Neutral Clouds Research Articles

A Comparative Study of a Client Based Vendor Neutral Cloud QoS Monitoring Tool and Cloud Providers’ Platform Integrated QoS Monitoring Tools

Cloud service providers have a QoS monitoring capability integrated in their cloud platforms. This is to aid in monitoring the performance of the platform as well as for Service Level Agreement confirmation to the clients. Unfortunately this arrangement serves the interest of the cloud provider more than the cloud client since the service providers gauge their services using their own tools. This paper performs a comparative study on the capabilities of the client based vendor neutral QoS tool, developed from a vendor neutral QoS monitoring model against the cloud provider integrated QoS monitoring tools. The comparison was done on four global SaaS cloud service providers, namely SalesForce, Google, Hubspot and Shopify. From the comparative study, it emerged that the client based vendor neutral tool has more capabilities than the cloud provider integrated tools since it has the capability to monitor three key QoS metrics, namely service response time, service availability and service stability as opposed to the cloud providers’ tools which only have one quantitative capability. Further the vendor neutral model can be used across any cloud platform that is accessible via the web browser. This provides a capability for cross platform performance comparison for the various cloud providers. This can aid in decision making with regards to which cloud service provider to procure based on the desired performance.

Comparison between ionospheric disturbances caused by barium and cesium

After being released in the ionosphere, alkali-metal atoms will be rapidly photoionized by solar UV, producing positive ions and electrons, and forming artificial plasma cloud. Based on a three-dimensional two-species fluid model, considering both the loss of barium atoms due to photoionization and oxidation and the influence of horizontal wind field in the release region, the spatial-temporal evolution of the artificial plasma cloud is discussed. By taking into account the electromagnetic field force, pressure gradient, particle collisions and ion inertia, the ionospheric disturbance effects caused by barium and cesium are compared with each other. The simulation results show that the alkali metal rapidly expands after being released in the ionosphere, and the generated plasma cloud gradually forms an ellipsoidal structure from the inside to the outside under the constraint of magnetic field with considering no wind. Meanwhile, the expanded plasma cloud pushes away the background oxygen ions, forming an oxygen ion density hole in the release center and two symmetrical density bumps on both sides. In the absence of neutral wind, the plasma cloud is dominated by the movement along magnetic field, while considering the background neutral wind, the plasma cloud and background disturbance area will move along the direction of wind, so that the density gradient of plasma cloud becomes steepening on the upwind side. Although the movement of ion cloud across the magnetic field is constrained, the neutrals can pass through the magnetic field freely, so the ion cloud and neutral cloud will separate from each other slowly. Also, the presence of horizontal wind field will make a greater disturbance to the background oxygen ion. By comparing the simulation results of barium and cesium we can see that, qualitatively, the expansion characteristics of Cs<sup>+</sup> and Ba<sup>+</sup> as well as their effects on the background O<sup>+</sup> are similar. Due to the small diffusion coefficient of cesium, the barium cloud expands more rapidly and the coverage area of Ba<sup>+</sup> cloud is wider. Because of the large photoionization rate of cesium, the ionization yield of cesium is higher than that of barium when the same mass is released. In addition, the snowplow effect of Cs<sup>+</sup> is stronger than that of Ba<sup>+</sup>, and the oxygen ion density holes and bumps caused by Cs<sup>+</sup> are also larger.

Observation of Acceleration of H i Clouds within the Fermi Bubbles

Abstract The ∼200 H i clouds observed to be entrained in the Fermi bubble wind show a trend of increasing maximum with Galactic latitude. We analyze previous observations and present new data from the Green Bank Telescope that rule out systematic effects as the source of this phenomenon. Instead, it is likely evidence for acceleration of the clouds. The data suggest that clouds in the lower 2 kpc of the Fermi bubbles, within the bubble boundaries established from X-ray studies, have an outflow velocity that rises from ≈150 to 200 close to the Galactic center and reaches ≈330 at a distance of 2.5–3.5 kpc. These parameters are also consistent with the kinematics of ultraviolet absorption lines from highly ionized species observed against two targets behind the Fermi bubbles at b = −6.°6 and b = +11.°2. The implied neutral cloud lifetime is 4–10 Myr.

