661 research outputs found
Classical String Solutions in Effective Infrared Theory of SU(3) Gluodynamics
We investigate string solutions to the classical equations of motion
("classical QCD strings") for a dual Ginzburg-Landau model corresponding to
SU(3) gluodynamics in an abelian projection. For a certain relation between
couplings of the model the string solutions are defined by first order
differential equations. These solutions are related to vortex configurations of
the Abelian Higgs model in the Bogomol'ny limit. An analytic expression for the
string tension is derived and the string-string interactions are discussed. Our
results imply that the vacuum of SU(3) gluodynamics is near a border between
type-I and type-II dual superconductivity.Comment: 7 pages, LaTeX2e; v2: references added and typos correcte
Disruption management in passenger railway transportation.
This paper deals with disruption management in passengerrailway transportation. In the disruption management process, manyactors belonging to different organizations play a role. In this paperwe therefore describe the process itself and the roles of thedifferent actors.Furthermore, we discuss the three main subproblems in railwaydisruption management: timetable adjustment, and rolling stock andcrew re-scheduling. Next to a general description of these problems,we give an overview of the existing literature and we present somedetails of the specific situations at DSB S-tog and NS. These arethe railway operators in the suburban area of Copenhagen, Denmark,and on the main railway lines in the Netherlands, respectively.Since not much research has been carried out yet on OperationsResearch models for disruption management in the railway context,models and techniques that have been developed for related problemsin the airline world are discussed as well.Finally, we address the integration of the re-scheduling processesof the timetable, and the resources rolling stock and crew.
Aharonov-Bohm effect, Center Monopoles and Center Vortices in SU(2) Lattice Gluodynamics
SU(2) gluodynamics is investigated numerically and analytically in the
(Indirect) Maximal Center gauge at finite temperature. The center vortices are
shown to be condensed in the confinement phase and dilute in the deconfinement
phase. A new physical object, center monopole, is constructed. We show that the
center monopole condensate is the order parameter of deconfinement phase
transition. The linking of the vortex worldsheets and quark trajectories is
identified with the Aharonov-Bohm interaction in an effective Abelian Higgs
theory. We conclude that the confinement in the Maximal Center gauge can be
explained by a new mechanism called "the real superconductor mechanism".Comment: LATTICE98(confine), 3 pages, LaTeX, 2 eps figures, uses espcrc2.st
Negotiating safety practice in small construction companies
AbstractSmall construction companies have high rates of work related injuries and pervasive challenges in preventing them. This article examines safety practice from the employee perspective, taking into account the role of the ownerâmanager and interactions with customers in everyday work settings. Data were derived from a qualitative multi-case study of ten small construction companies (carpentry/plumbing/masonry) involving one or two-man work crews. The analytic approach is phenomenological, based on thematic content analysis of interviews and participant-observations. The employeesâ general approach to safety was âto take care of oneselfâ, which, in addition to standardized rule-based knowledge, drew on individual feelings, personal experience and the balancing of various concerns in different work settings, e.g. workflow, customer satisfaction, good work relations and safety issues. In the context of small companies, safety practice was negotiated in the tension between ownerâmanager decisions and employeesâ self-administration, which also was reflected in the way safety was communicated and learned within the companies as a matter of professionalism and individual mastering. Safety was rarely in explicit focus among employees in the small construction companies. It was an intrinsic part of their craftsmanship, established and negotiated in work situations and in interactions, in particular with customers. Safety issues were rarely shared or communicated as a common issue within the company. Consequently ownerâmanagers had limited impact on the employeesâ daily safety practices. Injury prevention approaches should take into account the limited impact that ownerâmanagers had on the day-to-day safety practices, as well as the importance of the employeesâ relationships with the customers
Aharonov--Bohm Effect in 3D Abelian Higgs Theory
We study a field--theoretical analogue of the Aharonov--Bohm effect in the 3D
Abelian Higgs Model: the corresponding topological interaction is proportional
to the linking number of the vortex and the particle world trajectories. We
show that the Aharonov--Bohm effect gives rise to a nontrivial interaction of
tested charged particles.Comment: LaTeX, 3 pages, 1 figure, uses epsf.sty; talk presented at
