6,922 research outputs found
Effective Action and Measure in Matrix Model of IIB Superstrings
We calculate an effective action and measure induced by the integration over
the auxiliary field in the matrix model recently proposed to describe IIB
superstrings. It is shown that the measure of integration over the auxiliary
matrix is uniquely determined by locality and reparametrization invariance of
the resulting effective action. The large-- limit of the induced measure for
string coordinates is discussed in detail. It is found to be ultralocal and,
thus, possibly is irrelevant in the continuum limit. The model of the GKM type
is considered in relation to the effective action problem.Comment: 9pp., Latex; v2: the discussion of the large N limit of the induced
measure is substantially expande
Direct thrust measurement of a 30-cm ion thruster
A direct thrust measurement of a 30-cm diameter ion thruster was accomplished by means of a laser interferometer thrust stand. The thruster was supported in a pendulum manner by three 3.65-m long wires. Electrical power was provided by means of 18 mercury filled pots. A movable 23-button planar probe rake was used to determine thrust loss due to ion beam divergence. Values of thrust, thrust loss due to ion beam divergence, and thrust loss due to multiple ionization were measured for ion beam currents ranging from 0.5 A to 2.5 A. Measured thrust values indicate an accuracy of approximately 1% and are in good agreement with thrust values calculated by indirect measurements
Black Holes of a Minimal Size in String Gravity
A lower limit for a neutral black hole size is obtained in the frames of the
string gravity model with the second order curvature correction. It is shown
that this effect remains when the third order curvature correction is also
taken into account and argued that such restriction does exist in all
perturbative orders of curvature expansions.Comment: 6 LaTeX pages, 1 PostScript figure (epsfig.sty), minor changes in the
text and references, submitted to Int.J.Mod.Phy
Ten Dimensional Black Hole and the D0-brane Threshold Bound State
We discuss the ten dimensional black holes made of D0-branes in the regime
where the effective coupling is large, and yet the 11D geometry is unimportant.
We suggest that these black holes can be interpreted as excitations over the
threshold bound state. Thus, the entropy formula for the former is used to
predict a scaling region of the wave function of the latter. The horizon radius
and the mass gap predicted in this picture agree with the formulas derived from
the classical geometry.Comment: 11 pages, harvmac; v2: typos corrected, argument for the convergence
of two integrals improved, v3: one ref. adde
Some comments about Schwarzschield black holes in Matrix theory
In the present paper we calculate the statistical partition function for any
number of extended objects in Matrix theory in the one loop approximation. As
an application, we calculate the statistical properties of K clusters of D0
branes and then the statistical properties of K membranes which are wound on a
torus.Comment: 15 page
Comment about quasi-isotropic solution of Einstein equations near cosmological singularity
We generalize for the case of arbitrary hydrodynamical matter the
quasi-isotropic solution of Einstein equations near cosmological singularity,
found by Lifshitz and Khalatnikov in 1960 for the case of radiation-dominated
universe. It is shown that this solution always exists, but dependence of terms
in the quasi-isotropic expansion acquires a more complicated form.Comment: 7 pages, The collective of authors is enlarged and some comments and
references are adde
Space-Time and Matter in IIB Matrix Model - gauge symmetry and diffeomorphism -
We pursue the study of the type IIB matrix model as a constructive definition
of superstring. In this paper, we justify the interpretation of space-time as
distribution of eigenvalues of the matrices by showing that some low energy
excitations indeed propagate in it. In particular, we show that if the
distribution consists of small clusters of size , low energy theory acquires
local SU(n) gauge symmetry and a plaquette action for the associated gauge
boson is induced, in addition to a gauge invariant kinetic term for a massless
fermion in the adjoint representation of the SU(n). We finally argue a possible
identification of the diffeomorphism symmetry with permutation group acting on
the set of eigenvalues, and show that the general covariance is realized in the
low energy effective theory even though we do not have a manifest general
covariance in the IIB matrix model action.Comment: 25 page
Measurement of beam divergence of 30-centimeter dished grids
The beam divergence of a 30-centimeter diameter thruster with dished grids was calculated from current densities measured with a probe rake containing seventeen planar molybdenum probes. The measured data were analyzed as a function of a number of parameters. The most sensitive parameters were the amount of compensation of the accelerator grid and the ratio of net to total accelerating voltage. The thrust losses were reduced by over 5 percent with the use of compensated grids alone, and by variation of other parameters the overall thrust losses due to beam divergence were reduced to less than 2 percent
Carbon-13 in groundwater from English and Norwegian crystalline rock aquifers: a tool for deducing the origin of alkalinity?
The 13C signature is evaluated for various environmental compartments (vegetation, soils, soil gas, rock and groundwater) for three crystalline rock terrains in England and Norway. The data are used to evaluate the extent to which stable carbon isotopic data can be applied to deduce whether the alkalinity in crystalline bedrock groundwaters has its origin in hydrolysis of carbonate or silicate minerals by CO2. The resolution of this issue has profound implications for the role of weathering of crystalline rocks as a global sink for CO2. In the investigated English terrain (Isles of Scilly), groundwaters are hydrochemically immature and DIC is predominantly in the form of carbonic acid with a soil gas signature. In the Norwegian terrains, the evidence is not conclusive but is consistent with a significant fraction of the groundwater DIC being derived from silicate hydrolysis by CO2. A combined consideration of pH, alkalinity and carbon isotope data, plotted alongside theoretical evolutionary pathways on bivariate diagrams, strongly suggests real evolutionary pathways are likely to be hybrid, potentially involving both open and closed CO2 conditions
Nonsingular Lagrangians for Two Dimensional Black Holes
We introduce a large class of modifications of the standard lagrangian for
two dimensional dilaton gravity, whose general solutions are nonsingular black
holes. A subclass of these lagrangians have extremal solutions which are
nonsingular analogues of the extremal Reissner-Nordstrom spacetime. It is
possible that quantum deformations of these extremal solutions are the endpoint
of Hawking evaporation when the models are coupled to matter, and that the
resulting evolution may be studied entirely within the framework of the
semiclassical approximation. Numerical work to verify this conjecture is in
progress. We point out however that the solutions with non-negative mass always
contain Cauchy horizons, and may be sensitive to small perturbations.Comment: 27 pages, three figures, RU-92-61. (Replaced version contains some
corrections to incorrect equations. The zero temperature extremal geometry
(the conjectured end-point of the Hawking evaporation) is not as stated in
the previous version, but rather is a nonsingular analogue of the zero
temperature Reissner-Nordstrom space-time.
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