Transient Change of Io's Neutral Oxygen Cloud and Plasma Torus Observed by Hisaki

AbstractIo's atmospheric oxygen atoms are heated by atmospheric sputtering and escape from Io's gravity, forming a neutral oxygen cloud around Io's orbit. This neutral cloud is important as a source of the Io oxygen plasma torus. Previous studies derived the distribution and density of the equilibrium neutral oxygen cloud. However, little is known about the evolution of the neutral cloud. In this study, we analyzed Hisaki satellite observations of the spatial distribution of OI 130.4 nm emissions around Io's orbit during transient strong density enhancement in the torus in 2015 (called high density period). Comparing time variations of OI and OII 83.4 nm emissions, we estimated that the lifetimes of O+ in this period were about 21 days in the high density period and 41 days in the normal density period. Hisaki observations are consistent with a decrease in the lifetime of O+ when the density in the torus increases. The radial distribution showed the neutral oxygen cloud spread outward up to 8.6 Jupiter radii during the high density period. We also show that during the high density period, the neutral oxygen number density at Io's orbit (where north‐south thickness is assumed to be 1.2 Jupiter radii) increased to cm−3, more than three times the value during the normal density period ( cm−3). The azimuthal distribution showed a dense region around Io and a longitudinally uniform, diffuse region distributed along Io's orbit that enlarges during the high density period.

Simulation of Io’s plumes and Jupiter’s plasma torus

Io is a highly volcanic satellite of Jupiter. Its giant plumes rise hundreds of kilometers, creating large targets for incoming ions as Jupiter’s plasma torus overtakes Io in its orbit. Neutral material from Io’s sublimation atmosphere and volcanic plumes supplies the plasma torus, but the details of the interaction between neutral gas at Io and ions in the torus are not well understood. This paper suggests a process by which plume material is energized and ionized so as to supply the torus. We present three-dimensional direct simulation Monte Carlo simulations of giant plumes being bombarded by S+ and O+ ions which are moved based on precomputed electric and magnetic fields. The dependence of the plume/plasma interaction on the plume’s location on Io is investigated. The plume/plasma interaction is seen to be asymmetric even for a plume at the subplasma point because of the electric field that arises in an Io-fixed reference frame. Plasma is found to inflate and heat plume canopies and to give rise to a large, diffuse neutral cloud over the plume’s entire hemisphere. We also find that plasma can explain the thickness of red deposition rings observed on Io.

On the Formation of Density Filaments in the Turbulent Interstellar Medium

Abstract This study is motivated by recent observations of ubiquitous interstellar density filaments and guided by modern theories of compressible magnetohydrodynamic (MHD) turbulence. The interstellar turbulence shapes the observed density structures. As the fundamental dynamics of compressible MHD turbulence, perpendicular turbulent mixing of density fluctuations entails elongated density structures aligned with the local magnetic field, accounting for low-density parallel filaments seen in diffuse atomic and molecular gas. The elongation of low-density parallel filaments depends on the turbulence anisotropy. When taking into account the partial ionization, we find that the minimum width of parallel filaments in the cold neutral medium and molecular clouds is determined by the neutral–ion decoupling scale perpendicular to magnetic field. In highly supersonic MHD turbulence in molecular clouds, both low-density parallel filaments due to anisotropic turbulent mixing and high-density filaments due to shock compression exist.

Through thick or thin: multiple components of the magneto-ionic medium towards the nearby H ii region Sharpless 2–27 revealed by Faraday tomography

