bluuebunny/crossref_metadata_2025 huggingface dataset:
Solving the Heterogeneous VHTR Core with Efficient Grid Computing
Authors: John Connolly Kevin , Rahnema Farzad
Published: June 2014

This paper uses the coarse mesh transport method COMET to solve the eigenvalue and pin fission density distribution of the Very High Temperature Reactor (VHTR). It does this using the Boltzmann transport equation without such low-order approximations as diffusion, and it does not simplify the reactor core problem through homogenization techniques. This method is chosen as it makes highly efficient use of grid computing resources: it conducts a series of calculations at the block level using Monte Carlo to model the explicit geometry within the core without approximation, and compiles a compendium of data with the solution set. From there, it is able to solve the desired core configuration on a single processor in a fraction of the time necessary for whole-core deterministic or stochastic transport calculations. Thus, the method supplies a solution which has the accuracy of a whole-core Monte Carlo solution via the computing power available to the user.

The core solved herein, the VHTR, was chosen due to its complexity. With a high level of detailed heterogeneity present from the core level to the pin level, and with asymmetric blocks and control material present outside of the fueled region of the core, this reactor geometry creates problems for methods which rely on homogenization or diffusion methods. Even transport methods find it challenging to solve. As it is desirable to reduce the number of assumptions necessary for a whole core calculation, this choice of reactor and solution method combination is an appropriate choice for a demonstration on an efficient use of grid computing.
SAMPSON Parallel Computation for Sensitivity Analysis of TEPCO's Fukushima Daiichi Nuclear Power Plant Accident
Authors: Pellegrini M. , Bautista Gomez L. , Maruyama N. , Naitoh M. , Matsuoka S. , Cappello F.
Published: June 2014

On March 11th 2011 a high magnitude earthquake and consequent tsunami struck the east coast of Japan, resulting in a nuclear accident unprecedented in time and extents. After scram started at all power stations affected by the earthquake, diesel generators began operation as designed until tsunami waves reached the power plants located on the east coast. This had a catastrophic impact on the availability of plant safety systems at TEPCO's Fukushima Daiichi, leading to the condition of station black-out from unit 1 to 3. In this article the accident scenario is studied with the SAMPSON code. SAMPSON is a severe accident computer code composed of hierarchical modules to account for the diverse physics involved in the various phases of the accident evolution. A preliminary parallelization analysis of the code was performed using state-of-the-art tools and we demonstrate how this work can be beneficial to the nuclear safety analysis. This paper shows that inter-module parallelization can reduce the time to solution by more than 20%. Furthermore, the parallel code was applied to a sensitivity study for the alternative water injection into TEPCO's Fukushima Daiichi unit 3. Results show that the core melting progression is extremely sensitive to the amount and timing of water injection, resulting in a high probability of partial core melting for unit 3.
A highly heterogeneous 3D PWR core benchmark: deterministic and Monte Carlo method comparison
Authors: Jaboulay J.-C. , Damian F. , Douce S. , Lopez F. , Guenaut C. , Aggery A. , Poinot-Salanon C.
Published: June 2014

Physical analyses of the LWR potential performances with regards to the fuel utilization require an important part of the work dedicated to the validation of the deterministic models used for theses analyses. Advances in both codes and computer technology give the opportunity to perform the validation of these models on complex 3D core configurations closed to the physical situations encountered (both steady-state and transient configurations). In this paper, we used the Monte Carlo Transport code TRIPOLI-4®; to describe a whole 3D large-scale and highly-heterogeneous LWR core. The aim of this study is to validate the deterministic CRONOS2 code to Monte Carlo code TRIPOLI-4®; in a relevant PWR core configuration. As a consequence, a 3D pin by pin model with a consistent number of volumes (4.3 millions) and media (around 23,000) is established to precisely characterize the core at equilibrium cycle, namely using a refined burn-up and moderator density maps. The configuration selected for this analysis is a very heterogeneous PWR high conversion core with fissile (MOX fuel) and fertile zones (depleted uranium). Furthermore, a tight pitch lattice is selcted (to increase conversion of 238U in 239Pu) that leads to harder neutron spectrum compared to standard PWR assembly. In these conditions two main subjects will be discussed: the Monte Carlo variance calculation and the assessment of the diffusion operator with two energy groups for the core calculation.
Ab initio and Atomic kinetic Monte Carlo modelling of segregation in concentrated FeCrNi alloys
Authors: Piochaud J.B. , Becquart C.S. , Domain C.
Published: June 2014

Internal structure of pressurised water reactors are made of austenitic materials. Under irradiation, the microstructure of these concentrated alloys evolves and solute segregation on grain boundaries or irradiation defects such as dislocation loops are observed to take place. In order to model and predict the microstructure evolution, a multiscale modelling approach needs to be developed, which starts at the atomic scale. Atomic Kinetic Monte Carlo (AKMC) modelling is the method we chose to provide an insight on defect mediated diffusion under irradiation. In that approach, we model the concentrated commercial steel as a FeCrNi alloy (γ-Fe70Cr20Ni10). As no reliable empirical potential exists at the moment to reproduce faithfully the phase diagram and the interactions of the elements and point defects, we have adjusted a pair interaction model on large amount of DFT calculations. The point defect properties in the Fe70Cr20Ni10, and more precisely, how their formation energy depends on the local environment will be presented and some AKMC results on thermal non equilibrium segregation and radiation induce segregation will be presented. The effect of Si on the segregation will also be discussed.
Modelisation of the SECMin molten salts environment
Authors: Lucas M. , Slim C. , Delpech S. , di Caprio D. , Stafiej J.
Published: June 2014

