466 research outputs found
Remarks on 2+1 Self-dual Chern-Simons Gravity
We study 2+1 Chern-Simons gravity at the classical action level. In
particular we rederive the linear combinations of the ``standard'' and
``exotic'' Einstein actions, from the (anti) self-duality of the ``internal''
Lorentzian indices. The relation to a genuine four-dimensional (anti)self-dual
topological theory greatly facilitates the analysis and its relation to
hyperbolic three-dimensional geometry. Finally a non-abelian vector field
``dual'' action is also obtained.Comment: 16+1 pages, LaTeX file, no figures, clarifications and comments
added, typos corrected and one reference adde
Decoupling Inflation From the String Scale
When Inflation is embedded in a fundamental theory, such as string theory, it
typically begins when the Universe is already substantially larger than the
fundamental scale [such as the one defined by the string length scale]. This is
naturally explained by postulating a pre-inflationary era, during which the
size of the Universe grew from the fundamental scale to the initial
inflationary scale. The problem then arises of maintaining the [presumed]
initial spatial homogeneity throughout this era, so that, when it terminates,
Inflation is able to begin in its potential-dominated state. Linde has proposed
that a spacetime with compact negatively curved spatial sections can achieve
this, by means of chaotic mixing. Such a compactification will however lead to
a Casimir energy, which can lead to effects that defeat the purpose unless the
coupling to gravity is suppressed. We estimate the value of this coupling
required by the proposal, and use it to show that the pre-inflationary
spacetime is stable, despite the violation of the Null Energy Condition
entailed by the Casimir energy.Comment: 24 pages, 5 eps figures, references added, stylistic changes, version
to appear in Classical and Quantum Gravit
In Vitro and in Vivo Study of Sustained Nitric Oxide Release Coating Using Diazeniumdiolate-doped Poly(vinyl chloride) Matrix with Poly(lactide-co-glycolide) Additive
Nitric oxide (NO) is an endogenous vasodilator as well as natural inhibitor of platelet adhesion and activation that can be released from a NO donor species, such as diazeniumdiolated dibutylhexanediamine (DBHD/N2O2) within a polymer coating. In this study, various Food and Drug Administration approved poly(lactic-co-glycolic acid) (PLGA) species were evaluated as additives to promote a prolonged NO release from DBHD/N2O2 within a plasticized poly(vinyl chloride) (PVC) matrix. When using an ester-capped PLGA additive with a slow hydrolysis time, the resulting coatings continuously release between 7 and 18 × 10−10 mol cm−2 min−1 NO for 14 days at 37 °C in PBS buffer. The corresponding pH changes within the polymer films were visualized using pH sensitive indicators and are shown to correlate with the extended NO release pattern. The optimal combined diazeniumdiolate/PLGA-doped NO release (NOrel) PVC coating was evaluated in vitro and its effect on the hemodynamics was also studied within a 4 h in vivo extracorporeal circulation (ECC) rabbit model of thrombogenicity. Four out of 7 control circuits clotted within 3 h, whereas all the NOrel coated circuits were patent after 4 h. Platelet counts on the NOrel ECC were preserved (79 ± 11% compared to 54 ± 6% controls). The NOrel coatings showed a significant decrease in the thrombus area as compared to the controls. Results suggest that by using ester-capped PLGAs as additives to a conventional plasticized PVC material containing lipophilic diazeniumdiolates, the NO release can be prolonged for up to 2 weeks by controlling the pH within the organic phase of the coating
Electromagnetic Form Factors of the SU(3) Octet Baryons in the semibosonized SU(3) Nambu-Jona-Lasinio Model
The electromagnetic form factors of the SU(3) octet baryons are investigated
in the semibosonized SU(3) Nambu--Jona-Lasinio model (chiral quark-soliton
model). The rotational and strange quark mass corrections in linear
order are taken into account. The electromagnetic charge radii of the nucleon
and magnetic moments are also evaluated. It turns out that the model is in a
remarkable good agreement with the experimental data.Comment: RevTex is used. 37 pages. The final version to appear in Phys. Rev.
