Miracle-dz/UniFAR-FTUs huggingface dataset:
A new theory of the instability of a uniform fluidized bed

The form of the momentum equation for one-dimensional (vertical) unsteady mean motion of solid particles in a fluidized bed or a sedimenting dispersion is established from physical arguments. In the case of a fluidized bed that is slightly non-uniform this equation contains two dependent variables, the local mean particle velocity V and the local concentration ϕ, and several statistical parameters of the particle motion in a uniform bed. All these parameters are functions of ϕ with clear physical meanings, and the important ones are measurable. It is a novel feature of the equation that it contains two explicit contributions to the bulk modulus of elasticity of the particle configuration, one arising from the transfer of particle momentum by velocity fluctuations and one arising from the effective repulsive force exerted between particles in random motion. This latter contribution, which proves to be the more important of the two, is related to the gradient diffusivity of the particles, a key quantity in the new theory. The equation of mean motion of the particles and the equation of particle conservation are sufficient to determine the behaviour of a small disturbance with sinusoidal variation of V and ϕ in the vertical direction. Particle inertia forces in such a propagating wavy disturbance may promote amplitude growth, whereas particle diffusion tends to suppress it, and instability occurs when the particle Froude number exceeds a critical value. Rough estimates of the relevant parameters allow the criterion for instability to be put in approximate numerical from for both gas-fluidized beds (for which the flow Reynolds number at marginal stability is small) and liquid-fluidized beds of solid spherical particles (for which the Reynolds number is well above unity), although more information about the particle diffusivity in particular is needed. The predictions of the theory appear to be in qualitative accord with the available observational data on instability of gas- and liquid-fluidized beds.
Quantum Walk on the Line

Motivated by the immense success of random walk and Markov chain methods in the design of classical algorithms, we consider {\em quantum\/} walks on graphs. We analyse in detail the behaviour of unbiased quantum walk on the line, with the example of a typical walk, the ``Hadamard walk''''. In particular, we show that after~$t$ time steps, the probability distribution on the line induced by the Hadamard walk is almost uniformly distributed over the interval~$[-t/\sqrt{2},\;t/\sqrt{2}]$. This implies that the same walk defined on the circle mixes in {\em linear\/} time. This is in direct contrast with the quadratic mixing time for the corresponding classical walk. We conclude by indicating how our techniques may be applied to more general graphs.
Fermi-Surface Instabilities in the Organic Conductor (TMTSF)2NO3: High-Pressure Studies

The study of the magnetoresistance in the organic quasi-one-dimensional conductor (TMTSF)2NO3 at a pressure (8 kbar) exceeding the critical pressure required for the stabilization of a conducting state at low temperature has revealed the existence of quantum oscillations with a frequency of 190 T in good agreement with an extended Huckel-type calculation of the band structure. Unlike other members of the (TMTSF)2X series the ambient pressure SDW ground state in (TMTSF)2NO3 can be understood in terms of an instability involving the nesting of 2D semi-metallic Fermi surfaces.
Dynamical regimes of a multistripe laser array with external off-axis feedback

We theoretically study the dynamics of a multistripe laser array with an external cavity formed by either one or two off-axis feedback mirrors, which allow us to select a single lateral supermode with transversely modulated intensity distribution. We derive and analyze a reduced model of such an array based on a set of delay differential equations, taking into account transverse carrier grating in the semiconductor medium. With the help of the bifurcation analysis of the reduced model, we show the existence of single and multimode instabilities leading to periodic and irregular pulsations of the output intensity. In particular, we observe a multimode instability leading to a periodic regime with antiphase oscillating intensities of the two counter-propagating waves in the external cavity. This is in agreement with the result obtained earlier with the help of a 2+1 dimensional traveling wave model.
Equilibrium phase-space distributions and space charge limits in linacs

