893 research outputs found
A linear programming based heuristic framework for min-max regret combinatorial optimization problems with interval costs
This work deals with a class of problems under interval data uncertainty,
namely interval robust-hard problems, composed of interval data min-max regret
generalizations of classical NP-hard combinatorial problems modeled as 0-1
integer linear programming problems. These problems are more challenging than
other interval data min-max regret problems, as solely computing the cost of
any feasible solution requires solving an instance of an NP-hard problem. The
state-of-the-art exact algorithms in the literature are based on the generation
of a possibly exponential number of cuts. As each cut separation involves the
resolution of an NP-hard classical optimization problem, the size of the
instances that can be solved efficiently is relatively small. To smooth this
issue, we present a modeling technique for interval robust-hard problems in the
context of a heuristic framework. The heuristic obtains feasible solutions by
exploring dual information of a linearly relaxed model associated with the
classical optimization problem counterpart. Computational experiments for
interval data min-max regret versions of the restricted shortest path problem
and the set covering problem show that our heuristic is able to find optimal or
near-optimal solutions and also improves the primal bounds obtained by a
state-of-the-art exact algorithm and a 2-approximation procedure for interval
data min-max regret problems
Thunderstorm dynamics in a scale interaction
This paper presents a review of thunderstorm dynamics through the use of the vorticity equation with a focus on the development of rotation, an indicator of storm severity. The processes involved in the scale interaction are basically the tilting of vortex tubes while the divergence (or ballerina) term, being highly non-linear, provides intensification of incipient vorticity. A brief account of numerically simulated storms in Brazil with well defined wind shear in the storm environment is presented
Thermal Effects on Photon-Induced Quantum Transport
We theoretically investigate laser induced quantum transport in a two-level
quantum dot attached to electric contacts. Our approach, based on
nonequilibrium Green function technique, allows to include thermal effects on
the photon-induced quantum transport and excitonic coherent dynamics. By
solving a set of coupled integrodifferential equations, involving correlation
and propagator functions, we obtain the photocurrent and the dot occupations as
a function of time. The characteristic coherent Rabi oscillations are found in
both occupations and photocurrent, with two distinct sources of decoherence:
incoherent tunneling and thermal fluctuations. In particular, for increasing
temperature the dot becomes more thermally occupied which shrinks the amplitude
of the Rabi oscillations, due to Pauli blockade. Finally, due to the interplay
between photon and thermal induced electron populations, the photocurrent can
switch sign as time evolves and its stationary value can be maximized by
tunning the laser intensity.Comment: 5 pages, 4 figure
Relativistic Bose-Einstein condensate in the rainbow gravity
In this paper, we study the effects of a modified theory of gravity - the
rainbow gravity - on the relativistic Bose-Einstein condensate (BEC). We
initially discuss some formal aspects of the model in order to compute the
corrections to the relevant quantities of the condensate. Following, we
evaluate the generating functional from which obtain some thermodynamic
parameters. Then we calculate the corrected critical temperature that
sets the relativistic Bose-Einstein condensate considering the three principal
rainbow functions, finding, in addition, a phenomenological upper bound for the
parameters involved in the model. Finally, we discuss how harder is for the
particles at an arbitrary temperature to enter the condensed state
compared to the usual scenario, {\it i.e.}, without rainbow gravity.Comment: 13 pages, 2 figure, matches version accepted in EP
Dressing approach to the nonvanishing boundary value problem for the AKNS hierarchy
We propose an approach to the nonvanishing boundary value problem for
integrable hierarchies based on the dressing method. Then we apply the method
to the AKNS hierarchy. The solutions are found by introducing appropriate
vertex operators that takes into account the boundary conditions.Comment: Published version Proc. Quantum Theory and Symmetries 7
(QTS7)(Prague, Czech Republic, 2011
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