The Initial Stage of Physical Investigations of the Gas Electric Discharge in the Quasi-Optical MW Beam in Real Conditions

2012 ◽  
Author(s):  
Konstantin Alexandrov ◽  
Vladimir Bychkov ◽  
Dmitry Bychkov ◽  
Igor Esakov ◽  
Lev Grachev
Keyword(s):  
Electric Discharge ◽  
Initial Stage

scholarly journals A distinct negative leader propagation mode

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
O. Scholten ◽  
B. M. Hare ◽  
J. Dwyer ◽  
N. Liu ◽  
C. Sterpka ◽  
...  
Keyword(s):  
Radio Telescope ◽  
Electric Discharge ◽  
Radio Astronomy ◽  
Propagation Mode ◽  
Common Phenomenon ◽  
High Charge ◽  
Initial Stage ◽  
Lightning Initiation ◽  
The Common

AbstractThe common phenomenon of lightning still harbors many secrets such as what are the conditions for lightning initiation and what is driving the discharge to propagate over several tens of kilometers through the atmosphere forming conducting ionized channels called leaders. Since lightning is an electric discharge phenomenon, there are positively and negatively charged leaders. In this work we report on measurements made with the LOFAR radio telescope, an instrument primarily build for radio-astronomy observations. It is observed that a negative leader rather suddenly changes, for a few milliseconds, into a mode where it radiates 100 times more VHF power than typical negative leaders after which it spawns a large number of more typical negative leaders. This mode occurs during the initial stage, soon after initiation, of all lightning flashes we have mapped (about 25). For some flashes this mode occurs also well after initiation and we show one case where it is triggered twice, some 100 ms apart. We postulate that this is indicative of a small (order of 5 km$$^2$$ 2 ) high charge pocket. Lightning thus appears to be initiated exclusively in the vicinity of such a small but dense charge pocket.

scholarly journals A Distinct Negative Leader Propagation Mode

2021 ◽  
Author(s):  
O. Scholten ◽  
B. M. Hare ◽  
J. Dwyer ◽  
N. Liu ◽  
C. Sterpka ◽  
...  
Keyword(s):  
Radio Telescope ◽  
Electric Discharge ◽  
Radio Astronomy ◽  
Propagation Mode ◽  
Common Phenomenon ◽  
High Charge ◽  
Initial Stage ◽  
Lightning Initiation ◽  
The Common

Abstract The common phenomenon of lightning still harbors many secrets such as what are the conditions for lightning initiation and what is driving the discharge to propagate over several tens of kilometers through the atmosphere forming conducting ionized channels called leaders. Since lightning is an electric discharge phenomenon, there are positively and negatively charged leaders. In this work we report on measurements made with the LOFAR radio telescope, an instrument primarily build for radio-astronomy observations. It is observed that a negative leader rather suddenly changes, for a few milliseconds, into a mode where it radiates 100 times more VHF power than typical negative leaders after which it spawns a large number of more typical negative leaders.This mode occurs during the initial stage, soon after initiation, of all lightning flashes we have mapped (about 25). For some flashes this mode occurs also well after initiation and we show one case where it is triggered twice, some 100 ms apart.We postulate that this is indicative of a small (order of 5 km2) high charge pocket.Lightning thus appears to be initiated exclusively in the vicinity of such a small but dense charge pocket.

Reaction couples of ceramic thin films prepared by CVD

1988 ◽  
Vol 46 ◽  
pp. 798-799
Author(s):  
D.W. Susnitzky ◽  
S.R. Summerfelt ◽  
C.B. Carter
Keyword(s):  
Thin Film ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Solid State Reactions ◽  
Spatial Distributions ◽  
Diffusion Couples ◽  
Kinetics Studies ◽  
Ceramic Thin Films ◽  
Initial Stage

Solid-state reactions have traditionally been studied in the form of diffusion couples. This ‘bulk’ approach has been modified, for the specific case of the reaction between NiO and Al2O3, by growing NiAl2O4 (spinel) from electron-transparent Al2O3 TEM foils which had been exposed to NiO vapor at 1415°C. This latter ‘thin-film’ approach has been used to characterize the initial stage of spinel formation and to produce clean phase boundaries since further TEM preparation is not required after the reaction is completed. The present study demonstrates that chemical-vapor deposition (CVD) can be used to deposit NiO particles, with controlled size and spatial distributions, onto Al2O3 TEM specimens. Chemical reactions do not occur during the deposition process, since CVD is a relatively low-temperature technique, and thus the NiO-Al2O3 interface can be characterized. Moreover, a series of annealing treatments can be performed on the same sample which allows both Ni0-NiAl2O4 and NiAl2O4-Al2O3 interfaces to be characterized and which therefore makes this technique amenable to kinetics studies of thin-film reactions.

