Miracle-dz/UniFAR-FTUs huggingface dataset:
Inviscid axisymmetric absolute instability of swirling jets

The propagation characteristics of inviscid axisymmetric linearized disturbances to swirling jets are investigated for two families of model velocity profiles. Briggs' method is applied to dispersion relations to determine when the basic swirling jets are absolutely or convectively unstable. The method is also applied to the neutral inertial waves used by Benjamin to characterize the subcritical or supercritical nature of the flow. Although these waves are neutral, Briggs' method nonetheless indicates a qualitative change in behaviour at Benjamin's criticality condition. The first model jet has uniform axial velocity, rigid-body rotation and issues into still fluid. A known difficulty in the application of Briggs' method to the analytical dispersion relation for inviscid waves in this flow is resolved. The difficulty is that the pinch point can cross into the left half of the complex-wavenumber plane, where waves grow exponentially with radius and fail to satisfy homogeneous boundary conditions. In this paper the physical consequences of this behaviour are explained. It is shown that if the still fluid is of infinite extent in the radial direction, then the jet is convectively unstable to axisymmetric waves, but if the jet is confined by an outer cylinder concentric with the jet axis, then it becomes absolutely unstable to axisymmetric waves provided that the swirl (ratio of azimuthal to axial velocity) is large enough. This destabilizing effect of confinement occurs however large the radius of the outer cylinder. A second family of model swirling jets with smooth profiles and a finite thickness shear layer at the jet edge is also studied. The inviscid stability equations are solved numerically in this case. The results from the analytical dispersion relations are reproduced as the shear layer thickness tends to zero. However, increasing this thickness acts to destabilize the absolute instability of axisymmetric waves, apparently due to the centrifugal instability present in the shear layer. It is suggested that the transition from convective to absolute instability could be associated with the onset of an unsteady vortex breakdown. The swirl required to produce this transition can be either greater, or less, than the swirl required to produce the transition from supercritical to subcritical flow, depending on the details of the basic velocity profiles. A codimension-two point in parameter space can exist where the unsteady bifurcation associated with the convective–absolute transition coincides with the steady bifurcation associated with the supercritical–subcritical transition. Such codimension-two points can control a rich variety of nonlinear dynamical behaviour.
A Comparative Study of Implicit and Explicit Methods Using Unstructured Voronoi Meshes in Petroleum Reservoir Simulation

This work presents a comparative study among three linearization schemes widely used in petroleum reservoir simulation, namely the Implicit Pressure Explicit Saturation (IMPES), Fully Implicit (FI) and Adaptive Implicit Method (AIM). Attention is given to the criterion used for switching from IMPES to FI and vice-versa. The black-oil model considering the oil-water flow is employed. The equations are discretized using an unstructured Voronoi mesh in a finite-volume framework. The numerical results are analyzed based on the number of iterations in the Newton and solver procedures, number of implicit volumes, and mass balance error of components. The effect of the stopping criterion on Newton's iterations is also investigated. The outcome of the study reveals that adaptive implicit methodologies can be a good choice when unstructured grids are present, allowing the use of time steps with the same order of magnitude as the ones used in FI procedures, but with reduction in the computational effort.
Biennial variability in aerosol optical depth associated with QBO modulated tropical tropopause

The role of quasi‐biennial oscillation (QBO) in determining the distribution of atmospheric aerosols over the north Indian region has been investigated. The results reveal that aerosol optical depth (AOD) undergoes a biennial variability in response to positive and negative phases of QBO. Large aerosol loading occurring in the pre‐monsoon season during westerly phase (positive phase) of QBO is concurrent with a quasi‐horizontal advection, diffusion and gravitational sedimentation. Further analysis of tropopause anomalies confirm that warming (cooling) of the tropical tropopause during the positive (negative) phase of QBO is accompanied by an increase (decrease) in AOD over the study region. Copyright © 2011 Royal Meteorological Society
A positive finite-difference advection scheme

