126,481 research outputs found
Relativistic Coulomb Green's function in -dimensions
Using the operator method, the Green's functions of the Dirac and
Klein-Gordon equations in the Coulomb potential are derived for
the arbitrary space dimensionality . Nonrelativistic and quasiclassical
asymptotics of these Green's functions are considered in detail.Comment: 9 page
Screening for colorectal cancer in a factory-based population with Fecatest.
This report concerns a screening programme for colorectal cancer using Fecatest, a relatively sensitive test for faecal occult blood, in a factor-based population. A total of 2420 workers between 40 and 65 years of age returned kits for testing following suitable dietary restriction. In Factory A, in which screening was offered as part of an annual medical examination, 989 men agreed to participate, a compliance rate of 45%. In Factory B, in which screening was offered in their weekly pay packets, 1431 men participated, a compliance rate of 22%. An overall positivity rate of 5.8% was found, 4.6% in Factory A and 6.6% in Factory B. Five cancers were found, two of the rectum, one at the recto-sigmoid junction, one in the sigmoid colon and one in the transverse colon. Two of these lesions were at Dukes Stage A, one at Stage B and two at Stage C. In addition, 25 adenomatous polyps were found in 17 men. In 13 these were characterized as tubular adenomata and in 4 as tubulovillous adenomata. The mean age at diagnosis in the polyp cases was 52.6 years and in the cancer cases 58.8 years. Increased specificity is obtained by excluding participants below 46 years of age. The detection rate in the 46-65 year range is approximately 1 in 100 for adenomatous polyps and 1 in 300 for cancer in the population screened. This detection rate is higher than most comparable studies using a less sensitive Guaiac test on older populations
Acetylene terminated matrix resins
The synthesis of resins with terminal acetylene groups has provided a promising technology to yield high performance structural materials. Because these resins cure through an addition reaction, no volatile by-products are produced during the processing. The cured products have high thermal stability and good properties retention after exposure to humidity. Resins with a wide variety of different chemical structures between the terminal acetylene groups are synthesized and their mechanical properties studied. The ability of the acetylene cured polymers to give good mechanical properties is demonstrated by the resins with quinoxaline structures. Processibility of these resins can be manipulated by varying the chain length between the acetylene groups or by blending in different amounts of reactive deluents. Processing conditions similar to the state-of-the-art epoxy can be attained by using backbone structures like ether-sulfone or bis-phenol-A. The wide range of mechanical properties and processing conditions attainable by this class of resins should allow them to be used in a wide variety of applications
Electronic, optical and thermal properties of the hexagonal and fcc Ge2Sb2Te5 chalcogenide from first-principle calculations
We present a comprehensive computational study on the properties of
face-centered cubic and hexagonal chalcogenide Ge2Sb2Te5. We calculate the
electronic structure using density functional theory (DFT); the obtained
density of states (DOS) compares favorably with experiments, also looking
suitable for transport analysis. Optical constants including refraction index
and absorption coefficient capture major experimental features, aside from an
energy shift owed to an underestimate of the band gap that is typical of DFT
calculations. We also compute the phonon DOS for the hexagonal phase, obtaining
a speed of sound and thermal conductivity in good agreement with the
experimental lattice contribution. The calculated heat capacity reaches ~ 1.4 x
106 J/(m3 K) at high temperature, in agreement with experimental data, and
provides insight into the low-temperature range (< 150 K), where data are
unavailable.Comment: 19 pages, 8 figure
Chiral Properties of Pseudoscalar Mesons on a Quenched Lattice with Overlap Fermions
The chiral properties of the pseudoscalar mesons are studied numerically on a
quenched lattice with the overlap fermion. We elucidate the role of the
zero modes in the meson propagators, particularly that of the pseudoscalar
meson. The non-perturbative renormalization constant is determined from
the axial Ward identity and is found to be almost independent of the quark mass
for the range of quark masses we study; this implies that the error is
small. The pion decay constant, , is calculated from which we
determine the lattice spacing to be 0.148 fm. We look for quenched chiral log
in the pseudoscalar decay constants and the pseudoscalar masses and we find
clear evidence for its presence. The chiral log parameter is
determined to be in the range 0.15 -- 0.4 which is consistent with that
predicted from quenched chiral perturbation theory.Comment: Version accepted for publication by PRD. A few minor typographical
errors have been corrected. 24 pages, 11 figure
Theoretical Isochrones with Extinction in the K Band. II. J - K versus K
We calculate theoretical isochrones in a consistent way for five filter pairs
near the J and K band atmospheric windows (J-K, J-K', J-Ks, F110W-F205W, and
F110W-F222M) using the Padova stellar evolutionary models of Girardi et al. We
present magnitude transformations between various K-band filters as a function
of color. Isochrones with extinction of up to 6 mag in the K band are also
presented. As found for the filter pairs composed of H & K band filters, we
find that the reddened isochrones of different filter pairs behave as if they
follow different extinction laws, and that the extinction curves of Hubble
Space Telescope NICMOS filter pairs in the color-magnitude diagram are
considerably nonlinear. Because of these problems, extinction values estimated
with NICMOS filters can be in error by up to 1.3 mag. Our calculation suggests
that the extinction law implied by the observations of Rieke et al for
wavelengths between the J and K bands is better described by a power-law
function with an exponent of 1.66 instead of 1.59, which is commonly used with
an assumption that the transmission functions of J and K filters are Dirac
delta functions.Comment: Published in PASP, 118, 62 (Jan. 2006
Radiolabeling human peripheral blood stem cells for positron emission tomography (PET) imaging in young rhesus monkeys.
