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2022 ◽  
Vol 12 (1) ◽  
pp. 1-26
Author(s):  
V. S. R. Annapareddy ◽  
T. Bore ◽  
M. Bajodek ◽  
A. Scheuermann

This letter proposes semi-analytical methods to obtain the local permeability for granular soils based on indirect measurements of the local porosity profile in a large coaxial cell permeameter using spatial time domain reflectometry. The porosity profile is used to obtain the local permeability using the modified Kozeny-Carman and Katz-Thompson equations, which incorporated an effective particle diameter that accounted for particle migration within the permeameter. The profiles of the local permeability obtained from the proposed methods are compared with experimentally obtained permeability distributions using pressure measurements and flow rate. The permeabilities obtained with the proposed methods are comparable with the experimentally obtained permeabilities and are within one order of magnitude deviation, which is an acceptable range for practical applications.


Atmosphere ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 141
Author(s):  
Yan Yang ◽  
Wei Zhou ◽  
Qian Gao ◽  
Delong Zhao ◽  
Xiange Liu ◽  
...  

Many studies have shown that air pollutants have complex impacts on urban precipitation. Meteorological weather station and satellite Aerosol Optical Depth (AOD) product data from the last 20 years, combined with simulation results from the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), this paper focuses on the effects of air pollutants on summer precipitation in different regions of Beijing. These results showed that air pollution intensity during the summer affected the precipitation contribution rate (PCR) of plains and mountainous regions in the Beijing area, especially in the plains. Over the past 20 years, plains PCR increased by ~10% when the AOD augmented by 0.15, whereas it decreased with lower pollution levels. In contrast, PCR in mountainous areas decreased with higher pollution levels and increased with lower pollution levels. Our analysis from model results indicated that aerosol increases reduce the effective particle size of cloud droplets and raindrops. Smaller cloud raindrops more readily transport to high air layers and participate in the generation of ice-phase substances in the clouds, increasing the total amount of cloud water in the air in a certain time, which ultimately enhanced precipitation intensity on the plains. The removal of pollutants caused by increased precipitation in the plains decreased rainfall levels in mountainous areas.


2022 ◽  
Author(s):  
Thierry Kremeyer ◽  
Ralf König ◽  
Sebastijan Brezinsek ◽  
Oliver Schmitz ◽  
Yuhe Feng ◽  
...  

Abstract A single-reservoir particle balance for the main plasma species hydrogen has been established for Wendelstein 7-X (W7-X). This has enabled the quantitative characterization of the particle sources in the standard island divertor configuration for the first time. Findings from attached scenarios with two different island sizes with a boronized wall and turbo molecular pumping are presented. Fueling efficiencies, particle flows and source locations were measured and used to infer the total particle confinement time $\tau_{\rm{p}}$. Perturbative gas injection experiments served to measure the effective particle confinement time $\tau_{\rm{p}}^*$. Combining both confinement times provides access to the global recycling coefficient $\bar{R}$. Hydrogen particle inventories have been addressed and the knowledge of particle sources and sinks reveals the core fueling distribution and provides insight into the capability of the magnetic islands to control exhaust features. Measurements of hydrogen fueling efficiencies were sensitive to the precise fueling location and measured between 12~\% and 31~\% with the recycling fueling at the strike line modeled at only 6~\%, due to much higher densities. 15~\% of the total \SI{5.2E+22}{a/s} recycling flow ionizes far away from the recycling surfaces in the main chamber. It was shown that 60~\% of recycled particles ionize above the horizontal and 18~\% above the vertical divertor target, while the remainder of the recycling flow ionizes above the baffle (7~\%). Combining these source terms with their individual fueling efficiencies resolves the core fueling distribution. Due to the higher fueling efficiency in the main chamber, up to 51~\% of the total \SI{5.1E+21}{1/s} core fueling particles are entering the confined plasma from the main chamber. $\tau_{\rm{p}}$ values in the range of 260 ms were extracted for these discharges. Together with $\tau_{\rm{p}}$, the global recycling coefficient $\bar{R}$ was resolved for every $\tau_{\rm{p}}^*$ measurement and a typical value close to unity was obtained. An increase of the island size, resulted in no change of $\tau_{\rm{p}}$, but doubled $\tau_{\rm{p}}^*$, indicating the feasibility of the control coils as an actuator to control exhaust features without affecting core confinement properties.


Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1173
Author(s):  
John Falk ◽  
Kimmo Korhonen ◽  
Vilhelm B. Malmborg ◽  
Louise Gren ◽  
Axel C. Eriksson ◽  
...  

The immersion freezing ability of soot particles has in previous studies been reported in the range of low/insignificant to very high. The aims of this study were to: (i) perform detailed physico-chemical characterisation of freshly produced soot particles with very different properties, (ii) investigate the immersion freezing ability of the same particles, and (iii) investigate the potential links between physico-chemical particle properties and ice-activity. A miniCAST soot generator was used to produce eight different soot samples representing a wide range of physico-chemical properties. A continuous flow diffusion chamber was used to study each sample online in immersion mode over the temperature (T) range from −41 to −32 °C, at a supersaturation of about 10% with respect to liquid water. All samples exhibited low to no heterogeneous immersion freezing. The most active sample reached ice-activated fractions (AF) of 10−3 and 10−4 at temperatures of 1.7 and 1.9 K , respectively, above the homogeneous freezing temperature. The samples were characterized online with respect to a wide range of physico-chemical properties including effective particle density, optical properties, particle surface oxidation and soot maturity. We did observe indications of increasing immersion freezing ice-activity with increasing effective particle density and increasing particulate PAH fraction. Hence, those properties, or other properties co-varying with those, could potentially enhance the immersion freezing ice-activity of the studied soot particle types. However, we found no significant correlation between the physico-chemical properties and the observed ice-nucleating ability when the particle ensemble was extended to include previously published results including more ice-active biomass combustion soot particles. We conclude that it does not appear possible in general and in any straightforward way to link observed soot particle physico-chemical properties to the ice-nucleating ability using the online instrumentation included in this study. Furthermore, our observations support that freshly produced soot particles with a wide range of physico-chemical properties have low to insignificant immersion freezing ice-nucleating ability.


2021 ◽  
pp. 137-150
Author(s):  
Ankit Tomar ◽  
Bhaskar Pant ◽  
Vikas Tripathi ◽  
Kamal Kant Verma ◽  
Saurabh Mishra

2021 ◽  
Author(s):  
Soorya Pradeep ◽  
Thomas A Zangle

Transport of mass within cells helps maintain homeostasis and is disrupted by disease and stress. Here, we develop quantitative phase velocimetry (QPV) as a label-free approach to make the invisible flow of mass within cells visible and quantifiable. We benchmark our approach against alternative image registration methods, a theoretical error model, and synthetic data. Our method tracks not just individual labeled particles or molecules, but the entire flow of material through the cell. This enables us to measure diffusivity within distinct cell compartments using a single approach, which we use here for direct comparison of nuclear and cytoplasmic diffusivity. As a label-free method, QPV can be used for long-term tracking to capture dynamics through the cell cycle. Finally, based on the known effective particle size, we show that QPV is an accessible method to measure intracellular viscosity.


2021 ◽  
Vol 81 (8) ◽  
Author(s):  
Recai Erdem ◽  
Kemal Gültekin

AbstractWe introduce a method where particle physics processes in cosmology may be calculated by the usual perturbative flat space quantum field theory through an effective Minkowski space description at small time intervals provided that the running of the effective particle masses are sufficiently slow. We discuss the necessary conditions for the applicability of this method and illustrate the method through a simple example. This method has the advantage of avoiding the effects of gravitational particle creation in the calculation of rates and cross sections i.e. giving directly the rates and the cross sections due to the scatterings or the decay processes.


2021 ◽  
Author(s):  
David Jewitt ◽  
Yoonyoung Kim ◽  
Max Mutchler ◽  
Jessica Agarwal ◽  
Jing Li ◽  
...  

