575 research outputs found
Biodegradable polymeric prodrugs of naltrexone
The development of a biodegradable polymeric drug delivery system for the narcotic antagonist naltrexone may improve patient compliance in the treatment of opiate addiction. Random copolymers consisting of the ¿-amino acids N5-(3-hydroxypropyl--glutamine and -leucine were synthesized with equimolar initial monomer feeds. The molecular weight of this chemical carrier was determined by viscometry and wide-angle light scattering. In order to get selective covalent coupling of drug to polymer the 3-acetate derivative and the 14-acetate derivative of naltrexone were synthesized and characterized by NMR. Hydrolytic conversion of each monoacetate to parent drug was monitored by HPLC and the rate constant was determined. Both derivatives were coupled via hydrolytically labile carbonate linkages to the polymer hydroxyl groups. The drug conjugates were prepared as particles of various size ranges between 20 and 350 ¿. In vitro studies in phosphate-buffered saline (pH 7.4) demonstrated a release rate dependence on particle size. Nearly constant plasma levels of naltrexone were obtained for one month after subcutaneous injection in rats
Improving the low-lying spectrum of the overlap kernel
The action of the overlap-Dirac operator on a vector is typically implemented
in directly through a multi-shift conjugate gradient solver. The compute-time
this takes to evaluate depends upon the condition number of the matrix
that is used as the overlap kernel. We examine the low-lying spectra of various
candidate kernels in an effort to optimise , thereby speeding up the
overlap evaluation.Comment: 5 pages, 8 figure
Magnetic moments of the 3/2 resonances and their quark spin structure
We discuss magnetic moments of the baryons based on an earlier model
for the baryon magnetic moments, allowing for flavor symmetry breaking in the
quark magnetic moments as well as a general quark spin structure. From our
earlier analysis of the nucleon-hyperon magnetic moments and the measured
values of the magnetic moments of and we predict the
other magnetic moments and deduce the spin structure of the resonance
particles. We find from experiment that the total spin polarization of the
decuplet baryons, , is considerably smaller than the
non-relativistic quark model value of 3, although the data is still not good
enough to give a precise determination.Comment: 13 pages, REVTeX, 2 figures, minor clarifying change
Gauge-fixing, semiclassical approximation and potentials for graded Chern-Simons theories
We perform the Batalin-Vilkovisky analysis of gauge-fixing for graded
Chern-Simons theories. Upon constructing an appropriate gauge-fixing fermion,
we implement a Landau-type constraint, finding a simple form of the gauge-fixed
action. This allows us to extract the associated Feynman rules taking into
account the role of ghosts and antighosts. Our gauge-fixing procedure allows
for zero-modes, hence is not limited to the acyclic case. We also discuss the
semiclassical approximation and the effective potential for massless modes,
thereby justifying some of our previous constructions in the Batalin-Vilkovisky
approach.Comment: 46 pages, 4 figure
Supersymetry on the Noncommutative Lattice
Built upon the proposal of Kaplan et.al. [hep-lat/0206109], we construct
noncommutative lattice gauge theory with manifest supersymmetry. We show that
such theory is naturally implementable via orbifold conditions generalizing
those used by Kaplan {\sl et.al.} We present the prescription in detail and
illustrate it for noncommutative gauge theories latticized partially in two
dimensions. We point out a deformation freedom in the defining theory by a
complex-parameter, reminiscent of discrete torsion in string theory. We show
that, in the continuum limit, the supersymmetry is enhanced only at a
particular value of the deformation parameter, determined solely by the size of
the noncommutativity.Comment: JHEP style, 1+22 pages, no figure, v2: two references added, v3:
three more references adde
A geometric discretisation scheme applied to the Abelian Chern-Simons theory
We give a detailed general description of a recent geometrical discretisation
scheme and illustrate, by explicit numerical calculation, the scheme's ability
to capture topological features. The scheme is applied to the Abelian
Chern-Simons theory and leads, after a necessary field doubling, to an
expression for the discrete partition function in terms of untwisted
Reidemeister torsion and of various triangulation dependent factors. The
discrete partition function is evaluated computationally for various
triangulations of and of lens spaces. The results confirm that the
discretisation scheme is triangulation independent and coincides with the
continuum partition functionComment: 27 pages, 5 figures, 6 tables. in late
Supersymmetric Deformations of Type IIB Matrix Model as Matrix Regularization of N=4 SYM
We construct a supersymmetry and global symmetry
preserving deformation of the type IIB matrix model. This model, without
orbifold projection, serves as a nonperturbative regularization for
supersymmetric Yang-Mills theory in four Euclidean dimensions.
Upon deformation, the eigenvalues of the bosonic matrices are forced to reside
on the surface of a hypertorus. We explicitly show the relation between the
noncommutative moduli space of the deformed matrix theory and the Brillouin
zone of the emergent lattice theory. This observation makes the transmutation
of the moduli space into the base space of target field theory clearer. The
lattice theory is slightly nonlocal, however the nonlocality is suppressed by
the lattice spacing. In the classical continuum limit, we recover the
SYM theory. We also discuss the result in terms of D-branes and
interpret it as collective excitations of D(-1) branes forming D3 branes.Comment: Version 2: Extended discussion of moduli space, added a referenc
Towards the deconstruction of M-theory
We argue that there is an equivalence of M-theory on T^3 \times A_{N-1} with
a four-dimensional non-supersymmetric quiver gauge theory on the Higgs branch.
The quiver theory in question has gauge group SU(N)^{N_4N_6N_8} and is
considered in a strong coupling and large N_{4,6,8} limit. We provide field-
and string-theoretical evidence for the equivalence making use of the
deconstruction technique. In particular, we find wrapped M2-branes in the mass
spectrum of the quiver theory at low energies.Comment: LaTeX, 15 pages, 4 figures, added reference
Regularization of Non-commutative SYM by Orbifolds with Discrete Torsion and SL(2,Z) Duality
We construct a nonperturbative regularization for Euclidean noncommutative
supersymmetric Yang-Mills theories with four (N= (2,2)), eight (N= (4,4)) and
sixteen (N= (8,8)) supercharges in two dimensions. The construction relies on
orbifolds with discrete torsion, which allows noncommuting space dimensions to
be generated dynamically from zero dimensional matrix model in the
deconstruction limit. We also nonperturbatively prove that the twisted
topological sectors of ordinary supersymmetric Yang-Mills theory are equivalent
to a noncommutative field theory on the topologically trivial sector with
reduced rank and quantized noncommutativity parameter. The key point of the
proof is to reinterpret 't Hooft's twisted boundary condition as an orbifold
with discrete torsion by lifting the lattice theory to a zero dimensional
matrix theory.Comment: 36 pages, references added, minor typos fixe
Magnetohydrodynamics and Plasma Cosmology
We study the linear magnetohydrodynamic (MHD) equations, both in the
Newtonian and the general-relativistic limit, as regards a viscous magnetized
fluid of finite conductivity and discuss instability criteria. In addition, we
explore the excitation of cosmological perturbations in anisotropic spacetimes,
in the presence of an ambient magnetic field. Acoustic, electromagnetic (e/m)
and fast-magnetosonic modes, propagating normal to the magnetic field, can be
excited, resulting in several implications of cosmological significance.Comment: 9 pages, RevTeX, To appear in the Proceedings of the Peyresq X
Meeting, IJTP Conference Serie
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