Spread Of Cloud Research Articles

A Software Evolution Process Model under the Circumstances of Cloud Computing

With the wide spread of cloud computing technologies, we assume that increasing amount of attentions will be given to the area of software evolution processes in the context of cloud computing environments. Some major problems we are here facing now include: What kind of process a software evolution model under the circumstances of cloud computing must possess What properties a software process must have as an attribute in order to effectively support the software evolution How to modeling a process in the context of software evolution While aiming to solve these mentioned problems, we focused our research on establishing a software evolution process model with independent functions as a component. In this article, the detailed discussion of our thoughts has been given and the in-depth analysis of our model is shown. Through a realistic case to which this model is applied, we concluded that our model provided the software evolution process with an effective support under the circumstances of cloud computing.

Volcanic ash hazard climatology for an eruption of Hekla Volcano, Iceland

Ash produced by a volcanic eruption on Iceland can be hazardous for both the transatlantic flight paths and European airports and airspace. In order to begin to quantify the risk to aircraft, this study explored the probability of ash from a short explosive eruption of Hekla Volcano (63.98°N, 19.7°W) reaching European airspace. Transport, dispersion and deposition of the ash cloud from a three hour ‘explosive’ eruption with an initial plume height of 12 km was simulated using the Met Office's Numerical Atmospheric-dispersion Modelling Environment, NAME, the model used operationally by the London Volcanic Ash Advisory Centre. Eruptions were simulated over a six year period, from 2003 until 2008, and ash clouds were tracked for four days following each eruption. Results showed that a rapid spread of volcanic ash is possible, with all countries in Europe facing the possibility of an airborne ash concentration exceeding International Civil Aviation Organization (ICAO) limits within 24 h of an eruption. An additional high impact, low probability event which could occur is the southward spread of the ash cloud which would block transatlantic flights approaching and leaving Europe. Probabilities of significant concentrations of ash are highest to the east of Iceland, with probabilities exceeding 20% in most countries north of 50°N. Deposition probabilities were highest at Scottish and Scandinavian airports. There is some seasonal variability in the probabilities; ash is more likely to reach southern Europe in winter when the mean winds across the continent are northerly. Ash concentrations usually remain higher for longer during summer when the mean wind speeds are lower.

How does wall slippage affect hydrodynamic dispersion?

How hydrodynamic dispersion is affected by wall slip remains to be fully understood. An attempt is made in this article looking into this issue for dispersion in some elementary pressure-driven flows. Both the long-time Taylor–Aris dispersion and the early-phase convection-dominated dispersion are investigated, analytically and numerically, respectively. The mean and the variance of the residence time distribution are also examined. In the basic case where the walls of a parallel-plate channel have equal slip lengths, the slip is in general to reduce the spread of a solute cloud in a finite channel by either increasing the convection speed or decreasing the dispersivity. However, the decreasing effect of slip on dispersion can be diminished or even reversed by unequal slip lengths and/or phase exchange with the wall. The convection-dominated regime is investigated, following a recently proposed transport-based method, to determine how the mean residence time and variance of elution profiles may change with axial positions depending on the slip.

Simulation of the Lpg Release, Dispersion, and Explosion in the Viareggio Railway Accident

The manuscript analyzes the accident that occurred in the railway station of Viareggio (Italy) on June 2009. A freight train carrying LPG went off the rails and five out of fourteen wagons derailed and overturned. A hole formed in the first tank car due to the impact with a signaling stake. The pressurized LPG was released as a two-phase jet: the liquid phase formed a boiling pool on the ballast while the dense gas dispersed in the atmosphere. The dense cloud spread and moved towards the neighboring houses. Afterwards, the cloud was ignited and exploded. The overpressure destroyed some residential buildings in the area closest to the explosion epicenter, while glasses were shattered in a larger area. Thirty-one people died and a number of residents were injured due to the fires that engulfed the surrounding houses. Starting from the data related to the tank cars, meteorological data, pictures of the site after the accident, aerial photos, witnesses of both civilians, and rescue teams, the manuscript reconstructs the dynamics of the accident by means of a dedicated software.

