363 research outputs found
An Electron-Tracking Compton Telescope for a Survey of the Deep Universe by MeV gamma-rays
Photon imaging for MeV gammas has serious difficulties due to huge
backgrounds and unclearness in images, which are originated from incompleteness
in determining the physical parameters of Compton scattering in detection,
e.g., lack of the directional information of the recoil electrons. The recent
major mission/instrument in the MeV band, Compton Gamma Ray
Observatory/COMPTEL, which was Compton Camera (CC), detected mere
persistent sources. It is in stark contrast with 2000 sources in the GeV
band. Here we report the performance of an Electron-Tracking Compton Camera
(ETCC), and prove that it has a good potential to break through this stagnation
in MeV gamma-ray astronomy. The ETCC provides all the parameters of
Compton-scattering by measuring 3-D recoil electron tracks; then the Scatter
Plane Deviation (SPD) lost in CCs is recovered. The energy loss rate (dE/dx),
which CCs cannot measure, is also obtained, and is found to be indeed helpful
to reduce the background under conditions similar to space. Accordingly the
significance in gamma detection is improved severalfold. On the other hand, SPD
is essential to determine the point-spread function (PSF) quantitatively. The
SPD resolution is improved close to the theoretical limit for multiple
scattering of recoil electrons. With such a well-determined PSF, we demonstrate
for the first time that it is possible to provide reliable sensitivity in
Compton imaging without utilizing an optimization algorithm. As such, this
study highlights the fundamental weak-points of CCs. In contrast we demonstrate
the possibility of ETCC reaching the sensitivity below erg
cm s at 1 MeV.Comment: 19 pages, 12 figures, Accepted to the Astrophysical Journa
The Origin of the Charge Ordering and Its Relevance to Superconductivity in -(BEDT-TTF)X: The Effect of the Fermi Surface Nesting and the Distant Electron-Electron Interactions
The origin of the charge ordering in organic compounds -(BEDT-TTF) ((SCN), Tl,Rb,Co, Cs,Zn) is studied using an extended
Hubbard model. Calculating the charge susceptibility within random phase
approximation (RPA), we find that the charge
ordering observed at relatively high temperatures can be considered as a
consequence of a cooperation between the Fermi surface nesting, controlled by
the hopping integral in the direction, and the electron-electron
interactions, where the distant (next nearest neighbor) interactions that have
not been taken into account in most of the previous studies play an important
role.Mean field analysis at T=0 also supports the RPA results, and further
shows that in the charge ordered state, some portions of the Fermi
surface remain ungapped and are nested with a nesting vector close to the
modulation wave vector of the horizontal stripe ordering observed at low
temperatures in (SCN). We further study the possibility of
superconductivity by taking into account the distant off-site repulsions and
the band structure corresponding to I, in which superconductivity is
experimentally observed. We find that there is a close competition between
-wave-like singlet pairing and -wave-like triplet pairing due
to a cooperation between the charge and the spin fluctuations. The present
analysis provides a possible unified understanding of the experimental phase
diagram of the -(BEDT-TTF) family, ranging from a charge ordered
insulator to a superconductor.Comment: 13 pages, 18 figures (Figs.5,6,7,14,15,18 compressed using jpeg2ps
Validation of U.S. mortality prediction models for hospitalised heart failure in the United Kingdom and Japan
Aims Prognostic models for hospitalized heart failure (HHF) were developed predominantly for patients of European origin in the United States of America; it is unclear whether they perform similarly in other health care systems or for different ethnicities. We sought to validate published prediction models for HHF in the United Kingdom (UK) and Japan. Methods and results Patients in the UK (n =894) and Japan (n =3158) were prospectively enrolled and were similar in terms of sex (∼60% men) and median age (∼77 years). Models predicted that British patients would have a higher mortality than Japanese, which was indeed true both for in‐hospital (4.8% vs. 2.5%) and 180‐day (20.7% vs. 9.5%) mortality. The model c‐statistics for the published/derivation (range 0.70–0.76) and Japanese (range 0.75–0.77) cohorts were similar and higher than for the UK (0.62–0.75) but models consistently overestimated mortality in Japan. For in‐hospital mortality, the OPTIMIZE‐HF model performed best, providing similar discrimination in published/derivation, UK and Japanese cohorts [c‐indices: 0.75 (0.74–0.77); 0.75 (0.68–0.81); and 0.77 (0.70–0.83), respectively], and least overestimated mortality in Japan. For 180‐day mortality, the c‐statistics for the ASCEND‐HF model were similar in published/derivation (0.70) and UK [0.69 (0.64–0.74)] cohorts but higher in Japan [0.75 (0.71–0.79)]; calibration was good in the UK but again overestimated mortality in Japan. Conclusion Calibration of published prediction models appears moderately accurate and unbiased when applied to British patients but consistently overestimates mortality in Japan. Identifying the reason why patients in Japan have a better than predicted prognosis is of great interest
Validation of U.S. mortality prediction models for hospitalized heart failure in the United Kingdom and Japan: Validation of risk models in decompensated heart failure