Decoration technique and surface physics

1978 ◽  
Vol 36 (1) ◽  
pp. 436-437 ◽  
Author(s):  
H. Bethge
Keyword(s):  
Diffusion Path ◽  
Special Importance ◽  
Surface Physics ◽  
Step Structure ◽  
Initial Stage ◽  
Special Cases ◽  
Atomic Surface ◽  
The Mean ◽  
Bulk Structure ◽  
Decoration Technique

Besides the atomic surface structure, diverging in special cases with respect to the bulk structure, the real structure of a surface Is determined by the step structure. Using the decoration technique /1/ it is possible to image step structures having step heights down to a single lattice plane distance electron-microscopically. For a number of problems the knowledge of the monatomic step structures is important, because numerous problems of surface physics are directly connected with processes taking place at these steps, e.g. crystal growth or evaporation, sorption and nucleatlon as initial stage of overgrowth of thin films.To demonstrate the decoration technique by means of evaporation of heavy metals Fig. 1 from our former investigations shows the monatomic step structure of an evaporated NaCI crystal. of special Importance Is the detection of the movement of steps during the growth or evaporation of a crystal. From the velocity of a step fundamental quantities for the molecular processes can be determined, e.g. the mean free diffusion path of molecules.

Nucleation and initial growth of Pd2Si crystals on Si(111)

1993 ◽  
Vol 51 ◽  
pp. 844-845
Author(s):  
Xianghong Tong ◽  
Oliver Pohland ◽  
J. Murray Gibson
Keyword(s):  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Initial Growth ◽  
Surface And Interface ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Initial Stage ◽  
Effect Of Surface

The nucleation and initial stage of Pd2Si crystals on Si(111) surface is studied in situ using an Ultra-High Vacuum (UHV) Transmission Electron Microscope (TEM). A modified JEOL 200CX TEM is used for the study. The Si(111) sample is prepared by chemical thinning and is cleaned inside the UHV chamber with base pressure of 1x10−9 τ. A Pd film of 20 Å thick is deposited on to the Si(111) sample in situ using a built-in mini evaporator. This room temperature deposited Pd film is thermally annealed subsequently to form Pd2Si crystals. Surface sensitive dark field imaging is used for the study to reveal the effect of surface and interface steps.The initial growth of the Pd2Si has three stages: nucleation, growth of the nuclei and coalescence of the nuclei. Our experiments shows that the nucleation of the Pd2Si crystal occurs randomly and almost instantaneously on the terraces upon thermal annealing or electron irradiation.

Anisotropy of interfacial defects in the initial stage of MOVPE GaAs growth On Si

1990 ◽  
Vol 48 (4) ◽  
pp. 592-593
Author(s):  
C. Vannuffel ◽  
C. Schiller ◽  
J. P. Chevalier
Keyword(s):  
Early Stage ◽  
Threading Dislocations ◽  
Mbe Growth ◽  
Detailed Mechanism ◽  
Si Substrates ◽  
Initial Stage ◽  
Interfacial Defects ◽  
Interfacial Dislocations ◽  
Step Growth ◽  
Essential Problem

Recently, interest has focused on the epitaxy of GaAs on Si as a promising material for electronic applications, potentially for integration of optoelectronic devices on silicon wafers. The essential problem concerns the 4% misfit between the two materials, and this must be accommodated by a network of interfacial dislocations with the lowest number of threading dislocations. It is thus important to understand the detailed mechanism of the formation of this network, in order to eventually reduce the dislocation density at the top of the layers.MOVPE growth is carried out on slightly misoriented, (3.5°) from (001) towards , Si substrates. Here we report on the effect of this misorientation on the interfacial defects, at a very early stage of growth. Only the first stage, of the well-known two step growth process, is thus considered. Previously, we showed that full substrate coverage occured for GaAs thicknesses of 5 nm in contrast to MBE growth, where substantially greater thicknesses are required.

