Miracle-dz/UniFAR-FTUs huggingface dataset:
Optimal filtering for discrete-time linear systems with multiplicative and time-correlated additive measurement noises

The filtering problem for discrete-time linear systems with multiplicative and time-correlated additive measurement noises is considered where the multiplicative noises are zero-mean white noise sequences, and the time-correlated additive measurement noise is described by a linear system model with white noise. Using the method of measurement differencing and some results obtained in this study, a novel algorithm for optimal filtering of the system under consideration is proposed in the sense of linear minimum mean-square error. The proposed algorithm is recursive, and does not increase computation and storage load with time. The convergence of the proposed algorithm is investigated. Computer simulations are carried out to demonstrate the performance of the proposed algorithm. The simulation results show the superiority of the proposed algorithm.
Local-moment fluctuations in the optimally doped high- T c superconductor YBa 2 Cu 3 O 6.95

We present results of neutron scattering experiments on ${\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{6.95}$ (YBCO) $({T}_{c}=93\text{ }\text{K})$. Our results indicate that magnetic collective modes due to correlated local moments are present both above and below ${T}_{c}$ in optimally doped YBCO. The magnon-like modes are robust and not overdamped by itinerant particle-hole excitations. We compare the experimental results to predictions of the Fermi-liquid (FL) theory in the random phase approximation.
Mental space embeddings, counterfactuality, and the use of unless

Unless-constructions have often been compared with conditionals. It was noted that unless can in most cases be paraphrased with if not, but that its meaning resembles that of except if (Geis, 1973; von Fintel, 1991). Initially, it was also assumed that, unlike if-conditionals, unless-sentences with counterfactual (or irrealis) meanings are not acceptable. In recent studies by Declerck and Reed (2000, 2001), however, the acceptability of such sentences was demonstrated and a new analysis was proposed. The present article argues for an account of irrealis unless-sentences in terms of epistemic distance and mental space embeddings. First, the use of verb forms in irrealis sentences is described as an instance of the use of distanced forms, which are widely used in English to mark hypotheticality. In the second part, the theory of mental spaces is introduced and applied to show how different mental space set-ups (in conjunction with distanced forms) account for the construction of different hypothetical meanings. The so-called irrealis unless-sentences are then interpreted as a number of instances of mental space embeddings. Finally, it is shown how the account proposed explains the fact that some unless-constructions can be paraphrased only with if not while others only with except if.
Numerical investigation of the propagation of the quasi-two-day wave into the lower thermosphere

We present results of a series of numerical experiments for January conditions using a linearized spectral model which includes realistic mean winds and dissipation. These experiments were designed to characterize the propagation characteristics of the (3,0) mixed Rossby-gravity mode through the middle atmosphere and into the lower thermosphere. Our results suggest that the wave magnitude is extremely sensitive to the zonal mean winds assumed in the calculations. In particular, our results suggest that a comparatively weak eastward stratomesospheric jet during northern hemisphere winter can account for a shift in the resonant frequency of the quasi-two-day wave response. Further, the inclusion of a realistic lower thermospheric jet in the summer lower thermosphere sets up a reflecting layer and an associated enhancement of the summer mesospheric wave signature. These features are in keeping with meteor and partial reflection drift radar observations.
Scattering transform for nonstationary Schrödinger equation with bidimensionally perturbed N-soliton potential

In the framework of the extended resolvent approach the direct and inverse scattering problems for the nonstationary Schrodinger equation with a potential being a perturbation of the N-soliton potential by means of a generic bidimensional smooth function decaying at large spaces are introduced and investigated. The initial value problem of the Kadomtsev-Petviashvili I equation for a solution describing N wave solitons on a generic smooth decaying background is then linearized, giving the time evolution of the spectral data.
State-space model of freely vibrating and surface-coupled cantilever dynamics in atomic force microscopy

