Miracle-dz/UniFAR-FTUs huggingface dataset:
Optimal operation solutions of power systems with transient stability constraints

The computation of an optimal operation point in power systems is a nonlinear optimization problem in functional space, which is not easy to deal with precisely, even for small-scale power systems. On the other hand, the emergence of competitive power markets makes optimal power flow (OPF) with transient stability constraints increasingly important because the conventionally heuristic evaluation for the operation point can produce a discrimination among market players in the deregulated power systems. Instead of directly tackling this tricky problem, in this paper, OPF with transient stability constraints (OTS) is equivalently converted into an optimization problem in the Euclidean space via a constraint transcription, which can be viewed as an initial value problem for all disturbances and solved by any standard nonlinear programming techniques adopted by OPF. The transformed OTS problem has the same variables as those of OPF in form, and is tractable even for the large-scale power systems with a large number of transient stability constraints. This paper also derives the Jacobian matrices of the transient stability constraints and gives two computation algorithms based on the relaxation scheme. The numerical simulation verified the effectiveness of the proposed approach.
Micromechanical magnetometer using an all-silicon nonlinear torsional resonator

In this work, a micromagnetometer employing a nonlinear torsional resonator with a high quality factor Q is presented experimentally. Oscillatory rotation of a conducting plate in the sensed magnetic field H induces eddy currents that dissipate energy. Due to the nonlinear response of the oscillator, the resulting mechanical damping originates frequency shifts in the resonance curve that depend on H. Nonlinearity results from the electrostatic detection, which introduces high order electrical spring constants. The device is fabricated with a standard silicon process and does not incorporate ferromagnetic materials. An analytical nonlinear model that correctly describes the device is also introduced.
SCATTERING POLARIZATION IN THE Fe i 630 nm EMISSION LINES AT THE EXTREME LIMB OF THE SUN

Spectro-polarimetric observations with the Solar Optical Telescope onboard Hinode reveal the emission spectrum of the Fe i 630 nm lines at the solar limb. The emission shell extends for less than 1″ thereby making it extremely difficult to detect from ground-based observatories viewing the limb through the Earth's atmosphere. The linear polarization signal is clearly due to scattering and it is predominantly oriented in the radial direction. Using a comprehensive atomic model of iron, we are able to interpret qualitatively the observed signals, including the radial orientation of the linear polarization. The Hanle effect causes the linear polarization of the Fe i 630 nm lines to be sensitive to magnetic fields between ∼0.1 G and ∼40 G, and also to be sensitive to the field's topology for stronger fields. The overall degree of observed polarization can be reproduced by randomly oriented horizontal magnetic fields of strength ≈2 G. The discovery of their scattering polarization signals thus opens a new diagnostic opportunity for these lines.
Factor Frequencies in Languages Invariant Under Symmetries Preserving Factor Frequencies

Abstract. The number of frequencies of factors of length in a recurrent aperiodic infinite word does not exceed , where is the first difference of factor complexity, as shown by Boshernitzan. Pelantová together with the author derived a better upper bound for infinite words whose language is closed under reversal. In this paper, we further diminish the upper bound for uniformly recurrent infinite words whose language is invariant under all elements of a finite group of symmetries and we prove the optimality of the obtained upper bound.
New null screen design for corneal topography

In this work we report the design of a null screen for corneal topography. Here we assume that the corneal surface is an ellipsoid with a diameter of 12 mm and a curvature radius of 7.8 mm. To avoid the difficulties in the alignment of the test system due to the face contour (eyebrows, nose, or eyelids), we design a conical null-screen with spots (similar to ellipses) drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact radial array of circular spots if the surface is perfect. Additionally, we performed a numerical simulation introducing Gaussian random errors in the coordinates of the centroids of the spots on the image plane, and in the coordinates of the sources (spots on the null-screen) in order to obtain the conical null-screen that reduces the error in the evaluation of the topography.
Logistic Regression Multivariate Life Tables

The use of logistic regression to estimate a discrete-time hazard model is discussed. The derivation of linkage between the results of the estimation of the logistic regression equations and the summary measures of the life table is presented. We argue that the method is responsive to the needs of a variety of researchers, requires few assumptions, and is straightforward to implement. An example is presented where the determinants of the timing of entry into motherhood in eight Asian countries is analyzed.
Parallel universal approach to mesh motion and application to rotors in forward flight

