Static Amplitudes Research Articles

A Stochastic Wavelet Finite Element Method for 1D and 2D Structures Analysis

A stochastic finite element method based on B-spline wavelet on the interval (BSWI-SFEM) is presented for static analysis of 1D and 2D structures in this paper. Instead of conventional polynomial interpolation, the scaling functions of BSWI are employed to construct the displacement field. By means of virtual work principle and BSWI, the wavelet finite elements of beam, plate, and plane rigid frame are obtained. Combining the Monte Carlo method and the constructed BSWI elements together, the BSWI-SFEM is formulated. The constructed BSWI-SFEM can deal with the problems of structural response uncertainty caused by the variability of the material properties, static load amplitudes, and so on. Taking the widely used Timoshenko beam, the Mindlin plate, and the plane rigid frame as examples, numerical results have demonstrated that the proposed method can give a higher accuracy and a better constringency than the conventional stochastic finite element methods.

Nulls and side lobe levels control in a time modulated linear antenna array by optimizing excitations and element locations using RGA

In this paper a novel approach based on the Real coded Genetic Algorithm (RGA) is proposed to improve nulling performance as well as suppression of Side Lobe Level (SLL) of a Time Modulated Linear Antenna Arrays (TMLA). RGA adjusts the static excitation amplitudes as well as the location of each element from the origin to place deeper nulls in the desired direction. Three design examples are presented that illustrate the use of the RGA, and the optimization goal in each example is easily achieved.

A single objective approach for suppressing sideband radiations of ultra-low side lobe patterns in time-modulated antenna arrays

In this paper, a novel optimization method based on single objective, that is, minimization of sideband radiation (SBR) of ultra-low side lobe, narrow beam patterns in time modulated antenna arrays (TMAAs) is proposed. The proposed method utilizes the weighting vectors of the low side lobe Dolph-Chebyshev/Taylor series patterns as the dynamic excitation coefficients of the desired pattern at fundamental radiation. Differential evolution algorithm is employed to distribute the static amplitudes and switch-on time durations in such a way that in the optimization process, dynamic excitation distribution remains the same. Static amplitudes are perturbed in a predefined search range of (0.25, 1), whereas the weighted values of switch-on time durations are obtained by dividing dynamic excitation coefficients by static amplitudes. The technique greatly simplifies the difficulties of multi-objective TMAA synthesizing problem by reducing it to a single-objective optimization problem. Numerical examples for a 32-element linear array are presented to produce ultra low side lobe Taylor and Dolph-Chebyshev pattern with low value of maximum sideband radiation (SBRmax). The optimization results of the proposed method are also compared with those obtained by other optimization techniques, which have been reported previously.

DIFFERENTIAL EVOLUTION ALGORITHM FOR OPTIMIZING THE CONFLICTING PARAMETERS IN TIME-MODULATED LINEAR ARRAY ANTENNAS

In this paper, a new technique is proposed to optimize the con∞icting parameters like low value of maximum side lobe level (SLL), narrow beam-width of the main beam and low value of maximum sideband radiation level (SRL) of time-modulated linear antenna arrays (TMLAAs). The method is based on minimizing a multi-objective fltness function by using single-objective difierential evolution algorithm (DEA) technique. The method is applied to both uniformly excited TMLAA (UE-TMLAA) and non-uniformly excited TMLAA (NUE-TMLAA) to synthesize low side lobe optimum pattern at operating frequency by suppressing the sideband radiation level to a su-ciently low value. For UE-TMLAA only the switch- on time durations of the array elements and for NUE-TMLAA the switch-on time durations and the static amplitudes with predetermined dynamic range ratio (DRR) of static amplitudes are taken as the optimization parameters for the DEA. To show efiectiveness of the proposed approach, the single-objective DEA optimized results are compared with those obtained by other single objective and multi- objective techniques that has been reported previously. Also, flrst null beam width (FNBW) and half power beam width (HPBW) of the DEA optimized patterns at fundamental radiation are compared with those of the Dolph-Chebyshev (D-C) pattern of same SLL.

High temperature limit in static backgrounds

We prove that the hard thermal loop contribution to static thermal amplitudes can be obtained by setting all the external four-momenta to zero before performing the Matsubara sums and loop integrals. At the one-loop order we do an iterative procedure for all the one-particle irreducible one-loop diagrams, and at the two-loop order we consider the self-energy. Our approach is sufficiently general to the extent that it includes theories with any kind of interaction vertices, such as gravity in the weak field approximation, for $d$ space-time dimensions. This result is valid whenever the external fields are all bosonic.

