scholarly journals Variable inflaton equation-of-state and reheating

2021 ◽  
pp. 2150095
Author(s):  
Alessandro Di Marco ◽  
Gianfranco Pradisi
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Coupled System ◽  
Radiation Energy ◽  
Entropy Density ◽  
Time Dependent ◽  
Thermal Bath ◽  
Eos Parameter ◽  
Radiation Energy Density ◽  
Primordial Gravitational Waves

We explore the consequences of a time-dependent inflaton equation-of-state (EoS) parameter in the context of the post-inflationary perturbative Boltzmann reheating. In particular, we numerically solve the perturbative coupled system of Boltzmann equations involving the inflaton energy density, the radiation energy density and the related entropy density and temperature of the produced particle thermal bath. We exploit reasonable Ansätze for the EoS and discuss the robustness of the Boltzmann system. We also comment on the possible microscopic origin related to a time-dependent inflaton potential, discussing the consequences on a preheating stage and the related (primordial) gravitational waves.

Measurement facility for the relative radiation energy density distribution for pulse-periodic lasers

1988 ◽  
Vol 31 (10) ◽  
pp. 966-967
Author(s):  
V. I. Andreev ◽  
A. P. Palivoda ◽  
S. P. Fetisov ◽  
N. V. Shalomeeva ◽  
V. A. Yakovlev
Keyword(s):  
Energy Density ◽  
Density Distribution ◽  
Radiation Energy ◽  
Measurement Facility ◽  
Radiation Energy Density ◽  
Energy Density Distribution

Features of Brass Processing with Powerful Ultraviolet Lasers of Nanosecond Duration

2022 ◽  
Vol 1049 ◽  
pp. 11-17
Author(s):  
Ivan Kaplunov ◽  
Taras Malinskiy ◽  
S.I. Mikolutskiy ◽  
Vladimir Rogalin ◽  
Yuriy Khomich ◽  
...  
Keyword(s):  
Energy Density ◽  
Metal Structure ◽  
Radiation Energy ◽  
Laser Heat Treatment ◽  
Absorbed Energy ◽  
Radiation Energy Density ◽  
Nanosecond Duration ◽  
Third Harmonic ◽  
Accumulation Of Damage ◽  
Ultraviolet Lasers

We investigated the process of laser heat treatment of polished brass samples (36% zinc, containing a small amount of lead, which does not dissolve in the alloy and is in the form of inclusions, having micron and submicron size) by impacting to a series of 25 - 30 ultraviolet (UV) pulses of a Nd:YAG laser (third harmonic, wavelength λ = 355 nm, duration τ = 10 ns, pulse repetition rate f = 10 Hz, pulse energy density ~ 0.15 - 1.0 J/cm2) in the stationary spot mode. Copper and its alloys absorb up to 90% of the energy of this laser. It is found that the relaxation of the absorbed energy of laser radiation in the metal occurs nonuniformly. Defects in the metal structure such as grain boundaries and lead inclusions are visualized. Traces of crystallographic sliding appear inside some grains. With an increase in the number of impacting impulses, accumulation of damage is observed. A further increase in the radiation energy density leads to an aggravation of the observed phenomena.

Ponderomotive pressure effects in laser driven high-temperature plasma flows

1981 ◽  
Vol 25 (2) ◽  
pp. 193-213 ◽  
Author(s):  
J. L. Bobin
Keyword(s):  
High Temperature ◽  
Mach Number ◽  
Energy Density ◽  
Density Ratio ◽  
Radiation Energy ◽  
Pressure Effects ◽  
Initial State ◽  
Temperature Plasma ◽  
Radiation Energy Density ◽  
Plasma Effects

Gasdynamical equations taking radiation energy density and ponderomotive pressure into account are investigated. Conditions for these quantities to be important are stated: low absorption, reflexion at cut-off. The density ratio in a discontinuity is studied as a function of ponderomotive pressure, absorbed intensity and Mach number in the initial state. Chapman–Jouguet conditions are defined. Compressive (R type) flows and rarefaction (D type) appear. The structure of the latter is discussed including plasma effects.

Radiation Energy Density and Radiation Heat Flux in Small Rectangular Cavities

1972 ◽  
Vol 94 (3) ◽  
pp. 289-294 ◽  
Author(s):  
R. P. Caren
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Energy Density ◽  
Classical Theory ◽  
Radiant Energy ◽  
Radiation Energy ◽  
Radiant Heat ◽  
Radiant Heat Transfer ◽  
Radiation Heat ◽  
Radiation Energy Density

The present paper investigates the impact of one or more small cavity dimensions on the radiation energy density and radiation heat flux in rectangular metallic cavities. The emphasis of the present analysis is the exact treatment of the modal structure of the electromagnetic field in a small cavity in determining the properties of the thermal radiation field in the cavity. The excitation spectrum of the modes is assumed to be given by the Planck distribution function. The Poynting theorem is invoked in order to determine the radiative heat flux absorbed by the walls from the radiation in the cavity. Variation of the dimensions of the rectangular cavity allows the effects of cavity size and shape on the radiant energy density and radiant heat transfer to be assessed, particularly in several interesting limiting cases. It is found that significant deviations from the classical theory occur whenever any of the cavity dimensions satisfy the inequality lT ≤ 1 cm-deg K. It is further found that, when two or more of the cavity dimensions satisfy the above inequality, the radiant energy density and radiant heat transfer are significantly reduced in comparison to the results of classical theory. However, when only one dimension is limited, as in the case of a closely spaced parallel-surface geometry, the radiant energy density and radiant heat transfer are significantly increased compared to the classical theory.