Mechanism of irregular crack-propagation in thermal controlled fracture of ceramics induced by microwave

2020 ◽  
Vol 21 (6) ◽  
pp. 610
Author(s):  
Xiaoliang Cheng ◽  
Chunyang Zhao ◽  
Hailong Wang ◽  
Yang Wang ◽  
Zhenlong Wang
Keyword(s):  
Crack Propagation ◽  
Industrial Application ◽  
Ceramic Materials ◽  
Advanced Technology ◽  
Analytical Models ◽  
Propagation Mechanism ◽  
Unstable Crack ◽  
Fracture Simulation ◽  
Initial Stage ◽  
Controlled Fracture

Microwave cutting glass and ceramics based on thermal controlled fracture method has gained much attention recently for its advantages in lower energy-consumption and higher efficiency than conventional processing method. However, the irregular crack-propagation is problematic in this procedure, which hinders the industrial application of this advanced technology. In this study, the irregular crack-propagation is summarized as the unstable propagation in the initial stage, the deviated propagation in the middle stage, and the non-penetrating propagation in the end segment based on experimental work. Method for predicting the unstable propagation in the initial stage has been developed by combining analytical models with thermal-fracture simulation. Experimental results show good agreement with the prediction results, and the relative deviation between them can be <5% in cutting of some ceramics. The mechanism of deviated propagation and the non-penetrating propagation have been revealed by simulation and theoretical analysis. Since this study provides effective methods to predict unstable crack-propagation in the initial stage and understand the irregular propagation mechanism in the whole crack-propagation stage in microwave cutting ceramics, it is of great significance to the industrial application of thermal controlled fracture method for cutting ceramic materials using microwave.

Natural Language and a Computer System in Medical Research*)

1979 ◽  
Vol 18 (01) ◽  
pp. 15-17 ◽  
Author(s):  
Ileana C. Johnson ◽  
S. L. Tsao ◽  
I. D. J. Bross ◽  
D. P. Shedd
Keyword(s):  
Head And Neck Cancer ◽  
Natural Language ◽  
Roswell Park Memorial Institute ◽  
Basic Form ◽  
Specialized Knowledge ◽  
Complete Control ◽  
Processing Data ◽  
Remote Terminal ◽  
Initial Stage ◽  
Cancer Project

A series of computer programs are now available for processing data whose basic form is narrative (natural language), numerical or a combination of the two. This system was developed in the Department of Biostatistics of Roswell Park Memorial Institute, to enable an investigator to have complete control of the data — from the initial stage of entering the data to the final stage of analysis. Specialized knowledge of computers is not necessary in order to implement the different procedures. By following the instructions specified in various manuals and by basically just pushing a button of a remote terminal the procedures are activated and executed. This system is actually used for maintaining the data of a head and neck cancer project.

A Study on Knowledge, Attitude, Awareness and Practice About HIV/AIDS among different age group of Karachi, Pakistan

2017 ◽  
Vol 3 (3) ◽  
pp. 328-333
Author(s):  
Safia Mehmood ◽  
Sheema Zia ◽  
Nida Aziz ◽  
Omama Sajid
Keyword(s):  
Hiv Transmission ◽  
Age Groups ◽  
World Population ◽  
Major Barrier ◽  
Initial Stage ◽  
Awareness Programs ◽  
And Gender ◽  
Strongly Agree ◽  
High Level ◽  
Lack Of Knowledge

The AIDS is one of the most complicated health problems of the 21st century and it threatens the world population. AIDS spread at an alarming rate. This was a descriptive study to determine the knowledge, awareness, and practice about HIV among different age groups. The study carried out in Karachi, Pakistan during the period of January 2016-april 2016, in which 82 peoples are participated; 65 peoples having age in between 18-30, people’s lies in 31-40 years, while only 4 peoples having age above 40. From which 91% peoples thought HIV is dangerous virus and 51% peoples having misconception that it cause AIDS on initial stage and does not have any effect on CD4+. Majority of peoples aware about transmission of AIDS through intercourse, and during pregnancy. But the study show the high level of misbelieve also in mode of transmission that HIV transmit through sweat, saliva etc. Majority of the peoples have knowledge that HIV-1 is the most common type found worldwide. Also large number of peoples have knowledge that HIV weak immune system by destroying CD4+ and require long exposure to progress AIDS. Less than 15% of peoples strongly agree that AIDS is common in women. This misconception reflex the lack of knowledge and awareness in the HIV transmission and gender relation. Also majority of peoples thought that lack of knowledge is major barrier in the proper cure of disease. So increasing knowledge by awareness programs; sexual prevention; by starting national testing resources and curing poverty will cured AIDS in Pakistan. Newly drugs are introduced which can stop the progression of AIDS.

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