Quantification of source-level turbulence during LNG spills onto a water pond

The use of computational fluid dynamics (CFD) models to simulate LNG vapor dispersion scenarios has been growing steadily over the last few years, with applications to LNG spills on land as well as on water. Before a CFD model may be used to predict the vapor dispersion hazard distances for a hypothetical LNG spill scenario, it is necessary for the model to be validated with respect to relevant experimental data. As part of a joint-industry project aimed at validating the CFD methodology, the LNG vapor source term, including the turbulence level associated with the evaporation process vapors was quantified for one of the Falcon tests. This paper presents the method that was used to quantify the turbulent intensity of evaporating LNG, by analyzing the video images of one of the Falcon tests, which involved LNG spills onto a water pond. The measured rate of LNG pool growth and spreading and the quantified turbulence intensity that were obtained from the image analysis were used as the LNG vapor source term in the CFD model to simulate the Falcon-1 LNG spill test. Several CFD simulations were performed, using a vaporization flux of 0.127 kg/m 2 s, radial and outward spreading velocities of 1.53 and 0.55 m/s respectively, and a range of turbulence kinetic energy values between 2.9 and 28.8 m 2/s 2. The resulting growth and spread of the vapor cloud within the impounded area and outside of it were found to match the observed behavior and the experimental measured data. The results of the analysis presented in this paper demonstrate that a detailed and accurate definition of the LNG vapor source term is critical in order for any vapor cloud dispersion simulation to provide useful and reliable results.

Coagulation of nanoparticles in a plasma

Coagulation of nanoparticles in a low-pressure radio frequency plasma was studied by means of a detailed numerical model for the spatiotemporal evolution of the nanoparticle-plasma system. Simulation results indicate that the occurrence of coagulation to any significant degree in such systems requires the existence of two effects: first, gas-phase nucleation is not limited to a brief burst, but rather continues in regions that are sufficiently free of nanoparticles; and second, coagulation coefficients for collisions between neutral and negatively charged nanoparticles are enhanced by the image potential induced in the neutral particle. Accounting for these effects, coagulation is predicted to be dominated by coagulation between very small (approximately 1 or 2 nm in diameter) neutral particles and larger negatively charged particles that are trapped in the plasma. Coagulation ceases when the spreading of the nanoparticle cloud across the plasma quenches gas-phase nucleation.

Electrical discharge occurring between a negatively charged particle cloud and a grounded sphere electrode

Electrostatic discharge occurring between a space-charge cloud and a grounded object was investigated using a large-scale charged particle cloud formed by using three set of cloud generators consisting of a blower and corona charger. The ejecting velocity of the particles affects the formation of the charged cloud. At the lower velocity, the charged cloud spread due to electrostatic repulsion force, while at the higher velocity cloud forms an elongated conical shape. To cause electrostatic discharge between the cloud and a grounded object, a grounded sphere electrode with 100 mm in diameter was set at the inside or outside of the cloud. The brush-like discharge channels reached the maximum length of 0.55 m. The discharge current has a waveform with single or multi-peak, a current peak of several amperes, the maximum charge quantity of 2 μC, and the duration of several microseconds. The relationship between the charge quantity and the current peak or the duration in each discharge was examined. The discharge between the cloud and the electrode placed at the outside of the cloud has relatively longer channels and multi-peak current with the longer duration, while that at the inside of the cloud has the lower charge quantity with single peak.

