A study of breakdown delay in electrically pumped laser gases

1977 ◽  
Vol 55 (4) ◽  
pp. 325-336 ◽  
Author(s):  
P. Savic ◽  
M. M. Kekez
Keyword(s):  
Roughness Element ◽  
Surface Phenomena ◽  
Cathode Sheath ◽  
Sheath Region ◽  
Hot Gas ◽  
Deposited Energy ◽  
History Of ◽  
Laser Development ◽  
Time Required ◽  
Experimental Findings

When a steep-fronted voltage step is applied to the electrodes in a preionized gas, the high electric field in the cathode sheath, together with current continuity across the sheath causes preferential heating and pressure increase of the gas in the sheath region. The situation is somewhat analogous to that in a shock tube at the instant of diaphragm rupture. However, owing to the current, the cathode sheath goes unstable, forming filaments of hot gas from the sheath. Expressions are derived for the breakdown delay in the two extreme cases of high and low power deposited in the gas, in terms of four time constants, i.e. the relaxation time, the 'power time', being the time required for the electric power to raise the pressure level of the gas to ambient, the 'asperity time', i.e. the time taken by a sound wave to traverse a roughness element or asperity of the electrode surface, and the 'sheath time', being the time of the wave's traverse of the sheath thickness. It is shown that the theory is in substantial agreement with existing experimental findings, including those of the authors. It is further indicated to what extent the new theory goes beyond older concepts, namely in that not only thermoacoustic but also surface phenomena are taken into account.The history of gas laser development is illustrated graphically in the theoretical and experimental curves of breakdown delay vs. surface asperity and deposited energy.

The Enrichment History of Hot Gas in Poor Galaxy Groups

1999 ◽  
Vol 511 (1) ◽  
pp. 34-40 ◽  
Author(s):  
David S. Davis ◽  
John S. Mulchaey ◽  
Richard F. Mushotzky
Keyword(s):  
Galaxy Groups ◽  
Hot Gas ◽  
History Of

A short history of laser development

2010 ◽  
Vol 49 (25) ◽  
pp. F99 ◽  
Author(s):  
Jeff Hecht
Keyword(s):  
Short History ◽  
History Of ◽  
Laser Development

Studies on the life-history of Bunostomum phlebotomum (Railliet, 1900), a hookworm parasite of cattle

Parasitology ◽  
1946 ◽  
Vol 37 (3-4) ◽  
pp. 192-201 ◽  
Author(s):  
J. F. A. Sprent
Keyword(s):  
Infective Larva ◽  
Stage Larva ◽  
Fourth Stage ◽  
Larval Stages ◽  
The Third ◽  
Third Stage ◽  
History Of ◽  
Time Required ◽  
Cutaneous Blood ◽  
Fourth Stage Larva

A description is given of the processes of copulation, formation of the egg and spermatozoon, cleavage, embryogeny and hatching in B. phlebotomum. These processes were found to be essentially similar to those in other strongyle nematodes.The anatomy of the first three larval stages is described and the observations of Conradi & Barnette (1908) and Schwartz (1924) were largely confirmed.Penetration of the skin of calves by the infective larva was observed histologically. The larvae were found to have reached the dermis within 30 min. and to have penetrated the cutaneous blood vessels within 60 min. of application to the skin. The larvae were found in the lung where the third ecdysis was in progress 10 days after penetration of the skin. A description is given of the growth of the third-stage larva in the lung, the changes which take place during the third ecdysis, and the anatomy of the fourth-stage larva.The fourth-stage larvae exsheath in the lungs and travel to the intestine. After a period of growth in which sexual differentiation takes place, the fourth ecdysis occurs and the adult parasite emerges. The time required for the attainment of maturity was found to be somewhere between 30 and 56 days after penetration of the skin.This paper was written at the Ministry of Agriculture and Fisheries Veterinary Laboratories, Wey-bridge, and the writer would like to express his gratitude to the Director, Prof. T. Dalling, also to Dr W. R. Wooldridge, chairman of the Council of the Veterinary Educational Trust for their help and encouragement. The writer's thanks are also due to Dr H. A. Baylis, Prof. R. T. Leiper and Dr E. L. Taylor for their advice and help on technical points, and to Mr R. A. O. Shonekan, African laboratory assistant, for his able co-operation.

scholarly journals THE LIFE-HISTORY OF THE NORTHERN MOLE-CRICKET—GRYLLOTALPA BOREALIS

1892 ◽  
Vol 24 (11) ◽  
pp. 270-273
Author(s):  
E. W. Doran
Keyword(s):  
United States ◽  
Life History ◽  
The United States ◽  
General Distribution ◽  
Mole Cricket ◽  
History Of ◽  
Time Required

Although this is a common insect in many parts of the United States, it is not generally found in great numbers in any locality, and, notwith standing its general distribution, the various staes of the insect seem not to have been describe or figured.While I am not yet able to clear up all the points in its history, I have studied the insect in all its stages, though I have not reared it from the egg to maturity, on account of the time required for it to develop—in all probability three years.