Abstract This paper examines a class of explicit finite-difference advection schemes derived along the method of lines. An important application field is large-scale atmospheric transport. The paper therefore focuses on the demand of positivity. For the spatial discretization, attention is confined to conservative schemes using five points per direction. The fourth-order central scheme and the family of κ-schemes, comprising the second-order central, the second-order upwind, and the third-order upwind biased, are studied. Positivity is enforced through flux limiting. It is concluded that the limited third-order upwind discretization is the best candidate from the four examined. For the time integration attention is confined to a number of explicit Runge-Kutta methods of orders two up to four. With regard to the demand of positivity, these integration methods turn out to behave almost equally and no best method could be identified.
Pulse broadening of the enhanced backscattering from rough surfaces

Recently, the authors presented a study of pulse scattering by rough surfaces based on the first order Kirchhoff approximation which is applicable to rough surfaces with rms slope less than 0.5 and correlation distance l/spl ges//spl lambda/. However, there has been an increasing interest in enhanced backscattering from rough surfaces, and this requires inclusion of the second order Kirchhoff approximation with shadowing corrections. This paper presents a theory for the two-frequency mutual coherence function in this region and shows that the multiple scattering on the surface gives rise to an additional pulse tail in the direction of enhanced backscattering. The theory predicts pulse broadening approximately 20% greater than that caused by single scattering alone for a delta-function incident pulse and typical surface parameters. Analytical results are compared with Monte Carlo simulations and millimeter wave experiments for the one-dimensional rough surface with rms height of 1/spl lambda/, and correlation distance of 1/spl lambda/, showing good agreement. <<ETX>>
Algebraic Statistics: Computational Commutative Algebra in Statistics

INTRODUCTION History and Motivation Overview Computer Algebra Summary ALGEBRAIC MODELS Models Polynomials and Polynomial Ideals Term-Orderings Division Algorithm All Ideals Are Finitely Generated Varieties and Equations Grobner Bases Properties of Grobner Basis Elimination Theory Polynomial Functions and Quotients by Ideals Hilbert Function Further Topics THE DIRECT THEORY Designs and Design Ideals Computing the Grobner basis of a design Operations with Designs Examples Span of a Design Models and Identifiability Quotients Examples The Fan of an Experimental Design Subsets and Sequential Algorithms Regression Analysis Other Topics TWO-LEVEL DESIGNS. APPLICATION IN LOGIC AND RELIABILITY The binary case: Boolean Representations Reliability: Coherent Systems are Minimal Fan Designs Two Level Factorial Design: Contrasts and Orthogonality PROBABILITY AND STATISTICS Random Variables on a Finite Support Moments Probability Algebraic Representation of Exponentials Generating Functions Generating Functions and Exponential Models Examples and Further Applications Statistical Modelling Likelihoods and Sufficient Statistics A Ring of Random Variables Score Function and Information
Eigenmode analysis of dielectric loaded top-hat monopole antennas

Eigenmode expansions are used for computing the currents on a dielectric loaded top-hat monopole radiating above an infinite conducting ground plane. The approach is facilitated by adding a parallel ground plane above the antenna, thus allowing use of cylindrical harmonic field expansions in each of three regions. Expansion coefficients are found by enforcing boundary and continuity conditions at conducting surfaces and regional interfaces. Convergence and accuracy are assessed using comparisons with three other methodologies, namely an integral equation solution, a quasi-static analysis, and multi-octave experimental measurements. >
Subcritical bifurcation and bistability in thermoacoustic systems

