bluuebunny/crossref_metadata_2025 huggingface dataset:
Isotope fractionation in surface ionization ion source of alkaline-earth iodides
Authors: Suzuki T. , Kanzaki C. , Nomura M. , Fujii Y.
Published: February 2012

The relationship between the isotope fractionation of alkaline-earth elements in the surface ionization ion source and the evaporation filament current, i.e., filament temperature, was studied. It was confirmed that the isotope fractionation depends on the evaporation filament temperature; the isotope fractionation in the case of higher temperature of filament becomes larger. The ionization and evaporation process in the surface ionization ion source was discussed, and it was concluded that the isotope fractionation is suppressed by setting at the lower temperature of evaporation filament because the dissociations are inhibited on the evaporation filament.
Transport of intense ion beams and space charge compensation issues in low energy beam lines (invited)
Authors: Chauvin N. , Delferrière O. , Duperrier R. , Gobin R. , Nghiem P. A. P. , Uriot D.
Published: February 2012

Over the last few years, the interest of the international scientific community for high power accelerators in the megawatt range has been increasing. For such machines, the ion source has to deliver a beam intensity that ranges from several tens up to a hundred of mA. One of the major challenges is to extract and transport the beam while minimizing the emittance growth and optimizing its injection into the radio frequency quadrupole. Consequently, it is crucial to perform precise simulations and cautious design of the low energy beam transport (LEBT) line. In particular, the beam dynamics calculations have to take into account not only the space charge effects but also the space charge compensation of the beam induced by ionization of the residual gas. The physical phenomena occurring in a high intensity LEBT and their possible effects on the beam are presented, with a particular emphasis on space charge compensation. Then, beam transport issues in different kind of LEBTs are briefly reviewed. The SOLMAXP particle-in-cell code dedicated to the modeling of the transport of charge particles under a space charge compensation regime is described. Finally, beam dynamics simulations results obtained with SOLMAXP are presented in the case of international fusion materials irradiation facility injector.
Wave frequency dependence of H− ion production and extraction in a transformer coupled plasma H− ion source at SNU
Authors: An YoungHwa , Cho WonHwi , Chung Kyoung-Jae , Lee Kern , Jang SeungBin , Lee Seok-Geun , Hwang Y. S.
Published: February 2012

The effect of rf wave frequencies on the production of H− ion is investigated in a transformer coupled plasma H− ion source at Seoul National University. A Langmuir probe is installed to measure the plasma density and temperature, and these plasma parameters are correlated to the extracted H− beam currents at various frequencies. The Langmuir probe is also used to measure the density of H− ions at the ion source by generating photodetachment with an Nd:YAG laser. The extracted H− currents decrease to a minimum value until 13 MHz and then, increase as the driving frequency increases from 13 MHz while the relative H− population measured by photodetachment monotonically decreases as the driving rf frequency increases from 11 MHz to 15 MHz. A potential well formed at the extraction region at high frequencies of more than 13 MHz is considered responsible for the increased H− beam extraction even with a lower photodetachment signal. The variation in the driving rf frequency not only affects the density and temperature of the plasma but also modifies the plasma potential with the existence of a filtering magnetic field and consequently, influences the extracted H− current through the extraction as well as formation of H− ions.
Status of the ion sources developments for the Spiral2 project at GANIL
Authors: Lehérissier P. , Bajeat O. , Barué C. , Canet C. , Dubois M. , Dupuis M. , Flambard J. L. , Frigot R. , Jardin P. , Leboucher C. , Lemagnen F. , Maunoury L. , Osmond B. , Pacquet J. Y. , Pichard A. , Thuillier T. , Peaucelle C.
Published: February 2012

The SPIRAL 2 facility is now under construction and will deliver either stable or radioactive ion beams. First tests of nickel beam production have been performed at GANIL with a new version of the large capacity oven, and a calcium beam has been produced on the heavy ion low energy beam transport line of SPIRAL 2, installed at LPSC Grenoble. For the production of radioactive beams, several target/ion-source systems (TISSs) are under development at GANIL as the 2.45 GHz electron cyclotron resonance ion source, the surface ionization source, and the oven prototype for heating the uranium carbide target up to 2000 °C. The existing test bench has been upgraded for these developments and a new one, dedicated for the validation of the TISS before mounting in the production module, is under design. Results and current status of these activities are presented.
Investigation of ISIS and Brookhaven National Laboratory ion source electrodes after extended operation
Authors: Lettry J. , Alessi J. , Faircloth D. , Gerardin A. , Kalvas T. , Pereira H. , Sgobba S.
Published: February 2012

