Miracle-dz/UniFAR-FTUs huggingface dataset:
Numerical simulation of turbulent free surface flow with two‐equation k–ε eddy‐viscosity models

This paper presents a finite difference technique for solving incompressible turbulent free surface fluid flow problems. The closure of the time‐averaged Navier–Stokes equations is achieved by using the two‐equation eddy‐viscosity model: the high‐Reynolds k–ε (standard) model, with a time scale proposed by Durbin; and a low‐Reynolds number form of the standard k–ε model, similar to that proposed by Yang and Shih. In order to achieve an accurate discretization of the non‐linear terms, a second/third‐order upwinding technique is adopted. The computational method is validated by applying it to the flat plate boundary layer problem and to impinging jet flows. The method is then applied to a turbulent planar jet flow beneath and parallel to a free surface. Computations show that the high‐Reynolds k–ε model yields favourable predictions both of the zero‐pressure‐gradient turbulent boundary layer on a flat plate and jet impingement flows. However, the results using the low‐Reynolds number form of the k–ε model are somewhat unsatisfactory. Copyright © 2004 John Wiley & Sons, Ltd.
The structure of the coma cluster of galaxies.

Analysis of radial velocities in the coma cluster (many of them new) in conjunction with previous data on the density distribution. The cluster extends more than 200 min in radius, with bright and faint galaxies distributed in nearly the same way. Some spirals are members. Several different determinations of M/L give values around 250. The cluster is stabilized by a 'missing mass' some seven times the mass of the galaxies, which must be distributed in the same way as the galaxies.
Simulations of dissipative galaxy formation in hierarchically clustering universes – II. Dynamics of the baryonic component in galactic haloes

We present self-consistent 3D simulations of the formation of virialized systems containing both gas and dark matter. Using a fully Lagrangian code based on the smooth particle hydrodynamics technique and a tree data structure, we follow the evolution of regions of comoving radius 2-3 Mpc with proper inclusion of the tidal effects of surrounding material. Initial conditions at high redshifts assume an Einstein-de Sitter universe, a biased cold dark matter perturbation spectrum (b=2.5), and a baryonic mass fraction of 10 per cent. The gas is initially cold and radiates in the manner expected for a plasma of primordial composition. We neglect star formation and associated processes. We find that most of the gas settles rapidly into centrifugally supported discs at the centres of small dark matter clumps
A dense molecular ring surrounding the nonthermal Galactic center radio shell G359.1-0.5

A new 12 CO survey of the Galactic center region reveals a nearly continuous ring of molecular gas that is centered on and concentric with the nonthermal radio continuum shell G359.1-0.5. The molecular feature has high radial velocities, between -60 and -190 km/s, indicating that it is likely to be located at the distance of the Galactic center; its diameter is then about 75 pc. The mass of the ring, based on its integrated CO line emission, is about 2.5 x 10 6 M ⊙
On the structure of the irreducible polynomials over local fields

The paper is concerned with the structure of irreducible polynomials in one variable over a local field (K, v). The main achievement is the definition of a system P(ƒ) of invariant factors for each monic irreducible polynomial ƒ ∈ K[X]. It is proved that these invariants are characteristic, i.e., by using invariants we may describe the set of irreducible polynomials over a local field.
Quasi-periodic solutions with Sobolev regularity of NLS on $\mathbb {T}^d$ with a multiplicative potential

We prove the existence of quasi-periodic solutions for Schrodinger equations with a multiplicative potential on T, d ≥ 1, finitely differentiable nonlinearities, and tangential frequencies constrained along a pre-assigned direction. The solutions have only Sobolev regularity both in time and space. If the nonlinearity and the potential are C∞ then the solutions are C∞. The proofs are based on an improved Nash-Moser iterative scheme, which assumes the weakest tame estimates for the inverse linearized operators (“Green functions”) along scales of Sobolev spaces. The key off-diagonal decay estimates of the Green functions are proved via a new multiscale inductive analysis. The main novelty concerns the measure and “complexity” estimates.
A CO Survey of the LMC with NANTEN: III. Formation of Stellar Clusters and Evolution of Molecular Clouds

In order to elucidate star formation in the LMC, we made a complete study of CO clouds with NANTEN. In the present paper, we compare 55 giant molecular clouds (GMCs), whose physical quantities were well determined, with young objects, such as young stellar clusters and H II regions. We find that the GMCs are actively forming stars and clusters; 23 and 40 are found to be associated with the clusters and the H II regions, respectively. The clusters associated with the GMCs are significantly young; ∼ 85% of them are younger than∼ 10Myr. In addition, compact groups of the young clusters are often found at the peak position of the GMCs, e.g., N 159 and N 44, while much looser groups are away from the GMCs. This suggests that the clusters are formed in groups and disperse as they become old. The distributions of the CO, [C II], and UV indicate that the GMCs are likely to be rapidly dissipated within several Myr due to UV photons from the clusters. We also estimate the evolutionary time scale of the GMCs; they form stars in a few Myr after their birth, and form clusters during the next few Myr, and are dissipated in the subsequent few Myr.
Laser phase errors in seeded free electron lasers

