Miracle-dz/UniFAR-FTUs huggingface dataset:
Decrement of spanwise vortices by a drag-reducing riblet surface

In this paper, the spanwise vortices in a turbulent flow over drag-reducing V-shaped riblet grooves have been investigated experimentally. The height and lateral spacing of each V-shaped riblet groove are 176.8 μm and 300 μm, respectively. A high-resolution PIV system was employed to measure the instantaneous velocity fields of the turbulent boundary layer developed over the riblet surface under a drag-reducing condition of s + = 10.4. The contours of the spanwise vortices which show a locally swirling motion were derived by using a vortex-identification technique. After extracting the cores of the spanwise vortices from instantaneous PIV velocity fields, the number distributions of the vortex cores were analyzed statistically. In addition, the spatial distributions of mean velocity, turbulence intensity and Reynolds stress were also obtained. All experimental results were compared with those over a flat smooth surface. As a result, the number distributions of the small-scale spanwise vortices were significantly decreased on the riblet surface. The turbulence intensity and Reynolds stress were also reduced by the drag-reducing effect of the riblet grooves. The decrease of small-scale vortices observed in this study indicates the reduction of small-scale coherent structures in the boundary layer.
On the origin of near-radial magnetic fields in the heliosphere: Numerical simulations

[1] Deviations from the direction of the “Parker spiral” can be found in in situ measurements of the interplanetary magnetic field on essentially all scales. One intriguing subset is the intervals of near-radial magnetic field, lasting for many hours. Some such intervals are obviously associated with coronal mass ejections, while others appear to be embedded within the ambient solar wind. Most occur on declining speed profiles, such that, when mapped back to the Sun, an entire radial field interval appears to have been launched at approximately the same time. It has been proposed that these events are the result of abrupt, semipermanent speed decreases on these field lines close to the Sun, and that such speed changes might be due to interchange reconnection. In this study, we use a three-dimensional, time-dependent magnetohydrodynamic model to assess to what extent this can account for near-radial magnetic fields observed relatively far out in the heliosphere. We find that sudden speed drops on the trailing portions of high-speed flows can produce strongly underwound (that is near radial) field lines in the heliosphere, although significantly larger speed gradients are required than are typically observed. Moreover, the simulations also reproduce the decreases in density, temperature, and magnetic field strength that are also commonly observed within these events. The question of what produces the abrupt speed drops remains to be answered.
SPECTRAL PROPERTIES OF BRIGHT FERMI-DETECTED BLAZARS IN THE GAMMA-RAY BAND

The gamma-ray energy spectra of bright blazars of the LAT Bright AGN Sample (LBAS) are investigated using Fermi-LAT data. Spectral properties (hardness, curvature, and variability) established using a data set accumulated over 6 months of operation are presented and discussed for different blazar classes and subclasses: flat spectrum radio quasars (FSRQs), low-synchrotron peaked BLLacs (LSP-BLLacs), intermediate-synchrotron peaked BLLacs (ISP-BLLacs), and high-synchrotron peaked BLLacs (HSP-BLLacs). The distribution of photon index (Γ, obtained from a power-law fit above 100 MeV) is found to correlate strongly with blazar subclass. The change in spectral index from that averaged over the 6 months observing period is < 0.2–0.3 when the flux varies by about an order of magnitude, with a tendency toward harder spectra when the flux is brighter for FSRQs and LSP-BLLacs. A strong departure from a single power-law spectrum appears to be a common feature for FSRQs. This feature is also present for some high-luminosity LSP-BLLacs, and a small number of ISP-BLLacs. It is absent in all LBAS HSP-BLLacs. For 3C 454.3 and AO 0235+164, the two brightest FSRQ source and LSP-BLLac source, respectively, a broken power law (BPL) gives the most acceptable of power law, BPL, and curved forms. The consequences of these findings are discussed.
Realization and electrical characterization of ultrathin crystals of layered transition-metal dichalcogenides

