Large Volume Of Space Research Articles

Experimental reconstruction of sound fields over large spatial domains

This talk discusses sensing methods and reconstruction techniques for characterizing sound fields over large spatial domains. We focus specifically on reconstructing reverberant soundfields in rooms and enclosures. Two complementary approaches are presented in the talk: on the one hand, we present a method that leverages on modeling the spatio-temporal and statistical properties of enclosed sound fields via wave expansions, enabling to estimate the sound field over a large volume of space. On the other hand, we present a Physics Informed Neural Network, which learns the governing wave equation using a small set of measured data and enables to meaningfully interpolate and extrapolate the sound field to any position where no observations are available. Experiments in real rooms are presented, including an opera hall and an auditoria for oral communication. The experiments successfully demonstrate the volumetric acquisition and three-dimensional characterization of the sound fields. The presented techniques can be of relevance in applications pertaining to immersive and navigable audio, architectural acoustics and heritage preservation.

Development of two-dimensional hydrogen distribution model in small-scale spaces under severe accidents

Hydrogen distribution and combustion are important problems in nuclear reactor safety analysis under severe accident conditions.IPWR (Integrated pressurized water reactor) are very different from conventional nuclear power plants in design, structure and operating power. In particular, the nuclear power plant containment has a large space volume, and there are multiple compartments inside, while the small reactor containment has a small volume and a simple and compact internal layout. This makes the hydrogen in the containment behave differently in a severe accident. Thus, the hydrogen flow distribution characteristics of IPWR under severe accidents need further study.In this paper, a two-dimensional continuum model of hydrogen distribution in small-scale under severe accident conditions is established by using finite volume method and staggered grid scheme based on hydrodynamics calculation method. SIMPER (Semi-Implicit Method for Pressure Linked Equations Revised) algorithm is used to construct the pressure correction equation, alternate direction implicit algorithm is used to solve the algebraic equations, and block correction algorithm is used to accelerate the iterative convergence. Compared with the experimental study of hydrogen flow distribution characteristics in local compartments, the model can predict the change of hydrogen volume fraction distribution well with time in the experiment. After that, the flow distribution characteristics of hydrogen in the RPV (Reactorpressurevessel) and containment under the low-pressure core melt accident were analyzed with IPWR-IP200 as the research object. The results show that the coolant level in the lower head of the RPV is still about 0.8 m during hydrogen generation, so there is no hydrogen in the lower head area. The highest hydrogen volume fraction in the RPV is at the outlet of the core, which is about 23 %. The highest volume fraction of hydrogen in the containment is the outlet above the pressurizer relief valve, which is up to 17 %. Because of the high volume fraction of water vapor in the RPV, there is no risk of hydrogen combustion in the RPV. During hydrogen generation, there is a risk of hydrogen combustion within the containment, and the risk area is located in the upper space of the containment. After hydrogen production ceases, as water vapor continues to enter the containment, the hydrogen volume fraction gradually decreases, and the risk of hydrogen combustion will also decrease.The two-dimensional continuum model established in this paper can predict the hydrogen distribution under severe accidents, which can provide a reference for the hydrogen mitigation strategy of IPWR.

Investigation of a Portable Wind Tunnel for Energy Harvesting

Current wind tunnels possess a large space volume and high manufacturing cost, which are not suitable for investigating micro energy harvesters. This paper aims to design and fabricate a small, portable and low-speed wind tunnel for energy harvesting. A wind tunnel structure was first designed, a finite element analyses is then utilized to obtain the airflow velocity and turbulence intensity at the testing section, and the influence of the structural parameters of the wind tunnel on the flow field performance is finally investigated to achieve better performance. An experimental prototype of the wind tunnel was fabricated to verify the simulation results. Results demonstrated that the distribution uniformity and average turbulence intensity at the test section decrease first and then increase with the increase of both the diffuser and contraction lengths. The rectifying and damping effect of the honeycomb increase with increasing porosity and thickness. When the diffuser and contraction lengths are 850 mm and 480 mm, respectively, a better distribution uniformity and a lower turbulence intensity can be achieved. Experimental results were in good agreement with the simulation values. The maximum airflow velocity can reach up to 24.74 m/s, and the minimum error was only 1.23%. The designed wind tunnel achieved low-speed, small, portable and stable functions. This work provides an important guidance for further investigating the piezoelectric energy harvesting.