Harmonic seeding of free electron lasers has attracted significant attention from the promise of transform-limited pulses in the soft X-ray region. Harmonic multiplication schemes extend seeding to shorter wavelengths, but also amplify the spectral phase errors of the initial seed laser, and may degrade the pulse quality. In this paper we consider the effect of seed laser phase errors in high gain harmonic generation and echo-enabled harmonic generation. We use simulations to confirm analytical results for the case of linearly chirped seed lasers, and extend the results for arbitrary seed laser envelope and phase.
A simple method for the estimation of power losses in silicon iron sheets under alternating pulse voltage excitation

The prediction of iron losses in magnetic steels submitted to alternating pulse voltages is studied and an efficient method is proposed. It is developed by coupling the pulse voltage form factor and the loss separation model. Prediction of iron losses becomes possible directly from the loss model corresponding to the sinusoidal flux density. This method is validated on silicon iron grain-oriented and non-oriented magnetic steels. The predetermined iron losses are coherent with those measured and this approach allows both simplicity and precision well appreciated by industry. >
Base pressure in laminar supersonic flow

An asymptotic description is proposed for supersonic laminar flow over a wedge or a backward-facing step, for large Reynolds number and for a base or step height which is small compared with the boundary-layer length. The analysis is carried out for adiabatic wall conditions and a viscosity coefficient proportional to temperature. In a particular limit corresponding to a very thick boundary layer, a similarity law is obtained for the base pressure $\overline{p}_b$. For a thinner boundary layer an asymptotic form for $\overline{p}_b$ is obtained which shows the dependence on the parameters explicitly and which permits good agreement with experiment. This latter result is based on an inviscid-flow approximation for the corner expansion and for reattachment, with viscous forces important primarily in a thin sublayer about the dividing streamline. A prediction of the pressure distribution at reattachment is given and the result is compared with experimental pressure distributions.
Statistical mechanics of a spin-polarized plasma

The statistical mechanics of a spin-polarized plasma is investigated in detail. A rigorous quantum-mechanical description is constructed in terms of a generalized matrix Wigner function. In order to ensure the manifest gauge invariance of the theory, the non-canonical variables q (position) and π (mechanical momentum) are used for the particles. The evolution equation for the phase-space Wigner function, as well as the BBGKY hierarchy for the reduced distribution functions, are derived. A general expression is found for the quantum-mechanical realization of the Lie bracket of any pair of dynamical functions. In the quasi-classical limit, the equations of evolution and the Lie bracket reduce to a simple form. Our approach is compared with the previous semi-phenomenological theory of Cowley, Kulsrud and Valeo.
Extraction of short wind wave spectra from stereo images of the sea surface

A combined method is proposed to estimate the spectra of short wind waves. The spectra extracted from stereo pairs of the sea surface are used for the absolute calibration of the slope spectra obtained with Fourier-processing of the same high-resolution photo images. The calibration extends significantly the range of scales of stereo-retrieved waves toward the shortest ones. The method was adjusted and validated in situ. Algorithms and their experimental validation are presented, covering a range of wavelengths from 30 cm up to 6 mm, for different wind speeds. Spectral shapes and levels are consistent with earlier experimental data and models.
A note on deletion diagnostics for estimating equations

We describe an algorithm based upon the Sherman--Morrison--Woodbury formula for the inversion of matrices with special structure that occur in formulae for deletion diagnostics. Substantial computational savings relative to a method based upon Cholesky's decomposition are illustrated. The result has broad application to regression diagnostics for clustered data. Copyright 2008, Oxford University Press.
The complex Monge-Ampère equation and pluripotential theory

Positive currents and plurisubharmonic functions Siciak's extremal function and a related capacity The Dirichlet problem for the Monge-Ampere equation with continuous data The Dirichlet problem continued The Monge-Ampere equation for unbounded functions The complex Monge-Ampere equation on a compact Kahler manifold Bibliography.
Cross-Equatorial Response to Middle-Latitude Forcing in a Zonally Varying Basic State

Abstract A nonlinear model based on the shallow water equations is used to study cross-equatorial propagation of forced waves in the presence of a longitudinally varying time-mean basic-state zonal wind field. It is found that global-scale planetary waves are unable to propagate past a critical latitude where the mean zonal wind speed vanishes. However, if the longitudinally-asymmetric basic state includes a “duet” in which the zonal winds are westerly, waves of zonal scale less than the zonal scale of the westerly duct may propagate from one hemisphere to the other even though the zonally-symmetric mean zonal wind remains easterly in the equatorial region. The amplitude of the response in one hemisphere to forcing in the opposite hemisphere increases strongly with the magnitude of the westerlies in the equatorial duct. The existence and annual variations of a westerly duct region in the upper troposphere in the eastern Pacific appear to account for some features of the low-frequency variability in the No.
Interplanetary magnetic field periodicity of ∼153 days