Linac4 accelerator of Centre Européen de Recherches Nucléaires is under construction and a RF-driven H− ion source is being developed. The beam current requirement for Linac4 is very challenging: 80 mA must be provided. Cesiated plasma discharge ion sources such as Penning or magnetron sources are also potential candidates. Accelerator ion sources must achieve typical reliability figures of 95% and above. Investigating and understanding the underlying mechanisms involved with source failure or ageing is critical when selecting the ion source technology. Plasma discharge driven surface ion sources rely on molybdenum cathodes. Deformation of the cathode surfaces is visible after extended operation periods. A metallurgical investigation of an ISIS ion source is presented. The origin of the deformation is twofold: Molybdenum sputtering by cesium ions digs few tenths of mm cavities while a growth of molybdenum is observed in the immediate vicinity. The molybdenum growth under hydrogen atmosphere is hard and loosely bound to the bulk. It is, therefore, likely to peel off and be transported within the plasma volume. The observation of the cathode, anode, and extraction electrodes of the magnetron source operated at BNL for two years are presented. A beam simulation of H−, electrons, and Cs− ions was performed with the IBSimu code package to qualitatively explain the observations. This paper describes the operation conditions of the ion sources and discusses the metallurgical analysis and beam simulation results.
Study of ion beam transport from the SECRAL electron cyclotron resonance ion source at the Institute of Modern Physics
Authors: Cao Y. , Lu W. , Zhang W. H. , Sha S. , Yang Y. , Ma B. H. , Wang H. , Zhu Y. H. , Guo J. W. , Fang X. , Lin S. H. , Li X. X. , Feng Y. C. , Li J. Y. , Zhao H. Y. , Ma H. Y. , Zhang X. Z. , Guo X. H. , Wu Q. , Sun L. T. , Zhao H. W. , Xie D. Z.
Published: February 2012

Ion beam transport from the Superconducting Electron Cyclotron Resonance ion source with Advanced design in Lanzhou (SECRAL) electron cyclotron resonance ion source was studied at the Institute of Modern Physics during 2010. Particle-in-cell simulations and experimental results have shown that both space charge and magnetic aberrations lead to a larger beam envelope and emittance growth. In the existing SECRAL extraction beam line, it has been shown that raising the solenoid lens magnetic field reduces aberrations in the subsequent dipole and results in lower emittance. Detailed beam emittance measurements are presented in this paper.
Plasma studies on electron cyclotron resonance light ion source at CEA/Saclay
Authors: Nyckees S. , Delferrière O. , Duperrier R. , Harrault F. , Tuske O.
Published: February 2012

By the 90s, the CEA has undertaken to develop the production of intense light ion beams from unconfined ECR plasma. Today, three sources for IPHI, SPIRAL2, and IFMIF projects (respectively, 100 mA of H+, 8 mA of D+, and 140 mA of D+) are installed at CEA/Saclay. In order to improve performances and decrease dimensions of these sources, it is necessary to better understand the mechanisms involved in the production and extraction of particles. As a consequence, theoretical and experimental studies are being carried out. We present a theoretical study based on SOLMAXP, a home-made particle-in-cell code. The aim is to investigate the possibility of reducing the plasma chamber size without loss of beam characteristics. This code has been validated by beam intensity measurements on a permanent magnet based source, producing a proton beam of 30 mA at 40 kV on the test bench BETSI. In order to reduce experimentally the dimensions of plasma chamber, a new source, named ALISES with variable plasma chamber volume, is under assembly.
Laser measurement of H– ions in a field-effect-transistor based radio frequency ion source
Authors: Tanaka N. , Matsuno T. , Funaoi T. , Ando A. , Tauchi Y. , Nakano H. , Tsumori K. , Takeiri Y.
Published: February 2012

Hydrogen negative ion density measurements are required to clarify the characteristics of negative ion production and ion source performance. Both of laser photodetachment and cavity ring down (CRD) measurements have been implemented to a field-effect-transistor based radio-frequency ion source. The density ratio of negative hydrogen ions to electrons was successfully measured by laser photodetachment and effect of magnetic filter field on negative ion density was confirmed. The calculated CRD signal showed that CRD mirrors with >99.990% reflectivity are required and loss of reflectivity due to cesium contamination should be minimized.
Laser ion sources for radioactive beams (invited)
Authors: Lecesne N.
Published: February 2012

Resonant ionisation laser ion sources are nowadays extensively used, when available, at many leading on-line facilities. Moreover, new laser ion sources are now under development in most of the recent on-line facility projects under construction worldwide. This success is mainly due to the reliability, the ionization efficiency and the high purity that this type of source can achieve for the production of radioactive species and for a large range of chemical elements. Laser ion sources for radioactive beams gather many different systems such as dye laser or all-solid state titanium:sapphire laser systems, high or low repetition rates, hot cavities or gas cells, additional selectivity by using chemical techniques, or the LIST technique (laser ion source trap). In this paper, the physics of laser ion sources will be described with the current limitations and challenges for the future. An overview of the laser ion source facilities will be given, with an emphasis on the ongoing developments and perspectives on LIS.
Invited Review Article: The statistical modeling of atomic clocks and the design of time scales
Authors: Levine Judah
Published: February 2012

I will show how the statistical models that are used to describe the performance of atomic clocks are derived from their internal design. These statistical models form the basis for time scales, which are used to define international time scales such as International Atomic Time and Coordinated Universal Time. These international time scales are realized by ensembles of clocks at national laboratories such as the National Institute of Standards and Technology, and I will describe how ensembles of atomic clocks are characterized and managed.
Collisional electron transfer to photoexcited acceptor radical anions
Authors: Wyer Jean Ann , Støchkel Kristian , Nielsen Steen Brøndsted
Published: February 2012