Limits on beam current and emittance in proton and heavy ion linear accelerators resulting from space charge forces are calculated. The method involves determining equilibrium distributions in phase space using a continuous focusing, no acceleration, model in two degrees of freedom using the coordinates r and z. A nonlinear Poisson equation must be solved numerically. This procedure is a matching between the longitudinal and transverse directions to minimize the effect of longitudinal-transverse coupling which is believed to be the main problem in emittance growth due to space charge in linacs. Limits on the Clinton P. Anderson Meson Physics Facility (LAMPF) accelerator performance are calculated as an example. The beam physics is described by a few space charge parameters so that accelerators with different physical parameters can be compared in a natural way. The main result of this parameter study is that the requirement of a high-intensity beam is best fulfilled with a low-frequency accelerator whereas the requirement of a high-brightness beam is best fulfilled with a high-frequency accelerator.
A 5 Hz flashlamp pumped Cr:LiSAF multipass amplifier for ultrashort pulses

We report here the operation, at 5 Hz, of a multipass flashlamp pumped Cr:LiSAF ultrashort pulse amplifier, presenting peak powers over 0.3 TW. This unusual high repetition rate was obtained by using a two-flashlamp pumping scheme, aiming at the minimization of the thermal load on the gain medium by the use of intracavity absorption filters. This cavity was used as a four-pass multipass amplifier in a hybrid Ti:sapphire/Cr:LiSAF system. The maximum amplification factor was 150, and the compressed pulse duration was 60 fs.
Dispersion characteristic and stability analysis for an arbitrary MRTD scheme with variable mesh

Variable mesh allows volumic methods such as MRTD to provide a better description of complex structure details with some substantial saving in terms of computer execution time and memory. However, irregular meshing produces some local increase of velocity error and raises some issue about stability. The dispersion characteristic of S‐MRTD‐Battle‐Lemarie schemes is derived for irregular meshing and the stability of the algorithm investigated. Then, the S‐MRTD is coupled with FDTD to accelerate computations when irregular meshing technique is required. Finally, examples of applications demonstrate the relevance of the hybrid procedure. Copyright © 2010 John Wiley & Sons, Ltd.
Active Pixel Sensors for Direct Detection of Soft X-rays

The imaging of soft X-ray images is typically performed with charge coupled devices (CCDs). However, these can have limited readout speed, dynamic range and can also require significant cooling to obtain the required signal to noise ratio. Active pixel sensors (APS) are able to combine faster readout speeds and higher dynamic range with in-pixel intelligence to allow region of interest readout and adaptive gain. To obtain high detection efficiency and 100% pixel fill factor the sensor is back thinned and illuminated from the backside. We report on the characterization of a back-thinned APS (Vanilla); an array of 512 ? 512 pixels of size 25 ? 25 microns. The sensor has a 12-bit digital output for full frame mode, as well as being able to be readout in a fully programmable Region-Of-Interest (ROI) analogue mode. In full frame, the sensor can operate at a readout rate of more than 100 frames per second. Characterization of the detector was carried out through the analysis of photon transfer curves to yield measurements of the full well capacity, noise levels, gain constants and device linearity. Spectral response measurements were made to show the improvement in detection efficiency using a backthinned sensor. A typical synchrotron experiment was performed at the Diamond Light Source (DLS) using Soft X-rays ( ~ 700 eV) to produce a diffraction pattern from a permalloy sample. The pattern was imaged at a range of frame rates, up to 20Hz, and a range of temperatures for both a back-thinned Vanilla and a Princeton PIXIS-XO: 2048B CCD. The results of which are compared. The detection efficiency of the APS is shown to be comparable to the CCD for a given frame rate (0.1Hz), with similar noise levels. We suggest that the back-thinned APS are a viable technology choice for the direct detection of soft X-rays for synchrotron applications.
Turbulence Structure of Particle-Laden Flow in a Vertical Plane Channel Due to Vortex Shedding

