Showing papers on "Amplitude published in 1994"

Numerical and Theoretical Investigations on the Possibilities and Limitations of Nakamura's Technique

Abstract: Numerical simulation of noise is used to investigate the characteristics of the spectral ratio between horizontal and vertical components (H/V ratio) and its sensitivity to various parameters in order to better appreciate the reliability of the technique proposed by Nakamura (1989) to estimate site amplification effects from single station noise recordings. Noise is simulated as the signal produced at a single site by a set of superficial sources (unidirectional forces or dipoles) disposed all around with random amplitude and time delay. Individual signals from a single source are computed by the discrete wave number technique. Synthetic calculations for 15 soil profiles show that this ratio exhibits a single, clear peak, the location of which is independent of the source excitation function, but strongly correlated with the local geological structure: its frequency is very close to the S wave resonance frequency. This peak appears to be mainly controlled by the polarization curve of the fundamental Rayleigh waves, which in turn exhibits a sharp peak around the fundamental resonance mode of the sedimentary structure. A similar result is found for the H/V ratio obtained for incident plane SV waves. In contrast, the amplitude of this peak exhibits a poor correlation with the ground motion amplification of S waves at resonance frequency. It is shown to be related with a high sensitivity on the value of the Poisson's ratio in the uppermost layer presumed to be the noise source layer, and, though to a much lesser extent, on the mean distance between site and noise sources. It is concluded that Nakamura's method can clearly allow the resonance frequency of a given sedimentary site to be measured very efficiently and very cheaply, but that its use for deriving the amplification at resonance frequency seems still premature from a theoretical point of view.

Patterns and quasi-patterns in the Faraday experiment

Abstract: Parametric excitation of surface waves via forced vertical oscillation of a container filled with fluid (the Faraday instability) is investigated experimentally in a small-depth large-aspect-ratio system, with a viscous fluid and with two simultaneous forcing frequencies. The asymptotic pattern observed just above the threshold for the first instability of the flat surface is found to depend strongly on the frequency ratio and the amplitudes and phases of the two sinusoidal components of the driving acceleration. Parallel lines, squares, and hexagons are observed. With viscosity 100 cS, these stable standing-wave patterns do not exhibit strong sidewall effects, and are found in containers of various shapes including an irregular shape. A ‘quasi-pattern’ of twelvefold symmetry, analogous to a two-dimensional quasi-crystal, is observed for some even/odd frequency ratios. Many of the experimental phenomena can be modelled via cubic-order amplitude equations derived from symmetry arguments.

Complex wave-field reconstruction using phase-space tomography.

Abstract: A method is proposed for the experimental determination of the amplitude and phase structure of a quasimonochromatic wave field in a plane normal to its propagation direction. The wave field may represent either a scalar electromagnetic (EM) field or the quantum mechanical (QM) wave function of a matter wave. For coherent EM fields or pure QM states, the method uniquely reconstructs the complex wave fields. For partially coherent EM fields or mixed QM states, it reconstructs the two-point correlation function or density matrix. The experiment uses only intensity measurements and refractive optics (lenses), and the data analysis algorithm is noniterative and requires no deconvolution.

Tidal propagation in strongly convergent channels

Abstract: Simple first- and second-order analytic solutions, which diverge markedly from classical views of cooscillating tides, are derived for tidal propagation in strongly convergent channels. Theoretical predictions compare well with observations from typical examples of shallow, “funnel-shaped” tidal estuaries. A scaling of the governing equations appropriate to these channels indicates that at first order, gradients in cross-sectional area dominate velocity gradients in the continuity equation and the friction term dominates acceleration in the momentum equation. Finite amplitude effects, velocity gradients due to wave propagation, and local acceleration enter the equations at second order. Applying this scaling, the first-order governing equation becomes a first-order wave equation, which is inconsistent with the presence of a reflected wave. The solution is of constant amplitude and has a phase speed near the frictionless wave speed, like a classical progressive wave, yet velocity leads elevation by 90°, like a classical standing wave. The second-order solution at the dominant frequency is also a unidirectional wave; however, its amplitude is exponentially modulated. If inertia is finite and convergence is strong, amplitude increases along channel, whereas if inertia is weak and convergence is limited, amplitude decays. Compact solutions for second-order tidal harmonics quantify the partially canceling effects of (1) time variations in channel depth, which slow the propagation of low water, and (2) time variations in channel width, which slow the propagation of high water. Finally, it is suggested that phase speed, along-channel amplitude growth, and tidal harmonics in strongly convergent channels are all linked by morphodynamic feedback.