Large-scale clustering amongst Fermi blazars; evidence for axis alignments?

ABSTRACT We find evidence for large-scale clustering amongst Fermi-selected BL Lac objects but not amongst Fermi-selected flat spectrum radio quasars (FSRQs). Using two-point correlation functions, we have investigated the clustering properties of different classes of objects from the Fermi–LAT(Large Area Telescope) 4FGL catalogue. We wanted to test the idea based on optical polarization observations that there might be large volumes of space in which AGN axes are aligned. To do this, we needed a clean sample of blazars as these are objects with their jet axes pointing towards the observer and Fermi sources provide such a sample. We find that high latitude Fermi sources taken as a whole show a significant clustering signal on scales up to 30°. To investigate if all blazars behave in the same way we used he machine learning classifications from the literature, which are based only on gamma-ray information, to separate BL Lac-like objects from FSRQ-like objects. A possible explanation for the clustering signal we find amongst the BL Lac-like objects is that there are indeed large volumes of space in which AGN axes are aligned. This signal might be washed out in FSRQs since they occupy a much larger volume of space. Thus, our results support the idea that large scale polarization alignments could originate from coherent alignments of AGN axes. We speculate that these axis alignments may be related to the well-known intrinsic alignments of galaxy optical position angles.

Concentration and size distribution of particulate matter in a new aviary system for laying hens in China

ABSTRACTParticulate matter (PM) from poultry production facilities may strongly affect the health of animals and workers in the houses, and PM emitted to the ambient air is an important pollution source to the surrounding areas. Aviary system is considered as a welfare friendly production system for laying hens. However, its air quality is typically worse as compared with conventional cage systems, because of the higher PM concentration of indoor air and other airborne contaminants. Furthermore, PM’s physical property, which has a direct impact on the penetration depth into the lungs of the birds and humans, is largely unknown for the aviary system. Therefore, a systematic method was utilized to investigate the characteristics of particles in the aviary house with large cage aviary unit system (LCAU) in Beijing, China. For the field measurements, three measuring locations were selected with two inside and one outside the house with LCAU to continuously monitor PM concentrations and collect the samples for particle size distribution (PSD) analysis. Results showed that PM2.5, PM10, and total suspended particulate (TSP) concentrations averaged at 0.037 ± 0.025 mg/m3, 0.42 ± 0.10 mg/m3, and 1.92 ± 1.91 mg/m3, respectively. Particle concentrations increased from October to December due to less ventilation as the weather got colder, and were generally affected by stocking density, ventilation rate, birds’ activities, and housing system. Meanwhile, indoor PM2.5 concentration was easily impacted by the ambient air quality. Mass median diameter (MMD) and mass geometric standard deviation (MGSD) of the TSP during the measurement were 18.92 ± 7.08 μm and 3.11 ± 0.31, respectively. Count median diameter (CMD) and count geometric standard deviation (CGSD) were 1.94 ± 0.14 μm and 1.48 ± 0.08, respectively. Results indicated that the aviary system can attain a good indoor condition by suitable system design and environment control strategy.Implications: Indoor PM2.5 concentration of the layer house can be significantly affected by ambient air quality when the air quality index (AQI) was larger than 100. PM2.5 and PM10 concentrations of the layer house with a LCAU system were comparable to the cage system. TSP concentration was higher, and PM size was larger than most of the cage system. System design, larger space volume, and higher ventilation rate were the main influence factors. Good indoor environment of the aviary system can be achieved through the reasonable design of the production system and appropriate environment control strategy.

Dark Matter: An Unforeseen Gravitational Property of Relativistic Space-Time?

If the wave functions of matter expanded with time dilation for an outside observer in the same way as photons do in gravitational redshift; with some modifications the general relativity might alone explain dark matter, galaxy rotation curves, and part of the energy released in supernova explosions. Also, the event horizons of black holes couldn’t be formed when packing matter more and more densely together. Essentially, if the time dilation increases enough, the particles turn less localized to outside observers and the mass distribution of the same particles would expand into larger volume of space. Small particles deep inside a black hole might seem like dark matter instead by their gravitational influence if the time dilation alters their size enough for outside observers. At the same time, the surface particles of the black hole would be less dispersed, creating the Newtonian gravitational potential we see closer to black holes. The following research doesn’t attempt to reformulate the general relativity itself, but only proposes the idea while approximating the Milky way gravity profile to compare the hypothesis with measurements. Therefore, actually proving the hypothesis is still far off while the idea is sound at its core.