Ocular Mucin Visualization by Confocal Laser Scanning Microscopy

To describe a new method of visualizing human conjunctiva goblet cell mucin secretion by using a combination of impression cytology and laser scanning microscopy. By assembling a Z-stack of confocal microscopy images taken from human impression cytology samples, we obtained 3-dimensional information about the release and spread of goblet cell secretions above the conjunctival surface. After reconstruction and rendering of these images, analysis of the shape and spreading characteristics of the mucins permitted definition of the following parameters related to goblet cell secretion: mucin cloud height as the height of the top of the cloudlike mucin structure visible above the goblet cell opening and spread mucin thickness, which is the thickness of the mucin layer distributed over the surface of the conjunctiva. Several impression cytology samples of control and muco-deficient patients have been analyzed through the confocal laser scanning technique, and significant differences between these groups were found. Mucin cloud height and spread mucin thickness values for controls were 8.81 +/- 4.00 and 2.77 +/- 1.00 microm, respectively (n = 25). These values decreased by approximately 70% and 40%, respectively, for moderately mucodeficient subjects and by 84% and 48% for those with severe mucodeficiency. Classifying those individuals having mucin-related pathology may thus be possible on the basis of application of these techniques. In summary, we present a method of objectively identifying those individuals with problems associated with either a lack of mucins or a reduction in the distribution of these proteins over the ocular surface.

Numerical simulation of plasma motion in a magnetic field. Two-dimensional case

A model of dynamics and heating of a plasma cloud in a magnetic field is considered in a two-temperature approximation. Based on a predictor-corrector-type implicit difference scheme, spreading of a plasma cloud in an external magnetic field is numerically simulated, and the influence of this field on spread dynamics is evaluated.

Direct charge sharing observation in single-photon-counting pixel detector

In photon-counting imaging devices, charge sharing can limit the detector spatial resolution and contrast, as multiple counts can be induced in adjacent pixels as a result of the spread of the charge cloud generated from a single X-ray photon of high energy in the detector bulk. Although debated for a long time, the full impact of charge sharing has not been completely assessed. In this work, the importance of charge sharing in pixellated CdTe and silicon detectors is studied by exposing imaging devices to different low activity sources. These devices are made of Si and CdTe pixel detector bump-bonded to Medipix2 single-photon-counting chips with a 55 μm pixel pitch. We will show how charge sharing affects the spatial detector resolution depending on incident particle type (alpha, beta and gamma), detector bias voltage and read-out chip threshold. This study will give an insight on the impact on the design and operation of pixel detectors coupled to photon-counting devices for imaging applications.

Information-theoretic measures for Morse and Pöschl–Teller potentials

The spreading of the quantum-mechanical probability cloud for the ground state of the Morse and modified Pöschl–Teller potentials, which controls the chemical and physical properties of some molecular systems, is studied in position and momentum space by means of global (Shannon's information entropy, variance) and local (Fisher's information) information-theoretic measures. We establish a general relation between variance and Fisher's information, proving that, in the case of a real-valued and symmetric wavefunction, the well-known Cramer–Rao and Heisenberg uncertainty inequalities are equivalent. Finally, we discuss the asymptotics of all three information measures, showing that the ground state of these potentials saturates all the uncertainty relations in an appropriate limit of the parameter.

Charge-sharing observations with a CdTe pixel detector irradiated with a57Co source

Abstract Charge sharing is a limiting factor of detector spatial resolution and contrast in photon counting imaging devices because multiple counts can be induced in adjacent pixels as a result of the spread of the charge cloud generated from a single X-ray photon of high energy in the detector bulk. Although this topic has been debated for a long time, the full impact of charge sharing has not been completely assessed. In this work, we look at the importance of charge sharing in CdTe pixel detectors by exposing such a device to a low-activity (37 kBq)57Co source, whose main emission line is at 122 keV.The detectors used are 1 mm thick with a pixel pitch of 55 μm. These detectors are bump-bonded to Medipix2 photon-counting chips. This study gives an insight of the impact on the design and operation of pixel detectors coupled to photon-counting devices for imaging applications.

