502 research outputs found
Black Hole with Quantum Potential
In this work, we investigate black hole (BH) physics in the context of
quantum corrections. These quantum corrections were introduced recently by
replacing classical geodesics with quantal (Bohmian) trajectories and hence
form a quantum Raychaudhuri equation (QRE). From the QRE, we derive a modified
Schwarzschild metric, and use that metric to investigate BH singularity and
thermodynamics. We find that these quantum corrections change the picture of
Hawking radiation greatly when the size of BH approaches the Planck scale. They
prevent the BH from total evaporation, predicting the existence of a quantum BH
remnant, which may introduce a possible resolution for the catastrophic
behavior of Hawking radiation as the BH mass approaches zero. Those corrections
also turn the spacelike singularity of the black hole to be timelike, and hence
this may ameliorate the information loss problem.Comment: 16 pages, 6 figures; Accepted in Nucl.Phys.
A Proposal for Testing Gravity's Rainbow
Various approaches to quantum gravity such as string theory, loop quantum
gravity and Horava-Lifshitz gravity predict modifications of the
energy-momentum dispersion relation. Magueijo and Smolin incorporated the
modified dispersion relation (MDR) with the general theory of relativity to
yield a theory of gravity's rainbow. In this paper, we investigate the
Schwarzschild metric in the context of gravity's rainbow. We investigate
rainbow functions from three known modified dispersion relations that were
introduced by Amelino-Camelia, et el. in [arXiv:hep-th/9605211,
arXiv:0806.0339v2, arXiv:astro-ph/9712103] and by Magueijo-Smolin in
[arXiv:hep-th/0112090]. We study the effect of the rainbow functions on the
deflection of light, photon time delay, gravitational red-shift, and the weak
equivalence principle. We compare our results with experiments to obtain upper
bounds on the parameters of the rainbow functions.Comment: 6 pages, no figures, to appear in Europhysics Letter
Remnant for all Black Objects due to Gravity's Rainbow
We argue that a remnant is formed for all black objects in gravity's rainbow.
This will be based on the observation that a remnant depends critically on the
structure of the rainbow functions, and this dependence is a model independent
phenomena. We thus propose general relations for the modified temperature and
entropy of all black objects in gravity's rainbow. We explicitly check this to
be the case for Kerr, Kerr-Newman-dS, charged-AdS, and higher dimensional
Kerr-AdS black holes. We also try to argue that a remnant should form for black
Saturn in gravity's rainbow. This work extends our previous results on remnants
of Schwarzschild black holes [ arXiv:1402.5320] and black rings
[arXiv:1409.5745].Comment: 21 pages, 13 figures, Accepted in Nucl.Phys.
Remnants of Black Rings from Gravity's Rainbow
In this paper, we investigate a spinning black ring and a charged black ring
in the context of gravity's rainbow. By incorporating rainbow functions
proposed by Amelino-Camelia, et al. in [arXiv:hep-th/9605211,
arXiv:0806.0339v2] in the metric of the black rings, a considerable
modification happens to their thermodynamical properties. We calculate
corrections to the temperature, entropy and heat capacity of the black rings.
These calculations demonstrate that the behavior of Hawking radiation changes
considerably near the Planck scale in gravity's rainbow, where it is shown that
black rings do not evaporate completely and a remnant is left as the black
rings evaporate down to Planck scale.Comment: 14 pages, 6 figure
Does folic acid reduce congenital anomalies and adverse pregnancy outcomes in women received long-term low dose methotrexate?
