1,144 research outputs found
Pharmaceutical Properties of Nanoparticulate Formulation Composed of TPGS and PLGA for Controlled Delivery of Anticancer Drug
A suitable management of the pharmaceutical property is needed and helpful to design a desired nanoparticulate delivery system, which includes the carrier nature, particle size and size distribution, morphology, surfactant stabiliser according to the technique applied, drug-loading ratio and encapsulation efficiency, surface property, etc. All will influence the in vitro release, in vivo behaviour and tissue distribution of administered particulate drug loaded nanoparticles. The main purpose of the present work was to determine the effect of drug loading ratio when employing TPGS as surfactant stabiliser and/or matrix material to improve the nanoparticulate formulation. The model drug employed was paclitaxel.Singapore-MIT Alliance (SMA
Electrostatic potentials at Cu In,Ga Se2 grain boundaries Experiment and simulations
In the present Letter, we report on a combined ab initio density functional theory calculation, multislice simulation, and electron holography study, performed on a amp; 931;9 grain boundary GB in a CuGaSe2 bicrystal, which exhibits a lower symmetry compared with highly symmetric amp; 931; 3 GBs. We find an electrostatic potential well at the amp; 931;9 GB of 0.8 V in depth and 1.3 nm in width, which in comparison with results from amp; 931;3 and random GBs exhibits the trend of increasing potential well depths with lower symmetry. The presence of this potential well at the amp; 931; 9 GB can be explained conclusively by a reduced density of atoms at the GB. Considering experimental limitations in resolution, we demonstrate quantitative agreement of experiment and theor
Exceptional Collections and del Pezzo Gauge Theories
Stacks of D3-branes placed at the tip of a cone over a del Pezzo surface
provide a way of geometrically engineering a small but rich class of
gauge/gravity dualities. We develop tools for understanding the resulting
quiver gauge theories using exceptional collections. We prove two important
results for a general quiver gauge theory: 1) we show the ordering of the nodes
can be determined up to cyclic permutation and 2) we derive a simple formula
for the ranks of the gauge groups (at the conformal point) in terms of the
numbers of bifundamentals. We also provide a detailed analysis of four node
quivers, examining when precisely mutations of the exceptional collection are
related to Seiberg duality.Comment: 26 pages, 1 figure; v2 footnote 2 amended; v3 ref adde
Dibaryon Spectroscopy
The AdS/CFT correspondence relates dibaryons in superconformal gauge theories
to holomorphic curves in Kaehler-Einstein surfaces. The degree of the
holomorphic curves is proportional to the gauge theory conformal dimension of
the dibaryons. Moreover, the number of holomorphic curves should match, in an
appropriately defined sense, the number of dibaryons. Using AdS/CFT backgrounds
built from the generalized conifolds of Gubser, Shatashvili, and Nekrasov
(1999), we show that the gauge theory prediction for the dimension of
dibaryonic operators does indeed match the degree of the corresponding
holomorphic curves. For AdS/CFT backgrounds built from cones over del Pezzo
surfaces, we are able to match the degree of the curves to the conformal
dimension of dibaryons for the n'th del Pezzo surface, n=1,2,...,6. Also, for
the del Pezzos and the A_k type generalized conifolds, for the dibaryons of
smallest conformal dimension, we are able to match the number of holomorphic
curves with the number of possible dibaryon operators from gauge theory.Comment: 30 pages, 6 figures, corrected refs; v3 typos correcte
Dibaryons from Exceptional Collections
We discuss aspects of the dictionary between brane configurations in del
Pezzo geometries and dibaryons in the dual superconformal quiver gauge
theories. The basis of fractional branes defining the quiver theory at the
singularity has a K-theoretic dual exceptional collection of bundles which can
be used to read off the spectrum of dibaryons in the weakly curved dual
geometry. Our prescription identifies the R-charge R and all baryonic U(1)
charges Q_I with divisors in the del Pezzo surface without any Weyl group
ambiguity. As one application of the correspondence, we identify the cubic
anomaly tr R Q_I Q_J as an intersection product for dibaryon charges in large-N
superconformal gauge theories. Examples can be given for all del Pezzo surfaces
using three- and four-block exceptional collections. Markov-type equations
enforce consistency among anomaly equations for three-block collections.Comment: 47 pages, 11 figures, corrected ref
New checks and subtleties for AdS/CFT and a-maximization
We provide a cross-check of AdS/CFT and a-charge maximization for a four
dimensional =1 SCFT with irrational R-charges. The gauge theory is the low
