High Frequency Terms Research Articles

A Parallel Method for Backward Parabolic Problems Based on the Laplace Transformation

A parallel method for time discretization of backward parabolic problems is proposed. The problem is reformulated to a set of Helmholtz‐type problems with a parameter on a suitably chosen contour in the complex plane. After solving the resulting elliptic equations, which can be solved in parallel, we obtain a regularized solution with high frequency terms cut off by the inverse Laplace transforms without requiring the knowledge of the eigenfunctions of the differential operator. Since the regularized solution is obtained without artificial perturbation and high frequency components of the noise are suppressed, the quality of the solution is improved significantly compared to those obtained by other methods. Two different numerical inversions of Laplace transforms, with an arbitrary high order of accuracy and spectral accuracy, respectively, are used. Error estimates and numerical examples are presented.

Design and fabrication of in situ UV-LIGA assembled robust nickel micro check valves for compact hydraulic actuators

Compact robust hydraulic actuators (pumps) are very important for space-related applications because of their capabilities in producing much larger forces per unit volume/mass than existing technologies. PZT stacks (pusher) have been widely identified for developing compact actuators (pump), but valves to match the inherent properties of PZT, in terms of high frequency (up to 100 kHz), load support (up to 100 MPa) and desired flow rate, are missing. The authors have developed novel robust solid nickel microvalve arrays using an in situ UV-LIGA assembling process. A high frequency and large pressure support capability has been realized analytically by elaborating the scaling law, in combination with a stiff material such as nickel. Large flow rate was realized by utilizing a microvalve array, instead of using a single valve. By doing this, all major requirements, in terms of frequency match, load support, as well as small amount of valve mass (payload), have been met. The reliability of the valve is assured by using a curved valve flap so that low stress can be maintained, in combination with a mechanical robust nickel valve stopper.

Effect of the magnetic field on the ferroelectric transition of KD 2PO 4 measured by a high resolution and super-sensitive differential scanning calorimeter

The magnetic effect on the ferroelectric transition of single crystalline KD 2PO 4 (DKDP) was measured by using a high resolution and super-sensitive differential scanning calorimeter (DSC) working in a magnetic bore. The transition temperature of KD 2PO 4 with the magnetic field of 5 T along a-axis and along c-axis was 5.6 ± 0.8 and 2.8 ± 0.9 mK, respectively, higher than that without the magnetic field. The calculated temperature shifts of the transition due to the magnetic field along a-axis and along c-axis using the magneto-Clapeyron equation and the data of magnetic susceptibility were negative values, being contradictory to the experimental results. These results demand to consider another contribution in magnetic susceptibility. The high frequency term of magnetic susceptibility due to molecular motions was considered to play an important role in order to explain the positive experimental values.

Building a protein name dictionary from full text: a machine learning term extraction approach

BackgroundThe majority of information in the biological literature resides in full text articles, instead of abstracts. Yet, abstracts remain the focus of many publicly available literature data mining tools. Most literature mining tools rely on pre-existing lexicons of biological names, often extracted from curated gene or protein databases. This is a limitation, because such databases have low coverage of the many name variants which are used to refer to biological entities in the literature.ResultsWe present an approach to recognize named entities in full text. The approach collects high frequency terms in an article, and uses support vector machines (SVM) to identify biological entity names. It is also computationally efficient and robust to noise commonly found in full text material. We use the method to create a protein name dictionary from a set of 80,528 full text articles. Only 8.3% of the names in this dictionary match SwissProt description lines. We assess the quality of the dictionary by studying its protein name recognition performance in full text.ConclusionThis dictionary term lookup method compares favourably to other published methods, supporting the significance of our direct extraction approach. The method is strong in recognizing name variants not found in SwissProt.

Proposal and design of a new SiC-emitter lateral NPM Schottky collector bipolar transistor on SOI for VLSI applications

A novel bipolar transistor structure, namely, a SiC emitter lateral NPM Schottky collector bipolar transistor (SCBT) with a silicon-on-insulator (SOI) substrate is explored using two-dimensional (2-D) simulation. A comprehensive comparison of the proposed structure with its equivalent Si lateral NPN BJT and an SiC emitter lateral NPN HBT is presented. Based on simulation results, the authors demonstrate for the first time that the proposed SiC emitter lateral NPM transistor shows superior performance in terms of high current gain and cut-off frequency, reduced collector resistance, negligible reverse recovery time and suppressed Kirk effect over its equivalent Si lateral NPN BJT and SiC emitter lateral NPN HBT. A simple fabrication process compatible with BiCMOS technology is also discussed.

