bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of solid-density ultraintense ion beams by a picosecond laser pulse of circular polarization
Authors: Jablonski S. , Badziak J.
Published: February 2012

This contribution reports particle-in-cell numerical studies of deuteron beam acceleration by a picosecond laser pulse of circular polarization. The effect of laser wavelength λ and the ILλ2 product (IL is laser intensity) on the ion beam parameters is investigated. It is shown that at the ILλ2 product fixed, the beam parameters (〈Ei〉, Ii, Fi) as well as the laser-ions energy conversion efficiency quickly increase with a decrease in the laser wavelength and the best results are achieved for a KrF laser (λ = 0.248 μm). In particular, a 2-ps KrF laser pulse of ILλ2 ∼ 2 × 1020 Wcm−2 μm2 interacting with a 10-μm deuteron target produces a quasi-monoenergetic, solid-density deuteron beam of parameters approaching those required for inertial confinement fusion fast ignition.
Influence of the shear flow on electron cyclotron resonance plasma confinement in an axisymmetric magnetic mirror trap of the electron cyclotron resonance ion source
Authors: Izotov I. V. , Razin S. V. , Sidorov A. V. , Skalyga V. A. , Zorin V. G. , Bagryansky P. A. , Beklemishev A. D. , Prikhodko V. V.
Published: February 2012

Influence of shear flows of the dense plasma created under conditions of the electron cyclotron resonance (ECR) gas breakdown on the plasma confinement in the axisymmetric mirror trap (“vortex” confinement) was studied experimentally and theoretically. A limiter with bias potential was set inside the mirror trap for plasma rotation. The limiter construction and the optimal value of the potential were chosen according to the results of the preliminary theoretical analysis. This method of “vortex” confinement realization in an axisymmetric mirror trap for non-equilibrium heavy-ion plasmas seems to be promising for creation of ECR multicharged ion sources with high magnetic fields, more than 1 T.
Design of a compact electron cyclotron resonance ion source for medium charge state light ions
Authors: Button D. , Hotchkis M. A. C. , Milford G. N.
Published: February 2012

At the Australian Nuclear Science and Technology Organization we are developing a new isotope ratio mass spectrometer based on the measurement of multiple charge state ions. We have carried out a review of our existing ECR ion source and identified a number of design flaws. For the new instrument, we are producing a new ECR source and have refined the design, in particular by using 3D simulations to improve the magnetic confinement field and by a combination of simulations and experiments to improve the design of the microwave coupling.
Progress towards the development of a realistic electron cyclotron resonance ion source extraction model
Authors: Winklehner D. , Leitner D. , Benitez J. Y. , Lyneis C. M. , Strohmeier M. M.
Published: February 2012

In this paper, an ongoing effort to provide a simulation and design tool for electron cyclotron resonance ion source extraction and low energy beam transport is described and benchmarked against experimental results. Utilizing the particle-in-cell code WARP, a set of scripts has been developed: A semiempirical method of generating initial conditions, a 2D-3D hybrid method of plasma extraction and a simple beam transport deck. Measured emittances and beam profiles of uranium and helium beams are shown and the influence of the sextupole part of the plasma confinement field is investigated. The results are compared to simulations carried out using the methods described above. The results show that the simulation model (with some additional refinements) represents highly charged, well-confined ions well, but that the model is less applicable for less confined, singly charged ions.
Synthesis, microstructure and magnetic properties of low Nd content Fe90Nd5B3.5M1.5 (M = Hf, Ti and Ta) alloys
Authors: Zhang Zeqiang , Sharma Parmanand , Yubuta Kunio , Makino Akihiro
Published: February 2012

We have investigated the effects of Hf, Ti and Ta addition on crystallization behavior, microstructure and magnetic properties of melt-spun Fe90Nd5B3.5M1.5 (M = Hf, Ti and Ta) alloy ribbons. Optimization of processing conditions lead to the development of nano-composite magnets, made from high Bs soft magnetic bcc α-Fe (grain size ∼20 nm) and tetragonal Nd2Fe14B (grain size ∼18 nm) hard magnetic phases. Hf is most effective in restraining the growth of α-Fe and Nd2Fe14B phases during annealing. The Fe90Nd5B3.5Hf1.5 ribbon annealed at 1003 K for 600 s exhibits very high maximum energy product (BH)max ∼127 kJ/m3 and reduced remanence ∼1.34 T. Strong exchange coupling among the nano-sized soft and hard magnetic phases is shown to be responsible for the excellent magnetic properties. Among low Nd-containing NdFeB nano-composite magnets, the present alloy seems to have highest (BH)max.
Room temperature ferromagnetism in monoclinic Mn-doped ZrO2 thin films
Authors: Hoa Hong Nguyen , Park C.-K. , Raghavender A. T. , Ciftja O. , Bingham N. S. , Phan M. H. , Srikanth H.
Published: February 2012

