703 research outputs found
Hydrostatic and Physiologic Contributions to Intraocular Pressure Change During Postural Change
Many studies have observed that intraocular pressure (IOP) is dependent on tilt angle () during postural change. In this work, we aggregated 36 independent datasets from 30 published articles, representing 821 subjects, which reported data on IOP during postural change. From this data, we developed a generalized quantitative relationship between IOP and . We then compared the experimentally derived results to simulated predictions generated by our lumped parameter model of the eye, LPEye, considering only hydrostatic effects. The difference between the analytical and simulated values of IOP can be used to quantify the physiologic regulatory contribution
Decay Modes of Intersecting Fluxbranes
Just as the single fluxbrane is quantum mechanically unstable to the
nucleation of a locally charged spherical brane, so intersecting fluxbranes are
unstable to various decay modes. Each individual element of the intersection
can decay via the nucleation of a spherical brane, but uncharged spheres can
also be nucleated in the region of intersection. For special values of the
fluxes, however, intersecting fluxbranes are supersymmetric, and so are
expected to be stable. We explicitly consider the instanton describing the
decay modes of the two--element intersection (an F5-brane in the string theory
context), and show that in dimensions greater than four the action for the
decay mode of the supersymmetric intersection diverges. This observation allows
us to show that stable intersecting fluxbranes should also exist in type 0A
string theory.Comment: 19 pages, 6 figures. References adde
Entropy in the RST Model
The RST Model is given boundary term and Z-field so that it is well-posed and
local. The Euclidean method is described for general theory and used to
calculate the RST intrinsic entropy. The evolution of this entropy for the
shockwave solutions is found and obeys a second law.Comment: 10 pages, minor revisions, published version in Late
Neutron/proton ratio of nucleon emissions as a probe of neutron skin
The dependence between neutron-to-proton yield ratio () and neutron
skin thickness () in neutron-rich projectile induced reactions is
investigated within the framework of the Isospin-Dependent Quantum Molecular
Dynamics (IQMD) model. The density distribution of the Droplet model is
embedded in the initialization of the neutron and proton densities in the
present IQMD model. By adjusting the diffuseness parameter of neutron density
in the Droplet model for the projectile, the relationship between the neutron
skin thickness and the corresponding in the collisions is obtained.
The results show strong linear correlation between and
for neutron-rich Ca and Ni isotopes. It is suggested that may be used
as an experimental observable to extract for neutron-rich nuclei,
which is very significant to the study of the nuclear structure of exotic
nuclei and the equation of state (EOS) of asymmetric nuclear matter.Comment: 7 pages, 5 figures; accepted by Phys. Lett.
Two-dimensional quantum-corrected black hole in a finite size cavity
We consider the gravitation-dilaton theory (not necessarily exactly
solvable), whose potentials represent a generic linear combination of an
exponential and linear functions of the dilaton. A black hole, arising in such
theories, is supposed to be enclosed in a cavity, where it attains thermal
equilibrium, whereas outside the cavity the field is in the Boulware state. We
calculate quantum corrections to the Hawking temperature , with the
contribution from the boundary taken into account. Vacuum polarization outside
the shell tend to cool the system. We find that, for the shell to be in the
thermal equilibrium, it cannot be placed too close to the horizon. The quantum
corrections to the mass due to vacuum polarization vanish in spite of non-zero
quantum stresses. We discuss also the canonical boundary conditions and show
that accounting for the finiteness of the system plays a crucial role in some
theories (e.g., CGHS), where it enables to define the stable canonical
ensemble, whereas consideration in an infinite space would predict instability.Comment: 21 pages. In v.2 misprints corrected. To appear in Phys. Rev.
A New Cosmological Scenario in String Theory
We consider new cosmological solutions with a collapsing, an intermediate and
an expanding phase. The boundary between the expanding (collapsing) phase and
the intermediate phase is seen by comoving observers as a cosmological past
(future) horizon. The solutions are naturally embedded in string and M-theory.
In the particular case of a two-dimensional cosmology, space-time is flat with
an identification under boost and translation transformations. We consider the
corresponding string theory orbifold and calculate the modular invariant
one-loop partition function. In this case there is a strong parallel with the
BTZ black hole. The higher dimensional cosmologies have a time-like curvature
singularity in the intermediate region. In some cases the string coupling can
be made small throughout all of space-time but string corrections become
important at the singularity. This happens where string winding modes become
light which could resolve the singularity. The new proposed space-time casual
structure could have implications for cosmology, independently of string
theory.Comment: 28 pages, 3 figures; v2: Added new subsection relating
two-dimensional model to BTZ black hole, typos corrected and references
added; v3: minor corrections, PRD versio
Penrose Limits, Deformed pp-Waves and the String Duals of N=1 Large n Gauge Theory
A certain conformally invariant N=1 supersymmetric SU(n) gauge theory has a
description as an infra-red fixed point obtained by deforming the N=4
supersymmetric Yang-Mills theory by giving a mass to one of its N=1 chiral
multiplets. We study the Penrose limit of the supergravity dual of the large n
limit of this N=1 gauge theory. The limit gives a pp-wave with R-R five-form
flux and both R-R and NS-NS three-form flux. We discover that this new solution
preserves twenty supercharges and that, in the light-cone gauge, string theory
on this background is exactly solvable. Correspondingly, this latter is the
stringy dual of a particular large charge limit of the large n gauge theory. We
are able to identify which operators in the field theory survive the limit to
form the string's ground state and some of the spacetime excitations. The full
string model, which we exhibit, contains a family of non-trivial predictions
for the properties of the gauge theory operators which survive the limit.Comment: 39 pages, Late
N=1* in 5 dimensions: Dijkgraaf-Vafa meets Polchinski-Strassler
One of the powerful techniques to analyze the 5 dimensional Super Yang Mills
theory with a massive hypermultiplet (N=1*) is provided by the AdS/CFT
correspondence. It predicts that, for certain special values of the
hypermultiplet mass, this theory develops nonperturbative branches of the
moduli space as well as new light degrees of freedom.
We use the higher dimensional generalization of the matrix model/gauge theory
correspondence and recover all the prediction of the supergravity analysis. We
construct the map between the four dimensional holomorphic superpotential and
the five dimensional action and explicitly show that the superpotential is flat
along the nonperturbative branches. This is the first instance in which the
Dijkgraaf-Vafa method is used to analyze intrinsically higher dimensional
phenomena.Comment: 28 pages, Late
On unquenched N=2 holographic flavor
The addition of fundamental degrees of freedom to a theory which is dual (at
low energies) to N=2 SYM in 1+3 dimensions is studied. The gauge theory lives
on a stack of Nc D5 branes wrapping an S^2 with the appropriate twist, while
the fundamental hypermultiplets are introduced by adding a different set of Nf
D5-branes. In a simple case, a system of first order equations taking into
account the backreaction of the flavor branes is derived (Nf/Nc is kept of
order 1). From it, the modification of the holomorphic coupling is computed
explicitly. Mesonic excitations are also discussed.Comment: 25 pages, 4 figure
Strings in Gravimagnetic Fields
We provide a complete solution of closed strings propagating in Nappi-Witten
space. Based on the analysis of geodesics we construct the coherent
wavefunctions which approximate as closely as possible the classical
trajectories. We then present a new free field realization of the current
algebra using the gamma, beta ghost system. Finally we construct the quantum
vertex operators, for the tachyon, by representing the wavefunctions in terms
of the free fields. This allows us to compute the three- and four-point
amplitudes, and propose the general result for N-point tachyon scattering
amplitude.Comment: final version, 29 pages + 4 app
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