Distributions Of Various Parameters Research Articles

Particle dynamics in viscoelastic media: Effects of non-thermal white noise on barrier crossing rates.

The growing interest in the dynamics of self-driven particle motion has brought increased attention to the effects of non-thermal noise on condensed phase diffusion. Thanks to data recently collected by Ferrer et al. on activated dynamics in the presence of memory [Phys. Rev. Lett. 126, 108001 (2021)], some of these effects can now be characterized quantitatively. In the present paper, the data collected by Ferrer et al. are used to calculate the extent to which non-thermal white noise alters the time taken by single micron-sized silica particles in a viscoelastic medium to cross the barrier separating the two wells of an optically created bistable potential. The calculation-based on a generalized version of Kramers's flux-over-population approach-indicates that the added noise causes the barrier crossing rate (compared to the noise-free case) to first increase as a function of the noise strength and then to plateau to a constant value. The precise degree of rate enhancement may depend on how the data from the experiments conducted by Ferrer et al. are used in the flux-over-population approach. As claimed by Ferrer et al., this approach predicts barrier crossing times for the original silica-fluid system that agree almost perfectly with their experimental counterparts. However, this near-perfect agreement between theory and experiment is only achieved if the theoretical crossing times are obtained from the most probable values of a crossing time distribution constructed from the distributions of various parameters in Kramers's rate expression. If the mean values of these parameters are used in the expression instead, as would be commonly done, the theoretical crossing times are found to be as much as 1.5 times higher than the experimental values. However, these times turn out to be consistent with an alternative model of viscoelastic barrier crossing based on a mean first passage time formalism, which also uses mean parameter values in its rate expression. The rate enhancements predicted for barrier crossing under non-thermal noise are based on these mean parameter values and are open to experimental verification.

Population Synthesis of Black Hole Binaries with Normal-star Companions. I. Detached Systems

Abstract Optical observations of normal stars in binary systems with massive unseen objects have been proposed to search for candidate black holes (BHs) and provide a direct measurement of their dynamical masses. In this paper, we have performed binary population synthesis calculations to simulate the potential population of detached binaries containing BHs and normal-star companions in the Galaxy. We focus on the influence of the BH progenitors. In the traditional model, BHs in binaries evolve from stars more massive than ∼25M ⊙. However, it is difficult for this model to produce BH low-mass X-ray binaries. Recent investigations of massive star evolution have suggested that the BH progenitors have masses as low as ∼15M ⊙. Based on this model, we provide the expected distributions of various parameters for detached BH binaries with normal-star companions, including the component masses, the orbital parameters of the binary systems, the radial velocity semi-amplitudes, and the astrometric signatures of the optical companions. Our calculations show that there are thousands of such detached binaries in the Galaxy, and hundreds of them are potentially observable systems with luminous companions brighter than 20 mag. In addition, detached BH binaries are dominated by those with main-sequence companions and only a small percent of them are expected to have giant companions.

Model-based downdraft biomass gasifier operation and design for synthetic gas production

In this study, three-phase flow model together with a thermal-equilibrium model was developed to study the operation of downdraft biomass gasifiers. Gasification experiments were conducted to obtain pyrolysis kinetics and validate the models. A good agreement was found between experiment data and model predictions, in terms of syngas composition and temperature, respectively. Kinetics based on experimental study improves the accuracy of simulation. The thermal-equilibrium model was applied to study the effects of air to biomass ratio on gas composition, LHV (lower heating value), and temperature. The 3D multiphase flow model was applied to investigate the spatial distributions of various parameters (i.e. pressure, gas velocity, temperature, and gas composition) inside the gasifier that are critical to the design of gasifier. A rough division of four gasification zones was determined based on temperature profile. It was also found that the cold gas efficiency was around 63% based on CFD (computational fluid dynamic) simulation. The temperature distributions could be used to guide the application of heat resistant materials inside the gasifier. In addition, the simulation results indicated that blockage of the gasifier has a high chance to occur at the top of reduction bell when using feedstock of high metal contents. Effects of reduction bell dimension and operation conditions on the temperature distribution and syngas production were also investigated by the 3D CFD model, which sheds light on the improvement of the design and operation of reactor. The syngas production could be enhanced by varying the size of reduction bell.