Nonparametric H Density Estimation Based on Regularized Nonlinear Inversion of the Lyman Alpha Emission in Planetary Atmospheres

AbstractInversion of space‐borne remote sensing measurements of the resonantly scattered solar Lyman alpha (121.6‐nm) emission in planetary atmospheres is the most promising means of quantifying the H density in a vast volume of space near terrestrial planets. Owing to the highly nonlinear nature of the inverse problem and the lack of sufficient data constraints over the large volume of space where H atoms are present, previous inversion methods relied on physics‐based parametric formulations of the H density distributions to guarantee solution uniqueness. Those physical formulations, such as the Chamberlain model, were developed with simple assumptions of the atmospheric conditions. The use of such formulations as constraints significantly limits the range of possible solutions, which might lead to large errors in the case when those assumptions are invalid. In this study, we demonstrate for the first time the feasibility of estimating the H density through regularized nonlinear inversion of the Ly‐α emission in an optically thick atmosphere, without using parametric formulations. Specifically, Occam's inversion algorithm is used to demonstrate that the H density can be estimated in a large volume of space near the planet, with accuracy in different atmospheric regions depending on the observation scheme. Two distinctly different schemes are examined, including a low‐Earth orbit and a geostationary orbit. Modeling results show that the low‐Earth orbit is better for H density estimation in the thermosphere, while the high‐altitude orbit is better for estimation in the exosphere. Our results could provide useful information for designing the observation schemes of future missions.

Image-based deep learning for classification of noise transients in gravitational wave detectors

The detection of gravitational waves has inaugurated the era of gravitational astronomy and opened new avenues for the multimessenger study of cosmic sources. Thanks to their sensitivity, the Advanced LIGO and Advanced Virgo interferometers will probe a much larger volume of space and expand the capability of discovering new gravitational wave emitters. The characterization of these detectors is a primary task in order to recognize the main sources of noise and optimize the sensitivity of interferometers. Glitches are transient noise events that can impact the data quality of the interferometers and their classification is an important task for detector characterization. Deep learning techniques are a promising tool for the recognition and classification of glitches. We present a classification pipeline that exploits convolutional neural networks to classify glitches starting from their time-frequency evolution represented as images. We evaluated the classification accuracy on simulated glitches, showing that the proposed algorithm can automatically classify glitches on very fast timescales and with high accuracy, thus providing a promising tool for online detector characterization.

Electrochemical lithiation and delithiation performance of SnSb–Ag/carbon nanonube composites for lithium-ion batteries

SnSb–Ag/Carbon nanonube (CNT) composites materials are synthesised using chemical reduction methods. The microstructure, morphologies and electrochemical properties of these materials are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), constant current charge/discharge tests and cyclic voltammetry tests. The results indicate that Ag promotes the entire charge–discharge process during the complex multi-step reaction process and, to some extent, prevent the reunion of nanoparticles. At the same time, CNTs, with a large space volume and form a network structure, prevent particles aggregation and increase the buffer space between the alloy particles, which greatly reduce the diffusion distance of lithium ions and the occurrence of lithium trapping in the active electrode materials. CNTs also have excellent mechanical properties and toughness, they effectively buffer enormous stresses during the volume expansion of alloy particles, weakening the forces between the particles and reducing the rate of formation of powder particles. All these factors cause the SnSbAg0.1/6% CNT composites exhibit excellent cycle life by controlling the lithiation of the anode material; the reversible capacity for the 50th cycle is 639.6 mAh g−1 between 0.05 and 1.5 V.

