Miracle-dz/UniFAR-FTUs huggingface dataset:
Assessment and Modification of One-Equation Models of Turbulence for Wall-Bounded Flows

This work assesses the performance of two single-equation eddy viscosity transport models that are based on Menter's transformation of the k-s and the k-ω closures. The coefficients of both models are set exactly the same and follow directly from the constants of the standard k-e closure. This in turn allows a cross-comparison of the effect of two different destruction terms on the performance of single-equation closures. Furthermore, some wall-free modifications to production and destruction terms are proposed and applied to both models. An assessment of the baseline models with and without the proposed modifications against experiments, and the Spalart-Allmaras turbulence model is provided via several boundary-layer computations. Better performance is indicated with the proposed modifications in wall-bounded nonequilibrium flows.
A linear model of the Antarctic circumpolar current

A simple frictional wind-driven model of the Antarctic circumpolar current is examined. The geometry includes what are thought to be the main features effecting the current, namely a gap corresponding to Drake Passage and a partial barrier corresponding to the South American peninsula. Solutions obtained by both numerical and analytical methods are presented. The analytic solution, valid for small values of a friction parameter, enables the total rate of transport of water by the current to be calculated as a function of the friction parameter and the wind stress distribution. The width which controls the rate of transport by the current tends to be the narrowest encountered rather than the average width as assumed in earlier zonal models. However, the current spreads out to several times this width due to frictional effects. The values of the eddy viscosity required to give a rate of transport of the observed order are about 103 cm2/s for a bottom-friction model and of the order of 108 cm2/s for a lateral friction model.
Effective plasma heat conductivity in 'braided' magnetic field-I. Quasi-linear limit

Anomalous cross-field electron transport in a specified magnetic field with weakly-destroyed flux surfaces is discussed. Following the approach developed previously in the present paper the regimes of effective transverse plasma transport are studied systematically, both in the collisional and collisionless limits. The present analysis incorporates the nonstationary of magnetic perturbations, which was not included in the previous works. Part I of this study deals with the quasi-linear approximation, which may be written as b0L0/ delta > chi perpendicular to ) for time-independent magnetic perturbations. However, these regimes can exist in the presence a finite-frequency magnetic flutter. A unified classification of quasi-linear regimes of anomalous transport is introduced in order to further extend the analysis to the strong magnetic turbulence limit b0L0/ delta >>1 (see Part II), which is considered as a companion paper. (Isichenko, ibid., vol.33, no.7, p.809-26 (1991)).
X-ray studies of quasars with the Einstein observatory

Using the Einstein Observatory, we have carried out X-ray observations of 107 quasars and have detected 79. From the analysis of this sample of objects we find a correlation between optical emission and X-ray emission. Our data for radio-loud quasars also show a correlation between radio emission and X-ray emission. For a given optical luminosity, the average X-ray emission of radio-loud quasars is approx.3 times higher than that of ratio-quiet quasars. In addition, our data suggest that the radio of X-ray to optical luminosity is decreasing with increasing redshift and/or optical luminosity. Taking into account the differences in X-ray luminosity between radio-loud and radio-quiet quasars, and between low-redshift and high-redshift quasars, we estimate that approx.30% of the observed X-ray background is contributed by quasars brighter than m/sub B/roughly-equal20, while much of the remainder can be contributed by still fainter quasars. Our data also imply that the optical log N--m/sub B/ relation for quasars cannot be extrapolated much beyond m/sub B/roughly-equal20 with the steep slope used to characterize optical source counts at brighter magnitudes. This situation supports the picture in which luminosity evolution, rather than pure density evolution, describes the quasar behavior as a function of redshift. We briefly discuss themore » observed correlation of X-ray luminosity with radio luminosity in the context of current quasar models. « less
A new type of recurrence relations for the secant method

