Compressive Dust Research Articles

Dust acoustic solitary waves and double layers in a dusty plasma with two-temperature trapped ions

The combined effects of trapped ion distribution, two-ion-temperature, dust charge fluctuation, and dust fluid temperature are incorporated in the study of nonlinear dust acoustic waves in an unmagnetized dusty plasma. It is found that, owing to the departure from the Boltzmann ion distribution to the trapped ion distribution, the dynamics of small but finite amplitude dust acoustic waves is governed by a modified Korteweg–de Vries equation. The latter admits a stationary dust acoustic solitary wave solution, which has stronger nonlinearity, smaller amplitude, wider width, and higher propagation velocity than that involving adiabatic ions. The effect of two-ion-temperature is found to provide the possibility for the coexistence of rarefactive and compressive dust acoustic solitary structures and double layers. Although the dust fluid temperature increases the amplitude of the small but finite amplitude solitary waves, the dust charge fluctuation does the opposite effect. The present investigation should help us to understand the salient features of the nonlinear dust acoustic waves that have been observed in a recent numerical simulation study.

Effects of trapped electron temperature, dust charge variations, and grain radius on the existence of the dust-ion-acoustic waves

The ionization source model is considered to study the effects of trapped electron temperature, dust charge variations, and grain radius on the nonlinear dust ion acoustic waves (DIAWs) in dusty plasmas having trapped electrons. It has been shown that the nonlinear DIAWs damp waves and these waves are governed by a damped modified Korteweg–de Vries equation. It is found that only compressive dust ion acoustic solitons can propagate in dusty plasmas with trapped electrons. The amplitude and the width of the solitons depend mainly on the trapped electron temperature, dust charge variations and grain radius. The existence of the solitons is independent of the trapped electron temperature. The findings of this investigation may be useful in understanding laboratory plasma phenomena and astrophysical situations.

Molecular Tracers of the Central 12 Parsecs of the Galactic Center

We have used the BIMA array to image the Galactic center with a 19 pointing mosaic in HCN(1-0), HCO+(1-0), and H 42α emission with 5 km s-1 velocity resolution and 13'' × 4'' angular resolution. The 5' field includes the circumnuclear ring (CND) and parts of the 20 and 50 km s-1 clouds. HCN(1-0) and HCO+ trace the CND and nearby giant molecular clouds, while the H 42α emission traces the ionized gas in Sgr A West. We find that the CND has a definite outer edge in HCN and HCO+ emission at ~45'' radius and appears to be composed of two or three distinct streams of molecular gas rotating around the nucleus. Outside the CND, HCN and HCO+ trace dense clumps of high-velocity gas in addition to optically thick emission from the 20 and 50 km s-1 clouds. A molecular ridge of compressed gas and dust, traced in NH3 emission and self-absorbed HCN and HCO+, wraps around the eastern edge of Sgr A East. Just inside this ridge are several arcs of gas that have been accelerated by the impact of Sgr A East with the 50 km s-1 cloud. HCN and HCO+ emission trace the extension of the northern arm of Sgr A West, which appears to be an independent stream of neutral and ionized gas and dust originating outside the CND. Broad line widths and OH maser emission mark the intersection of the northern arm and the CND. Comparison to previous NH3 and 1.2 mm dust observations shows that HCN and HCO+ preferentially trace the CND and are weaker tracers of the GMCs than NH3 and dust. We discuss possible scenarios for the emission mechanisms and environment at the Galactic center that could explain the differences in these images.

Large amplitude electrostatic solitary structures in a hot non-thermal dusty plasma

A rigorous theoretical investigation has been made of large amplitude compressive and rarefactive dust–acoustic solitary waves in an unmagnetized hot dusty plasma consisting of a negatively charged hot dust fluid and non-thermally distributed ions. The pseudo-potential approach, which is valid for arbitrary amplitude solitary waves, has been employed. It is shown that the presence of the fast or non-thermal ions may allow compressive and rarefactive solitary waves to coexist. It is found that the effect of the dust fluid temperature changes the minimum values of α (a parameter determining the number of fast ions present in our dusty plasma model) and M (the Mach number) for which the compressive and rarefactive solitary waves can coexist. It is also observed that as the dust fluid temperature rises, the amplitude of both the compressive and rarefactive solitary waves decrease, whereas their width increases. The implications of these results to some space and astrophysical dusty plasma situations are briefly discussed.