Aeroelastic analysis and nonlinear dynamics of an elastically mounted wing

The response of an elastically mounted wing that is free to plunge and pitch, supported by nonlinear translational and torsional springs, and interacting with an incoming stream is analyzed. A tightly coupled model of the wing flow interaction is developed. A three-dimensional code based on the unsteady vortex lattice method is used for the prediction of the unsteady aerodynamic loads. The response of the wing shows a sequence of static and dynamic bifurcations and chaotic motions when increasing the flow speed. Pairs of stable solutions are observed over the different response regimes. The effects of the gust and structural nonlinearity on the wing's response are also investigated. The results show that gust may lead to jumps between the pairs of solutions for static and dynamic equilibrium responses without impacting the boundaries of the different response regimes. As for the effect of the structural nonlinearity, increasing the nonlinear coefficient of the stiffness of the torsional spring yields lower static deflections and amplitudes of the limit cycle oscillations.

Monte Carlo Calculations of THz Generation in Nitrides

The electromagnetic power generation associated with the optical-phonon transit-time resonance of a nitride-based maser is analyzed by Monte Carlo simulations under small- and large-signal regimes. Numerical results show that a dynamic negative differential mobility occurs in a wide frequency range with an optimal generation frequency easily tunable in the terahertz range by varying the static electric field strength. The generation phenomena are present up to the liquid nitrogen temperature with reasonably high values of the amplification coefficient. The efficiency of the amplification and generation is found to depend nonmonotonously on static and microwave electric field amplitudes, generation frequency, and doping level, so that for each generation frequency there exists an optimal range of parameter values. A comparative study among the performances of different nitrides is also reported.

Monte Carlo Calculations of THz Generation in Nitrides

The electromagnetic power generation associated with the optical-phonon transit-time resonance of a nitride-based maser is analyzed by Monte Carlo simulations under small- and large-signal regimes. Numerical results show that a dynamic negative differential mobility occurs in a wide frequency range with an optimal generation frequency easily tunable in the terahertz range by varying the static electric field strength. The generation phenomena are present up to the liquid nitrogen temperature with reasonably high values of the amplification coefficient. The efficiency of the amplification and generation is found to depend nonmonotonously on static and microwave electric field amplitudes, generation frequency, and doping level, so that for each generation frequency there exists an optimal range of parameter values. A comparative study among the performances of different nitrides is also reported.

Sideband suppression in time-modulated linear arrays by the differential evolution algorithm

A novel approach based on the differential evolution (DE) algorithm is proposed to suppress the sideband radiation patterns in time modulated linear antenna arrays. The sideband level of a time modulated linear array can be reduced significantly by rearranging the static excitation amplitudes as well as the switch-on time intervals of each element. The approach is illustrated through a 32-element linear array.

Electron-density distribution in stishovite, SiO2: a new high-energy synchrotron-radiation study.

The electron-density distribution of the high-pressure polymorph of SiO2, stishovite [a = 4.177 (1), c = 2.6655 (5) A, space group P4(2)/mnm, Z = 2], has been redetermined by single-crystal diffractometry using synchrotron radiation of 100.42 and 30.99 keV, respectively, in order to obtain essentially absorption- and extinction-free data. Room-temperature diffraction experiments on two samples of irregular shape were carried out on two different diffractometers installed at HASYLAB/DESY, Hamburg, Germany. The structure refinement on the high-energy data converged at R(F) = 0.0047, wR(F) = 0.0038, GoF = 0.78, for a multipole model with neutral atoms and multipole expansions up to seventh order. For each atom, the radial expansion coefficients of the multipole orders (l > 0) were constrained to a common value. The absence of extinction was indicated by a refined correction parameter equalling zero within error limit. The excellent quality of the data is also illustrated by a high-order (HO) refinement (s > 0.7 A(-1)) yielding R(F) = 0.0060, wR(F) = 0.0048, GoF = 0.85. Both static deformation electron-density distribution and structure amplitudes compare well with corresponding results obtained from band-structure calculations using the linearized-augmented-plane-wave (LAPW) method. Ensuing topological analysis of the total model electron density distribution revealed bond critical point properties for the two unique Si--O bonds, indicating a predominantly closed-shell interaction mixed with a significant shared interaction contribution that decreases with increasing interatomic distance. Calculation of atomic basins yielded charges of +3.39 e and -1.69 e for Si and O, respectively, in good agreement with the theoretically calculated values of +3.30 e and -1.65 e. The volumina of the Si and O basins are 2.32 and 10.48 A3, corresponding to spheres with radii of 0.82 and 1.36 A, respectively. The results also conform well with correlations between bond length and bond critical point properties reported in the literature for geometry-optimized hydroxyacid molecules. Estimates of the Si cation electronegativity indicate that the change of Si coordination by oxygen from 4 to 6 is accompanied by an increase of the ionicity of the Si--O bond of about 7%.