Theory has predicted that high temperature ferromagnetism (FM) should be found in cubic Mn-doped ZrO2. Our experimental data reveal room temperature FM in Mn-doped ZrO2 thin films grown on LaAlO3 substrates. The largest saturated magnetic moment (Ms) is found to be about 13.8 μB/Mn for the cubic Mn0.05Zr0.95O2 films and it decreases as the Mn content increases. In this case, the intrinsic FM is strongly associated with the cubic structure of Mn-doped ZrO2, and the Mn-Mn exchange interactions via intermediate oxygen atoms is important. Room temperature FM is also observed in monoclinic Mn-doped ZrO2 thin films grown on Yttrium Stabilized Zirconia (YSZ) substrates, however, with a completely different nature. Though pristine monoclinic ZrO2 films are already ferromagnetic, doping Mn can enhance the magnetic moment by about 40% (Ms is 2.68 μB/Mn). Differently from the cubic case, FM in monoclinic Mn-doped ZrO2 films does not come only via exchange interactions, but also from defects.
Fabrication of Fe@mSiO2 nanowires with large remanence and low cytotoxicity for targeted drug delivery
Authors: Song Meng-Meng , Bi Hong , Zhang Ye
Published: February 2012

Core-shell structured Fe@mSiO2 nanowires for targeted drug delivery have been prepared through electrodeposition followed by a CTAB-template sol-gel process. The magnetic Fe nanowire core has a diameter of ∼40 nm and the mesoporous silica shell has a uniform thickness of ∼40 nm with an average pore size of ∼2.45 nm. The drug loading experiment indicates Fe@mSiO2 nanowires have a good capability for loading drug molecules due to the large surface area of the mesoporous silica shell. Furthermore, MDA-MB-231 human breast cancer cells were chosen as model cells to investigate cyototoxicity of the nanowires by 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) and lactate dehydrogenase (LDH) assays. MTT results show low cytotoxicity of the nanowires, which is concentration-dependent and the cell viability is still nearly 80% while the concentration reaches as high as 250 μg/mL. Moreover, LDH assay has demonstrated that the nanowires have no influence on the integrity of the cell membrane. All results indicate that the as-prepared Fe@mSiO2 nanowires have a potential application as a drug nanocarrier for magnetic-targeted drug delivery.
Tuning of magnetization dynamics in sputtered CoFeB thin film by gas pressure
Authors: Xu Feng , Huang Qijun , Liao Zhiqin , Li Shandong , Ong C. K.
Published: February 2012

The influences of sputtering gas pressure on the high-frequency magnetization dynamics of as-sputtered CoFeB thin films are studied with permeability spectra based on the Landau-Lifshitz-Gilbert (LLG) equation. Results show that with the pressure increasing, both the anisotropy field and resonance frequency have minimums, while the initial permeability shows a maximum. The damping factor deceases monotonously with the pressure increasing, similar as with the coercivity. The high tunability of the damping factor indicates that controlling sputtering gas pressure could be an effective method in tuning the magnetization dynamics. All these dependences on gas pressure are suggested to be related to the inner stress of these sputtered films.
Surface morphologies and magnetic properties of Fe and Co magnetic thin films on polyethylene naphthalate organic substrates
Authors: Kaiju Hideo , Abe Taro , Kondo Kenji , Ishibashi Akira
Published: February 2012

We have studied the surface morphologies and magnetic properties of Fe and Co thin films evaporated on polyethylene naphthalate (PEN) organic substrates toward the fabrication of spin quantum cross devices. As a result, the surface roughnesses of Co (6.1 nm)/PEN and Co (12 nm)/PEN are as small as 0.1 and 0.09 nm, respectively, corresponding to less than one atomic layer, in the same scanning scale as the thickness. As for the magnetic properties, the coercive force of the Co/PEN shows the constant value of 2 kA/m upon decreasing the Co thickness from 35 to 10 nm, and it increases up to 7 kA/m upon decreasing the Co thickness from 10 to 5 nm. It decreases when the Co thickness is less than 5 nm. These results can be explained by the competition between the shape magnetic anisotropy and the induced magnetic anisotropy.
Structure and properties of metal-exchanged zeolites studied using gradient-corrected and hybrid functionals. III. Energetics and vibrational spectroscopy of adsorbates
Authors: Göltl Florian , Hafner Jürgen
Published: February 2012

The influence of the exchange-correlation functional (semilocal gradient corrected or hybrid functional) on density-functional studies of the adsorption of CO and NO in Cu- and Co-exchanged chabazite has been investigated, extending the studies of the structural and electronic properties of these materials [F. Göltl and J. Hafner, J. Chem. Phys. 136, 064501 (2012)10.1063/1.3676408; F. Göltl and J. Hafner, J. Chem. Phys. 136, 064502 (2012)10.1063/1.3676409] and including for comparison carbonyls and nitrosyls of Cu and Co. Hybrid functionals predict much lower adsorption energies than conventional semilocal functionals, in better agreement with experiment as far as data are available for comparison. The calculated adsorption energies show a strong linear correlation with the stability of the cation sites. For Cu(I)-chabazite the calculated adsorption energies span almost the interval between the adsorption energies calculated for pure neutral and positively charged Cu-carbonyls and nitrosyls. For divalent Cu(II) and Co(II) the adsorption energies at cations in chabazite are much lower than the metal-molecule binding energies in the free carbonyls or nitrosyls, especially for the most stable cation location in a six-membered ring of the chabazite structure. For the stretching modes of adsorbed CO only hybrid functionals reproduce the blueshift of the frequency reported for all Cu(I)- and Co(II)-zeolites. For Cu(II)-chabazite both types of functionals predict a blueshift, the larger value calculated with hybrid functionals being in better agreement with observation. For NO adsorbed on Cu(I)-chabazite all functionals produce a redshift, the smaller value derived with hybrid functionals being in better agreement with experiment. For NO adsorbed in Cu(II)- and Co(II)-chabazite gradient-corrected functionals produce the best agreement with experiment for cations located in a six-membered ring. Semilocal functionals tend to underestimate the frequencies, while hybrid functionals tend to overestimate. The decisive factors determining the influence of the functionals are the larger HOMO-LUMO gap and the larger bandgap of the zeolite host, as well as the larger exchange-splitting of the cation eigenstates predicted with hybrid functionals. For Co(II)-chabazite the tendency to overestimate the exchange-splitting and to stabilize a high-spin state lead to better results with semilocal functionals. Finally, a comprehensive discussion of the influence of the exchange-correlation functional on the physico-chemical properties of these complex systems, based all three papers of this series is presented.
Analysis of temporal jitter in a copper vapor laser system
Authors: Kumar D. Durga Praveen , Gantayet L. M. , Singh Sunita , Rawat A. S. , Rana Paramjit , V Rajasree , Agarwalla Sandeep K. , Chakravarthy D. P.
Published: February 2012