Turbulence modulation in particle-laden flow, especially the influence of vortex shedding, was investigated by means of the direct numerical simulation. To this end, we developed a finite-difference scheme to resolve the flow around each particle moving in turbulence. The method was applied to the flow around a sphere and the accuracy was confirmed up to the Reynolds number range with vortex shedding. The agreement between our 4th-order central finite-difference method and spectral method for turbulent channel flow without particles was also fine. Then, we simulated upward flow in a vertical channel including solid particles. The velocity and vorticity fluctuations as well as Reynolds shear stress were strongly affected by wakes from particles. The shed vortices were elongated in the mainstream direction by the velocity gradient and resulted in the hairpin vortices. They increased the energy production rate in couple with production due to particle-turbulence correlation.
On mappings contractive in the sense of Kannan

Let f: X -* X be a continuous compact mapping of a metric space (X, d) into itself with the property that x, y E X and x 9 y implies d(f(x),f(y)) < J[d(x,f(x)) + d(y,f(y))]. It is shown that under these conditions f has a unique fixed point and, moreover, f is a Banach contraction relative to a suitable remetrization of the space X. A similar result concerning condensing mappings is also obtained.
ASCA Observations of the Lensing Clusters CL 0500–24, CL 2244–02, and A370: Mass Determinations and Comparisons

ASCA observations of three gravitational lensing clusters, CL 0500-24, CL 2244-02, and A370, are presented. The X-ray temperatures of the three clusters are determined, respectively, at 7.2 (5.4-10.9), 6.5 (5.2-8.3), and 6.6 (5.7-7.7) keV (90% error), while the X-ray luminosities are determined to be 1.7, 1.3, and 8.3 × 1044 ergs s-1 in the 2-10 keV band. We also obtained significant constraints on the surface brightness profile assuming the β-model and the King model (i.e., the β-model with β = 1) profiles. The mass of the cluster estimated from these X-ray data is smaller by a factor of 2-3 than the mass estimated from lens models for two of the clusters, CL 0500-24 and A370, while the two independent mass estimates are consistent with each other for CL 2244-02. We suspect that the major cause of mass discrepancy of CL 0500-24 and A370 is in the projection effect of substructures of these clusters.
Understanding bursty behavior in midlatitude geomagnetic activity

[1] We provide a new example of a natural system exhibiting statistical signatures of complex scaling behavior predicted by the contemporary theory of nonequilibrium phase transitions. We examine statistical properties of bursty multiscale energy dissipation in the inner magnetosphere of Earth based on the dynamics of the SYM-H index, a global marker of low-latitude geomagnetic fluctuations. We show that on average, and for time scales shorter than 2 h, temporal development of SYM-H bursts follows an algebraic form consistent with the predictions from the theory of nonequilibrium phase transitions. Probability distributions of sizes and lifetimes of the activity bursts reveal no characteristic scales other than the scales imposed by technical limitations of the analysis. This behavior is observed for a wide range of SYM-H burst durations starting from about 5 min up to 10–15 days. The power law exponents describing the probability distributions suggest that the main energy dissipation in the inner magnetosphere takes place because of large activity bursts such as major space storms as opposed to smaller activations whose contribution is less significant despite their much higher relative occurrence. The results obtained provide statistical evidence that the energy dissipation mechanisms associated with magnetospheric activity in the inner magnetosphere are essentially “scale-free,” displaying dynamical and statistical self-similarity. Our results can also be used for validating existing and future ring current models in terms of their ability to correctly represent the cross-scale coupling effects in this system. They show what could be the first quantitative evidence for the same universality class as directed percolation in a natural system.
The linear evolution of centrifugal instabilities in curved, compressible mixing layers

The linear development of Gortler vortices in a curved compressible mixing layer is studied. It has been shown both experimentally and theoretically that the curved mixing layer can support a centrifugal mode, which is believed to be similar to the Gortler vortex mode. This study follows the corresponding incompressible study of Otto, Jackson, and Hu, and attempts to demonstrate the effects compressibility has on the growth of such modes [J. Fluid Mech. 315, 85 (1996)]. The ultimate downstream fate of the modes is studied in the high Taylor/Gortler number regime. The problem of the third boundary condition inherent to the mixing layer model is addressed using the set of boundary conditions for both subsonic and supersonic flows derived by Ting [J. Math. Phys. 28, 153 (1959)]. A class of modes is discussed that have no counterpart in the uniform temperature incompressible case.
Pipe performance analysis with nonparametric regression