Ultrathin crystals of the layered transition-metal dichalcogenide MoS2 (semiconducting) and TaS2 (metallic) were obtained by mechanical peeling or chemical exfoliation techniques and electrically contacted using electron-beam lithography. The MoS2 devices showed high field-effect mobility in the tens of cm2∕Vs and an on/off ratio higher than 105. The TaS2 devices remained metallic despite the fabrication process and showed an enhancement of the superconducting transition temperature and disappearance of the charge density wave phase anomaly at low temperature.
Flare loop radiative hydrodynamics. I. Basic methods

Many phenomena occurring in flaring loops involve both the corona and chromosphere: two distinctly different physical environments which nevertheless are strongly coupled by the exchange of matter, energy, and momentum. The aim of the present study is twofold: first, to examine the role of energy transport mechanisms: for instance, thermal conduction in the corona and radiative transfer in the chromosphere: in flare dynamics, and second, to provide diagnostics of flare energization processes by predicting the evolutionary behavior of concurrent emissions from all regions of the flaring atmosphere. To attain these ends, we have developed a numerical method for the simultaneous solution of the continuity, momentum, and energy equations; the time-dependent atomic rate equations describing ionization and excitation; and the radiative transfer equations.
The relaxed CQ algorithm solving the split feasibility problem

Let C and Q be nonempty closed convex sets in RN and RM, respectively, and A is an M by N real matrix. The split feasibility problem (SFP) is to find x C with Ax Q, if such x exists. Byrne proposed an iterative method called the CQ algorithm that involves only the orthogonal projections onto C and Q and does not need to compute the matrix inverse, which may be the main advantage compared with other algorithms. The CQ algorithm is as follows: where γ (0, 2/L), with L being the largest eigenvalue of the matrix ATA and PC and PQ denote the orthogonal projections onto C and Q, respectively. Byrne (2002 Inverse Problems 18 441–53, 2004 Inverse Problems 20 103–20) proved the convergence of the CQ algorithm for arbitrary nonzero matrix A. In his algorithm, Byrne assumed that the projections PC and PQ are easily calculated. In this paper, a modification of the CQ algorithm, called the relaxed CQ algorithm, is given, in which we replace PC and PQ by and , respectively, and the latter are easy to implement. Under mild assumptions, the convergence of the proposed algorithm is established. Then another algorithm for SFP is given; with the help of the CQ algorithm and its relaxed version, it is easy to obtain the convergence of this algorithm and corresponding relaxed scheme.
High-resolution positron scattering from helium: Grand total and positronium-formation cross sections

Measurements of the grand total and positronium-formation cross sections for positrons scattered by helium within the impact energy range from 10 to 60 eV are presented. All measurements presented here use a high-resolution $(\ensuremath{\sim}70\text{ }\text{meV})$ trap-based pulsed positron beam. Scattering is studied using a high-magnetic field, and absolute measurements of the scattering cross sections are obtained without the need for normalization to other cross sections. We also present single center, convergent close coupling calculations of the total cross section. A detailed study of the cross section to investigate the possibility of scattering resonances and channel coupling has been made. Comparisons with previous cross-section measurements and theoretical calculations are also included.
Global control of nonlinear systems with uncertain output function using homogeneous domination approach

This paper addresses the problem of using output feedback to globally control a class of nonlinear systems whose output functions are not precisely known. First, for the nominal linear system, we design a homogeneous state compensator without requiring precise information of the output function, and construct a nonlinear stabilizer with adjustable coefficients by using the generalized adding a power integrator technique. Then based on the homogeneous domination approach, a scaling gain is introduced into the proposed output feedback controller, which can be used by tuning the scaling gain to solve: (i) the problem of global output feedback stabilization for a class of upper‐triangular systems; and (ii) the problem of global practical output tracking for a class of lower‐triangular systems. Copyright © 2011 John Wiley & Sons, Ltd.
Shielding of a slowly moving test charge in a dusty plasma with dynamical grain charging