The dynamics of the microcantilever in atomic force microscopy (AFM) is represented by a multiple-degrees-of-freedom state-space model and is discussed within the framework of system theory. The cantilever dynamics is modeled as a linear time-invariant system with a nonlinear output feedback due to the tip-sample interaction. This allows one to use the same model to analyze different aspects of atomic force microscopy such as the dynamics of contact-mode or the dynamics of tapping-mode AFM. The state-space approach to the dynamic response of the AFM cantilever allows for numerically efficient simulations. We show that not only the eigenfrequency but also the modal damping of a cantilever interacting with a surface strongly depends on the contact stiffness. This is important for a quantitative characterization of elastic sample properties. Additionally, our model shows the presence of higher harmonics in tapping-mode AFM. The excitation of higher eigenmodes can strongly distort the system response. The results illustrate that higher eigenmodes have to be considered in the analysis of dynamic AFM.
Determination of Elastic and Piezoelectric Constants for Crystals in Class (3m)

Determination of the elastic and piezoelectric constants for crystals in class (3m) is complicated by the large number of independent constants and the many possible ways in which they may be combined. An experimental and analytical procedure has been developed to determine all the constants using primarily thickness‐mode measurements made on small, plate‐shaped samples of various crystallographic orientations, and results using this procedure have been obtained for lithium tantalate and lithium niobate, two recently developed synthetic crystals. The resonant and antiresonant frequency constants for thickness modes have been calculated as functions of a plate's rotation angle. Information in this form makes possible the selection of plate orientations that might be useful as resonators and transducers.
Pickup ion acceleration by turbulent electric fields in the slow solar wind

Recent spacecraft observations reveal that energetic tails in ion spectra are present continually in the slow low‐latitude solar wind, even in the absence of nearby shocks. To explain this phenomenon we take into account growing evidence that MHD turbulence in the solar wind has a strong two‐dimensional (2D) component. 2D MHD turbulence simulations exhibit large‐scale field‐aligned electric field fluctuations which are also observable in the solar wind. We explore pickup ion propagation and acceleration between the Sun and Earth with a newly developed kinetic numerical model which includes a random distribution of large‐scale field‐aligned electric field fluctuations consistent with observations in the low‐latitude solar wind. The model is found to qualitatively reproduce the accelerated interstellar pickup He+ spectra observed at Earth. Like the observations, the simulated accelerated “tail” is approximately a power law f(υ) ∝ υ−4.5 until it reaches particle speeds about ten times the solar wind speed where a rollover occurs.
Water as a standard in the measurements of speed of sound in liquids

The speeds of sound in water measured by Del Grosso and Mader [J. Acoust. Soc. Am. 52, 1442–1446 (1972)], Kroebel and Mahrt [Acustica 35, 154–164 (1976)], and Fujii and Masui [J. Acoust. Soc. Am. 93, 276–282 (1993)] were compared. A fairly good agreement was found. A new fifth-order polynomial describing the dependence of the speed of sound in water on temperature (ITS-90) within the limits 0–95 °C was proposed. The importance of the effect of impurities of water on the systematic errors of the measurement results was pointed out. The accuracy of the relative measurements of speed of sound in liquids was discussed in the context of the proper choice of a standard (“true”) value of the speed in water.
Articulating and Stationary PARSIVEL Disdrometer Measurements in Conditions with Strong Winds and Heavy Rainfall

AbstractThe influence of strong winds on the quality of optical Particle Size Velocity (PARSIVEL) disdrometer measurements is examined with data from Hurricane Ike in 2008 and from convective thunderstorms observed during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) in 2010. This study investigates an artifact in particle size distribution (PSD) measurements that has been observed independently by six stationary PARSIVEL disdrometers. The artifact is characterized by a large number concentration of raindrops with large diameters (>5 mm) and unrealistic fall velocities (<1 m s−1). It is correlated with high wind speeds and is consistently observed by stationary disdrometers but is not observed by articulating disdrometers (instruments whose sampling area is rotated into the wind). The effects of strong winds are further examined with a tilting experiment, in which drops are dripped through the PARSIVEL sampling area while the instrument is tilted at various angles, s.
Experimental investigations of plasma bullets

