1,358 research outputs found
Gravity from self-interaction redux
I correct some recent misunderstandings about, and amplify some details of,
an old explicit non-geometrical derivation of GR.Comment: Final, amplified, published version; GRG (2009
Gauss-Bonnet Gravity with Scalar Field in Four Dimensions
We give all exact solutions of the Einstein-Gauss-Bonnet Field Equations
coupled with a scalar field in four dimensions under certain assumptions.Comment: Latex file, 7 page
Exact solutions of Dirac equation on (1+1)-dimensional spacetime coupled to a static scalar field
We use a generalized scheme of supersymmetric quantum mechanics to obtain the
energy spectrum and wave function for Dirac equation in (1+1)-dimensional
spacetime coupled to a static scalar field.Comment: 7 pages, Late
Massive Gravity Simplified: A Quadratic Action
We present a simplified formulation of massive gravity where the Higgs fields
have quadratic kinetic term. This new formulation allows us to prove in a very
explicit way that all massive gravity theories considered so far inevitably
have Boulware-Deser ghost in non-trivial fluctuations of background metric.Comment: 8 pages, paragraph added proving that Bianchi identity does not imply
vanishing of linearized curvatur
Causal Structure of Vacuum Solutions to Conformal(Weyl) Gravity
Using Penrose diagrams the causal structure of the static spherically
symmetric vacuum solution to conformal (Weyl) gravity is investigated. A
striking aspect of the solution is an unexpected physical singularity at
caused by a linear term in the metric. We explain how to calculate the
deflection of light in coordinates where the metric is manifestly conformal to
flat i.e. in coordinates where light moves in straight lines.Comment: 18 pages, 2 figures, title and abstract changed, contents essentially
unaltered accepted for publication in General Relativity and Gravitatio
Racial and Ethnic Disparities in Dermatology Office Visits among Insured Patients, 2005-2010
Objective:To determine whether differences in race and ethnicity affect the usage of dermatological services.
Methods: Data from the National Ambulatory Medical Care Survey were used to study trends in ethnic/race rates of outpatient dermatology office visits among publicly and privately insured patients from 2005-2010. In multivariable models, we explored the magnitude of ethnic/race differences in dermatology visit attendance for patients with public vs. private insurance.
Results: From 2005-2010, dermatology visit utilization increased among insured Hispanics, but not among insured non-Hispanic Blacks or whites. Visits were less frequent by those with public insurance compared to private insurance. Privately and publicly insured visits were less common for non-Hispanic Blacks and Hispanics compared to whites after adjustment for patient demographics and primary visit diagnosis. Racial and ethnic differences in visit utilization rates were most apparent among non-referred visits. However, primary diagnoses for non-referred visits were similar across races and ethnicities, which suggests that differences in utilization may result from factors unrelated to clinical indications for care.
Conclusion: Ethnic/race differences in the use of dermatological services in the United States may result from patient preferences for dermatologic care or health system related factors (e.g., insurance coverage regulations)
GEODYN programmer's guide, volume 2, part 2
A computer program for executive control routine for orbit integration of artificial satellites is presented. At the beginning of each arc, the program initiates required constants as well as the variational partials at epoch. If epoch needs to be reset to a previous time, the program negates the stepsize, and calls for integration backward to the desired time. After backward integration is completed, the program resets the stepsize to the proper positive quantity
On the instability of classical dynamics in theories with higher derivatives
The development of instability in the dynamics of theories with higher
derivatives is traced in detail in the framework of the Pais-Uhlenbeck fourth
oder oscillator. For this aim the external friction force is introduced in the
model and the relevant solutions to equations of motion are investigated. As a
result, the physical implication of the energy unboundness from below in
theories under consideration is revealed.Comment: 9 pages, no figures and no tables, revtex4; a few misprints are
correcte
Brane Cosmology from Heterotic String Theory
We consider brane cosmologies within the context of five-dimensional actions
with O(a') higher curvature corrections. The actions are compatible with bulk
string amplitude calculations from heterotic string theory. We find wrapped
solutions that satisfy the field equations in an approximate but acceptable
manner given their complexity, where the internal four-dimensional scale factor
is naturally inflating, having an exponential De-Sitter form. The temporal
dependence of the metric components is non-trivial so that this metric cannot
be factored as in a conformally flat case. The effective Planck mass is finite
and the brane solutions localize four-dimensional gravity, while the
four-dimensional gravitational constant varies with time. The Hubble constant
can be freely specified through the initial value of the scalar field, to
conform with recent data.Comment: 15 pages, 3 figures, LaTeX, Accepted for Publication in IJT
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