Asbestos cement (AC) water mains were installed extensively in North America, Europe, and Australia during 1920s-1980s and subject to a high breakage rate in recent years in some utilities. It is essential to understand how the influential factors contribute to the degradation and failure of AC pipes. The historical failure data collected from twenty utilities are used in this study to explore the correlation between pipe condition and its working environment. In this paper, we applied four nonparametric regression methods to model the relationship between pipe failure represented by average break rates and influential variables including pipe age and internal and external working environmental parameters. The nonparametric regression models do not take a predetermined form but it needs information derived from data. The feasibility of using a nonparametric regression model for the condition assessment of AC pipes is investigated and understood.
Optical Characteristic of the Strain‐Controlled GaN Epitaxial Layer Grown on 6H‐SiC Substrate by an Adapting (GaN/AlN) Multibuffer Layer

GaN epitaxial layers were grown on a (0001) 6H-SiC substrate by metalorganic vapor phase epitaxy by adapting a (GaN/AlN) multibuffer layer. Successful control of residual strain in the epitaxial layers was achieved by changing the layer structure of the (GaN/AlN) multibuffer layer. The lattice constant c of the thin GaN epitaxial layer (as thin as 0.1 μm) was close to that of freestanding GaN, where the thin GaN layer was grown on the substrate by adapting the multibuffer layer. In addition, the (GaN/AIN) multibuffer layer is effective not only for control of the residual strain included in a GaN epitaxial layer, but also for improving the quality of a GaN epitaxial layer.
An abstract ultraparabolic integrodifferential equation

We prove an existence and uniqueness result for a ultraparabolic integrodifferential equation in the strip [0, T1 ] × [0, T2 ] in the context of the spaces of continuous functions with values in a Banach space X and we give some applications to specific partial integrodifferential problems.
HPV Testing Can Be Used As a Primary Screening Method for Cervical Lesions among Women in Western China

Objective : Cervical cancer screening has gradually changed from single cytology to diversification, and HPV testing has steadily become a primary screening method. The purpose of our study is to explore screening strategies suitable for cervical cancer and precancerous lesions in Western Chinese women. Methods : Between January 2010 and December 2020, a total of 7009 patients were diagnosed with high-grade squamous intraepithelial neoplasia (CIN2+) after HPV testing, cytology screening or a combination of both. Results : The mean age of these patients was 40±1 years, the positive rate of human papillomavirus (HPV) was 91.2% and the cytology was 75.1%. The positive rate and negative rate of co-testing were 68.8% and 2% respectively. The positive rate of HPV16/18 was 50.6% and that of HPV52/58/33 was 50.4%, the difference was 0.2%. HPV16/18-positive and cytology-negative infection rate was 54.5%, HPV52/58/33-positive and cytology-negative infection rate was 44.7%, the difference was 9.8%. Conclusion : The common genotypes of HPV infection are HPV16, 58, 52, 33 and 18. Cytology negative patients with HPV52/58/33 positive are recommended to be referred for colposcopy as soon as possible. HPV testing is the primary method of cervical cancer or cervical lesions screening among women in western China, and HPV testing is more sensitive than cytology in predicting cervical lesions.
Improved subgrid-scale models for large-eddy simulation

The paper analyzes models for subgrid-scale turbulence. The analysis indicates that there is sufficient information in the resolved scales to determine some characteristics of the complete flow field. The kinetic energy of the small-scale motions can be decomposed into two parts: one results from the large scales and is correlated with them, and the other part is uncorrelated which leads to a two-component eddy-viscosity model. The 'production equals dissipation' argument does not apply to the small scales in the decay of turbulence because it does not account for the uncorrelated component. The exchange between the large and small scales takes place mainly between the smallest scales of the former and the largest scales of the latter; this argument is the basis of a new model shown to be superior to the Smagorinsky model (1963).
Mathematical Theory of a Kinetic Model for Dispersion of Previously Distributed Chemicals in a Sorbing Porous Medium

