144 research outputs found
Prospects for future very high-energy gamma-ray sky survey: impact of secondary gamma rays
Very high-energy gamma-ray measurements of distant blazars can be well
explained by secondary gamma rays emitted by cascades induced by
ultra-high-energy cosmic rays. The secondary gamma rays will enable one to
detect a large number of blazars with future ground based gamma-ray telescopes
such as Cherenkov Telescope Array (CTA). We show that the secondary emission
process will allow CTA to detect 100, 130, 150, 87, and 8 blazars above 30 GeV,
100 GeV, 300 GeV, 1 TeV, and 10 TeV, respectively, up to assuming the
intergalactic magnetic field (IGMF) strength G and an unbiased all
sky survey with 0.5 hr exposure at each Field of View, where total observing
time is hr. These numbers will be 79, 96, 110, 63, and 6 up to
in the case of G. This large statistics of sources will
be a clear evidence of the secondary gamma-ray scenarios and a new key to
studying the IGMF statistically. We also find that a wider and shallower survey
is favored to detect more and higher redshift sources even if we take into
account secondary gamma rays.Comment: 8 pages, 3 figures, accepted for publication in Astroparticle Physic
Upper Limit on the Cosmological Gamma-ray Background
We show that the current extragalactic gamma-ray background (EGB) measurement
below 100 GeV sets an upper limit on EGB itself at very high energy (VHE) above
100 GeV. The limit is conservative for the electromagnetic cascade emission
from VHE EGB interacting with the cosmic microwave-to-optical background
radiation not to exceed the current EGB measurement. The cascade component fits
the measured VHE EGB spectrum rather well. However, once we add the
contribution from known source classes, the Fermi VHE EGB observation exceeds
or even violates the limit, which is approximated as E^2dN/dE < 4.5x10^-5
(E/100 GeV)^-0.7 MeV/cm^2/s/sr. The upper limit above 100 GeV is useful in the
future to probe the EGB origin and the new physics like axion-like particles
and Lorentz-invariance violation.Comment: 8 pages, 8 figures, accepted for publication in PRD, Interested
readers may wish to consult the recent paper by Murase, Beacom and Takami
(arXiv:1205.5755
Upper Bound on the First Star Formation History
Our understanding of the nature of the extragalactic background light (EBL)
has improved with the recent development of gamma-ray observation techniques.
An open subject in the context of the EBL is the reionization epoch, which is
an important probe of the formation history of first stars, the so-called
Population III (Pop III) stars. Although the mechanisms for the formation of
Pop III stars are rather well understood on theoretical grounds, their
formation history is still veiled in mystery because of their faintness. To
shed light into this matter, we study jointly the gamma-ray opacity of distant
objects and the reionization constraints from studies of intergalactic gas. By
combining these studies, we obtain a sensitive upper bound on the Pop III star
formation rate density as at
, where and are the escape fraction of ionizing
photons from galaxies and the clumping factor of the intergalactic hydrogen
gas. This limit is a times tighter constraint compared with previous
studies that take into account gamma-ray opacity constraints only. Even if we
do not include the current gamma-ray constraints, the results do not change.
This is because the detected gamma-ray sources are still at where
the reionization has already finished.Comment: 5 pages, 2 figures, accepted for publication in ApJ
A phase diagram of the pinch-off-type behavior of impulsively-induced viscoelastic liquid jets
In this study, we systematically investigate the jet behaviors of
viscoelastic liquids, focusing on the region of high velocity and high
viscoelasticity, which has not been investigated in previous studies. We
generate viscoelastic jets using an impulsive force and categorize the
resulting jets into two types: pinch-off jets (jets that break up during
elongation after ejection) and no-pinch-off jets (jets that pull back to the
nozzle after maximum elongation or jets that return without elongation after
ejection). We then propose criteria to characterize these regions using the
Weissenberg number and the Reynolds number, which are dimensionless numbers
composed of the rheological properties of the solution and the initial
conditions of the jet injection. It is found that pinch-off jets occur at in regions of high elasticity , and at in regions of low elasticity . We also show that
the phase diagram can be explained by modeling a focused jet using the finitely
extensible non-linear elastic dumbbell model with the Chilcott-Rallison closure
approximation (FENE-CR)
Renormalization for Discrete Optimization
The renormalization group has proven to be a very powerful tool in physics
for treating systems with many length scales. Here we show how it can be
adapted to provide a new class of algorithms for discrete optimization. The
heart of our method uses renormalization and recursion, and these processes are
embedded in a genetic algorithm. The system is self-consistently optimized on
