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Linear Regime (linear + regime)

Distribution by Scientific Domains

Physics and Astronomy	57%

Selected Abstracts

Analysis and selection criteria of BSIM4 flicker noise simulation models

INTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 7 2008
T. Noulis
Abstract CMOS transistors' noise performance is mainly dominated by flicker (1/f) noise. BSIM4.X MOSFET simulation model develops two distinct models, SPICE-Flicker and BSIM-Flicker, to calculate flicker noise. In this paper, these two models are analytically examined and compared to noise measurements, using an NMOS and a PMOS device fabricated in 0.6µm process by Austria Mikro Systeme (AMS). MOSFET 1/f noise measurements and the respective simulations were obtained under various bias conditions, as to study which flicker noise model is the optimum in each operating region. Measurement temperature was constant at 295,K. Comparisons suggest that in an NMOS transistor operating in the triode or saturation region, BSIM-Flicker model is accurate and therefore preferable. In a PMOS transistor, the most suitable model to describe its 1/f noise performance in the linear regime is also BSIM-Flicker, whereas SPICE-Flicker is more preferable in saturation. In NMOS transistors, the selected model provides a great accurate description of flicker noise, contrary to PMOS transistors, where simulation models appear to be quite unreliable and need further improvement. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Synthesis and characterization of catalytic nanoporous carbon membranes

AICHE JOURNAL, Issue 1 2001
Michael S. Strano
A method is reported for the synthesis of nobel catalyic nanoporous carbon membranes. Defect-free, nanoporous carbon films of 12.5,,m average thickness containing a dispersion of Ptx were synthesized on macroporous stainless-steel supports. Ideal gas selectivities for the catalytic membranes were simliar to those of inert nanoporous carbon membranes with He,N2=58.6 and O2N2=4.9. The selective hydrogenation of monoolefins (propylen, l-buiene, isobutylene) was used to probe the shape-selective catalytic proerties nad the transport selectivities of the membranes. The results were modeled using the linear regime of coupled sdsorption, transport and rection in the membrane. Model regression yielded 14.9, 19.7. and 18.4 kJ/mol for the activation energies of permeation for propylene, isobutylene, and l-butene, respectively. The system demonstrated selective reaction and transport favoring propane production with selectiveity ratios of 28.9:3.2.I for propane:n-butane:isobutane at 125°C. [source]

Temperature Dependence of Tensile Strength for a Woven Boron-Nitride-Coated Hi-NicalonÔ SiC Fiber-Reinforced Silicon-Carbide-Matrix Composite

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001
Shuqi Guo
The temperature dependence of tensile fracture behavior and tensile strength of a two-dimensional woven BN-coated Hi-NicalonÔ SiC fiber-reinforced SiC matrix composite fabricated by polymer infiltration pyrolysis (PIP) were studied. A tensile test of the composite was conducted in air at temperatures of 298 (room temperature), 1200, 1400, and 1600 K. The composite showed a nonlinear behavior for all the test temperatures; however, a large decrease in tensile strength was observed above 1200 K. Young's modulus was estimated from the initial linear regime of the tensile stress,strain curves at room and elevated temperatures, and a decrease in Young's modulus became significant above 1200 K. The multiple transverse cracking that occurred was independent of temperature, and the transverse crack density was measured from fractographic observations of the tested specimens at room and elevated temperatures. The temperature dependence of the effective interfacial shear stress was estimated from the measurements of the transverse crack density. The temperature dependence of in situ fiber strength properties was determined from fracture mirror size on the fracture surfaces of fibers. The decrease in the tensile strength of the composite up to 1400 K was attributed to the degradation in the strength properties of in situ fibers, and to the damage behavior exception of the fiber properties for 1600 K. [source]

