Density Distribution Characteristics Research Articles

Ring-shaped hollow multi-Gaussian schell-model array beams

We introduced a new kind of partially coherent beam source which can produce the far field with ring-shaped hollow array profile, and the distribution characteristics of the far-zone spectral density generated by such beam source are investigated in detail. It is shown that the characteristics of the far-zone spectral density, including the size of the hollow of the each lobe, the distance of the adjacent lobes, the orientation of the each lobe, and the number of the lobes, can be effectively manipulated by adjusting the corresponding parameters of the beam source.

Study on the plasma spatial distribution characteristics of laser-induced breakdown on the oil-water interface

The technology of oil-water separation is very important for the improvement of water resources and environment. The detection of oil-water interface characteristics is one of the key requirements of the technology. In this paper, the laser plasma spectroscopy is used to detect the oil-water interface, and the theoretical research and verification are carried out. The spatial distribution characteristics of plasma electron temperature and electron density are experimentally studied. The semi-ellipsoid model of laser plasma spatial distribution is proposed, combined with the laser focusing characteristic. The position of oil-water interface was determined by the laser-induced plasma spectroscopy based on the difference of element luminescent characteristics. According to the relationship between the intensity of spectral lines and the concentration of elements, the relationship between the intensity of characteristic spectral lines and the number of elements is obtained based on the semi-ellipsoid model. Furthermore, the relationship between the intensity ratio of characteristic elements and the thickness of the oil film is studied, and the spectral measurement of oil layers with different thickness is realized. In this paper, the law of the self-absorption effect of C and H elements with the thickness of the oil film is analyzed, and the rationality of the direct judgment of oil film thickness by the relative strength ratio of the characteristic elements of the detection spectrum signal is verified. According to the intensity ratio of spectral lines, the scatter distribution of oil thickness, and the simulation curve, the variation rule of experimental error with oil thickness are obtained. The relative error is less than 20%, which also verifies the reliability of the method.

Ring-shaped twisted Gaussian Schell-model array beams.

A new partially coherent source which can generate a beam field with a ring-shaped twisted array profile is presented, and the distribution characteristics of spectral density and degree of coherence of the field are discussed. It is shown that both the spectral density and degree of coherence will rotate along the propagating direction, but in opposite rotating directions. Furthermore, we find that the distribution properties of the ring-shaped array of the spectral density, including the number of the rings, the number of the lobes of each ring, and the distance of all adjacent lobes, can be properly controlled by adjusting structural parameters of the source.

Density distribution characteristics of fluid inside vortex in supersonic mixing layer

Based on the large eddy simulation, the boundary of a vortex and the coordinates of its core are both obtained by using the Lagrangian coherent structure method and the location extraction method of the vortex core, and thus the method of representing fluid density inside a vortex is proposed. The density distribution characteristics of fluid inside the vortex in a supersonic mixing layer are revealed by analyzing the changes in density of the fluid inside a vortex under different conditions (e.g. spatial size of the vortex, compressibility of the supersonic mixing layer, and merging process of the two paired vortices) as follows. For the weak and medium compressive supersonic mixing layers, the density distribution of the fluid inside a vortex is symmetrical about both the flow direction (<i>x</i>-axis) and longitudinal direction (<i>y</i>-axis), the fluid density at the vortex core is lowest while it is highest at the vortex boundary, and fluid density increases monotonically and nearly uniformly along the ray connecting the vortex core and the vortex boundary. For the strongly compressible supersonic mixing layer, however, the density distribution of the fluid inside the vortex is no longer symmetrical about any flow direction and moreover it shows the fluctuation characteristics of fluid density distribution. With the increase of the spatial size of a vortex and the compressibility of a supersonic mixing layer, the fluid density at the vortex core decreases (the maximum reduction is about 31%–56%) while it changes about 6%–27% at the vortex boundary. In the merging process of two adjacent vortices, the variation of fluid density in the two vortices is slight, which shows that the merging process is probably of a peer-to-peer combination of fluid inside the two adjacent vortices. Considering the practical engineering applications, the density distribution characteristics of fluid inside the vortex in the supersonic mixing layer with different inflow densities of its upper and lower layers are also investigated, and the results show that the density distribution of the fluid inside a vortex is symmetrical about the longitudinal direction (<i>y</i>-axis), but not the flow direction (<i>x</i>-axis). It is also found that the density distribution near the vortex boundary is determined by the inflow density there, so a good strategy of reducing the aero-optical effects caused by the supersonic mixing layer is that the difference in density between the upper and lower layers should be as small as possible.

