16,125 research outputs found
Analytical approach to the transition to thermal hopping in the thin- and thick-wall approximations
The nature of the transition from the quantum tunneling regime at low
temperatures to the thermal hopping regime at high temperatures is investigated
analytically in scalar field theory. An analytical bounce solution is
presented, which reproduces the action in the thin-wall as well as thick-wall
limits. The transition is first order for the case of a thin wall while for the
thick wall case it is second order.Comment: Latex file, 22 pages, 4 Postscript figure
Microphysical, microchemical and adhesive properties of lunar material. 3: Gas interaction with lunar material
Knowledge of the reactivity of lunar material surfaces is important for understanding the effects of the lunar or space environment upon this material, particularly its nature, behavior and exposure history in comparison to terrestrial materials. Adsorptive properties are one of the important techniques for such studies. Gas adsorption measurements were made on an Apollo 12 ultrahigh vacuum-stored sample and Apollo 14 and 15 N2-stored samples. Surface area measurements were made on the latter two. Adsorbate gases used were N2, A, O2 and H2O. Krypton was used for the surface area determinations. Runs were made at room and liquid nitrogen temperature in volumetric and gravimetric systems. It was found that the adsorptive/desorptive behavior was in general significantly different from that of terrestrial materials of similar type and form. Specifically (1) the UHV-stored sample exhibited very high initial adsorption indicative of high surface reactivity, and (2) the N2-stored samples at room and liquid nitrogen temperatures showed that more gas was desorbed than introduced during adsorption, indicative of gas release from the samples. The high reactivity is a scribed cosmic ray track and solar wind damage
Kinematical Analogy for Marginal Dyon Decay
We describe a kinematical analogy for the marginal decay of 1/4-BPS dyons in
4-dimensional N=4 string compactifications. In this analogy, the electric and
magnetic charges play the role of spatial momenta, the BPS mass plays the role
of energy, and 1/2-BPS dyons correspond to massless particles. Using SO(12,1)
"Lorentz" invariance and standard kinematical formulae in particle physics, we
provide simple derivations of the curves of marginal stability. We also show
how these curves map into the momentum ellipsoid, and propose some applications
of this analogy.Comment: 10 pages, minor revision
An existence theorem for optimal control with nonstandard cost functionals
An existence theorem for optimal control is obtained for a general nonstandard cost functional of fractional type in this work. As an application of our result we can derive an existence theorem for optimal control given by M. B. Subrahamanyam for a cost functional, which is a ratio of two given integral cost functionals
Doping, density of states and conductivity in polypyrrole and poly(p-phenylene vinylene)
The evolution of the density of states (DOS) and conductivity as function of
well controlled doping levels in OC_1C_10-poly(p-phenylene vinylene)
[OC_1C_10-PPV] doped by FeCl_3 and PF_6, and PF_6 doped polypyrrole (PPy-PF_6
have been investigated. At a doping level as high as 0.2 holes per monomer, the
former one remains non-metallic, while the latter crosses the metal-insulator
transition. In both systems a similar almost linear increase in DOS as function
of charges per unit volume c* has been observed from the electrochemical gated
transistor data. In PPy-PF_6, when compared to doped OC_1C_10-PPV, the energy
states filled at low doping are closer to the vacuum level; by the higher c* at
high doping more energy states are available, which apparently enables the
conduction to change to metallic. Although both systems on the insulating side
show log(sigma) proportional to T^-1/4 as in variable range hopping, for highly
doped PPy-PF_6 the usual interpretation of the hopping parameters leads to
seemingly too high values for the density of states.Comment: 4 pages (incl. 6 figures) in Phys. Rev.
Various aspects of fines in separation and processing of beach sand minerals in India
In the present study, formation and occurance of beach sand deposits of India and recovery of heavy minerals, viz., ilmenite , rutile, zircon,monazite, sillimanite and garnet have been reported. Separation processes adopted for concentration of heavy minerals at different plants
of Indian Rear Earth Limited (IREL) have been discussed
Status of Waste Treatment in Titanium Mineral Industries
The titanium mineral industries encompassing mining, mineral separation and value addition activities generate considerable quantities of wastes primarily in the form of iron chloride/sulphate, iron oxide and acidic effluents.This paper presents a brief review of various value addition activities and associated waste generation issues. Special reference is made of the problems faced by Indian plants engaged in the processing of titanium minerals
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