We apply the Secant method to solve nonlinear operator equations in Banach spaces. We establish a Newton-Kantorovich convergence theorem using a new system of recurrence relations and give an explicit expression for the a priori error bounds. Moreover, we apply our results to the numerical resolution of a nonlinear boundary value problem of second order and improve the error bounds obtained by other authors.
An experimental study of the flow of thin liquid sheets in hot atmospheres

A study has been made of the flow and disintegration of thin liquid sheets in combustion gases up to temperatures of 950°C. It is found that below 300°C sheet breakdown occurs through the growth of antisymmetric Kelvin–Helmholtz waves. Above this temperature high frequency symmetric waves and localized disturbances are superimposed on the sheet and disintegration then occurs by the combined action of aerodynamic waves and perforations, the contribution of the latter predominating with increasing temperature. It is demonstrated that the new wave system is electrohydrodynamic in origin, the electric field being generated by the charged species present in the gas. The drop size is found to be critically dependent upon the nature of the disintegration process.
Northeasterly Cold Surges and Near-Equatorial Disturbances over the Winter MONEX Area during December 1974. Part I: Synoptic Aspects

Abstract This is a pre-Winter Monsoon Experiment (Winter MONEX) pilot study to examine the possible interactions between the northeasterly cold surges off the Asia continent and the convective disturbances in the near equatorial region. Based on surface and 850 mb wind and temperature analyses, satellite data, and synoptic weather charts of the Hong Kong Royal Observatory, a sequence of synoptic events associated with two cold air surges and near-equatorial disturbances over the Winter MONEX area of South China Sea and its vicinity during December 1974 is discussed. The results lead to the tentative conclusions that due to the varying degree of air-sea interactions between cold air originating from the southeastern China coast, Taiwan and Luzon Straits, and that originating from the South China coast, the near-equatorial latitudes of the South China Sea will experience a freshening of the low-level northeasterly monsoon Winds prior to a decrease in surface temperature which, if it occurs, is confined to t.
Robust Active Ranking from Sparse Noisy Comparisons

From sporting events to sociological surveys, ranking from pairwise comparisons is a tool of choice for many applications. When certain pairs of items are difficult to compare, outcomes can be noisy, and it is necessary to develop robust strategies. In this work, we show how a simple active sampling scheme that uses a standard black box sorting algorithm enables the efficient recovery of the ranking, achieving low error with sparse samples. Both in theory and practice, this active strategy performs systematically better than selecting comparisons at random. As a detour, we show a link between Rank Centrality, a recently proposed algorithm for rank aggregation, and the ML estimator for the Bradley-Terry model. This enables us to develop a new, provably convergent iterative algorithm for computing the ML estimate.
Magellanic type galaxies throughout the Universe

Abstract The Magellanic Clouds are often characterized as “irregular” galaxies, a term that implies an overall lack of organized structure. While this may be a fitting description of the Small Cloud, the Large Magellanic Cloud, contrary to popular opinion, should not be considered an irregular galaxy. It is characterized by a distinctive morphology of having an offset stellar bar and single spiral arm. Such morphology is relatively common in galaxies of similar mass throughout the local Universe, although explaining the origin of these features has proven challenging. Through a number of recent studies we are beginning to get a better grasp on what it means to be a Magellanic spiral. One key result of these works is that we now recognize that the most unique aspect of the Magellanic Clouds is not their structure, but, rather, their proximity to a larger spiral such as the Milky Way.
Differentiation in Star-Invariant Subspaces II. Schatten Class Criteria

Abstract Given an inner function θ on the upper half-plane C + , let K θ ≔ H 2 ⊖ θ H 2 be the corresponding star-invariant subspace of the Hardy space H 2 . Earlier we showed that the differentiation operator d dx : K θ → L 2 ( R ) is bounded iff θ ′∈ L ∞ ( R ) and compact iff θ ′∈ C 0 ( R ). The current problem is to determine when the above operator belongs to the Schatten–von Neumann class S p . The most important cases are p =1 and p =2, and for these p 's we solve the problem completely. The S 1 and S 2 criteria that arise involve the decay rate of θ′ at infinity or (alternatively) the distribution of the zero sequence { z j } of θ . Moreover, explicit formulae for the trace and the Hilbert–Schmidt norm are provided. For other values of p , we point out some necessary and some sufficient conditions in order that d dx ∈ S p . The gap is presumably quite small, and we are able to eliminate it for special classes of zero sequences { z j }.
Flow characteristics within the recirculation region of three-dimensional turbulent offset jet