In this article, we show that photoexcitation of radical anions facilitates electron transfer from sodium atoms in femtosecond encounters. Thus, excitation of 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and fluorinated TCNQ (TCNQ-F4) anions to the second optically active state at 478 nm led to increases in the yields of dianions of about 20% and 10%, respectively. Photoexcitation with a nanosecond-long laser pulse was done a few microseconds before the ions entered the sodium collision cell so that none of the ions would be in any of the initially reached doublet-excited states. We suggest an explanation for the higher electron capture cross section based on the formation of long-lived quartet state anions. Excitation of TCNQ anions within the lowest-energy absorption band, where there are no accessible quartet states, led instead to a lower yield of dianions. There are at least three explanations for the lower dianion yields: (1) Depletion of the monoanion beam due to photodetachment after the absorption of minimum two photons; (2) Formation of short-lived vibrationally excited dianions that decay by electron autodetachment prior to identification; and (3) Lower electron capture cross sections of vibrationally excited monoanions. Similar losses in dianion signal can occur at 478 nm so the actual yield of dianions at this wavelength due to the population of quartet states is therefore greater than that observed. Our methodology devises a more efficient route for the production of molecular dianions, and at the same time it may provide information on long-lived electronic states.
Interface nature of oxidized single-crystal arrays of etched Si nanowires on (100)Si
Authors: Jivanescu M. , Stesmans A. , Kurstjens R. , Dross F.
Published: February 2012

Low temperature electron spin resonance studies have been carried out on single crystalline arrays of sub-10 nm Si nanowires (NWs) manufactured on (100)Si by top down etching and oxidation thinning. This reveals the presence of a substantial inherent density of Pb0 (Si3 ≡ Si•) defects (traps) at the NW Si/SiO2 interfaces, due to particular faceting and enhanced interface strain, leaving NW interfaces of reduced electrical quality. Perusal of the specific properties of the occurring Pb-type defect system points to a nanopillar morphology compatible with NWs predominantly bordered by {110} facets, with cross sectional shape of 〈100〉 truncated {110} squares. The inherent interface quality appears limited by the wire-narrowing thermal oxidation procedure.
In search of the next Holy Grail of polyoxide chemistry: Explicitly correlated ab initio full quartic force fields for HOOH, HOOOH, HOOOOH, and their isotopologues
Authors: Hollman David S. , Schaefer Henry F.
Published: February 2012

Explicitly correlated ab initio methods have been used to compute full quartic force fields for the three chain minima for HOOOOH, which are found to lie within 1 kcal mol−1. The CCSD(T)-F12 method with the cc-pVTZ-F12 basis set was used to compute equilibrium structures, anharmonic vibrational frequencies, and rotational constants for HOOH, HOOOH, and three chain isomers of HOOOOH, with the two former force fields being used as benchmarks for the latter three. The full quartic force fields were computed in such a way as to yield fundamental frequencies for all isotopologues at once. The present research confirms the recent experimental identification of HOOOH and provides reliable force fields in support of future experimental work on the enigmatic bonding paradigms involved in the HOOOOH chain.
H− beam extraction from a cesium seeded field effect transistor based radio frequency negative hydrogen ion source
Authors: Ando A. , Matsuno T. , Funaoi T. , Tanaka N. , Tsumori K. , Takeiri Y.
Published: February 2012

H− beam was successfully extracted from a cesium seeded ion source operated using a field effect transistor inverter power supply as a radio frequency (RF) wave source. High density hydrogen plasma more than 1019 m−3 was obtained using an external type antenna with RF frequency of lower than 0.5 MHz. The source was isolated by an isolation transformer and H− ion beam was extracted from a single aperture. Acceleration current and extraction current increased with the increase of extraction voltage. Addition of a small amount of cesium vapor into the source enhanced the currents.
Tin doped indium oxide core—TiO2 shell nanowires on stainless steel mesh for flexible photoelectrochemical cells
Authors: Hong Noh Jun , Ding Bo , Soo Han Hyun , Seong Kim Ju , Hoon Park Jong , Baek Park Sang , Suk Jung Hyun , Lee Jung-Kun , Sun Hong Kug
Published: February 2012

Photoanode architecture is built on highly conductive tin doped indium oxide (ITO) nanowires (NWs) on a flexible stainless steel mesh (SSM). ITO nanowires were coated with the atomic layer deposition grown TiO2 layer and the photoelectrochemical performance of the stainless steel mesh based photoanode were examined as a function of wire-length and shell-thickness. The photoanode consisting of 20 μm-long nanowire core and 36 nm thick shell increased the photocurrent of the testing cell by 4 times, compared to a reference cell. This enhanced photochemical activity is attributed to higher light harvesting efficiency of nanowire arrays and suppressed charge recombination of core-shell structure.
Unexpected effects of third-order cross-terms in heteronuclear spin systems under simultaneous radio-frequency irradiation and magic-angle spinning NMR
Authors: Tatton Andrew S. , Frantsuzov Ilya , Brown Steven P. , Hodgkinson Paul
Published: February 2012

We recently noted [R. K. Harris, P. Hodgkinson, V. Zorin, J.-N. Dumez, B. Elena, L. Emsley, E. Salager, and R. Stein, Magn. Reson. Chem. 48, S103 (2010)10.1002/mrc.2636] anomalous shifts in apparent 1H chemical shifts in experiments using 1H homonuclear decoupling sequences to acquire high-resolution 1H NMR spectra for organic solids under magic-angle spinning (MAS). Analogous effects were also observed in numerical simulations of model 13C,1H spin systems under homonuclear decoupling and involving large 13C,1H dipolar couplings. While the heteronuclear coupling is generally assumed to be efficiently suppressed by sample spinning at the magic angle, we show that under conditions typically used in solid-state NMR, there is a significant third-order cross-term from this coupling under the conditions of simultaneous MAS and homonuclear decoupling for spins directly bonded to 1H. This term, which is of the order of 100 Hz under typical conditions, explains the anomalous behaviour observed on both 1H and 13C spins, including the fast dephasing observed in 13C{1H} heteronuclear spin-echo experiments under 1H homonuclear decoupling. Strategies for minimising the impact of this effect are also discussed.
Modeling molecular mixing in a spatially inhomogeneous turbulent flow
Authors: Meyer Daniel W. , Deb Rajdeep
Published: February 2012