Temporal jitter in a magnetic pulse compression based copper vapor laser (CVL) system is analyzed by considering ripple present in the input dc power supply and ripple present in the magnetic core resetting power supply. It is shown that the jitter is a function of the ratio of operating voltage to the designed voltage, percentage ripple, and the total propagation delay of the magnetic pulse compression circuit. Experimental results from a CVL system operating at a repetition rate of 9 kHz are presented.
A plastic miniature x-ray emission spectrometer based on the cylindrical von Hamos geometry
Authors: Mattern B. A. , Seidler G. T. , Haave M. , Pacold J. I. , Gordon R. A. , Planillo J. , Quintana J. , Rusthoven B.
Published: February 2012

We present a short working distance miniature x-ray emission spectrometer (miniXES) based on the cylindrical von Hamos geometry. We describe the general design principles for the spectrometer and detail a specific implementation that covers Kβ and valence level emission from Fe. Large spatial and angular access to the sample region provides compatibility with environmental chambers, microprobe, and pump/probe measurements. The primary spectrometer structure and optic is plastic, printed using a 3-dimensional rapid-prototype machine. The spectrometer is inexpensive to construct and is portable; it can be quickly set up at any focused beamline with a tunable narrow bandwidth monochromator. The sample clearance is over 27 mm, providing compatibility with a variety of environment chambers. An overview is also given of the calibration and data processing procedures, which are implemented by a multiplatform user-friendly software package. Finally, representative measurements are presented. Background levels are below the level of the Kβ2, 5 valence emission, the weakest diagram line in the system, and photometric analysis of count rates finds that the instrument is performing at the theoretical limit.
Dynamics and efficiency of a self-propelled, diffusiophoretic swimmer
Authors: Sabass Benedikt , Seifert Udo
Published: February 2012

Active diffusiophoresis—swimming through interaction with a self-generated, neutral, solute gradient—is a paradigm for autonomous motion at the micrometer scale. We study this propulsion mechanism within a linear response theory. First, we consider several aspects relating to the dynamics of the swimming particle. We extend established analytical formulae to describe small swimmers, which interact with their environment on a finite lengthscale. Solute convection is also taken into account. Modeling of the chemical reaction reveals a coupling between the angular distribution of reactivity on the swimmer and the concentration field. This effect, which we term “reaction induced concentration distortion,” strongly influences the particle speed. Building on these insights, we employ irreversible, linear thermodynamics to formulate an energy balance. This approach highlights the importance of solute convection for a consistent treatment of the energetics. The efficiency of swimming is calculated numerically and approximated analytically. Finally, we define an efficiency of transport for swimmers which are moving in random directions. It is shown that this efficiency scales as the inverse of the macroscopic distance over which transport is to occur.
Plasma resonances in a microwave-driven microdischarge
Authors: Xue J. , Urdahl R. S. , Cooley J. E.
Published: February 2012

This work investigates resonances in a capacitively coupled, low pressure krypton microdischarge operated at 2.5 GHz. A circuit model for the device, which has a length dimension of approximately 1 mm, calculates impedance values for a range of electron densities. The model results predict several “parallel” and “series” resonances at the driving frequency when the electron density is approximately 8 × 1011 cm−3 and 5 × 1012 cm−3. The series resonance occurs when the resistance approaches the output impedance of the radio-frequency signal source, minimizing the reflected power. These resonances explain an experimentally observed jump in intensity with increasing input power.
Sodium-ion conduction in complex hydrides NaAlH4 and Na3AlH6
Authors: Oguchi H. , Matsuo M. , Kuromoto S. , Kuwano H. , Orimo S.
Published: February 2012

We have studied sodium-ion conduction in complex hydrides NaAlH4 and Na3AlH6. The electrical conductivities of these complex hydrides were studied using ac impedance measurements at temperatures up to 363 K for NaAlH4 and 433 K for Na3AlH6. Nyquist plots obtained by the measurements indicated the sodium-ion conduction. Also, dc measurements showed that sodium-ion transference numbers of NaAlH4 and Na3AlH6 were almost unity. Na3AlH6 exhibited the sodium-ion conduction of 4.1 × 10−4 S/cm at 433 K. This study will open up research on complex hydrides as solid-state sodium-ion conductors.
Thermal carrier emission and nonradiative recombinations in nonpolar (Al,Ga)N/GaN quantum wells grown on bulk GaN
Authors: Corfdir P. , Dussaigne A. , Teisseyre H. , Suski T. , Grzegory I. , Lefebvre P. , Giraud E. , Ganière J.-D. , Grandjean N. , Deveaud-Plédran B.
Published: February 2012

