Software compensation of eddy current fields in multislice high order dynamic shimming
Sengupta, Saikat; Avison, Malcolm J; Gore, John C.; Welch, E. Brian
2011-01-01
Dynamic B0 shimming (DS) can produce better field homogeneity than static global shimming by dynamically updating slicewise shim values in a multislice acquisition. The performance of DS however is limited by eddy current fields produced by the switching of 2nd and 3rd order unshielded shims. In this work, we present a novel method of eddy field compensation (EFC) applied to higher order shim induced eddy current fields in multislice DS. This method does not require shim shielding, extra hard...
Software compensation of eddy current fields in multislice high order dynamic shimming
Sengupta, Saikat; Avison, Malcolm J.; Gore, John C.; Welch, E. Brian
2011-01-01
Dynamic B0 shimming (DS) can produce better field homogeneity than static global shimming by dynamically updating slicewise shim values in a multislice acquisition. The performance of DS however is limited by eddy current fields produced by the switching of 2nd and 3rd order unshielded shims. In this work, we present a novel method of eddy field compensation (EFC) applied to higher order shim induced eddy current fields in multislice DS. This method does not require shim shielding, extra hardware for eddy current compensation or subject specific prescanning. The interactions between shim harmonics are modeled assuming steady state of the medium and long time constant, cross and self term eddy fields in a DS experiment and ‘correction factors’ characterizing the entire set of shim interactions are derived. The correction factors for a given time between shim switches are shown to be invariable with object scanned, shim switching pattern and actual shim values, allowing for their generalized prospective use. Phantom and human head, 2nd and 3rd order DS experiments performed without any hardware eddy current compensation using the technique show large reductions in field gradients and offsets leading to significant improvements in image quality. This method holds promise as an alternative to expensive hardware based eddy current compensation required in 2nd and 3rd order DS. PMID:21458339
Automatic Palmprint Identification based on High Order Zernike Moment
Directory of Open Access Journals (Sweden)
R. Gayathri
2012-01-01
Full Text Available Problem statement: Hand geometry contains relatively invariant features of an individual. Palmprint recognition is an efficient biometric solution for authentication system. The existence of several hand-based authentication commercial systems indicates the effectiveness of this type of biometric. Approach: We proposed a palmprint verification system using high order Zernike moment that was robust to rotation, translation and occlusion. Zernike moment was an efficient algorithm for representing the shape features of an image. The design consists of feature extraction and matching of image using high order Zernike moment. Zernike moments at high orders was calculated from the image and the image was classified using K-Nearest Neighborhood (KNN. The reason for using Zernike moment was that it was the best algorithm due to its orthogonality and rotation invariance property. Results and Conclusion: Computational cost can be reduced by detecting the common term of Zernike moment. Experiments and classifications have been performed using Hong Kong PolyU palm print database with 125 individuals left hand palm images; every person has 5 samples, totaling up to 625. We then get every persons palm images as a template (totaling 125. The remaining 500 are used as the training samples. The proposed palmprint authentication system achieves a recognition accuracy of 98% and interesting working point with False Acceptance Rate (FAR of = 1.062% and False Rejection Rate (FRR of = 0%. Experimental evaluation demonstrates the efficient recognition performance of the proposed algorithm compared with conventional palmprint recognition algorithms.
International Nuclear Information System (INIS)
A function minimising method embodied in an available standard computer library routine VA04A applied to the normally tedious business of magnet shimming has been shown to hold great promise in saving time and effort. Application of the method to the overall problem of magnet design will make the process almost automatic. (UK)
Gradient shimming based on regularized estimation for B0-field and shim functions.
Song, Kan; Bao, Qingjia; Chen, Fang; Huang, Chongyang; Feng, Jiwen; Liu, Chaoyang
2016-07-01
Mapping B0-field and shim functions spatially is a crucial step in the gradient shimming. The conventional estimation method used in the phase difference imaging technique takes no account for noise and T2(∗) effects, and is prone to create noisy and distorted field maps. This paper describes a new gradient shimming based on the regularized estimation for B0-field and shim functions. Based on a statistical model, the B0-field and shim function maps are estimated by a Penalized Maximum Likelihood method that minimizes two regularized least-squares cost functions, respectively. The first cost function of B0-field exploits the two facts that the noise in the phase difference measurements is Gaussian and the B0-field maps tend to be smooth. And the other one adds an additional fact that each shim function corresponds to a given spherical harmonic of the magnetic field. Significant improvements in the quality of field mapping and in the final shimming results are demonstrated through computer simulations as well as experiments, especially when the magnetic field homogeneity is poor. PMID:27131476
A new gradient shimming method based on undistorted field map of B0 inhomogeneity
Bao, Qingjia; Chen, Fang; Chen, Li; Song, Kan; Liu, Zao; Liu, Chaoyang
2016-04-01
Most existing gradient shimming methods for NMR spectrometers estimate field maps that resolve B0 inhomogeneity spatially from dual gradient-echo (GRE) images acquired at different echo times. However, the distortions induced by B0 inhomogeneity that always exists in the GRE images can result in estimated field maps that are distorted in both geometry and intensity, leading to inaccurate shimming. This work proposes a new gradient shimming method based on undistorted field map of B0 inhomogeneity obtained by a more accurate field map estimation technique. Compared to the traditional field map estimation method, this new method exploits both the positive and negative polarities of the frequency encoded gradients to eliminate the distortions caused by B0 inhomogeneity in the field map. Next, the corresponding automatic post-data procedure is introduced to obtain undistorted B0 field map based on knowledge of the invariant characteristics of the B0 inhomogeneity and the variant polarity of the encoded gradient. The experimental results on both simulated and real gradient shimming tests demonstrate the high performance of this new method.
AA, shims and washers on quadrupole ends
CERN PhotoLab
1981-01-01
Due to the fact that much of the field of the quadrupoles was outside the iron (in particular with the wide quadrupoles) and that thus the fields of quadrupoles and bending magnets interacted, the lattice properties of the AA could not be predicted with the required accuracy. After a first running period in 1980, during which detailed measurements were made with proton test beams, corrections to the quadrupoles were made in 1981, in the form of laminated shims at the ends of the poles, and with steel washers. With the latter ones, further refinements were made in an iterative procedure with measurements on the circulating beam. This eventually resulted, amongst other things, in a very low chromaticity, with the Q-values being constant to within +- 0.001 over the total momentum range of 6 %. Here we see the shims and washers on a narrow qudrupole (QFN, QDN). See also 8103203, 8103204, 8103205, 8103206.
Dynamic Shimming of the Human Brain at 7 Tesla
Juchem, Christoph; Nixon, Terence W.; Diduch, Piotr; Rothman, Douglas L.; Starewicz, Piotr; de Graaf, Robin A.
2010-01-01
Dynamic shim updating (DSU) of the zero- to second-order spherical harmonic field terms has previously been shown to improve the magnetic field homogeneity in the human brain at 4 Tesla. The increased magnetic field inhomogeneity at 7 Tesla can benefit from inclusion of third-order shims during DSU. However, pulsed higher-order shims can generate a multitude of temporally varying magnetic fields arising from eddy-currents that can strongly degrade the magnetic field homogeneity.
SHIMS -- A Spatial Heterodyne Interferometer for Methane Sounding Project
National Aeronautics and Space Administration — This project develops the Spatial Heterodyne Interferometer for Methane Sounding (SHIMS), a lightweight, compact, robust spectrometer system for remote sensing of...
Phase error reduction in superconductive undulators using induction shimming
International Nuclear Information System (INIS)
As shown in a first proof of principle experiment, induction shimming can constitute a simple and efficient method of increasing the field quality of superconductive undulators. Although previous measurements on a single undulator half were successful in giving a qualitative understanding on hysteresis in the shim coils, it was found that the measurement setup needs improvement for meaningful calculations of the phase error reduction. Presented here are the first results on phase error reduction with induction shimming, using a measurement setup with improved accuracy. Theoretical results on the coupling between shim coils, important for the function of the shim system and for an extension to full length undulators, are also presented in this contribution.
Effect of Shim Arm Depletion in the NBSR
Energy Technology Data Exchange (ETDEWEB)
Hanson A. H.; Brown N.; Diamond, D.J.
2013-02-22
The cadmium shim arms in the NBSR undergo burnup during reactor operation and hence, require periodic replacement. Presently, the shim arms are replaced after every 25 cycles to guarantee they can maintain sufficient shutdown margin. Two prior reports document the expected change in the 113Cd distribution because of the shim arm depletion. One set of calculations was for the present high-enriched uranium fuel and the other for the low-enriched uranium fuel when it was in the COMP7 configuration (7 inch fuel length vs. the present 11 inch length). The depleted 113Cd distributions calculated for these cores were applied to the current design for an equilibrium low-enriched uranium core. This report details the predicted effects, if any, of shim arm depletion on the shim arm worth, the shutdown margin, power distributions and kinetics parameters.
Enabling Object Storage via shims for Grid Middleware
Skipsey, Samuel Cadellin; Dewhurst, Alastair; Britton, David; Roy, Gareth; Crooks, David
2015-01-01
The Object Store model has quickly become the basis of most commercially successful mass storage infrastructure, backing so-called "Cloud" storage such as Amazon S3, but also underlying the implementation of most parallel distributed storage systems. Many of the assumptions in Object Store design are similar, but not identical, to concepts in the design of Grid Storage Elements, although the requirement for "POSIX-like" filesystem structures on top of SEs makes the disjunction seem larger. As modern Object Stores provide many features that most Grid SEs do not (block level striping, parallel access, automatic file repair, etc.), it is of interest to see how easily we can provide interfaces to typical Object Stores via plugins and shims for Grid tools, and how well experiments can adapt their data models to them. We present evaluation of, and first-deployment experiences with, (for example) Xrootd-Ceph interfaces for direct object-store access, as part of an initiative within GridPP\\cite{GridPP} hosted at RAL....
Dynamic shim updating (DSU) for multislice signal acquisition.
de Graaf, Robin A; Brown, Peter B; McIntyre, Scott; Rothman, Douglas L; Nixon, Terence W
2003-03-01
Dynamic shim updating (DSU) is a technique for achieving optimal magnetic field homogeneity over extended volumes by dynamically updating an optimal shim setting for each individual slice in a multislice acquisition protocol. Here the practical implementation of DSU using all first- and second-order shims is described. In particular, the hardware modifications and software requirements are demonstrated. Furthermore, the temporal effects of dynamically switching shim currents are investigated and a Z(2)-to-Z(0) compensation unit is described and implemented to counteract the temporal Z(0) variations following a change in the Z(2) shim current. The optimal shim settings for all slices are determined with a quantitative and user-independent, multislice phase-mapping sequence. The performance of DSU is evaluated from multislice phase maps and spectroscopic images acquired on rat brain in vivo. DSU improved the magnetic field homogeneity over all spatial slices, with a more pronounced effect on the slices positioned away from the magnet isocenter, thereby making the magnetic field homogeneity highly uniform over an extended volume. PMID:12594742
High-order harmonic generation
Czech Academy of Sciences Publication Activity Database
Jakubczak, Krzysztof
Rijeka: InTech, 2010 - (Duarte, F.), s. 61-82 ISBN 978-953-307-405-4 R&D Projects: GA AV ČR KAN300100702; GA ČR GA202/08/1734; GA ČR GC202/07/J008; GA MŠk 7E09113 Grant ostatní: AV ČR(CZ) M100100911 Institutional research plan: CEZ:AV0Z10100523 Keywords : high-order harmonic (HHG) * x-ray * laser * gaseous media * multilayer mirror Subject RIV: BH - Optics, Masers, Lasers http://www.intechopen.com/articles/show/title/high-order-harmonic-generation
Iwasa, Yukikazu; Hahn, Seungyong; Voccio, John; Keun Park, Dong; Kim, Youngjae; Bascuñán, Juan
2013-01-01
Design, fabrication, and test results of a type persistent-mode high-temperature superconductor (HTS) shim coil are presented. A prototype Z1 rectangle-loop shim, cut from 46-mm wide Y-Ba-Cu-O tape manufactured by AMSC, was fabricated and tested at 77 K. The HTS shim, much thinner than the conventional NbTi shim, is placed inside the main magnet and immune to its diamagnetic wall effects. Combined with the >12-T and >10-K operation capability, the HTS shim offers a versatile design option for nuclear magnetic resonance (NMR) magnets, liquid-helium-free as well as conventional, and is particularly attractive in the next generation NMR magnets. PMID:23983275
The use of iron shims to reduce the toroidal field ripple in Tokamaks
International Nuclear Information System (INIS)
A study was performed to investigate the use of laminated ferromagnetic material, iron shims, to reduce the toroidal field, TF, ripple in Tokamaks. Fixed geometry shims can reduce the TF ripple and will behave linearly for Low Field Tokamaks with central fields under 2 Tesla. For High Field Tokamaks with central fields under 6 Tesla, fixed geometry shims can reduce the TF ripple but will have some non-linear behavior. Variable geometry shims can reduce the field ripple significantly with complete linearity for High Field Tokamaks
Kind, J.; Thiele, C. M.
2015-11-01
In order to enable monitoring of rapidly occurring reactions Wagner et al. recently presented a simple scheme for 1D NMR experiments with continuous data acquisition, without inter-scan delays, using a spatially-selective and frequency-shifted excitation approach (Wagner et al., 2013). This scheme allows acquisition of proton spectra with temporal resolutions on the millisecond timescale. Such high temporal resolutions are desired in the case of reaction monitoring using stopped flow setups. In regular 1H NMR-spectra without spatial selection the line width increases for a given shim setting with changes in sample volume, susceptibility, convection and temperature or concentration gradients due to the disturbance of magnetic field homogeneity. Concerning reaction monitoring this is unfortunate as shimming prior to acquisition becomes necessary to obtain narrow signals after injection of a reactant into an NMR sample. Even automatic shim routines may last up to minutes. Thus fast reactions can hardly be monitored online without large hardware dead times in a single stopped flow experiment. This problem is reduced in the spatially-selective and frequency-shifted continuous NMR experiment as magnetic field inhomogeneties are less pronounced and negative effects on the obtained line shapes are reduced as pointed out by Bax and Freeman (1980) [2] and demonstrated by Wagner et al. (2013). Here we present the utilization of this technique for observation of reactions in small molecule systems in which chemical conversion and longitudinal relaxation occur on the same timescale. By means of the alkaline ethyl acetate hydrolysis, a stoichiometric reaction, we show advantages of spatially-selective excitation on both temporal resolution and line shapes in stopped flow experiments. Results are compared to data obtained by non-selective small angle excitation experiments.
Passive shimming of a superconducting magnet using the L1-norm regularized least square algorithm
Kong, Xia; Zhu, Minhua; Xia, Ling; Wang, Qiuliang; Li, Yi; Zhu, Xuchen; Liu, Feng; Crozier, Stuart
2016-02-01
The uniformity of the static magnetic field B0 is of prime importance for an MRI system. The passive shimming technique is usually applied to improve the uniformity of the static field by optimizing the layout of a series of steel shims. The steel pieces are fixed in the drawers in the inner bore of the superconducting magnet, and produce a magnetizing field in the imaging region to compensate for the inhomogeneity of the B0 field. In practice, the total mass of steel used for shimming should be minimized, in addition to the field uniformity requirement. This is because the presence of steel shims may introduce a thermal stability problem. The passive shimming procedure is typically realized using the linear programming (LP) method. The LP approach however, is generally slow and also has difficulty balancing the field quality and the total amount of steel for shimming. In this paper, we have developed a new algorithm that is better able to balance the dual constraints of field uniformity and the total mass of the shims. The least square method is used to minimize the magnetic field inhomogeneity over the imaging surface with the total mass of steel being controlled by an L1-norm based constraint. The proposed algorithm has been tested with practical field data, and the results show that, with similar computational cost and mass of shim material, the new algorithm achieves superior field uniformity (43% better for the test case) compared with the conventional linear programming approach.
High order limit in bunch compressor
International Nuclear Information System (INIS)
This paper studies the high order effect in bunch compressing. There exists the limit of high order effect which is from RF accelerating field and bunch compressor, the bunch length obtained from high order theory is longer than that from linear theory, the initial uniform distribution bunch is easier to compress than the initial Gaussian distribution. Finally, a numerical simulation has been carried out, and the results agree with the theory well. (authors)
High-Order Hamilton's Principle and the Hamilton's Principle of High-Order Lagrangian Function
Institute of Scientific and Technical Information of China (English)
ZHANG Ming-Jiang; ZHAO Hong-Xia; FANG Jian-Hui; MA Shan-Jun; LU Kai
2008-01-01
In this paper, based on the theorem of the high-order velocity energy, integration and variation principle, the high-order Hamilton's principle of general holonomic systems is given. Then, three-order Lagrangian equations and four-order Lagrangian equations are obtained from the high-order Hamilton's principle. Finally, the Hamilton's principle of high-order Lagrangian function is given.
High-order polarization vortex spatial solitons
International Nuclear Information System (INIS)
We investigate the formation of high-order polarization vortex spatial solitons. The high-order polarization vortex solitons have novel polarization states which are different from fundamental polarization vortex solitons and have rotational symmetry only in intensity. It is proved that the polarization vortex solitons cannot carry vortex phase. The existence domain and dynamical characteristic of these high-order polarization vortex solitons in Bessel optical lattices are discussed in detail. -- Highlights: ► It is proved that the polarization vortex solitons cannot carry vortex phase. ► Polarization vortex solitons formed by cylindrical vector beams must be first-order solitons. ► New high-order polarization vortex solitons are investigated in Bessel optical lattices.
High order Poisson Solver for unbounded flows
DEFF Research Database (Denmark)
Hejlesen, Mads Mølholm; Rasmussen, Johannes Tophøj; Chatelain, Philippe;
2015-01-01
This paper presents a high order method for solving the unbounded Poisson equation on a regular mesh using a Green’s function solution. The high order convergence was achieved by formulating mollified integration kernels, that were derived from a filter regularisation of the solution field. The...... performing the differentiation as a multiplication of the Fourier coefficients. In this way, differential operators such as the divergence or curl of the solution field could be solved to the same high order convergence without additional computational effort. The method was applied and validated using the...... equations of fluid mechanics as an example, but can be used in many physical problems to solve the Poisson equation on a rectangular unbounded domain. For the two-dimensional case we propose an infinitely smooth test function which allows for arbitrary high order convergence. Using Gaussian smoothing as...
MULTISYMPLECTIC COMPOSITION INTEGRATORS OF HIGH ORDER
Institute of Scientific and Technical Information of China (English)
Jing-bo Chen; Meng-zhao Qin
2003-01-01
A composition method for constructing high order multisymplectic integrators is pre-sented in this paper. The basic idea is to apply composition method to both the time andthe space directions. We also obtain a general formula for composition method.
Dynamic simulation and study of Mechanical Shim (MSHIM) core control strategy for AP1000 reactor
International Nuclear Information System (INIS)
Highlights: • A reactor core fast simulation program RCFSP is developed for AP1000. • A nodal core model and the MSHIM control strategy are implemented in RCFSP. • Load follow results for the original and revised MSHIM strategies are given. • Parameter sensitivity analysis and optimization of MSHIM control system are performed. - Abstract: The advanced Mechanical Shim (MSHIM) core control strategy is implemented in the AP1000 reactor by a digital rod control system. This control system comprises of two separate rod controllers that automatically control the core reactivity and axial power distribution using the gray and black M control banks and the axial offset (AO) control bank respectively. It has been demonstrated that the MSHIM control system can provide superior reactor control capabilities via automatic rod control only, which needs it to take more burdens than many other traditional core control systems during load change transients. This paper presents the dynamic simulation, and the parameter sensitivity analysis and optimization of the MSHIM control system for AP1000 reactor. A nodal core model is used to describe the dynamic behavior of the reactor core first. Then the nodal model and the original and revised MSHIM strategies are implemented in the AP1000 reactor to develop a fast simulation program in MATLAB/SIMULINK. Based on the simulation program, the MSHIM load follow and load regulation operations are simulated, the results of which demonstrate that the core reactivity and axial power distribution can be well-controlled via automatic rod control only. To show the effects of key factors on the control system behavior, the MSHIM load follow simulations with different control parameter values are performed. According to the simulation results and subsequent quantitative analysis, the mechanisms by which the key factors affect the control system behavior are illustrated and the optimum numerical ranges of these parameters are obtained. These
High-order beam optics - an overview
International Nuclear Information System (INIS)
Beam-transport codes have been around for as long as thirty years and high order codes, second-order at least, for close to twenty years. Before this period of design-code development, there was considerable high-order treatment, but it was almost entirely analytical. History has a way of repeating itself, and the current excitement in the field of high-order optics is based on the application of Lie algebra and the so-called differential algebra to beam-transport codes, both of which are highly analytical in foundation. The author will describe some of the main design tools available today, giving a little of their history, and will conclude by trying to convey some of the excitement in the field through a brief description of Lie and differential algebra. 30 refs., 7 figs., 1 tab
Stages: sub-Fourier dynamic shim updating using nonlinear magnetic field phase preparation.
Witschey, Walter R T; Littin, Sebastian; Cocosco, Chris A; Gallichan, Daniel; Schultz, Gerrit; Weber, Hans; Welz, Anna; Hennig, Jürgen; Zaitsev, Maxim
2014-01-01
Heterogeneity of the static magnetic field in magnetic resonance imaging may cause image artifacts and degradation in image quality. The field heterogeneity can be reduced by dynamically adjusting shim fields or dynamic shim updating, in which magnetic field homogeneity is optimized for each tomographic slice to improve image quality. A limitation of this approach is that a new magnetic field can be applied only once for each slice, otherwise image quality would improve somewhere to its detriment elsewhere in the slice. The motivation of this work is to overcome this limitation and develop a technique using nonlinear magnetic fields to dynamically shim the static magnetic field within a single Fourier-encoded volume or slice, called sub-Fourier dynamic shim updating. However, the nonlinear magnetic fields are not used as shim fields; instead, they impart a strong spatial dependence to the acquired MR signal by nonlinear phase preparation, which may be exploited to locally improve magnetic field homogeneity during acquisition. A theoretical description of the method is detailed, simulations and a proof-of-principle experiment are performed using a magnet coil with a known field geometry. The method is shown to remove artifacts associated with magnetic field homogeneity in balanced steady-state free-precession pulse sequences. We anticipate that this method will be useful to improve the quality of magnetic resonance images by removing deleterious artifacts associated with a heterogeneous static magnetic field. PMID:23440677
Juchem, Christoph; Umesh Rudrapatna, S; Nixon, Terence W; de Graaf, Robin A
2015-01-15
Gradient-echo echo-planar imaging (EPI) is the primary method of choice in functional MRI and other methods relying on fast MRI to image brain activation and connectivity. However, the high susceptibility of EPI towards B0 magnetic field inhomogeneity poses serious challenges. Conventional magnetic field shimming with low-order spherical harmonic (SH) functions is capable of compensating shallow field distortions, but performs poorly for global brain shimming or on specific areas with strong susceptibility-induced B0 distortions such as the prefrontal cortex (PFC). Excellent B0 homogeneity has been demonstrated recently in the human brain at 7 Tesla with the DYNAmic Multi-coIl TEchnique (DYNAMITE) for magnetic field shimming (J Magn Reson (2011) 212:280-288). Here, we report the benefits of DYNAMITE shimming for multi-slice EPI and T2* mapping. A standard deviation of 13Hz was achieved for the residual B0 distribution in the human brain at 7 Tesla with DYNAMITE shimming and was 60% lower compared to conventional shimming that employs static zero through third order SH shapes. The residual field inhomogeneity with SH shimming led to an average 8mm shift at acquisition parameters commonly used for fMRI and was reduced to 1.5-3mm with DYNAMITE shimming. T2* values obtained from the prefrontal and temporal cortices with DYNAMITE shimming were 10-50% longer than those measured with SH shimming. The reduction of the confounding macroscopic B0 field gradients with DYNAMITE shimming thereby promises improved access to the relevant microscopic T2* effects. The combination of high spatial resolution and DYNAMITE shimming allows largely artifact-free EPI and T2* mapping throughout the brain, including prefrontal and temporal lobe areas. DYNAMITE shimming is expected to critically benefit a wide range of MRI applications that rely on excellent B0 magnetic field conditions including EPI-based fMRI to study various cognitive processes and assessing large-scale brain connectivity
Highly-Ordered Ferroelectric Photonic Crystals
Institute of Scientific and Technical Information of China (English)
Naomi Matsuura; Suxia Yang; Ping Sun; Harry E. Ruda
2003-01-01
Highly-ordered, ferroelectric, Pb-doped Ba0.7Sr0.3TiO3, inverse opal thin films were fabricated using a sol-gel spin coating technique. The excellent crystal quality is evident from the SEM images and the good agreement between the theory and experiments.
ADAPTIVE REGULATION OF HIGH ORDER NONHOLONOMIC SYSTEMS
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The problem of adaptive regulation of a class of high-order parametric nonholonomic systems in chained-form was discussed. Using adding a power integrator technique and state scaling with discontinuous projection technique, a discontinuous adaptive dynamic controller was constructed. The controller guarantees the estimated value of unknown parameter is in the prescribed extent.
Enhancement of PARR-2 core reactivity by beryllium shim plate addition
International Nuclear Information System (INIS)
PARR-2 is a 30 kW research reactor. Its excess reactivity decreased after 10 years operation. Reactor could not be operated continuously for 5 hours during a day to meet the demand of users, because of negative temperature co-efficient of reactivity which is 0.13 mk per degree centigrade. The average temperature increase in the coolant (water) around the core is about 6 deg. C at the end of 5 hours operation. Reactivity of - 0.78 mk is added due to this temperature increase and has to be made available. Beryllium metal shim plate of 1.5mm thickness has been added into the reflector tray of reactor. Reactivity of core increased from 2.96 mk to 3.96 mk. Report covers procedure, preparations for shimming operation and post shimming measurements. (author)
Method and apparatus for magnetic field shimming in an isochronous cyclotron
International Nuclear Information System (INIS)
In a cyclotron having ferrous material structures associated with the orbital gap, a means is provided of obtaining radial and azimuthal field shimming by altering the geometry of such structures. More specifically, in an isochronous cyclotron of the superconducting type having ferrous material sectors there is provided a flutter field giving a hill and valley effect as a means of obtaining radial and azimuthal field shimming. This is done by mechanically altering the configuration of the ferrous material in the structures, that is, in the magnetic pole pieces or raised sectors defining flutter poles. This is achieved by a system of movable shim rods adapted for movement into and through openings in the pole pieces or flutter pole sectors such as to change the geometry of the poles. (LL)
Directory of Open Access Journals (Sweden)
Amine Dhraief
2011-11-01
Full Text Available Multihoming is a solution that enables a fault-tolerant access to the Internet by configuring on each network entity several IP addresses associated with distinct ISPs. IPv6 natively allows end-hosts and end-sites to be multihomed where nodes and routers can have multiple IP addresses. However, a specific support is required to take full advantage of multihoming. The SHIM6 protocol provides such a support.We study in this paper to what extent the mobility impacts the SHIM6 protocol component in general and more specifically the context establishment as it is a \\textit{sine qua none} condition for session survivability. We focus on possible consequences of mobility before, during, and after the context establishment. We find that in some mobility scenarios, the SHIM6 context is never established and the session survivability cannot be ensured.
Development of Antiwear Shim Inserts Utilizing Segment-Structured DLC Coatings
Takashima, Mai; Kuroda, Tsuyoshi; Saito, Masanori; Ohtake, Naoto; Matsuo, Makoto; Iwamoto, Yoshinao
Wear and fretting fatigue are important technological problems in automotive, railway and aerospace fields. The purpose of this study is to find a method of reducing the wear of cast-iron (FCD)/aluminum components, which are often applied to automotives, and thus extend their lifetime. First, a stainless-steel (SUS) shim was designed, which can be inserted between an FCD plate and an aluminum plate. Second, diamond-like carbon (DLC) coatings were applied to the shim inserts to prevent the FCD and aluminum plates from wear. Then, the tribological and fatigue characteristics of the shim were evaluated by a ball-on-disk (BoD) test and a bending fatigue test of up to 1×106 cycles. Each substrate was coated with DLC by Plasma-Based Ion Implantation and Deposition (PBII&D). A unique feature of our shim is that a segment-structured DLC film (S-DLC) is employed as well as a continuous DLC (C-DLC) film. The effect of the DLC coating on reducing the damage to the Al plate was apparent, because the surface roughness of the Al plate abraded with the DLC-coated shim was significantly smaller than that abraded directly with the FCD plate. Moreover, the average damage fraction to the C-DLC coating is approximately 20-fold larger than that to the S-DLC coating. The C-DLC film suffers severe damage near the bolt hole, whereas the S-DLC film suffered almost no damage even after 1×106 bending cycles. In conclusion, an S-DLC-coated SUS shim has a marked effect on reducing the wear of Al/FCD components and improving their lifetime.
Institute of Scientific and Technical Information of China (English)
ZHANG; Tian-jue; LV; Yin-long; ZHONG; Jun-qing; XING; Jian-sheng; CAO; Lei; YANG; Jian-jun; WANG; Chuan; YAO; Hong-juan; CUI; Tao; LI; Ming; YIN; Zhi-guo; WANG; Zhen-hui; LIU; Geng-shou; LEI; Yu; ZOU; Jian; ZHAO; Jiang-bin
2012-01-01
<正>In 2012, the magnetic mapping and shimming for the main magnet of CYCIAE-100 has been carried out 4 times in the temporary building, realizing the goal of reducing the phase shift of the accelerating proton by 80%. A number of large scale equipments, including the main magnet, main coils, hydraulic elevating system, RF amplifier, magnetic mapper and vacuum chamber, have been in place for installation in the main building. The final stage magnetic mapping and shimming has started out as well.
A high-order material point method.
Ghaffari Motlagh, Y.; Coombs, W.M.
2016-01-01
The material point method (MPM) is a version of the particle-in-cell (PIC) which has substantial advantages over pure Lagrangian or Eulerian methods in numerical simulations of problems involving large deformations. Using MPM helps to avoid mesh distortion and tangling problems related to Lagrangian methods and the advection errors associated with Eulerian methods are avoided. In this paper a novel high-order material point method within an isogeomeric analysis (IGA) framework is developed. U...
Shimming Halbach magnets utilizing genetic algorithms to profit from material imperfections
Parker, Anna J.; Zia, Wasif; Rehorn, Christian W. G.; Blümich, Bernhard
2016-04-01
In recent years, permanent magnet-based NMR spectrometers have resurfaced as low-cost portable alternatives to superconducting instruments. While the development of these devices as well as clever shimming methods have yielded impressive advancements, scaling the size of these magnets to miniature lengths remains a problem to be addressed. Here we present the results of a study of a discrete shimming scheme for NMR Mandhalas constructed from a set of individual magnet blocks. While our calculations predict a modest reduction in field deviation by a factor of 9.3 in the case of the shimmed ideal Mandhala, a factor of 28 is obtained in the case of the shimmed imperfect Mandhala. This indicates that imperfections of magnet blocks can lead to improved field homogeneity. We also present a new algorithm to improve the homogeneity of a permanent magnet assembly. Strategies for future magnet construction can improve the agreement between simulation and practical implementation by using data from real magnets in these assemblies as the input to such an algorithm to optimize the homogeneity of a given design.
High order harmonic generation from plasma mirror
International Nuclear Information System (INIS)
When an intense laser beam is focused on a solid target, its surface is rapidly ionized and forms a dense plasma that reflects the incident field. For laser intensities above few 1015 W/cm2, high order harmonics of the laser frequency, associated in the time domain to a train of atto-second pulses (1 as = 1018 s), can be generated upon this reflection. Because such a plasma mirror can be used with arbitrarily high laser intensities, this process should eventually lead to the production of very intense pulses in the X-ray domain. In this thesis, we demonstrate that for laser intensities about 1019 W/cm2, two mechanisms can contribute to the generation of high order harmonics: the coherent wake emission and the relativistic emission. These two mechanisms are studied both theoretically and experimentally. In particular, we show that, thanks to very different properties, the harmonics generated by these two processes can be unambiguously distinguished experimentally. We then investigate the phase properties of the harmonic, in the spectral and in the spatial domain. Finally, we illustrate how to exploit the coherence of the generation mechanisms to get information on the dynamics of the plasma electrons. (author)
High order generalized permutational fractional Fourier transforms
Institute of Scientific and Technical Information of China (English)
Ran Qi-Wen; Yuan Lin; Tan Li-Ying; Ma Jing; Wang Qi
2004-01-01
We generalize the definition of the fractional Fourier transform (FRFT) by extending the new definition proposed by Shih. The generalized FRFT, called the high order generalized permutational fractional Fourier transform (HGPFRFT),is a generalized permutational transform. It is shown to have arbitrary natural number M periodic eigenvalues not only with respect to the order of Hermite-Gaussian functions but also to the order of the transform. This HGPFRFT will be reduced to the original FRFT proposed by Namias and Liu's generalized FRFT and Shih's FRFT at the three limits with M = +∞,M = 4k (k is a natural number), and M = 4, respectively. Therefore the HGPFRFT introduces a comprehensive approach to Shih's FRFT and the original definition. Some important properties of HGPFRFT are discussed. Lastly the results of computer simulations and symbolic representations of the transform are provided.
High order generalized permutational fractional Fourier transforms
Ran, Qi-Wen; Yuan, Lin; Tan, Li-Ying; Ma, Jing; Wang, Qi
2004-02-01
We generalize the definition of the fractional Fourier transform (FRFT) by extending the new definition proposed by Shih. The generalized FRFT, called the high order generalized permutational fractional Fourier transform (HGPFRFT), is a generalized permutational transform. It is shown to have arbitrary natural number M periodic eigenvalues not only with respect to the order of Hermite-Gaussian functions but also to the order of the transform. This HGPFRFT will be reduced to the original FRFT proposed by Namias and Liu's generalized FRFT and Shih's FRFT at the three limits with M = +infty, M = 4k (k is a natural number) and M = 4, respectively. Therefore the HGPFRFT introduces a comprehensive approach to Shih's FRFT and the original definition. Some important properties of HGPFRFT are discussed. Lastly the results of computer simulations and symbolic representations of the transform are provided.
High order harmonic generation from plasma mirrors
International Nuclear Information System (INIS)
When an intense laser beam is focused on a solid target, the target's surface is rapidly ionized and forms dense plasma that reflects the incident field. For laser intensities above few 10 to the power of 15 Wcm-2, high order harmonics of the laser frequency, associated in the time domain to a train of atto-second pulses (1 as 10-18 s), can be generated upon this reflection. In this thesis, we developed numerical tools to reveal original aspects of harmonic generation mechanisms in three different interaction regime: the coherent wake emission, the relativistic emission and the resonant absorption. In particular, we established the role of these mechanisms when the target is a very thin foil (thickness of the order of 100 nm). Then we study experimentally the spectral, spatial and coherence properties of the emitted light. We illustrate how to exploit these measurements to get information on the plasma mirror dynamics on the femtosecond and atto-second time scales. Last, we propose a technique for the single-shot complete characterization of the temporal structure of the harmonic light emission from the laser-plasma mirror interaction. (author)
High order harmonic generation in rare gases
Energy Technology Data Exchange (ETDEWEB)
Budil, K.S.
1994-05-01
The process of high order harmonic generation in atomic gases has shown great promise as a method of generating extremely short wavelength radiation, extending far into the extreme ultraviolet (XUV). The process is conceptually simple. A very intense laser pulse (I {approximately}10{sup 13}-10{sup 14} W/cm{sup 2}) is focused into a dense ({approximately}10{sup l7} particles/cm{sup 3}) atomic medium, causing the atoms to become polarized. These atomic dipoles are then coherently driven by the laser field and begin to radiate at odd harmonics of the laser field. This dissertation is a study of both the physical mechanism of harmonic generation as well as its development as a source of coherent XUV radiation. Recently, a semiclassical theory has been proposed which provides a simple, intuitive description of harmonic generation. In this picture the process is treated in two steps. The atom ionizes via tunneling after which its classical motion in the laser field is studied. Electron trajectories which return to the vicinity of the nucleus may recombine and emit a harmonic photon, while those which do not return will ionize. An experiment was performed to test the validity of this model wherein the trajectory of the electron as it orbits the nucleus or ion core is perturbed by driving the process with elliptically, rather than linearly, polarized laser radiation. The semiclassical theory predicts a rapid turn-off of harmonic production as the ellipticity of the driving field is increased. This decrease in harmonic production is observed experimentally and a simple quantum mechanical theory is used to model the data. The second major focus of this work was on development of the harmonic {open_quotes}source{close_quotes}. A series of experiments were performed examining the spatial profiles of the harmonics. The quality of the spatial profile is crucial if the harmonics are to be used as the source for experiments, particularly if they must be refocused.
Juchem, Christoph; Rudrapatna, S. Umesh; Nixon, Terence W.; de Graaf, Robin A.
2014-01-01
Gradient-echo echo-planar imaging (EPI) is the primary method of choice in functional MRI and other methods relying on fast MRI to image brain activation and connectivity. However, the high susceptibility of EPI towards B0 magnetic field inhomogeneity poses serious challenges. Conventional magnetic field shimming with low-order spherical harmonic (SH) functions is capable of compensating shallow field distortions, but performs poorly for global brain shimming or on specific areas with strong ...
Iguchi, S.; Piao, R.; Hamada, M.; Matsumoto, S.; Suematsu, H.; Takao, T.; Saito, A. T.; Li, J.; Nakagome, H.; Jin, X.; Takahashi, M.; Maeda, H.; Yanagisawa, Y.
2016-04-01
This paper describes a field shimming technology to obtain a spatially homogeneous magnetic field required for a high-resolution nuclear magnetic resonance (NMR) magnet under the influence of a screening current in a (RE)Ba2Cu3O7-x (REBCO) coil. Use of REBCO inner coils is one solution to realize a super-high field (>23.5 T, 1 GHz) NMR magnet. However, a REBCO coil generates a large amount of field error harmonics due to the inhomogeneous coil winding introduced by a thin tape conductor. In addition, the performance of a field correction coil and outer superconducting (SC) shim coils are significantly reduced due to the shielding effect of the screening current in the REBCO coil. Therefore, conventional shimming technology using SC shim coils and room temperature shim coils cannot adequately compensate those field error harmonics and high-resolution NMR measurements are not possible. In the present paper, an advanced field shimming technology including an inner SC shim coil and a novel type of ferromagnetic shim were installed in a 400 MHz low-temperature SC/REBCO NMR magnet. The inner SC shim coil and the ferromagnetic shim compensated for the reduction in the performances of the field correction coil and the SC shim coils, respectively. The field error harmonics were greatly compensated with the technology and a high NMR resolution <0.01 ppm was obtained. The results from the present work suggest an optimal shimming procedure for a super-high field NMR magnet with high-temperature superconductors inner coils, i.e. the best mix of shims.
Dynamic Multi-Coil Shimming of the Human Brain at 7 Tesla
Juchem, Christoph; Nixon, Terence W.; McIntyre, Scott; Boer, Vincent O.; Rothman, Douglas L.; de Graaf, Robin A.
2011-01-01
High quality magnetic field homogenization of the human brain (i.e. shimming) for MR imaging and spectroscopy is a demanding task. The susceptibility differences between air and tissue are a longstanding problem as they induce complex field distortions in the prefrontal cortex and the temporal lobes. To date, the theoretical gains of high field MR have only been realized partially in the human brain due to limited magnetic field homogeneity.
Evaluation of two polyurethane resins for injection shimming of the MFTF magnet
International Nuclear Information System (INIS)
This work was conducted to support selection of a filler for the injection shimming of the MFTF Magnet (Reference 1). Two candidate polyurethanes (Pplycast RG256-57-3 and Polycast 1009-78 manufactured by CPR Upjohn Co.) were evaluated with respect to their physical and mechanical properties. Physical properties examined include thermal contraction, viscosity, and cure shrinkage. Mechanical properties include thermal shock resistance, compression modulus, and compression strength at LH2 temperature
Clark, D. S.; Weber, C. R.; Smalyuk, V. A.; Robey, H. F.; Kritcher, A. L.; Milovich, J. L.; Salmonson, J. D.
2016-07-01
Current indirect drive implosion experiments on the National Ignition Facility (NIF) [Moses et al., Phys. Plasmas 16, 041006 (2009)] are believed to be strongly impacted by long wavelength perturbations driven by asymmetries in the hohlraum x-ray flux. To address this perturbation source, active efforts are underway to develop modified hohlraum designs with reduced asymmetry imprint. An alternative strategy, however, is to modify the capsule design to be more resilient to a given amount of hohlraum asymmetry. In particular, the capsule may be deliberately misshaped, or "shimmed," so as to counteract the expected asymmetries from the hohlraum. Here, the efficacy of capsule shimming to correct the asymmetries in two recent NIF implosion experiments is assessed using two-dimensional radiation hydrodynamics simulations. Despite the highly time-dependent character of the asymmetries and the high convergence ratios of these implosions, simulations suggest that shims could be highly effective at counteracting current asymmetries and result in factors of a few enhancements in neutron yields. For higher compression designs, the yield improvement could be even greater.
Development of a minimal kinase ensemble receptor (MKER) for surrogate AutoShim.
Mukherjee, Prasenjit; Martin, Eric
2011-10-24
The target-tailored 3-D virtual screening (VS) method "Surrogate AutoShim" adds pharmacophoric shims to a 16-kinase crystal structure "Universal Kinase Ensemble Receptor" (UKER) to generate highly predictive, target-customized docking models. Predocking a corporate archive of millions of compounds into the 16-structure ensemble takes months. However, since the 16 UKER structures are always the same, docking need only be done once. The predocked results are then "shimmed" to reproduce experimental training data for any number of additional kinases far more accurately than conventional docking. Training new kinase models and predicting activity for millions of predocked compounds against dozens of kinases takes only hours. However reducing the predocking time would make the method even more advantageous. Sequential Floating Forward Search (SFFS) was employed to rationally identify a reduced subset using only 8 of the 16 structures, a "Minimal Kinase Ensemble Receptor" (MKER) that preserved the predictive accuracy for 20 kinase models. Furthermore, a performance evaluation of this subset on an extended set of 52 kinase targets and 100,000 compounds showed statistical model performance comparable to the original UKER. The MKER has halved the time for predocking large databases of internal and commercial compounds. For ad hoc virtual libraries, where predocking is not possible, 2- or 3-kinases "Approximate Kinase Ensemble Receptors" (AKER) were also identified with only a modest loss of prediction accuracy. PMID:21848284
Comparison of volume-selective z-shim and conventional EPI in fMRI studies using face stimuli
Fukunaga, Hu Cheng Srikanth Padmala Rena
2013-01-01
Single-shot gradient recalled echo planar imaging (EPI) is the primary tool for functional magnetic resonance imaging (fMRI). The image often suffers from signal drop near the air-tissue interface, such as the amygdala and regions of the orbitofrontal lobe. An effective way to correct for this type of artifact is by applying multi-shot EPI using different z-shimming. Unfortunately, the scanning efficiency is significantly lowered. More recently, a new technique called volume-selective z-shim was proposed to implement z-shim compensation to only specific slices with large susceptibility effects. The high imaging efficiency of volume selective z-shim makes it possible to substitute conventional EPI for whole brain studies. In this study two fMRI experiments were conducted to compare volume- selective z-shim and conventional EPI while subjects performed tasks on face stimuli. The comparison was focused on three brain regions: amygdala, hippocampus, and fusiform gyrus. Our results indicate that despite fewer volu...
A rigorous analysis of high order electromagnetic invisibility cloaks
Weder, Ricardo
2007-01-01
There is currently a great deal of interest in the invisibility cloaks recently proposed by Pendry et al. that are based in the transformation approach. They obtained their results using first order transformations. In recent papers Hendi et al. and Cai et al. considered invisibility cloaks with high order transformations. In this paper we study high order electromagnetic invisibility cloaks in transformation media obtained by high order transformations from general anisotropic media. We cons...
High-order harmonic generation from eld-distorted orbitals
DEFF Research Database (Denmark)
Spiewanowski, Maciek; Etches, Adam; Madsen, Lars Bojer
We investigate the eect on high-order harmonic generation of the distortion of molecular orbitals by the driving laser eld. Calculations for high-order harmonic generation including orbital distortion are performed for N2 (high polarizability). Our results allow us to suggest that field...
Experiments towards establishing of design rules for R2R-UV-NIL with polymer working shims
Nees, Dieter; Ruttloff, Stephan; Palfinger, Ursula; Stadlober, Barbara
2016-03-01
Roll-to-Roll-UV-nanoimprint lithography (R2R-UV-NIL) enables high resolution large area patterning of flexible substrates and is therefore of increasing industrial interest. We have set up a custom-made R2R-UV-NIL pilot machine which is able to convert 10 inch wide web with velocities of up to 30 m/min. In addition, we have developed self-replicable UV-curable resins with tunable surface energy and Young's modulus for UV-imprint material as well as for polymer working stamp/shim manufacturing. Now we have designed test patterns for the evaluation of the impact of structure shape, critical dimension, pitch, depth, side wall angle and orientation relative to the web movement onto the imprint fidelity and working shim life time. We have used female (recessed structures) silicon masters of that design with critical dimensions between CD = 200 nm and 1600 nm, and structure depths of d = 500 nm and 1000 nm - all with vertical as well as inclined side walls. These entire master patterns have been transferred onto single male (protruding structures) R2R polymer working shims. The polymer working shims have been used for R2R-UV-NIL runs of several hundred meters and the imprint fidelity and process stability of the various test patterns have been compared. This study is intended as a first step towards establishing of design rules and developing of nanoimprint proximity correction strategies for industrial R2R-UV-NIL processes using polymer working shims.
Testing of Compact Bolted Fasteners with Insulation and Friction-Enhanced Shims for NCSX
Energy Technology Data Exchange (ETDEWEB)
L. E. Dudek, J.H. Chrzanowski, G. Gettelfinger, P. Heitzenroeder, S. Jurczynski, M. Viola and K. Freudenberg
2009-02-04
The fastening of the National Compact Stellarator Experiment's (NCSX) modular coils presented a number of engineering and manufacturing challenges due to the high magnetic forces, need to control induced currents, tight tolerances and restrictive space envelope. A fastening method using high strength studs, jack nuts, insulating spacers, bushings and alumina coated shims was developed which met the requirements. A test program was conducted to verify the design. The tests included measurements of flatness of the spacers, determination of contact area, torque vs. tension of the studs and jack nuts, friction coefficient tests on the alumina and G-10 insulators, electrical tests, and tension relaxation tests due to temperature excursions from room temperature to liquid nitrogen temperatures. This paper will describe the design and the results of the test program.
Testing of Compact Bolted Fasteners with Insulation and Friction-Enhanced Shims for NCSX
International Nuclear Information System (INIS)
The fastening of the National Compact Stellarator Experiment's (NCSX) modular coils presented a number of engineering and manufacturing challenges due to the high magnetic forces, need to control induced currents, tight tolerances and restrictive space envelope. A fastening method using high strength studs, jack nuts, insulating spacers, bushings and alumina coated shims was developed which met the requirements. A test program was conducted to verify the design. The tests included measurements of flatness of the spacers, determination of contact area, torque vs. tension of the studs and jack nuts, friction coefficient tests on the alumina and G-10 insulators, electrical tests, and tension relaxation tests due to temperature excursions from room temperature to liquid nitrogen temperatures. This paper will describe the design and the results of the test program.
Numerical dissipation control in high order shock-capturing schemes for LES of low speed flows
Kotov, D. V.; Yee, H. C.; Wray, A. A.; Sjögreen, B.; Kritsuk, A. G.
2016-02-01
The Yee & Sjögreen adaptive numerical dissipation control in high order scheme (High Order Filter Methods for Wide Range of Compressible Flow Speeds, ICOSAHOM 09, 2009) is further improved for DNS and LES of shock-free turbulence and low speed turbulence with shocklets. There are vastly different requirements in the minimization of numerical dissipation for accurate turbulence simulations of different compressible flow types and flow speeds. Traditionally, the method of choice for shock-free turbulence and low speed turbulence are by spectral, high order central or high order compact schemes with high order linear filters. With a proper control of a local flow sensor, appropriate amount of numerical dissipation in high order shock-capturing schemes can have spectral-like accuracy for compressible low speed turbulent flows. The development of the method includes an adaptive flow sensor with automatic selection on the amount of numerical dissipation needed at each flow location for more accurate DNS and LES simulations with less tuning of parameters for flows with a wide range of flow speed regime during the time-accurate evolution, e.g., time varying random forcing. An automatic selection of the different flow sensors catered to the different flow types is constructed. A Mach curve and high-frequency oscillation indicators are used to reduce the tuning of parameters in controlling the amount of shock-capturing numerical dissipation to be employed for shock-free turbulence, low speed turbulence and turbulence with strong shocks. In Kotov et al. (High Order Numerical Methods for LES of Turbulent Flows with Shocks, ICCFD8, Chengdu, Sichuan, China, July 14-18, 2014) the LES of a turbulent flow with a strong shock by the Yee & Sjögreen scheme indicated a good agreement with the filtered DNS data. A work in progress for the application of the adaptive flow sensor for compressible turbulence with time-varying random forcing is forthcoming. The present study examines the
High-Order Supervised Discriminant Analysis for Visual Data
Institute of Scientific and Technical Information of China (English)
Xiao-Ling Xia; Hang-Hui Huang
2014-01-01
In practical applications, we often have to deal with high-order data, for example, a grayscale image and a video clip are intrinsically a 2nd-order tensor and a 3rd-order tensor, respectively. In order to satisty these high-order data, it is conventional to vectorize these data in advance, which often destroys the intrinsic structures of the data and includes the curse of dimensionality. For this reason, we consider the problem of high-order data representation and classification, and propose a tensor based fisher discriminant analysis (FDA), which is a generalized version of FDA, named as GFDA. Experimental results show our GFDA outperforms the existing methods, such as the 2-directional 2-dimensional principal component analysis ((2D)2PCA), 2-directional 2-dimensional linear discriminant analysis ((2D)2LDA), and multilinear discriminant analysis (MDA), in high-order data classification under a lower compression ratio.
Adaptive high-order methods in computational fluid dynamics
Wang, Z J
2011-01-01
This book consists of important contributions by world-renowned experts on adaptive high-order methods in computational fluid dynamics (CFD). It covers several widely used, and still intensively researched methods, including the discontinuous Galerkin, re
High-order correlation of chaotic bosons and fermions
Liu, Hong-Chao
2016-08-01
We theoretically study the high-order correlation functions of chaotic bosons and fermions. Based on the different parity of the Stirling number, the products of the first-order correlation functions are well classified and employed to represent the high-order correlation function. The correlation of bosons conduces a bunching effect, which will be enhanced as order N increases. Different from bosons, the anticommutation relation of fermions leads to the parity of the Stirling number, which thereby results in a mixture of bunching and antibunching behaviors in high-order correlation. By further investigating third-order ghost diffraction and ghost imaging, the differences between the high-order correlations of bosons and fermions are discussed in detail. A larger N will dramatically improve the ghost image quality for bosons, but a good strategy should be carefully chosen for the fermionic ghost imaging process due to its complex correlation components.
Illuminating Molecular Symmetries with Bicircular High-Order-Harmonic Generation
Reich, Daniel M
2016-01-01
We present a complete theory of bicircular high-order-harmonic emission from N-fold rotationally symmetric molecules. Using a rotating frame of reference we predict the complete structure of the high-order-harmonic spectra for arbitrary driving frequency ratios and show how molecular symmetries can be directly identified from the harmonic signal. Our findings reveal that a characteristic fingerprint of rotational molecular symmetries can be universally observed in the ultrafast response of molecules to strong bicircular fields.
Determination of rod insertion limits of the AP600'S M-shim bank at low power operating mode
International Nuclear Information System (INIS)
A series of calculation works had been conducted to determine the AP00's M-shim bank insertion limits during low-power operating mode. This activity was a part of the preliminary studies toward the plan on implementation a Rapid Power Reduction System (RPRS) in AP00's control / operating system, that enable it to operate under low power level (below 50% RTP). The calculations were performed for cycle 1 and equilibrium cycle as function of power levels and the fraction of AO-bank insertion. The results show that the M-shim insertion limits for both cycle 1 and equilibrium cycle were determined based on the limiting conditions at low-burn-up level (BOL), and high burn-up level (EOL) respectively
Electrochemical Hydrogen Storage in a Highly Ordered Mesoporous Carbon
Directory of Open Access Journals (Sweden)
Dan eLiu
2014-10-01
Full Text Available A highly order mesoporous carbon has been synthesized through a strongly acidic, aqueous cooperative assembly route. The structure and morphology of the carbon material were investigated using TEM, SEM and nitrogen adsorption-desorption isotherms. The carbon was proven to be meso-structural and consisted of graphitic micro-domain with larger interlayer space. AC impedance and electrochemical measurements reveal that the synthesized highly ordered mesoporous carbon exhibits a promoted electrochemical hydrogen insertion process and improved capacitance and hydrogen storage stability. The meso-structure and enlarged interlayer distance within the highly ordered mesoporous carbon are suggested as possible causes for the enhancement in hydrogen storage. Both hydrogen capacity in the carbon and mass diffusion within the matrix were improved.
Dynamic Stability Analysis Using High-Order Interpolation
Directory of Open Access Journals (Sweden)
Juarez-Toledo C.
2012-10-01
Full Text Available A non-linear model with robust precision for transient stability analysis in multimachine power systems is proposed. The proposed formulation uses the interpolation of Lagrange and Newton's Divided Difference. The High-Order Interpolation technique developed can be used for evaluation of the critical conditions of the dynamic system.The technique is applied to a 5-area 45-machine model of the Mexican interconnected system. As a particular case, this paper shows the application of the High-Order procedure for identifying the slow-frequency mode for a critical contingency. Numerical examples illustrate the method and demonstrate the ability of the High-Order technique to isolate and extract temporal modal behavior.
Airfoil noise computation use high-order schemes
DEFF Research Database (Denmark)
Zhu, Wei Jun; Shen, Wen Zhong; Sørensen, Jens Nørkær
2007-01-01
) finite difference schemes and optimized high-order compact finite difference schemes are applied for acoustic computation. Acoustic equations are derived using so-called splitting technique by separating the compressible NS equations into viscous (flow equation) and inviscid (acoustic equation) parts......High-order finite difference schemes with at least 4th-order spatial accuracy are used to simulate aerodynamically generated noise. The aeroacoustic solver with 4th-order up to 8th-order accuracy is implemented into the in-house flow solver, EllipSys2D/3D. Dispersion-Relation-Preserving (DRP...
