966 research outputs found
Big Bang Nucleosynthesis and the Missing Hydrogen Mass in the Universe
It is proposed that when the era of the big-bang nucleosynthesis ended,
almost all of the 75 percent of the observed total baryonic matter remained in
the form of hydrogen and continued to exist in the form of protons and
electrons. They are present today as baryonic dark matter in the form of
intergalactic hydrogen plasma. To test our hypothesis we have investigated the
effects of Thomson scattering by free electrons on the reported dimming of Type
Ia supernovae. The quantitative results of our calculation suggest that the
dimming of these supernovae, which are dimmer than expected and hence more
distant than predicted by Hubble expansion, is a result of Thomson scattering
without cosmic acceleration.Comment: A typographical error in equation (7) page 3 has been correcte
Van der Waals Correction to Nuclear Fusion by Mechanical Adiabatic Compression of a Dense Plasma
We consider fusion processes initiated by the rapid adiabatic compression by a piston of a deuterium plasma contained in a wellâinsulated chamber. To exploit the n2 factor in the fusion reaction rate, we consider one mole of deuterium which, at ambient temperature and pressure, provides a particle density of ~ 10^19 cm^â3. The reaction rate is enhanced by the application of magnetic and electric fields to reduce the number of degrees of freedom of the gas, thereby lowering its heat capacity and producing a higher temperature increase for a given energy input. Previous studies have shown that the combination of adiabatic operation, high particle density and reduced degrees of freedom can result in appreciable fusion rates at temperatures lower than those in magnetic confinement experiments. Prior work treated the deuterium gas as an ideal gas while the present work incorporates the corrections of a van der Waals gas. Both primary D-D reactions and secondary D-T reactions are considered. Conditions of energy-break-even and excess energy release were found at temperatures of the order of 10^6 K
A Mathematical Framework for the Energy Spectrum of Primary Cosmic Rays
Primary cosmic rays are nucleons from outer space incident upon the Earthâs atmosphere. Their flux varies with energy E as \u1d438^(â\u1d6fe) in which the exponent assumes values between 2.5 and 3.2. We provide herein a framework to account for these values. We consider the particlesâ kinetic temperature T and introduce a damping factor \u1d447^(â\u1d45a) to account for non head-on collisions. It is the presence of the index m which can provide values of Îł
Implications of Unchecked Exponential Growth
Treatments of the exponential function in Calculus textbooks are often cursory in that they treat unchecked (Malthusian) growth processes without examination of their consequences. Through the use of problems posed to students, we illustrate the implications of such processes when applied to growth of populations and to growth in the rates of consumption of nonrenewable resources
A Novel Approach to Fusion Power Generation
A poster discussing the use of mechanical adiabatic compression in nuclear fusion
Evolution of Asteroid Orbits in a Restricted Three-Body Simulation
We study the evolution of asteroid orbits in a restricted threeÂbody problem formulation consisting of the Sun, the planet Jupiter and an unspecified asteroid of negligible mass. It was discovered by Kirkwood that the distribution of asteroid orbits contains gaps for orbits whose period is commensurate with that of Jupiter. Detailed computations in three-dimensional, many-body formulations found that test bodies initially placed in a forbidden orbit did not develop large eccentricities or leave the gap even after the passage of 10^5 years. In the present two-dimensional simulation, an extension of earlier work, we perform numerical integrations of the coupled equations of motion for Jupiter and the asteroid. Under assumptions of a stationary Sun and a circular orbit for Jupiter, we find that test bodies initially placed in a forbidden orbit can develop a large eccentricity after relatively few orbits
Secondary Fusion Reactions in the Mechanical Adiabatic Compression of a Dense Plasma
We consider fusion processes initiated by the rapid adiabatic compression by a piston of a deuterium plasma contained in a wellâinsulated chamber. To exploit the n^2 factor in the fusion reaction rate, we consider one mole of deuterium which, at ambient temperature and pressure, provides a particle density of ~ 10^19 cm^â3. The reaction rate is enhanced by the application of magnetic and electric fields to reduce the number of degrees of freedom of the gas, thereby lowering its heat capacity and producing a higher temperature increase for a given energy input. Previous studies have shown that the combination of adiabatic operation, high particle density and reduced degrees of freedom can result in appreciable fusion rates at temperatures lower than those in magnetic confinement experiments. The prior work considered only primary D-D fusion reactions while the present work also includes D-T reactions. Conditions of energy-break-even and excess energy release were found at temperatures of the order of 10^6 K
Multistage Fusion Reaction Rates in an Adiabatically Compressed Plasma
A poster discussing fusion reaction rates in adiabatically compressed plasma
Evolution of Asteroid Orbits in a Restricted Three-Body Simulation
We study the evolution of asteroid orbits in a restricted three-body problem formulation in two dimensions, consisting of the Sun, the planet Jupiter and an unspecified asteroid of negligible mass. It was discovered by Kirkwood [l] that the distribution of asteroid orbits contains gaps for orbits whose period is commensurate with that of Jupiter. Detailed computations in three-dimensional, many-body formulations found that test bodies initially placed in a forbidden orbit did not develop large eccentricities or leave the gap even after the passage of 10 5 years [2]. While previous two-dimensional, three-body simulations, an extension of earlier work [3], showed significant departure of asteroids placed in forbidden orbits in fewer than 10 revolutions, our present work shows such orbits to be stable for at least 25,000 years. The results suggest two things: One, the two-dimensional, three-body, reduced problem (modeled in figure 3) is consistent with more detailed three-dimensional, many-body models, contrary to previous work. Secondly, the numerical integrations of the coupled equations of motion for Jupiter and the asteroid are highly sensitive to the precision in the method of computation. The demand for precise calculations for accurate predictions brings forth a problem of time complexity. With the resources available, simulations longer than 25,000 years were not practically possible
Irregular sloshing cold fronts in the nearby merging groups NGC 7618 and UGC 12491: evidence for Kelvin-Helmholtz instabilities
We present results from two \sim30 ks Chandra observations of the hot
atmospheres of the merging galaxy groups centered around NGC 7618 and UGC
12491. Our images show the presence of arc-like sloshing cold fronts wrapped
around each group center and \sim100 kpc long spiral tails in both groups. Most
interestingly, the cold fronts are highly distorted in both groups, exhibiting
'wings' along the fronts. These features resemble the structures predicted from
non-viscous hydrodynamic simulations of gas sloshing, where Kelvin-Helmholtz
instabilities (KHIs) distort the cold fronts. This is in contrast to the
structure seen in many other sloshing and merger cold fronts, which are smooth
and featureless at the current observational resolution. Both magnetic fields
and viscosity have been invoked to explain the absence of KHIs in these smooth
cold fronts, but the NGC 7618/UGC 12491 pair are two in a growing number of
both sloshing and merger cold fronts that appear distorted. Magnetic fields
and/or viscosity may be able to suppress the growth of KHIs at the cold fronts
in some clusters and groups, but clearly not in all. We propose that the
presence or absence of KHI-distortions in cold fronts can be used as a measure
of the effective viscosity and/or magnetic field strengths in the ICM.Comment: ApJ, accepted. Uses emulateapj styl
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