2,238 research outputs found
Stable Fermion Bag Solitons in the Massive Gross-Neveu Model: Inverse Scattering Analysis
Formation of fermion bag solitons is an important paradigm in the theory of
hadron structure. We study this phenomenon non-perturbatively in the 1+1
dimensional Massive Gross-Neveu model, in the large limit. We find,
applying inverse scattering techniques, that the extremal static bag
configurations are reflectionless, as in the massless Gross-Neveu model. This
adds to existing results of variational calculations, which used reflectionless
bag profiles as trial configurations. Only reflectionless trial configurations
which support a single pair of charge-conjugate bound states of the associated
Dirac equation were used in those calculations, whereas the results in the
present paper hold for bag configurations which support an arbitrary number of
such pairs. We compute the masses of these multi-bound state solitons, and
prove that only bag configurations which bear a single pair of bound states are
stable. Each one of these configurations gives rise to an O(2N) antisymmetric
tensor multiplet of soliton states, as in the massless Gross-Neveu model.Comment: 10 pages, revtex, no figures; v2: typos corrected, references added;
v3: version accepted for publication in the PRD. referencess added. Some
minor clarifications added at the beginning of section
Adaptive Subcarrier PSK Intensity Modulation in Free Space Optical Systems
We propose an adaptive transmission technique for free space optical (FSO)
systems, operating in atmospheric turbulence and employing subcarrier phase
shift keying (S-PSK) intensity modulation. Exploiting the constant envelope
characteristics of S-PSK, the proposed technique offers efficient utilization
of the FSO channel capacity by adapting the modulation order of S-PSK,
according to the instantaneous state of turbulence induced fading and a
pre-defined bit error rate (BER) requirement. Novel expressions for the
spectral efficiency and average BER of the proposed adaptive FSO system are
presented and performance investigations under various turbulence conditions
and target BER requirements are carried out. Numerical results indicate that
significant spectral efficiency gains are offered without increasing the
transmitted average optical power or sacrificing BER requirements, in
moderate-to-strong turbulence conditions. Furthermore, the proposed variable
rate transmission technique is applied to multiple input multiple output (MIMO)
FSO systems, providing additional improvement in the achieved spectral
efficiency as the number of the transmit and/or receive apertures increases.Comment: Submitted To IEEE Transactions On Communication
Metabolite concentrations, fluxes and free energies imply efficient enzyme usage.
In metabolism, available free energy is limited and must be divided across pathway steps to maintain a negative ΔG throughout. For each reaction, ΔG is log proportional both to a concentration ratio (reaction quotient to equilibrium constant) and to a flux ratio (backward to forward flux). Here we use isotope labeling to measure absolute metabolite concentrations and fluxes in Escherichia coli, yeast and a mammalian cell line. We then integrate this information to obtain a unified set of concentrations and ΔG for each organism. In glycolysis, we find that free energy is partitioned so as to mitigate unproductive backward fluxes associated with ΔG near zero. Across metabolism, we observe that absolute metabolite concentrations and ΔG are substantially conserved and that most substrate (but not inhibitor) concentrations exceed the associated enzyme binding site dissociation constant (Km or Ki). The observed conservation of metabolite concentrations is consistent with an evolutionary drive to utilize enzymes efficiently given thermodynamic and osmotic constraints
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