Simulations of spatially inhomogeneous turbulent mixing in decaying grid turbulence with a joint velocity–concentration probability density function (PDF) method were conducted. The inert mixing scenario involves three streams with different compositions. The mixing model of Meyer [“A new particle interaction mixing model for turbulent dispersion and turbulent reactive flows,” Phys. Fluids 22(3), 035103 (2010)], the interaction by exchange with the mean (IEM) model and its velocity-conditional variant, i.e., the IECM model, were applied. For reference, the direct numerical simulation data provided by Sawford and de Bruyn Kops [“Direct numerical simulation and lagrangian modeling of joint scalar statistics in ternary mixing,” Phys. Fluids 20(9), 095106 (2008)] was used. It was found that velocity conditioning is essential to obtain accurate concentration PDF predictions. Moreover, the model of Meyer provides significantly better results compared to the IECM model at comparable computational expense.
A momentum imaging microscope for dissociative electron attachment
Authors: Adaniya H. , Slaughter D. S. , Osipov T. , Weber T. , Belkacem A.
Published: February 2012

We describe an experimental approach to image the three-dimensional (3D) momentum distribution of the negative ions arising from dissociative electron attachment (DEA). The experimental apparatus employs a low energy pulsed electron gun, an effusive gas source and a 4π solid-angle ion momentum imaging spectrometer consisting of a pulsed ion extraction field, an electrostatic lens, and a time- and position-sensitive detector. The time-of-flight and impact position of each negative ion are measured event by event in order to image the full 3D ion momentum sphere. The system performance is tested by measuring the anion momentum distributions from two DEA resonances, namely H− from H2O− (2B1) and O− from \documentclass[12pt]{minimal}\begin{document}${\rm O}_2^-$\end{document}O2− (2Πu). The results are compared with existing experimental and theoretical data.
Alfvénic turbulence generated by a beam of energetic ions via spontaneous process
Authors: Wu D. J. , Chen L. , Wu C. S.
Published: February 2012

Turbulent Alfvén waves exist ubiquitously in space and astrophysical plasmas. They may be generated by many different source mechanisms. Among them, ion beam instability is well known. Almost all instability theories are interested in the discussion whether a perturbation will grow or be damped in a given unperturbed state. Few papers elaborate the meaning of growth or amplification in terms of the initial condition. This brief communication complements the existing discussions by considering the effect of spontaneous generation of the waves. In the present study, we estimate the level of spectral energy of Alfvénic turbulence due to the presence of a beam of energetic ions. It is found that the spectral energy may be much higher than the average kinetic energy of the background plasma particles.
Metastable atom and electron density diagnostic in the initial stage of a pulsed discharge in Ar and other rare gases by emission spectroscopy
Authors: Adams S. F. , Bogdanov E. A. , Demidov V. I. , Koepke M. E. , Kudryavtsev A. A. , Williamson J. M.
Published: February 2012

Temporal measurements of the emission intensities of the Ar 419.8 and 420.1 nm spectral lines combined with Ar plasma modeling were used to examine the metastable atom and electron density behavior in the initial stage of a pulsed dc discharge. The emission intensity measurements of these spectral lines near the start of a pulsed dc discharge in Ar demonstrated a sharp growth of metastable atom and electron densities which was dependent on the applied reduced electric fields. For lower electric fields, the sharp growth of metastable atom density started earlier than the sharp electron density growth. The reverse situation was observed for larger electric fields. This presents the possibility for controlling plasma properties which may be useful for technological applications. Similar measurements with spectral lines of corresponding transitions in other rare gases are examined.
ZnO coated nanospring-based chemiresistors
Authors: Dobrokhotov Vladimir , Oakes Landon , Sowell Dewayne , Larin Alexander , Hall Jessica , Kengne Alex , Bakharev Pavel , Corti Giancarlo , Cantrell Timothy , Prakash Tej , Williams Joseph , McIlroy D. N.
Published: February 2012

Chemiresistors were constructed using 3-D silica nanospring mats coated with a contiguous film of ZnO nanocrystals. Chemiresistors with an average ZnO nanocrystal radius <3 nm, or >20 nm, were found to exhibit a relative change in conductance of a factor of 50 upon exposure to a gas flow of 20% O2 and 80% N2 with ∼500 ppm of toluene and an operational temperature of 400 °C. Samples with an average ZnO nanocrystal radius of 15 nm were found to be the most responsive with a relative conductance change of a factor of 1000. The addition of metal nanoparticles (average radius equal to 2.4 nm) onto the surface of the ZnO nanocrystals (average radius equal to 15 nm) produced a relative change in conductance of a factor of 1500. For the optimum conditions (T = 400 °C, grain size ∼15 nm) well-defined spikes in conductance to explosive vapors (TNT, TATP) were obtained for 0.1 ms exposure time at ppb levels.
Single-particle tunneling in doped graphene-insulator-graphene junctions
Authors: Feenstra R. M. , Jena Debdeep , Gu Gong
Published: February 2012