Abstract This paper analyses subcritical transition to instability, also known as triggering in thermoacoustic systems, with an example of a Rijke tube model with an explicit time delay. Linear stability analysis of the thermoacoustic system is performed to identify parameter values at the onset of linear instability via a Hopf bifurcation. We then use the method of multiple scales to recast the model of a general thermoacoustic system near the Hopf point into the Stuart–Landau equation. From the Stuart–Landau equation, the relation between the nonlinearity in the model and the criticality of the ensuing bifurcation is derived. The specific example of a model for a horizontal Rijke tube is shown to lose stability through a subcritical Hopf bifurcation as a consequence of the nonlinearity in the model for the unsteady heat release rate. Analytical estimates are obtained for the triggering amplitudes close to the critical values of the bifurcation parameter corresponding to loss of linear stability. The unstable limit cycles born from the subcritical Hopf bifurcation undergo a fold bifurcation to become stable and create a region of bistability or hysteresis. Estimates are obtained for the region of bistability by locating the fold points from a fully nonlinear analysis using the method of harmonic balance. These analytical estimates help to identify parameter regions where triggering is possible. Results obtained from analytical methods compare reasonably well with results obtained from both experiments and numerical continuation.
Comparisons of the radiation protection standards for air kerma of the NIST and the BIPM for 60Co and 137Cs gamma radiation

An indirect comparison of the standards for air kerma of the National Institute of Standards and Technology (NIST), USA, and of the Bureau International des Poids et Mesures (BIPM) was carried out in the 60Co and 137Cs radiation protection-level beams of the BIPM in September 2011. The comparison results, based on the calibration coefficient for two transfer standards and expressed as a ratio of the NIST and the BIPM standards for air kerma, are 1.0023 with a combined standard uncertainty of 3.2 × 10−3 in 60Co, and 0.9990 with a combined standard uncertainty of 3.5 × 10−3 in 137Cs. The result in the 60Co beam for radiation protection agrees within the uncertainties with the result of the comparison carried out at the same time in the CIS Bio 60Co beam for radiotherapy-level air kerma. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm. org/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
Complex Formation History of the Lenticular Galaxies with Stellar Counterrotation: NGC 4138 and NGC 4550

Two lenticular galaxies with counterrotating stellar components in their disks have been studied with the Multi-Pupil Fiber Spectrograph of the 6 m telescope (at the Special Astrophysical Observatory). In NGC 4138 the nucleus is certainly chemically distinct, with the central concentration of magnesium enhancement marginally exceeding that of iron. The ionized gas within R = 4″ of the nucleus rotates circularly in an inclined ring, perhaps a kind of a circumnuclear polar ring surrounding a compact stellar minibar. NGC 4550 exhibits complex extended structures in its center that can be identified by enhanced levels of magnesium and iron indices; the stellar population of the unresolved nucleus is younger than that of the circumnuclear region. We conclude that although NGC 4550 does not possess a chemically distinct nucleus in the ordinary sense of the term, there are nevertheless clear signatures of a secondary star formation burst confined perhaps to the counterrotating stellar gaseous disk. We argue that the inclination of the counterrotating disk differs from that of the main stellar disk, implying that the two disks are not coplanar. Both galaxies seem to have possessed bars, either actually present or already dissolved.
The soliton: A new concept in applied science

The term soliton has recently been coined to describe a pulselike nonlinear wave (solitary wave) which emerges from a collision with a similar pulse having unchanged shape and speed. To date at least seven distinct wave systems, representing a wide range of applications in applied science, have been found to exhibit such solutions. This review paper covers the current status of soliton research, paying particular attention to the very important "inverse method" whereby the initial value problem for a nonlinear wave system can be solved exactly through a succession of linear calculations.
Quotients and Homomorphisms of Relational Systems

Relational systems containing one binary relation are investigated. Quotient relational systems are introduced and some of their properties are characterized. Moreover, homomorphisms, strong mappings and cone preserving mappings are introduced and the interplay between these notions is considered. Finally, the connection between directed relational systems and corresponding groupoids is investigated.
Mixing across an interface due to turbulence generated by an oscillating grid

Many experimenters have used oscillating grids to produce turbulence for various laboratory purposes, especially in studies of mixing, but there have been few direct measurements of the properties of the turbulence itself. In the present paper we report experiments which attempt to relate the turbulent velocity and length scales to the external parameters, the frequency and amplitude, for three forms of grid oscillated in a tank of water. Turbulent velocities have been measured in the absence of a mean flow by using a hot film moved through the fluid to provide its own mean velocity. The output is stored and analysed in a small computer, which rapidly evaluates velocity and length scale statistics from an ensemble of records. The spatial variation of these quantities with distance from the stirrer is of special interest. It agrees with results suggested by an inertial-decay theory, and with previous measurements made by Bouvard & Dumas (1967) using a different form of stirrer. A particular purpose of the work has been to ‘calibrate’ the entrainment experiments of Turner (1968), by providing absolute scales of velocity and length in the fluid near a mixing interface, for the same grid as was used in the earlier experiments. Evidence is presented which suggests that other forms of grid may not be calibrated simply by extrapolating these results.
Barium and Sodium Abundances in the Globular Clusters M15 and M92

