Miracle-dz/UniFAR-FTUs huggingface dataset:
Meteoritic, Asteroidal, and Theoretical Constraints on the 500 Ma Disruption of theLChondrite Parent Body

The high abundance of heavily shocked and degassedLchondrites with Ar–Ar ages around 500 Myr shows that theLchondrite parent body suffered a major impact 500 Myr ago. We infer from constraints on the thermal evolution of impact heated rocks after the 500-Myr event and the high abundance of shockedLchondrites that the parent body was catastrophically disrupted. The slow cooling rates of some shocked and degassedLchondrites (0.01–1°C year−1) show that they were derived from kilometer-sized impact-heated fragments or rubble piles that were ejected from near the impact point. We suggest that the catastrophic dispersion of the parent body provided some fragments with sufficiently high velocities to put them into resonances and that this initiated the orbital evolution which resulted in the high flux ofLchondrite meteoroids impacting the Earth at present. It appears likely that this was a “slow-track” type of dynamical evolution, with most objects avoiding drastic resonant changes of orbital eccentricity, and undergoing a slow random walk in orbital element space, driven by a sequence of random encounters with Mars and, later on, with the Earth. The ν6secular resonance provides a plausible mechanism to start this evolution, since fragments inserted into it in the main belt frequently have their eccentrici_ties raised to values of about 0.4, sufficient for Mars-crossing but not for Earth-crossing orbits; on the other hand, recent numerical work has shown that the 3:1 mean motion resonance leads almost always to a fast-track evolution, ending up with a solar collision or a hyperbolic ejection within a few Myr.
Modal approach to the morphology of spiral galaxies. II: Dynamical mechanisms

Au moyen d'une relation de dispersion cubique, developpee anterieurement, on fait une approche modale des modes spiraux qui permet de montrer le processus d'entretien et d'excitation des modes spiraux pour diverses morphologies: d'une part, pour des modes spiraux normaux et, d'autre part, pour des modes spiraux ouverts. Des relations algebriques simples caracterisent les regions de parametres
Dynamics of the snow grain size in a windy coastal area of Antarctica from continuous in situ spectral-albedo measurements

Abstract. The grain size of the superficial snow layer is a key determinant of the surface albedo in Antarctica. Its evolution is the result of multiple interacting processes, such as dry and wet metamorphism, melt, snow drift, and precipitation. Among them, snow drift has the least known and least predictable impact. The goal of this study is to relate the variations in surface snow grain size to these processes in a windy location of the Antarctic coast. For this, we retrieved the daily grain size from 5-year-long in situ observations of the spectral albedo recorded by a new multi-band albedometer, unique in terms of autonomy and described here for the first time. An uncertainty assessment and a comparison with satellite-retrieved grain size were carried out to verify the reliability of the instrument, and an RMSE up to 0.16 mm in the observed grain size was found. By relating these in situ measurements to time series of snow drift, surface temperature, snow surface height and snowfall, we established that the evolution of the grain size in the presence of snow drift is complex and follows two possible pathways: (1) a decrease in the grain size (about half of our measurements) resulting from the deposition of small grains advected by the wind (surprisingly, this decrease is often – 2/3 of the cases– associated with a decrease in the surface height, i.e., a net erosion over the drift episode), (2) an increase in the grain size (the other half) due to either the removal of the surface layer or metamorphism. However, we note that this increase is often limited with respect to the increase predicted by a theoretical metamorphism model, suggesting that a concomitant deposition of small grains is likely. At last, we found that wind also completely impedes the deposition of snowfall during half of the observed precipitation events. When this happens, the grain size evolves as if precipitation were not occurring. As a result of all these processes, we conclude that the grain size in a windy area remains more stable than it would be in the absence of snow drift, hence limiting the variations in the albedo and in the radiative energy budget.
The ionization structure of planetary nebulae. V - NGC 3242