The characteristics of tunnel junctions formed between n- and p-doped graphene are investigated theoretically. The single-particle tunnel current that flows between the two-dimensional electronic states of the graphene (2D–2D tunneling) is evaluated. At a voltage bias such that the Dirac points of the two electrodes are aligned, a large resonant current peak is produced. The magnitude and width of this peak are computed, and its use for devices is discussed. The influences of both rotational alignment of the graphene electrodes and structural perfection of the graphene are also discussed.
Effect of nonmagnetic Sc ion on the intrachain coupling in spin-chain compounds Ca3Co2−xScxO6
Authors: Ruan M. Y. , Ouyang Z. W. , Chen J. , Sheng S. S. , Xia Z. C. , Li L.
Published: February 2012

We have demonstrated that in Ca3Co2−xScxO6, substitution of nonmagnetic Sc3+ (S = 0) for high-spin Cotrig, even up to the solid solubility limit of x = 0.5−0.6, does not dramatically modify the intrachain ferromagnetic (FM) interaction. This is quite different from the cases of Ir- and Rh-doping, which much enhance the intrachain FM interaction, and the cases of Mn-, Fe-, and Cr-doping, which gradually reduce the intrachain FM interaction, simultaneously introducing antiferromagnetic interaction. The results of band-structure calculations of x = 0.5 are qualitatively consistent with our magnetization data.
Influence of plastic deformation on the magnetostrictive behavior of [126]-oriented Fe–Ga alloy single crystals
Authors: Saha Biswadeep , Ramanathan Meenakshisundaram , Ren Chai , Guruswamy Sivaraman
Published: February 2012

Dislocation arrays were introduced through controlled deformation of Fe–20 at. % Ga alloy single crystal samples with ⟨100⟩ and ⟨126⟩ orientations. Alloy single crystals were obtained through vertical Bridgman growth process. Magnetostriction measurements show a large decrease in magnetostriction after deforming just past the yield point when only a single slip system is operative as in the case of [126]-oriented crystal deformation. Magnetostriction values showed a much lower decrease with deformation for the case of [100]-oriented crystal deformation, where eight different slip systems were operative and consequently eight different sets of dislocation arrays are expected. The results suggest that the nature of strain modulation introduced by the dislocation arrays has a strong influence on the magnetostrictive behavior of magnetostrictive alloys.
The reduction of effective doping with extra dopant: n-Type doping of tris(8-hydroxyquinoline) aluminum with K
Authors: Lee Hyunbok , Cho Sang Wan , Lee Jeihyun , Jeon Pyung Eun , Jeong Kwangho , Lee Jin Woo , Yi Yeonjin
Published: February 2012

We studied the n-type doping effect of K deposited on tris(8-hydroxyquinoline) aluminum (Alq3), which has been used for efficient organic semiconducting devices for the last decade. The K doped or inserted at the interface region of the Alq3/cathode has shown highly enhanced device characteristics and yet, peculiarly, extra doping of K has always deteriorated the device properties. We study the interfacial electronic structures of the Alq3–K system using in situ photoemission spectroscopy and a theoretical model to understand the origin of such deterioration. As the K doping progresses, the lowest unoccupied molecular orbital (LUMO) of pristine Alq3 is gradually filled and it becomes an occupied gap state. This reduction of LUMO density of states makes the electron injection diminished, which is the origin of the device deterioration.
Structural study of GaP layers on misoriented silicon (001) substrates by transverse scan analysis
Authors: Jussila H. , Nagarajan S. , Huhtio T. , Lipsanen H. , Tuomi T. O. , Sopanen M.
Published: February 2012

This paper examines the structural properties of gallium phosphide layers by high resolution x-ray diffraction and atomic force microscopy measurements. GaP layers are grown on misoriented and nominally exactly oriented silicon (001) substrates by metalorganic vapor phase epitaxy. Structural characterization is performed by reciprocal lattice map and transverse scan measurements of (00l)-reflections (l = 2, 4, 6). Transverse scan line profiles of GaP layers on exactly oriented and misoriented substrates are compared thoroughly and antiphase disorder related satellite peaks are observed on exactly oriented substrates. In addition, results imply that antiphase disorder is self-annihilated on misoriented substrates. The dependence of crystallographic tilt on growth temperature indicates structural coherence. Williamson-Hall-like plot of transverse scans reveals the lateral correlation length of crystalline defects of 79 nm which gives the average size of the mosaic crystallites. In addition, the mosaicity of the GaP layer is 0.042°.
Spin-filtering and switching effects of a single-molecule magnet Mn(dmit)2
Authors: An Yipeng , Yang Zhongqin
Published: February 2012

We investigated spin-dependent transport properties of a single-molecule magnet Mn(dmit)2 with a coplanar or perpendicular conformation using first-principles density functional theory combined with nonequilibrium Green’s function method. It was found that the current flowing through the junction comprised of two Au leads and a Mn(dmit)2 molecule is high spin-polarized, up to a high efficiency of 82%, if the two ligands of the molecule are orientated in the same plane. The current is strongly suppressed when a ligand is rotated and perpendicular to the other. These results suggest that Mn(dmit)2 is a potential candidate for spin filters or molecular switches.
Ab initio many-body study of the electronic and optical properties of MgAl2O4 spinel
Authors: Jiang Shengli , Lu Tiecheng , Long Yao , Chen Jun
Published: February 2012

