bluuebunny/crossref_metadata_2025 huggingface dataset:
IBSIMU: A three-dimensional simulation software for charged particle optics
Authors: Kalvas T. , Tarvainen O. , Ropponen T. , Steczkiewicz O. , Ärje J. , Clark H.
Published: February 2010

A general-purpose three-dimensional (3D) simulation code IBSIMU for charged particle optics with space charge is under development at JYFL. The code was originally developed for designing a slit-beam plasma extraction and nanosecond scale chopping for pulsed neutron generator, but has been developed further and has been used for many applications. The code features a nonlinear FDM Poisson’s equation solver based on fast stabilized biconjugate gradient method with ILU0 preconditioner for solving electrostatic fields. A generally accepted nonlinear plasma model is used for plasma extraction. Magnetic fields can be imported to the simulations from other programs. The particle trajectories are solved using adaptive Runge–Kutta method. Steady-state and time-dependent problems can be modeled in cylindrical coordinates, two-dimensional (slit) geometry, or full 3D. The code is used via C++ programming language for versatility but it features an interactive easy-to-use postprocessing tool for diagnosing fields and particle trajectories. The open source distribution and public documentation make the code well suited for scientific use. IBSIMU has been used for modeling the 14 GHz ECR ion source extraction and for designing a four-electrode extraction for a 2.45 GHz microwave ion source at Jyväskylä. A grid extraction has also been designed for producing large uniform beam for creating conditions similar to solar wind. The code has also been used to design a H− extraction with electron dumping for the Cyclotron Institute of Texas A&M University.
Three-dimensional simulations of ion dynamics in an Electron Cyclotron Resonance Ion Source
Authors: Beijers J. P. M. , Mironov V.
Published: February 2010

We present a three-dimensional simulation of the ion dynamics in an electron cyclotron resonance ion source. Ion trajectories in the min-B field of the source are calculated taking ion-ion and electron-ion collisions into account. The electrons are not tracked but considered as a neutralizing background with a Maxwell–Boltzmann velocity distribution. Some applications of the code are discussed, e.g., the calculated charge-state and phase-space distributions of extracted ion beams and the ionization dynamics in the plasma.
The effect of rf pulse pattern on bremsstrahlung and ion current time evolution of an ECRIS
Authors: Ropponen T. , Tarvainen O. , Toivanen V. , Peura P. , Jones P. , Kalvas T. , Koivisto H. , Noland J. , Leitner D.
Published: February 2010

Time-resolved helium ion production and bremsstrahlung emission from JYFL 14 GHz ECRIS is presented with different radio frequency pulse lengths. rf on times are varied from 5 to 50 ms and rf off times from 10 to 1000 ms between different measurement sets. It is observed that the plasma breakdown occurs a few milliseconds after launching the rf power into the plasma chamber, and in the beginning of the rf pulses a preglow transient is seen. During this transient the ion beam currents are increased by several factors compared to a steady state situation. By adjusting the rf pulse separation the maximum ion beam currents can be maintained during the so-called preglow regime while the amount of bremsstrahlung radiation is significantly decreased.
Gridless, very low energy, high-current, gaseous ion source
Authors: Vizir A. V. , Shandrikov M. V. , Yushkov G. Yu. , Oks E. M.
Published: February 2010

We have made and tested a very low energy gaseous ion source in which the plasma is established by a gaseous discharge with electron injection in an axially diverging magnetic field. A constricted arc with hidden cathode spot is used as the electron emitter (first stage of the discharge). The electron flux so formed is filtered by a judiciously shaped electrode to remove macroparticles (cathode debris from the cathode spot) from the cathode material as well as atoms and ions. The anode of the emitter discharge is a mesh, which also serves as cathode of the second stage of the discharge, providing a high electron current that is injected into the magnetic field region where the operating gas is efficiently ionized. In this discharge configuration, an electric field is formed in the ion generation region, accelerating gas ions to energy of several eV in a direction away from the source, without the use of a gridded acceleration system. Our measurements indicate that an argon ion beam is formed with an energy of several eV and current up to 2.5 A. The discharge voltage is kept at less than 20 V, to keep below ion sputtering threshold for cathode material, a feature which along with filtering of the injected electron flow, results in extremely low contamination of the generated ion flow.
A high-current light-ion injector for tandem accelerators
Authors: Quax G. W. W. , Gottdang A. , Mous D. J. W.
Published: February 2010

A dual-source injector for tandem accelerators to produce negative ion currents of H, D, and He has been developed and built. The system consists of a central vacuum enclosure that accommodates two multicusp ion sources. Beam currents of several mA of H− and D− have been obtained by direct negative extraction of one of the multicusp ion sources. The yield for He− was optimized applying differentially pumped vacuum sections that support space compensation in the He+ transport section a well as low neutralization loss of He− after charge exchange. In addition, an optimized extraction geometry and beam transport system enabled in excess of 10 mA He+ within the low acceptance of the charge exchange canal. Early measurements yielded ∼50 μA for He− using Li as a charge exchange medium, but currents over 100 μA are anticipated if Na would be used.
ITEP MEVVA ion beam for rhenium silicide production
Authors: Kulevoy T. , Gerasimenko N. , Seleznev D. , Kropachev G. , Kozlov A. , Kuibeda R. , Yakushin P. , Petrenko S. , Medetov N. , Zaporozhan O.
Published: February 2010

