Miracle-dz/UniFAR-FTUs huggingface dataset:
Measurements of acoustic impedance in a free field with two microphones and a spectrum analyzer

A technique is presented for evaluating the normal acoustic impedance at the surface of a panel of absorbing material in a free field. The evaluation is achieved by measuring the pressure and the acoustic velocity with two microphones set very close to the panel. This technique allows measurements of impedance for panels of area about 1 m2, the two microphones being located very close to the panel so that, contrary to other methods, the effect of the finite dimension of the panel is negligible. Because of the very small spacing between both microphones, this technique allows precise measurements only for frequencies higher than 500 Hz.
Gaussian Maximum Likelihood Estimation For ARMA Models. I. Time Series

Abstract. We provide a direct proof for consistency and asymptotic normality of Gaussian maximum likelihood estimators for causal and invertible autoregressive moving‐average (ARMA) time series models, which were initially established by Hannan [Journal of Applied Probability (1973) vol. 10, pp. 130–145] via the asymptotic properties of a Whittle's estimator. This also paves the way to establish similar results for spatial processes presented in the follow‐up article by Yao and Brockwell [Bernoulli (2006) in press].
Production of chemically active species in the air by a single positive streamer in a nonuniform field

We report the results of a two-dimensional (2-D) simulation of a cylindrically symmetric positive streamer in atmospheric pressure air between a positively stressed point and a grounded plate. A hydrodynamic diffusion drift model was used. It is shown that a streamer propagates with the constant velocity and constant field at the tip (/spl sime/140 kV/cm) and constant electron density in the head (/spl sime/10/sup 14/ cm/sup -3/). Special attention has been paid to the generation of excited molecules, radicals, and atoms [chemically active species (CAS)] by the streamer, 2-D distributions of CAS are obtained. The total number of CAS linearly increases with time (except excited oxygen molecules) in accordance with the constant velocity of streamer propagation. The mean energy cost of each active specie is 35 eV.
Application of compact neural network for drag reduction in a turbulent channel flow at low Reynolds numbers

The aim of the present work is to develop neural networks for flow estimation and control in a turbulent channel flow at low Reynolds number. The control strategy considered here is the opposition strategy of Choi et al. [“Active turbulence control for drag reduction in wall-bounded flows,” J. Fluid Mech. 267, 75 (1994)]. The idea is to identify which velocity length scales are associated with substantial drag reduction, and to determine how the flow at these length scales can be estimated from a grid of sensors with limited extent and finite spacing. Numerical experiments are carried out in a restricted computational domain at Rτ=140 as well as in a full flow unit at Rτ=180. Evidence is shown that the flow is more complex in the larger domain than in the reduced one. In the larger domain, the estimation is performed on independent subdomains spanning at most a few coherent structures. We obtain up to 13% drag reduction in the simplified flow and 12% in the full flow unit. The essential scales for control.
H II Regions and Abundances in the “Dark Galaxy” DDO 154 and the Chemical Evolution of Dwarf Irregular Galaxies

We present Hα imaging and optical spectrophotometry of H II regions in the low surface brightness dwarf irregular galaxy DDO 154. The galaxy possesses a very small population of faint discrete H II regions and larger diffuse H II regions and ionized shells. We confirm the very low star formation rate and extremely long gas consumption times reported previously by van Zee, Haynes, & Salzer. The current star formation rate is ∼2–4 times lower than its average past rate, confirming the previous characterization of DDO 154 as a "quiescent" dwarf irregular galaxy. Spectrophotometry of two of the brightest H II regions yields a relatively low oxygen abundance of 0.055 ± 0.008 (O/H)⊙, in agreement with the previous determination by van Zee et al., and in accordance with the previously determined metallicity-luminosity relationship for dwarf irregular galaxies. We also find an N/O ratio of 0.037 ± 0.003, which is marginally higher than the typical value of 0.025 found in low-metallicity blue compact galaxies. Although DDO 154 has been labeled "the dark galaxy" and is a prototype for low surface brightness galaxies with large H I content, its chemical abundances are consistent with an average, low-mass, dwarf irregular galaxy. Assuming that the neutral gas is chemically homogeneous, we derive an effective oxygen yield of roughly 50% of the solar value, a value that is close to the theoretically favored values for the true oxygen yield. Thus, it is possible that DDO 154 is evolving nearly as a closed system. On the other hand, if the abundances in the extended H I disk are lower than in the H II regions, the derived value of the effective yield has been artificially inflated, and DDO 154 may have experienced significant loss of metal-enriched gas.
Stochastic String Models with Continuous Semimartingales