Analysis of an LPG explosion and fire

AbstractIn September 1997, an LPG release occurred at the Hindustan Petroleum Corporation, Ltd. refinery in Visakhapatnam, India. The resulting explosion and fire destroyed most of the facility's administrative buildings, numerous LPG storage vessels, processing units, and an adjacent petroleum liquid storage terminal. Fifty‐six people were declared dead, but the fatality number could have been as high as 3 times the official estimate. Property damage was estimated at US $15 million.It is known that a leak occurred during receipt of LPG cargo from a pressurized ship. The subsequent vapor cloud spread throughout the refinery tank farm, administrative complex, utilities area, and at least one process unit before eventually finding an ignition source. The investigation team developed numerous release theories. However, none of these theories could be substantiated by first hand witnesses' testimonies since all personnel directly involved in the tank filling operation were killed. Vapor cloud dispersion computer modeling was used to evaluate the credibility of various release scenarios. This paper discusses the events leading up to the explosion, the damages sustained, and compares quantitative dispersion modeling results to the physical damage and witness testimony obtained during the investigation.

Anomalous behaviour of a passive tracer in wave turbulence

We consider the behaviour of a passive tracer in multiscale velocity field, when there is no separation of scales; the energy spectrum of the velocity field extends into the region of long waves and even can be singular there. We suppose that the velocity field is a superposition of random waves. The turbulence of various ocean or atmospheric waves provides examples. We find anomalous diffusion (sub- and super-diffusion), anomalous drift (super-drift), and anomalous spreading of a passive tracer cloud. For the latter we find the existence of two regimes: (i) ‘close’ passive tracer particles diverge sub- or supper-exponentially in time, and (ii) a ‘large’ passive tracer cloud spreads as a power-law in time. The exponents, as well as the corresponding pre-factors, are found. The theory is confirmed by numerical simulations.

The Effect of Swirl on Flow Stability in Spray Dryers

The effect of varying the amount of inlet air swirl on the stability of the flow patterns in a small-scale, co-current spray dryer has been investigated. The objective of this work was better understanding of the effect of the vane angle on the flow patterns and to determine whether a particular vane angle provided superior performance. The dryer studied was a cylinder on cone unit, with a drying chamber 0.8 m in diameter and 1.61 m tall, and fitted with adjustable swirl vanes tightly surrounding a Delavan GA1 two-fluid atomiser. Swirl vane angles between 0° and 45°, in 5° increments, were investigated using a complementary combination of flow visualisation and laser Doppler velocimetry (LDV) techniques. No single swirl vane angle resulted in behaviour that was clearly steady throughout the dryer, but a swirl vane angle of about 25° was considered to be an appropriate selection. This vane angle, corresponding to a Swirl number of approximately 0.45, gave an observable degree of stability in much of the flow domain and good air-spray mixing without excessive spreading of the spray cloud and wall deposition. The introduction of spray had a significant effect on the flow behaviour, so that air-only studies did not adequately represent the flow conditions with spray.

The Spark‐associated Soliton Model for Pulsar Radio Emission

We propose a new, self-consistent theory of coherent pulsar radio emission based on the nonstationary sparking model of Ruderman & Sutherland, modified by Gil & Sendyk. The polar cap is populated by a number of sparks with a characteristic perpendicular dimension D approximately equal to the polar gap height scale h, separated from each other also by about D ≈ h. Each spark reappears in approximately the same place on the polar cap for a timescale much longer than its 10 μs lifetime and delivers to the open magnetosphere a sequence of e-e+ clouds that flow orderly along a flux tube of dipolar magnetic field lines. The overlapping of particles with different momenta from consecutive clouds leads to effective two-stream instability, which triggers electrostatic Langmuir waves at the altitudes of about 50 stellar radii. The electrostatic oscillations are modulationally unstable, and their nonlinear evolution results in formation of plasma solitons. Because of relative streaming of electrons and positrons and the corresponding difference in relativistic masses, the pondermotive Miller force acts on them at different rates, which results in the net soliton charge. A characteristic soliton length along magnetic field lines is about 30 cm, so they are capable of emitting coherent curvature radiation at radio wavelengths. A perpendicular cross section of each soliton at radiation altitudes follows from a dipolar spread of a plasma cloud with a characteristic dimension near the star surface of about D ≈ h ≈ 50 m. If Δγ = |γ+ - γ-| ~ 100, then the net soliton charge is about 1021 fundamental charges contained within a volume of about 1014 cm3. For a typical pulsar, there are about 105 solitons associated with each of about 25 sparks operating on the polar cap at any instant. One soliton moving relativistically along dipolar field lines with a Lorentz factor of the order of 100 generates a power of about 1021 ergs s-1 by means of curvature radiation. Then the total power of a typical radio pulsar can be estimated as being about 1027-1028 ergs s-1. The energy of the soliton curvature radiation is supported by kinetic energy of secondary electron-positron plasma created by the primary beam produced by the accelerating potential drop within the polar gap. A significant fraction of kinetic energy generated by sparks is radiated away in the form of the observed coherent radio emission.