Numerical simulation of unsteady flows including moving boundaries, whether rigid, prescribed, or deforming, requires the mesh to move/deform also. Many approaches to mesh motion have been considered, but the approach adopted often depends on both the meshing approach used and the proposed application. A universal approach to grid motion is presented here. The method developed has several important properties, the most significant of which is that the scheme requires no grid point connectivity information, i.e. each point can be moved totally independently to its neighbours. This has two major implications: first, it means the scheme is universal, i.e. applicable to any grid type, unstructured, hybrid or structured single‐ and multiblock. Second, and equally as important, is that the scheme is perfectly parallel, as no communication is required between points/blocks. Each block can be updated independently to its neighbours so there is no connectivity data required, and this also means the flow‐solver does not have to carry the grid motion parameterization data in memory. The scheme accounts for moving surface rotations as well as displacements, and this ensures grid quality is preserved by maintaining orthogonality. The method is applied to a four‐bladed lifting rotor in forward flight. This is a particularly challenging unsteady problem as there are multiple bodies in relative motion, each one with its own axis system, as each blade has a cyclic pitch variation. Grid quality is proven to be preserved even when a large deformation case is considered and, significantly, the scheme adds only around 1% to the cost of a flow solution real time step. Copyright © 2006 John Wiley & Sons, Ltd.
A Two-Step Scheme for the Advection Equation with Minimized Dissipation and Dispersion Errors

Abstract A two-step advection scheme of the Lax-Wendroff type is derived which has accuracy and phase characteristics similar to that of a third-order scheme. The scheme is exactly third-order accurate in time and space for uniform flow. The new scheme is compared with other currently used methods, and is shown to simulate well the advection of localized disturbances with steep gradients. The scheme is derived for constant flow and generalized to two-dimensional nonuniform flow.
Switched chattering control vs. backlash/friction phenomena in electrical servo-motors

A switched control algorithm is developed to globally stabilize an electrical servo-motor operating under uncertainty conditions in the presence of complex non-linear phenomena such as backlash, stick-slip motion, etc. The controller constructed is referred to as a chattering controller and it does not rely on the generation of sliding motions while providing robustness features similar to those possessed by their sliding mode counterparts. Particularly, the chattering controller ensures robustness against external disturbances with the a priori known norm bounds, thus rejecting the influence of undesired backlash/friction effects on the motor. Stability analysis, given within the Lyapunov functions framework extended to discontinuous dynamic systems, additionally reveals a finite time convergence of the system trajectories to the equilibrium point. Performance issues of the controller are illustrated in a simulation study.
Azimuth preprocessing for monostatic and bistatic spotlight synthetic aperture radar maging based on spectral analysis convolution

Dechirping is a technique widely used to reduce sampling rate. It is well suited for the illumination of small scenes. In this paper, we extend this idea to mono/bistatic spotlight synthetic aperture radar (SAR) imaging. An azimuth preprocessor based on the spectral analysis (SPECAN) convolution is presented. The convolution overcomes the Doppler aliasing of echoed signals, while the wavenumber analytic formula keeps unchanged. Since the spatial characteristic of the signal is preserved, the preprocessing is well compatible with conventional focusing approaches, such as chirp scaling algorithm and frequency scaling algorithm The proposed method is validated by simulations in both monostatic and bistatic cases.
On model predictions of the power spectral density of radial solar p modes

We investigate the frequency dependence of the power spectral density of low-degree solar p modes by comparing measurements with the results of a stochastic-excitation model. In the past it was common practice to use the total power in such investigations. Using the maximum of the power spectral density instead provides a direct comparison with the measured mode heights in the observed power spectrum. This method permits a more careful calibration of the adjustable parameters in the excitation model, a model which we present here, for the first time, in a format that precisely and unambiguously relates the amplitudes of the modes of oscillation to the Reynolds stress in the equilibrium model. We find that errors in the theory of the linear mode damping rates, particularly at low frequency, have a dramatic impact on the predictions of the mode heights in the spectral density, whereas parameter changes in the stochastic excitation model, within a plausible domain of parameter space, have a comparatively small effect.
Optical polarimetry of BL Lacertae objects and violent variable quasars.

Recent optical polarimetric and photometric data on 24 BL Lacertae objects and optically violent variable quasars are presented. Out of 12 objects for which the polarimetric S/N is greater than 9, statistically significant wavelength dependence in the percent polarization was detected in five objects (OJ 287, Mrk 421, Ton 599, 1308 + 326, and 3C 345), with marginal evidence for such an effect in two more (3C 279 and BL Lac). Polarization in excess of 25 percent was detected at some time in eight objects out of 24. In BL Lac and 3C 345, there is evidence that the planes of optical polarization were fairly well aligned with the milliarsecond radio structures as determined by contemporaneous VLBI observations. 45 references.
Optically observed microbubble coalescence and collapse