We develop a cellular automata modelisation of SECM experiments to study corrosion in molten salt media for generation IV nuclear reactors. The electrodes used in these experiments are cylindrical glass tips with a coaxial metal wire inside. As the result of simulations we obtain the current approach curves of the electrodes with geometries characterized by several values of the ratios of glass to metal area at the tip. We compare these results with predictions of the known analytic expressions, solutions of partial differential equations for flat uniform geometry of the substrate. We present the results for other, more complicated substrate surface geometries e. g. regular saw modulated surface, surface obtained by Eden model process, ...
Corrections and Design Studies of Borehole Logging Tools with the help of Monte Carlo Simulations
Authors: Reinhardt Heiko
Published: June 2014

Borehole logging tools are used for measuring a detailed record of a geological formation that is penetrated by a borehole. Values of interest of a geological formation are for example its density, chemical composition and porosity. Density of a formation can be measured using tools based on a chemical CS-137 gamma ray source. Porosity can be measured using a chemical AmBe neutron source. The resulting measurement of the tool, for example the density of a formation, has to be corrected for borehole influences such as borehole fluid or borehole size. These corrections depend on the individual tool design. The best way to calculate this vast number of corrections is using Monte-Carlo simulations. The software of choice is the MCNP5 package(1) . At Antares Datensysteme simulations are further used in pre design studies, to get the best physical layout of a tool.
Estimation of Secondary Neutron Dose during Proton Therapy
Authors: Urban Tomas , Klusoň Jaroslav
Published: June 2014

During proton radiotherapy, secondary neutrons are produced by nuclear interactions in the material along the beam path, in the treatment nozzle (including the fixed scatterer, range modulator, etc.) and, of course, after entering the patient. The dose equivalent deposited by these neutrons is usually not considered in routine treatment planning. In this study, there has been estimated the neutron dose in patient (in as well as around the target volume) during proton radiotherapy using scattering and scanning techniques.

The proton induced neutrons (and photons) have been simulated in the simple geometry of the single scattering and the pencil beam scanning universal nozzles and in geometry of the plastic phantom (made of tissue equivalent material – RW3 – imitate the patient). In simulations of the scattering nozzle, different types of brass collimators have been used as well. Calculated data have been used as an approximation of the radiation field in and around the chosen/potential target volume in the patient (plastic phantom). For the dose equivalent evaluation, fluence-to-dose conversion factors from ICRP report have been employed.

The results of calculated dose from neutrons in various distances from the spot for different treatment technique and for different energies of incident protons have been compared and evaluated in the context of the dose deposited in the target volume.

This work was supported by RVO: 68407700 and Grant Agency of the CTU in Prague, grant No. SGS12/200/OHK4/3T/14.
The Application of Elliptic Cylindrical Phantom in Brachytherapy Dosimetric Study of HDR 192Ir Source
Authors: Sang Ahn Woo , Ho Park Sung , Hoon Jung Sang , Choi Wonsik , Do Ahn Seung , Soo Shin Seong
Published: June 2014

The purpose of this study is to determine the radial dose function of HDR 192Ir source based on Monte Carlo simulation using elliptic cylindrical phantom, similar to realistic shape of pelvis, in brachytherapy dosimetric study. The elliptic phantom size and shape was determined by analysis of dimensions of pelvis on CT images of 20 patients treated with brachytherapy for cervical cancer. The radial dose function obtained using the elliptic cylindrical water phantom was compared with radial dose functions for different spherical phantom sizes, including the Williamsion’s data loaded into conventional planning system. The differences in the radial dose function for the different spherical water phantoms increase with radial distance, r, and the largest differences in the radial dose function appear for the smallest phantom size. The radial dose function of the elliptic cylindrical phantom significantly decreased with radial distance in the vertical direction due to different scatter condition in comparison with the Williamson’s data. Considering doses to ICRU rectum and bladder points, doses to reference points can be underestimated up to 1-2% at the distance from 3 to 6 cm. The radial dose function in this study could be used as realistic data for calculating the brachytherapy dosimetry for cervical cancer.
PRIZMA predictions of in-core detection indications in the VVER-1000 reactor
Authors: Kandiev Yadgar Z. , Kashayeva Elena A. , Malyshin Gennady N. , Modestov Dmitry G. , Khatuntsev Kirill E.
Published: June 2014

The paper describes calculations which were done by the PRIZMA code(1) to predict indications of in-core rhodium detectors in the VVER-1000 reactor for some core fragments with allowance for fuel and rhodium burnout.
Octree Ray Tracing Method for Complicated Reactor Geometry
Authors: Poveshchenko Oxana Yu. , Vujic Jasmina L.
Published: June 2014

This paper presents the new approach to ray tracing for nuclear reactor neutron transport computer simulation analysis. This method is aimed for Monte-Carlo methods as well as for deterministic neutron transport methods. Special attention is attended for reactor core composed of a set of material zones with complicate geometrical boundaries.