This paper reformulates the stochastic string model of Santa-Clara and Sornette using stochastic calculus with continuous semimartingales. We present some new results, such as: (a) the dynamics of the short-term interest rate, (b) the PDE that must be satisfied by the bond price, and (c) an analytic expression for the price of a European bond call option. Additionally, we clarify some important features of the stochastic string model and show its relevance to price derivatives and the equivalence with an infinite dimensional HJM model to price European options.
Transient analysis of an electromagnetic actuator using an overlapping finite element scheme

The authors describe the modeling of the transient dynamic behavior of a solenoidal core type electromagnetic actuator using an overlapping finite element (FE) scheme. The FE scheme allows two topologically unconnected 2D finite element meshes to slide over and overlap each other, whilst still coupled together electromagnetically in a consistent manner. The result is that the same set of FE meshes can be used to model directly a continuously shrinking or expanding air gap. This paper demonstrates, for the first time, that such a FE scheme can be used to model accurately the dynamic closing of the air gap of a linear actuator. The results of the simulation were compared with experimental measurements. It is shown that good agreement between simulated and measured results is obtained.
Experimental observations of thermo-optical bistability and self-pulsation in silicon microring resonators

Optical bistability and self-pulsation (SP) in silicon microring resonators (MRRs) are experimentally observed. The waveforms and frequencies of SP can be controlled by changing input light power and its wavelength, and the region of SP can be modulated readily by applying a reverse voltage on the PN junction embedded in the MRR. These phenomena are theoretically studied by adopting the coupled-mode theory and linear stability analysis method for differential equations, with theoretical results fitting well with the experimental ones.
Computer model of propagated excitation in the anisotropic human heart. II. Simulation of extracardiac fields

For pt.1 see ibid., p.545-8 (1991). The authors have developed a computer model of propagated excitation in the three-dimensional anisotropic human ventricular myocardium. The present report deals with simulations of excitation waves associated with the preexcitation syndrome. For each of the 14 simulated cases, the calculated electrocardiographic and magnetocardiographic maps at 40 ms into the delta wave are presented. The objective of the initial simulations with the heart-torso model, whose results are presented, was to perform a simple validation that would assure that the basic anatomical structure of the model is correct. <<ETX>>
The FU Orionis binary system RNO 1B/1C

Observations of CS (7→6) emission reveal a ≥3M_⊙ core, 1.8×10^4 AU in size, surrounding the FU Orionis binary system RNO 1B/1C. Fractional chemical abundances, calculated from LVG and LTE codes, are mostly similar to those in the cold core TMC 1. However, values for Si0/H_2 and CH_(3)0H/H_2 are enhanced, possibly by sputtering reactions or grain-grain collisions in tile outflow associated with the young stars. Aperture syntllesis maps of tile 2.6 and 3.1 mm continuum emission at ~5" and ~9" resolution, respectively, reveal that RNO 1C is surrounded by a flattened, dusty envelope, ~5000 AU in size, with mass ≥1.1 M_⊙. High spatial resolution (~3") interferometer observations of CS (2→1) emission may trace the dense walls of ail outflow cavity comprised of two concentric arcs with dynamical ages of 4×10^3 and 1×10^4 yr. The velocity structure of lower density gas imaged in the CO (1→0) transition is consistent with the arcs being formed by two energetic FU Orionis outbursts. Each event may have imparted more than 4 M_⊙km s^(-1) to the outflow, implying outburst mass loss rates of ~10^(-4) M_⊙ yr^(-1). It appears that RNO 1C is probably the driving source for the outflow and tllat, while pre-main sequence stars are in tile FU Orionis stage, outbursts may dominate both outflow morphology and energetics.
Experiments on supersonic combustion ramjet propulsion in a shock tunnel