Understanding the mechanisms of microbubble destruction is needed for the development of ultrasound guided drug and gene delivery methods and for the improvement of diagnostic ultrasonic contrast agent (UCA) detection methods. We performed 482 experiments on the coalescence and collapse mechanisms of a soft-shelled and a hard-shelled contrast agent, by subjecting an experimental lipid-shelled UCA and the hard-shelled UCA Quantison/spl trade/ to 500 kHz, high-pressured ultrasound (MI/spl ap/1.0), and recording microscopic images of these events with a fast-framing camera. Results showed that bubble fragmentation into smaller bubbles is the primary mechanism for lipid-shelled contrast microbubble destruction during the first cycles after ultrasound arrival. In 28% of our experimental events with a lipid-shelled UCA, we observed bubble coalescence. The coalescence mechanism was observed to be analog to the process described for larger gas bubbles. Repetitive coalescence and fragmentation was clearly recorded with a fast-framing camera. We also demonstrated the formation and collapse of large lipid-shelled bubbles and bubble clusters. Furthermore we showed that sonic cracking is feasible for the hard-shelled contrast agent Quantison/spl trade/.
Autonomous star referenced attitude determination

A general star pattern recognition algorithm has been used to develop JPL's redundant, microcomputer-equipped ASTROS II CCD star tracker into a full-sky autonomous star tracker (FAST), capable of determining its attitude about all three axes without requiring any a priori attitude knowledge. A large field of view allows the number of guide stars in the all-sky data-base of the tracker to be limited to a manageable number, while high accuracy ensures that the pattern formed by the observed guide stars is unique. The recognition algorithm can also be used for automating the acquisition of celestial targets by astronomy telescopes, for autonomously updating the attitude of gyro-based attitude control systems, and for automating ground-based attitude recognition. Using both Monte Carlo simulations and a quasi-analytical method, it is shown that the general recognition algorithm and a less software-intensive special algorithm can be used to reliably automate the acquisition of celestial targets by astronomy telescopes.
State space characterization and robust stabilization of dissipative LTI systems

Dissipative linear time-invariant (LTI) systems represent a large class of systems, which include bounded real, positive real and sector bounded systems as special cases, In this paper, a sufficient condition is developed for stability of the feedback interconnection of two dissipative LTI systems. The stability result generalizes and unifies previous stability results such as small gain, passivity and sector-boundedness theorems. State-space characterization of dissipative LTI systems is presented in terms of a "dissipativity lemma", which extends the positive realness (Kalman-Yakubovich), bounded realness and sector-boundedness lemmas. These conditions are equivalently expressed as linear matrix inequalities.
The interaction of waves with a row of circular cylinders

The two-dimensional acoustics problem of the scattering of an obliquely incident plane wave by a row of equally-spaced circular cylinders is solved using multipole expansions. The method is superior to existing techniques available for this problem as it allows the far-field behaviour of the solution to be evaluated in a straightforward manner, and extensive results for the reflection and transmission coefficients are given. The problem described above has a direct analogue in the theory of water waves and this is also discussed.
Galactic spiral patterns and dynamo action

Abstract The theory of mean-field galactic dynamos is generalized by allowing for a finite response time of the mean electromotive force (emf) to variations in the mean magnetic field and small-scale turbulence. A non-axisymmetric forcing of the dynamo by a spiral pattern (either stationary or transient) is invoked. The resulting magnetic spiral arms are phase-shifted from the spiral arms of the pattern by an angle 15°–40°, opposite to the sense of galactic rotation. Our findings may help to explain the phase shift between material and magnetic arms observed in NGC 6946 and other galaxies.
Auroral electrodynamics with current and voltage generators

The electrodynamic structure of auroral currents is studied in the steady state by coupling Maxwell's equations with effective Ohm's laws for ionospheric Pedersen currents, field-aligned currents and currents in the generator region. An effective generator conductivity is introduced which allows consideration of a variety of states from pure current (ΣG = 0) to pure voltage (ΣG → ∞) generators. On short time scales when Alfven waves are important, this conductivity mapped to the ionosphere is lower than the ionospheric conductivity, implying a currentlike generator. This is in contrast with previous electrodynamic models of the aurora, which have assumed voltage-fixed generators. Current generators differ from the voltage generators in that the natural scale size is smaller for current generators, indicating that the narrow discrete arcs may be current driven, while the overall large-scale auroral currents are voltage driven. In addition, reversals of the electric field occur naturally in the current-driven case, leading to V-shaped potential structures. Examination of the effects of ionospheric conductivity gradients and comparison with a time-dependent MHD model of auroral currents indicate that either regions of nonlinear resistivity or generator motions can decouple the ionospheric currents from the generator. In this case the effective conductivity becomes the Alfven wave conductivity, which, being small compared to the ionospheric conductivity, leads to a structure typical of a current-driven system. This implies that the current structure is not affected by ionospheric conductivity gradients, while the ionospheric electric field is enhanced on the low-conductivity side.
Extrapolation strategies in numerical schemes for transient magnetic field simulations