Background: Methotrexate (MTX) which is folic acid antagonist is used to treat many diseases, including rheumatic, inflammatory, autoimmune disorders or malignancies; it is also used for the medical treatment of ectopic pregnancy and termination of pregnancy. The objective of this study was to assess the impact of folic acid in preventing congenital anomalies (CAs) in the fetus of pregnant that take long-term low dose methotrexate.Methods: The study included 1569 with history of low dose methotrexate therapy <25 mg/week that stopped one month before pregnancy, they were divided into 3 groups; Group 1 comprised 272 pregnant women, Group 2 comprised 367 pregnant women both groups take folic acid 4-5 weeks preconception and for the first 12-13 weeks gestation, the dose in the 1st group was 0.4 mg/day while in 2nd Group 4 mg/day, Group 3 comprised of 930 pregnant disease-matched with no folic acid. Group 4 comprised of 1015 pregnant no underlying autoimmune and no folic acid intake.Results: The overall rate of CAs and cardiovascular CAs were higher in fetuses of Group 3 (OR: 1.7; 95% CI: 1.1-2.7) and (OR: 2.7; 95% CI: 1.4-5.2) respectively compared to the overall rate of CAs and cardiovascular CAs in other groups. Other adverse outcomes as abortion, preterm delivery, preeclampsia, placenta abruption, PROM, low birth weight, admission to NICU, IUGR and IUFD were higher in Group 3 and 4 than in Group 1 and 2. There were no significant differences in umbilical arterial PH. The Apgar scores <7 at 1, 5 min and gestational age at delivery were higher in Group 1 and 2 than Group 3 and 4.Conclusions: There was a certain reduction in methotrexate teratogenic effect on the fetuses with folic acid intake during pregnancy, these pregnancies might benefit from taking of folic acid in high doses before conception and during the first trimester of pregnancy and improvement in fetal and maternal outcomes but the explanation of this effect requires further study
Absence of Black Holes at LHC due to Gravity's Rainbow
In this paper, we investigate the effect of Planckian deformation of quantum
gravity on the production of black holes at colliders using the framework of
gravity's rainbow. We demonstrate that a black hole remnant exists for
Schwarzschild black holes in higher dimensions using gravity's rainbow. The
mass of this remnant is found to be greater than the energy scale at which
experiments were performed at the LHC. We propose this as a possible
explanation for the absence of black holes at the LHC. Furthermore, we
demonstrate that it is possible for black holes in six (and higher) dimensions
to be produced at energy scales that will be accessible in the near future.Comment: 16 pages, 5 figures, to appear in Phys. Lett.
GUP parameter and black hole temperature
Motivated by a recent work of Scardigli, Lambiase and Vagenas (SLV), we
derive the GUP parameter, i.e. , when the GUP has a linear and
quadratic term in momentum. The value of the GUP parameter is obtained by
conjecturing that the GUP-deformed black hole temperature of a Schwarzschild
black hole and the modified Hawking temperature of a quantum-corrected
Schwarzschild black hole are the same. The leading term in both cases is the
standard Hawking temperature and since the corrections are considered as
thermal, the modified and deformed expressions of temperature display a slight
shift in the Hawking temperature. Finally, by equating the first correction
terms, we obtain a value for the GUP parameter. In our analysis, the GUP
parameter is not a pure number but depends on the ratio \mpl /M with \mpl
to be the Planck mass and the black hole mass.Comment: v1: 10 pages, no figures, REVTeX 4; v2: typos corrected and
references updated to match published versio
Kristalna struktura i optička svojstva sustava Bi-Sb-Te-Se
The quaternary systems of Bi-Sb-Te-Se were synthesized by direct fusion technique. Thin films of these compounds were prepared by thermal evaporation under vacuum of 10−4 Pa. The structural properties of these compounds in powder and thin film forms were investigated by X-ray diffraction. The optical constants (absorption coefficient and band gap) of the thin films were determined by measurements of IR absorbance in the region 2.5 – 10 µm. Analysis of the optical absorption spectra revealed the existence of two direct energy gaps.Sintetizirali smo sustave Bi-Sb-Te-Se sa četiri sastavnice izravnom metodom staljivanja. Tanke slojeve tih spojeva pripremali smo isparavanjem u vakuumu (na 10−4 Pa). Primjenom rendgenske difrakcije odredili smo strukturna svojstva praha i tankih slojeva tih spojeva. Optičke konstante tankih slojeva (koeficijent apsorpcije i procijep med–u vrpcama) odredili smo mjerenjem apsorpcije u području 2.5 – 10 µm. Analiza optičkih apsorpcijskih spektara pokazuje dva izravna procijepa
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