Measurements have been made of the propulsive effect of supersonic combustion ramjets incorporated into a simple axisymmetric model in a free piston shock tunnel. The nominal Mach number was 6, and the stagnation enthalpy varied from 2.8 to 8.5 MJ kg−1. A mixture of 13% silane and 87% hydrogen was used as fuel, and experiments were conducted at equivalence ratios up to approximately 0.8. The measurements involved the axial force on the model, and were made using a stress wave force balance, which is a recently developed technique for measuring forces in shock tunnels. A net thrust was experienced up to a stagnation enthalpy of 3.7 MJ kg−1, but as the stagnation enthalpy increased, an increasing net drag was recorded. Pilot and static pressure measurements showed that the combustion was supersonic. The results were found to compare satisfactorily with predictions based on established theoretical models, used with some simplifying approximations. The rapid reduction of net thrust with increasing stagnation enthalpy was seen to arise from increasing precombustion temperature, showing the need to control this variable if thrust performance was to be maintained over a range of stagnation enthalpies. Both the inviscid and viscous drag were seen to be relatively insensitive to stagnation enthalpy, with the combustion chambers making a particularly significant contribution to drag. The maximum fuel specific impulse achieved in the experiments was only 175 s, but the theory indicates that there is considerable scope for improvement on this through aerodynamic design.
The scattering matrix for the Schrödinger operator with a long-range electromagnetic potential

We consider the Schrodinger operator H=(i∇+A)2+V in the space L2(Rd) with long-range electrostatic V(x) and magnetic A(x) potentials. Using the scheme of smooth perturbations, we give an elementary proof of the existence and completeness of modified wave operators for the pair H0=−Δ, H. Our main goal is to study spectral properties of the corresponding scattering matrix S(λ). We obtain its stationary representation and show that its singular part (up to compact terms) is a pseudodifferential operator with an oscillating amplitude which is an explicit function of V and A. Finally, we deduce from this result that, in general, for each λ>0 the spectrum of S(λ) covers the whole unit circle.
The Hall effect in accelerating and stationary conductors

The acceleration of the ions in an unconstrained current-carrying conductor in an external magnetic field is shown to be produced solely by an electric field due to a modified Hall effect, despite the fact that the total force on the conductor is proportional to only the magnetic field. The modification of the Hall field from the conventional one is typically of the order of one part in 104 or less, but it is essential to obtain self-consistent results. The same modified Hall electric field results from a single-particle model, a model consisting of two rigid charge distributions, and a plasma model. The latter two models predict the existence and the widths of the surfacelike charge sheaths that are the sources of the Hall electric field. For a conductor held at rest, the three models yield the correct total force of constraint, but an additional assumption must be made in the single-particle and the rigid charge distribution models to obtain the Hall field. The plasma model predicts a unique modified Ha.
VLBI Observations of Southern EGRET Identifications. II. VLBA Observations and the Importance of Jet Bending in Gamma-Ray Sources

We present VLBI images of six southern hemisphere radio sources that have been identified by EGRET as sources of greater-than-100 MeV gamma-ray emission, PKS 0521-365, PKS 1127-145, PKS 1622-253, PKS 1622-297, PKS 1730-130, and PKS 1908-201. We quantitatively investigate the suggestion of von Montigny et al. that jet bending may be a significant factor affecting the gamma-ray identification of radio-loud flat-spectrum active galactic nuclei (AGNs), using samples of EGRET-identified and gamma-ray-quiet radio sources. From this investigation, we find evidence to suggest that jet bending properties, as observed in parsec-scale radio jets, are correlated with gamma-ray identification for this class of source. The parsec-scale jets in gamma-ray-quiet AGNs appear to have more and larger bends than do the parsec-scale jets in EGRET-identified AGNs. Caution should be exercised when interpreting these results, however, since we point out that significant, but difficult to quantify, observational biases may also be at work in these samples.
Cotorsion pairs in C(R-Mod)

