Miracle-dz/UniFAR-FTUs huggingface dataset:
Closed-Loop Performance Control of Dielectric-Barrier-Discharge Plasma Actuators

The counteraction of changing environmental conditions (i.e., changes of pressure level and airflow speed) on the resulting plasma-actuator performance is demonstrated in the present work. The impact of these changing (fluctuating and/or transient) airflow conditions on the performance of dielectric-barrier-discharge plasma actuators is suppressed using a novel closed-loop performance-control procedure. The goal of controlling a preset plasma-actuator performance online and in situ is achieved and successfully demonstrated. This novel approach represents the first step toward optimal-discharge-based flow control because, beyond the common purpose of favorably manipulating the airflow, any advanced dielectric-barrier-discharge-based flow-control system will necessarily require an appropriate closed-loop performance control of the discharge device.
Effect of free rotation on the motion of a solid sphere in linear shear flow at moderate Re

The effect of free rotation on the drag and lift forces on a solid sphere in unbounded linear shear flow is investigated. The sphere Reynolds number, Re=|ur|d/ν, is in the range 0.5–200, where ur is the slip velocity. Direct numerical simulations of three-dimensional flow past an isolated sphere are performed using spectral methods. The sphere is allowed to rotate and translate freely in the shear flow in response to the hydrodynamic forces and torque acting on it. The effect of free rotation is studied in a systematic way by considering three sets of simulations. In the first set of simulations, we study how fast a pure rotational or translational motion of the sphere approaches steady state. The “history” effect of rotational and translational motions are compared. Results at high Re are found to be significantly different from the analytical prediction based on low Re theory. In steady simulations, the sphere is allowed to rotate in a torque-free condition. The torque-free rotation rate and the drag an.
A NUMERICAL MODEL OF STANDARD TO BLOWOUT JETS

We report on three-dimensional (3D) MHD simulations of the formation of jets produced during the emergence and eruption of solar magnetic fields. The interaction between an emerging and an ambient magnetic field in the solar atmosphere leads to (external) reconnection and the formation of “standard” jets with an inverse Y-shaped configuration. Eventually, low-atmosphere (internal) reconnection of sheared fieldlines in the emerging flux region produces an erupting magnetic flux rope and a reconnection jet underneath it. The erupting plasma blows out the ambient field and, moreover, it unwinds as it is ejected into the outer solar atmosphere. The fast emission of the cool material that erupts together with the hot outflows due to external/internal reconnection form a wider “blowout” jet. We show the transition from “standard” to “blowout” jets and report on their 3D structure. The physical plasma properties of the jets are consistent with observational studies.
Axisymmetric flow within a torsionally oscillating sphere

The flow of an incompressible Newtonian fluid inside a torsionally oscillating spherical cavity is considered. The three-dimensional Navier-Stokes and continuity equations are solved by means of a Galerkin projection spectral method, based on a second-order incremental fractional-step approach. Legendre and Jacobi polynomial expansions are used in the zenithal and radial directions, respectively. Axisymmetric solutions are sought for a relatively wide set of the parameters controlling the flow, namely, the Rossby and the Womersley numbers. In particular, the behaviour of the flow for relatively large amplitudes of oscillation is studied, with emphasis on the generation of centrifugal instabilities. Numerical results are compared with experimental observations and semi-analytical solutions in the small-amplitude regime, showing good agreement.
Analysis of Newton’s Method at Irregular Singularities

Recent work on Newton’s method at singularities of the Jacobian has established linear convergence under certain regularity assumptions. Here, Newton’s method is analyzed in the neighborhood of irregular singularities which include all minimizers at which the Hessian has a one-dimensional null space. Depending on a parameter specific to the underlying optimization problem or system of simultaneous equations, Newton’s method is found either to converge with a limiting ratio of about $\frac{2} {3}$, or to diverge from arbitrarily close starting points, or to behave in a certain sense chaotically.
Characterization of Palm measures via bijective point-shifts

