15,802 research outputs found
Mars: The Viking discoveries
An overview of the Viking Mars probe is presented. The Viking spacecraft is described and a brief history of the earlier observations and exploration of Mars is provided. A number of the Viking photographs of the Martian surface are presented and a discussion of the experiments Viking performed including a confirmation of the general theory of relativity are reported. Martian surface chemistry is discussed and experiments to study the weather on Mars are reported
Improved linings for integrating spheres
Sphere surface is covered with plain weave of glass fibers coated with polytetrafluoroethylene and one or two layers of magnesium oxide vapor. The resultant lining is suitable for measurement of radiation in the ultraviolet, visible, and near-infrared wavelengths, is not damage prone, and is easily cleaned
Duality Between the Weak and Strong Interaction Limits for Randomly Interacting Fermions
We establish the existence of a duality transformation for generic models of
interacting fermions with two-body interactions. The eigenstates at weak and
strong interaction U possess similar statistical properties when expressed in
the U=0 and U=infinity eigenstates bases respectively. This implies the
existence of a duality point U_d where the eigenstates have the same spreading
in both bases. U_d is surrounded by an interval of finite width which is
characterized by a non Lorentzian spreading of the strength function in both
bases. Scaling arguments predict the survival of this intermediate regime as
the number of particles is increased.Comment: RevTex4, 4 pages, 4 figures. Accepted for publication at Phys. Rev.
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Underlying symmetries of realistic interactions and the nuclear many-body problem
The present study brings forward important information, within the framework
of spectral distribution theory, about the types of forces that dominate three
realistic interactions, CD-Bonn, CDBonn+ 3terms and GXPF1, in nuclei and their
ability to account for many-particle effects such as the formation of
correlated nucleon pairs and enhanced quadrupole collective modes.
Like-particle and proton-neutron isovector pairing correlations are described
microscopically by a model interaction with Sp(4) dynamical symmetry, which is
extended to include an additional quadrupole-quadrupole interaction. The
analysis of the results for the 1f7/2 level shows that both CD-Bonn+3terms and
GXPF1 exhibit a well-developed pairing character compared to CD-Bonn, while the
latter appears to build up more (less) rotational isovector T = 1 (isoscalar T
= 0) collective features. Furthermore, the three realistic interactions are in
general found to correlate strongly with the pairing+quadrupole model
interaction, especially for the highest possible isospin group of states where
the model interaction can be used to provide a reasonable description of the
corresponding energy spectra.Comment: 12 pages, 4 figure
Loschmidt echoes in two-body random matrix ensembles
Fidelity decay is studied for quantum many-body systems with a dominant
independent particle Hamiltonian resulting e.g. from a mean field theory with a
weak two-body interaction. The diagonal terms of the interaction are included
in the unperturbed Hamiltonian, while the off-diagonal terms constitute the
perturbation that distorts the echo. We give the linear response solution for
this problem in a random matrix framework. While the ensemble average shows no
surprising behavior, we find that the typical ensemble member as represented by
the median displays a very slow fidelity decay known as ``freeze''. Numerical
calculations confirm this result and show, that the ground state even on
average displays the freeze. This may contribute to explanation of the
``unreasonable'' success of mean field theories.Comment: 9 pages, 5 figures (6 eps files), RevTex; v2: slight modifications
following referees' suggestion
1/f noise in the Two-Body Random Ensemble
We show that the spectral fluctuations of the Two-Body Random Ensemble (TBRE)
exhibit 1/f noise. This result supports a recent conjecture stating that
chaotic quantum systems are characterized by 1/f noise in their energy level
fluctuations. After suitable individual averaging, we also study the
distribution of the exponent \alpha in the 1/f^{\alpha} noise for the
individual members of the ensemble. Almost all the exponents lie inside a
narrow interval around \alpha=1 suggesting that also individual members exhibit
1/f noise, provided they are individually unfoldedComment: 4 pages, 3 figures, Accepted for publication in Phys. Rev.
Progress in Developing High Energy Nozzle Beams
Electron beam studies of skimmer phenomena and effect on high energy nozzle beam formatio
AIDS patients have increased surfactant protein D but normal mannose binding lectin levels in lung fluid.
BACKGROUND: Surfactant protein D (SP-D) and Mannose Binding Lectin (MBL) are collectins that have opsonic and immunoregulatory functions, are found in lung fluid and interact with the human immunodeficiency virus (HIV). We compared collectin levels in lung fluid and serum from HIV infected and normal subjects to determine if alterations in lung collectin levels were associated with HIV infection and might result in increased susceptibility to other pulmonary infections. METHODS: Blood and bronchoalveolar lavage samples were collected from 19 HIV-infected individuals and 17 HIV-uninfected individuals, all with normal chest X ray at time of study. HIV viral loads and peripheral blood CD4+ T cell counts were measured in all subjects. SP-D was measured in lung fluid, and MBL in both lung fluid and serum. RESULTS: SP-D levels were not significantly different in lung fluid from HIV-uninfected (median 406.72 ng/ml) and HIV-infected individuals with high CD4 count (CD4 >200) (median 382.60 ng/ml) but were elevated in HIV-infected individuals with low CD4 count (median 577.79 ng/ml; Kruskall Wallis p < 0.05). MBL levels in serum were not significantly different between HIV-uninfected and HIV-infected individuals (median 1782.70 ng/ml vs 2639.73 ng/ml) and were not detectable in lung fluid. CONCLUSION: SP-D levels are increased in lung fluid from AIDS patients but not in patients with early HIV infection. MBL levels are not altered by HIV infection or AIDS. There is no evidence that altered pulmonary collectin levels result in susceptibility to infection in these patients
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A Raman spectroscopic study of carbon phases in impact melt rocks and breccias from the Gardnos impact structure, Norway
Raman spectroscopy suggests that the C was emplaced in at least two separate episodes into the impactites of the Gardnos impact structure
Studies of Autumn calving suckler cows, bulls at pasture and winter grazing
End of project reportMost beef and dairy cows are spring calving leading to distinct seasonality of supply. Calving
a proportion of the beef herd in the autumn would lead to a more uniform annual supply of
cattle for slaughter and potentially increase the proportion of grazed grass in the diet of the
suckler progeny. Autumn calving sucklers also facilitate the use of AI, which should enhance
the product quality.
This project aimed to address the technical aspects of autumn calving sucklers, which differ
from those of spring calvers. The currently available international energy models were
evaluated for autumn calving lactating suckler cows using the type of cow typically found in
Irish suckler herds (Experiment 1). The winter accommodation of the suckler cow and calf
unit and its impact on cow reproductive performance was evaluated (Experiment 2).
The final part of the project evolved into component studies to determine the effect of
supplementary feed on the performance of grazing bulls (Experiment 3), and the
consequences of weanling cattle grazing pasture in winter as an alternative to housing them in winter (Experiments 4 to 7)
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