LATTICE96(topology), St. Louis, US
Vortex profiles and vortex interactions at the electroweak crossover
Local correlations of Z-vortex operators with gauge and Higgs fields (lattice
quantum vortex profiles) as well as vortex two-point functions are studied in
the crossover region near a Higgs mass of 100 GeV within the 3D SU(2) Higgs
model. The vortex profiles resemble certain features of the classical vortex
solutions in the continuum. The vortex-vortex interactions are analogous to the
interactions of Abrikosov vortices in a type-I superconductor.Comment: talk at LATTICE99(electroweak), 3 pages and 5 EPS figure
Experimental evidence of a change of exchange anisotropy sign with temperature in Zn-substituted Cu2OSeO3
We report small-angle neutron scattering from the conical state in a single crystal of Zn-substituted Cu 2 OSeO 3 . Using a 3D vector-field magnet to reorient the conical wave vector, our measurements show that the magnitude of the conical wave vector changes as a function of crystallographic direction. These changes are explained using the anisotropic exchange interaction (AEI) within the continuum model, whose magnitude in free-energy transitions from a maxima to a minima along the âš 111 â© and âš 100 â© crystallographic directions respectively. We further find that the AEI free-energy constant undergoes a change of sign from positive to negative with decreasing temperature. Unlike in the related compound FeGe, where similar behavior of the AEI induces a reorientation of the helical wave vector, we show that the zero field helical wave vector in ( Cu 0.98 Zn 0.02 ) 2 OSeO 3 remains along the âš 100 â© directions at all temperatures due to the competing fourth-order magnetocrystalline anisotropy becoming dominant at lower temperatures
Electromagnetic superconductivity of vacuum induced by strong magnetic field
The quantum vacuum may become an electromagnetic superconductor in the
presence of a strong external magnetic field of the order of 10^{16} Tesla. The
magnetic field of the required strength (and even stronger) is expected to be
generated for a short time in ultraperipheral collisions of heavy ions at the
Large Hadron Collider. The superconducting properties of the new phase appear
as a result of a magnetic-field-assisted condensation of quark-antiquark pairs
with quantum numbers of electrically charged rho mesons. We discuss
similarities and differences between the suggested superconducting state of the
quantum vacuum, a conventional superconductivity and the Schwinger pair
creation. We argue qualitatively and quantitatively why the superconducting
state should be a natural ground state of the vacuum at the sufficiently strong
magnetic field. We demonstrate the existence of the superconducting phase using
both the Nambu-Jona-Lasinio model and an effective bosonic model based on the
vector meson dominance (the rho-meson electrodynamics). We discuss various
properties of the new phase such as absence of the Meissner effect, anisotropy
of superconductivity, spatial inhomogeneity of ground state, emergence of a
neutral superfluid component in the ground state and presence of new
topological vortices in the quark-antiquark condensates.Comment: 37 pages, 14 figures, to appear in Lect. Notes Phys. "Strongly
interacting matter in magnetic fields" (Springer), edited by D. Kharzeev, K.
Landsteiner, A. Schmitt, H.-U. Ye
Monopole Chains in the Compact Abelian Higgs Model with doubly-charged Matter Field
We study the properties of topological defects in the lattice compact Abelian
Higgs Model with charge Q=2 matter field. We find that monopoles and
antimonopoles form chain-like structures which are dense in the
confinement/symmetric phase. In this phase the mentioned structures explain
both the confinement of single-charged and the breaking of strings spanned
between doubly-charged test particles. This observation helps to understand how
the non-diagonal gluons, once taken into consideration in the Abelian
projection of gluodynamics, could reproduce in this framework the string
breaking for adjoint charges.Comment: 11 pages, 8 figures; Revision 1: two figures added, percolation
properties discussed, title changed, enlarged version; Revision 2: misprints
are corrected, to be published in Phys.Lett.
The Case for Quantum Key Distribution
Quantum key distribution (QKD) promises secure key agreement by using quantum
mechanical systems. We argue that QKD will be an important part of future
cryptographic infrastructures. It can provide long-term confidentiality for
encrypted information without reliance on computational assumptions. Although
QKD still requires authentication to prevent man-in-the-middle attacks, it can
make use of either information-theoretically secure symmetric key
authentication or computationally secure public key authentication: even when
using public key authentication, we argue that QKD still offers stronger
security than classical key agreement.Comment: 12 pages, 1 figure; to appear in proceedings of QuantumComm 2009
Workshop on Quantum and Classical Information Security; version 2 minor
content revision
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