28,669 research outputs found
Engineering estimates for supersonic flutter of curved shell segments
Engineering estimates for supersonic flutter of curved shell panel
High Input Impedance Voltage-Mode Universal Biquadratic Filters With Three Inputs Using Three CCs and Grounding Capacitors
Two current conveyors (CCs) based high input impedance voltage-mode universal biquadratic filters each with three input terminals and one output terminal are presented. The first circuit is composed of three differential voltage current conveyors (DVCCs), two grounded capacitors and four resistors. The second circuit is composed of two DVCCs, one differential difference current conveyor (DDCC), two grounded capacitors and four grounded resistors. The proposed circuits can realize all the standard filter functions, namely, lowpass, bandpass, highpass, notch and allpass filters by the selections of different input voltage terminals. The proposed circuits offer the features of high input impedance, using only grounded capacitors and low active and passive sensitivities. Moreover, the x ports of the DVCCs (or DDCC) in the proposed circuits are connected directly to resistors. This design offers the feature of a direct incorporation of the parasitic resistance at the x terminal of the DVCC (DDCC), Rx, as a part of the main resistance
The spectral dimension of random brushes
We consider a class of random graphs, called random brushes, which are
constructed by adding linear graphs of random lengths to the vertices of Z^d
viewed as a graph. We prove that for d=2 all random brushes have spectral
dimension d_s=2. For d=3 we have {5\over 2}\leq d_s\leq 3 and for d\geq 4 we
have 3\leq d_s\leq d.Comment: 15 pages, 1 figur
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Influence of spatial resolution on diurnal variability during the north American monsoon
Diurnal variability is an important yet poorly understood aspect of the warm-season precipitation regime over southwestern North America. In an effort to improve its understanding, diurnal variability is investigated numerically using the fifth-generation Pennsylvania State University (PSU)-NCAR Mesoscale Model (MM5). The goal herein is to determine the possible influence of spatial resolution on the diurnal cycle. The model is initialized every 48 h using the operational NCEP Eta Model 212 grid (40 km) model analysis. Model simulations are carried out at horizontal resolutions of both 9 and 3 km. Overall, the model reproduces the basic features of the diurnal cycle of rainfall over the core monsoon region of northwestern Mexico and the southwestern United States. In particular, the model captures the diurnal amplitude and phase, with heavier rainfall at high elevations along the Sierra Madre Occidental in the early-afternoon that shifts to lower elevations along the west slopes in the evening. A comparison to observations (gauge and radar data) shows that the high-resolution (3 km) model generates better rainfall distributions on time scales from monthly to hourly than the coarse-resolution (9 km) model, especially along the west slopes of the Sierra Madre Occidental. The model has difficulty with nighttime rainfall along the slopes, over the Gulf of California, and over Arizona. A comparison of surface wind data from three NCAR Integrated Sounding System (ISS) stations and the Quick Scatterometer (QuikSCAT) to the model reveals a low bias in the strength of the Gulf of California low-level jet, even at high resolution. The model results indicate that outflow from convection over northwestern Mexico can modulate the low-level jet, though the extent to which these relationships occur in nature was not investigated. © 2008 American Meteorological Society
Interpenetration as a Mechanism for Liquid-Liquid Phase Transitions
We study simple lattice systems to demonstrate the influence of
interpenetrating bond networks on phase behavior. We promote interpenetration
by using a Hamiltonian with a weakly repulsive interaction with nearest
neighbors and an attractive interaction with second-nearest neighbors. In this
way, bond networks will form between second-nearest neighbors, allowing for two
(locally) distinct networks to form. We obtain the phase behavior from analytic
solution in the mean-field approximation and exact solution on the Bethe
lattice. We compare these results with exact numerical results for the phase
behavior from grand canonical Monte Carlo simulations on square, cubic, and
tetrahedral lattices. All results show that these simple systems exhibit rich
phase diagrams with two fluid-fluid critical points and three thermodynamically
distinct phases. We also consider including third-nearest-neighbor
interactions, which give rise to a phase diagram with four critical points and
five thermodynamically distinct phases. Thus the interpenetration mechanism
provides a simple route to generate multiple liquid phases in single-component
systems, such as hypothesized in water and observed in several model and
experimental systems. Additionally, interpenetration of many such networks
appears plausible in a recently considered material made from nanoparticles
functionalized by single strands of DNA.Comment: 12 pages, 9 figures, submitted to Phys. Rev.
Transverse force generated by an electric field and transverse charge imbalance in spin-orbit coupled systems
We use linear response theory to study the transverse force generated by an
external electric field and hence possible charge Hall effect in spin-orbit
coupled systems. In addition to the Lorentz force that is parallel to the
electric field, we find that the transverse force perpendicular to the applied
electric field may not vanish in a system with an anisotropic energy
dispersion. Surprisingly, in contrast to the previous results, the transverse
force generated by the electric field does not depend on the spin current, but
in general, it is related to the second derivative of energy dispersion only.
Furthermore, we find that the transverse force does not vanish in the
Rashba-Dresselhaus system. Therefore, the non-vanishing transverse force acts
as a driving force and results in charge imbalance at the edges of the sample.
The estimated ratio of the Hall voltage to the longitudinal voltage is . The disorder effect is also considered in the study of the
Rashba-Dresselhaus system. We find that the transverse force vanishes in the
presence of impurities in this system because the vertex correction and the
anomalous velocity of the electron accidently cancel each other
Temperature-Dependent Rate Constants and Substituent Effects for the Reactions of Hydroxyl Radicals With Three Partially Fluorinated Ethers
Rate constants and temperature dependencies for the reactions of OH with CF3OCH3 (HFOC-143a), CF2HOCF2H (HFOC-134), and CF3OCF2H (HFOC-125) were studied using a relative rate technique in the temperature range 298-393 K. The following absolute rate constants were derived: HFOC-143a, 1.9E-12 exp(-1555/T); HFOC-134, 1.9E-12 exp(-2006/T); HFOC-125, 4.7E-13 exp(-2095/T). Units are cm(exp 3)molecule(exp -1) s(exp -1). Substituent effects on OH abstraction rate constants are discussed, and it is shown that the CF3O group has an effect on the OH rate constants similar to that of a fluorine atom. The effects are related to changes in the C-H bond energies of the reactants (and thereby the activation energies) rather than changes in the preexponential factors. On the basis of a correlation of rate constants with bond energies, the respective D(C-H) bond strengths in the three ethers are found to be 102, 104, and 106 kcal/mol, with an uncertainty of about 1 kcal/mol
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