Thickness Of Dust Layer Research Articles

On the crossing of thin shells

The crossing of two dust shells is considered as a simplified model of a collapsing thick layer of dust. We use the Israel's formalism to describe the development of two shells of dust which interact only gravitationally. The formalism is developed in both Schwarzschild and Kruskal coordinates.

A Microwave Technique for Online Monitoring and Control of Dust Layer Thickness Inside Electrostatic Precipitators

A procedure is proposed for real time non-intrusive measuring of the thickness of the ash layer on the plates of electrostatic precipitators (ESP) commonly used in energy plants. The method is based on the measurement of the phase shift of a surface electromagnetic wave, which propagates on the plate under test, equipped with input-output electromagnetic couplers.It is shown that the phase shift depends on the mean thickness of the ash layer. Results are reported that were obtained from a laboratory-scale experimental ESP model, using a microwave test signal at 2500 MHz.The experiments confirm the possibility of using the proposed technique for on line determination of the collection efficiency of ESP and also to prevent electrostatic discharge.

Are galaxy discs optically thick?

The classical optical evidence for the low optical depths traditionally assigned to spiral disks is reexamined, suggesting that it is highly model-dependent and unconvincing. In particular, layered models with a physically thin but optically thick dust layer behave like optically thin disks. The opposite hypothesis, that such disks are optically thick is then examined in the light of modern evidence. It is found to be consistent with the near IR and IRAS observations, with the surface brightnesses, with the H I and CO column densities and with the H-alpha measurements.

Evidence for a molecule heavier than methane in the atmosphere of Pluto

THE recent occultation of a 12th magnitude star by Pluto provided a unique opportunity for studying its atmosphere. Analyses of measurements made at the Hobart observatory in Australia and the Kuiper Airborne Observatory (KAO) have been published1,2. It is generally agreed that Pluto possesses a substantial atmosphere, with a surface pressure of ∼l0µbar. Both occultation measurements are sensitive primarily to the atmospheric conditions at the 1-μbar level. Analysis of the Hobart data reveals an atmospheric scale height of 46–57 km at a radial distance of 1,240–1,290 km, whereas the scale height derived from the KAO data is 59.7 ± 1.5 km at 1,214 ± 20 km. The existence of an optically thick dust layer along the line of sight at the limb has been inferred from the KAO measurements, raising doubts about the true surface radius of Pluto2. The measured scale heights are consistent with a purely methane atmosphere at a temperature of 50–61 K for the Hobart data1 and 67±6K for the KAO data2. These values are close to the surface temperature3. Here we examine the energy balance in the atmosphere and conclude that the temperature near 1 μ bar is ∼100K rather than the surface temperature; consequently, the mean molecular weight of the atmosphere is close to 25a.m.u., and a molecule heavier than (and in addition to) methane must be present in the atmosphere.

The Onset of Electrical Breakdown in Dust Layers: II. Effective Dielectric Constant and Local Field Enhancement

Part I of this work has shown that electrical breakdown in dust layers obeys Paschen's Law, but occurs at applied field values which appear too small to initiate the breakdown. In this paper we will show how an effective dielectric constant characterizing the dust layer can be determined from ac dielectric measurements and the theory of Debye. When combined with an expression for the enhanced local electric field in the void spaces between particles in the layer, field strengths which are large enough to initiate electrical breakdown in the layer are predicted at relatively low values of applied field. The effect of temperature and dust layer thickness on the onset of electrical breakdown within the dust layer can also be explained by the dependence of the effective dielectric constant on these parameters.

Impact on the earth, ocean and atmosphere

On the basis of finite-difference techniques, cratering flow calculations are used to obtain the spatial attenuation of shock pressure with radius along the impact axis for the impact of silicate rock and iron impactors on a silicate half-space at speeds of 5 to 45 km/sec. Upon impact of a 10 to 30 km diameter silicate or water object onto a 5 km deep ocean overlying a silicate half-space planet at 30 km/sec, it is found that from 12 to 15 percent of the incident energy is coupled into the water. The mass of atmosphere lost due to impacts of 1 to 5 km radius projectiles is calculated.

Flashover measurements of back discharge

The mode change and flashover voltage of back discharge under different gaseous conditions were studied with special attention to the effects of dust layer thickness and alkaline components contained in dust. It was found that back discharge took either a streamer or a steady-glow mode depending upon the gas mean-free-path. These modes have their own characteristics flashover voltage as a function of gas mean-free-path, where its value for the former mode is much lower than that for the latter. The thickness of the dust layer and the existence of the alkaline components also govern the initiation of a streamer so that the flashover voltage is affected greatly by these factors.

Thermal Decomposition of Grain Dust: An Early Warning for Incipient Fire or Explosion

ABSTRACT TESTS were conducted to eval-uate the response of ionization-type detectors and combustible gas detectors to invisible aerosols and gases evolved from heated grain dust at temperatures below the igni-tion temperature. The concentration of aerosol particles as a func-tion of temperature and dust layer thickness was determined. The aerosol concentration from a heated surface is sensitive to dust layer thickness and at a given temperature and heating rate, it decreases quite rapidly for thicknesses greater than 0.03 cm. Thin dust layers heated at 24 C/min triggered a Pyr-A-Larm detector unit (set to respond at (2-3) x 105 particles/cm3) when the dust reached a temperature of 200 C, and at 225 C when the aerosol was drawn through a fiberglass filter. A combustible gas detector could be set to respond at temperatures well below the ignition temperature and did not appear to be sensitive to dust layer thickness of up to 0.64 cm. The potential application of such detectors in an early warning system to detect hot spots approaching dust ignition temperatures in a grain elevator or feed mill environment is dis-cussed.

Interaction of the solar wind with the moon and formation of a lunar limb shock wave

The interaction of the solar wind with a two-layered moon is considered from the point of view of the induction generator model of Sonett and Colburn (1967). We show that a highly conducting lunar core, shielded by a thin insulating outer layer, cannot reasonably be consistent with the observed absence of a lunar bow shock, since a 10-meter thick surface dust layer would require a conductivity less than 10−10 mho/m, while a 10-kilometer thick layer would require a conductivity less than 10−7 mho/m to shield the core; conductivities in this low range do not seem reasonable. We thus establish an upper limit of 10−5 mho/m for the core conductivity, but point out that this figure can be consistent with the existence of a highly conducting surface layer. Two mechanisms are suggested for the formation of a lunar limb shock wave. It is shown that in the steady-state unipolar generator model a limb shock will be expected to form in the vicinity of the plane defined by the solar wind velocity and magnetic field directions, while a limb shock may be expected to form also in the nonsteady state if the moon possesses a conducting outer layer (10−4 < σ < 10−3 mho/m) of thickness between one-tenth and several kilometers.