Input cavity for high-order asymmetric-mode gyroklystron
Danilov, Yu. Yu.
2012-06-01
A new input cavity design for a high-order asymmetric-mode gyroklystron is proposed. Methods of the selective excitation of a resonant mode with a rotating field structure and the prevention of cavity self-excitation at harmonics of the gyrofrequency are proposed. Results of experimental investigation of the H711 mode cavity for a multimegawatt pulsed gyroklystron are presented.
A high order solver for the unbounded Poisson equation
DEFF Research Database (Denmark)
Hejlesen, Mads Mølholm; Rasmussen, Johannes Tophøj; Chatelain, Philippe; Walther, Jens Honore
2013-01-01
method is extended to directly solve the derivatives of the solution to Poissonʼs equation. In this way differential operators such as the divergence or curl of the solution field can be solved to the same high order convergence without additional computational effort. The method, is applied and...
A high order solver for the unbounded Poisson equation
DEFF Research Database (Denmark)
Hejlesen, Mads Mølholm; Rasmussen, Johannes Tophøj; Chatelain, Philippe; Walther, Jens Honore
2012-01-01
This work improves upon Hockney and Eastwood's Fourier-based algorithm for the unbounded Poisson equation to formally achieve arbitrary high order of convergence without any additional computational cost. We assess the methodology on the kinematic relations between the velocity and vorticity fields....
High order finite volume methods for singular perturbation problems
Institute of Scientific and Technical Information of China (English)
CHEN ZhongYing; HE ChongNan; WU Bin
2008-01-01
In this paper we establish a high order finite volume method for the fourth order singular perturbation problems. In conjunction with the optimal meshes, the numerical solutions resulting from the method have optimal convergence order. Numerical experiments are presented to verify our theoretical estimates.
High-Order Dispersion Coefficients for Alkali-metal Atoms
Institute of Scientific and Technical Information of China (English)
KANG Shuai; DING Chi-Kun; CHEN Chang-Yong; WU Xue-Qing
2013-01-01
High-order dispersion coefficients C9,C11,C12,and C13 for the ground-state alkali-metals were calculated by combining the l-dependent model potential of alkali-metal atoms and linear variation method based on B-spline basis functions.The results were compared.
High order finite volume methods for singular perturbation problems
Institute of Scientific and Technical Information of China (English)
2008-01-01
In this paper we establish a high order finite volume method for the fourth order singular perturbation problems.In conjunction with the optimal meshes,the numerical solutions resulting from the method have optimal convergence order.Numerical experiments are presented to verify our theoretical estimates.
Recycler Chromaticities and End Shims for NOvA at Fermilab
Xiao, M
2013-01-01
In era of NOvA operation, it is planned to slip-stack six on six Booster proton batches in the Recycler ring for a total intensity of 5 1013 protons/cycle. During the slip-stacking, the chromaticities are required to be jumped from (-2,-2) to (-20,-20). However, they can only be adjusted to (-12,-12) from (-2,-2) using existing 2 families of powered sextupoles. On the other hand, the presently designed Recycler lattice for Nova replaces the 30 straight section with 8 D-D half FODO cells . We use 3 quads in a half-cell to obtain the working point under the limit of the feasible quad strength, and the maximum beta-function in this section cannot be less than 80 m. In this paper, we re-designed the end shims of the permanent magnets in the ring lattice with appropriate quadrupole and sextupole components to meet both chromaticity and tune requirements. We are able to use 2 quads in a half cell in RR30 straight section within feasible quad strength. The maximum beta-functions are also lowered to around 55 m. The ...
Shimming techniques for the ultraprecise muon g-2 storage ring at the AGS
International Nuclear Information System (INIS)
Major components are in an advanced state of construction for a 7 meter radius 0.1 PPM precision storage ring. Detailed techniques are planned for static shimming of the assembly to at least 10 PPM magnetic field uniformity prior to the use of field correction coils. An air gap behind each ultra-pure iron pole piece strongly decouples the aperture field shape from the properties of the 1,006 iron yoke. Iron wedges whose thickness varies across the width of the poles with slope of ∼ 1/60 are used to eliminate the gradient produced by the C-magnet shape required for open access for the decay electron counter on the inside radius of the storage ring magnet. These wedges are 10 cm in azimuthal length and can be radially adjusted for short wavelength field adjustments. A horizontal motion of 50 μm effectively adjusts the 10 cm half-gap aperture by 1 μm (or 10 PPM). This and other techniques to adjust dipole, quadrupole, sextuple, etc. multipoles will be described
7 T body MRI: B1 shimming with simultaneous SAR reduction
International Nuclear Information System (INIS)
The high frequency of the radiofrequency (RF) fields used in high field magnetic resonance imaging (MRI) results in electromagnetic field variations that can cause local regions to have a large specific absorption rate (SAR) and/or a low excitation. In this study, we evaluated the use of a B1 shimming technique which can simultaneously improve the B+1 homogeneity and reduce the SAR for whole body imaging at 7 T. Optimizations for four individual anatomies showed a reduction up to 74% of the peak SAR values with respect to a quadrature excitation and a simultaneous improvement of the B+1 homogeneity varying between 39 and 75% for different optimization parameters. The average SAR was reduced with approximately 50% for all optimizations. The optimized phase and amplitude settings from an elliptical phantom model were applied to four realistic human anatomy models to evaluate whether a generic application without prior knowledge of the detailed human anatomy is possible. This resulted in an average improvement of the B+1 homogeneity of 37% and an average reduction of the maximum and average SAR of 50 and 55%, respectively. It can be concluded that this generic method can be used as a simple method to improve the prospects of 7 T body imaging
International Nuclear Information System (INIS)
The present paper contains a comprehensive literature survey on helicopter flow analyses and describes some true unsteady flows past helicopter rotors obtained using low and high order CFD models. The low order model is based on a panel method coupled with a viscous boundary layer approach and a compressibility correction. The USAERO software is used for the computations. The high order model is based on Euler and Navier-Stokes equations. For the high order models, a true unsteady scheme, as implemented in the CFD-FASTRAN code using the Euler equations, is considered for flows past hovering rotor. On the other hand, a quasi-steady approach, using the WIND code with the Navier-Stokes equations and the SST turbulence model, is used to assess the validity of the approach for the simulation of flows past a helicopter in forward flight conditions. When using the high order models, a Chimera grid technique is used to describe the blade motions within the parent stationary grid. Comparisons with experimental data are performed and the true unsteady simulations provide a reasonable agreement with the available experimental data. The panel method and the quasisteady approach are found to overestimate the loads on the helicopter rotors. The USAERO panel code is found to produce more thrust owing to some error sources in the computations when a wake-surface collision occurs, as the blades interact with their own wakes. The automatic cutting of the wake sheets, as they approach the model surface, is not working properly at every time step. (author)
Parallel preconditioners and high order elements for microwave imaging
Bonazzoli, M; Rapetti, F; Tournier, P -H
2016-01-01
This paper combines the use of high order finite element methods with parallel preconditioners of domain decomposition type for solving electromagnetic problems arising from brain microwave imaging. The numerical algorithms involved in such complex imaging systems are computationally expensive since they require solving the direct problem of Maxwell's equations several times. Moreover, wave propagation problems in the high frequency regime are challenging because a sufficiently high number of unknowns is required to accurately represent the solution. In order to use these algorithms in practice for brain stroke diagnosis, running time should be reasonable. The method presented in this paper, coupling high order finite elements and parallel preconditioners, makes it possible to reduce the overall computational cost and simulation time while maintaining accuracy.
Spectral Shifts of Nonadiabatic High-Order Harmonic Generation
Directory of Open Access Journals (Sweden)
André D. Bandrauk
2013-03-01
Full Text Available High-order harmonic generation (HHG is a nonlinear nonperturbative process in ultrashort intense laser-matter interaction. It is the main source of coherent attosecond (1 as = 10−18 s laser pulses to investigate ultrafast electron dynamics. HHG has become an important table-top source covering a spectral range from infrared to extreme ultraviolet (XUV. One way to extend the cutoff energy of HHG is to increase the intensity of the laser pulses. A consequence of HHG in such intense short laser fields is the characteristic nonadiabatic red and blue shifts of the spectrum, which are reviewed in the present work. An example of this nonperturbative light-matter interaction is presented for the one-electron nonsymmetric molecular ion HeH2+, as molecular systems allow for the study of the laser-molecule orientation dependence of such new effects including a four-step model of MHOHG (Molecular High-order Harmonic Generation.
High-order harmonic generation in laser plasma plumes
Ganeev, Rashid A
2013-01-01
This book represents the first comprehensive treatment of high-order harmonic generation in laser-produced plumes, covering the principles, past and present experimental status and important applications. It shows how this method of frequency conversion of laser radiation towards the extreme ultraviolet range matured over the course of multiple studies and demonstrated new approaches in the generation of strong coherent short-wavelength radiation for various applications. Significant discoveries and pioneering contributions of researchers in this field carried out in various laser scientific centers worldwide are included in this first attempt to describe the important findings in this area of nonlinear spectroscopy. "High-Order Harmonic Generation in Laser Plasma Plumes" is a self-contained and unified review of the most recent achievements in the field, such as the application of clusters (fullerenes, nanoparticles, nanotubes) for efficient harmonic generation of ultrashort laser pulses in cluster-containin...
High-order Hamiltonian splitting for Vlasov-Poisson equations
Casas, Fernando; Faou, Erwan; Mehrenberger, Michel
2015-01-01
We consider the Vlasov-Poisson equation in a Hamiltonian framework and derive new time splitting methods based on the decomposition of the Hamiltonian functional between the kinetic and electric energy. Assuming smoothness of the solutions, we study the order conditions of such methods. It appears that these conditions are of Runge-Kutta-Nystr{\\"o}m type. In the one dimensional case, the order conditions can be further simplified, and efficient methods of order 6 with a reduced number of stages can be constructed. In the general case, high-order methods can also be constructed using explicit computations of commutators. Numerical results are performed and show the benefit of using high-order splitting schemes in that context. Complete and self-contained proofs of convergence results and rigorous error estimates are also given.
High-order dispersion effects in two-photon interference
Mazzotta, Z; Cipriani, D; Olivares, S; Paris, M G A
2016-01-01
Two-photon interference and Hong-Ou-Mandel (HOM) effect are relevant tools for quantum metrology and quantum information processing. In optical coherence tomography, HOM effect is exploited to achieve high-resolution measurements with the width of the HOM dip being the main parameter. On the other hand, applications like dense coding require high-visibility performances. Here we address high-order dispersion effects in two-photon interference and study, theoretically and experimentally, the dependence of the visibility and the width of the HOM dip on both the pump spectrum and the downconverted photon spectrum. In particular, a spatial light modulator is exploited to experimentally introduce and manipulate a custom phase function to simulate the high-order dispersion effects.
The Observation of Highly Ordered Domains in Membranes with Cholesterol
Energy Technology Data Exchange (ETDEWEB)
Armstrong, Clare L [McMaster University; Marquardt, Drew [Brock University, St. Catharines, ON, Canada; Dies, Hannah [McMaster University; Kucerka, Norbert [Canadian Neutron Beam Centre and Comelius University (Slovakia); Yamani, Zahra [Canadian Neutron Beam Centre, National Research Council, Chalk River Laboratorie; Harroun, Thad [Brock University, St. Catharines, ON, Canada; Katsaras, John [ORNL; Shi, A-C [McMaster University; Rheinstadter, Maikel C [McMaster University
2013-01-01
Rafts, or functional domains, are transient nano- or mesoscopic structures in the exoplasmic leaflet of the plasma membrane, and are thought to be essential for many cellular processes. Using neutron diffraction and computer modelling, we present evidence for the existence of highly ordered lipid domains in the cholesterol-rich (32.5 mol%) liquid-ordered (lo) phase of dipalmitoylphosphatidylcholine membranes. The liquid ordered phase in one-component lipid membranes has previously been thought to be a homogeneous phase. The presence of highly ordered lipid domains embedded in a disordered lipid matrix implies non-uniform distribution of cholesterol between the two phases. The experimental results are in excellent agreement with recent computer simulations of DPPC/cholesterol complexes [Meinhardt, Vink and Schmid (2013). Proc Natl Acad Sci USA 110(12): 4476 4481], which reported the existence of nanometer size lo domains in a liquid disordered lipid environment.
Tunneling spectroscopy of highly ordered organic thin films
Törker, Michael
2003-01-01
In this work, a Au(100) single crystal was used as substrate for organic molecular beam epitaxy. Highly ordered organic thin films of the molecules 3,4,9,10-perylenetetracarboxylic-3,4,9,10-dianhydrid (PTCDA) and hexa-peri-hexabenzo-coronene (HBC) as well as organic-organic heterostructures on reconstructed Au(100) were prepared. The molecular arrangement was characterized in Scanning Tunneling Microscopy and Low Energy Electron Diffraction investigations. Scanning Tunneling Spectroscopy data...
High-Order Harmonic Generation in the Ionization Process
Institute of Scientific and Technical Information of China (English)
CHEN Jing; CHEN Shi-Gang; LIU Jie
2000-01-01
Based on the nonperturbative quantum electrodynamics scattering theory for multiphoton ionization developed recently, high-order harmonic generated in the ionization process is discussed. The influence of the Coulomb potential is treated as a perturbation in the expansion of the transition matrix. It is deduced that the harmonic photons are emitted in the resonant process during ionization and the width of the harmonic peaks is just the ionization rate of the atom.
Divergence-free Wavelets and High Order Regularization
Kadri Harouna, Souleymane; Dérian, Pierre; Héas, Patrick; Mémin, Etienne
2013-01-01
International audience Expanding on a wavelet basis the solution of an inverse problem provides several advantages. Wavelet bases yield a natural and efficient multiresolution analysis. The continuous representation of the solution with wavelets enables analytical calculation of regularization integrals over the spatial domain. By choosing differentiable wavelets, high-order derivative regularizers can be designed, either taking advantage of the wavelet differentiation properties or via th...
High-order WENO scheme for Polymerization-type equations
Gabriel, Pierre
2010-01-01
Polymerization of proteins is a biochimical process involved in different diseases. Mathematically, it is generally modeled by aggregation-fragmentation-type equations. In this paper we consider a general polymerization model and propose a high-order numerical scheme to investigate the behavior of the solution. An important property of the equation is the mass conservation. The fifth-order WENO scheme is built to preserve the total mass of proteins along time.
Double-peak Splitting in High-order Harmonics Generation
Institute of Scientific and Technical Information of China (English)
WANG Yingsong; LIU Yaqing; YANG Xiaodong; XU Zhizhan
2000-01-01
When the intensity of the driving pulse is much higher than the saturation intensity of the media involved, the double-peak splitting in frequency domain emerges in the generated high-order harmonic spectra. The possible origins of this splitting are carefully investigated. The ionization of the gas media and the propagation effect of harmonic field are the main reason for the double-peak splitting observed.
High--order jamming crossovers and density anomalies
Ciamarra, Massimo Pica; Sollich, Peter
2012-01-01
We demonstrate the existence of high--order jamming crossovers in systems of particles with repulsive contact interactions, which originate from the collapse of successive coordination shells. At zero temperature, these crossovers induce an anomalous behavior of the bulk modulus, which varies non--monotonically with the density, while at finite temperature they induce density anomalies consisting in an increased diffusivity upon isothermal compression and in a negative thermal expansion coeff...
High order Nyström method for elastodynamic scattering
Chen, Kun; Gurrala, Praveen; Song, Jiming; Roberts, Ron
2016-02-01
Elastic waves in solids find important applications in ultrasonic non-destructive evaluation. The scattering of elastic waves has been treated using many approaches like the finite element method, boundary element method and Kirchhoff approximation. In this work, we propose a novel accurate and efficient high order Nyström method to solve the boundary integral equations for elastodynamic scattering problems. This approach employs high order geometry description for the element, and high order interpolation for fields inside each element. Compared with the boundary element method, this approach makes the choice of the nodes for interpolation based on the Gaussian quadrature, which renders matrix elements for far field interaction free from integration, and also greatly simplifies the process for singularity and near singularity treatment. The proposed approach employs a novel efficient near singularity treatment that makes the solver able to handle extreme geometries like very thin penny-shaped crack. Numerical results are presented to validate the approach. By using the frequency domain response and performing the inverse Fourier transform, we also report the time domain response of flaw scattering.
Institute of Scientific and Technical Information of China (English)
Yuming Gong; Gang Liang; Lifeng Zhao; Yong Zhang; Yong Zhao; Xuyong Chen
2014-01-01
Superconducting magnetic levitation perfor-mance, including levitation force and guidance force, is important for the application of high-temperature super-conducting maglev. Both of them are not only affected by different arrays of superconductors and magnets, but also by the thickness of the iron shim between permanent magnets. In order to obtain the best levitation performance, the magnetic field distribution, levitation force, and guid-ance force of a new type of three magnetic hills of per-manent magnet guideway with iron shim of different thicknesses (4, 6, and 8 mm) are discussed in this paper. Simulation analysis and experiment results show that the guideway with iron shim of 8 mm thickness possesses the strongest magnetic field and levitation performance when the suspension gap is larger than 10 mm. However, with the decreasing of suspension gap, the guideway with iron shim of 4 mm thickness possesses the best levitation per-formance. The phenomena can be attributed to the density distribution of flux and magnetization of iron shim.
Highly Ordered Architecture of MicroRNA Cluster
Bing Shi; Mingxuan Zhu; Shuang Liu; Mandun Zhang
2013-01-01
Although it is known that the placement of genes in a cluster may be critical for proper expression patterns, it remains largely unclear whether the orders of members in an miRNA cluster have biological insights. By investigating the relationship between expression and orders for miRNAs from the oncogenic miR-17-92 cluster, we observed a highly ordered architecture in this cluster. A significant correlation between miRNA expression level and its placement was revealed. More importantly, the p...
High-order harmonic generation with short-pulse lasers
International Nuclear Information System (INIS)
Recent progress in the understanding of high-order harmonic conversion from atoms and ions exposed to high-intensity, short-pulse optical lasers is reviewed. We find that ions can produce harmonics comparable in strength to those obtained from neutral atoms, and that the emission extends to much higher order. Simple scaling laws for the strength of the harmonic emission and the maximium observable harmonic are suggested. These results imply that the photoemission observed in recent experiments in helium and neon contains contributions from ions as well as neutrals
On high-order perturbative calculations at finite density
Ghisoiu, Ioan; Kurkela, Aleksi; Romatschke, Paul; Säppi, Matias; Vuorinen, Aleksi
2016-01-01
We discuss the prospects of performing high-order perturbative calculations in systems characterized by a vanishing temperature but finite density. In particular, we show that the determination of generic Feynman integrals containing fermionic chemical potentials can be reduced to the evaluation of three-dimensional phase space integrals over vacuum on-shell amplitudes. Applications of these rules will be discussed in the context of the thermodynamics of cold and dense QCD, where it is argued that they facilitate an extension of the Equation of State of cold quark matter to higher perturbative orders.
Attosecond Synchronization of High-Order Harmonics from Midinfrared Drivers
International Nuclear Information System (INIS)
The group delay dispersion, also known as the attochirp, of high-order harmonics generated in gases has been identified as the main intrinsic limitation to the duration of Fourier-synthesized attosecond pulses. Theory implies that the attochirp, which is inversely proportional to the laser wavelength, can be decreased at longer wavelength. Here we report the first measurement of the wavelength dependence of the attochirp using an all-optical, in situ method [N. Dudovich et al., Nature Phys. 2, 781 (2006)]. We show that a 2 μm driving wavelength reduces the attochirp with respect to 0.8 μm at comparable intensities
Fast calibration of high-order adaptive optics systems
Kasper, Markus; Fedrigo, Enrico; Looze, Douglas P.; Bonnet, Henri; Ivanescu, Liviu; Oberti, Sylvain
2004-06-01
We present a new method of calibrating adaptive optics systems that greatly reduces the required calibration time or, equivalently, improves the signal-to-noise ratio. The method uses an optimized actuation scheme with Hadamard patterns and does not scale with the number of actuators for a given noise level in the wave-front sensor channels. It is therefore highly desirable for high-order systems and/or adaptive secondary systems on a telescope without a Gregorian focal plane. In the latter case, the measurement noise is increased by the effects of the turbulent atmosphere when one is calibrating on a natural guide star.
A high order solver for the unbounded Poisson equation
DEFF Research Database (Denmark)
Hejlesen, Mads Mølholm; Rasmussen, Johannes Tophøj; Chatelain, Philippe; Walther, Jens Honore
In mesh-free particle methods a high order solution to the unbounded Poisson equation is usually achieved by constructing regularised integration kernels for the Biot-Savart law. Here the singular, point particles are regularised using smoothed particles to obtain an accurate solution with an order...... of convergence consistent with the moments conserved by the applied smoothing function. In the hybrid particle-mesh method of Hockney and Eastwood (HE) the particles are interpolated onto a regular mesh where the unbounded Poisson equation is solved by a discrete non-cyclic convolution of the mesh...
Enhanced Optomechanical Cooling at High-Order Exceptional Points
Jing, H; Lü, H; Nori, Franco
2016-01-01
We study mechanical cooling in systems of coupled passive (lossy) and active (with gain) optical resonators. We find that for a driving laser which is red-detuned with respect to the cavity frequency, the supermode structure of the system is radically changed, featuring the emergence of genuine high-order exceptional points. This in turn leads to giant enhancement of both the mechanical damping and the spring stiffness, facilitating low-power mechanical cooling in the vicinity of gain-loss balance. This opens up new avenues of steering micromechanical devices with exceptional points beyond the lowest-order two.
High-order total variation minimization for interior tomography
International Nuclear Information System (INIS)
Recently, an accurate solution to the interior problem was proposed based on the total variation (TV) minimization, assuming that a region of interest (ROI) is piecewise constant. In this paper, we generalize that assumption to allow a piecewise polynomial ROI, introduce the high-order TV (HOT), and prove that an ROI can be accurately reconstructed from projection data associated with x-rays through the ROI via the HOT minimization if the ROI is piecewise polynomial. Then, we verify our theoretical results in numerical simulation
Ellermann, J; Goerke, U; Morgan, P; Ugurbil, K; Tian, J; Schmitter, S; Vaughan, T; Van De Moortele, P-F
2012-10-01
The objective of this study was to demonstrate the feasibility of simultaneous bilateral hip imaging at 7 Tesla. Hip joint MRI becomes clinically critical since recent advances have made hip arthroscopy an efficacious approach to treat a variety of early hip diseases. The success of these treatments requires a reliable and accurate diagnosis of intraarticular abnormalities at an early stage. Articular cartilage assessment is especially important to guide surgical decisions but is difficult to achieve with current MR methods. Because of gains in tissue contrast and spatial resolution reported at ultra high magnetic fields, there are strong expectations that imaging the hip joint at 7 Tesla will improve diagnostic accuracy. Furthermore, there is growing evidence that the majority of these hip abnormalities occur bilaterally, emphasizing the need for bilateral imaging. However, obtaining high quality images in the human torso, in particular of both hips simultaneously, must overcome a major challenge arising from the damped traveling wave behaviour of RF waves at 7 Tesla that leads to severe inhomogeneities in transmit B1 (B(1) (+) ) phase and magnitude, typically resulting in areas of low signal and contrast, and consequently impairing use for clinical applications. To overcome this problem, a 16-channel stripline transceiver RF coil was used, together with a B1 shimming algorithm aiming at maximizing B(1) (+) in six regions of interest over the hips that were identified on axial scout images. Our successful results demonstrate that this approach effectively reduces inhomogeneities observed before B1 shimming and provides high joint tissue contrast in both hips while reducing the required RF power. Critical to this success was a fast small flip angle B(1) (+) calibration scan that permitted the computation of subject-specific B1 shimming solutions, a necessary step to account for large spatial variations in B(1) (+) phase observed in different subjects. PMID:22311346
Haeseler, Friedrich
2003-01-01
Automatic sequences are sequences which are produced by a finite automaton. Although they are not random they may look as being random. They are complicated, in the sense of not being not ultimately periodic, they may look rather complicated, in the sense that it may not be easy to name the rule by which the sequence is generated, however there exists a rule which generates the sequence. The concept automatic sequences has special applications in algebra, number theory, finite automata and formal languages, combinatorics on words. The text deals with different aspects of automatic sequences, in particular:· a general introduction to automatic sequences· the basic (combinatorial) properties of automatic sequences· the algebraic approach to automatic sequences· geometric objects related to automatic sequences.
High-order finite element methods for cardiac monodomain simulations
Directory of Open Access Journals (Sweden)
Kevin P Vincent
2015-08-01
Full Text Available Computational modeling of tissue-scale cardiac electrophysiology requires numerically converged solutions to avoid spurious artifacts. The steep gradients inherent to cardiac action potential propagation necessitate fine spatial scales and therefore a substantial computational burden. The use of high-order interpolation methods has previously been proposed for these simulations due to their theoretical convergence advantage. In this study, we compare the convergence behavior of linear Lagrange, cubic Hermite, and the newly proposed cubic Hermite-style serendipity interpolation methods for finite element simulations of the cardiac monodomain equation. The high-order methods reach converged solutions with fewer degrees of freedom and longer element edge lengths than traditional linear elements. Additionally, we propose a dimensionless number, the cell Thiele modulus, as a more useful metric for determining solution convergence than element size alone. Finally, we use the cell Thiele modulus to examine convergence criteria for obtaining clinically useful activation patterns for applications such as patient-specific modeling where the total activation time is known a priori.
Enhancing narrowband high order harmonic generation by Fano resonances
Rothhardt, Jan; Demmler, Stefan; Krebs, Manuel; Fritzsche, Stephan; Limpert, Jens; Tünnermann, Andreas
2014-01-01
Resonances in the photo-absorption spectrum of the generating medium can modify the spectrum of high order harmonics. In particular, window-type Fano resonances can reduce photo-absorption within a narrow spectral region and, consequently, lead to an enhanced emission of high-order harmonics in absorption-limited generation conditions. For high harmonic generation in argon it is shown that the 3s3p6 np 1P1 window resonances (n=4,5,6) give rise to enhanced photon yield. In particular, the 3s3p6 4p 1P1 resonance at 26.6 eV allows a relative enhancement up to a factor of 30 compared to the characteristic photon emission of the neighboring harmonic order. This enhanced, spectrally isolated and coherent photon emission line has a relative energy bandwidth of only {\\Delta}E/E=3*10-3. Therefore, it might be directly applied for precision spectroscopy or coherent diffractive imaging without the need of additional spectral filtering. The presented mechanism can be employed for tailoring and controlling the high harmon...
Accelerating experimental high-order spatial statistics calculations using GPUs
Li, Xue; Huang, Tao; Lu, De-Tang; Niu, Cong
2014-09-01
High-order spatial statistics have been widely used to describe the spatial phenomena in the field of geology science. Spatial statistics are subject to extremely heavy computational burden for large geostatistical models. To improve the computational efficiency, a parallel approach based on GPU (Graphics Processing Unit) is proposed for the calculation of high-order spatial statistics. The parallel scheme is achieved by utilizing a two-stage method to calculate the replicate of a moment for a given template simultaneously termed as the node-stage parallelism, and transform the spatial moments to cumulants for all lags of a template simultaneously termed as the template-stage parallelism. Also, a series of optimization strategies are proposed to take full advantage of the computational capabilities of GPUs, including the appropriate task allocation to the CUDA (Compute Unified Device Architecture) threads, proper organization of the GPU physical memory, and optimal improvement of the existed parallel routines. Tests are carried out on two training images to compare the performance of the GPU-based method with that of the serial implementation. Error analysis results indicate that the proposed parallel method can generate accurate cumulant maps, and the performance comparisons on various examples show that all the speedups for third-order, fourth-order and fifth-order cumulants calculation are over 17 times.
Shaping Neural Circuits by High Order Synaptic Interactions
Ravid Tannenbaum, Neta; Burak, Yoram
2016-01-01
Spike timing dependent plasticity (STDP) is believed to play an important role in shaping the structure of neural circuits. Here we show that STDP generates effective interactions between synapses of different neurons, which were neglected in previous theoretical treatments, and can be described as a sum over contributions from structural motifs. These interactions can have a pivotal influence on the connectivity patterns that emerge under the influence of STDP. In particular, we consider two highly ordered forms of structure: wide synfire chains, in which groups of neurons project to each other sequentially, and self connected assemblies. We show that high order synaptic interactions can enable the formation of both structures, depending on the form of the STDP function and the time course of synaptic currents. Furthermore, within a certain regime of biophysical parameters, emergence of the ordered connectivity occurs robustly and autonomously in a stochastic network of spiking neurons, without a need to expose the neural network to structured inputs during learning. PMID:27517461
Hybrid overlay metrology for high order correction by using CDSEM
Leray, Philippe; Halder, Sandip; Lorusso, Gian; Baudemprez, Bart; Inoue, Osamu; Okagawa, Yutaka
2016-03-01
Overlay control has become one of the most critical issues for semiconductor manufacturing. Advanced lithographic scanners use high-order corrections or correction per exposure to reduce the residual overlay. It is not enough in traditional feedback of overlay measurement by using ADI wafer because overlay error depends on other process (etching process and film stress, etc.). It needs high accuracy overlay measurement by using AEI wafer. WIS (Wafer Induced Shift) is the main issue for optical overlay, IBO (Image Based Overlay) and DBO (Diffraction Based Overlay). We design dedicated SEM overlay targets for dual damascene process of N10 by i-ArF multi-patterning. The pattern is same as device-pattern locally. Optical overlay tools select segmented pattern to reduce the WIS. However segmentation has limit, especially the via-pattern, for keeping the sensitivity and accuracy. We evaluate difference between the viapattern and relaxed pitch gratings which are similar to optical overlay target at AEI. CDSEM can estimate asymmetry property of target from image of pattern edge. CDSEM can estimate asymmetry property of target from image of pattern edge. We will compare full map of SEM overlay to full map of optical overlay for high order correction ( correctables and residual fingerprints).
The pyramid wavefront sensor for the high order testbench (HOT)
Pinna, E.; Puglisi, A. T.; Quiros-Pacheco, F.; Busoni, L.; Tozzi, A.; Esposito, S.; Aller-Carpentier, E.; Kasper, M.
2008-07-01
The High Order Testbench (HOT) is a joint experiment of ESO, Durham University and Arcetri Observatory to built and test in laboratory the performance of Shack-Hartmann and pyramid sensor in a high-order correction loop using a 32x32 actuators MEMS DM. This paper will describe the pyramid wavefront sensor unit developed in Arcetri and now installed in the HOT bench at ESO premises. In the first part of this paper we will describe the pyramid wavefront sensor opto-mechanics and its real-time computer realized with a commercial Linux-PC. In the second part we will show the sensor integration and alignment in the HOT bench and the experimental results obtained at ESO labs. Particular attention will be paid to the implementation of the modal control strategy, like modal basis definition, orthogonalization on the real pupil, and control of edge actuators. A stable closed loop controlling up to 667 modes has been achieved obtaining a Strehl ratio of 90 -- 93% in H band.
Desorption mechanisms in PMMA irradiated by high order harmonics
Czech Academy of Sciences Publication Activity Database
De Grazia, M.; Merdji, H.; Auguste, T.; Carré, B.; Gaudin, J.; Geoffroy, G.; Guizard, S.; Krejčí, F.; Kuba, J.; Chalupský, J.; Cihelka, Jaroslav; Hájková, Věra; Ledinský, Martin; Juha, Libor
Bellingham: SPIE, 2011 - (Juha, L.; Bajt, S.; London, R.), 80770L/1-80770L/10. (Proceedings of SPIE. 8077). ISBN 9780819486677. ISSN 0277-786X. [Conference on Damage to VUV, EUV, and X-ray Optics III. Prague (CZ), 18.04.2011-20.04.2011] R&D Projects: GA AV ČR KAN300100702; GA MŠk LC510; GA MŠk(CZ) LC528; GA MŠk LA08024; GA MŠk(CZ) ME10046 Institutional research plan: CEZ:AV0Z10100523 Keywords : XUV pulses * high order harmonics * PMMA * desorption * chain scission * cross-linking Subject RIV: BH - Optics, Masers, Lasers http://dx.doi.org/ 10.1117/12.890093
Genuine High-Order Einstein-Podolsky-Rosen Steering
Li, Che-Ming; Chen, Kai; Chen, Yueh-Nan; Zhang, Qiang; Chen, Yu-Ao; Pan, Jian-Wei
2015-07-01
Einstein-Podolsky-Rosen (EPR) steering demonstrates that two parties share entanglement even if the measurement devices of one party are untrusted. Here, going beyond this bipartite concept, we develop a novel formalism to explore a large class of EPR steering from generic multipartite quantum systems of arbitrarily high dimensionality and degrees of freedom, such as graph states and hyperentangled systems. All of these quantum characteristics of genuine high-order EPR steering can be efficiently certified with few measurement settings in experiments. We faithfully demonstrate for the first time such generality by experimentally showing genuine four-partite EPR steering and applications to universal one-way quantum computing. Our formalism provides a new insight into the intermediate type of genuine multipartite Bell nonlocality and potential applications to quantum information tasks and experiments in the presence of untrusted measurement devices.
High-order Primordial Perturbations with Quantum Gravitational Effects
Zhu, Tao; Kirsten, Klaus; Cleaver, Gerald; Sheng, Qin
2016-01-01
In this paper, we provide a systematic investigation of high-order primordial perturbations with nonlinear dispersion relations due to quantum gravitational effects in the framework of {\\em uniform asymptotic approximations}. Because of these effects, the equation of motion of the mode function in general has multiple-turning points. After obtaining analytically approximated solutions in different regions, associated with different types of turning points, to any order, we match them to the third one. To this order the errors are less than $0.15\\%$. General expressions of the power spectra of the primordial tensor and scalar perturbations are derived explicitly. We also investigate effects of back-reactions of the quantum gravitational corrections, and make sure that inflation lasts long enough in order to solve underlying problems, such as flatness, horizon and monopole. Various features of the spectra that are observationally relevant are investigated. In particular, under a moderate assumption about the en...
Fabrication of highly ordered metallic nanowire arrays by electrodeposition
International Nuclear Information System (INIS)
Highly ordered hexagonal arrays of parallel metallic nanowires (Ni, Bi) with diameters of about 50 nm and lengths up to 50 μm were synthesized by electrodeposition. Hexagonal-close-packed nanochannel anodized aluminum oxide film was used as the deposition template. The deposition was performed in an organic bath of dimethylsulfoxide with metal chloride as the electrolyte. A high degree of ordering and uniformity in these arrays can be obtained with this technique by fine-tuning the electrodeposition parameters. Moreover, an unprecedentedly high level of uniformity and control of the wire length was achieved. The arrays are unique platforms for explorations of collective behavior in coupled mesoscopic systems, and are useful for applications in high-density data storage, field emission displays, and sensors. Copyright 2001 American Institute of Physics
Tuning the topological charge of laser high-order harmonics
Gauthier, D; Adhikary, G; Camper, A; Chappuis, C; Cucini, R; Dovillaire, G; Géneaux, R; Poletto, L; Ressel, B; Ruchon, T; Spezzani, C; Stupar, M; De Ninno, G
2016-01-01
We report on the generation of optical vortices carrying a controllable amount of orbital angular momentum in laser high-order harmonics in gas. The experiment is based on two-color wave mixing, where a vortex and a Gaussian beam are spatially overlapped in the generation medium. Such a setup allows efficient and robust generation of lower order orbital angular momentum modes. The results constitute the first experimental verification of the conservation rule for orbital angular momentum in high-harmonic generation using two driving beams. Our findings significantly extend the capability of controlling the spatial properties of femtosecond extreme-ultraviolet pulses and could lead to entirely new experiments in the field of light-matter interactions.
XAO coronagraphy with the High-Order Test bench
Directory of Open Access Journals (Sweden)
Kasper M.
2011-07-01
Full Text Available Extreme adaptive optics systems dedicated to the search for extra solar planets are currently being developed for 8–10 meter class telescopes. The High-Order Test bench (HOT is a high-contrast imaging adaptive optics bench developed at ESO. Its objective is to test and optimize different techniques and technologies (e.g. wave front sensors, coronagraphs, speckle calibration methods…. It mimics realistic conditions at a telescope (e.g. VLT, including turbulence generator, XAO, and various near-IR coronagraphs. Here we provide a short overview of the system, and present results of recent AO-closed loop coronagraphic runs obtained with an Apodized Pupil Lyot Coronagraph (APLC.
High-order multiphoton ionization photoelectron spectroscopy of NO
International Nuclear Information System (INIS)
Photoelectron energy and angular distributions of NO following three different high-order multiphoton ionization (MPI) schemes have been measured. The 3+3 resonantly enhanced multiphoton ionization (REMPI) via the A2Σ+ (v=0) level yielded a distribution of electron energies corresponding to all accessible vibrational levels (v+=0--6) of the nascent ion. Angular distributions of electrons corresponding to v+=0 and v+=3 were significantly different. The 3+2 REMPI via the A2Σ+ (v=1) level produced only one low-energy electron peak (v+=1). Nonresonant MPI at 532 nm yielded a distribution of electron energies corresponding to both four- and five-photon ionization. Prominent peaks in the five-photon photoelectron spectrum (PES) suggest contributions from near-resonant states at the three-photon level
Mechanism of High-Order Harmonic Generation from Periodic Potentials
Du, Tao-Yuan
2016-01-01
We study numerically the Bloch electron wave-packet dynamics in periodic potentials to simulate laser-solid interactions. We introduce a quasi-classical model in the \\emph{k} space combined with the energy band structure to understand the high-order harmonic generation (HHG) process occurring in a subcycle timescale. This model interprets the multiple plateau structure in HHG spectra well and the linear dependence of cutoff energies on the amplitude of vector potential of the laser fields. It also predicts the emission time of HHG, which agrees well with the results by solving the time-dependent Schr\\"{o}dinger equation (TDSE). It provides a scheme to reconstruct the energy dispersion relations in Brillouin zone and to control the trajectories of HHG by varying the shape of laser pulses. This model is instructive for experimental measurements.
Role of Rydberg States In High-order Harmonic Generation
Beaulieu, Samuel; Comby, Antoine; Wanie, Vincent; Petit, Stéphane; Légaré, François; Catoire, Fabrice; Mairesse, Yann
2016-01-01
The role of Rydberg states in strong field physics has known a renewed interest in the past few years with the study of resonant high-order harmonic generation. In addition to its fundamental in- terest, this process could create bright sources of coherent vacuum and extreme ultraviolet radiation with controlled polarization state. We investigate the spectral, spatial and temporal characteristics of the radiation produced near the ionization threshold of argon by few-cycle laser pulses. The intensity-dependence of the emission shows that two different pathways interfere to populate the Rydberg states. Furthermore, we show that the population of Rydberg states can lead to different emission mecanisms: either direct emission through XUV Free Induction Decay, or sequentially with absorption of additional photons, in processes similar to resonance-enhanced multiphoton above- threshold ionization. Last, using the attosecond lighthouse technique we show that the resonant emission from Rydberg states is not temporal...
High-order jamming crossovers and density anomalies.
Pica Ciamarra, Massimo; Sollich, Peter
2013-10-28
We demonstrate that particles interacting via core-softened potentials exhibit a series of successive density anomalies upon isothermal compression, leading to oscillations in the diffusivity and thermal expansion coefficient, with the latter reaching negative values. These finite-temperature density anomalies are then shown to correspond to zero-temperature high-order jamming crossovers. These occur when particles are forced to come into contact with neighbours in successive coordination shells upon increasing the density. The crossovers induce anomalous behavior of the bulk modulus, which oscillates with density. We rationalize the dependence of these crossovers on the softness of the interaction potential, and relate the jamming crossovers and the anomalous diffusivity via the properties of the vibrational spectrum. PMID:26029762
A New CMOS Current Reference with High Order Temperature Compensation
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
A new high order CMOS temperature compensated current reference is proposed in this paper, which is accomplished by two first order temperature compensation current references. The novel circuit exploits the temperature characteristics of integrated-circuit resistors and gate-source voltage of MOS transistors working in weak inversion. The proposed circuit, designed with a 0.6 (m standard CMOS technology, gives a good temperature coefficient of 31ppm/℃ [(50～100℃] at a 1.8 V supply, and also achieves line regulation of 0.01%/V and (120 dB PSR at 1 MHz. Comparing with other presented work, the proposed circuit shows better temperature coefficient and Line regulation.
High order source approximation for the EFEN method
International Nuclear Information System (INIS)
The flat source approximation in one dimensional Exponential Function Expansion Nodal (EFEN) method is extended to a high order polynomial approximation while maintaining the simplicity of the nodal response matrix. By applying the new method to a one dimensional PWR pin-by-pin problem, it has been observed that quadratic source approximation is good enough for PWR pin-by-pin calculation, while the flat source approximation causes about 5% of relative error to the thermal flux. By applying the new method to a one dimensional assembly homogenized problem, it has been found that the EFEN method with cubic source approximation can be employed to handle PWR core diffusion problems. Numerical results suggest the optimization of source approximation order for different energy groups and different spacial locations to achieve more accurate results with less computing effort. (author)
High-Order Wave Propagation Algorithms for Hyperbolic Systems
Ketcheson, David I.
2013-01-22
We present a finite volume method that is applicable to hyperbolic PDEs including spatially varying and semilinear nonconservative systems. The spatial discretization, like that of the well-known Clawpack software, is based on solving Riemann problems and calculating fluctuations (not fluxes). The implementation employs weighted essentially nonoscillatory reconstruction in space and strong stability preserving Runge--Kutta integration in time. The method can be extended to arbitrarily high order of accuracy and allows a well-balanced implementation for capturing solutions of balance laws near steady state. This well-balancing is achieved through the $f$-wave Riemann solver and a novel wave-slope WENO reconstruction procedure. The wide applicability and advantageous properties of the method are demonstrated through numerical examples, including problems in nonconservative form, problems with spatially varying fluxes, and problems involving near-equilibrium solutions of balance laws.
Frequency shift in high order harmonic generation from isotopic molecules
He, Lixin; Zhai, Chunyang; Wang, Feng; Shi, Wenjing; Zhang, Qingbin; Zhu, Xiaosong; Lu, Peixiang
2016-01-01
We report the first experimental observation of frequency shift in high order harmonic generation (HHG) from isotopic molecules H2 and D2 . It is found that harmonics generated from the isotopic molecules exhibit obvious spectral red shift with respect to those from Ar atom. The red shift is further demonstrated to arise from the laser-driven nuclear motion in isotopic molecules. By utilizing the red shift observed in experiment, we successfully retrieve the nuclear vibrations in H2 and D2, which agree well with the theoretical calculations from the time-dependent Schrodinger equation (TDSE) with Non-Born-Oppenheimer approximation. Moreover, we demonstrate that the frequency shift can be manipulated by changing the laser chirp.
High-order hydrodynamic algorithms for exascale computing
Energy Technology Data Exchange (ETDEWEB)
Morgan, Nathaniel Ray [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-02-05
Hydrodynamic algorithms are at the core of many laboratory missions ranging from simulating ICF implosions to climate modeling. The hydrodynamic algorithms commonly employed at the laboratory and in industry (1) typically lack requisite accuracy for complex multi- material vortical flows and (2) are not well suited for exascale computing due to poor data locality and poor FLOP/memory ratios. Exascale computing requires advances in both computer science and numerical algorithms. We propose to research the second requirement and create a new high-order hydrodynamic algorithm that has superior accuracy, excellent data locality, and excellent FLOP/memory ratios. This proposal will impact a broad range of research areas including numerical theory, discrete mathematics, vorticity evolution, gas dynamics, interface instability evolution, turbulent flows, fluid dynamics and shock driven flows. If successful, the proposed research has the potential to radically transform simulation capabilities and help position the laboratory for computing at the exascale.
High-order total variation minimization for interior SPECT
International Nuclear Information System (INIS)
Recently, we developed an approach for solving the computed tomography (CT) interior problem based on the high-order TV (HOT) minimization, assuming that a region-of-interest (ROI) is piecewise polynomial. In this paper, we generalize this finding from the CT field to the single-photon emission computed tomography (SPECT) field, and prove that if an ROI is piecewise polynomial, then the ROI can be uniquely reconstructed from the SPECT projection data associated with the ROI through the HOT minimization. Also, we propose a new formulation of HOT, which has an explicit formula for any n-order piecewise polynomial function, while the original formulation has no explicit formula for n ⩾ 2. Finally, we verify our theoretical results in numerical simulation, and discuss relevant issues. (paper)
A highly ordered cubic mesoporous silica/graphene nanocomposite
Lee, Chang-Wook; Roh, Kwang Chul; Kim, Kwang-Bum
2013-09-01
A highly ordered cubic mesoporous silica (KIT-6)/graphene nanocomposite and 2D KIT-6 nanoflakes were synthesized using a novel synthesis methodology. The non-ionic triblock copolymer, P123, played a dual role as a structure-directing agent in the formation of the cubic mesoporous structure and as a cross-linking agent between mesoporous silica and graphene. The prepared (KIT-6)/graphene nanocomposite could act as a template for the preparation of mesoporous material/graphene nanocomposites.A highly ordered cubic mesoporous silica (KIT-6)/graphene nanocomposite and 2D KIT-6 nanoflakes were synthesized using a novel synthesis methodology. The non-ionic triblock copolymer, P123, played a dual role as a structure-directing agent in the formation of the cubic mesoporous structure and as a cross-linking agent between mesoporous silica and graphene. The prepared (KIT-6)/graphene nanocomposite could act as a template for the preparation of mesoporous material/graphene nanocomposites. Electronic supplementary information (ESI) available: S1: TEM images of disordered mesoporous silica/graphene nanocomposite; S2: TEM images of KIT-6/GO nanocomposite; S3: Thermogravimetric analysis of KIT-6/GO and KG-400-700; S4: SEM and TEM images of KIT-6; S5: Low angle XRD, Raman spectra, N2 adsorption isotherms, pore size distribution and photographic images of the prepared samples; S6: TEM image and N2 adsorption isotherms of mesoporous carbon/graphene nanocomposite; S7: XPS C1s spectra of the prepared samples. See DOI: 10.1039/c3nr03108j
High-Order Space-Time Methods for Conservation Laws
Huynh, H. T.
2013-01-01
Current high-order methods such as discontinuous Galerkin and/or flux reconstruction can provide effective discretization for the spatial derivatives. Together with a time discretization, such methods result in either too small a time step size in the case of an explicit scheme or a very large system in the case of an implicit one. To tackle these problems, two new high-order space-time schemes for conservation laws are introduced: the first is explicit and the second, implicit. The explicit method here, also called the moment scheme, achieves a Courant-Friedrichs-Lewy (CFL) condition of 1 for the case of one-spatial dimension regardless of the degree of the polynomial approximation. (For standard explicit methods, if the spatial approximation is of degree p, then the time step sizes are typically proportional to 1/p(exp 2)). Fourier analyses for the one and two-dimensional cases are carried out. The property of super accuracy (or super convergence) is discussed. The implicit method is a simplified but optimal version of the discontinuous Galerkin scheme applied to time. It reduces to a collocation implicit Runge-Kutta (RK) method for ordinary differential equations (ODE) called Radau IIA. The explicit and implicit schemes are closely related since they employ the same intermediate time levels, and the former can serve as a key building block in an iterative procedure for the latter. A limiting technique for the piecewise linear scheme is also discussed. The technique can suppress oscillations near a discontinuity while preserving accuracy near extrema. Preliminary numerical results are shown
Highly ordered periodic mesoporous organosilica nanoparticles with controllable pore structures
Guan, Buyuan; Cui, Yan; Ren, Zhongyuan; Qiao, Zhen-An; Wang, Li; Liu, Yunling; Huo, Qisheng
2012-09-01
A general synthetic procedure for highly ordered and well-dispersed periodic mesoporous organosilica (PMO) nanoparticles is reported based on a single cationic surfactant cetyltrimethylammonium bromide (CTAB) and simple silica sources with organic bridging groups via an ammonia-catalyzed sol-gel reaction. By changing the bridging group in the silica sources, the pore structures of the as-made particles with three-dimensional hexagonal (P63/mmc), cubic (Pm3n), two-dimensional hexagonal (P6mm), and wormlike structure were evidenced by powder X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The size range of the nanoparticles can be adjusted from 30 nm to 500 nm by variation of the ammonia concentration or the co-solvent content of the reaction medium. The PMO nanoparticles with high concentration of organic groups in the framework offered good thermal stability, good dispersion in low polarity solvent and high adsorption of small hydrophobic molecules. Finally, the dye functionalized PMO nanoparticles show low cytotoxicity and excellent cell permeability, which offers great potential for biomedical applications.A general synthetic procedure for highly ordered and well-dispersed periodic mesoporous organosilica (PMO) nanoparticles is reported based on a single cationic surfactant cetyltrimethylammonium bromide (CTAB) and simple silica sources with organic bridging groups via an ammonia-catalyzed sol-gel reaction. By changing the bridging group in the silica sources, the pore structures of the as-made particles with three-dimensional hexagonal (P63/mmc), cubic (Pm3n), two-dimensional hexagonal (P6mm), and wormlike structure were evidenced by powder X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The size range of the nanoparticles can be adjusted from 30 nm to 500 nm by variation of the ammonia concentration or the co-solvent content of the reaction medium. The PMO nanoparticles with high concentration of organic
Template synthesis and characterization of highly ordered lamellar hydroxyapatite
International Nuclear Information System (INIS)
Surfactant template synthesis attracts great attention in the fields of biomaterials and functional materials. In this study, highly ordered lamellar hydroxyapatite (Lα-HA) powder was synthesized by a surfactant templating method in water-ethanol. Ca(NO3)2 and (NH4)2HPO4 were used as calcium and phosphorus sources, respectively. Sodium dodecyl sulphonate (SDS, C12H25SO3Na) acted as the template. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses showed that HA is the only crystal phase in Lα-HA. Transmission electron microscope (TEM) observation further proved this regular lamellar structure detected by XRD. The repeat periodicity of the structure is about 3.6 nm observed by TEM, which is in well accordance with the XRD data (3.16 nm). The selected area electron diffraction (SAED) results indicated that Lα-HA was a polycrystalline structure. The formation of Lα-HA could be explained by a surfactant template
Central Command Architecture for High Order Autonomous Unmanned Systems
Bieber, Chad Michael
This dissertation describes a High-Order Central Command (HOCC) architecture and presents a flight demonstration where a single user coordinates 4 unmanned fixed-wing aircraft. HOCC decouples the user from control of individual vehicles, eliminating human limits on the size of the system, and uses a non-iterative sequence of algorithms that permit easy estimation of how computational complexity scales. The Hungarian algorithm used to solve a min-sum assignment with a one-task planning horizon becomes the limiting complexity, scaling at O(x3) where x is the larger number of vehicles or tasks in the assignment. This method is shown to have a unique property of creating non-intersecting routes which is used to drastically reduce the computational cost of deconflicting planned routes. Results from several demonstration flights are presented where a single user commands a system of 4 fixed-wing aircraft. The results confirm that autonomous flight of a large number of UAVs is a bona fide engineering sub-discipline, which is expected to be of interest to engineers who will find its utility in the aviation industry and in other emerging markets.
Nonlinear high-order mode locking in stochastic sensory neurons
Rowe, Michael; Afghan, Muhammad; Neiman, Alexander
2004-03-01
Excitable systems demonstrate various mode locking regimes when driven by periodic external signals. With noise taken into account, such regimes represent complex nonlinear responses which depend crucially on the frequency and amplitude of the periodic drive as well as on the noise intensity. We study this using a computational model of a stochastic Hodgkin-Huxley neuron in combination with the turtle vestibular sensory system as an experimental model. A bifurcation analysis of the model is performed. Extracellular recordings from primary vestibular afferent neurons with two types of stimuli are used in the experimental study. First, mechanical stimuli applied to the labyrinth allow us to study the responses of the entire system, including transduction by the hair cells and spike generation in the primary afferents. Second, a galvanic stimuli applied directly to an afferent are used to study the responses of afferent spike generator directly. The responses to galvanic stimuli reveal multiple high-order mode locking regimes which are well reproduced in numerical simulation. Responses to mechanical stimulation are characterized by larger variability so that fewer mode-locking regimes can be observed.
A high-order Godunov method for multiple condensed phases
Energy Technology Data Exchange (ETDEWEB)
Miller, G.H. [Univ. of Chicago, IL (United States); Puckett, E.G. [Univ. of California, Davis, CA (United States)
1996-10-01
We present a numerical algorithm for computing strong shock waves in problems involving multiple condensed phases. This method is based on a conservative high-order Godunov method in Eulerian form, similar to those that have been used extensively for gas dynamics computations, with an underlying thermodynamic model based on the Mie-Grueneisen equation of state together with a linear Hugoniot. This thermodynamic model is appropriate for a wide variety of nonporous condensed phases. We model multiple phases by constructing an effective single phase in which the density, specific energy, and elastic properties are given by self-consistent averages of the individual phase properties, including their relative abundances. We use a second-order volume-of-fluid interface reconstruction algorithm to decompose the effective single-phase fluxes back into the appropriate individual component phase quantities. We have coupled a two-dimensional operator-split version of this method to an adaptive mesh refinement algorithm and used it to model problems that arise in experimental shock wave geophysics. Computations from this work are presented. 56 refs., 15 figs., 3 tabs.
A high-order Godunov method for multiple condensed phases
International Nuclear Information System (INIS)
We present a numerical algorithm for computing strong shock waves in problems involving multiple condensed phases. This method is based on a conservative high-order Godunov method in Eulerian form, similar to those that have been used extensively for gas dynamics computations, with an underlying thermodynamic model based on the Mie-Grueneisen equation of state together with a linear Hugoniot. This thermodynamic model is appropriate for a wide variety of nonporous condensed phases. We model multiple phases by constructing an effective single phase in which the density, specific energy, and elastic properties are given by self-consistent averages of the individual phase properties, including their relative abundances. We use a second-order volume-of-fluid interface reconstruction algorithm to decompose the effective single-phase fluxes back into the appropriate individual component phase quantities. We have coupled a two-dimensional operator-split version of this method to an adaptive mesh refinement algorithm and used it to model problems that arise in experimental shock wave geophysics. Computations from this work are presented. 56 refs., 15 figs., 3 tabs
Integrated high-order surface diffraction gratings for diode lasers
Zolotarev, V. V.; Leshko, A. Yu; Pikhtin, N. A.; Slipchenko, S. O.; Sokolova, Z. N.; Lubyanskiy, Ya V.; Voronkova, N. V.; Tarasov, I. S.