The idea of this approach is described. Method works for 3-D space in general case. Algorithms of octree map generation and the tracing phases for typical geometric bodies are given. Simple 2-D numerical benchmark is given to demonstrate the advantage of new approach.
Uncertainty Quantification in Monte Carlo Simulation: Theoretical Foundations and Heuristic Investigations
Authors: Saracco P. , Batic M. , Pia M.G.
Published: June 2014

We present advances in the development of methods to predict the effect that uncertainties in physical data needed for generic Monte Carlo simulations induce on the observables resulting from the simulation. Under wide conditions the PDF for the input (uncertain) physical data determine univocally the PDF for the output of the simulation: this general result has clear and powerful applications both in the case of a single (or few) uncertain input data and in the case of many unknown variables, provided they are totally correlated or uncorrelated. Although this is a typical example of forward propagation problem, our results can be applicable also in the backward case, for instance when one is trying to assess conditions for a robust design.
Assessment of the neutron activation of a stainless steel sample in a Research Nuclear Reactor using the Monte Carlo method and CINDER’90
Authors: Lázaro Ignacio , Ródenas José , Marques José G. , Gallardo Sergio
Published: June 2014

Materials in a nuclear reactor are activated by neutron irradiation. When they are withdrawn from the reactor and placed in some storage, the potential dose received by workers in the surrounding area must be taken into account. In previous papers, activation of control rods in a NPP with BWR and dose rates around the storage pool have been estimated using the MCNP5 code based on the Monte Carlo method. Models were validated comparing simulation results with experimental measurements. As the activation is mostly produced in stainless steel components of control rods the activation model can be also validated by means of experimental measurements on a stainless steel sample after being irradiated in a reactor. This has been done in the Portuguese Research Reactor at Instituto Tecnológico e Nuclear. The neutron activation has been calculated by two different methods, Monte Carlo and CINDER’90, and results have been compared. After irradiation, dose rates at the water surface of the reactor pool were measured, with the irradiated stainless steel sample submerged at different positions under water. Experimental measurements have been compared with simulation results using Monte Carlo. The comparison shows a good agreement confirming the validation of models.
Validation of the MORET 5 code for Criticality Safety Applications
Authors: Cochet B. , Leclaire N. , Heulers L. , Le Dauphin F. X. , Mijonnet A.
Published: June 2014

The MORET 5 Monte Carlo code includes two calculation routes: a multi-group route based on cross-sections calculated from various preliminary cell codes and a continuous energy calculation route. The criticality experimental validation database is made up of 2255 benchmarks, mainly taken from the Handbook of the International Criticality Safety Benchmark Evaluated Experiments Project or performed in French facilities. Most of them have been investigated with the two different routes. The calculation results are generally in good agreement with the benchmarks, depending on the nuclear data used.
A technique for estimating neutron fluxes in a large number of in-core detectors by the Monte Carlo code PRIZMA for a full-scale model of a water-moderated reactor core
Authors: Kandiev Y.Z. , Kashaeva E.A. , Malyshkin G.N. , Khatuntsev K.E.
Published: June 2014

The paper describes a technique implemented in the PRIZMA code for calculating neutron flux in a large number of small detectors arranged in the core of the VVER-1000 reactor.
Benchmarking of Proton Transport in Super Monte Carlo Simulation Program
Authors: Wang Yongfeng , Li Gui , Song Jing , Zheng Huaqing , Sun Guangyao , Hao Lijuan , Wu Yican
Published: June 2014

The Monte Carlo (MC) method has been traditionally applied in nuclear design and analysis due to its capability of dealing with complicated geometries and multi-dimensional physics problems as well as obtaining accurate results. The Super Monte Carlo Simulation Program (SuperMC) is developed by FDS Team in China for fusion, fission, and other nuclear applications. The simulations of radiation transport, isotope burn-up, material activation, radiation dose, and biology damage could be performed using SuperMC. Complicated geometries and the whole physical process of various types of particles in broad energy scale can be well handled. Bi-directional automatic conversion between general CAD models and full-formed input files of SuperMC is supported by MCAM, which is a CAD/image-based automatic modeling program for neutronics and radiation transport simulation. Mixed visualization of dynamical 3D dataset and geometry model is supported by RVIS, which is a nuclear radiation virtual simulation and assessment system. Continuous-energy cross section data from hybrid evaluated nuclear data library HENDL are utilized to support simulation. Neutronic fixed source and critical design parameters calculates for reactors of complex geometry and material distribution based on the transport of neutron and photon have been achieved in our former version of SuperMC.

Recently, the proton transport has also been intergrated in SuperMC in the energy region up to 10 GeV. The physical processes considered for proton transport include electromagnetic processes and hadronic processes. The electromagnetic processes include ionization, multiple scattering, bremsstrahlung, and pair production processes. Public evaluated data from HENDL are used in some electromagnetic processes. In hadronic physics, the Bertini intra-nuclear cascade model with exitons, preequilibrium model, nucleus explosion model, fission model, and evaporation model are incorporated to treat the intermediate energy nuclear reactions for proton. Some other hadronic models are also being developed now.