A New Modeling Approach for the Probability Density Distribution Function of Wind power Fluctuation

With the rapid development of grid-connected wind power, analysing and describing the probability density distribution characteristics of wind power fluctuation has always been a hot and difficult problem in the wind power field. In traditional methods, a single distribution function model is used to fit the probability density distribution of wind power output fluctuation; however, the results are unsatisfying. Therefore, a new distribution function model is proposed in this work for fitting the probability density distribution to replace a single distribution function model. In form, the new model includes only four parameters which make it easier to implement. Four statistical index models are used to evaluate the distribution function fits with the measured probability data. Simulations are designed to compare the new model with the Gaussian mixture model, and results illustrate the effectiveness and advantages of the newly developed model in fitting the wind power fluctuation probability density distribution. Besides, the fireworks algorithm is adopted for determining the optimal parameters in the distribution function model. The comparison experiments of the fireworks algorithm with the particle swarm optimization (PSO) algorithm and the genetic algorithm (GA) are carried out, which shows that the fireworks algorithm has faster convergence speed and higher accuracy than the two common intelligent algorithms, so it is useful for optimizing parameters in power systems.

Biomechanical and Bone Material Properties of Schnurri-3 Null Mice.

ABSTRACT Schnurri‐3 (Shn3) is an essential regulator of postnatal skeletal remodeling. Shn3‐deficient mice (Shn3–/–) have high bone mass; however, their bone mechanical and material properties have not been investigated to date. We performed three‐point bending of femora, compression tests of L3 vertebrae. We also measured intrinsic material properties, including bone mineralization density distribution (BMDD) and osteocyte lacunae section (OLS) characteristics by quantitative backscatter electron imaging, as well as collagen cross‐linking by Fourier transform infrared microspectroscopy of femora from Shn3–/– and WT mice at different ages (6 weeks, 4 months, and 18 months). Moreover, computer modeling was performed for the interpretation of the BMDD outcomes. Femora and L3 vertebrae from Shn3–/– aged 6 weeks revealed increased ultimate force (2.2‐ and 3.2‐fold, p < .01, respectively). Mineralized bone volume at the distal femoral metaphysis was about twofold (at 6 weeks) to eightfold (at 4 and 18 months of age) in Shn3–/– (p < .001). Compared with WT, the average degree of trabecular bone mineralization was similar at 6 weeks, but increased at 4 and 18 months of age (+12.6% and +7.7%, p < .01, respectively) in Shn3–/–. The analysis of OLS characteristics revealed a higher OLS area for Shn3–/– versus WT at all ages (+16%, +23%, +21%, respectively, p < .01). The collagen cross‐link ratio was similar between groups. We conclude that femora and vertebrae from Shn3–/– had higher ultimate force in mechanical testing. Computer modeling demonstrated that in cases of highly increased bone volume, the average degree of bone matrix mineralization can be higher than in WT bone, which was actually measured in the older Shn3–/– groups. The area of 2D osteocyte lacunae sections was also increased in Shn3‐deficiency, which could only partly be explained by larger remnant areas of primary cortical bone. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Non-Gaussian Features of Local Wind Pressure for Typical Gable Roof of Low-rise Building

The non-Gaussian characteristics of local wind pressure of typical gable roof of low-rise building with a slop angle of 18.4° were monitored by means of the wind tunnel test under terrain roughness regimes of A,B and C. The probability density distribution features of wind pressure coefficient series are investigated, the characteristics of non-Gaussian zones distribution of wind pressure relative to different wind angles and different terrain conditions are analyzed and the relationships between non-Gaussian pressure and distinctions of flow field on roof are discussed. The studying results indicate that GEV distribution and Gamma distribution fit the probability density distribution of wind pressure coefficient better than Gaussian distribution and Lognormal distribution, but the fitting effect for long trailing tail part is undesirable, when skewness and kurtosis are large in magnitude (absolute value). The variation of terrain roughness and wind directions have significant influence on the distribution of non-Gaussian pressure regions on low-rise building roof. Under the oblique wind direction, the Gaussian pressure zone is divided into three sections along the approaching wind direction, along which the areas move with the change of terrain roughness regimes. The non-Gaussian features of wind pressure is positively related to mutual correlation coefficient of it’s time-history.