Monte Carlo Shielding Analysis Capabilities with MAVRIC

Monte Carlo shielding analysis capabilities in SCALE 6 are centered on the Consistent Adjoint Driven Importance Sampling (CADIS) methodology. CADIS is used to create an importance map for space/energy weight windows as well as a biased source distribution. New to SCALE 6 are the Monaco functional module, a multigroup fixed-source Monte Carlo transport code, and the Monaco with Automated Variance Reduction using Importance Calculations (MAVRIC) sequence. MAVRIC uses the Denovo code (also new to SCALE 6) to compute coarse-mesh discrete ordinates solutions that are used by CADIS to form an importance map and biased source distribution for the Monaco Monte Carlo code. MAVRIC allows the user to optimize the Monaco calculation for a specific tally using the CADIS method with little extra input compared with a standard Monte Carlo calculation. When computing several tallies at once or a mesh tally over a large volume of space, an extension of the CADIS method called FW-CADIS can be used to help the Monte Carlo simulation spread particles over phase space to obtain more uniform relative uncertainties.

Stellar black holes at the dawn of the universe

It is well established that between 380000 and 1 billion years after the Big Bang the Inter Galactic Medium (IGM) underwent a "phase transformation" from cold and fully neutral to warm (~10^4 K) and ionized. Whether this phase transformation was fully driven and completed by photoionization by young hot stars is a question of topical interest in cosmology. AIMS. We propose here that besides the ultraviolet radiation from massive stars, feedback from accreting black holes in high-mass X-ray binaries (BH-HMXBs) was an additional, important source of heating and reionization of the IGM in regions of low gas density at large distances from star-forming galaxies. METHODS. We use current theoretical models on the formation and evolution of primitive massive stars of low metallicity, and the observations of compact stellar remnants in the near and distant universe, to infer that a significant fraction of the first generations of massive stars end up as BH-HMXBs. The total number of energetic ionizing photons from an accreting stellar black hole in an HMXB is comparable to the total number of ionizing photons of its progenitor star. However, the X-ray photons emitted by the accreting black hole are capable of producing several secondary ionizations and the ionizing power of the resulting black hole could be greater than that of its progenitor. Feedback by the large populations of BH-HMXBs heats the IGM to temperatures of ~10^4 K and maintains it ionized on large distance scales. BH-HMXBs determine the early thermal history of the universe and mantain it as ionized over large volumes of space in regions of low density. This has a direct impact on the properties of the faintest galaxies at high redshifts, the smallest dwarf galaxies in the local universe, and on the existing and future surveys at radio wavelengths of atomic hydrogen in the early universe.

Topological inference for EEG and MEG

Neuroimaging produces data that are continuous in one or more dimensions. This calls for an inference framework that can handle data that approximate functions of space, for example, anatomical images, time–frequency maps and distributed source reconstructions of electromagnetic recordings over time. Statistical parametric mapping (SPM) is the standard framework for whole-brain inference in neuroimaging: SPM uses random field theory to furnish p-values that are adjusted to control family-wise error or false discovery rates, when making topological inferences over large volumes of space. Random field theory regards data as realizations of a continuous process in one or more dimensions. This contrasts with classical approaches like the Bonferroni correction, which consider images as collections of discrete samples with no continuity properties (i.e., the probabilistic behavior at one point in the image does not depend on other points). Here, we illustrate how random field theory can be applied to data that vary as a function of time, space or frequency. We emphasize how topological inference of this sort is invariant to the geometry of the manifolds on which data are sampled. This is particularly useful in electromagnetic studies that often deal with very smooth data on scalp or cortical meshes. This application illustrates the versatility and simplicity of random field theory and the seminal contributions of Keith Worsley (1951–2009), a key architect of topological inference.

Stellar black holes: Cosmic history and feedback at the dawn of the universe

AbstractSignificant historic cosmic evolution for the formation rate of stellar black holes is inferred from current theoretical models of the evolution of massive stars, the multiple observations of compact stellar remnants in the near and distant universe, and the cosmic chemical evolution. The mean mass of stellar black holes, the fraction of black holes/neutron stars, and the fraction of black hole high mass X-ray binaries (BH-HMXBs)/solitary black holes increase with redshift. The energetic feedback from large populations of BH-HMXBs form in the first generations of star burst galaxies has been overlooked in most cosmological models of the reionization epoch of the universe. The powerful radiation, jets, and winds from BH-HMXBs heat the intergalactic medium over large volumes of space and keep it ionized until AGN take over. It is concluded that stellar black holes constrained the properties of the faintest galaxies at high redshifts. I present here the theoretical and observational grounds for the historic cosmic evolution of stellar black holes. Detailed calculations on their cosmic impact are presented elsewhere (Mirabel, Dijkstra, Laurent, Loeb, & Pritchard 2011).