Relation Between Current Density Distribution in Land-Channel Direction and Presence of Liquid Water in Proton Exchange Membrane Fuel Cell Flow Channel

Since most of the PEMFCs have land-channel geometry in their flow field, the distance between the flow channel to the catalyst layer is not uniform. The distance is longer from the flow channel to the catalyst layer under the land area than to the catalyst layer under the channel area. This difference causes the non-uniform current density in land-channel direction, and the distribution largely depends on the operating conditions. As the inlet gas humidity in the operating condition decreases, the trend in the current density distribution changes from high local current under the channel to relatively uniform, and to higher local current under the land (Figure 1). This trend is due to the combined effects of (1) non-uniform oxygen transport resistance, (2) non-uniform liquid water transport distance causing the local flooding under the land area at wet condition, and (3) the tendency of faster membrane dryout under the channel area at dry condition. In order to investigate the distributions of various parameters in the land-channel direction, a small-scale segmented cell with about 300-micron resolution was developed by the authors’ group, and successfully measured the current and high-frequency resistance distribution in the land-channel direction. Distribution of oxygen transport resistance from the flow channel to the catalyst layer was also measured using limiting current technique. In this study a new segmented cell is developed. Using the transparent cathode plate the behavior of liquid water in cathode flow channel can be observed, and simultaneously the current density distribution is measured in land-channel direction. With this cell the relation between the current density distribution in the land-channel direction and the presence of liquid water is investigated. First, it is studied that at what gas humidity and at what overall current density the liquid water starts emerging from the gas diffusion layer surface to the flow channel. This provides us the information about the dependency of the liquid water emergence location on the current density distribution is studied. Then, how the presence of liquid water in the flow channel changes the current distribution is studied. Figure 1

Effect of Flow Field Configuration on Oxygen Transport Resistances in Proton Exchange Membrane Fuel Cell Cathode

Land-channel geometry is necessary for proton exchange membrane fuel cells to transport electron and at the same time to transport reactants/products. However, this configuration causes the difference in transport distance between the flow channel to the catalyst layer, and results in the non-uniform distribution of various factors, such as species concentration, current generation, and rate of degradation. In order to investigate the distributions of various parameters in the land-channel direction, a small-scale segmented cell with about 300-micron resolution was developed by the authors’ group, and successfully measured the current and high-frequency resistance distribution in the land-channel direction. Distribution of oxygen transport resistance from the flow channel to the catalyst layer was also measured using limiting current technique. The oxygen transport mechanism is completely different in the conventional flow field and in the interdigitated flow field. In the conventional flow field, the oxygen transport is mostly driven by the duffusion due to the concentration gradient. In the interdigitated flow field, on the other hand, the convective flow through gas diffusion layer (GDL) makes the diffusion distance shorter than the conventional flow field case, and therefore the lower oxygen transport resistance is expected. In this study the oxygen transport resistance distribution in land-channel direction is measured in two different flow field configurations, that is, conventional flow field and interdigitated flow field. The comparison of the results from these two flow fields reveals the impact of the convective transport through GDL on the oxygen transport resistance and on the distribution.

Influence of statistical distributions on the electrical properties of disordered and aligned carbon nanotube networks

We have studied the influence of different statistical distributions of various parameters describing the structural and physical properties of carbon nanotube (CNT) networks on their electrical properties. We observed a significant dependence on the distribution of structural parameters (length, diameter, and angle), but nearly no impact for a statistical distribution of the tube-tube resistance beyond percolation threshold. The variation of the conductance of the CNT network as a function of the CNT density observed experimentally can be accurately reproduced through simulations by considering a tube-tube resistance centered at 0.1–1.0 MΩ, in agreement with the experimental estimation. Since the number of tube-tube contacts is increasing rapidly with the size of the simulated network, a statistical representation of tube-tube resistances for large CNT network models does not introduce a significant variation.