Complex wave-field reconstruction by using phase-space tomography

Abstract: A new class of phase-retrieval methods for 2-D fields is introduced. Phase-space tomography can be used for the experimental determination of the amplitude and phase structure of a quasi-monochromatic wave field in a plane normal to its propagation direction. The wave field ψ(r) may represent either a scalar electromagnetic (EM) field or the quantum-mechanical (QM) wave function of a matter wave. The complex wave field may be coherent or partially coherent, in which case the method reconstructs the two-point spatial correlation function, Γ(r, r′) = ⟨ψ(r)ψ*(r′)⟩. (In the QM case, the analogous quantity is the density matrix.) The experiment uses only intensity measurements and refractive optics (lenses), and the data-analysis algorithm is noniterative and requires no deconvolution.

The shape of the sunspot cycle

Abstract: The temporal behavior of a sunspot cycle, as described by the International sunspot numbers, can be represented by a simple function with four parameters: starting time, amplitude, rise time, and asymmetry. Of these, the parameter that governs the asymmetry between the rise to maximum and the fall to minimum is found to vary little from cycle to cycle and can be fixed at a single value for all cycles. A close relationship is found between rise time and amplitude which allows for a representation of each cycle by a function containing only two parameters: the starting time and the amplitude. These parameters are determined for the previous 22 sunspot cycles and examined for any predictable behavior. A weak correlation is found between the amplitude accurate to within about 30% right at the start of the cycle. As the cycle progresses, the amplitude can be better determined to within 20% at 30 months and to within 10% at 42 months into the cycle, thereby providing a good prediction both for the timing and size of sunspot maximum and for the behavior of the remaining 7-12 years of the cycle.

Solitary wave dynamics of film flows

Abstract: The development and interaction of solitary wave pulses is critical to understanding wavy film flows on an inclined (or vertical) surface. Sufficiently far downstream, the wave structure consists of a generally irregular sequence of solitary waves independent of the conditions at the inlet. The velocity of periodic solitary waves is found to depend on their frequency and amplitude. Larger pulses travel faster; this property, plus a strong inelasticity, causes larger pulses to absorb others during interactions, leaving a nearly flat interface behind. These wave interactions lead to the production of solitary wave trains from periodic small amplitude waves. The spacings between solitary waves can be irregular for several different reasons, including the amplification of ambient noise, and the interaction process itself. On the other hand, this irregularity is suppressed by the addition of periodic forcing.

Effects of multiple phase transitions in a three-dimensional spherical model of convection in Earth's mantle

Abstract: Numerical models of mantle convection that incorporate the major mantle phase changes of the transition zone reveal an inherently three-dimensional flow pattern, with cylindrical features and linear features that behave differently in their ability to penetrate the 670-km discontinuity. The dynamics are dominated by accumulation of cold linear downwellings into rounded pools above the endothermic phase change at 670 km depth, resulting in frequent “avalanches” of upper mantle material into the lower mantle. The effect of the exothermic phase transition at 400 km depth is to reduce the overall degree of layering by pushing material through the 670-km phase change, resulting in smaller and more frequent avalanches, and a wider range of morphologies. Large quantities of avalanched cold material accumulate above the coremantle boundary (CMB), resulting in a region of strongly depressed mean temperature at the base of the mantle. The 670-km phase change has a strong effect on the temperature field, with three-distinct regions being visible: (1) the upper mantle, containing linear downwellings and pools of cold material in the transition zone and characterized by a high amplitude long wavelength spectrum; (2) the midmantle, containing quasi-cylindrical avalanche conduits and characterized by a low amplitude, broad spectrum; and (3) the deep mantle, containing large pools of cold, avalanched material and characterized by a high amplitude, ultra-red (i.e., long wavelength) spectrum. The effect on the velocity field is very different. Flow penetration across the 670-km phase change is strongly wavelength-dependent, with easy penetration at long wavelengths but strong inhibition at short wavelengths. Thus, when comparing numerical models with long wavelength seismic tomography, diagnostics based on the density field, such as the radial correlation function, are much more sensitive to the effects of phase transitions than those based on the velocity field. The amplitude of the geoid is not significantly affected by the partial layering, because the contribution from the strong heterogeneity in the transition zone is almost perfectly balanced by the contribution from deflection of the 670-km discontinuity. Avalanches are associated with geoid lows. However, a more complex viscosity structure is required to correctly match the sign of the geoid over slabs in Earth.