We investigate, via time-resolved photoluminescence, the temperature-dependence of charge carrier recombination mechanisms in nonpolar (Al,Ga)N/GaN single quantum wells (QWs) grown via molecular beam epitaxy on the a-facet of bulk GaN crystals. We study the influence of both QW width and barrier Al content on the dynamics of excitons in the 10-320 K range. We first show that the effective lifetime of QW excitons τ increases with temperature, which is evidence that nonradiative mechanisms do not play any significant role in the low-temperature range. The temperature range for increasing τ depends on the QW width and Al content in the (Al,Ga)N barriers. For higher temperatures, we observe a reduction in the QW emission lifetime combined with an increase in the decay time for excitons in the barriers, until both exciton populations get fully thermalized. Based on analysis of the ratio between barrier and QW emission intensities, we demonstrate that the main mechanism limiting the radiative efficiency in our set of samples is related to nonradiative recombination in the (Al,Ga)N barriers of charge carriers that have been thermally emitted from the QWs.
Angular and frequency dependence of standing spin waves in FePt films
Authors: Jacobi D. M. , Sallica Leva E. , Álvarez N. , Vásquez Mansilla M. , Gómez J. , Butera A.
Published: February 2012

We present a detailed analysis of the dynamic response of the magnetization in as-made FePt thin films, particularly studying the angular dependence of standing spin waves that can be observed when the external field is applied close to the film normal. We have found that the field separation between the uniform and the first excited mode depends strongly on angle and microwave frequency. To explain the observed behavior we have adopted the surface inhomogeneity model in the circular precession approximation. Using this model the experimental data could be very well fitted assuming that spins are not totally pinned at the surfaces by introducing a finite surface anisotropy. The experimental angular behavior of the resonance field at three different frequencies could be fitted with a single set of parameters indicating that the reported changes in the surface anisotropy as a function of film thickness are intrinsic to the samples.
Molecular dynamics simulations of damage production by thermal spikes in Ge
Authors: López Pedro , Pelaz Lourdes , Santos Iván , Marqués Luis A. , Aboy María
Published: February 2012

Molecular dynamics simulation techniques are used to analyze damage production in Ge by the thermal spike process and to compare the results to those obtained for Si. As simulation results are sensitive to the choice of the inter-atomic potential, several potentials are compared in terms of material properties relevant for damage generation, and the most suitable potentials for this kind of analysis are identified. A simplified simulation scheme is used to characterize, in a controlled way, the damage generation through the local melting of regions in which energy is deposited. Our results show the outstanding role of thermal spikes in Ge, since the lower melting temperature and thermal conductivity of Ge make this process much more efficient in terms of damage generation than in Si. The study is extended to the modeling of full implant cascades, in which both collision events and thermal spikes coexist. Our simulations reveal the existence of bigger damaged or amorphous regions in Ge than in Si, which may be formed by the melting and successive quenching induced by thermal spikes. In the particular case of heavy ion implantation, defect structures in Ge are not only bigger, but they also present a larger net content in vacancies than in Si, which may act as precursors for the growth of voids and the subsequent formation of honeycomb-like structures.
Prediction of glass-forming ability and characterization of atomic structure of the Co-Ni-Zr metallic glasses by a proposed long range empirical potential
Authors: Ye Dai , Jiahao Li , Baixin Liu
Published: February 2012

An interatomic potential is constructed for the Co-Ni-Zr ternary metal system under long range empirical formalism and applied to conduct molecular dynamics simulations and Voronoi tessellations. Using solid solution models with varying solute concentrations, the simulations reveal that the physical origin of metallic glass formation is the crystalline lattice collapsing while solute concentration exceeding the critical solid solubility and determine a series of critical values. In the composition triangle, the determined critical solid solubilities define a quadrilateral region, in which the formation of Co-Ni-Zr ternary metallic glasses is favored and could therefore be considered as the quantitative glass-forming ability of the system. Voronoi tessellations indicate that the atomic structure of the Co-Ni-Zr ternary metallic glasses is obviously affected by the concentration of the component metals and that the differences of the atomic radii play the key role in influencing the atomic structure of the metallic glasses, e.g., for the Co50 − x/2Ni50 − x/2Zrx (15 < x < 80) metallic glasses, the {0, 0, 12, 0} icosahedrons are the most popular polyhedrons, and they are almost Co- or Ni-centered. With increasing Zr concentration, the average coordination numbers of Co, Ni, or Zr decrease. When the Zr concentration is greater than 50 at. %, the fractions of {0, 0, 12, 0} icosahedrons and {0, 1, 12, 0} icosidihedrons decrease and the fraction of {0, 2, 8, 1} octadecahedrons remarkably increases. It turns out that the predicted glass-forming ability is well supported by the experimental observations so far reported in the literature.
Crystal and electronic structures of CuxS solar cell absorbers
Authors: Xu Qiang , Huang Bing , Zhao Yufeng , Yan Yanfa , Noufi Rommel , Wei Su-Huai
Published: February 2012