These studies focused on a new radiolabeling technique with copper ((64)Cu) and zirconium ((89)Zr) for positron emission tomography (PET) imaging using a CD45 antibody. Synthesis of (64)Cu-CD45 and (89)Zr-CD45 immunoconjugates was performed and the evaluation of the potential toxicity of radiolabeling human peripheral blood stem cells (hPBSC) was assessed in vitro (viability, population doubling times, colony forming units). hPBSC viability was maintained as the dose of (64)Cu-TETA-CD45 increased from 0 (92%) to 160 µCi/mL (76%, p>0.05). Radiolabeling efficiency was not significantly increased with concentrations of (64)Cu-TETA-CD45 >20 µCi/mL (p>0.50). Toxicity affecting both growth and colony formation was observed with hPBSC radiolabeled with ≥40 µCi/mL (p<0.05). For (89)Zr, there were no significant differences in viability (p>0.05), and a trend towards increased radiolabeling efficiency was noted as the dose of (89)Zr-Df-CD45 increased, with a greater level of radiolabeling with 160 µCi/mL compared to 0-40 µCi/mL (p<0.05). A greater than 2,000 fold-increase in the level of (89)Zr-Df-CD45 labeling efficiency was observed when compared to (64)Cu-TETA-CD45. Similar to (64)Cu-TETA-CD45, toxicity was noted when hPBSC were radiolabeled with ≥40 µCi/mL (p<0.05) (growth, colony formation). Taken together, 20 µCi/mL resulted in the highest level of radiolabeling efficiency without altering cell function. Young rhesus monkeys that had been transplanted prenatally with 25×10(6) hPBSC expressing firefly luciferase were assessed with bioluminescence imaging (BLI), then 0.3 mCi of (89)Zr-Df-CD45, which showed the best radiolabeling efficiency, was injected intravenously for PET imaging. Results suggest that (89)Zr-Df-CD45 was able to identify engrafted hPBSC in the same locations identified by BLI, although the background was high
Subset currents on free groups
We introduce and study the space of \emph{subset currents} on the free group
. A subset current on is a positive -invariant locally finite
Borel measure on the space of all closed subsets of consisting of at least two points. While ordinary geodesic currents
generalize conjugacy classes of nontrivial group elements, a subset current is
a measure-theoretic generalization of the conjugacy class of a nontrivial
finitely generated subgroup in , and, more generally, in a word-hyperbolic
group. The concept of a subset current is related to the notion of an
"invariant random subgroup" with respect to some conjugacy-invariant
probability measure on the space of closed subgroups of a topological group. If
we fix a free basis of , a subset current may also be viewed as an
-invariant measure on a "branching" analog of the geodesic flow space for
, whose elements are infinite subtrees (rather than just geodesic lines)
of the Cayley graph of with respect to .Comment: updated version; to appear in Geometriae Dedicat
Atomistic origins of the phase transition mechanism in Ge2Sb2Te5
Combined static and molecular dynamics first-principles calculations are used
to identify a direct structural link between the metastable crystalline and
amorphous phases of Ge2Sb2Te5. We find that the phase transition is driven by
the displacement of Ge atoms along the rocksalt [111] direction from the
stable-octahedron to high-energy-unstable tetrahedron sites close to the
intrinsic vacancy regions, which give rise to the formation of local 4-fold
coordinated motifs. Our analyses suggest that the high figures of merit of
Ge2Sb2Te5 are achieved from the optimal combination of intrinsic vacancies
provided by Sb2Te3 and the instability of the tetrahedron sites provided by
GeTe
- …