Recently several investigators reported on various means of generating cold plasma jets at atmospheric pressure. More interestingly, these jets turned out to be not continuous plasmas but trains of small high velocity plasma packets/bullets. However, until now little is known of the nature of these ‘bullets’. Here we present experimental insights into the physical and chemical characteristics of bullets. We show that their time of initiation, their velocity and the distance they travel are directly dependent on the value of the applied voltage. We also show that these bullets can be controlled by the application of an external electric field. Using an intensified charge coupled device camera we report on their geometrical shape, which was revealed to be ‘donut’ shaped, therefore giving an indication that solitary surface ionization waves may be responsible for the creation of these bullets. In addition, using emission spectroscopy, we follow the evolution of various species along the trajectory of the bullets, in this way correlating the bullet propagation with the evolution of their chemical activity.
Misconceptions about astronomical magnitudes

The present system of astronomical magnitudes was created as an inverse scale by Claudius Ptolemy in about 140 A.D. and was defined to be logarithmic in 1856 by Norman Pogson, who believed that human eyes respond logarithmically to the intensity of light. Although scientists have known for some time that the response is instead a power law, astronomers continue to use the Pogson magnitude scale. The peculiarities of this system make it easy for students to develop numerous misconceptions about how and why to use magnitudes. We present a useful exercise in the use of magnitudes to derive a cosmologically interesting quantity (the mass-to-light ratio for spiral galaxies), with potential pitfalls pointed out and explained.
Positive Streamer Spark Breakdown at Low Pressures in Air

No data existed as to the lower pressure limits of streamer breakdown in positive point‐to‐plane geometry. Using a combination of Lichtenberg figure techniques in the coplanar mode and a two‐photomultiplier analysis of the movement of luminous pulses between the electrodes, the streamer mechanism has been observed to 4 Torr in room air; below this pressure, it is too faint to observe. A primary streamer starts from the anode. Its speed of the order of 107 cm/sec varies across the gap, depending on overvoltage and pressure. It is influenced by encounter with photoelectrically initiated avalanches from the cathode and by streamer‐tip‐cathode fields. On arrival at the cathode, fast space waves of potential gradient travel up the branch tips. Where such waves converge at the junction of the channel branches near the anode, a bright secondary streamer pulse appears. The tips of the midgap event move towards cathode and anode as secondary positive and negative streamers, respectively, at speeds around 106 cm/se.
Micromechanical modelling of erosion due to evaporation in a partially wet granular slope

Small quantities of water in a granular slope increase the overall stability and justify the large slope angle which is sometime observable in nature. However, the evaporation usually changes the water content of soil, especially in very shallow layers, leading to a soil strength reduction and the trigger of erosion processes. This work presents some numerical tests simulating a small slope physical model constituted of monosized glass ballotini in a pendular state. After a brief review of the different theories describing the capillary bridge which forms between two spheres and its effects on inter‐particle forces, this paper deals with the implementation of the minimum energy approach within a discrete element model (DEM). Some numerical triaxial tests with different water contents and confinement stresses were performed: the analyses permitted to emphasize the shear strength increase occurring at low water content. Moreover, moving from the observations performed in the physical model, a law relating the evaporation rate with depth and air–water interface was also included in the DEM. Finally, the improved DEM was successfully adopted in the simulation of the erosion process occurring in the physical model: it very well captures the formation of a talus slope profile, typical of the long‐term evolution of granular slopes. The monitoring of soil displacements and suction distribution during the numerical test also allows for the evaluation of erosion mechanisms: for instance, both in experimental and numerical tests, it was observed a rigid displacement at the slope toe after the initial phase of shallow erosion. Copyright © 2011 John Wiley & Sons, Ltd.
Detailed Analysis of Balmer Lines in a Sloan Digital Sky Survey Sample of 90 Broad-Line Active Galactic Nuclei