Influence of Volumetric Damage Parameters on Patch Antenna Sensor-Based Damage Detection of Metallic Structure.

Antenna sensors have been employed for crack monitoring of metallic materials. Existing studies have mainly focused on the mathematical relationship between the surface crack length of metallic material and the resonant frequency. The influence of the crack depth on the sensor output and the difference of whether the crack is depth-penetrated remains unexplored. Therefore, in this work, a numerical simulation method was used to investigate the current density distribution characteristics of the ground plane (metallic material) with different crack geometric parameters. The data reveals that, compared with the crack length, the crack depth has a greater influence on the resonant frequency. The relationship between the frequency and the crack geometric parameters was discussed by characterizing the current density and sensor output under different crack lengths and depths. Therefore, the feasibility of monitoring another common damage of metallic materials, i.e., corrosion pit, was explored. Furthermore, the influences of crack and corrosion pit geometric parameters on the output results were validated by experiments.

Probability distribution characteristics of stock density in offshore of northern South China Sea.

Based on catch data from the bottom trawl survey by eight cruises in offshore of northern South China Sea during 2014-2017, we analyzed the stock density distribution and explored its probability distribution with statistical method, which was further used to estimate the mean stock density in this region. The results showed that the coefficient of variation (CV) for stock density ranged from 0.67 to 1.03 for all the periods, indicating a highly uneven spatial distribution of stock density. The frequency distribution of fishery resource density was characterized by obvious right-skewed, which was dominated by stock density of 0-1000 kg·km-2. The results of one sample Kolmogorov-Smirnov test indicated that three probability distribution patterns were suitable for stock density in this region, including Lognormal, Gamma and Weibull distributions. In terms of the mean stock density estimation, the values from Lognormal showed no statistically significant difference from those from others, but the opposite result was obtained between Gamma and Weibull distributions. Compared with 1960s-1970s, the appropriate probability distribution pattern of stock density has changed from single to multiple types. Variation of the proportion of low catch resulted from the changes in the structure of fishery resources, fishing effort and climate change might cause the alte-ration of probability distribution.

Experimental investigation of wind-induced internal pressures in nominally sealed building structures

The action of internal pressure cannot be neglected in wind-resistant design of large-span structures, high-rise buildings, and low-rise residential buildings. In this study, the internal pressure characteristics were first measured in still air in a completely closed building structure without any leakage. Then a series of wind tunnel tests were conducted to study the probability density distribution characteristics of the internal pressure responses in a nominally sealed building with background leakage. The mean and peak internal pressure responses associated with different background leakage distributions and wind directions were further investigated, and the experimental results were compared with those suggested by the Chinese wind load code GB50009-2012. The results indicated that the internal pressure in the completely closed building was non-stationary, and varied significantly when collected at different time points. Furthermore, a period of about 24 h was observed from the measured time history of internal pressure over 9 d. The internal pressure in a nominally sealed building structure nearly fitted a normal Gaussian distribution. When background leakage was uniformly arranged on the surface of the building, the mean internal pressure coefficient remained unchanged with increasing background leakage, varying within the range from −0.15 to −0.14, indicating lower magnitudes than the value of −0.2 suggested by the Chinese wind load code. The minimum negative peak internal pressure coefficient was −0.255 when the peak factor was 3.5, indicating a lower magnitude than the value of −0.326 calculated in the Chinese wind load code.