Method and apparatus for providing a respiratory effort waveform for the treatment of obstructive sleep apnea

Abstract: A method and device for stimulation of an upper airway muscle of a patient to relieve an airway obstruction employs a digital respiratory effort waveform. The waveform is provided by sensing a signal having an output characteristic of respiratory effort of the patient and sampling the sensed signal at a predetermined interval. To bring the signal into the center of the maximum digital range for the device, an average offset for the digitized waveform is determined and the sensed signal is adjusted to bring the average offset into the center of a predetermined maximum digital range. To provide an appropriate amplitude for the waveform, an average peak-to-peak amplitude for the digitized waveform is determined and the average peak-to-peak amplitude is then adjusted to bring the average peak-to-peak amplitude into the range of about 60-90% of the maximum digital range. By selecting an appropriate sampling interval and digital range for the waveform, the resolution of the waveform can allow parameters characteristic of valid respiratory signals to be evaluated which will allow stimulation output from the apnea treatment device to be synchronized with the inspiratory phase of the patient's respiratory cycle.

Correction of ultrasonic wavefront distortion using backpropagation and a reference waveform method for time-shift compensation.

Abstract: A model is introduced to describe ultrasonic pulse amplitude and shape distortion as well as arrival time fluctuation produced by propagation through specimens of human abdominal wall. In the model, amplitude and shape distortion develops as the wavefront propagates in a uniform medium after passing through a phase screen that only causes time shifts. This distortion is compensated by a backpropagation of the wavefront using the angular spectrum method. The compensation employed waveforms emitted by a pointlike source and measured after propagation through the tissue. The waveforms were first corrected for geometric path and then were backpropagated over a sequence of increasing distances. At each distance, a waveform similarity factor was calculated to find the backpropagation distance at which the waveforms were most similar. A new method was devised to estimate pulse arrival time for geometric correction as well as to perform time‐shift compensation. The method adaptively derives a reference waveform that is then cross correlated with all the waveforms in the aperture to obtain a surface of arrival times. The surface was smoothed iteratively to remove outlying points due to waveform distortion. The mean (±s.d.) of the waveform similarity factor for 14 specimens was found to be 0.938 (±0.025) initially. After backpropagation of waveforms to the distance of maximum waveform similarity for each specimen, the waveform similarity factor improved to 0.967 (±0.015). The corresponding energy level fluctuation in the wavefront was 4.2 (±0.4) dB initially and became 3.3 (±0.3) dB after backpropagation. For wavefronts focused at 180 mm, the −30 dB mean (±s.d.) effective radius of the focus was 4.2 (±1.2) mm with time‐shift compensation in the aperture and became 2.5 (±0.5) mm with backpropagation followed by time‐shift compensation. These results indicate that a phase screen placed some distance away from the aperture is an improved model for the description of wavefront distortion produced by human abdominal wall and that wavefront backpropagation followed by time‐shift estimation and compensation is an effective method to compensate for such distortion.

Asymptotic decay of correlations in liquids and their mixtures

Abstract: We consider the asymptotic decay of structural correlations in pure fluids, fluid mixtures, and fluids subject to various types of inhomogeneity. For short ranged potentials, both the form and the amplitude of the longest range decay are determined by leading order poles in the complex Fourier transform of the bulk structure factor. Generically, for such potentials, asymptotic decay falls into two classes: (i) controlled by a single simple pole on the imaginary axis (monotonic exponential decay) and (ii) controlled by a conjugate pair of simple poles (exponentially damped oscillatory decay). General expressions are given for the decay length, the amplitude, and [in class (ii)] the wavelength and phase involved. In the case of fluid mixtures, we find that there is only one decay length and (if applicable) one oscillatory wavelength required to specify the asymptotic decay of all the component density profiles and all the partial radial distribution functions gij(r). Moreover, simple amplitude relations link the amplitudes associated with the decay of correlation of individual components. We give explicit results for the case of binary systems, expanding on and partially correcting recent work by Martynov. In addition, numerical results for g(r) for the pure fluid square‐well model and for gij(r) for binary hard sphere mixtures are presented in order to illustrate the fact that the asymptotic forms remain remarkably accurate at intermediate range. This is seen to arise because the higher order poles are typically well‐separated from the low order ones. We also discuss why the asymptotics of solvation forces for confined fluids and of density profiles of inhomogeneous fluids (embracing wetting phenomena) fall within the same theoretical framework. Finally, we comment on possible modifications to the theory arising from the presence of power‐law attractive potentials (dispersion forces).