Monte Carlo simulation of terahertz generation innitrides

The conditions for microwave power generation under thequasi-periodic motion of carriers caused by the combined action ofcarrier acceleration in a constant electric field and optical phononemission at low temperatures are analysed by means of Monte Carlosimulations of both small- and large-signal responses in bulknitrides such as GaN and InN. It is shown that, as a consequence ofthe high value of the optical phonon energy and the strongelectron-phonon interaction, a dynamic negative differentialmobility caused by transit-time resonance occurs over a wide frequencyrange which covers practically the whole submillimetre range andpersists in the THz frequency range up to liquid nitrogentemperature. The efficiency of the amplification and generation isfound to depend nonmonotonically on: (i) the static and microwaveelectric field amplitudes, (ii) the generation frequency, and(iii) the carrier concentration. Accordingly, for each generationfrequency there exists an optimal range of parameter values. Underoptimal conditions we predict a generation efficiency of about1-2% in the 0.5-1.5 THz frequency range.

Monte Carlo simulation of the generation of terahertz radiation in GaN

The conditions for microwave power generation at low temperatures under optical phonon emission are analyzed by Monte Carlo simulations of both small- and large-signal responses in bulk zinc blende and wurtzite GaN. As a result of the high optical phonon energy and the strong interaction of electrons with optical phonons in GaN a general improvement on the transit-time resonance and a considerable increase in the maximum generation frequency and power can be achieved in comparison to the widely studied III–V materials such as GaAs and InP. A dynamic negative differential mobility caused by transit-time resonance occurs in a wide frequency range of about 0.05–3 THz and persists in the THz frequency range up to the liquid nitrogen temperature with doping levels up to about 5×1016 cm−3. The efficiency of the amplification and generation is found to depend nonmonotonously on static and microwave electric field amplitudes, generation frequency, and doping level so that for each generation frequency there exists an optimal range of parameter values. Under optimal conditions a generation efficiency of about 1% to 2% can be achieved in the 0.5–1.5 THz frequency range.

Ba6CoNb9O30 and Ba6FeNb9O30: Two New Tungsten-Bronze-Type Ferroelectrics. Centrosymmetry of Ba5.2K0.8U2.4Nb7.6O30 at 300 K

Ba6CoNb9O30 and Ba6FeNb9O30 in space group P4bm are shown to satisfy the structural criteria for ferroelectricity. Ba6CoNb9O30 undergoes a diffuse phase transition at 660 (11) K, as observed calorimetrically, in addition to a dielectric permittivity anomaly with an onset temperature of 685 (10) K. The demonstration of dielectric hysteresis at room temperature under the application of a varied DC field reaching a maximum of ± 300 kV m−1, corresponding to a spontaneous polarization of 1.2 (5) × 10−2C m−2, provides unambiguous verification that it is a new ferroelectric. Ba6FeNb9O30 also undergoes a diffuse phase transition at 605 (16) K, with a dielectric anomaly at 583 (5) K, and exhibits dielectric hysteresis at room temperature under a varied DC field ranging to ± 310 kV m−1 corresponding to a spontaneous polarization of 2.2(5) × 10−2Cm−2; it too is demonstrably a new ferroelectric. Although Ba5.2K0.8U2.4Nb7.6O30 has also been reported in space group P4bm, all atomic displacements from the corresponding centrosymmetric positions are less than their refined root-mean-square thermal or static amplitudes. Such an arrangement is likely to be thermodynamically unstable. Either its space group has been incorrectly assigned, and reinvestigation will show the space group is P4/mbm, or the structural refinement is incomplete.

The temperature dependence of the reflection intensities of the modulated composite structure Hg0.776(BEDT-TTF)SCN

The temperature dependence between 30 and 300 K of the intensities of 24 reflections of the column-composite structure Hg0.776(BEDT-TTF)SCN [Wang, Beno, Carlson, Thorup, Murray, Porter, Williams, Maly, Bu, Petricek, Cisarova, Coppens, Jung, Whangbo, Schirber & Overmyer (1991). Chem. Mater. 3, 508–513; BEDT-TTF = 3,4,3′,4′-bis(ethylenedithio)-2,2′,5,5′-tetrathiafulvalene] has been analyzed in terms of a model including phason temperature factors. The temperature dependence of the main and first-order satellite reflections is reasonably well reproduced in a refinement with 236 observations and four variables. The results are interpreted in terms of a temperature independence of the static displacement amplitudes. The room-temperature r.m.s. phason fluctuations of the mercury sublattice are 50 (2)°. This value implies that the mean mercury displacement amplitude will increase by ∼ 60% on lowering of the temperature to within the liquid-helium range. The thermal contraction on cooling is the same for the two sublattices.

