Miracle-dz/UniFAR-FTUs huggingface dataset:
Measurement of the transfer function of the steering filter of the Virgo super attenuator suspension

The optical elements of the Virgo antenna are supported and isolated from seismic noise disturbances by super attenuator (SA) suspensions. The steering filter (SF) is a component of the SA, designed for the mirror control. The dynamical properties of the SF are described by transfer functions, which have been measured in order to define the control strategy; the results have made it possible to set and tune the parameters of a simulation of the SA. The measuring devices were linear voltage differential transducers: they were found to be quite effective and flexible in usage. An auto-regressive model was used to fit the experimental data, implementing the linear relation between the input forces and the resulting motion. The ability of the model to reproduce the experimental behavior was a clear indication of the good data quality, showing that the contaminating noise was under control. The simulation was able to reproduce the qualitative behavior, and the simulation parameters were estimated, with 10% and.
From NBODY1 to NBODY6: The Growth of an Industry

I review the development of direct N‐body codes at Cambridge over nearly 40 years, highlighting the main stepping stones. The first code (NBODY1) was based on the simple concepts of a force polynomial combined with individual time steps, where numerical problems due to close encounters were avoided by a softened potential. Fortuitously, the elegant Kustaanheimo‐Stiefel two‐body regularization soon permitted small star clusters to be studied (NBODY3). Subsequent extensions to unperturbed three‐body and four‐body regularization proved beneficial in dealing with multiple interactions. Investigations of larger systems became possible with the Ahmad‐Cohen neighbor scheme which was used more than 20 years ago for expanding universe models of 4000 galaxies (NBODY2). Combining the neighbor scheme with the regularization procedures enabled more realistic star clusters to be considered (NBODY5). After a period of simulations with no apparent technical progress, chain regularization replaced the treatment of compact subsystems (NBODY3, NBODY5). More recently, the Hermite integration method provided a major advance and has been implemented on the special‐purpose HARP computers (NBODY4) together with an alternative version for workstations and supercomputers (NBODY6). These codes also include a variety of algorithms for stellar evolution based on fast lookup functions. The treatment of primordial binaries contains efficient procedures for chaotic two‐body motion as well as tidal circularization, and special attention is paid to hierarchical systems and their stability. This family of N‐body codes constitutes a powerful tool for dynamical simulations which is freely available to the astronomical community, and the massive effort owes much to collaborators.
Average intersection and pivoting densities

For the purposes of quantifying efficiency of more-than-one codimension piecewise-linear continuation algorithms, higher dimensional analogues of the average directional density are defined and studied. Two such are explicitly considered—the average intersection density, which measures the local density of intersections of an implicitly defined piecewise-linear manifold with complementing faces of a decomposition of Euclidean space, and average pivoting density, which considers the number of pivots such an intersection entails. General results are established which relate the densities to geometric properties of the decomposition. Explicit, closed formulae are presented for the most interesting case of the Freudenthal–Kuhn triangulation and asymptotic expressions are developed.
Site-specific growth of Zno nanorods using catalysis-driven molecular-beam epitaxy

We report on catalyst-driven molecular beam epitaxy of ZnO nanorods. The process is site specific, as single crystal ZnO nanorod growth is realized via nucleation on Ag films or islands that are deposited on a SiO2-terminated Si substrate surface. Growth occurs at substrate temperatures on the order of 300–500 °C. The nanorods are uniform cylinders, exhibiting diameters of 15–40 nm and lengths in excess of 1 μm. With this approach, nanorod placement can be predefined via location of metal catalyst islands or particles. This, coupled with the relatively low growth temperatures needed, suggests that ZnO nanorods could be integrated on device platforms for numerous applications, including chemical sensors and nanoelectronics.
Subharmonics and vortex merging in mixing layers

In the present study, it is shown that the spreading rate of a mixing layer can be greatly manipulated at very low forcing level if the mixing layer is perturbed near a subharmonic of the most-amplified frequency. The subharmonic forcing technique is able to make several vortices merge simultaneously and hence increases the spreading rate dramatically. A new mechanism, ‘collective interaction’, was found which can bypass the sequential stages of vortex merging and make a large number of vortices (ten or more) coalesce. A deeper physical insight into the evolution of the coherent structures is revealed through the investigation of a forced mixing layer. The stability and the forcing function play important roles in determining the initial formation of the vortices. The subharmonic starts to amplify at the location where the phase speed of the subharmonic matches that of the fundamental. The position where vortices are seen to align vertically coincides with the position where the measured subharmonic reaches its peak. This location is defined as the merging location, and it can be determined from the feedback equation (Ho & Nosseir 1981). The spreading rate and the velocity profiles of the forced mixing layer are distinctly different from the unforced case. The data show that the initial condition has a longlasting effect on the development of the mixing layer.
Visuelle Helligkeitsbeobachtungen von Neuen Sternen