Spectrophotometric observations of emission line intensities over the spectral range 1400 A to 9600 A were made in five positions in the planetary nebula NGC 3242. In two of the positions, both the weakness of the 1548 A, 1550 A C IV resonance lines and the steepness of the Balmer decrement suggest the possibility of internal dust in the nebula. The measured electron temperature varies little from the average value of 11,100 K, which is in reasonably good agreement with the less accurate value of 12,900 K measured from the Balmer continuum. The 4267 A C II line implies a C(2+) abundance that is much higher than that determined from the 1906 A, 1908 A C III lines. This discrepancy decreases with increasing distance from the central star. Equations used to correct for the existence of elements in other than the optically-observable ionization stages give results that are consistent and in agreement with abundances calculated using ultraviolet lines. This discrepancy decreases with increasing distance from the central star. Equations used to correct for the existence of elements in other than the optically-observable ionization stages give results that are consistent and in agreement with abundances calculated using ultraviolet lines. The logarithmicmore » abundances are He = 10.96, O = 8.64, N = 7.96, Ne = 8.04, C = 8.41, Ar = 6.15, and S = 6.51. 22 references. « less
Measurement of the twist elastic constant of nematic liquid crystals using pi-cell devices

We present a fast and accurate method for measurement of the twist elastic constant of nematic liquid crystals using pi-cell devices. We observe that there are two bifurcations during the transition from the bend state to the planar 180° twisted state, each of which leads to a voltage threshold. The Freedericksz threshold voltage due to a tilt bifurcation occurs at a lower voltage and is “softened” by the required surface pretilt in the device. The higher of the two thresholds is due to a bifurcation between left- and right-handed 180° twisted states and we term this the T to V state threshold. This voltage threshold is independent of device thickness, and is not softened by the pretilt. We show that the T to V state threshold is highly sensitive to changes in the twist elastic constant, K22, and use this threshold to evaluate the magnitude of K22 for a variety of materials. These results show very good agreement with those obtained using the standard magnetic Freedericksz twist threshold experiment. This.
Simultaneous localization of photons and phonons in two-dimensional periodic structures

We demonstrate theoretically the simultaneous localization of photons and phonons in the same spatial region by introducing lattice defects in a periodic array of dielectric/elastic material that exhibits gaps for both electromagnetic and elastic waves. Transverse electromagnetic waves, pure shear elastic waves, and mixed shear and dilatation elastic waves were simultaneously localized. The coexistent localization of light and sound can have a strong influence on photon-phonon interactions (i.e., optical cooling) and the possibility of dual acoustic-optical devices that can integrate the management of sound, heat, and light.
Feedforward artificial neural networks for solving discrete multiple criteria decision making problems

Decision making involves choosing some course of action among various alternatives. In almost all decision making problems, there are several criteria for judging possible alternatives. The main concern of the Decision Maker DM is to fulfill his conflicting goals while satisfying the constraints of the system. In this paper, we present an Adaptive Feedforward Artificial Neural Network AF-ANN approach to solve discrete Multiple Criteria Decision Making MCDM problems. The AF-ANN is used to capture and represent the DM's preferences and then to select the most desirable alternative. The AF-ANN can adjust and improve its representation as more information from the DM becomes available. We begin with the assumption that an AF-ANN topology is given, i.e., specific numbers of nodes and links are predetermined. To adjust the parameters of the AF-ANN, we present an iterative learning algorithm consisting of two steps. a generating a direction, and b a one-dimensional search along that direction. We then present a methodology to obtain the most appropriate AF-ANN topology and set its parameters. The procedure starts with a small number of nodes and links and then adaptively increases the number of nodes and links until the proper topology is obtained. Furthermore, when the set of training patterns alternatives with their associated evaluations by the DM changes, the AF-ANN model can adapt itself by re-training or expanding the existing model. Some illustrative examples are presented. To solve discrete MCDM problems by an AF-ANN, we show how to incorporate basic properties of efficiency, concavity, and convexity into the AF-ANN. We formulate the MCDM problems and use the AF-ANN to rank the set of discrete alternatives where each alternative is associated with a set of conflicting and noncommensurate criteria. We present a method for solving discrete MCDM problems through AF-ANNs which consists of. a formulating and assessing the utility function by eliciting information from the DM and then training the AF-ANN, and b ranking a rating alternatives by using the trained AF-ANN model. Some computational experiments are presented to show the effectiveness of the method.
Measurement of Air Film Damping Effectiveness