The paper considers a stationary point process N in R d . A point-map picks a point of N in a measurable way. It is called bijective [Thorisson, H. (2000). Coupling, Stationarity, and Regeneration. Springer, New York] if it is generating (by suitable shifts) a bijective mapping on N. Mecke [Math. Nachr. 65 (1975) 335-344] proved that the Palm measure of N is point-stationary in the sense that it is invariant under bijective point-shifts. Our main result identifies this property as being characteristic for Palm measures. This generalizes a fundamental classical result for point processes on the line (see, e.g., Theorem 11.4 in [Kallenberg, O. (2002). Foundations of Modern Probability, 2nd ed. Springer, New York]) and solves a problem posed in [Thorisson, H. (2000). Coupling, Stationarity, and Regeneration. Springer, New York] and [Ferrari, P. A. , Landim, C. and Thorisson, H. (2004). Ann. Inst. H. Poincare Probab. Statist. 40 141-152]. Our second result guarantees the existence of bijective point-maps that have (almost surely with respect to the Palm measure of N) no fixed points. This answers another question asked by Thorisson. Our final result shows that there is a directed graph with vertex set N that is defined in a translation-invariant way and whose components are almost surely doubly infinite paths. This generalizes and complements one of the main results in [Holroyd, A. E. and Peres, Y. (2003). Electron. Comm. Prohab. 8 17-27]. No additional assumptions (as ergodicity, nonlattice type conditions, or a finite intensity) are made in this paper.
Sucient conditions for a digraph to be Hamiltonian

We describe a new type of sufficient condition for a digraph to be Hamiltonian. Conditions of this type combine local structure of the digraph with conditions on the degrees of non-adjacent vertices. The main difference from earlier conditions is that we do not require a degree condition on all pairs of non-adjacent vertices. Our results generalize the classical conditions by Ghouila-Houri and Woodall.
Operational Wave Guidance at the U.S. National Weather Service during Tropical/Post–Tropical Storm Sandy, October 2012*

AbstractWaves generated during Hurricane Sandy (October 2012) contributed significantly to life and property losses along the eastern U.S. seaboard. Extreme waves generated by Sandy propagated inland riding high water levels, causing direct destruction of property and infrastructure. High waves also contributed to the observed record-breaking storm surges. Operational wave-model guidance provided by the U.S. National Weather Service, via numerical model predictions made at NOAA’s National Centers for Environmental Prediction (NCEP), gave decision makers accurate information that helped mitigate the severity of this historical event. The present study provides a comprehensive performance assessment of operational models used by NCEP during Hurricane Sandy, and makes a brief review of reports issued by government agencies, private industry, and universities, indicating the importance of the interplay of waves and surges during the hurricane. Performance of wave models is assessed through validation made rel.
A variational approach to a nonlinear Steklov problem

Synopsis We study the Steklov problem which consists in finding a complex function w(z) = U(z) + iV(z) holomorphic in the open unit disc G of the complex plane, continuous on its closure, such that V(0) = 0 and verifying on its boundary the condition (d/ds)V(eis)+g(s, U(eis))=h(s), where g and h are given functions. Using the Hilbert transform, the problem is reduced to the search for periodic solutions of an equivalent singular integro-differential equation which is treated by the direct method of the calculus of variations. When g(s,.) is non-decreasing, we obtain a necessary and sufficient condition for the solvability. The case of a non-monotone nonlinearity is also considered.
Steady-state mode interactions in the presence of 0(2)-symmetry