Measuring the Radiation Energy Density of a Pulsed X-Ray Source

2019 ◽  
Vol 62 (2) ◽  
pp. 232-235
Author(s):  
R. R. Akhmetshin ◽  
E. A. Babichev ◽  
D. N. Grigoriev ◽  
V. R. Groshev ◽  
V. F. Kazanin ◽  
...  
Keyword(s):  
Energy Density ◽  
Radiation Energy ◽  
Radiation Energy Density ◽  
X Ray

Radiation hydrodynamical self-similar funnel jets

2021 ◽  
Vol 503 (1) ◽  
pp. 1367-1373
Author(s):  
J Fukue
Keyword(s):  
Energy Density ◽  
Outer Part ◽  
Radiation Energy ◽  
Polar Axis ◽  
The Self ◽  
Flow Density ◽  
Radiation Energy Density ◽  
Similar Treatment ◽  
Various Boundary Conditions ◽  
Self Similar

ABSTRACT Two-dimensional funnel flows driven by radiation pressure in the conical funnel formed by the critical accretion disc are examined using the self-similar treatment. The flow is assumed to be steady and axisymmetric, and other forces such as viscosity and magnetic fields are ignored. For various boundary conditions on the funnel wall at the disc surface, the self-similar solutions are found to be classified into three types: funnel-filled solutions, where the flow gas fills the whole region of the funnel; polar-hollow ones, where there appears a cavity around the polar axis, and unphysical ones in a sense that, e.g. the radiation energy density becomes negative. For the physically reasonable solutions, the flow gas generally concentrates to the funnel wall, and the flow density and the radiation energy density monotonically decrease from the funnel wall towards the polar axis, while the radial flux becomes negative near the polar axis. The vertical velocity increases towards the polar axis, while the vertical flux has often the maximum between the polar axis and the funnel wall. As a result, the present self-similar funnel jets are such a flow with a slow dense outer part and a fast rarefied inner part.

scholarly journals GRAVITATIONAL INSTANTON AND COSMOLOGICAL TERM

2009 ◽  
Vol 24 (20n21) ◽  
pp. 3865-3891 ◽  
Author(s):  
SHE-SHENG XUE
Keyword(s):  
Black Holes ◽  
Energy Density ◽  
Radiation Energy ◽  
Flat Space ◽  
Cosmological Term ◽  
Radiation Energy Density ◽  
Gravitational Instantons ◽  
Gravitational Instanton ◽  
Inflationary Phase ◽  
The Universe

Quantum fluctuation of unstable modes about gravitational instantons causes the instability of flat space at finite temperature, leading to the spontaneous process of nucleating quantum black holes. The energy-density of quantum black holes, depending on the initial temperature, gives the cosmological term, which naturally accounts for the inflationary phase of the early universe. The reheating phase is attributed to the Hawking radiation and annihilation of these quantum black holes. Then, the radiation energy-density dominates over the energy-density of quantum black holes, the universe started the standard cosmology phase. In this phase the energy-density of quantum black holes depends on the reheating temperature. It asymptotically approaches to the cosmological constant in matter domination phase, consistently with current observations.

scholarly journals Multimode flux-limited diffusion theory

1992 ◽  
Vol 10 (2) ◽  
pp. 239-251 ◽  
Author(s):  
G. C. Pomraning
Keyword(s):  
Energy Density ◽  
Diffusion Approximation ◽  
Exponential Growth ◽  
Diffusion Theory ◽  
Radiation Energy ◽  
Radiation Hydrodynamics ◽  
Diffusion Approximations ◽  
Radiation Energy Density ◽  
Weak Gradient ◽  
Limited Diffusion

We present a diffusion approximation describing the flow of thermal radiation that preserves several important features of the underlying equation of radiative transfer. Specifically, this diffusion description: (1) is flux limited; (2) reduces to the correct transport weak gradient limit; (3) allows correct and simultaneous exponential growth and Decay for a certain class of problems; (4) gives correct transport results for certain contiguous half-space problems; and (5) allows the radiative flux and the gradient of the radiation energy density to point in independent directions. This treatment extends and generalizes earlier flux-limited diffusion approximations that are widely used in radiation–hydrodynamics calculations.

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