Estimation of heterogeneous aquifer parameters from piezometric data using ridge functions and neural networks

Inverse modeling aims to estimate transmissivity and other parameters needed by distributed aquifer models, using piezometric measurements. While these parameters are highly variable in space, the two-dimensional aquifer area is essentially empty of measurements (“curse of dimensionality”). To address this problem, a representation of the two-dimensional transmissivity map based on ridge functions and neural networks is introduced and applied to inverse aquifer modeling. The proposed representation has good expressive power, i.e. it is concise and convergences quickly as the number of parameters are increased, and it is expected to express complex transmissivity variations with relatively few parameters which can be estimated from the piezometric measurements. A simple regularization that can dampen erratic high frequency terms in the estimated parameters is suggested. Several examples indicate that the proposed parameterization can handle diverse types of transmissivity variations while it is particularly suited when the true transmissivity map exhibits specific sorts of heterogeneity with large anisotropies or abrupt changes along lines.

SOME GENERAL EFFECTS OF STRONG HIGH-FREQUENCY EXCITATION: STIFFENING, BIASING AND SMOOTHENING

Mechanical high-frequency (HF) excitation provides a working principle behind many industrial and natural applications and phenomena. This paper concerns three particular effects of HF excitation, that may change the apparent characteristics of mechanical systems: (1) stiffening, by which the apparent linear stiffness associated with an equilibrium is changed, along with derived quantities such as stability and natural frequencies; (2) biasing by which the system is biased towards a particular state, static or dynamic, which does not exist or is unstable in the absence of the HF excitation; and (3) smoothening, referring to a tendency for discontinuities to be effectively “smeared out” by HF excitation. Illustrating first these effects for a few specific systems, analytical results are provided that quantify them for a quite general class of mechanical systems. This class covers systems that can be modelled by a finite number of second order ordinary differential equations, generally non-linear, with periodically oscillating excitation terms of high frequency and small amplitude. The results should be useful for understanding the effects in question in a broader perspective than is possible with specific systems, for calculating effects for specific systems using well-defined formulas, and for possibly designing systems that display prescribed characteristics in the presence of HF excitation.

Comparison of Results of Calculations and Measurements of DYSAF-tests, a research project to investigate safety limits of Derailment at High Speeds

Test runs have been carried out in Velim, Czech Republic, to analyse derailment conditions at higher speeds up to 160 kph. In the research program ‘DYSAF’ a test running gear was developed which enabled to test derailment of a wheelset in guiding and unloaded conditions. With the aid of a lateral force actuator static and dynamic Y/Q derailment situations were measured for different velocities and angle of attack. In this paper a comparison of test and simulation results of the multi body program MEDYNA is presented.Identifying the parameters of nominal wheel loads of the test running gear and friction coefficients in tread and flange simulation results show a very good and promising agreement for the compared signals. Only higher frequency terms are lacking. To include them dynamic properties of track, hydraulic device and wheel roundness have to be improved.Derailment simulation with a MBS tool is a possibility to analyse derailment cases and to develop safety criteria against derailment of railway vehicles. Necessary is a wheel-rail element, which can describe multi non-elliptic contact patches in tread and flange, which can describe creepages in curved contact patches and which uses an extended creep force theory for non-elliptic contact patches. The wheel-rail element of ArgeCare is such an element.

New Definition for the Celestial Pole and the Celestial Origin in the ICRS

AbstractTwo Resolutions have been submitted to the 24thGeneral Assembly of the IAU concerning the definition and use of the celestial pole of reference and the celestial origin. The aim of both resolutions is to provide new parameters for Earth rotation which are consistent with the properties of the International Celestial Reference System (ICRS), adopted from 1 January 1998 as the IAU celestial reference system. The definition of the parameters have also to be consistent with the precision and the temporal resolution of the current Earth rotation measurements as well as with the theory for nutation and polar motion at the microarcsecond level. This paper explains the basis of the resolutions as well as their practical application. One of the resolutions defines the “Celestial Intermediate Pole” (CIP) in order to replace the “Celestial Ephemeris Pole” (CEP) for the new IAU precession-nutation model; its specifies the way for taking into account the constant offset from the ICRS and the high frequency terms in polar motion and nutation. The other resolution recommends the use of the “non-rotating origin” (Guinot 1979) on the moving equator, for defining Earth rotation and UT1; it also recommends the use of the celestial and terrestrial coordinates of the CIP in the transformation from the celestial to the terrestrial systems.

