6,235 research outputs found
Polytropic stars in three-dimensional spacetime
We investigate three-dimensional perfect fluid stars with polytropic equation
of state, matched to the exterior three-dimensional black hole geometry of
Banados, Teitelboim and Zanelli. A new class of exact solutions for a generic
polytropic index is found and analysed.Comment: 3 pages, revte
Stem Cell Therapy: a Novel Approach for Vision Restoration in Retinitis Pigmentosa
Unfortunately, at present, degenerative retinal diseases such as retinitis pigmentosa remains untreatable. Patients with these conditions suffer progressive visual decline resulting from continuing loss of photoreceptor cells and outer nuclear layers. However, stem cell therapy is a promising approach to restore visual function in eyes with degenerative retinal diseases such as retinitis pigmentosa. Animal studies have established that pluripotent stem cells when placed in the mouse retinitis pigmentosa models have the potential not only to survive, but also to differentiate, organize into and function as photoreceptor cells. Furthermore, there is early evidence that these transplanted cells provide improved visual function. These groundbreaking studies provide proof of concept that stem cell therapy is a viable method of visual rehabilitation among eyes with retinitis pigmentosa. Further studies are required to optimize these techniques in human application. This review focuses on stem cell therapy as a new approach for vision restitution in retinitis pigmentosa
Structure and genetic diversity in wild and cultivated populations of Zapote mamey (Pouteria sapota, Sapotaceae) from southeastern Mexico: its putative domestication center
Tropical fruit trees are an important component of the human diet; however, little is known about their genetic diversity levels. Zapote mamey (Pouteria sapota) is a tree native to southeastern Mexico and Central America, and Mexico is the leading producer in the world. Studies of the genetic diversity of Zapote mamey have been based on cultivated materials using morphological and biochemical characterization or dominant molecular markers. To gain a deeper understanding about the conservation status of Zapote mamey in its center of origin and domestication, we collected 188 individuals from eight wild and five cultivated populations in southeastern Mexico and characterized them using eight microsatellite loci. STRUCTURE, 3D-PCoA, and neighbor-joining analyses showed three groups in the wild gene pool and one group in the cultivated gene pool. FST values were significant between wild and cultivated gene pools, among the four groups observed and among the 13 populations collected (0.13, 0.25, and 0.36, respectively). Overall, we found low levels of genetic diversity (A = 2.77, HO = 0.29, HE = 0.39), permutation tests did not show significant differences between wild and cultivated gene pools. The Garza–Williamson index showed low values in both gene pools (wild = 0.16, cultivated = 0.11) and the Bottleneck program indicated a decrease in genetic diversity in both gene pools (wild, P = 0.027; cultivated, P = 0.054); both analyses suggest a potential genetic bottleneck within this species. This study can help to generate adequate sampling techniques and to develop effective management strategies for Zapote mamey of southeastern Mexico
Current data are consistent with flat spatial hypersurfaces in the CDM cosmological model but favor more lensing than the model predicts
We study the performance of three pairs of tilted CDM cosmological
models, two pairs allowing for non-flat spatial hypersurfaces with CMB
temperature and polarization power spectrum data (P18) from Planck, P18 lensing
(lensing), and non-CMB data (non-CMB). For the six models, we measure
cosmological parameters and study whether or not pairs of the data sets are
mutually consistent in these models. Half of these models allow the lensing
consistency parameter to be an additional free parameter, while the other
three have . The tilted spatially-flat models assume the usual
primordial spatial inhomogeneity power spectrum. The tilted non-flat models
assume either the primordial power spectrum used in the Planck group analyses
[Planck ] or a recently computed power spectrum [new ]. In the
tilted non-flat models with we find differences between P18 data and
non-CMB data cosmological parameter constraints, which are large enough to rule
out the Planck model at 3 but not the new model. While
both P18 data and non-CMB data separately favor a closed geometry when
P18+non-CMB data are jointly analyzed the evidence in favor of non-flat
hypersurfaces subsides. Differences between P18 data and non-CMB data
cosmological constraints subside when is allowed to vary. From the most
restrictive P18+lensing+non-CMB data combination we get almost
model-independent constraints and find that the option is preferred
over the one, with the parameter, for all models, being
larger than unity by . According to the deviance information
criterion, in the P18+lensing+non-CMB analysis, the varying option is on
the verge of being strongly favored over the one, which could indicate
a problem for the standard tilted flat CDM model (Abridged abstract).Comment: 83 pages, 39 figure
(2+1)-Dimensional Black Hole with Coulomb-like Field
A (2+1)-static black hole solution with a nonlinear electric field is
derived. The source to the Einstein equations is a nonlinear electrodynamics,
satisfying the weak energy conditions, and it is such that the energy momentum
tensor is traceless. The obtained solution is singular at the origin of
coordinates. The derived electric field E(r) is given by , thus it