The rhenium silicides are very attractive materials for semiconductor industry. In the Institute for Theoretical and Experimental Physics (ITEP) at the ion source test bench the research program of rhenium silicide production by ion beam implantation are going on. The investigation of silicon wafer after implantation of rhenium ion beam with different energy and with different total dose were carried out by secondary ions mass spectrometry, energy-dispersive x-ray microanalysis, and x-ray diffraction analysis. The first promising results of rhenium silicide film production by high intensity ion beam implantation are presented.
Two-stage plasma gun based on a gas discharge with a self-heating hollow emitter
Authors: Vizir A. V. , Tyunkov A. V. , Shandrikov M. V. , Oks E. M.
Published: February 2010

The paper presents the results of tests of a new compact two-stage bulk gas plasma gun. The plasma gun is based on a nonself-sustained gas discharge with an electron emitter based on a discharge with a self-heating hollow cathode. The operating characteristics of the plasma gun are investigated. The discharge system makes it possible to produce uniform and stable gas plasma in the dc mode with a plasma density up to 3×109 cm−3 at an operating gas pressure in the vacuum chamber of less than 2×10−2 Pa. The device features high power efficiency, design simplicity, and compactness.
Laser ion source: A direct plasma injection scheme for two-beam type interdigital-H radio frequency quadrupole linac
Authors: Ishibashi T. , Hayashizaki N. , Tamura J. , Oka K. , Shimaya Y. , Hattori T. , Kashiwagi H.
Published: February 2010

We developed a laser ion source using a direct plasma injection scheme (DPIS) as an injection system for a two-beam type radio frequency quadrupole (RFQ) linac with an interdigital-H (IH) type cavity. The laser ion source in the DPIS is directly connected to the RFQ cavity without the low energy beam transport system. We achieved a high current C2+ beam above 60 mA per beam channel from the ion source. The beam will be injected to the two-beam type IH-RFQ linac, and the linac will generate a beam current of approximately 44 mA per beam channel.
Precessional dynamics of Ni45Fe55 thin films for ultrahigh frequency integrated magnetics
Authors: Godsell Jeffrey F. , Kulkarni Santosh , O’Donnell Terence , Roy Saibal
Published: February 2010

Future monolithic point of load switched mode power supplies will be expected to meet the energy requirements of miniaturized, high functionality electronic devices. Recently, Ni45Fe55 has emerged as a potentially important material choice for use as a soft magnetic core material within high frequency integrated passive magnetic components. The operating frequency range of the integrated passives which form a key part of the point of load power supply must increase to allow for inductor/transformer miniaturization to become monolithic with power integrated circuits. In this work, an analysis of the high frequency permeability spectra of an electroplated Ni45Fe55 thin film has been carried out to quantitatively analyze the material’s high frequency performance. Complex permeability spectra of the film have been investigated at frequencies up to 9 GHz to identify both the film’s spectroscopic splitting factor (g) and its effective dimensionless damping parameter (α). The Kittel equation is utilized to identify g as 2.128, while α is determined to be approximately 0.045. The critically damped condition for the film is also examined to extract α in the critically damped case under a range of externally applied bias fields. It is concluded that for monolithic power inductors, improved device performance can be achieved when the ferromagnetic core is in an underdamped state up to a critical frequency.
The jump phenomenon in the angular dependence of the off-aligned exchange bias
Authors: Bai Yuhao , Yun Guohong , Bai Narsu
Published: February 2010

Based on the principle of minimal energy, the angular dependence of exchange bias has been investigated in detail with noncollinear easy axes of unidirectional and uniaxial anisotropies in the ferromagnetic/antiferromagnetic bilayers. The competition between unidirectional and uniaxial anisotropies divides the initial magnetization state of the bilayers into monostable state and bistable state, which determine the angular dependence of exchange bias directly. When the external field is applied along the intrinsic easy axes and intrinsic hard axes, it is found that one of the coercive fields at the descending or ascending branch of the hysteresis loop makes an abrupt change, whereas the other coercive field keeps continuity by analyzing the magnetization reversal processes. Consequently, the exchange bias field and the coercivity will show the jump phenomenon in the angular dependence of exchange bias. This jump phenomenon of the exchange bias is found to be an intrinsic property of the bilayers which is dependent on the relative magnitudes and orientations between unidirectional and uniaxial anisotropies. The numerical calculations indicate that both the exchange bias field and the coercivity are larger in the magnitude at the points of the jumps. At the jumping points of the intrinsic easy axes, the coercivity reaches the maximum; at the jumping points of the intrinsic hard axes, the exchange bias field reaches the maximum, at the meantime the coercivity can vanish itself suddenly. These features of the jump phenomenon are useful in the technological applications to achieve the largest exchange bias field.
Instability of a moving liquid sheet in the presence of acoustic forcing
Authors: Mulmule Aditya S. , Tirumkudulu Mahesh S. , Ramamurthi K.
Published: February 2010