Properties of Substrate Phonon Events in Superconducting Tunnel Junctions Induced by X-Ray Absorption

The spectra of substrate phonon events induced by illuminating with X-rays obtained with Nb-based superconducting tunnel junctions (STJs) fabricated on a sapphire substrate were examined. We constructed a geometrical model in which the collection efficiency of phonons is proportional to the solid angle subtended to the STJ from the position of the absorption. By using the Monte-Carlo simulation, we succeeded in fairly reproducing the features of the spectra obtained by our measurements. A comparison of the model spectra with the measured ones revealed that a mismatch of the acoustic impedance at the junction-substrate interface and the spatial spread of a phonon cloud play an important role in the determination of the spectra. By including these effects, we show that the measured spectra can be well reproduced by adjusting only one free parameter, the radius of the phonon cloud. We estimated this radius in a sapphire substrate to be ∼20 µm under 5.9 keV X-ray illumination.

The spread of the hot electron cloud in the solar corona

The spread of the electron cloud generating solar type III bursts is discussed. It is shown that the maximum velocity of the electron distribution function, plateau, cannot exceed the velocity of free propagation u= x/ t. It appeared that despite the plateau formation at the electron distribution function the asymptotic self-similar solution u( x, t)=2 x/ t never occurred.

A study of breakdown limits in microstrip gas counters with preamplification structures

We have studied the charge and breakdown limits of Microstrip Gas Counters (MSGC's) with two different preamplification structures: the Gas Electron Multiplier (GEM) and the Parallel-Plate Avalanche Counter (PPAC). It was found that in both cases the breakdown limit was increased by 1–2 orders of magnitude compared to the bare MSGC and that this was due to the spreading of the primary electron cloud during pre-amplification. This spreading reduces the charge density in the final MSGC avalanche, permitting much higher total gains before streamers form. The real practical gain limitations in these two-stage detectors arose not from sparking, but from a loss of proportionality due to space charge effects.

Boundary versus internal diapycnal mixing in stratified natural waters

Using the fluorescent dye uranin, tracer release experiments to study the contribution of bottom boundary mixing to diapycnal transport in stratified natural waters were performed in Lake Alpnach (central Switzerland) during 1992–1995. A first experiment involved injecting the tracer from a point source into the center of the hypolimnion (that part of the lake below the surface mixed layer). An in situ fluorometer was then employed to detect the horizontal and vertical spreading of the tracer cloud, allowing rates of diapycnal diffusivity to be determined. As long as the tracer was confined to the interior water region, the diapycnal diffusivity was relatively small. However, after the tracer cloud had reached the lake boundary, the diapycnal diffusivity increased by approximately one order of magnitude. In a second experiment, the tracer was released near the sediment‐water interface. In this case the dynamics of vertical tracer spreading were opposite. During the first few hours after tracer release, diapycnal diffusivities were large, subsequently decreasing as the tracer cloud drifted away from the lake boundary. Basin‐wide diapycnal diffusivities calculated from heat flux measurements based on temperature profiles obtained from thermistor chains or conductivity‐temperature‐depth casts agreed well with the values obtained from the vertical tracer diffusion after horizontal homogenization. The results of the tracer experiments corroborate the hypothesis that diapycnal fluxes are determined predominantly by mixing in the bottom boundary region.