2015-12-01
High-order surface diffraction gratings acting as a distributed Bragg reflector (DBR) in mesa stripe semiconductor lasers (λ = 1030 nm) have been studied theoretically and experimentally. Higher order interfering radiation modes (IRMs), which propagate off the plane of the waveguide, have been shown to have a crucial effect on the reflection and transmission spectra of the DBR. The decrease in the reflectivity of the DBR in response to the increase in the diffraction efficiency of these modes may reach 80% and more. According to theoretical analysis results, the intensity of the higher order IRMs is determined by the geometry of the DBR groove profile. Experimental data demonstrate that the noncavity modes are responsible for parasitic light leakage losses in the laser cavity. It has been shown that, in the case of nonoptimal geometry of the grating groove profile, the overall external differential quantum efficiency of the parasitic laser emission may exceed 45%, which is more than half of the laser output power. The optimal geometry of the DBR groove profile is trapezoidal, with the smallest possible lower base. Experimental evidence has been presented that this geometry considerably reduces the power of the higher order IRMs and minimises the parasitic light leakage loss.
High-order accurate dissipative weighted compact nonlinear schemes
Institute of Scientific and Technical Information of China (English)
DENG; Xiaogang(邓小刚)
2002-01-01
Based on the method deriving dissipative compact linear schemes (DCS), novel high-order dissipative weighted compact nonlinear schemes (DWCNS) are developed. By Fourier analysis,the dissipative and dispersive features of DWCNS are discussed. In view of the modified wave number, the DWCNS are equivalent to the fifth-order upwind biased explicit schemes in smooth regions and the interpolations at cell-edges dominate the accuracy of DWCNS. Boundary and near boundary schemes are developed and the asymptotic stabilities of DWCNS on both uniform and stretching grids are analyzed. The multi-dimensional implementations for Euler and Navier-Stokes equations are discussed. Several numerical inviscid and viscous results are given which show the good performances of the DWCNS for discontinuities capturing, high accuracy for boundary layer resolutions, good convergent rates (the root-mean-square of residuals approaching machine zero for solutions with strong shocks) and especially the damping effect on the spudous oscillations which were found in the solutions obtained by TVD and ENO schemes.
High-order WENO scheme for polymerization-type equations*
Directory of Open Access Journals (Sweden)
Gabriel Pierre
2010-12-01
Full Text Available Polymerization of proteins is a biochemical process involved in different diseases. Mathematically, it is generally modeled by aggregation-fragmentation-type equations. In this paper we consider a general polymerization model and propose a high-order numerical scheme to investigate the behavior of the solution. An important property of the equation is the mass conservation. The WENO scheme is built to preserve the total mass of proteins along time. Le processus biophysique de polymérisation de protéines entre en jeu dans différentes maladies. Mathématiquement, ceci est généralement modélisé par des équations de type agrégation-fragmentation. Dans cet article nous considérons un modèle général de polymérisation et proposons un schéma d’ordre élevé pour sa résolution numérique. Une propriété importante de l’équation est la conservation de la masse. Le schéma WENO est construit pour conserver la masse totale de protéines au cours du temps.
A 1D analysis of two high order MOC methods
International Nuclear Information System (INIS)
The work presented here provides two different methods for evaluating angular fluxes along long characteristics. One is based off a projection of the 1D transport equation onto a complete set of Legendre polynomials, while the other uses the 1D integral transport equation to evaluate the angular flux values at specific points along each track passing through a cell. The Moment Long Characteristic (M-LC) method is shown to provide 2(P+1) spatial convergence and significant gains in accuracy with the addition of only a few spatial degrees of freedom. The M-LC method, though, is shown to be ill-conditioned at very high order and for optically thin geometries. The Point Long Characteristic (P-LC) method, while less accurate, significantly improves stability to problems with optically thin cells. The P-LC method is also more flexible, allowing for extra angular flux evaluations along a given track to give a more accurate representation of the shape along each track. This is at the expense of increasing the degrees of freedom of the system, though, and requires an increase in memory storage. This work concludes that both may be used simultaneously within the same geometry to provide the best mix of accuracy and stability possible. (authors)
A Novel QAM Technique for High Order QAM Signaling
Directory of Open Access Journals (Sweden)
A. Ozen
2011-09-01
Full Text Available The paper proposes a novel spread quadrature amplitude modulation (S-QAM technique with high SNR improvement for high-order QAM channels. Simulated and experimental bit error rate (BER performance analyses of the proposed technique in blind and non-blind equalizers are obtained by using single carrier (SC WiMAX (IEEE 802.16-2004 radio. Instead of using any one particular type of channel profile, this study concentrates on true frequency selective Rayleigh fading channels in the real-time WiMAX radio environment around 3.5 GHz. The Constant Modulus Algorithm (CMA blind equalizer has been compared with the popular non-blind equalizers, Recursive Least Squares (RLS and Least Mean Squares (LMS algorithm, as benchmarks. It has been proven in experimental and simulated channels that CMA blind equalizer, using the proposed technique, can be considered as a low complexity, spectrum efficient and high performance time domain equalizations to be embedded in a transceiver for the next generation communications. Furthermore the proposed technique has also reduced approximately till 5 dB and 7.5 dB performance differences between non-blind and blind equalizers for 16-QAM and 64-QAM, respectively. The simulation results have demonstrated that the simulated and experimental studies of the proposed technique are compatible with each other and extremely satisfying.
The high-order quantum coherence of thermal light
Chen, Hui
Thermal light, such as sunlight, is usually considered classical light. In a macroscopic picture, classical theory successfully explained the first-order coherence phenomena of thermal light. The macroscopic theory, based on the statistical behavior of light intensity fluctuations, however, can only phenomenologically explain the second- or higher-order coherence phenomena of thermal light. This thesis introduces a microscopic quantum picture, based on the interferences of a large number of randomly distributed and randomly radiated subfields, wavepackets or photons, to the study of high-order coherence of thermal light. This thesis concludes that the second-order intensity fluctuation correlation is caused by nonlocal interference: a pair of wavepackets, which are randomly paired together, interferes with the pair itself at two distant space-time coordinates. This study has the following practical motivations: (1) to simulate N-qbits. Practical quantum computing requires quantum bits(qubits) of N-digit to represent all possible integers from 0 to 2N-1 simultaneously. A large number of independent particles can be prepared to represent a large set of N orthogonal |0> and |1> bits. In fact, based on our recent experiments of simulating the high-order correlation of entangled photons, thermal radiation is suggested as a promising source for quantum information processing. (2) to achieve sunlight ghost imaging. Ghost imaging has three attractive non-classical features: (a) the ghost camera can "see" targets that can never be seen by a classic camera; (2) it is turbulence-free; and (3) its spatial resolution is mainly determined by the angular diameter of the light source. For example, a sunlight ghost image of an object on earth may achieve a spatial resolution of 200 micrometer because the angular diameter of sun is 0.53 degree with respect to Earth. Although ghost imaging has been experimental demonstrated by using entangled photon pairs and "pseudo-thermal light
Mode of conception of triplets and high order multiple pregnancies.
LENUS (Irish Health Repository)
Basit, I
2012-03-01
A retrospective audit was performed of all high order multiple pregnancies (HOMPs) delivered in three maternity hospitals in Dublin between 1999 and 2008. The mode of conception for each pregnancy was established with a view to determining means of reducing their incidence. A total of 101 HOMPs occurred, 93 triplet, 7 quadruplet and 1 quintuplet. Information regarding the mode of conception was available for 78 (81%) pregnancies. Twenty eight (27.7%) were spontaneous, 34 (33.7%) followedlVF\\/ICSI\\/FET treatment (in-vitro fertilisation, intracytoplasmic sperm injection, frozen embryo transfer), 16 (15.8%) resulted from Clomiphene Citrate treatment and 6 (6%) followed ovulation induction with gonadotrophins. Triplet and HOMPs are a major cause of maternal, feta land neonatal morbidity. Many are iatrogenic, arising from fertility treatments including Clomiphene. Reducing the numbers of embryos transferred will address IVF\\/ICSI\\/FET-related multiple pregnancy rates and this is currently happening in Ireland. Clomiphene and gonadotrophins should only be prescribed when appropriate resources are available to monitor patients adequately.
A Multilevel Parallelization Framework for High-Order Stencil Computations
Dursun, Hikmet; Nomura, Ken-Ichi; Peng, Liu; Seymour, Richard; Wang, Weiqiang; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya
Stencil based computation on structured grids is a common kernel to broad scientific applications. The order of stencils increases with the required precision, and it is a challenge to optimize such high-order stencils on multicore architectures. Here, we propose a multilevel parallelization framework that combines: (1) inter-node parallelism by spatial decomposition; (2) intra-chip parallelism through multithreading; and (3) data-level parallelism via single-instruction multiple-data (SIMD) techniques. The framework is applied to a 6 th order stencil based seismic wave propagation code on a suite of multicore architectures. Strong-scaling scalability tests exhibit superlinear speedup due to increasing cache capacity on Intel Harpertown and AMD Barcelona based clusters, whereas weak-scaling parallel efficiency is 0.92 on 65,536 BlueGene/P processors. Multithreading+SIMD optimizations achieve 7.85-fold speedup on a dual quad-core Intel Clovertown, and the data-level parallel efficiency is found to depend on the stencil order.
Highly ordered ultralong magnetic nanowires wrapped in stacked graphene layers
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Abdel-Aziz El Mel
2012-12-01
Full Text Available We report on the synthesis and magnetic characterization of ultralong (1 cm arrays of highly ordered coaxial nanowires with nickel cores and graphene stacking shells (also known as metal-filled carbon nanotubes. Carbon-containing nickel nanowires are first grown on a nanograted surface by magnetron sputtering. Then, a post-annealing treatment favors the metal-catalyzed crystallization of carbon into stacked graphene layers rolled around the nickel cores. The observed uniaxial magnetic anisotropy field oriented along the nanowire axis is an indication that the shape anisotropy dominates the dipolar coupling between the wires. We further show that the thermal treatment induces a decrease in the coercivity of the nanowire arrays. This reflects an enhancement of the quality of the nickel nanowires after annealing attributed to a decrease of the roughness of the nickel surface and to a reduction of the defect density. This new type of graphene–ferromagnetic-metal nanowire appears to be an interesting building block for spintronic applications.
Control of high order harmonic emission using attosecond pulse trains
International Nuclear Information System (INIS)
Full text: We show that attosecond pulse trains (APTs) are a natural tool for controlling strong field processes such as high order harmonic generation. When used in combination with an intense infrared laser field, the timing of the APT with respect to the infrared (IR) laser field can be used to microscopically select a single quantum path contribution to a process that would otherwise consist of many interfering components. It is through this timing that we predict control over the release of the electron into the continuum, its excursion inside the continuum and consequently influence the yield and coherence properties of the harmonics. Since our initial calculation was based on the time-dependent Schroedinger equation, only single atom effects could be predicted. We have carried out an initial experiment in which we generate the APT from harmonic generation in a xenon fiber target, and focus the APT together with the remaining IR field with an Ag mirror into an He gas jet. The photon spectrum for a fixed time delay between APT and IR field is shown: a clear enhancement of the harmonic spectrum at the cutoff region is seen only when both the APT and the IR field are present. We have predicted control over quantum paths of electron wavepackets using a combination of APT and an IR field, manifesting in the harmonic photon spectrum as order-of-magnitude enhancement of the harmonic yield and spectral cleanup. First experimental results, for a fixed time delay, clearly confirm the enhancement and spectral control, whereas in a future experiment we plan to vary the time delay. Refs. 3 (author)
International Nuclear Information System (INIS)
Objective: To characterize the clinical factors which influence water suppression and auto-shimming line width for liver 3.0 T 1H-MRS. Methods: Fifty-seven cases with liver 1H-MR spectroscopy (1H-MRS) were retrospectively studied, including chronic type B hepatitis (n=5), fatty liver (n=14), chronic type B hepatitis combining fatty liver (n=3) and normal situation (n=35). Independent t test was used to characterize the difference of general condition (height, weight, body mass index etc.) between different water suppression effect groups and between different shimming effect groups. Using Chi-square test to analyze whether water suppression rate and auto-shimming line width between fatty liver groups and non-fatty liver exist significance difference. Results: By comparing WS ≥90% (n=47) group with WS 2 respectively] and LW [(17.7±3.7) and (24.6±6.3) Hz respectively] than the latter (t=-3.488, -3.415, -4.002 and -3.327, P 20 Hz (n=16) group, the former showed better water suppression rate [(93.0±2.7)% and (86.1±8.5)% respectively] than the latter (t=3.213, P2 respectively] (t=-2.516, -2.024, P2=11.347, P2=28.536, P<0.05). Conclusion: Hepatic steatosis exerts an adverse effect in water suppression and shimming. (authors)
De Basabe, Jonás D.
2010-04-01
We investigate the stability of some high-order finite element methods, namely the spectral element method and the interior-penalty discontinuous Galerkin method (IP-DGM), for acoustic or elastic wave propagation that have become increasingly popular in the recent past. We consider the Lax-Wendroff method (LWM) for time stepping and show that it allows for a larger time step than the classical leap-frog finite difference method, with higher-order accuracy. In particular the fourth-order LWM allows for a time step 73 per cent larger than that of the leap-frog method; the computational cost is approximately double per time step, but the larger time step partially compensates for this additional cost. Necessary, but not sufficient, stability conditions are given for the mentioned methods for orders up to 10 in space and time. The stability conditions for IP-DGM are approximately 20 and 60 per cent more restrictive than those for SEM in the acoustic and elastic cases, respectively. © 2010 The Authors Journal compilation © 2010 RAS.
High-order distance-based multiview stochastic learning in image classification.
Yu, Jun; Rui, Yong; Tang, Yuan Yan; Tao, Dacheng
2014-12-01
How do we find all images in a larger set of images which have a specific content? Or estimate the position of a specific object relative to the camera? Image classification methods, like support vector machine (supervised) and transductive support vector machine (semi-supervised), are invaluable tools for the applications of content-based image retrieval, pose estimation, and optical character recognition. However, these methods only can handle the images represented by single feature. In many cases, different features (or multiview data) can be obtained, and how to efficiently utilize them is a challenge. It is inappropriate for the traditionally concatenating schema to link features of different views into a long vector. The reason is each view has its specific statistical property and physical interpretation. In this paper, we propose a high-order distance-based multiview stochastic learning (HD-MSL) method for image classification. HD-MSL effectively combines varied features into a unified representation and integrates the labeling information based on a probabilistic framework. In comparison with the existing strategies, our approach adopts the high-order distance obtained from the hypergraph to replace pairwise distance in estimating the probability matrix of data distribution. In addition, the proposed approach can automatically learn a combination coefficient for each view, which plays an important role in utilizing the complementary information of multiview data. An alternative optimization is designed to solve the objective functions of HD-MSL and obtain different views on coefficients and classification scores simultaneously. Experiments on two real world datasets demonstrate the effectiveness of HD-MSL in image classification. PMID:25415948
ESP pedagogy: Blending low and high order thinking
Directory of Open Access Journals (Sweden)
Yuvienco, Janette Custodio
2012-06-01
Full Text Available Conventional teaching of English has followed a gradual and linear procedure of learning –from vocabulary to phrase to sentence to paragraph. We are familiar with classroom situations where the teacher starts with lecturing about the target language: Firstly, going through a list of vocabulary, then translating words; singling out phrases where a word may be used, then, reading a sentence where the words may be used; finally, walking students through paragraphs, slowly and carefully explaining the grammatical and contextual information in them. In the present Techo-Info Age, however, this approach to learning may prove irrelevant given the amount of information we see, read and hear in different parts of the world at varying contexts and at distinct phases of the development of the language. This paper reports a study on Technology-based pedagogy; it describes and defines the elements of Genre-based pedagogical framework, an ICT-supported set of procedures of teaching Business English at Higher Education which includes showcasing, highlighting, transferring, in order for students to notice, compare and integrate - cognitive skills that encompass both low and high order thinking. Adopting Fink’s (2003 instructional procedures and taking into account Schmidt’s (1990 Noticing Hypothesis; the framework identifies three aspects of consciousness within language learning: awareness, intention and knowledge thus, seeking to arrive at significant, deliberate learning. Guided by this principle, the last section of the paper proposes a proto-syllabus (Breen, 1989 which elaborates the components of a Business English course. Intermeshing knowledge and skills into teaching, the proto-syllabus contains the following: (1 authentic materials which include genre-specific resources (e.g., writing training course leaflet, writing press release, etc. and straightforwardly demonstrate the elements of commercial documents and the criteria for evaluating
Law, Yan Nei; Lieng, Monica Keiko; Li, Jingmei; Khoo, David Aik-Aun
2014-03-01
Breast cancer is the most common cancer and second leading cause of cancer death among women in the US. The relative survival rate is lower among women with a more advanced stage at diagnosis. Early detection through screening is vital. Mammography is the most widely used and only proven screening method for reliably and effectively detecting abnormal breast tissues. In particular, mammographic density is one of the strongest breast cancer risk factors, after age and gender, and can be used to assess the future risk of disease before individuals become symptomatic. A reliable method for automatic density assessment would be beneficial and could assist radiologists in the evaluation of mammograms. To address this problem, we propose a density classification method which uses statistical features from different parts of the breast. Our method is composed of three parts: breast region identification, feature extraction and building ensemble classifiers for density assessment. It explores the potential of the features extracted from second and higher order statistical information for mammographic density classification. We further investigate the registration of bilateral pairs and time-series of mammograms. The experimental results on 322 mammograms demonstrate that (1) a classifier using features from dense regions has higher discriminative power than a classifier using only features from the whole breast region; (2) these high-order features can be effectively combined to boost the classification accuracy; (3) a classifier using these statistical features from dense regions achieves 75% accuracy, which is a significant improvement from 70% accuracy obtained by the existing approaches.
A high order multi-resolution solver for the Poisson equation with application to vortex methods
DEFF Research Database (Denmark)
Hejlesen, Mads Mølholm; Spietz, Henrik Juul; Walther, Jens Honore
A high order method is presented for solving the Poisson equation subject to mixed free-space and periodic boundary conditions by using fast Fourier transforms (FFT). The high order convergence is achieved by deriving mollified Green’s functions from a high order regularization function which...
High-Order Bessel-Gaussian Beam and its Propagation Properties
Institute of Scientific and Technical Information of China (English)
陆璇辉; 陈许敏; 张蕾; 薛大建
2003-01-01
A high-order Bessel-Gaussian mode is introduced to describe hollow beams. The results for high-order BesselGaussian beams propagating through lens focusing system and free space are derived in terms of Collins integral formula. The diffraction patterns and profile for high-order Bessel-Gaussian beams propagating through the above-mentioned optical systems are illustrated.
Esterhazy, Sofi; Schneider, Felix; Schöberl, Joachim; Perugia, Ilaria; Bokelmann, Götz
2016-04-01
The research on purely numerical methods for modeling seismic waves has been more and more intensified over last decades. This development is mainly driven by the fact that on the one hand for subsurface models of interest in exploration and global seismology exact analytic solutions do not exist, but, on the other hand, retrieving full seismic waveforms is important to get insides into spectral characteristics and for the interpretation of seismic phases and amplitudes. Furthermore, the computational potential has dramatically increased in the recent past such that it became worthwhile to perform computations for large-scale problems as those arising in the field of computational seismology. Algorithms based on the Finite Element Method (FEM) are becoming increasingly popular for the propagation of acoustic and elastic waves in geophysical models as they provide more geometrical flexibility in terms of complexity as well as heterogeneity of the materials. In particular, we want to demonstrate the benefit of high-order FEMs as they also provide a better control on the accuracy. Our computations are done with the parallel Finite Element Library NGSOLVE ontop of the automatic 2D/3D mesh generator NETGEN (http://sourceforge.net/projects/ngsolve/). Further we are interested in the generation of synthetic seismograms including direct, refracted and converted waves in correlation to the presence of an underground cavity and the detailed simulation of the comprehensive wave field inside and around such a cavity that would have been created by a nuclear explosion. The motivation of this application comes from the need to find evidence of a nuclear test as they are forbidden by the Comprehensive Nuclear-Test Ban Treaty (CTBT). With this approach it is possible for us to investigate the wave field over a large bandwidth of wave numbers. This again will help to provide a better understanding on the characteristic signatures of an underground cavity, improve the protocols for
A high order energy preserving scheme for the strongly coupled nonlinear Schrödinger system
International Nuclear Information System (INIS)
A high order energy preserving scheme for a strongly coupled nonlinear Schrödinger system is proposed by using the average vector field method. The high order energy preserving scheme is applied to simulate the soliton evolution of the strongly coupled Schrödinger system. Numerical results show that the high order energy preserving scheme can well simulate the soliton evolution, moreover, it preserves the discrete energy of the strongly coupled nonlinear Schrödinger system exactly. (general)
Linear High-Order Distributed Average Consensus Algorithm in Wireless Sensor Networks
Directory of Open Access Journals (Sweden)
Xiong Gang
2010-01-01
Full Text Available This paper presents a linear high-order distributed average consensus (DAC algorithm for wireless sensor networks. The average consensus property and the convergence rate of the high-order DAC algorithm are analyzed. In particular, the convergence rate is determined by the spectral radius of a network topology-dependent matrix. Numerical results indicate that this simple linear high-order DAC algorithm can accelerate the convergence without additional communication overhead and reconfiguration of network topology.
Generation of High-order Group-velocity-locked Vector Solitons
Jin, X X; Zhang, Q; Li, L; Tang, D Y; Shen, D Y; Fu, S N; Liu, D M; Zhao, L M
2015-01-01
We report numerical simulations on the high-order group-velocity-locked vector soliton (GVLVS) generation based on the fundamental GVLVS. The high-order GVLVS generated is characterized with a two-humped pulse along one polarization while a single-humped pulse along the orthogonal polarization. The phase difference between the two humps could be 180 degree. It is found that by appropriate setting the time separation between the two components of the fundamental GVLVS, the high-order GVLVS with different pulse width and pulse intensity could be obtained. 1+2 and 2+2 type high-order GVLVS could be either obtained.
Practical aspects of spherical near-field antenna measurements using a high-order probe
DEFF Research Database (Denmark)
Laitinen, Tommi; Pivnenko, Sergey; Nielsen, Jeppe Majlund; Breinbjerg, Olav
2006-01-01
Two practical aspects related to accurate antenna pattern characterization by probe-corrected spherical near-field antenna measurements with a high-order probe are examined. First, the requirements set by an arbitrary high-order probe on the scanning technique are pointed out. Secondly, a channel...
Convergency analysis of the high-order mimetic finite difference method
Energy Technology Data Exchange (ETDEWEB)
Lipnikov, Konstantin [Los Alamos National Laboratory; Veiga Da Beirao, L [UNIV DEGLI STUDI; Manzini, G [NON LANL
2008-01-01
We prove second-order convergence of the conservative variable and its flux in the high-order MFD method. The convergence results are proved for unstructured polyhedral meshes and full tensor diffusion coefficients. For the case of non-constant coefficients, we also develop a new family of high-order MFD methods. Theoretical result are confirmed through numerical experiments.
Numerical Study on Turbulent Airfoil Noise with High-Order Schemes
DEFF Research Database (Denmark)
Zhu, Wei Jun; Shen, Wen Zhong; Sørensen, Jens Nørkær
2009-01-01
High-order finite difference schemes are introduced in the flow/acoustics splitting technique for predicting flow generated noise. The flow equations are solved by a second-order finite volume method whereas the acoustic equations are solved by high-order finite difference schemes. At each time...
Effects of high-order dispersions on dark-bright vector soliton propagation and interaction
Institute of Scientific and Technical Information of China (English)
Hong Li; Dongning Wang
2011-01-01
The dynamics of dark-bright vector solitons is investigated in a birefringent fiber with the high-order dispersions, and their effects on vector soliton propagation and interaction are analyzed using the numerical method. The combined role of the high-order dispersions, such as the third-order dispersion (TOD) and the fourth-order dispersion (FOD), may cause various deformation of the vector soliton and enhance interaction. These effects depend strictly on the sign of the high-order dispersions. Results indicate that the disadvantageous effects can be reduced effectively via proper mapping of the high-order dispersions.%@@ The dynamics of dark-bright vector solitons is investigated in a birefringent fiber with the high-order dispersions, and their effects on vector soliton propagation and interaction are analyzed using the numerical method.The combined role of the high-order dispersions, such as the third-order dispersion (TOD) and the fourth-order dispersion (FOD), may cause various deformation of the vector soliton and enhance interaction.These effects depend strictly on the sign of the high-order dispersions.Results indicate that the disadvantageous effects can be reduced effectively via proper mapping of the high-order dispersions.
Institute of Scientific and Technical Information of China (English)
Li Yu-Qing; Ma Jie; Wu Ji-Zhou; Zhang Yi-Chi; Zhao Yan-Ting; Wang Li-Rong; Xiao Lian-Tuan; Jia Suo-Tang
2012-01-01
We report on the observation of enhanced high-order partial wave scattering from atom-atom interaction via changing the temperature of a magneto-optical trap in the process of photoassociation. The high-order scattering partial wave is directly manifested through the large signal amplitude of the rovibrational resonance levels of trap-loss spectroscopy from photoassociation.
Quantum and quasi-classical analyses of high order emission processes
Energy Technology Data Exchange (ETDEWEB)
Schafer, K.J.; Kulander, K.C.
1993-06-01
High-order harmonic generation from atoms and ions cuts off in accord with the simple rule: E{sub c} {approximately} I{sub p} + 3U{sub p}. This cutoff rule as well as the lack of a cutoff in high- order electron energy spectra can be understood via a simple extension of existing two step quasi-classical models.
Quantitative Analysis of Zero and High Order Laue Zones Effects on the Exit Wave Function
Institute of Scientific and Technical Information of China (English)
Canying CAI; Qibin YANG; Hongrong LIU; Yanguo WANG
2004-01-01
The exit wave function including zero and high order Laue zones has been simulated by both multi-slice method and electron dynamic diffraction analytical expression. Coincidence of the simulations by these two methods was achieved. The calculated results showed that the exit wave function highly dominated by zero order Laue zone,while high order ones modify the exit wave function to some extent depending on the situation. High order Laue zone effects become important for the following cases: sample consists of light elements, the thickness is very thin,lattice planar spacing perpendicular to the direction of the incident beam is large, and the electron beam has long wavelength. In these cases the exit wave function should be corrected by adding high order Laue zone effects. The analytical expression is effective and convenient for dealing with high order Laue zone effects.
High-Order Calderón Preconditioned Time Domain Integral Equation Solvers
Valdes, Felipe
2013-05-01
Two high-order accurate Calderón preconditioned time domain electric field integral equation (TDEFIE) solvers are presented. In contrast to existing Calderón preconditioned time domain solvers, the proposed preconditioner allows for high-order surface representations and current expansions by using a novel set of fully-localized high-order div-and quasi curl-conforming (DQCC) basis functions. Numerical results demonstrate that the linear systems of equations obtained using the proposed basis functions converge rapidly, regardless of the mesh density and of the order of the current expansion. © 1963-2012 IEEE.
Application of high-order diamond differencing schemes to 3D Cartesian geometries
International Nuclear Information System (INIS)
An innovative high-order discrete ordinate method for the resolution of the time-independent Boltzmann transport equation in 3D Cartesian geometries is presented. This approach consists in a generalization of the classical diamond differencing scheme to high-order spatial approximations. To insure convergence of the source iteration in presence of high diffusive and strong heterogeneous media, diffusion synthetic acceleration (DSA) has been implemented, conjugated with a Krylov subspace method, GMRES(m). We provide numerical comparisons of this 3D high-order SN method with SPn and Monte- Carlo reference calculations. (authors)
A Novel Method for Decoding Any High-Order Hidden Markov Model
Fei Ye; Yifei Wang
2014-01-01
This paper proposes a novel method for decoding any high-order hidden Markov model. First, the high-order hidden Markov model is transformed into an equivalent first-order hidden Markov model by Hadar’s transformation. Next, the optimal state sequence of the equivalent first-order hidden Markov model is recognized by the existing Viterbi algorithm of the first-order hidden Markov model. Finally, the optimal state sequence of the high-order hidden Markov model is inferred from the optimal stat...
Expanding the plateau of high-order harmonic spectrum by multi-color synthesized laser field
International Nuclear Information System (INIS)
We propose a scheme to extend the plateau of high-order harmonic spectrum by using multi- color synthesized laser field. Firstly, the two-color and three-color laser fields are synthesized by adding control laser pulse to the 800 nm fundamental pulse. Secondly, the high-order harmonic spectra are presented via numerically solving the one-dimensional time-dependent Schrodinger equation in multi-color synthesized laser field, and the results show that the width can be expended effectively. Finally, the high-order harmonic spectra are explained reasonably by means of classical returning kinetic-energy map and the time-frequency distribution. (authors)
International Nuclear Information System (INIS)
We present the two results of high-order harmonic generation experiment by using an ultrafast near infrared (NIR) pulse, one is the generation of a coherent water window x-ray under a neutral-medium condition, and the other is the generation of a continuum high-order harmonic spectrum by mixing multicycle two-color NIR laser fields. Our proposed generation scheme, combining an NIR (1600 nm) laser driver and a neutral medium, is efficient and scalable in output yields of the water window x-ray. And also, by optimizing the wavelength of a supplementary NIR pulse in a two-color field, a continuum harmonic spectrum was created around the cutoff region without carrier-envelope phase stabilization. The obtained harmonic spectra clearly show the possibility of generating isolated attosecond pulses from multicycle two-color laser fields. This concept opens the door to create an intense, isolated attosecond pulse using a conventional femtosecond laser system. (author)
Hong, Kyung-Han; Gkortsas, Vasileios-Marios; Huang, Shu-Wei; Moses, Jeffrey; Granados, Eduardo; Bhardwaj, Siddharth; Kärtner, Franz X
2012-01-01
We experimentally and numerically study the atomic response and pulse propagation effects of high-order harmonics generated in Xe, Kr, and Ar driven by a 2.1-\\mu m infrared femtosecond light source. The light source is an optical parametric chirped-pulse amplifier, and a modified strong-field approximation and 3-dimensional pulse propagation code are used for the numerical simulations. The extended cutoff in the long-wavelength driven high-harmonic generation has revealed the spectral shaping of high-order harmonics due to the atomic structure (or photo-recombination cross-section) and the macroscopic effects, which are the main factors of determining the conversion efficiency besides the driving wavelength. Using precise numerical simulations to determine the macroscopic electron wavepacket, we are able to extract the photo-recombination cross-sections from experimental high-order harmonic spectra in the presence of macroscopic effects. We have experimentally observed that the macroscopic effects shift the o...
High Order Wavelet-Based Multiresolution Technology for Airframe Noise Prediction Project
National Aeronautics and Space Administration — An integrated framework is proposed for efficient prediction of rotorcraft and airframe noise. A novel wavelet-based multiresolution technique and high-order...
High-order Finite Elements on Pyramids: Approximation Spaces, Unisolvency and Exactness
Nigam, Nilima; Phillips, Joel
2010-01-01
We present a family of high-order finite element approximation spaces on a pyramid, and associated unisolvent degrees of freedom. These spaces consist of rational basis functions. We establish conforming, exactness and polynomial approximation properties.
Phase Random Walk Trace in High-order Coherence of Two First-order Incoherent Sources
Hong, Peilong
2014-01-01
High-order coherence effects between two first-order incoherent sources with fully independent phases have been well studied in the literature, which shows interference fringes with respect to the position separations among different space points. Here we show that this is not the whole story, and find that the high-order coherence effects depend on the mode of the phase random walk of the first-order incoherent sources, which can be controlled artificially and represented geometrically by vectorial polygons. Interestingly, by scanning the detectors along the same direction with the position separations between them kept constant, a set of high-order coherence fringes, which fingerprint the phase random walk of the first-order incoherent sources, can be observed. Our results show that it is possible to control the high-order coherence of two first-order incoherent sources, which could have important practical applications such as superhigh resolution optical lithography.
Moiseev, N. Ya.
2011-04-01
An approach to the construction of high-order accurate monotone difference schemes for solving gasdynamic problems by Godunov's method with antidiffusion is proposed. Godunov's theorem on monotone schemes is used to construct a new antidiffusion flux limiter in high-order accurate difference schemes as applied to linear advection equations with constant coefficients. The efficiency of the approach is demonstrated by solving linear advection equations with constant coefficients and one-dimensional gasdynamic equations.
High-order harmonic generation in carbon-nanotube-containing plasma plumes
International Nuclear Information System (INIS)
High-order harmonic generation (HHG) in carbon-nanotube (CNT)-containing plasma plumes has been demonstrated. Various targets were ablated to produce the plasma plumes containing nanotubes for the HHG in these media. Harmonics up to the 29th order were generated. Odd and even harmonics were generated using a two-color pump. The integrity of CNTs within the plasma plume, indicating nanotubes as the source of high-order harmonics, was confirmed by structural studies of plasma debris.
Technical Training on High-Order Spectral Analysis and Thermal Anemometry Applications
Maslov, A. A.; Shiplyuk, A. N.; Sidirenko, A. A.; Bountin, D. A.
2003-01-01
The topics of thermal anemometry and high-order spectral analyses were the subject of the technical training. Specifically, the objective of the technical training was to study: (i) the recently introduced constant voltage anemometer (CVA) for high-speed boundary layer; and (ii) newly developed high-order spectral analysis techniques (HOSA). Both CVA and HOSA are relevant tools for studies of boundary layer transition and stability.
A High-Order Finite Spectral Volume Method for Conservation Laws on Unstructured Grids
Wang, Z. J.; Liu, Yen; Kwak, Dochan (Technical Monitor)
2001-01-01
A time accurate, high-order, conservative, yet efficient method named Finite Spectral Volume (FSV) is developed for conservation laws on unstructured grids. The concept of a 'spectral volume' is introduced to achieve high-order accuracy in an efficient manner similar to spectral element and multi-domain spectral methods. In addition, each spectral volume is further sub-divided into control volumes (CVs), and cell-averaged data from these control volumes is used to reconstruct a high-order approximation in the spectral volume. Riemann solvers are used to compute the fluxes at spectral volume boundaries. Then cell-averaged state variables in the control volumes are updated independently. Furthermore, TVD (Total Variation Diminishing) and TVB (Total Variation Bounded) limiters are introduced in the FSV method to remove/reduce spurious oscillations near discontinuities. A very desirable feature of the FSV method is that the reconstruction is carried out only once, and analytically, and is the same for all cells of the same type, and that the reconstruction stencil is always non-singular, in contrast to the memory and CPU-intensive reconstruction in a high-order finite volume (FV) method. Discussions are made concerning why the FSV method is significantly more efficient than high-order finite volume and the Discontinuous Galerkin (DG) methods. Fundamental properties of the FSV method are studied and high-order accuracy is demonstrated for several model problems with and without discontinuities.
An adaptive high-order hybrid scheme for compressive, viscous flows with detailed chemistry
Ziegler, Jack L.; Deiterding, Ralf; Shepherd, Joseph E.; Pullin, D. I.
2011-08-01
A hybrid weighted essentially non-oscillatory (WENO)/centered-difference numerical method, with low numerical dissipation, high-order shock-capturing, and structured adaptive mesh refinement (SAMR), has been developed for the direct numerical simulation of the multicomponent, compressible, reactive Navier-Stokes equations. The method enables accurate resolution of diffusive processes within reaction zones. The approach combines time-split reactive source terms with a high-order, shock-capturing scheme specifically designed for diffusive flows. A description of the order-optimized, symmetric, finite difference, flux-based, hybrid WENO/centered-difference scheme is given, along with its implementation in a high-order SAMR framework. The implementation of new techniques for discontinuity flagging, scheme-switching, and high-order prolongation and restriction is described. In particular, the refined methodology does not require upwinded WENO at grid refinement interfaces for stability, allowing high-order prolongation and thereby eliminating a significant source of numerical diffusion within the overall code performance. A series of one-and two-dimensional test problems is used to verify the implementation, specifically the high-order accuracy of the diffusion terms. One-dimensional benchmarks include a viscous shock wave and a laminar flame. In two-space dimensions, a Lamb-Oseen vortex and an unstable diffusive detonation are considered, for which quantitative convergence is demonstrated. Further, a two-dimensional high-resolution simulation of a reactive Mach reflection phenomenon with diffusive multi-species mixing is presented.
Tumor Classification Using High-Order Gene Expression Profiles Based on Multilinear ICA
Directory of Open Access Journals (Sweden)
Ming-gang Du
2009-01-01
Full Text Available Motivation. Independent Components Analysis (ICA maximizes the statistical independence of the representational components of a training gene expression profiles (GEP ensemble, but it cannot distinguish relations between the different factors, or different modes, and it is not available to high-order GEP Data Mining. In order to generalize ICA, we introduce Multilinear-ICA and apply it to tumor classification using high order GEP. Firstly, we introduce the basis conceptions and operations of tensor and recommend Support Vector Machine (SVM classifier and Multilinear-ICA. Secondly, the higher score genes of original high order GEP are selected by using t-statistics and tabulate tensors. Thirdly, the tensors are performed by Multilinear-ICA. Finally, the SVM is used to classify the tumor subtypes. Results. To show the validity of the proposed method, we apply it to tumor classification using high order GEP. Though we only use three datasets, the experimental results show that the method is effective and feasible. Through this survey, we hope to gain some insight into the problem of high order GEP tumor classification, in aid of further developing more effective tumor classification algorithms.
Arbitrary Truncated Levy Flight: Asymmetrical Truncation and High-Order Correlations
Vinogradov, Dmitry V
2012-01-01
The generalized correlation approach, which has been successfully used in statistical radio physics to describe non-Gaussian random processes, is proposed to describe stochastic financial processes. The generalized correlation approach has been used to describe a non-Gaussian random walk with independent, identically distributed increments in the general case, and high-order correlations have been investigated. The cumulants of an asymmetrically truncated Levy distribution have been found. The behaviors of asymmetrically truncated Levy flight, as a particular case of a random walk, are considered. It is shown that, in the Levy regime, high-order correlations between values of asymmetrically truncated Levy flight exist. The source of high-order correlations is the non-Gaussianity of the increments: the increment skewness generates threefold correlation, and the increment kurtosis generates fourfold correlation.
DEFF Research Database (Denmark)
Madsen, Christian Bruun; Abu-Samha, Mahmoud; Madsen, Lars Bojer
2010-01-01
We present a generic approach for treating the effect of nuclear motion in high-order harmonic generation from polyatomic molecules. Our procedure relies on a separation of nuclear and electron dynamics where we account for the electronic part using the Lewenstein model and nuclear motion enters as...... a nuclear correlation function. We express the nuclear correlation function in terms of Franck-Condon factors, which allows us to decompose nuclear motion into modes and identify the modes that are dominant in the high-order harmonic generation process. We show results for the isotopes CH4 and CD4...... and thereby provide direct theoretical support for a recent experiment [S. Baker et al., Science 312, 424 (2006)] that uses high-order harmonic generation to probe the ultrafast structural nuclear rearrangement of ionized methane....
Weinan, E.; Shu, Chi-Wang
1992-01-01
High order essentially non-oscillatory (ENO) schemes, originally designed for compressible flow and in general for hyperbolic conservation laws, are applied to incompressible Euler and Navier-Stokes equations with periodic boundary conditions. The projection to divergence-free velocity fields is achieved by fourth order central differences through Fast Fourier Transforms (FFT) and a mild high-order filtering. The objective of this work is to assess the resolution of ENO schemes for large scale features of the flow when a coarse grid is used and small scale features of the flow, such as shears and roll-ups, are not fully resolved. It is found that high-order ENO schemes remain stable under such situations and quantities related to large-scale features, such as the total circulation around the roll-up region, are adequately resolved.
Vibrational resonance: a study with high-order word-series averaging
Murua, Ander
2016-01-01
We study a model problem describing vibrational resonance by means of a high-order averaging technique based on so-called word series. With the tech- nique applied here, the tasks of constructing the averaged system and the associ- ated change of variables are divided into two parts. It is first necessary to build recursively a set of so-called word basis functions and, after that, all the required manipulations involve only scalar coefficients that are computed by means of sim- ple recursions. As distinct from the situation with other approaches, with word- series, high-order averaged systems may be derived without having to compute the associated change of variables. In the system considered here, the construction of high-order averaged systems makes it possible to obtain very precise approxima- tions to the true dynamics.
Giant Faraday rotation of high-order plasmonic modes in graphene-covered nanowires
Kuzmin, Dmitry A; Shavrov, Vladimir G; Temnov, Vasily V
2016-01-01
Plasmonic Faraday rotation in nanowires manifests itself in the rotation of the spatial intensity distribution of high-order surface plasmon polariton (SPP) modes around the nanowire axis. Here we predict theoretically the giant Faraday rotation for SPP propagating on graphene-coated magneto-optically active nanowires. Upon the reversal of the external magnetic field pointing along the nanowire axis some high-order plasmonic modes may be rotated by up to ~ 100 degrees on scale of about 500 nm at mid-infrared frequencies. Tuning carrier concentration in graphene by chemical doping or gate voltage allows for controlling SPP-properties and notably the rotation angle of high-order azimuthal modes. Our results open the door to novel plasmonic applications ranging from nanowire-based Faraday isolators to the magnetic control in quantum-optical applications.
Very High Order $\\PNM$ Schemes on Unstructured Meshes for the Resistive Relativistic MHD Equations
Dumbser, Michael
2009-01-01
In this paper we propose the first better than second order accurate method in space and time for the numerical solution of the resistive relativistic magnetohydrodynamics (RRMHD) equations on unstructured meshes in multiple space dimensions. The nonlinear system under consideration is purely hyperbolic and contains a source term, the one for the evolution of the electric field, that becomes stiff for low values of the resistivity. For the spatial discretization we propose to use high order $\\PNM$ schemes as introduced in \\cite{Dumbser2008} for hyperbolic conservation laws and a high order accurate unsplit time discretization is achieved using the element-local space-time discontinuous Galerkin approach proposed in \\cite{DumbserEnauxToro} for one-dimensional balance laws with stiff source terms. The divergence free character of the magnetic field is accounted for through the divergence cleaning procedure of Dedner et al. \\cite{Dedneretal}. To validate our high order method we first solve some numerical test c...
Consensus Analysis of High-Order Multiagent Systems with General Topology and Asymmetric Time-Delays
Directory of Open Access Journals (Sweden)
Fangcui Jiang
2014-01-01
Full Text Available This paper focuses on the consensus problem for high-order multiagent systems (MAS with directed network and asymmetric time-varying time-delays. It is proved that the high-order multiagent system can reach consensus when the network topology contains a spanning tree and time-delay is bounded. The main contribution of this paper is that a Lyapunov-like design framework for the explicit selection of protocol parameters is provided. The Lyapunov-like design guarantees the robust consensus of the high-order multiagent system with respect to asymmetric time-delays and is independent of the exact knowledge of the topology when the communication linkages among agents are undirected and connected.
DEFF Research Database (Denmark)
Hejlesen, Mads Mølholm
the appropriate regularised Green’s functions. Using an analogy to the particle-particle particle-mesh method, a framework for calculating multi-resolution solutions using local refinement patches is presented. The regularised Poisson solver is shown to maintain a high order converging solution for different...... configurations of the refinement patches.The regularised Poisson solver has been implemented in a high order particle-mesh based vortex method for simulating incompressible fluid flow. A re-meshing of the vortex particlesis used to ensure the convergence of the method and a re-projection of the vorticity field...... is included to explicitly fulfil the kinematic constraints of the flow field. The high order, unbounded particle-mesh based vortex method is used to simulate the instability, transition to turbulence and eventual destruction of a single vortex ring. From the simulation data, a novel analysis on the vortex...
He, Yang; Zhang, Ruili; Wang, Yulei; Liu, Jian; Qin, Hong
2016-01-01
We construct high order symmetric volume-preserving methods for the relativistic dynamics of a charged particle by the splitting technique with processing. Via expanding the phase space to include time $t$, we give a more general construction of volume-preserving methods that can be applied to systems with time-dependent electromagnetic fields. The newly derived methods provide numerical solutions with good accuracy and conservative properties over long time of simulation. Furthermore, because of the use of processing technique the high order methods are explicit, and cost less than the methods derived from standard compositions, thus are more efficient. The results are verified by the numerical experiments. Linear stability analysis of the methods show that the high order processed method allows larger time step size during integration.
Multipass relativistic high-order-harmonic generation for intense attosecond pulses
Edwards, Matthew R.; Mikhailova, Julia M.
2016-02-01
We demonstrate that the total reflected field produced by the interaction of a moderately relativistic laser with dense plasma is itself an efficient driver of high-order-harmonic generation. A system of two or more successive interactions of an incident laser beam on solid targets may therefore be an experimentally realizable method of optimizing conversion of laser energy to high-order harmonics. Particle-in-cell simulations suggest that attosecond pulse intensity may be increased by up to four orders of magnitude in a multipass system, with decreased duration of the attosecond pulse train. We discuss high-order-harmonic wave-form engineering for enhanced attosecond pulse generation with an electron trajectory model, present the behavior of multipass systems over a range of parameters, and offer possible routes towards experimental implementation of a two-pass system.
High order filtering methods for approximating hyberbolic systems of conservation laws
Lafon, F.; Osher, S.
1990-01-01
In the computation of discontinuous solutions of hyperbolic systems of conservation laws, the recently developed essentially non-oscillatory (ENO) schemes appear to be very useful. However, they are computationally costly compared to simple central difference methods. A filtering method which is developed uses simple central differencing of arbitrarily high order accuracy, except when a novel local test indicates the development of spurious oscillations. At these points, the full ENO apparatus is used, maintaining the high order of accuracy, but removing spurious oscillations. Numerical results indicate the success of the method. High order of accuracy was obtained in regions of smooth flow without spurious oscillations for a wide range of problems and a significant speed up of generally a factor of almost three over the full ENO method.
Bernuzzi, Sebastiano
2016-01-01
The theoretical modeling of gravitational waveforms from binary neutron star mergers requires precise numerical relativity simulations. Assessing convergence of the numerical data and building the error budget is currently challenging due to the low accuracy of general-relativistic hydrodynamics schemes and to the grid resolutions that can be employed in (3+1)-dimensional simulations. In this work, we explore the use of high-order weighted-essentially-non-oscillatory (WENO) schemes in neutron star merger simulations and investigate the accuracy of the waveforms obtained with such methods. We find that high-order WENO schemes can be robustly employed for simulating the inspiral-merger phase and they significantly improve the assessment of the waveform's error budget with respect to finite-volume methods. High-order WENO schemes can be thus efficiently used for high-quality waveforms production, also in future large-scale investigations of the binary parameter space.
Giant Faraday Rotation of High-Order Plasmonic Modes in Graphene-Covered Nanowires.
Kuzmin, Dmitry A; Bychkov, Igor V; Shavrov, Vladimir G; Temnov, Vasily V
2016-07-13
Plasmonic Faraday rotation in nanowires manifests itself in the rotation of the spatial intensity distribution of high-order surface plasmon polariton (SPP) modes around the nanowire axis. Here we predict theoretically the giant Faraday rotation for SPPs propagating on graphene-coated magneto-optically active nanowires. Upon the reversal of the external magnetic field pointing along the nanowire axis some high-order plasmonic modes may be rotated by up to ∼100° on the length scale of about 500 nm at mid-infrared frequencies. Tuning the carrier concentration in graphene by chemical doping or gate voltage allows for controlling SPP-properties and notably the rotation angle of high-order azimuthal modes. Our results open the door to novel plasmonic applications ranging from nanowire-based Faraday isolators to the magnetic control in quantum-optical applications. PMID:27348746
Papanicolaou, N. C.; Aristotelous, A. C.
2015-10-01
In this work, we develop a High-Order Symmetric Interior Penalty (SIP) Discontinuous Galerkin (DG) Finite Element Method (FEM) to investigate convective flows in a rectangular cavity subject to both vertical and horizontal temperature gradients. The whole cavity is subject to gravity modulation (g-jitter), simulating a microgravity environment. The sensitivity of the bifurcation problem makes the use of a high-order accurate and efficient technique essential. Our method is validated by solving the plane-parallel flow problem and the results were found to be in good agreement with published results. The numerical method was designed to be easily extendable to even more complex flows.
Computational Aero-Acoustic Using High-order Finite-Difference Schemes
Zhu, Wei Jun; Shen, Wen Zhong; Sørensen, Jens Nørkær
2007-01-01
In this paper, a high-order technique to accurately predict flow-generated noise is introduced. The technique consists of solving the viscous incompressible flow equations and inviscid acoustic equations using a incompressible/compressible splitting technique. The incompressible flow equations are solved using the in-house flow solver EllipSys2D/3D which is a second-order finite volume code. The acoustic solution is found by solving the acoustic equations using high-order finite difference sc...
Preparation of highly-ordered carbon nanotube arrays in the anodized alumina template
International Nuclear Information System (INIS)
A highly-ordered, hexagonally arranged alumina nanopore template was prepared by self-organized two-step anodization process of aluminium in oxalic acid solution. Highly parallel pores were obtained within domains of a few micrometers. Highly-ordered, parallel carbon nanotube arrays were successfully grown in the alumina template nanopores by chemical vapor deposition catalyzed by alumina itself. The nanotube arrays are suitable for channeling of particle beams. The structures of aluminium, alumina template and carbon nanotubes were characterized by scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD). The growth mechanism and formation condition of both alumina template and carbon nanotube were discussed. (authors)
Neurodynamics-Based Robust Pole Assignment for High-Order Descriptor Systems.
Le, Xinyi; Wang, Jun
2015-11-01
In this paper, a neurodynamic optimization approach is proposed for synthesizing high-order descriptor linear systems with state feedback control via robust pole assignment. With a new robustness measure serving as the objective function, the robust eigenstructure assignment problem is formulated as a pseudoconvex optimization problem. A neurodynamic optimization approach is applied and shown to be capable of maximizing the robust stability margin for high-order singular systems with guaranteed optimality and exact pole assignment. Two numerical examples and vehicle vibration control application are discussed to substantiate the efficacy of the proposed approach. PMID:26357408
Quasi phase matching for high order harmonic generation induced by the carrier-envelope phase
Faccio, Daniele; Serrat, Carles; Cela, Jose M.; Di Trapani, Albert Farres Paolo; Biegert, Jens
2009-01-01
We report a novel quasi-phase matching technique for high-order harmonic generation in low-density gases. Numerical simulations show that in few-optical cycle pulsed Bessel beams it is possible to control the pulse envelope and phase velocities which in turn allows to control the carrier-envelope phase during propagation. The resulting oscillations in the peak intensity allow to phase-match the high-order harmonic generation process with a nearly two decade enhancement in the XUV power spectrum.
Flat-top phase-matched high-order harmonics in gas-filled cell
Institute of Scientific and Technical Information of China (English)
Xinhua Xie(谢新华); Zhinan Zeng(曾志男); Ruxin Li(李儒新); Yunpei Deng(邓蕴沛); Haihe Lu(陆海鹤); Dingjun Yin(印定军); Zhizhan Xu(徐至展)
2004-01-01
Phase-matched high-order harmonic generation in Ar gas-filled cell is investigated experimentally. We obtain phase-matched 27th order harmonic driven by a commercially available solid-state femtosecond laser system at 0.55 m J/pulse energy level and 1-kHz repetition rate. Moreover, we find that the spatial distribution of intensity of high-order harmonics is flat-top profile other than a Gaussian one under the condition of optimized conversion efficiency in the static gas cell.
High-Order Entropy Stable Finite Difference Schemes for Nonlinear Conservation Laws: Finite Domains
Fisher, Travis C.; Carpenter, Mark H.
2013-01-01
Developing stable and robust high-order finite difference schemes requires mathematical formalism and appropriate methods of analysis. In this work, nonlinear entropy stability is used to derive provably stable high-order finite difference methods with formal boundary closures for conservation laws. Particular emphasis is placed on the entropy stability of the compressible Navier-Stokes equations. A newly derived entropy stable weighted essentially non-oscillatory finite difference method is used to simulate problems with shocks and a conservative, entropy stable, narrow-stencil finite difference approach is used to approximate viscous terms.
Benchmarking with the multigroup diffusion high-order response matrix method
International Nuclear Information System (INIS)
The benchmarking capabilities of the high-order response matrix eigenvalue method, which was developed more than a decade ago, are demonstrated by means of the numerical analysis of a variety of two-dimensional Cartesian geometry light-water reactor test problems. These problems are typical of those generally used for the benchmarking of coarse-mesh (nodal) diffusion methods and the numerical results show that the high-order response matrix eigenvalue method is well suited to be used as an alternative to fine-mesh finite-difference and refined mesh nodal methods for the purpose of generating reference solutions to such problems. (author)
A Rapid Method for the Synthesis of Highly Ordered MCM-41
Directory of Open Access Journals (Sweden)
Mohammad Teymouri
2011-01-01
Full Text Available In the present work MCM-41 material was synthesized by a rapid method. The calcined material was characterized using XRD, scanning electron microscopy and nitrogen physisorption. The XRD pattern of calcined sample shows five well-defined peaks that indicates highly ordered MCM-41 material was synthesized. The SEM image reveals that the sample particles are in nanometer range. The isotherm of Nitrogen demonstrates a nearly reversible behavior which implies highly ordered MCM-41 material was synthesized by this method. The BET specific surface area of the sample is about 910 m3g-1. This method is also rapid and simple and results in high quality MCM-41 material.
High order single step time delay compensation algorithm for structural active control
Institute of Scientific and Technical Information of China (English)
王焕定; 耿淑伟; 王伟
2002-01-01
The optimal instantaneous high order single step algorithm for active control is first discussed andthen, the n + 1 time step controlling force vector of the instantaneous optimal algorithm is derived from way of ntime state vector. An estimating algorithm, is developed from this to solve the problem of active control withtime delay compensation. The estimating algorithm based on this high order single step β method (HSM) foun-dation, is proven by simulation and experiment analysis, to be a valid solution to problem of active control withtime delay compensation.
Room temperature NO2 sensor based on highly ordered porphyrin nanotubes.