The benchmarking of proton transport in SuperMC has been performed according to Accelerator Driven subcritical System (ADS) benchmark data and model released by IAEA from IAEA’s Cooperation Research Plan (CRP). The incident proton energy is 1.0 GeV. The neutron flux and energy deposition were calculated. The results simulated using SupeMC and FLUKA are in agreement within the statistical uncertainty inherent in the Monte Carlo method. The proton transport in SuperMC has also been applied in China Lead-Alloy cooled Reactor (CLEAR), which is designed by FDS Team for the calculation of spallation reaction in the target.
GPU-Accelerated Monte Carlo Electron Transport Methods: Development and Application for Radiation Dose Calculations Using Six GPU cards
Authors: Su Lin , Du Xining , Liu Tianyu , George Xu X.
Published: June 2014

An electron-photon coupled Monte Carlo code ARCHER ─ Accelerated Radiation-transport Computations in Heterogeneous EnviRonments ─ is being developed at Rensselaer Polytechnic Institute as a software testbed for emerging heterogeneous high performance computers that utilize accelerators such as GPUs. This paper presents the preliminary code development and the testing involving radiation dose related problems. In particular, the paper discusses the electron transport simulations using the class-II condensed history method. The considered electron energy ranges from a few hundreds of keV to 30 MeV. For photon part, photoelectric effect, Compton scattering and pair production were modeled. Voxelized geometry was supported. A serial CPU code was first written in C++. The code was then transplanted to the GPU using the CUDA C 5.0 standards. The hardware involved a desktop PC with an Intel Xeon X5660 CPU and six NVIDIA Tesla™ M2090 GPUs. The code was tested for a case of 20 MeV electron beam incident perpendicularly on a water-aluminum-water phantom. The depth and later dose profiles were found to agree with results obtained from well tested MC codes. Using six GPU cards, 6x106 electron histories were simulated within 2 seconds. In comparison, the same case running the EGSnrc and MCNPX codes required 1645 seconds and 9213 seconds, respectively. On-going work continues to test the code for different medical applications such as radiotherapy and brachytherapy.
Monte Carlo Application ToolKit (MCATK)
Authors: Adams Terry , Nolen Steve , Sweezy Jeremy , Zukaitis Anthony , Campbell Joann , Goorley Tim , Greene Simon , Aulwes Rob
Published: June 2014

The Monte Carlo Application ToolKit (MCATK) is a component-based software library designed to build specialized applications and to provide new functionality for existing general purpose Monte Carlo radiation transport codes. We will describe MCATK and its capabilities along with presenting some verification and validations results.
PRIZMA Status
Authors: Kandiev Y.Z. , Kashaeva E.A. , Khatuntsev K.E. , Kuropatenko E.S. , Lobanova L.V. , Lukin G.N. , Malakhov A.A. , Malyshkin G.N. , Modestov D.G. , Mukhamadiev R.F. , Orlov V.G. , Samarin S.I. , Serova E.V. , Spirina S.G. , Vakhonina T.V. , Voronina N.A. , Zatsepin O.V.
Published: June 2014

For more than thirty years the code PRIZMA has been used at RFNC-VNIITF for solving radiation transport problems with the Monte Carlo method. The code models the separate and coupled transport of neutrons, photons, electrons, positrons and ions in one-, two-, and three-dimensional geometry. For criticality calculations the code implements the method of generations with a constant number of fission sites in one generation. Now the code is extending its capabilities for nuclear reactor calculations. The paper describes the current status of the code and gives examples of its application to particle transport in nuclear reactors and other physical facilities.
Downstream plasma transport and metal ionization in a high-powered pulsed-plasma magnetron
Authors: Meng Liang , Yu He , Szott Matthew M. , McLain Jake T. , Ruzic David N.
Published: June 2014

Downstream plasma transport and ionization processes in a high-powered pulsed-plasma magnetron were studied. The temporal evolution and spatial distribution of electron density (ne) and temperature (Te) were characterized with a 3D scanning triple Langmuir probe. Plasma expanded from the racetrack region into the downstream region, where a high ne peak was formed some time into the pulse-off period. The expansion speed and directionality towards the substrate increased with a stronger magnetic field (B), largely as a consequence of a larger potential drop in the bulk plasma region during a relatively slower sheath formation. The fraction of Cu ions in the deposition flux was measured on the substrate using a gridded energy analyzer. It increased with higher pulse voltage. With increased B field from 200 to 800 Gauss above racetrack, ne increased but the Cu ion fraction decreased from 42% to 16%. A comprehensive model was built, including the diffusion of as-sputtered Cu flux, the Cu ionization in the entire plasma region using the mapped ne and Te data, and ion extraction efficiency based on the measured plasma potential (Vp) distribution. The calculations matched the measurements and indicated the main causes of lower Cu ion fractions in stronger B fields to be the lower Te and inefficient ion extraction in a larger pre-sheath potential.
Exponential time differencing methods with Chebyshev collocation for polymers confined by interacting surfaces
Authors: Liu Yi-Xin , Zhang Hong-Dong
Published: June 2014

