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Wave Frequency (wave + frequency)
Selected AbstractsScreening Breakdown in a Plasma by Two Laser Fields and Strong DC Magnetic FieldCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1 2005D. F. Miranda Abstract The effective static dielectric constant of an electron plasma system in the simultaneous presence of two electromagnetic waves and a strong DC magnetic field is calculated. It is found that as the difference ,, of the two electromagnetic wave frequencies matches the plasma frequency ,, a breakdown in screening occurs thereby increasing the plasma heating rate via the external fields due to inverse Bremmstrahlung. An application is made by considering the typical parameters of a hot plasma. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The stress dependent elastic properties of thermally induced microfractures in aeolian Rotliegend sandstoneGEOPHYSICAL PROSPECTING, Issue 3 2007Colin MacBeth ABSTRACT The impact of thermally induced microfractures on the stress-sensitive elastic wave properties of aeolian Rotliegend sandstone samples is analysed. It is found that to identify the effects of the microfracture contribution accurately, a correction must first be made to account for water loss (representing a mass loss of 4,6%) from the pore throats and clays due to the heating process, despite care being taken to ensure that the thermally fractured samples re-adsorb room moisture. Both the original and thermally fractured rocks are stress-sensitive at the ultrasonic wave frequencies of the laboratory. However, a distinct shift in the estimated distribution of internal rock compliance indicates that the population of thermal microfractures differs in nature from that caused solely by core-plug extraction damage. In particular, the ratio of normal to tangential compliance is observed to be higher for the thermally generated microfractures than for the broken grain-grain contacts created by extraction unloading. This can be explained by the intragranular thermal-fracture surfaces being smoother when compared to the intergranular boundaries. Mechanical hysteresis is observed between the up- and downgoing test cycles for both the original and, to a greater extent, the thermally fractured rock. This indicates that there is compaction-induced movement of the fractures in the samples during application of stress in the laboratory. [source] Contactless monitoring of Si substrate permittivity and resistivity from microwave to millimeter wave frequenciesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 11 2010A. Elhawil Abstract A contactless and nondestructive technique is employed for characterizing single-sided metallised silicon wafers. The reflection spectra are measured using a quasi-optical millmeter-wave setup in the frequency range 40,320 GHz. The results are compared with those provided by the coplanar waveguide method, in terms of accuracy and range of applicability. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2500,2505, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25524 [source] Iterative design of moth-eye antireflective surfaces at millimeter wave frequenciesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2010Mark S. Mirotznik Abstract A method for synthesizing broadband antireflective (AR) surfaces at millimeter wave frequencies is demonstrated. AR surfaces were formed by machining a multilayer subwavelength structures into nonabsorptive dielectrics. This created low-reflected energies (<,25 dB) over large bandwidths and incidence angles. Experimental results are provided demonstrating the validity of the method. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 561,568, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24973 [source] Photoinduced spin waves in Fe/AlGaAs (001) heterostructurePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2008H. B. Zhao Abstract Photoinduced spin waves are investigated for Fe films on AlGaAs (001) using the time resolved magneto-optical Kerr effect. We observe first and second order standing spin waves as well as uniform magnetization precession. The anisotropy fields and exchange stiffness constant are obtained from the field and azimuthal dependence of the spin wave frequencies using the Landau-Lifshitz-Gilbert equation. A comparison with spin wave resonance measurements reveals a more pronounced interface effect on the low order standing spin waves in thin films. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dispersion of Dust Acoustic Modes and Perturbations of Plasma Flux BalanceCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3 2007V. Tsytovich Abstract Previous considerations of dust acoustic waves is demonstrated to be inconsistent - the required equilibrium state for perturbations was not defined since balance of plasma fluxes was neglecting. The self-consistent treatment shows that plasma flux perturbations are accompanying any collective waves propagating in dusty plasmas and can play an important role in wave dispersion, wave damping and can create instabilities. This is illustrated by the derivation of dispersion relation for dust acoustic modes taking into account the plasma flux balances and plasma flux perturbations by waves. The result of this approach shows that the dust acoustic waves with linear dependence of wave frequency on the wave number exist only in restricted range of the wave numbers. Only for wave numbers larger than some critical wave number for low frequency modes the frequency can be have approximately a linear dependence on wave number and can be called as dust acoustic wave but the phase velocity of these waves is different from that which can be obtained neglecting the flux balance and depends on grain charge variations which are determined by the balance of fluxes. The presence of plasma fluxes previously neglected is the main typical feature of dusty plasmas. The dispersion relation in the range of small wave numbers is found to be mainly determined by the change of the plasma fluxes and is quite different from that of dust acoustic type, namely it is found to have the same form as the well known dispersion relation for the gravitational instability. This result proves in general way the existence of the collective grain attractions of negatively charged grains for for large distances between them and for any source of ionization. The attraction of grains found from dispersion relation of the dust acoustic branch coincides with that found previously for pair grain interactions using some models for the ionization source. For the existing experiments the effective Jeans length for such attraction is estimated to be about 8 , 10 times larger than the ion Debye length and the effective gravitational constant for the grain attraction is estimated to be several orders of magnitude larger than the usual gravitational constant. The grain attraction at large inter-grain distances described by the gravitationlike grain instability is considered as the simplest explanation for observed dust cloud clustering, formation of dust structures including the plasma crystals. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Trivelpiece-Gould mode produced gas-discharges in a diffusion-controlled regimeCONTRIBUTIONS TO PLASMA PHYSICS, Issue 3-4 2003H. Schlüter Abstract The study presents a numerical fluid-plasma model of waveguide discharges sustained by travelling azimuthallysymmetric Trivelpiece-Gould modes. The results describe weakly-magnetized (, , ,e) plasma production in a diffusion-controlled regime (, being the wave frequency, ,e the electron gyro-frequency). However, with respect to the influence of the external magnetic field on the transverse ambipolar-diffusion coefficient, cases of both weak and strong impact of the magnetic field are covered. In its electrodynamical part, the model involves detailed description of the behaviour of the Trivelpiece-Gould waves in radially-inhomogeneous collisional plasmas. The gas-discharge part of the model specifies plasma production in an argon gas. The results are for the self-consistent structure of the discharge composed out of the interrelated variations of wavenumber, space damping rate, plasma density, electron temperature and power absorbed on average by an electron. The analysis is in terms of influence of gas-pressure and magnetic-field changes. [source] Considerations of the discontinuous deformation analysis on wave propagation problemsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2009Jiong Gu Abstract In rock engineering, the damage criteria of the rock mass under dynamic loads are generally governed by the threshold values of wave amplitudes, such as the peak particle velocity and the peak particle acceleration. Therefore, the prediction of wave attenuation across fractured rock mass is important on assessing the stability and damage of rock mass under dynamic loads. This paper aims to investigate the applications of the discontinuous deformation analysis (DDA) for modeling wave propagation problems in rock mass. Parametric studies are carried out to obtain an insight into the influencing factors on the accuracy of wave propagations, in terms of the block size, the boundary condition and the incident wave frequency. The reflected and transmitted waves from the interface between two materials are also numerically simulated. To study the tensile failure induced by the reflected wave, the spalling phenomena are modeled under various loading frequencies. The numerical results show that the DDA is capable of modeling the wave propagation in jointed rock mass with a good accuracy. Copyright © 2009 John Wiley & Sons, Ltd. [source] A viscoelastic model for the dynamic response of soils to periodical surface water disturbanceINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2006P. C. Hsieh Abstract In many instances soils can be assumed to behave like viscoelastic materials during loading/unloading cycles, and this study is aimed at setting up a viscoelastic model