Expansion Of Cloud Research Articles

Antiparticle cloud temperatures for antihydrogen experiments

A simple rate-equation description of the heating and cooling of antiparticle clouds under conditions typical of those found in antihydrogen formation experiments is developed and analyzed. We include single-particle collisional, radiative, and cloud expansion effects and, from the modeling calculations, identify typical cooling phenomena and trends and relate these to the underlying physics. Some general rules of thumb of use to experimenters are derived.

The development of a new model to simulate the dispersion of rocket exhaust clouds

This study presents the development of a new model named MSRED, which was designed to simulate the formation, rise, expansion, stabilisation and dispersion of rocket exhaust clouds for short-range assessment, using a three-dimensional semi-analytical solution of the advection–diffusion equation based on the ADMM method. For long-range modelling, the MSRED was built to generate a ready-to-use initial conditions file to be input to the CMAQ model, as it represents the state-of-the-art in regional and chemical transport air quality modelling. Simulations and analysis were carried out in order to evaluate the application of this integrated modelling system for different rocket launch cases and atmospheric conditions, for the Alcantara Launching Center (ALC, the Brazilian gate to the space) region. This hybrid, modern and multidisciplinary system is the basis of a modelling framework that will be employed at ALC for pre- and post-launching simulations of the environmental effects of rocket operations.

Synthetic Lorentz force in an expanding cold atomic gas

We implement a synthetic Lorentz force in a cold atomic gas released from a magneto-optical trap. The signature of this is an angular deflection of a rotationally asymmetrical cloud. The effect is a consequence of thermal expansion of the cold atomic cloud under the influence of the applied synthetic Lorentz force. The synthetic Lorentz force is based on radiation pressure and the Doppler effect, making it straightforward to implement. The introduction of synthetic magnetism into our system, together with the fact that it is readily described by the Fokker–Planck equation, makes it an excellent candidate to emulate numerous complex classical systems.

Flame propagation and dust transient movement in a dust cloud explosion process

In recent years, dust explosion accidents have been reported frequently. More and more studies on dust explosions have been published. However, there are few reports concerning flame propagation and dust particle movement of a large-scale dust explosion process in open space. In this study, a large-scale corn starch dust explosion was simulated using computational fluid dynamics software. Flame propagation and particle transient movement during the explosion were monitored. The initial dust cloud, with a concentration of about 300 g m−3, is approximately an ellipsoid with a 4 m major axis (horizontal) and a 3 m minor axis (vertical); its center is at about 1.5 m distance from the ground. At the time of 700 ms when the explosion process basically finishes, the dust cloud expands to a semi ellipsoid with a 14 m major axis (vertical) and a 10 m minor axis (horizontal). The dust cloud volume expands to 366.92 m3, which is 14.60 times of its initial value (25.13 m3). During the explosion, both the flame and the dust cloud expansion are first accelerated and then decelerated, but overall, variation of dust cloud expansion velocity lags behind the variation of flame velocity. Before 400 ms, dust cloud expansion velocity is notably lower than flame velocity, then dust cloud and flame expand outwards together basically at the same speed, and the distance between dust cloud boundary and flame boundary stabilizes at around 0.5 m.

Protection properties of stuffed corrugated sandwich structures under hypervelocity impact: Numerical simulation

The stuffed corrugated sandwich structure was proposed for the application in the protection of the spacecraft against orbital debris. In order to investigate the protection properties of the stuffed corrugated sandwich structure under hypervelocity impact, numerical simulations were carried out to analyze the impact characteristics. The hypervelocity impact process was presented and the properties such as shock waves propagation, energy absorption, and expansion of the debris cloud were discussed; corresponding properties of mass equal Whipple structure under impact were analyzed for comparison. The results illustrate the protection mechanism of the stuffed corrugated sandwich subject to hypervelocity impact and show that it has superior protection performance to monolithic plate, which prove that the stuffed corrugated sandwich structure has potentially broad application prospect in the field of spacecraft protection against the orbital debris. The research can provide reference for the design of protection shield of the spacecraft.

Scheme for suppressing atom expansion induced contrast loss in atom interferometers

The loss of contrast due to atom expansion induced non-perfect Raman pulse area in atom interferometers is investigated systematically. Based on the theoretical simulation, we find that the expansion of the atomic cloud results in a decrease of the π pulse fidelity and a change of the π pulse duration, which lead to a significant reduction in fringe contrast. We propose a mitigation strategy of increasing the intensities of the second and third Raman pulses. Simulation results show that the fringe contrast can be improved by 13.6% in a typical atom interferometer gravimeter using this intensity compensation strategy. We also evaluate the effects of this mitigation strategy in the case of a lower atomic cloud temperature and a larger Raman beam size under different Raman pulse time interval conditions. This mitigation strategy has potential applications in increasing the sensitivity of atom interferometer-based precision measuring, including precision measuring of the gravity, gravity gradient, rotation, and magnetic field gradient, as well as testing of the Einstein equivalence principle.