ABSTRACT The present study investigates the flow characteristics within the recirculation region of three-dimensional offset jets using a particle image velocimetry technique. Measurements were performed for four nozzle offset height ratios of 0, 2, 4 and 8. The discharged jet entrained the ambient fluid as depicted by streamlines superimposed on the mean velocity contours. Analysis of the flow field showed that the maximum streamwise mean velocity decay rate increased with increasing offset height ratio. Wall-normal spread rates of 0.066 and 0.016 were obtained for jets with offset height ratios of 0 and 2, respectively, and lateral spread rates of 0.116, 0.114 and 0.096 for jets with offset height ratios of 0, 2 and 4, respectively. The reattachment lengths of the jets increased with increasing offset height ratio. Profiles of the mean velocities, Reynolds stresses and some of the budget terms (specifically, production, diffusion and convective terms) of the turbulent kinetic energy have been investigated. It was observed that increasing the offset height ratio influenced the distribution of these quantities within the recirculation region. A two-point velocity correlation analysis was performed to analyse the flow structures within the recirculation region. The two-point correlation revealed some large-scale structures which were observed to increase in size as the offset height ratio increased. The two-point correlation analysis also revealed that the estimated integral length scales within the recirculation region of the flow increased with increasing offset height ratio.
Non-linear MHD simulation of ELM energy deposition

The mechanisms of edge-localized mode (ELM) energy deposition are studied by means of non-linear magnetohydrodynamic (MHD) simulation of ELMs. The footprint of the ELM heat flux at the divertor is found to increase approximately linearly with the total ELM energy loss for JET-scale plasmas, which is similar to the experimentally observed broadening of the ELM energy deposition with ELM energy loss. For these relatively large ELMs, in which conductive losses dominate, the divertor footprint broadening is due to an increase in the magnetic perturbation of the ballooning mode with increasing ELM energy loss, which results in a widening of the homoclinic tangles intersecting the target. The first results from ELM simulations in the ITER Q = 10 scenario indicate that on the ITER scale the broadening is similar for conductive and convective ELMs at least up to an ELM energy loss of 4 MJ. For the larger conductive-type ELMs the magnetic perturbation and its homoclinic tangles determine the pattern of the ELM heat flux at the divertor target similar to the JET-scale results. For the smaller convective ELMs, the ELM footprint is determined by the radial distance travelled by plasma filaments expelled by the ELM and the loss of the plasma energy in the filaments along the magnetic field lines.
Lasing properties of near-infrared laser dyes in the liquid and solid state

The photophysical and lasing properties of a number of near infrared laser dyes from different dye classes - extended rhodamines, oxazines, cyanine and styryl dyes - predominantly in liquids but also in poly(methyl methacrylate) (PMMA) based hosts are reported in this paper. The different dyes have been found to exhibit fluorescence quantum efficiencies in the range of 0.01-0.88 in solution. The fluorescence efficiency for a number of the dyes has been found to be heavily dependent on the solvent characteristics. Laser slope efficiencies in the range of 20-66% have been recorded for the dyes under nanosecond laser pumping at or close to the wavelength of their absorption maximum. The lasing wavelengths of the samples were found to range from 647 nm to 815 nm. Some differences in the lasing efficiency has been noted between the behaviour of the liquid and solid-state dye samples, in particular for the dye Oxazine 1. A number of the dye/solvent combinations have been further tested in a flashlamp pumped dye laser apparatus with success, with moderate laser efficiency at lasing wavelengths ranging from 692 to 824 nm having been achieved.
Föhn in the Rhine Valley during MAP: A review of its multiscale dynamics in complex valley geometry

