires, with 100 nm typical diameters, were grown by chemical vapor deposition method, using Pt catalyst, and characterized by cathodoluminescence and electron beam induced current (EBIC) measurements at 5 K. The near band edge emission was found to be asymmetric and broad, with full width half maximum of around 150 meV, peaking at 3.55 eV, well above the GaN bulk band gap. This blueshift was ascribed to band filling effect resulting from unintentional n-type doping in the range 1019–1020 cm−3. Despite of this heavy doping, EBIC experiments showed that minority carriers can diffuse over 0.2 μm.
Photon reabsorption in fluorescent solar collectors
Authors: Fang L. , Parel T. S. , Danos L. , Markvart T.
Published: April 2012

Understanding photon transport losses in fluorescence solar collectors is very important for increasing optical efficiencies. We present an analytical expression to characterize photon reabsorption in fluorescent solar collectors, which represent a major source of photon loss. A particularly useful universal form of this expression is found in the limit of high reabsorption, which gives the photon reabsorption probability in a simple form as a function of the absorption coefficient and the optical étendue of the emitted photon beam. Our mathematical model predicts fluorescence spectra emitted from the collector edge, which are in excellent agreement with experiment and provide an effective characterization tool for photon transport in light absorbing media.
Spectra of Rashba- and Dresselhaus-type circular photogalvanic effect at inter-band excitation in GaAs/AlGaAs quantum wells and their behaviors under external strain
Authors: Yu J. L. , Chen Y. H. , Liu Y. , Jiang C. Y. , Ma H. , Zhu L. P.
Published: April 2012

Spectra of Rashba- and Dresselhaus-type circular photogalvanic effect (CPGE) at inter-band excitation in symmetric GaAs/Al0.3Ga0.7As quantum wells have been investigated at room temperature. The lineshape of Rashba and Dresselhaus-type CPGE spectra is similar, and the Rashba-type is about five times larger than that of Dresselhaus-type. The CPGE current for 1HH-1E (the first valence subband of heavy hole to the first conduction) has the same sign with that of 1LH-1E, while the strain-induced Rashba-type CPGE has different sign for them, and no detectable strain-induced Dresselhaus-type CPGE is observed.
Design and micromagnetic simulation of the L1-FePt/Fe multilayer graded film
Authors: Zhang Jun , Liu Yang , Wang Fang , Zhang Jing , Zhang Ruiqiang , Wang Zhenfeng , Xu Xiaohong
Published: April 2012

The magnetic properties of the L10-FePt20 nm/Fe5 nm exchange spring bilayer were investigated using the micromagnetic simulation software object oriented micromagnetic framework (OOMMF). The results indicate that coercivity increases and thermal stability improves as the magnetocrystalline anisotropy constant (KFePt) of the L10-FePt hard layer increases. When KFePt reaches the critical value of 2.8 × 106 J/m3, an additional step appears in the hysteresis loop, and the magnetization process shows a two-phase reversal behavior, which is disadvantageous for practical applications of the recording media. However, setting KFePt as a graded variation removes the step of the hysteresis loop and reduces coercivity while allowing the thermal stability of the system to remain constant. These results can serve as a significant basis for the experimental preparation of exchange-coupled graded media.
Mechanically tunable magnetism on graphene nanoribbon adsorbed SiO2 surface
Authors: Guo Yufeng , Guo Wanlin
Published: April 2012

Our first-principle calculations reveal that the O-terminated surface of zigzag graphene nanoribbon adsorbed (100) α-quartz SiO2 exhibits antiferromagnetic ground state. This is due to unpaired electrons of dangling O atoms forming on the SiO2 surface, which are caused by the edge C atoms of the adsorbed nanoribbon. The resulting magnetism and spin-resolved states on the SiO2 surface can be effectively tuned by mechanical strain applied on the substrate, with the antiferromagnetic state transforming into ferromagnetic state as well as the total magnetic moment varying from negative to positive when the strain turns from tensile to compressive. We elucidate the mechanism for the modification of the surface magnetism by orbital hybridization between C and O atoms and part of dangling O atoms bonding with the nanoribbon under strain.
Fano resonance in two-intersecting nanorings: Multiple layers of plasmon hybridizations
Authors: Liu Hailong , Wu Xijun , Li Bing , Xu Chenxi , Zhang Guangbiao , Zheng Longjiang
Published: April 2012