Song, Feifei; Ma, Pan; Chen, Changlong; Jia, Jingna; Wang, Yucheng; Zhu, Peihua
2016-07-15
Highly ordered nanotubes of 5, 10, 15, 20-tetrakis(4-aminophenyl)porphyrin zinc (ZnTAP) are fabricated by using nanoporous anodized aluminum oxide (AAO) membrane as the template. Electronic absorption spectra, fluorescence spectra, transmission electron microscope (TEM), scanning electronic microscopy (SEM), low-angle X-ray diffraction (XRD) techniques are adopted to characterize these nanotubes. The highly ordered nanotubes of ZnTAP show good conductivity and present an efficient gas sensor platform for the ultrasensitive detection of NO2 under room temperature. The proposed sensor shows high sensitivity, reproducibility and fast response/recovery behavior, and provides a promising avenue for improving the sensing performance. PMID:27100904
High Order Centrifugal Distortion Corrections to Energy Levels of Asymmetric Top Molecules
Institute of Scientific and Technical Information of China (English)
LIU Yu-Yan; LIU Xiao-Yong; LIU Hong-Ping; GUO Yuan-Qing; HUANG Guang-Ming; LIN Jie-Li; GAO Hui
2000-01-01
High order centrifugal distortion terms have been derived and added to the effective Hamiltonian of asymmetric top molecules. Based on this Hamiltonian, a program in Fortran 77 has been developed for spectral analysis of asymmetric top molecules. The high order centrifugal distortion terms are found to be non-negligible even for the low-lying rotational transitions of molecules, such as Ha 18O, subjected to severe centrifugal distortion effect,and for the high-lying rotational transitions of molecules, such as 14N16O2 subjected to the moderate centrifugal distortion effect.
Probing rotational wave-packet dynamics with the structural minimum in high-order harmonic spectra
Qin, Meiyan; Li, Yang; Zhang, Qingbin; Lan, Pengfei; Lu, Peixiang
2014-01-01
We investigate the alignment-dependent high-order harmonic spectrum generated from nonadiabatically aligned molecules around the first half rotational revival. It is found that the evolution of the molecular alignment is encoded in the structural minima. To reveal the relation between the molecular alignment and the structural minimum in the high-order harmonic spectrum, we perform an analysis based on the two-center interference model. Our analysis shows that the structural minimum position depends linearly on the inverse of the alignment parameter $$. This linear relation indicates the possibility of probing the rotational wave-packet dynamics by measuring the spectral minima.
High order filtering methods for approximating hyperbolic systems of conservation laws
Lafon, F.; Osher, S.
1991-01-01
The essentially nonoscillatory (ENO) schemes, while potentially useful in the computation of discontinuous solutions of hyperbolic conservation-law systems, are computationally costly relative to simple central-difference methods. A filtering technique is presented which employs central differencing of arbitrarily high-order accuracy except where a local test detects the presence of spurious oscillations and calls upon the full ENO apparatus to remove them. A factor-of-three speedup is thus obtained over the full-ENO method for a wide range of problems, with high-order accuracy in regions of smooth flow.
International Nuclear Information System (INIS)
Using a quantum-mechanical three-step model, we present numerical calculations of the high-order harmonic generation from four polyatomic molecules. Ethylene (C2H4) serves as an example where orbital symmetry directly affects the harmonic yield. We treat the case of methane (CH4) to address the high-order harmonic generation resulting from a molecule with degenerate orbitals. To this end we illustrate how the single-orbital contributions show up in the total high-order harmonic signal. This example illustrates the importance of adding coherently the amplitude contributions from the individual degenerate orbitals. Finally, we study the high-order harmonic generation from propane (C3H8) and butane (C4H10). These two molecules, being extended and far from spherical in structure, produce harmonics with nontrivial orientational dependencies. In particular, propane can be oriented so that very high-frequency harmonics are favored, and thus the molecule contains prospects for the generation of uv attosecond pulses
Approximate high-order eigenvalues in two-medium, one-speed neutron transport
International Nuclear Information System (INIS)
Earlier work on high-order criticality eigenvalues in homogeneous systems with neutrons of one speed has been extended to two-medium systems. Reflected spheres as well as reflected infinite slabs and cylinders have been studied. Values from the derived formulae have been compared with numerical results obtained recently by Garis for spheres and slabs. The agreement is generally good. (author)
A high-order external distributed feedback polymer laser with low working threshold
Huang, Wenbin; Pu, Donglin; Yang, Xiaofei; Wei, Guojun; Fang, Zongbao; Zhou, Xiaohong; Qiao, Wen; Chen, Linsen
2016-05-01
In this paper, we report a high-order distributed feedback (DFB) polymer laser with low working threshold. Using the high-order grating increases the lithographic tolerances, providing coherent light sources that are more amenable to mass-manufacturing techniques, such as laser direct writing lithography and roll-to-roll processing. To enable high-order DFB lasing, an unconventional working configuration is designed in which the grating is situated on top of the uniform conjugated polymer film. In addition, a novel Forster energy transfer blend of two conjugated polymers is used as the gain medium. Upon pumping, the device emits lasing around 603.6 nm with a bandwidth of 0.5 nm. The threshold is around 20.5 μJ cm‑2 (~2.56 kW cm‑2), about to enter the regime of inexpensive LED pumping. A further increase in pump energy results in simultaneous oscillations at the 29th and 30th Bragg orders. Operating principles of the high-order DFB polymer laser, including spectral performance and threshold dependence on pump length, are investigated. This approach represents a step towards low-cost, even ‘disposable’ polymer lasers.
High-order Finite Difference Solution of Euler Equations for Nonlinear Water Waves
DEFF Research Database (Denmark)
Christiansen, Torben Robert Bilgrav; Bingham, Harry B.; Engsig-Karup, Allan Peter
2012-01-01
with a two-dimensional implementation of the model are compared with highly accurate stream function solutions to the nonlinear wave problem, which show the approximately expected convergence rates and a clear advantage of using high-order finite difference schemes in combination with the Euler equations....
Efficient High Order Central Schemes for Multi-Dimensional Hamilton-Jacobi Equations: Talk Slides
Bryson, Steve; Levy, Doron; Biegel, Brian R. (Technical Monitor)
2002-01-01
This viewgraph presentation presents information on the attempt to produce high-order, efficient, central methods that scale well to high dimension. The central philosophy is that the equations should evolve to the point where the data is smooth. This is accomplished by a cyclic pattern of reconstruction, evolution, and re-projection. One dimensional and two dimensional representational methods are detailed, as well.
High Order Finite Difference Methods, Multidimensional Linear Problems and Curvilinear Coordinates
Nordstrom, Jan; Carpenter, Mark H.
1999-01-01
Boundary and interface conditions are derived for high order finite difference methods applied to multidimensional linear problems in curvilinear coordinates. The boundary and interface conditions lead to conservative schemes and strict and strong stability provided that certain metric conditions are met.
International Nuclear Information System (INIS)
A 3 x 3 matrix spectral problem and a Liouville integrable hierarchy are constructed by designing a new subalgebra of loop algebra A2. Furthermore, high-order binary symmetry constraints of the corresponding hierarchy are obtained by using the binary nonlinearization method. Finally, according to another new subalgebra of loop algebra A2, its integrable couplings are established.
Guided Assemblies of Ferritin Nanocages: Highly Ordered Arrays of Monodisperse Nanoscopic Elements
Energy Technology Data Exchange (ETDEWEB)
Hu, Y.; Chen, D; Park, S; Emrick, T; Russell, T
2010-01-01
High-density arrays of highly ordered ferritin nanocages are fabricated through the guided assembly of thiol-modified ferritin on prepatterned gold nanodots, which are prepared by block copolymer micelle lithography. One and only one ferritin nanocage is anchored to each gold nanodot, as confirmed by scanning electron and scanning force microscopy.
Developing Student-Centered Learning Model to Improve High Order Mathematical Thinking Ability
Saragih, Sahat; Napitupulu, Elvis
2015-01-01
The purpose of this research was to develop student-centered learning model aiming to improve high order mathematical thinking ability of junior high school students of based on curriculum 2013 in North Sumatera, Indonesia. The special purpose of this research was to analyze and to formulate the purpose of mathematics lesson in high order…
DEFF Research Database (Denmark)
Wang, Shaofei; Guo, Hairun; Bai, Xuekun;
2014-01-01
We numerically investigate the influence of high-order dispersion (HOD) on temporal and spectral characteristics of microresonator-based optical frequency combs. Theoretical analysis based on the moment method associated with numerical simulations are utilized to study the comb evolution dynamics...
Optimal Design of High-Order Passive-Damped Filters for Grid-Connected Applications
DEFF Research Database (Denmark)
Beres, Remus Narcis; Wang, Xiongfei; Blaabjerg, Frede;
2016-01-01
Harmonic stability problems caused by the resonance of high-order filters in power electronic systems are ever increasing. The use of passive damping does provide a robust solution to address these issues, but at the price of reduced efficiency due to the presence of additional passive components...
High order mode damping in the NSLS accelerating RF cavities by the use of damping antennae
Fewell, N.; Wen, Z.
High order modes were successfully damped in the existing NSLS accelerating cavities by the insertion of damping antennae. The location of the antennae was aided by cavity field plots using superfish and their lengths determined experimentally. A description of their construction is presented together with the results of their insertion upon higher order cavity modes and beam stability.
DEFF Research Database (Denmark)
Etches, Adam; Madsen, Christian Bruun; Madsen, Lars Bojer
A correction term is introduced in the stationary-point analysis on high-order harmonic generation (HHG) from aligned molecules. Arising from a multi-centre expansion of the electron wave function, this term brings our numerical calculations of the Lewenstein model into qualitative agreement with...
Guided transmission of slow Ne ions through the nanochannels of highly ordered anodic alumina
DEFF Research Database (Denmark)
Mátéfi-Tempfli, Stefan; Mátéfi-Tempfli, M.; Piraux, L.;
2006-01-01
A highly ordered hexagonally close-packed nanochannels array was prepared using the self-ordering phenomena during a two-step anodization process of a high purity aluminium foil. The anodized aluminium oxide, with pore diameters of about 280nm and interpore distances of about 450nm was prepared as...
High Order Adjoint Derivatives using ESDIRK Methods for Oil Reservoir Production Optimization
DEFF Research Database (Denmark)
Capolei, Andrea; Stenby, Erling Halfdan; Jørgensen, John Bagterp
2012-01-01
In production optimization, computation of the gradients is the computationally expensive step. We improve the computational efficiency of such algorithms by improving the gradient computation using high-order ESDIRK (Explicit Singly Diagonally Implicit Runge-Kutta) temporal integration methods and...
Highly ordered three-dimensional macroporous carbon spheres for determination of heavy metal ions
International Nuclear Information System (INIS)
Highlights: ► Highly ordered three dimensional macroporous carbon spheres (MPCSs) were prepared. ► MPCS was covalently modified by cysteine (MPCS–CO–Cys). ► MPCS–CO–Cys was first time used in electrochemical detection of heavy metal ions. ► Heavy metal ions such as Pb2+ and Cd2+ can be simultaneously determined. -- Abstract: An effective voltammetric method for detection of trace heavy metal ions using chemically modified highly ordered three dimensional macroporous carbon spheres electrode surfaces is described. The highly ordered three dimensional macroporous carbon spheres were prepared by carbonization of glucose in silica crystal bead template, followed by removal of the template. The highly ordered three dimensional macroporous carbon spheres were covalently modified by cysteine, an amino acid with high affinities towards some heavy metals. The materials were characterized by physical adsorption of nitrogen, scanning electron microscopy, and transmission electron microscopy techniques. While the Fourier-transform infrared spectroscopy was used to characterize the functional groups on the surface of carbon spheres. High sensitivity was exhibited when this material was used in electrochemical detection (square wave anodic stripping voltammetry) of heavy metal ions due to the porous structure. And the potential application for simultaneous detection of heavy metal ions was also investigated.
High-order finite difference solution for 3D nonlinear wave-structure interaction
DEFF Research Database (Denmark)
Ducrozet, Guillaume; Bingham, Harry B.; Engsig-Karup, Allan Peter;
2010-01-01
This contribution presents our recent progress on developing an efficient fully-nonlinear potential flow model for simulating 3D wave-wave and wave-structure interaction over arbitrary depths (i.e. in coastal and offshore environment). The model is based on a high-order finite difference scheme...
Rotating-frame perspective on high-order-harmonic generation of circularly polarized light
Reich, Daniel M.; Madsen, Lars Bojer
2016-04-01
We employ a rotating frame of reference to elucidate high-order-harmonic generation of circularly polarized light by bicircular driving fields. In particular, we show how the experimentally observed circular components of the high-order-harmonic spectrum can be directly related to the corresponding quantities in the rotating frame. Supported by numerical simulations of the time-dependent Schrödinger equation, we deduce an optimal strategy for maximizing the cutoff in the high-order-harmonic plateau while keeping the two circular components of the emitted light spectrally distinct. Moreover, we show how the rotating-frame picture can be more generally employed for elliptical drivers. Finally, we point out how circular and elliptical driving fields show a near-duality to static electric and magnetic fields in a rotating-frame description. This demonstrates how high-order-harmonic generation of circularly polarized light under static electromagnetic fields can be emulated in practice even at static field strengths beyond current experimental capabilities.
High-order harmonics in a quantum dot and metallic nanorod complex.
Yang, Wen-Xing
2015-11-01
We investigate the high-order harmonic generation (HHG) in a semiconductor quantum dot (SQD) and metallic nanorod (MNR) complex driven by a moderate intensity (supercontinuum harmonics (25 eV maximal photon energy) and isolated ultrashort pulses (2.67-4.36 fs FWHM) are achievable. PMID:26512479
High-order inertial phase shifts for time-domain atom interferometers
Bongs, Kai; Launay, Romain; Kasevich, Mark A.
2002-01-01
High-order inertial phase shifts are calculated for time-domain atom interferometers. We obtain closed-form analytic expressions for these shifts in accelerometer, gyroscope, optical clock and photon recoil measurement configurations. Our analysis includes Coriolis, centrifugal, gravitational, and gravity gradient-induced forces. We identify new shifts which arise at levels relevant to current and planned experiments.
A family of high-order targeted ENO schemes for compressible-fluid simulations
Fu, Lin; Hu, Xiangyu Y.; Adams, Nikolaus A.
2016-01-01
Although classical WENO schemes have achieved great success and are widely accepted, they exhibit several shortcomings. They are too dissipative for direct simulations of turbulence and lack robustness when very-high-order versions are applied to complex flows. In this paper, we propose a family of high-order targeted ENO schemes which are applicable for compressible-fluid simulations involving a wide range of flow scales. In order to increase the numerical robustness as compared to very-high-order classical WENO schemes, the reconstruction dynamically assembles a set of low-order candidate stencils with incrementally increasing width. While discontinuities and small-scale fluctuations are efficiently separated, the numerical dissipation is significantly diminished by an ENO-like stencil selection, which either applies a candidate stencil with its original linear weight, or removes its contribution when it is crossed by a discontinuity. The background linear scheme is optimized under the constraint of preserving an approximate dispersion-dissipation relation. By means of quasi-linear analyses and practical numerical experiments, a set of case-independent parameters is determined. The general formulation of arbitrarily high-order schemes is presented in a straightforward way. A variety of benchmark-test problems, including broadband waves, strong shock and contact discontinuities are studied. Compared to well-established classical WENO schemes, the present schemes exhibit significantly improved robustness, low numerical dissipation and sharp discontinuity capturing. They are particularly suitable for DNS and LES of shock-turbulence interactions.
Very high-order finite volume method for one-dimensional convection diffusion problems
Clain, Stéphane; Diot, Steven; Loubère, Raphaël; Machado, Gaspar; Ralha, Rui; Pereira, Rui
2011-01-01
We propose a new finite volume method to provide very high-order accuracy for the convection diffusion problem. The main tool is a polynomial reconstruction baesd on the mean values to provide the optimal order. Numerical examples are proposed to show the method efficiency.
HIGH-ORDER NYSTR(``O)M METHOD FOR THE EFIE OF EM SCATTERING PROBLEMS
Institute of Scientific and Technical Information of China (English)
Zhang Xiaojuan
2004-01-01
Nystrom method is a new method for solving electromagnetic scattering problems.This paper gives the detailed description on high-order Nystrom method used for the electric field integral equation of electromagnetic scattering problems. The numerical solutions of two examples are correct compared with Method Of Moment(MOM).
A Reconstruction Approach to High-Order Schemes Including Discontinuous Galerkin for Diffusion
Huynh, H. T.
2009-01-01
We introduce a new approach to high-order accuracy for the numerical solution of diffusion problems by solving the equations in differential form using a reconstruction technique. The approach has the advantages of simplicity and economy. It results in several new high-order methods including a simplified version of discontinuous Galerkin (DG). It also leads to new definitions of common value and common gradient quantities at each interface shared by the two adjacent cells. In addition, the new approach clarifies the relations among the various choices of new and existing common quantities. Fourier stability and accuracy analyses are carried out for the resulting schemes. Extensions to the case of quadrilateral meshes are obtained via tensor products. For the two-point boundary value problem (steady state), it is shown that these schemes, which include most popular DG methods, yield exact common interface quantities as well as exact cell average solutions for nearly all cases.
Pricing Exotic Options under a High-Order Markovian Regime Switching Model
Directory of Open Access Journals (Sweden)
Wai-Ki Ching
2007-01-01
by a discrete-time Markovian regime-switching process driven by an observable, high-order Markov model (HOMM. We assume that the market interest rate, the drift, and the volatility of the underlying risky asset's return switch over time according to the states of the HOMM, which are interpreted as the states of an economy. We will then employ the well-known tool in actuarial science, namely, the Esscher transform to determine an equivalent martingale measure for option valuation. Moreover, we will also investigate the impact of the high-order effect of the states of the economy on the prices of some path-dependent exotic options, such as Asian options, lookback options, and barrier options.
A wavelet-optimized, very high order adaptive grid and order numerical method
Jameson, Leland
1996-01-01
Differencing operators of arbitrarily high order can be constructed by interpolating a polynomial through a set of data followed by differentiation of this polynomial and finally evaluation of the polynomial at the point where a derivative approximation is desired. Furthermore, the interpolating polynomial can be constructed from algebraic, trigonometric, or, perhaps exponential polynomials. This paper begins with a comparison of such differencing operator construction. Next, the issue of proper grids for high order polynomials is addressed. Finally, an adaptive numerical method is introduced which adapts the numerical grid and the order of the differencing operator depending on the data. The numerical grid adaptation is performed on a Chebyshev grid. That is, at each level of refinement the grid is a Chebvshev grid and this grid is refined locally based on wavelet analysis.
Enhancement of high-order harmonic generation in the presence of noise
International Nuclear Information System (INIS)
We report on our simulations of the generation of high-order harmonics from atoms driven by an intense femtosecond laser field in the presence of noise. We numerically solve the non-perturbative stochastic time-dependent Schroedinger equation and observe how varying noise levels affect the frequency components of the high harmonic spectrum. Our calculations show that when an optimum amount of noise is present in the driving laser field, roughly a factor of 45 net enhancement can be achieved in high-order harmonic yield, especially, around the cut-off region. We observe that, for a relatively weak noise, the enhancement mechanism is sensitive to the carrier-envelope phase. We also investigate the possibility of generating ultra-short intense attosecond pulses by combining the laser field and noise and observe that a roughly four orders of magnitude enhanced isolated attosecond burst can be generated.
Retrieval of interatomic separations of molecules from laser-induced high-order harmonic spectra
International Nuclear Information System (INIS)
We illustrate an iterative method for retrieving the internuclear separations of N2, O2 and CO2 molecules using the high-order harmonics generated from these molecules by intense infrared laser pulses. We show that accurate results can be retrieved with a small set of harmonics and with one or few alignment angles of the molecules. For linear molecules the internuclear separations can also be retrieved from harmonics generated using isotropically distributed molecules. By extracting the transition dipole moment from the high-order harmonic spectra, we further demonstrated that it is preferable to retrieve the interatomic separation iteratively by fitting the extracted dipole moment. Our results show that time-resolved chemical imaging of molecules using infrared laser pulses with femtosecond temporal resolutions is possible
Unstructured nodal DG-FEM solution of high-order Boussinesq-type equations
DEFF Research Database (Denmark)
Engsig-Karup, Allan Peter
2007-01-01
high-order Boussinesq equations. Remarkably, it is demonstrated that the linear eigenspectra of the linearized semi-discrete equation system is bounded and hence the stable time increment is not dictated by the spatial discretization. This is a favorable property for explicit time-integration schemes...... equations constitute a highly complex system of coupled equations which put any numerical method to the test. The main problems that need to be overcome to solve the equations are the treatment of strongly nonlinear convection-type terms and spatially varying coefficient terms; efficient and robust solution...... of the resultant time-dependent linear system; and the numerical treatment of high-order and cross-differential derivatives. The suggested solution strategy of the current work is based on a collocation approach where the DG-FEM is used to approximate spatial derivatives and the boundary conditions...
Wang, Junfeng; Miesch, Mark S
2015-01-01
We present a novel and powerful Compressible High-ORder Unstructured Spectral-difference (CHORUS) code for simulating thermal convection and related fluid dynamics in the interiors of stars and planets. The computational geometries are treated as rotating spherical shells filled with stratified gas. The hydrodynamic equations are discretized by a robust and efficient high-order Spectral Difference Method (SDM) on unstructured meshes. The computational stencil of the spectral difference method is compact and advantageous for parallel processing. CHORUS demonstrates excellent parallel performance for all test cases reported in this paper, scaling up to 12,000 cores on the Yellowstone High-Performance Computing cluster at NCAR. The code is verified by defining two benchmark cases for global convection in Jupiter and the Sun. CHORUS results are compared with results from the ASH code and good agreement is found. The CHORUS code creates new opportunities for simulating such varied phenomena as multi-scale solar co...
Xiao, Feng; Chen, Chungang; Li, Xingliang
2012-01-01
This paper presents a general formulation to construct high order numerical schemes by using multi-moment constraint conditions on the flux function reconstruction. The new formulation, so called multi-moment constrained flux reconstruction (MMC-FR), distinguishes itself essentially from the flux reconstruction formulation (FR) of Huynh (2007) by imposing not only the continuity constraint conditions on the flux function at the cell boundary, but also other types constraints which may include those on the spatial derivatives or the point values. This formulation can be also interprated as a blend of Lagrange interpolation the Hermite interpolation, which provides a numerical framework to accomodate a wider spectrum of high order schemes. Some representative schemes will be presented and evaluated through Fourier analysis and numerical tests.
A high-order Legendre-WENO kernel density function method for modeling disperse flows
Smith, Timothy; Pantano, Carlos
2015-11-01
We present a high-order kernel density function (KDF) method for disperse flow. The numerical method used to solve the system of hyperbolic equations utilizes a Roe-like update for equations in non-conservation form. We will present the extension of the low-order method to high order using the Legendre-WENO method and demonstrate the improved capability of the method to predict statistics of disperse flows in an accurate, consistent and efficient manner. By construction, the KDF method already enforced many realizability conditions but others remain. The proposed method also considers these constraints and their performance will be discussed. This project was funded by NSF project NSF-DMS 1318161.
Different time scales in plasmonically enhanced high-order harmonic generation
Zagoya, C; Chomet, H; Slade, E; Faria, C Figueira de Morisson
2016-01-01
We investigate high-order harmonic generation in inhomogeneous media for reduced dimensionality models. We perform a phase-space analysis, in which we identify specific features caused by the field inhomogeneity. We compute high-order harmonic spectra using the numerical solution of the time-dependent Schr\\"odinger equation, and provide an interpretation in terms of classical electron trajectories. We show that the dynamics of the system can be described by the interplay of high-frequency and slow-frequency oscillations, which are given by Mathieu's equations. The latter oscillations lead to an increase in the cutoff energy, and, for small values of the inhomogeneity parameter, take place over many driving-field cycles. In this case, the two processes can be decoupled and the oscillations can be described analytically.
Retrieval of interatomic separations of molecules from laser-induced high-order harmonic spectra
Energy Technology Data Exchange (ETDEWEB)
Le, Van-Hoang; Nguyen, Ngoc-Ty [Department of Physics, University of Pedagogy, 280 An Duong Vuong, Ward 5, Ho Chi Minh City (Viet Nam); Jin, C; Le, Anh-Thu; Lin, C D [J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS 66506 (United States)
2008-04-28
We illustrate an iterative method for retrieving the internuclear separations of N{sub 2}, O{sub 2} and CO{sub 2} molecules using the high-order harmonics generated from these molecules by intense infrared laser pulses. We show that accurate results can be retrieved with a small set of harmonics and with one or few alignment angles of the molecules. For linear molecules the internuclear separations can also be retrieved from harmonics generated using isotropically distributed molecules. By extracting the transition dipole moment from the high-order harmonic spectra, we further demonstrated that it is preferable to retrieve the interatomic separation iteratively by fitting the extracted dipole moment. Our results show that time-resolved chemical imaging of molecules using infrared laser pulses with femtosecond temporal resolutions is possible.
Duru, Kenneth
2014-12-01
© 2014 Elsevier Inc. In this paper, we develop a stable and systematic procedure for numerical treatment of elastic waves in discontinuous and layered media. We consider both planar and curved interfaces where media parameters are allowed to be discontinuous. The key feature is the highly accurate and provably stable treatment of interfaces where media discontinuities arise. We discretize in space using high order accurate finite difference schemes that satisfy the summation by parts rule. Conditions at layer interfaces are imposed weakly using penalties. By deriving lower bounds of the penalty strength and constructing discrete energy estimates we prove time stability. We present numerical experiments in two space dimensions to illustrate the usefulness of the proposed method for simulations involving typical interface phenomena in elastic materials. The numerical experiments verify high order accuracy and time stability.
Highly ordered palladium nanodots and nanowires from switchable block copolymer thin films
Energy Technology Data Exchange (ETDEWEB)
Bhoje Gowd, E; Nandan, Bhanu; Vyas, Mukesh Kumar; Stamm, Manfred [Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, 01069, Dresden (Germany); Bigall, Nadja C; Eychmueller, Alexander [Physical Chemistry and Electrochemistry, TU Dresden, Bergstrasse 66b, 01062, Dresden (Germany); Schloerb, Heike, E-mail: gowd@ipfdd.d, E-mail: nandan@ipfdd.d [Leibniz Institute for Solid State and Materials Research Dresden, PO Box 27 00 16, D-01171, Dresden (Germany)
2009-10-14
We demonstrate a new approach to fabricate highly ordered arrays of nanoscopic palladium dots and wires using switchable block copolymer thin films. The surface-reconstructed block copolymer templates were directly deposited with palladium nanoparticles from a simple aqueous solution. The preferential interaction of the nanoparticles with one of the blocks is mainly responsible for the lateral arrangement of the nanoparticles inside the pores of the templates in addition to the capillary forces. A subsequent stabilization by UV-irradiation followed by pyrolysis in air at 450 {sup 0}C removes the polymer to produce highly ordered metallic nanostructures. We extended this approach to micellar films to obtain metallic nanostructures. This method is highly versatile as the procedure used here is simple, eco-friendly and provides a simple approach to fabricate a broad range of nanoscaled architectures with tunable lateral spacing, and can be extended to systems with even smaller dimensions.
Del Zanna, L; Bucciantini, N; Londrillo, P
2007-01-01
We present a new numerical code, ECHO, based on an Eulerian Conservative High Order scheme for time dependent three-dimensional general relativistic magnetohydrodynamics (GRMHD) and magnetodynamics (GRMD). ECHO is aimed at providing a shock-capturing conservative method able to work at an arbitrary level of formal accuracy (for smooth flows), where the other existing GRMHD and GRMD schemes yield an overall second order at most. Moreover, our goal is to present a general framework, based on the 3+1 Eulerian formalism, allowing for different sets of equations, different algorithms, and working in a generic space-time metric, so that ECHO may be easily coupled to any solver for Einstein's equations. Various high order reconstruction methods are implemented and a two-wave approximate Riemann solver is used. The induction equation is treated by adopting the Upwind Constrained Transport (UCT) procedures, appropriate to preserve the divergence-free condition of the magnetic field in shock-capturing methods. The limi...
Amplified high order harmonic light for high coherent x-ray laser
International Nuclear Information System (INIS)
We proposed a method to generate high spatial and temporal coherent x-ray laser, in which high order harmonic light is used as a seed light of a laser-produced x-ray amplifier. The high order harmonic light is very suitable for this purpose because it has high spatial and temporal coherence. In this report, we conducted an experiment for the amplification of the 29th order harmonic light of the Ti;Sapphire laser with the neon-like manganese x-ray laser medium (λ=26.9 nm) pumped by the Nd:Glass laser. The divergence of Ne-like Mu x-ray laser with the seed light was preserved form the divergence of the seed light. We succeed in amplification of the harmonic light for the purpose of high coherent x-ray laser. (author)
High order convergent multigrid methods on domains containing holes for black hole initial data
Natchu, Vishnu
2007-01-01
It is well known that multigrid methods are optimally efficient for solution of elliptic equations (O(N)), which means that effort is proportional to the number of points at which the solution is evaluated). Thus this is an ideal method to solve the initial data/constraint equations in General Relativity for (for instance) black hole interactions, or for other strong-field gravitational configurations. Recent efforts have produced finite difference multigrid solvers for domains with holes (excised regions). We present here the extension of these concepts to higher order (fourth-, sixth- and eigth-order). The high order convergence allows rapid solution on relatively small computational grids. Also, general relativity evolution codes are moving to typically fourth-order; data have to be computed at least as accurately as this same order for straightfoward demonstration of the proper order of convergence in the evolution. Our vertex-centered multigrid code demonstrates globally high-order-accurate solutions of ...
High-order harmonic characterization using different schemes of extended plasma formation
Ganeev, R. A.
2015-10-01
The review of the characterization of the high-order harmonics of ultrashort pulses produced in the extended plasmas is presented. We analyze the spatial and coherence characteristics of the harmonics generated in the extended plasmas produced by 370 ps pulses. We discuss the advanced properties of extended manganese and zinc plasma plumes for the harmonic generation in the shorter and longer wavelength regions of extreme ultraviolet compared with the short-length plasmas used in previous studies. The conversion efficiency of the 11th-19th orders at these conditions was estimated to be 5 × 10-5. The reviewed studies demonstrate the limits of most extended harmonic cut-off in the plasma media. We also discuss the harmonic generation using the two femtosecond pulses propagating in the vicinity of solid and powdered targets. This method allows the simplified analysis of the high-order nonlinear optical properties of the media.
Large eddy simulation of a muffler with the high-order spectral difference method
Parsani, Matteo; Lacor, Chris
2013-01-01
The combination of the high-order accurate spectral difference discretization on unstructured grids with subgrid-scale modelling is investigated for large eddy simulation of a muffler at Re = 4.64 10^4 and low Mach number. The subgrid-scale stress tensor is modelled by the wall-adapting local eddy-viscosity model with a cut-off length which is a decreasing function of the order of accuracy of the scheme. Numerical results indicate that although the high-order solver without subgrid-scale modelling is already able to capture well the features of the flow, the coupling with the wall-adapting local eddy-viscosity model improves the quality of the solution.
High-order ghost imaging with N-colour thermal light
International Nuclear Information System (INIS)
High-order ghost imaging with thermal light consisting of N different frequencies is investigated. The high-order intensity correlation and intrinsic correlation functions are derived for such N-colour light. It is found that they are similar in form to those for the monochromatic case, thus most of the conclusions we obtained previously for monochromatic Nth-order ghost imaging are still applicable. However, we find that the visibility of the N-colour ghost image depends strongly on the wavelength used to illuminate the object, and increases as this wavelength increases when the test arm is fixed. On the contrary, changes of wavelength in the reference arms do not lead to any change of the visibility. (rapid communication)
Energy Technology Data Exchange (ETDEWEB)
Lehner, Luis [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States); Reula, Oscar [FaMAF, Universidad Nacional de Cordoba, Ciudad Universitaria, 5000 Cordoba (Argentina); Tiglio, Manuel [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States); Center for Computation and Technology, 302 Johnston Hall, Louisiana State University, Baton Rouge, LA 70803-4001 (United States); Center for Radiophysics and Space Research, Cornell University, Ithaca, NY 14853 (United States)
2005-12-21
The need to smoothly cover a computational domain of interest generically requires the adoption of several grids. To solve a given problem under this grid structure, one must ensure the suitable transfer of information among the different grids involved. In this work, we discuss a technique that allows one to construct finite-difference schemes of arbitrary high order which are guaranteed to satisfy linear numerical and strict stability. The method relies on the use of difference operators satisfying summation by parts and penalty terms to transfer information between the grids. This allows the derivation of semi-discrete energy estimates for problems admitting such estimates at the continuum. We analyse several aspects of this technique when used in conjunction with high-order schemes and illustrate its use in one-, two- and three-dimensional numerical relativity model problems with non-trivial topologies, including truly spherical black hole excision.
European Workshop on High Order Nonlinear Numerical Schemes for Evolutionary PDEs
Beaugendre, Héloïse; Congedo, Pietro; Dobrzynski, Cécile; Perrier, Vincent; Ricchiuto, Mario
2014-01-01
This book collects papers presented during the European Workshop on High Order Nonlinear Numerical Methods for Evolutionary PDEs (HONOM 2013) that was held at INRIA Bordeaux Sud-Ouest, Talence, France in March, 2013. The central topic is high order methods for compressible fluid dynamics. In the workshop, and in this proceedings, greater emphasis is placed on the numerical than the theoretical aspects of this scientific field. The range of topics is broad, extending through algorithm design, accuracy, large scale computing, complex geometries, discontinuous Galerkin, finite element methods, Lagrangian hydrodynamics, finite difference methods and applications and uncertainty quantification. These techniques find practical applications in such fields as fluid mechanics, magnetohydrodynamics, nonlinear solid mechanics, and others for which genuinely nonlinear methods are needed.
High-order harmonic spectroscopy for molecular imaging of polyatomic molecules
Negro, M; Faccialà, D; De Silvestri, S; Vozzi, C; Stagira, S
2014-01-01
High-order harmonic generation is a powerful and sensitive tool for probing atomic and molecular structures, combining in the same measurement an unprecedented attosecond temporal resolution with a high spatial resolution, of the order of the angstrom. Imaging of the outermost molecular orbital by high-order harmonic generation has been limited for a long time to very simple molecules, like nitrogen. Recently we demonstrated a technique that overcame several of the issues that have prevented the extension of molecular orbital tomography to more complex species, showing that molecular imaging can be applied to a triatomic molecule like carbon dioxide. Here we report on the application of such technique to nitrous oxide (N2O) and acetylene (C2H2). This result represents a first step towards the imaging of fragile compounds, a category which includes most of the fundamental biological molecules.
Forward-smooth high-order uniform Aharonov–Bohm asymptotics
Berry, M. V.
2016-07-01
The Aharonov–Bohm (AB) function, describing a plane wave scattered by a flux line, is expanded asymptotically in a Fresnel-integral based series whose terms are smooth in the forward direction and uniformly valid in angle and flux. Successive approximations are valid for large distance r from the flux (or short wavelength) but are accurate even within one wavelength of it. Coefficients of all the terms are exhibited explicitly for the forward direction, enabling the high-order asymptotics to be understood in detail. The series is factorally divergent, with optimal truncation error exponentially small in r. Systematic resummation gives further exponential improvement. Terms of the series satisfy a resurgence relation: the high orders are related to the low orders. Discontinuities in the backward direction get smaller order by order, with systematic cancellation by successive terms. The relation to an earlier scheme based on the Cornu spiral is discussed.
High order fluid model for streamer discharges: I. Derivation of model and transport data
Dujko, S; White, R D; Ebert, U
2013-01-01
Streamer discharges pose basic problems in plasma physics, as they are very transient, far from equilibrium and have high ionization density gradients; they appear in diverse areas of science and technology. The present paper focuses on the derivation of a high order fluid model for streamers. Using momentum transfer theory, the fluid equations are obtained as velocity moments of the Boltzmann equation; they are closed in the local mean energy approximation and coupled to the Poisson equation for the space charge generated electric field. The high order tensor in the energy flux equation is approximated by the product of two lower order moments to close the system. The average collision frequencies for momentum and energy transfer in elastic and inelastic collisions for electrons in molecular nitrogen are calculated from a multi term Boltzmann equation solution. We then discuss, in particular, (1) the correct implementation of transport data in streamer models; (2) the accuracy of the two term approximation f...
Multi-input partial eigenvalue assignment for high order control systems with time delay
Zhang, Lei
2016-05-01
In this paper, we consider the partial eigenvalue assignment problem for high order control systems with time delay. Ram et al. (2011) [1] have shown that a hybrid method can be used to solve partial quadratic eigenvalue assignment problem of single-input vibratory system. Based on this theory, a rather simple algorithm for solving multi-input partial eigenvalue assignment for high order control systems with time delay is proposed. Our method can assign the expected eigenvalues and keep the no spillover property. The solution can be implemented with only partial information of the eigenvalues and the corresponding eigenvectors of the matrix polynomial. Numerical examples are given to illustrate the efficiency of our approach.
Computational Aero-Acoustic Using High-order Finite-Difference Schemes
DEFF Research Database (Denmark)
Zhu, Wei Jun; Shen, Wen Zhong; Sørensen, Jens Nørkær
2007-01-01
In this paper, a high-order technique to accurately predict flow-generated noise is introduced. The technique consists of solving the viscous incompressible flow equations and inviscid acoustic equations using a incompressible/compressible splitting technique. The incompressible flow equations are...... discretizations of the acoustic equations. The classical fourth-order Runge-Kutta time scheme is applied to the acoustic equations for time discretization....
Generation of high-order optical vortices using directly machined spiral phase mirrors
Campbell, Geoff; Hage, Boris; Buchler, Ben; Lam, Ping Koy
2011-01-01
We report on the generation of high-order optical vortices by spiral phase mirrors. The phase mirrors are produced by direct machining with a diamond tool and are shown to produce high-quality optical vortices with topological charges ranging from 1 to 1000 at a wavelength of 532 nm. The direct machining technique is flexible and offers the promise of high-precision, large-diameter spiral phase mirrors that are compatible with high optical powers.
Highly Ordered Carbon Nanotube Arrays with Open Ends Grown in Anodic Alumina Nanoholes
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
Highly ordered multiwalled carbon nanotube arrays were fabricated by pyrolysis of acetylene within anodic alumina templates.Nanotubes are very uniform in diameter and open at both ends. High resolution transmission electron microscopy and electron diffraction analysis show that the carbon nanotubes are well graphitized. These standing and open carbon nanotubes are possible to offer a potential elegant technique for electron emitting devices,chemical functionalization and nanotube composites.
Formation of highly ordered arrays of dimples on tantalum at the nanoscale.
El-Sayed, Hany; Singh, Sherdeep; Greiner, Mark T; Kruse, Peter
2006-12-01
We show that electropolishing of tantalum metal in a single step of about 5 min can reproducibly lead to dimples tens of nanometers in diameter, regular in shape, monodispersed in size, and arranged in highly ordered arrays which even transverse grain boundaries. Dimpled tantalum is ductile, high melting, and chemically inert, which makes it suitable for nanostructure synthesis even under extreme conditions, as demonstrated with a simple sputter coating and flame annealing procedure for gold nanoparticles. PMID:17163747
Entropy Viscosity Method for High-Order Approximations of Conservation Laws
Guermond, J. L.
2010-09-17
A stabilization technique for conservation laws is presented. It introduces in the governing equations a nonlinear dissipation function of the residual of the associated entropy equation and bounded from above by a first order viscous term. Different two-dimensional test cases are simulated - a 2D Burgers problem, the "KPP rotating wave" and the Euler system - using high order methods: spectral elements or Fourier expansions. Details on the tuning of the parameters controlling the entropy viscosity are given. © 2011 Springer.
High order P-G finite elements for convection-dominated problems
International Nuclear Information System (INIS)
From the error analysis presented in this paper it is shown that de CCAU method derived by Dutra do Carmo and Galeao [3] preserves the same order of approximation obtained with SUPH (cf. Books and Hughes [2]) when advection-diffusion regular solutions are considered, and improves the accuracy of the approximate boundary layer solution when high order interpolating polynomials are used near sharp layers
High-Order Central WENO Schemes for 1D Hamilton-Jacobi Equations
Bryson, Steve; Levy, Doron; Biegel, Bryan A. (Technical Monitor)
2002-01-01
In this paper we derive fully-discrete Central WENO (CWENO) schemes for approximating solutions of one dimensional Hamilton-Jacobi (HJ) equations, which combine our previous works. We introduce third and fifth-order accurate schemes, which are the first central schemes for the HJ equations of order higher than two. The core ingredient is the derivation of our schemes is a high-order CWENO reconstructions in space.
Quasi-phase-matching of high-order-harmonic generation using multimode polarization beating
Liu, Lewis Z.; O'Keeffe, Kevin; Hooker, Simon M.
2013-01-01
The generalization of quasi-phase-matching using polarization beating and of multimode quasi-phase-matching (MMQPM) for the generation of high-order harmonics is explored, and a method for achieving polarization beating is proposed. If two (and in principle more) modes of a waveguide are excited, modulation of the intensity, phase, and/or polarization of the guided radiation will be achieved. By appropriately matching the period of this modulation to the coherence length, quasi-phase-matching...
Dissipative issue of high-order shock capturing schemes with non-convex equations of state
International Nuclear Information System (INIS)
It is well known that, closed with a non-convex equation of state (EOS), the Riemann problem for the Euler equations allows non-standard waves, such as split shocks, sonic isentropic compressions or rarefaction shocks, to occur. Loss of convexity then leads to non-uniqueness of entropic or Lax solutions, which can only be resolved via the Liu-Oleinik criterion (equivalent to the existence of viscous profiles for all admissible shock waves). This suggests that in order to capture the physical solution, a numerical scheme must provide an appropriate level of dissipation. A legitimate question then concerns the ability of high-order shock capturing schemes to naturally select such a solution. To investigate this question and evaluate modern as well as future high-order numerical schemes, there is therefore a crucial need for well-documented benchmarks. A thermodynamically consistent C∞ non-convex EOS that can be easily introduced in Eulerian as well as Lagrangian hydrocodes for test purposes is here proposed, along with a reference solution for an initial value problem exhibiting a complex composite wave pattern (the Bizarrium test problem). Two standard Lagrangian numerical approaches, both based on a finite volume method, are then reviewed (vNR and Godunov-type schemes) and evaluated on this Riemann problem. In particular, a complete description of several state-of-the-art high-order Godunov-type schemes applicable to general EOSs is provided. We show that this particular test problem reveals quite severe when working on high-order schemes, and recommend it as a benchmark for devising new limiters and/or next-generation highly accurate schemes
Wavelet Expansion and High-order Regularization for Multiscale Fluid-motion Estimation
Dérian, Pierre; Héas, Patrick; Herzet, Cédric; Memin, Etienne
2010-01-01
We consider a novel optic flow estimation algorithm based on a wavelet expansion of the velocity field. In particular, we propose an efficient gradient-based estimation algorithm which naturally encompasses the estimation process into a multiresolution framework while avoiding most of the drawbacks common to this kind of hierarchical methods. We then emphasize that the proposed methodology is well-suited to the practical implementation of high-order regularizations. The powerfulness of the pr...
Two dimensional high-order C IP numerical method and applications
International Nuclear Information System (INIS)
Employing a function and its derivatives to construct a fifth-order interpolation function to approximate to the real solution in a cell, we have improved the CIP (Constrained Interpolation Profile) numerical algorithm. A direct two-dimensional high-order CIP method differing from adopting a time-splitting technology has been developed on the basis of the previous one-dimensional case. The improved method is an explicit scheme with the fifth-order accuracy. (authors)
Modulated phase matching and high-order harmonic enhancement mediated by the carrier-envelope phase
International Nuclear Information System (INIS)
The process of high-order harmonic generation in gases is numerically investigated in the presence of a few-cycle pulsed-Bessel-beam pump, featuring a periodic modulation in the peak intensity due to large carrier-envelope-phase mismatch. A two-decade enhancement in the conversion efficiency is observed and interpreted as the consequence of a mechanism known as a nonlinearly induced modulation in the phase mismatch.
On The Integration of Decision Diagrams in High Order Logic Based Theorem Provers: a Survey
Sa'ed Abed; Otmane O. Mohamed; Ghiath A. Sammane
2007-01-01
This survey discuss approaches that integrate Decision Diagrams inside High Order Logic based Theorem provers. The approaches can be divided in two kinds, one is based on building a translation between model checker and theorem prover, the second is based on embedding the model checker algorithms inside the theorem prover. A comparison between both is discussed in detail. The paper also tries to answer which is the best decision graphs formalization for theorem provers as what is the optimize...
High Order Numerical Solution of Integral Transport Equation in Slab Geometry
Institute of Scientific and Technical Information of China (English)
沈智军; 袁光伟; 沈隆钧
2002-01-01
@@ There are some common numerical methods for solving neutron transport equation, which including the well-known discrete ordinates method, PN approximation and integral transport methods[1]. There exists certain singularities in the solution of transport equation near the boundary and interface[2]. It gives rise to the difficulty in the construction of high order accurate numerical methods. The numerical solution obtained by now can not attain the second order convergent accuracy[3,4].
Implementation of the high-order schemes QUICK and LECUSSO in the COMMIX-1C Program
International Nuclear Information System (INIS)
Multidimensional analysis computer programs based on the finite volume method, such as COMMIX-1C, have been commonly used to simulate thermal-hydraulic phenomena in engineering systems such as nuclear reactors. In COMMIX-1C, the first-order schemes with respect to both space and time are used. In many situations such as flow recirculations and stratifications with steep gradient of velocity and temperature fields, however, high-order difference schemes are necessary for an accurate prediction of the fields. For these reasons, two second-order finite difference numerical schemes, QUICK (Quadratic Upstream Interpolation for Convective Kinematics) and LECUSSO (Local Exact Consistent Upwind Scheme of Second Order), have been implemented in the COMMIX-1C computer code. The formulations were derived for general three-dimensional flows with nonuniform grid sizes. Numerical oscillation analyses for QUICK and LECUSSO were performed. To damp the unphysical oscillations which occur in calculations with high-order schemes at high mesh Reynolds numbers, a new FRAM (Filtering Remedy and Methodology) scheme was developed and implemented. To be consistent with the high-order schemes, the pressure equation and the boundary conditions for all the conservation equations were also modified to be of second order. The new capabilities in the code are listed. Test calculations were performed to validate the implementation of the high-order schemes. They include the test of the one-dimensional nonlinear Burgers equation, two-dimensional scalar transport in two impinging streams, von Karmann vortex shedding, shear driven cavity flow, Couette flow, and circular pipe flow. The calculated results were compared with available data; the agreement is good
A high-order q-difference equation for q-Hahn multiple orthogonal polynomials
DEFF Research Database (Denmark)
Arvesú, J.; Esposito, Chiara
2012-01-01
A high-order linear q-difference equation with polynomial coefficients having q-Hahn multiple orthogonal polynomials as eigenfunctions is given. The order of the equation coincides with the number of orthogonality conditions that these polynomials satisfy. Some limiting situations when are studie....... Indeed, the difference equation for Hahn multiple orthogonal polynomials given in Lee [J. Approx. Theory (2007), ), doi: 10.1016/j.jat.2007.06.002] is obtained as a limiting case....
10th International Conference on Spectral and High-Order Methods
Berzins, Martin; Hesthaven, Jan
2015-01-01
The book contains a selection of high quality papers, chosen among the best presentations during the International Conference on Spectral and High-Order Methods (2014), and provides an overview of the depth and breadth of the activities within this important research area. The carefully reviewed selection of papers will provide the reader with a snapshot of the state-of-the-art and help initiate new research directions through the extensive biography.
Laser-induced bound-state phases in high-order harmonic generation
DEFF Research Database (Denmark)
Etches, Adam; B. Gaarde, Mette; Bojer Madsen, Lars
2012-01-01
We present single-molecule and macroscopic calculations showing that laser-induced Stark shifts contribute significantly to the phase of high-order harmonics from polar molecules. This is important for orbital tomography, where phases of field-free dipole matrix elements are needed in order to...... reconstruct molecular orbitals. We derive an analytical expression that allows the first-order Stark phase to be subtracted from experimental measurements....
High-Order Stochastic Adaptive Controller Design with Application to Mechanical System
Jie Tian; Wei Feng; Yuzhen Wang
2012-01-01
The main purpose of this paper is to apply stochastic adaptive controller design to mechanical system. Firstly, by a series of coordinate transformations, the mechanical system can be transformed to a class of special high-order stochastic nonlinear system, based on which, a more general mathematical model is considered, and the smooth state-feedback controller is designed. At last, the simulation for the mechanical system is given to show the effectiveness of the design scheme.
Tarasevitch, A. P.; Kohn, R.; von der Linde, D.
2009-07-01
The advantages of using two beam high order harmonic generation (HOHG) from solids are discussed. The two-pulse technique allows additional control of the parameters essential for the attosecond pulse generation. We show that spectral filtering is not necessary for the generation of attosecond pulses. The simple oscillating mirror model is in qualitative agreement with the computer simulations. We present the results of first experiments using two beams for HOHG.
Bonazzoli, M.; Dolean, V.; Rapetti, F.; Tournier, P. -H.
2016-01-01
This paper combines the use of high order finite element methods with parallel preconditioners of domain decomposition type for solving electromagnetic problems arising from brain microwave imaging. The numerical algorithms involved in such complex imaging systems are computationally expensive since they require solving the direct problem of Maxwell's equations several times. Moreover, wave propagation problems in the high frequency regime are challenging because a sufficiently high number of...
An Efficient Method Based on Lucas Polynomials for Solving High-Order Linear Boundary Value Problems
Çetin, Muhammed; Sezer, Mehmet; Kocayiğit, Hüseyin
2015-01-01
In this paper, a new collocation method based on Lucas polynomials for solving high-order linear differential equations with variable coefficients under the boundary conditions is presented by transforming the problem into a system of linear algebraic equations with Lucas coefficients. The proposed approach is applied to fourth, fifth, sixth and eighth-order two-point boundary values problems occurring in science and engineering, and compared by existing methods. The technique gives better ap...
Demonstration of a spatial filtering amplifier for high-order harmonics
Czech Academy of Sciences Publication Activity Database
Goddet, J.Ph.; Sebban, S.; Morlens, A.S.; Gautier, J.; Rousseau, J. P.; Burgy, F.; Zeitoun, P.; Valentin, C.; Hauri, C.; Maynard, G.; Boudaa, A.; Caumes, J.P.; Merdji, H.; Mocek, Tomáš; Kozlová, Michaela; Jakubczak, K.
2007-01-01
Roč. 32, č. 11 (2007), s. 1498-1500. ISSN 0146-9592 Grant ostatní: European Union(XE) HPRI-1999-CT-00086; Barrande(XE) 2-06-16 Institutional research plan: CEZ:AV0Z10100523 Keywords : X-ray laser * high-order harmonic generation * seeding * amplification * spatial filtering Subject RIV: BH - Optics, Masers, Lasers Impact factor: 3.711, year: 2007
Deng, Quanling; Ginting, Victor
2016-01-01
We propose a simple post-processing technique for linear and high order continuous Galerkin Finite Element Methods (CGFEMs) to obtain locally conservative flux field. The post-processing technique requires solving an auxiliary problem on each element independently which results in solving a linear algebra system whose size is low for any order CGFEM. The post-processing could have been done directly from the finite element solution that results in locally conservative flux on the element. How...
On global exponential stability of high-order neural networks with time-varying delays
International Nuclear Information System (INIS)
This Letter investigates the problem of stability analysis for a class of high-order neural networks with time-varying delays. The delays are bounded but not necessarily differentiable. Based on the Lyapunov stability theory together with the linear matrix inequality (LMI) approach and the use of Halanay inequality, sufficient conditions guaranteeing the global exponential stability of the equilibrium point of the considered neural networks are presented. Two numerical examples are provided to demonstrate the effectiveness of the proposed stability criteria
MIMO Detection for High-Order QAM Based on a Gaussian Tree Approximation
Goldberger, Jacobb; Leshem, Amir
2010-01-01
This paper proposes a new detection algorithm for MIMO communication systems employing high order QAM constellations. The factor graph that corresponds to this problem is very loopy; in fact, it is a complete graph. Hence, a straightforward application of the Belief Propagation (BP) algorithm yields very poor results. Our algorithm is based on an optimal tree approximation of the Gaussian density of the unconstrained linear system. The finite-set constraint is then applied to obtain a loop-fr...
Research on Appraisal System of Procurator Performance by Using High-Order CFA Model
Directory of Open Access Journals (Sweden)
Yong-mao Huang
2014-01-01
Full Text Available The prosecutor is the main body of procuratorial organs. The performance appraisal system plays an important role in promoting the work efficiency of procurator. In this paper, we establish the performance appraisal system of procurators by high-order confirmatory factor analysis method and evaluate procurators’ performance by fuzzy comprehensive evaluation method based on the 360 degrees. The results have some help to performance management of procuratorial organs.
Research on Appraisal System of Procurator Performance by Using High-Order CFA Model
Yong-mao Huang
2014-01-01
The prosecutor is the main body of procuratorial organs. The performance appraisal system plays an important role in promoting the work efficiency of procurator. In this paper, we establish the performance appraisal system of procurators by high-order confirmatory factor analysis method and evaluate procurators’ performance by fuzzy comprehensive evaluation method based on the 360 degrees. The results have some help to performance management of procuratorial organs.
Haider, F.; Bertier, N.; Courbet, B.; Vuillot, F.; Croisille, J.P.
2015-01-01
This paper presents a high order finite volume scheme built on a new k-exact reconstruction algorithm for general unstructured grids. The algorithm is capable of computing accurate polynomial approximations using data from adjacent cells only, overcoming a major obstacle to extend classical finite volume schemes beyond 2 nd order spatial accuracy. Moreover, it can easily be integrated in a cell or vertex centered finite volume method that uses the cell averages as the only unknown per grid ce...
High order discontinuous finite-volume/finite-element method for CFD applications
Ramezani A; Stipcich G.
2014-01-01
The proposed method naturally merges the desirable conservative properties and intuitive physical formulation of the widely used finite-volume (FV) technique, with the capability of local arbitrary high-order accuracy and high-resolution which is distinctive in the discontinuous finite-element (FE) framework. This relatively novel scheme, the discontinuous hybrid control-volume/finite-element method (DCVFEM), has been already applied to the solution of advection-diffusion problems and shallow...
Discontinuous high-order finite-volume/finite-element method for inviscid compressible flows
Ramezani A; Stipcich G.; Remaki L.
2015-01-01
The discontinuous, hybrid control-volume/finite-element method merges the desirable conservative properties and intuitive physical formulation of the finite-volume technique, with the capability of local arbitrary high-order accuracy distinctive of the discontinuous finite-element method. This relatively novel scheme has been previously applied to the solution of advection-diffusion problems and the shallow-water equations, and is in the present work extended to the Euler equations. The deriv...
The effect of dressing on high-order harmonic generation in vibrating H$_2$ molecules
Chirila, C. C.; Lein, M.