to investigate the dynamic response of a porous soil layer of finite thickness under the effect of periodically linear water waves. The waves and homogeneous water are described by potential theory and the porous material is described by a viscoelastic model, which is modified from Biot's poroelastic theory (1956). The distributions of pore water pressures and effective stresses of various soils such as silt, sand, and gravel are demonstrated by employing the proposed viscoelastic model. The discrepancies of the dynamic response between the simulations of viscoelastic model and elastic model are found to be strongly dependent on the wave frequency. Copyright © 2006 John Wiley & Sons, Ltd. [source] Dual pulse intestinal electrical stimulation normalizes intestinal dysrhythmia and improves symptoms induced by vasopressin in fed state in dogsNEUROGASTROENTEROLOGY & MOTILITY, Issue 5 2007H. Qi Abstract, To assess effects of dual pulse intestinal electrical stimulation (DPIES) on intestinal dysrhythmia and motility, and symptoms induced by vasopressin in conscious dogs. The study was performed in three postprandial sessions (control; vasopressin; DPIES) in six dogs with two pairs of electrodes chronically implanted on the serosal surface of the proximal jejunum and with a chronic duodenal fistula. A manometric catheter was advanced into the small intestine via the intestinal cannula. Motility and intestinal slow waves were recorded. Symptoms were assessed. During vasopressin infusion, the percentage of normal intestinal slow wave frequency was decreased (P < 0.01), reflected as a significant increase in the percentage of both bradygastria and tachygastria; the motility index decreased (P < 0.01) and the symptom score increased (P < 0.01). In the session of DPIES, the percentage of normal slow wave frequency was recovered (P < 0.05 vs vasopressin), attributed to a reduction in both bradyarrhythmia and tachyarrhythmia; the symptom score was reduced (P < 0.05 vs vasopressin); the motility index was not significantly increased. These results suggest that vasopressin induces intestinal dysrhythmia and emetic symptoms and inhibits intestinal motility. Dual pulse intestinal electrical stimulation is capable of improving intestinal dysrhythmia and emetic symptoms but not impaired intestinal motility induced by vasopressin. [source] Surface integral methods for high-frequency electromagnetic scatteringPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2007M. Ganesh Surface integral equation based methods are advantageous for simulation of electromagnetic waves scattered by three dimensional obstacles, because they efficiently reduce the dimension of the problem and are robust for high-frequency problems. However, the cost of setting up the associated discretized dense linear systems is prohibitive due to evaluation of highly oscillatory magnetic and electric dipole surface integral operators using standard cubatures. The computational complexity of evaluating such integrals depends on the incident wave frequency, and the size and shape of the obstacles. In this work we discuss a surface integral reformulation of the scattering problem that involves evaluation of surface integrals with a highly oscillatory physical density, and discuss methods for efficient evaluation of such integrals for a class of smooth three dimensional scatterers whose diameter is a large multiple of the incident wavelength. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mitochondrial modulation of Ca2+ sparks and transient KCa currents in smooth muscle cells of rat cerebral arteriesTHE JOURNAL OF PHYSIOLOGY, Issue 3 2004Serguei Y. Cheranov Mitochondria sequester and release calcium (Ca2+) and regulate intracellular Ca2+ concentration ([Ca2+]i) in eukaryotic cells. However, the regulation of different Ca2+ signalling modalities by mitochondria in smooth muscle cells is poorly understood. Here, we investigated the regulation of Ca2+ sparks, Ca2+ waves and global [Ca2+]i by mitochondria in cerebral artery smooth muscle cells. CCCP (a protonophore; 1 ,m) and rotenone (an electron transport chain complex I inhibitor; 10 ,m) depolarized mitochondria, reduced Ca2+ spark and wave frequency, and elevated global [Ca2+]i in smooth muscle cells of intact arteries. In voltage-clamped (,40 mV) cells, mitochondrial depolarization elevated global [Ca2+]i, reduced Ca2+ spark amplitude, spatial spread and the effective coupling of sparks to large-conductance Ca2+ -activated potassium (KCa) channels, and decreased transient KCa current frequency and amplitude. Inhibition of Ca2+ sparks and transient KCa currents by mitochondrial depolarization could not be explained by a decrease in intracellular ATP or a reduction in sarcoplasmic reticulum Ca2+ load, and occurred in the presence of diltiazem, a voltage-dependent Ca2+ channel blocker. Ru360 (10 ,m), a mitochondrial Ca2+ uptake blocker, and lonidamine (100 ,m), a permeability transition pore (PTP) opener, inhibited transient KCa currents similarly to