Study on Distribution Characteristics of Key Target Personnel Density and Earthquake Rescue Strategy

The first priority after a catastrophic earthquake is to carry out emergency rescue for people buried in collapsed buildings. Some large public buildings often have a high concentration of personnel and are the key targets for emergency rescue during earthquakes. This paper summarized four survey methods for the indoor personnel density of key buildings, carried out a sampling survey on indoor personnel density in different time periods in some schools, hospitals, shopping malls, and cinemas in Yanjiao District of Sanhe City in China using these methods, investigated the changing raw of the personnel density in these key target buildings within a period of one day and the changing characteristics of the personnel density in working days and holidays, compared the differences in the time distribution of the personnel density among different types of key targets, and initially explored the strategies and attention points of rescue for indoor personnel in different key targets at different original times of earthquake, thus providing reference for rescue decision-making of indoor personnel in key buildings in the event of a sudden disaster.

A threshold voltage definition for modeling asymmetric dual-gate amorphous InGaZnO thin-film transistors with parameter extraction technique

A physical definition of threshold voltage has been proposed for asymmetric dual-gate amorphous InGaZnO (a-IGZO) thin-film transistors. Based on the definition, a compact model for drain current has been derived with complete parameter extraction methods. According to the distribution characteristics of density of states (DOS) in the a-IGZO bandgap, the threshold voltage of bottom-gate (BG)-driven devices is defined by the ratio of the trapped-carrier density to the free-carrier density at the bottom surface of the channel layer. This definition has proven to give appropriate values of threshold voltage for devices with DOS parameters varying in a wide range. The trapped-charge density in the above-threshold region can be expressed based on the defined threshold voltage, with the form related to the BG voltage, the top-gate voltage, and the potential along the channel. The free-charge density and analytical drain current can thus be obtained in the above-threshold region. Finally, the continuous drain current expression is developed covering all operation regions. In the modeling process, the determination and extraction strategies for parameters are also presented.

Physical properties of niobium-based intermetallics (Nb3B; B = Os, Pt, Au): a DFT-based ab-initio study

Structural, elastic and electronic band structure properties of A-15 type Nb-based intermetallic compounds Nb3B (B = Os, Pt, Au) have been revisited using first principles calculations based on the density functional theory (DFT). All these show excellent agreement with previous reports. More importantly, electronic bonding, charge density distribution and Fermi surface features have been studied in detail for the first time. Vickers hardness of these compounds is also calculated. The Fermi surfaces of Nb3B contain both hole- and electron-like sheets, the features of which change systematically as one move from Os to Au. The electronic charge density distribution implies that Nb3Os, Nb3Pt and Nb3Au have a mixture of ionic and covalent bondings with a substantial metallic contribution. The charge transfer between the atomic species in these compounds has been explained via the Mulliken bond population analysis and the Hirshfeld population analysis. The bonding properties show a good correspondence to the electronic band structure derived electronic density of states (DOS) near the Fermi level. Debye temperature of Nb3B (B = Os, Pt, Au) has been estimated from the elastic constants and shows a systematic behavior as a function of the B atomic species. A good correspondence among the elastic, electronic and charge density distribution properties are found. The superconducting transition temperature is found to be dominated by the electronic density of states at the Fermi level. We have discussed possible implications of the results obtained in this study in details in this paper.

ROVvstrawling approaches in the study of benthic communities: the case ofPennatula rubra(Cnidaria: Pennatulacea)

Megabenthic soft bottom communities of trawlable grounds have been studied since the first few decades of the last century, thanks to trawl fishing technologies. Despite providing an extensive amount of presence data, trawling cannot be considered reliable from a quantitative point of view, frequently giving only weak information about sessile species density, large and small-scale distribution and main habitat features. The recent development of visual technologies on remotely operated vehicles (ROVs) can give a more accurate approach for the study of mega-epibenthic communities. The present study reports the application of both ROV imaging and trawling approaches for the study of a large aggregation (i.e. field) of the red sea penPennatula rubrain the Ionian Sea. Density, biomass and population structure were studied in the same population ofP. rubra. The density assessed by ROV was significantly higher than that estimated with a three-year series of trawling surveys. Trawling gear efficiency in the removal ofP. rubrawas low overall. Incidental mortality can be very high due to damage to those specimens that encounter the trawl net but are not directly captured. However, sampling of several colonies by trawling was necessary to establish biometric correlations to estimates of size and biomass from ROV imaging. Trawling catch abundance/biomass data could be useful to identify areas of higher concentration of sea pens, while ROV imaging can be used to monitor these fields in a non-destructive manner that would be consistent with protection measures.

