Critical Conditions for Impact- and Shock-Induced Hot Spots in Solid Explosives†

1996 ◽  
Vol 100 (14) ◽  
pp. 5794-5799 ◽  
Author(s):  
Craig M. Tarver ◽  
Steven K. Chidester ◽  
Albert L. Nichols
Keyword(s):  
Hot Spots ◽  
Critical Conditions ◽  
Solid Explosives

Hot-spot reaction under transient pressure conditions

1987 ◽  
Vol 413 (1845) ◽  
pp. 329-350 ◽  
Keyword(s):  
Hot Spots ◽  
Hot Spot ◽  
Thermodynamic Description ◽  
Exothermic Reaction ◽  
Pressure Change ◽  
Variable Pressure ◽  
Transient Pressure ◽  
Physical Mechanisms ◽  
Solid Explosives ◽  
Condensed Phase Explosives

The initiation of condensed-phase explosives is often caused by hot spots; that is, localized regions of high temperature created by a variety of physical mechanisms, particularly in solid explosives. Once the hot spots are created, further temperature change is governed by (i) self-heating due to chemical reaction, (ii) heat loss by conduction and radiation, and (iii) adiabatic effects due to pressure and specific volume variation. The last effect includes both self-induced pressure change due to thermal expansion against the surroundings, and externally generated pressure change when initiation is attempted by mechanical impact. This paper presents a thermodynamic description of exothermic reaction under conditions of variable pressure and volume. The reaction rate is assumed to be a function of temperature only. The effect of variable pressure enters through its influence on temperature. It is demonstrated that the effects of self-induced pressure change are small. In the case of externally generated pressure change, explosion times can be affected drastically. These results are discussed in terms of initiation by shock waves of finite duration.

scholarly journals Initiation of solid explosives by impact and friction: the influence of grit

1949 ◽  
Vol 198 (1054) ◽  
pp. 337-349 ◽  
Keyword(s):  
Melting Point ◽  
Hot Spots ◽  
Hot Spot ◽  
Threshold Value ◽  
Maximum Temperature ◽  
Melting Points ◽  
Solid Explosives ◽  
Lower Melting Point ◽  
Determining Factor ◽  
Spot Temperature

This paper describes an experimental study of the initiation of solid explosives, and in particular the effect of artificially introducing transient hot spots of known maximum temperature. This was done by adding small foreign particles (or grit) of known melting-point. The minimum transient hot-spot temperature for the initiation of a number of secondary and primary explosives has been determined in this way. It is shown that the melting-point of the grit is the determining factor , and all the grits which sensitize these explosives to initiation either by friction or impact have melting-points above a threshold value which lies between 400 and 550 ° C. Grit particles of lower melting-point do not sensitize the explosives. The same explosives initiated by the adiabatic compression of air required, for initiation, minimum transient temperatures of the same order as the threshold melting-point values. The results provide strong evidence that the initiation of solids as well as of liquids by friction and impact is thermal in origin and is due to the formation of localized hot spots. There is evidence that in the case of the majority of secondary explosives which melt at comparatively low temperatures, intergranular friction is not able to cause explosion and the hot spots must be formed in some other way. With the primary explosives which explode at temperatures below their melting-points, hot spots formed by intergranular friction can be important.

scholarly journals Ranking and Clustering Iranian Provinces Based on COVID-19 Spread: K-Means Cluster Analysis

2021 ◽  
Author(s):  
Farzan Madadizadeh ◽  
Reyhane Sefidkar
Keyword(s):  
Cluster Analysis ◽  
Hot Spots ◽  
Human Development Index ◽  
Cross Sectional Study ◽  
Critical Conditions ◽  
Spearman Correlation ◽  
Sectional Study ◽  
Cross Sectional ◽  
Real Picture ◽  
Sistan And Baluchestan