Simultaneous liquid viscosity and density determination with piezoelectric unimorph cantilevers

We have examined both experimentally and theoretically a piezoelectric unimorph cantilever as a liquid viscosity-and-density sensor. The fabricated piezoelectric unimorph consisted of a PbO⋅ZrO2⋅TiO2 (PZT) layer on a thin stainless-steel plate. In addition to a driving electrode, a sensing electrode was placed on top of the PZT layer, permitting the direct measurement of the resonance frequency. The cantilever was tested using water–glycerol solutions of different compositions. In all three of the tested modes, the resonance frequency decreased while the width of the resonance peak increased with increasing glycerol content. To account for the liquid effect, we consider the cantilever as a sphere of radius R oscillating in a liquid. By including the high and low frequency terms in the induced mass and the damping coefficient of the liquid, we show that for a given liquid density and viscosity the oscillating-sphere model predicts a resonance frequency and peak width that closely agree with experiment. Furthermore, the viscosity and the density of a liquid have been determined simultaneously using the experimentally measured resonance frequency and peak width as inputs to the oscillating-sphere model. The calculated liquid viscosity and density closely agreed with the known values, indicating that our cantilever-based sensor is effective in determining viscosity and density, simultaneously. We also show that scaling analysis predicts an increase in the width of the resonance peak with decreasing cantilever size, an observation in agreement with the large peak widths observed for microcantilevers.

Effects of repeated atropine injection on heart rate variability in Thoroughbred horses.

To investigate the effects of repeated atropine injection on heart rate (HR) variability in resting Thoroughbred horses, two microg/ kg of atropine as parasympathetic nervous blockade was injected intravenously every 6 min to a total of 8 microg/kg after intravenous administration of 0.2 mg/kg of propranolol as sympathetic nervous blockade. We recorded electrocardiograms and obtained the HR, then evaluated variation in HR from the power spectrum in terms of low frequency (LF, 0.01-0.07 Hz) power and high frequency (HF, 0.07-0.6 Hz) power. Administration of atropine decreased parasympathetic nervous activity in a dose-dependent manner, affecting first the LF power, then the HF power and finally HR. These responses may provide valuable information for evaluating autonomic nervous activity in Thoroughbred horses.

A corpus-based approach to comparative evaluation of statistical term association measures

Statistical association measures have been widely applied in information retrieval research, usually employing a clustering of documents or terms on the basis of their relationships. Applications of the association measures for term clustering include automatic thesaurus construction and query expansion. This research evaluates the similarity of six association measures by comparing the relationship and behavior they demonstrate in various analyses of a test corpus. Analysis techniques include comparisons of highly ranked term pairs and term clusters, analyses of the correlation among the association measures using Pearson's correlation coefficient and MDS mapping, and an analysis of the impact of a term frequency on the association values by means of z-score. The major findings of the study are as follows: First, the most similar association measures are mutual information and Yule's coefficient of colligation Y, whereas cosine and Jaccard coefficients, as well as χ2 statistic and likelihood ratio, demonstrate quite similar behavior for terms with high frequency. Second, among all the measures, the χ2 statistic is the least affected by the frequency of terms. Third, although cosine and Jaccard coefficients tend to emphasize high frequency terms, mutual information and Yule's Y seem to overestimate rare terms.

A corpus‐based approach to comparative evaluation of statistical term association measures

Statistical association measures have been widely applied in information retrieval research, usually employing a clustering of documents or terms on the basis of their relationships. Applications of the association measures for term clustering include automatic thesaurus construction and query expansion. This research evaluates the similarity of six association measures by comparing the relationship and behavior they demonstrate in various analyses of a test corpus. Analysis techniques include comparisons of highly ranked term pairs and term clusters, analyses of the correlation among the association measures using Pearson's correlation coefficient and MDS mapping, and an analysis of the impact of a term frequency on the association values by means of z-score. The major findings of the study are as follows: First, the most similar association measures are mutual information and Yule's coefficient of colligation Y, whereas cosine and Jaccard coefficients, as well as χ2 statistic and likelihood ratio, demonstrate quite similar behavior for terms with high frequency. Second, among all the measures, the χ2 statistic is the least affected by the frequency of terms. Third, although cosine and Jaccard coefficients tend to emphasize high frequency terms, mutual information and Yule's Y seem to overestimate rare terms.

When Ottoman is Easier than Chair: An Inverse Frequency Effect in Jargon Aphasia

This paper presents evidence of an inverse frequency effect in jargon aphasia. The subject (JP) showed a pre-disposition for low frequency word production on a range of tasks, including picture naming, sentence completion and naming in categories. Her real word errors were also striking, in that these tended to be lower in frequency than the target. Reading data suggested that the inverse frequency effect was present only when production was semantically mediated. It was therefore hypothesised that the effect was at least partly due to the semantic characteristics of low frequency items. Some support for this was obtained from a comprehension task showing that JP's understanding of low frequency terms, which she often produced as errors, was superior to her understanding of high frequency terms. Possible explanations for these findings are considered.