Sharpless 2-27 (Sh2-27) is a nearby ${\rm H\,{\small II}}$ region excited by $\zeta$Oph. We present observations of polarized radio emission from 300 to 480$\,$MHz towards Sh2-27, made with the Parkes 64$\,$m Radio Telescope as part of the Global Magneto-Ionic Medium Survey. These observations have an angular resolution of $1.35^{\circ}$, and the data are uniquely sensitive to magneto-ionic structure on large angular scales. We demonstrate that background polarized emission towards Sh2-27 is totally depolarized in our observations, allowing us to investigate the foreground. We analyse the results of Faraday tomography, mapping the magnetised interstellar medium along the 165$\,$pc path to Sh2-27. The Faraday dispersion function in this direction has peaks at three Faraday depths. We consider both Faraday thick and thin models for this observation, finding that the thin model is preferred. We further model this as Faraday rotation of diffuse synchrotron emission in the Local Bubble and in two foreground neutral clouds. The Local Bubble extends for 80$\,$pc in this direction, and we find a Faraday depth of $-0.8 \pm 0.4\,$rad$\,$m$^{-2}$. This indicates a field directed away from the Sun with a strength of $-2.5\pm1.2\,\mu$G. The near and far neutral clouds are each about 30$\,$pc thick, and we find Faraday depths of $-6.6\pm0.6\,$rad$\,$m$^{-2}$ and $+13.7\pm0.8\,$rad$\,$m$^{-2}$, respectively. We estimate that the line-of-sight magnetic strengths in the near and far cloud are $B_{\parallel, \text{near}} \approx -15\,\mu\text{G}$ and $B_{\parallel, \text{far}} \approx +30\,\mu\text{G}$. Our results demonstrate that Faraday tomography can be used to investigate the magneto-ionic properties of foreground features in front of nearby ${\rm H\,{\small II}}$ regions.

Observation of Electron Density Depletion Due to Maneuver Operation of H‐II Transfer Vehicle

AbstractThe plasma sensor on the sixth H‐II Transfer Vehicle (HTV) measured the depletion of electron density during some maneuver operations for attitude or altitude control. In this paper, we first discuss the on‐orbit observation of electron density depletion during the entire lifetime of the HTV. On‐orbit data showed that both altitude and attitude control maneuvers caused the depletion effect. The geocentric coordinates and universal time were also shown to confirm the depletion effect around the HTV by using other techniques, such as total electron content based on the Global Navigation Satellite System network. In the latter part of the paper, we discuss the cause of the depletion effect based on past literature. To analyze the interaction between thruster plume gas and ionospheric plasma, computational fluid dynamics simulations were conducted to analyze the number density distribution of molecules around the HTV. It was found that the combination of charge exchange and dissociative recombination possibly caused the depletion of electron density during altitude control maneuvers, due to neutral particles being ejected from the thrusters and a time delay in the reaction response. During attitude control maneuvers, the electrons of ionospheric plasma were pushed away from the plasma sensor by dense neutral clouds.

Net Neutrality: Unexpected Solution to Blockchain Scaling

Provably neutral clouds are undoubtedly a viable solution to blockchain scaling. By optimizing the transport layer, not only can the throughput be fundamentally scaled up, but the latency could be dramatically reduced. Indeed, the latency distribution in today’s data centers is already biased toward microsecond timescales for most of the flows, with millisecond timescales residing only at the tail of the distribution. There is no reason why a BDN point of presence would not be able to achieve a similar performance. Adding dedicated optical infrastructure among such BDN points of presence would further alleviate throughput and reduce latency, creating the backbone of an advanced BDN. The key to this vision, however, lies in establishing trust by the blockchain ecosystem into the underlying networking infrastructure. This, in turn, is achieved by decoupling authority from infrastructure via a provably neutral network design.

Three-dimensional fluid simulations of the Cs plasma release in the ionosphere

Releasing plasma cloud is an efficient way to manage ionosphere properties. In this paper, we establish a three-dimensional fluid model to simulate the spatiotemporal evolution of released Cs plasma. Four types of particles are taken into account: released neutral Cs, ambient O, Cs+ and electron, among which the Cs+ and electron move according to the classical ambipolar diffusion. Meanwhile, photoionization induced by solar radiation and recombination of Cs+/electron are included in model as two chemical reactions. Based on this model, we investigate the influence of three factors: initial velocity of neutral Cs cloud, photoionization rate and altitude. The initial velocity can change the whole distribution of plasma cloud. When there is no velocity or velocity along the background magnetic field, the plasma cloud shows an ellipsoid shape and moves with neutral cloud. If the velocity is perpendicular to the magnetic field line, the cloud will be stretched in the same direction and does not move. We investigate the influence of photoionization rate under different initial velocities, and find that with the photoionization rate increasing, more and more particles remain in the initial release position. Moreover, the altitude affects the density of ambient O and temperature result in the diffusion coefficient and drifting velocity reducing and then the size of bulk plasma inclines to be reduced at lower altitude.