EU Data Protection Reform: Challenges for Cloud Computing

The EC adopted a strategy to unleash the potential of cloud computing, where it marked data protection legislation as one of the main barriers for the development and expansion of cloud computing in Europe. In light of the EC goal to ensure a stimulating environment for the development of cloud computing in the EU, this paper aims to assess the consequences of the new roles and responsibilities of cloud service providers and the new rights for individuals under the GDPR. The analyses show that, in line with the position of data protection in the EU as a fundamental right, the GDPR considerably raises standards of data protection in cloud computing, which faces EU cloud service providers with a more demanding position than their non-EU competition. Further analysis shows that by promoting privacy enabling technology and by the extraterritorial application of the GDPR, together with the hefty fines for non-compliance, the GDPR provides tools that might force non-EU service providers to adjust their business model to EU standards, thus rebalancing possible market disruption in cloud computing. The paper concludes that the GDPR provides tools that might result in raised standards of data protection globally and in cloud computing in particular.

FORMING CHONDRULES IN IMPACT SPLASHES. II. VOLATILE RETENTION

ABSTRACT Solving the mystery of the origin of chondrules is one of the most elusive goals in the field of meteoritics. Recently, the idea of planet(esimal) collisions releasing splashes of lava droplets, long considered out of favor, has been reconsidered as a possible origin of chondrules by several papers. One of the main problems with this idea is the lack of quantitative and simple models that can be used to test this scenario by directly comparing to the many known observables of chondrules. In Paper I of this series, we presented a simple thermal evolution model of a spherically symmetric expanding cloud of molten lava droplets that is assumed to emerge from a collision between two planetesimals. The production of lava could be either because the two planetesimals were already in a largely molten (or almost molten) state due to heating by 26Al, or due to impact jetting at higher impact velocities. In the present paper, number II of this series, we use this model to calculate whether or not volatile elements such as Na and K will remain abundant in these droplets or whether they will get depleted due to evaporation. The high density of the droplet cloud (e.g., small distance between adjacent droplets) causes the vapor to quickly reach saturation pressure and thus shuts down further evaporation. We show to what extent, and under which conditions, this keeps the abundances of these elements high, as is seen in chondrules. We find that for most parameters of our model (cloud mass, expansion velocity, initial temperature) the volatile elements Mg, Si, and Fe remain entirely in the chondrules. The Na and K abundances inside the droplets will initially stay mostly at their initial values due to the saturation of the vapor pressure, but at some point start to drop due to the cloud expansion. However, as soon as the temperature starts to decrease, most or all of the vapor recondenses again. At the end, the Na and K elements retain most of their initial abundances, albeit occasionally somewhat reduced, depending on the parameters of the expanding cloud model. These findings appear to be qualitatively consistent with the analysis of Semarkona Type II chondrules by Hewins et al. who found evidence for sodium evaporation followed by recondensation.

The Stefan outflow in a multicomponent vapor–gas atmosphere around a droplet and its role for cloud expansion

A new comprehensive analysis of Stefan׳s flow caused by a free growing droplet in the vapor–gas atmosphere with several condensing components is presented. This analysis, based on the nonstationary heat and material balance and diffusion transport equations, shows the appearance of the Stefan inflow in the vicinity of the growing droplet and the Stefan outflow at large distances from the droplet as a consequence of nonisothermal condensation. For an ensemble of droplets in the atmospheric cloud, this outflow provides an increase of the total volume of the cloud, which can be treated as cloud thermal expansion and leads to the rise of the cloud as a whole due to increasing its buoyancy. We have formulated the self-similar solutions of the nonstationary diffusion and heat conduction equations for a growing multicomponent droplet and have derived analytical expressions for the nonstationary velocity profile of Stefan׳s flow and the expansion volume of the vapor–gas mixture around the growing droplet. To illustrate the approach, we computed these quantities in the case of droplet of stationary composition in air with several specific vapors (C2H5OH/H2O; H2SO4/H2O; H2O).

Density and velocity distribution function for freely expanding matter

For a system of noninteracting particles being initially in a spherical volume of a given radius, the density evolution and the distribution function are considered for various initial conditions. In particular, the conditions under which the density during free expansion of a sphere-shaped cloud of noninteracting particles remains spatially constant, while the boundary remains sharp, are determined. Alternative variants of free spherically symmetric expansion of a particle cloud are considered. The results of this consideration are applicable to various problems of the centrosymmetric explosion, and have astrophysical applications.

