5,852 research outputs found

    Multiphase gas in the circumgalactic medium: relative role of tcool/tfft_{\rm cool}/t_{\rm ff} and density fluctuations

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    We perform a suite of simulations with realistic gravity and thermal balance in shells to quantify the role of the ratio of cooling time to the free-fall time (tcool/tfft_{\rm cool}/t_{\rm ff}) and the amplitude of density perturbations (δρ/ρ\delta \rho/\rho) in the production of multiphase gas in the circumgalactic medium (CGM). Previous idealized simulations, focussing on small amplitude perturbations in the intracluster medium (ICM), found that cold gas can condense out of the hot ICM in global thermal balance when the background tcool/tff10t_{\rm cool}/t_{\rm ff} \lesssim 10. Recent observations suggest the presence of cold gas even when the background profiles have somewhat large values of tcool/tff{t_{\rm cool}/t_{\rm ff}}. This partly motivates a better understanding of additional factors such as large density perturbations that can enhance the propensity for cooling and condensation even when the background tcool/tff{t_{\rm cool}/t_{\rm ff}} is high. Such large density contrasts can be seeded by galaxy wakes or dense cosmological filaments. From our simulations, we introduce a condensation curve in the (δρ/ρ)(\delta \rho/\rho) - min(tcool/tff)(t_{\rm cool}/t_{\rm ff}) space, that defines the threshold for condensation of multiphase gas in the CGM. We show that this condensation curve corresponds to (tcool/tff)blob10{(t_{\rm cool}/t_{\rm ff})}_{\rm blob} \lesssim 10 applied to the overdense blob instead of the background for which tcool/tfft_{\rm cool}/t_{\rm ff} can be higher. We also study the modification in the condensation curve by varying entropy stratification. Steeper (positive) entropy gradients shift the condensation curve to higher amplitudes of perturbations (i.e., make condensation difficult). A constant entropy core, applicable to the CGM in smaller halos, shows condensation over a larger range of radii as compared to the steeper entropy profiles in the ICM.Comment: 17 pages, 14 figures, 2 tables, the version accepted in MNRA

    Liquid gating elastomeric porous system with dynamically controllable gas/liquid transport

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    【Abstract】The development of membrane technology is central to fields ranging from resource harvesting to medicine, but the existing designs are unable to handle the complex sorting of multiphase substances required for many systems. Especially, the dynamic multiphase transport and separation under a steady-state applied pressure have great benefits for membrane science, but have not been realized at present. Moreover, the incorporation of precisely dynamic control with avoidance of contamination of membranes remains elusive. We show a versatile strategy for creating elastomeric microporous membrane-based systems that can finely control and dynamically modulate the sorting of a wide range of gasesandliquids underasteady-stateapplied pressure,nearlyeliminate fouling,and can be easily applied over many size scales, pressures, and environments. Experiments and theoretical calculation demonstrate the stability of our system and the tunability of the critical pressure. Dynamic transport of gas and liquid can be achieved through our gating interfacial design and the controllable pores’ deformation without changing the applied pressure. Therefore, we believe that this system will bring new opportunities for many applications, such as gas-involved chemical reactions, fuel cells, multiphase separation, multiphase flow, multiphase microreactors, colloidal particle synthesis, and sizing nano/microparticles.This work was supported by the National Natural Science Foundation of China (grant no. 21673197), the Young Overseas High-level Talents Introduction Plan, the 111 Project (grant no. B16029). 研究工作得到国家自然科学基金委(项目批准号:21673197)和厦门大学校长基金(项目批准号:20720170050)等资助与支持

    The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

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    The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future

    Multiphase Stirred Tank Bioreactors – New Geometrical Concepts and Scale‐up Approaches

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    Mainly with respect to biotechnological cases, current developments in the field of impeller geometries and findings for multistage configurations with a specific view on aerated stirred tanks are reviewed. Although often the first choice, in the given case the 6‐straight blade disc turbine is usually not the best option. Furthermore, quantities usable for scale‐up, specifically applicable in this field are discussed. Only quantities taking local conditions into account appear to be able to actually compare different stirrer types and scales.DFG, 56091768, TRR 63: Integrierte chemische Prozesse in flüssigen MehrphasensystemenDFG, 315464571, Interaktion der mechanischen Beanspruchung und der Produktivität von biologischen Agglomeraten in RührfermenternDFG, 256647858, Stoffübergang von aufsteigenden Blasen in reagierenden FlüssigphasenTU Berlin, Open-Access-Mittel - 201

    Petrophysical and rock physics analyses for characterization of complex sands in deepwater Niger delta, Nigeria

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    Characterization of complex sand reservoirs in deepwater of Niger Delta was carried out through petrophysical and rock physics evaluation of well log data from three wells. Petrophysical analysis to determine clay volume, porosity, lithologies and hydrocarbon saturation were made. Rock physics was studied in velocity-porosity plane to analyze the influence of depositional and diagenetic features on the reservoirs. Cross-plots of different elastic parameters, using linear regression and cluster analysis, were generated for lithologic and fluid fill identification and to differentiate between the hydrocarbon bearing sands, brine sands and shale. Variance attribute was extracted on seismic time slice in order to image the complex sand distribution in the area. Three reservoirs of turbidite origin were identified within the upper fan to lower fan area. Petrophysical results revealed gas bearing reservoir units with less than 20% shale volume and porosity of 25-31%. Lambda-Mu-Rho (LMR) cross-plots for the reservoirs show gas saturated data cloud and trend. Ratio-Difference (R-D) cluster analysis of elastic rock properties shows a distinct trend and data cloud that represents lithofacies units and fluid fills. The study concludes that the reservoirs simulated contact cement and friable models with properties that ranged from highly porous, well sorted and poorly consolidated sand to fairly sorted and highly cemented sands. The results provide a model that increases the possibility of finding reservoir sand, while mitigating the risk involved in finding hydrocarbons
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