Time Dependent Magnetic Switching in Spin Valve Structures

1995 ◽  
Vol 384 ◽  
Author(s):  
J. B. Restorff ◽  
M. Wun-Fogle ◽  
S. F. Cheng ◽  
K. B. Hathaway
Keyword(s):  
Giant Magnetoresistance ◽  
Spin Valve ◽  
Time History ◽  
Time Dependent ◽  
Si Substrates ◽  
Magnetic Switching ◽  
Magnetic Aftereffect ◽  
Magnetron Sputter Deposition ◽  
History Of ◽  
Time Required

ABSTRACTWe have observed time dependent magnetic switching in spin-valve sandwich structures of Cu/Co/Cu/Fe films grown on silicon and Kapton substrates and Permalloy/Co/Cu/Co films grown on NiO or NiO/CoO coated Si substrates. The giant magnetoresistance (MR) values ranged from 1 to 3 percent at room temperature. The films were grown by DC magnetron sputter deposition. Measurements were made on the time required for the MR to stabilize to about 1 part in 104 after the applied field was incremented. This time depends almost linearly on the amplitude of the timedependent MR change with a slope (time / ΔMR) of 20 000 to 30 000 s. Some samples took as long as 70 s to stabilize. The time dependent effects may be important for devices operating in these regions of the magnetoresistance curve. In addition, measurements were made on the time history of the MR value for a period of 75 s following a step change in the field from saturation. We observed that the time dependent behavior of the MR values of both experiments produced an excellent fit to a function of the form ΔMR(t) = α + β;ln(t) where ɑ and β are constants. This time dependence was consistent with the behavior of the magnetic aftereffect.

scholarly journals Short history of laser development

2010 ◽  
Vol 49 (9) ◽  
pp. 091002 ◽  
Author(s):  
Jeff Hecht
Keyword(s):  
Short History ◽  
History Of ◽  
Laser Development

Food Security-Related Issues and Solutions

2020 ◽  
pp. 43-62
Author(s):  
Olga Pasko ◽  
Natalia Staurskaya
Keyword(s):  
Food Security ◽  
Anthropogenic Pollution ◽  
Environmentally Safe ◽  
History Of ◽  
Quality Of Food ◽  
High Yields ◽  
Time Required ◽  
Food Reserves ◽  
Sufficient Food

The food problem has been and has remained relevant throughout the history of mankind. At the end of 20th and the beginning of the 21st century, in the lives of many nations and countries, there have been significant changes. Health status and level of education of the population, such as, for example, food security, is the priority in many countries since, in the absence of sufficient food reserves, there is an economic and political dependence of some countries on others. Having not yet received the required amount of food, the world is faced with the problem of ensuring security in its quality. Anthropogenic pollution of the environment complicates the problem with the quality of food and the exception of harmful chemicals in food. There is a problem of using environmentally friendly agrotechnical means, ensuring the production of high yields of environmentally safe products with a desirable reduction in their cost, and shortening the time required for their production.

scholarly journals Evidence for AGN Feedback in Galaxy Clusters and Groups

2012 ◽  
Vol 2012 ◽  
pp. 1-24 ◽  
Author(s):  
Myriam Gitti ◽  
Fabrizio Brighenti ◽  
Brian R. McNamara
Keyword(s):  
Galaxy Clusters ◽  
Galaxy Evolution ◽  
Large Scale ◽  
Current Knowledge ◽  
Dynamical Evolution ◽  
Large Scale Structures ◽  
Hot Gas ◽  
History Of ◽  
Initial Idea ◽  
Scale Structures

The current generation of flagship X-ray missions,ChandraandXMM-Newton, has changed our understanding of the so-called “cool-core” galaxy clusters and groups. Instead of the initial idea that the thermal gas is cooling and flowing toward the center, the new picture envisages a complex dynamical evolution of the intracluster medium (ICM) regulated by the radiative cooling and the nongravitational heating from the active galactic nucleus (AGN). Understanding the physics of the hot gas and its interplay with the relativistic plasma ejected by the AGN is key for understanding the growth and evolution of galaxies and their central black holes, the history of star formation, and the formation of large-scale structures. It has thus become clear that the feedback from the central black hole must be taken into account in any model of galaxy evolution. In this paper, we draw a qualitative picture of the current knowledge of the effects of the AGN feedback on the ICM by summarizing the recent results in this field.

scholarly journals Acoustic Agglomeration of Power Plant Fly Ash for Environmental and Hot Gas Clean-up

1988 ◽  
Vol 110 (4) ◽  
pp. 552-557 ◽  
Author(s):  
G. Reethof
Keyword(s):  
Fly Ash ◽  
Power Plant ◽  
Pollution Control ◽  
Flue Gases ◽  
Analytical Models ◽  
Particle Removal ◽  
Air Pollution Control ◽  
Hot Gas ◽  
History Of ◽  
Viable Method

Acoustic agglomeration of power plant fly ash is an intermediate treatment of the flue gases to increase the size of the small micron (1–5) and submicron (0.1–1) particulates to large micron sizes (5–10) so that the conventional particle removal devices such as bag houses, electrostatic precipitators, and scrubbers can operate more efficiently. This paper provides a brief history of the topic, introduces some of the fundamental issues and gives some recent results of analytical models of the processes. The experimental facility is briefly described and some analytical results are shown which compare well with the experimental results. Most important of all, the paper shows that acoustic agglomeration is a technically and potentially economically viable method to improve air pollution control.

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