<p class="p1">We discuss the development of activity in the extraordinary, distant long-period comet C/2017 K2 over the heliocentric distance range<span class="Apple-converted-space"> </span>9 < r<sub>H</sub> < 16 AU.<span class="Apple-converted-space">  C/2017 K2 is an incoming long-period comet with a period so long (~ 3 Myr) that no heat from the previous perihelion can be retained; we can be sure that the observed mass-loss is driven by the current insolation and not by a thermal lag.  </span>The comet is characterized by a steady-state coma of sub-millimeter and larger particles ejected at low (4 m/s) velocity, filling a roughly spheroidal coma with a characteristic scale of 80,000 km.<span class="Apple-converted-space">  </span>In a fixed, co-moving volume around the nucleus we find that the scattering cross-section of the coma, C, is related to the heliocentric distance by a power law, C ~ r<sub>H</sub><sup>-s</sup>, with heliocentric index s = 1.14+/-0.05. This dependence is significantly weaker than the r<sub>H</sub><sup>-2</sup>, variation of the<span class="Apple-converted-space"> </span>insolation as a result of two effects.<span class="Apple-converted-space">  </span>These are, first, the heliocentric dependence of the dust velocity and, second, a lag effect due to very slow-moving<span class="Apple-converted-space"> </span>particles ejected long before the observations were taken. <span class="Apple-converted-space">  </span>A Monte Carlo<span class="Apple-converted-space"> </span>model of the photometry shows that dust production beginning at r<sub>H</sub> ~ 35 AU is needed to match the measured heliocentric index, with only a slight dependence on the particle size distribution.<span class="Apple-converted-space">  </span>Dust mass loss rates at 10 AU are of order dM/dt ~ 10<sup>3 </sup>a<sub>1</sub> kg/s, where 0.1 < a<sub>1</sub> < 1 is the effective particle radius expressed in millimeters.</p> <p class="p1">The expulsion of submillimeter and larger grains, beginning at Kuiper belt distances, is likely the result of the sublimation of near-surface supervolatile ice (probably CO, as suggested by the recent detection of this molecule at 6.7 AU; Yang et al. Ap. J. Letters, in press). Water ice is involatile over the observed distance range and even the energy and gas release triggered by the crystallization of amorphous ice, if present, cannot produce activity at 35 AU.  Comet C/2017 K2 will reach perihelion near Mars' orbit in December 2022.  </p> <p class="p1"> </p> <p class="p1">This work is described in D. Jewitt, Y. Kim. M. Mutchler, J. Agarwal, J. Li and H. Weaver (2021).  Astronomical Journal, 161:188 (11pp) </p>


2021 ◽  
Vol 23 (3) ◽  
Author(s):  
Niklas Meyer ◽  
Robert Seifried

AbstractParticle damping is a promising damping technique for a variety of technical applications. However, their non-linear behavior and multitude of influence parameters, hinder currently its wide practical use. So far, most researchers focus either on determining the energy dissipation inside the damper or on the overall damping behavior when coupled to a structure. Indeed, currently almost no knowledge exchange between both approaches occurs. Here, a bridge is build to combine both techniques for systems under forced vibrations by coupling the energy dissipation field and effective particle mass field of a particle damper with a reduced model of a vibrating structure. Thus, the overall damping of the structure is estimated very quickly. This combination of both techniques is essential for an overall efficient dimensioning process and also provides a deeper understanding of the dynamical processes. The accuracy of the proposed coupling method is demonstrated via a simple application example. Hereby, the energy dissipation and effective mass of the particle damper are analyzed for a large excitation range first using a shaker setup. The particle damper exhibits multiple areas of different efficiency. The underlying structure is modeled using FEM and modal reduction techniques. By coupling both parts it is shown that multiple eigenmodes of the structure are highly damped using the particle damper. The damping prediction using the developed coupling procedure is validated via experiments of the overall structure with particle damper.


2021 ◽  
Author(s):  
Prakash Tamboli

The paper presents an effective particle filtering using the Ensemble Kalman Filter based proposal density to improve the computational efficiency


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