The excitation of thin planar liquid sheets formed by impinging two collinear water jets to acoustic waves was studied at varying frequencies and sound pressure levels (SPLs). Experiments were conducted over a range of liquid velocities that encompassed the stable and flapping regimes of the sheet. For a given frequency, there was a threshold value of SPL below which the sheet was unaffected. The threshold SPL increased with frequency. Further, the sheet was observed to respond to a set of specific frequencies lying in the range of 100–300 Hz, the frequency set varying with the Weber number of the liquid sheet. The magnitude of the response for a fixed pressure level, characterized by the reduction in the extent of the sheet, was larger at lower frequencies. The droplet sizes formed by the disintegration of the sheet reduced with an increase in the measured response and the drop-shedding frequency was near the imposed frequency. Model equations for inviscid flow and accounting for the varying pressure field across the moving liquid sheet of constant thickness was solved to determine the linear stability of the system. Numerical solution shows that the most unstable wavelengths in the presence of the forcing to be smaller than in the absence, which is in line with observations. Both the dilatational and sinuous modes are coupled at the lowest order and become significant for the range of acoustic forcing studied. The model calculation suggests that the parametric resonance involving the dilatational mode may be responsible for the observed instability although the model was unable to predict the observed variation of threshold SPL with frequency.
Positron annihilation study in SmFeAsO and SmFeAsO0.82F0.18
Authors: Hao Y. P. , Chen X. L. , Liu R. H. , Kong W. , Cheng B. , Xu H. X. , Chen X. H. , Han R. D. , Weng H. M. , Du H. J. , Ye B. J.
Published: February 2010

SmFeAsO 1 − x F x polycrystalline samples were first studied by positron annihilation lifetime spectroscopy and Doppler-broadening spectroscopy, combined with the calculated results of positron lifetime. The experimental results agree well with the calculated positron bulk lifetime in SmFeAsO and SmFeAsF crystals. The temperature dependence of S-parameter shows a remarkable difference between the parent and superconductor. An abrupt jump of S-parameter is detected around 150 K in parent sample, however, two different slopes were shown below and above superconducting transition. The linearity S-T plot determines one-type of defects through the superconducting transition which must play an important role in superconductivity.
Laser-plasma debris from a rotating cryogenic–solid-Xe target
Authors: Amano Sho , Inaoka Yutaka , Hiraishi Hiroki , Miyamoto Shuji , Mochizuki Takayasu
Published: February 2010

We investigate the characteristics of laser plasma debris that is responsible for damaging optics. The debris is composed of fast ions, neutral particles, and fragments, and originates from a solid Xe target on a rotating drum that we developed as an extreme ultraviolet (EUV) source. The ice fragments appear to be a problem most notably with solid Xe targets; however, we find that the damage induced by Xe ice fragments can be avoided by simply reducing the laser pulse energy. We find the number of fast neutral particles to be an order of magnitude less than the number of ions, and we clarify that the plasma debris is primarily composed of fast ions. In addition, we find that the number of fast ions having a few dozen keV of energy decreases when using the rotating target compared with the rest target. We attribute this to a gas curtain effect from the Xe gas localized at the rotating target surface. We estimate the sputtering rate of the Mo/Si mirror, which is caused primarily by the fast ions, to be 104 nm/1×106 shots at 190 mm from the source plasma and at an 11.25° angle from the incident laser beam. Up to the 1×106 shots exposure, remarkable degradation of the mirror reflectivity is not observed though the sputtering damages the mirror. Mitigation of the ions by using gas and/or magnetic fields will further improve the mirror lifetime. By comparing with a liquid jet Xe target, we conclude that the sputtering rate per conversion efficiency when using the solid Xe targets on the rotating drum is the same as that when using the liquid Xe targets. The high conversion efficiency of 0.9% in the rotating drum solid Xe target makes this technique useful for developing laser plasma EUV sources.
Surface plasmon excitation in silver nanowires directly deposited on a laser diode chip
Authors: Ma Zhe , Zhang Xining , Guo Xin , Yang Qing , Ma Yaoguang , Tong Limin
Published: February 2010

We demonstrate surface plasmon (SP) excitation in silver nanowires directly deposited on the emission facet of a laser diode (LD) chip. Evident light output from the silver nanowires is observed. The output is linear-polarized and is strongly dependent on the nanowire orientation. SP excitation at the central part of a silver nanowire is also observed. The possibility of direct SP excitation on an LD chip may open opportunities for realizing plasmonic and photonic circuits or components with high compactness.
Methane dissociation and adsorption on Ni(111), Pt(111), Ni(100), Pt(100), and Pt(110)-(1×2): Energetic study
Authors: Nave Sven , Tiwari Ashwani Kumar , Jackson Bret
Published: February 2010