Active Noise Control as a Solution to Low Frequency Noise Problems

The control of low frequency noise presents special problems which do not occur at higher frequencies. These problems relate mainly to the long wavelength at low frequencies, which leads to little absorption by conventional means, unless large quantities of absorbing material or large volumes of space are used. There are many examples of low frequency noise problems which can be solved by active attenuation, without the use of thick absorbing material. Some of these are given in this paper.

Influence of balancing parameters in achieving magnetic field uniformity in a large cylindrical volume

Large diameter, air-cored, coaxially configured magnetic coils of rectangular winding cross sections have been envisaged for generating extremely homogenous magnetic fields over a large volume of space. Optimized magnetic field balancing parameters and dimensions for a coil configuration were experimentally developed, verified, and their results are presented. The developed design has made it possible to generate extremely homogenous magnetic fields in a large extended cylindrical region of more than 12 of the coil’s diameter, which requires the winding cross-section thickness to have a width ratio of a relatively small integer. Furthermore, field uniformity regions can be extended to more than one and a half times as can be achieved with coils of negligible winding cross section by employing balancing parameters method.

Comments on “On Internal Waves in a Lagrangian Reference Frame”

Broutman et al. (2004, henceforth BGE1) have entered a current discussion that compares and contrasts gravity wave formulations in Lagrangian and Eulerian analyses. They derived a Lagrangian dispersion relation that takes some account of the nonlinear multiwave ambiance that is at issue, and then they showed that there is “a complete equivalence between the Lagrangian ray equations (46) and the Eulerian ray equations (18).” In doing so, they have negated my own speculation (Hines 2002, henceforth H02) that Lagrangian and Eulerian ray paths might differ, but at the same time they have given guarded confirmation of certain conditions I established for minimal Lagrangian nonlinearity, and they appear to anticipate further study of my suggestion that there are advantages to be gained from a Lagrangian approach to ray tracing in corresponding circumstances. I welcome these developments as a positive contribution to the field, but I must respond to one portion of their related discussion. Their analysis was set in the context of studies by Allen and Joseph (1989, henceforth AJ), Hines (2001), and Chunchuzov (2002)—henceforth collectively the AJHCh papers—and they question those studies in their section 5. Specifically, they question whether a certain “nonwavelike” behavior found by the AJHCh papers in Eulerian spectra at large wavenumbers might have been produced by the use of a Lagrangian dispersion relation that differs from their own, with the implication that their own would have been more appropriate and might have produced only “wavelike” Eulerian behavior. The answer is an unreserved no. What BGE1 call “the” Lagrangian dispersion relation is more properly and more fully described as “a” Lagrangian dispersion relation, one that is applicable locally to waves of small space–time scales propagating in the presence of fluctuations of fluid velocity, fluid displacement, density, and pressure that occur at, and only at, much larger scales. Since the AJHCh papers deal with a continuum of scales, the BGE1 dispersion relation really has nothing to say about the AJHCh results: it could not even have been validly employed. Moreover, there is no mechanism by which it could have been employed, validly or not, given the quite different nature of the AJHCh analyses. Nor, if there were, would “wavelike” behavior have been found in the Eulerian results at large wavenumbers. With its ray-tracing point of view, the BGE1 study focuses on local conditions found in the immediate vicinity of a wave packet, and it follows changes of those conditions as the packet progresses along its ray. The AJHCh analyses, on the contrary, take a more global view: they deal with a large volume of space–time in its entirety, and they contemplate a four-dimensional Fourier decomposition of the fluctuations that are found within it. For the result to be wavelike within the operative definition of that word, each wavevector k would have to have been associated with a single frequency k (k) to yield a dispersion relation applicable to the volume as a whole. Such behavior is not found even locally in the BGE1 Eulerian analysis, which produces at best a single intrinsic frequency for a given k wherever and whenever that k is found locally in various packets as they weave their way through the ever-changing background. This intrinsic frequency would have to be Doppler shifted, by a variable amount dependent on the local flow, before being recorded for use as a frequency in the fixed Eulerian coordinates of the AJHCh analyses. How could those analyses—or any others employing a single Eulerian coordinate system—possibly be expected to find a single frequency in association with a chosen k? It is inherent in the nature of multiwave nonlinearity that, if a “wave” defined by its globally applicable k is subject to significant modification through Eulerian nonlinear effects, it cannot have a single corresponding frequency in a single Eulerian frame of reference. Such a “wave”—in truth, a Corresponding author address: Dr. C. O. Hines, 15 Henry Street, Toronto, ON M5T 1W9, Canada. E-mail: hines@stpl.cress.yorku.ca JANUARY 2005 N O T E S A N D C O R R E S P O N D E N C E 251