We report on the finding of a 153‐day periodicity in the magnetic field strength and solar wind speed measured at 1 AU during the years 1978–1982. The period and the occurence epoch are consistent with the “154‐day” periodicity previously reported for events occurring at the Sun. In particular, the variations in the field strength and the occurence rate of energetic (tens of MeV) solar particle events are in phase. The similar periodicities in the interplanetary field and solar phenomena are consistent with a global phenomenon. Whereas this periodicity is quite strong for the magnetic field magnitude, there is only a weak periodicity for the individual field components. The field magnitude shows essentially no periodicity at this period during the previous and following solar maxima. The lack of persistence, and of significant harmonic components of the observed periodicity, does not support the proposal of a solar “clock” mechanism. The most significant variations in the complete near‐earth magnetic field data base (1963–1997) with periods of less than 200 days occur at 166 and 146 days.
Experimental study and analysis of corona discharge parameters on an ice surface

The objective of this investigation is to understand the inception of ice surface corona streamers. A validated onset criterion that is useful for practical electrode geometries is presented. High-speed streak photography techniques were used to observe the streamers propagating over an ice surface. The effects of several experimental parameters such as freezing water conductivity and HV electrode radius on the streamer inception parameters of an ice surface have been examined. Empirical models have been proposed, based on elements derived from the inception parameters to account for corona streamer propagation velocity and inception voltage/field on an ice surface. Since the propagation velocity is a power function of the electric field, its value has been expressed in terms of the inception voltage.
Higher-order Noether symmetries and constants of the motion

The authors identify a class of symmetries for Lagrangian systems, called higher-order Noether symmetries, which yield a corresponding first integral without further integrations. First, a version of Noether's theorem is recalled in which Noether symmetries are considered to be symmetries of the two-form d theta , theta being the Cartan form. nth-order Noether symmetries are then defined by the requirement LYnd theta =0. The picture is further generalised by exploring various ways in which the computation of repeated Lie derivatives of d theta can lead to the identification of first integrals. A number of illustrative examples are discussed.
Testing for the symmetric component in skew distributions

Many models of asymmetric distributions proposed in the statistical literature are obtained by transforming an arbitrary symmetric distribution by means of a skewing mechanism. In certain important cases, the resultant skewed distribution shares some properties of its symmetric antecedent. Because of this inheritance, it would be interesting to test if the symmetric generator belongs to a certain family, that is to say, testing goodness‐of‐fit for the symmetric component. This work proposes a test of such hypothesis. Taking into account that the normal law is perhaps the most studied distribution, as a particular case of unquestionable interest, the generalized skew‐normal family is studied in detail, because the symmetric component of the distributions in this family is normal. Copyright © 2015 John Wiley & Sons, Ltd.
The Effect of Nanostructure Distribution on Subcooled Boiling Heat Transfer Enhancement over Nanostructured Plates Integrated Into a Rectangular Channel

In this study, subcooled flow boiling is investigated over nanostructured plates at flow rates ranging from 69 mL/min to 145 mL/min. The first configuration of the nanostructured plate includes ˜600-nm-long, closely packed copper nanorod arrays distributed randomly upon the surface with an average nanorod diameter of ˜150 nm, and the second configuration consists of a periodic structure having ˜600-nm-long copper (Cu) nanorods with an average nanorod diameter of ˜550 nm and a center-to-center nanorod separation of ˜1 μm. The nanorod arrays are deposited utilizing glancing angle deposition (GLAD) technique on the copper thin film (˜50 nm thick) coated on silicon wafer substrates. Dimensions of the test section, heat flux values, and flow rates are chosen to ensure that nanostructured plates remain intact along with their nanorods in their original shape and position, so that the nanostructured plates could be used for many experiments. A consistent increase (up to 30%) in heat transfer coefficients is observed on nanostructured plates compared to the Cu thin film, which is used as the control sample. However, no significant difference in the boiling heat transfer performance between the random and periodic nanorods was observed, which indicates that the distribution of nanostructures may not be very critical in achieving enhanced heat transfer. In light of the obtained promising results, channels with nanostructured surfaces are proven to be useful, particularly in applications such as cooling of small electronic devices, where conventional surface modification techniques are not applicable.
Structure and dynamics of perovskite‐type crystals

The connection between Landau's theory of phase transitions and the lattice-dynamical theory of a displacive transition in a crystal is discussed. At a second-order displacive transition the frequency of one normal mode becomes zero. By investigating the displacements of the atoms from special positions of the lattice for a number of crystals having the distorted perovskite structure, we have shown that several modes are involved in the various transitions, except in the case of LaAlO3, where the transition is probably second-order or nearly so, and is associated with a mode of low frequency. The wave vector of this mode is at the point (1/2 1/2 1/2) of the Brillouin zone, and its irreducible representation is Γ25.
The luminosity function for stars with minus 0.6 less than or equal to M (sub nu) less than or equal to 6.5 in the globular cluster M30: Is there a problem with stellar evolution models?