The dynamical charging of grains in a dusty plasma enhances the shielding of test charges. Time scales for charging are determined by the ambient plasma parameters and the grain dimensions. They can be very short, approaching the ion plasma period for grain sizes of the order of an electron Debye length. For a slowly moving test charge the response potential is found as a power series in the test charge velocity. Collisional effects are included. Analytical expressions for the response potential, valid for all radial distances, are found up to second order in the test charge velocity. The first-order dynamical charging term is shown to be the consequence of the delay in the shielding due to the dynamics of the charging process. The remaining first-order terms are given by analytical expressions that yield the well known asymptotic power law forms for large distances.
A classification of well‐posed kinetic layer problems

In the first part of this paper, we study the half space boundary value problem for the Boltzmann equation with an incoming distribution, obtained when considering the boundary layer arising in the kinetic theory of gases as the mean free path tends to zero. We linearize it about a drifting Maxwellian and prove that, as conjectured by Cercignani [4], the problem is well-posed when the drift velocity u exceeds the sound speed c, but that one (respectively four, five) additional conditions must be imposed when 0 < u < c (respectively - c < u < 0 and u < - c). In the second part, we show that the well-posedness and the asymptotic behavior results for kinetic layers equations with prescribed incoming flux can be extended to more general and realistic boundary conditions.
Comparing cone-partitioned plate and cone-standard plate shear rheometry of a polystyrene melt

For a polystyrene melt with a zero shear rate viscosity of 44.5 kPa s at 190 °C, shear stress and first normal stress difference in step shear rate experiments with cone-standard plate and cone-partitioned plate tools are compared. The cone angle α is 8.5° throughout. With the partitioned plate and a central stem of radius 4 mm, steady state viscosities can be obtained up to shear rates of 100 s−1, about a factor of 3 higher than for the standard plate tool. The strain at the maximum viscosity grows from 2.3 below γ=3 s−1 to 6.5 at γ=100 s−1. This increase can hardly be seen with the standard plate tool. The ratio of the maximum to the steady state viscosity shows a tendency to saturate beyond γ=30 s−1 and reaches 1.75 at γ=100 s−1. This finding is again beyond the scope of the standard plate tool. The ratio of the maximum to the steady state first normal stress difference only shows a minor increase to 1.03 at γ=30 s−1. N1 beyond this strain rate cannot be determined because the maximum thrust of 20 N narrows the range of sample radii too much. It is found that experiments at high shear rates are not limited by edge fracture but by insufficient normal force transducer capacities and by viscous dissipation heating. Calculations show that small cone angles (below 6°) should be used beyond γ=30 s−1 to deal with this. Small cone angles necessarily require very stiff rheometers for a good short time resolution.For a polystyrene melt with a zero shear rate viscosity of 44.5 kPa s at 190 °C, shear stress and first normal stress difference in step shear rate experiments with cone-standard plate and cone-partitioned plate tools are compared. The cone angle α is 8.5° throughout. With the partitioned plate and a central stem of radius 4 mm, steady state viscosities can be obtained up to shear rates of 100 s−1, about a factor of 3 higher than for the standard plate tool. The strain at the maximum viscosity grows from 2.3 below γ=3 s−1 to 6.5 at γ=100 s−1. This increase can hardly be seen with the standard plate tool. The ratio of the maximum to the steady state viscosity shows a tendency to saturate beyond γ=30 s−1 and reaches 1.75 at γ=100 s−1. This finding is again beyond the scope of the standard plate tool. The ratio of the maximum to the steady state first normal stress difference only shows a minor increase to 1.03 at γ=30 s−1. N1 beyond this strain rate cannot be determined because the maximum thrust of 20.
Le grand crible dans la théorie analytique des nombres

© Société mathématique de France, 1974, tous droits réservés. L’accès aux archives de la collection « Astérisque » (http://smf4.emath.fr/ Publications/Asterisque/) implique l’accord avec les conditions générales d’utilisation (http://www.numdam.org/conditions). Toute utilisation commerciale ou impression systématique est constitutive d’une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright.
Study of $CP$ asymmetry in the neutral $B$ meson decays to two charged pions

