6,603 research outputs found
On Exact and Approximate Solutions for Hard Problems: An Alternative Look
We discuss in an informal, general audience style the da Costa-Doria conjecture about the independence of the P = NP hypothesis and try to briefly assess its impact on practical situations in economics. The paper concludes with a discussion of the Coppe-Cosenza procedure, which is an approximate, partly heuristic algorithm for allocation problems.P vs. NP , allocation problem, assignment problem, traveling salesman, exact solution for NP problems, approximate solutions for NP problems, undecidability, incompleteness
Effect of the boundary condition on the vortex patterns in mesoscopic three-dimensional superconductors - disk and sphere
The vortex state of mesoscopic three-dimensional superconductors is
determined using a minimization procedure of the Ginzburg-Landau free energy.
We obtain the vortex pattern for a mesoscopic superconducting sphere and find
that vortex lines are naturally bent and are closest to each other at the
equatorial plane. For a superconducting disk with finite height, and under an
applied magnetic field perpendicular to its major surface, we find that our
method gives results consistent with previous calculations. The matching
fields, the magnetization and , are obtained for models that differ
according to their boundary properties. A change of the Ginzburg-Landau
parameters near the surface can substantially enhance as shown here.Comment: 7 pages, 4 figures (low resolution
The Average Kinetic Energy of the Superconducting State
Isothermal magnetization curves are plotted as the magnetization times the
magnetic induction, , versus the applied field, H. We show
here that this new curve is the average kinetic energy of the superconducting
state versus the applied field, for type-II superconductors with a high
Ginzburg-Landau parameter . The maximum of occurs at
a field, , directly related to the upper critical field, ,
suggesting that may be extracted from such plots even in cases when
it is too high for direct measurement. We obtain these plots both
theoretically, from the Ginzburg-Landau theory, and experimentally, using a
Niobium sample with , and compare them.Comment: 11 pages, 9 postscript figure
Yang-Mills Families
The Yang-Mills theory structure is based on group theory. It rules the symmetry relationship where the number of potential fields transforming under a same group must be equal to the number of group generators. It defines the group valued expression from where the corresponding non-abelian symmetry properties are derived. Nevertheless based on different origins as Kaluza-Klein, fibre bundles, supersymmetry, s-model , BRST and anti-BRST algorithm, counting degrees of freedom leads to a Yang-Mills extension under the existence of different potential fields rotating under a same single group. They establish for SU(N) the relationship where and is a flavor index, . Physically, it says that different Yang-Mills families can share a common symmetry group. They develop a whole non-abelian gauge theory. The effort in this work is to explore such non-abelian extension. First, to build up it on the so-called constructor basis where gauge symmetry is more available for expressing the corresponding fields strengths, Lagrangian and classical equations. After that, given that the physical fields are those associated to the poles of two-point Green functions, one derives the physical Lagrangian L written in the physical basis . A new physical Lagrangian associated to symmetry is generated. The meaning of Yang-Mills families appears. A symmetry of difference is realized. Where every quanta is distinguished from each other. It yields a quanta diversity associated to corresponding Yang-Mills families. There are N-spin 1 and N-spin 0 quanta separated by different quantum numbers through a whole N-dynamics. An extension to QCD becomes possible
New Faraday lines through Four Bosons EM
Field physics was founded by Faraday introducing magnetic fields (1831),
electric fields (1837) and light as an EM wave (1846), initiating the process
where nature is made by matter and fields. Consider that, ordinary space is
full of fields. The Faraday view is basis for modern quantum field theory. The
concept of fields set up a physicality in development. Physics would like to
know how far matter is created by fields. Generate matter from nonlinear
fields. Faraday lines of force relating physical entities as electric charge
and mass depending on fields. Our purpose is on Faraday lines for nonlinear
abelian electromagnetism. Introduce the Four Bosons EM. The phenomenology of a
generic charge transmitted by four bosons . Nonlinear equations constituted. New Faraday lines were