HST Observations of 3 More Old LMC Clusters

We present color-magnitude diagrams (CMDs) based on HST F555W (“V”) and F814W (“I”) observations of three old LMC clusters: NGC 2210, NGC 1786, and Reticulum. The fiducial derived from the CMD of NGC 2257, another LMC cluster, provided a good fit to the data for the new clusters. Because NGC 2257 has a similar metallicity ([Fe/H]∼ −1.8) to NGC 2210, NGC 1786, and Reticulum, the agreement between the CMDs of all four clusters indicates that they have the same age. This preliminary analysis suggests that any age differences are smaller than 2 Gyr. These new results mean that there are now 11 old LMC clusters with similar ages. An initial epoch of star cluster formation therefore happened in a short period over a large volume of space, a volume much larger than is now covered by the present-day optical LMC.

Ionospheric effects of the solar eclipse of March 9, 1997, as deduced from data from the GPS-radio interferometer at Irkutsk

This paper presents data from first measurements of total electron content (TEC) and its gradient variations during the solar eclipse of March 9, 1997, obtained with the GPS-radio interferometer at Irkutsk. The interferometer consists of three receivers located at the vertices of a triangle and spaced by about 3–5 km. The measured TEC variations are indicative of profound changes in the ion production process in the ionosphere attendant on the solar eclipse, simultaneously in a large volume of space with a radius of 400 km at 300 km altitude. The delay of a minimum value of TEC with respect to the maximum phase of eclipse at 300 km altitude was about 10 min, and the depression depth of TEC growth varies from 1÷3×1016 m−2. By analyzing the data on TEC gradient variations, one is led to conclude that the depression of TEC growth during the eclipse is essentially independent of the longitude and of the latitude (within the observation ranges 52±6° N and 104±11° E).

The Ages of the Globular Clusters in the Fornax Dwarf Galaxy

From observations with the Hubble Space Telescope, color-magnitude diagrams (CMDs) have been constructed for the four most metal-poor globular clusters in the Fornax dSph galaxy. These diagrams confirm that cluster 1 has a redder horizontal-branch (HB) morphology than the other three clusters despite its similarity in metallicity (the second parameter effect). The near coincidence of the fiducial lines of the CMDs indicates that the ages of the Fornax clusters are identical to within 1 Gyr. Since a larger range is predicted if age is the second parameter, we conclude that either the sensitivity of the HB to age has been underestimated or some parameter besides age is acting as a second parameter. The Fornax clusters exhibit a correlation between HB morphology and central density that is similar to the one among galactic globular clusters, which suggests that some mechanism related to density is influencing HB morphology. No significant differences in age have been found between the Fornax clusters and the metal-poor galactic globular clusters M68 and M92, which suggests that cluster formation began nearly simultaneously over a large volume of space.

Ionospheric effects of the solar eclipse of March 9, 1997, as deduced from GPS data

This paper presents data from first measurements of total electron content (TEC) and its gradient during the solar eclipse of March 9, 1997, obtained with the GPS‐radio interferometer at Irkutsk. The interferometer consists of three receivers (one Turbo‐Rogue SNR‐8000, and two Ashtech Z‐12) located at the vertices of a triangle and spaced by about 3–5 km. The measured TEC variations are indicative of profound changes in the ion production process in the ionosphere attendant on the solar eclipse, simultaneously in a large volume of space with a radius of at height 300 km at 300 km altitude. The delay of a minimum value of TEC with respect to the maximum phase of eclipse at 300 km altitude was about 10 min, and the depression depth of TEC growth varies from l÷3×1016m−2. By analyzing the data on TEC gradient variations, one is led to conclude that the depression of TEC growth during the eclipse is essentially independent of the longitude and of the latitude (within the observation ranges 52±6° N and 104±11° E).