We theoretically investigate the optical properties of two-intersecting nanorings (TINR), which exhibit a pronounced Fano resonance in the near-infrared region. A multiple-layer plasmon hybridization model is proposed to explain the reasons and forming processes of the Fano resonance. The dependence of the Fano resonance on the intersecting distance is also demonstrated. Moreover, the presented two-intersecting nanorings are employed as a biosensor exhibiting a 3-fold improvement of the figure of merit than that of a single-ring biosensor with the same resonant wavelength.
Bolometric response in graphene based superconducting tunnel junctions
Authors: Vora Heli , Kumaravadivel Piranavan , Nielsen Bent , Du Xu
Published: April 2012

We fabricate graphene-TiOx-aluminum tunnel junctions and characterize their radio frequency response. Below the superconducting critical temperature of aluminum and when biased within the superconducting gap, the devices show enhanced dynamic resistance which increases with decreasing temperature. Application of radio frequency radiation affects the dynamic resistance through electronic heating. The relation between the electron temperature rise and the absorbed radiation power is measured, from which the bolometric parameters, including heat conductance, noise equivalent power, and responsivity, are characterized.
Coupling distance between Eu3+ emitters and Ag nanoparticles
Authors: Pillonnet A. , Berthelot A. , Pereira A. , Benamara O. , Derom S. , Colas des Francs G. , Jurdyc A.-M.
Published: April 2012

Emission by rare earth emitters has been experimentally investigated based on their position relative to metallic nanoparticles by using Ag/Y2O3/Eu:Y2O3/Y2O3/Ag multilayer samples on- or off-plasmon resonance. Comparison with simple models revealed two different coupling regimes at short and long distances. The optimal coupling distance was determined.
Core/shell structural transformation and brittle-to-ductile transition in nanowires
Authors: Yuan Zaoshi , Nomura Ken-ichi , Nakano Aiichiro
Published: April 2012

Nanowires (NWs) exhibit thermo-mechanical properties that are distinct from their bulk properties, and their understanding is critical for the reliability, manufacturability, and optimization of a wide range of devices consisting of NWs. Here, molecular-dynamics simulation reveals a rich size-temperature “phase diagram” for the mechanical response of a zinc-oxide NW under tension. For smaller diameters and higher temperatures, transitions are found from brittle cleavage to structural transformation-mediated brittle cleavage to ductile failure. Atomistic mechanisms of the unique nano-thermo-mechanical behavior are elucidated as a consequence of surface-structural relaxation, which in particular predicts spontaneous formation of a core/shell structure under tension. The nano-thermo-mechanical phase diagram resolves controversies between previous experiments and theory, and the predicted “intrinsic” core/shell structure may find device applications.
Thermal emission in type-II GaSb/GaAs quantum dots and prospects for intermediate band solar energy conversion
Authors: Hwang Jinyoung , Martin Andrew J. , Millunchick Joanna M. , Phillips Jamie D.
Published: April 2012

The electronic structure and thermal carrier capture and escape mechanisms are studied for GaSb/GaAs quantum dots with a type-II band alignment using admittance spectroscopy. Clear signatures are observed corresponding to confined quantum dot states with extracted activation energy of 0.337 eV and the thermal capture cross section in the range from 2.10 × 10−16 to 1.19 × 10−13 cm2. The thermal emission rates in the GaSb/GaAs quantum dots are significantly lower than prior reports for type-I systems, where optical emission is predicted to be the dominant process in an intermediate band solar cells under solar concentration.
Effects of DNA nucleotide adsorption on the conductance of graphene nanoribbons from first principles
Authors: Lee Eun-Cheol
Published: April 2012