2FHL J0826.1–4500: Discovery of a Possible Shock–Cloud Interaction on the Western Edge of the Vela Supernova Remnant

Abstract We report on the investigation of a very high-energy, Galactic γ-ray source recently discovered at >50 GeV using the Large Area Telescope on board Fermi. This object, 2FHL J0826.1−4500, displays one of the hardest >50 GeV spectra (photon index Γ γ ∼ 1.6) in the 2FHL catalog, and a follow-up observation with XMM-Newton has uncovered diffuse, soft thermal emission at the position of the γ-ray source. A detailed analysis of the available multi-wavelength data shows that this source is located on the western edge of the Vela supernova remnant (SNR): the observations and the modeling of the spectral energy distribution support a scenario where this γ-ray source is the byproduct of the interaction between the SNR shock and a neutral hydrogen cloud. If confirmed, this shock–cloud interaction would make 2FHL J0826.1−4500 a promising candidate for efficient particle acceleration.

The impact of fast electrons on pellet injection in the stellarator TJ-II

Efficient plasma core fuelling is a critical issue for achieving steady-state scenarios in magnetically confined fusion devices. The current preferred method to achieve this goal is cryogenic pellet injection (PI). PI’s are now installed in most medium- and large-sized fusion devices. In this paper, recent results from PI experiments in the stellarator TJ-II are reported. Of particular interest is the influence of fast electrons. Whilst edge populations of such electrons do not affect PI in the TJ-II, fast electrons residing in its hot core have significant influence on both pellet ablation and fuelling efficiency. If present in the core, their radial location can be determined from the light emission profile produced by an ablating pellet as it traverses the plasma and confirmed from the power spectral distribution spectrograph of the total secondary beam current collected by a scanning heavy ion beam probe system. Moreover, it is found that if a pellet is subject to excess ablation due to core fast electron impacts, the resultant pellet efficiency (deposited particles/delivered particles) increases by up to 50% with respect to injections into similar, fast-electron free, plasmas. This is consistently found for microwave-heated plasmas, where pellet penetration is shallower than the magnetic axis in TJ-II, when such a population is present, as well as for neutral beam created and heated plasmas in which fast-electrons, generated during magnetic field ramp-up, persist in the core along a discharge. Similarly, when polystyrene pellets (TESPEL) are injected into the same machine sector, an analogous increase in post-injection particle deposition is seen. It is postulated that vaporization of the pellet through heating by fast electrons modifies normal neutral cloud and plasmoid development and hence affects outwards drifting that is inherent to magnetic fusion devices.

Is Dark Matter Needed in Galaxies?

We present arguments indicating that galaxies and their clusters should be considered as open developing systems. Galaxies interact with the intergalactic medium and are not in a virial equilibrium (which is determined by the gravity and rotation). In this case, the conventional interpretation of the rotation curves of galaxy outer regions outside the visible stellar disk (i.e. the presence of high mass dark matter haloes) may be erroneous. If there is an accretion of the intergalactic medium in these regions, then the orbital velocities of neutral hydrogen clouds are determined not only by the gravitation of the mass inside their orbits. Galaxy clusters accrete the material (intergalactic gas and galaxies) from filaments of the large-scale structure, at the intersections of which they are located. Only their central regions can approach the virial equilibrium. Therefore, the high velocities of galaxies and the high temperatures of the intergalactic gas in a cluster do not necessarily indicate the presence of a large mass of dark matter in the cluster.