Upper giant branch members of the Galactic globular clusters M15 and M92 have been surveyed with the WIYN 3.5 m telescope and Hydra multiobject fiber-fed spectrometer. Medium-resolution spectra (R ≡ λ/δλ ∼ 20000) in the wavelength range 5740–5980 Å were obtained for 31 stars in M15 and 34 stars in M92. The stellar samples range over the top three magnitudes of the cluster color-magnitude diagrams; the faintest of the stars are at or below the luminosity of the horizontal branch. Ca, Ba, and Na abundances have been derived for all stars from the Ca I λ5857. 4, the Ba II λ5853. 7, and the Na I D λλ5889. 9, 5895.9 lines, and Fe, Si, and Ti abundances have also been derived for the coolest, most luminous stars near the cluster red giant branch tips. The Fe metallicities and abundance ratios of the tip giants are in general agreement with literature values for these two clusters. The derived ⟨[Ca/H]⟩ abundance in M15 is about 0.05 dex larger than in M92, consistent with earlier suggestions of a very small overall metallicity difference between these two clusters. Using the Ca abundance as a surrogate for cluster metallicity, the overall relative abundances of Ba indicated by the ⟨[Ba/Ca]⟩ ratios are significantly different in M15 and M92: -0.1 and -0.4. The large star-to-star scatter (σ ∼ 0.4) in [Na/Ca] at all giant branch positions in both clusters confirms the existence of large proton-capture abundance variations down to stellar luminosities comparable to the horizontal branch.
A Super-Star Cluster in NGC 253: Mid-Infrared Properties

We observed the nearby starburst galaxy NGC 253 in the mid-infrared to obtain a three-dimensional data set with arcsecond angular resolution and 0.2 μm spectral resolution. The observations show the major spectral features in the upper half of the mid-IR window: the 11.3 μm polycyclic aromatic hydrocarbon (PAH) line and the 12.8 μm [Ne II] line as well as the broad silicate absorption feature at 9.7 μm. We use the [Ne II] line to determine the emission measure of the ionized gas, and in combination with radio observations to predict the thermal and nonthermal contributions to the radio continuum. The amount of ionized gas is related to the rate of star formation. Based on the mid-IR spectra, we identify three major components in the nucleus of NGC 243: an AGN in the center of the galaxy, a super-star cluster also seen in optical images, and a larger scale diffuse envelope composed of an older population of supernova remnants and lower mass stars.
Seasonal Cycle of the Climatological Stationary Waves in the NCEP–NCAR Reanalysis

Abstract The maintenance mechanisms of the climatological stationary waves and their seasonal cycle are investigated with a linear stationary wave model and the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis data from 1985 to 1993. The stationary wave model is linearized about the zonal-mean flow and subjected to the zonally asymmetric stationary wave forcings. It has rhomboidal wavenumber 30 truncation and 14 vertical sigma levels. The forcings for the linear model include diabatic heating, orography, stationary nonlinearity, and transient vorticity and heat flux convergences. The NCEP–NCAR reanalysis provides a high quality global dataset for this study. When the linear model is subjected to all forcings, it reproduces reasonably well the climatological stationary wave seasonal cycle. The linear stationary wave theory is quantitatively valid at the upper-tropospheric levels for all months and the lower-tropospheric levels for the northern su.
Mackey formula in type A