has the Coulomb form of a point charge in the Minkowski spacetime. This
solution describes charged (anti)--de Sitter spaces. An interesting
asymptotically flat solution arises for .Comment: 6 pages, Latex, Phys. Lett. B. 484, 154 (2000
The cross helicity at the solar surface by simulations and observations
The quasilinear mean-field theory for driven MHD turbulence leads to the
result that the observed cross helicity may directly yield the
magnetic eddy diffusivity \eta_{T} of the quiet Sun. In order to model the
cross helicity at the solar surface, magnetoconvection under the presence of a
vertical large-scale magnetic field is simulated with the nonlinear MHD code
NIRVANA. The very robust result of the calculations is that \simeq 2
independent of the applied magnetic field amplitude. The
correlation coefficient for the cross helicity is about 10%. Of similar
robustness is the finding that the rms value of the magnetic perturbations
exceeds the mean-field amplitude (only) by a factor of five. The characteristic
helicity speed u_{\eta} as the ratio of the eddy diffusivity and the density
scale height for an isothermal sound velocity of 6.6 km/s proves to be 1 km/s
for weak fields. This value well coincides with empirical results obtained from
the data of the HINODE satellite and the Swedish 1-m Solar Telescope (SST)
providing the cross helicity component . Both simulations and
observations thus lead to a numerical value of \eta_{T} \simeq 10^12 cm^2 /s as
characteristic for the surface of the quiet Sun.Comment: 6 pages, 6 figure
Stem Cell Therapy: a Novel Approach for Vision Restoration in Retinitis Pigmentosa
Unfortunately, at present, degenerative retinal diseases such as retinitis pigmentosa remains untreatable. Patients with these conditions suffer progressive visual decline resulting from continuing loss of photoreceptor cells and outer nuclear layers. However, stem cell therapy is a promising approach to restore visual function in eyes with degenerative retinal diseases such as retinitis pigmentosa. Animal studies have established that pluripotent stem cells when placed in the mouse retinitis pigmentosa models have the potential not only to survive, but also to differentiate, organize into and function as photoreceptor cells. Furthermore, there is early evidence that these transplanted cells provide improved visual function. These groundbreaking studies provide proof of concept that stem cell therapy is a viable method of visual rehabilitation among eyes with retinitis pigmentosa. Further studies are required to optimize these techniques in human application. This review focuses on stem cell therapy as a new approach for vision restitution in retinitis pigmentosa
Wormholes in String Theory
A wormhole is constructed by cutting and joining two spacetimes satisfying
the low energy string equations with a dilaton field. In spacetimes described
by the "string metric" the dilaton energy-momentum tensor need not satisfy the
weak or dominant energy conditions. In the cases considered here the dilaton
field violates these energy conditions and is the source of the exotic matter
required to maintain the wormhole. There is also a surface stress-energy, that
must be produced by additional matter, where the spacetimes are joined. It is
shown that wormholes can be constructed for which this additional matter
satisfies the weak and dominant energy conditions, so that it could be a form
of "normal" matter. Charged dilaton wormholes with a coupling between the
dilaton and the electromagnetic field that is more general than in string
theory are also briefly discussed.Comment: 9 pages, LaTex, submitted to Phys. Rev.
Utilization and Predictors of adjuvant Metformin For Children and adolescents On Mixed Receptor antagonists (Second-Generation antipsychotics)
OBJECTIVE: to examine utilization and predictors of adjuvant metformin among pediatric recipients of second-generation antipsychotics (SGAs) (mixed receptor antagonist).
METHOD: This study used 2016-2021 data of a national electronic medical record database. Eligible participants were children aged 6 to 17 with a new SGA prescription for at least 90 days. Predictors of prescribing adjuvant metformin in general and to nonobese pediatric SGA recipients in particular were assessed using conditional logistic regression and logistic regression analyses, respectively.
RESULTS: Of 30,009 pediatric SGA recipients identified, 2.3% (n = 785) received adjuvant metformin. Among 597 participants with a body mass index z score documented during the 6-month period before metformin initiation, 83% were obese, and 34% had either hyperglycemia or diabetes. Significant predictors for metformin prescribing were high baseline body mass index z score (odds ratio [OR] 3.5, 95% CI 2.8-4.5, p \u3c .0001), having hyperglycemia or diabetes (OR 5.3, 95% CI 3.4-8.3, p \u3c .0001), and undergoing a switch from a higher metabolic risk SGA to a lower risk one (OR 9.9, 95% CI 3.5-27.5, p = .0025) or a switch in the opposite direction (OR 4.1, 95% CI 2.1-7.9, p = .0051) compared with no switch. Nonobese metformin users were more likely to have a positive body mass index z score velocity before metformin initiation than their obese counterparts. Receiving the index SGA prescribed by a mental health specialist was associated with higher likelihood of receiving adjuvant metformin and receiving metformin before the development of obesity.
CONCLUSION: Utilization of adjuvant metformin among pediatric SGA recipients is uncommon, and early introduction of the medication among nonobese children is rare
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