The crystal and electronic band structures of CuxS(1.25 < x ≤ 2) are systematically studied using the density-functional theory method. For Cu2S, all the three chalcocite phases, i.e., the low-chalcocite, the high-chalcocite, and the cubic-chalcocite phases have direct band gaps around 1.3–1.5 eV, with the low-chalcocite being the most stable one. However, Cu vacancies can form spontaneously in these compounds, causing instability of Cu2S. We find that under Cu-rich condition, the anilite Cu1.75S is the most stable structure. It has a predicted band gap of 1.4 eV and could a promising solar cell absorber.
Epitaxial growth and demonstration of hexagonal BN/AlGaN p-n junctions for deep ultraviolet photonics
Authors: Majety S. , Li J. , Cao X. K. , Dahal R. , Pantha B. N. , Lin J. Y. , Jiang H. X.
Published: February 2012

Recent advances in epitaxial growth and demonstration of p-type conductivity in hexagonal boron nitride (hBN) epilayers represent an exceptional opportunity to revolutionize p-layer approach and overcome the intrinsic problem of low p-type conductivity in Al-rich AlGaN for deep ultraviolet (DUV) device applications. Nevertheless, the ability of epitaxial growth of hBN on AlGaN is a prerequisite for the incorporation of p-type hBN in AlGaN DUV device structures. We report on the epi-growth of hBN on Al-rich AlGaN/AlN/Al2O3 templates using metal organic chemical vapor deposition. X-ray diffraction measurement revealed a 2θ peak at 26.5° which indicates that the BN epilayers are hexagonal and consist of a single phase. Mg doped hBN epilayers were also grown on highly insulating AlN and n-type AlGaN templates with an attempt to demonstrate hBN/AlGaN p-n junctions. Mg doped hBN epilayers grown on insulating templates were p-type with an in-plane resistivity of ∼2.3 Ω cm. Diode behavior in the p-n structures of p-hBN/n-AlxGa1−xN (x ∼ 0.62) has been demonstrated. The results here reveal the feasibility of using highly conductive p-type hBN as an electron blocking and p-contact layers for AlGaN deep UV emitters.
Enhancement of photoluminescence signal from ultrathin layers with silicon nanocrystals
Authors: Dyakov S. A. , Zhigunov D. M. , Hartel A. , Zacharias M. , Perova T. S. , Timoshenko V. Yu.
Published: February 2012

Using the model of oscillating dipoles, we simulated the photoluminescence intensity of a triple-layered structure where the silicon nanocrystals layer was enclosed by buffer and capping silicon dioxide layers. It was found that a structure with an optimized buffer layer thickness exhibited photoluminescence which was approximately 20 times more intense than that from the structure without a buffer layer. Theoretical simulations were verified by photoluminescence measurements for the corresponding structures with silicon nanocrystals fabricated by plasma enhanced chemical vapour deposition.
Enhancement of ferromagnetism in Ni excess Cu1−xNixMnSb half Heusler alloys
Authors: Ahuja B. L. , Dashora Alpa , Tiwari Shailja , Mund H. S. , Halder Madhumita , Yusuf S. M. , Itou M. , Sakurai Y.
Published: February 2012

Spin momentum densities of Cu1−xNixMnSb (for x = 0.17 and 0.22), derived from experimental magnetic Compton profiles (MCPs), show an increase in magnetic moment while going from x = 0.17 → 0.22, which is attributed to Mn 3d states. MCPs along with magnetization data suggest a negligible contribution of orbital moment. The MCPs and spin moments at Mn 3d states computed using the spin polarized relativistic Korringa-Kohn-Rostoker technique are in good agreement with the experimental data. An unusual increase in magnetic moment (2.77 ± 0.03 μB/f.u. for x = 0.17 to 3.94 ± 0.03 μB/f.u. for x = 0.22) is due to significant rise in local magnetic moment on Mn site. For x = 0.22 (0.17), presence of antiferromagnetic phase is observed to be 2 (31)%.
A neural network potential-energy surface for the water dimer based on environment-dependent atomic energies and charges
Authors: Morawietz Tobias , Sharma Vikas , Behler Jörg
Published: February 2012

Understanding the unique properties of water still represents a significant challenge for theory and experiment. Computer simulations by molecular dynamics require a reliable description of the atomic interactions, and in recent decades countless water potentials have been reported in the literature. Still, most of these potentials contain significant approximations, for instance a frozen internal structure of the individual water monomers. Artificial neural networks (NNs) offer a promising way for the construction of very accurate potential-energy surfaces taking all degrees of freedom explicitly into account. These potentials are based on electronic structure calculations for representative configurations, which are then interpolated to a continuous energy surface that can be evaluated many orders of magnitude faster. We present a full-dimensional NN potential for the water dimer as a first step towards the construction of a NN potential for liquid water. This many-body potential is based on environment-dependent atomic energy contributions, and long-range electrostatic interactions are incorporated employing environment-dependent atomic charges. We show that the potential and derived properties like vibrational frequencies are in excellent agreement with the underlying reference density-functional theory calculations.
Growth and electrical characterisation of δ-doped boron layers on (111) diamond surfaces
Authors: Edgington Robert , Sato Syunsuke , Ishiyama Yuichiro , Morris Richard , Jackman Richard B. , Kawarada Hiroshi
Published: February 2012