Small amplitude theory of Richtmyer–Meshkov instability

Abstract: This paper presents a new analysis of small amplitude Richtmyer–Meshkov instability. The linear theory for the case of reflected rarefaction waves, a problem not treated in previous work, is formulated and numerically solved. This paper also carries out a systematic comparison of Richtmyer’s impulsive model to the small amplitude theory, which has identified domains of agreement as well as disagreement between the two. This comparison includes both the reflected shock and reflected rarefaction cases. Additional key results include the formulation of criteria determining the reflected wave type in terms of preshocked quantities, identification of parameter regimes corresponding to total transmission of the incident wave, discussion of an instability associated with a rarefaction wave, investigation of phase inversions and the related phenomenon of freeze‐out, and study of the sensitivity of the numerical solutions to initial conditions.

Couple-stresses in peristaltic transport of fluids

Abstract: Peristaltic pumping by a sinusoidal travelling wave in the walls of a two-dimensional channel filled with a viscous incompressible couple-stress fluid, is investigated theoretically. A perturbation solution is obtained, which satisfies the momentum equation for the case in which the amplitude ratio (wave amplitude:channel half width) is small. The results show that the mean axial velocity decreases with increasing couple-stress parameter eta . The phenomenon of reflux (mean flow reversal) is discussed. A reversal of velocity in the neighbourhood of the centre line occurs when the pressure gradient is greater than that of the critical reflux condition. It is found that the critical reflux pressure increases with the couple-stress parameter. Numerical results are reported for various values of the physical parameters of interest.

Amplitude expansions for instabilities in populations of globally-coupled oscillators

Abstract: We analyze the nonlinear dynamics near the incoherent state in a mean-field model of coupled oscillators. The population is described by a Fokker-Planck equation for the distribution of phases, and we apply center-manifold reduction to obtain the amplitude equations for steady-state and Hopf bifurcation from the equilibrium state with a uniform phase distribution. When the population is described by a native frequency distribution that is reflection-symmetric about zero, the problem has circular symmetry. In the limit of zero extrinsic noise, although the critical eigenvalues are embedded in the continuous spectrum, the nonlinear coefficients in the amplitude equation remain finite, in contrast to the singular behavior found in similar instabilities described by the Vlasov-Poisson equation. For a bimodal reflection-symmetric distribution, both types of bifurcation are possible and they coincide at a codimension-two Takens-Bogdanov point. The steady-state bifurcation may be supercritical or subcritical and produces a time-independent synchronized state. The Hopf bifurcation produces both supercritical stable standing waves and supercritical unstable traveling waves. Previous work on the Hopf bifurcation in a bimodal population by Bonilla, Neu, and Spigler and by Okuda and Kuramoto predicted stable traveling waves and stable standing waves, respectively. A comparison to these previous calculations shows that the prediction of stable traveling waves results from a failure to include all unstable modes.

A minimal model of the single capacitor biphasic defibrillation waveform.

Abstract: UNLABELLED A quantitative model of the single capacitor biphasic defibrillation waveform is proposed. The primary hypothesis of this model is that the first phase leaves a residual charge on the membranes of the unsynchronized cells, which can then reinitiate fibrillation. The second phase diminishes this charge, reducing the potential for refibrillation. To suppress this potential refibrillation, a monophasic shock must be strong enough to synchronize a critical mass of nearly 100% of the myocytes. Since the biphasic waveform performs this protection function by removing the residual charge (with its second phase), its first phase may be of a lower strength than a monophasic shock of equivalent performance. A quantitative model was developed to calculate the residual membrane voltage, Vm, assuming a capacitive membrane being alternately charged and discharged by the first and second phases, respectively. It was further assumed that the amplitude of the first phase would be predicted by a minimum value plus a term proportional to Vm2. The model was evaluated on the pooled data of three relevant published studies comparing biphasic waveforms. The model explained 79% of the variance in the first phase amplitude and predicted optimal durations for various defibrillator capacitances and electrode resistances. Assuming a first phase of optimal duration, the optimal second phase duration appears to be about 2.5 msec for all capacitances and resistances now seen clinically. CONCLUSION The effectiveness of the single capacitor biphasic waveform may be explained by the second phase "burping" of the deleterious residual charge of the first phase that, in turn, reduces the synchronization requirement and the amplitude requirements of the first phase.