We present a fast and accurate numerical method for the self-consistent field theory calculations of confined polymer systems. It introduces an exponential time differencing method (ETDRK4) based on Chebyshev collocation, which exhibits fourth-order accuracy in temporal domain and spectral accuracy in spatial domain, to solve the modified diffusion equations. Similar to the approach proposed by Hur et al. [Macromolecules 45, 2905 (2012)], non-periodic boundary conditions are adopted to model the confining walls with or without preferential interactions with polymer species, avoiding the use of surface field terms and the mask technique in a conventional approach. The performance of ETDRK4 is examined in comparison with the operator splitting methods with either Fourier collocation or Chebyshev collocation. Numerical experiments show that our exponential time differencing method is more efficient than the operator splitting methods in high accuracy calculations. This method has been applied to diblock copolymers confined by two parallel flat surfaces.
Accuracy of the centrifugal sudden approximation in the H + CHD3 → H2 + CD3 reaction
Authors: Zhang Zhaojun , Chen Jun , Liu Shu , Zhang Dong H.
Published: June 2014

The initial state selected time-dependent wave packet method has been extended to calculate the coupled-channel reaction probabilities with total angular momentum Jtot > 0 for the title reaction with seven degrees of freedom included. Fully converged integral cross sections were obtained for the ground and a number of vibrational excited initial states on a new potential energy surface recently constructed by this group using neural network fitting. As found from a previous study with the centrifugal sudden (CS) approximation, all these initial vibrational excitations investigated in this study enhance the reactivity considerably at a given collision energy, in particular the CH stretch excited state. The energy initially deposited in CH stretch motion is more effective than translational energy on promoting the reaction in the entire energy region, while for CH bending or CD3 umbrella excitations only at the high collision energy the vibrational energy becomes more effective. Our calculations also revealed that the accuracy of the CS approximation considerably deteriorates with the increase of Jtot, in particular on the threshold energy. The CS approximation underestimates the integral cross sections for all these initial states, albeit not very severely. In general, it works better at high collision energies and for vibrationally excited initial states, with the increase of integral cross section.
Prediction of porous dielectric line wiggling phenomenon with metallic hard mask: From simulation to experiment
Authors: Ducoté J. , Possémé N. , David T. , Darnon M. , Chevolleau T. , Guillermet M.
Published: June 2014

The patterning of narrow trenches in porous SiOCH with a metallic hard mask can lead to the undulation of the dielectric lines between the trenches, also called wiggling. This phenomenon is attributed to the relaxation of the residual stress of the highly compressive hard mask by deforming the mechanically weak porous dielectric. This work analyses the parameters (titanium nitride stress and thickness, lines width and height, and materials Young modulus) potentially responsible for dielectric lines undulations using finite element mechanical modeling. These simulations are experimentally validated.
Phonon mean free path spectrum and thermal conductivity for Si1−xGex nanowires
Authors: Xie Guofeng , Guo Yuan , Wei Xiaolin , Zhang Kaiwang , Sun Lizhong , Zhong Jianxin , Zhang Gang , Zhang Yong-Wei
Published: June 2014

We reformulate the linearized phonon Boltzmann transport equation by incorporating the direction-dependent phonon-boundary scattering, and based on this equation, we study the thermal conductivity of Si1−xGex nanowires and derive their phonon mean free path spectrum. Due to the severe suppression of high-frequency phonons by alloy scattering, the low frequency phonons in Si1−xGex nanowires have a much higher contribution to the thermal conductivity than pure silicon nanowires. We also find that Si1−xGex nanowires possess a stronger length-dependent, weaker diameter-dependent, and weaker surface roughness-dependent thermal conductivity than silicon nanowires. These findings are potentially useful for engineering Si1−xGex nanowires for thermoelectric applications.
Biofield-effect protein-sensor: Plasma functionalization of polyaniline, protein immobilization, and sensing mechanism
Authors: Cho Chae-Ryong , Lee Hyun-Uk , Ahn Kyun , Jeong Se-Young , Choi Jun-Hee , Kim Jinwoo , Cho Jiung
Published: June 2014

We report the fabrication of a biofield-effect protein-sensor (BioFEP) based on atmospheric-pressure plasma (AP) treatment of a conducting polyaniline (PANI) film. Successive H2 and O2 AP (OHAP) treatment generated dominant hydrophilic –OH and O=CO– functional groups on the PANI film surface, which served as strong binding sites to immobilize bovine serum albumin (BSA) protein molecules. The output current changes of the BioFEP as a function of BSA concentration were obtained. The resistance of the OHAP surface could be sensitively increased from 2.5 × 108 Ω to 2.0 × 1012 Ω with increasing BSA concentrations in the range of 0.025–4 μg/ml. The results suggest that the method is a simple and cost-effective tool to determine the concentration of BSA by measuring electrical resistance.
Characterization of plasma expansion dynamics in a high power diode with a carbon-fiber-aluminum cathode
Authors: Ju J.-C. , Liu L. , Cai D.
Published: June 2014