In [8] Salce introduced the notion of a cotorsion pair (A,B) in the category of abelian groups. But his definitions and basic results carry over to more general abelian categories and have proved useful in a variety of settings. In this article we will consider complete cotorsion pairs (C,D) in the category C(R-Mod) of complexes of left R-modules over some ring R. If (C,D) is such a pair, and if C is closed under taking suspensions, we will show when we regard K(C) and K(D) as subcategories of the homotopy category K(RMod), then the embedding functors K(C) → K(R-Mod) and K(D) → K(R-Mod) have left and right adjoints, respectively. In finding examples of such pairs, we will describe a procedure for using Hoveys results in [5] to find a new model structure on C(R-Mod).
Challenges in Mesoscale Prediction of a Nocturnal Stratocumulus-Topped Marine Boundary Layer and Implications for Operational Forecasting

Abstract A numerical study using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) was performed to assess the impact of initial and boundary conditions, the parameterization of turbulence transfer and its coupling with cloud-driven radiation, and cloud microphysical processes on the accuracy of mesoscale predictions and forecasts of the cloud-capped marine boundary layer. Aircraft, buoy, and satellite data and the large eddy simulation (LES) results during the Dynamics and Chemistry of Marine Stratocumulus field experiment (DYCOMS II) in July 2001 were used in the assessment. Three of the tested input fields (Eta, NCEP, and ECMWF) show deficiencies, mainly in the thermodynamic structure of the lowest 1500 m of the marine atmosphere. On a positive note, the simulated marine-layer depth showed good agreement with aircraft observations using the Eta fields, while using the NCEP and ECMWF datasets underestimated the marine-layer depth by about 2.
Detection of the YORP effect in asteroid (1620) Geographos

Aims. The rotation state of small asteroids is affected by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) torque. The directly observable consequence of the YORP effect is the secular change of the asteroid’s rotation period. We carried out new photometric observations of asteroid (1620) Geographos in 2008 to extend the time line that, if long enough, would enable us to see possible deviations from a constant period rotation. Methods. We used the lightcurve inversion method to model the shape and spin state of Geographos. We assumed that the rotation rate evolves in time as ω(t) = ω0 + υt, where both the constant term of the rotation rate ω0 and the linear term υ are parameters to be optimized. In total, we used 94 lightcurves observed in 1969−2008. Results. We show that for υ = 0, a constant-period model, the whole dataset of lightcurves cannot be satisfactorily fitted. However, when relaxing υ in the optimization process we obtain an excellent agreement between the model and observations. The best-fit value υ = (1.15 ± 0.15) × 10 −8 rad d −2 implies that Geographos’ rotation rate accelerates by � 2. 7m s yr −1 . This is in agreement with the theoretically predicted value 1.4 × 10 −8 rad d −2 obtained from numerical integration of YORP torques acting on our convex shape model. Geographos is only the third asteroid (after (1862) Apollo and (54509) YORP) for which the YORP effect has been detected. It is also the largest object for which effects of thermal torques were revealed.
A unified approach to the optimization of fault detection systems

In this paper, problems of optimizing observer-based fault detection (FD) systems in the sense of increasing the robustness to the unknown inputs and simultaneously enhancing the sensitivity to the faults are studied. The core of the study is the development of an approach that simultaneously solves four optimization problems. Different algorithms are derived for the application of this approach to the optimal selection of post-filters as well as optimization of fault detection filters, and to the systems with and without structure constraints. The achieved results also reveal some interesting relationships among the optimization problems considered. Copyright © 2000 John Wiley & Sons, Ltd.
Spherical averages of Fourier transforms of measures with finite energy; dimensions of intersections and distance sets

Let μ, be a positive Radon measure with compact support in the euclidean n -space ℝ n . Introducing the Fourier transform and the averages over the spheres we can write the α-energy, 0 α n , of μ as where the positive constants c 1 and c 2 depend only on n and α. The second equality is based on the Plancherel formula and the fact that where .
On the amplitude of surface waves obtained by noise correlation and the capability to recover the attenuation: a numerical approach