We use density functional theory to examine 24 transition states for methane dissociation on five different metal surfaces. In our calculations, the nonlocal exchange-correlation effects are treated within the generalized gradient approximation using the Perdew–Burke–Ernzerhof functional. In all cases, the minimum energy path for dissociation is over a top site. The barriers are large, 0.66–1.12 eV, and relatively insensitive to the rotational orientation of the (nonreacting) methyl group and the azimuthal orientation of the reactive C–H bond. There is a strong preference on the Pt surfaces for the methyl fragment to bond on the top site, while on the Ni surfaces there is a preference for the hollow or bridge sites. Thus, during the dissociation on Pt, only the low mass H atom needs to significantly move or tunnel, while on Ni, both the dissociating H and the methyl fragment move away from the top site. For all 24 configurations there is a strong force at the transition state to pucker the metal atom over which the reaction occurs. The resulting magnitude of the variation in the barrier height with the motion of this atom varies a bit from surface-to-surface, but is of the order of 1 eV/Å. We derive a model for the effective reaction barrier height that includes the effects of lattice motion and substrate temperature and compare with recent experiments and other theoretical studies.
A dual-beam photothermal reflection based system for thermal diffusivity measurement of optically dense liquids
Authors: Jaimes Blanca , Pulgar Dervin , Ranaudo María Antonieta , Chirinos José , Caetano Manuel
Published: February 2010

A dual-beam photothermal reflection based system capable to measure thermal diffusivities of optically dense liquids has been designed and implemented. The large optical absorption coefficient of these liquids inhibits the possibility to use conventional transmission instruments for direct thermal diffusivity measurements. To overcome this problem, a front heating front detection photothermal reflection system has been proposed. This method expands the range of application and simplifies the experimental procedure of traditional photothermal methods, allowing precise measurement of thermal diffusivity of a variety of liquids. Measurements of the change in thermal diffusivity with the concentration of asphaltene in toluene solutions are described to test the applicability of this technique for reliable measurements of thermal diffusivities of optically dense liquids.
Emission zone control in blue organic electrophosphorescent devices through chemical modification of host materials
Authors: Polikarpov Evgueni , Swensen James S. , Cosimbescu Lelia , Koech Phillip K. , Rainbolt James E. , Padmaperuma Asanga B.
Published: February 2010

We report blue organic light-emitting devices with iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2′] picolinate as an emitter doped into a series of phosphine oxide-based host materials that have significantly different charge transport properties: 4-(diphenylphosphoryl)-N,N-diphenylaniline (HM-A1), N-(4-diphenylphosphoryl phenyl) carbazole (PO12), 9-[6-(diphenylphosphoryl)pyridin-3-yl]-9H-carbazole (HM-A5), and 6-(diphenylphosphoryl)-N,N-diphenylpyridin-3-amine (HM-A6). Depending on the nature of the host material, the location of the emission zone can be moved within the emissive layer from the hole transport layer interface to the electron-transport layer interface. The charge transport properties of the materials were evaluated using single carrier devices.
Note: Construction of x-ray scattering and x-ray absorption fine structure beamline at the Pohang Light Source
Authors: Lee Ik-Jae , Yu Chung-Jong , Yun Young-Duck , Lee Chae-Soon , Seo In Deuk , Kim Hyo-Yun , Lee Woul-Woo , Chae Keun Hwa
Published: February 2010

A new hard x-ray beamline, 10B KIST-PAL beamline (BL10B), has been designed and constructed at the Pohang Light Source (PLS) in Korea. The beamline, operated by Pohang Accelerator Laboratory-Korean Institute of Science and Technology consortium, is dedicated to x-ray scattering (XRS) and x-ray absorption fine structure (XAFS) experiments. X rays with photon energies from 4.0 to 16.0 keV are delivered to the experimental station passing a collimating mirror, a fixed-exit double-crystal Si(111) monochromator, and a toroidal mirror. Basic experimental equipments for XAFS measurement, a high resolution diffractometry, an image plate detector system, and a hot stage have been prepared for the station. From our initial commissioning and performance testing of the beamline, it is observed that BL10B beamline can perform XRS and XAFS measurements successfully.
Electrical properties of ZnO nanowire field effect transistors with varying high-k Al2O3 dielectric thickness
Authors: Choe Minhyeok , Jo Gunho , Maeng Jongsun , Hong Woong-Ki , Jo Minseok , Wang Gunuk , Park Woojin , Lee Byoung Hun , Hwang Hyunsang , Lee Takhee
Published: February 2010

We investigated the electronic properties of ZnO nanowire combined with the scaled high-k Al2O3 dielectrics using metal-oxide-semiconductor and field effect transistor (FET) device structures. We found that Al2O3 dielectric material can significantly reduce leakage currents when the applied voltage was restricted less than the transition voltage of direct tunneling to Fowler–Nordheim tunneling. The ZnO nanowire FETs with Al2O3 dielectrics exhibited the increase in electrical conductance, transconductance, and mobility and the threshold voltage shifted to the negative gate bias direction with decreasing Al2O3 dielectric layer thickness.
Mayer problem for quantum stochastic control
Authors: Ogundiran M. O. , Ayoola E. O.
Published: February 2010

This paper is concerned with the value function for optimal quantum stochastic control. We established the Lipschitz continuity of the value function, which is inherent from the Lipschitz property of the set-valued map describing the quantum stochastic control. By using a feedback multivalued map, we also prove a characterization of optimal solutions relating to a noncommutative generalization of Mayer problem.
Surface-induced magnetism in C-doped SnO2
Authors: Rahman Gul , García-Suárez Víctor M.
Published: February 2010