For transient three-dimensional eddy current simulations, algorithmic improvements are presented based on the observation that, in the required implicit time stepping scheme, the iterative solvers applied to the large sparse (non-)linear systems of equations converge faster if more accurate start solutions are available. Different extrapolation techniques for new time-step solutions are compared in combination with the preconditioned conjugate gradient algorithm. Simple extrapolation schemes based on Taylor series expansion are used and compared to schemes derived especially for multistage implicit Runge-Kutta time stepping methods. Numerical tests show the resulting improvements in terms of computational efficiency for several test problems.
Maximum Likelihood Estimation for MA(1) Processes with a Root on or near the Unit Circle

This paper considers maximum likelihood estimation for the moving average parameter θ in an MA(1) model when θ is equal to or close to 1. A derivation of the limit distribution of the estimate θLM, defined as the largest of the local maximizers of the likelihood, is given here for the first time. The theory presented covers, in a unified way, cases where the true parameter is strictly inside the unit circle as well as the noninvertible case where it is on the unit circle. The asymptotic distribution of the maximum likelihood estimator subMLE is also described and shown to differ, but only slightly, from that of θLM. Of practical significance is the fact that the asymptotic distribution for either estimate is surprisingly accurate even for small sample sizes and for values of the moving average parameter considerably far from the unit circle.
Transport properties of free carriers in semiconductors studied by terahertz time-domain magneto-optical ellipsometry

We have developed a terahertz time-domain magneto-optical ellipsometry to deduce the effective mass, scattering time, density, and type (n or p) of free carriers independently. The parameters are derived from diagonal and off-diagonal components of the complex dielectric tensor obtained by measurements of magneto-optical Kerr effects under a magnetic field of 0.46 T using the generalized Drude model. The derivation of these parameters for n-type InAs wafers with different carrier densities is demonstrated. The carrier density dependence of the effective mass agrees well with previously reported experimental results and theoretical calculations that take into account nonparabolicity of conduction bands.
A novel measuring implementation of femtosecond pulse amplitude and phase based on frequency-resolved optical gating

A novel measuring implementation based on second-harmonic generation frequency-resolved optical gating (SHG-FROG) has been presented. Both the intensity and phase of arbitrary-shaped ultra-short laser pulses can be got. According to SHG-FROG, the femtosecond pulse produced by a laser resource is split into two beams which variable time delay one another is controlled by a stepped electromotor. The second-harmonic signal field is generated by focusing these two beams to a 100um BBO crystal. Changing the delay from 0 to N (N is the samples number of time domain or frequency domain) delay units, the two-dimensional spectrum data of the second-harmonic signal field are acquired by PC2000-ISA card spectrometer and OOIwinIP of Ocean Optics. These data are provided to a pulse amplitude and phase retrieval algorithm to retrieve the parameters of the pulse. An experimental system is erected and the all software modules, including spectrum data acquiring, pulse retrieving and displaying, are based on Labwindows/CVI of National Instrument Corp. The stepped electromotor is driven by the commands coming from RS-232 interface. The results show that after 50 times iterations or so, the iterative error of the algorithm can be reduced to an enough small value and then the pulse amplitude, phase and other parameters are the desired parameters. The whole measuring process can be finished in 2~3 seconds while the spectrum data is a 64x64 matrix and the iterative times are set to 50.
Experimental set-up and procedures for the investigation of XUV free electron laser interactions with solids

In this article, we describe the experimental station and procedures for investigating the interaction of short-wavelength free-electron lasers (FELs) pulses with solids. With the advent of these sources, a unique combination of radiation properties (including wavelength range from tens of nanometers down to sub-Angstroms, femtosecond pulse duration, and high pulse energy reaching milli-Joules level) creates new research possibilities for the systematic studies of radiation-induced structural changes in solids. However, the properties of the intense FEL radiation generate, apart from the new experimental opportunities, extreme demands on the experimental set-up (mostly in terms of radiation hardness of detectors and their saturation levels). Thus, radiation-induced phase transitions in solids, beyond the fundamental scientific interest, are of importance for the design of FEL beamlines and instruments which interact with the direct beam. In this report, we focus on the instrumentation and experimental techniques used in the recent studies performed at the FLASH facility in Hamburg.
Suppression of runaway electron avalanches by radial diffusion

The kinetic theory of runaway electron avalanches caused by close Coulomb collisions is extended to account for radial diffusion. This is found to slow down the growth of avalanches. An approximate analytical formula for the growth rate is derived and is verified by a three-dimensional Monte Carlo code constructed for this purpose. As the poloidal magnetic flux that is available to induce an electric field in a tokamak is limited, avalanches can be prevented altogether by sufficiently strong radial diffusion. The requisite magnetic fluctuation level is sensitive to the mode structure and the speed of the disruption. It is estimated to be δB/B∼10−3 for parameters typical of large tokamaks.