2,473 research outputs found
The Evolution of Multicomponent Systems at High Pressures: VI. The Thermodynamic Stability of the Hydrogen-Carbon System: The Genesis of Hydrocarbons and the Origin of Petroleum
The spontaneous genesis of hydrocarbons which comprise natural petroleum have
been analyzed by chemical thermodynamic stability theory. The constraints
imposed upon chemical evolution by the second law of thermodynamics are briefly
reviewed; and the effective prohibition of transformation, in the regime of
temperatures and pressures characteristic of the near-surface crust of the
Earth, of biological molecules into hydrocarbon molecules heavier than methane
is recognized.
A general, first-principles equation of state has been developed by extending
scaled particle theory (SPT) and by using the technique of the factored
partition function of the Simplified Perturbed Hard Chain Theory (SPHCT). The
chemical potentials, and the respective thermodynamic Affinity, have been
calculated for typical components of the hydrogen-carbon (H-C) system over a
range pressures between 1-100 kbar, and at temperatures consistent with those
of the depths of the Earth at such pressures. The theoretical analyses
establish that the normal alkanes, the homologous hydrocarbon group of lowest
chemical potential, evolve only at pressures greater than approximately thirty
kbar, excepting only the lightest, methane. The pressure of thirty kbar
corresponds to depths of approximately 100 km.
Special high-pressure apparatus has been designed which permits
investigations at pressures to 50 kbar and temperatures to 2000 K, and which
also allows rapid cooling while maintaining high pressures. The high-pressure
genesis of petroleum hydrocarbons has been demonstrated using only the solid
reagents iron oxide, FeO, and marble, CaCO3, 99.9% pure and wet with
triple-distilled water
Search for cold and hot gas in the ram pressure stripped Virgo dwarf galaxy IC3418
We present IRAM 30m sensitive upper limits on CO emission in the ram pressure
stripped dwarf Virgo galaxy IC3418 and in a few positions covering HII regions
in its prominent 17 kpc UV/Ha gas-stripped tail. In the central few arcseconds
of the galaxy, we report a possible marginal detection of about 1x10^6 M_sun of
molecular gas (assuming a Galactic CO-to-H_2 conversion factor) that could
correspond to a surviving nuclear gas reservoir. We estimate that there is less
molecular gas in the main body of IC3418, by at least a factor of 20, than
would be expected from the pre-quenching UV-based star formation rate assuming
the typical gas depletion timescale of 2 Gyr. Given the lack of star formation
in the main body, we think the H_2-deficiency is real, although some of it may
also arise from a higher CO-to-H_2 factor typical in low-metallicity, low-mass
galaxies. The presence of HII regions in the tail of IC3418 suggests that there
must be some dense gas; however, only upper limits of < 1x10^6 M_sun were found
in the three observed points in the outer tail. This yields an upper limit on
the molecular gas content of the whole tail < 1x10^7 M_sun, which is an amount
similar to the estimates from the observed star formation rate over the tail.
We also present strong upper limits on the X-ray emission of the stripped gas
in IC3418 from a new Chandra observation. The measured X-ray luminosity of the
IC3418 tail is about 280 times lower than that of ESO 137-001, a spiral galaxy
in a more distant cluster with a prominent ram pressure stripped tail.
Non-detection of any diffuse X-ray emission in the IC3418 tail may be due to a
low gas content in the tail associated with its advanced evolutionary state
and/or due to a rather low thermal pressure of the surrounding intra-cluster
medium.Comment: 15 pages, 11 figures, A&A accepte
Random sequential adsorption of shrinking or spreading particles
We present a model of one-dimensional irreversible adsorption in which
particles once adsorbed immediately shrink to a smaller size or expand to a
larger size. Exact solutions for the fill factor and the particle number
variance as a function of the size change are obtained. Results are compared
with approximate analytical solutions.Comment: 9 pages, 8 figure
Magnetic field configuration associated with solar gamma ray flares in June, 1991
The vector magnetic field configuration of the solar active region AR 6659 that produced very high levels of flare activity in Jun. 1991 is described. The morphology and evolution of the photospheric fields are described for the period 7-10 Jun., and the flares taking place around these dates and their locations relative to the photospheric fields are indicated. By comparing the observed vector field with the potential field calculated from the observed line-of-sight flux, we identify the nonpotential characteristics of the fields along the magnetic neutral lines where the flares were observed. These results are compared with those from the earlier study of gamma-ray flares
The microcanonical thermodynamics of finite systems: The microscopic origin of condensation and phase separations; and the conditions for heat flow from lower to higher temperatures
Microcanonical thermodynamics allows the application of statistical mechanics
both to finite and even small systems and also to the largest, self-gravitating
ones. However, one must reconsider the fundamental principles of statistical
mechanics especially its key quantity, entropy. Whereas in conventional
thermostatistics, the homogeneity and extensivity of the system and the
concavity of its entropy are central conditions, these fail for the systems
considered here. For example, at phase separation, the entropy, S(E), is
necessarily convex to make exp[S(E)-E/T] bimodal in E. Particularly, as
inhomogeneities and surface effects cannot be scaled away, one must be careful
with the standard arguments of splitting a system into two subsystems, or
bringing two systems into thermal contact with energy or particle exchange. Not
only the volume part of the entropy must be considered. As will be shown here,
when removing constraints in regions of a negative heat capacity, the system
may even relax under a flow of heat (energy) against a temperature slope. Thus
the Clausius formulation of the second law: ``Heat always flows from hot to
cold'', can be violated. Temperature is not a necessary or fundamental control
parameter of thermostatistics. However, the second law is still satisfied and
the total Boltzmann entropy increases. In the final sections of this paper, the
general microscopic mechanism leading to condensation and to the convexity of
the microcanonical entropy at phase separation is sketched. Also the
microscopic conditions for the existence (or non-existence) of a critical
end-point of the phase-separation are discussed. This is explained for the
liquid-gas and the solid-liquid transition.Comment: 23 pages, 2 figures, Accepted for publication in the Journal of
Chemical Physic
Scattering a pulse from a chaotic cavity: Transitioning from algebraic to exponential decay
The ensemble averaged power scattered in and out of lossless chaotic cavities
decays as a power law in time for large times. In the case of a pulse with a
finite duration, the power scattered from a single realization of a cavity
closely tracks the power law ensemble decay initially, but eventually
transitions to an exponential decay. In this paper, we explore the nature of
this transition in the case of coupling to a single port. We find that for a
given pulse shape, the properties of the transition are universal if time is
properly normalized. We define the crossover time to be the time at which the
deviations from the mean of the reflected power in individual realizations
become comparable to the mean reflected power. We demonstrate numerically that,
for randomly chosen cavity realizations and given pulse shapes, the probability
distribution function of reflected power depends only on time, normalized to
this crossover time.Comment: 23 pages, 5 figure
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