The electronic structure and optical properties of MgAl2O4 spinel with and without oxygen vacancies have been studied in the framework of many-body perturbation theory. By considering the self-energy of electrons, we reasonably describe the bandgap of perfect MgAl2O4 and the defect energy levels of MgAl2O4 containing oxygen vacancies. With the inclusion of electron-hole interaction by solving Bethe-Salpeter equation, the calculated dielectric functions and reflectivity spectrum all are in agreement well with the experimental results for perfect MgAl2O4. Our results show that the sharp peak near 7.8 eV in the experimental absorption spectrum is attributed to the excitonic states. The oxygen vacancies produce some new defect energy levels in the forbidden gap. The optical absorption peaks at 5.3 eV, 4.75 eV and 3.2 eV are induced by the VO0 and VO1+ vacancies.
Low-order harmonic generation in metal ablation plasmas in nanosecond and picosecond laser regimes
Authors: López-Arias M. , Oujja M. , Sanz M. , Ganeev R. A. , Boltaev G. S. , Satlikov N. Kh. , Tugushev R. I. , Usmanov T. , Castillejo M.
Published: February 2012

Low-order harmonics, third and fifth, of IR (1064 nm) laser emission have been produced in laser ablation plasmas of the metals manganese, copper and silver. The harmonics were generated in a process triggered by laser ablation followed by frequency up-conversion of a fundamental laser beam that propagates parallel to the target surface. These studies were carried out in two temporal regimes by creating the ablation plasma using either nanosecond or picosecond pulses and then probing the plasma plume with pulses of the same duration. The spatiotemporal behavior of the generated harmonics was characterized and reveals the distinct composition and dynamics of the plasma species that act as nonlinear media, allowing the comparison of different processes that control the generation efficiency. These results serve to guide the choice of laser ablation plasmas to be used for efficient high harmonic generation of laser radiation.
Nonlinear dynamics of the membrane potential of a bursting pacemaker cell
Authors: González-Miranda J. M.
Published: February 2012

This article presents the results of an exploration of one two-parameter space of the Chay model of a cell excitable membrane. There are two main regions: a peripheral one, where the system dynamics will relax to an equilibrium point, and a central one where the expected dynamics is oscillatory. In the second region, we observe a variety of self-sustained oscillations including periodic oscillation, as well as bursting dynamics of different types. These oscillatory dynamics can be observed as periodic oscillations with different periodicities, and in some cases, as chaotic dynamics. These results, when displayed in bifurcation diagrams, result in complex bifurcation structures, which have been suggested as relevant to understand biological cell signaling.
The effect of the spatial nonlocality of the Kirkwood g-factor on the determination of the long wavelength dielectric functions in dipolar fluids
Authors: Fulton Robert L.
Published: February 2012

The Kirkwood g-factor that determines the long wavelength dielectric constant of a simple, isotropic, translationally invariant dipolar fluid is given by an integral of a dipole-dipole correlation function over a spherical region of a nonzero radius \documentclass[12pt]{minimal}\begin{document}$\mathcal {R}_{\mathrm{K}}$\end{document}RK chosen such that any further increase in the radius leads to no change in the value of the integral, thereby defining a Kirkwood correlation length \documentclass[12pt]{minimal}\begin{document}$\mathcal {R}_{\mathrm{K}}$\end{document}RK. For radii less than the correlation length the integral defines a radius dependent (nonlocal) Kirkwood g-factor, implying a nonlocal dielectric function. The nonlocal nature of these quantities has important consequences for the determination of the long wavelength dielectric function from dipole fluctuations via the Kirkwood-Fröhlich connection. The dipole-dipole correlation function (the volume dipole auto-correlation function) commonly used in this determination involves particles residing solely within a sphere of radius \documentclass[12pt]{minimal}\begin{document}$\mathcal {R}$\end{document}R, unlike the correct correlation function which involves either a single particle with those particles in a spherical volume of radius \documentclass[12pt]{minimal}\begin{document}$\mathcal {R}_\mathrm{K}$\end{document}RK or those particles in a spherical volume of radius \documentclass[12pt]{minimal}\begin{document}$\mathcal {R}$\end{document}R with those residing within a spherical volume of radius \documentclass[12pt]{minimal}\begin{document}$\mathcal {R}+\mathcal {R}_{\mathrm{K}}$\end{document}R+RK. A procedure is suggested for extracting the infinite system dipole-dipole correlation function from results of simulations performed on finite spherical samples. Using some results reported in the recent literature, relative to the accurate correlation function the commonly used correlation function ranges from 27% too small for a sphere having a radius comparable to the Kirkwood correlation length to 4% too small at a radius of seven times that correlation length. As a result, the apparent dielectric constants, as determined by the conventional procedure of using the fluctuations of the sum of dipoles in a finite fixed volume, are also too small. This suggests that a dielectric constant extracted from computer simulations using a total dipole-total dipole correlation function in a given volume with other geometries and/or boundary conditions will result in similar errors.
An ellipsoid-chain model for conjugated polymer solutions
Authors: Lee Cheng K. , Hua Chi C. , Chen Show A.
Published: February 2012