Zahlreiche visuelle Helligkeitsbeobachtungen, die zum Teil auch mit Farbfiltern an den funf Novae WZ Sge, CT Ser. V 465 Cyg, EU Set und DK Lac angestellt wurden, liefern zuverlassige Aufschlusse uber den Verlauf der Lichtabnahme dieser Sterne. Die Filterbeobachtungen spiegeln die spektralen Veranderungen bei der Entwicklung zum Nebelstadium wider und lassen bemerkenswerte Beziehungen zwischen Farbung und Helligkeit erkennen.
Analytic Expressions of Magnetic Multipole Field Generated by a Row of Permanent Magnets

Analytic expressions of a magnetic multipole field generated by a row of permanent magnets which are arranged on a same plane have been obtained. Each magnet is replaced by two sheet currents flowing in opposite directions through each side of the magnet. The results have been compared with measured values and both have been in good agreement. These expressions are simple and very convenient for design of a plasma source surrounded by magnetic multipole fields.
Interaction of an Asymmetric Double Vortex and Trochoidal Motion of a Tropical Cyclone with the Concentric Eyewall Structure

Radar echo images demonstrate that mature tropical cyclones frequently have a concentric eyewall structure, which consists of the inner eyewall, echo-free moat, and outer eyewall regions. Near the inner and outer eyewalls, well-defined wind maxima are generally observed. This indicates that two large vertical vorticity regions exist just inside radii of the two wind maxima near the inner and outer eyewalls. Therefore, the concentric eyewall structure can be considered to be a double vortex composed of the inner vortex and the outer vortex ring. In this study, the contour dynamics model is used on the f plane to analyze the characteristics of flows with either a symmetric double vortex or an asymmetric one, and examined the relationship between the movement of the inner vortex in an asymmetric double vortex and a trochoidal motion of a tropical cyclone with an asymmetric concentric eyewall structure. Results show that, depending on the degree of an interaction of a double vortex, the evolution of the inner vortex is classified into three patterns: the first is that the center of the inner vortex is stationary, which is seen only for the symmetric double vortex; the second is that the track of the center of the inner vortex draws a circle; and the third is that it draws a spiral. A numerical experiment based on an observed flow around Typhoon Herb was also performed. The time evolution of the double vortex is very similar to that of radar echo intensity of Typhoon Herb. Also the rotation period and amplitude of the inner vortex in the numerical experiment were comparable with those of the trochoidal motion in the observation. These suggest that, in tropical cyclones with the concentric eyewall structure, the interaction of an asymmetric double vortex can become a cause of trochoidal motion.
Investigation of intrinsic defects in core-shell structured ZnO nanocrystals

Nanocrystalline ZnO particles were prepared using the high-energy ball milling technique and investigated with electron paramagnetic resonance (EPR), impedance, and Raman spectroscopy to reveal the origin of surface and core defects. We observed two distinct EPR signals with different g-factors, g ∼ 2.0 and ∼1.96, indicating EPR-active defects on the surface and core, respectively. Using the semi-empirical core-shell model, we identified that sufficiently small nanocrystals (below 30 nm) can show p-type character. The model can also explain the origin of the non-linearity of the U-I behaviour in nanocrystalline ZnO.
Nonlinear aspects of hydrodynamic instabilities in laser ablation

We report on our investigation of the Rayleigh–Taylor and Kelvin–Helmholtz (KH) instabilities in laser ablatively accelerated targets for a series of single mode perturbations. We find linear growth rates well below classical values and a cutoff in the growth rates for wavelengths less than the foil thickness. However, the striking result is the dominance of nonlinear effects, i.e., the KH rollup, for the short wavelength perturbations. Although the linear growth rate increases as k1/2 up to the cutoff, the KH rollup dominates at large k, drastically reducing the penetration rate of the dense spike below its free fall value in the nonlinear phase and effectively doubling the aspect ratio before foil breakup.
Solar wind double ion beams and the heliospheric current sheet

Double ion beams are often observed in the solar wind, but little work has been done in relating these beams to structures within the solar wind. Double ion beams are observed as beams of a given ion species and charge state occurring at two different energies. We use the three-dimensional ion plasma instrument on board the Ulysses spacecraft to look for evidence of such beams associated with the heliospheric current sheet. In a subset chosen independently of plasma parameters consisting of 8 of over 47 crossings of the current sheet made during the in-ecliptic phase of the Ulysses mission we find that these double ion beams are always present on either side of the current sheet. The double beams are present in both the proton and helium species. The secondary beam typically has a higher helium abundance, which suggests that these beams are formed in the helium-rich corona rather than in interplanetary space. The double beams are not present in the interior of the current sheet. Neither collisions nor effects of plasma beta can account for the disappearance of the double beams inside the current sheet in all eight cases. We postulate that these beams are formed by reconnection occurring near the Sun in the boundary region between the open field lines of the coronal holes and the closed field line region of the heliospheric current sheet. Such a scenario would be consistent with previous X ray measurements which suggest that reconnection is occurring in this region.
Semiparametric Estimators for Limited Dependent Variable (LDV) Models with Endogenous Regressors