This paper summarizes the findings of seven years of research on föhn conducted within the project ‘Föhn in the Rhine Valley during MAP’ (FORM) of the Mesoscale Alpine Programme (MAP). It starts with a brief historical review of föhn research in the Alps, reaching back to the middle of the 19th century. Afterwards, it provides an overview of the experimental and numerical challenges identified before the MAP field experiment and summarizes the key findings made during MAP in observation, simulation and theory. We specifically address the role of the upstream and cross‐Alpine flow structure on föhn at a local scale and the processes driving föhn propagation in the Rhine Valley. The crucial importance of interactions between the föhn and cold‐air pools frequently filling the lower Rhine Valley is highlighted. In addition, the dynamics of a low‐level flow splitting occurring at a valley bifurcation between the Rhine Valley and the Seez Valley are examined. The advances in numerical modelling and forecasting of föhn events in the Rhine Valley are also underlined. Finally, we discuss the main differences between föhn dynamics in the Rhine Valley area and in the Wipp/Inn Valley region and point out some open research questions needing further investigation. Copyright © 2007 Royal Meteorological Society
Stark Width Regularities within Neutral Calcium Spectral Series

Abstract Dependences of electron and proton impact Stark width on the upper level ionization potential within different series of the neutral calcium spectral lines have been evaluated and discussed. The similar dependences previously found for the electron impact contribution were also obtained for the proton impact contribution to the Stark broadening. The emphasis is on the term structure influence on the studied Stark width dependences. The influence of the lower transition level and transition term is higher at low temperatures. After establishing these dependences, predictions were made for Stark widths of neutral calcium spectral lines not measured experimentally or calculated theoretically until now.
Frequency control characteristics of a single-frequency fiber laser with an external light injection

Characteristics of a single-frequency erbium-doped fiber laser (EDFL) controlled by an external light source is investigated. The frequency control is achieved by cooperatively induced spatial hole-burning (SHB) formed by the interference between the lasing light and the external light. We evaluate the frequency stability of several cavity designs of the fiber laser and the frequency control characteristics in detail. Tunable operation as wide as 30 nm wavelength range with a good frequency stability is also demonstrated.
Generate disaggregated soil allocation data using a Minimum Cross Entropy Model

Montado ecosystem in the Alentejo Region, south of Portugal, has enormous agro-ecological and economics heterogeneities. A definition of homogeneous sub-units among this heterogeneous ecosystem was made, but for them is disposal only partial statistical information about soil allocation agro-forestry activities. The paper proposal is to recover the unknown soil allocation at each homogeneous sub-unit, disaggregating a complete data set for the Montado ecosystem area using incomplete information at sub-units level. The methodological framework is based on a Generalized Maximum Entropy approach, which is developed in thee steps concerning the specification of a r order Markov process, the estimates of aggregate transition probabilities and the disaggregation data to recover the unknown soil allocation at each homogeneous sub-units. The results quality is evaluated using the predicted absolute deviation (PAD) and the "Disagegation Information Gain" (DIG) and shows very acceptable estimation errors.
Experimental Investigation of the Production and Containment of a Laser‐Produced Plasma

The results of optical interferometric measurements in a laser produced plasma are presented. Two processes are studied. First, the quantity of charge in the plasma, as a function of the power density at the focal spot; agreement is found with the theoretical one‐dimensional heating model. Second, expansion in a uniform magnetic field. Here, confinement occurs in the first stage and is rapidly perturbed by a large flow of the plasma across the field. This flow is explained by a charge separation when a highly directed velocity exists.
On the structure of vortex rings from inclined nozzles