Air film damping systems have attracted considerable interest within the gas turbine industry because of their effectiveness at controlling modes of vibration without environmental limitations. Though still in the early stages of development, air film dampers have promise for improving the high cycle fatigue characteristics of solid gas turbine airfoils. This study used experimental methods to compare the vibrational response of a solid flat plate with the response of an identically sized plate that incorporated an air film damper. It also investigated the influence of elevated pressures on air film damping effectiveness, the impact of the damper on the various vibration modes, and the relative strain levels of the air film cover plate to the solid backing. The results show that the air film damper is very effective in controlling the two-stripe mode for which it was designed. Increasing the surrounding air pressure makes the damper more effective and shifts the resonant frequencies lower.
Whistler mode waves in the magnetotail

Whistler mode waves in the magnetotail, especially the plasma sheet and the plasma sheet boundary layer, are frequently detected by a waveform capture on board Geotail satellite. The whistler mode waves with frequencies above 10 Hz are often narrowband and short-lived. Statistical study shows that these whistler mode waves propagate in a direction quasi-parallel to the ambient magnetic field with an average wave normal angle of 23°. This suggests that the electron cyclotron resonance is dominant for excitation of the whistler mode waves. Their frequencies range mainly from 0.05 to ∼ 0. 5Ωe, where Ωe is the electron cyclotron frequency. Their average frequency is 0. 21Ωe. Amplitudes of the whistler mode waves cover a range from a few picoteslas to ∼100 pT. Their mean amplitude is 44 pT or 10−2 B0, where B0 is the magnitude of the ambient magnetic field. One interesting feature is that the whistler mode waves propagate mostly in a direction either parallel or antiparallel to B0. The whistler mode waves are very likely excited by energetic electron beams, which arise from reconnections in the near/deep magnetotail. Another significant feature of the whistler mode waves is that the correlation between their amplitudes and phase speeds. A higher phase speed usually associates with a lower amplitude. Whistler mode waves in the near magnetotail (−100 RE < x <−10 RE) and the deep magnetotail (−210 RE < x < −100 RE) are very much the same in many respects. However, one significant difference is that the average electron resonant energy is higher in the near magnetotail (11 keV) than that in the deep magnetotail (1.6 keV). Observations of whistler mode waves may provide a way to monitor energetic electrons and processes of reconnection in the magnetotail.
Identification of the extraction structure of H− ions by Hα imaging spectroscopy

Extraction structure of negative hydrogen ions (H−) (i.e. the regions where H− ions are effectively extracted from the plasma) was obtained using hydrogen Balmer-α (Hα) imaging spectroscopy and cavity ring-down spectroscopy. The H− ion density increases after caesium (Cs) seeding through a surface conversion process on a Cs-covered plasma-grid (PG) surface. We found a reduction in the H− density during beam extraction after Cs conditioning, and the same signal reduction appeared in the Hα intensity caused by the reduction in the excited hydrogen (n = 3) population, which in turn is caused by the decrease in the mutual neutralization process between positive and negative hydrogen ions. We clearly observed the reduction structure of the Hα emissions in the extraction region; the structure expands at optimal Cs conditioning. From this result, the H− ions, which are produced at the PG surface, release to the extraction region and widely distribute during arc discharge. We conclude that the reduction of the H− density is caused by the particle loss due to beam extraction from the PG apertures.
The broad-line regions of active galaxies

We attempt to classify the observed profiles of the broad emission lines from active galactic nuclei into a number of types. We propose a model for the broad-line region in which clouds are injected into an outflowing wind from a rotating disc. We then show how the characteristic scales in the model relate to features in our classification of the observations by comparing the observed profiles with those from the model in each class
Determination of Autoionization Rates by Means of Optical Emission Spectroscopy

