scholarly journals The transition of a gravitationally radiating, dissipative fluid to equilibrium

2018 ◽  
Vol 96 (9) ◽  
pp. 1010-1015 ◽  
Author(s):  
L. Herrera ◽  
A. Di Prisco ◽  
J. Ospino
Keyword(s):  
Relaxation Time ◽  
Equilibrium State ◽  
Physical Properties ◽  
Gravitational Radiation ◽  
Time Scale ◽  
Thermal Relaxation ◽  
Static Case ◽  
The Past ◽  
Adjustment Time ◽  
Dissipative Fluid

We describe the transition of a gravitationally radiating, axially and reflection symmetric, dissipative fluid to a non-radiating state. It is shown that very shortly after the end of the radiating regime, at a time scale on the order of the thermal relaxation time, the thermal adjustment time, or the hydrostatic time (whichever is larger), the system reaches the equilibrium state. This result is at variance with all the studies carried out in the past on gravitational radiation outside the source, which strongly suggest that after a radiating period, the conditions for a return to a static case look rather forbidding. As we shall see, the reason for such a discrepancy resides in the fact that some elementary, but essential, physical properties of the source have been overlooked in these latter studies.

scholarly journals The Stability of Mars’s Annular Polar Vortex

2017 ◽  
Vol 74 (5) ◽  
pp. 1533-1547 ◽  
Author(s):  
William J. M. Seviour ◽  
Darryn W. Waugh ◽  
Richard K. Scott
Keyword(s):  
Relaxation Time ◽  
Time Scales ◽  
Time Scale ◽  
Thermal Relaxation ◽  
Polar Vortex ◽  
Radiative Relaxation ◽  
Equilibrium Profile ◽  
Rotating Shallow Water ◽  
The Stability ◽  
Topographic Forcing

Abstract The Martian polar atmosphere is known to have a persistent local minimum in potential vorticity (PV) near the winter pole, with a region of high PV encircling it. This finding is surprising, since an isolated band of PV is barotropically unstable, a result going back to Rayleigh. Here the stability of a Mars-like annular vortex is investigated using numerical integrations of the rotating shallow-water equations. The mode of instability and its growth rate is shown to depend upon the latitude and width of the annulus. By introducing thermal relaxation toward an annular equilibrium profile with a time scale similar to that of the instability, a persistent annular vortex with similar characteristics as that observed in the Martian atmosphere can be simulated. This time scale, typically 0.5–2 sols, is similar to radiative relaxation time scales for Mars’s polar atmosphere. The persistence of an annular vortex is also shown to be robust to topographic forcing, as long as it is below a certain amplitude. It is therefore proposed that the persistence of this barotropically unstable annular vortex is permitted owing to the combination of short radiative relaxation time scales and relatively weak topographic forcing in the Martian polar atmosphere.

Correlating Blocking Temperatures in Single Molecule Magnets with Raman Relaxation

2018 ◽  
Author(s):  
Marcus J. Giansiracusa ◽  
Andreas Kostopoulos ◽  
George F. S. Whitehead ◽  
David Collison ◽  
Floriana Tuna ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Single Molecule ◽  
Energy Barrier ◽  
Thermal Relaxation ◽  
Relaxation Mechanism ◽  
Blocking Temperature ◽  
Single Molecule Magnets ◽  
Single Molecule Magnet ◽  
Key Parameter

We report a six coordinate DyIII single-molecule magnet<br>(SMM) with an energy barrier of 1110 K for thermal relaxation of<br>magnetization. The sample shows no retention of magnetization<br>even at 2 K and this led us to find a good correlation between the<br>blocking temperature and the Raman relaxation regime for SMMs.<br>The key parameter is the relaxation time (𝜏<sub>switch</sub>) at the point where<br>the Raman relaxation mechanism becomes more important than<br>Orbach.