Thermal plasma expansion is characterised during the operation of a high power diode with an explosive emission carbon-fiber-aluminum cathode driven by a 250 kV, 150 ns accelerating pulse. It is found that a quasi-stationary state of plasma expansion is obtained during the main part of the accelerating pulse and the whole plasma expansion exhibits an “U”-shape velocity evolution. A theoretical model describing the dynamics of plasma expansion is developed, which indicates that the plasma expansion velocity is determined by equilibrium between the diode current density and plasma thermal electron current density.
3C-SiC nanocrystals/TiO2 nanotube heterostructures with enhanced photocatalytic performance
Authors: Zhang J. , Liu L. Z. , Yang L. , Gan Z. X. , Wu X. L. , Chu Paul K.
Published: June 2014

p-type ultrathin 3C-SiC nanocrystals are coated on heat-treated n-type TiO2 nanotube arrays formed by electrochemical etching of Ti sheets to produce heterostructured photocatalysts. Depending on the amounts of 3C-SiC nanocrystals on the TiO2 nanotubes, photocatalytic degradation of organic species can be enhanced. The intrinsic electric field induced by the heterojunction promotes separation of the photoexcited electrons-holes in both the TiO2 nanotubes and 3C-SiC nanocrystals. Hence, holes can more effectively travel to the surface of 3C-SiC nanocrystals and there are more electrons on the surface of TiO2 nanotubes consequently forming more •O2− and •OH species to degrade organic molecules.
Microscopic mechanisms of graphene electrolytic delamination from metal substrates
Authors: Fisichella G. , Di Franco S. , Roccaforte F. , Ravesi S. , Giannazzo F.
Published: June 2014

In this paper, hydrogen bubbling delamination of graphene (Gr) from copper using a strong electrolyte (KOH) water solution was performed, focusing on the effect of the KOH concentration (CKOH) on the Gr delamination rate. A factor of ∼10 decrease in the time required for the complete Gr delamination from Cu cathodes with the same geometry was found increasing CKOH from ∼0.05 M to ∼0.60 M. After transfer of the separated Gr membranes to SiO2 substrates by a highly reproducible thermo-compression printing method, an accurate atomic force microscopy investigation of the changes in Gr morphology as a function of CKOH was performed. Supported by these analyses, a microscopic model of the delamination process has been proposed, where a key role is played by graphene wrinkles acting as nucleation sites for H2 bubbles at the cathode perimeter. With this approach, the H2 supersaturation generated at the electrode for different electrolyte concentrations was estimated and the inverse dependence of td on CKOH was quantitatively explained. Although developed in the case of Cu, this analysis is generally valid and can be applied to describe the electrolytic delamination of graphene from several metal substrates.
The topological insulator in a fractal space
Authors: Song Zhi-Gang , Zhang Yan-Yang , Li Shu-Shen
Published: June 2014

We investigate the band structures and transport properties of a two-dimensional model of topological insulator, with a fractal edge or a fractal bulk. A fractal edge does not affect the robust transport even when the fractal pattern has reached the resolution of the atomic-scale, because the bulk is still well insulating against backscattering. On the other hand, a fractal bulk can support the robust transport only when the fractal resolution is much larger than a critical size. Smaller resolution of bulk fractal pattern will lead to remarkable backscattering and localization, due to strong couplings of opposite edge states on narrow sub-edges which appear almost everywhere in the fractal bulk.
Electric-field tunable magnetic-field-sensor based on CoFeB/MgO magnetic tunnel junction
Authors: Naik V. B. , Meng H. , Liu R. S. , Luo P. , Yap S. , Han G. C.
Published: June 2014

We demonstrate an electric-field-tunable magnetic-field-sensor based on CoFeB/MgO magnetic tunnel junction with interfacial perpendicular magnetic anisotropy (PMA). From the dynamic lock-in measurements, we show that an applied electric-field induces a peak in sensor voltage (VSENSOR) around the free layer magnetization switching regime in response to external a.c. magnetic field. Detailed measurements of VSENSOR as functions of free layer thickness, a.c. magnetic field amplitude and frequency reveal that the sensitivity of the sensor can be up to 80.8 V cm−1 Oe−1 under −0.5 V, which can be controlled by the strength and polarity of the applied electric-field via electric-field controlled PMA. We discuss the origin of our observations based on the oscillations in the tunnel magnetoresistance, and this may trigger the development of magnetoelectrically controlled magnetic-field-sensor based on magnetic tunnel junctions.
An electrostatic microwell–based biochip for phytoplanktonic cell trapping
Authors: Kuntanawat Panwong , Ruenin Jirapat , Phatthanakun Rungrueang , Kunhorm Phongsakorn , Surareungchai Werasak , Sukprasong Sompong , Chomnawang Nimit
Published: June 2014

A simple microwell-based microfluidic chip for microalgal cells trapping was fabricated. An electrostatic cell trapping mechanism, enabled by a positively charged glass surface, was used. The chip was capable of capturing multiple algal cell types. In the case of filamentous Spirulina platensis, we observed single filament occupancy of up to ∼30% available wells, as high as some previously proposed methods. Captured filaments were not of any preferential size, suggesting well randomized cell trapping. It was found that the electrostatic attraction did not affect the cell growth. Total replacement of liquid inside the wells could be achieved by pumping new solutions via the inlet, making single cell experiments in controlled chemical conditions possible. After the top layer of the chip was removed, cells in the wells could be simply transferred using a micropipette, turning the chip into a platform for strain selection.
Ordinary and extraordinary dielectric functions of rutile SnO2 up to 20 eV
Authors: Feneberg Martin , Lidig Christian , Lange Karsten , Goldhahn Rüdiger , Neumann Maciej D. , Esser Norbert , Bierwagen Oliver , White Mark E. , Tsai Min Y. , Speck James S.
Published: June 2014