Spatial Distribution of Io's Neutral Oxygen Cloud Observed by Hisaki

AbstractWe report on the spatial distribution of a neutral oxygen cloud surrounding Jupiter's moon Io and along Io's orbit observed by the Hisaki satellite. Atomic oxygen and sulfur in Io's atmosphere escape from the exosphere mainly through atmospheric sputtering. Some of the neutral atoms escape from Io's gravitational sphere and form neutral clouds around Jupiter. The extreme ultraviolet spectrograph called EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) installed on the Japan Aerospace Exploration Agency's Hisaki satellite observed the Io plasma torus continuously in 2014–2015, and we derived the spatial distribution of atomic oxygen emissions at 130.4 nm. The results show that Io's oxygen cloud is composed of two regions, namely, a dense region near Io and a diffuse region with a longitudinally homogeneous distribution along Io's orbit. The dense region mainly extends on the leading side of Io and inside of Io's orbit. The emissions spread out to 7.6 Jupiter radii (RJ). Based on Hisaki observations, we estimated the radial distribution of the atomic oxygen number density and oxygen ion source rate. The peak atomic oxygen number density is 80 cm−3, which is spread 1.2 RJ in the north‐south direction. We found more oxygen atoms inside Io's orbit than a previous study. We estimated the total oxygen ion source rate to be 410 kg/s, which is consistent with the value derived from a previous study that used a physical chemistry model based on Hisaki observations of ultraviolet emission ions in the Io plasma torus.

Blowing in the Milky Way Wind: Neutral Hydrogen Clouds Tracing the Galactic Nuclear Outflow

Abstract We present the results of a new sensitive survey of neutral hydrogen above and below the Galactic Center with the Green Bank Telescope. The observations extend up to Galactic latitude with an effective angular resolution of 9.′5 and an average rms brightness temperature noise of 40 mK in a 1 channel. The survey reveals the existence of a population of anomalous high-velocity clouds extending up to heights of about 1.5 kpc from the Galactic plane and showing no signature of Galactic rotation. These clouds have local standard of rest velocities , and assuming a Galactic Center origin, they have sizes of a few tens of parsec and neutral hydrogen masses spanning . Accounting for selection effects, the cloud population is symmetric in longitude, latitude, and V LSR. We model the cloud kinematics in terms of an outflow expanding from the Galactic Center and find the population consistent with being material moving with radial velocity distributed throughout a bicone with opening angle . This simple model implies an outflow luminosity erg s−1 over the past 10 Myr, consistent with star formation feedback in the inner region of the Milky Way, with a cold gas mass-loss rate . These clouds may represent the cold gas component accelerated in the nuclear wind driven by our Galaxy, although some of the derived properties challenge current theoretical models of the entrainment process.

Development of a new gas puff imaging diagnostic on the HL-2A tokamak

A new gas puff imaging (GPI) diagnostic has been developed on the HL-2A tokamak to study two-dimensional plasma edge turbulence in poloidal vs. radial plane. During a discharge, neutral helium or deuterium gas is puffed at the edge of the plasma through a rectangular multi\ obreakdash-capillaries nozzle to generate a gas cloud on the observing plane. Then a specially designed telescope and a high-speed camera are used to observe and photograph the emission from the neutral gas cloud. The brightness and contrast in the 2-D poloidal vs. radial frames reveal the structures and movements of the turbulence. The diagnostic was put into the first experiment during the latest campaign and successfully captured blob structures of different shapes and sizes in scrape-off layer (SOL).

Gemini Follow-up of Two Massive H i Clouds Discovered with the Australian Square Kilometer Array Pathfinder

Abstract Using the Gemini Multi Object Spectrograph (GMOS) we search for optical counterparts of two massive (∼109 M ⊙) neutral hydrogen clouds near the spiral galaxy IC 5270, located in the outskirts of the IC 1459 group. These two H i clouds were recently discovered using the Australian Square Kilometer Array Pathfinder (ASKAP). Two low surface brightness optical counterparts to one of these H i clouds are identified in the new Gemini data that reaches down to magnitudes of ∼27.5 mag in the g-band. The observed H i mass-to-light ratio derived with these new data, , is among the highest reported to date. We are also able to rule out that the two H i clouds are dwarf companions of IC 5270. Tidal interactions and ram pressure stripping are plausible explanations for the physical origin of these two clouds.

