Gravitational mechanism of variation of period of fundamental oscillations of pulsars

1979 ◽  
Vol 22 (6) ◽  
pp. 677-677
Author(s):  
Yu. G. Ignat'ev
Keyword(s):  
Gravitational Mechanism

Gravitational Mechanism for Sea-Floor Spreading

Science ◽  
1969 ◽  
Vol 163 (3863) ◽  
pp. 176-177 ◽  
Author(s):  
H. N. Pollack
Keyword(s):  
Sea Floor ◽  
Sea Floor Spreading ◽  
Gravitational Mechanism

scholarly journals A GRAVITATIONAL MECHANISM FOR COSMOLOGICAL SCREENING

2011 ◽  
Vol 20 (14) ◽  
pp. 2847-2851 ◽  
Author(s):  
N. C. TSAMIS ◽  
R. P. WOODARD
Keyword(s):  
Kinetic Energy ◽  
Time Evolution ◽  
Vacuum Energy ◽  
Accelerated Expansion ◽  
Spatial Volume ◽  
The Universe ◽  
Gravitational Mechanism

Infrared gravitons are continually produced during inflation. Like all particles, their contribution to the vacuum energy comes not only from their bare kinetic energy but also from the interactions they have with other gravitons. These interactions can be substantial — despite the particles being highly infrared — because they occur over the enormous spatial volume of the universe. Furthermore, the interactions grow with time evolution because more and more such gravitons come into causal contact with one another. Since gravity is universally attractive, these interactions can act to slow and eventually stop accelerated expansion.

A flow-front instability in viscous gravity currents

1998 ◽  
Vol 369 ◽  
pp. 1-21 ◽  
Author(s):  
DON SNYDER ◽  
STEPHEN TAIT
Keyword(s):  
Gravitational Instability ◽  
Gravity Current ◽  
High Viscosity ◽  
Gravity Currents ◽  
Ambient Fluid ◽  
Cell Width ◽  
Dense Fluid ◽  
Unstable Layer ◽  
Gravitational Mechanism ◽  
Hele Shaw Cell

We describe an instability that appears at the front of laminar gravity currents as they intrude into a viscous, miscible ambient fluid. The instability causes a current to segment into fingers aligned with its direction of flow. In the case of currents flowing along a rigid floor into a less dense fluid, the case of primary interest here, two mechanisms can produce this instability. The first is gravitational and arises because the nose of the gravity current is elevated above the floor and overrides a buoyantly unstable layer of ambient liquid. The second is a form of viscous fingering analogous to a Saffman–Taylor instability in a Hele-Shaw cell. Whereas the ambient fluid must be more viscous than the current in order for the latter instability to occur, the gravitational instability can occur even if the ambient fluid is less viscous, as long as it is viscous enough to elevate the nose of the current and trap a layer of ambient fluid. For the gravitational mechanism, which is most important when the current and ambient fluids have comparable viscosities, the wavelength when the instability first appears is proportional to a length scale constructed with the viscosity, the flux and the buoyancy. The Saffman–Taylor-type mechanism is most important when the ambient liquid is much more viscous than the current. We have carried out experiments with miscible fluids in a Hele-Shaw cell that show that, at the onset of instability, the ratio of the finger wavelength to the cell width is a constant approximately equal to 2. This result is explained by using the principle that the flow tends to minimize the dissipation associated with the finger perturbation. For the gravity currents with high viscosity ratios, the ratio of the wavelength to the current thickness is also a constant of about 2, apparently consistent with the same mechanism. But, further analysis of this instability mechanism is required in order to assess its role in wavelength selection for gravity currents.

scholarly journals A gravitational mechanism for the acceleration of ultrarelativistic particles

2005 ◽  
Vol 14 (11-12) ◽  
pp. 751-763 ◽  
Author(s):  
C. Chicone ◽  
B. Mashhoon
Keyword(s):  
Gravitational Mechanism

scholarly journals Maculopathy Development Mechanism in Choroid Tumor Localization Outside the Foveolar Zone

2019 ◽  
Vol 16 (1S) ◽  
pp. 49-55
Author(s):  
A. F. Brovkina ◽  
A. S. Stoyukhina ◽  
M. V. Budzinskaya ◽  
I. V. Musatkina
Keyword(s):  
Normal Values ◽  
Choroidal Melanoma ◽  
Subretinal Fluid ◽  
Careful Examination ◽  
Tumor Localization ◽  
Macular Area ◽  
Symptom Development ◽  
Biometric Parameters ◽  
Eye Examination ◽  
Gravitational Mechanism

The term “distant maculopathy” (DM) means the changes in the macular region, when the tumor is located at the distant from it. Purpоse: to study the peculiarities of the DM development, according to the tumor localization and present a possible mechanism of this symptom development. Patients and Methods. The study involved 53 patients with choroidal tumors localized outside the macular area, including 18 patients with neuroepithelial detachment (NED) in the macular area. In addition to the standard eye examination, all patients underwent EDI OCT. Results. In 1/3 cases of extrafoveolar located choroidal tumors according to OCT, exudative changes in the macular zone were revealed. In extrafoveral choroidal melanoma (CM), the biometric tumor parameters in patients with DM were slightly higher than the average in patients of this group, however, there was no correlation between the height of NED and tumor parameters. In extrafoveolar choroidal hemangioma (CH), a significant direct relationship between the height of the NED in the foveolar zone and the biometric parameters of the CH was found. In all cases, there was not choroidal elevation in the foveolar zone. The thickness and structure of the choroid in the subfoveolar zone in CM did not differ from the paired eye and the normal values. The thickness of the choroid in CH also did not differ from the paired eye, however, there was a slight expansion of the outer layers of the choroid (as in the paired eye) and an increase in its thickness compared with the norm. When a tumor is located above the macular zone, there is a “gravitational” mechanism for the development of DM, due to the spread of subretinal fluid (or blood) under the action of gravity. In case of juxtapapillar tumor localization, the appearance of DM is caused by microvascular disorders in the foveo-macular region of the retina and impaired axoplasmic current. In CM, the occurrence of NED may be associated with a retinal tension on the steeper side of the tumor. Conclusion. The development of distant maculopathy in CM is a sign of “active” tumor growth, in CH it develops later and depends on the size of the tumor. In identifying a high prevalent NED in the macular area, a careful examination of not only the central fundus zone, but also its peripheral parts is necessary. 

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