energy effective theory of N D3-branes at the tip of the complex cone over the
first del Pezzo surface. By carefully taking into account the subtle issue of
flavor symmetry breaking at the fixed point, we show, using a-maximization,
that this theory has in fact irrational central charge and R-charges. Our
results perfectly match with those inherited from the recently discovered
supergravity dual background. Along analogous lines, we make novel predictions
for the still unknown AdS dual of the quiver theory for the second del Pezzo
surface. This should flow to a SCFT with irrational charges, too. All of our
results differ from previous findings in the literature and outline interesting
subtleties in a-maximization and AdS/CFT techniques overlooked in the past.Comment: Latex, 16 pagex, 2 figures; v2, comments and a reference added; v3,
typos correcte
The Physical Role of Gravitational and Gauge Degrees of Freedom in General Relativity - II: Dirac versus Bergmann observables and the Objectivity of Space-Time
(abridged)The achievements of the present work include: a) A clarification of
the multiple definition given by Bergmann of the concept of {\it (Bergmann)
observable. This clarification leads to the proposal of a {\it main conjecture}
asserting the existence of i) special Dirac's observables which are also
Bergmann's observables, ii) gauge variables that are coordinate independent
(namely they behave like the tetradic scalar fields of the Newman-Penrose
formalism). b) The analysis of the so-called {\it Hole} phenomenology in strict
connection with the Hamiltonian treatment of the initial value problem in
metric gravity for the class of Christoudoulou -Klainermann space-times, in
which the temporal evolution is ruled by the {\it weak} ADM energy. It is
crucial the re-interpretation of {\it active} diffeomorphisms as {\it passive
and metric-dependent} dynamical symmetries of Einstein's equations, a
re-interpretation which enables to disclose their (nearly unknown) connection
to gauge transformations on-shell; this is expounded in the first paper
(gr-qc/0403081). The use of the Bergmann-Komar {\it intrinsic
pseudo-coordinates} allows to construct a {\it physical atlas} of 4-coordinate
systems for the 4-dimensional {\it mathematical} manifold, in terms of the
highly non-local degrees of freedom of the gravitational field (its four
independent {\it Dirac observables}), and to realize the {\it physical
individuation} of the points of space-time as {\it point-events} as a
gauge-fixing problem, also associating a non-commutative structure to each
4-coordinate system.Comment: 41 pages, Revtex
Cold Dark Matter Hypotheses in the MSSM
We perform a Bayesian model selection analysis in the the R-parity conserving
MSSM to compare two different assumptions: whether the lightest neutralinos
make all or only part of the cold dark matter. This corresponds to either
imposing full WMAP relic density limits or just its upper bound for
constraining the MSSM parameters. We consider several realisations of the MSSM,
namely, three GUT-scale SUSY breaking scenarios with a handful of parameters
corresponding to the CMSSM, anomaly mediation and the large volume string
scenarios as well as the weak-scale 25-parameter phenomenological MSSM (pMSSM).
The results give a data-based quantitative evidence for a multicomponent cold
dark matter. The pMSSM posterior samples indicate that the choice of imposing
full WMAP limits or just its upper bound affects mostly the gaugino-higgsino
content of the neutralino and, against naive expectations, essentially not any
other sector.Comment: version to appear in Physcis Letters
Holographic Cosmic Quintessence on Dilatonic Brane World
Recently quintessence is proposed to explain the observation data of
supernova indicating a time-varying cosmological constant and accelerating
universe. Inspired by this and its mysterious origin, we look for the
possibility of quintessence as the holographic dark matters dominated in the
late time in the brane world scenarios. We consider both the cases of static
and moving brane in a dilaton gravity background. For the static brane we use
the Hamilton-Jacobi method motivated by holographic renormalization group to
study the intrinsic FRW cosmology on the brane and find out the constraint on
the bulk potential for the quintessence. This constraint requires a negative
slowly varying bulk potential which implies an anti-de Sitter-like bulk
geometry and could be possibly realized from the higher dimensional
supergravities or string theory. We find the similar constraint for the moving
brane cases and that the quintessence on it has the effect as a mildly
time-varying Newton constant.Comment: 16pages, no figure, Latex; revised version, references added, typos
corrected, abstract and comments improved; final version, will appear in PR
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