2008-01-01
We develop the strong-field approximation for high-order harmonic generation in hydrogen molecules, including the vibrational motion and the laser-induced coupling of the lowest two Born-Oppenheimer states in the molecular ion that is created by the initial ionization of the molecule. We show that the field dressing becomes important at long laser wavelengths ($\\approx 2 \\mu$m), leading to an overall reduction of harmonic generation and modifying the ratio of harmonic signals from different i...
High-order lattice Boltzmann models for wall-bounded flows at finite Knudsen numbers
Feuchter, C
2015-01-01
We analyze a large number of high-order discrete velocity models for solving the Boltzmann-BGK equation for finite Knudsen number flows. Using the Chapman-Enskog formalism, we prove for isothermal flows a relation identifying the resolved flow regimes for low Mach numbers. Although high-order lattice Boltzmann models recover flow regimes beyond the Navier-Stokes level we observe for several models significant deviations from reference results. We found this to be caused by their inability to recover the Maxwell boundary condition exactly. By using supplementary conditions for the gas-surface interaction it is shown how to systematically generate discrete velocity models of any order with the inherent ability to fulfill the diffuse Maxwell boundary condition accurately. Both high-order quadratures and an exact representation of the boundary condition turn out to be crucial for achieving reliable results. For Poiseuille flow, we can reproduce the mass flow and slip velocity up to the Knudsen number of 1. Moreov...
Jiang, Zhen-Hua; Yan, Chao; Yu, Jian
2013-08-01
Two types of implicit algorithms have been improved for high order discontinuous Galerkin (DG) method to solve compressible Navier-Stokes (NS) equations on triangular grids. A block lower-upper symmetric Gauss-Seidel (BLU-SGS) approach is implemented as a nonlinear iterative scheme. And a modified LU-SGS (LLU-SGS) approach is suggested to reduce the memory requirements while retain the good convergence performance of the original LU-SGS approach. Both implicit schemes have the significant advantage that only the diagonal block matrix is stored. The resulting implicit high-order DG methods are applied, in combination with Hermite weighted essentially non-oscillatory (HWENO) limiters, to solve viscous flow problems. Numerical results demonstrate that the present implicit methods are able to achieve significant efficiency improvements over explicit counterparts and for viscous flows with shocks, and the HWENO limiters can be used to achieve the desired essentially non-oscillatory shock transition and the designed high-order accuracy simultaneously.
Energy Technology Data Exchange (ETDEWEB)
Wang, Wei [Deprartment of Mathematics. Florida Intl Univ., Miami, FL (United States); Shu, Chi-Wang [Division of Applied Mathematics. Brown Univ., Providence, RI (United States); Yee, H.C. [NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States); Sjögreen, Björn [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2012-01-01
A new high order finite-difference method utilizing the idea of Harten ENO subcell resolution method is proposed for chemical reactive flows and combustion. In reaction problems, when the reaction time scale is very small, e.g., orders of magnitude smaller than the fluid dynamics time scales, the governing equations will become very stiff. Wrong propagation speed of discontinuity may occur due to the underresolved numerical solution in both space and time. The present proposed method is a modified fractional step method which solves the convection step and reaction step separately. In the convection step, any high order shock-capturing method can be used. In the reaction step, an ODE solver is applied but with the computed flow variables in the shock region modified by the Harten subcell resolution idea. For numerical experiments, a fifth-order finite-difference WENO scheme and its anti-diffusion WENO variant are considered. A wide range of 1D and 2D scalar and Euler system test cases are investigated. Studies indicate that for the considered test cases, the new method maintains high order accuracy in space for smooth flows, and for stiff source terms with discontinuities, it can capture the correct propagation speed of discontinuities in very coarse meshes with reasonable CFL numbers.
Time-Frequency Analysis Using Warped-Based High-Order Phase Modeling
Directory of Open Access Journals (Sweden)
Ioana Cornel
2005-01-01
Full Text Available The high-order ambiguity function (HAF was introduced for the estimation of polynomial-phase signals (PPS embedded in noise. Since the HAF is a nonlinear operator, it suffers from noise-masking effects and from the appearance of undesired cross-terms when multicomponents PPS are analyzed. In order to improve the performances of the HAF, the multi-lag HAF concept was proposed. Based on this approach, several advanced methods (e.g., product high-order ambiguity function (PHAF have been recently proposed. Nevertheless, performances of these new methods are affected by the error propagation effect which drastically limits the order of the polynomial approximation. This phenomenon acts especially when a high-order polynomial modeling is needed: representation of the digital modulation signals or the acoustic transient signals. This effect is caused by the technique used for polynomial order reduction, common for existing approaches: signal multiplication with the complex conjugated exponentials formed with the estimated coefficients. In this paper, we introduce an alternative method to reduce the polynomial order, based on the successive unitary signal transformation, according to each polynomial order. We will prove that this method reduces considerably the effect of error propagation. Namely, with this order reduction method, the estimation error at a given order will depend only on the performances of the estimation method.
PROPAGATION CHARACTERISTICS OF HIGH ORDER LONGITUDINAL MODES IN STEEL STRANDS AND THEIR APPLICATIONS
Institute of Scientific and Technical Information of China (English)
Zenghua Liu; Su Liu; Bin Wu; Yinong Zhang; Cunfu He
2008-01-01
Propagation characteristics of high order longitudinal modes of ultrasonic guided waves in seven-wire steel strands are investigated theoretically and experimentally. According to these analysis results, proper longitudinal modes are selected for defect detection in steel strands.Dispersion curves for helical and central wires in a 17.80 mm nominal diameter seven-wire steel strand are numerically obtained firstly, and propagation characteristics of high-order longitudinal modes, such as wave structures, attenuation and dispersion, are analyzed. In experiments, the signals of ultrasonic guided wave at different high frequencies are excited and received at one end of a steel strand by using the same single piezoelectric transducer. The identification of longitudinal modes in the received signals is achieved based on short time Fourier transform. Furthermore,appropriate L(0, 5) mode at 2.54 MHz is chosen for detecting an artificial defect in a helical wire of the steel strand. Results show that high order longitudinal modes in a high frequency range with low dispersion and attenuation whose energy propagates mainly in the center of the wires can be used for defect detection in long range steel strands.
Energy Technology Data Exchange (ETDEWEB)
Rieben, R N
2004-07-20
The goal of this dissertation is twofold. The first part concerns the development of a numerical method for solving Maxwell's equations on unstructured hexahedral grids that employs both high order spatial and high order temporal discretizations. The second part involves the use of this method as a computational tool to perform high fidelity simulations of various electromagnetic devices such as optical transmission lines and photonic crystal structures to yield a level of accuracy that has previously been computationally cost prohibitive. This work is based on the initial research of Daniel White who developed a provably stable, charge and energy conserving method for solving Maxwell's equations in the time domain that is second order accurate in both space and time. The research presented here has involved the generalization of this procedure to higher order methods. High order methods are capable of yielding far more accurate numerical results for certain problems when compared to corresponding h-refined first order methods , and often times at a significant reduction in total computational cost. The first half of this dissertation presents the method as well as the necessary mathematics required for its derivation. The second half addresses the implementation of the method in a parallel computational environment, its validation using benchmark problems, and finally its use in large scale numerical simulations of electromagnetic transmission devices.
photon-plasma: A modern high-order particle-in-cell code
Energy Technology Data Exchange (ETDEWEB)
Haugbølle, Troels [Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen (Denmark); Frederiksen, Jacob Trier [Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Nordlund, Åke [Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen (Denmark)
2013-06-15
We present the photon-plasma code, a modern high order charge conserving particle-in-cell code for simulating relativistic plasmas. The code is using a high order implicit field solver and a novel high order charge conserving interpolation scheme for particle-to-cell interpolation and charge deposition. It includes powerful diagnostics tools with on-the-fly particle tracking, synthetic spectra integration, 2D volume slicing, and a new method to correctly account for radiative cooling in the simulations. A robust technique for imposing (time-dependent) particle and field fluxes on the boundaries is also presented. Using a hybrid OpenMP and MPI approach, the code scales efficiently from 8 to more than 250.000 cores with almost linear weak scaling on a range of architectures. The code is tested with the classical benchmarks particle heating, cold beam instability, and two-stream instability. We also present particle-in-cell simulations of the Kelvin-Helmholtz instability, and new results on radiative collisionless shocks.
photon-plasma: A modern high-order particle-in-cell code
International Nuclear Information System (INIS)
We present the photon-plasma code, a modern high order charge conserving particle-in-cell code for simulating relativistic plasmas. The code is using a high order implicit field solver and a novel high order charge conserving interpolation scheme for particle-to-cell interpolation and charge deposition. It includes powerful diagnostics tools with on-the-fly particle tracking, synthetic spectra integration, 2D volume slicing, and a new method to correctly account for radiative cooling in the simulations. A robust technique for imposing (time-dependent) particle and field fluxes on the boundaries is also presented. Using a hybrid OpenMP and MPI approach, the code scales efficiently from 8 to more than 250.000 cores with almost linear weak scaling on a range of architectures. The code is tested with the classical benchmarks particle heating, cold beam instability, and two-stream instability. We also present particle-in-cell simulations of the Kelvin-Helmholtz instability, and new results on radiative collisionless shocks
Narrow-bandwidth high-order harmonics driven by long-duration hot spots
Kozlov, Maxim; Kfir, Ofer; Fleischer, Avner; Kaplan, Alex; Carmon, Tal; Schwefel, Harald G. L.; Bartal, Guy; Cohen, Oren
2012-06-01
We predict and investigate the emission of high-order harmonics by atoms that cross intense laser hot spots that last for a nanosecond or longer. An atom that moves through a nanometer-scale hot spot at characteristic thermal velocity can emit high-order harmonics in a similar fashion to an atom that is irradiated by a short-duration (picosecond-scale) laser pulse. We analyze the collective emission from a thermal gas and from a jet of atoms. In both cases, the line shape of a high-order harmonic exhibits a narrow spike with spectral width that is determined by the bandwidth of the driving laser. Finally, we discuss a scheme for producing long-duration laser hot spots with intensity in the range of the intensity threshold for high-harmonic generation. In the proposed scheme, the hot spot is produced by a long laser pulse that is consecutively coupled to a high-quality micro-resonator and a metallic nano-antenna. This system may be used for generating ultra-narrow bandwidth extreme-ultraviolet radiation through frequency up-conversion of a low-cost compact pump laser.
Minimum in the high-order harmonic generation spectrum from molecules: role of excited states
DEFF Research Database (Denmark)
Han, Yong-Chang; Madsen, Lars Bojer
2010-01-01
We model the process of high-order harmonic generation by solving the time-dependent Schrödinger equation for H+2 in the fixed nuclei approximation including full 3D electron motion for nonvanishing angles between the nuclear axis and the linear polarization of the driving pulse. We show that the...... coherent laser coupling induced between the 2Σ+g(1sσg) ground state and the first excited 2Σ+u(2pσu) state leads to two dominating amplitudes for the high-order harmonic generation that may interfere: amplitudes describing recombination back into the σg and σu states, respectively. These two amplitudes may...... interfere destructively or constructively. The effect of a destructive interference is very clear through the occurrence of a minimum in the high-order harmonic spectrum. We show cases where such a minimum in the spectrum is approximately at the position predicted by the simple two-centre interference...
Brown, J.; Ahmadia, A.; Knepley, M. G.; Smith, B.
2011-12-01
The cost of memory, especially memory bandwidth, is becoming increasingly expensive on modern high performance computing architectures including GPUs and multi-core systems. In contrast, floating point operations are relatively inexpensive when they can be vectorized (e.g. thread blocks on a GPU or vector registers on a CPU). This relative cost of memory to flops will continue to become even more pronounced due to fundamental issues of power utilization, therefore it is important to rethink algorithms to effectively utilize hardware. Commonly used methods for implicit solves with finite element methods involve assembly of a sparse matrix. Unfortunately, sparse matrix kernels have an arithmetic intensity (ratio of flops to bytes of memory movement) that is orders of magnitude less than that delivered by modern hardware, causing the floating point units to be massively under-utilized. The ``free flops'' can be effectively utilized by higher order methods which deliver improved accuracy for the same number of degrees of freedom. Effective use of high order methods require eschewing assembled data structures for matrix storage in exchange for unassembled representations. The resulting computation reduces to small dense tensor-product operations and indepedent ``physics'' kernels at each quadrature point, both of which are amenable to vectorization and capable of delivering a high fraction of peak performance. To reduce the effort required to implement new physics (e.g. constitutive relations and additional fields), retain code verifiability, and experiment with different vectorization strategies and solver algorithms, we express the continuum equations in Python and use automatic differentiation, symbolic methods, and code generation techniques to create vectorized kernels for residual evaluation, Jacobian storage, Jacobian application, and adjoints for each block of the system. The performance and effectiveness of these methods is demonstrated for free-surface Stokes
A comparison of high-order polynomial and wave-based methods for Helmholtz problems
Lieu, Alice; Gabard, Gwénaël; Bériot, Hadrien
2016-09-01
The application of computational modelling to wave propagation problems is hindered by the dispersion error introduced by the discretisation. Two common strategies to address this issue are to use high-order polynomial shape functions (e.g. hp-FEM), or to use physics-based, or Trefftz, methods where the shape functions are local solutions of the problem (typically plane waves). Both strategies have been actively developed over the past decades and both have demonstrated their benefits compared to conventional finite-element methods, but they have yet to be compared. In this paper a high-order polynomial method (p-FEM with Lobatto polynomials) and the wave-based discontinuous Galerkin method are compared for two-dimensional Helmholtz problems. A number of different benchmark problems are used to perform a detailed and systematic assessment of the relative merits of these two methods in terms of interpolation properties, performance and conditioning. It is generally assumed that a wave-based method naturally provides better accuracy compared to polynomial methods since the plane waves or Bessel functions used in these methods are exact solutions of the Helmholtz equation. Results indicate that this expectation does not necessarily translate into a clear benefit, and that the differences in performance, accuracy and conditioning are more nuanced than generally assumed. The high-order polynomial method can in fact deliver comparable, and in some cases superior, performance compared to the wave-based DGM. In addition to benchmarking the intrinsic computational performance of these methods, a number of practical issues associated with realistic applications are also discussed.
Large-eddy simulation in a mixing tee junction: High-order turbulent statistics analysis
International Nuclear Information System (INIS)
Highlights: • Mixing and thermal fluctuations in a junction are studied using large eddy simulation. • Adiabatic and conducting steel wall boundaries are tested. • Wall thermal fluctuations are not the same between the flow and the solid. • Solid thermal fluctuations cannot be predicted from the fluid thermal fluctuations. • High-order turbulent statistics show that the turbulent transport term is important. - Abstract: This study analyses the mixing and thermal fluctuations induced in a mixing tee junction with circular cross-sections when cold water flowing in a pipe is joined by hot water from a branch pipe. This configuration is representative of industrial piping systems in which temperature fluctuations in the fluid may cause thermal fatigue damage on the walls. Implicit large-eddy simulations (LES) are performed for equal inflow rates corresponding to a bulk Reynolds number Re = 39,080. Two different thermal boundary conditions are studied for the pipe walls; an insulating adiabatic boundary and a conducting steel wall boundary. The predicted flow structures show a satisfactory agreement with the literature. The velocity and thermal fields (including high-order statistics) are not affected by the heat transfer with the steel walls. However, predicted thermal fluctuations at the boundary are not the same between the flow and the solid, showing that solid thermal fluctuations cannot be predicted by the knowledge of the fluid thermal fluctuations alone. The analysis of high-order turbulent statistics provides a better understanding of the turbulence features. In particular, the budgets of the turbulent kinetic energy and temperature variance allows a comparative analysis of dissipation, production and transport terms. It is found that the turbulent transport term is an important term that acts to balance the production. We therefore use a priori tests to evaluate three different models for the triple correlation
Landing gear noise prediction using high-order finite difference schemes
Liu, W.; Kim, J. W.; Zhang, X; Angland, D.; BASTIEN, C
2012-01-01
Aerodynamic noise from a generic two-wheel landing-gear model is predicted by a CFD/FW-H hybrid approach. The unsteady flow-field is computed using a compressible Navier–Stokes solver based on high-order finite difference schemes and a fully structured grid. The calculated time history of the surface pressure data is used in an FW-H solver to predict the far-field noise levels. Both aerodynamic and aeroacoustic results are compared to wind tunnel measurements and are found to be in good agree...
High-order harmonic generation in Ar and Ne with a 45fs intense laser field
Institute of Scientific and Technical Information of China (English)
徐至展; 王迎松; 翟侃; 李学信; 刘亚青; 杨晓东; 张正泉; 李儒新; 张文琦
1999-01-01
Experimental results of high-order harmonic generation (HHG) in Ar and Ne gas driven with a 45fs Ti: sapphire laser are presented. The shortest-wavelength harmonic emission corresponding to the 91st order harmonic (8.63nm) is observed in argon. In neon, the harmonics up to order 131 (5.99nm) is also observed. The effects of gas density, laser intensity, free electron and the focusing geometry parameters of the laser beam on the process of harmonic generation are investigated. The direct experimental evidence that an increased electron density causes a degenerated harmonic radiation is obtained.
Free Electron Lasers Seeded by ir Laser Driven High-order Harmonic Generation
Energy Technology Data Exchange (ETDEWEB)
Wu, Juhao; Bolton, Paul R.; /SLAC; Murphy, James B.; /BNL, NSLS; Zhong, Xinming; /Beijing Normal U.
2007-03-12
Coherent x-ray production by a seeded free electron laser (FEL) is important for next generation synchrotron light sources. We examine the feasibility and features of FEL emission seeded by a high-order harmonic of an infrared laser (HHG). In addition to the intrinsic FEL chirp, the longitudinal profile and spectral bandwidth of the HHG seed are modified significantly by the FEL interaction well before saturation. This smears out the original attosecond pulselet structure. We introduce criteria for this smearing effect on the pulselet and the stretching effect on the entire pulse. We discuss the noise issue in such a seeded FEL.
Explicit high-order symplectic integrators for charged particles in general electromagnetic fields
Tao, Molei
2016-01-01
This article considers non-relativistic charged particle dynamics in both static and non-static electromagnetic fields, which are governed by nonseparable, possibly time-dependent Hamiltonians. For the first time, explicit symplectic integrators of arbitrary high-orders are constructed for accurate and efficient simulations of such mechanical systems. Performances superior to the standard non-symplectic method of Runge-Kutta are demonstrated on two examples: the first is on the confined motion of a particle in a static toroidal magnetic field used in tokamak; the second is on how time-periodic perturbations to a magnetic field inject energy into a particle via parametric resonance at a specific frequency.
Unstructured nodal DG-FEM solution of high-order Boussinesq-type equations
Engsig-Karup, Allan Peter; Madsen, Per A.; Bingham, Harry B.; Thomsen, Per Grove
2007-01-01
The main objective of the present study has been to develop a numerical model and investigate solution techniques for solving the recently derived high-order Boussinesq equations of \\cite{MBL02} in irregular domains in one and two horizontal dimensions. The Boussinesq-type methods are the simplest alternative to solving full three-dimensional wave problems by e.g. Navier-Stokes equations, which can capture all the important wave phenomena such as diffraction, refraction, nonlinear wave-wave i...
International Nuclear Information System (INIS)
High-order harmonic generation efficiency is theoretically modeled and compared with experiments using 400 and 800 nm driver pulses. It is shown that, for a short drive wavelength and a Keldysh parameter larger than 1, the Ammosov-Delone-Krainov (ADK) ionization model does not give a good agreement between theory and experiment. Since the ADK ionization model only accounts for tunnel ionization, it underestimates the yield of low-order harmonics from the wings of the driver pulse. In contrast, the Yudin-Ivanov ionization model [Phys. Rev. A 64, 013409 (2001)], which accounts for both tunnel and multiphoton ionization, gives much better agreement with the experimental results.
Electrochemical properties of modified highly ordered pyrolytic graphite by using ambient plasma
Kim, Ho Jun; Yang, Cheol-Soo; Jeong, HaeKyung
2016-01-01
Surface of highly ordered pyrolytic graphite (HOPG) is reformed by using ambient plasma. The HOPG film shows various pore structures after the plasma treatment, indicating improved electrochemical properties for supercapacitor applications because of the increase of the surface area. We also compare water effect on the film during the plasma treatment. Water might protect HOPG surface from the plasma and provide oxygen functional groups onto it, resulting in lower infected pores and higher impedance compared with them of HOPG film without water. Ambient plasma, therefore, could be considered as an economic and effective method for sample reformations.
Orbital angular momentum of a high-order Bessel light beam
Energy Technology Data Exchange (ETDEWEB)
Volke-Sepulveda, K [Instituto Nacional de Astrofisica, Optica y Electronica, Apdo. Postal 51/216, Puebla, Pue., Mexico 72000 (Mexico); Garces-Chavez, V [School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, Scotland (United Kingdom); Chavez-Cerda, S [Instituto Nacional de Astrofisica, Optica y Electronica, Apdo. Postal 51/216, Puebla, Pue., Mexico 72000 (Mexico); Arlt, J [School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, Scotland (United Kingdom); Dholakia, K [School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS, Scotland (United Kingdom)
2002-04-01
The orbital angular momentum density of Bessel beams is calculated explicitly within a rigorous vectorial treatment. This allows us to investigate some aspects that have not been analysed previously, such as the angular momentum content of azimuthally and radially polarized beams. Furthermore, we demonstrate experimentally the mechanical transfer of orbital angular momentum to trapped particles in optical tweezers using a high-order Bessel beam. We set transparent particles of known dimensions into rotation, where the sense of rotation can be reversed by changing the sign of the singularity. Quantitative results are obtained for rotation rates. This paper's animations are available from the Multimedia Enhancements page.
High Order Sliding Mode Control of Doubly-fed Induction Generator under Unbalanced Grid Faults
DEFF Research Database (Denmark)
Zhu, Rongwu; Chen, Zhe; Wu, Xiaojie; Liu, Hongzhi
This paper deals with a doubly-fed induction generator-based (DFIG) wind turbine system under grid fault conditions such as: unbalanced grid voltage, three-phase grid fault, using a high order sliding mode control (SMC). A second order sliding mode controller, which is robust with respect to......) control. In order to improve control performance of the overall system, electromagnetic power and active power oscillations elimination strategies are proposed respectively. Lastly, the effective of the proposed control strategy is verified by the simulation results of a 2 MW DFIG system....
Nonlinear wave-structure interactions with a high-order Boussinesq model
DEFF Research Database (Denmark)
Fuhrman, David R.; Bingham, Harry; Madsen, Per A.
2005-01-01
This paper describes the extension of a finite difference model based on a recently derived highly accurate Boussinesq formulation to include domains having arbitrary piecewise-rectangular bottom-mounted (surface-piercing) structures. The resulting linearized system is analyzed for stability on a...... system is receptive to dissipation, and these problems can be overcome in practice using high-order filtering techniques. The resulting model is verified through numerical simulations involving classical linear wave diffraction around a semi-infinite breakwater, linear and nonlinear gap diffraction, and...
High-performance and high-order numerical methods for 2D Navier-Stokes equations
Aurichio, Vinicius Henrique; Cucchieri, Attilio; Oliveira, Maria Luisa Bambozzi De
2015-11-01
Since numerical simulation of a flow is a computationally-intensive problem, our main goal is to develop numerical methods - to solve the fluid equations of motion (compressible Navier-Stokes) in 2D - that are also suitable for the high-performance computing framework. We study known methods, such as flux-splitting, MacCormack, and compact schemes, to guide our search. In particular, we consider some high-order versions of these methods, since they allow for high-resolution with less grid points, possibly reducing the computation times. Our effort is focused on obtaining shock-capturing, multiscale, low-numerical dissipation methods. CNPq-Brazil.
HIERtalker: A default hierarchy of high order neural networks that learns to read English aloud
Energy Technology Data Exchange (ETDEWEB)
An, Z.G.; Mniszewski, S.M.; Lee, Y.C.; Papcun, G.; Doolen, G.D.
1988-01-01
A new learning algorithm based on a default hierarchy of high order neural networks has been developed that is able to generalize as well as handle exceptions. It learns the ''building blocks'' or clusters of symbols in a stream that appear repeatedly and convey certain messages. The default hierarchy prevents a combinatoric explosion of rules. A simulator of such a hierarchy, HIERtalker, has been applied to the conversion of English words to phonemes. Achieved accuracy is 99% for trained words and ranges from 76% to 96% for sets of new words. 8 refs., 4 figs., 1 tab.
Spin-controlled orbital motion in tightly focused high-order Laguerre-Gaussian beams.
Cao, Yongyin; Zhu, Tongtong; Lv, Haiyi; Ding, Weiqiang
2016-02-22
Spin angular momentum can contribute to both optical force and torque exerted on spheres. Orbit rate of spheres located in tightly focused LG beams with the same azimuthal mode index l is spin-controlled due to spin-orbit coupling. Laguerre-Gaussian beams with high-order azimuthal mode are used here to study the orbit rate of dielectric spheres. Orbit rates of spheres with varying sizes and refravtive indices are investigated as well as optical forces acting on spheres in LG beams with different azimuthal modes. These results would be much helpful to investigation on optical rotation and transfer of spin and orbital angular momentum. PMID:26906996
Properties of high-order transverse modes in astigmatic laser cavities
International Nuclear Information System (INIS)
A theory of the modes in a resonator bounded by the surface of a triaxial ellipsoid was given previously by Weinstein. We have applied this theory to characterize the modes observed in a large-aperture Brewster-window laser. Recognizing that Brewster windows impart astigmatism to the laser cavity, we can find an equivalent ellipsoidal cavity with which to associate the modes. The theory predicts various forms of mode structure, depending on the total astigmatism present. We have verified the theory experimentally and show that high-order modes having rectangular symmetry may be obtained even though a circular aperture is used in the cavity. (auth)
Rows of optical vortices from elliptically perturbing a high-order beam
Dennis, M R
2006-01-01
An optical vortex (phase singularity) with a high topological strength resides on the axis of a high-order light beam. The breakup of this vortex under elliptic perturbation into a straight row of unit strength vortices is described. This behavior is studied in helical Ince-Gauss beams and astigmatic, generalized Hermite-Laguerre-Gauss beams, which are perturbations of Laguerre-Gauss beams. Approximations of these beams are derived for small perturbation, in which a neighborhood of the axis can be approximated by a polynomial in the complex plane: a Chebyshev polynomial for Ince-Gauss beams, and a Hermite polynomial for astigmatic beams.
Satisfactory PI-P Controller Design for High-order Servo System
Institute of Scientific and Technical Information of China (English)
MA Jian-wei; GUO Zhi; WU Qin
2005-01-01
The paper presents an output feedback controller design method for high-order servo system with the constraints of multiple indices by using satisfactory control theory. The control strategy is to convert transfer-function form of two-loop servo system into state-space form and assign the system poles in the specified region and H∞ attenuation degree in the given range with the Riccati matrix inequality so that the closed-loop system has good dynamics and robust quality. A numeric example is given to show the effectiveness of the proposed approach.
Controllable synthesis of highly ordered Ag nanorod arrays by chemical deposition method
International Nuclear Information System (INIS)
Highly ordered Ag nanorod arrays were successfully fabricated using a simple chemical deposition method with the assistance of porous alumina membrane (PAM) template. The products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ag+ ions in the PAM nanochannels were reduced by acetaldehyde reagent and resulting in the formation of rod array structures. It is found that the diameter of the Ag nanorods is determined by the PAM template, and the length of the Ag nanorods is depended on the reaction temperature. The growth mechanism of the Ag nanorod arrays is investigated in the study.
A generic mode selection strategy for high-order mode gyrotrons operating at multiple frequencies
Franck, Joachim; Avramidis, Konstantinos; Gantenbein, Gerd; Illy, Stefan; Jin, Jianbo; Thumm, Manfred; Jelonnek, John
2015-01-01
High-power, high-frequency gyrotrons for electron cyclotron resonance heating and current drive, such as proposed for the demonstration thermonuclear fusion reactor DEMO, require operating modes of very high order. As it is shown, the selection of the operating modes for such gyrotrons can be based on multi-frequency operability. A general selection strategy is derived, suitable for multi-purpose multi-frequency gyrotrons with quasi-optical mode converter and single-disc output window. Two examples, one of them relevant for future DEMO gyrotron designs, are discussed.
Photoemission with high-order harmonics: A tool for time-resolved core-level spectroscopy
DEFF Research Database (Denmark)
Christensen, Bjarke Holl; Raarup, Merete Krog; Balling, Peter
2010-01-01
A setup for femtosecond time-resolved photoelectron spectroscopy of solid surfaces is presented. The photon energies for core-level spectroscopy experiments are created by high-order harmonic generation from infrared 120-femtosecond laser pulses focused in a Ne gas jet. The present experimental r...... from the sample are collected by a large-solid-angle time-of-flight electron spectrometer based on a parabolic-grid reflector. Results from experiments probing the Bi 5d core-levels are presented, and the results of preliminary pump-probe experiments are described....
On The Integration of Decision Diagrams in High Order Logic Based Theorem Provers: a Survey
Directory of Open Access Journals (Sweden)
Sa'ed Abed
2007-01-01
Full Text Available This survey discuss approaches that integrate Decision Diagrams inside High Order Logic based Theorem provers. The approaches can be divided in two kinds, one is based on building a translation between model checker and theorem prover, the second is based on embedding the model checker algorithms inside the theorem prover. A comparison between both is discussed in detail. The paper also tries to answer which is the best decision graphs formalization for theorem provers as what is the optimized set of operations to efficiently manipulate the decision graphs inside theorem provers. Then, we contrast between them according to their efficiency, complexity and feasibility.
High Order Adjoint Derivatives using ESDIRK Methods for Oil Reservoir Production Optimization
DEFF Research Database (Denmark)
Capolei, Andrea; Stenby, Erling Halfdan; Jørgensen, John Bagterp
2012-01-01
continuous adjoints . The high order integration scheme allows larger time steps and therefore faster solution times. We compare gradient computation by the continuous adjoint method to the discrete adjoint method and the finite-difference method. The methods are implemented for a two phase flow reservoir...... simulator. Computational experiments demonstrate that the accuracy of the sensitivities obtained by the adjoint methods are comparable to the accuracy obtained by the finite difference method. The continuous adjoint method is able to use a different time grid than the forward integration. Therefore, it can...
High order numerical methods for the space non-homogeneous Boltzmann equation
International Nuclear Information System (INIS)
In this paper we present accurate methods for the numerical solution of the Boltzmann equation of rarefied gas. The methods are based on a time splitting technique. The transport is solved by a third order accurate (in space) positive and flux conservative (PFC) method. The collision step is treated by a Fourier approximation of the collision integral, which guarantees spectral accuracy in velocity, coupled with several high order integrators in time. Strang splitting is used to achieve second order accuracy in space and time. Several numerical tests illustrate the properties of the methods
Natural Dye-Sensitized Solar Cells Based on Highly Ordered TiO2 Nanotube Arrays
Na Li; Nengqian Pan; Danhong Li; Shiwei Lin
2013-01-01
The dye-sensitized solar cells (DSSCs) have been fabricated using highly ordered TiO2 nanotube arrays as photoelectrode and natural dyes as photosensitizers. The natural dyes were extracted from the abundant plants in the tropical region, such as Tradescantia zebrina, kapok, and pitaya. The dyes could chemically couple with TiO2 nanotubes and effectively convert visible light into electricity in DSSCs. A power conversion efficiency could be achieved up to 0.3% in the solar cell sensitized by ...
Guiding of low-energy electrons by highly ordered Al2 O3 nanocapillaries
DEFF Research Database (Denmark)
Milosavljević, A.R.; Víkor, G.; Pešić, Z.D.; Kolarž, P.; Šević, D.; Marinković, B.P.; Mátéfi-Tempfli, Stefan; Mátéfi-Tempfli, M.; Piraux, L.
2007-01-01
We report an experimental study of guided transmission of low-energy (200-350 eV) electrons through highly ordered Al2 O3 nanocapillaries with large aspect ratio (140 nm diameter and 15 μm length). The nanochannel array was prepared using self-ordering phenomena during a two-step anodization...... process of a high-purity aluminum foil. The experimental results clearly show the existence of the guiding effect, as found for highly charged ions. The guiding of the electron beam was observed for tilt angles up to 12°. As seen for highly charged ions, the guiding efficiency increases with decreasing...
DEFF Research Database (Denmark)
Etches, Adam; Madsen, Christian Bruun; Madsen, Lars Bojer
2010-01-01
A recent paper reported elliptically polarized high-order harmonics from aligned N2 using a linearly polarized driving field [X. Zhou et al., Phys. Rev. Lett. 102, 073902 (2009)]. This observation cannot be explained in the standard treatment of the Lewenstein model and has been ascribed to many...... additional contributions, which can be interpreted as quantum orbits in which the active electron is ionized at one atomic center within the molecule and recombines at another. The associated exchange harmonics are responsible for the nonvanishing ellipticity and result from a correlation between the...
High-Order Non-Reflecting Boundary Scheme for Time-Dependent Waves
Givoli, Dan; Neta, Beny
2002-01-01
A new non-reflecting boundary scheme is proposed for time-dependent wave problems in unbounded domains. The linear time-dependent wave equation, with or without a disper- sive term, is considered outside of an obstacle or in a semi-infinite wave guide. The infinite domain is truncated via an artificial boundary B, and a high-order Non-Reflecting Boundary Condition (NRBC) is imposed on B. Then the problem is solved numerically in the finite domain bounded by B. The new boundary scheme is based...
Application of the Arbitrarily High Order Method to Coupled Electron Photon Transport
International Nuclear Information System (INIS)
This work is about the application of the Arbitrary High Order Nodal Method to coupled electron photon transport.A Discrete Ordinates code was enhanced and validated which permited to evaluate the advantages of using variable spatial development order per particle.The results obtained using variable spatial development and adaptive mesh refinement following an a posteriori error estimator are encouraging.Photon spectra for clinical accelerator target and, dose and charge depositio profiles are simulated in one-dimensional problems using cross section generated with CEPXS code.Our results are in good agreement with ONELD and MCNP codes
Comparison of high order modes damping techniques for 800 MHz single cell superconducting cavities
Shashkov, Ya V; Zobov, M M
2014-01-01
Currently, applications of 800 MHz harmonic cavities in both bunch lengthening and shortening regimes are under consideration and discussion in the framework of the High Luminosity LHC project. In this paper we study electromagnetic characteristics of high order modes (HOM) for a single cell 800 MHz superconducting cavity and arrays of such cavities connected by drifts tubes. Different techniques for the HOM damping such as beam pipe grooves, coaxial-notch loads, fluted beam pipes etc. are investigated and compared. The influence of the sizes and geometry of the drift tubes on the HOM damping is analyzed.
International Nuclear Information System (INIS)
The isotopic effect on the molecular high-order harmonics generation is studied by numerically solving the one-dimensional time-dependent Schrodinger equation when the model H2+/HD+ ions are exposed to an intense laser pulse. To explain the effect more clearly, not only the ionization probabilities but also the time-frequency profiles are calculated. The results show that the interference minimum is sensitive to the laser intensity and the initial vibrational level for H2+ ions; in contrast, it is only dependent on the initial vibrational level for HD+ ions. (authors)
High-order-harmonic generation driven by pulses with angular spatial chirp
Hernández-García, Carlos; Jaron-Becker, Agnieszka; Hickstein, Daniel D.; Becker, Andreas; Durfee, Charles G.
2016-02-01
We present and analyze a technique to drive high-order harmonics by laser pulses with an angular spatial chirp. Results of our numerical simulations show that each harmonic is emitted with an angular chirp which scales inversely with the harmonic order and leads to additional control of the spatial and temporal resolution of the spectrum. In particular, the use of angular chirp leads to separation of the harmonics in two dimensions where (i) high spectral resolution can be achieved and (ii) the temporal periodicity of the harmonic pulse trains can be controlled. We show that this technique does not require carrier-envelope-phase stabilization when using few-cycle laser pulses.
Stability predictions for high-order ΣΔ modulators based on quasilinear modeling
DEFF Research Database (Denmark)
Risbo, Lars
This paper introduces a novel interpretation of the instability mechanisms in high-order one-bit Sigma-Delta modulators. Furthermore, it is demonstrated how the maximum stable amplitude range can be predicted very well. The results are obtained using an extension of the well known quasilinear...... modeling of the one-bit quantizer. The theoretical results are verified by numerical simulations of a number of realistic 4th order modulators designed by means of standard filter design tools. The results are useful for automated design and optimization of loop filters...
Long, Fan; Ganesh, Vijay; Carbin, Michael James; Sidiroglou, Stelios; Rinard, Martin
2012-01-01
We present a novel technique, automatic input rectification, and a prototype implementation, SOAP. SOAP learns a set of constraints characterizing typical inputs that an application is highly likely to process correctly. When given an atypical input that does not satisfy these constraints, SOAP automatically rectifies the input (i.e., changes the input so that it satisfies the learned constraints). The goal is to automatically convert potentially dangerous inputs into typical inputs that the ...
Directory of Open Access Journals (Sweden)
Narcis Eduard Mitu
2013-11-01
Full Text Available Policies or institutions (built into an economic system that automatically tend to dampen economic cycle fluctuations in income, employment, etc., without direct government intervention. For example, in boom times, progressive income tax automatically reduces money supply as incomes and spendings rise. Similarly, in recessionary times, payment of unemployment benefits injects more money in the system and stimulates demand. Also called automatic stabilizers or built-in stabilizers.
Automatic differentiation bibliography
Energy Technology Data Exchange (ETDEWEB)
Corliss, G.F. (comp.)
1992-07-01
This is a bibliography of work related to automatic differentiation. Automatic differentiation is a technique for the fast, accurate propagation of derivative values using the chain rule. It is neither symbolic nor numeric. Automatic differentiation is a fundamental tool for scientific computation, with applications in optimization, nonlinear equations, nonlinear least squares approximation, stiff ordinary differential equation, partial differential equations, continuation methods, and sensitivity analysis. This report is an updated version of the bibliography which originally appeared in Automatic Differentiation of Algorithms: Theory, Implementation, and Application.
Propagation evolution of an off-axis high-order cylindrical vector beam.
Li, Yang; Zhu, Zhuqing; Wang, Xiaolei; Gong, Liping; Wang, Ming; Nie, Shouping
2014-11-01
The propagation characteristics of an off-axis high-order cylindrical vector beam (OHCVB) are studied in this paper. The analytic expressions for the electric field and intensity distribution of the OHCVB propagating in free space are presented, to our knowledge for the first time. The transverse intensity of the OHCVB, different from that of the input Gaussian beam, does not have an axially symmetric distribution, owing to a slight dislocation between the polarization singularity located in the vector field generator and the center point of the Gaussian beam. Numerical results show that the intensity distribution during propagation strongly depends on the propagation distance, dislocation displacement, and topological charge. Accompanied by beam expansion, the intensity distribution of the OHCVB tends to eventually become steady, and the dark core of the vector beam will disappear gradually during the process of propagation. Moreover, with the increase of the topological charge, more energy will be transferred from the x axis to the y axis, and the annular intensity is split into two parts along the y-axis direction. The results help us to investigate the dynamic propagation behaviors of the HCVB under the off-axis condition and also guide the calibration of the off-axis high-order cylindrical vector field in practice. PMID:25401345
Domain structure and defects of highly ordered Bi4Si3O12 micro-crystals
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Highly ordered Bi4Si3O12 micro-crystals were prepared at normal atmosphere. Phase identification of the prepared crystals was accomplished by X-ray diffractometer (XRD). Domain structure and defects were characterized by environmental scanning electron microscopy (ESEM). XRD shows that the obtained micro-crystals are of eulytite structure with chemical formulation of Bi4Si3O12. A highly ordered growth pattern is confirmed due to the faster growth of the {124} faces than that of the {204} faces by ESEM. The growing process of the domain structure is of pollen parent and filial generation pattern. The filial generations of Bi4Si3O12 crystals are generated from the pollen parent. Cracks generate from the defect areas and propagate along the {124} faces due to their lower binding energy under a proper temperature gradient, contributing to the total transcrystalline fracture. It is confirmed that the generation and development of the voids in the crystal grains can be developed when unmatched dimensions of the two opposite faces are formed. And the development of the voids is dependent on the dimensions and orientations of the two opposite faces.
Experimental study of conversion from atomic high-order harmonics to x-ray emissions
Institute of Scientific and Technical Information of China (English)
王骐; 陈建新; 夏元钦; 陈德应
2003-01-01
There are two physical phenomena in a strong laser intensity. One is the high-order harmonic emission; the other is x-ray emission from optical-field ionized plasmas. The experiment of conversion from high-order harmonics to x-ray emissions was given with a 105fs Ti:sapphire laser by adjusting laser intensities. The ingredient in plasma was investigated by the numerical simulations. Our experimental results suggested that the free electrons have detrimental effects on harmonic generation but are favourable for x-ray emission from optical-field ionized plasmas. If we want to obtain more intense harmonic signals as a coherent light source in the soft x-ray region, we must avoid the production of free electrons in plasmas. At the same time, if we want to observe x-rays for the development of high-repetition-rate table-top soft x-ray lasers, we should strip all atoms in the plasmas to a necessary ionized stage by the optical-fieldionization in the field of a high-intensity laser pulse.
Quantum-optical model for the dynamics of high-order-harmonic generation
Gombkötő, Ákos; Czirják, Attila; Varró, Sándor; Földi, Péter
2016-07-01
We investigate a two-level atom in the field of a strong laser pulse. The resulting time-dependent polarization is the source of a radiation the frequency components of which are essentially harmonics of the driving field's carrier frequency. The time evolution of this secondary radiation is analyzed in terms of the expectation values of the photon-number operators for a large number of electromagnetic modes that are initially in the vacuum state. Our method is based on a multimode version of the Jaynes-Cummings-Paul model and can be generalized to different radiating systems as well. We show that, after the exciting pulse, the final distribution of the photon numbers is close to the conventional (Fourier-transform-based) power spectrum of the secondary radiation. The details of the high-order-harmonic spectra (HHG spectra) are also analyzed; for many-cycle excitations a clear physical interpretation is given in terms of the Floquet quasienergies. A first step towards the determination of the photon statistics of the high-order-harmonic modes reveals states with slightly super-Poissonian distribution.
The effects of molecular vibration on the yield of high-order harmonic generation.
Xia, Jiangfan
2005-05-01
It is well-accepted that the high-order harmonic spectrum is the results of interference between many attosecond pulses. Each of the attosecond pulse is produced by a three-step process taking place within one laser cycle. For light molecules such as H2, the first step is the ionization of one electron. When the freed electron returns to the H2^+, the internuclear distance is changed. This may cause the electron to miss the ion during its revisit, thus reducing its probability to recombine with the parent ion. As a result, the high harmonic generation yield is lower for H2 than D2, since D2 has a longer vibration period (˜21 fs) than that of H2 (˜15 fs). Here we report, to the best of our knowledge, the first experimental observation of the effects of vibration on the yield of HHG in molecules. We compared the high-order harmonic spectra of H2, HD and D2. The shortest pulses were ˜8 fs, which is almost the same as one half of the vibration period of H2. Using such short pulses assures that the internuclear distances of all three types of molecules are in the increasing phase of a cycle when the harmonics are generated. From the HHG spectra it is evident that the yield of D2 is a factor of two higher than that of H2, while that of HD is in between. This is consistent with the theoretical predictions.
A high-order Godunov-type scheme for shock interactions in ideal magnetohydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Dai, W.; Woodward, P.R. [Univ. of Minnesota, Minneapolis, MN (United States)
1997-07-01
A high-order Godunov-type scheme is developed for the shock interactions in ideal magnetohydrodynamics (MHD). The scheme is based on a nonlinear Riemann solver and follows the basic procedure in the piecewise parabolic method. The scheme takes into account all the discontinuities in ideal MHD and is in a strict conservation form. The scheme is applied to numerical examples, which include shock-tube problems in ideal MHD and various interactions between strong MHD shocks. All the waves involved in the corresponding Riemann problems are resolved and are correctly displayed in the simulation results. The correctness of the scheme is shown by the comparison between the simulation results and the solutions of the Riemann problems. The robustness of the scheme is demonstrated through the numerical examples. It is shown that the scheme offers the principle advantages of a high-order Godunov-type scheme: robust operation in the presence of very strong waves, thin shock fronts, and thin contact and slip surface discontinuities.
A high-order Godunov-type scheme for shock interactions in ideal magnetohydrodynamics
International Nuclear Information System (INIS)
A high-order Godunov-type scheme is developed for the shock interactions in ideal magnetohydrodynamics (MHD). The scheme is based on a nonlinear Riemann solver and follows the basic procedure in the piecewise parabolic method. The scheme takes into account all the discontinuities in ideal MHD and is in a strict conservation form. The scheme is applied to numerical examples, which include shock-tube problems in ideal MHD and various interactions between strong MHD shocks. All the waves involved in the corresponding Riemann problems are resolved and are correctly displayed in the simulation results. The correctness of the scheme is shown by the comparison between the simulation results and the solutions of the Riemann problems. The robustness of the scheme is demonstrated through the numerical examples. It is shown that the scheme offers the principle advantages of a high-order Godunov-type scheme: robust operation in the presence of very strong waves, thin shock fronts, and thin contact and slip surface discontinuities
Verification of high-order mixed FEM solution of transient Magnetic diffusion problems
Energy Technology Data Exchange (ETDEWEB)
Rieben, R; White, D A
2005-05-12
We develop and present high order mixed finite element discretizations of the time dependent electromagnetic diffusion equations for solving eddy current problems on 3D unstructured grids. The discretizations are based on high order H(grad), H(curl) and H(div) conforming finite element spaces combined with an implicit and unconditionally stable generalized Crank-Nicholson time differencing method. We develop three separate electromagnetic diffusion formulations, namely the E (electric field), H (magnetic field) and the A-{phi} (potential) formulations. For each formulation, we also provide a consistent procedure for computing the secondary variables F (current flux density) and B (magnetic flux density), as these fields are required for the computation of electromagnetic force and heating terms. We verify the error convergence properties of each formulation via a series of numerical experiments on canonical problems with known analytic solutions. The key result is that the different formulations are equally accurate, even for the secondary variables J and B, and hence the choice of which formulation to use depends mostly upon relevance of the Natural and Essential boundary conditions to the problem of interest. In addition, we highlight issues with numerical verification of finite element methods which can lead to false conclusions on the accuracy of the methods.
High Order Finite Volume Nonlinear Schemes for the Boltzmann Transport Equation
Energy Technology Data Exchange (ETDEWEB)
Bihari, B L; Brown, P N
2005-03-29
The authors apply the nonlinear WENO (Weighted Essentially Nonoscillatory) scheme to the spatial discretization of the Boltzmann Transport Equation modeling linear particle transport. The method is a finite volume scheme which ensures not only conservation, but also provides for a more natural handling of boundary conditions, material properties and source terms, as well as an easier parallel implementation and post processing. It is nonlinear in the sense that the stencil depends on the solution at each time step or iteration level. By biasing the gradient calculation towards the stencil with smaller derivatives, the scheme eliminates the Gibb's phenomenon with oscillations of size O(1) and reduces them to O(h{sup r}), where h is the mesh size and r is the order of accuracy. The current implementation is three-dimensional, generalized for unequally spaced meshes, fully parallelized, and up to fifth order accurate (WENO5) in space. For unsteady problems, the resulting nonlinear spatial discretization yields a set of ODE's in time, which in turn is solved via high order implicit time-stepping with error control. For the steady-state case, they need to solve the non-linear system, typically by Newton-Krylov iterations. There are several numerical examples presented to demonstrate the accuracy, non-oscillatory nature and efficiency of these high order methods, in comparison with other fixed-stencil schemes.
Bai, Yushi; Luo, Quan; Zhang, Wei; Miao, Lu; Xu, Jiayun; Li, Hongbin; Liu, Junqiu
2013-07-31
Protein self-assembly into exquisite, complex, yet highly ordered architectures represents the supreme wisdom of nature. However, precise manipulation of protein self-assembly behavior in vitro is a great challenge. Here we report that by taking advantage of the cooperation of metal-ion-chelating interactions and nonspecific protein-protein interactions, we achieved accurate control of the orientation of proteins and their self-assembly into protein nanorings. As a building block, we utilized the C2-symmetric protein sjGST-2His, a variant of glutathione S-transferase from Schistosoma japonicum having two properly oriented His metal-chelating sites on the surface. Through synergic metal-coordination and non-covalent interactions, sjGST-2His self-assembled in a fixed bending manner to form highly ordered protein nanorings. The diameters of the nanorings can be regulated by tuning the strength of the non-covalent interaction network between sjGST-2His interfaces through variation of the ionic strength of the solution. This work provides a de novo design strategy that can be applied in the construction of novel protein superstructures. PMID:23865524
Frequency dependence of quantum path interference in non-collinear high-order harmonic generation
Shi-Yang, Zhong; Xin-Kui, He; Hao, Teng; Peng, Ye; Li-Feng, Wang; Peng, He; Zhi-Yi, Wei
2016-02-01
High-order harmonic generation (HHG) driven by two non-collinear beams including a fundamental and its weak second harmonic is numerically studied. The interference of harmonics from adjacent electron quantum paths is found to be dependent on the relative delay of the driving pulse, and the dependences are different for different harmonic orders. This frequency dependence of the interference is attributed to the spatial frequency chirp in the HHG beam resulting from the harmonic dipole phase, which in turn provides a potential way to gain an insight into the generation of high-order harmonics. As an example, the intensity dependent dipole phase coefficient α is retrieved from the interference fringe. Project supported by the National Key Basic Research Program of China (Grant Nos. 2013CB922401 and 2013CB922402), the National Key Scientific Instrument and Equipment Development Projects, China (Grant No. 2012YQ12004704), the National Natural Science Foundation of China (Grant No. 11374356), and the International Joint Research Program of National Natural Science Foundation of China (Grant No. 61210017).
A high-order staggered finite-element vertical discretization for non-hydrostatic atmospheric models
Guerra, Jorge E.; Ullrich, Paul A.
2016-06-01
Atmospheric modeling systems require economical methods to solve the non-hydrostatic Euler equations. Two major differences between hydrostatic models and a full non-hydrostatic description lies in the vertical velocity tendency and numerical stiffness associated with sound waves. In this work we introduce a new arbitrary-order vertical discretization entitled the staggered nodal finite-element method (SNFEM). Our method uses a generalized discrete derivative that consistently combines the discontinuous Galerkin and spectral element methods on a staggered grid. Our combined method leverages the accurate wave propagation and conservation properties of spectral elements with staggered methods that eliminate stationary (2Δx) modes. Furthermore, high-order accuracy also eliminates the need for a reference state to maintain hydrostatic balance. In this work we demonstrate the use of high vertical order as a means of improving simulation quality at relatively coarse resolution. We choose a test case suite that spans the range of atmospheric flows from predominantly hydrostatic to nonlinear in the large-eddy regime. Our results show that there is a distinct benefit in using the high-order vertical coordinate at low resolutions with the same robust properties as the low-order alternative.
A unified approach for a posteriori high-order curved mesh generation using solid mechanics
Poya, Roman; Sevilla, Ruben; Gil, Antonio J.
2016-06-01
The paper presents a unified approach for the a posteriori generation of arbitrary high-order curvilinear meshes via a solid mechanics analogy. The approach encompasses a variety of methodologies, ranging from the popular incremental linear elastic approach to very sophisticated non-linear elasticity. In addition, an intermediate consistent incrementally linearised approach is also presented and applied for the first time in this context. Utilising a consistent derivation from energy principles, a theoretical comparison of the various approaches is presented which enables a detailed discussion regarding the material characterisation (calibration) employed for the different solid mechanics formulations. Five independent quality measures are proposed and their relations with existing quality indicators, used in the context of a posteriori mesh generation, are discussed. Finally, a comprehensive range of numerical examples, both in two and three dimensions, including challenging geometries of interest to the solids, fluids and electromagnetics communities, are shown in order to illustrate and thoroughly compare the performance of the different methodologies. This comparison considers the influence of material parameters and number of load increments on the quality of the generated high-order mesh, overall computational cost and, crucially, the approximation properties of the resulting mesh when considering an isoparametric finite element formulation.
Impact of electron ionization on the generation of high-order harmonics from molecules
International Nuclear Information System (INIS)
When the laser frequency is tuned to be equal to the molecular electronic excitation, high-order harmonics are generated due to the electronic dipole transitions between the corresponding two potential-energy surfaces (PES). A natural, often taken, choice is the PES of the field-free molecular system. In this special choice the ionization phenomenon is not considered. Only the effect of the dissociation is considered. The method we developed enables one to remain within the framework of the 2-PES approximation and yet to include also the ionization effect in the calculations of molecular high-order harmonic generation spectra. In this approach the coupling between the electronic and nuclear motions is taken into consideration by using coupled complex adiabatic PES. As an illustrative numerical example, we calculated the high harmonic generation (HHG) spectra of H2+ in a 730-nm laser with the intensity of 8.77x1013 W/cm2. The inclusion of the ionization in our approach not only enables the electrons to tunnel through the effective static potential barrier, but also apply an asymmetric force which accelerates the electron before ionization takes place. Therefore, indirectly the inclusion of the ionization by the laser field may lead eventually to an enhanced HHG spectra in comparison with the calculated one when the ''natural'' choice of the field-free 2PES is taken
Exponential quantum spreading in a class of kicked rotor systems near high-order resonances
Wang, Hailong; Wang, Jiao; Guarneri, Italo; Casati, Giulio; Gong, Jiangbin
2013-11-01
Long-lasting exponential quantum spreading was recently found in a simple but very rich dynamical model, namely, an on-resonance double-kicked rotor model [J. Wang, I. Guarneri, G. Casati, and J. B. Gong, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.107.234104 107, 234104 (2011)]. The underlying mechanism, unrelated to the chaotic motion in the classical limit but resting on quasi-integrable motion in a pseudoclassical limit, is identified for one special case. By presenting a detailed study of the same model, this work offers a framework to explain long-lasting exponential quantum spreading under much more general conditions. In particular, we adopt the so-called “spinor” representation to treat the kicked-rotor dynamics under high-order resonance conditions and then exploit the Born-Oppenheimer approximation to understand the dynamical evolution. It is found that the existence of a flat band (or an effectively flat band) is one important feature behind why and how the exponential dynamics emerges. It is also found that a quantitative prediction of the exponential spreading rate based on an interesting and simple pseudoclassical map may be inaccurate. In addition to general interests regarding the question of how exponential behavior in quantum systems may persist for a long time scale, our results should motivate further studies toward a better understanding of high-order resonance behavior in δ-kicked quantum systems.