We present the measurement of CP -violatingasymmetries inB → π+π− decays based on a 78 fb−1 data sample collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We fully reconstruct one neutral B meson as a B → π+π− CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we obtain the CP -violating asymmetry parameters Aππ = +0.77 ± 0.27(stat) ± 0.08(syst) and Sππ = −1.23 ± 0.41(stat) +0.08 −0.07(syst), where the statistical uncertainties are determined from Monte Carlo pseudo-experiments. We rule out the CP -conserving hypothesis, Aππ = Sππ = 0, at a 99.93% confidence level.We discuss how these results constrain the value of CKM angle φ2.
New colour and Zanstra temperatures for 15 central stars of planetary nebulae

On presente les observations spectrophotometriques de l'emission continue des noyaux de 15 nebuleuses planetaires. On en deduit les couleurs et les temperatures de Zanstra. On donne les caracteristiques de chaque objet et on les compare aux resultats d'etudes anterieures
COMPARISON OF DIFFERENT NUMERICAL SCHEMES FOR THE CAHN-HILLIARD EQUATION

In this work, we numerically analyze a class of time discretizations for the Cahn-Hilliard equation. It is useful to investigate the performance of different schemes in terms of accuracy and efficiency since these schemes are frequently used in various science applications. In this work, comparisons of the explicit Euler’s, implicit Euler’s, Crank-Nicolson, semi-implicit Euler’s, linearly stabilized splitting, and non-linearly stabilized splitting schemes are presented. The continuous problem has the conservation of mass and the decrease of the total energy. We check the same properties hold for the discrete problem.
Compactness criteria for Riemannian manifolds

Ambrose, Calabi and others have obtained Ricci curvature conditions (weaker than Myers' condition) which ensure the compactness of a complete Riemamnan manifold. Using standard index form techniques we relate the problem of finding such Ricci curvature criteria to that of establishing the conjugacy of the scalar Jacobi equation. Using this relationship we obtain a Ricci curvature condition for compactness which is weaker than that of Ambrose and, in fact, which is best among a certain class of conditions. One of the most well-known results relating the curvature and topology of a complete Riemannian manifold M is the classical theorem of Myers [8] which states that if the Ricci curvature with respect to unit vectors on M has a positive lower bound then M is compact. (Myers also gives a diameter estimate in terms of this bound.) In 1957 Ambrose [1] published an interesting generalization of Myers' theorem. He proved that if there is a point q M in such that along each geodesic y: [0, oo) -M emanating from q (and parameterized by arc length t) the Ricci curvature satisfies f Ric(dY dtY ) dt = +oo then M is compact. One of the important features of this result is that the Ricci curvature is not required to be everywhere nonnegative. The author, together with T. Frankel, has applied Ambrose's theorem to certain problems in general relativity (see [4]). In this paper we present a general technique for establishing compactness criteria for complete Riemannian manifolds. As an application of this technique we obtain a generalization of Ambrose's theorem, which, with respect to a certain class of curvature conditions, is best. This generalization can be used to improve some of the results in [4]. (See, especially, Theorem 5 and Corollary 6 of that paper.) We take a moment to introduce some notation and terminology. Throughout, let M denote a smooth complete Riemannian manifold of dimension n > 2. Let be the Riemannian metric on M and let V be the associated Levi-Civita connection. If t -y(t) is a curve in M, let D/dt be the covariant derivative operator on vector fields along y induced by the connection V. For vector fields X and Y let R(X, Y) be the Riemann curvature transformation, i.e. R(X, Y)Z = VxV yZ-V yVxZ -V[XyZ Received by the editors October 3, 1980. 1980 Mathematics Subject Classificatio. Primary 53C20. o 1982 American Mathematical Society 0002-9939/82/0000-0025/$02.25
Convergence properties of algorithms for nonlinear optimization

This paper reviews some of the most successful methods for unconstrained, constrained and nondifferentiable optimization calculations. Particular attention is given to the contribution that theoretical analysis has made to the development of algorithms. It seems that practical considerations provide the main new ideas, and that subsequent theoretical studies give improvements to algorithms, coherence to the subject, and better understanding.
New rotational velocities for eclipsing binaries, and a comparison of spectroscopic and photometric rotations

