The Micrometeoroid in the Upper Atmosphere

International Astronomical Union Colloquium ◽

10.1017/s0252921100067002 ◽

1991 ◽

Vol 126 ◽

pp. 303-306 ◽

Cited By ~ 1

Author(s):

F. Kamijo

Keyword(s):

Deep Sea ◽

Initial Velocity ◽

Upper Atmosphere ◽

Meteor Stream ◽

Secondary Particles ◽

Radius Variation ◽

Gas Molecules

AbstractThe temperature and the radius variation of micrometeoroids in the thermosphere and the mesosphere are calculated theoretically. If the radius and the initial velocity are 100μm and 30 km/sec respectively, the evaporation height and the velocity coincide almost exactly with those of the Capricornids and the Virginids from the meteor stream observation.Moreover, it is shown that the not evaporated debris till the end of the sublimation may become spherules in the bottom of deep sea; and that fluffy micrometeoroids (10μsize) floating in the stratosphere are also consistent with our calculation.The recondensation and the coagulation of the evaporated gas molecules from the meteoroid are also calculated, and it is shown that these secondary particles are very small and few.

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Influence of Low Dosage Green Extracts on CO2 Hydrate Formation

Petroleum & Petrochemical Engineering Journal ◽

10.23880/ppej-16000234 ◽

2020 ◽

Vol 4 (3) ◽

pp. 1-10

Author(s):

Prasad PSR

Keyword(s):

Deep Sea ◽

Hydrate Formation ◽

Economic Loss ◽

Extraction Process ◽

High Demand ◽

Leaf Extracts ◽

Gas Molecules ◽

Plug Formation ◽

Low Dosage ◽

Petroleum Extraction

Gas clathrates or the gas hydrates are the solid ice particles encapsulating gas molecules (commonly methane - CH 4 and carbon dioxide - CO 2 ) within the water cavities, at moderately high-pressure and low-temperature conditions. The petroleum extraction process from the deep-sea environment favours the occurrence of hydrates, and CO 2 hydrates require milder p, T conditions than CH 4 hydrates. Thus, chocking the pipeline network and obstructing the petroleum flow; leading to a substantial economic loss and hazardous. Conventional hydrate inhibitors (methanol, ethanol, glycols, Amino acids, and ionic liquids, etc.) are used, which are chemically toxic, costly, and required in large volumes (30-50 wt %). Therefore a suitable additive preventing plug formation is on high demand. The present study disclosures the use of three green leaf extracts Azadirachta indica (Neem - NL), Piper betel (betel - BL), and Nelumbo nucifera (Indian lotus - LL) in low dosage (0.5 wt %) on the CO 2 hydrate formation. Experiments are conducted in the isochoric method, with 0.5 wt % green-additives. The hydrates nucleate at higher subcooling (̴ 7-9 K), and the conversion is about ̴ 33-40 %. The induction time is nearly the same both pure- H 2 O and H2O with LL, whereas, it is ̴3 and 4 times higher for NL and BL. The hydrate growth kinetics also indicate significant retardation (2 – 4 times). Thus, these bio-additives, in low-dosage, could be an effective THI and also KHI for preventing the CO 2 hydrates plugs.

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The effects of surface absorbed monolayer microdiffraction patterns

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100105461 ◽

1988 ◽

Vol 46 ◽

pp. 680-681

Author(s):

M. Pan ◽

J.M. Cowley

Keyword(s):

Surface Potential ◽

Electron Probe ◽

Potential Distribution ◽

Crystal Surface ◽

Normal Direction ◽

Surface Image ◽

Extended Surface ◽

Gas Molecules ◽

Surface Nature ◽

Electron Microdiffraction

Electron microdiffraction patterns, obtained when a small electron probe with diameter of 10-15 Å is directed to run parallel to and outside a flat crystal surface, are sensitive to the surface nature of the crystals. Dynamical diffraction calculations have shown that most of the experimental observations for a flat (100) face of a MgO crystal, such as the streaking of the central spot in the surface normal direction and (100)-type forbidden reflections etc., could be explained satisfactorily by assuming a modified image potential field outside the crystal surface. However the origin of this extended surface potential remains uncertain. A theoretical analysis by Howie et al suggests that the surface image potential should have a form different from above-mentioned image potential and also be smaller by several orders of magnitude. Nevertheless the surface potential distribution may in practice be modified in various ways, such as by the adsorption of a monolayer of gas molecules.