Directory of Open Access Journals (Sweden)
Elhadj BOUNADJA
2016-07-01
Full Text Available The present work examines a direct torque control strategy using a high order sliding mode controllers of a doubly-fed induction generator (DFIG incorporated in a wind energy conversion system and working in saturated state. This research is carried out to reach two main objectives. Firstly, in order to introduce some accuracy for the calculation of DFIG performances, an accurate model considering magnetic saturation effect is developed. The second objective is to achieve a robust control of DFIG based wind turbine. For this purpose, a Direct Torque Control (DTC combined with a High Order Sliding Mode Control (HOSMC is applied to the DFIG rotor side converter. Conventionally, the direct torque control having hysteresis comparators possesses major flux and torque ripples at steady-state and moreover the switching frequency varies on a large range. The new DTC method gives a perfect decoupling between the flux and the torque. It also reduces ripples in these grandeurs. Finally, simulated results show, accurate dynamic performances, faster transient responses and more robust control are achieved.
High-order numerical solution of the nonlinear Helmholtz equation with axial symmetry
Baruch, G.; Fibich, G.; Tsynkov, S.
2007-07-01
The nonlinear Helmholtz (NLH) equation models the propagation of intense laser beams in a Kerr medium. The NLH takes into account the effects of nonparaxiality and backward scattering that are neglected in the more common nonlinear Schrodinger model. In [G. Fibich, S. Tsynkov, High-order two-way artificial boundary conditions for nonlinear wave propagation with backscattering, J. Comput. Phys., 171 (2001) 632-677] and [G. Fibich, S. Tsynkov, Numerical solution of the nonlinear Helmholtz equation using nonorthogonal expansions, J. Comput. Phys., 210 (2005) 183-224], a novel high-order numerical method for solving the NLH was introduced and implemented in the case of a two-dimensional Cartesian geometry. The NLH was solved iteratively, using the separation of variables and a special nonlocal two-way artificial boundary condition applied to the resulting decoupled linear systems. In the current paper, we propose a major improvement to the previous method. Instead of using LU decomposition after the separation of variables, we employ an efficient summation rule that evaluates convolution with the discrete Green's function. We also extend the method to a three-dimensional setting with cylindrical symmetry, under both Dirichlet and Sommerfeld-type transverse boundary conditions.
A high order special relativistic hydrodynamic code with space-time adaptive mesh refinement
Zanotti, Olindo
2013-01-01
We present a high order one-step ADER-WENO finite volume scheme with space-time adaptive mesh refinement (AMR) for the solution of the special relativistic hydrodynamics equations. By adopting a local discontinuous Galerkin predictor method, a high order one-step time discretization is obtained, with no need for Runge-Kutta sub-steps. This turns out to be particularly advantageous in combination with space-time adaptive mesh refinement, which has been implemented following a "cell-by-cell" approach. As in existing second order AMR methods, also the present higher order AMR algorithm features time-accurate local time stepping (LTS), where grids on different spatial refinement levels are allowed to use different time steps. We also compare two different Riemann solvers for the computation of the numerical fluxes at the cell interfaces. The new scheme has been validated over a sample of numerical test problems in one, two and three spatial dimensions, exploring its ability in resolving the propagation of relativ...
Adaptation strategies for high order discontinuous Galerkin methods based on Tau-estimation
Kompenhans, Moritz; Rubio, Gonzalo; Ferrer, Esteban; Valero, Eusebio
2016-02-01
In this paper three p-adaptation strategies based on the minimization of the truncation error are presented for high order discontinuous Galerkin methods. The truncation error is approximated by means of a τ-estimation procedure and enables the identification of mesh regions that require adaptation. Three adaptation strategies are developed and termed a posteriori, quasi-a priori and quasi-a priori corrected. All strategies require fine solutions, which are obtained by enriching the polynomial order, but while the former needs time converged solutions, the last two rely on non-converged solutions, which lead to faster computations. In addition, the high order method permits the spatial decoupling for the estimated errors and enables anisotropic p-adaptation. These strategies are verified and compared in terms of accuracy and computational cost for the Euler and the compressible Navier-Stokes equations. It is shown that the two quasi-a priori methods achieve a significant reduction in computational cost when compared to a uniform polynomial enrichment. Namely, for a viscous boundary layer flow, we obtain a speedup of 6.6 and 7.6 for the quasi-a priori and quasi-a priori corrected approaches, respectively.
Towards high-order modulation using complex modulation of semiconductor lasers.
Che, Di; Yuan, Feng; Shieh, William
2016-03-21
Optical communication using high-speed on-off-keying signal by directly modulated semiconductor lasers (DML) was one of the most significant breakthroughs for telecommunication in 1960s. The wide deployment of 2.5-Gb/s per-channel transoceanic optical fiber links in 1990s drove the internet as a global phenomenon. However, the detrimental frequency chirp of DML prevents its application to the subsequent internet capacity evolution. Today, the state-of-the-art long-haul optical transponder uses external modulators to support high-order complex modulation. In contrast, this paper shows that the "detrimental" chirp effect can be exploited to generate complex modulation with a single DML, which achieves dramatic sensitivity gain of signal-to-noise-ratio compared to the conventional intensity modulation of DML. By using large chirp parameters, complex-modulated DML paves an attractive pathway towards high-order pulse-amplitude modulation with an ultra-low transmitter cost, which has great potential in future medium reach optical communications. PMID:27136852
Scattering of high order guided wave modes around a through-thickness circular hole
Travaglini, Christophe; Bescond, Christophe; França, Demartonne Ramos; Kruger, Silvio E.; Viens, Martin; Bélanger, Pierre
2016-02-01
Ultrasonic guided waves have the ability to propagate long distances with minimal attenuation, which makes them particularly interesting in structural health monitoring (SHM) applications. Using the baseline subtraction approach, the signal from a defect-free structure is compared with the actual monitoring signal to detect and locate defects. There are many scientific publications on low-frequency guided waves for SHM purposes, and the interaction between guided wave fundamental modes and defects is also well documented. There is however a very limited number of studies on high order modes. High-frequency guided waves may enable the detection of smaller cracks related to conventional low-frequency guided wave SHM. The main difficulty at high frequency is the existence of several modes with different velocities. This study investigates the scattering of high order guided wave modes around a through-thickness hole with a view to developing a highly sensitive SHM method. A 3D finite element model of a 305 mm × 305 mm × 1.6 mm aluminium plate was used to determine the scattering of cracks on the circumference of a through-thickness hole in the middle of the plate. Crack properties such as orientation, length and depth were studied. A subset of the finite element simulations were validated against experimental results. The experimental setup comprised a film type PZT actuator bonded on the side of the plate and a laser interferometer detector. An input signal centered at 4 MHz was used in all simulations and experiments.
Institute of Scientific and Technical Information of China (English)
LIU Xiang-zhi; XU Ming-xia; TIAN Yu-ming; SHANG Meng; ZHANG Ping
2006-01-01
A two-step anodizing process was used to prepare wide-range highly ordered porous anodic alumina membrane (PAA) in the electrolyte of oxalic acid. The effects of anodic voltage,anodizing time,size of aluminium foil and additives on the regularity of PAA membrane were also studied in the process of two-step anodization. The template method was combined with the sol-electrophoresis deposition and sol-gel method respectively to prepare highly ordered titania nanostructures. The diameter and length of the obtained nanostructures were determined by the pore size and depth of the PAA template. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the morphology and phase structure of the PAA template and the titania nanostructures. The results show that the anodizing time and the additive of ethanol have a great effect on the regularity of PAA template. This can be explained from the self-organized process and the current density theory. A theoretical model based on the self-organized process was established to discuss the formation mechanism of PAA template from the chemical perspective. The titania nanostructures prepared with this method has a high specific surface area. Furthermore,the photocatalytic activity of titania nanostructures on methyl orange were studied. Compared with ordinary titania membranes,the titania nanostructures synthesized with this method have higher photodegradation activity.
Preparation and photocatalytic activity of highly ordered mesoporous TiO{sub 2}-SBA-15
Energy Technology Data Exchange (ETDEWEB)
Qiao Wenting [School of Chemical Engineering, Shandong Institute of Light Industry, Jinan, 250353, Shandong (China); Zhou Guowei, E-mail: guoweizhou@hotmail.com [School of Chemical Engineering, Shandong Institute of Light Industry, Jinan, 250353, Shandong (China); Zhang Xiaotong; Li Tianduo [School of Chemical Engineering, Shandong Institute of Light Industry, Jinan, 250353, Shandong (China)
2009-05-05
TiO{sub 2}-SBA-15 complex materials with highly ordered mesostructures have been prepared by a one-step hydrothermal synthesis method of titanium tetraisopropoxide (TTIP) and tetraethoxysilane (TEOS) in an acidic solution using surfactant P123 (EO{sub 20}PO{sub 70}EO{sub 20}) as structure-directing reagent. The prepared materials were characterized by transmission electron microscopy (TEM), small-angle X-ray diffraction patterns (SAXRD), Fourier transformed infrared spectroscopy (FT-IR) and N{sub 2} adsorption-desorption experiments. The resulting TiO{sub 2}-SBA-15 complex materials showed highly ordered mesoporous structure with uniform pore sizes of 5.95 and 8.24 nm, high specific surface areas S{sub BET} of 689 m{sup 2} g{sup -1} and 347 m{sup 2} g{sup -1} at different hydrothermal temperatures (100 deg. C and 130 deg. C). The photocatalytic activity of these TiO{sub 2}-SBA-15 mesoporous materials has been studied by 4-chlorophenol decomposition under UV light irradiation. The TiO{sub 2}-SBA-15 mesoporous materials prepared at the TiO{sub 2}:SiO{sub 2} mass ratios of 25:75, 40:60 and 50:50 showed higher photocatalytic activity than that prepared at the TiO{sub 2}:SiO{sub 2} mass ratio of 75:25.
High-intensity attosecond high-order harmonic generation driven by a synthesized laser field
International Nuclear Information System (INIS)
The scheme of high-intensity attosecond high-order harmonic generation driven by a synthesized laser field is proposed. The synthesized laser field is obtained by an appropriate superposition of a few-cycle laser pulse and a relatively long pulse of several tens of femtoseconds. Calculated results show that the intensity of the attosecond high-order harmonic pulse in helium driven by the synthesized laser field with a 8.8x1013 W/cm2/5 fs laser pulse and a 3.51x1014 W/cm2/50 fs laser pulse is several orders of magnitude higher than that driven by a single 8.8x1013 W/cm2/5 fs laser pulse, and it is even stronger than that driven by a single 7.9x1014 W/cm2/5 fs laser pulse, although the single and the synthesized pulses have the same peak electric-field strength
High-Intensity High-order Harmonics Generated from Low-Density Plasma
International Nuclear Information System (INIS)
We study the generation of high-order harmonics from lowly ionized plasma, using the 10 TW, 10 Hz laser of the Advanced Laser Light Source (ALLS). We perform detailed studies on the enhancement of a single order of the high-order harmonic spectrum generated in plasma using the fundamental and second harmonic of the ALLS beam line. We observe quasi-monochromatic harmonics for various targets, including Mn, Cr, Sn, and In. We identify most of the ionic/neutral transitions responsible for the enhancement, which all have strong oscillator strengths. We demonstrate intensity enhancements of the 13th, 17th, 29th, and 33rd harmonics from these targets using the 800 nm pump laser and varying its chirp. We also characterized the attosecond nature of such plasma harmonics, measuring attosecond pulse trains with 360 as duration for chromium plasma, using the technique of ''Reconstruction of Attosecond Beating by Interference of Two-photon Transitions''(RABBIT). These results show that plasma harmonics are intense source of ultrashort coherent soft x-rays.
Adaptive terminal sliding mode control for high-order nonlinear dynamic systems
Institute of Scientific and Technical Information of China (English)
庄开宇; 苏宏业; 张克勤; 褚健
2003-01-01
An adaptive terminal sliding mode control (SMC) technique is proposed to deal with the tracking problem for a class of high-order nonlinear dynamic systems. It is shown that a function augmented sliding hyperplane can be used to develop a new terminal sliding mode for high-order nonlinear systems. A terminal SMC controller based on Lyapunov theory is designed to force the state variables of the closed-loop system to reach and remain on the terminal sliding mode, so that the output tracking error then converges to zero in finite time which can be set arbitrarily. An adaptive mechanism is introduced to estimate the unknown parameters of the upper bounds of system uncertainties. The estimates are then used as controller parameters so that the effects of uncertain dynamics can be eliminated. It is also shown that the stability of the closed-loop system can be guaranteed with the proposed control strategy. The simulation of a numerical example is provided to show the effectiveness of the new method.
High-order moments of spin-orbit energy in a multielectron configuration.
Na, Xieyu; Poirier, M
2016-07-01
In order to analyze the energy-level distribution in complex ions such as those found in warm dense plasmas, this paper provides values for high-order moments of the spin-orbit energy in a multielectron configuration. Using second-quantization results and standard angular algebra or fully analytical expressions, explicit values are given for moments up to 10th order for the spin-orbit energy. Two analytical methods are proposed, using the uncoupled or coupled orbital and spin angular momenta. The case of multiple open subshells is considered with the help of cumulants. The proposed expressions for spin-orbit energy moments are compared to numerical computations from Cowan's code and agree with them. The convergence of the Gram-Charlier expansion involving these spin-orbit moments is analyzed. While a spectrum with infinitely thin components cannot be adequately represented by such an expansion, a suitable convolution procedure ensures the convergence of the Gram-Charlier series provided high-order terms are accounted for. A corrected analytical formula for the third-order moment involving both spin-orbit and electron-electron interactions turns out to be in fair agreement with Cowan's numerical computations. PMID:27575229
High-order harmonic generation with resonant core excitation by ultra-intense X-rays
International Nuclear Information System (INIS)
It is known that atoms can generate high-order harmonic (HHG) in intense optical laser fields. In this article, HHG is combined with resonant X-ray excitation of a core electron into the transient valence vacancy that is created in the course of the HHG process. To describe this setting, I develop a two-active-electron quantum theory for a single atom assuming no Coulomb interaction among the electrons; one electron performs a typical HHG three-step process whereas another electron is excited (or even Rabi flops) by intense X-rays from the core shell into the valence hole after the first electron has left the atom. Depending on the amplitude to find a vacancy in the valence and the core, the returning continuum electron recombines with the valence and the core, respectively, emitting high-order harmonic (HH) radiation that is characteristic of the combined process. After presenting the theory of X-ray boosted HHG for continuous-wave light fields, I develop a description for X-ray pulses with a time varying amplitude and phase. My prediction offers novel prospects for nonlinear X-ray physics, atto-second X-rays, and HHG-based time-dependent chemical imaging involving core orbitals. (author)
Generation of very-high order Laguerre-Gaussian modes in Yb:YAG ceramic laser
International Nuclear Information System (INIS)
The use of a simple short-focus plano-convex glass lens with strong spherical aberration for Laguerre-Gaussian mode selection in a continuous wave (CW) LD-end-pumped Yb:YAG ceramic laser is demonstrated. Mode selection was obtained in a nearly meter long plane-parallel cavity by shifting an intra-cavity lens of 2.5 cm focal length along the resonator axis. Sequence of Laguerre-Gaussian (LGp,l) modes with different combinations of radial (p) and azimuthal (l) indices from low to high orders (p = 0 – 12, l = 0 – 28) with output beam diameters 2 – 13 mm and power up to 30 mW was produced. Along with many low order modes, the whole lineage of very high order pure ''hollow'' LGp,l modes (p = 5 – 10, l = 7 – 28) was produced by this method for the first time. The region of stability of the resonator with an intra-cavity aberrating lens was found to be enclosed between ''focusing'' and ''imaging'' configurations in the cavity, which the aberrating lens could provide simultaneously. The mechanism of LGp,l mode selection in such a cavity and possible applications of the proposed laser scheme are considered
Liu, Yen; Vinokur, Marcel; Wang, Z. J.
2004-01-01
A three-dimensional, high-order, conservative, and efficient discontinuous spectral volume (SV) method for the solutions of Maxwell's equations on unstructured grids is presented. The concept of discontinuous 2nd high-order loca1 representations to achieve conservation and high accuracy is utilized in a manner similar to the Discontinuous Galerkin (DG) method, but instead of using a Galerkin finite-element formulation, the SV method is based on a finite-volume approach to attain a simpler formulation. Conventional unstructured finite-volume methods require data reconstruction based on the least-squares formulation using neighboring cell data. Since each unknown employs a different stencil, one must repeat the least-squares inversion for every cell at each time step, or to store the inversion coefficients. In a high-order, three-dimensional computation, the former would involve impractically large CPU time, while for the latter the memory requirement becomes prohibitive. In the SV method, one starts with a relatively coarse grid of triangles or tetrahedra, called spectral volumes (SVs), and partition each SV into a number of structured subcells, called control volumes (CVs), that support a polynomial expansion of a desired degree of precision. The unknowns are cell averages over CVs. If all the SVs are partitioned in a geometrically similar manner, the reconstruction becomes universal as a weighted sum of unknowns, and only a few universal coefficients need to be stored for the surface integrals over CV faces. Since the solution is discontinuous across the SV boundaries, a Riemann solver is thus necessary to maintain conservation. In the paper, multi-parameter and symmetric SV partitions, up to quartic for triangle and cubic for tetrahedron, are first presented. The corresponding weight coefficients for CV face integrals in terms of CV cell averages for each partition are analytically determined. These discretization formulas are then applied to the integral form of
Further study on the high-order double-Fourier-series spectral filtering on a sphere
Cheong, Hyeong-Bin; Kwon, In-Hyuk; Goo, Tae-Young
2004-01-01
A high-order harmonic spectral filter (HSF) is further studied using double Fourier series (DFS), which performs filtering in terms of successive inversion of tridiagonal matrices with complex-valued elements. The high-order harmonics filter equation is split into multiple Helmholtz equations. It is found that the filter provides the same order of accuracy as the spectral filter in [J. Comput. Phys. 177 (2002) 313] that consists of the pentadiagonal matrices with real-valued elements. The advantage of the filter over the previous one lies on the simplicity and easiness of numerical implementation or computer coding, just requiring the same complexity as Poisson's equation solver. However, the operation count associated with the filter increases by a factor of about 2. To circumvent the inefficiency while preserving the simplicity, an easy way to construct pentadiagonal matrices associated with the biharmonic equation is presented in which the tridiagonal matrices related with Poisson's equation are manipulated. Computational efficiency of the spectral filter is discussed in terms of the relative computing time to the spectral transform. It is revealed that the computing cost (requiring O( N2) operations with N being the truncation) for the spectral filtering, even with the complex-valued matrices, is not significant in the DFS spectral model that is characterized by O( N2log 2N) operations. Filtering with different DFS expansions is discussed with a focus on the accuracy and pole condition. It is shown that the DFS violating the pole conditions produces a discontinuity at poles in case of wave truncation, and its influence spreads over the globe. The spectral filter is applied to two kinds of uniform-grid data, the regular and the shifted grids, and the results are compared with each other. The operator splitting (or spherical harmonics factorization) makes it feasible to apply the finite difference method to the high-order harmonics filter with ease because only
A high-order Petrov-Galerkin method for the Boltzmann transport equation
International Nuclear Information System (INIS)
We describe a new Petrov-Galerkin method using high-order terms to introduce dissipation in a residual-free formulation. The method is developed following both a Taylor series analysis and a variational principle, and the result has much in common with traditional Petrov-Galerkin, Self Adjoint Angular Flux (SAAF) and Even Parity forms of the Boltzmann transport equation. In addition, we consider the subtleties in constructing appropriate boundary conditions. In sub-grid scale (SGS) modelling of fluids the advantages of high-order dissipation are well known. Fourth-order terms, for example, are commonly used as a turbulence model with uniform dissipation. They have been shown to have superior properties to SGS models based upon second-order dissipation or viscosity. Even higher-order forms of dissipation (e.g. 16.-order) can offer further advantages, but are only easily realised by spectral methods because of the solution continuity requirements that these higher-order operators demand. Higher-order operators are more effective, bringing a higher degree of representation to the solution locally. Second-order operators, for example, tend to relax the solution to a linear variation locally, whereas a high-order operator will tend to relax the solution to a second-order polynomial locally. The form of the dissipation is also important. For example, the dissipation may only be applied (as it is in this work) in the streamline direction. While for many problems, for example Large Eddy Simulation (LES), simply adding a second or fourth-order dissipation term is a perfectly satisfactory SGS model, it is well known that a consistent residual-free formulation is required for radiation transport problems. This motivated the consideration of a new Petrov-Galerkin method that is residual-free, but also benefits from the advantageous features that SGS modelling introduces. We close with a demonstration of the advantages of this new discretization method over standard Petrov
Three-Dimensional High-Order Spectral Finite Volume Method for Unstructured Grids
Liu, Yen; Vinokur, Marcel; Wang, Z. J.; Kwak, Dochan (Technical Monitor)
2002-01-01
Many areas require a very high-order accurate numerical solution of conservation laws for complex shapes. This paper deals with the extension to three dimensions of the Spectral Finite Volume (SV) method for unstructured grids, which was developed to solve such problems. We first summarize the limitations of traditional methods such as finite-difference, and finite-volume for both structured and unstructured grids. We then describe the basic formulation of the spectral finite volume method. What distinguishes the SV method from conventional high-order finite-volume methods for unstructured triangular or tetrahedral grids is the data reconstruction. Instead of using a large stencil of neighboring cells to perform a high-order reconstruction, the stencil is constructed by partitioning each grid cell, called a spectral volume (SV), into 'structured' sub-cells, called control volumes (CVs). One can show that if all the SV cells are partitioned into polygonal or polyhedral CV sub-cells in a geometrically similar manner, the reconstructions for all the SVs become universal, irrespective of their shapes, sizes, orientations, or locations. It follows that the reconstruction is reduced to a weighted sum of unknowns involving just a few simple adds and multiplies, and those weights are universal and can be pre-determined once for all. The method is thus very efficient, accurate, and yet geometrically flexible. The most critical part of the SV method is the partitioning of the SV into CVs. In this paper we present the partitioning of a tetrahedral SV into polyhedral CVs with one free parameter for polynomial reconstructions up to degree of precision five. (Note that the order of accuracy of the method is one order higher than the reconstruction degree of precision.) The free parameter will be determined by minimizing the Lebesgue constant of the reconstruction matrix or similar criteria to obtain optimized partitions. The details of an efficient, parallelizable code to solve
Nikkar, Samira; Nordström, Jan
2015-06-01
A time-dependent coordinate transformation of a constant coefficient hyperbolic system of equations which results in a variable coefficient system of equations is considered. By applying the energy method, well-posed boundary conditions for the continuous problem are derived. Summation-by-Parts (SBP) operators for the space and time discretization, together with a weak imposition of boundary and initial conditions using Simultaneously Approximation Terms (SATs) lead to a provable fully-discrete energy-stable conservative finite difference scheme. We show how to construct a time-dependent SAT formulation that automatically imposes boundary conditions, when and where they are required. We also prove that a uniform flow field is preserved, i.e. the Numerical Geometric Conservation Law (NGCL) holds automatically by using SBP-SAT in time and space. The developed technique is illustrated by considering an application using the linearized Euler equations: the sound generated by moving boundaries. Numerical calculations corroborate the stability and accuracy of the new fully discrete approximations.
Strong-field-approximation theory of high-order harmonic generation by polyatomic molecules
Odžak, S.; Hasović, E.; Milošević, D. B.
2016-04-01
A theory of high-order harmonic generation by arbitrary polyatomic molecules is introduced. A polyatomic molecule is modeled by an (N +1 ) -particle system, which consists of N heavy atomic (ionic) centers and an electron. After the separation of the center-of-mass coordinate, the dynamics of this system is reduced to the relative electronic and nuclear coordinates. Various versions (with or without the dressing of the initial and/or final molecular state) of the molecular strong-field approximation are introduced. For neutral polyatomic molecules the derived expression for the T -matrix element takes a simple form. The interference minima in the harmonic spectrum are explained as a multiple-slit type of interference. This is illustrated by numerical examples for the ozone (O3) and carbon dioxide (CO2) molecules.
High-order methods for decaying two-dimensional homogeneous isotropic turbulence
San, Omer; 10.1016/j.compfluid.2012.04.006
2012-01-01
Numerical schemes used for the integration of complex flow simulations should provide accurate solutions for the long time integrations these flows require. To this end, the performance of various high-order accurate numerical schemes is investigated for direct numerical simulations (DNS) of homogeneous isotropic two-dimensional decaying turbulent flows. The numerical accuracy of compact difference, explicit central difference, Arakawa, and dispersion-relation-preserving schemes are analyzed and compared with the Fourier-Galerkin pseudospectral scheme. In addition, several explicit Runge-Kutta schemes for time integration are investigated. We demonstrate that the centered schemes suffer from spurious Nyquist signals that are generated almost instantaneously and propagate into much of the field when the numerical resolution is insufficient. We further show that the order of the scheme becomes increasingly important for increasing cell Reynolds number. Surprisingly, the sixth-order schemes are found to be in pe...
Explicit high-order noncanonical symplectic algorithms for ideal two-fluid systems
Xiao, Jianyuan; Morrison, Philip J; Liu, Jian; Yu, Zhi; Zhang, Ruili; He, Yang
2016-01-01
An explicit high-order noncanonical symplectic algorithm for ideal two-fluid systems is developed. The fluid is discretized as particles in the Lagrangian description, while the electromagnetic fields and internal energy are treated as discrete differential form fields on a fixed mesh. With the assistance of Whitney interpolating forms, this scheme preserves the gauge symmetry of the electromagnetic field, and the pressure field is naturally derived from the discrete internal energy. The whole system is solved using the Hamiltonian splitting method discovered by He et al., which was been successfully adopted in constructing symplectic particle-in-cell schemes. Because of its structure preserving and explicit nature, this algorithm is especially suitable for large-scale simulations for physics problems that are multi-scale and require long-term fidelity and accuracy. The algorithm is verified via two tests: studies of the dispersion relation of waves in a two-fluid plasma system and the oscillating two-stream ...
A fast high-order finite difference algorithm for pricing American options
Tangman, D. Y.; Gopaul, A.; Bhuruth, M.
2008-12-01
We describe an improvement of Han and Wu's algorithm [H. Han, X.Wu, A fast numerical method for the Black-Scholes equation of American options, SIAM J. Numer. Anal. 41 (6) (2003) 2081-2095] for American options. A high-order optimal compact scheme is used to discretise the transformed Black-Scholes PDE under a singularity separating framework. A more accurate free boundary location based on the smooth pasting condition and the use of a non-uniform grid with a modified tridiagonal solver lead to an efficient implementation of the free boundary value problem. Extensive numerical experiments show that the new finite difference algorithm converges rapidly and numerical solutions with good accuracy are obtained. Comparisons with some recently proposed methods for the American options problem are carried out to show the advantage of our numerical method.
Single attosecond pulse from terahertz-assisted high-order harmonic generation
International Nuclear Information System (INIS)
High-order harmonic generation by few-cycle 800 nm laser pulses in neon gas in the presence of a strong terahertz (THz) field is investigated numerically with propagation effects taken into account. Our calculations show that the combination of THz fields with up to 12 fs laser pulses can be an effective gating technique to generate single attosecond pulses. We show that in the presence of the strong THz field only a single attosecond burst can be phase matched, whereas radiation emitted during other half cycles disappears during propagation. The cutoff is extended and a wide supercontinuum appears in the near-field spectra, extending the available spectral width for isolated attosecond pulse generation from 23 to 93 eV. We demonstrate that phase-matching effects are responsible for the generation of isolated attosecond pulses, even in conditions when single-atom response yields an attosecond pulse train.
A fast high-order method to calculate wakefield forces in an electron beam
Energy Technology Data Exchange (ETDEWEB)
Qiang, Ji; Mitchell, Chad; Ryne, Robert D.
2012-03-22
In this paper we report on a high-order fast method to numerically calculate wakefield forces in an electron beam given a wake function model. This method is based on a Newton-Cotes quadrature rule for integral approximation and an FFT method for discrete summation that results in an O(Nlog(N)) computational cost, where N is the number of grid points. Using the Simpson quadrature rule with an accuracy of O(h4), where h is the grid size, we present numerical calculation of the wakefields from a resonator wake function model and from a one-dimensional coherent synchrotron radiation (CSR) wake model. Besides the fast speed and high numerical accuracy, the calculation using the direct line density instead of the first derivative of the line density avoids numerical filtering of the electron density function for computing the CSR wakefield force. I. INTRODUCTION
International Nuclear Information System (INIS)
We present a time-dependent density functional theory (TDDFT) approach with proper asymptotic long-range potential for nonperturbative treatment of high-order harmonic generation (HHG) of diatomic molecules with their molecular axis parallel to the laser field polarization. A time-dependent two-center generalized pseudospectral method in prolate spheroidal coordinate system is used for accurate and efficient treatment of the TDDFT equations in space and time. The theory is applied to a detailed all-electron nonperturbative investigation of HHG processes of homonuclear (N2 and F2) and heteronuclear (CO, BF, and HF) molecules in intense ultrashort laser pulses with the emphasis on the role of multiple molecular orbitals (MOs). The results reveal intriguing and substantially different nonlinear optical response behaviors for homonuclear and heteronuclear molecules. In particular, we found that the HHG spectrum for homonuclear molecules features a destructive interference of MO contributions while heteronuclear molecules show mostly constructive interference of orbital contributions.
Institute of Scientific and Technical Information of China (English)
无
1998-01-01
Using Nd:YAG second harmonic pulse (100 ps), the optical storage properties of two novel polyesters, poly [4'-bis (N, N-oxyethylene) imino-4-nitroazobenzene succinyl] and poly [2'-chloro-4'-bis (N, N-oxyethylene) imino-4-nitroazobenzene succinyl] have been studied by multiwave mixing. The high-order diffractions of the orientation gratingsinduced by anisotropy via the reorientation of nitroazobenzene groups and optical information storage with long-term stability have been realized by multiwave mixing in their films. Up to 3rd order forward diffraction was detected in two wave mixing, while up to 4th order backward diffraction was observed in degenerated four wave mixing. The recording mechanism was explained by the trans-cis-trans isomerization cycles of azobenzene groups.The isomerization of these azobenzene groups probably undergoes with inversion mechanism under the experimental conditions. The information recorded in these films has been kept for more than 6 months.
HIGH ORDER FUZZY TIME SERIES MODEL AND ITS APLICATION TO IMKB
Directory of Open Access Journals (Sweden)
Çağdaş Hakan ALADAĞ
2010-12-01
Full Text Available The observations of some real time series such as temperature and stock market can take different values in a day. Instead of representing the observations of these time series by real numbers, employing linguistic values or fuzzy sets can be more appropriate. In recent years, many approaches have been introduced to analyze time series consisting of observations which are fuzzy sets and such time series are called fuzzy time series. In this study, a novel approach is proposed to analyze high order fuzzy time series model. The proposed method is applied to IMKB data and the obtained results are discussed. IMKB data is also analyzed by using some other fuzzy time series methods available in the literature and obtained results are compared to results obtained from the proposed method. As a result of the comparison, it is seen that the proposed method produce accurate forecasts.
Enzyme-mediated self-assembly of highly ordered structures from disordered proteins
International Nuclear Information System (INIS)
Wheat gluten is an amorphous storage protein. Trypsin hydrolysis of wheat gluten produced glutamine-rich peptides. Some peptides were able to self-assemble into fibrous structures extrinsic to native wheat gluten. The final material was an in situ formed peptide composite of highly ordered nanometer-sized fibrils and micron-sized fibers embedded in an unassembled peptide matrix. Fourier transform infrared spectroscopic and x-ray diffraction data suggested that the new structures resembled that of cross- β fibrils found in some insect silk and implicated in prion diseases. The largest self-assembled fibers were about 10 µm in diameter with right-handed helicity and appeared to be bundles of smaller nanometer-sized fibrils. Results demonstrated the potential for utilizing natural mechanisms of protein self-assembly to design advanced materials that can provide a wide range of structural and chemical functionality
A high-order public domain code for direct numerical simulations of turbulent combustion
Babkovskaia, N; Brandenburg, A
2010-01-01
A high-order scheme for direct numerical simulations of turbulent combustion is discussed. Its implementation in the massively parallel and publicly available Pencil Code is validated with the focus on hydrogen combustion. Ignition delay times (0D) and laminar flame velocities (1D) are calculated and compared with results from the commercially available Chemkin code. The scheme is verified to be fifth order in space. Upon doubling the resolution, a 32-fold increase in the accuracy of the flame front is demonstrated. Finally, also turbulent and spherical flame front velocities are calculated and the implementation of the non-reflecting so-called Navier-Stokes Characteristic Boundary Condition is validated in all three directions.
A fast high-order method to calculate wakefields in an electron beam
Qiang, Ji; Mitchell, Chad; Ryne, Robert D.
2012-08-01
In this paper, we report on a high-order fast method to numerically calculate wakefields in an electron beam given a wake function model. This method is based on a Newton-Cotes quadrature rule for integral approximation and an FFT method for discrete summation that results in an O(N log(N)) computational cost, where N is the number of grid points. Using the Simpson quadrature rule with an accuracy of O(h4), where h is the grid size, we present numerical calculation of the wakefields from a resonator wake function model and from a one-dimensional coherent synchrotron radiation (CSR) wake model. Besides the fast speed and high numerical accuracy, the calculation using the direct line density instead of the first derivative of the line density avoids numerical filtering of the electron density function for computing the CSR wakefield.
Rad-Hydro with a High-Order, Low-Order Method
Energy Technology Data Exchange (ETDEWEB)
Wollaber, Allan Benton [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Park, HyeongKae [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Lowrie, Robert Byron [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Rauenzahn, Rick M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Cleveland, Mathew Allen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-08-04
Moment-based acceleration via the development of “high-order, low-order” (HO-LO) algorithms has provided substantial accuracy and efficiency enhancements for solutions of the nonlinear, thermal radiative transfer equations by CCS-2 and T-3 staff members. Accuracy enhancements over traditional, linearized methods are obtained by solving a nonlinear, timeimplicit HO-LO system via a Jacobian-free Newton Krylov procedure. This also prevents the appearance of non-physical maximum principle violations (“temperature spikes”) associated with linearization. Efficiency enhancements are obtained in part by removing “effective scattering” from the linearized system. In this highlight, we summarize recent work in which we formally extended the HO-LO radiation algorithm to include operator-split radiation-hydrodynamics.
DEFF Research Database (Denmark)
Han, Yong-Chang; Madsen, Lars Bojer
2010-01-01
We solve the time-dependent Schrödinger equation for atomic hydrogen in an intense field using spherical coordinates with a radial grid and a spherical harmonic basis for the angular part. We present the high-order harmonic spectra based on three different forms, the dipole, dipole velocity, and...... acceleration forms, and two gauges, the length and velocity gauges. The relationships among the harmonic phases obtained from the Fourier transform of the three forms are discussed in detail. Although quantum mechanics is gauge invariant and the length and velocity gauges should give identical results, the two...... gauges present different computation efficiencies, which reflects the different behavior in terms of characteristics of the physical couplings acting in the two gauges. In order to obtain convergence, more angular momentum states are required in the length gauge, while more grid points are required in...
High-order optical vortex harmonics generated by relativistic femtosecond laser pulse
Han, Yu-Jing; Liao, Guo-Qian; Chen, Li-Ming; Li, Yu-Tong; Wang, Wei-Min; Zhang, Jie
2015-06-01
Harmonics generated by an intense femtosecond Gaussian laser pulse normally incident on a spiral-shaped thin foil target were studied. By using two-dimensional (2D) particle-in-cell (PIC) simulation, we observed evident odd harmonics signals in the reflection direction and found that the reflected field has a helical structure determined by the target shape. This method provides a new way to generate an intense ultraviolet vortex with high-order topological charge by use of ultrahigh intense laser-driven harmonics. Project supported by the National Basic Research Program of China (Grant Nos. 2013CBA01501 and 2013CBA01504), the National Key Scientific Instrument and Equipment Development Project, China (Grant No. 2012YQ120047), CAS Key Program and National Natural Science Foundation of China (Grant Nos. 11135012 and 11375262), and a Project of Higher Educational Science and Technology Program of Shandong Province, China (Grant No. J11LA52).
High-order harmonic generation from Rydberg atoms driven by plasmonic-enhanced laser fields
Tikman, Y; Ciappina, M F; Chacon, A; Altun, Z; Lewenstein, M
2015-01-01
We theoretically investigate high-order harmonic generation (HHG) in Rydberg atoms driven by spatially inhomogeneous laser fields, induced, for instance, by plasmonic enhancement. It is well known that the laser intensity should to exceed certain threshold in order to generate HHG, when noble gas atoms in their ground state are used as an active medium. One way to enhance the coherent light coming from a conventional laser oscillator is to take advantage of the amplification obtained by the so-called surface plasmon polaritons, created when a low intensity laser field is focused onto a metallic nanostructure. The main limitation of this scheme is the low damage threshold of the materials employed in the nanostructures engineering. In this work we propose to use Rydberg atoms, driven by spatially inhomogeneous, plasmonic-enhanced laser fields, for HHG. We exhaustively discuss the behaviour and efficiency of these systems in the generation of coherent harmonic emission. To this aim we numerically solve the time...
Alternative interpretation of high-order harmonic generation using Bohmian trajectories
Sanz, A S; Wu, J; Faria, C Figueira de Morisson
2012-01-01
A full quantum model of high-order harmonic generation is presented from a Bohmian-mechanical perspective. According to the three-step model, this phenomenon occurs due to the laser-induced recombination of an electron ejected by tunnel ionization with its parent ion. However, when revisited within the Bohmian scenario, we find that the high-harmonic spectrum is generated by those trajectories that reside well inside the core rather than by those that undergo excursions out of it. This agrees with the outcome of quantum mechanical studies, in which the spectrum is obtained through the dipole acceleration. Nevertheless, one may relate time-frequency maps from these central Bohmian trajectories to classical electrons behaving according to the three-step model. This happens because the quantum phase carried by each Bohmian trajectory is influenced by the whole wavefunction and, therefore, also by those trajectories that leave the core.
High-order harmonic generation with Rydberg atoms by using an intense few-cycle pulse
Zhai, Zhen; Zhu, Qiren; Chen, Jing; Yan, Zong-Chao; Fu, Panming; Wang, Bingbing
2011-04-01
We demonstrate that high-order harmonic generation (HHG) with both high cutoff frequency and high conversion efficiency can be realized by using a Rydberg atom in a few-cycle laser pulse. This is because a Rydberg state has a large electron orbital radius and small binding energy; therefore an electron in the Rydberg state can be ionized easily and accelerated directly toward the core under the interaction of a few-cycle laser pulse, leading to emission of harmonic photons. In this case, the tunneling process of the electron is not involved and, hence, the conversion efficiency and the cutoff frequency of harmonic generation can be higher than that predicted by the conventional three-step model.
High order surface aberration contributions from phase space analysis of differential rays.
Chen, Bo; Herkommer, Alois M
2016-03-21
Phase space methods are very popular for illumination systems or paraxial system analysis. In this paper it will be shown that it is also a promising tool to visualize and quantify surface aberration contributions, including all orders. The method is based on the calculation and propagation of a differential ray pair. In order to validate the method we compare to Aldis calculus, an exact method to determine high order aberrations in rotational symmetric systems. A triplet lens is used as an example to visualize the results. The analysis indicates that the phase space method is a very good approximation to Aldis calculus and moreover it is not limited to any symmetry assumptions. PMID:27136789
High-order continuum kinetic method for modeling plasma dynamics in phase space
International Nuclear Information System (INIS)
Continuum methods offer a high-fidelity means of simulating plasma kinetics. While computationally intensive, these methods are advantageous because they can be cast in conservation-law form, are not susceptible to noise, and can be implemented using high-order numerical methods. Advances in continuum method capabilities for modeling kinetic phenomena in plasmas require the development of validation tools in higher dimensional phase space and an ability to handle non-cartesian geometries. To that end, a new benchmark for validating Vlasov-Poisson simulations in 3D (x,vx,vy) is presented. The benchmark is based on the Dory-Guest-Harris instability and is successfully used to validate a continuum finite volume algorithm. To address challenges associated with non-cartesian geometries, unique features of cylindrical phase space coordinates are described. Preliminary results of continuum kinetic simulations in 4D (r,z,vr,vz) phase space are presented
Lee, Lee-Min; Jean, Fu-Rong
2016-08-01
The hidden Markov models have been widely applied to systems with sequential data. However, the conditional independence of the state outputs will limit the output of a hidden Markov model to be a piecewise constant random sequence, which is not a good approximation for many real processes. In this paper, a high-order hidden Markov model for piecewise linear processes is proposed to better approximate the behavior of a real process. A parameter estimation method based on the expectation-maximization algorithm was derived for the proposed model. Experiments on speech recognition of noisy Mandarin digits were conducted to examine the effectiveness of the proposed method. Experimental results show that the proposed method can reduce the recognition error rate compared to a baseline hidden Markov model. PMID:27586781
Carrier-wave Rabi flopping signatures in high-order harmonic generation for alkali atoms
Ciappina, M F; Landsman, A S; Zimmermann, T; Lewenstein, M; Roso, L; Krausz, F
2015-01-01
We present the first theoretical investigation of carrier-wave Rabi flopping in real atoms by employing numerical simulations of high-order harmonic generation (HHG) in alkali species. Given the short HHG cutoff, related to the low saturation intensity, we concentrate on the features of the third harmonic of sodium (Na) and potassium (K) atoms. For pulse areas of 2$\\pi$ and Na atoms, a characteristic unique peak appears, which, after analyzing the ground state population, we correlate with the conventional Rabi flopping. On the other hand, for larger pulse areas, carrier-wave Rabi flopping occurs, and is associated with a more complex structure in the third harmonic. These new characteristics observed in K atoms indicate the breakdown of the area theorem, as was already demonstrated under similar circumstances in narrow band gap semiconductors.
CgWind: A high-order accurate simulation tool for wind turbines and wind farms
Energy Technology Data Exchange (ETDEWEB)
Chand, K K; Henshaw, W D; Lundquist, K A; Singer, M A
2010-02-22
CgWind is a high-fidelity large eddy simulation (LES) tool designed to meet the modeling needs of wind turbine and wind park engineers. This tool combines several advanced computational technologies in order to model accurately the complex and dynamic nature of wind energy applications. The composite grid approach provides high-quality structured grids for the efficient implementation of high-order accurate discretizations of the incompressible Navier-Stokes equations. Composite grids also provide a natural mechanism for modeling bodies in relative motion and complex geometry. Advanced algorithms such as matrix-free multigrid, compact discretizations and approximate factorization will allow CgWind to perform highly resolved calculations efficiently on a wide class of computing resources. Also in development are nonlinear LES subgrid-scale models required to simulate the many interacting scales present in large wind turbine applications. This paper outlines our approach, the current status of CgWind and future development plans.
High order expanding domain methods for the solution of Poisson's equation in infinite domains
Anderson, Christopher R.
2016-06-01
In this paper we present a discrete Fourier transform based procedure to evaluate the infinite domain solution of Poisson's equation at points in a rectangular computational region. The numerical procedure is a modification of an "expanding domain" type method where one obtains approximations of increasing accuracy by expanding the computational domain. The modification presented here is one that leads to approximations that converge with high order rates of convergence with respect to domain size. Spectrally accurate approximations are used to approximate differential operators and so the method possesses very high rates of convergence with respect to mesh size as well. Computational results on both two and three dimensional test problems are presented that demonstrate the accuracy and computational efficiency of the procedure.
A simple Riemann solver and high-order Godunov schemes for hyperbolic systems of conservation laws
International Nuclear Information System (INIS)
A simple approximate Riemann solver for hyperbolic systems of conservation laws is developed for its use in Godunov schemes. The solver is based on characteristic formulations and is illustrated through Euler and ideal magnetohydrodynamical (MHD) equations. The procedure of a high-order Godunov scheme incorporated with the Riemann solver for one-dimensional hyperbolic systems of conservation laws is described in detail. The correctness of the scheme is shown by comparison with the piecewise parabolic method for Euler equations and by comparison with exact solutions of Riemann problems for ideal MHD equations. The robustness of the scheme is demonstrated through numerical examples involving more than one strong shock at the same time. It is shown that the scheme offers the principle advantages of Godunov schemes: robust operation in the presence of strong waves, thin shock fronts, thin contact and slip surface discontinuities
A simple Riemann solver and high-order Godunov schemes for hyperbolic systems of conservation laws
Energy Technology Data Exchange (ETDEWEB)
Dai, W.; Woodward, P.R. [Univ. of Minnesota, Minneapolis, MN (United States)
1995-10-01
A simple approximate Riemann solver for hyperbolic systems of conservation laws is developed for its use in Godunov schemes. The solver is based on characteristic formulations and is illustrated through Euler and ideal magnetohydrodynamical (MHD) equations. The procedure of a high-order Godunov scheme incorporated with the Riemann solver for one-dimensional hyperbolic systems of conservation laws is described in detail. The correctness of the scheme is shown by comparison with the piecewise parabolic method for Euler equations and by comparison with exact solutions of Riemann problems for ideal MHD equations. The robustness of the scheme is demonstrated through numerical examples involving more than one strong shock at the same time. It is shown that the scheme offers the principle advantages of Godunov schemes: robust operation in the presence of strong waves, thin shock fronts, thin contact and slip surface discontinuities.
High order sliding mode control of a DFIM supplied by two power inverters
Directory of Open Access Journals (Sweden)
Zinelaabidine Boudjema
2015-06-01
Full Text Available Traditional vector control structures which include proportional-integral (PI regulator for the speed of a doubly fed induction motor (DFIM driven have some disadvantages such as parameter tuning complications, mediocre dynamic performances and reduced robustness. Thus, based on the analysis of the mathematical model of a DFIM supplied by two indirect inverters, this paper addresses a nonlinear control algorithm based on high order sliding mode. The conventional sliding mode control has large chattering on the electromagnetic torque developed by the DFIM. In order to solve this problem, the second order sliding mode technique is used. The simulation results show the effectiveness of the proposed method especially in chattering-free behavior, response to sudden load torque variations and robustness against machine parameters variations.
High-order cyclo-difference techniques: An alternative to finite differences
Carpenter, Mark H.; Otto, John C.
1993-01-01
The summation-by-parts energy norm is used to establish a new class of high-order finite-difference techniques referred to here as 'cyclo-difference' techniques. These techniques are constructed cyclically from stable subelements, and require no numerical boundary conditions; when coupled with the simultaneous approximation term (SAT) boundary treatment, they are time asymptotically stable for an arbitrary hyperbolic system. These techniques are similar to spectral element techniques and are ideally suited for parallel implementation, but do not require special collocation points or orthogonal basis functions. The principal focus is on methods of sixth-order formal accuracy or less; however, these methods could be extended in principle to any arbitrary order of accuracy.
Institute of Scientific and Technical Information of China (English)
WANG Gang; RAO NiNi; ZHANG Ying
2008-01-01
The analysis and the characterization of atrial fibrillation (AF) requires,in a previous key step,the extraction of the atrial activity (AA) free from 12-lead electrocardiogram (ECG).This contribution proposes a novel non-invasive approach for the AA estimation in AF episodes.The method is based on blind source extraction (BSE) using high order statistics (HOS).The validity and performance of this algorithm are confirmed by extensive computer simulations and experiments on realworld data.In contrast to blind source separation (BSS) methods,BSE only extract one desired signal,and it is easy for the machine to judge whether the extracted signal is AA source by calculating its spectrum concentration,while it is hard for the machine using BSS method to judge which one of the separated twelve signals is AA source.Therefore,the proposed method is expected to have great potential in clinical monitoring.
Exploring arbitrarily high orders of optimized perturbation theory in QCD with nf -> 16.5
Stevenson, P M
2016-01-01
Perturbative QCD with nf flavours of massless quarks becomes simple in the hypothetical limit nf -> 16.5, where the leading beta-function coefficient vanishes. The Banks-Zaks (BZ) expansion in a0=(8/321)(16.5-nf) is straightforward to obtain from perturbative results in MSbar or any renormalization scheme (RS) whose nf dependence is `regular.' However, `irregular' RS's are perfectly permissible and should ultimately lead to the same BZ results. We show here that the `optimal' RS determined by the Principle of Minimal Sensitivity does yield the same BZ-expansion results when all orders of perturbation theory are taken into account. The BZ limit provides an arena for exploring optimized perturbation theory at arbitrarily high orders. These explorations are facilitated by a `master equation' expressing the optimization conditions in the fixed-point limit. We find an intriguing strong/weak coupling duality a -> a*^2/a about the fixed point a*.
A Novel High-Order, Entropy Stable, 3D AMR MHD Solver with Guaranteed Positive Pressure
Derigs, Dominik; Gassner, Gregor J; Walch, Stefanie
2016-01-01
We describe a high-order numerical magnetohydrodynamics (MHD) solver built upon a novel non-linear entropy stable numerical flux function that supports eight travelling wave solutions. By construction the solver conserves mass, momentum, and energy and is entropy stable. The method is designed to treat the divergence-free constraint on the magnetic field in a similar fashion to a hyperbolic divergence cleaning technique. The solver described herein is especially well-suited for flows involving strong discontinuities. Furthermore, we present a new formulation to guarantee positivity of the pressure. We present the underlying theory and implementation of the new solver into the multi-physics, multi-scale adaptive mesh refinement (AMR) simulation code $\\texttt{FLASH}$ (http://flash.uchicago.edu). The accuracy, robustness and computational efficiency is demonstrated with a number of tests, including comparisons to available MHD implementations in $\\texttt{FLASH}$.
A novel high-order, entropy stable, 3D AMR MHD solver with guaranteed positive pressure
Derigs, Dominik; Winters, Andrew R.; Gassner, Gregor J.; Walch, Stefanie
2016-07-01
We describe a high-order numerical magnetohydrodynamics (MHD) solver built upon a novel non-linear entropy stable numerical flux function that supports eight travelling wave solutions. By construction the solver conserves mass, momentum, and energy and is entropy stable. The method is designed to treat the divergence-free constraint on the magnetic field in a similar fashion to a hyperbolic divergence cleaning technique. The solver described herein is especially well-suited for flows involving strong discontinuities. Furthermore, we present a new formulation to guarantee positivity of the pressure. We present the underlying theory and implementation of the new solver into the multi-physics, multi-scale adaptive mesh refinement (AMR) simulation code FLASH (http://flash.uchicago.edu)
A fast high-order method to calculate wakefields in an electron beam
International Nuclear Information System (INIS)
In this paper, we report on a high-order fast method to numerically calculate wakefields in an electron beam given a wake function model. This method is based on a Newton–Cotes quadrature rule for integral approximation and an FFT method for discrete summation that results in an O(Nlog(N)) computational cost, where N is the number of grid points. Using the Simpson quadrature rule with an accuracy of O(h4), where h is the grid size, we present numerical calculation of the wakefields from a resonator wake function model and from a one-dimensional coherent synchrotron radiation (CSR) wake model. Besides the fast speed and high numerical accuracy, the calculation using the direct line density instead of the first derivative of the line density avoids numerical filtering of the electron density function for computing the CSR wakefield.
High Order Moment Model for Polydisperse Evaporating Sprays Towards Interfacial Geometry
Essadki, Mohamed; Laurent, Frédérique; Massot, Marc
2016-01-01
In this paper we propose a new Eulerian modeling and related accurate and robust numerical methods, describing polydisperse evaporating sprays, based on high order moment methods in size. The main novelty of this model is its capacity to describe some geometrical variables of the droplet-gas interface, by analogy with the liquid-gas interface in interfacial flows. For this purpose, we use fractional size-moments, where the size variable is taken as the droplet surface. In order to evaluate the evaporation of the polydisperse spray, we use a smooth reconstruction which maximizes the Shannon entropy. However, the use of fractional moments introduces some theoretical and numerical difficulties, which need to be tackled. First, relying on a study of the moment space, we extend the Maximum Entropy (ME) reconstruction of the size distribution to the case of fractional moments. Then, we propose a new accurate and realizable algorithm to solve the moment evolution due to evaporation, which preserves the structure of ...
A fast high-order method to calculate wakefield forces in an electron beam
Qiang, Ji; Ryne, Robert D
2012-01-01
In this paper we report on a high-order fast method to numerically calculate wakefield forces in an electron beam given a wake function model. This method is based on a Newton-Cotes quadrature rule for integral approximation and an FFT method for discrete summation that results in an $O(Nlog(N))$ computational cost, where $N$ is the number of grid points. Using the Simpson quadrature rule with an accuracy of $O(h^4)$, where $h$ is the grid size, we present numerical calculation of the wakefields from a resonator wake function model and from a one-dimensional coherent synchrotron radiation (CSR) wake model. Besides the fast speed and high numerical accuracy, the calculation using the direct line density instead of the first derivative of the line density avoids numerical filtering of the electron density function for computing the CSR wakefield force.
Wang, Guanghui; Zhang, Weifeng; Lu, Jiahui; Zhao, Huijun
2016-08-01
We analytically study dispersion properties and optical gradient forces of different-order transverse magnetic (TM) modes in two coupled hyperbolic metamaterial waveguides (HMMWs). According to Maxwell's equations, we obtain the dispersion relation of symmetric and antisymmetric modes, and calculate optical gradient forces of different-order modes by using Maxwell stress tensor. Numerical results show that the dispersion properties are dependent on the filling ratio, and the optical gradient forces of high-order TM modes are larger than the fundamental mode when the gap between two HMMWs is very narrow, but they weaken much faster than the case of low-order TM modes with the gap width increasing. In addition, the effects of the dielectric surrounding of waveguides on the coupling effect and optical gradient force are clarified. These properties offer an avenue for various optomechanical applications in optical sensors and actuators.
High Order Projection Plane Method for Evaluation of Supersingular Curved Boundary Integrals in BEM
Directory of Open Access Journals (Sweden)
Miao Cui
2016-01-01
Full Text Available Boundary element method (BEM is a very promising approach for solving various engineering problems, in which accurate evaluation of boundary integrals is required. In the present work, the direct method for evaluating singular curved boundary integrals is developed by considering the third-order derivatives in the projection plane method when expanding the geometry quantities at the field point as Taylor series. New analytical formulas are derived for geometry quantities defined on the curved line/plane, and unified expressions are obtained for both two-dimensional and three-dimensional problems. For the two-dimensional boundary integrals, analytical expressions for the third-order derivatives are derived and are employed to verify the complex-variable-differentiation method (CVDM which is used to evaluate the high order derivatives for three-dimensional problems. A few numerical examples are given to show the effectiveness and the accuracy of the present method.