Global m= 1 instabilities and lopsidedness in disc galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
V. Dury
ABSTRACT Lopsidedness is common in spiral galaxies. Often, there is no obvious external cause, such as an interaction with a nearby galaxy, for such features. Alternatively, the lopsidedness may have an internal cause, such as a dynamical instability. In order to explore this idea, we have developed a computer code that searches for self-consistent perturbations in razor-thin disc galaxies and performed a thorough mode-analysis of a suite of dynamical models for disc galaxies embedded in an inert dark matter halo with varying amounts of rotation and radial anisotropy. Models with two equal-mass counter-rotating discs and fully rotating models both show growing lopsided modes. For the counter-rotating models, this is the well-known counter-rotating instability, becoming weaker as the net rotation increases. The m= 1 mode of the maximally rotating models, on the other hand, becomes stronger with increasing net rotation. This rotating m= 1 mode is reminiscent of the eccentricity instability in near-Keplerian discs. To unravel the physical origin of these two different m= 1 instabilities, we studied the individual stellar orbits in the perturbed potential and found that the presence of the perturbation gives rise to a very rich orbital behaviour. In the linear regime, both instabilities are supported by aligned loop orbits. In the non-linear regime, other orbit families exist that can help support the modes. In terms of density waves, the counter-rotating m= 1 mode is due to a purely growing Jeans-type instability. The rotating m= 1 mode, on the other hand, grows as a result of the swing amplifier working inside the resonance cavity that extends from the disc centre out to the radius where non-rotating waves are stabilized by the model's outwardly rising Q profile. [source]

Modelling angular-momentum history in dark-matter haloes

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002
Ariyeh H. Maller
We model the acquisition of spin by dark-matter haloes in semi-analytic merger trees. We explore two different algorithms: one in which halo spin is acquired from the orbital angular momentum of merging satellites, and another in which halo spin is gained via tidal torquing on shells of material while still in the linear regime. We find that both scenarios produce the characteristic spin distribution of haloes found in N -body simulations, namely, a log-normal distribution with mean , 0.04 and standard deviation , 0.5 in the log. A perfect match requires fine-tuning of two free parameters. Both algorithms also reproduce the general insensitivity of the spin distribution to halo mass, redshift and cosmology seen in N -body simulations. The spin distribution can be made strictly constant by physically motivated scalings of the free parameters. In addition, both schemes predict that haloes that have had recent major mergers have systematically larger spin values. These algorithms can be implemented within semi-analytic models of galaxy formation based on merger trees. They yield detailed predictions of galaxy properties that strongly depend on angular momentum (such as size and surface brightness) as a function of merger history and environment. [source]

Cosmic momentum field and mass fluctuation power spectrum

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2000
Changbom Park
We introduce the cosmic momentum field as a new measure of the large-scale peculiar velocity and matter fluctuation fields. The momentum field is defined as the peculiar velocity field traced and weighted by galaxies, and is equal to the velocity field in the linear regime. We show that the radial component of the momentum field can be considered as a scalar field with the power spectrum which is practically one-third of that of the total momentum field. We present a formula for the power spectrum directly calculable from the observed radial peculiar velocity data. The momentum power spectrum is measured for the MAT sample in the Mark III catalogue of peculiar velocities of galaxies. Using the momentum power spectrum we find the amplitude of the matter power spectrum is and at the wavenumbers 0.049 and 0.074 h Mpc,1, respectively, where , is the density parameter. The 68 per cent confidence limits include the cosmic variance. The measured momentum and density power spectra together indicate that the parameter or where bO is the bias factor for optical galaxies. [source]

Planar distribution of the galaxies in the Local Group

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2008
S. Pasetto
Abstract Adopting known data on positions and distances, we make use of analytical geometry and look for the plane that minimizes the distances of all galaxies to it. A planar distribution is found. We apply Hamilton's principle of minimum action to investigate the dynamics of the two major systems of the Local Group, the Milky Way and Andromeda, under the action of forces exerted by nearby galaxies or groups external to the Local Group. We find that the planar distribution is fully compatible with the minimum action and that the external force field is likely parallel to the plane. It pulls the galaxies of the Local Group without altering their planar distribution. Special care is paid to evaluate the robustness of this result. We present an explanation in the linear regime of the numerical results based on the compression effect described with the tidal tensor. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]