This paper studies the multiple bifuraction phenomenon of steady-state mode interactions in the presence of 0(2)-symmetry. For such problems the flow on the centre manifold is determined by a vector field in or that is equivariant under an action of 0(2). The action is related to the wave numbers of the unstable modes. The unfolded normal forms for these equivariant bifurcation problems admit primary bifurcations to single-mode solutions, secondary bifurcations to mixed-mode solutions and, in some instances, tertiary bifurcations to travelling and standing waves. The bifurcation behaviour depends crucially on the wave numbers. For small wave numbers, the mixed-mode solutions encounter subordinate saddle-node bifurcations.
Hidden symmetry breaking in a generalized valence-bond solid model

A 'boson' representation for the ground state of the generalized valence-bond solid model is derived. The relation between this expression and the matrix-product representation of Klumper et al. (1991,1992) is discussed. It is shown that the hidden Z2*Z2-symmetry is partially broken in this model. Elementary excitations of this system have a topological nature similar to that in the Affleck, Kennedy, Lieb and Tasaki (1988) model.
Bifurcation analysis of an inverted pendulum with delayed feedback control near a triple-zero eigenvalue singularity

We investigate a delay differential equation that models a pendulum stabilized in the upright position by a delayed linear horizontal control force. Linear stability analysis reveals that the region of stability of the origin (the upright position of the pendulum) is bounded for positive delay. We find that a codimension-three triple-zero eigenvalue bifurcation acts as an organizing centre of the dynamics. It is studied by computing and then analysing a reduced three-dimensional vector field on the centre manifold. The validity of this analysis is checked in the full delay model with the continuation software DDE-BIFTOOL. Among other things, we find stable small-amplitude solutions outside the region of linear stability of the pendulum, which can be interpreted as a relaxed form of successful control.
Response of Earth's Ionosphere to Interplanetary Shocks

This paper presents three-dimensional, global numerical simulations of the dynamic response of the Earth's ionosphere to interplanetary shocks. The background interplanetary magnetic field is spiral with a vanishing south-north component, the initial ionosphere is dominated by the region I field-aligned current (FAC) and the corresponding dawn-dusk electric field, and the interplanetary shock collides with the Earth along the Sun-Earth line. It is shown that with the impact of interplanetary shocks, the region I current moves towards the midnight sector, accompanied by a successive occurrence of two FAC structures: an anomalous FAC pair of opposite direction to the region I current and a new region I current of the same direction. The anomalous FAC pair creates a transient dusk-dawn electric field over the polar cap, tailing behind the original region I current and drifting towards the night side until it falls into oblivion. In the meantime, the new region I current keeps increasing and expanding towards the night and equator side, and it eventually replaces the original region I current, so the polar cap returns to a state similar to the original with a dawn-dusk electric field. Such a response depends on the strength of the interplanetary shock. For a stronger shock, the new region I current gets stronger, extends for a longer distance towards the equator, and reaches a lower latitude. These results agree with the observations associated with traveling convection vortices and midday sub-auroral patches.
On the Gauss–Bonnet Formula in Riemann–Finsler Geometry

Using Chern's method of transgression, the Euler class of a compact orientable Riemann–Finsler space is represented by polynomials in the connection and curvature matrices of a torsion‐free connection. When using the Chern connection (and hence the Christoffel–Levi–Civita connection in the Riemannian case), this result extends the Gauss–Bonnet formula of Bao and Chern to Finsler spaces whose indicatrices need not have constant volume.
Quantum mechanical compact modeling of symmetric double-gate MOSFETs using variational approach

A physics-based analytical model for symmetrically biased double-gate (DG) MOSFETs considering quantum mechanical effects is proposed. Schrödinger's and Poisson's equations are solved simultaneously using a variational approach. Solving the Poisson and Schrödinger equations simultaneously reveals quantum mechanical effects (QME) that influence the performance of DG MOSFETs. The inversion charge and electrical potential distributions perpendicular to the channel are expressed in closed forms. We systematically evaluated and analyzed the potentials and inversion charges, taking QME into consideration, in Si based double gate devices. The effect of silicon thickness variation in inversion-layer charge and potentials are quantitatively defined. The analytical solutions provide good physical insight into the quantization caused by quantum confinement under various gate biases.
Optical image hiding in the Fresnel domain

