14,361 research outputs found
Drive mechanism for production of simulated human breath
Simulated breath drive mechanism was developed as subsystem to breathing metabolic simulator. Mechanism reproduces complete range of human breath rate, breath depth, and breath waveform, as well as independently controlled functional residual capacity. Mechanism was found capable of simulating various individual human breathing characteristics without any changes of parts
Meteoroid hazards in deep space Final report
Design and development of Sisyphus meteoroid detection system for interplanetary spacecraf
Rubidium and lead abundances in giant stars of the globular clusters M4 and M5
We present measurements of the neutron-capture elements Rb and Pb for bright
giants in the globular clusters M4 and M5. The clusters are of similar
metallicity ([Fe/H] = -1.2) but M4 is decidedly s-process enriched relative to
M5: [Ba/Fe] = +0.6 for M4 but 0.0 for M5. The Rb and Pb abundances were derived
by comparing synthetic spectra with high-resolution, high signal-to-noise ratio
spectra obtained with MIKE on the Magellan telescope. Abundances of Y, Zr, La,
and Eu were also obtained. In M4, the mean abundances from 12 giants are
[Rb/Fe] = 0.39 +/- 0.02 (sigma = 0.07), [Rb/Zr] = 0.17 +/- 0.03 (sigma = 0.08),
and [Pb/Fe] = 0.30 +/- 0.02 (sigma = 0.07). In M5, the mean abundances from two
giants are [Rb/Fe] = 0.00 +/- 0.05 (sigma = 0.06), [Rb/Zr] = 0.08 +/- 0.08
(sigma = 0.11), and [Pb/Fe] = -0.35 +/- 0.02 (sigma = 0.04). Within the
measurement uncertainties, the abundance ratios [Rb/Fe], [Pb/Fe] and [Rb/X] for
X = Y, Zr, La are constant from star-to-star in each cluster and none of these
ratios are correlated with O or Na abundances. While M4 has a higher Rb
abundance than M5, the ratios [Rb/X] are similar in both clusters indicating
that the nature of the s-products are very similar for each cluster but the gas
from which M4's stars formed had a higher concentration of these products.Comment: Accepted for publication in Ap
Giant Backscattering Peak in Angle-Resolved Andreev Reflection
It is shown analytically and by numerical simulation that the angular
distribution of Andreev reflection by a disordered normal-metal --
superconductor junction has a narrow peak at the angle of incidence. The peak
is higher than the well-known coherent backscattering peak in the normal state,
by a large factor G/G_0 (where G is the conductance of the junction and
G_0=2e^2/h). The enhanced backscattering can be detected by means of ballistic
point contacts.Comment: Instituut-Lorentz, Leiden, The Netherlands, 4 pages, REVTeX-3.0, 3
figure
Suppression of Giant Magnetoresistance by a superconducting contact
We predict that current perpendicular to the plane (CPP) giant
magnetoresistance (GMR) in a phase-coherent magnetic multilayer is suppressed
when one of the contacts is superconducting. This is a consequence of a
superconductivity-induced magneto-resistive (SMR) effect, whereby the
conductance of the ferromagnetically aligned state is drastically reduced by
superconductivity. To demonstrate this effect, we compute the GMR ratio of
clean (Cu/Co)_nCu and (Cu/Co)_nPb multilayers, described by an ab-initio spd
tight binding Hamiltonian. By analyzing a simpler model with two orbitals per
site, we also show that the suppression survives in the presence of elastic
scattering by impurities.Comment: 5 pages, 4 figures. Submitted to PR
Rubidium in Metal-Deficient Disk and Halo Stars
We report the first extensive study of stellar Rb abundances. High-resolution
spectra have been used to determine, or set upper limits on, the abundances of
this heavy element and the associated elements Y, Zr, and Ba in 44 dwarfs and
giants with metallicities spanning the range -2.0 <[Fe/H] < 0.0. In
metal-deficient stars Rb is systematically overabundant relative to Fe; we find
an average [Rb/Fe] of +0.21 for the 32 stars with [Fe/H] < -0.5 and measured
Rb. This behavior contrasts with that of Y, Zr, and Ba, which, with the
exception of three new CH stars (HD 23439A and B and BD +5 3640), are
consistently slightly deficient relative to Fe in the same stars; excluding the
three CH stars, we find the stars with [Fe/H] < -0.5 have average [Y/Fe],
[Zr/Fe], and [Ba/Fe] of --0.19 (24 stars), --0.12 (28 stars), and --0.06 (29
stars), respectively. The different behavior of Rb on the one hand and Y, Zr,
and Ba on the other can be attributed in part to the fact that in the Sun and
in these stars Rb has a large r-process component while Y, Zr, and Ba are
mostly s-process elements with only small r-process components. In addition,
the Rb s-process abundance is dependent on the neutron density at the
s-processing site. Published observations of Rb in s-process enriched red
giants indicate a higher neutron density in the metal-poor giants. These
observations imply a higher s-process abundance for Rb in metal-poor stars. The
calculated combination of the Rb r-process abundance, as estimated for the
stellar Eu abundances, and the s-process abundance as estimated for red giants
accounts satisfactorily for the observed run of [Rb/Fe] with [Fe/H].Comment: 23 pages, 5 tables, 7 figure
Emerging Biological Principles of Metastasis
Metastases account for the great majority of cancer-associated deaths, yet this complex process remains the least understood aspect of cancer biology. As the body of research concerning metastasis continues to grow at a rapid rate, the biological programs that underlie the dissemination and metastatic outgrowth of cancer cells are beginning to come into view. In this review we summarize the cellular and molecular mechanisms involved in metastasis, with a focus on carcinomas where the most is known, and we highlight the general principles of metastasis that have begun to emerge
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