introduced. The potentials fields of physics are developed. Granular and
collective fields strengths expressed. Four types of fields charges are
derived. They are electric charge, modulated, neutral, Bianchi. This work
introduces a systematic procedure of associative physics. Mass and charge are
generated due to the four fields interrelationships. Masses are derived without
spontaneous symmetry breaking. It is obtained naturally from gauge symmetry,
London, and mixing terms. Electric charge is written by fields through the
Noether theorem. EM interactions not necessarily coupled with electric charge
are proposed. An enlargement of EM energy is derived.Comment: 20 pages, 0 figure
Landau and Ott scaling for the kinetic energy density and the low conventional superconductors, and Nb
The scaling approach recently proposed by Landau and Ott for isothermal
magnetization curves is extended to the average kinetic energy density of the
condensate. Two low superconductors, Nb and are studied
and their isothermal reversible magnetization shown to display Landau and Ott
scaling. Good agreement is obtained for the upper critical field ,
determined from the Abrikosov approximation for the reversible region (standard
linear extrapolation of the magnetization curve), and from the maximum of the
kinetic energy curves. For the full range of data, which includes the
irreversible region, the isothermal curves for show an
impressive collapse into a single curve over the entire range of field
measurements. The Nb isothermal curves exhibit the interesting
feature of a constant and temperature independent minimum value
Electric Charge Mutation by Four Vector Bosons
A general theory of electric charge is proposed. It is based on two
phenomenologies. Electric charge mutation and conservation law. Three charges
transformations physics succeeds. Quantum field theory underlies
corresponding creations and annihilation. A potential field's quadruplet is
ruled. Microscopic electromagnetism is processed by four vectors bosons
intermediations. The electromagnetism closure is accomplished. The quadruplet
completeness introduces the
most generic EM energy flux between electric charges. Charge mutation includes
that besides usual photon, EM phenomena is enlarged by massive and charged
photons. Charge conservation associates these four vector fields. Electric
charge symmetry, extends EM for an abelian symmetry . A new EM Lagrangian beyond Maxwell results. A symmetry
equation for electric charge is established through Noether theorem. The
electric charge transfer physics extends the EM phenomenon. Nonlinear
Electromagnetic fields modified electric charge symmetry, new EM regimes.
Potential fields become a physical entity producing conglomerates, collective
fields, mass, sources, charges, monopoles, forces. EM features ruled from an
extended electric charge abelian symmetry. Systemic, nonlinear, neutral,
spintronics, photonics, electroweak EM regimes are constituted.Comment: 45 pages, not figur
Vanishing of the upper critical field in Bi_2Sr_2CaCu_2O_{8+\delta} from Landau-Ott scaling
We apply Landau-Ott scaling to the reversible magnetization data of
BiSrCaCuO published by Y. Wang et al. [\emph{Phys.
Rev. Lett. \textbf{95} 247002 (2005)}] and find that the extrapolation of the
Landau-Ott upper critical field line vanishes at a critical temperature
parameter, T^*_c, a few degrees above the zero resistivity critical
temperature, T_c. Only isothermal curves below and near to T_c were used to
determine this transition temperature. This temperature is associated to the
disappearance of the mixed state instead of a complete suppression of
superconductivity in the sample.Comment: 3 figure
Using imprecise continuous time Markov chains for assessing the reliability of power networks with common cause failure and non-immediate repair.
We explore how imprecise continuous time Markov
chains can improve traditional reliability models based
on precise continuous time Markov chains. Specifically,
we analyse the reliability of power networks under very
weak statistical assumptions, explicitly accounting for
non-stationary failure and repair rates and the limited
accuracy by which common cause failure rates can be
estimated. Bounds on typical quantities of interest
are derived, namely the expected time spent in system
failure state, as well as the expected number of
transitions to that state. A worked numerical example
demonstrates the theoretical techniques described.
Interestingly, the number of iterations required for
convergence is observed to be much lower than current
theoretical bounds
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