The effects of DNA nucleotide adsorption on the conductance of graphene nanoribbons are investigated through first-principles calculations. We find that, for the adsorption of a single nucleotide, the negatively charged phosphate produces conductance dips associated with quasibound states, reducing the hole conductance. The conductance of conduction electrons is also reduced by electron scattering at the Coulomb potential barriers produced by the phosphate, with no noticeable conductance dips near the Fermi level. Our results indicate that graphene nanoribbon is promising for the application to DNA sensor utilizing quantum carrier conductance.
Note: Reliable and reusable ultrahigh vacuum optical viewports
Authors: Arora P. , Gupta A. Sen
Published: April 2012

We report a simple technique for the realization of ultrahigh vacuum optical viewports. The technique relies on using specially designed thin copper knife-edges and using a thin layer of Vacseal® on tip of the knife-edges between the optical flat and the ConFlat® (CF) flange. The design of the windows is such that it gives uniform pressure on the flat without breaking it. The assembled window is a complete unit, which can be mounted directly onto a CF flange of the vacuum chamber. It can be removed and reused without breaking the window seal. The design is reliable as more than a dozen such windows have survived several bake out and cooling cycles and have been leak tested up to 10−11 Torr l/s level with a commercial Helium leak detector. The advantages of this technique are ease of assembly and leak proof sealing that survives multiple temperature cycling making the windows reliable and reusable.
Note: Improved sensitivity of photoreflectance measurements with a combination of dual detection and electronic compensation
Authors: Mukherjee Amlan , Ghosh Sandip , Sugunakar Vasam
Published: April 2012

A setup is described for performing photoreflectance (PR) measurements using two photodetectors, wherein the photodetectors need not be identical. The second detector monitors the photoluminescence and scattered pump laser background signal in real time. It is then eliminated from the measured PR signal using electronic circuits that compensate for amplitude and phase differences between the background signals from the two detectors. The technique overcomes the adverse effect of short-term fluctuations in the pump laser intensity. The signal-to-noise ratio is shown to improve significantly, enabling measurement of weak PR signals.
Selection for yearling fleece weight and its effect on fleece shedding in New Zealand Wiltshire sheep
Authors: O'Connell D. , Scobie D. R. , Hickey S. M. , Sumner R. M. W. , Pearson A. J.
Published: April 2012

A flock of New Zealand Wiltshire sheep was divided into two lines and selected for increased greasy fleece weight or decreased greasy fleece weight as yearlings. Wiltshires shed their fleece annually, and although these yearlings may have expressed shedding as lambs in the preceding summer, they were shorn in autumn at 5 months and again in spring at 12 months of age to determine fleece weight before the subsequent shedding. A rapid separation in fleece weight was observed within 8 years, with ewe (0.89 kg) and ram yearlings (0.92 kg) selected for increased fleece weight producing significantly more wool (P < 0.001) than ewe (0.43 kg) or ram yearlings (0.39 kg) from the line selected for decreased fleece weight. There was no significant difference between sexes, and the sex × line interaction was not significant. Clearly this was very low wool production, but fleece weight was heritable (h2 = 0.57 ± 0.04).
Shedding was scored from 0 (not shed) to 5 (completely shed) for all animals (n = 2505 records) and was found to be heritable in December (h2 = 0.39 ± 0.04) and again in January (h2 = 0.52 ± 0.05), but less so in September at shearing (h2 = 0.24 ± 0.03). Fleece weight in spring was negatively correlated with shedding score in January, both phenotypically (–0.52 ± 0.02) and genetically (–0.81 ± 0.04). Selecting yearlings for low fleece weight developed a shedding sheep with negligible fleece, which may not require shearing. Selecting for shedding of lambs in January would likely achieve a similar outcome.
Power-law decay of the spatial correlation function in exciton-polariton condensates
Authors: Roumpos Georgios , Lohse Michael , Nitsche Wolfgang H. , Keeling Jonathan , Szymańska Marzena Hanna , Littlewood Peter B. , Löffler Andreas , Höfling Sven , Worschech Lukas , Forchel Alfred , Yamamoto Yoshihisa
Published: April 2012