scholarly journals The properties of early-type stars in the Magellanic Clouds

2008 ◽  
Vol 4 (S256) ◽  
pp. 325-336
Author(s):  
Christopher J. Evans
Keyword(s):  
Physical Properties ◽  
Mass Loss ◽  
Temperature Scale ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Early Type ◽  
The Past ◽  
The Galaxy ◽  
Stellar Temperature ◽  
Early Type Stars

AbstractThe past decade has witnessed impressive progress in our understanding of the physical properties of massive stars in the Magellanic Clouds, and how they compare to their cousins in the Galaxy. I summarise new results in this field, including evidence for reduced mass-loss rates and faster stellar rotational velocities in the Clouds, and their present-day compositions. I also discuss the stellar temperature scale, emphasizing its dependence on metallicity across the entire upper-part of the Hertzsprung-Russell diagram.

Introductory remarks

1977 ◽  
Vol 280 (972) ◽  
pp. 105-105
Keyword(s):  
Climatic Change ◽  
Food Supply ◽  
Time Scale ◽  
Food Production ◽  
Rapid Change ◽  
Climatic Fluctuations ◽  
The Past ◽  
Wide Range ◽  
The Subject ◽  
Different Sources

In the last year or two there has been a remarkable increase in the interest, both popular and scientific, in the subject of climatic change. This stems from a recognition that even a highly technological society is vulnerable to the effects of climatic fluctuations and indeed may become more so, as margins of surplus food production are reduced, and nations become more interdependent for their food supply. In this respect our concern is with quite small changes - a degree (Celsius) or less in temperature and 10 % or so in rainfall. Probably we may discount some of the more alarmist suggestions of an imminent and rapid change towards near glacial conditions as these are based on very sketchy evidence. However, whatever the time-scale of climatic fluctuations with which we are concerned, we may hope to learn a great deal which is relevant to the factors which will control our future climate from the study of its more extreme vagaries in the past. Information relevant to the weather in such extreme periods is coming forward in increasing detail and volume from a wide range of disciplines. The variety of the evidence, its lack of precision as a strict measure of climate, and the number of different sources all make it difficult for an individual to build up a clear picture of past climates. However such a picture is needed, if explanations and interpretation are to be possible. Ideally one would need a synchronous picture of the climate of the whole world at selected epochs in the past. Various international programmes are directed to forming such pictures.

On measurement of the thermal relaxation time in transient thermal processes of solids

2015 ◽  
Vol 58 (3) ◽  
pp. 251-257 ◽  
Author(s):  
Yu. A. Kirsanov ◽  
A. Yu. Kirsanov ◽  
K. Kh. Gil’fanov ◽  
A. E. Yudakhin
Keyword(s):  
Relaxation Time ◽  
Thermal Relaxation ◽  
Thermal Relaxation Time ◽  
Thermal Processes ◽  
Transient Thermal

scholarly journals Kekasaran Permukaan Resin Komposit Nanofilled dan Nanohybrid Setelah Paparan Asap Rokok Kretek

2019 ◽  
Vol 8 (1) ◽  
pp. 30
Author(s):  
Johanna Chandra ◽  
Laksmiari Setyowati ◽  
Setyabudi Setyabudi
Keyword(s):  
Surface Roughness ◽  
Physical Properties ◽  
Cigarette Smoke ◽  
Public Health Problem ◽  
Composite Resins ◽  
Dental Composites ◽  
Distilled Water ◽  
Control Groups ◽  
The Past ◽  
Nanohybrid Composite