A technique of optical image hiding in the Fresnel domain is proposed. In our method, a secret image can be hidden in the watermarked image through the phase only masks that are efficiently generated by the phase retrieval algorithm. The corresponding key distribution scheme is also investigated. Since the watermarked image can be the same as the host image and the secret image’s available dimension is equal to the host one, the imperceptibility and the capacity requirements of the image hiding are both satisfied excellently in the proposed system. The properties of the phase keys are discussed and their dominating role in the system is revealed, which provides the system with robustness to attacks and distortions to the amplitude of the watermarked image. Due to the particularly employed optical keys, including the wavelength key and the mask position key, in this Fresnel hiding system, the system’s security is further improved and the flexibility of the designs for different application purposes is introduced. Further, we also analyse the implementation of this lensless system by the pure digital method and the opt-digital method.
Nasal spectra for forensic voice comparison

For features to be effective in forensic voice comparison, they must have relatively low within-speaker variability and relatively high between-speaker variability. An understudied source of features, which potentially meets these criteria is the acoustic spectrum of nasals. Nasals spectra contain poles and zeros dependent upon nasal cavities. The latter are complex static structures which vary from person to person. Theoretically, nasal spectra may therefore have low within-speaker and high between-speaker variabilities. This study evaluates different methods for extracting spectral features (e.g., pole-zero models, all-pole models, and cepstra) and using them as part of a likelihood-ratio forensic-voice-comparison system. The validity and reliability of each system is empirically evaluated using /m/ and /n/ token extracted from a database of voice recordings of 60 female speakers of Chinese.
Estimating the underlying change in unemployment in the UK

By setting up a suitable time series model in state space form, the latest estimate of the underlying current change in a series may be computed by the Kalman filter. This may be done even if the observations are only available in a time‐aggregated form subject to survey sampling error. A related series, possibly observed more frequently, may be used to improve the estimate of change further. The paper applies these techniques to the important problem of estimating the underlying monthly change in unemployment in the UK measured according to the definition of the International Labour Organisation by the Labour Force Survey. The fitted models suggest a reduction in root‐mean‐squared error of around 10% over a simple estimate based on differences if a univariate model is used and a further reduction of 50% if information on claimant counts is taken into account. With seasonally unadjusted data, the bivariate model offers a gain of roughly 40% over the use of annual differences. For both adjusted and unadjusted data, there is a further gain of around 10% if the next month's figure on claimant counts is used. The method preferred is based on a bivariate model with unadjusted data. If the next month's claimant count is known, the root‐mean‐squared error for the estimate of change is just over 10000.
ALFVÉN WAVES IN SHEAR FLOWS REVISITED

We revisit our earlier study of the evolution of an initial propagating Alfvén wave in a magnetic-field-aligned flow with a cross-field velocity shear. Our goal is to show how the Alfvén wave drives up plasma density fluctuations which might be observed and serve as a signature of the presence of Alfvén waves in regions such as the solar corona which are inaccessible to direct observations. Here, we introduce a new initial condition which takes into account the initial distortion of the streamlines by the Alfvén wave, and we present new analytical results for the driven waves. We find that the density fluctuations of a properly placed linearly polarized Alfvén wave in a shear flow are much smaller than we originally estimated.
A minimax control problem for sampled linear systems

A linear differential system is subject to a bounded control and a bounded disturbance. The controller receives the value of the state at a finite number of fixed sampling times. The cost is a convex or concave function of the state at a fixed final time. Given any control law, there is a maximum cost over all perturbations, the guaranteed performance for this control law. It is desired to find the minimum of this number over all control laws. Fenchel's theory of conjugate convex functions is used to set up an algorithm dual to the dynamic programming approach. This algorithm deals with the support functions of reachable sets, more easily determined than other descriptions of these sets. A discrete minimax principle is generally incorrect for problems of this class.
TEMPORARY CAPTURE OF PLANETESIMALS BY A PLANET FROM THEIR HELIOCENTRIC ORBITS