The V band luminosity function (LF) for stars ranging from the tip of the giant branch to approximately 2.5 mag fainter than the main-sequence turnoff (MSTO) in M30 (=NGC 7099, GC 2137-234) is derived from CCD observations. Comparison with the theoretical LFs of Bergbusch & VandenBerg (1992) for (M/H) = -2, 16 Gyr models shows discrepancies which can be described either of two ways: (1) If the observations are normalized to the models over a few magnitudes fainter than the MSTO, then there is an excess (N (sub obs) greater than N(sub predicted)) of subgiant stars within 0.5 mag of the MSTO at the level of 4.8 sigma and an excess of stars (approximately 20%) compared to the models all along the giant branch. (2) If the normalization is made to match predicted and observed numbers of stars on the giant branch, then there is a discrepancy between models and observations in the sense that there is a broad depression in the observed LF fainter than the MSTO that is not present in the models. Consideration of LFs generated from 12 Gyr models or models adjusted to a shorter (m - M)(sub nu) = 14.5) distance modulus diminishes the magnitude of some of these discrepancies but introduces other mismatches between the observations and models. LFs constructed from stellar models that have 10% of the stellar mass in an isothermal core qualitatively match the observations better than the 'standard' models.
Bayesian selection of threshold autoregressive models

Abstract. An approach to Bayesian model selection in self‐exciting threshold autoregressive (SETAR) models is developed within a reversible jump Markov chain Monte Carlo (RJMCMC) framework. Our approach is examined via a simulation study and analysis of the Zurich monthly sunspots series. We find that the method converges rapidly to the optimal model, whilst efficiently exploring suboptimal models to quantify model uncertainty. A key finding is that the parsimony of the model selected is influenced by the specification of prior information, which can be examined and subjected to criticism. This is a strength of the Bayesian approach, allowing physical understanding to constrain the model selection algorithm.
Challenges in microstructural metrology for advanced engineered materials

Measurement of microstructural parameters is essential for both controlling and modelling properties of and production processes for advanced materials. In the past decade new techniques such as electron backscatter diffraction have enabled a considerable increase in the amount of data and degree of detail in microstructural measurements of, for example, the extent of recrystallization in a metal deformed at high temperatures. However, the many parameters involved and automated nature of the methods can lead to artefacts and bias in calculated values, and increased resolution will lead to disagreement with more conventional methods. Examples are given of the range of microstructural measurements possible by new techniques and how different results can be obtained from the same underlying data. The need is stressed for interlaboratory comparisons to enable underpinning data to be derived on the validity, repeatability and reproducibility of measurements of key microstructural parameters.
Non-local optics of the near field lens

The effects of non-locality on the focusing properties of a thin metal slab, with the real part of the permittivity equal to −1, are evaluated. Non-local effects are introduced by employing the wavenumber-dependent plasmon energy of the hydrodynamic model. Non-locality affects the dispersion of the surface plasmons, the transmissivity of the slab, and hence also its imaging ability. The results of numerical calculations for silver slabs are presented.
Numerical convergence studies of the mixed finite element method for natural convection flow in a fluid-saturated porous medium

This paper describes a numerical approximation scheme for the natural convection (NC) flow in a fluid-saturated porous medium. Our formulation of the problem is based on the mixed finite element method (FEM). Using the so-called consistent splitting scheme, a second-order accuracy in time and in space is verified by the numerical calculation. The resulting flow patterns and heat transfer for different Rayleigh numbers, Darcy numbers and porosities are numerically studied by the proposed scheme.
Empirical Prediction of the Summer Monsoon Rainfall over India

Abstract We have examined 46 years (1939–84) of observed data to study synoptic and statistical relationships between the summer monsoon rainfall over India, the Southern Oscillation, and the midtropospheric circulation over India. The change in Darwin pressure from January to April and the latitudinal position of the April 500-mb ridge along 75°E are taken as two quasi-independent predictor parameters to develop a regression equation to predict the summer monsoon rainfall. Verification of predictions on independent data shows that the root-mean-square error for predicted rainfall is 36 mm, which is less than half of the standard deviation (82 mm) and only about 4% of the mean rainfall (857 mm). Since the observations needed to define the predictor parameters would be available well before the monsoon season, and since the performance of the empirical prediction formula is reasonably good, this method can be of some possible use for long-range forecasting of seasonal mean rainfall over India.