40,999 research outputs found
Deconvolution and analysis of wide-angle longwave radiation data from Nimbus 6 Earth radiation budget experiment for the first year
One year of longwave radiation data from July 1975 through June 1976 from the Nimbus 6 satellite Earth radiation budget experiment is analyzed by representing the radiation field by a spherical harmonic expansion. The data are from the wide field of view instrument. Contour maps of the longwave radiation field and spherical harmonic coefficients to degree 12 and order 12 are presented for a 12 month data period
Towards Loop Quantum Supergravity (LQSG) II. p-Form Sector
In our companion paper, we focussed on the quantisation of the
Rarita-Schwinger sector of Supergravity theories in various dimensions by using
an extension of Loop Quantum Gravity to all spacetime dimensions. In this
paper, we extend this analysis by considering the quantisation of additional
bosonic fields necessary to obtain a complete SUSY multiplet next to graviton
and gravitino in various dimensions. As a generic example, we study concretely
the quantisation of the 3-index photon of 11d SUGRA, but our methods easily
extend to more general p-form fields. Due to the presence of a Chern-Simons
term for the 3-index photon, which is due to local SUSY, the theory is
self-interacting and its quantisation far from straightforward. Nevertheless,
we show that a reduced phase space quantisation with respect to the 3-index
photon Gauss constraint is possible. Specifically, the Weyl algebra of
observables, which deviates from the usual CCR Weyl algebras by an interesting
twist contribution proportional to the level of the Chern-Simons theory, admits
a background independent state of the Narnhofer-Thirring type.Comment: 12 pages. v2: Journal version. Minor clarifications and correction
Quantum Moduli Spaces of String Theories
Generically, string models with supersymmetry are not expected to have
moduli beyond perturbation theory; stringy non-perturbative effects as well as
low energy field-theoretic phenomena such as gluino condensation will lift any
flat directions. In this note, we describe models where some subspace of the
moduli space survives non-perturbatively. Discrete symmetries forbid any
inherently stringy effects, and dynamical considerations control the
field-theoretic effects. The surviving subspace is a space of high symmetry;
the system is attracted to this subspace by a potential which we compute.
Models of this type may be useful for considerations of duality and raise
troubling cosmological questions about string theory. Our considerations also
suggest a mechanism for fixing the expectation value of the dilaton.Comment: 26 pages; uses harvmac. Footnote re fixing dilaton adde
Duality and higher derivative terms in M theory
Dualities of M-theory are used to determine the exact dependence on the
coupling constant of the D^6R^4 interaction of the IIA and IIB superstring
effective action. Upon lifting to eleven dimensions this determines the
coefficient of the D^6R^4 interaction in eleven-dimensional M-theory. These
results are obtained by considering the four-graviton two-loop scattering
amplitude in eleven-dimensional supergravity compactified on a circle and on a
two-torus -- extending earlier results concerning lower-derivative
interactions. The torus compactification leads to an interesting
SL(2,Z)-invariant function of the complex structure of the torus (the IIB
string coupling) that satisfies a Laplace equation with a source term on the
fundamental domain of moduli space. The structure of this equation is in accord
with general supersymmetry considerations and immediately determines tree-level
and one-loop contributions to D^6R^4 in perturbative IIB string theory that
agree with explicit string calculations, and two-loop and three-loop
contributions that have yet to be obtained in string theory. The complete
solution of the Laplace equation contains infinite series' of single
D-instanton and double D-instanton contributions, in addition to the
perturbative terms. General considerations of the higher loop diagrams of
eleven-dimensional supergravity suggest extensions of these results to
interactions of higher order in the low energy expansion.Comment: harvmac. 41 pages. 3 figures. v2 typos corrected and reference list
updated. v3. Significant new subsection deriving the non-zero coefficient of
the IIB string theory three-loop contributio
D3-branes on the Coulomb branch and instantons
The relative coefficients of higher derivative interactions of the IIB
effective action of the form C^4, (D F_5)^4, F_5^8, ... (where C is the Weyl
tensor and F_5 is the five-form field strength) are motivated by supersymmetry
arguments. It is shown that the classical supergravity solution for N parallel
D3-branes is unaltered by this combination of terms. The non-vanishing of
\zeroC^2 in this background (where \zero C is the background value of the Weyl
tensor) leads to effective O(1/alpha') interactions, such as C^2 and Lambda^8
(where Lambda is the dilatino). These contain D-instanton contributions in
addition to tree and one-loop terms. The near horizon limit of the N D3-brane
system describes a multi-AdS_5xS^5 geometry that is dual to \calN=4 SU(N)
Yang-Mills theory spontaneously broken to S(U(M_1)x...xU(M_r)). Here, the N
D3-branes are grouped into r coincident bunches with M_r in each group, with
M_r/N = m_r fixed as N goes to infinity. The boundary correlation function of
eight Lambda's is constructed explicitly. The second part of the paper
considers effects of a constrained instanton in this large-N Yang-Mills theory
by an extension of the analysis of Dorey, Hollowood and Khoze of the
one-instanton measure at finite N. This makes precise the correspondence with
the supergravity D-instanton measure at leading order in the 1/N expansion.
However, the duality between instanton-induced correlation functions in
Yang-Mills theory and the dual supergravity is somewhat obscured by
complications relating to the structure of constrained instantons.Comment: 30 pages, JHEP style. Typos corrected and minor clarifications adde
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Preliminary results from the dust flux monitoring instrument during the encounter of Stardust spacecraft with Wild-2 comet
On January 2, 2004, the Stardust spacecraft successfully encountered the Wild-2 comet. The Dust Flux Monitoring Instrument (DFMI) provided quantitative measurements of dust particle fluxes and particle mass distributions throughout the entire flythrough
A robust pseudo-inverse spectral filter applied to the Earth Radiation Budget Experiment (ERBE) scanning channels
Computer simulations of a least squares estimator operating on the ERBE scanning channels are discussed. The estimator is designed to minimize the errors produced by nonideal spectral response to spectrally varying and uncertain radiant input. The three ERBE scanning channels cover a shortwave band a longwave band and a ""total'' band from which the pseudo inverse spectral filter estimates the radiance components in the shortwave band and a longwave band. The radiance estimator draws on instantaneous field of view (IFOV) scene type information supplied by another algorithm of the ERBE software, and on a priori probabilistic models of the responses of the scanning channels to the IFOV scene types for given Sun scene spacecraft geometry. It is found that the pseudoinverse spectral filter is stable, tolerant of errors in scene identification and in channel response modeling, and, in the absence of such errors, yields minimum variance and essentially unbiased radiance estimates
Computational fluid dynamics calculations of binary representation of Ni-base superalloy solidification in frustum geometries
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