The problem of mass transport and dispersion of materials through porous media has been increasingly becoming important in industry, agriculture, biophysical and biochemical studies. The existing mathematical treatment of these problems consists in assuming simple distribution laws relating the free phase chemical concentration in the medium and the resulting field equations are generally solved numerically. In the present investigation we have developed a physically realistic dynamic model for the free and sorbed phase distributions and we have obtained exact solutions of the field equations by analytical means using operational and repeated contour integration methods involving convolutions. This is an important step in the development of this direction of study since these analytical models and mass transport predictions pave the way for a better and more complete understanding of the dispersion phenomena than what the numerical techniques alone can provide. Furthermore, many interesting new results ha.
The abundance of interstellar chlorine in the galaxy

Des largeurs equivalentes nouvellement deduites de spectres IUE ont ete combinees a des largeurs equivalentes de Copernicus pour evaluer les abondances interstellaires du chlore pour plus de 40 lignes de visee galactiques. L'abondance presente une decroissance marquee avec l'augmentation de n(H) suivant la relation approchee a(Cl)≃4,9-0,3 log [n(H) cm −3 ]. Le chlore semble adherer aux grains de poussiere plus qu'on ne le pensait
Wavelengths of Forbidden Transitions Arising from Levels Within the Fe+19 2s22p3 Ground Configuration

In this paper we report the identification of all remaining unidentified forbidden lines arising from transitions within levels of the Fe+19 ground configuration. These lines were identified using data from the SOHO/SUMER spectrograph and Skylab. Adjusted wavelength values are also given for some previously observed lines. Forbidden lines that are the result of transitions within levels of the ground configuration of a highly ionized astrophysically abundant element generally have longer wavelengths than resonance lines emitted by the same ion. Many of these forbidden lines are fairly prominent in low-density plasmas and traditionally have been used in determining properties of high-temperature astrophysical plasmas. The identified Fe+19 forbidden lines span the 300-2665 Å wavelength range. Since spontaneous decay rates of forbidden transitions arising from the same upper level are known quite accurately, these lines can be used for calibrating spectrometers over wide wavelength ranges.
Light incoherence theory revisited by Heisenberg time-energy uncertainty challenges solar cell optimization

Optimization of the efficiency of solar cells is a major challenge for renewable energies. Using a rigorous theoretical approach, we show that the photocurrent generated in a solar cell depends strongly on the degree of coherence of the incident light. In accordance with Heisenberg uncertainty time-energy, incoherent light at photons of carrier energy lower than the active material bandgap can be absorbed whereas coherent light at the same carrier energy cannot. We identify cases where incoherence does enhance efficiency. This result has a dramatical impact on the way solar cells must be optimized regarding sunlight. As an illustration, surface-corrugated GaAs and c-Si thin-film solar cells are considered.
Signal Detection Theory Applied to Size Constancy in Virtual Environments

Pictorial depth cues and instructional set are two factors that influence the degree to which size constancy maintains in static two-dimensional perspective displays. Signal detection theory (SDT) allows the determination of whether these factors influence observers' sensitivity to perceived size (d') versus their subjective criteria (bias) for making ”same” or ”different” discriminative responses. Two objects were presented at various perceived distances in static perspective displays that varied in number of available pictorial depth cues. Observers made comparative size judgments regarding the objects' apparent distal size (phenomenal instructions) or objective distal size (objective instructions). Observers showed greater sensitivity to distal size differences when responding to apparent, rather than objective size differences. The presence of more pictorial depth cues produced greater sensitivity than a reduced-cue condition, especially under objective instructions. Overall, results indicate that SDT reveals aspects of size perception in pictorial displays not assessed through more traditional analyses based solely on accuracy.