A spherical harmonic approach to redshift distortion and a measurement of $\Omega_0$ from the 1.2-Jy IRAS Redshift Survey

Abstract: We examine the nature of galaxy clustering in redshift space, using a method based on an expansion of the galactic density field in spherical harmonics and linear theory. Our approach provides a compact and self-consistent expression for the distortion when applied to flux-limited redshift surveys. The amplitude of the distortion is controlled by the combination of the density and bias parameters, beta = OMEGA0(0.6)/b; we exploit this fact to derive a maximum-likelihood estimator for beta. We check our formalism using N-body simulations, and demonstrate that it provides an unbiased estimate of beta when the amplitude and shape of the galaxy power spectrum are known. Application of the technique to the 1.2-Jy IRAS Redshift Survey yields beta almost-equal-to 1.0; both random errors (from counting statistics and the uncertainties in the power-spectrum normalization) and systematic errors (from the uncertainty in the shape of the power spectrum) individually contribute 20 per cent uncertainties in this estimate. This estimate of beta is comparable (both in amplitude and uncertainty) with previous measurements based on comparisons of the IRAS density field with direct measurements of peculiar velocities and analyses of the acceleration of the Local Group, but the spherical harmonic analysis has the advantage of being easy to implement and largely free of systematic errors.

Diffusive filtering theory of gravity wave spectra in the atmosphere

Abstract: Shear and convective instabilities, Doppler spreading, and nonlinear wave-wave interactions are mechanisms which have been proposed to explain the form of the gravity wave vertical wave number spectrum of horizontal winds. In this paper we present an alternative explanation by assuming that the damping effects of molecular viscosity, turbulence, and off-resonance wave-wave interactions can all be characterized in terms of a scale-independent diffusivity (D) which increases with altitude. The components of the gravity wave source spectrum are assumed to grow exponentially with increasing altitude in response to decreasing atmospheric density until they are removed by diffusive damping. A wave of intrinsic frequency Cu and vertical wave number m is assumed to be completely damped when the effective vertical velocity of momentum diffusion (mD) exceeds the vertical phase velocity of the wave (ω/m). Only waves satisfying mD < ω/m, or equivalently m2D < ω and m < (ω/D)½ are permitted to grow in amplitude as they propagate upward in the atmosphere. If the gravity wave temporal spectrum of horizontal winds varies as ω−p, we show that the vertical wave number spectrum must vary as m−2p + 1 and the zonal (or meridional) wave number spectrum must vary as ω−p we show that the vertical wave number spectrum must very as k−(2p + 1)/3. For p = 2, and ω m and ω spectra are and where N is the buoyancy frequency, ƒ is the inertial frequency, is a form of the Richardson number, and is the variance of the vertical shear of the horizontal wind. Similar models are developed for scale-dependent diffusion. In this case the spectra are proportional to ω−p, m−3 and k(−p - 1)/(p + 1). Because the joint (m, ω) intrinsic spectra for both scale-independent and scale-dependent diffusive filtering are not separable, the theory predicts that the m spectra of vertical winds are proportional to m5 - 2p for scale-independent diffusion and m(7 - 3p)/(p - 1) for scale-dependent diffusion. The model spectra compare favorably with recent lidar and radar observations of middle atmosphere density, temperature, and wind fluctuations.

Constant Q attenuation of subsurface radar pulses

Abstract: Q is a measure of the energy stored to the energy dissipated in a propagating wave and can be estimated from the ratio of attenuation and frequency. For seismic waves, Q has been found to be essentially independent of frequency. As a result, attenuation is an approximately linear function of frequency and the impulse response function of the earth. Hence, the distortion of a seismic pulse as it propagates can be described by a single parameter. Laboratory measurements show that the attenuation of radio waves in some geological materials can also be approximated by a linear function of frequency over the bandwidths of typical subsurface radar pulses. We define a new parameter Q* to describe the slope of this linear region. The impulse response of the transfer function for a given value of Q* differs from that of the same value of Q only in total amplitude. Thus the change of shape of a radar pulse as it travels through these materials can also be described by a single parameter. The constant Q* model succe...

Noise in an ac biased junction: Nonstationary Aharonov-Bohm effect.

Abstract: We study excess noise in a quantum conductor in the presence of constant voltage and alternating external field. Becasue of a two-particle interference effect caused by Fermi correlations the noise is sensitive to the phase of the time-dependent transmission amplitude. We compute spectral density and show that at T=0 the noise has singular dependence on the dc voltage V and the ac frequency \ensuremath{\Omega} with cusplike singularities at integer eV/\ensuremath{\Elzxh}\ensuremath{\Omega}. For a metallic loop with an alternating flux the phase sensitivity leads to an oscillating dependence of the strength of the cusps on the flux amplitude.