The magnetism of C-doped SnO2 (001) surfaces is studied using first-principles calculations. It is found that carbon does not induce magnetism in bulk SnO2 when located at the oxygen site but shows a large magnetic moment at the SnO2 (001) surface. The magnetic moment is mainly contributed by the carbon atoms due to empty minority spins of p orbitals and is localized at the surface and subsurface atoms. No magnetism is observed when the carbon atom is located at the subsurface oxygen sites. The origin of magnetism is discussed in the context of surface bonding.
Effective work function tuning in high-κ dielectric metal-oxide-semiconductor stacks by fluorine and lanthanide doping
Authors: Fet A. , Häublein V. , Bauer A. J. , Ryssel H. , Frey L.
Published: February 2010

In this letter, an ion implantation approach to engineer the effective work function is discussed and an empirical model to explain the mechanisms of work function change is proposed. It is shown that by doping a TiN/HfSiOx stack with La and F, a silicon conduction band edge and valence band edge metal effective work function of 3.8 and 5.4 eV, respectively, can be achieved. The empirical correlation of the achieved effective work function to the electronegativity of the dopant element is explained.
Dual wavelength emission from a terahertz quantum cascade laser
Authors: Freeman Joshua R. , Madéo Julien , Brewer Anthony , Dhillon Sukhdeep , Marshall Owen P. , Jukam Nathan , Oustinov Dimitri , Tignon Jerome , Beere Harvey E. , Ritchie David A.
Published: February 2010

We describe a heterogeneous terahertz (THz) quantum cascade laser that is composed of two different active region designs. This device emits simultaneously at around 2.5 and 2.9 THz with certain frequency tunability by applied current. We also investigate the spectral gain in the structure by THz time-domain spectroscopy and correlate the gain spectral bandwidth with the alignment and wavelength emission behavior of the two stack device.
Cloaking a metal object from an electromagnetic pulse: A comparison between various cloaking techniques
Authors: Alitalo Pekka , Kettunen Henrik , Tretyakov Sergei
Published: February 2010

Electromagnetic cloaks are devices that can be used to reduce the total scattering cross section of various objects. An ideal cloak removes all scattering from an object and thus makes this object “invisible” to the electromagnetic fields that impinge on the object. However, ideal cloaking appears to be possible only at a single frequency. To study cloaking from an electromagnetic pulse, we consider propagation of a pulse inside a waveguide with a cloaked metal object inside. There are several ways to achieve cloaking, and in this paper, we study three such methods, namely, the coordinate-transformation cloak, the transmission-line cloak, and the metal-plate cloak. In the case of the two last cloaks, pulse propagation is studied using experimental data, whereas the coordinate-transformation cloak is studied with numerical simulations. The results show that, at least in the studied cases where the cloaked object’s diameter is smaller than the wavelength, the cloaks based on transmission-line meshes and metal plates have wider bandwidth than the coordinate-transformation cloak and are thus more efficient in hiding objects from electromagnetic pulses.
Effect of V/III flux ratio on luminescence properties and defect formation of Er-doped GaN
Authors: Chen Shaoqiang , Uedono Akira , Ishibashi Shoji , Tomita Shigeo , Kudo Hiroshi , Akimoto Katsuhiro
Published: February 2010

Erbium-doped GaN samples grown with different V/III ratios through gas source molecular beam epitaxy were prepared to investigate the influence of the V/III ratio on the defect formation and the optical activity of the Er-related luminescence center. Obvious V/III ratio dependence was observed in photoluminescence measurement. Positron annihilation spectroscopy measurements suggested that VGa-VN vacancy-complexes formed in these samples and that the VN/VGa ratio depended on the V/III ratio. The generation of Er-VN defect complexes, which act as high optical active luminescence centers, is suggested as the cause of improved optical properties of Er-doped GaN grown with a lower V/III ratio.
Correlation consistent basis sets for molecular core-valence effects with explicitly correlated wave functions: The atoms B–Ne and Al–Ar
Authors: Hill J. Grant , Mazumder Shivnath , Peterson Kirk A.
Published: February 2010

Correlation consistent basis sets have been optimized for accurately describing core-core and core-valence correlation effects with explicitly correlated F12 methods. The new sets, denoted cc-pCVnZ-F12 (n=D, T, Q) and aug-cc-pCF12VnZ (n=D, T, Q, 5), were developed by augmenting the cc-pVnZ-F12 and aug-cc-pVnZ families of basis sets with additional functions whose exponents were optimized based on the difference between all-electron and valence-electron correlation energies. The number of augmented functions added is fewer, in general, than in the standard cc-pCVnZ and cc-pwCVnZ families of basis sets. Optimal values of the geminal Slater exponent for use with these basis sets in MP2-F12 calculations are presented and are also recommended for CCSD-F12b calculations. Auxiliary basis sets for use in the resolution of the identity approximation in explicitly correlated calculations have also been optimized and matched to the new cc-pCVnZ-F12 series of orbital basis sets. The cc-pCVnZ-F12 basis sets, along with the new auxiliary sets, were benchmarked in CCSD(T)-F12b calculations of spectroscopic properties on a series of homo- and heteronuclear first and second row diatomic molecules. Comparing the effects of correlating the outer core electrons in these molecules with those from conventional CCSD(T) at the complete basis set limit, which involved calculations with new cc-pCV6Z basis sets for the second row elements that were also developed in the course of this work, it is observed that the F12 values are reasonably well converged already at just the triple-ζ level.
Reinvestigation of the Rb2 (2)Π3g−a Σ3u+ band on helium nanodroplets
Authors: Auböck G. , Aymar M. , Dulieu O. , Ernst W. E.
Published: February 2010

