On the Origin of Mass and Angular Momentum of Stellar Objects

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Thermal diffusivity measurement of silicon samples by a combined piezoelectric and pyroelectric method

In the past, when thermal diffusivity measurement of materials were carried out by photoacoustic signal detection using transducers, only the piezoelectric or the pyroelectric property of the transducers was considered. In case the transducer exhibits both piezoelectric and pyroelectric properties, one of these properties had been suppressed during the experimentation, obviously more errors are introduced this way. We use polyvinylidene difluoride ~PVDF! as the detector for thermal waves. Since PVDF has both piezoelectric and pyroelectric properties, we show in this article that the signal detected by the transducer is a sum of both the piezoelectric and pyroelectric effects. Silicon semiconductor samples are considered in this article to compare the theory with experimental results. Although both the piezoelectric and pyroelectric properties are found in the resultant signal at all the frequency ranges considered, we find that when the samples are thermally thick, the piezoelectric contribution to the detected signal is slightly more than the pyroelectric contribution and vice versa when the sample is thermally thin. This behavior of the combined signal can be explained by the fact that in an optically opaque solid heat is generated very close to the surface, following absorption. This heat is communicated to the PVDF as long as the thermal diffusion length is larger than the thickness ~i.e., the sample is thermally thin!. At high frequencies the solid becomes thermally thick and the pyroelectric nature decreases as both the optical and thermal contact of the sample with the detector diminishes. Since both the properties are considered in our theory, we can measure the thermal diffusivity of a general sample without ‘‘artificial suppression.’’ Moreover, from our analysis we can deduce the physical thickness of the sample from the critical frequency, which is the frequency at which the sample changes from thermally thin to thermally thick. This transition is clearly evident in the amplitude curve as a change in slope is detected at the critical frequency. © 1999 American Institute of Physics.published_or_final_versio

Pseudocoloring for a dual-phase grating method

A simple method for adjusting pseudocolor distributions of photographic images is described and demonstrated experimentally. This method is based on the technique for photographic phase image pseudocolor modulated by a grating. A reflecting ray path is introduced into a 4f system to produce diffraction of the dual-phase grating so that the pseudocolor at the output plane can be adjusted. The merit of this method is that many pseudocolor images with different color distributions can be obtained for each diffraction order. ©1996 Society of Photo – Optical Instrumentation Engineers.published_or_final_versio

Dissipation function of the first-order phase transformation in solids via internal-friction measurements

Reconstruction and displacement of crystal structure and motion of the phase interface induces dissipation of energy, and latent heat appears during a first-order phase transition (FOPT) in solids. In this series of investigations, we first express the energy dissipation as a function of four physical parameters. Since there are more unknowns than the number of equations, we introduce four more equations describing the dynamics of the system on which internal friction (IF, the dissipation of vibration energy) measurements are conducted. Via IF measurements during FOPT, we can then calculate the relevant four parameters and hence the dissipation function. We have completed the first step in establishing a phenomenological theory to describe FOPT in solids.published_or_final_versio

Dissipation function of the first-order phase transformation in VO2 ceramics by internal-friction measurements

In order to apply the concept of the dissipation function during the first-order phase transition (FOPT) in solids, we measured the internal friction Q-1 and shear modulus μ for a range of frequencies of polycrystalline ceramics VO2 as the sample passed through a FOPT across the temperature range of 300–420 K. The experiment was repeated for different temperature variation rate Ṫ. We have found that for each frequency, a maximum of Q-1 and a minimum of μ occurred at the same temperature Tp when Ṫ was kept constant. The numerical values of the dissipation function ΔGR plus other FOPT parameters have been deduced using Q-1 data. The general trend of ΔGR-T and other results are found to be consistent with known physical aspects.published_or_final_versio

Plasma membrane cholesterol homeostasis is essential for preventing oxidative damage in wild-type Chinese hamster ovary cells

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Melatonin protects against focal cerebral ischemia in rats via inhibition of ischemia-induced overproduction of nitric oxide

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Thermal-diffusivity measurements of an oriented superconducting-film–substrate composite using the mirage technique

When one measures the thermal diffusivity χ of a thin film on a substrate by the mirage method, the photothermal deflection of the probe beam is caused by the heat field contributed by both the film and the substrate which are heated by the pump beam. To include the effects due to the presence of the substrate, we present a method to measure the diffusivities of both the film and substrate in one set of mirage detection. Using the off-axis magnetron sputtering process, we fabricated YBa2Cu3O7-δ thin films of suitable thickness (∼60 nm) on SrTiO3 as our sample for χ measurements along the c and b axes. Our results are consistent with published ones.published_or_final_versio

Multi-channel Fourier packet transform of EEG: optimal representation and time-varying coherence

Multi-channel recording of electroencephalogram (EEG) provides a measure of spatial-temporal pattern of cognitive processes. When oscillatory activities are going to be studied, the time-domain EEG signal can be analyzed via Fourier or wavelet transform. However the loss of temporal information after Fourier transform and the unavailability of phase information in wavelet transform limit their applicability in EEG analysis. In this paper, multi-channel Fourier packet transform is introduced. The algorithm resembles the wavelet packet transform by its binary tree search for an optimal selection of orthogonal basis, but extends the application to the multi-channel scenario. It aims to provide a sparse signal representation to localize features in the spatial-spectral-temporal domain. Since the decomposed atoms are spatially coherent components, analysis of time-varying synchrony across scalp locations is then possible.published_or_final_versio

Asymptotic properties of order statistics correlation coefficient in the normal cases

We have previously proposed a novel order statistics correlation coefficient (OSCC), which possesses some desirable advantages when measuring linear and monotone nonlinear associations between two signals. However, the understanding of this new coefficient is far from complete. A lot of theoretical questions, such as the expressions of its distribution and moments, remain to be addressed. Motivated by this unsatisfactory situation, in this paper we prove that for samples drawn from bivariate normal populations, the distribution of OSCC is asymptotically equivalent to that of the Pearson's product moment correlation coefficient (PPMCC). We also reveal its close relationships with the other two coefficients, namely, Gini correlation (GC) and Spearman's rho (SR). Monte Carlo simulation results agree with the theoretical findings. © 2008 IEEE.published_or_final_versio