In order to contribute to the general effort aiming at the improvement of our knowledge about the physical conditions within the broad-line regions (BLRs) of active galactic nuclei (AGNs), here we present the results achieved by our analysis of the spectral properties of a sample of 90 broad-line-emitting sources, collected from the Sloan Digital Sky Survey database. By focusing our attention mainly on the Balmer series of hydrogen emission lines, which is the dominant feature in the optical wavelength range of many BLR spectra, we extracted several flux and profile measurements, which we related to other source properties, such as optical continuum luminosity, inferred black hole mass, and accretion rate. Using the Boltzmann plot method to investigate the Balmer-line flux ratios as a function of the line profiles, we found that AGNs that emit broader lines typically have larger Hα/Hβ and smaller Hγ/Hβ and Hδ/Hβ line ratios. With the help of some recent investigations, we model the structure of the BLR, and we study the influence of the accretion process on the properties of BLR plasma.
The soft X-ray characteristics of solar flares, both with and without associated CMEs

The complex relationship between solar flares and coronal mass ejections is investigated using a comparison of flare parameters for a total of 69 ejective and non-ejective flares. In the case of solar flares which do not show mass ejection there seems to be a clear relationship between the peak intensity and duration, with higher intensity events being of longer duration. Systematic differences in the relationship between peak temperature and intensity for the two types of event are also evident, with flares associated with CMEs tending to have lower peak temperatures than non-ejective events of the same intensity. Whilst there appears to be a clear relationship between the length of rise and decay phase in a flare, there are no systematic differences in these parameters for ejective and non-ejective flares. A total of eleven "EIT waves" were found, all of which were associated with CMEs. There is no apparent correlation between the occurrence of an EIT wave and the peak temperature, intensity or rise time of the associated flare.
A cost‐effective sparse communication strategy for networked linear control systems: an SVD‐based approach

In networked control, there is often an incentive to communicate only what is absolutely necessary to achieve the desired performance goals. This is true to both the downlink (between a control base station and actuators) and the uplink (between the sensors and base station). Here, we present a strategy aimed at this problem based on a singular value decomposition of the Hessian of the quadratic performance index generally considered in Model Predictive Control. The singular vectors are employed to generate an orthonormal basis function expansion of the unconstrained solution to the finite horizon optimal control problem. These are preloaded into each actuator and each sensor. On the downlink, the actuators are informed, in real‐time, about which basis functions they should use. On the uplink, after a ‘burn in period’, the sensors need only communicate when their response departs from that pre‐calculated for the given basis functions. We show that this strategy facilitates communication in both the downlink and uplink in a cost‐effective fashion. We also show that the strategy can be modified so that input constraints are satisfied. We illustrate the proposed results by applying them to a simulation of the cross direction control of a paper machine. Potential extensions and other applications of the proposed strategy are also discussed. Copyright © 2014 John Wiley & Sons, Ltd.
Convective Snowbands Downstream of the Rocky Mountains in an Environment with Conditional, Dry Symmetric, and Inertial Instabilities

Abstract Convective snowbands moved slowly over Wyoming and northern Colorado on 16–17 February 2007 and produced up to 71 mm (2.8 in.) of snow that was unpredicted by operational numerical weather prediction models and human forecasters. The northwest–southeast-oriented bands lasted for over 6 h, comprising both a single major band (more than 30 km wide) and multiple minor bands (about 10 km wide). The convective bands initiated within the ascending branch of a secondary circulation associated with both near-surface and elevated frontogenesis, but the bands remained nearly stationary while the near-surface frontogenesis moved quickly equatorward. The bands occurred downstream of complex terrain on the anticyclonic-shear side of a midlevel jet streak, where conditional, dry symmetric (negative potential vorticity), and inertial (negative absolute vorticity) instabilities were present. To determine the mechanisms responsible for the development and organization of these bands, simulations using a convectio.
Impacts of Convectively Coupled Kelvin Waves on Environmental Conditions for Atlantic Tropical Cyclogenesis