A plasma enhanced chemical vapor deposition protocol for the growth of δ-doping of boron in diamond is presented, using the (111) diamond plane as a substrate for diamond growth. AC Hall effect measurements have been performed on oxygen terminated δ-layers and desirable sheet carrier densities (∼1013 cm−2) for field-effect transistor application are reported with mobilities in excess of what would expected for equivalent but thicker heavily boron-doped diamond films. Temperature-dependent impedance spectroscopy and secondary ion mass spectroscopy measurements show that the grown layers have metallic-like electrical properties with high cut-off frequencies and low thermal impedance activation energies with estimated boron concentrations of approximately 1020 cm−3.
An electrooptic probe to determine internal electric fields in a piezoelectric transformer
Authors: Norgard Peter , Kovaleski Scott
Published: February 2012

A technique using the electrooptic effect to determine the output voltage of an optically clear LiNbO3 piezoelectric transformer was developed and explored. A brief mathematical description of the solution is provided, as well as experimental data demonstrating a linear response under ac resonant operating conditions. A technique to calibrate the diagnostic was developed and is described. Finally, a sensitivity analysis of the electrooptic response to variations in angular alignment between the LiNbO3 transformer and the laser probe are discussed.
Consequences of spontaneous reconnection at a two-dimensional non-force-free current layer
Authors: Fuentes-Fernández J. , Parnell C. E. , Hood A. W. , Priest E. R. , Longcope D. W.
Published: February 2012

Magnetic neutral points, where the magnitude of the magnetic field vanishes locally, are potential locations for energy conversion in the solar corona. The fact that the magnetic field is identically zero at these points suggests that for the study of current sheet formation and of any subsequent resistive dissipation phase, a finite beta plasma should be considered, rather than neglecting the plasma pressure as has often been the case in the past. The rapid dissipation of a finite current layer in non-force-free equilibrium is investigated numerically, after the sudden onset of an anomalous resistivity. The aim of this study is to determine how the energy is redistributed during the initial diffusion phase, and what is the nature of the outward transmission of information and energy. The resistivity rapidly diffuses the current at the null point. The presence of a plasma pressure allows the vast majority of the free energy to be transferred into internal energy. Most of the converted energy is used in direct heating of the surrounding plasma, and only about 3% is converted into kinetic energy, causing a perturbation in the magnetic field and the plasma which propagates away from the null at the local fast magnetoacoustic speed. The propagating pulses show a complex structure due to the highly non-uniform initial state. It is shown that this perturbation carries no net current as it propagates away from the null. The fact that, under the assumptions taken in this paper, most of the magnetic energy released in the reconnection converts internal energy of the plasma, may be highly important for the chromospheric and coronal heating problem.
Wafer-scale fabrication of high-aspect ratio nanochannels based on edge-lithography technique
Authors: Xie Quan , Zhou Qing , Xie Fei , Sang Jianming , Wang Wei , Zhang Haixia Alice , Wu Wengang , Li Zhihong
Published: February 2012

This paper introduced a wafer-scale fabrication approach for the preparation of nanochannels with high-aspect ratio (the ratio of the channel depth to its width). Edge lithography was used to pattern nanogaps in an aluminum film, which was functioned as deep reactive ion etching mask thereafter to form the nanochannel. Nanochannels with aspect ratio up to 172 and width down to 44 nm were successfully fabricated on a 4-inch Si wafer with width nonuniformity less than 13.6%. A microfluidic chip integrated with nanometer-sized filters was successfully fabricated by utilizing the present method for geometric-controllable nanoparticle packing.
Room temperature single photon emission from an epitaxially grown quantum dot
Authors: Fedorych O. , Kruse C. , Ruban A. , Hommel D. , Bacher G. , Kümmell T.
Published: February 2012

Single photon emission from an epitaxially grown quantum dot at room temperature is presented. CdSe/ZnSSe quantum dots are embedded into MgS barriers, providing dominant radiative recombination up to 300 K. Under continuous wave optical excitation, the autocorrelation function g(2)(t) exhibits a sharp dip at (t = 0) with g(2)(0) = 0.16 ± 0.15 at T = 300 K, revealing excellent suppression of multiphoton emission even at room temperature.
Thermal model for an early prototype of concentrating photovoltaic for active solar panel initiative system
Authors: Kumar Natarajan Sendhil , Katz Matty , Kumar Mallick Tapas
Published: February 2012