Failure Mechanism of a Low-Energy-Triggered Bulk Gallium Arsenide Avalanche Semiconductor Switch: Simulated Analysis and Experimental Results

The failure mechanism is discussed numerically and experimentally in a low-energy-triggered bulk gallium arsenide avalanche semiconductor switch with ultrafast switching. The characteristics of current density distribution along contacts are investigated, and the density at the contact neighboring the active region is found to be higher than that of the average of the structure. In particular, the peak amplitude of the current density by cathode triggering is higher than that by anode triggering. The ultrahigh current density first damages the contacting metal neighboring the active region, and the switch is vulnerable to degrade by cathode triggering. Longevity improvement was achieved experimentally in the anode-triggered switches in contrast with cathode-triggered switches, which validates the deduction of numerical analysis.

Ono-Kondo lattice model for propane multilayer adsorption in organic nanopores in relation to shale gas

Accurate characterization of shale gas adsorption capacity is of great importance to the gas-in-place estimation and prediction of well productivity. Propane is one of major constituents in shale gases which can have multilayer adsorption behavior on pore surfaces. While experiments can measure excess adsorption, the absolute adsorption, which describes adsorbed gas capacity, has to be converted from the excess adsorption. In previous works, absolute adsorption is usually calculated from excess adsorption with adsorbed phase volume or density based on the single-layer adsorption model. However, for heavier alkanes, such as ethane and propane, which can have multilayer adsorption behavior, single-layer adsorption model becomes invalid. While molecular simulation can characterize the multilayer adsorption behavior, it comes with expensive computational costs. Currently, there is no viable model to characterize the absolute adsorption of hydrocarbons which can have multilayer adsorption behavior. In this work, we conduct grand canonical Monte Carlo (GCMC) simulation to study propane adsorption in shale nanopores over a wide range of pressures at temperature higher than the critical temperature. We find that propane can form multiple adsorption layers, thus, using single-layer adsorption model to obtain the absolute adsorption becomes unjustifiable. Based on the propane density distribution characteristics, we propose a multilayer adsorption model and use Ono-Kondo (OK) lattice model with multilayer structures to regress propane excess adsorption and subsequently obtain the absolute adsorption in each layer. For propane, we take into account the correlation effect arising from strong adsorbate–adsorbate interactions beyond mean field theory (MFT) and the only predetermined parameters are number of layers and adsorption layer width. The proposed OK model shows an excellent agreement with GCMC simulations on the excess adsorption and absolute adsorption in each layer, with discrepancies less than 6% above 50 bar. The proposed OK model can readily take into account the propane multilayer adsorption behavior, while significantly reducing calculation time. Our method presents a reliable and highly-efficient approach for accurate characterization of adsorption of hydrocarbons with multilayer structures and provide important insights into the gas-in-place estimation in shale.

A nonlinear magneto-mechanical-thermal-electric coupling model of Terfenol-D/PZT/Terfenol-D and Ni/PZT/Ni laminates

A nonlinear magneto-mechanical-thermo-electric coupling finite element model is established for the Terfenol-D/PZT and Ni/PZT laminates structure respectively, based on Maxwell electromagnetic equations and nonlinear constitutive equations of giant magnetostrictive materials. The magnetoelectric (ME) coefficients of the two laminates with considering the coupling stress or without considering the coupling stress are calculated respectively. The results indicate that the predicted values of ME coefficient of our model are very well in agreement with the experimental datas both in the low, intermediate and high magnetic field for the two kinds of materials structures at different temperatures (most of previous theoretical models just give the well comparison in low and intermediate field). The coupling stress has a significant effect on the ME coefficient for the Terfenol-D/PZT laminate, but little effect for the Ni/PZT laminate. The ME coefficient with considering coupling stress is smaller than that without considering coupling stress. Besides, the magnetic flux density, displacement and voltage distribution characteristics of ME laminates at different temperatures and pre-stresses are also detailed investigated. It has been shown a noteworthy phenomenon that the sensitivity of ME effect on temperature and/or pre-stress can be tuned by the pre-stress and/or temperature, respectively. Adjusting pre-stress can reduce the sensitivity of ME effect on temperature, which may promote the stability of ME devices operating in complex environments.