Aims: Prognostic models for hospitalised heart failure (HHF) were developed predominantly for patients of European origin in the United States of America; it is unclear whether they perform similarly in other health-care systems or for different ethnicities. We sought to validate published prediction models for HHF in the United Kingdom (UK) & Japan.Methods and Results: Patients in the UK (894) and Japan (3,158) were prospectively enrolled and similar in terms of sex (~60% men) and median age (~77 years). Models predicted that British patients would have a higher mortality than Japanese, which was indeed true both for in-hospital [4.8% vs 2.5%] and 180-day [20.7% vs 9.5%] mortality. The model c-statistics for the published/derivation [range 0.70-0.76] and Japanese [range 0.75-0.77] cohorts were similar and higher than for the UK [0.62-0.75] but models consistently over-estimated mortality in Japan. For in-hospital mortality, OPTIMIZE-HF performed best, providing similar discrimination in published/derivation, UK and Japanese cohorts [c-indices: 0.75 (0.74-0.77); 0.75 (0.68 - 0.81) and 0.77 (0.70 - 0.83)], and least over-estimated mortality in Japan. For 180-day mortality, the cstatistics for ASCEND-HF were similar in published/derivation [0.70] and UK [0.69 (0.64 - 0.74)] cohorts but higher in Japan [0.75 (0.71 - 0.79)]; calibration was good in the UK but again over-estimated mortality in Japan.Conclusion: Calibration of published prediction models appear moderately accurate and unbiased when applied to British patients but consistently overestimate mortality in Japan. Identifying the reason why patients in Japan have a better than predicted prognosis is of great interest
Variational Monte Carlo Study of a Spinless Fermion t-V Model on a Triangular Lattice: Formation of a Pinball Liquid
We analyze a model of spinless fermions on a triangular lattice at
half-filling interacting via strong nearest-neighbor repulsive interactions, V,
using the variational Monte Carlo simulation technique. The existence of
three-sublattice long-range order is confirmed by the finite-size scaling
analysis of the charge structural factor at V_c/t > 12. This ordered phase
shows characteristics expected for a so called "pinball liquid" state, which
has the spontaneous separation of fermionic degrees of freedom into coexisting
Wigner crystal-like charge order (pin) and a metal (ball). The pins are fixed
in order to maximize the kinetic energy gain of balls which move almost freely.
The Fermi surface is reconstructed at V=V_c and remains towards the strong
coupling limit. These features reminiscent of the strong correlation together
with the large value of V_c/t distinguishes the pinball liquid from the
conventional charge-density-wave.Comment: 7 pages, 7 figure
Vascular endothelial growth factor acts as an osteolytic factor in breast cancer metastases to bone
Vascular endothelial growth factor (VEGF) is a proangiogenic cytokine that is expressed highly in many solid tumours often correlating with a poor prognosis. In this study, we investigated the expression of VEGF and its receptors in bone metastases from primary human breast tumours and further characterised its effects on osteoclasts in vitro. Breast cancer metastases to bone were immunohistochemically stained for VEGF, its receptors VEGFR1 and 2 (vascular endothelial growth factor receptor 1 and 2), demonstrating that breast cancer metastases express VEGF strongly and that surrounding osteoclasts express both VEGFR1 and VEGFR2. RAW 264.7 cells (mouse monocyte cell line) and human peripheral blood mononuclear cells (PBMCs) were cultured with VEGF, RANKL and M-CSF. VEGF and RANKL together induced differentiation of multinucleated, tartrate-resistant acid phophatase (TRAP)-positive cells in similar numbers to M-CSF and RANKL. The PBMCs were also able to significantly stimulate resorption of mineralised matrix after treatment with M-CSF with RANKL and VEGF with RANKL. We have shown that VEGF in the presence of RANKL supports PBMC differentiation into osteoclast-like cells, able to resorb substrate. Vascular endothelial growth factor may therefore play a role in physiological bone resorption and in pathological situations. Consequently, VEGF signalling may be a therapeutic target for osteoclast inhibition in conditions such as tumour osteolysis
Augmentation of Neovascularizaiton in Hindlimb Ischemia by Combined Transplantation of Human Embryonic Stem Cells-Derived Endothelial and Mural Cells
BACKGROUND: We demonstrated that mouse embryonic stem (ES) cells-derived vascular endothelial growth factor receptor-2 (VEGF-R2) positive cells could differentiate into both endothelial cells (EC) and mural cells (MC), and termed them as vascular progenitor cells (VPC). Recently, we have established a method to expand monkey and human ES cells-derived VPC with the proper differentiation stage in a large quantity. Here we investigated the therapeutic potential of human VPC-derived EC and MC for vascular regeneration. METHODS AND RESULTS: After the expansion of human VPC-derived vascular cells, we transplanted these cells to nude mice with hindlimb ischemia. The blood flow recovery and capillary density in ischemic hindlimbs were significantly improved in human VPC-derived EC-transplanted mice, compared to human peripheral and umbilical cord blood-derived endothelial progenitor cells (pEPC and uEPC) transplanted mice. The combined transplantation of human VPC-derived EC and MC synergistically improved blood flow of ischemic hindlimbs remarkably, compared to the single cell transplantations. Transplanted VPC-derived vascular cells were effectively incorporated into host circulating vessels as EC and MC to maintain long-term vascular integrity. CONCLUSIONS: Our findings suggest that the combined transplantation of human ES cells-derived EC and MC can be used as a new promising strategy for therapeutic vascular regeneration in patients with tissue ischemia
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