903 research outputs found
No Ghost State in the Brane World
We discuss the role of the trace part of metric fluctuations in the
Randall-Sundrum scenario of gravity. Without the matter, this field
() is a gauge-dependent term, and thus it can be gauged
away. But, including the uniform source , this field satisfies
the linearized equation . This may
correspond to the scalar in the bending of the brane due to the
localized source. Considering the case of longitudinal perturbations (), one finds the source relation
, which leads to the ghost states in the
massive modes. In addition, if one requires , it is
found that in the limit of we have the massless spin-2
propagation without the ghost state. This exactly corresponds to the same
situation as in the intermediate scales of Gregory-Rubakov-Sibiryakov (GRS)
model.Comment: 7 pages, no figure, the version to appear in PLB, comments on the
matter source and references added, main results unchange
Randall-Sundrum Gauge in the Brane World
We discuss the Randall-Sundrum (RS) choice for in the brane-world.
We begin with the de Donder gauge (transverse-tracefree) including
scalar(), vector() and tensor() in five
dimensions for comparison. One finds that and . This
leads to the RS choice. It appears that the RS choice is so restrictive for the
five massless states, whereas it is unique for describing the massive states.
Furthermore, one can establish the stability of the RS solution with the RS
choice only.Comment: corrected some typographical mistakes, 11 pages with ReVTeX, no
figur
Assessment of Ionizing Radiation Induced Dicentric Chromosome and Micronuclei in Human Peripheral Blood Lymphocytes for Preliminary Reconstruction of Cytogenetic Biodosimetry
Cytological biodosimetry methodology has been widely used for determining and estimating the precise irradiation dose received by victims in the situation of emergency irradiation exposure. The aim of this study was to assess the gamma-ray induced dicentric chromosomes and micronuclei (MN) in peripheral blood lymphocytes for preliminary reconstruction of cytogenetic biodosimetry. The study was performed by exposing blood samples taken from seven healthy donors to gamma rays at dose range of 0.1 to 4.0 Gy, followed by culturing them for 48-72 hours at 37 °C by the standard technique. After being harvested, the chromosome spread at metaphase and MN were stained with Giemsa's solution. The results showed that the frequency of both dicentrics and MN of samples were increased with the increase of radiation dose. Considerable increases of both cytologic damages were found in the samples exposed to higher doses (>2 Gy). Significant differences (p>0.05) only found in mean frequencies of MN for all doses tested. Reconstruction of the relationship of these frequencies with doses was found to follow linear-quadratic curve lines and was consistent with that of other studies. Due to the aforementioned advantages namely the dependence of radiation dose and dose rate on the frequency of of both dicentric and MN, despite some limitations, these assays have been found to be suitable to be used as biological dosimetry. It is concluded that in order for this cytogenetic biodosimety method by means of scoring/assessing the radiation-induced dicentrics and MN could be used in radiation emergency and protection, and further studies with larger numbers of samples need to be done.Received: 12 November 2015; Revised: 18 Mei 2016; Accepted: 08 December 201
U(1) Gauge Field of the Kaluza-Klein Theory in the Presence of Branes
We investigate the zero mode dimensional reduction of the Kaluza-Klein
unifications in the presence of a single brane in the infinite extra dimension.
We treat the brane as fixed, not a dynamical object, and do not require the
orbifold symmetry. It seems that, contrary to the standard Kaluza-Klein models,
the 4D effective action is no longer invariant under the U(1) gauge
transformations due to the explicit breaking of isometries in the extra
dimension by the brane. Surprisingly, however, the linearized perturbation
analysis around the RS vacuum shows that the Kaluza-Klein gauge field does
possess the U(1) gauge symmetry at the linear level. In addition, the
graviscalar also behaves differently from the 4D point of view. Some physical
implications of our results are also discussed.Comment: 10 pages, revtex, no figure, version to appear in Phys. Rev. D,
possible caveats of our results due to the zero mode ansatz we used are
explained in more detai
Stability of the GRS Model
We discuss the compatibility between the weaker energy condition and the
stability of Gregory, Rubakov and Sibiryakov (GRS) model. Because the GRS
spacetime violates the weak energy condition, it may cause the instability. In
the GRS model, the four dimensional gravity can be described by the massive KK
modes with the resonance. Hence, instead of considering the weaker energy
condition, we require for the stability of this model: no tachyon and no ghost
condition for graviton modes (). No tachyonic condition () is satisfied because the lowest state is supersymmetric vacuum
state. Further, no ghost state condition is achieved if one requires some
relations for the matter source: . It
turns out that, although the GRS spacetime does not satisfy the weaker energy
condition, it is stable against small perturbation.Comment: Revtex, 1 figure, 10 pages, a wrong citation correcte
Embryonic stem cell-derived extracellular vesicle-mimetic nanovesicles rescue erectile function by enhancing penile neurovascular regeneration in the streptozotocin-induced diabetic mouse