Let G be a connected reductive group defined over a finite field with q elements and let F: G → G be the corresponding Frobenius endomorphism. We prove that the Mackey formula for Lusztig induction and restriction holds in GF if all the simple components of G are of type A. Our result holds for every Frobenius endomorphism (split or non‐split) and for every q. 1991 Mathematics Subject Classification: 20G05, 20G40.
FIXED POINT RESULTS FOR '-CONTRACTIONS ON A SET WITH TWO SEPARATING GAUGE STRUCTURES

The purpose of this article is to present some fixed point theorems for Ciric-type generalized φ-contractions on a set with two separating gauge structures. Fixed point theorems and a homotopy result are given in Section 2. Then, as applications, some existence results for a multivalued Cauchy problem and a Volterra-type integral inclusion are presented in Section 3. Our theorems extend and generalize some previous results in the literature, such as: [1], [3], [7], [10], [11], [13].
The sharp existence of constrained minimizers for a class of nonlinear Kirchhoff equations

In this paper, we study the existence of solutions with prescribed L2‐norm for the following Kirchhoff type equation: −a+b∫RN|∇u|2Δu−|u|p−2u=λu,x∈RN,λ∈R,where N≤3,a,b > 0 are constants, p∈(2,2*),2*=6 if N = 3, and 2*=+∞ if N = 1,2. We obtain the sharp existence of global constraint minimizers for 2
A review of cancer screening evaluation techniques, with some particular examples in breast cancer screening

Summary. The instigation of mass screening for breast cancer has, over the last three decades, raised various statistical issues and led to the development of new statistical approaches. Initially, the design of screening trials was the main focus of research but, as the evidence in favour of population‐based screening programmes mounts, a variety of other applications have also been identified. These include administrative and quality control tasks, for monitoring routine screening services, as well as epidemiological modelling of incidence and mortality. We review the commonly used methods of cancer screening evaluation, highlight some current issues in breast screening and, using examples from randomized trials and established screening programmes, illustrate the role that statistical science has played in the development of clinical research in this field.
Radiation of Seismic Body Waves from a Finite Moving Source in the Earth

Body waves from a finite moving source are investigated. Ray theory is used to obtain a long-range approximation for the surface displacements from a buried horizontal force. A weak velocity gradient in the medium is assumed, and the curvature of the earth is replaced by an equivalent additional velocity gradient. The displacements are then integrated over a finite line to simulate a disturbance moving with constant speed. Results indicate that the finiteness of the source is manifested in a factor of the form e-iXsinX/X and that the derivation of the fault length and the velocity of rupture of earthquakes from the spectra of body waves is possible. The results are similar to those obtained earlier for seismic surface waves, except that for body waves X depends on both polar coordinates of the station with respect to the source. The method can be extended to other types of common faulting.
Algebraic multigrid method for nonsymmetric matrices arising in electromagnetic finite-element analyses

Algebraic multigrid (AMG) methods were originally developed for linear systems of equations with symmetric coefficient matrices. The objective of this paper is to investigate the applicability of the AMG solvers in electromagnetic finite-element analyses, which lead to nonsymmetric matrices. The excellent performances of the AMG solvers are demonstrated in (two-dimensional and three-dimensional) electromagnetic analyses of a magnetohydrodynamic generator and in a three-dimensional eddy-current analysis including a moving conductor.
Stable solution zone for fluid flow through curved pipe with circular cross-section

Numerical study is performed to examine numerically the stable solution for the incompressible viscous steady flow through a curved pipe with circular cross-section. Also the combined effects of high Dean Number Dn and curvature δ on the flow are investigated. Spectral method is applied as a main tool for the numerical technique; where, Fourier series, Chebyshev polynomials, Collocation methods, and Iteration method are used as secondary tools. The flow patterns have been shown graphically for large Dean Numbers and a wide range of curvature, 0.01≤δ≤0.9. Two vortex solutions have been found for secondary flow. Axial velocity has been found to increase with the increase of Dean number and decrease with the increase of curvature. For high Dean number and low curvature almost all the fluid particles leave the inner half of the cross-section. The stable solution zone increases with the increase of curvature up to a certain limit, then decrease. DOI: 10.3329/jname.v7i1. 3630