303核融合炉事故事象時における熱流動挙動に関する数値解析

Numerical analyses on thermal-hydraulic characteristics in fusion reactors at accident events such as ICE (Ingress-of-Coolant Event) and LOVA (Loss-of-Vacuum Event) were carried out due to make sure adequacy of the safety design in ITER (International Thermonuclear Experimental Reactor) and the results were visualized numerically to enhance the understanding of physical phenomena during ICE and LOVA events. Relation between pressure rise and void fraction in ITER at the ICE event was obtained with a TRAC code. Air-ingress behavior into water was also clarified quantitatively with a CIP code. Furthermore, exchange flow and dust mobilization behavior through breaches on the fusion reactor during the LOVA event were analyzed based on equations of compressible fluid and dust momentum. It was found from the results of present numerical visualization that a suppression tank system which will be used in ITER is very effective and the ITER pressure suppression system during ICE and LOVA events is adequate.

Dust acoustic solitons in a two-ion-temperature plasma with isothermal ions and warm adiabatic dusty fluid

Both compressive and rarefactive solitons are found to exist in a warm adiabatic dusty plasma with two-temperature isothermal ions. The Korteweg-de Vries (KdV) equation for isothermal ions and KdV-type equations at a critical density of low-temperature ions are derived in order to discuss the properties of dust acoustic solitons. Using a quasipotential analysis, critical Mach numbers M 1c and M 2c are obtained such that rarefactive dust acoustic solitons exist when 1<M <M 1c and compressive dust acoustic solitons exist when 1 <M <M 2c .

Simulation of the long-term behaviour of regenerateable dust filters

Periodically regenerateable cake-forming filters have assumed a commercially dominant role in air purification because of their excellent dust collection capabilities. However, due to the absence of calculation models, intensive experimental investigations are usually necessary to optimally design such filters especially with respect to a residual pressure drop after regeneration that is as small and stable as possible. The simulation model described in this work is capable of simulating the build-up of a compressible dust filter cake on a needle-felt including the regeneration of the filter medium and the calculation of the pressure drop during filtration and after regeneration. This model was used to examine the influence of the two most important operation parameters of such filters - the filtration velocity and the maximum pressure drop Δp max, where regeneration is performed - on the residual pressure drop: It is shown why a high maximum pressure drop Δp max and a high filtration velocity can lead to a long-term increase of the residual pressure drop of a filter - an effect, that is well known from experiments and of course has to be avoided.

Simulation of the filtration behaviour of dust filters

Periodically regenerable cake-forming filters have assumed a commercially dominant role in air purification due to their excellent dust collection capabilities. These filters are used to separate particles from gases with high dust concentrations, whereby the separation arises as the dust-gas mixture passes through the filter medium and the particles are retained. As soon as a certain maximum pressure drop over the filter medium is reached the filter medium is regenerated. In order to optimally design such filters, there are three important parameters for the economical evaluation of the filter: the correlating pressure drop increase of the filter during filtration which is mainly influenced by the compressibility of the dust cake, the dust separation efficiency especially at the beginning of the filtration and the rise of the residual pressure drop of the filter after several cycles of filtration and regeneration. In this work a 2-dimensional computer simulation model for the compressible dust cake build-up on widely used non-woven fabrics (needle-felts) is introduced. First this model is used to investigate the mechanism causing compression inside dust filter cakes and to clarify different compression phenomena. Second it is shown that this simulation program is capable of describing the particle penetration inside and through the filter medium, the clogging of the filter medium and the growing of the dust filter cake out of the filter medium, whereby the corresponding pressure drop and the number of particles in the clean gas as an function of the filtration time show good qualitative agreement with known experimental data.

Dust-acoustic solitary waves and double layers in dusty plasma consisting of cold dust particles and two-temperature isothermal ions

It is found that a dusty plasma with inertial dust fluid and two-temperature isothermal ions admits both compressive and rarefactive solitary waves, as well as compressive and rarefactive double layers (depending on the concentration of low-temperature ions). In this paper, Korteweg-de Vries equation (KdV-type equations) with cubic and fourth-order nonlinearity at the critical density of low-temperature isothermal ions are derived to discuss properties of dust-acoustic solitary waves. In the vicinity of critical density of low-temperature ions, KdV-type equation with mixed nonlinearity is discussed. By using quasipotential analysis, critical Mach numbers M1c and M2c are obtained such that rarefactive dust-acoustic solitons exist when 1&amp;lt;M&amp;lt;M1c and compressive dust acoustic solitons exist when 1&amp;lt;M&amp;lt;M2c.