Extraction of accurate values of autoionization rates from broadened emission lines in optical spectra is discussed. Results for autoionizing states in He I and Li I are given and compared with theory. Spin-induced autoionization is proposed to cause the discrepancy between theoretical and experimental lifetimes for some Li I quartet levels.
Improved Shepard's Method for the Optimization of Composite Structures

a, b = length and width of a rectangular plate, mm A = membrane stiffness matrix B = membrane/bending coupling stiffness matrix D = bending stiffness matrix dAD = AD distance E11 = Young modulus in longitudinal (fiber) direction, GPa E22 = Young modulus in transverse (matrix) direction, GPa G12 = in-plane shear modulus, GPa h = laminate thickness, mm L, R = length and radius of a cylinder, mm Nx, N , Nx = resultants of axial compression, external pressure and torsion for a cylinder, N=mm Nx, Ny, Nxy = in-plane stress resultants for a plate, N=mm r = inverse of the buckling factor Vi = in-plane lamination parameters, i 1; . ; 4 Wi = out-of-plane lamination parameters, i 1; . ; 4 = buckling factor
Comments on “Preferential Concentration of Cloud Droplets by Turbulence:Effects on the Early Evolution of Cumulus Cloud Droplet Spectra”

Shaw et al. (1998, hereafter SRCV98) discussed effects of turbulence on spatial distribution of cloud droplets and their growth by the diffusion of water vapor inside adiabatic cores of convective clouds. They proposed an idealized model of cloud droplet growth in a turbulent environment that is based on the assumption that cloud droplets are not randomly distributed in space but are preferentially concentrated in regions of low vorticity. In the context of this model, SRCV98 obtain droplet spectra significantly wider than predicted by a classic parcel model, significant activation is possible well above the cloud base, and a large droplet tail is present. The inspiration for the SRCV98 study comes from a vast body of evidence, mostly from laboratory studies, suggesting that preferential concentration of particles occurs in dilute particle-laden turbulent flows (e.g., Eaton and Fessler 1994). However, there are significant differences between laboratory and numerical model flows reported in the literature on one side, and atmospheric flows on the other side. In particular, flows with considerably higher eddy dissipation rates are usually considered in laboratory flows as compared to typical flows in cumulus clouds. This is especially true for the case of adiabatic cores of convective clouds. As a result, the relevant parameters in the atmospheric case are outside the range of values explored previously in laboratory experiments and in numerical simulations. In par-
Measurements of High-, Room-, and Low-Temperature Photoabsorption Cross Sections of SO2 in the 2080- to 2950-Å Region, with Application to Io

Abstract Using synchrotron radiation as a continuum light source, we have measured the absolute absorption cross sections of SO 2 from 2080 to 2950 A with a resolution bandwidth (FWHM) of 0.5 A and under temperature conditions of 400, 295, and 200 K. Significant temperature effects are clearly observable throughout the studied wavelength region. Many hot bands have been observed, including some in the 2080- to 2220-A region, where no such transitions were previously known. It was also found that the apparent continuum cross section underlying the vibrational features increases by an order of magnitude when the gaseous SO 2 temperature increases from 200 to 400 K. The new laboratory cross section data should be useful in constraining both the temperature and abundance differences between the leading and the trailing sides of the Io's atmosphere.
Hubble Space Telescope Observations of Oxygen-rich Supernova Remnants in the Magellanic Clouds. II. Elemental Abundances in N132D and 1E 0102.2–7219

We present Hubble Space Telescope (HST) Wide Field and Planetary Camera 2 images and Faint Object Spectrograph data of two young supernova remnants in the Magellanic Clouds, N132D (LMC) and 1E 0102.2-7219 (SMC). The spectra cover essentially the entire UV/optical range available to HST and provide the first true comparison of UV/optical line intensities from astrophysical shocks that do not depend on scalings from different aperture sizes or instruments. For the spectra, we isolated specific knots and filaments that contain fast-moving debris of nuclear-processed material that are devoid of hydrogen and appear to have originated from the cores of the progenitor stars. In N132D we also observed a knot on the outer rim of the remnant that represents a shocked interstellar cloud. In the debris from both remnants, we identify only the elements O, Ne, C, and Mg. We find no evidence for oxygen-burning products, such as S, Ca, Ar, etc., which are seen in Cas A and are expected from models of Type II supernovae. We suggest that the progenitor stars of N132D and 1E 0102.2-7219 had large, oxygen-rich mantles (perhaps Wolf-Rayet stars) and may be the products of Type Ib supernovae. Shock modeling demonstrates systematic differences in the relative abundances in the O-rich debris, possibly pointing to different progenitor masses for these two objects. The shocked interstellar knot in N132D shows that we are probably seeing a range of conditions within the ~1'' aperture and that no evidence is present for enrichment by a precursor star wind.
Biased galaxy formation in a universe dominated by cold dark matter