Estimating the spatiotemporal distribution of geochemical parameters associated with biostimulation using spectral induced polarization data and hierarchical Bayesian models

We developed a hierarchical Bayesian model to estimate the spatiotemporal distribution of aqueous geochemical parameters associated with in‐situ bioremediation using surface spectral induced polarization (SIP) data and borehole geochemical measurements collected during a bioremediation experiment at a uranium‐contaminated site near Rifle, Colorado (USA). The SIP data were first inverted for Cole‐Cole parameters, including chargeability, time constant, resistivity at the DC frequency, and dependence factor, at each pixel of two‐dimensional grids using a previously developed stochastic method. Correlations between the inverted Cole‐Cole parameters and the wellbore‐based groundwater chemistry measurements indicative of key metabolic processes within the aquifer (e.g., ferrous iron, sulfate, uranium) were established and used as a basis for petrophysical model development. The developed Bayesian model consists of three levels of statistical submodels: (1) data model, providing links between geochemical and geophysical attributes, (2) process model, describing the spatial and temporal variability of geochemical properties in the subsurface system, and (3) parameter model, describing prior distributions of various parameters and initial conditions. The unknown parameters were estimated using Markov chain Monte Carlo methods. By combining the temporally distributed geochemical data with the spatially distributed geophysical data, we obtained the spatiotemporal distribution of ferrous iron, sulfate, and sulfide, and their associated uncertainty information. The obtained results can be used to assess the efficacy of the bioremediation treatment over space and time and to constrain reactive transport models.

The structure of mesoscale convective systems in central Russia

Described is the organization of 216 summertime mesoscale convective systems (MCSs) in Moscow region. Initially, the horizontal radioecho fields corresponding to the stage of MCS reflectivity maximum were divided into 92 lines with the length of more than 200 km and 124 nonlinear MCSs. Subsequently, three types of lines were separated: lines with solid segments of reflectivity of more than 40 dBZ of ∼100 km long, discontinuous convection bands representing the combinations of linear and node-like amorphous thunderstorms, and convex or concave bow-shaped systems frequently forming the families of spirals or occlusions. The nonlinear MCSs contain circular radar cells (similar to open mesoscale cells) or small bow segments of ∼30 km; however, the most intensive storms have a propagation axis connecting the major MCSs. Finally, an objective classification of MCSs is proposed based on the quantiles of climatological distributions of various parameters describing the intensity, morphology, and kinematics of MCSs.

Neutrino spectra from low and high luminosity populations of gamma ray bursts

The detection of GRB 060218 at z = 0.033 by Swift within 1.5 years of operation, together with the detection of GRB 980425 at z = 0.0085 by BeppoSAX, suggest that these low luminosity (LL) GRBs have a much higher event rate than the canonical high luminosity (HL) GRBs, and they form a distinct new component in the GRB luminosity function. We explore the contribution of this previously neglected GRB population to the diffuse neutrino background within the internal shock model and compare it with that of the canonical HL population. By considering a wide range of distributions of various parameters (e.g. luminosity, spectral break energy, duration, variability time, Lorentz factor, redshift) for both populations, we find that although it is difficult to detect neutrinos from the individual LL GRBs, the contribution of the LL population to the diffuse neutrino background is more than the HL population above about 10 8 GeV.

Earth's Bow Shock and Its Interaction with Interplanetary Shocks

AbstractGiven the interplanetary conditions near the Earth's orbit and the geometrical configuration of the Earth's bow shock, this paper discusses the distributions of various parameters of shock strength over the sunward shock front, and the interaction between the bow shock and interplanetary shocks. For the case of axisymmetrical bow shock front with respect to the Sun‐Earth line, we arrive at the following conclusions: (1) The parameters of shock strength are distributed symmetrically with respect to the plane of reference defined by the interplanetary magnetic field (IMF) and the Sun‐Earth line, and their maxima appear in the plane of reference. The ratio of magnetic pressure is larger on the side containing the perpendicular‐shock line, whereas the ratio of gas pressure is larger on the side containing the parallel‐shock point, leading to a distribution of the ratio of total pressure that is largely axisymmetrical with respect to the Sun‐Earth line. (2) When the angle between the IMF and the Sun‐Earth line increases, the maxima of shock strength parameters of the bow shock decrease and the maximum points shift away from the subsolar point, but the distributions of gas‐pressure ratio and total pressure ratio are essentially not affected. (3) After an interplanetary shock is transmitted through the bow shock, the ratio of tangential field strength becomes closer to 1, whereas the jump of total magnetic field strength increases in amplitude. (4) After transmission through the bow shock, the ratio of total magnetic field strength becomes closer to 1 for quasi‐perpendicular interplanetary shocks but farther away from 1 for quasi‐parallel ones.

