Miracle-dz/UniFAR-FTUs huggingface dataset:
Analysis of flow through heterogeneous random aquifers: 2. Unsteady flow in confined formations

The direct problem of determining the head field in a formation of given stationary isotropic random structure is solved approximately for unsteady flow conditions. Under restrictive assumptions of sufficiently small conductivity variance and average head gradient slowly varying in time and space, closed form expressions are derived for the effective conductivity or storativity and for the head variogram. Two types of unsteady flow are considered: transients and periodic flows. In the case of transients, it is assumed that initially the head is constant (no flow) and that ultimately the flow becomes uniform. It is found that the effective conductivity and transmissivity are time-dependent and drop from the arithmetic mean (initially) to the steady state value during a relaxation time. The latter is much larger for one-dimensional flows than for two- or three-dimensional ones. The head variogram also relaxes from the one corresponding to the initial lack of correlation to the steady state variogram during a relaxation time which grows with the lag. While in three-dimensional structure the relaxation time scales are relatively short and steady state analysis can be used accurately even under transient conditions, the tendency to steady state may be very slow in the case of transmissivity because of its large integral scale. Hence steady state analysis for transients might not be warranted for regional transient flows. In the case of periodic flows of seasonal nature, the head gradient is assumed to be made up from a steady component and a periodic one. If the amplitude of the latter is sufficiently small compared to the steady one, steady state value of effective transmissivity and storativity can be adopted. The head variogram has also its steady state form for large lags and quasisteady for small lags. Hence the variogram lies between the steady one (steady component of head gradient) and the quasisteady one (instantaneous head gradient).
Evolution of radio quasars for z of less than 2

A sample of 72 radio quasars is used to study the cosmic and individual evolution of quasars in the 1-2 redshift range. It is shown that the most luminous sources at all redshifts are unresolved, and that one-sided and two-sided structures correspond to progressively lower core (and total) luminosities. The sizes and fractional population of triple sources are found to fall steadily with increasing redshift to z of about 1.7. A correlation over many orders of magnitude is noted between the optical and maximum radio-core luminosity. 15 refs.
A digital acoustic recording tag for measuring the response of marine mammals to sound

There is growing concern about the effect on marine mammals of underwater sound sources such as vessels, industrial equipment, and sonar. In order to quantify the reaction of these animals to sound, controlled exposure experiments have been attempted using surface observations or vocal monitoring to estimate response. However, the short surface time of most marine mammals, and their often unknown vocalization rates, limit the effectiveness of such experiments. To address these problems, a small digital recording tag, the DTAG, has been developed capable of simultaneously sampling the acoustic environment of the host animal, together with its orientation, heading, and depth. The tag has a 400‐Mbyte memory array sufficient to record audio and sensor signals for several hours. The tag is encapsulated in a plastic resin and can operate at a water depth up to 3000 m. Programing and data off‐load are accomplished with an infrared communications link to a personal computer. The DTAG has been deployed on northern.
Liquid Sheet Formed by Impingement of Two Viscous Jets

Impinging-jet injectors are commonly used in liquid-propellant rocket engines. Previous theoretical studies on sheets formed by two impinging liquid jets have largely ignored the affect of liquid viscosity, however, several experimental results have illustrated that liquid viscosity could greatly influence sheet characteristics. This paper proposes an improved theoretical analysis model for two viscous liquid impinging jets, in which viscosity and energy dissipation are taken into account; experiments were also performed to validate the theory. Furthermore, based on this model, the effects of impingement angle, jet velocity profile, Weber number, and Reynolds number on sheet characteristics, such as sheet shape, thickness, and velocity distribution, were investigated.
Molecular doping for control of gate bias stress in organic thin film transistors

The key active devices of future organic electronic circuits are organic thin film transistors (OTFTs). Reliability of OTFTs remains one of the most challenging obstacles to be overcome for broad commercial applications. In particular, bias stress was identified as the key instability under operation for numerous OTFT devices and interfaces. Despite a multitude of experimental observations, a comprehensive mechanism describing this behavior is still missing. Furthermore, controlled methods to overcome these instabilities are so far lacking. Here, we present the approach to control and significantly alleviate the bias stress effect by using molecular doping at low concentrations. For pentacene and silicon oxide as gate oxide, we are able to reduce the time constant of degradation by three orders of magnitude. The effect of molecular doping on the bias stress behavior is explained in terms of the shift of Fermi Level and, thus, exponentially reduced proton generation at the pentacene/oxide interface.
Use of Phase for the Detection of Hidden Periodicites