Spectroscopic ellipsometry at room temperature is applied in order to determine the ordinary (ε⊥) and extraordinary (ε∥) dielectric functions (DFs) of rutile SnO2 corresponding to electric field (E) polarization perpendicular (E⊥c) and parallel (E∥c) to the optical axis (c), respectively. Strong anisotropic behavior is found for the full spectral range from 0.5 up to 20 eV. The onsets of strong absorption are found at 4.28 eV and 5.42 eV for E⊥c and E∥c, respectively. A dipole-forbidden band gap at (3.59 ± 0.2) eV at room temperature is found by line shape fits to the imaginary parts of the DFs. Further high-energy transitions are resolved. Their accurate energy values are obtained by fitting the second derivatives of the DFs. Comparison to published DFs calculated by ab-initio theory demonstrates that the electron-hole interaction in SnO2 is strong and has to be included for interpretation.
The effect of mix on capsule yields as a function of shell thickness and gas fill
Authors: Bradley P. A.
Published: June 2014

An investigation of direct drive capsules with different shell thicknesses and gas fills was conducted to examine the amount of shock induced (Richtmyer-Meshkov) mix versus Rayleigh-Taylor mix from deceleration of the implosion. The RAGE (Eulerian) code with a turbulent mix model was used to model these capsules for neutron yields along with time-dependent mix amounts. The amount of Richtmyer-Meshkov induced mix from the shock breaking out of the shell is about 0.1 μg (0.15 μm of shell material), while the Rayleigh-Taylor mix is of order 1 μg and determines the mixed simulation yield. The simulations were able to calculate a yield over mix (YOM) ratio (experiment/mix simulation) between 0.5 and 1.0 for capsules with shell thicknesses ranging from 7.5 to 20 μm and with gas fills between 3.8 and 20 atm of D2 or DT. The simulated burn averaged Tion values typically lie with 0.5 keV of the data, which is within the measurement error. For capsules with shell thicknesses >25 μm, the YOM values drop to 0.10 ± 0.05, suggesting that some unmodeled effect needs to be accounted for in the thickest capsules.
A semi-analytic power balance model for low (L) to high (H) mode transition power threshold
Authors: Singh R. , Jhang Hogun , Kaw P. K. , Diamond P. H. , Nordman H. , Bourdelle C. , Loarte A.
Published: June 2014

We present a semi-analytic model for low (L) to high (H) mode transition power threshold (Pth). Two main assumptions are made in our study. First, high poloidal mode number drift resistive ballooning modes (high-m DRBM) are assumed to be the dominant turbulence driver in a narrow edge region near to last closed flux surface. Second, the pre-transition edge profile and turbulent diffusivity at the narrow edge region pertain to turbulent equipartition. An edge power balance relation is derived by calculating the dissipated power flux through both turbulent conduction and convection, and radiation in the edge region. Pth is obtained by imposing the turbulence quench rule due to sheared E × B rotation. Evaluation of Pth shows a good agreement with experimental results in existing machines. Increase of Pth at low density (i.e., the existence of roll-over density in Pth vs. density) is shown to originate from the longer scale length of the density profile than that of the temperature profile.
Global coherence of dust density waves
Authors: Killer Carsten , Melzer André
Published: June 2014

The coherence of self-excited three-dimensional dust density waves has been experimentally investigated by comparing global and local wave properties. For that purpose, three-dimensional dust clouds have been confined in a radio frequency plasma with thermophoretic levitation. Global wave properties have been measured from the line-of-sight integrated dust density obtained from homogenous light extinction measurements. Local wave properties have been obtained from thin, two-dimensional illuminated laser slices of the cloud. By correlating the simultaneous global and local wave properties, the spatial coherence of the waves has been determined. We find that linear waves with small amplitudes tend to be fragmented, featuring an incoherent wave field. Strongly non-linear waves with large amplitudes, however, feature a strong spatial coherence throughout the dust cloud, indicating a high level of synchronization.
Note: Active optical detection of cloud from a balloon platform
Authors: Harrison R. G. , Nicoll K. A.
Published: June 2014

A disposable backscatter instrument is described for optical detection of cloud in the atmosphere from a balloon-carried platform. It uses an ultra-bright light emitting diode (LED) illumination source with a photodiode detector. Scattering of the LED light by cloud droplets generates a small optical signal which is separated from background light fluctuations using a lock-in technique. The signal to noise obtained permits cloud detection using the scattered LED light, even in daytime. The response is interpreted in terms of the equivalent visual range within the cloud. The device is lightweight (150 g) and low power (∼30 mA), for use alongside a conventional meteorological radiosonde.
Deformation of red blood cells using acoustic radiation forces
Authors: Mishra Puja , Hill Martyn , Glynne-Jones Peter
Published: June 2014

