109 research outputs found
Counting Closed String States in a Box
The computation of the microcanonical density of states for a string gas in a
finite volume needs a one by one count because of the discrete nature of the
spectrum. We present a way to do it using geometrical arguments in phase space.
We take advantage of this result in order to obtain the thermodynamical
magnitudes of the system. We show that the results for an open universe exactly
coincide with the infinite volume limit of the expression obtained for the gas
in a box. For any finite volume the Hagedorn temperature is a maximum one, and
the specific heat is always positive. We also present a definition of pressure
compatible with R-duality seen as an exact symmetry, which allows us to make a
study on the physical phase space of the system. Besides a maximum temperature
the gas presents an asymptotic pressure.Comment: 16 pages, 5 Postscript figure
Non-perturbative Thermodynamics in Matrix String Theory
A study of the thermodynamics in IIA Matrix String Theory is presented. The
free string limit is calculated and seen to exactly reproduce the usual result.
When energies are enough to excite non-perturbative objects like D-particles
and specially membranes, the situation changes because they add a large number
of degrees of freedom that do not appear at low energies. There seems to be a
negative specific heat (even in the Microcanonical Ensemble) that moves the
asymptotic temperature to zero. Besides, the mechanism of interaction and
attachment of open strings to D-particles and D-membranes is analyzed.Comment: 30 pages, 3 figures. Several points are clarified. Final version to
appear in Nucl. Phys. B. Also available at http://condmat1.ciencias.uniovi.e
Thermodynamic nonextensivity in a closed string gas
Well known results in string thermodynamics show that there is always a
negative specific heat phase in the microcanonical description of a gas of
closed free strings whenever there are no winding modes present. We will
carefully compute the number of strings in the gas to show how this negative
specific heat is related to the fact that the system does not have
thermodynamic extensivity. We will also discuss the consequences for a system
of having a microcanonical negative specific heat versus the exact result that
such a thing cannot happen in any canonical (fixed temperature) description.Comment: Title + 13 pages, more typos correcte
Editorial: Hydroinformatics for water distribution systems analysis and management
Urban water distribution systems (WDS) analysis and management is a very complex challenge for researchers and technicians. Such a labyrinth contains numerous processes, sub-processes, states of being with their associated causative factors, feedback loops and interrelationships (Colombo & Karney 2003). This special issue is an occasion to study and analyse specific processes in the broader and stronger view of the entire labyrinth. The selected papers focus on some of the most important problems of urban WDS management, trying to help orientate researchers and planners, like Theseus and the Minotaur, in the labyrinth of the various concerns and processes involved in urban WDS planning (Figure 1). Figure 1 The labyrinth of WDS (modified by Macaulay 1976). This issue contains 10 papers that have been selected among those presented at the 16th Conference on Water Distribution System Analysis, WDSA 2014 (Bari, Italy, 14-17 July 2014), as very interesting studies and applications of Hydroinformatics techniques to WDS analysis and management. The selected papers have been fully rewritten, completed and improved and have undergone a rigorous peer-review process. The key points of the issue are
Data Mining for Management and Rehabilitation of Water Systems: The Evolutionary Polynomial Regression Approach
Finite Temperature Matrix Theory
We present the way the Lorentz invariant canonical partition function for
Matrix Theory as a light-cone formulation of M-theory can be computed. We
explicitly show how when the eleventh dimension is decompactified, the N = 1
eleven dimensional SUGRA partition function appears. We also provide a high
temperature expansion which captures some structure of the canonical partition
function when interactions amongst D-particles are on. The connection with the
semi-classical computations thermalizing the open superstrings attached to a
D-particle is also clarified through a Born-Oppenheimer approximation. Some
ideas about how Matrix Theory would describe the complementary degrees of
freedom of the massless content of eleven dimensional SUGRA are discussed.
Comments about possible connections to black hole physics are also made.Comment: 32 pages. LaTeX, 1 epsf figure. Corrections and changes made in
Section 4. One reference adde
WDNetXL: Efficient Research Transfer For Management, Planning And Design Of Water Distribution Networks
The WDNetXL system (www.hydroinformatics.it) is aimed at promoting transfer of research achievements in water distribution network (WDN) analysis, planning and management to practitioners, students and researchers. In order to facilitate the technology transfer, the WDNetXL functions are integrated into the worldwide known MS-Excel data-management environment. Advanced hydraulic modeling and topological analyses of WDN are combined with efficient optimization strategies to make readily available the latest, even customized, decision support tools for planning and management of WDNs. All these features make WDNetXL of practical support for technicians as well as a privileged platform to test innovations coming from research in WDN analysis, planning and management area. This, contribution illustrates the WDNetXL research transfer paradigm and its architecture, providing also few details about the main advancements in WDN analysis, which represents the primary support for engineersâ activities and the base component for other functions
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