Standard tests for the detection of hidden periodicities in time series are largely ignored by applied workers. Various simple but inappropriate methods are used instead. Therefore a method is suggested which is both simple and appropriate but which requires the prior knowledge of certain characteristics of the suspected periodicity. For illustration, this method is applied to a set of data from a chronobiological study.
The screening effect in Kriging

When predicting the value of a stationary random field at a location x in some region in which one has a large number of observations, it may be difficult to compute the optimal predictor. One simple way to reduce the computational burden is to base the predictor only on those observations nearest to x. As long as the number of observations used in the predictor is sufficiently large, one might generally expect the best predictor based on these observations to be nearly optimal relative to the best predictor using all observations. Indeed, this phenomenon has been empirically observed in numerous circumstances and is known as the screening effect in the geostatistical literature. For linear predictors, when observations are on a regular grid, this work proves that there generally is a screening effect as the grid becomes increasingly dense. This result requires that, at high frequencies, the spectral density of the random field not decay faster than algebraically and not vary too quickly. Examples demonstrate that there may be no screening effect if these conditions on the spectral density are violated.
Simulation of the Kelvin-Helmholtz Instability in the Magnetized Slab Jet

Two-dimensional magnetohydrodynamic simulations are performed to study the evolution of the Kelvin-Helmholtz instability for a slab jet moving parallel to the magnetic field. Surface waves are excited at each of the side boundaries, and the time evolution of the individual mode, as well as its interaction with the mode excited at the opposite boundary, is observed. The instability is very disruptive when the excited perturbations on the two side boundaries are antisymmetric. The long-term evolution of the antisymmetric perturbation shows a kinklike magnetic field structure after multiple reconnection events, while the symmetric perturbation yields wavy signatures only around the jet boundaries. Three different cases of the thin slab jet are considered with the antisymmetric perturbation: a hydrodynamic jet, a jet embedded in a uniform magnetic field, and a thermally confined magnetized jet. Although the imposed magnetic fields are weak, they show quite different evolutions. In the hydrodynamic case, the density and flow patterns associated with the vortices survive until the end of the simulation without significant changes after the initial development of the instability. For the jet embedded in a uniform magnetic field, the density pattern associated with the vortex is destroyed as magnetic reconnection develops, and a steady increase in density from the central jet region toward the side boundaries is seen at the final stage when the magnetic field becomes flat again. The density and flow structures in the thermally confined magnetized jet are similar to those of the hydrodynamic case, but they change slowly with the evolution of the magnetic field. Also, it is seen that the magnetic fields that originally reside in the jet are expelled out to the side boundaries. Similar results are obtained for both the transonic jet and the supersonic jet, but the density variation is more significant in the supersonic case.
FLOW CHARACTERISTICS AROUND AN INCLINED ELLIPTIC CYLINDER IN A TURBULENT BOUNDARY LAYER

Abstract The flow characteristics around an inclined elliptic cylinder located near a flat plate were investigated experimentally. The axis ratio of the elliptic cylinder was AR=2. The pressure distributions along the surface of the cylinder and the flat plate were measured by varying the angle of attack of the elliptic cylinder. The velocity profiles behind the cylinder were measured using hot-wire anemometry. When the angle of attack varies, the peak pressure location on the windward cylinder surface moves towards the rear edge of the cylinder, while that on the leeward surface moves towards the front edge of the cylinder. The vortex-shedding frequency also gradually decreases, defining a critical angle of attack for each gap ratio. The location of the minimum pressure on the flat plate surface moves downstream for positive angles of attack, while it moves upstream for negative angles of attack. Negative angles of attack cause a greater disturbance in the boundary layer near the wall compared to positive angles of attack. This shows that the separated wall shear layer from the boundary layer and the lower shear layer of the cylinder wake are strongly merged compared to other cases.
Gas Flow Resistance Measurements Through Packed Beds at High Reynolds Numbers

Abstract : This work reviews the literature on gaseous flow pressure resistance in packed beds and found important differences depending on test conditions and Reynolds number ranges. A test apparatus was constructed which allowed for the testing over a wide range of pressures, test conditions, and Reynolds number range several orders of magnitude higher than previously tested. From the resulting data it was ascertained that the classical Reynolds number dependency of the coefficient of drag is not correct for Reynolds numbers greater than 1000. A new correlation for the coefficient of drag was developed, which indicated that a new factor, the kinetic energy of the gases being forced through the bed, must be taken into account. This formula was shown to be valid for a Reynolds number range 1,000 - 100,000, for particles ranging in diameter from 1 mm through 6 mm. This correlation of transient two-phase flows at high pressures, as needed in the modeling effort for deflagration-to-detonation (DDT) in granular beds of propellant.
On the Possibility of Acceleration of Heavy Solar and Cosmic Nuclei To GeV, TeV Energies and Beyond