It is well known that alkali-metal molecules are preferentially observed in the weak van der Waals-bound high spin states by helium droplet isolation spectroscopy. In [F. R. Brühl et al., J. Chem. Phys. 115, 10275 (2001)] the Rb2 (2)Π3g−a Σ3u+ band on He droplets was investigated by laser-induced fluorescence and dispersed emission spectroscopy. At that time no information on the magnitude of spin-orbit coupling was available for the (2)Π3g state which connects to the atomic 5s+4d asymptote and it was neglected. In this work we reinvestigate the observed spectra. The dispersed emission spectra, which resulted from free molecules, are consistent with state-of-the-art nonrelativistic potential energy surfaces and effective spin-orbit coupling matrix elements obtained from resonance-enhanced multiphoton ionization spectroscopy of cold Rb dimers [J. Lozeille et al., Eur. Phys. J. D 39, 261 (2006)]. Having validated the theoretical description of the free molecule state, we use the laser-induced fluorescence spectrum to discuss the influence of the He droplet on the excitation band.
Electric field dependence of nonlinearity parameters and third order elastic constants of 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 single crystal
Authors: Liu Xiaozhou , Zhang Shujun , Luo Jun , Shrout Thomas R. , Cao Wenwu
Published: February 2010

Through second harmonic measurements, the ultrasonic nonlinearity parameters of [001]c and [111]c polarized 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3(PMN–0.3PT) single crystals have been measured as a function of bias electric field. It was found that the nonlinearity parameter increases almost linearly with field at low field but shows a drastic increase near the coercive field. The [111]c polarized single domain crystal has much smaller nonlinearity parameter than that of the [001]c polarized multidomain crystal. Based on effective symmetries of these crystals, we were able to derive the field dependence of several third order elastic constants, which are important parameters for high field applications.
Observation of an electrically tunable exciton g factor in InGaAs/GaAs quantum dots
Authors: Klotz F. , Jovanov V , Kierig J. , Clark E. C. , Rudolph D. , Heiss D. , Bichler M. , Abstreiter G. , Brandt M. S. , Finley J. J.
Published: February 2010

The electric field dependence of the exciton g factor and the fine structure splitting in self-assembled InGaAs/GaAs quantum dots grown via a flush-overgrowth technique is studied by photocurrent and photoluminescence experiments. Both the fine structure and the Zeeman splitting can be tuned over a wide range via electric fields applied in growth direction of the quantum dot. For the g factor, a tunability of 250% is demonstrated from g=0.12 to 0.42.
Delaying sheep grazing after wildfire in sagebrush steppe may not affect vegetation recovery
Authors: Roselle Lovina , Seefeldt Steven S. , Launchbaugh Karen
Published: February 2010

Although many land managers prohibit grazing for 2 years after a fire, little research has been conducted to determine the interaction of grazing with vegetation recovery after fire. In a study conducted in sagebrush steppe rangelands after a 2000 wildfire at the United States Sheep Experiment Station in Idaho, the influence of delay and season of sheep grazing on vegetation recovery was measured. A moderate level of sheep grazing was started 1, 2, or 3 years after fire in the autumn or 2 or 3 years after fire in the spring. Pseudoroegneria spicata, the dominant perennial grass, and Crepis acuminata increased in the autumn and non-grazed treatments, whereas perennial forb and Crepis acuminata cover declined in the spring grazing treatments beginning the second year after fire. There was no impact of sheep grazing on cover of Bromus tectorum, an important exotic winter annual grass, probably owing to the lack of autumn germination. In this study, moderate sheep grazing had subtle impacts on vegetation recovery after fire, with spring grazing having more negative consequences. Management decisions on when to start grazing livestock after fire should consider pre-fire ecological conditions, post-fire climatic conditions, and current knowledge of impacts of grazing on plant recovery.
Integrating values and risk perceptions into a decision support system
Authors: Morehouse Barbara J. , O'Brien Sara , Christopherson Gary , Johnson Peter
Published: February 2010

One of the thorniest challenges to effective wildland fire management is integration of public perceptions and values into science-based adaptive management. One promising alternative is incorporation of public values into place-based decision support technologies that are accessible to lay citizens as well as to fire-management experts. A survey of individuals, including residents, fire and fuels managers, volunteer firefighters, and others living in or near four mountain areas of the US Southwest, identified a set of personal values and perceptions about wildland fire risk that could be spatially represented in a geographic information science-based decision support system designed for wildland fire strategic planning efforts. We define values, in this context, as phenomena that are not necessarily quantifiable but that strongly attract and connect individuals for whatever reasons to particular areas. Inclusion of this type of information into interactive decision tools for fire management may contribute to improved understanding and finer-scale spatial visualisation of public perceptions of fire risk. The integration of such factors in decision support tools offers opportunities for improving interactions between managers and the public involved in strategic planning processes for fire management.
Repeated disturbance through chaining and burning differentially affects recruitment among plant functional types in fire-prone heathlands
Authors: Gosper Carl R. , Prober Suzanne M. , Yates Colin J.
Published: February 2010