Synchronisation of high-order MIMO nonlinear systems using distributed neuro-adaptive control
Ghiti Sarand, Hassan; Karimi, Bahram
2016-07-01
This paper addresses synchronisation problem of high-order multi-input/multi-output (MIMO) multi-agent systems. Each agent has unknown nonlinear dynamics and is subject to uncertain external disturbances. The agents must follow a reference trajectory. An adaptive distributed controller based on relative information of neighbours of each agent is designed to solve the problem for any undirected connected communication topology. A radial basis function neural network is used to represent the controller's unknown structure. Lyapunov stability analysis is employed to guarantee stability of the overall system. By the theoretical analysis, the closed-loop control system is shown to be uniformly ultimately bounded. Finally, simulations are provided to show effectiveness of the proposed control method against uncertainty and disturbances.
Laser-Duration Dependence of Emission Properties of High-Order Harmonic Generation
Institute of Scientific and Technical Information of China (English)
GE Yu-Cheng
2008-01-01
@@ Quantitative investigations are made for the laser-duration dependence of the emission properties of high-order harmonic generation (HHG). HHG emission properties produced by few-cycle lasers show some useful characteristics. The cutoff energy is less than that by laser for infinite duration. The single energy distribution pulse decreases much faster than its duration as the laser duration grows. A two-cycle laser with carrier-envelope phase of O°can produce a single distribution pulse peaked at the laser carrier phase 1.22rad and spanned 1.18 rad with the cutoff energy 2.9Uρ + Iρ and a bandwidth 0.63Uρ, where Uρ is the ponderomotive potential of the laser field and Iρ is the atomic ionization potential.
High-order Composite Likelihood Inference for Max-Stable Distributions and Processes
Castruccio, Stefano
2015-09-29
In multivariate or spatial extremes, inference for max-stable processes observed at a large collection of locations is a very challenging problem in computational statistics, and current approaches typically rely on less expensive composite likelihoods constructed from small subsets of data. In this work, we explore the limits of modern state-of-the-art computational facilities to perform full likelihood inference and to efficiently evaluate high-order composite likelihoods. With extensive simulations, we assess the loss of information of composite likelihood estimators with respect to a full likelihood approach for some widely-used multivariate or spatial extreme models, we discuss how to choose composite likelihood truncation to improve the efficiency, and we also provide recommendations for practitioners. This article has supplementary material online.
Orbital geometry determined by orthogonal high-order harmonic polarization components
International Nuclear Information System (INIS)
We study the polarization state of high-order harmonics produced by linearly polarized light interacting with two-center molecules. By generating high-harmonic 'polarization maps' from Radon transformations of excited electronic wave functions, we show that the polarization of the harmonic radiation can be linked to the geometry of the molecular orbital. While in the Radon transformation the plane-wave approximation for the rescattered electron is implicitly assumed, numerical solutions of the two-dimensional time-dependent Schro··dinger equation, in which this approximation is not made, confirm the validity of this topological connection. We also find that measuring two orthogonal amplitude components of the harmonics provides a method for quantum tomography that substantially improves the quality of reconstructed molecular states.
High-order optical processes in intense laser field: Towards nonperturbative nonlinear optics
Strelkov, V. V.
2016-05-01
We develop an approach describing nonlinear-optical processes in the strong-field domain characterized by the nonperturbative field-with-matter interaction. The polarization of an isolated atom in the external field calculated via the numerical solution of the time-dependent Schrödinger equation agrees with our analytical findings. For the practically important case of one strong laser field and several weaker fields, we derive and analytically solve propagation equations describing high-order (HO) wave mixing, HO parametric amplification, and HO stimulated scattering. These processes provide a way of efficient coherent xuv generation. Some properties of HO processes are new in nonlinear optics: essentially complex values of the coefficients in the propagation equations, the superexponential (hyperbolic) growing solutions, etc. Finally, we suggest conditions for the practical realization of these processes and discuss published numerical and experimental results where such processes could have been observed.
Design of high-order elliptic filter from a versatile mode generic OTA-C structure
Ghosh, K.; Ray, B. N.
2015-03-01
A new synthesis methodology for high-order versatile mode programmable Operational transconductance amplifier and capacitor (OTA-C) generic filter structure is proposed. The structure fulfills the three main criteria of high frequency operation i.e it uses (1) less number of components (2) only single ended input OTAs (3) only grounded capacitors. Any nth order transfer function can be realised from it. Elliptic filter is designed from the generic structure using optimisation technique to reduce the number of OTAs. SPICE simulation with BSIM level 53 model and 0.13 μm process confirms the theoretical analysis. Frequency response of third-order and fourth-order elliptic filter is shown as representative set of simulated result. Sensitivity and non-ideal effect of the designed filter are studied.
High-order threshold corrections for top-pair and single-top production
Kidonakis, Nikolaos
2015-01-01
I present results for high-order corrections from threshold resummation to cross sections and differential distributions in top-antitop pair production and in single-top production. I show aN$^3$LO results for the total $t{\\bar t}$ cross section as well as for the top-quark transverse momentum ($p_T$) and rapidity distributions, and the top-quark forward-backward asymmetry in $t{\\bar t}$ production. I compare with the most recent Tevatron and LHC data, including at 13 TeV. I also present aNNLO results for cross sections and $p_T$ distributions in $t$-channel, $s$-channel, and $tW$-channel single-top production.
Energy Technology Data Exchange (ETDEWEB)
Leng, Wei [Chinese Academy of Sciences; Ju, Lili [University of South Carolina; Gunzburger, Max [Florida State University; Price, Stephen [Los Alamos National Laboratory; Ringler, Todd [Los Alamos National Laboratory,
2012-01-01
The numerical modeling of glacier and ice sheet evolution is a subject of growing interest, in part because of the potential for models to inform estimates of global sea level change. This paper focuses on the development of a numerical model that determines the velocity and pressure fields within an ice sheet. Our numerical model features a high-fidelity mathematical model involving the nonlinear Stokes system and combinations of no-sliding and sliding basal boundary conditions, high-order accurate finite element discretizations based on variable resolution grids, and highly scalable parallel solution strategies, all of which contribute to a numerical model that can achieve accurate velocity and pressure approximations in a highly efficient manner. We demonstrate the accuracy and efficiency of our model by analytical solution tests, established ice sheet benchmark experiments, and comparisons with other well-established ice sheet models.
High-order quantum back-reaction and quantum cosmology with a positive cosmological constant
Bojowald, Martin; Hernandez, Hector H; Koop, Michael J; Morales-Tecotl, Hugo A
2010-01-01
When quantum back-reaction by fluctuations, correlations and higher moments of a state becomes strong, semiclassical quantum mechanics resembles a dynamical system with a high-dimensional phase space. Here, systematic numerical methods to derive the dynamical equations including all quantum corrections to high order in the moments are introduced, together with a quantum cosmological example to illustrate some implications. The results show, for instance, that the initial Gaussian form of an initial state is maintained only briefly, but that the evolving state settles down to a new characteristic shape afterwards. At some point during the evolution all moments considered become of equal size and no truncation to finite order is possible. But until that time is reached, numerical evaluations provide a large amount of information about dynamical quantum states.
High-order harmonic generation in polyatomic molecules induced by a bicircular laser field
Odžak, Senad; Milošević, Dejan B
2016-01-01
High-order harmonic generation by a bicircular field, which consists of two coplanar counter-rotating circularly polarized fields of frequency $r\\omega$ and $s\\omega$ ($r$ and $s$ are integers), is investigated for a polyatomic molecule. This field possesses dynamical symmetry, which can be adjusted to the symmetry of the molecular Hamiltonian and used to investigate the molecular symmetry. For polyatomic molecules having the $C_{r+s}$ symmetry only the harmonics $n=q(r+s)\\pm r$, $q=1,2,\\ldots$, are emitted having the ellipticity $\\varepsilon_n=\\pm 1$. We illustrate this using the example of the planar molecules BH$_3$ and BF$_3$, which obey the $C_3$ symmetry. We show that for the BF$_3$ molecule, similarly to atoms with a $p$ ground state, there is a strong asymmetry in the emission of high harmonics with opposite helicities. This asymmetry depends on the molecular orientation.
Real-Time Wavefront Control for the PALM-3000 High Order Adaptive Optics System
Truong, Tuan N.; Bouchez, Antonin H.; Dekany, Richard G.; Guiwits, Stephen R.; Roberts, Jennifer E.; Troy, Mitchell
2008-01-01
We present a cost-effective scalable real-time wavefront control architecture based on off-the-shelf graphics processing units hosted in an ultra-low latency, high-bandwidth interconnect PC cluster environment composed of modules written in the component-oriented language of nesC. The architecture enables full-matrix reconstruction of the wavefront at up to 2 KHz with latency under 250 us for the PALM-3000 adaptive optics systems, a state-of-the-art upgrade on the 5.1 meter Hale Telescope that consists of a 64 x 64 subaperture Shack-Hartmann wavefront sensor and a 3368 active actuator high order deformable mirror in series with a 241 active actuator tweeter DM. The architecture can easily scale up to support much larger AO systems at higher rates and lower latency.
Chen, Zi-Yu
2016-01-01
Ultrafast extreme ultraviolet (XUV) sources with controllable polarization state are powerful tools in investigating not only structural and electronic, but also magnetic properties of materials. However, such light sources are still limited to a few free electron laser facilities and very recently to high-order harmonic generation (HHG) from noble gases. Here we propose and numerically demonstrate a new laser-plasma scheme to generate bright XUV pulses with fully controlled polarization. An elliptically polarized laser pulse is obliquely incident on a plasma surface. The reflected radiation contains trains and isolated circularly or highly elliptically polarized attosecond XUV pulses. The harmonic polarization state is fully controlled by the laser-plasma parameters. The mechanism can be explained within the relativistically oscillating mirror model. This scheme opens a practical and promising route to generate bright attosecond XUV pulses with desirable ellipticities in a straightforward and efficient way f...
Probe of Multi-electron Dynamics in Xenon by Caustics in High Order Harmonic Generation
Faccialà, Davide; Bruner, Barry D; Ciriolo, Anna G; De Silvestri, Sandro; Devetta, Michele; Negro, Matteo; Soifer, Hadas; Stagira, Salvatore; Dudovich, Nirit; Vozzi, Caterina
2016-01-01
We investigated the giant resonance in Xenon by high-order harmonic generation spectroscopy driven by a two-color field. The addition of a non-perturbative second harmonic component parallel to the driving field breaks the symmetry between neighboring sub-cycles resulting in the appearance of spectral caustics at two distinct cut-off energies. By controlling the phase delay between the two color components it is possible to tailor the harmonic emission in order to amplify and isolate the spectral feature of interest. In this paper we demonstrate how this control scheme can be used to investigate the role of electron correlations that give birth to the giant resonance in Xenon. The collective excitations of the giant dipole resonance in Xenon combined with the spectral manipulation associated with the two color driving field allow to see features that are normally not accessible and to obtain a quantitative good agreement between the experimental results and the theoretical predictions.
Mohan, Ranjini R.; Varma, Sreekanth J.; Sankaran, Jayalekshmi
2016-04-01
The present work highlights the remarkably high shielding effectiveness of about 68 dB, exhibited by highly ordered and doped polyaniline films, in the microwave frequency range 4-12 GHz, obtained by self-stabilized dispersion polymerization as the synthesis route. The observed shielding effectiveness is found to depend quite sensitively on the electrical conducting properties, which are predominantly controlled by the nature and concentration of the dopants. The structural and morphological characterization of the films using XRD and TEM techniques reveals surprisingly high extent of crystallinity, which contributes significantly towards enhancing the electrical conductivity of the films. Most of the available reports on the microwave response of conducting polymer film samples deal with much thicker films, compared to the micrometer thick films of the present studies. The shielding effectiveness of acid doped, micrometer thick polyaniline films reported in the present work far exceeds most of the previously reported values and meets the commercial requirements.
Multi-dimensional high-order numerical schemes for Lagrangian hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Dai, William W [Los Alamos National Laboratory; Woodward, Paul R [Los Alamos National Laboratory
2009-01-01
An approximate solver for multi-dimensional Riemann problems at grid points of unstructured meshes, and a numerical scheme for multi-dimensional hydrodynamics have been developed in this paper. The solver is simple, and is developed only for the use in numerical schemes for hydrodynamics. The scheme is truely multi-dimensional, is second order accurate in both space and time, and satisfies conservation laws exactly for mass, momentum, and total energy. The scheme has been tested through numerical examples involving strong shocks. It has been shown that the scheme offers the principle advantages of high-order Codunov schemes; robust operation in the presence of very strong shocks and thin shock fronts.
Laser plasma as a source of intense attosecond pulses via high-order harmonic generation
International Nuclear Information System (INIS)
The incredible progress in ultrafast laser technology and Ti:sapphire lasers have lead to many important applications, one of them being high-order harmonic generation (HHG). HHG is a source of coherent extreme ultraviolet (XUV) radiation, which has opened new frontiers in science by extending nonlinear optics and time-resolved spectroscopy to the XUV region, and pushing ultrafast science to the attosecond domain. Progress in attosecond science has revealed many new phenomena that have not been seen with femtosecond pulses. Clearly, the next frontier is to study nonlinear effects at the attosecond timescale and in the XUV. However, a problem with present-day attosecond pulses is that they are just too weak to induce measurable nonlinearities, which severely limits the application of this source. While HHG from solid targets has shown promise for higher conversion efficiency, there is no experiment so far that demonstrates isolated attosecond pulse generation. The generation of isolated, several 100-as pulses with few-µJ energy will enable us to enter a completely new phase in attoscience. In past works, we have demonstrated that high-order harmonics from lowly ionized plasma is a highly efficient method to generate coherent XUV pulses. For example, indium plasma has been shown to generate intense 13th harmonic of the Ti:sapphire laser, with conversion efficiency of 10-4. However, the quasi-monochromatic nature of indium harmonics would make it difficult to generate attosecond pulses. We have also demonstrated that one could increase the harmonic yield by using nanoparticle targets. Specifically, we showed that by using indium oxide nanoparticles or C60 film, we could obtain intense harmonics between wavelengths of 50 to 90 nm. The energy in each of these harmonic orders was measured to be a few µJ, which is sufficient for many applications. However, the problem of using nanoparticle or film targets is the rapid decrease in the harmonic intensity, due to the rapid
Coherent diffractive imaging microscope with a high-order harmonic source.
Dinh, Khuong Ba; Le, Hoang Vu; Hannaford, Peter; Dao, Lap Van
2015-06-10
We report the generation of highly coherent extreme ultraviolet sources with wavelengths around 30 and 10 nm by phase-matched high-order harmonic generation (HHG) in a gas cell filled with argon and helium, respectively. We then perform coherent diffractive imaging (CDI) by using a focused narrow-bandwidth HHG source with wavelength around 30 nm as an illumination beam for two kinds of samples. The first is a transmission sample and the second is a absorption sample. In addition, we report the successful reconstruction of a complex absorption sample using a tabletop high-harmonic source. This will open the path to the realization of a compact soft x-ray microscope to investigate biological samples such as membrane proteins. PMID:26192827
Coherent Sources of XUV Radiation Soft X-Ray Lasers and High-Order Harmonic Generation
Jaeglé, Pierre
2006-01-01
Extreme ultraviolet radiation, also referred to as soft X-rays or XUV, offers very special optical properties. The X-UV refractive index of matter is such that normal reflection cannot take place on polished surfaces whereas beam transmission through one micrometer of almost all materials reduces to zero. Therefore, it has long been a difficult task to imagine and to implement devices designed for complex optics experiments in this wavelength range. Thanks to new sources of coherent radiation - XUV-lasers and High Order Harmonics - the use of XUV radiation, for interferometry, holography, diffractive optics, non-linear radiation-matter interaction, time-resolved study of fast and ultrafast phenomena and many other applications, including medical sciences, is ubiquitous.
Carbon coatings for extreme-ultraviolet high-order laser harmonics
Energy Technology Data Exchange (ETDEWEB)
Coraggia, S.; Frassetto, F. [CNR-Institute of Photonics and Nanotechnologies, Laboratory for UV and X-Ray Optical Research, via Trasea 7, 35131 Padova (Italy); Aznarez, J.A.; Larruquert, J.I.; Mendez, J.A. [GOLD-Instituto de Optica-Consejo Superior de Investigaciones Cientificas, Serrano 144, 28006 Madrid (Spain); Negro, M.; Stagira, S.; Vozzi, C. [Department of Physics-Politecnico of Milano and CNR-Institute of Photonics and Nanotechnologies, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Poletto, L., E-mail: poletto@dei.unipd.i [CNR-Institute of Photonics and Nanotechnologies, Laboratory for UV and X-Ray Optical Research, via Trasea 7, 35131 Padova (Italy)
2011-04-11
The experimental study of the optical properties of thin carbon films to be used as grazing-incidence coatings for extreme-ultraviolet high-order harmonics is presented. The carbon samples were deposited on plane glass substrates by the electron beam evaporation technique. The optical constants (real and imaginary parts of the refraction index) have been calculated through reflectivity measurements. The results are in good agreement with what reported in the literature, and confirm that carbon-coated optics operated at grazing incidence have a remarkable gain over conventional metallic coatings in the extreme ultraviolet. Since the harmonics co-propagate with the intense infrared laser generating beam, the carbon damage threshold when exposed to ultrashort infrared laser pulses has been measured.
High order spatial expansion for the method of characteristics applied to 3-D geometries
International Nuclear Information System (INIS)
The method of characteristics is an efficient and flexible technique to solve the neutron transport equation and has been extensively used in two-dimensional calculations because it permits to deal with complex geometries. However, because of a very fast increase in storage requirements and number of floating operations, its direct application to three-dimensional routine transport calculations it is not still possible. In this work we introduce and analyze several modifications aimed to reduce memory requirements and to diminish the computing burden. We explore high-order spatial approximation, the use of intermediary trajectory-dependent flux expansions and the possibility of dynamic trajectory reconstruction from local tracking for typed subdomains. (authors)
High-order Boussinesq-type modelling of nonlinear wave phenomena in deep and shallow water
DEFF Research Database (Denmark)
Madsen, Per A.; Fuhrman, David R.
2010-01-01
fully nonlinear and highly dispersive waves traveling over a rapidly varying bathymetry. Finally, we cover applications of this Boussinesq model, and we study a number of nonlinear wave phenomena in deep and shallow water. These include (1) Kinematics in highly nonlinear progressive deep-water waves; (2......In this work, we start with a review of the development of Boussinesq theory for water waves covering the period from 1872 to date. Previous reviews have been given by Dingemans,1 Kirby,2,3 and Madsen & Schäffer.4 Next, we present our most recent high-order Boussinesq-type formulation valid for......) Kinematics in progressive solitary waves; (3) Reflection of solitary waves from a vertical wall; (4) Reflection and diffraction around a vertical plate; (5) Quartet and quintet interactions and class I and II instabilities; (6) Extreme events from focused directionally spread waveelds; (7) Bragg scattering...
Effect of nuclear motion on spectral broadening of high-order harmonic generation.
Yuan, Xiaolong; Wei, Pengfei; Liu, Candong; Ge, Xiaochun; Zheng, Yinghui; Zeng, Zhinan; Li, Ruxin
2016-04-18
High-order harmonic generation (HHG) in molecular targets is experimentally investigated in order to reveal the role of the nuclear motion played in the harmonic generation process. An obvious broadening in the harmonic spectrum from the H2 molecule is observed in comparison with the harmonic spectrum generated from other molecules with relatively heavy nuclei. We also find that the harmonic yield from the H2 molecule is much weaker than the yield from those gas targets with the similar ionization potentials, such as Ar atom and N2 molecule. The yield suppression and the spectrum broadening of HHG can be attributed to the vibrational motion of nuclear induced by the driving laser pulse. Moreover, the one-dimensional (1D) time-dependent Schrödinger equation (TDSE) with the non-Born-Oppenheimer (NBO) treatment is numerically solved to provide a theoretical support to our explanation. PMID:27137258
Schaal, Kevin; Chandrashekar, Praveen; Pakmor, Rüdiger; Klingenberg, Christian; Springel, Volker
2015-01-01
Solving the Euler equations of ideal hydrodynamics as accurately and efficiently as possible is a key requirement in many astrophysical simulations. It is therefore important to continuously advance the numerical methods implemented in current astrophysical codes, especially also in light of evolving computer technology, which favours certain computational approaches over others. Here we introduce the new adaptive mesh refinement (AMR) code TENET, which employs a high-order Discontinuous Galerkin (DG) scheme for hydrodynamics. The Euler equations in this method are solved in a weak formulation with a polynomial basis by means of explicit Runge-Kutta time integration and Gauss-Legendre quadrature. This approach offers significant advantages over commonly employed finite volume (FV) solvers. In particular, the higher order capability renders it computationally more efficient, in the sense that the same precision can be obtained at significantly less computational cost. Also, the DG scheme inherently conserves a...
High-order harmonic generation in laser surface ablation: current trends
International Nuclear Information System (INIS)
We review emerging concepts that have increased the efficiency of coherent XUV (extreme ultraviolet) generation through the use of laser frequency conversion in specially prepared plasmas and which have enabled high-order harmonic generation (HHG) spectroscopy to be used in spectral and structural analysis. We also present the current status of plasma HHG and examine what new trends have evolved in the field since it was reviewed last [Phys. Usp. 52 55 (2009)]. In particular, we consider new techniques for generating higher harmonics from various plasmas for the purpose of studying the physical properties of materials. It has been shown recently that HHG has application potential for many, sometimes unexpected, areas of laser radiation-matter interaction. It is argued that plasma HHG is—along with alternative coherent XUV generation—a powerful tool for a variety of spectroscopic and analytical applications. (reviews of topical problems)
High-order harmonic generation and multi-photon ionization of Na2 in laser fields
Institute of Scientific and Technical Information of China (English)
Zhang Yan-Ping; Zhang Feng-Shou; Meng Ke-Lai; Xiao Guo-Qing
2007-01-01
In this paper high-order harmonic generation (HHG) spectra and the ionization probabilities of various charge states of small cluster Na2 in the multiphoton regimes are calculated by using time-dependent local density approximation (TDLDA) for one-colour (1064 nm) and two-colour (1064 nm and 532 nm) ultrashort (25 fs) laser pulses. HHG spectra of Na2 have not the large extent of plateaus due to pronounced collective effects of electron dynamics. In addition, the two-colour laser field can result in the breaking of the symmetry and generation of the even order harmonic such as the second order harmonic. The results of ionization probabilities show that a two-colour laser field can increase the ionization probability of higher charge state.
Engineering of highly ordered TiO2 nanopore arrays by anodization
Wang, Huijie; Huang, Zhennan; Zhang, Li; Ding, Jie; Ma, Zhaoxia; Liu, Yong; Kou, Shengzhong; Yang, Hangsheng
2016-07-01
Finite element analysis was used to simulate the current density distributions in the TiO2 barrier layer formed at the initial stage of Ti anodization. The morphology modification of the barrier layer was found to induce current density distribution change. By starting the anodization with proper TiO2 barrier layer morphology, the current density distribution can be adjusted to favor the formation of either nanotube arrays or nanopore arrays of anodic TiO2. We also found that the addition of sodium acetate into the electrolyte suppressed both the field-assisted chemical dissolution of TiO2 and the TiF62- hydrolysis induced TiO2 deposition during anodization, and thus further favored the nanopore formation. Accordingly, highly ordered anodic TiO2 nanopore arrays, similar to anodic aluminum oxide nanopore arrays, were successfully prepared.
A single-electron approach for many-electron dynamics in high-order harmonic generation
Schild, Axel
2016-01-01
We present a novel ab-initio single-electron approach to correlated electron dynamics in strong laser fields. By writing the electronic wavefunction as a product of a marginal one-electron wavefunction and a conditional wavefunction, we show that the exact harmonic spectrum can be obtained from a single-electron Schr\\"odinger equation. To obtain the one-electron potential in practice, we propose an adiabatic approximation, i.e. a potential is generated that depends only on the position of one electron. This potential, together with the laser interaction, is then used to obtain the dynamics of the system. For a model Helium atom in a laser field, we show that by using our approach, the high-order harmonic generation spectrum can be obtained to a good approximation.
High order forces and nonlocal operators in a Kohn-Sham Hamiltonian.
Bobbitt, N Scott; Schofield, Grady; Lena, Charles; Chelikowsky, James R
2015-12-21
Real space pseudopotentials have a number of advantages in solving for the electronic structure of materials. These advantages include ease of implementation, implementation on highly parallel systems, and great flexibility for describing partially periodic systems. One limitation of this approach, shared by other electronic structure methods, is the slow convergence of interatomic forces when compared to total energies. For real space methods, this requires a fine grid to converge a solution of the Kohn-Sham problem, which is accompanied by concurrent increase in memory and additional matrix-vector multiplications. Here we introduce a method to expedite the computation of interatomic forces by employing a high order integration technique. We demonstrate the usefulness of this technique by calculating accurate bond lengths and vibrational frequencies for molecules and nanocrystals without using fine real space grids. PMID:26106967
Effects of High-Order Co-occurrences on Word Semantic Similarities
Lemaire, Benoît
2008-01-01
A computational model of the construction of word meaning through exposure to texts is built in order to simulate the effects of co-occurrence values on word semantic similarities, paragraph by paragraph. Semantic similarity is here viewed as association. It turns out that the similarity between two words W1 and W2 strongly increases with a co-occurrence, decreases with the occurrence of W1 without W2 or W2 without W1, and slightly increases with high-order co-occurrences. Therefore, operationalizing similarity as a frequency of co-occurrence probably introduces a bias: first, there are cases in which there is similarity without co-occurrence and, second, the frequency of co-occurrence overestimates similarity.
Institute of Scientific and Technical Information of China (English)
Huafeng Yang; Guilin Liu; Changhui Rao; Yudong Zhang; Wenhan Jiang
2007-01-01
A new kind of adaptive optics (AO) system, in which several low spatial frequency deformable mirrors(DMs) with optical conjugation relationship are combined to correct high-order aberrations, is proposed.The phase compensation principle and the control method of the combinational AO system are introduced.The numerical simulations for the AO system with two 60-element DMs are presented. The results indicate that the combinational DM in the AO system can correct different aberrations effectively as one single DM with more actuators, and there is no change of control method. This technique can be applied to a large telescope AO system to improve the spatial compensation capability for wavefront by using current DM.
Enhanced high-order harmonic generation from periodic potentials in inhomogeneous laser fields
Du, Tao-Yuan; Zhou, Xiao-Xin; Bian, Xue-Bin
2016-01-01
We theoretically study high-order harmonic generation (HHG) from solid-phase systems in spatially inhomogeneous strong laser fields originated by resonant plasmons within a metallic nanostructure. The intensity of the second plateau in HHG may be enhanced by two-three orders and be comparable with the intensity of the first plateau. This is due to bigger transition probabilities to higher conduction bands. It provides us a practical way to increase the yields of HHG with laser intensity below the damage threshold. It presents a promising way to triple the range of HHG spectra in experimental measurements. It also allows to generate intense isolated attosecond pulse from solids driven by few-cycle laser fields.
Translational symmetry of high order tokamak flux surface shaping in gyrokinetics
Ball, Justin; Barnes, Michael
2015-01-01
A particular translational symmetry of the local nonlinear $\\delta f$ gyrokinetic model is demonstrated analytically and verified numerically. This symmetry shows that poloidally translating all the flux surface shaping effects with large poloidal mode number by a single tilt angle has an exponentially small effect on the transport properties of a tokamak. This is shown using a generalization of the Miller local equilibrium model to specify an arbitrary flux surface geometry. With this geometry specification we find that, when performing an expansion in large flux surface shaping mode number, the governing equations of gyrokinetics are symmetric in the poloidal translation of the high order shaping effects. This allows us to take the fluxes from a single configuration and calculate the fluxes in any configuration that can be produced by translating the large mode number shaping effects. This creates a distinction between tokamaks with mirror symmetric flux surfaces and tokamaks without mirror symmetry, which ...
Efficient simulation of cardiac electrical propagation using high order finite elements
Arthurs, Christopher J.; Bishop, Martin J.; Kay, David
2012-05-01
We present an application of high order hierarchical finite elements for the efficient approximation of solutions to the cardiac monodomain problem. We detail the hurdles which must be overcome in order to achieve theoretically-optimal errors in the approximations generated, including the choice of method for approximating the solution to the cardiac cell model component. We place our work on a solid theoretical foundation and show that it can greatly improve the accuracy in the approximation which can be achieved in a given amount of processor time. Our results demonstrate superior accuracy over linear finite elements at a cheaper computational cost and thus indicate the potential indispensability of our approach for large-scale cardiac simulation.
High-order harmonic and attosecond pulse generation on plasma mirrors: basic mechanisms
Energy Technology Data Exchange (ETDEWEB)
Thaury, C; Quere, F, E-mail: fabien.quere@cea.f [Service des Photons, Atomes et Molecules, Commissariat l' Energie Atomique, DSM/IRAMIS, CEA Saclay, 91191 Gif sur Yvette (France)
2010-11-14
When an intense femtosecond laser pulse hits an optically polished surface, it generates a dense plasma that itself acts as a mirror, known as the plasma mirror. As this mirror reflects the high-intensity laser field, its nonlinear temporal response can lead to a periodic temporal distortion of the reflected wave, associated with a train of attosecond light pulses, and, in the frequency domain, to the generation of high-order harmonics of the laser. This tutorial presents detailed theoretical and numerical analysis of the two dominant harmonic generation mechanisms identified so far, coherent wake emission and the relativistic oscillating mirror. Parametric studies of the emission efficiency are presented for these two regimes, and the phase properties of the corresponding harmonics are discussed. This theoretical study is complemented by a synthesis of recent experimental results, which establishes that these two mechanisms indeed dominate harmonic generation on plasma mirrors. (phd tutorial)
High-order harmonic and attosecond pulse generation on plasma mirrors: basic mechanisms
International Nuclear Information System (INIS)
When an intense femtosecond laser pulse hits an optically polished surface, it generates a dense plasma that itself acts as a mirror, known as the plasma mirror. As this mirror reflects the high-intensity laser field, its nonlinear temporal response can lead to a periodic temporal distortion of the reflected wave, associated with a train of attosecond light pulses, and, in the frequency domain, to the generation of high-order harmonics of the laser. This tutorial presents detailed theoretical and numerical analysis of the two dominant harmonic generation mechanisms identified so far, coherent wake emission and the relativistic oscillating mirror. Parametric studies of the emission efficiency are presented for these two regimes, and the phase properties of the corresponding harmonics are discussed. This theoretical study is complemented by a synthesis of recent experimental results, which establishes that these two mechanisms indeed dominate harmonic generation on plasma mirrors. (phd tutorial)
Single attosecond pulse from terahertz-assisted high-order harmonic generation
Energy Technology Data Exchange (ETDEWEB)
Balogh, Emeric [Department of Optics and Quantum Electronics, University of Szeged, H-6701 Szeged (Hungary); Kovacs, Katalin [Department of Optics and Quantum Electronics, University of Szeged, H-6701 Szeged (Hungary); National Institute for R and D of Isotopic and Molecular Technologies, RO-400293 Cluj-Napoca (Romania); Dombi, Peter; Farkas, Gyozo [Research Institute for Solid State Physics and Optics, H-1525 Budapest (Hungary); Fulop, Jozsef A.; Hebling, Janos [Department of Experimental Physics, University of Pecs, H-7624 Pecs (Hungary); Tosa, Valer [National Institute for R and D of Isotopic and Molecular Technologies, RO-400293 Cluj-Napoca (Romania); Varju, Katalin [HAS Research Group on Laser Physics, University of Szeged, H-6701 Szeged (Hungary)
2011-08-15
High-order harmonic generation by few-cycle 800 nm laser pulses in neon gas in the presence of a strong terahertz (THz) field is investigated numerically with propagation effects taken into account. Our calculations show that the combination of THz fields with up to 12 fs laser pulses can be an effective gating technique to generate single attosecond pulses. We show that in the presence of the strong THz field only a single attosecond burst can be phase matched, whereas radiation emitted during other half cycles disappears during propagation. The cutoff is extended and a wide supercontinuum appears in the near-field spectra, extending the available spectral width for isolated attosecond pulse generation from 23 to 93 eV. We demonstrate that phase-matching effects are responsible for the generation of isolated attosecond pulses, even in conditions when single-atom response yields an attosecond pulse train.
Electron path control of high-order harmonic generation by a spatially inhomogeneous field
Mohebbi, Masoud; Nazarpoor Malaei, Sakineh
2016-04-01
We theoretically investigate the control of high-order harmonics cut-off and as-pulse generation by a chirped laser field using a metallic bow tie-shaped nanostructure. The numerical results show that the trajectories of the electron wave packet are strongly modified, the short quantum path is enhanced, the long quantum path is suppressed and the low modulated spectrum of the harmonics can be remarkably extended. Our calculated results also show that, by confining electron motion, a broadband supercontinuum with the width of 1670 eV can be produced which directly generates an isolated 34 as-pulse without phase compensation. To explore the underlying mechanism responsible for the cut-off extension and the quantum path selection, we perform time-frequency analysis and a classical simulation based on the three-step model.
Single attosecond pulse from terahertz-assisted high-order harmonic generation
Balogh, Emeric; Dombi, Peter; Fulop, Jozsef A; Farkas, Gyozo; Hebling, Janos; Tosa, Valer; Varju, Katalin; 10.1103/PhysRevA.84.023806
2011-01-01
High-order harmonic generation by few-cycle 800 nm laser pulses in neon gas in the presence of a strong terahertz (THz) field is investigated numerically with propagation effects taken into account. Our calculations show that the combination of THz fields with up to 12 fs laser pulses can be an effective gating technique to generate single attosecond pulses. We show that in the presence of the strong THz field only a single attosecond burst can be phase matched, whereas radiation emitted during other half-cycles disappears during propagation. The cutoff is extended and a wide supercontinuum appears in the near-field spectra, extending the available spectral width for isolated attosecond pulse generation from 23 to 93 eV. We demonstrate that phase matching effects are responsible for the generation of isolated attosecond pulses, even in conditions when single atom response yields an attosecond pulse train.
High order recombination and an application to cubature on Wiener space
Litterer, Christian
2010-01-01
Particle methods are widely used because they can provide accurate descriptions of evolving measures. Recently it has become clear that by stepping outside the Monte-Carlo paradigm these methods can be of higher order with effective and transparent error bounds. A weakness of particle methods(particularly in the higher order case) is the tendency for the number of particles to explode if the process is iterated and accuracy preserved. In this paper we identify a new approach that allows dynamic recombination in such methods and retains the high order accuracy by simplifying the support of the intermediate measures used in the iteration. We describe an algorithm that can be used to simplify the support of a discrete measure and give an application to the cubature on Wiener space method developed by Lyons, Victoir [12].
Optical properties of dyes with/without metal nanoparticles doped in a highly ordered nanostructure
Institute of Scientific and Technical Information of China (English)
SUN Li-ping; LI Yu-dong; QI Ji-wei; XU Jing-jun; SUN Qian
2011-01-01
Highly ordered nanocomposite arrays of Rh6G-Au-AAO are formed by filling anodized aluminum oxide (AAO) with Rhodamine 6G (Rh6G) and gold nanoparticles. The optical properties of Rh6G-Au-AAO are studied by visible absorptive and fluorescent spectroscopy. Compared with the fluorescence spectra of Rh6G-Au in the solution environment, the fluorescence peak intensities of Rh6G-Au-AAO are significantly enhanced, the maximum enhancement rate is 5.5, and a constant blue shift of～ 12 nm of peak positions is presented. The effects come from the spatial confinement of AAO and the inhibition of the fluorescence quenching effect induced by gold nanoparticles. The results show that the nanocomposite structures of fluorescence molecules-metal nanoparticles-AAO have a considerable potential in engineering molecular assemblies and creating functional materials of superior properties for future nanophotonics.
Electrodeposition and Characteristics of Highly Ordered Macroporous β-PbO2 Electrodes
Directory of Open Access Journals (Sweden)
Yusairie Mohd
2011-09-01
Full Text Available Highly ordered macroporous β-PbO2 deposits were successfully produced on gold using polystyrene microsphere templates through electrodeposition technique from acidic nitrate baths containing Pb(II ions using a constant current at 298 K. The morphology, catalytic activity and chemical stability of the deposits have been investigated. The morphology of the deposits has been analysed by Scanning Electron Microscopy (SEM. The catalytic activity of the deposited β-PbO2 electrodes as anodes for dimethylsulfoxide (DMSO oxidation has been investigated using cyclic voltammetry. The chemical stability of the electrode in acidic solution was monitored and observed by the SEM. The deposits were shown to be active for the oxidation of DMSO due to their high surface area. It was also found that decomposition of the electrodes occurred when they were kept standing in acidic solution containing an oxidisable organic compound (ie: DMSO on open circuit.
Formation of high-order acoustic Bessel beams by spiral diffraction gratings
Jiménez, Noé; Sánchez-Morcillo, Víctor; Romero-García, Vicent; García-Raffi, Lluis M; Staliunas, Kestutis
2016-01-01
The formation of high-order Bessel beams by a passive acoustic device consisting of an Archimedes' spiral diffraction grating is theoretically, numerically and experimentally reported in this work. These beams are propagation-invariant solutions of the Helmholtz equation and are characterized by an azimuthal variation of the phase along its annular spectrum producing an acoustic vortex in the near field. In our system, the scattering of plane acoustic waves by the spiral grating leads to the formation of the acoustic vortex with zero pressure on-axis and the angular phase dislocations characterized by the spiral geometry. The order of the generated Bessel beam and, as a consequence, the size of the generated vortex can be fixed by the number of arms in the spiral diffraction grating. The obtained results allow to obtain Bessel beams with controllable vorticity by a passive device, which has potential applications in low-cost acoustic tweezers and acoustic radiation force devices.
A Scalable Auxiliary Space Preconditioner for High-Order Finite Element Methods
Lee, Young-Ju; Zhang, Chen-Song
2012-01-01
In this paper, we revisit an auxiliary space preconditioning method proposed by Xu [Computing 56, 1996], in which low-order finite element spaces are employed as auxiliary spaces for solving linear algebraic systems arising from high-order finite element discretizations. We provide a new convergence rate estimate and parallel implementation of the proposed algorithm. We show that this method is user-friendly and can play an important role in a variety of Poisson-based solvers for more challenging problems such as the Navier--Stokes equation. We investigate the performance of the proposed algorithm using the Poisson equation and the Stokes equation on 3D unstructured grids. Numerical results demonstrate the advantages of the proposed algorithm in terms of efficiency, robustness, and parallel scalability.
Two-center interference in high-order harmonic generation from heteronuclear diatomic molecules.
Zhu, Xiaosong; Zhang, Qingbin; Hong, Weiyi; Lan, Pengfei; Lu, Peixiang
2011-01-17
Two-center interference for heteronuclear diatomic molecules (HeDM) is investigated. The minimum in the high-order harmonic spectrum, as a consequence of the destructive interference, is shifted to lower harmonic orders compared with that in a homonuclear case. This phenomenon is explained by performing phase analysis. It is found that, for an HeDM, the high harmonic spectrum contains information not only on the internuclear separation but also on the properties of the two separate centers, which implies the potential application of estimating the asymmetry of molecules and judging the linear combination of atomic orbitals (LCAO) for the highest occupied molecular orbital (HOMO). Moreover, the possibility to monitor the evolution of HOMO itself in molecular dynamics is also promised. PMID:21263583
International Nuclear Information System (INIS)
To explore the kinetics of photoelectrocatalytic degradation of salicylic acid, one of the important PPCPs, highly ordered TiO2 nanotube arrays (NTs) were prepared by the electrochemical anodization and characterized with scanning electron microscopy and X-ray diffraction techniques. The effect of TiO2 NTs properties, bias potential, initial salicylic acid concentration and solution pH on the degradation efficiency was studied and carefully analyzed. The results revealed that the salicylic acid degradation follows quasi-first order kinetics in the photoelectrocatalytic process, and the fastest decay kinetics was achieved in acidic environment (pH 2). The result was further interpreted through the electrochemical impedance spectroscopy. It is confirmed that the electrochemical assisted photocatalysis is a synergetic approach to combat stable organic substances with improved efficiency.
Energy Technology Data Exchange (ETDEWEB)
Sjogreen, B; Yee, H C
2007-12-12
Flows containing steady or nearly steady strong shocks in parts of the flow field, and unsteady turbulence with shocklets on other parts of the flow field are difficult to capture accurately and efficiently employing the same numerical scheme even under the multiblock grid or adaptive grid refinement framework. On one hand, sixth-order or higher shock-capturing methods are appropriate for unsteady turbulence with shocklets. On the other hand, lower order shock-capturing methods are more effective for strong steady shocks in terms of convergence. In order to minimize the shortcomings of low order and high order shock-capturing schemes for the subject flows, a multi-block overlapping grid with different orders of accuracy on different blocks is proposed. Test cases to illustrate the performance of the new solver are included.
Directory of Open Access Journals (Sweden)
Benedetto Farina
2015-04-01
Full Text Available The state-of-the-art in studies on mentalization suggests that capacity to understand other minds (mindreading, self introspection and consciousness, mental time travel in the past and the present, linguistic communication, are different components of a hierarchical organization of several functions reflecting the evolutionary development of the specie and integrates increasingly complex, mutually coordinated brain levels. The understanding of the precise hierarchical relations between them, that reflect the phylo- and ontogenetic evolutionary pathway for adaptation to the complex interpersonal and socio-cultural environment, has an essential application in psychopathology and psychotherapy, in particular for those clinical conditions where the normal integration of high order mental functions is hampered by developmental relational trauma.
Depict noise-driven nonlinear dynamic networks from output data by using high-order correlations
Chen, Yang; Chen, Tianyu; Wang, Shihong; Hu, Gang
2016-01-01
Many practical systems can be described by dynamic networks, for which modern technique can measure their output signals, and accumulate extremely rich data. Nevertheless, the network structures producing these data are often deeply hidden in these data. Depicting network structures by analysing the available data turns to be significant inverse problems. On one hand, dynamics are often driven by various unknown facts, called noises. On the other hand, network structures of practical systems are commonly nonlinear, and different nonlinearities can provide rich dynamic features and meaningful functions of realistic networks. So far, no method, both theoretically or numerically, has been found to systematically treat the both difficulties together. Here we propose to use high-order correlation computations (HOCC) to treat nonlinear dynamics; use two-time correlations to treat noise effects; and use suitable basis and correlator vectors to unifiedly depict all dynamic nonlinearities and topological interaction l...
A novel high-order, entropy stable, 3D AMR MHD solver with guaranteed positive pressure
Derigs, Dominik; Winters, Andrew R.; Gassner, Gregor J.; Walch, Stefanie
2016-07-01
We describe a high-order numerical magnetohydrodynamics (MHD) solver built upon a novel non-linear entropy stable numerical flux function that supports eight travelling wave solutions. By construction the solver conserves mass, momentum, and energy and is entropy stable. The method is designed to treat the divergence-free constraint on the magnetic field in a similar fashion to a hyperbolic divergence cleaning technique. The solver described herein is especially well-suited for flows involving strong discontinuities. Furthermore, we present a new formulation to guarantee positivity of the pressure. We present the underlying theory and implementation of the new solver into the multi-physics, multi-scale adaptive mesh refinement (AMR) simulation code FLASH (http://flash.uchicago.edu).
Dynamic modification of the fragmentation of COq+ excited states generated with high-order harmonics
International Nuclear Information System (INIS)
The dynamic process of fragmentation of COq+ excited states is investigated using a pump-probe approach. EUV radiation (32-48 eV) generated by high-order harmonics was used to ionize and excite CO molecules and a time-delayed infrared (IR) pulse (800 nm) was used to influence the evolution of the dissociating multichannel wave packet. Two groups of states, separable experimentally by their kinetic-energy release (KER), are populated by the EUV and lead to C+-O+ fragmentation: direct double ionization of the neutral molecule and fragmentation of the cation leading to C+-O*, followed by autoionization of O*. The IR pulse was found to modify the KER of the latter group in a delay-dependent way which is explained with a model calculation.
Tunable generation of high-order harmonics by IR and THz fields
Kovács, K.; Balogh, E.; Toşa, V.; Varjú, K.
2013-11-01
We numerically investigate high-order harmonic generation where a properly tailored THz pulse assists the process of regular HHG in a static cell. The strong IR pulse (800 nm, 20 fs, 0.16-0.3 mJ pulse energy) propagates along the cell while the assisting THz pulse illuminates the cell laterally. We demonstrate that the phase mismatch can be compensated during propagation and the macroscopic cutoff can be extended up to the single-dipole cutoff. The amplified spectral domain can be controlled by adjusting the IR pulse energy and the THz pulse parameters. We obtain two orders of magnitude increase in the harmonic efficiency in the cutoff region (150-200 eV), in a quasi-phasematching regime.
High-order harmonics with frequency-varying polarization within each harmonic
Fleischer, Avner; Sidorenko, Pavel; Cohen, Oren
2014-01-01
We predict high-order harmonics in which the polarization within the spectral bandwidth of each harmonic varies continuously and significantly. For example, the interaction of counter-rotating circularly-polarized bichromatic drivers having close central frequencies with isotropic gas leads to the emission of polarization-fan harmonics which are nearly circularly-polarized in one tail of the harmonic peak, linear in the center of the peak and nearly circular with the opposite helicity in the opposite tail. Polarization fan harmonics are obtained as a result of multiple (at least two) head-on recollisions of electrons with their parent ions occurring from different angles. The process can be phase-matched using standard methods (e.g. pressure tuning phase matching) and maintains the single-atom polarization property through propagation. These polarization-fan harmonics may be used for exploring non-repetitive ultrafast chiral phenomena, e.g. dynamics of magnetic domains, in a single shot
High order one-step monotonicity-preserving schemes for unsteady compressible flow calculations
International Nuclear Information System (INIS)
This paper deals with the development of accurate one-step schemes for the numerical simulation of unsteady compressible flows. Pursuing our work in Daru and Tenaud [V. Daru, C. Tenaud, Comput. Fluids 30 (2001) 89] where third-order schemes were considered, we follow the Lax-Wendroff approach to develop high order TVD combined time-space schemes by correcting the successive modified equations. In the scalar case, TVD schemes accurate up to seventh order (OSTVD7) in time and space are obtained (in smooth regions and away from extrema). To avoid the clipping and the loss of accuracy that is common to the TVD schemes near extrema, we develop monotonicity-preserving (MP) conditions derived from Suresh and Huynh [A. Suresh, H.T. Huynh, J. Comput. Phys. 136 (1997) 83] to locally relax the TVD limitation for this family of one-step schemes. Numerical results for long time integration in the scalar case show that the MP one-step approach gives the best results compared to several multistage schemes, including WENO schemes. The extension to systems and to the multidimensional case is done in a simplified way which does not preserve the scalar order of accuracy. However we show that the resulting schemes have a very low level of error. For validation, the present algorithm has been checked on several classical one-dimensional and multidimensional test cases, including both viscous and inviscid flows: a moving shock wave interacting with a sine wave, the Lax shock tube problem, the 2D inviscid double Mach reflection and the 2D viscous shock wave-vortex interaction. By computing these various test cases, we demonstrate that very accurate results can be obtained by using the one-step MP approach which is very competitive compared to multistage high order schemes
Direct Simulations of Transition and Turbulence Using High-Order Accurate Finite-Difference Schemes
Rai, Man Mohan
1997-01-01
In recent years the techniques of computational fluid dynamics (CFD) have been used to compute flows associated with geometrically complex configurations. However, success in terms of accuracy and reliability has been limited to cases where the effects of turbulence and transition could be modeled in a straightforward manner. Even in simple flows, the accurate computation of skin friction and heat transfer using existing turbulence models has proved to be a difficult task, one that has required extensive fine-tuning of the turbulence models used. In more complex flows (for example, in turbomachinery flows in which vortices and wakes impinge on airfoil surfaces causing periodic transitions from laminar to turbulent flow) the development of a model that accounts for all scales of turbulence and predicts the onset of transition may prove to be impractical. Fortunately, current trends in computing suggest that it may be possible to perform direct simulations of turbulence and transition at moderate Reynolds numbers in some complex cases in the near future. This seminar will focus on direct simulations of transition and turbulence using high-order accurate finite-difference methods. The advantage of the finite-difference approach over spectral methods is that complex geometries can be treated in a straightforward manner. Additionally, finite-difference techniques are the prevailing methods in existing application codes. In this seminar high-order-accurate finite-difference methods for the compressible and incompressible formulations of the unsteady Navier-Stokes equations and their applications to direct simulations of turbulence and transition will be presented.
Study and development of a soft X-ray laser seeded by high-order harmonic
International Nuclear Information System (INIS)
The work in this thesis aimed to study a geometry of X-UV lasers inspired by high power laser. This architecture, consisting of an injector (a source of high-order harmonics) coupled to an amplifier (plasma created by laser), corresponds to that of a laser chain in the spectral range of the X-UV. The laser at 32.8 nm studied here, is produced by the injection of high-order harmonic in a krypton plasma created by Optical Field Ionization (OFI). This scheme, initially tested by T. Ditmire in 1995, was validated in 2003 with a plasma amplifier created by the interaction of intense laser and a gaseous medium. This thesis is a continuation of that work in trying to address different aspects, not only a better understanding of the physical processes involved, but also of the spatio-temporal characterization of this type of source. We have demonstrated experimentally for the first time a source in the X-UV, which can be highly compact, energetic (1 μJ per pulse), close to the diffraction limit and Fourier transform limited. Indeed, through the spatial filtering of harmonics by the amplifying medium, the injected X-UV laser at 32.8 nm shows a Gaussian spatial profile with a divergence of 0.7 mrad (at 1/e2). The wavefront was measured with a Hartmann sensor and presents a value of λ/17 in standard deviation, demonstrating that the X-UV source is diffraction limited. The temporal characterization of laser shows that the coherence time is of the order of the duration of spontaneous emission of the amplifier. The temporal coherence presents a Gaussian profile with a relative spectral width Δλ/λ equal to 10-5 (FWHM) corresponding to a pulse duration of about 5 ps. (author)
Using pattern classification to measure adaptation to the orientation of high order aberrations.
Directory of Open Access Journals (Sweden)
Lucie Sawides
Full Text Available BACKGROUND: The image formed by the eye's optics is blurred by the ocular aberrations, specific to each eye. Recent studies demonstrated that the eye is adapted to the level of blur produced by the high order aberrations (HOA. We examined whether visual coding is also adapted to the orientation of the natural HOA of the eye. METHODS AND FINDINGS: Judgments of perceived blur were measured in 5 subjects in a psychophysical procedure inspired by the "Classification Images" technique. Subjects were presented 500 pairs of images, artificially blurred with HOA from 100 real eyes (i.e. different orientations, with total blur level adjusted to match the subject's natural blur. Subjects selected the image that appeared best focused in each random pair, in a 6-choice ranked response. Images were presented through Adaptive Optics correction of the subject's aberrations. The images selected as best focused were identified as positive, the other as negative responses. The highest classified positive responses correlated more with the subject's Point Spread Function, PSF, (r = 0.47 on average than the negative (r = 0.34 and the difference was significant for all subjects (p<0.02. Using the orientation of the best fitting ellipse of angularly averaged integrated PSF intensities (weighted by the subject's responses we found that in 4 subjects the positive PSF response was close to the subject's natural PSF orientation (within 21 degrees on average whereas the negative PSF response was almost perpendicularly oriented to the natural PSF (at 76 degrees on average. CONCLUSIONS: The Classification-Images inspired method is very powerful in identifying the internally coded blur of subjects. The consistent bias of the Positive PSFs towards the natural PSF in most subjects indicates that the internal code of blur appears rather specific to each subject's high order aberrations and reveals that the calibration mechanisms for normalizing blur also operate using
International Nuclear Information System (INIS)
High-order triangle-based discontinuous Galerkin (DG) methods for hyperbolic equations on a rotating sphere are presented. The DG method can be characterized as the fusion of finite elements with finite volumes. This DG formulation uses high-order Lagrange polynomials on the triangle using nodal sets up to 15th order. The finite element-type area integrals are evaluated using order 2N Gauss cubature rules. This leads to a full mass matrix which, unlike for continuous Galerkin (CG) methods such as the spectral element (SE) method presented in Giraldo and Warburton [A nodal triangle-based spectral element method for the shallow water equations on the sphere, J. Comput. Phys. 207 (2005) 129-150], is small, local and efficient to invert. Two types of finite volume-type flux integrals are studied: a set based on Gauss-Lobatto quadrature points (order 2N - 1) and a set based on Gauss quadrature points (order 2N). Furthermore, we explore conservation and advection forms as well as strong and weak forms. Seven test cases are used to compare the different methods including some with scale contractions and shock waves. All three strong forms performed extremely well with the strong conservation form with 2N integration being the most accurate of the four DG methods studied. The strong advection form with 2N integration performed extremely well even for flows with shock waves. The strong conservation form with 2N - 1 integration yielded results almost as good as those with 2N while being less expensive. All the DG methods performed better than the SE method for almost all the test cases, especially for those with strong discontinuities. Finally, the DG methods required less computing time than the SE method due to the local nature of the mass matrix
Highly ordered Ni–Ti–O nanotubes for non-enzymatic glucose detection
International Nuclear Information System (INIS)
Anodization is used to fabricate Ni–Ti–O nanotube (NT) electrodes for non-enzymatic glucose detection. The morphology, microstructure and composition of the materials are characterized by field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Our results show amorphous and highly ordered NTs with diameter of 50 nm, length of 800 nm, and Ni/Ti ratio (at %) of 0.35 can be fabricated in ethylene glycol electrolyte supplemented with 0.2 wt.% NH4F and 0.5 vol.% H2O at 30 °C and 25 V for 1 h. Electrochemical experiments indicate that at an applied potential of 0.60 V vs. Ag/AgCl, the electrode exhibits a linear response window for glucose concentrations from 0.002 mM to 0.2 mM with a response time of 10 s, detection limit of 0.13 μM (S/N = 3), and sensitivity of 83 μA mM−1 cm−2. The excellent performance of the electrode is attributed to its large specific area and fast electron transfer between the NT walls. The good electrochemical performance of the Ni–Ti–O NTs as well as their simple and low-cost preparation method make the strategy promising in non-enzymatic glucose detection. - Highlights: • Highly ordered Ni–Ti–O nanotubes have been fabricated by one-step anodization. • We find H2O contents in the electrolyte is critical to successful fabrication of the NTs. • The Ni–Ti–O nanotubes are ideal electrode materials for non-enzymatic glucose detection
Highly ordered Ni–Ti–O nanotubes for non-enzymatic glucose detection
Energy Technology Data Exchange (ETDEWEB)
Hang, Ruiqiang, E-mail: hangruiqiang@tyut.edu.cn [Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Liu, Yanlian [Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Gao, Ang [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China); Bai, Long; Huang, Xiaobo; Zhang, Xiangyu; Lin, Naiming [Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Tang, Bin, E-mail: tangbin@tyut.edu.cn [Research Institute of Surface Engineering, Taiyuan University of Technology, Taiyuan 030024 (China); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)
2015-06-01
Anodization is used to fabricate Ni–Ti–O nanotube (NT) electrodes for non-enzymatic glucose detection. The morphology, microstructure and composition of the materials are characterized by field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Our results show amorphous and highly ordered NTs with diameter of 50 nm, length of 800 nm, and Ni/Ti ratio (at %) of 0.35 can be fabricated in ethylene glycol electrolyte supplemented with 0.2 wt.% NH{sub 4}F and 0.5 vol.% H{sub 2}O at 30 °C and 25 V for 1 h. Electrochemical experiments indicate that at an applied potential of 0.60 V vs. Ag/AgCl, the electrode exhibits a linear response window for glucose concentrations from 0.002 mM to 0.2 mM with a response time of 10 s, detection limit of 0.13 μM (S/N = 3), and sensitivity of 83 μA mM{sup −1} cm{sup −2}. The excellent performance of the electrode is attributed to its large specific area and fast electron transfer between the NT walls. The good electrochemical performance of the Ni–Ti–O NTs as well as their simple and low-cost preparation method make the strategy promising in non-enzymatic glucose detection. - Highlights: • Highly ordered Ni–Ti–O nanotubes have been fabricated by one-step anodization. • We find H{sub 2}O contents in the electrolyte is critical to successful fabrication of the NTs. • The Ni–Ti–O nanotubes are ideal electrode materials for non-enzymatic glucose detection.