This article reviews semiparametric estimators for limited dependent variable (LDV) models with endogenous regressors, where nonlinearity and nonseparability pose difficulties. We first introduce six main approaches in the linear equation system literature to handle endogenous regressors with linear projections: (i) ‘substitution’ replacing the endogenous regressors with their projected versions on the system exogenous regressors x, (ii) instrumental variable estimator (IVE) based on E{(error) × x} = 0, (iii) ‘model-projection’ turning the original model into a model in terms of only x-projected variables, (iv) ‘system reduced form (RF)’ finding RF parameters first and then the structural form (SF) parameters, (v) ‘artificial instrumental regressor’ using instruments as artificial regressors with zero coefficients, and (vi) ‘control function’ adding an extra term as a regressor to control for the endogeneity source. We then check if these approaches are applicable to LDV models using conditional mean/quantiles instead of linear projection. The six approaches provide a convenient forum on which semiparametric estimators in the literature can be categorized, although there are a few exceptions. The pros and cons of the approaches are discussed, and a small-scale simulation study is provided for some reviewed estimators.
Electrostatic structure around spacecraft in tenuous plasmas

[1] Most satellite-based in situ plasma experiments are affected in some manner by the electrostatic structure surrounding the spacecraft. In order to better understand this structure, we have developed a fully three-dimensional self-consistent model that can accept realistic spacecraft geometry, including both thin (∼10−4 m) wires and long (∼102 m) booms, with open boundary conditions. The model uses an integral formulation incorporating boundary element, multigrid and fast multipole methods to overcome problems associated with the large range in scale sizes and inherently three-dimensional structure. By applying the model to the Cluster spacecraft, we show that the electric potential structure is dominated by the charge on the wire booms, with the spacecraft body contributing at small distances. Consequently, the potential near the EFW (Electric Fields and Waves experiment) probes at the end of the wire booms is typically significantly above the true plasma potential. For the Cluster spacecraft, we show that this effect causes a 19% underestimation of the spacecraft potential and 13% underestimation of the ambient electric field. We further assess the electric field due to the sunward-oriented photoelectron cloud, showing that the cloud contributes little to the observed spurious sunward field in the EFW data.
An immersed interface method for flow past circular cylinder in the vicinity of a plane moving wall

Two‐dimensional flows past a stationary circular cylinder near a plane boundary are numerically simulated using an immersed interface method with second‐order accuracy. Instead of a fixed wall, a moving wall with no‐slip boundary is considered to avoid the complex involvement of the boundary layer and to focus only on the shear‐free wall proximity effects for investigating the force dynamics and flow fields. To analyze the convergence and accuracy of our implementation, numerical studies have been first performed on a simple test problem of rotational flow, where the second order of convergence is confirmed through numerical experiments and an optimal range of relative grid‐match ratio of Lagrangian to Eulerian grid sizes has been recommended. By comparing the force quantities and the Strouhal number, the accuracy of this method has been demonstrated on the flow past a stationary isolated cylinder. The cylinder is then put in proximity to the wall to investigate the shear‐free wall proximity effects in the low Reynolds number regime (20≤Re≤200). The gap ratio, e/D, where e denotes the gap between the cylinder and the moving wall and D denotes the diameter of the cylinder, is taken from 0.10 to 2.00 to determine the critical gap ratio, (e/D)critical, for the alternate vortex shedding, where the fluid forces, flow fields and the streamwise velocity profiles are studied. One of the key findings is that the (e/D)critical for the alternate vortex shedding decreases as the Reynolds number increases. We also find that, in this low Reynolds number regime, the mean drag coefficient increases and peaks at e/D = 0.5 with the increase of e/D and keeps decreasing gently from e/D = 0.5 to e/D = 2.0, while the mean lift coefficient decreases monotonically with the increase of e/D. New correlations are then proposed for computing force coefficients as a function of Re and e/D for a cylinder in the vicinity of a moving plane wall. Copyright © 2015 John Wiley & Sons, Ltd.
Propagation of Pinched Electron Beams for Pellet Fusion

We present results which are encouraging for a multibeam approach to relativistic-electron-beam--induced pellet fusion. A self-pinched relativistic electron beam with nominal parameters of 1.1 MV, 200 kA, and 5-mm radius has been propagated at atmospheric pressure over distances of up to 1 m. Gross beam beam stability and reasonable energy transport efficiency has been achieved. A simple Alfven-type calculation corroborates the propagation result, and a self-consistent particle simulation indicates the possibility of scaling to very high-. nu. /. gamma. beams.
Fractal properties of rain, and a fractal model