Distribution characteristics and factors influencing the ecosystem in western Hubei

Western Hubei is the most concentrated area of forest resources in Hubei Province, and the knowledge of the distribution characteristics of ecosystem carbon density is important to understand the regional characteristics of carbon density and its mechanism of formation. Carbon density and factors influencing different layers in the ecosystem were studied by using field data. The average carbon density of ecosystems in western Hubei was 159.05t/hm2; the carbon density of different forest types in descending order was Abies fargesii forests (362.25t/hm2), mixed broadleaf-conifer forests (154.13t/hm2), broad-leaved forests (146.09t/hm2), and coniferous forests (135.76t/hm2), and ecosystem carbon density increased with increasing age. The carbon density of the arborous layer, shrub layer, and soil layer of A. fargesii forests was significant higher than that of the other forests (P<0.05), indicating the carbon storage per unit area of A. fargesii forests, which grow at higher elevations, was the greatest. The carbon density in arborous layers of broad-leaved forests, mixed broadleaf-conifer forests, and coniferous forests was 39.29t/hm2, 48.99t/hm2, and 48.39t/hm2, respectively. Those of the soil layer were 102.96t/hm2, 100.97t/hm2, and 82.37t/hm2, respectively, and there were no significant differences among them. Among the three forest types, carbon density in the litter layer was greater than that of the shrub layer, which indicated the litter layer plays an important role in carbon storage. The carbon density of mixed broadleaf-conifer forests was greatest, excluding A. fargesii forests, in medium (58.71t/hm2) and mature forests (79.66t/hm2). Thus, the carbon sink of mixed broadleaf-conifer forests had more potential than the others at the medium and mature forest stage. The soil layer carbon density in different forests constituted 60.67—70.48% of the entire ecosystem, and was 1.70—2.62 times greater than that of the arborous layer. There are many factors influencing ecosystem carbon density, which result from the interaction of environmental and topographical factors. The main explanatory variables of carbon density of the region were altitude, precipitation, and canopy density. The vegetation and soil layer carbon density increased as altitude increased, and the rate of change for every vertical 100m was 1.3t/hm2 and 1.9t/hm2, respectively (P<0.05). Although the annual average precipitation only affected the carbon density of the vegetation, it increased to 4t/hm2 (P<0.01) when average precipitation was >100mm.

The Correlation Analysis of Henan Population Distribution Evolution and Terrain Characteristics

Aiming at the relationship between population distribution evolution and terrain characteristics, based on 30m × 30m DEM and 1km2×1km2 population density raster data, and using spatial analysis methods, this paper studies the evolution characteristics of the population spatial distribution, the population vertical distribution and the population slope distribution in Henan province from 1995 to 2015. The results show that, there are significant imbalances in the population development in the province, the population aggregation in urban built-up area is very obvious. The gradually decreasing regions with the density of 500-1000 person/km2 are still the main density distribution characteristics of the province's population. With the rapid increase of population, many people are migrating out from complex terrain. With rapid urbanization, major cities in the province have attracted a large number of immigrants. Excluding the natural population growth factors, the relative growth rate of population is inversely proportional to elevation and slope, there are a lot of people above 6°slope migrating out.

On the evaluation of dislocation densities in pure tantalum from EBSD orientation data

We analyze measurements of dislocation densities carried out independently by several teams using three different methods on orientation maps obtained by Electron Back Scattered Diffraction on commercially pure tantalum samples in three different microstructural states. The characteristic aspects of these three methods: the Kernel average method, the Dillamore method and the determination of the lattice curvature-induced Nye’s tensor component fields are reviewed and their results are compared. One of the main features of the uncovered dislocation density distributions is their strong heterogeneity over the analyzed samples. Fluctuations in the dislocation densities, amounting to several times their base level and scaling as power-laws of their spatial frequency are observed along grain boundaries, and to a lesser degree along sub-grain boundaries. As a result of such scale invariance, defining an average dislocation density over a representative volume element is hardly possible, which leads to questioning the pertinence of such a notion. Field methods allowing to map the dislocation density distributions over the samples therefore appear to be mandatory.