Cake Formation in Fabric Filtration of Gases

The formation of dust cakes on the surface of a flat square polyester felt has been studied. Cake porosity was estimated from pressure drop and deposited mass measurements, utilizing correlations from the literature. These results have been compared to direct porosity measurements, obtained by image analysis of cake cross sections. Cakes of limestone particles with four different size ranges (median Sauter diameters of 2.5, 3.3, 6.9, and 10.7 μm) and four thicknesses, ranging from 130 to 1200 μm, were tested. The results have shown cake porosity to be increasing considerably with decreasing particle diameter. Also, the porosity was found to be dependent on cake thickness and position, indicating compressible dust layers. The porosity estimated from the correlations agreed reasonably well with the measured average in a cross section and could be used in practical cases in which overall values are required, provided that the cake is not too thin. Finally, an expression for pressure drop in a compressible ca...

Probing the properties of planetary ring dust by the observation of Mach cones

Compressive dust acoustic waves can be excited in dusty plasmas. Big boulders in planetary rings move at the Keplerian velocity, while smaller dust particles move at a slightly different velocity due to the action of the Lorentz force. If the difference in velocity Δυ is larger than the dust acoustic wave velocity, αd, a wake will be formed with an opening angle of 2θ where sin θ = |αd/Δυ|. The discovery of wakes and the measurement of their opening angles by the space experiment Cassini to Saturn will yield added information on the dusty plasma conditions in regions through which Cassini will not pass. We find that in some regions the waves that are excited by the boulders may be weak because a large fraction of the interacting dust is absorbed rather than deflected by the boulder. For a given dust size the most favourable conditions for the observations of wakes exist in two fairly narrow regions, one inside and one outside the corotation radius. The favorable regions are closest to the corotation radius for the smallest dust particles and progressively further away for larger dust particles.

A new dust-dynamics-induced interchange instability in dusty plasmas

A nonuniform dusty plasma held in equilibrium in a magnetic field against gravity has a polarization electric field E 0 in the direction of gravity for negatively charged dust grains. It is shown that the E 0 × B 0 drift of the plasma which carries a positive current induces, in combination with compressible dust dynamics, a novel flute-like interchange instability that is different from the usual Rayleigh-Taylor mode.

A new dust-dynamics-induced interchange instability in dusty plasmas

A nonuniform dusty plasma held in equilibrium in a magnetic field against gravity has a polarization electric field E 0 in the direction of gravity for negatively charged dust grains. It is shown that the E 0 × B 0 drift of the plasma which carries a positive current induces, in combination with compressible dust dynamics, a novel flute-like interchange instability that is different from the usual Rayleigh-Taylor mode.

Magnetic Hysteresis at Low Flux Densities

The energy loss per cycle in a ferromagnetic material subjected to small alternating fields is sometimes separated into three parts; the first due to eddy current loss, the second to hysteresis presumed to follow Rayleigh's laws at these flux densities. The origin of the remainder is unknown and is the subject of much controversy; it has been variously termed ``magnetic viscosity,'' ``after effect'' and ``square law hysteresis.'' In studying energy loss in a ring of compressed iron dust, hysteresis loops have been measured ballistically by a new method with a relative error in Bm as low as 0.01 percent. The range in maximum flux density is from 2 to 100 gauss. The loops are lenticular and very slender, Bm being about 1500 times the remanence for the smallest loop. The smaller loops are at flux densities considerably below those investigated by Rayleigh. His findings as to variation of area, of remanence, and of permeability with loop amplitude are confirmed and extended through the new range of flux densities, though the shape of the loops is not as simple as that he proposed. The energy loss per cycle is proportional to Bm3 while the remanence is proportional to Bm2. The ballistic measurements have been compared with a.c. bridge measurements on the same specimen. The loss of unknown origin is not included in the hysteresis loss measured ballistically. Comparison is made between the third harmonic induced voltage computed by a Fourier series analysis of the ballistic loops and the harmonic actually generated by the specimen. Agreement is found between the measured and the computed values. Possible explanations of the discrepancy between the ballistic observed energy losses and a.c. findings are discussed.