This paper amplifies upon earlier theories and observations by the authors, advances a probabilistic model ofrain fields, and exhibits realistic simulations, which the reader is advised to scan before continuing with the text. The model is also compared with other approaches. The theory of fractals has been in part motivated by the Hurst effect, which is an empirical observation in hydrology and climatology. A fractal is an unsmooth shape that is scaling, that is, where shape appears unchanged when examined by varying magnifications. The study offractals is characterized by the prevalence ofhyperbolically distributed random variables, for which Pr({.r ) u) a: z o, where Pr is the probability that the value of the variable exceeds z, and o is a positive exponent. Lovejoy established the applicability of fractals in meteorology, by showing that cloud and rain areas project on the Earth along shapes whose boundaries are fractal curves, and that the temporal and spatial structure ofrain is rife with hyperbolically distributed features. These observations, as amplified in this paper, set up the challenge ofconstructing fractal models with the observed properties. The models presented here belong to a very versatile family of random processes devised in Mandelbrot: fractal sums of (simple) pulses. or FSP processes. The simulations to be presented reveal that these processes involve a scaling heirarchy of "bands", "fronts", and "clusters", as well as other complex shapes, none of which had been deliberately incorporated in the process. This very rich morphology and the related statistical distributions exemplify the power of simple fractal models to generate complex structures, and are in accord with the wide diversity ofactual rainfall shapes. It is argued that this model already provides a useful context in which the basic statistical properties of the rainfield, including the relationship between the temporal and spatial structure, may be studied.
Drag coefficient prediction analysis for heavy duty trucks

In this paper application of a standard CFD code to analyse the flow and aerodynamic drag around heavy duty vehicles is elaborated by using the Sandia Ground Transportation System (GTS) model. It is assumed that all unsteady effects are taken care for by the RNG κ-e turbulence model. Within this context, a methodology for an accurate prediction of the drag coefficient is proposed, where special emphasis is placed upon the grid resolution, results indicating the importance of the discretisation of the wake area.
Theoretical and experimental study of space charge in intense ion beams

The highly collimated beams of energetic neutral atoms used in controlled thermonuclear fusion research (CTR) require the virtual elimination of space-charge forces in the primary ion beam in order to minimize the angular divergence. A model is presented which describes the behavior of an intense ion beam passing through a gas cell. This theory is used to derive the space-charge field produced by such a beam and shows how its effect can be minimized. This model agrees well with experimental measurements and enables emittance-dominated beams of very high brightness to be obtained which could find applications in fields other than CTR.
Compactness properties of weighted summation operators on trees-the critical case

The aim of this paper is to provide upper bounds for the entropy numbers of summation operators on trees in a critical case. In a recent paper [10] we elaborated a framework of weighted summation operators on general trees where we related the entropy of the operator with those of the underlying tree equipped with an appropriate metric. However, the results were left incomplete in a critical case of the entropy behavior, because this case requires much more involved techniques. In the present article we fill the gap left open in [10]. To this end we develop a method, working in the context of general trees and general weighted summation operators, which was recently proposed in [9] for a particular critical operator on the binary tree. Those problems appeared in natural way during the study of compactness properties of certain Volterra integral operators in a critical case.
Screening, predicting, and computer experiments

Many scientific phenomena are now investigated by complex computer models or codes. Given the input values, the code produces one or more outputs via a complex mathematical model. Often the code is expensive to run, and it may be necessary to build a computationally cheaper predictor to enable, for example, optimization of the inputs. If there are many input factors, an initial step in building a predictor is identifying (screening) the active factors. We model the output of the computer code as the realization of a stochastic process. This model has a number of advantages. First, it provides a statistical basis, via the likelihood, for a stepwise algorithm to determine the important factors. Second, it is very flexible, allowing nonlinear and interaction effects to emerge without explicitly modeling such effects. Third, the same data are used for screening and building the predictor, so expensive runs are efficiently used. We illustrate the methodology with two examples, both having 20 input variables. I.
New square-root smoothing algorithms

New square-root smoothing algorithms are suggested for the four kinds of smoothing formulas: (1) Bryson-Frazier (BF) formulas, (2) Rauch-Tung-Striebel (RTS) formulas, (3) backward RTS formulas and (4) two-filter formulas. These algorithms are compared on the basis of constraints, speed in real-time or batch processing, array size, memory size, and so on. The main features of the new algorithms are to implement all the formulas with square-root arrays composed of the filtered or smoothed estimates and their error covariances, and to avoid inversion or backwards substitution in all the formulas: these features provide many advantages over the conventional algorithms with respect to systolic array and parallel implementations as well as numerical stability and conditioning. <<ETX>>