When planetesimals encounter a planet, they can be temporarily captured by the planet's gravity and orbit about it for an extended period of time before escaping from the planet's vicinity. Such a process may have played an important role in the origin of irregular satellites or the dynamical evolution of short-period comets. Using three-body orbital integration, we study the temporary capture of planetesimals by a planet from their heliocentric eccentric orbits. We examine the dependence of the orbital characteristics during temporary capture as well as the rate of capture on the pre-capture heliocentric orbital parameters. We find that typical orbital size and direction of revolution around the planet change depending on planetesimals' initial eccentricity and energy. When initial eccentricity is so small that Kepler shear dominates the relative velocity between planetesimals and the planet, temporary capture typically occurs in the retrograde direction in the vicinity of the planet's Hill sphere, while large retrograde capture orbits outside the Hill sphere are predominant for large eccentricities. Long prograde capture occurs in a very narrow range of planetesimal eccentricity and energy. We obtain the rate of temporary capture of planetesimals and find that the rate of long capture increases with increasing eccentricity at low and high eccentricities, but decreases with increasing eccentricity in intermediate values of eccentricity. We also examine the dependence of capture rate on the duration of capture and find an approximate power-law dependence.
Experimental and theoretical statistics of microwave amplitude scintillations on satellite down-links

Extensive experimental results are presented on the statistics of tropospheric amplitude scintillations on an X -band satellite down-link obtained using the orbital test satellite beacon transmissions. The experimentally found distribution is shown to depart significantly from the expected log-normal distribution, and this is explained in terms of a Gaussian process with a time variable standard deviation from which a universal model is derived. It has been found that on average no less than about 100 h of data are required before the probability density and cumulative probability distribution functions approach stationarity. The statistics of the scintillation intensity are also presented, and a log-normal distribution of intensity is shown to be in good agreement with observations from other experimental sites. Link budget implications are outlined together with a simple strategy for the investigation of the scintillation process at any ground station.
Animated models coarsening with local area distortion and deformation degree control

In computer graphics applications, mesh coarsening is an important technique to alleviate the workload of visualization processing. Compared to the extensive works on static model approximation, very little attentions have been paid to animated models. In this paper, we propose a new method to approximate animated models with local area distortion and deformation degree control. Our method uses an improved quadric error metric guided by a local area distortion measurement as a basic hierarchy. Also, we define a deformation degree parameter to be embedded into the aggregated quadric errors, so areas with large deformation during the animation can be successfully preserved. Finally, a mesh optimization process is proposed to further reduce the geometric distortion for each frame. Our approach is fast, easy to implement, and as a result good quality dynamic approximations with well-preserved sharp features can be generated at any given frame.
Tornadoes in the New York Metropolitan Region: Climatology and Multiscale Analysis of Two Events

AbstractThis paper describes the climatology of tornadoes around New York City (NYC) and Long Island (LI), New York, and the structural evolution of two tornadic events that affected NYC on 8 August 2007 and 16 September 2010. Nearly half (18 of 34 events from 1950 to 2010) of NYC–LI tornadoes developed between 0500 and 1300 EDT, and August is the peak tornado month as compared to July for most of the northeast United States. A spatial composite highlights the approaching midlevel trough, moderate most unstable convective available potential energy (MUCAPE), and frontogenesis along a low-level baroclinic zone. Shortly before the early morning tornadoes on 8 August 2007, a mesoscale convective system intensified in the lee of the Appalachians in a region of low-level frontogenesis and moderate MUCAPE (~1500 J kg−1). Warm advection at low levels and evaporative cooling within an elevated mixed layer (EML) ahead of the mesoscale convective system (MCS) helped steepen the low-level lapse rates. Meanwhile, a s.