Similarity measurement using term negative weight and its application to word similarity

A “term weighting” is a useful technique for keyword extraction and document classification. The traditional approach depends on high frequency terms, called positive weight ( PW) function. This paper presents a new weighting method that depends on low frequency terms, called negative weight ( NW) function. In this paper word similarity for typical verbs and objects is focused as an example for the application field. Negative weighted inverse verb frequency ( NWIVF) function is well defined in this study and new similarity measurement is presented by combining the NWIVF and PWIVF ( positive weighted inverse verb frequency) functions. The proposed method is applied to 11,000 relationships between verbs and nouns extracted from a large tagged corpus. By using this new method both recall and precision have improved by 33% and 18% respectively, over the positive weight method.

Optimal signal multi-resolution by genetic algorithms to support artificial neural networks for exchange-rate forecasting

Detecting the features of significant patterns from historical data is crucial for good performance in time-series forecasting. Wavelet analysis, which processes information effectively at different scales, can be very useful for feature detection from complex and chaotic time series. In particular, the specific local properties of wavelets can be useful in describing the signals with discontinuous or fractal structure in financial markets. It also allows the removal of noise-dependent high frequencies, while conserving the signal bearing high frequency terms of the signal. However, one of the most critical issues to be solved in the application of the wavelet analysis is to choose the correct wavelet thresholding parameters. If the threshold is small or too large, the wavelet thresholding parameters will tend to overfit or underfit the data. The threshold has so far been selected arbitrarily or by a few statistical criteria. This study proposes an integrated thresholding design of the optimal or near-optimal wavelet transformation by genetic algorithms (GAs) to represent a significant signal most suitable in artificial neural network models. This approach is applied to Korean won/US dollar exchange-rate forecasting. The experimental results show that this integrated approach using GAs has better performance than the other three wavelet thresholding algorithms (cross-validation, best basis selection and best level tree).

Multilevel Methods in Space and Time for the Navier--Stokes Equations

We investigate the discretization in time of numerical schemes based on multilevel spatial splittings for the two-dimensional periodic Navier--Stokes equations. The approximate solution is computed as the sum of a low frequency component and a high frequency one. These two terms are advanced in time using different stepsizes. We show improved stability conditions (with respect to the classical Galerkin method). We derive error estimates that indicate that the high frequency term can be integrated less often. We address implementation issues and show that the method should yield a significant gain in computing time.

Determination of quadrupolar spin coupling for spin 7/2 using two pulse sequences

The response of a spin 7/2 system subject to a first-order quadrupolar interaction and excited by two in-phase pulses separated by time delay τ is calculated ignoring high frequency terms. The results obtained are valid for any ratio of the quadrupolar coupling to the amplitude of an RF pulse. It is shown here that single- and multiple-quantum coherences developed during the first pulse can be detected at the end of the second pulse. Other pulse sequences with various phase cycling are also discussed. The results are applied to 51V nuclei in a single ferroelastic crystal of BiVO4.

Higher-order correction for rotating wave approximation, Rabi transformation, and its applications in the Jaynes-Cummings model

Taking into account the consistence of the quantum adiabatic approximation and the rotating wave approximation in essence, we propose a method to study the interaction between atom and radiation field in a quantized cavity systematically. By using the exact solution of Jaynes-Cummings model as the lowest-order approximation, the effect of high frequency terms on the dynamics of atom-cavity field system is studied analytically.

The complex envelope signal and an application to structural modal parameter estimation

Complex demodulation is a useful technique in fields such as communication, speech and seismic data processing. In this work, the complex demodulation technique is applied to the modal parameter estimation of mechanical systems. This method was developed for an efficient estimation of a dynamic system when impulse response measurements are truncated or estimating in the frequency domain is difficult. First, impulse responses of a structural system are measured in the time domain, then resonance frequencies are selected from its discrete Fourier transform. Next, the complex envelope of each mode is obtained by shifting the signal associated with the selected resonance frequency to zero frequency and filtering the remaining high frequency terms. When estimating the modal parameters from the obtained complex envelope of a specific mode, the so-called estimation and correction methods are used. A method of extracting parameters for a system having closely spaced modes is presented and discussed. The proposed method has been tested numerically and has many advantages over conventional frequency domain methods.