AbstractHigh-amplitude convectively coupled equatorial atmospheric Kelvin waves (CCKWs) are explored over the tropical Atlantic during the boreal summer (1989–2009). Focus is given to the atmospheric environmental conditions that are important for tropical cyclogenesis.CCKWs are characterized by deep westerly vertical wind shear to the east of its convectively active phase and easterly vertical wind shear to the west of it. This dynamical signature increases vertical wind shear over the western tropical Atlantic ahead of the convectively active phase, and reduces vertical wind shear after its passage. The opposite is true over the eastern tropical Atlantic where the climatological vertical wind shear is easterly.Positive total column water vapor (TCWV) anomalies progress eastward with the convectively active phase of the CCKW, whereas negative TCWV anomalies progress eastward with the convectively suppressed phase. During the passage of the convectively active phase of the CCKW, a zonally oriented strip o.
On A Thermoelastic Three-Phase-Lag Model

A three-phase-lag model of the linearized theory of coupled thermoelasticity is formulated by considering the heat condition law that includes temperature gradient and the thermal displacement gradient among the constitutive variables. The Fourier law is replaced by an approximation to a modification of the Fourier law with three different translations for the heat flux vector, the temperature gradient and also for the thermal displacement gradient. The model formulated is an extension of the thermoelastic models proposed by Lord–Shulman, Green–Naghdi and Tzou.
On the stability of steep gravity waves

Previous calculations of the normal mode perturbations of steep gravity waves have suggested that the lowest superharmonic mode n = 2 becomes unstable at around ak = 0.436, where 2a is the crest-to-trough height of the unperturbed wave and k is the wavenumber. This would correspond to the wave steepness at which the phase speed c is a maximum (considered as a function of ak). However, numerical calculations at such high wave steepnesses can become inaccurate. The present paper studies analytically the conditions for the existence of a normal mode at zero limiting frequency. It is proved that for superharmonic perturbations such conditions will occur only for a pure phase-shift (corresponding to n = 1) or when the speed c is stationary with respect to the wave steepness, that is when dc = 0. Hence the limiting form of the instability found by Tanaka (J. phys. Soc. Japan 52, 3047-3055 (1983)) near the value ak = 0.429 must be a pure phase-shift.
The flow field in a suddenly enlarged combustion chamber

The characteristics and dynamics of an abruptly expanded flow in a model combustion chamber (combustor) were investigated experimentally. The combustion chamber consisted of a plexiglass, circular duct with a suddenly enlarged section followed by a nozzle. The Reynolds number, based on the inlet duct diameter and center velocity, was 64,000. The wall pressure measurements were carried out with a laser-Doppler anemometer (LDA). Detailed profiles of mean velocities, turbulent intensities, turbulent shear stresses, and wall pressure distribution were developed. The dividing streamline, the reattachment point, and the magnitudes of the mean kinetic energy and turbulent kinetic energy were also determined.
Theoretical investigation of the second-order harmonic distortion in the AM response of 1.55 mu m F-P and DFB lasers

Numerical calculations of the second-order harmonic distortion in the amplitude modulation-response of Fabry-Perot, and distributed feedback (DFB) lasers are presented, and the influence of several nonlinearities, such as longitudinal spatial hole burning, gain suppression, and relaxation oscillations are considered. This analysis is valid for modulation frequencies ranging from a few megahertz to well beyond the resonance frequency of the relaxation oscillation. The distortion of Fabry-Perot lasers for which the effects of spontaneous emission and gain suppression can be clearly illustrated is investigated. The distortion of DFB lasers where the emphasis is on the influence of spatial hole burning and its combination with other nonlinearities is discussed. Various effects are discussed. >