Dynamical zeroing of spin-wave momentum to suppress motional dephasing in an atomic-ensemble quantum memory

Motion-induced dephasing is a dominant decoherence mechanism for atom-gas quantum memories. In this paper, we develop a new coherent manipulation technique which enables arbitrary engineering of the spin-wave momentum with neglectable noise. By zeroing the spin-wave momentum, motion-induced dephasing can be frozen completely. We experimentally demonstrate this scheme with laser-cooled atoms in a DLCZ configuration. By applying the freezing pulses, memory lifetime gets extended significantly to the limit of atom cloud expansion and does not depend on the detection angle anymore. The observed high cross-correlation above 20 proves that high-fidelity memory operation is well preserved after coherent manipulation.

Volcanic lightning and plume behavior reveal evolving hazards during the April 2015 eruption of Calbuco volcano, Chile

AbstractSoon after the onset of an eruption, model forecasts of ash dispersal are used to mitigate the hazards to aircraft, infrastructure, and communities downwind. However, it is a significant challenge to constrain the model inputs during an evolving eruption. Here we demonstrate that volcanic lightning may be used in tandem with satellite detection to recognize and quantify changes in eruption style and intensity. Using the eruption of Calbuco volcano in southern Chile on 22 and 23 April 2015, we investigate rates of umbrella cloud expansion from satellite observations, occurrence of lightning, and mapped characteristics of the fall deposits. Our remote sensing analysis gives a total erupted volume that is within uncertainty of the mapped volume (0.56 ± 0.28 km3 bulk). Observations and volcanic plume modeling further suggest that electrical activity was enhanced both by ice formation in the ash clouds >10 km above sea level and development of a low‐level charge layer from ground‐hugging currents.

The dynamics of dense particle clouds subjected to shock waves. Part 1. Experiments and scaling laws

We quantify experimentally the dispersal characteristics of dense particle clouds in high-speed interactions with an atmosphere. Focused on the fundamentals, the experiments, conducted in a large-scale shock tube, involve a well-characterized ‘curtain’ of (falling) particles that fully occupies the cross-sectional area of the expansion section. The particle material (glass) and size (${\sim}$1 mm) are fixed, as is the curtain thickness (${\sim}$30 mm) and the particle volume fractions in it, varying from ${\sim}$58 % at the top of the curtain to ${\sim}$24 % near the bottom. Thus, the principal experimental variable is the impacting shock strength, with Mach numbers varying from 1.2 to 2.6, and flow speeds that cover from subsonic ($M_{IS}\sim 0.3$) to transonic and supersonic ($M_{IS}\sim 1.2$). The peak shock pressure ratio, 7.6, yields a flow speed of ${\sim}\!630~\text{m}~\text{s}^{-1}$, and a curtain expansion rate at ${\sim}$20 000 g. We record visually (high-speed, particle-resolving shadowgraphic method) the reflected/transmitted pressure waves and the transmitted contact wave, as well as the curtain displacements, and we measure the reflected/transmitted pressure transients. Data analysis yields simple rules for the amplitudes of the reflected pressure waves and the rapid cloud expansions observed, and we discover a time scaling that hints at a universal regime for cloud expansion. The data and these data-analysis results can provide the validation basis for numerical simulations meant to enable a deeper understanding of the key physics that drive this rather complex dispersal process.

The role of recombination in formation of charge composition of ions in a laser plasma upon mass spectrometric analysis of solids

A numerical experiment is used to study expansion of a plasma cloud with complex composition into a vacuum. Under the assumption that the density and temperature of the laser plasma are homogeneous throughout the cloud, the system of differential equations describing the plasma cloud expansion with allowance for inelastic processes is reduced to a system of ordinary differential equations for ions of five elements (Fe, Mn, Cr, Ni, Mo) with the charges z = 1, 2, 3, 4. The velocity of the plasma cloud boundary and its temperature as functions of the expansion time are determined. It is demonstrated that, after recombination stops, thermodynamically nonequilibrium plasma is created as a result of “quenching,” and in this plasma the residual degree of ionization and ion charge distribution depend on the initial plasma parameters T0, N0, and R0. In the course of recombination, the dependence of ion charge distribution on ionization potential weakens.

Perception of cloud computing in developing countries

Purpose – The purpose of this paper is to explore the perceptions of librarians engaged in Indian academic libraries towards cloud computing. Design/methodology/approach – A structured questionnaire was used to collect responses from the library professionals engaged in Indian academic libraries. Overall, 339 respondents participated in the survey. Descriptive survey method was used in the study. Findings – The findings of the study reveal that library professionals are using cloud-computing tools in their daily works. They want to adopt cloud computing in the libraries to improve library services and avoid redundancy of works. Ubiquitous availability, economy and the various service layers are the core drivers of its adoption in the libraries. The respondents showed their concern over security and data privacy in cloud. Practical implications – The study establishes the fact that the benefits of cloud computing are inadequate to convince the libraries to migrate from the traditional computing paradigm to the cloud. Technological advancement may not transform the cloud into a mainstream technology. To motivate the expansion of cloud computing adoption, emphasis has to be laid upon collaboration between the cloud service providers supplemented by solid cloud legislations which need to be worked out. Originality/value – The paper provides the perceptions of library professionals in response to the adoption of cloud computing.