Managing fire regimes is increasingly recognised as important for biodiversity conservation in fragmented agricultural landscapes in fire-prone regions. In the global biodiversity hotspot of south-west Western Australia, chaining and burning is a novel technique for facilitating fire management. Vegetation is first dislodged using a chain, then after a period of curing, burnt. The effects on plant communities are largely unstudied, despite the potential consequences of combining two disturbance events. We hypothesised that outcomes would vary depending on plant functional types defined by disturbance response. We compared plant community composition and recruitment and resprouting of plant functional types in mallee-heath subject to chaining and burning, burning only and neither of these. The effects of chaining and burning did not differ from only burning at the community level. Importantly, however, we recorded 90% fewer recruits of serotinous, obligate seeders in chained and burnt compared with only burnt plots, and a 44% decrease in their species richness. By contrast, recruits of obligate seeding shrubs and fire-ephemeral herbs with persistent soil-stored seed banks increased by 166% in chained and burnt plots. Sprouters showed little difference. We conclude that chaining and burning is likely to significantly alter vegetation composition, and potentially poses a significant threat to serotinous, obligate seeders. These impacts require consideration in fire management planning.
Mechanical amplification by hair cells in the semicircular canals
Authors: Rabbitt Richard D. , Boyle Richard , Highstein Stephen M.
Published: February 2010

Sensory hair cells are the essential mechanotransducers of the inner ear, responsible not only for the transduction of sound and motion stimuli but also, remarkably, for nanomechanical amplification of sensory stimuli. Here we show that semicircular canal hair cells generate a mechanical nonlinearity in vivo that increases sensitivity to angular motion by amplification at low stimulus strengths. Sensitivity at high stimulus strengths is linear and shows no evidence of amplification. Results suggest that the mechanical work done by hair cells contributes ∼
97
zJ/cell of amplification per stimulus cycle, improving sensitivity to angular velocity stimuli below ∼
5
°/s (0.3-Hz sinusoidal motion). We further show that mechanical amplification can be inhibited by the brain via activation of efferent synaptic contacts on hair cells. The experimental model was the oyster toadfish,
Opsanus tau
. Physiological manifestation of mechanical amplification and efferent control in a teleost vestibular organ suggests the active motor process in sensory hair cells is ancestral. The biophysical basis of the motor(s) remains hypothetical, but a key discriminating question may involve how changes in somatic electrical impedance evoked by efferent synaptic action alter function of the motor(s).
Autologous engineering of cartilage
Authors: Emans Pieter J. , van Rhijn Lodewijk W. , Welting Tim J. M. , Cremers Andy , Wijnands Nina , Spaapen Frank , Voncken J. Willem , Shastri V. Prasad
Published: February 2010

Treatment of full-thickness damage to hyaline cartilage is hampered by the limited availability of autologous healthy cartilage and the lengthy, cost-prohibitive cell isolation and expansion steps associated with autologous cartilage implantation (ACI). Here we report a strategy for de novo engineering of ectopic autologous cartilage (EAC) within the subperiosteal space (in vivo bioreactor), through the mere introduction of a biocompatible gel that might promote hypoxia-mediated chondrogenesis, thereby effectively overcoming the aforementioned limitations. The EAC is obtained within 3 wk post injection of the gel, and can be press-fit into an osteochondral defect where it undergoes remodeling with good lateral and subchondral integration. The implanted EAC showed no calcification even after 9 mo and attained an average O’Driscoll score of 11 (versus 4 for controls). An “on demand” autologous source of autologous cartilage with remodeling capacity is expected to significantly impact the clinical options in repair of trauma to articular cartilage.
Impaired geometric reorientation caused by genetic defect
Authors: Lakusta Laura , Dessalegn Banchiamlack , Landau Barbara
Published: February 2010

The capacity to reorient in one’s environment is a fundamental part of the spatial cognitive systems of both humans and nonhuman species. Abundant literature has shown that human adults and toddlers, rats, chicks, and fish accomplish reorientation through the construction and use of geometric representations of surrounding layouts, including the lengths of surfaces and their intersection. Does the development of this reorientation system rely on specific genes and their action in brain development? We tested reorientation in individuals who have Williams syndrome (WS), a genetic disorder that results in abnormalities of hippocampal and parietal areas of the brain known to be involved in reorientation. We found that in a rectangular chamber devoid of surface feature information, WS individuals do not use the geometry of the chamber to reorient, failing to find a hidden object. The failure among people with WS cannot be explained by more general deficits in visual-spatial working memory, as the same individuals performed at ceiling in a similar task in which they were not disoriented. We also found that performance among people with WS improves in a rectangular chamber with one blue wall, suggesting that some individuals with WS can use the blue wall feature to locate the hidden object. These results show that the geometric system used for reorientation in humans can be selectively damaged by specific genetic and neural abnormalities in humans.
Structural basis for inhibition of complement C5 by the SSL7 protein fromStaphylococcus aureus
Authors: Laursen Nick S. , Gordon Natasha , Hermans Stefan , Lorenz Natalie , Jackson Nicola , Wines Bruce , Spillner Edzard , Christensen Jesper B. , Jensen Morten , Fredslund Folmer , Bjerre Mette , Sottrup-Jensen Lars , Fraser John D. , Andersen Gregers R.
Published: February 2010