SUMMARY Cross-correlation of ambient seismic noise recorded by a pair of stations is now commonly recognized to contain the Green’s function between the stations. Although traveltimes extracted from such data have been extensively used to get images of the Earth interior, very few studies have attempted to exploit the amplitudes. In this work, we investigate the information contained in the amplitudes and we probe the capability of noise correlations to recover anelastic attenuation. To do so, we carry out numerical experiments in which we generate seismic noise at the surface of a 1-D Earth model. One of the advantages of our approach is that both uniform and non-uniform distributions of noise sources can be taken into account. In the case of a uniform distribution, we find that geometrical spreading as well as intrinsic attenuation are retrieved, even after strong non-linear operations such as one-bit normalization and spectral whitening applied to the noise recordings. In the case of a non-uniform distribution of sources, the geometrical spreading of the raw noise correlations depends on the distribution, but intrinsic attenuation is preserved. For the one-bit noise and whitened noise correlations, the interpretation of observed amplitude decays requires further study.
Substructure in the Galactic Halo

Abstract Giant stars make particularly useful tracer stars for halo substructure because they are very bright and very common. I discuss several projects that use giant-star tracers to search the Galactic halo for tidal debris from known Galactic satellites, including that from the Sagittarius dwarf galaxy, and to search for tidal debris features from former, now destroyed satellites. Several cross-sections of the halo reveal it to be networked with extended, coherent substructures, indicating that it is likely to be predominantly made up of accreted satellites.
Strain-induced darkening of trapped excitons in coupled quantum wells at low temperature

In GaAs/AlGaAs coupled quantum wells, strain-induced traps may be used to confine excitons in in-plane, harmonic traps. Using these traps, we have pursued Bose-Einstein condensation (BEC) of long-lived, spatially indirect excitons. Here, we report a remarkable transition of the indirect exciton luminescence pattern with increasing strain, increasing exciton density, and decreasing temperature, to a spatial pattern exhibiting a large dark spot at the trap center, where we expect the exciton density to be maximum. The mechanism of particle loss is ruled out as an explanation for this dark spot. While the onset criteria are approximately consistent with the conditions for BEC of a weakly interacting gas, the conspicuous proximity in energy of the indirect light-hole states suggests that an explanation employing the single-particle physics of light-hole-heavy-hole mixing may explain the phenomenon. The effect of the strain is modeled, and the resulting landscape of indirect exciton spin states is discussed. The relative oscillator strengths of these states are predicted by an exact numerical solution of the two-particle Schrodinger equation for electrons and holes in coupled quantum wells and an electric field. The contrast in oscillator strengths is sufficient to produce this luminescence pattern, but this analysis suggests a strongly diminished lifetime as stress is increased. The opposite lifetime dependence is observed experimentally. Additionally, the temperature dependence eludes explanation by this mechanism.
Geometrical properties of MDO polytypes and procedures for their derivation. I. General concept and applications to polytype families consisting of OD layers all of the same kind

The concept of MDO structures (structures of maximum degree of order) is explained in detail and defined. This concept corresponds closely to the concepts of standard, simple or regular polytypes, it seems, however, to be more adequate for complicated examples. MDO polytypes consisting of equivalent OD layers are treated in detail. For the six subcategories, simple tests showing whether a given polytype is an MDO polytype or not are given, and stepwise procedures for obtaining a complete list of all MDO polytypes of a polytypic substance are introduced. The approach is demonstrated by examples.
Instability of Three‐Layer Viscous Stratified Flow

Instability of plane Couette flow of three superposed layers of fluids of different viscosity between two horizontal planes is investigated. It is found that there are two modes of disturbance dominated, respectively, by the two interfaces. The flow is found to be unstable in the zero‐order approximation of wavenumber α for certain values of the depth and viscosity ratios. This is owing to a sort of resonance which prevails when a free wave at the lower interface forces a free wave at the upper interface. As is known from results previously obtained, the existence of a single surface of viscosity discontinuity will cause instability. The presence of an additional surface of discontinuity may or may not be stabilizing, depending upon the values of the depth and viscosity ratios at the additional interface.