Acoustic radiation forces have been used to manipulate cells and bacteria in a number of recent microfluidic applications. The net force on a cell has been subject to careful investigation over a number of decades. We demonstrate that the radiation forces also act to deform cells. An ultrasonic standing wave field is created in a 0.1 mm glass capillary at a frequency of 7.9 MHz. Using osmotically swollen red-blood cells, we show observable deformations up to an aspect ratio of 1.35, comparable to deformations created by optical tweezing. In contrast to optical technologies, ultrasonic devices are potentially capable of deforming thousands of cells simultaneously. We create a finite element model that includes both the acoustic environment of the cell, and a model of the cell membrane subject to forces resulting from the non-linear aspects of the acoustic field. The model is found to give reasonable agreement with the experimental results, and shows that the deformation is the result of variation in an acoustic force that is directed outwards at all points on the cell membrane. We foresee applications in diagnostic devices, and in the possibility of mechanically stimulating cells to promote differentiation and physiological effects.
Effects of film growth modes on light trapping in silicon thin film solar cells
Authors: Wiesendanger S. , Bischoff T. , Jovanov V. , Knipp D. , Burger S. , Lederer F. , Rockstuhl C.
Published: June 2014

In this work, the impact of two different growth modes on the efficiency of an amorphous thin film solar cell comprising randomly textured interfaces is investigated. The two modes are the commonly used conformal growth which assumes identical textured interfaces and the isotropic growth, in which deposited material grows in the direction of the local surface normal. In the latter, the texture's morphology can change significantly. The rivalling impact of these two growth modes on the solar cell absorption is not yet fully understood. Here, we show that the efficiency of a solar cell crucially depends on the growth mode. In different size regimes, they may outperform each other with regard to efficiency by almost 15%. The insights gained by this study will guide experimentalists in the future in selecting the optimised growth mode.
Surfacing behaviour and ecology of the marsupial mole (Notoryctes typhlops) at Uluru-Kata Tjuta National Park
Authors: Bennison Kerrie , Clayton Jim , Godfree Robert , Pavey Chris , Wilson Melinda
Published: June 2014

Little is known about the distribution and ecology of the cryptic and unique marsupial mole. In this paper we report on the habitat preferences and surfacing behaviour of marsupial moles on the basis of surface sign surveys conducted in Uluru-Kata Tjuta National Park and Ayers Rock Resort over a 12-month period by Uluru-Kata Tjuta National Park staff and traditional owners. A key aim of the study was to assess the potential viability of using surface sign as a rapid, non-intrusive alternative to traditional survey methods. We found that surfacing occurred widely across the study area, but that it was highly variable both across survey sites and over time. Significant relationships existed between surface sign counts and environmental variables, including fire age, timing of significant rainfall events, presence of infrastructure and the cumulative rainfall received in the preceding three months. We concluded that the use of marsupial mole surface sign is likely to be a useful method for monitoring the distribution, abundance and habitat requirements of this cryptic species.
Review on shape formation in epidermal pavement cells of the Arabidopsis leaf
Authors: Jacques Eveline , Verbelen Jean-Pierre , Vissenberg Kris
Published: June 2014

Epidermal pavement cells appear with a fascinating irregular wavy shape in the Arabidopsis thaliana leaf. This review addresses the questions of why this particular shape is produced during leaf development and how this is accomplished. To answer the first question most probably waviness offers some biomechanical benefits over other organisations. Different positions of lobe-formation are therefore explored and discussed. At the moment, however, no hard evidence that favours any one morphology is available. The latter question comprises the biomechanical accomplishment of shape and refers to the cell wall and cytoskeletal involvement herein. A current model for pavement cell development is discussed but remaining questions and pitfalls are put forward. Moreover, an overview of the genetic and biochemical regulatory pathways that are described up to date in the literature is presented.
Health actions prompted by health assessments for people with intellectual disability exceed actions recorded in general practitioners' records
Authors: Byrne Jacqueline H. , Ware Robert S. , Lennox Nicholas G.
Published: June 2014

People with intellectual disability experience inadequate health care and have unmet health needs that can go unidentified or be poorly managed. Health assessments have been shown to significantly increase short-term clinical activity for people with intellectual disability. The aim of this study was to more accurately quantify the effect of health assessments for people with intellectual disability by comparing health actions recorded in health assessment booklets to actions recorded in general practitioners’ (GPs) records in the 12-month period following the health assessment. Participants were people with intellectual disability who had received a Comprehensive Health Assessment Program (CHAP), living in the community. The CHAP is a health assessment that is demonstrated to significantly increase health actions, compared with usual care, for people with intellectual disability. Data collected from three randomised controlled trials conducted in South-East Queensland, Australia, from 2000 to 2010 were pooled and analysed. The health assessment booklet contained significantly more information on health actions than GPs’ records. Notably, hearing tests (risk ratio (RR) = 5.9; 95% confidence interval (CI) = 4.7–7.4), breast checks (RR = 3.9; 95% CI = 2.7–5.7), and skin examinations (RR = 7.9; 95% CI = 5.9–10.7) were more likely to be recorded in the CHAP booklet. Health assessments increase health actions for people with intellectual disability to a significantly greater extent than previously demonstrated.
Requirements and limits for life in the context of exoplanets
Authors: McKay Christopher P.
Published: June 2014

Significance

Our understanding of life on exoplanets and exomoons must be based on what we know about life on Earth. Liquid water is the common ecological requirement for Earth life. Temperature on an exoplanet is the first parameter to consider both because of its influence on liquid water and because it can be directly estimated from orbital and climate models of exoplanetary systems. Life needs some water, but deserts show that even a little can be enough. Only a small amount of light from the central star is required to provide for photosynthesis. Some nitrogen must be present for life and the presence of oxygen would be a good indicator of photosynthesis and possibly complex life.