On acceleration of relativistic electrons by any means, the coherent pinch effect brings the relativistic electrons together. The inclusion of a suitable number of positive ions, preferentially heavy ions would stabilize the beam. The heavy trapped nuclei would have to go with the electrons, thus acquire relativistic speeds. The electron beam may be divided into small bunches. This mechanism can accelerate positive nuclei to GeV and TeV energies during solar flares, stellar and galactic high energy events. During the acceleration of 1000 GeV electron bunches, the energy gained by trapped positive nuclei is estimated to reach 10$^{15}$ eV per nucleon. Higher energies can be achieved by head on collision as the energy gained by the target nucleus is proportional to $\gamma^{2},$ however fission reactions and very high energy gamma rays may occur. The principle of this mechanism is applied in electron-ring accelerators.To search for other articles by the author(s) go to: http://adsabs.harvard. edu/abstract_service. html
Phase Front Instability in Periodically Forced Oscillatory Systems

Multiplicity of phase states within frequency locked bands in periodically forced oscillatory systems may give rise to front structures separating states with different phases. A new front instability is found within bands where $\omega_{forcing}/\omega_{system}=2n$ ($n>1$). Stationary fronts shifting the oscillation phase by $\pi$ lose stability below a critical forcing strength and decompose into $n$ traveling fronts each shifting the phase by $\pi/n$. The instability designates a transition from stationary two-phase patterns to traveling $n$-phase patterns.
Blue luminescent silicon nanocrystals prepared by ns pulsed laser ablation in water

Here the authors report on a simple and cost-effective procedure to prepare blue luminescent colloidal silicon nanocrystals (Si-ncs) in de-ionized water at room temperature and atmospheric pressure by nanosecond pulsed laser ablation. At low laser fluences well-separated and spherical Si-ncs aggregates are formed. The fluence increase leads to fragmentation of spherical aggregates and the generation of finer Si-ncs with quantum confinement size effect. After aging in de-ionized water, such irregular Si-ncs fragments get stabilized into quite regular spheres and ovals. During the aging process the increase of blue room temperature photoluminescence centered around 2.9eV is recorded.
Adhesive elastic plastic contact: theory and numerical simulation

We examine the adhesive contact of an elastic‐plastic sphere and a rigid plane. We assume that the contact is normal and frictionless. First, a Molecular Dynamics (MD) simulation of the contact of an amorphous van der Waals solid is performed. Next, a simple model (EP) for the elastic plastic contact is presented, which has as asymptotic limit the singular model (SS) developed by Mesarovic and Johnson in [1]. Finally, the numerical results are quantitatively compared and discussed in relation to the EP and SS models, and qualitatively with Tomas' model [2]. Acknow This work has been supported by the Ministerio de Educación y Ciencia of the Spanish Government under contract number BFM2003‐1739, and by the Junta de Andalucía under project FQM‐421. A significant technical part of this work has been additionally performed under the Project HPC‐EUROPA (RII3‐CT‐2003‐506079), with the support of the European Community – Research Infrastructure Action under the FP6 “Structuring the European Research Area” Programme.
Coherent state path integral approach to multi-time correlation functions and photon emission in a semiconductor microcavity

In this paper by using the coherent state path integral field theory approach, we calculate the grand canonical partition function of an interacting combined system in the presence of the relevant source terms. It allows us to calculate multi-time correlation functions of interacting systems without using the quantum regression theorem. Then, we investigate the power spectrum and the second-order correlation function of the emitted photons from a microcavity in the presence of excitations of a semiconductor quantum well. By using the Hubbard–Stratonovich transformation, we investigate the effects of reservoir, detuning, the Coulomb interaction and the phase space filling on the power spectrum and the second-order correlation function of the emitted photons.
A Sensitivity Study of Convective Cloud Formation by Vegetation Forcing with Different Atmospheric Conditions

Abstract Variable vegetation cover is a possible trigger for convection, especially in semiarid areas due to differential surface forcing. A two-dimensional numerical model with explicit cloud physics and a detailed vegetation parameterization scheme is used to investigate the role of vegetation differences in triggering convective cloud formation. The ground surface in all simulations includes two irrigated vegetation areas with a dry steppe in the center of the domain. The effects of atmospheric stability, ambient moisture profile, and horizontal heating scale are investigated. Atmospheric stability controls the growth of convective circulations. Thermal circulations form at the interfaces between the vegetated areas and the dry steppe. In the more stable environment, two distinct convective cells persist; they merge into one cell in the less stable cases. The existence of low-level moisture controls the timing and persistence of clouds that form. An interesting result is the earlier dissipation of clou.
Thermal Afterglow from Transient Energy Release in Neutron Stars