Theoretical and experimental approach of the propagation of high frequency waves in road tunnels

Abstract: Characterization of high frequency electromagnetic wave propagation in tunnels has important applications in the field of mobile communication. In long tunnels, the amplitude of the electric field radiated by a retransmitting antenna can be easily calculated from ray theory. However, for short tunnels, one of the most critical points is either the radiation towards free space of a mobile station emitting in the tunnel or, on the contrary, the penetration of an external wave inside the tunnel. This coupling between the inside and the outside is treated through the uniform theory of diffraction. By comparing theoretical and experimental results, it is shown that this theory leads to adequate prediction of the field variation and allows the authors to point out the influence of parameters, such as the position of the mobile in the tunnel and the influence of the angle of incidence, on the entrance plane of an incoming external wave. >

Turbulent channel flow with large-amplitude velocity oscillations

Abstract: Measurements in turbulent channel flow with forced oscillations covering a wide range of frequencies (ω + =0.03-0.0005) and amplitudes (10-70% of centreline velocity) are presented and discussed. Phase averages of the velocity across the flow, and of the wall shear stress , as well as the turbulent fluctuations and are obtained with LDA and hot-film techniques. The time-mean quantities, except u' 2 , are only slightly affected by the imposed oscillations whatever their frequency and amplitude. It is shown that the appropriate similarity parameter for the oscillating quantities u and τ is the non-dimensional Stokes length l g + (or the frequency ω + =2/l g +2 )

Electro-optic detection of Bloch oscillations.

Abstract: The coherent motion of electronic wave packets in the Wannier-Stark regime of extemally biased GaAs/AIxGal _xAs superlattices is investigated by a time-resolved electro-optic technique. As predicted by the semiclassical theory, electronic wave packets undergo Bloch oscillations. They are observed via anisotropie changes in the refractive index associated with a intraband polarization, which is set up by the coherent spatial motion of electronic wave packets relative to localized holes. The oscillation amplitude depends strongly on the initial excitation conditions. Frequency, amplitude, and dephasing of Bloch oscillations are investigated over a wide range of electric fields. Complementary results to four-wave mixing and THz emission experiments are obtained.

Large amplitude electric and magnetic field signatures in the inner magnetosphere during injection of 15 MeV electron drift echoes

Abstract: Electric and magnetic fields were measured by the CRRES spacecraft at an L-value of 22 to 26 near 0300 magnetic local time during a strong storm sudden commencement (SSC) on March 24, 1991 The electric field signature at the spacecraft at the time of the SSC was characterized by a large amplitude oscillation (80 mV/m peak to peak) with a period corresponding to the 150 second drift echo period of the simultaneously observed 15 MeV electrons Considerations of previous statistical studies of the magnitude of SSC electric and magnetic fields versus local time and analysis of the energization and cross-L transport of the particles imply the existence of 200 to 300 mV/m electric fields over much of the dayside magnetosphere These observations also suggest that the 15 MeV drift echo electrons were selectively energized because their gradient drift velocity allowed them to reside in the region of strong electric fields for the duration of the accelerating phase of the electric field 10 refs, 3 figs

Analysis of the pion wave function in the light-cone formalism.

Abstract: We analyze several general constraints on the pionic valence-state wave function. It is found that the present model wave functions used in the light-cone formalism of perturbative quantum chromodynamics have failed to reproduce the Chernyak-Zhitnitsky (CZ) distribution amplitude which is required to fit the pionic form factor data and the reasonable valence-state structure function which does not exceed the pionic structure function data for $x\ensuremath{\rightarrow}1$ simultaneously. A possible model wave function which can satisfy all the general constraints has been suggested and analyzed.

Harmonic heat flow in isotropic layered systems and its use for thin film thermal conductivity measurements

Abstract: A theoretical model is presented describing harmonic heat flow in a two layer system heated by a modulated Gaussian laser beam Amplitude and phase of the modulated temperature rise in the layers, as well as in the backing substrate and adjacent atmosphere, are calculated by solving the three‐dimensional heat conduction equation with a source term including exponential absorption of the laser light in one or two layers Heat conduction is assumed to be isotropic throughout the system, however, a thermal contact resistance between the two layers can be taken into account Results are presented for single and double layer systems of gold and various dielectric thin film materials on glass substrates Amplitude and phase of the harmonic temperature variation are calculated either as a function of position in the sample system or at the surface as a function of the laser beam modulation frequency It is found that both amplitude and phase of the calculated temperature rise exhibit typical thin film features i