Schaal, Kevin; Bauer, Andreas; Chandrashekar, Praveen; Pakmor, Rüdiger; Klingenberg, Christian; Springel, Volker
2015-11-01
Solving the Euler equations of ideal hydrodynamics as accurately and efficiently as possible is a key requirement in many astrophysical simulations. It is therefore important to continuously advance the numerical methods implemented in current astrophysical codes, especially also in light of evolving computer technology, which favours certain computational approaches over others. Here we introduce the new adaptive mesh refinement (AMR) code TENET, which employs a high-order discontinuous Galerkin (DG) scheme for hydrodynamics. The Euler equations in this method are solved in a weak formulation with a polynomial basis by means of explicit Runge-Kutta time integration and Gauss-Legendre quadrature. This approach offers significant advantages over commonly employed second-order finite-volume (FV) solvers. In particular, the higher order capability renders it computationally more efficient, in the sense that the same precision can be obtained at significantly less computational cost. Also, the DG scheme inherently conserves angular momentum in regions where no limiting takes place, and it typically produces much smaller numerical diffusion and advection errors than an FV approach. A further advantage lies in a more natural handling of AMR refinement boundaries, where a fall-back to first order can be avoided. Finally, DG requires no wide stencils at high order, and offers an improved data locality and a focus on local computations, which is favourable for current and upcoming highly parallel supercomputers. We describe the formulation and implementation details of our new code, and demonstrate its performance and accuracy with a set of two- and three-dimensional test problems. The results confirm that DG schemes have a high potential for astrophysical applications.
The fluctuation of high-order aberration's sensitivity in ArF immersion lithography
Zhang, Fei; Li, Yanqui
2006-01-01
To achieve smaller and smaller feature sizes in the semiconductor industry, extreme demands are placed on the lithographic optics, specifically the projection lens. Higher numerical aperture (NA) is adopted to obtain higher resolution. However, higher NA scales the impact of geometrical aberrations on lithography performance. Thus, a detailed understanding of the effect of geometrical aberrations on the lithographic process is indispensable. In this paper, we consider some of the surprising phenomena that occur at such high NA. We discuss the impact of flare, polarization state and MSD on higher-order aberration's sensitivity using ArF immersion lithography to print elbow pattern exposed features in photo resist on 65nm node. The higher-order aberration's sensitivity is analyzed when the annular illumination (NA=1.2, sigma out=0.76, sigma in=0.52) is employed. The 3rd, 5th, 7th, 9th geometrical aberrations according to the Fringe convention are discussed. The sensitivities to individual geometrical aberrations are calculated by introducing a fixed amount of aberration for each Zernike coefficient with all other aberrations being zero. On 65nm node, with annular illumination, the high-order aberration's sensitivity is calculated respectively according to the variation of flare, polarization state, and MSD. The results show that flare, polarization state, and MSD can contribute to the high-order aberration's sensitivity. The aberration sensitivities are increasing with the MSD and flare's value rising. The aberration sensitivities can be decreased when the horizontal linear polarized light is adopted. The merits of adjusting polarization state to choke back the aberration sensitivities are presented.
High-order multi-implicit spectral deferred correction methods for problems of reactive flow
International Nuclear Information System (INIS)
Models for reacting flow are typically based on advection-diffusion-reaction (A-D-R) partial differential equations. Many practical cases correspond to situations where the relevant time scales associated with each of the three sub-processes can be widely different, leading to disparate time-step requirements for robust and accurate time-integration. In particular, interesting regimes in combustion correspond to systems in which diffusion and reaction are much faster processes than advection. The numerical strategy introduced in this paper is a general procedure to account for this time-scale disparity. The proposed methods are high-order multi-implicit generalizations of spectral deferred correction methods (MISDC methods), constructed for the temporal integration of A-D-R equations. Spectral deferred correction methods compute a high-order approximation to the solution of a differential equation by using a simple, low-order numerical method to solve a series of correction equations, each of which increases the order of accuracy of the approximation. The key feature of MISDC methods is their flexibility in handling several sub-processes implicitly but independently, while avoiding the splitting errors present in traditional operator-splitting methods and also allowing for different time steps for each process. The stability, accuracy, and efficiency of MISDC methods are first analyzed using a linear model problem and the results are compared to semi-implicit spectral deferred correction methods. Furthermore, numerical tests on simplified reacting flows demonstrate the expected convergence rates for MISDC methods of orders three, four, and five. The gain in efficiency by independently controlling the sub-process time steps is illustrated for nonlinear problems, where reaction and diffusion are much stiffer than advection. Although the paper focuses on this specific time-scales ordering, the generalization to any ordering combination is straightforward
Ivan, L.; De Sterck, H.; Susanto, A.; Groth, C. P. T.
2015-02-01
A fourth-order accurate finite-volume scheme for hyperbolic conservation laws on three-dimensional (3D) cubed-sphere grids is described. The approach is based on a central essentially non-oscillatory (CENO) finite-volume method that was recently introduced for two-dimensional compressible flows and is extended to 3D geometries with structured hexahedral grids. Cubed-sphere grids feature hexahedral cells with nonplanar cell surfaces, which are handled with high-order accuracy using trilinear geometry representations in the proposed approach. Varying stencil sizes and slope discontinuities in grid lines occur at the boundaries and corners of the six sectors of the cubed-sphere grid where the grid topology is unstructured, and these difficulties are handled naturally with high-order accuracy by the multidimensional least-squares based 3D CENO reconstruction with overdetermined stencils. A rotation-based mechanism is introduced to automatically select appropriate smaller stencils at degenerate block boundaries, where fewer ghost cells are available and the grid topology changes, requiring stencils to be modified. Combining these building blocks results in a finite-volume discretization for conservation laws on 3D cubed-sphere grids that is uniformly high-order accurate in all three grid directions. While solution-adaptivity is natural in the multi-block setting of our code, high-order accurate adaptive refinement on cubed-sphere grids is not pursued in this paper. The 3D CENO scheme is an accurate and robust solution method for hyperbolic conservation laws on general hexahedral grids that is attractive because it is inherently multidimensional by employing a K-exact overdetermined reconstruction scheme, and it avoids the complexity of considering multiple non-central stencil configurations that characterizes traditional ENO schemes. Extensive numerical tests demonstrate fourth-order convergence for stationary and time-dependent Euler and magnetohydrodynamic flows on
A method to design aspheric spectacles for correction of high-order aberrations of human eye
Institute of Scientific and Technical Information of China (English)
LI Rui; WANG ZhaoQi; LIU YongJi; MU GuoGuang
2012-01-01
Aiming at the correction of high-order aberrations of human eye with spectacles,a design method of aspheric spectacles is proposed based on the eye's wavefront aberrations data.Regarding the eyeball and the spectacles as a whole system-the lens-eye system-the surface profiles of the spectacles are achieved by optimization procedure of lens design.Different from the conventional optometry,in which the refraction prescription is acquired with a visual chart,the design takes into account the two aspects of actual human viewing,eyeball rolling and certain distinct viewing field.The rotation angle of eyeball is set to be ±20° as wearing spectacles,and the field of view is set to be ∧7° which is especially important as watching screen display.The individual eye model is constructed as the main part of the lens-eye system.The Liou eye model is modified by sticking a thin meniscus lens to the crystalline lens.Then the defocus of the individual eye is transferred to the front surface of the meniscus lens,and the astigmatism and high-order aberrations are transferred to the front surface of the cornea.50 eyes are involved in this research,among which 36 eyes have good enough visual performance already after sphero-cylindrical correction.10 eyes have distinct improvement in vision and 4 eyes have no visual improvement by further aspheric correction.6 typical subject eyes are selected for the aberrations analysis and the spectacles design in this paper.It is shown that the validity of visual correction of aspheric lens depends on the characteristics of the eye's wavefront aberrations,and it is effective for the eye with larger astigmatism or spherical aberration.Compared with sphero-cylindrical correction only,the superiority taken by the aspheric correction is mainly on the improvement of MTF at a larger field of view.For the best aspheric correction,the MTF values increase by 18.87％,38.34％,44.36％,51.29％ and 57.32％ at the spatial frequencies of 40
Directory of Open Access Journals (Sweden)
Gao X
2015-11-01
Full Text Available Xiang Gao,1,2,* Xiaohong Zhang,3,* Jinlin Song,1,2 Xiao Xu,4 Anxiu Xu,1 Mengke Wang,4 Bingwu Xie,1 Enyi Huang,2 Feng Deng,1,2 Shicheng Wei2–41College of Stomatology, 2Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing Medical University, Chongqing, 3Center for Biomedical Materials and Tissue Engineering, Academy for Advanced Interdisciplinary Studies, Peking University, 4Department of Oral and Maxillofacial Surgery, Laboratory of Interdisciplinary Studies, Peking University School and Hospital of Stomatology, Beijing, People’s Republic of China*These authors contributed equally to this workAbstract: The construction of functional biomimetic scaffolds that recapitulate the topographical and biochemical features of bone tissue extracellular matrix is now of topical interest in bone tissue engineering. In this study, a novel surface-functionalized electrospun polycaprolactone (PCL nanofiber scaffold with highly ordered structure was developed to simulate the critical features of native bone tissue via a single step of catechol chemistry. Specially, under slightly alkaline aqueous solution, polydopamine (pDA was coated on the surface of aligned PCL nanofibers after electrospinning, followed by covalent immobilization of bone morphogenetic protein-7-derived peptides onto the pDA-coated nanofiber surface. Contact angle measurement, Raman spectroscopy, and X-ray photoelectron spectroscopy confirmed the presence of pDA and peptides on PCL nanofiber surface. Our results demonstrated that surface modification with osteoinductive peptides could improve cytocompatibility of nanofibers in terms of cell adhesion, spreading, and proliferation. Most importantly, Alizarin Red S staining, quantitative real-time polymerase chain reaction, immunostaining, and Western blot revealed that human mesenchymal stem cells cultured on aligned nanofibers with osteoinductive peptides exhibited enhanced osteogenic differentiation potential than
Automatic Implantable Cardiac Defibrillator
Full Text Available Automatic Implantable Cardiac Defibrillator February 19, 2009 Halifax Health Medical Center, Daytona Beach, FL Welcome to Halifax Health Daytona Beach, Florida. Over the next hour you' ...
Automatic Payroll Deposit System.
Davidson, D. B.
1979-01-01
The Automatic Payroll Deposit System in Yakima, Washington's Public School District No. 7, directly transmits each employee's salary amount for each pay period to a bank or other financial institution. (Author/MLF)
High-order accurate multi-phase simulations: building blocks and whats tricky about them
Kummer, Florian
2015-11-01
We are going to present a high-order numerical method for multi-phase flow problems, which employs a sharp interface representation by a level-set and an extended discontinuous Galerkin (XDG) discretization for the flow properties. The shape of the XDG basis functions is dynamically adapted to the position of the fluid interface, so that the spatial approximation space can represent jumps in pressure and kinks in velocity accurately. By this approach, the `hp-convergence' property of the classical discontinuous Galerkin (DG) method can be preserved for the low-regularity, discontinuous solutions, such as those appearing in multi-phase flows. Within the past years, several building blocks of such a method were presented: this includes numerical integration on cut-cells, the spatial discretization by the XDG method, precise evaluation of curvature and level-set algorithms tailored to the special requirements of XDG-methods. The presentation covers a short review on these building-block and their integration into a full multi-phase solver. A special emphasis is put on the discussion of the several pitfalls one may expire in the formulation of such a solver. German Research Foundation.
2D coherent charge transport in highly ordered conducting polymers doped by solid state diffusion
Kang, Keehoon; Watanabe, Shun; Broch, Katharina; Sepe, Alessandro; Brown, Adam; Nasrallah, Iyad; Nikolka, Mark; Fei, Zhuping; Heeney, Martin; Matsumoto, Daisuke; Marumoto, Kazuhiro; Tanaka, Hisaaki; Kuroda, Shin-Ichi; Sirringhaus, Henning
2016-08-01
Doping is one of the most important methods to control charge carrier concentration in semiconductors. Ideally, the introduction of dopants should not perturb the ordered microstructure of the semiconducting host. In some systems, such as modulation-doped inorganic semiconductors or molecular charge transfer crystals, this can be achieved by spatially separating the dopants from the charge transport pathways. However, in conducting polymers, dopants tend to be randomly distributed within the conjugated polymer, and as a result the transport properties are strongly affected by the resulting structural and electronic disorder. Here, we show that in the highly ordered lamellar microstructure of a regioregular thiophene-based conjugated polymer, a small-molecule p-type dopant can be incorporated by solid state diffusion into the layers of solubilizing side chains without disrupting the conjugated layers. In contrast to more disordered systems, this allows us to observe coherent, free-electron-like charge transport properties, including a nearly ideal Hall effect in a wide temperature range, a positive magnetoconductance due to weak localization and the Pauli paramagnetic spin susceptibility.
Landing-gear noise prediction using high-order finite difference schemes
Liu, Wen; Wook Kim, Jae; Zhang, Xin; Angland, David; Caruelle, Bastien
2013-07-01
Aerodynamic noise from a generic two-wheel landing-gear model is predicted by a CFD/FW-H hybrid approach. The unsteady flow-field is computed using a compressible Navier-Stokes solver based on high-order finite difference schemes and a fully structured grid. The calculated time history of the surface pressure data is used in an FW-H solver to predict the far-field noise levels. Both aerodynamic and aeroacoustic results are compared to wind tunnel measurements and are found to be in good agreement. The far-field noise was found to vary with the 6th power of the free-stream velocity. Individual contributions from three components, i.e. wheels, axle and strut of the landing-gear model are also investigated to identify the relative contribution to the total noise by each component. It is found that the wheels are the dominant noise source in general. Strong vortex shedding from the axle is the second major contributor to landing-gear noise. This work is part of Airbus LAnding Gear nOise database for CAA validatiON (LAGOON) program with the general purpose of evaluating current CFD/CAA and experimental techniques for airframe noise prediction.
Numerical pricing of options using high-order compact finite difference schemes
Tangman, D. Y.; Gopaul, A.; Bhuruth, M.
2008-09-01
We consider high-order compact (HOC) schemes for quasilinear parabolic partial differential equations to discretise the Black-Scholes PDE for the numerical pricing of European and American options. We show that for the heat equation with smooth initial conditions, the HOC schemes attain clear fourth-order convergence but fail if non-smooth payoff conditions are used. To restore the fourth-order convergence, we use a grid stretching that concentrates grid nodes at the strike price for European options. For an American option, an efficient procedure is also described to compute the option price, Greeks and the optimal exercise curve. Comparisons with a fourth-order non-compact scheme are also done. However, fourth-order convergence is not experienced with this strategy. To improve the convergence rate for American options, we discuss the use of a front-fixing transformation with the HOC scheme. We also show that the HOC scheme with grid stretching along the asset price dimension gives accurate numerical solutions for European options under stochastic volatility.
A High Order Theory for Linear Thermoelastic Shells: Comparison with Classical Theories
Directory of Open Access Journals (Sweden)
V. V. Zozulya
2013-01-01
Full Text Available A high order theory for linear thermoelasticity and heat conductivity of shells has been developed. The proposed theory is based on expansion of the 3-D equations of theory of thermoelasticity and heat conductivity into Fourier series in terms of Legendre polynomials. The first physical quantities that describe thermodynamic state have been expanded into Fourier series in terms of Legendre polynomials with respect to a thickness coordinate. Thereby all equations of elasticity and heat conductivity including generalized Hooke's and Fourier's laws have been transformed to the corresponding equations for coefficients of the polynomial expansion. Then in the same way as in the 3D theories system of differential equations in terms of displacements and boundary conditions for Fourier coefficients has been obtained. First approximation theory is considered in more detail. The obtained equations for the first approximation theory are compared with the corresponding equations for Timoshenko's and Kirchhoff-Love's theories. Special case of plates and cylindrical shell is also considered, and corresponding equations in displacements are presented.
High-order harmonic generation by H2+ in super-intense xuv ultrashort laser pulses
International Nuclear Information System (INIS)
Dynamics of the two-dimensional H2+ under 30- and 40-cycle xuv (45 and 90 nm) laser pulses is investigated by numerical solution of the time-dependent Schrödinger equation beyond the dipole and Born–Oppenheimer approximations for two orientations (θ = 0° and θ = 90° referenced to the molecular axis) of the laser polarization. Dynamics of the electron and nuclei are treated in quantum and classical approaches, respectively. The ground, first and second excited states of H2+ are considered as initial states for different laser field intensities in the range of (4 × 1016 – 4 × 1019 W cm−2). For parallel orientation (θ = 0°), a negligibly small difference is seen for high-order harmonic generation (HOHG) spectra obtained with the dipole and non-dipole Hamiltonians for all three electronic states. While, for the perpendicular orientation (θ = 90°), non-dipole forces attenuate the HOHG spectra for the initial ground and the second excited states. For the initial first excited state and orientation θ = 90°, the motion of nuclei considerably increases the HOHG yield within the dipole approximation, but decreases it partially beyond dipole approximation. It is shown that contribution of the motion of nuclei to the HOHG yield depends on the extent of the increase in the separation between nuclei. (paper)
High-order-harmonic generation in benzene with linearly and circularly polarized laser pulses
Wardlow, Abigail; Dundas, Daniel
2016-02-01
High-order-harmonic generation in benzene is studied using a mixed quantum-classical approach in which the electrons are described using time-dependent density-functional theory while the ions move classically. The interaction with both linearly and circularly polarized infrared (λ =800 nm) laser pulses of duration of ten cycles (26.7 fs) is considered. The effect of allowing the ions to move is investigated as is the effect of including self-interaction corrections to the exchange-correlation functional. Our results for circularly polarized pulses are compared with previous calculations in which the ions were kept fixed and self-interaction corrections were not included, while our results for linearly polarized pulses are compared with both previous calculations and experiment. We find that even for the short-duration pulses considered here, the ionic motion greatly influences the harmonic spectra. While ionization and ionic displacements are greatest when linearly polarized pulses are used, the response to circularly polarized pulses is almost comparable, in agreement with previous experimental results.
Structure/Processing Relationships of Highly Ordered Lead Salt Nanocrystal Superlattices
Hanrath, Tobias
2009-10-27
We investigated the influence of processing conditions, nanocrystal/substrate interactions and solvent evaporation rate on the ordering of strongly interacting nanocrystals by synergistically combining electron microscopy and synchrotron-based small-angle X-ray scattering analysis. Spin-cast PbSe nanocrystal films exhibited submicrometer-sized supracrystals with face-centered cubic symmetry and (001)s planes aligned parallel to the substrate. The ordering of drop-cast lead salt nanocrystal films was sensitive to the nature of the substrate and solvent evaporation dynamics. Nanocrystal films drop-cast on rough indium tin oxide substrates were polycrystalline with small grain size and low degree of orientation with respect to the substrate, whereas films drop-cast on flat Si substrates formed highly ordered face-centered cubic supracrystals with close-packed (111)s planes parallel to the substrate. The spatial coherence of nanocrystal films drop-cast in the presence of saturated solvent vapor was significantly improved compared to films drop-cast in a dry environment. Solvent vapor annealing was demonstrated as a postdeposition technique to modify the ordering of nanocrystals in the thin film. Octane vapor significantly improved the long-range order and degree of orientation of initially disordered or polycrystalline nanocrystal assemblies. Exposure to 1,2-ethanedithiol vapor caused partial displacement of surface bound oleic acid ligands and drastically degraded the degree of order in the nanocrystal assembly. © 2009 American Chemical Society.
Parallelization of a high-order accurate unstructured mesh finite-volume solver
International Nuclear Information System (INIS)
A generic solver eliminates the need to write new finite-volume codes for each type of physics. By separating the physics from the numerics of the solver, a modular design is achieved. New physics modules can easily be written with a minimal knowledge of the finite-volume method. A parallel solver allows simulation of complex physics on intricate domains in a timely manner by using numerous processors simultaneously. In this paper we describe the steps needed to adapt a high-order accurate unstructured mesh generic finite-volume solver to a parallel architecture. A message-passing approach is used which allows the solver to operate on a distributed memory system, such as a cluster of workstations. The reconstruction stencil is determined at the preprocessing stage and an appropriate parallel data structure for the solution is formed. Fluxes for faces on the partition boundary are evaluated by communicating the reconstruction coefficients to the adjacent processor. Good performance scalability is achieved for second and fourth-order accurate solutions on cell and vertex centered meshes. (authors)
A high-order public domain code for direct numerical simulations of turbulent combustion
Babkovskaia, N.; Haugen, N. E. L.; Brandenburg, A.
2011-01-01
A high-order scheme for direct numerical simulations of turbulent combustion is discussed. Its implementation in the massively parallel and publicly available PENCIL CODE is validated with the focus on hydrogen combustion. This is the first open source DNS code with detailed chemistry available. An attempt has been made to present, for the first time, the full set of evolution and auxiliary equations required for a complete description of single phase non-isothermal fluid dynamics with detailed chemical reactions. Ignition delay times (0D) and laminar flame velocities (1D) are calculated and compared with results from the commercially available Chemkin code. The scheme is verified to be fifth order in space. Upon doubling the resolution, a 32-fold increase in the accuracy of the flame front is demonstrated. Finally, also turbulent and spherical flame front velocities are calculated and the implementation of the non-reflecting so-called Navier-Stokes Characteristic Boundary Condition is validated in all three directions.
On fully multidimensional and high order non oscillatory finite volume methods, I
International Nuclear Information System (INIS)
A fully multidimensional flux formulation for solving nonlinear conservation laws of hyperbolic type is introduced to perform calculations on unstructured grids made of triangular or quadrangular cells. Fluxes are computed across dual median cells with a multidimensional 2D Riemann Solver (R2D Solver) whose intermediate states depend on either a three (on triangle R2DT solver) of four (on quadrangle, R2DQ solver) state solutions prescribed on the three or four sides of a gravity cell. Approximate Riemann solutions are computed via a linearization process of Roe's type involving multidimensional effects. Moreover, a monotonous scheme using stencil and central Lax-Friedrichs corrections on sonic curves are built in. Finally, high order accurate ENO-like (Essentially Non Oscillatory) reconstructions using plane and higher degree polynomial limitations are defined in the set up of finite element Lagrange spaces Pk and Qk for k≥0, on triangles and quadrangles, respectively. Numerical experiments involving both linear and nonlinear conservation laws to be solved on unstructured grids indicate the ability of our techniques when dealing with strong multidimensional effects. An application to Euler's equations for the Mach three step problem illustrates the robustness and usefulness of our techniques using triangular and quadrangular grids. (Author). 33 refs., 13 figs
Carrier Envelope Phase Controlled High-Order Harmonic Generation in Ultrashort Laser Pulse
Institute of Scientific and Technical Information of China (English)
WANG Bing-Bing; CHEN Jing; LIU Jie; LI Xiao-Feng; FU Pan-Ming
2005-01-01
@@ We investigate the carrier envelope phase (CEP) effects on high-order harmonic generation (HHG) in ultrashort pulses with the pulse duration 2.5fs when the laser intensity is high enough so that the initial state is ionized effectively during the laser pulse but remains about 20% population at the end of the laser pulse. We find that the ionization process of the initial state is very sensitive to the CEP during the laser pulse. The ionization process of the initial state determines the continuum state population and hence influences dramatically the weights of the classical trajectories that contribute to HHG. In such a case we can not predict the cutoff and the structure of the harmonic spectrum only by the number and the kinetic energy of the classical trajectories. The harmonic spectrum exhibits abundant characters for different CEP cases. As a result, we can control the cutoff frequency and the plateau structure of the harmonic spectrum with CEP by controlling the time behaviour of the ionization of the initial state.
Quantum interference during high-order harmonic generation from aligned molecules
Kanai, Tsuneto; Minemoto, Shinichirou; Sakai, Hirofumi
2005-05-01
High-order harmonic generation (HHG) from atoms and molecules offers potential application as a coherent ultrashort radiation source in the extreme ultraviolet and soft X-ray regions. In the three-step model of HHG, an electron tunnels out from the atom and may recombine with the parent ion (emitting a high-energy photon) after undergoing laser-driven motion in the continuum. Aligned molecules can be used to study quantum phenomena in HHG associated with molecular symmetries; in particular, simultaneous observations of both ion yields and harmonic signals under the same conditions serve to disentangle the contributions from the ionization and recombination processes. Here we report evidence for quantum interference of electron de Broglie waves in the recombination process of HHG from aligned CO2 molecules. The interference takes place within a single molecule and within one optical cycle. Characteristic modulation patterns of the harmonic signals measured as a function of the pump-probe delay are explained with simple formulae determined by the valence orbital of the molecules. We propose that simultaneous observations of both ion yields and harmonic signals can serve as a new route to probe the instantaneous structure of molecular systems.
Quantum interference during high-order harmonic generation from aligned molecules.
Kanai, Tsuneto; Minemoto, Shinichirou; Sakai, Hirofumi
2005-05-26
High-order harmonic generation (HHG) from atoms and molecules offers potential application as a coherent ultrashort radiation source in the extreme ultraviolet and soft X-ray regions. In the three-step model of HHG, an electron tunnels out from the atom and may recombine with the parent ion (emitting a high-energy photon) after undergoing laser-driven motion in the continuum. Aligned molecules can be used to study quantum phenomena in HHG associated with molecular symmetries; in particular, simultaneous observations of both ion yields and harmonic signals under the same conditions serve to disentangle the contributions from the ionization and recombination processes. Here we report evidence for quantum interference of electron de Broglie waves in the recombination process of HHG from aligned CO2 molecules. The interference takes place within a single molecule and within one optical cycle. Characteristic modulation patterns of the harmonic signals measured as a function of the pump-probe delay are explained with simple formulae determined by the valence orbital of the molecules. We propose that simultaneous observations of both ion yields and harmonic signals can serve as a new route to probe the instantaneous structure of molecular systems. PMID:15917803
High-order harmonic generation enhanced by x rays from free-electron lasers
Buth, Christian; Kohler, Markus C.; He, Feng; Hatsagortsyan, Karen Z.; Ullrich, Joachim; Keitel, Christoph H.
2012-06-01
We theoretically examine high-order harmonic generation (HHG), by an intense near-infrared (nir) laser, in the light of the emerging, intense x-ray free electron lasers (FELs) which have started to revolutionize x-ray science. We present two theories based on modified three-step models of HHG. Once, we combine HHG with resonant x-ray excitation of a core electron into the transient valence vacancy that is created in the course of the HHG process via tunnel ionization (first step of HHG) by the nir light. When the continuum electron is driven back to the parent ion, a recombination with the valence and the core hole may occur. Modified HHG spectra are determined and analyzed for krypton on the 3d ->4p resonance and for neon on the 1s ->2p resonance. Another time, we examine HHG where tunnel ionization by the nir light is replaced by direct x-ray ionization of a core electron. We use the boosted HHG radiation from 1s electrons of neon to predict single attosecond pulses in the kiloelectronvolt regime. For both presented schemes, we find substantial HHG yield from the recombination of the continuum electron with the core hole. Our research brings the capabilities of HHG-based sources to FELs.
Exploring the high-order harmonic generation from Rydberg states with a fixed Keldysh parameter
Ata Bleda, Erdi; Yavuz, Ilhan; Altun, Zikri; Topcu, Turker
2012-06-01
The commonly adopted viewpoint that the Keldysh parameter γ determines the dynamical regime of ionization in strong field physics has long been demonstrated to be a misleading one. One can then ask what happens in strong field ionization as relevant parameters, such as laser intensity and frequency, are varied while keeping γ fixed. We present results from our simulations of high-order harmonic generation (HHG) from Rydberg states of a hydrogen atom. We calculate high harmonic spectra from various initial states with n up to 42, where the laser intensities and the frequencies are scaled from those for n=1 in order to maintain a fixed Keldysh parameter γthree-step model for n=1. However, a secondary cut-off structure forms below this, which moves to lower harmonics as n is increased. This second cut-off splits the plateau into two regions, one higher in yield and below the second cut-off, and the second with lower yield following it. We further investigate the final n-distributions for some of the interesting cases to elucidate the physical mechanism leading to this structure
Martínez-Fonseca, Nadhynee; Castañeda, Luis Ángel; Uranga, Agustín; Luviano-Juárez, Alberto; Chairez, Isaac
2016-05-01
This study addressed the problem of robust control of a biped robot based on disturbance estimation. Active disturbance rejection control was the paradigm used for controlling the biped robot by direct active estimation. A robust controller was developed to implement disturbance cancelation based on a linear extended state observer of high gain class. A robust high-gain scheme was proposed for developing a state estimator of the biped robot despite poor knowledge of the plant and the presence of uncertainties. The estimated states provided by the state estimator were used to implement a feedback controller that was effective in actively rejecting the perturbations as well as forcing the trajectory tracking error to within a small vicinity of the origin. The theoretical convergence of the tracking error was proven using the Lyapunov theory. The controller was implemented by numerical simulations that showed the convergence of the tracking error. A comparison with a high-order sliding-mode-observer-based controller confirmed the superior performance of the controller using the robust observer introduced in this study. Finally, the proposed controller was implemented on an actual biped robot using an embedded hardware-in-the-loop strategy. PMID:26928517
Energy Technology Data Exchange (ETDEWEB)
Mattingly, J.K.
2001-03-08
The development of high order statistical analyses applied to measurements of the temporal evolution of fission chain-reactions is described. These statistics are derived via application of Bayes' rule to conditional probabilities describing a sequence of events in a fissile system beginning with the initiation of a chain-reaction by source neutrons and ending with counting events in a collection of neutron-sensitive detectors. Two types of initiating neutron sources are considered: (1) a directly observable source introduced by the experimenter (active initiation), and (2) a source that is intrinsic to the system and is not directly observable (passive initiation). The resulting statistics describe the temporal distribution of the population of prompt neutrons in terms of the time-delays between members of a collection (an n-tuplet) of correlated detector counts, that, in turn, may be collectively correlated with a detected active source neutron emission. These developments are a unification and extension of Rossi-a, pulsed neutron, and neutron noise methods, each of which measure the temporal distribution of pairs of correlated events, to produce a method that measures the temporal distribution of n-tuplets of correlated counts of arbitrary dimension n. In general the technique should expand present capabilities in the analysis of neutron counting measurements.
Application of a sensitivity analysis technique to high-order digital flight control systems
Paduano, James D.; Downing, David R.
1987-01-01
A sensitivity analysis technique for multiloop flight control systems is studied. This technique uses the scaled singular values of the return difference matrix as a measure of the relative stability of a control system. It then uses the gradients of these singular values with respect to system and controller parameters to judge sensitivity. The sensitivity analysis technique is first reviewed; then it is extended to include digital systems, through the derivation of singular-value gradient equations. Gradients with respect to parameters which do not appear explicitly as control-system matrix elements are also derived, so that high-order systems can be studied. A complete review of the integrated technique is given by way of a simple example: the inverted pendulum problem. The technique is then demonstrated on the X-29 control laws. Results show linear models of real systems can be analyzed by this sensitivity technique, if it is applied with care. A computer program called SVA was written to accomplish the singular-value sensitivity analysis techniques. Thus computational methods and considerations form an integral part of many of the discussions. A user's guide to the program is included. The SVA is a fully public domain program, running on the NASA/Dryden Elxsi computer.
A High Order Finite Difference Scheme with Sharp Shock Resolution for the Euler Equations
Gerritsen, Margot; Olsson, Pelle
1996-01-01
We derive a high-order finite difference scheme for the Euler equations that satisfies a semi-discrete energy estimate, and present an efficient strategy for the treatment of discontinuities that leads to sharp shock resolution. The formulation of the semi-discrete energy estimate is based on a symmetrization of the Euler equations that preserves the homogeneity of the flux vector, a canonical splitting of the flux derivative vector, and the use of difference operators that satisfy a discrete analogue to the integration by parts procedure used in the continuous energy estimate. Around discontinuities or sharp gradients, refined grids are created on which the discrete equations are solved after adding a newly constructed artificial viscosity. The positioning of the sub-grids and computation of the viscosity are aided by a detection algorithm which is based on a multi-scale wavelet analysis of the pressure grid function. The wavelet theory provides easy to implement mathematical criteria to detect discontinuities, sharp gradients and spurious oscillations quickly and efficiently.
Implicit high-order method for calculating rarefied gas flow in a planar microchannel
International Nuclear Information System (INIS)
An efficient numerical algorithm for calculating rarefied gas flows in planar microchannels on the basis of the Boltzmann kinetic equation with the linearized S-model collision integral is presented. The algorithm consists of a high-order spatial discretisation on unstructured meshes, conservative procedure to calculate macroscopic quantities and efficient one-step implicit time evolution method. It therefore works across all flow regimes from the free-molecular to nearly continuum ones and provides rapid convergence to steady state solutions. The parallel implementation is provided via MPI programming paradigm. The performance of the method is illustrated by computing the flow for length to the width ratios for up to 103 in the wide range of Knudsen numbers. Numerical estimates of efficiency of implicit time marching and parallel performance as well as convergence studies in both physical and velocity spaces are provided. The end effects and other essentially two-dimensional features of the flow are analysed and a detailed comparison with the case of an infinitely long channel is carried out. The presented numerical data can be used as reference for future studies of nonlinear flows as well as for comparison with other numerical approaches and flow models.
Focused Wave Properties Based on A High Order Spectral Method with A Non-Periodic Boundary
Institute of Scientific and Technical Information of China (English)
李金宣; 柳淑学
2015-01-01
In this paper, a numerical model is developed based on the High Order Spectral (HOS) method with a non-periodic boundary. A wave maker boundary condition is introduced to simulate wave generation at the incident boundary in the HOS method. Based on the numerical model, the effects of wave parameters, such as the assumed focused amplitude, the central frequency, the frequency bandwidth, the wave amplitude distribution and the directional spreading on the surface elevation of the focused wave, the maximum generated wave crest, and the shifting of the focusing point, are numerically investigated. Especially, the effects of the wave directionality on the focused wave properties are emphasized. The numerical results show that the shifting of the focusing point and the maximum crest of the wave group are dependent on the amplitude of the focused wave, the central frequency, and the wave amplitude distribution type. The wave directionality has a definite effect on multidirectional focused waves. Generally, it can even out the difference between the simulated wave amplitude and the amplitude expected from theory and reduce the shifting of the focusing points, implying that the higher order interaction has an influence on wave focusing, especially for 2D wave. In 3D wave groups, a broader directional spreading weakens the higher nonlinear interactions.
Effect of Tin+ defects on electrochemical properties of highly-ordered titania nanotube arrays
International Nuclear Information System (INIS)
In this paper, highly-ordered TiO2 nanotube (TNT) electrodes fabricated by anodization at 20 V in 0.1 M F--based solution were annealed in O2, N2 and CO respectively. The surface properties of the TiO2 electrodes after annealing treatment by different gases were studied by means of photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the TNT electrodes were investigated by cyclic voltammetry, steady-state polarization and photocurrent response measurements. The results showed that Tin+ (n = 0-3) cations and oxygen vacancies existed in the TNT electrode after annealing in CO, leading to a very efficient electron transfer rate of 1.34 x 10-3 cm/s. Steady-state polarization measurement and photocurrent response demonstrated that the electrode potential of oxygen evolution reaction (OER) reduced by 20% and the photocurrent response increased by 50% for CO-annealed TNT electrode compared with O2-annealed TNT electrode.
Udal'tsov, Alexander V.; Bolshakova, Anastasia V.; Vos, Johannes G.
2014-05-01
Large-scale aggregates assembled from protonated meso-tetraphenylporphine (TPP) dimers and water have been investigated by IR and resonance Raman spectroscopy and also by scanning electron microscopy (SEM). It was found that the properties of water confined in the aggregates depend on the physical state of the support. When the aggregates were deposited on a solid CaF2 plate, they showed properties consistent with a quasi-crystalline structure. But when the aggregates were dispersed in oil, their IR characteristics were different; the vibration bands of the confined water were like those of water in liquid state. A doublet at about 1000 cm-1, components of which have been attributed to specific vibrations of H3O+ and H2O bound in the structure of water-porphyrin dimeric complex, was found in IR and resonance Raman spectra (λex = 441.6 nm) of protonated TPP aggregates. This doublet indicates the hydrogen ion involving in the vibrational system of water-porphyrin dimeric complex with hydrogen bonding by similar way as in so-called Zundel cation. The resonance Raman spectrum shows evidence for proton sharing between protonated water dimer and N groups of the pyrrole rings. SEM results indicate that the large-scale aggregates of the protonated porphyrin possess highly ordered structure, are only observed when using extremely pure water.
Exploration of laser-driven electron-multirescattering dynamics in high-order harmonic generation.
Li, Peng-Cheng; Sheu, Yae-Lin; Jooya, Hossein Z; Zhou, Xiao-Xin; Chu, Shih-I
2016-01-01
Multiple rescattering processes play an important role in high-order harmonic generation (HHG) in an intense laser field. However, the underlying multi-rescattering dynamics are still largely unexplored. Here we investigate the dynamical origin of multiple rescattering processes in HHG associated with the odd and even number of returning times of the electron to the parent ion. We perform fully ab initio quantum calculations and extend the empirical mode decomposition method to extract the individual multiple scattering contributions in HHG. We find that the tunneling ionization regime is responsible for the odd number times of rescattering and the corresponding short trajectories are dominant. On the other hand, the multiphoton ionization regime is responsible for the even number times of rescattering and the corresponding long trajectories are dominant. Moreover, we discover that the multiphoton- and tunneling-ionization regimes in multiple rescattering processes occur alternatively. Our results uncover the dynamical origin of multiple rescattering processes in HHG for the first time. It also provides new insight regarding the control of the multiple rescattering processes for the optimal generation of ultrabroad band supercontinuum spectra and the production of single ultrashort attosecond laser pulse. PMID:27596056
Role of high-order aberrations in senescent changes in spatial vision
Energy Technology Data Exchange (ETDEWEB)
Elliot, S; Choi, S S; Doble, N; Hardy, J L; Evans, J W; Werner, J S
2009-01-06
The contributions of optical and neural factors to age-related losses in spatial vision are not fully understood. We used closed-loop adaptive optics to test the visual benefit of correcting monochromatic high-order aberrations (HOAs) on spatial vision for observers ranging in age from 18-81 years. Contrast sensitivity was measured monocularly using a two-alternative forced choice (2AFC) procedure for sinusoidal gratings over 6 mm and 3 mm pupil diameters. Visual acuity was measured using a spatial 4AFC procedure. Over a 6 mm pupil, young observers showed a large benefit of AO at high spatial frequencies, whereas older observers exhibited the greatest benefit at middle spatial frequencies, plus a significantly larger increase in visual acuity. When age-related miosis is controlled, young and old observers exhibited a similar benefit of AO for spatial vision. An increase in HOAs cannot account for the complete senescent decline in spatial vision. These results may indicate a larger role of additional optical factors when the impact of HOAs is removed, but also lend support for the importance of neural factors in age-related changes in spatial vision.
Development of a multi-block high-order DNS code for turbulent flow simulations
International Nuclear Information System (INIS)
A high-order finite-differences direct numerical simulation code is developed for studying turbulent flows over complex geometries. The solver uses a global mapping based multi-block arrangement, with each block consisting of a structured mesh and the adjacent blocks overlapping each other along the interfaces. The physical bounds of interfaces are determined by using a pre-processing, and a pre-compiler is developed to reduce the computational costs by simplifying the expensive Jacobian calculations. The code is validated for several benchmark tests including free-stream preservation on a single-block wavy grid. For multi-block application, simulation of a square jet in a turbulent cross flow has been performed. The flow conditions are Reynolds number Re∞ = 1000, based on the free-stream quantities and the jet exit width, and a jet to a cross flow velocity ratio of R = 0.5, 1.5, respectively. A counter-rotating vortex pair has been captured downstream of the jet exit and it was also found that the streamwise and the spanwise mean velocity profiles are in reasonable good agreements with available experimental measurements. However, some discrepancies are observed in other flow statistics such as the normal mean velocity and the kinetic energy distributions, and they are probably due to the low Reynolds number effect of the simulation.
Role of quantum trajectory in high-order harmonic generation in the Keldysh multiphoton regime.
Li, Peng-Cheng; Jiao, Yuan-Xiang; Zhou, Xiao-Xin; Chu, Shih-I
2016-06-27
We present a systematic study of spectral and temporal structure of high-order harmonic generation (HHG) by solving accurately the time-dependent Schrödinger equation for a hydrogen atom in the multiphoton regime where the Keldysh parameter is greater unity. Combining with a time-frequency transform and an extended semiclassical analysis, we explore the role of quantum trajectory in HHG. We find that the time-frequency spectra of the HHG plateau near cutoff exhibit a decrease in intensity associated with the short- and long-trajectories when the ionization process is pushed from the multiphoton regime into the tunneling regime. This implies that the harmonic emission spectra in the region of the HHG plateau near and before the cutoff are suppressed. To see the generality of this prediction, we also present a time-dependent density-functional theoretical study of the effect of correlated multi-electron responses on the spectral and temporal structure of the HHG plateau of the Ar atom. PMID:27410589
Bayesian Modeling of ChIP-chip Data Through a High-Order Ising Model
Mo, Qianxing
2010-01-29
ChIP-chip experiments are procedures that combine chromatin immunoprecipitation (ChIP) and DNA microarray (chip) technology to study a variety of biological problems, including protein-DNA interaction, histone modification, and DNA methylation. The most important feature of ChIP-chip data is that the intensity measurements of probes are spatially correlated because the DNA fragments are hybridized to neighboring probes in the experiments. We propose a simple, but powerful Bayesian hierarchical approach to ChIP-chip data through an Ising model with high-order interactions. The proposed method naturally takes into account the intrinsic spatial structure of the data and can be used to analyze data from multiple platforms with different genomic resolutions. The model parameters are estimated using the Gibbs sampler. The proposed method is illustrated using two publicly available data sets from Affymetrix and Agilent platforms, and compared with three alternative Bayesian methods, namely, Bayesian hierarchical model, hierarchical gamma mixture model, and Tilemap hidden Markov model. The numerical results indicate that the proposed method performs as well as the other three methods for the data from Affymetrix tiling arrays, but significantly outperforms the other three methods for the data from Agilent promoter arrays. In addition, we find that the proposed method has better operating characteristics in terms of sensitivities and false discovery rates under various scenarios. © 2010, The International Biometric Society.
Role of elastic scattering in high-order above threshold ionization
Chen, Zhang-Jin; Ye, Jian-Mian; Xu, Yang-Bing
2015-10-01
We investigate the target and intensity dependence of plateau in high-order above threshold ionization (HATI) by simulating the two-dimensional (2D) momentum distributions and the energy spectra of photoelectrons in HATI of rare gas atoms through using the quantitative rescattering model. The simulated results are compared with the existing experimental measurements. It is found that the slope of the plateau in the HATI photoelectron energy spectrum highly depends on the structure of elastic scattering differential cross section (DCS) of laser-induced returning electron with its parent ion. The investigations of the long- and short-range potential effects in the DCSs reveal that the short-range potential, which reflects the structure of the target, plays an essential role in generating the HATI photoelectron spectra. Project supported by the National Natural Science Foundation of China (Grant No. 11274219), the STU Scientific Research Foundation for Talents, and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, China.
Wu, Chwan-Hwa; Roland, David A.
1991-08-01
In this paper a high-order bidirectional associative memory (HOBAM) based image recognition system and a dynamically reconfigurable multiprocessor system that achieves real- time response are reported. The HOBAM has been utilized to recognize corrupted images of human faces (with hats, glasses, masks, and slight translation and scaling effects). In addition, the HOBAM, incorporated with edge detection techniques, has been used to recognize isolated objects within multiple-object images. Successful recognition rates have been achieved. A dynamically reconfigurable multiprocessor system and parallel software have been developed to achieve real-time response for image recognition. The system consists of Inmos transputers and crossbar switches (IMS C004). The communication links can be dynamically connected by circuit switching. This is the first time and the transputers and crossbar switches are reported to form a low-cost multiprocessor system connected by a switching network. Moreover, the switching network simplifies the design of the communication in parallel software without handling the message routing. Although the HOBAM is a fully connected network, the algorithm minimizes the amount of information that needs to be exchanged between processors using a data compression technique. The detailed design of both hardware and software are discussed in the paper. Significant speedup through parallel processing is accomplished. The architecture of the experimental system is a cost-effective design for an embedded system for neural network applications on computer vision.
Design and Simulation of a high order mode cavity bunch length monitor
Guo, Jiang; Luo, Qing
2015-01-01
A new bunch length measurement method based on high order mode cavity was proposed. Operating the harmonic cavity at mode TM0n0 so that its radius could be chosen, in order to break the limitation of beam pipe radius. A two-cavity bunch length monitor for linac of positron source was designed. Operating frequency selection for different bunch time structure was discussed and calculation formula of bunch length was deducted. Fundamental harmonic cavity resonates at 2.856 GHz with mode TM010. Fifth harmonic cavity resonates at 14.28 GHz (fifth harmonic of the linac fundamental frequency 2.856 GHz) with mode TM020, which could provide larger radius. Each cavity equipped with a filter to suppress unwanted signal. A simulation measurement was conducted in CST Particle Studio for beam current from 100-300mA, bunch length from 5-10ps, calculation results shows a fairly high accuracy (better than 3%). Several cases were discussed.
Radiation forces on a three-level atom in the high-order Bessel beams
Institute of Scientific and Technical Information of China (English)
Wang Zheng-Ling; Yin Jian-Ping
2008-01-01
The general expressions of the average dissipative and dipole forces acting on a A-configuration three-level atom in an arbitrary light field are derived by means of the optical Bloch equations based on the atomic density matrix elements, and the general properties of the average dissipative and dipole forces on a three-level atom in the linearly-polarized high-order Bessel beams (HBBs) are analysed. We find a resonant property (with two resonant peaks) of the dissipative force and a non-resonant property (with two pairs of non-resonant peaks) of the dipole force on the three-level atom, which are completely different from those on the two-level atom. Meanwhile we find a saturation effect of the average dissipative force in the HBB, which comes from the saturation of the upper-level population. Our study shows that the general expressions of the average dissipative and dipole forces on the three-level atom will be simplified to those of the two-level atom under the approximation of large detuning. Finally, we study the axial and azimuthal Doppler cooling of atoms in 1D optical molasses composed of two counter-propagating HBBs and discuss the azimuthal influence of the HBB on the Doppler cooling limit. We also find that the Doppler limit of atoms in the molasses HBB is slightly below the conventional Doppler limit of hг/(2кB) due to the orbital angular momentum lh of the HBB.
High-order harmonic generation by enhanced plasmonic near-fields in metal nanoparticules
Shaaran, T; Guichard, R; Pérez-Hernández, J A; Arnold, M; Siegel, T; Zaïr, A; Lewenstein, M
2013-01-01
We present theoretical investigations of high-order harmonic generation (HHG) resulting from the interaction of noble gases with localized surface plasmons. These plasmonic fields are produced when a metal nanoparticle is subject to a few-cycle laser pulse. The enhanced field, which largely depends on the geometrical shape of the metallic structure, has a strong spatial dependency. We demonstrate that the strong non-homogeneity of this laser field plays an important role in the HHG process and leads to a significant increase of the harmonic cut-off energy. In order to understand and characterize this new feature, we include the functional form of the laser electric field obtained from recent attosecond streaking experiments [F. S{\\"u}{\\ss}mann and M. F. Kling, Proc. of SPIE, {\\bf Vol. 8096}, 80961C (2011)] in the time dependent Schr\\"odinger equation (TDSE). By performing classical simulations of the HHG process we show consistency between them and the quantum mechanical predictions. These allow us to underst...
Phase properties of the cut-off high-order harmonics
Khokhlova, M A
2015-01-01
The cut-off regime of high-order harmonic generation (HHG) by atoms in an intense laser field is studied numerically and analytically. We find that the cut-off regime is characterized by equal dephasing between the successive harmonics. The change of the harmonic phase-locking when HHG evolves from the cut-off to the plateau regime determines the optimal bandwidth of the spectral region which should be used for attosecond pulse generation via amplitude gating technique. The cut-off regime is also characterized by a linear dependence of the harmonic phase on the fundamental intensity. The proportionality coefficient grows as the cube of the fundamental wavelength, thus this dependence becomes very important for the HHG by mid-infrared fields. Moreover, for every high harmonic there is a {\\it range} of laser intensities providing the generation in the cut-off regime and the atomic response magnitude in this regime can be greater than that in the plateau regime. Thus the cut-off regime substantially contributes ...
Directory of Open Access Journals (Sweden)
Reuter John E
2003-06-01
Full Text Available Abstract Background The complex and characteristic structures of dendrites are a crucial part of the neuronal architecture that underlies brain function, and as such, their development has been a focal point of recent research. It is generally believed that dendritic development is controlled by a combination of endogenous genetic mechanisms and activity-dependent mechanisms. Therefore, it is of interest to test the relative contributions of these two types of mechanisms towards the construction of specific dendritic trees. In this study, we make use of the highly complex Vertical System (VS of motion sensing neurons in the lobula plate of the Drosophila visual system to gauge the importance of visual input and synaptic activity to dendritic development. Results We find that the dendrites of VS1 neurons are unchanged in dark-reared flies as compared to control flies raised on a 12 hour light, 12 hour dark cycle. The dendrites of these flies show no differences from control in dendrite complexity, spine number, spine density, or axon complexity. Flies with genetically ablated eyes show a slight but significant reduction in the complexity and overall length of VS1 dendrites, although this effect may be due to a reduction in the overall size of the dendritic field in these flies. Conclusions Overall, our results indicate no role for visual experience in the development of VS dendrites, while spontaneous activity from photoreceptors may play at most a subtle role in the formation of fully complex dendrites in these high-order visual processing neurons.
Modeling fragmentation with new high order finite element technology and node splitting
Olovsson, Lars; Limido, Jérôme; Lacome, Jean-Luc; Grønsund Hanssen, Arve; Petit, Jacques
2015-09-01
The modeling of fragmentation has historically been linked to the weapons industry where the main goal is to optimize a bomb or to design effective blast shields. Numerical modeling of fragmentation from dynamic loading has traditionally been modeled by legacy finite element solvers that rely on element erosion to model material failure. However this method results in the removal of too much material. This is not realistic as retaining the mass of the structure is critical to modeling the event correctly. We propose a new approach implemented in the IMPETUS AFEA SOLVER® based on the following: New High Order Finite Elements that can easily deal with very large deformations; Stochastic distribution of initial damage that allows for a non homogeneous distribution of fragments; and a Node Splitting Algorithm that allows for material fracture without element erosion that is mesh independent. The approach is evaluated for various materials and scenarios: -Titanium ring electromagnetic compression; Hard steel Taylor bar impact, Fused silica Taylor bar impact, Steel cylinder explosion, The results obtained from the simulations are representative of the failure mechanisms observed experimentally. The main benefit of this approach is good energy conservation (no loss of mass) and numerical robustness even in complex situations.
Gómez, José J. Arroyo; Zubieta, Carolina; Ferullo, Ricardo M.; García, Silvana G.
2016-02-01
The electrochemical formation of Au nanoparticles on a highly ordered pyrolytic graphite (HOPG) substrate using conventional electrochemical techniques and ex-situ AFM is reported. From the potentiostatic current transients studies, the Au electrodeposition process on HOPG surfaces was described, within the potential range considered, by a model involving instantaneous nucleation and diffusion controlled 3D growth, which was corroborated by the microscopic analysis. Initially, three-dimensional (3D) hemispherical nanoparticles distributed on surface defects (step edges) of the substrate were observed, with increasing particle size at more negative potentials. The double potential pulse technique allowed the formation of rounded deposits at low deposition potentials, which tend to form lines of nuclei aligned in defined directions leading to 3D ordered structures. By choosing suitable nucleation and growth pulses, one-dimensional (1D) deposits were possible, preferentially located on step edges of the HOPG substrate. Quantum-mechanical calculations confirmed the tendency of Au atoms to join selectively on surface defects, such as the HOPG step edges, at the early stages of Au electrodeposition.
A new high-order accurate continuous Galerkin method for linear elastodynamics problems
Idesman, Alexander V.
2007-07-01
A new high-order accurate time-continuous Galerkin (TCG) method for elastodynamics is suggested. The accuracy of the new implicit TCG method is increased by a factor of two in comparison to that of the standard TCG method and is one order higher than the accuracy of the standard time-discontinuous Galerkin (TDG) method at the same number of degrees of freedom. The new method is unconditionally stable and has controllable numerical dissipation at high frequencies. An iterative predictor/multi-corrector solver that includes the factorization of the effective mass matrix of the same dimension as that of the mass matrix for the second-order methods is developed for the new TCG method. A new strategy combining numerical methods with small and large numerical dissipation is developed for elastodynamics. Simple numerical tests show a significant reduction in the computation time (by 5 25 times) for the new TCG method in comparison to that for second-order methods, and the suppression of spurious high-frequency oscillations.