Thermal afterglow from transient energy releases in neutron stars, such as may result from glitches or gamma-ray bursts, is considered. If observable, thermal afterglow may provide important information on the nature of these events and on neutron star structure. For standard neutron star models, the energy released is either reradiated within a short time of at most hours for energy release near the surface, or most of the energy is stored in the deep interior and then reradiated over thousands of years. Intermediate time scales of order months are possible for afterglow, but only when the prompt afterglow accounts for a very small fraction of the total energy release, and enormous energy releases of about 10 to the 42nd ergs are required to make the afterglow last much longer than a few hours. An observational program to detect afterglow will need to accommodate short time scales. 13 references.
Constructing all entanglement witnesses from density matrices

We demonstrate a general procedure to construct entanglement witnesses for any entangled state. This procedure is based on the trace inequality and a general form of entanglement witnesses, which is in the form W={rho}-c{sub {rho}}I, where {rho} is a density matrix, c{sub {rho}} is a non-negative number related to {rho}, and I is the identity matrix. The general form of entanglement witnesses is deduced from Choi-Jamiolkowski isomorphism, that can be reinterpreted as that all quantum states can be obtained by a maximally quantum entangled state pass through certain completely positive maps. Furthermore, we provide the necessary and sufficient condition of the entanglement witness W={rho}-c{sub {rho}}I in operation, as well as in theory.
Effect of fluid flow on the fluctuations at the surface of an elastic medium

The effect of a linear shear flow of a Newtonian fluid in the region 0<z<∞ on the fluctuations at the surface of an elastic medium of thickness H in the region −H<z<0 is analyzed in the regime Re≫1 and Λ∼1, where Re=ργH2/η is the Reynolds number and Λ=(ργ2H2/E)1/2 is the ratio of the inertial stresses in the fluid and the elastic stresses in the solid. Here ρ and η are the fluid density and viscosity, E is the coefficient of elasticity of the solid, and γ is the mean strain rate in the fluid. A linear analysis is used to determine the effect of the flow on the fluctuations in the surface displacement, and an asymptotic expansion in the small parameter e=(Λ/Re) is employed. The dynamics in the bulk of the fluid is inviscid in the leading approximation, and the leading order growth rate is imaginary because energy is conserved in the absence of viscous dissipation. There are multiple frequencies of oscillation, all of which satisfy the equations of motion. An increase in the fluid velocity increases the fre.
A brief historical development of classical mathematics before the Renaissance

‘If you wish to foresee the future of mathematics our proper course is to study the history and present condition of the science. ’ Henri Poincaré ‘It is India that gave us the ingenious method of expressing all numbers by ten symbols, each symbol receiving a value of position, as well as an absolute value. We shall appreciate the grandeur of the achievement when we remember that it escaped the genius of Archimedes and Apollonius. ’ P.S. Laplace ‘The Greeks were the first mathematicians who are still ‘real’ to us today. Oriental mathematics may be an interesting curiosity, but Greek mathematics is the real thing. The Greek first spoke of a language which modern mathematicians can understand. ’ G.H. Hardy This article deals with a short history of mathematics and mathematical scientists during the ancient and medieval periods. Included are some major developments of the ancient, Indian, Arabic, Egyptian, Greek and medieval mathematics and their significant impact on the Renaissance mathematics. Special attention is given to many results, theorems, generalizations, and new discoveries of arithmetic, algebra, number theory, geometry and astronomy during the above periods. A number of exciting applications of the above areas is discussed in some detail. It also contains a wide variety of important material accessible to college and even high school students and teachers at all levels. Included also is mathematical information that puts the professionals and prospective mathematical scientists at the forefront of current research.
Buckling and Wrinkling of a Functionally Graded Material (fgm) Thin Film

The instability of a functionally graded material (FGM) strip as a free standing film or a substrate-bound film is studied in this work, in which the stiffness of the film is assumed to change exponentially along the length. The buckling load and the buckling mode shapes for the free standing FGM film are determined analytically. For the substrate-bound film, the substrate is modeled as a Winkler foundation and the wrinkling load and wrinkling pattern are determined numerically by using a finite difference method and a series solution. In contrast with the wrinkling of homogenous thin films in which the wrinkles propagate in the entire domain, the wrinkles of the FGM films accumulate around the location with the least bending rigidity. The results of this work show that the sensitivity of the wrinkle accumulation around the weak locations of the system with lower stiffness is very high. This work is expected to provide a better understanding for localization of wrinkles around a region of substrate-bounded thin films in thin film technology.