226 research outputs found
The in-situ cometary particulate size distribution measured for one comet: P/Halley
The close approach of Giotto to comet Halley during its 1986 apparition offered an opportunity to study the particulate mass distribution to masses of up to one gram. Data acquired by the front end channels of the highly sensitive mass spectrometer PIA and the dust shield detector system, DIDSY, provide definition to the detected distribution as close as 1000 km to the nucleus. Dynamic motion of the particulates after emission leads to a spatial differentiation affecting the size distribution in several forms: (1) ejecta velocity dispersion; (2) radiation pressure; (3) varying heliocentric distance; and (4) anisotropic nucleus emission. Transformation of the in-situ distribution from PIA and DIDSY weighted heavily by the near-nucleus fluxes leads to a presumed nucleus distribution. The data lead to a puzzling distribution at large masses, not readily explained in an otherwise monotonous power law distribution. Although temporal changes in nucleus activity could and do modify the in-situ size distribution, such an explanation is not wholly possible, because the same form is observed at differing locations in the coma where the time of flight from the nucleus greatly varies. Thus neither a general change in comet activity nor spatial variations lead to a satisfactory explanation
Low Energy Action of "Covariant" Superstring Field Theory in the NS-NS pp-Wave Background
Exact construction of superstring field theory in some background fields is
very important. We construct the low energy NS-NS sector of superstring field
action in the pp-wave background with the flux of NS-NS antisymmetric tensor
field (NS-NS pp-wave) without gauge fixing up to the second-order where the
action is world-sheet BRST invariant. Here we use the word "covariant" in a
invariant theory for a symmetric transformation of the pp-wave background which
is not the Lorentz transformation in the flat background. Moreover we prove the
exact correspondence between this low energy action and the second-order
perturbation of supergravity action in the same background. We also prove the
correspondence of the gauge transformation in both the actions. This
construction is based on the BRST first quantization of superstrings in the
pp-wave background in our previous paper.Comment: 34 page
Strong Evidence In Favor OF The Existence Of S-Matrix For Strings In Plane Waves
Field theories on the plane wave background are considered. We discuss that
for such field theories one can only form 1+1 dimensional freely propagating
wave packets. We analyze tree level four point functions of scalar field theory
as well as scalars coupled to gauge fields in detail and show that these four
point functions are well-behaved so that they can be interpreted as S-matrix
elements for 2 particle 2 particle scattering amplitudes. Therefore, at
least classically, field theories on the plane wave background have S-matrix
formulation.Comment: Latex file, 26 pages, 4 eps figures. v3: In the end of paper there is
a "Note Added" as an update of the result
A Representation of Symmetry Generators for the Type IIB Superstring on a Plane Wave in the U(4) Formalism
We calculate the symmetry currents for the type IIB superstring on a
maximally supersymmetric plane wave background using the N=(2,2)
superconformally covariant U(4) formulation developed by Berkovits, Maldacena
and Maoz. An explicit realization of the U(4) generators together with 16
fermionic generators is obtained in terms of the N=(2,2) worldsheet fields.
Because the action is no longer quadratic, we use a light-cone version to
display the currents in terms of the covariant worldsheet variables.Comment: 9 pages, harvmac, Corrected some typographical errors, Added
reference
On the plane-wave cubic vertex
The exact bosonic Neumann matrices of the cubic vertex in plane-wave
light-cone string field theory are derived using the contour integration
techniques developed in our earlier paper. This simplifies the original
derivation of the vertex. In particular, the Neumann matrices are written in
terms of \mu-deformed Gamma-functions, thus casting them into a form that
elegantly generalizes the well-known flat-space solution. The asymptotics of
the \mu-deformed Gamma-functions allow one to determine the large-\mu behaviour
of the Neumann matrices including exponential corrections. We provide an
explicit expression for the first exponential correction and make a conjecture
for the subsequent exponential correction terms.Comment: 26 pages, 1 figure; harvmac (b); v4: minor corrections in appendix
BMN Gauge Theory as a Quantum Mechanical System
We rigorously derive an effective quantum mechanical Hamiltonian from N=4
gauge theory in the BMN limit. Its eigenvalues yield the exact one-loop
anomalous dimensions of scalar two-impurity BMN operators for all genera. It is
demonstrated that this reformulation vastly simplifies computations. E.g. the
known anomalous dimension formula for genus one is reproduced through a
one-line calculation. We also efficiently evaluate the genus two correction,
finding a non-vanishing result. We comment on multi-trace two-impurity
operators and we conjecture that our quantum-mechanical reformulation could be
extended to higher quantum loops and more impurities.Comment: 13 pages, v2: minor changes, v3: typo corrected, to appear in Phys.