Staphylococcus aureussecretes the SSL7 protein as part of its immune evasion strategy. The protein binds both complement C5 and IgA, yet it is unclear whether SSL7 cross-links these two proteins and, if so, what purpose this serves the pathogen. We have isolated a stable IgA-SSL7-C5 complex, and our crystal structure of the C5-SSL7 complex confirms that binding to C5 occurs exclusively through the C-terminal β-grasp domain of SSL7 leaving the OB domain free to interact with IgA. SSL7 interacts with C5 >70 Å from the C5a cleavage site without inducing significant conformational changes in C5, and efficient inhibition of convertase cleavage of C5 is shown to be IgA dependent. Inhibition of C5a production and bacteriolysis are all shown to require C5 and IgA binding while inhibition of hemolysis is achieved by the C5 binding SSL7 β-grasp domain alone. These results provide a conceptual and structural basis for the development of a highly specific complement inhibitor preventing only the formation of the lytic membrane attack complex without affecting the important signaling functions of C5a.
Computation of symmetric, time-periodic solutions of the vortex sheet with surface tension
Authors: Ambrose David M. , Wilkening Jon
Published: February 2010

A numerical method is introduced for the computation of time-periodic vortex sheets with surface tension separating two immiscible, irrotational, two-dimensional ideal fluids of equal density. The approach is based on minimizing a nonlinear functional of the initial conditions and supposed period that is positive unless the solution is periodic, in which case it is zero. An adjoint-based optimal control technique is used to efficiently compute the gradient of this functional. Special care is required to handle singular integrals in the adjoint formulation. Starting with a solution of the linearized problem about the flat rest state, a family of smooth, symmetric breathers is found that, at quarter-period time intervals, alternately pass through a flat state of maximal kinetic energy, and a rest state in which all the energy is stored as potential energy in the interface. In some cases, the interface overturns before returning to the initial, flat configuration. It is found that the bifurcation diagram describing these solutions contains several disjoint curves separated by near-bifurcation events.
Reactive and nonreactive quenching of O(1D) by the potent greenhouse gases SO2F2, NF3, and SF5CF3
Authors: Zhao Zhijun , Laine Patrick L. , Nicovich J. Michael , Wine Paul H.
Published: February 2010

A laser flash photolysis–resonance fluorescence technique has been employed to measure rate coefficients and physical vs. reactive quenching branching ratios for O(1D) deactivation by three potent greenhouse gases, SO2F2(k1), NF3(k2), and SF5CF3(k3). In excellent agreement with one published study, we find thatk1(T) = 9.0 × 10-11 exp(+98/T) cm3 molecule-1 s-1and that the reactive quenching rate coefficient isk1b = (5.8 ± 2.3) × 10-11 cm3 molecule-1 s-1independent of temperature. We find thatk2(T) = 2.0 × 10-11 exp(+52/T) cm3 molecule-1 s-1with reaction proceeding almost entirely (∼99%) by reactive quenching. Reactive quenching of O(1D) by NF3is more than a factor of two faster than reported in one published study, a result that will significantly lower the model-derived atmospheric lifetime and global warming potential of NF3. Deactivation of O(1D) by SF5CF3is slow enough (k3 < 2.0 × 10-13 cm3 molecule-1 s-1at 298 K) that reaction with O(1D) is unimportant as an atmospheric removal mechanism for SF5CF3. The kinetics of O(1D) reactions with SO2(k4) and CS2(k5) have also been investigated at 298 K. We find thatk4 = (2.2 ± 0.3) × 10-10andk5 = (4.6 ± 0.6) × 10-10 cm3 molecule-1 s-1; branching ratios for reactive quenching are 0.76 ± 0.12 and 0.94 ± 0.06 for the SO2and CS2reactions, respectively. All uncertainties reported above are estimates of accuracy (2σ) and rate coefficientski(T) (i = 1,2) calculated from the above Arrhenius expressions have estimated accuracies of ± 15% (2σ).
Argonautes ALG-3 and ALG-4 are required for spermatogenesis-specific 26G-RNAs and thermotolerant sperm in
Caenorhabditis elegans
Authors: Conine Colin C. , Batista Pedro J. , Gu Weifeng , Claycomb Julie M. , Chaves Daniel A. , Shirayama Masaki , Mello Craig C.
Published: February 2010

Gametogenesis is a thermosensitive process in numerous metazoans, ranging from worms to man. In
Caenorhabditis elegans
, a variety of RNA-binding proteins that associate with germ-line nuage (P granules), including the Piwi-clade argonaute PRG-1, have been implicated in maintaining fertility at elevated temperature. Here we describe the role of two AGO-class paralogs,
alg-3
(T22B3.2) and
alg-4
(ZK757.3), in promoting thermotolerant male fertility. A rescuing GFP::
alg-3
transgene is localized to P granules beginning at the late pachytene stage of male gametogenesis.
alg-3
/
4
double mutants lack a subgroup of small RNAs, the 26G-RNAs which target and appear to down-regulate numerous spermatogenesis-expressed mRNAs. These findings add to a growing number of AGO pathways required for thermotolerant fertility in
C. elegans
and support a model in which AGOs and their small RNA cofactors function to promote robustness in gene-expression networks.