In this paper, three dimensional thermal model is presented for an early prototype of novel concentrating PV design for active solar panel initiative system using ANSYS, CFX package. The system consists of series of Fresnel lens for 36 × 6 series-parallel configuration solar cells, bottom encapsulation layer, and back plate. Fresnel lens is placed at the top of the system. Each Fresnel lens has a thickness of 3 mm and dimension of 10 × 60 mm dimensions. In order to protect the lens from the ambient conditions, protective glass plate is used just above the lens. Each solar cell is 0.25 mm thickness and dimension of 2 × 60 mm, located at the base of the system. The system concentration ratio is 5×. The solar cells are placed along the focal line of the Fresnel lens. Thermally conductive adhesive thickness of 1 mm is placed at the bottom and side of the solar cells. In the present model, only three Fresnel lens and solar cells arrangement have considered. To reduce the solar cell temperature, the five numbers of fins are used at the base of the 5 mm back plate. Solar radiation of 1000 W/m2 is considered and absorption coefficient of 15% of the lens, glass plate, and optical frame is also considered in the present model. Based on the present model, the temperatures of the different components are predicted for focal lengths of 41 mm, 33 mm, 25 mm, and 5 mm. It is observed that the variations of the focal length abruptly change the fluid motion between the lens and the solar cells, as a result, the operating solar cell temperature first increases and then decreases.
Anisotropic magneto-resistance in a GaMnAs-based single impurity tunnel diode: A tight binding approach
Authors: Nestoklon M. O. , Krebs O. , Jaffrès H. , Ruttala S. , George J.-M. , Jancu J.-M. , Voisin P.
Published: February 2012

Using an advanced tight-binding approach, we estimate the anisotropy of the tunnel transmission associated with the rotation of the 5/2 spin of a single Mn atom forming an acceptor state in GaAs and located near an AlGaAs tunnel barrier. Significant anisotropies in both in-plane and out-of-plane geometries are found, resulting from the combination of the large spin-orbit coupling associated with the p-d exchange interaction, cubic anisotropy of heavy-hole dispersion and the low C2v symmetry of the chemical bonds.
Wavelength-selective and diffuse emitter enhanced by magnetic polaritons for thermophotovoltaics
Authors: Wang L. P. , Zhang Z. M.
Published: February 2012

Both wavelength selectivity and directional insensitivity are highly desired in thermophotovoltaic applications. A concept of a magnetic-polariton-enhanced thermophotovoltaic emitter is presented. The predicted normal emittance from such a nanoengineered surface exceeds 0.8 in the wavelength region from 0.62 to 1.98 μm and is below 0.2 at wavelengths longer than 2.4 μm. Furthermore, thermal emission from the proposed structure is diffuse-like as the emittance changes little with the direction up to 75° from the normal. The strip width allows tuning of the emittance spectrum to match particular photovoltaic cells to potentially enhance power generation with improved conversion efficiency.
Nanometer sized Ni-dot/Ag/Pt structure for high reflectance of p-type contact metal in InGaN light emitting diodes
Authors: Sang Kim Kyu , Gyun Suh Myoung , Cho S. N.
Published: February 2012

The Ni-dot/Ag/Pt layer, where Ni-dot layer is formed of nanometer sized Ni dots, has been used to improve the reflectivity from the surface of p-type GaN in a light emitting diode (LED). Comparing with Ni/Ag/Pt layer, where Ni layer is a thin film, the Ni-dot/Ag/Pt structure shows significantly improved reflectivity with stable contact resistivity. The optical output power and external quantum efficiency of InGaN LEDs with Ni-dot/Ag/Pt structure for p-metal have improved by 28% and 29%, respectively, over the results of Ni/Ag/Pt structure.
Well-arranged novel InGaN hexagonal nanoplates at the tops of nitrogen-polarity GaN nanocolumn arrays
Authors: Kouno Tetsuya , Kishino Katsumi
Published: February 2012

Periodically arranged novel InGaN hexagonal nanoplates were fabricated at the tops of square-lattice N-polarity GaN nanocolumn arrays. The key finding in this work is that the growth of InGaN on N-polarity GaN nanocolumns led to a peculiar nanoplate structure. The InGaN nanoplates with thicknesses of 50-100 nm extended outward from the narrow nanocolumns with diameters of 100-150 nm, to form larger hexagonal nanoplates with a typical side length of 250 nm.
Agronomic studies on irrigated soybean in southern New South Wales. II. Broadening options for sowing date
Authors: Gaynor L. G. , Lawn R. J. , James A. T.
Published: February 2012

The response of irrigated soybean to sowing date and to plant population was evaluated in field experiments over three years at Leeton, in the Murrumbidgee Irrigation Area (MIA) in southern New South Wales. The aim was to explore the options for later sowings to improve the flexibility for growing soybean in double-cropping rotations with a winter cereal. The experiments were grown on 1.83-m-wide raised soil beds, with 2, 4, or 6 rows per bed (years 1 and 2) or 2 rows per bed only (year 3). Plant population, which was manipulated by changing either the number of rows per bed (years 1 and 2) or the within-row plant spacing (year 3), ranged from 15 to 60 plants/m2 depending on the experiment. Two sowings dates, late November and late December, were compared in years 1 and 3, while in year 2, sowings in early and late January were also included. Three genotypes (early, medium, and late maturity) were grown in years 1 and 2, and four medium-maturing genotypes were grown in year 3. In general, machine-harvested seed yields were highest in the November sowings, and declined as sowing was delayed. Physiological analyses suggested two underlying causes for the yield decline as sowing date was delayed. First and most importantly, the later sown crops flowered sooner after sowing, shortening crop duration and reducing total dry matter (TDM) production. Second, in the late January sowings of the medium- and late-maturing genotypes, harvest index (HI) declined as maturity was pushed later into autumn, exposing the crops to cooler temperatures during pod filling. Attempts to offset the decline in TDM production as sowing was delayed by using higher plant populations were unsuccessful, in part because HI decreased, apparently due to greater severity of lodging. The studies indicated that, in the near term, the yield potential of current indeterminate cultivars at the late December sowing date is adequate, given appropriate management, for commercially viable double-cropping of soybean in the MIA. In the longer term, it is suggested that development of earlier maturing, lodging-resistant genotypes that retain high HI at high sowing density may allow sowing to be delayed to early January.
Water use, water use efficiency and drought resistance among warm-season turfgrasses in shallow soil profiles
Authors: Zhou Yi , Lambrides Christopher J. , Kearns Ryan , Ye Changrong , Fukai Shu
Published: February 2012