Lett.
Use of sweeteners in osmotic pretreatment before freeze-drying of pear and pineapple
The aim of the study was to analyse the influence of the type of osmotic substance (sucrose, glucose, xylitol, trehalose, and sorbitol) on the physicochemical properties of freeze-dried fruit (pear and pineapple). Controlling the functional properties of freeze-dried fruit after osmotic dehydration with aqueous solutions at water activity of a w=0.90 is presented. Decrease in the water adsorption index (WAI) was recorded for all dehydrated samples. The largest decrease (for pears and pineapples by 25 and 65%, respectively) was observed in osmoactive solutions containing trehalose. Considerable increase in the FAI was recorded in samples of dehydrated pineapple. In osmoactive trehalose solutions that increase hardly reached 46%, whereas in sorbitol and xylitol its value elevated to 39% and 13%, respectively. Regardless of the osmoactive sweetener applied prior to freeze-drying, an increase in specific surface area (SBET) of dried materials was observed. For dehydrated pears, SBET ranged from 96 to 697 m2 gâ1, and for pineapple, from 115 to 938 m2 gâ1. Osmotic dehydration before lyophilisation of fruit samples weakened rehydration relative to the control. The dehydration carried out with osmoactive sweeteners, that is, sorbitol, xylitol, and trehalose, allows obtaining a product with good functional properties that can be successfully used for supplementation of dietary products, in particular for diabetics
Graviton-Scalar Interaction in the PP-Wave Background
We compute the graviton two scalar off-shell interaction vertex at tree level
in Type IIB superstring theory on the pp-wave background using the light-cone
string field theory formalism. We then show that the tree level vertex vanishes
when all particles are on-shell and conservation of p_{+} and p_{-} are
imposed. We reinforce our claim by calculating the same vertex starting from
the corresponding SUGRA action expanded around the pp-wave background in the
light-cone gauge.Comment: 26 pages, harvmac One reference added. A few comments changed in the
introduction. The "cyclic perms." term removed from some equations as
unnecessary and equations (2.38) and (3.19) are corrected accordingl
Decay Modes of Unstable Strings in Plane-Wave String Field Theory
The cubic interaction vertex of light-cone string field theory in the
plane-wave background has a simple effective form when considering states with
only bosonic excitations. This simple effective interaction vertex is used in
this paper to calculate the three string interaction matrix elements for states
of arbitrary bosonic excitation and these results are used to examine certain
decay modes on the mass-shell. It is shown that the matrix elements of one
string to two string decays involving only bosonic excitations will vanish to
all orders in 1/mu on the mass-shell when the number of excitations on the
initial string is less than or equal to two, but in general will not vanish
when the number of excitations is greater than two. Also, a truncated
calculation of the mass-shell matrix elements for one string to three string
decays of two excitation states is performed and suggests that these matrix
elements do not vanish on the mass-shell. There is, however, a quantitative
discrepancy between this last result and its (also non-vanishing) gauge theory
prediction from the BMN correspondence.Comment: 11 pages; v2: references added; v3: normalization of interaction
vertex and corresponding amplitudes changed by a factor of mu to reflect SFT
normalization (must now divide by mu to compare with BMN dual gauge theory),
and minor errors correcte
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