Nonlinear large amplitude vibration of composite helicopter blade atlarge static deflection

The nonlinear, large amplitude nonrotating free vibration of composite helicopter blades under large static deflection is investigated analytically and experimentally. A new model capable of handling large amplitudes as well as large deflections was developed based on the use of Euler angles and a harmonic balance, finite difference solution of the basic large deflection equations. The behavior of the first and second bending, the first fore-and-aft, and the first torsional modes of [0/90]3s and [45/0]$ graphite/epoxy flat beams were explored analytically as tip static deflection and tip amplitudes vary* Free vibration tests of several different lay-ups of composite blades show good agreement between theory and experiment. It is found that both large static deflection and large amplitudes can affect the fore-and-aft and torsional modes significantly, but bending modes are not influenced much by the geometrical nonlinearities.

The effects of simulated traffic vibrations on a dwelling house : R. A. Hood and C. P. Marshall 1987 Transport and Road Laboratory, Crowthorne, Contractor Report 44. (95 pages, 42 figures, 0 tables, 41 references) (in English)

This report describes an experiment to investigate damage caused to buildings by traffic-induced vibrations. A vacant property founded on loose to medium dense sand was located and subjected to separately generated groundborne and airborne vibrations, designed to simulate the effects of heavy traffic. Groundborne vibrations were simulated using a geophysical vibrator, airborne vibrations with a loudspeaker system connected to a microcomputer. The dynamic response of the structure was monitored using a computer controlled data collection and analysis system. Throughout the period of the experiment the condition of the structure, movements within the structure and movements within the underlying soil were monitored, using a range of precise measuring techniques. In order to widen the scope of the study, six sections of foundation strip were constructed close to the test house. These were subjected to various static loads and amplitudes of vibration. The behaviour of the strips was also monitored throughout the experiment. The report describes the experimental work and results in detail. Possible damage mechanisms are postulated and dicussed in the context of the very small amounts of movement and damage actually recorded. The distinction is made between the effects of airborne and groundborne vibrations. Conclusions are drawn regarding the overall risks of damage from traffic vibrations and circumstances which increase this risk are highlighted.

Two Scaling Relations Between Static and Dynamical Threshold Exponents and Amplitudes

Dynamical threshold phenomena in non-equilibrium systems satisfying the potential condition are discussed. Two scaling relations between the static and dynamical threshold exponents and amplitudes are obtained.

Viscoplastic deformations of coarse-rubbly soils subject to cyclic effects

1. Under a cyclic loading, the strength of coarse-rubbly soils (over the entire investigated range of variation in the static stressed state and stress amplitudes) remains virtually constant as compared with a static loading. 2. Additional soil compaction, which depends on the level of the static stressed state, the amplitude of the event, and the soil density, and also additional development of plastic shear strains take place under deviator cyclic loading. 3. Stabilization of volume and shear strains in the sublimiting state under cyclic effects occurs over a prolonged period as computed for thousands of load cycles; the major portion of the deformation, however, is accumulated during the first several tens of cycles. 4. The failure of a saturated coarse-rubbly soil under cyclic loading occurs in conformity with Terzaghi's effective-stress principle.

Acoustic creep of glass-fiber-reinforced plastic

A method of investigating acoustic creep of polymer composites developing under the effect of static tensile forces and small amplitudes of dynamic stresses with a frequency of 20 kHz acting coaxially with the static loads is considered. Results of investigating acoustic creep of glass-fabric-reinforced plastic are presented. It is shown that the presence of a high-frequency stress component regularly accelerates relaxation processes and reduces considerably the deformation resistance of the material. Generalized curves simulating the long-time static creep of reinforced plastic are constructed by the method of temperature-time, stress-time, and vibration-time analogies. The results of prediction are compared with the control experiment.

Quark-loop dynamics and meson decays

From a set of lowest-order quark-loop diagrams for static mesic amplitudes involving vector and axial vector vertices, we determine the effective quark mass and the meson-quark-quark coupling constants for three types of quark models. These parameters are applied to evaluate certain mesic decays and theSU 3 mass splitting of the 0− octet and 1− nonet, which serve as tests for the quark models. Adler’s low-energy theorem for the π0 → 2γ decay is derived in our approach without invoking the Adler-Schwinger anomaly. The test favors the Nambu-Han model of integrally charged quarks. Critical examinations of the underlying assumption of the quark-loop dominance are made, and a speculation on a physical model which allows such a situation will be proposed.