7,274 research outputs found
Casimir Effect and Global Theory of Boundary Conditions
The consistency of quantum field theories defined on domains with external
borders imposes very restrictive constraints on the type of boundary conditions
that the fields can satisfy. We analyse the global geometrical and topological
properties of the space of all possible boundary conditions for scalar quantum
field theories. The variation of the Casimir energy under the change of
boundary conditions reveals the existence of singularities generically
associated to boundary conditions which either involve topology changes of the
underlying physical space or edge states with unbounded below classical energy.
The effect can be understood in terms of a new type of Maslov index associated
to the non-trivial topology of the space of boundary conditions. We also
analyze the global aspects of the renormalization group flow, T-duality and the
conformal invariance of the corresponding fixed points.Comment: 11 page
The 1973-1984 Solar Modulation of Cosmic Ray Nuclei
As a continuation of the program of solar modulation studies, new measurements were carried out with the cosmic ray telescope on the Earth satellite IMP-8, of the intensity time variations and the energy spectra of galactic cosmic ray protons, helium, carbon and oxygen from 1980 through 1984 including the recent solar maximum. In order to test the applicability of a steady state model of solar modulation during a period which includes times of rapidly changing modulation, these fluxes were equated with the predictions of a conventional model of solar modulation which assumes equilibrium between modulation mechanisms. It is found that for a reasonable range of variations of the diffusion coefficient the model predictions can be made to agree with the measurements at essentially all times during the studied period. The model can account also for the observed hysteresis effects between cosmic rays of different rigidities
Assessing the influence of the carbon oxidation-reduction state on organic pollutant biodegradation in algal-bacterial photobioreactors
The influence of the carbon oxidation-reduction state (CORS) of organic pollutants on their biodegradation in enclosed algal-bacterial photobioreactors was evaluated using a consortium of enriched wild-type methanotrophic bacteria and microalgae. Methane, methanol and glucose (with CORS -4, -2 and 0, respectively) were chosen as model organic pollutants. In the absence of external oxygen supply, microalgal photosynthesis was not capable of supporting a significant methane and methanol biodegradation due to their high oxygen demands per carbon unit, while glucose was fully oxidized by photosynthetic oxygenation. When bicarbonate was added, removal efficiencies of 37¿±¿4% (20 days), 65¿±¿4% (11 days) and 100% (2 days) were recorded for CH(4,) CH(3)OH and C(6)H(12)O(6), respectively due to the additional oxygen generated from photosynthetic bicarbonate assimilation. The use of NO(3)(-) instead of NH(4)(+) as nitrogen source (N oxidation-reduction state of +5 vs. -3) resulted in an increase in CH(4) degradation from 0 to 33¿±¿3% in the absence of bicarbonate and from 37¿±¿4% to 100% in the presence of bicarbonate, likely due to a decrease in the stoichiometric oxygen requirements and the higher photosynthetic oxygen production. Hypothetically, the CORS of the substrates might affect the CORS of the microalgal biomass composition (higher lipid content). However, the total lipid content of the algal-bacterial biomass was 19¿±¿7% in the absence and 16¿±¿2% in the presence of bicarbonat
Dynamics of active membranes with internal noise
We study the time-dependent height fluctuations of an active membrane
containing energy-dissipating pumps that drive the membrane out of equilibrium.
Unlike previous investigations based on models that neglect either curvature
couplings or random fluctuations in pump activities, our formulation explores
two new models that take both of these effects into account. In the first
model, the magnitude of the nonequilibrium forces generated by the pumps is
allowed to fluctuate temporally. In the second model, the pumps are allowed to
switch between "on" and "off" states. We compute the mean squared displacement
of a membrane point for both models, and show that they exhibit distinct
dynamical behaviors from previous models, and in particular, a superdiffusive
regime specifically arising from the shot noise.Comment: 7 pages, 4 figure
Latitudinal gradients of cosmic rays and the polarity reversal of the heliospheric magnetic field: A preliminary evaluation
Within the statistical limits imposed by the currently available data and the noise inherent in the determination of the latitudinal gradient, no evidence for the expected change in the latitudinal gradient from pre-1980 to post-1980 epochs can be found. In addition, the rigidity dependence of the gradient appears to be the same in the two epochs. Thus, no evidence is found for a sensitivity of the latitudinal gradient to the polarity of the largescale heliospheric magnetic field such as has been predicted by models incorporating particle drifts
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