29,657 research outputs found
Some exact results on the matter star-product in the half-string formalism
We show that the D25 sliver wavefunction, just as the D-instanton sliver,
factorizes when expressed in terms of half-string coordinates. We also
calculate analytically the star-product of two zero-momentum eigenstates of
using the vertex in the oscillator basis, thereby showing that the
star-product in the matter sector can indeed be seen as multiplication of
matrices acting on the space of functionals of half strings. We then use the
above results to establish that the matrices , conjectured by
Rastelli, Sen and Zwiebach to be left and right projectors on the sliver, are
indeed so.Comment: 27 pages; footnote adde
A description of the NSSL cases used for a simulated VAS retrieval study
A documentation of eight National Severe Storm Laboratory severe storm cases, which serve as a basis for a simulated VISSR Atmospheric Sounder retrieval study, is presented in this paper. Six of the selected cases provide a control data set to complete the statistical information needed for retrieval techniques based upon the use of regression matrices. The other two cases are to be used in the actual retrieval experiments. The selection was based upon the presence of moisture gradients in the analysis region, the availability of satellite images at the selected time periods, and the extent of cloud cover within the observing network
The microcanonical thermodynamics of finite systems: The microscopic origin of condensation and phase separations; and the conditions for heat flow from lower to higher temperatures
Microcanonical thermodynamics allows the application of statistical mechanics
both to finite and even small systems and also to the largest, self-gravitating
ones. However, one must reconsider the fundamental principles of statistical
mechanics especially its key quantity, entropy. Whereas in conventional
thermostatistics, the homogeneity and extensivity of the system and the
concavity of its entropy are central conditions, these fail for the systems
considered here. For example, at phase separation, the entropy, S(E), is
necessarily convex to make exp[S(E)-E/T] bimodal in E. Particularly, as
inhomogeneities and surface effects cannot be scaled away, one must be careful
with the standard arguments of splitting a system into two subsystems, or
bringing two systems into thermal contact with energy or particle exchange. Not
only the volume part of the entropy must be considered. As will be shown here,
when removing constraints in regions of a negative heat capacity, the system
may even relax under a flow of heat (energy) against a temperature slope. Thus
the Clausius formulation of the second law: ``Heat always flows from hot to
cold'', can be violated. Temperature is not a necessary or fundamental control
parameter of thermostatistics. However, the second law is still satisfied and
the total Boltzmann entropy increases. In the final sections of this paper, the
general microscopic mechanism leading to condensation and to the convexity of
the microcanonical entropy at phase separation is sketched. Also the
microscopic conditions for the existence (or non-existence) of a critical
end-point of the phase-separation are discussed. This is explained for the
liquid-gas and the solid-liquid transition.Comment: 23 pages, 2 figures, Accepted for publication in the Journal of
Chemical Physic
Regge Behavior of DIS Structure Functions
Building on previous works of the mid 1960's, we construct an integral
equation for forward elastic scattering (t=0) at arbitrary virtuality Q^2 and
large s=W^2. This equation sums the ladder production of massless intermediate
bosons to all orders, and the solution exhibits Regge behavior. The equation is
used to study scattering in a simple chi^2 phi scalar theory, where it is
solved appoximately and applied to the study of DIS at small x. We find that
the model can naturally describe the quark distribution in both the large x
region and the small x region dominated by Reggeon exchange.Comment: 13 pages with 5 figure
Emergent bipartiteness in a society of knights and knaves
We propose a simple model of a social network based on so-called
knights-and-knaves puzzles. The model describes the formation of networks
between two classes of agents where links are formed by agents introducing
their neighbours to others of their own class. We show that if the proportion
of knights and knaves is within a certain range, the network self-organizes to
a perfectly bipartite state. However, if the excess of one of the two classes
is greater than a threshold value, bipartiteness is not observed. We offer a
detailed theoretical analysis for the behaviour of the model, investigate its
behaviou r in the thermodynamic limit, and argue that it provides a simple
example of a topology-driven model whose behaviour is strongly reminiscent of a
first-order phase transitions far from equilibrium.Comment: 12 pages, 5 figure
Relativistic calculation of the triton binding energy and its implications
First results for the triton binding energy obtained from the relativistic
spectator or Gross equation are reported. The Dirac structure of the nucleons
is taken into account. Numerical results are presented for a family of
realistic OBE models with off-shell scalar couplings. It is shown that these
off-shell couplings improve both the fits to the two-body data and the
predictions for the binding energy.Comment: 5 pages, RevTeX 3.0, 1 figure (uses epsfig.sty
Nuclear Corrections to Hyperfine Structure in Light Hydrogenic Atoms
Hyperfine intervals in light hydrogenic atoms and ions are among the most
accurately measured quantities in physics. The theory of QED corrections has
recently advanced to the point that uncalculated terms for hydrogenic atoms and
ions are probably smaller than 0.1 parts per million (ppm), and the experiments
are even more accurate. The difference of the experiments and QED theory is
interpreted as the effect on the hyperfine interaction of the (finite) nuclear
charge and magnetization distributions, and this difference varies from tens to
hundreds of ppm. We have calculated the dominant component of the 1s hyperfine
interval for deuterium, tritium and singly ionized helium, using modern
second-generation potentials to compute the nuclear component of the hyperfine
splitting for the deuteron and the trinucleon systems. The calculated nuclear
corrections are within 3% of the experimental values for deuterium and tritium,
but are about 20% discrepant for singly ionized helium. The nuclear corrections
for the trinucleon systems can be qualitatively understood by invoking SU(4)
symmetry.Comment: 26 pages, 1 figure, latex - submitted to Physical Review
Ghost Kinetic Operator of Vacuum String Field Theory
Using the data of eigenvalues and eigenvectors of Neumann matrices in the
3-string vertex, we prove analytically that the ghost kinetic operator of
vacuum string field theory obtained by Hata and Kawano is equal to the ghost
operator inserted at the open string midpoint. We also comment on the values of
determinants appearing in the norm of sliver state.Comment: 19 pages, 1 figure, lanlmac; v2: typos correcte
Excited states of a static dilute spherical Bose condensate in a trap
The Bogoliubov approximation is used to study the excited states of a dilute
gas of atomic bosons trapped in an isotropic harmonic potential
characterized by a frequency and an oscillator length . The self-consistent static Bose condensate has
macroscopic occupation number , with nonuniform spherical condensate
density ; by assumption, the depletion of the condensate is small (). The linearized density fluctuation operator and velocity potential operator satisfy coupled equations
that embody particle conservation and Bernoulli's theorem. For each angular
momentum , introduction of quasiparticle operators yields coupled eigenvalue
equations for the excited states; they can be expressed either in terms of
Bogoliubov coherence amplitudes and that determine the
appropriate linear combinations of particle operators, or in terms of
hydrodynamic amplitudes and . The hydrodynamic picture
suggests a simple variational approximation for that provides an upper
bound for the lowest eigenvalue and an estimate for the
corresponding zero-temperature occupation number ; both expressions
closely resemble those for a uniform bulk Bose condensate.Comment: 5 pages, RevTeX, contributed paper accepted for Low Temperature
Conference, LT21, August, 199
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