17,902 research outputs found
A Transport Equation for Quantum Fields with Continuous Mass Spectrum
Within a relativistic real-time Green's function formalism, a quantum
transport equation for the phase-space distribution function is derived without
a quasi-particle approximation. Dissipation is due to a nonzero spectral width,
and can be separated into time-local and memory effects.Comment: 25 pages LaTeX, 1 figure uuencoded, GSI-Preprint 94-1
Quantum Fields and Dissipation
The description of thermal or non-equilibrium systems necessitates a quantum
field theory which differs from the usual approach in two aspects: 1.The
Hilbert space is doubled; 2.Stable quasi-particles do not exist in interacting
systems. A mini-review of these two aspects is given from a practical viewpoint
including two applications. For thermal states it is shown how infrared
divergences occuring in perturbative quasi-particle theories are avoided,
whereas for non-equilibrium states a memory effect is shown to arise in the
thermalization.Comment: Paper in ReVTeX, 12 pages. Figures and complete paper available via
anonymous ftp at ftp://tpri6c.gsi.de/pub/phenning/h96neq, contribution to the
Umezawa memorial volume of Physics Essay
Locating-total dominating sets in twin-free graphs: a conjecture
A total dominating set of a graph is a set of vertices of such
that every vertex of has a neighbor in . A locating-total dominating set
of is a total dominating set of with the additional property that
every two distinct vertices outside have distinct neighbors in ; that
is, for distinct vertices and outside , where denotes the open neighborhood of . A graph is twin-free if
every two distinct vertices have distinct open and closed neighborhoods. The
location-total domination number of , denoted , is the minimum
cardinality of a locating-total dominating set in . It is well-known that
every connected graph of order has a total dominating set of size at
most . We conjecture that if is a twin-free graph of order
with no isolated vertex, then . We prove the
conjecture for graphs without -cycles as a subgraph. We also prove that if
is a twin-free graph of order , then .Comment: 18 pages, 1 figur
A Social Dimension for Transatlantic Economic Relations
Transatlantic Economic Relations (TER) was neglected by politi¬cians for much of the twentieth century as international security issues took priority. Since the end of the Cold War, however, and as economic issues have come to prominence TER has assumed increasing importance and yet is largely overlooked in academic discussion. This report places TER in its historical context and demonstrates how the political agenda and institutional setup are both largely dysfunctional. Viewed through the prism of industrial relations and drawing on some real life examples from both sides of the Atlantic, it argues that the social dimension is a challenge central to the future development of the relationship and proposes institutional innovations which could also be replicated in other areas: for instance in support of environmental concerns. Presenting some guiding principles for transatlantic trade, this paper recommends the creation of a new secretariat to act as a permanent contact point and providing a variety of practical functions essential to making TER work
Transversals in -Uniform Hypergraphs
Let be a -regular -uniform hypergraph on vertices. The
transversal number of is the minimum number of vertices that
intersect every edge. Lai and Chang [J. Combin. Theory Ser. B 50 (1990),
129--133] proved that . Thomass\'{e} and Yeo [Combinatorica
27 (2007), 473--487] improved this bound and showed that .
We provide a further improvement and prove that , which is
best possible due to a hypergraph of order eight. More generally, we show that
if is a -uniform hypergraph on vertices and edges with maximum
degree , then , which proves a known
conjecture. We show that an easy corollary of our main result is that the total
domination number of a graph on vertices with minimum degree at least~4 is
at most , which was the main result of the Thomass\'{e}-Yeo paper
[Combinatorica 27 (2007), 473--487].Comment: 41 page
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