We propose an ellipsoid-chain model which may be routinely parameterized to capture large-scale properties of semiflexible, amphiphilic conjugated polymers in various solvent media. The model naturally utilizes the defect locations as pivotal centers connecting adjacent ellipsoids (each currently representing ten monomer units), and a variant umbrella-sampling scheme is employed to construct the potentials of mean force (PMF) for specific solvent media using atomistic dynamics data and simplex optimization. The performances, both efficacy and efficiency, of the model are thoroughly evaluated by comparing the simulation results on long, single-chain (i.e., 300-mer) structures with those from two existing, finer-grained models for a standard conjugated polymer (i.e., poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) or MEH-PPV) in two distinct solvents (i.e., chloroform or toluene) as well as a hybrid, binary-solvent medium (i.e., chloroform/toluene = 1:1 in number density). The coarse-grained Monte Carlo (CGMC) simulation of the ellipsoid-chain model is shown to be the most efficient—about 300 times faster than the coarse-grained molecular dynamics (CGMD) simulation of the finest CG model that employs explicit solvents—in capturing elementary single-chain structures for both single-solvent media, and is a few times faster than the coarse-grained Langevin dynamics (CGLD) simulation of another implicit-solvent polymer model with a slightly greater coarse-graining level than in the CGMD simulation. For the binary-solvent system considered, however, both of the two implicit-solvent schemes (i.e., CGMC and CGLD) fail to capture the effects of conspicuous concentration fluctuations near the polymer-solvent interface, arising from a pronounced coupling between the solvent molecules and different parts of the polymer. Essential physical implications are elaborated on the success as well as the failure of the two implicit-solvent CG schemes under varying solvent conditions. Within the ellipsoid-chain model, the impact of synthesized defects on local segmental ordering as well as bulk chain conformation is also scrutinized, and essential consequences in practical applications discussed. In future perspectives, we remark on strategy that takes advantage of the coordination among various CG models and simulation schemes to warrant computational efficiency and accuracy, with the anticipated capability of simulating larger-scale, many-chain aggregate systems.
Adsorbed liposome deformation studied with quartz crystal microbalance
Authors: Reviakine Ilya , Gallego Marta , Johannsmann Diethelm , Tellechea Edurne
Published: February 2012

Deformation of surface-adsorbed liposomes is an important parameter that governs the kinetics of their transformations, but one that is very difficult to measure in the case of nm-size liposomes. We investigate the deformation of dimyristoyl phosphatidyl choline liposomes by quartz crystal microbalance (QCM) as a function of temperature and show that it follows the dependence of this lipid's bending modulus on temperature, as expected from theoretical considerations. To corroborate our approach, we model QCM response from adsorbed liposomes by explicitly considering their shape and mechanical properties.
Design and analysis of a novel mechanical loading machine for dynamic in vivo axial loading
Authors: Macione James , Nesbitt Sterling , Pandit Vaibhav , Kotha Shiva
Published: February 2012

This paper describes the construction of a loading machine for performing in vivo, dynamic mechanical loading of the rodent forearm. The loading machine utilizes a unique type of electromagnetic actuator with no mechanically resistive components (servotube), allowing highly accurate loads to be created. A regression analysis of the force created by the actuator with respect to the input voltage demonstrates high linear correlation (R2 = 1). When the linear correlation is used to create dynamic loading waveforms in the frequency (0.5–10 Hz) and load (1–50 N) range used for in vivo loading, less than 1% normalized root mean square error (NRMSE) is computed. Larger NRMSE is found at increased frequencies, with 5%–8% occurring at 40 Hz, and reasons are discussed. Amplifiers (strain gauge, linear voltage displacement transducer (LVDT), and load cell) are constructed, calibrated, and integrated, to allow well-resolved dynamic measurements to be recorded at each program cycle. Each of the amplifiers uses an active filter with cutoff frequency at the maximum in vivo loading frequencies (50 Hz) so that electronic noise generated by the servo drive and actuator are reduced. The LVDT and load cell amplifiers allow evaluation of stress-strain relationships to determine if in vivo bone damage is occurring. The strain gauge amplifier allows dynamic force to strain calibrations to occur for animals of different sex, age, and strain. Unique features are integrated into the loading system, including a weightless mode, which allows the limbs of anesthetized animals to be quickly positioned and removed. Although the device is constructed for in vivo axial bone loading, it can be used within constraints, as a general measurement instrument in a laboratory setting.
Electrical properties of magnetic nanocontact devices computed using finite-element simulations
Authors: Petit-Watelot S. , Otxoa R. M. , Manfrini M.
Published: February 2012

We compute the electrical current flow and associated Oersted fields in magnetic nanocontact (NC) systems with finite-element simulations. Underneath the nanocontact, the current distribution is found to be mainly perpendicular to the film plane, while the flow is essentially in the film plane outside the nanocontact region. For circular nanocontacts, we provide criteria for which the cylindrical approximation remains valid for electrical flow in asymmetric rectangular devices. The nature of the current distribution, and the induced field, is a key to understanding spin-torque driven magnetization dynamics in such systems.
Biodiesel as an alternative fuel for direct injection diesel engines: A review
Authors: Kannan G. R. , Anand R.
Published: February 2012