Background: Cigarette smoking is a public health problem that may influence physical properties of dental composites. Surface roughness is one of the physical properties of restorative materials that can influence their success. The use of nanofilled and nanohybrid composites in dentistry has substantially increased over the past few years. Purpose: The purpose of this study was to evaluate the surface roughness of nanofilled and nanohybrid composite resins exposed to kretek cigarette smoke. Methods: Twelve cylindrical specimens were prepared of each material and divided into two groups (n=6). For the control groups, the specimens were immersed in distilled water for 24 hours at 37oC and the water was renewed daily. For the experimental groups, the specimens were exposed daily to kretek cigarette smoke, then washed and stored in distilled water at 37oC. After 21 days, specimens were measured using a Surface Roughness Tester and the data was statistically analyzed. Result: Independent-T Test revealed that there were statistically significant differences in the surface roughness between control and experimental groups both nanofilled and nanohybrid, and between experimental groups nanofilled and nanohybrid. Conclusion: The exposure to kretek cigarette smoke can significantly increase the surface roughness of nanohybrid composites more than nanofilled composites.

scholarly journals Coated Metal Powders for Laser Powder Bed Fusion (L-PBF) Processing: A Review

Metals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1831
Author(s):  
Robert Bidulsky ◽  
Federico Simone Gobber ◽  
Jana Bidulska ◽  
Marta Ceroni ◽  
Tibor Kvackaj ◽  
...  
Keyword(s):  
Physical Properties ◽  
Powder Bed Fusion ◽  
Metal Powders ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
The Past ◽  
Coated Metal ◽  
Mechanical And Physical Properties ◽  
Interesting Approach ◽  
Coating Methods

In the last years, functionalized powders are becoming of increasing interest in additive manufacturing (particularly in laser powder bed fusion processing, L-PBF), due to their improved flowability and enhanced processability, particularly in terms of laser absorbance. Functionalized powders may also provide higher final mechanical or physical properties in the manufactured parts, like an increased hardness, a higher tensile strength, and density levels close to theoretical. Coatings represent a possible interesting approach for powders’ functionalizing. Different coating methods have been studied in the past years, either mechanical or non-mechanical. This work aims to present an overview of the currently obtained coated powders, analyzing in detail the processes adopted for their production, the processability of the coated systems, and the mechanical and physical properties of the final parts obtained by using L-PBF for the powders processing.

scholarly journals Historia global o las geografías del pasado. Implicaciones de la perspectiva global y geográfica en la escritura de la historia / Global History or the Geographies of the Past: Implications of a Global and Geographical Perspective in the Writing of History

2017 ◽  
pp. 91
Author(s):  
Francisco Javier Navarro Jiménez
Keyword(s):  
Time Scale ◽  
Global Perspective ◽  
Global History ◽  
Field Of Study ◽  
The Past ◽  
Longue Duree ◽  
Longue Durée ◽  
Geographical Perspective ◽  
Ultimate Purpose ◽  
Sobre Todo

ResumenLa historia global es un campo de estudios emergente. En la aproximación al pasado desde esta perspectiva, el giro territorial y la escala de la larga duración son elementos centrales, con lo que ello supone de solapamientos metodológicos y epistemológicos con otras disciplinas, sobre todo con la geografía. Esta perspectiva ofrece abundantes beneficios, pero también se deben considerar los riesgos que supone. A través de ejemplos concretos de obras escritas desde este campo, el artículo discute la vigencia de conceptos como globalización y ecúmene, pero también cuestiones metodológicas como la larga duración y el determinismo geográfico. Se pretende con ello identificar posibilidades, fortalezas y riesgos en la escritura de la historia global.Palabras claveHistoria global, geografía, territorio, larga duración, solapamientos metodológicos.AbstractGlobal history is an emergent field of study today. To apprehend the past from a global perspective, territorial turn and longue durée time scale become pivotal concepts, with the corresponding methodologic and epistemological overlaps with other disciplines, especially geography. Many benefits can be obtained from this perspective, but there are also risks that need to be considered. Through specific examples of works written from this field, this article examines the validity of concepts of globalization and ecumene, and discusses methodologic aspects related to the longue durée and geographic determinism. The ultimate purpose of it is to identify possibilities, strengths and risks in the writing of global history.Key WordsGlobal history, geography, territory, longue durée, methodologic overlaps.

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