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Principles of Low-Vacuum SEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100131152 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1304-1305

Author(s):

Klaus-Ruediger Peters

Keyword(s):

New Technologies ◽

High Vacuum ◽

Optical Microscope ◽

Specimen Surface ◽

Electrical Field ◽

Gaseous Environment ◽

New Information ◽

Gas Molecules ◽

New Interactions ◽

Gas Pressures

Only recently it became possible to expand scanning electron microscopy to low vacuum and atmospheric pressure through the introduction of several new technologies. In principle, only the specimen is provided with a controlled gaseous environment while the optical microscope column is kept at high vacuum. In the specimen chamber, the gas can generate new interactions with i) the probe electrons, ii) the specimen surface, and iii) the specimen-specific signal electrons. The results of these interactions yield new information about specimen surfaces not accessible to conventional high vacuum SEM. Several microscope types are available differing from each other by the maximum available gas pressure and the types of signals which can be used for investigation of specimen properties.Electrical non-conductors can be easily imaged despite charge accumulations at and beneath their surface. At high gas pressures between 10-2 and 2 torr, gas molecules are ionized in the electrical field between the specimen surface and the surrounding microscope parts through signal electrons and, to a certain extent, probe electrons. The gas provides a stable ion flux for a surface charge equalization if sufficient gas ions are provided.

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Environmental cell studies of deformation and fracture

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100175715 ◽

1990 ◽

Vol 48 (4) ◽

pp. 516-517

Author(s):

H. K. Birnbaum ◽

I. M. Robertson

Keyword(s):

National Laboratory ◽

Argonne National Laboratory ◽

Damage Threshold ◽

Chromatic Aberration ◽

Good Choice ◽

Point Of View ◽

Deformation And Fracture ◽

Environmental Cell ◽

Gas Molecules ◽

The University

Studies of the effects of hydrogen environments on the deformation and fracture of fcc, bcc and hep metals and alloys have been carried out in a TEM environmental cell. The initial experiments were performed in the environmental cell of the HVEM facility at Argonne National Laboratory. More recently, a dedicated environmental cell facility has been constructed at the University of Illinois using a JEOL 4000EX and has been used for these studies. In the present paper we will describe the general design features of the JEOL environmental cell and some of the observations we have made on hydrogen effects on deformation and fracture.The JEOL environmental cell is designed to operate at 400 keV and below; in part because of the available accelerating voltage of the microscope and in part because the damage threshold of most materials is below 400 keV. The gas pressure at which chromatic aberration due to electron scattering from the gas molecules becomes excessive does not increase rapidly with with accelerating voltage making 400 keV a good choice from that point of view as well. A series of apertures were placed above and below the cell to control the pressures in various parts of the column.

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Recent Progress In High-Resolution Shadowing For Biological Transmission Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100181300 ◽

1990 ◽

Vol 48 (1) ◽

pp. 510-511 ◽

Cited By ~ 1

Author(s):

Heinz Gross ◽

Katarina Krusche ◽

Peter Tittmann

Keyword(s):

Heavy Metal ◽

High Resolution ◽

Freeze Drying ◽

Atmospheric Conditions ◽

Vacuum Equipment ◽

Transmission Electron ◽

Gas Atmosphere ◽

Gas Molecules ◽

Residual Gas ◽

Backing Layer

Freeze-drying followed by heavy metal shadowing is a long established and straight forward approach to routinely study the structure of dehydrated macromolecules. Very thin specimens such as isolated membranes or single macromolecules are directly adsorbed on C-coated grids. After rapid freezing the grids are transferred into a suitable vacuum equipment for freeze-drying and heavy metal shadowing.To improve the resolution power of shadowing films we introduced shadowing at very low specimen temperature (−250°C). To routinely do that without the danger of contamination we developed in collaboration with Balzers an UHV (p≤10-9 mbar) machine (BAF500K, Fig.2). It should be mentioned here that at −250°C the specimen surface acts as effective cryopump for practically all impinging residual gas molecules from the residual gas atmosphere.Common high resolution shadowing films (Pt/C, Ta/W) have to be protected from alterations due to air contact by a relatively thick C-backing layer, when transferred via atmospheric conditions into the TEM. Such an additional C-coat contributes disturbingly to the contrast at high resolution.

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