D. 13 figures are include
Electromagnetic Form Factors of the Nucleon in an Improved Quark Model
Nucleon electromagnetic form factors are studied in the cloudy bag model
(CBM) with center-of-mass and recoil corrections. This is the first
presentation of a full set of nucleon form factors using the CBM. The center of
mass motion is eliminated via several different momentum projection techniques
and the results are compared. It is found that the shapes of these form factors
are significantly improved with respect to the experimental data if the Lorentz
contraction of the internal structure of the baryon is also appropriately taken
into account.Comment: revtex, 28 pages, 8 ps figs include
Valuing the commons : an international study on the recreational benefits of the Baltic Sea
The Baltic Sea provides benefits to all of the nine nations along its coastline, with some 85 million people living within the catchment area. Achieving improvements in water quality requires international cooperation. The likelihood of effective cooperation is known to depend on the distribution across countries of the benefits and costs of actions needed to improve water quality. In this paper, we estimate the benefits associated with recreational use of the Baltic Sea in current environmental conditions using a travel cost approach, based on data from a large, standardized survey of households in each of the 9 Baltic Sea states. Both the probability of engaging in recreation (participation) and the number of visits people make are modeled. A large variation in the number of trips and the extent of participation is found, along with large differences in current annual economic benefits from Baltic Sea recreation. The total annual recreation benefits are close to 15 billion EUR. Under a water quality improvement scenario, the proportional increases in benefits range from 7 to 18% of the current annual benefits across countries. Depending on how the costs of actions are distributed, this could imply difficulties in achieving more international cooperation to achieve such improvements.PostprintPeer reviewe
Effect of recent R_p and R_n measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
The Gari-Krumpelmann (GK) models of nucleon electromagnetic form factors, in
which the rho, omega, and phi vector meson pole contributions evolve at high
momentum transfer to conform to the predictions of perturbative QCD (pQCD), was
recently extended to include the width of the rho meson by substituting the
result of dispersion relations for the pole and the addition of rho' (1450)
isovector vector meson pole. This extended model was shown to produce a good
overall fit to all the available nucleon electromagnetic form factor (emff)
data. Since then new polarization data shows that the electric to magnetic
ratios R_p and R_n obtained are not consistent with the older G_{Ep} and G_{En}
data in their range of momentum transfer. The model is further extended to
include the omega' (1419) isoscalar vector meson pole. It is found that while
this GKex cannot simultaneously fit the new R_p and the old G_{En} data, it can
fit the new R_p and R_n well simultaneously. An excellent fit to all the
remaining data is obtained when the inconsistent G_{Ep} and G_{En} is omitted.
The model predictions are shown up to momentum transfer squared, Q^2, of 8
GeV^2/c^2.Comment: 14 pages, 8 figures, using RevTeX4; email correspondence to
[email protected] ; minor typos corrected, figures added, conclusions
extende
Consistent Treatment of Relativistic Effects in Electrodisintegration of the Deuteron
The influence of relativistic contributions to deuteron electrodisintegration
is systematically studied in various kinematic regions of energy and momentum
transfer. As theoretical framework the equation-of-motion and the unitarily
equivalent S-matrix approaches are used. In a (p/M)-expansion, all leading
order relativistic -exchange contributions consistent with the Bonn OBEPQ
model are included. In addition, static heavy meson exchange currents including
boost terms, -currents, and -isobar contributions
are considered. Sizeable effects from the various relativistic two-body
contributions, mainly from -exchange, have been found in inclusive form
factors and exclusive structure functions for a variety of kinematic regions.Comment: 41 pages revtex including 15 postscript figure
Extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
Nucleon electromagnetic form factor data (including recent data) is fitted
with models that respect the confinement and asymptotic freedom properties of
QCD. Gari-Krumpelmann (GK) type models, which include the major vector meson
pole contributions and at high momentum transfer conform to the predictions of
perturbative QCD, are combined with Hohler-Pietarinen (HP) models, which also
include the width of the rho meson and the addition of higher mass vector meson
exchanges, but do not evolve into the explicit form of PQCD at high momentum
transfer. Different parameterizations of the GK model's hadronic form factors,
the effect of including the width of the rho meson and the addition of the next
(in mass) isospin 1 vector meson are considered. The quality of fit and the
consistency of the parameters select three of the combined HP/GK type models.
Projections are made to the higher momentum transfers which are relevant to
electron-deuteron experiments. The projections vary little for the preferred
models, removing much of the ambiguity in electron-nucleus scattering
predictions.Comment: 18pp, 7 figures, using RevTeX with BoxedEPS macros; 1 new figure,
minor textual changes; email correspondence to [email protected]
A Measurement of the Electric Form Factor of the Neutron through at (GeV/c)
We report the first measurement of the neutron electric form factor
via using a solid polarized target. was
determined from the beam-target asymmetry in the scattering of longitudinally
polarized electrons from polarized deuterated ammonia, ND. The
measurement was performed in Hall C at Thomas Jefferson National Accelerator
Facility (TJNAF) in quasi free kinematics with the target polarization
perpendicular to the momentum transfer. The electrons were detected in a
magnetic spectrometer in coincidence with neutrons in a large solid angle
segmented detector. We find at (GeV/c).Comment: Latex2e 5 pages, 3 figure
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