Biodiesel is an alternative fuel to diesel engine that can replace or reduce the use of petroleum diesel. Biodiesel is derived from vegetable oils, animal fats, and waste cooking oils through transesterification reaction. This paper reviews the optimization of transesterification process for different varieties of biodiesel by considering the factors such as alcohols, fatty acid content, molar ratio of alcohols to oil, catalyst concentration, reaction temperature, and reaction time. The review also addresses various technical aspects of biodiesel usage in diesel engine to improve the cold flow properties, performance, combustion characteristics and reduce the emission characteristics, particularly nitric oxide and smoke compared to diesel through either modifying engine parameters like fuel injection pressure and timing or fuel modification by blending with alcohols, diesel, and metal based additives.
Chemical, biological, radiological, and nuclear threats-Decontamination technologies and recent patents: A review
Authors: Wadood Khan Abdul , Kotta Sabna , Hussain Ansari Shahid , Kumar Sharma Rakesh , Kumar Vinod , Rana Sudha , Ali Javed
Published: February 2012

With the increase in the intensity of threats perception and possibility of mass casualties in case of a chemical, biological, radiological, and nuclear (CBRN) emergency, there is a need to develop novel and effective systems for decontamination. The natural calamity in Japan leading to world’s most critical nuclear emergency exposed lack of decontamination formulation and technologies globally. There is a need to develop novel and effective systems for decontamination as the current technologies are expensive and cannot be used by victim themselves. Decontamination formulations that can be used by victims themselves are need of time. The review gives a brief introduction about the various CBRN agents and a concise discussion about the decontamination technologies available globally. The article also provides a review of the existing patents on the methods, equipment/devices used in CBRN decontamination.
Thermoelectric properties and structural variations in Bi2Te3−xSx crystals
Authors: Wong-Ng W. , Joress H. , Martin J. , Zavalij P. Y. , Yan Y. , Yang J.
Published: February 2012

We report the application of a custom-designed, non-destructive Seebeck coefficient screening technique, in combination with x-ray diffraction and Hall measurements, to characterize the effect of S substitution on n-type Bi2Te3−xSx single crystals. The results elucidate the detailed distribution of Te/S in the Bi2Te3−xSx crystals, including the preferred substitution site, to correlate the compositional gradient with the transport properties in different locations on the same crystal. As the S substitution increases, the carrier concentration increases, and the absolute Seebeck coefficient decreases. The observed trends in the transport properties and the compositional variations are consistent with a narrow gap semiconductor model.
Effect of secondary structure on the self-assembly of amphiphilic molecules: A multiscale simulation study
Authors: Mondal Jagannath , Yethiraj Arun
Published: February 2012

The self-assembly of amphiphilic molecules is of interest from a fundamental and practical standpoint. There has been recent interest in a class of molecules made from β-amino acids (which contain an additional backbone carbon atom when compared with natural amino acids). Block copolymers of β-peptides, where one block is hydrophobic and the other is hydrophilic, self-assemble into micelles. In this work, we use computer simulations to provide insight into the effect of secondary structure on the self-assembly of these molecules. Atomistic simulations for the free energy of association of a pair of molecules show that a homochiral hydrophobic block promotes self assembly compared to a heterochiral hydrophobic block, consistent with experiment. Simulations of a coarse-grained model show that these molecules spontaneously form spherical micelles.
Non-resonant femtosecond laser control of the molecular dynamics in liquid chloroform
Authors: Nikiforov V. G. , Shmelev A. G. , Safiullin G. M. , Lobkov V. S.
Published: February 2012

The optical control of the molecular motions in chloroform CHCl3 at room temperature through the non-resonant excitation was enhanced by means of the double-pulse pump-probe technique. When the separation time of the pump pulses and their relative intensity were varied, the amplification or the cancellation of the coherent vibrations of the molecules was achieved. The molecular responses were detected by the time-resolved optically heterodyne-detected optical-Kerr-effect technique.
Size-dependent hydrogen uptake behavior of Pd nanoparticles revealed by photonic crystal surface waves
Authors: Konopsky Valery N. , Basmanov Dmitry V. , Alieva Elena V. , Sekatskii Sergey K. , Dietler Giovanni
Published: February 2012

We present an optical method of study of nanoparticle properties using photonic crystal surface waves. Palladium nanoparticles were deposited on a surface of a one-dimensional photonic crystal, which supports the propagation of p-polarized optical surface waves. The changes in the nanoparticle properties, such as its dimension and refractive index, were monitored through angle interrogation of the photonic crystal surface waves. The interaction of palladium nanoparticles with hydrogen was detected with this method. The size-different hydrogen uptake behavior by 2 and 6 nm diameter Pd nanoparticles results in qualitatively different response of the optical signal, viz., in the different signs of such a response. This not only confirms the absence of the α- to β-phase transformation for the smallest palladium nanoparticles, but is a plausible indication that hydrogen donates its electrons to a collective electron band of the metal.
Towards nonvolatile memory devices based on ferroelectric polymers
Authors: Tsutsumi Naoto , Bai Xue , Sakai Wataru
Published: February 2012

We show the ferroelectric switching of a thin film of the copolymer of 60 mol% vinylidene fluoride and 40 mol% trifluoroethylene when it is subjected to a sinusoidal electric field from 10 Hz to 100 kHz using a conductive probe chip of AFM. A switching speed of 1.6 ×106 s-1 (switching time of 660 ns) was measured at 100 kHz switching.