Extracellular vesicles (EVs) have attracted particular interest in various fields of biology and medicine. However, one of the major hurdles in the clinical application of EV-based therapy is their low production yield. We recently developed cell-derived EV-mimetic nanovesicles (NVs) by extruding cells serially through filters with diminishing pore sizes (10, 5, and 1 mu m). Here, we demonstrate in diabetic mice that embryonic stem cell (ESC)-derived EV-mimetic NVs (ESC-NVs) completely restore erectile function (similar to 96% of control values) through enhanced penile angiogenesis and neural regeneration in vivo, whereas ESC partially restores erectile function (similar to 77% of control values). ESC-NVs promoted tube formation in primary cultured mouse cavernous endothelial cells and pericytes under high-glucose condition in vitro; and accelerated microvascular and neurite sprouting from aortic ring and major pelvic ganglion under high-glucose condition ex vivo, respectively. ESC-NVs enhanced the expression of angiogenic and neurotrophic factors (hepatocyte growth factor, angiopoietin-1, nerve growth factor, and neurotrophin-3), and activated cell survival and proliferative factors (Akt and ERK). Therefore, it will be a better strategy to use ESC-NVs than ESCs in patients with erectile dysfunction refractory to pharmacotherapy, although it remains to be solved for future clinical application of ESC.11Ysciescopu
Soft phonons and structural phase transition in superconducting Ba0.59K0.41BiO3
We have observed a softening of phonons and a structural phase transition in
a superconducting Ba0.59K0.41BiO3 (Tc = 31 K) single crystal using elastic and
inelastic neutron scattering measurements. The soft phonon occurs for the [111]
transverse acoustic mode at the zone boundary. The phonon energies in this
vicinity are found to continuously decrease with decreasing temperature from
above room temperature to 200 K, where a structural phase transition from cubic
to tetragonal symmetry occurs. The overall results are consistent with previous
data that reported phonon softening and a (0.5, 0.5, 0.5) type superstructure
in several Ba1-xKxBiO3 systems. However, we also find weak (0.5, 0.5, 0) type
superstructure peaks that reveal an additional component to the modulation. No
significant change related to the superconductivity was observed for the soft
phonon energies or linewidths.Comment: 15 page
Testing Holographic Principle from Logarithmic and Higher Order Corrections to Black Hole Entropy
The holographic principle is tested by examining the logarithmic and higher
order corrections to the Bekenstein-Hawking entropy of black holes. For the BTZ
black hole, I find some disagreement in the principle for a holography screen
at spatial infinity beyond the leading order, but a holography with the screen
at the horizon does not, with an appropriate choice of a period parameter,
which has been undetermined at the leading order, in Carlip's horizon-CFT
approach for black hole entropy in any dimension. Its higher dimensional
generalization is considered to see a universality of the parameter choice. The
horizon holography from Carlip's is compared with several other realizations of
a horizon holography, including induced Wess-Zumino-Witten model approaches and
quantum geometry approach, but none of the these agrees with Carlip's, after
clarifications of some confusions. Some challenging open questions are listed
finally.Comment: To appear in JHEP. The corrections in Sec.2 with those that follow
are more clearly explained. Careful distingtion between the implications of
my results to AdS/CFT and to the holograhic principl
Structure of Schlafen13 reveals a new class of tRNA/rRNA- targeting RNase engaged in translational control
Cleavage of transfer (t)RNA and ribosomal (r)RNA are critical and conserved steps of translational control for cells to overcome varied environmental stresses. However, enzymes that are responsible for this event have not been fully identified in high eukaryotes. Here, we report a mammalian tRNA/rRNA-targeting endoribonuclease: SLFN13, a member of the Schlafen family. Structural study reveals a unique pseudo-dimeric U-pillow-shaped architecture of the SLFN13 N'-domain that may clamp base-paired RNAs. SLFN13 is able to digest tRNAs and rRNAs in vitro, and the endonucleolytic cleavage dissevers 11 nucleotides from the 3'-terminus of tRNA at the acceptor stem. The cytoplasmically localised SLFN13 inhibits protein synthesis in 293T cells. Moreover, SLFN13 restricts HIV replication in a nucleolytic activity-dependent manner. According to these observations, we term SLFN13 RNase S13. Our study provides insights into the modulation of translational machinery in high eukaryotes, and sheds light on the functional mechanisms of the Schlafen family
Impact loading during distracted running before and after auditory gait retraining.
Visual feedback gait retraining has been reported to successfully reduce impact loading in runners, even when the runners were distracted. However, auditory feedback is more feasible in real life application. Hence, this study compared the peak positive acceleration (PPA), vertical average (VALR) and instantaneous (VILR) loading rate during distracted running before and after a course of auditory feedback gait retraining in 16 runners. The runners were asked to land with softer footfalls with and without auditory feedback. Low or high sound pitch was generated according to the impact of particular footfall, when compared with the preset target. Runners then received a course of auditory gait retraining, and after the gait retraining, runners completed a reassessment. Runners before gait retraining exhibited lower PPA, VALR and VILR with augmented auditory feedback (p0.104). A small effect of auditory feedback on VILR in runners after gait retraining was observed (p=0.032). Real time auditory feedback gait retraining is effective in impact loading reduction, even when the runners were distracted
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