We create a large exciton-polariton condensate and employ a Michelson interferometer setup to characterize the short- and long-distance behavior of the first order spatial correlation function. Our experimental results show distinct features of both the two-dimensional and nonequilibrium characters of the condensate. We find that the gaussian short-distance decay is followed by a power-law decay at longer distances, as expected for a two-dimensional condensate. The exponent of the power law is measured in the range 0.9–1.2, larger than is possible in equilibrium. We compare the experimental results to a theoretical model to understand the features required to observe a power law and to clarify the influence of external noise on spatial coherence in nonequilibrium phase transitions. Our results indicate that Berezinskii–Kosterlitz–Thouless-like phase order survives in open-dissipative systems.
Colour and spatial cueing in low-prevalence visual search
Authors: Russell Nicholas C. C. , Kunar Melina A.
Published: April 2012

In visual search, 30–40% of targets with a prevalence rate of 2% are missed, compared to 7% of targets with a prevalence rate of 50% (Wolfe, Horowitz, & Kenner, 2005). This “low-prevalence” (LP) effect is thought to occur as participants are making motor errors, changing their response criteria, and/or quitting their search too soon. We investigate whether colour and spatial cues, known to improve visual search when the target has a high prevalence (HP), benefit search when the target is rare. Experiments 1 and 2 showed that although knowledge of the target's colour reduces miss errors overall, it does not eliminate the LP effect as more targets were missed at LP than at HP. Furthermore, detection of a rare target is significantly impaired if it appears in an unexpected colour—more so than if the prevalence of the target is high (Experiment 2). Experiment 3 showed that, if a rare target is exogenously cued, target detection is improved but still impaired relative to high-prevalence conditions. Furthermore, if the cue is absent or invalid, the percentage of missed targets increases. Participants were given the option to correct motor errors in all three experiments, which reduced but did not eliminate the LP effect. The results suggest that although valid colour and spatial cues improve target detection, participants still miss more targets at LP than at HP. Furthermore, invalid cues at LP are very costly in terms of miss errors. We discuss our findings in relation to current theories and applications of LP search.
Applications of depth-resolved cathodoluminescence spectroscopy
Authors: Brillson L J
Published: April 2012

Depth-resolved cathodoluminescence spectroscopy (DRCLS) has developed over the past few decades into a powerful technique for characterizing electronic properties of advanced materials structures and devices on a nanoscale. The lateral and depth-resolved capabilities of DRCLS enable researchers to probe native defects, impurities, chemical changes and local band structure inside state-of-the-art device structures on an unprecedented scale. A key strength of DRCLS is its ability to distinguish electronic features at buried interfaces within multilayer device structures, interfaces whose microscopic physical features can determine macroscopic electronic properties. This review provides a general overview of DRCLS and illustrates the wide array of applications now available using this technique.
Simulation studies of RF excited micro-cavity discharges for micro-propulsion applications
Authors: Sitaraman H , Raja L L
Published: April 2012