As the available water supply for urban turfgrass management is becoming limited in Australia, it will be crucial to identify drought-resistant turfgrass species and water-saving management strategies. Eight (pre-)commercial turfgrasses grown in Australia, two each of four species including the bermudagrasses (Cynodon dactylon L.), the Queensland blue couches (Digitaria didactyla Willd), the seashore paspalums (Paspalum vaginatum Swartz.) and St Augustinegrasses (Stenotaphrum secundatum (Walt.) Kuntze) were evaluated in two lysimeter experiments. Shallow lysimeters (28 and 40 cm) were used to represent shallow soil profiles typical of urban environments. We measured gravimetric water use for the eight cultivars and calculated water use efficiency (WUE, clipping yield to water use ratio) and WUEr (ratio of WUE under drought to that under irrigated conditions). WUEr measured in both experiments correlated strongly with survival period and this relationship was not affected by soil type or cutting height. Using survival period as the criterion for drought resistance, the best were the bermudagrasses and the worst were the seashore paspalums and Queensland blue couches. The bermudagrass genotypes had the lowest water use, highest WUE and WUEr and the Queensland blue couches and seashore paspalums had the greatest water use, lowest WUE and WUEr. The possible mechanisms of drought resistance included lower water use and lower stomatal conductance as indicated by higher canopy temperature in the early stage of water deficit.
Religious tolerance in Oman: addressing religious prejudice through educational intervention
Authors: Al Sadi Fatma H. , Basit Tehmina N.
Published: February 2012

This paper examines the impact of a school‐based intervention entitled ‘Our Brothers and Sisters in Humanity’ on 10th grade female Omani students' religious tolerance. A questionnaire was administered before and after an intervention to a sample of 241 girls, of whom 116 were in the experimental group and 125 in the control group. A semi‐structured interview was conducted before and after the intervention with 16 participants, of whom 8 were from the experimental group and 8 from the control group. Analysis of the quantitative data in the postintervention round reveals that there are statistically significant differences between the experimental group and the control group in favour of the experimental group in religious tolerance. Similarly the experimental group shows greater tolerance when compared to the control group in post‐intervention interviews. The study suggests that religion is one of the most salient components of Omani pupils' ‘identity’. The participants use religion to define their relations with, and determine their tolerance of, those who hold different religious beliefs. However, we conclude that education that capitalises on the perceived similarities between religions can be a means to suppress intolerance.
The upper limit of thermoelectric figure of merit: importance of electronic thermoelectric efficiency
Authors: Li Jing , Yeung Tin Cheung Au , Kam Chan Hin
Published: February 2012

To improve thermoelectric (TE) efficiency, the physical phenomenon of TE effect is revisited. The important TE figure of merit (FOM) is expressed in terms of powers, and it is mapped by two fundamental quantities. One is the electronic TE efficiency, which is purely determined by a probability distribution function of electron transport. Furthermore, electronic TE efficiency plays an important role in the upper limit of TE FOM, which is an important index to judge the quality of a TE device. For any TE device with FOM more than one, its electronic TE efficiency must be greater than 0.5. For demonstration purpose, the TE properties of silicon nanowire are investigated.
Use of the otolith shape analysis in stock identification of anglerfish (Lophius piscatorius) in the Northeast Atlantic
Authors: Cañás Lucía , Stransky Christoph , Schlickeisen Jürgen , Sampedro M. Paz , Fariña A. Celso
Published: February 2012

Cañás, L., Stransky, C., Schlickeisen, J., Sampedro, M. P., and Fariña, A. C. 2012. Use of the otolith shape analysis in stock identification of anglerfish (Lophius piscatorius) in the Northeast Atlantic. – ICES Journal of Marine Science, 69: 250–256. The geographical variability in the anglerfish Lophius piscatorius otolith shape was investigated to examine biological evidence for the current separation into Northern and Southern stocks of L. piscatorius established in the Southwest European waters (Southern Shelf area) by the International Council for the Exploration of the Sea (ICES). In all, 629 otoliths of L. piscatorius (12–90 cm total length) from commercial fishing and research surveys were collected in two consecutive years, 2008 and 2009. The otolith shape was compared between stocks for differences in univariate descriptors using non-parametric analysis of covariance, as well as elliptical Fourier shape descriptors, through a metric multidimensional scaling and a linear discriminant analysis (LDA). The differences found in the otolith shape between Northern and Southern stocks were not large enough to hold the current status of L. piscatorius regarding stock definition in the Southern Shelf area, although homogeneous mixing between both stocks is not expected as there were significant differences between three univariate descriptors and the LDA was significant. These results are in agreement with the previous L. piscatorius stock identification studies (genetics, body morphology, and migratory behaviour), which do not support the current separation of these stocks but found substructures within the area.