Resonant line transfer in a fog: using Lyman-alpha to probe tiny structures in atomic gas

Motivated by observational and theoretical work which both suggest very small scale ($\lesssim 1\,$pc) structure in the circum-galactic medium of galaxies and in other environments, we study Lyman-$\alpha$ (Ly$\alpha$) radiative transfer in an extremely clumpy medium with many "clouds" of neutral gas along the line of sight. While previous studies have typically considered radiative transfer through sightlines intercepting $\lesssim 10$ clumps, we explore the limit of a very large number of clumps per sightline (up to $f_{\mathrm{c}} \sim 1000$). Our main finding is that, for covering factors greater than some critical threshold, a multiphase medium behaves similar to a homogeneous medium in terms of the emergent Ly$\alpha$ spectrum. The value of this threshold depends on both the clump column density and on the movement of the clumps. We estimate this threshold analytically and compare our findings to radiative transfer simulations with a range of covering factors, clump column densities, radii, and motions. Our results suggest that (i) the success in fitting observed Ly$\alpha$ spectra using homogeneous "shell models" (and the corresponding failure of multiphase models) hints towards the presence of very small-scale structure in neutral gas, in agreement within a number of other observations; and (ii) the recurrent problems of reproducing realistic line profiles from hydrodynamical simulations may be due to their inability to resolve small-scale structure, which causes simulations to underestimate the effective covering factor of neutral gas clouds.

Survey of Voyager plasma science ions at Jupiter: 3. Protons and minor ions

AbstractWhen the Voyager 1 and 2 spacecraft flew through the Jovian system in March and July 1979, the Plasma Science instruments measured ions and electrons in the Io plasma torus and plasma sheet between 4.9 and 42 RJ. The dominant ions in the Jovian magnetosphere comprise the first few ionization states of atomic sulfur and oxygen. We present here an analysis of minor ion species H+, Na+, and SO2+. Protons are 1–20% of the plasma between 5 and 30 RJ with variable temperatures ranging by a factor of 10 warmer or colder than the heavy ions. We suggest that these protons, measured deep inside the magnetosphere, are consistent with a source from the ionosphere of ~1.5–7.5 × 1027 protons s−1 (2.5–13 kg/s). Na+ ions are detected between 5 and 40 RJ at an abundance of 1 to 10%, produced by the ionization of the extended neutral cloud emanating from Io that has been observed since 1974. SO2+ ions are detected between 5.31 and 5.07 RJ at an abundance of 0.1–0.6%. These ions clearly come from the plasma interaction with Io's atmosphere, but the exact processes whereby atmospheric molecules escape Io and end up as ions well inside Io's orbit are not clear.

The survival of gas clouds in the circumgalactic medium of Milky Way-like galaxies

Observational evidence shows that low-redshift galaxies are surrounded by extended haloes of multiphase gas, the so-called 'circumgalactic medium' (CGM). To study the survival of relatively cool gas (T < 10^5 K) in the CGM, we performed a set of hydrodynamical simulations of cold (T = 10^4 K) neutral gas clouds travelling through a hot (T = 2x10^6 K) and low-density (n = 10^-4 cm^-3) coronal medium, typical of Milky Way-like galaxies at large galactocentric distances (~ 50-150 kpc). We explored the effects of different initial values of relative velocity and radius of the clouds. Our simulations were performed on a two-dimensional grid with constant mesh size (2 pc) and they include radiative cooling, photoionization heating and thermal conduction. We found that for large clouds (radii larger than 250 pc) the cool gas survives for very long time (larger than 250 Myr): despite that they are partially destroyed and fragmented into smaller cloudlets during their trajectory, the total mass of cool gas decreases at very low rates. We found that thermal conduction plays a significant role: its effect is to hinder formation of hydrodynamical instabilities at the cloud-corona interface, keeping the cloud compact and therefore more difficult to destroy. The distribution of column densities extracted from our simulations are compatible with those observed for low-temperature ions (e.g. SiII and SiIII) and for high-temperature ions (OVI) once we take into account that OVI covers much more extended regions than the cool gas and, therefore, it is more likely to be detected along a generic line of sight.