Abstract We carry out numerical simulations to investigate the vortex dynamics of laminar, impulsively driven flows through inclined nozzles in a piston–cylinder apparatus. Our simulations are motivated by the need to provide a complete description of the intricate vortical structures and governing mechanisms emerging in such flows as documented in the experiments of Webster & Longmire (Phys. Fluids, vol. 10, 1998, pp. 400–416) and Troolin & Longmire (Exp. Fluids, vol. 48, 2010, pp. 409–420). We show that the flow is dominated by the interaction of two main vortical structures: the primary inclined vortex ring at the nozzle exit and the secondary stopping ring that arises due to the entrainment of the flow into the cylinder when the piston stops moving. These two structures are connected together with pairs of vortex tubes, which evolve from the continuous vortex sheet initially connecting the primary vortex ring with the interior cylinder wall. In the exterior of the nozzle the key mechanism responsible for the breakup of the vortical structure is the interaction of the stronger inclined primary ring with the weaker stopping ring near the longest lip of the nozzle. In the interior of the nozzle the dynamics is governed by the axial stretching of the secondary ring and the ultimate impingement of this ring on the cylinder wall. Our simulations also clarify the kinematics of the azimuthal flow along the core of the primary vortex ring documented in the experiments by Lim (Phys. Fluids, vol. 10, 1998, pp. 1666–1671). We show that the azimuthal flow is characterized by a pair of two spiral saddle foci at the long and short lips of the nozzle through which ambient flow enters and exits the primary vortex core.
Ionospheric plasma escape by high‐altitude electric fields: Magnetic moment "pumping"

Measurements of electric fields and the composition of upward flowing ionospheric ions by the Viking spacecraft have provided further insight into the mass dependent plasma escape process taking place in the upper ionosphere. The Viking results of the temperature and mass-composition of individual ion beams suggest that upward flowing ion beams can be generated by a magnetic moment “pumping” mechanism caused by low-frequency transverse electric field fluctuations, in addition to a field-aligned “quasi-electrostatic” acceleration process. Magnetic moment “pumping” within transverse electric field gradients can be described as a conversion of electric drift velocity to cyclotron velocity by the inertial drift in a time-dependent electric field. This gives an equal cyclotron velocity gain for all plasma species, irrespective of mass. Oxygen ions thus gain 16 times as much transverse energy as protons. In addition to a transverse energy gain above the escape energy, a field-aligned quasi-electrostatic acceleration is considered primarily responsible for the collimated upward flow of ions. The field-aligned acceleration adds a constant parallel energy to escaping ionospheric ions. Thus, ion beams at high altitudes can be explained by a bimodal acceleration from both a transverse (equal velocity) and a parallel (equal energy) acceleration process. The Viking observations also show that the thermal energy of ion beams, and the ion beam width are mass dependent. The average O+/H+ “temperature” ratio has been found to be 4.0 from the Viking observations. This is less than the factor of 16 anticipated from a coherent transverse electric field acceleration but greater than the factor of 1 (or even less than 1) expected from a turbulent acceleration process.
Mardia's Multivariate Kurtosis with Missing Data

Mardia's measure of multivariate kurtosis has been implemented in many statistical packages commonly used by social scientists. It provides important information on whether a commonly used multivariate procedure is appropriate for inference. Many statistical packages also have options for missing data. However, there is no procedure for applying Mardia's kurtosis to a data set with missing values. In this article Mardia's kurtosis is extended to a data set with missing values. Based on the complete data counterpart, the behavior of a standardized version of the extended sample kurtosis can be described by the standard normal distribution. Analytical and Monte-Carlo studies imply that the proposed distribution description is as good as its complete data counterpart when missing variables are either missing completely at random or missing at random when observed marginals do not sit in a cluster with a restricted range. Application of this procedure is illustrated with a real data set.
Optimization of TLM schemes based on the general symmetrical condensed node

A general symmetrical condensed node (GSCN) for the transmission-line modeling (TLM) method is derived from first principles, based on the establishment of a mapping between field quantities and voltage pulses, averaging at the node centers quantities at the boundaries and differencing of Maxwell's equations. The degrees of freedom offered by this formulation permit the development of adaptable nodes, where the mix of stubs and links can be chosen in a manner to optimize the dispersion characteristics. Results are shown confirming that the adaptable nodes can reduce substantially the dispersion and remove polarization-dependent errors.