Eye movements and psychiatric disease.

During the past year a number of studies have been published on eye movement dysfunction in patients with psychiatric disease. According to the mainstream of modern neuropsychiatric research, these studies cover either genetic aspects or the results of pharmacological manipulation. A few studies addressed impaired smooth pursuit eye movements (eye tracking dysfunction) in unaffected relatives of psychiatric patients, and were important in excluding non-specific effects (e.g. medication) and isolating genetic predisposition to the disease. This predisposition could be demonstrated in families of schizophrenic patients irrespective of whether the index case was sporadic or familial. One large study demonstrated pathological distributions of various parameters of smooth pursuit eye movement performance in groups of schizophrenic patients and their relatives. However, another study challenged the specificity of eye tracking dysfunction as a trait marker for schizophrenia by showing that its prevalence was identical among relatives of patients with affective disorder and schizophrenia. Eye tracking dysfunction was associated with two gene polymorphisms that interfere with dopamine metabolism and are thus reasonable candidate genes for the predisposition to schizophrenia. The influence of nicotine and neuroleptic drugs on eye movement performance was studied in schizophrenic patients. Nicotine improved smooth pursuit performance in three studies, one of which attributed this finding to enhanced attention. Two groups of schizophrenic patients treated with two different atypical neuroleptic drugs, risperidone and olanzapine, did not differ in a battery of saccadic tasks. Eye movements provide an important tool to measure pharmacological effects in patients and unravel genetic traits in psychiatric disease.

Magnetic Relaxations of Antiferromagnetic Nanoparticles in Magnetic Fields

We reexamine anomalous magnetic relaxations of ferritin in magnetic fields, the presence of which has been regarded as evidence suggesting the existence of thermally assisted macroscopic quantum tunneling in antiferromagnetic nanoparticles. In the present study, relaxation curves of ferritin are examined using an approach that is free from assumptions regarding distributions of various parameters of polydispersive particles. The results are not anomalous. In other words, the relaxation is accelerated by the field, as expected for classical superparamagnetic fluctuations.

Statistical properties of spectroscopic binary stars

As part of a study of the mass-ratio distribution of spectroscopic binary stars, the statistical properties of the systems in theEighth Catalogue of the Orbital Elements of Spectroscopic Binary Stars, compiled by Battenet al. (1989), are investigated. Histograms are presented of the distributions of various parameters of the systems in the catalogue as a whole, and compared to those of the previous edition. Histograms of binaries of various spectral types are presented. It is noted that the early-type binaries in the catalogue have on average higher radial-velocity amplitudes, shorter periods, and smaller semi-major axes than late-type binaries. Late-type binaries have relatively more eccentric orbits. Whether the differences noticed between the early- and late-type binaries have any significance with respect to the population of binary stars in the Galaxy is not clear, because it is very hard to assess the extent to which the catalogue is a statistically representative and complete sample. The distribution of semi-major axesa 1 sini varies considerably among different subsamples. The mass-ratio distribution of single-lined spectroscopic binaries is, for all (sub-)samples, characterized by a decrease in the number of systems according to a power law asq→1, forq=M sec/M prim>0.25. The mass-ratio distribution of double-lined spectroscopic binaries (SBII) is, for all (sub-)samples but one, characterized by an increase in numbers according to a power law, asq→1. The exception to this general behaviour is the sample of SBII systems with magnitudesm≤5 m , which has its maximum atq≈0.65. The distributions are presented ‘as they are’, without corrections for selection effects.

Scoliosis

A two and a half-year prospective study was carried out to determine incidence rates and distributions of various parameters associated with idiopathic scoliosis. Data were also collected on the progression curves detected at the initial screening. The results showed: (1) that the incidence rate was 13.6 per cent with a female-to-male ratio of 1.2:1, (2) that the most common type of curve was thoracolumbar, and (3) that spontaneous improvement occurred in approximately 22 per cent of those patients followed for an average of one year.