mitochondrial depolarization. In contrast, CGP37157 (10 ,m), a mitochondrial Na+,Ca2+ exchange blocker, activated these events. The PTP blockers bongkrekic acid and cyclosporin A both reduced inhibition of transient KCa currents by mitochondrial depolarization. These results indicate that mitochondrial depolarization leads to a voltage-independent elevation in global [Ca2+]i and Ca2+ spark and transient KCa current inhibition. Data also suggest that mitochondrial depolarization inhibits Ca2+ sparks and transient KCa currents via PTP opening and a decrease in intramitochondrial [Ca2+]. [source] Pacing of interstitial cells of Cajal in the murine gastric antrum: neurally mediated and direct stimulationTHE JOURNAL OF PHYSIOLOGY, Issue 2 2003Elizabeth A. H. Beckett Phase advancement of electrical slow waves and regulation of pacemaker frequency was investigated in the circular muscle layer of the gastric antra of wild-type and W/WV mice. Slow waves in the murine antrum of wild-type animals had an intrinsic frequency of 4.4 cycles min,1 and were phase advanced and entrained to a maximum of 6.3 cycles min,1 using 0.1 ms pulses of electrical field stimulation (EFS) (three pulses delivered at 3,30 Hz). Pacing of slow waves was blocked by tetrodotoxin (TTX) and atropine, suggesting phase advancement was mediated via intrinsic cholinergic nerves. Phase advancement and entrainment of slow waves via this mechanism was absent in W/WV mutants which lack intramuscular interstitial cells of Cajal (ICC-IM). These data suggest that neural regulation of slow wave frequency and regulation of smooth muscle responses to slow waves are mediated via nerve-ICC-IM interactions. With longer stimulation parameters (1.0,2.0 ms), EFS phase advanced and entrained slow waves in wild-type and W/WV animals. Pacing with 1,2 ms pulses was not inhibited by TTX or atropine. These data suggest that stimulation with longer pulse duration is capable of directly activating the pacemaker mechanism in ICC-MY networks. In summary, intrinsic excitatory neurons can phase advance and increase the frequency of antral slow waves. This form of regulation is mediated via ICC-IM. Longer pulse stimulation can directly activate ICC-MY in the absence of ICC-IM. [source] Effect of wave frequency of clinical electric shock: pain sensation and startle responseBEHAVIORAL INTERVENTIONS, Issue 2 2004P. C. Duker Contingent shock has been used in a number of studies to suppress health-threatening self-injurious behavior of individuals with mental retardation and autism. As sustained suppression is an issue of clinical concern, research into procedural variables of contingent shock is needed. As research on subjects who have mental retardation and who show self-injurious behavior is ethically impossible, we conducted research on healthy volunteers. In this study, we compared the effect of wave frequency (i.e. Hz) of electric shock on subjects' pain sensation and startle response. It was found that 60,Hz revealed a significantly stronger pain sensation rating than 30,Hz and that 90,Hz revealed a significantly stronger rating than 60,Hz. Also, the magnitude of subjects' startle response significantly increased as wave frequency increased from 30,Hz to 60,Hz and from 60 to 90,Hz. Copyright © 2004 John Wiley & Sons, Ltd. [source] Gastric electrical activity in patients with cholelithiasis undergoing laparoscopic cholecystectomy: A prospective controlled studyJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 6 2004SPIROS N SGOUROS Abstract Background:, The aim of the present study was to evaluate the effect of gallstone disease (GD) and laparoscopic cholecystectomy on gastric electrical activity of slow waves, which was recorded via transcutaneous electrogastrography (EGG). Methods:, Twenty-one consecutive patients (M/F: 12/9, 52.7 ± 15 years old) with GD and no previous history of abdominal operations or known disease affecting gastrointestinal motility were studied. The EGG was performed for 30 min prior to and 90 min after a standard meal, during a 4,6 month period prior to and after laparoscopic cholecystectomy. The percentile proportion of the three spectra of gastric slow waves frequency was studied, defined as follows: bradygastria, 1,2.1 cycles per min (c.p.m.); normogastria, 2.2,3.9 c.p.m.; and tachygastria, 4,9 c.p.m. The findings were compared to those of nine healthy subjects (M/F: 5/4, 49.5 ± 14.8 years old). Results:, No statistically significant difference was found in percentile distribution of bradygastria, normogastria and tachygastria, pre- or post-prandially, neither before or after laparoscopic cholecystectomy, nor between patients and controls. Conclusions:, Patients with GD do not exhibit differences in gastric electrical activity of slow waves in comparison to normal subjects and laparoscopic cholecystectomy does not alter gastric electrical activity. These findings suggest that cholelithiasis does not seem to cause dyspeptic symptoms due to gastric dysrythmias. [source] | ||||||||||||||||