The hypothesis that galaxies form from rare fluctuations in a universe dominated by cold, weakly interacting dark matter is shown to be in reasonable accord with most observed properties of the distribution of galaxies. The normalization of the primordial power spectrum is chosen to reproduce the observed coherence length of the galaxy distribution. In particular, we compute the rms galaxy peculiar velocities, the quadrupole anisotropy in the microwave background radiation induced by potential fluctuations, and the galaxy luminosity and multiplicity functions. We find that pancake-like structures develop which are associated with scales that have recently become nonlinear. Application is made to calculate the baryonic mass fraction not incorporated into galaxies. Inclusion of a threshold effect is necessary in order to suppress the low-sigma fluctuations from forming galaxies. For illustrative purposes, we consider a threshold in redshift at z = 3, associated with the peaking of quasar activity and presumed reionization of the intergalactic medium. This assumption allows us to determine the luminosity function of forming objects on all scales. Consideration of the cooling function appropriate to a primordial cloud allows us to identify all objects of scale greater than 10/sup 7/ M/sub sun/ and below 10/sup 12/ M/sub sun/ withmore » galaxies. The only potential difficulty encountered is that our relatively crude statistical treatment predicts a number density of low-luminosity galaxies that considerably exceeds most extrapolations of the bright-galaxy luminosity function. « less
On a finite-element method for solving the three-dimensional Maxwell equations

Abstract The aim of this paper is to present a method for solving the time-domain three-dimensional Maxwell equations, which can be coupled with a particle solver. For this purpose, Maxwell's equations are reformulated as a constrained wave equation system, with Lagrange multipliers associated to the conditions ∇ · β - 0 and ∇ · E - ρ/e 0 . We approximate both the fields and the Lagrange multipliers with a finite element method using a Taylor Hood element.
The Motion of Two Spheres in a Viscous Fluid

The problem of this paper is to determine the motion set up in a viscous fluid at rest at infinity by two solid spheres (equal or unequal) moving with equal small constant velocities parallel to their line of centres. The same analysis is immediately applicable to the corresponding problem in which the spheres are fixed and the fluid streams past them with constant velocity. The solution is based on the determination of Stokes’ stream-function for the motion of the fluid, and from this the forces necessary to maintain the motion of the spheres are calculated.
Direct observation of a resolvable spin separation in the spin Hall effect of light at an air-glass interface

We theoretically and experimentally demonstrate that it is possible to directly observe the resolvable spin separation in the spin Hall effect of light at an air-glass interface by choosing optimal parameters. When a P-polarized light with a beam waist of 10 μm is incident around Brewster's angle, the two spin components of the reflected beam can be completely separated by eliminating the influence of the in-plane wavevector spread. This not only obviously reveals the strong impacts of the polarization state, the incident angle, the beam waist, and the in-plane wavevector spread, but also intuitively visualizes the observation of the spin Hall effect of light.
Subband transitions in dual-band n-B-n InAs/GaSb superlattice infrared photodetector identified by photoresponse spectra

The subband transitions in dual-band n-B-n InAs/GaSb type-II superlattice infrared photodetector are identified by the photoresponse (PR) spectra. In the mid- and long-wavelength PR spectra measured by changing bias polarity, each spectrum individually shows a series of distinctive peaks related to the transitions from the hole subbands to the conduction one. The PR mechanism at each polarity is discussed in terms of diffusion and tunneling currents.