Sudden expansion and domain-wall melting of strongly interacting bosons in two-dimensional optical lattices and on multileg ladders

We numerically investigate the expansion of clouds of hard-core bosons in the two-dimensional square lattice using a matrix-product-state based method. This nonequilibrium set-up is induced by quenching the trapping potential to zero and our work is specifically motivated by a recent experiment with interacting bosons in an optical lattice [Ronzheimer et al., Phys. Rev. Lett. 110, 205301 (2013)]. As the anisotropy of the amplitudes $J_x$ and $J_y$ for hopping in different spatial directions is varied from the one- to the two-dimensional case, we observe a crossover from a fast ballistic expansion in the one-dimensional limit $J_x \gg J_y$ to much slower dynamics in the isotropic two-dimensional limit $J_x=J_y$. We further study the dynamics on multi-leg ladders and long cylinders. For these geometries we compare the expansion of a cloud to the melting of a domain wall, which helps us to identify several different regimes of the expansion as a function of time. By studying the dependence of expansion velocities on both the anisotropy $J_y/J_x$ and the number of legs, we observe that the expansion on two-leg ladders, while similar to the two-dimensional case, is slower than on wider ladders. We provide a qualitative explanation for this observation based on an analysis of the rung spectrum.

Problems and prospects of implementing cloud computing in university libraries

Purpose – The paper aims to examine the characteristic elements of various organizational factors to identify whether a favourable climate for implementing and sustaining cloud computing in Banaras Hindu University library system (BHULS) existed. Design/methodology/approach – After reviewing relevant literature on the topic, a list of 20 factors that affected an organization’s adoption to innovation was prepared. A questionnaire was personally administered to the library professionals engaged in BHULS. Respondents were asked to nominate the level of importance of each factor for validation of cloud computing adoption. Findings – Findings of the paper validate the fact that opportune time for the implementation of cloud computing existed in BHULS. Library staff showed high willingness toward the adoption of the cloud computing and were well prepared to grasp the challenges. Practical implications – The paper establishes the fact that the benefits of cloud computing are inadequate to convince organizations to migrate from the traditional computing paradigm to the cloud. Technological advancement may not transform the cloud into a mainstream technology. To motivate the expansion of cloud computing adoption, emphasis has to be laid upon collaboration between the cloud service providers supplemented by solid cloud legislations which need to be worked out. Originality/value – Because no empirical study on the cloud computing in conjunction with academic libraries of India has been carried out before, this paper closes this gap and provides guidelines to migrate to cloud environment. Also, it provides the perceptions of library professionals in response to its adoption.

Modeling of magnetic cloud expansion

Modeling of magnetic cloud expansion

Multi-dimensional key generation of ICMetrics for cloud computing

Despite the rapid expansion and uptake of cloud based services, lack of trust in the provenance of such services represents a significant inhibiting factor in the further expansion of such service. This paper explores an approach to assure trust and provenance in cloud based services via the generation of digital signatures using properties or features derived from their own construction and software behaviour. The resulting system removes the need for a server to store a private key in a typical Public/Private-Key Infrastructure for data sources. Rather, keys are generated at run-time by features obtained as service execution proceeds. In this paper we investigate several potential software features for suitability during the employment of a cloud service identification system. The generation of stable and unique digital identity from features in Cloud computing is challenging because of the unstable operation environments that implies the features employed are likely to vary under normal operating conditions. To address this, we introduce a multi-dimensional key generation technology which maps from multi-dimensional feature space directly to a key space. Subsequently, a smooth entropy algorithm is developed to evaluate the entropy of key space.

The dynamics of a gas–dust cloud expansion in the upper atmosphere at a shutdown of solid-propellant rocket engines

The velocity of spherical gas–dust cloud expansion in the situation when the stages of solid-propellant rocket separate in the upper atmosphere have been determined. The measured velocity vary from 2.5 to 7.5 km/s. The dispersed component accelerates at the front of a shock that develops at engine-thrust shutdown. The model calculations of the gas–dust cloud luminosity intensity qualitatively coincide with the photometric profiles of object images. Such formations can vary from almost homogeneous ball-shaped clouds to rather thin spherical shells depending on the gas–dust cloud mass and the matter distribution within this cloud.