Introduction: The Coronavirus has crossed geographical borders. This study was performed to rank and cluster Iranian provinces based on coronavirus disease (COVID-19) recorded cases from February 19 to March 22, 2020. Materials and Methods: This cross-sectional study was conducted in 31 provinces of Iran using the daily number of confirmed cases. Cumulative Frequency (CF) and Adjusted CF (ACF) of new cases for each province were calculated. Characteristics of provinces like population density, area, distance from the original epicenter (Qom province), altitude from sea level, and Human Development Index (HDI) were used to investigate their correlation with ACF values. Spearman correlation coefficient and K-Means Cluster Analysis (KMCA) were used for data analysis. Statistical analyses were conducted in RStudio. The significant level was set at 0.05. Results: There were 21,638 infected cases with COVID-19 in Iran during the study period. Significant correlations between ACF values and province HDI (r = 0.46) and distance from the original epicenter (r = -0.66) was observed. KMCA, based on both CF and ACF values, classified provinces into 10 clusters. In terms of ACF, the highest level of spreading belonged to cluster 1 (Semnan and Qom provinces), and the lowest one belonged to cluster 10 (Kerman, Sistan and Baluchestan, Chaharmahal and Bakhtiari and Busher provinces). Conclusion: This study showed that ACF gives a real picture of each province's spreading status. KMCA results based on ACF identify the provinces that have critical conditions and need attention. Therefore, using this accurate model to identify hot spots to perform quarantine is recommended.

A high-performance oil-free backing pump for electron microscopes

1978 ◽  
Vol 36 (1) ◽  
pp. 110-111
Author(s):  
G.K.W. Balkau ◽  
E. Bez ◽  
J.L. Farrant
Keyword(s):  
Molecular Weight ◽  
Electron Microscope ◽  
Hot Spots ◽  
High Performance ◽  
Carbonaceous Material ◽  
Contamination Rate ◽  
Low Molecular Weight ◽  
Principal Source ◽  
Rotary Pumps ◽  
Electron Microscopes

The earliest account of the contamination of electron microscope specimens by the deposition of carbonaceous material during electron irradiation was published in 1947 by Watson who was then working in Canada. It was soon established that this carbonaceous material is formed from organic vapours, and it is now recognized that the principal source is the oil-sealed rotary pumps which provide the backing vacuum. It has been shown that the organic vapours consist of low molecular weight fragments of oil molecules which have been degraded at hot spots produced by friction between the vanes and the surfaces on which they slide. As satisfactory oil-free pumps are unavailable, it is standard electron microscope practice to reduce the partial pressure of organic vapours in the microscope in the vicinity of the specimen by using liquid-nitrogen cooled anti-contamination devices. Traps of this type are sufficient to reduce the contamination rate to about 0.1 Å per min, which is tolerable for many investigations.

World Bank pinpoints disaster hot spots

Nature ◽  
2005 ◽  
Author(s):  
Deirdre Lockwood
Keyword(s):  
World Bank ◽  
Hot Spots

Preservation of Morphological Integrity and Clot Retraction Activity of Human Platelets After Freezing

1964 ◽  
Vol 11 (01) ◽  
pp. 222-229 ◽  
Author(s):  
Isaac Djerassi ◽  
Albert Roy ◽  
Jorge Alvarado ◽  
Keyword(s):  
Dimethyl Sulfoxide ◽  
Liquid Nitrogen ◽  
Human Platelets ◽  
Slow Freezing ◽  
Critical Conditions ◽  
Plasma Medium ◽  
Clot Retraction ◽  
Controlled Freezing ◽  
Direct Immersion

SummaryHuman platelets frozen at −195° C (liquid nitrogen) retain their morphological integrity and ability to promote clot retraction when 5% dimethyl-sulfoxide and 5% dextrose are added to the suspending plasma medium. Slow freezing was more effective than direct immersion in the liquid nitrogen. Although similar results may be achieved with dimethylsulfoxide alone with rigidly controlled freezing rates, the addition of sugars may permit freezing under less critical conditions.Dimethylsulfoxyd und 5% Dextrose dem Plasmamilieu hinzugefügt werden. Das langsame Einfrieren ist effektiver als das direkte Eintauchen in flüssigen Stickstoff. Obschon ähnliche Resultate mit Dimethylsulfoxyd allein unter exakter Kontrolle der Einfrierungsgeschwindig-keit erreicht werden können, erlaubt die Zugabe von Dextrose ein Einfrieren unter weniger kritischen Bedingungen.

Application of graphical analysis of taxonomical structure of diatom complexes in identification of critical conditions of the Neopleistocene lakes (on the example of Bibirevo section)

2019 ◽  
pp. 78-87
Author(s):  
Elena V. Bespalova
Keyword(s):  
Lake Sediments ◽  
Critical Points ◽  
Graphical Analysis ◽  
Volga Region ◽  
Critical Conditions ◽  
Ancient Lake ◽  
Diatom Complexes

Ancient lake sediments of Bibirevo section in the Yaroslavl and Kostroma Volga region are studied by means of graphical analysis of taxonomical structure of diatom complexes. This method allowed to record critical points (change of areas of stability) in the development of a Neopleistocene lake during the transition from stage to stage, as well as from phase to phase.

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