all scales, leading to a high probability of finding the ground state
configuration. To demonstrate the generality of such an approach, we perform
tests on traveling salesman and spin glass problems. The results show that our
``genetic renormalization algorithm'' is extremely powerful.Comment: 4 pages, no figur
Characterization of Zero-point Vibration in One-Component Crystals
We study the magnitude of zero-point vibration in one-component crystals. For
the crystals whose constituent atoms share the same bonding geometry, we prove
the existence of a characteristic temperature, T0, at which the magnitude of
zero-point vibrations equals to that of the excited vibrations. Within the
Debye model T0 is found to be ~1/3 of the Debye temperature. The results are
demonstrated in realistic systems.Comment: 18 pages, 1 figure
Anderson transition in three-dimensional disordered systems with symplectic symmetry
The Anderson transition in a 3D system with symplectic symmetry is
investigated numerically. From a one-parameter scaling analysis the critical
exponent of the localization length is extracted and estimated to be . The level statistics at the critical point are also analyzed
and shown to be scale independent. The form of the energy level spacing
distribution at the critical point is found to be different from that
for the orthogonal ensemble suggesting that the breaking of spin rotation
symmetry is relevant at the critical point.Comment: 4 pages, revtex, to appear in Physical Review Letters. 3 figures
available on request either by fax or normal mail from
[email protected] or [email protected]
The IG-DMR and the MEG3-DMR at Human Chromosome 14q32.2: Hierarchical Interaction and Distinct Functional Properties as Imprinting Control Centers
Human chromosome 14q32.2 harbors the germline-derived primary DLK1-MEG3 intergenic differentially methylated region (IG-DMR) and the postfertilization-derived secondary MEG3-DMR, together with multiple imprinted genes. Although previous studies in cases with microdeletions and epimutations affecting both DMRs and paternal/maternal uniparental disomy 14-like phenotypes argue for a critical regulatory function of the two DMRs for the 14q32.2 imprinted region, the precise role of the individual DMR remains to be clarified. We studied an infant with upd(14)pat body and placental phenotypes and a heterozygous microdeletion involving the IG-DMR alone (patient 1) and a neonate with upd(14)pat body, but no placental phenotype and a heterozygous microdeletion involving the MEG3-DMR alone (patient 2). The results generated from the analysis of these two patients imply that the IG-DMR and the MEG3-DMR function as imprinting control centers in the placenta and the body, respectively, with a hierarchical interaction for the methylation pattern in the body governed by the IG-DMR. To our knowledge, this is the first study demonstrating an essential long-range imprinting regulatory function for the secondary DMR
The Interaction of LFA-1 on Mononuclear Cells and ICAM-1 on Tubular Epithelial Cells Accelerates TGF-β1-Induced Renal Epithelial-Mesenchymal Transition
The epithelial-mesenchymal transition (EMT) of renal epithelial cells (RTECs) has pivotal roles in the development of renal fibrosis. Although the interaction of lymphocyte function-associated antigen 1 (LFA-1) on leukocytes and its ligand, intracellular adhesion molecule 1 (ICAM-1), plays essential roles in most inflammatory reactions, its pathogenetic role in the EMT of RTECs remains to be clarified. In the present study, we investigated the effect of the interaction of LFA-1 on peripheral blood mononuclear cells (PBMCs) and ICAM-1 on HK-2 cells after stimulation with TGF-β1 on the EMT of RTECs. ICAM-1 was highly expressed in HK-2 cells. After TGF-β1 stimulation, the chemokines CCL3 and CXCL12 increased on HK-2 cells. After co-culture of PBMCs and HK-2 cells pre-stimulated with TGF-β1 (0.1 ng/ml) (HK-2-TGF-β1 (0.1)), the expression of the active form of LFA-1 increased on PBMCs; however, total LFA-1 expression did not change. The expression of the active form of LFA-1 on PBMCs did not increase after co-culture with not CCL3 but CXCL12 knockdown HK-2-TGF-β1 (0.1). The expression of epithelial cell junction markers (E-cadherin and occludin) further decreased and that of mesenchymal markers (vimentin and fibronectin) further increased in HK-2-TGF-β1 (0.1) after co-culture with PBMCs for 24 hrs (HK-2-TGF-β1 (0.1)-PBMCs). The phosphorylation of ERK 1/2 but not smad2 and smad3 increased in HK-2-TGF-β1 (0.1)-PBMCs. The snail and slug signaling did not increase HK-2-TGF-β1 (0.1)-PBMCs. Although the migration and invasion of HK-2 cells induced full EMT by a high dose (10.0 ng/ml) and long-term (72–96 hrs) TGF-β1 stimulation increased, that of HK-2-TGF-β1 (0.1)-PBMCs did not increase. These results suggested that HK-2 cells stimulated with TGF-β1 induced conformational activation of LFA-1 on PBMCs by increased CXCL12. Then, the direct interaction of LFA-1 on PBMCs and ICAM-1 on HK-2 cells activated ERK1/2 signaling to accelerate the part of EMT of HK-2 cells induced by TGF-β1
- …