11,433 research outputs found
Fermi surface renormalization in Hubbard ladders
We derive the one-loop renormalization equations for the shift in the
Fermi-wavevectors for one-dimensional interacting models with four Fermi-points
(two left and two right movers) and two Fermi velocities v_1 and v_2. We find
the shift to be proportional to (v_1-v_2)U^2, where U is the Hubbard-U. Our
results apply to the Hubbard ladder and to the t_1-t_2 Hubbard model. The
Fermi-sea with fewer particles tends to empty. The stability of a saddle point
due to shifts of the Fermi-energy and the shift of the Fermi-wavevector at the
Mott-Hubbard transition are discussed.Comment: 5 pages, 4 Postscript figure
The role of spatial and temporal radiation deposition in inertial fusion chambers: the case of HiPER¿
The first wall armour for the reactor chamber of HiPER will have to face short energy pulses of 5 to 20 MJ mostly in the form of x-rays and charged particles at a repetition rate of 5–10 Hz. Armour material and chamber dimensions have to be chosen to avoid/minimize damage to the chamber, ensuring the proper functioning of the facility during its planned lifetime. The maximum energy fluence that the armour can withstand without risk of failure, is determined by temporal and spatial deposition of the radiation energy inside the material. In this paper, simulations on the thermal effect of the radiation–armour interaction are carried out with an increasing definition of the temporal and spatial deposition of energy to prove their influence on the final results. These calculations will lead us to present the first values of the thermo-mechanical behaviour of the tungsten armour designed for the HiPER project under a shock ignition target of 48 MJ. The results will show that only the crossing of the plasticity limit in the first few micrometres might be a threat after thousands of shots for the survivability of the armour
New Phenomenon of Nonlinear Regge Trajectory and Quantum Dual String Theory
The relation between the spin and the mass of an infinite number of particles
in a -deformed dual string theory is studied. For the deformation parameter
a root of unity, in addition to the relation of such values of with the
rational conformal field theory, the Fock space of each oscillator mode in the
Fubini-Veneziano operator formulation becomes truncated. Thus, based on general
physical grounds, the resulting spin-(mass) relation is expected to be
below the usual linear trajectory. For such specific values of , we find
that the linear Regge trajectory turns into a square-root trajectory as the
mass increases.Comment: 12 pages, Latex, HU-SEFT R 1994-0
Cord blood Lin(-)CD45(-) embryonic-like stem cells are a heterogeneous population that lack self-renewal capacity.
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Human umbilical cord blood (hUCB) has been proposed to contain not only haematopoietic stem cells, but also a rare pluripotent embryonic-like stem cell (ELSc) population that is negative for hematopoietic markers (Lin(-)CD45(-)) and expresses markers typical of pluripotent cells. The aim of this work was to isolate, characterise and expand this ELSc fraction from hUCB, as it may provide a valuable cell source for regenerative medicine applications. We found that we could indeed isolate a Lin(-)CD45(-) population of small cells (3-10 µm diameter) with a high nucleus to cytoplasm ratio that expressed the stem cell markers CD34 and CXCR4. However, in contrast to some previous reports, this fraction was not positive for CD133. Furthermore, although these cells expressed transcripts typical of pluripotent cells, such as SOX2, OCT3/4, and NANOG, they were not able to proliferate in any of the culture media known to support stem cell growth that we tested. Further analysis of the Lin(-)CD45(-) population by flow cytometry showed the presence of a Lin(-)CD45(-)Nestin(+) population that were also positive for CD34 (20%) but negative for CXCR4. These data suggest that the Lin(-)CD45(-) stem cell fraction present in the cord blood represents a small heterogeneous population with phenotypic characteristics of stem cells, including a Lin(-)CD45(-)Nestin(+) population not previously described. This study also suggests that heterogeneity within the Lin(-)CD45(-) cell fraction is the likely explanation for differences in the hUCB cell populations described by different groups that were isolated using different methods. These populations have been widely called "embryonic-like stem cell" on the basis of their phenotypical similarity to embryonic stem cells. However, the fact they do not seem to be able to self-renew casts some doubt on their identity, and warns against defining them as "embryonic-like stem cell" at this stage.Anthony Nolan and the Great Ormond Street Hospital Charity for financial support. Cesar Alvarez-Gonzalez is a fellowship from Consejo Nacional de Ciencia y Tecnologia (CONACyT) and Instituto Jaliscience de la Juventud (IJJ); Mexico
Prospects for observations of high-energy cosmic tau neutrinos
We study prospects for the observations of high-energy cosmic tau neutrinos
(E \geq 10^6 GeV) originating from proton acceleration in the cores of active
galactic nuclei. We consider the possibility that vacuum flavor neutrino
oscillations induce a tau to muon neutrino flux ratio greatly exceeding the
rather small value expected from intrinsic production. The criterias and event
rates for under water/ice light Cerenkov neutrino telescopes are given by
considering the possible detection of downgoing high-energy cosmic tau
neutrinos through characteristic double shower events.Comment: 10 pages, Revtex, 3 figures included with eps
OC-0480: External radiation therapy, extended surgery and intraoperative electrons for oligorrecurent pelvic cancer
Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068
We present sub-arcsecond 7.513 m imaging- and spectro-polarimetric
observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio
CANARIAS. At all wavelengths, we find:
(1) A 90 60 pc extended polarized feature in the northern ionization
cone, with a uniform 44 polarization angle. Its polarization
arises from dust and gas emission in the ionization cone, heated by the active
nucleus and jet, and further extinguished by aligned dust grains in the host
galaxy. The polarization spectrum of the jet-molecular cloud interaction at
24 pc from the core is highly polarized, and does not show a silicate
feature, suggesting that the dust grains are different from those in the
interstellar medium.
(2) A southern polarized feature at 9.6 pc from the core. Its
polarization arises from a dust emission component extinguished by a large
concentration of dust in the galaxy disc. We cannot distinguish between dust
emission from magnetically aligned dust grains directly heated by the jet close
to the core, and aligned dust grains in the dusty obscuring material
surrounding the central engine. Silicate-like grains reproduce the polarized
dust emission in this feature, suggesting different dust compositions in both
ionization cones.
(3) An upper limit of polarization degree of 0.3 per cent in the core. Based
on our polarization model, the expected polarization of the obscuring dusty
material is 0.1 per cent in the 813 m wavelength range. This
low polarization may be arising from the passage of radiation through aligned
dust grains in the shielded edges of the clumps.Comment: 17 pages, 10 figures, accepted for publication at MNRA
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