Rotational velocities are determined spectroscopically for 38 eclipsing binaries, including many long-period, nominally semidetached, systems. We note that spectroscopic rotations may differ from rotations derived from light-curve modeling using the Wilson-Devinney program. In direct-impact mass-transferring systems, or in most systems with periods smaller than about 7 days, observations suggest that the two rotations are usually about the same. In cases where the stream misses the gainer and an accretion disk forms, however, photometric rotation estimates often exceed spectroscopic determinations. The possible physical significance of this situation is briefly discussed. Doubt is cast on the likelihood that the rotation of the hot component of U Sge has changed detectably in the last 30 years
Mobile, Phased-Array, Doppler Radar Observations of Tornadoes at X Band

AbstractA mobile, phased-array Doppler radar, the Mobile Weather Radar, 2005 X-band, Phased Array (MWR-05XP), has been used since 2007 to obtain data in supercells and tornadoes. Rapidly updating, volumetric data of tornadic vortex signatures (TVSs) associated with four tornadoes are used to investigate the time–height evolution of TVS intensity, position, and dissipation up through storm midlevels. Both TVS intensity and position were highly variable in time and height even during tornado mature phases. In one case, a TVS associated with a tornado dissipated aloft and a second TVS formed shortly thereafter while there was one continuous TVS near the ground. In a second case, the TVS associated with a long-lived, violent tornado merged with a second TVS (likely a second cyclonic tornado) causing the original TVS to strengthen. TVS dissipation occurred first at a height of ~1.5 km AGL and then at progressively higher levels in two cases; TVS dissipation occurred last in the lowest 1 km in three cases exami.
Herding Behaviour: Does it Exist in the Indian Stock Market?*

This article examines the herding behaviour in the Indian stock market for the period January 2019 to March 2020. For testing the herding activity, we use three independent datasets viz., small-cap, mid-cap, and large-cap stocks. Our findings suggest that herding behaviour exists in mid-cap stocks. Further, it is confirmed that herding activity is more prominent during the periods of negative market returns and days with net negative foreign institutional inflows.
The flow past a rapidly rotating circular cylinder

This paper considers the two-dimensional flow past a circular cylinder immersed in a uniform stream, when the cylinder rotates about its axis so fast that separation in suppressed. The solution of the flow in the boundary layer on the cylinder is obtained in the form of a power series in the ratio of the stream velocity to the cylinder's peripheral velocity, and expressions are deduced for the value of the circulation and the torque on the cylinder. The terms calculated explicitly are sufficient to give reliable numerical values over the whole range of rotational speeds for which the postulate of non-separating flow is justifiable. The previously accepted theory, due to Prandtl, predicted that the circulation should not exceed a certain limit, while the present theory indicates that the circulation increases indefinitely with increase of rotaional speed. Strong arguments against the older theory are put forward, but the experimental evidence available is inconclusive.
On the Convergence of Solutions to a Second Order Difference Equation with Monotone Operator

We investigate asymptotic behavior of solutions to the following second order difference equation where A is a maximal monotone operator in a real Hilbert space H and {c i } is a positive real sequence. We show weak and strong convergence of solutions to an element of A −1(0), under appropriate assumptions on A and the sequence {c i }. Our results extend and improve previous results by Morosanu [21] and Mitidieri-Morosanu [18] (see also [19, pp. 156–168]) under more general assumptions on c i .
Solving the Stochastic Growth Model by Linear-Quadratic Approximation and by Value-Function Iteration

This article describes three approximation methods I used to solve the growth model (Model 1) studied by the National Bureau of Economic Research's nonlinear rational-expectations-modeling group project, the results of which were summarized by Taylor and Uhlig (1990). The methods involve computing exact solutions to models that approximate Model 1 in different ways. The first two methods approximate Model 1 about its nonstochastic steady state. The third method works with a version of the model in which the state space has been discretized. A value function iteration method is used to solve that model.