A detailed computational modelling study of the micro-cavity discharge (MCD) thruster is presented. The MCD thruster concept incorporates a microdischarge with dielectric covered electrodes operated using alternating current (ac) excitation. The thruster geometry comprises a constant area pipe section followed by a divergent micro-nozzle. Two ring electrodes are embedded in the wall of the pipe section with the downstream electrode close to the pipe-micronozzle intersection. A microdischarge plasma is generated in argon propellant gas flowing through the thruster. A detailed plasma dynamics model coupled with the compressible Navier–Stokes equations is used to study the flow and plasma phenomenon in the thruster. Results show a highly pulsed microdischarge with plasma densities of ∼1019 m−3 and current densities ∼700 mA cm−2 for an ac excitation in the radio frequency (RF) regime of 10 and 20 MHz. The dominant gas heating mechanism in these discharges is through ion Joule heating. Higher electron densities and spatially dominant thermal source terms are observed for the 20 MHz excitation compared with 10 MHz excitation. The addition of 20% nitrogen to the flow resulted in much better performance compared with the pure argon cases. A peak gas temperature rise ∼200 K is seen for a cycle-averaged power deposition of 76 mW. For the conditions explored in this study, the overall specific impulse of the thruster operating with the microdischarge plasma is found to be about 25% higher than a corresponding cold gas case.
NHERF1 acts as a molecular switch to program metastatic behavior and organotropism via its PDZ domains
Authors: Cardone Rosa Angela , Greco Maria Raffaella , Capulli Mattia , Weinman Edward J. , Busco Giovanni , Bellizzi Antonia , Casavola Valeria , Antelmi Ester , Ambruosi Barbara , Dell'Aquila Maria Elena , Paradiso Angelo , Teti Anna , Rucci Nadia , Reshkin Stephan Joel
Published: April 2012

Metastatic cells are highly plastic for differential expression of tumor phenotype hallmarks and metastatic organotropism. The signaling proteins orchestrating the shift of one cell phenotype and organ pattern to another are little known. Na+/H+ exchanger regulatory factor (NHERF1) is a molecular pathway organizer, PDZ-domain protein that recruits membrane, cytoplasmic, and cytoskeletal signaling proteins into functional complexes. To gain insight into the role of NHERF1 in metastatic progression, we stably transfected a metastatic breast cell line, MDA-MB-231, with an empty vector, with wild-type NHERF1, or with NHERF1 mutated in either the PDZ1- or PDZ2-binding domains to block their binding activities. We observed that NHERF1 differentially regulates the expression of two phenotypic programs through its PDZ domains, and these programs form the mechanistic basis for metastatic organotropism. The PDZ2 domain promotes visceral metastases via increased invadopodia-dependent invasion and anchorage-independent growth, as well as by inhibition of apoptosis, whereas the PDZ1 domain promotes bone metastases by stimulating podosome nucleation, motility, neoangiogenesis, vasculogenic mimicry, and osteoclastogenesis in the absence of increased growth or invasion. Collectively, these findings identify NHERF1 as an important signaling nexus for coordinating cell structure with metastatic behavior and identifies the “mesenchymal-to-vasculogenic” phenotypic transition as an essential step in metastatic progression.
A de novo metagenomic assembly program for shotgun DNA reads
Authors: Lai Binbin , Ding Ruogu , Li Yang , Duan Liping , Zhu Huaiqiu
Published: April 2012

Motivation: A high-quality assembly of reads generated from shotgun sequencing is a substantial step in metagenome projects. Although traditional assemblers have been employed in initial analysis of metagenomes, they cannot surmount the challenges created by the features of metagenomic data.

Result: We present a de novo assembly approach and its implementation named MAP (metagenomic assembly program). Based on an improved overlap/layout/consensus (OLC) strategy incorporated with several special algorithms, MAP uses the mate pair information, resulting in being more applicable to shotgun DNA reads (recommended as >200 bp) currently widely used in metagenome projects. Results of extensive tests on simulated data show that MAP can be superior to both Celera and Phrap for typical longer reads by Sanger sequencing, as well as has an evident advantage over Celera, Newbler and the newest Genovo, for typical shorter reads by 454 sequencing.

Availability and implementation: The source code of MAP is distributed as open source under the GNU GPL license, the MAP program and all simulated datasets can be freely available at http://bioinfo.ctb.pku.edu.cn/MAP/

Contact:  hqzhu@pku.edu.cn

Supplementary information:  Supplementary data are available at Bioinformatics online.