803 research outputs found
VEGA Pathfinder navigation for Giotto Halley encounter
Results of the VEGA Pathfinder concept which was used to successfully target the European Space Agnecy's Giotto spacecraft to a 600 km encounter with the comet Halley are presented. Pathfinder was an international cooperative navigation activity involving USSR, European and U.S. space agencies. The final Giotto targeting maneuver was based on a comet location determined from optical data acquired by the earlier arriving Soviet VEGA spacecraft. Inertial pointing angles extracted from optical images of the comet nucleus were combined with a precise estimate of the VEGA encounter orbits determined using VLBI data acquired by NASA's Deep Space Network to predict the location of Halley at Giotto encounter. This article describes the VLBI techniques used to determine the VEGA orbits and shows that the insensitivity of the VLBI data strategy to unmodeled dynamic error sources resulted in estimates of the VEGA orbits with an accuracy of 50 km
Probing NMSSM Scenarios with Minimal Fine-Tuning by Searching for Decays of the Upsilon to a Light CP-Odd Higgs Boson
Completely natural electroweak symmetry breaking is easily achieved in
supersymmetric models if there is a SM-like Higgs boson, , with m_h\lsim
100\gev. In the minimal supersymmetric model, such an decays mainly to
b\anti b and is ruled out by LEP constraints. However, if the MSSM Higgs
sector is expanded so that decays mainly to still lighter Higgs bosons,
e.g. , with , and if , then the LEP
constraints are satisfied. In this letter, we show that in the next-to-minimal
supersymmetric model the above and properties (for the lightest CP-even
and CP-odd Higgs bosons, respectively) imply a lower bound on BR(\Upsilon\to
\gam a) that dedicated runs at present (and future) factories can explore.Comment: 4 pages, 2 figure
Most CD4+ T cells from human immunodeficiency virus-1 infected patients can undergo prolonged clonal expansion
We have addressed the capacity of HIV-1 infection to alter the growth of primary CD4+ T cells, but at the clonal level. Single T cells were expanded in the presence of PHA, IL-2, and small numbers of accessory dendritic cells. We report two new findings. First, T cells from seropositive individuals, even those with AIDS and markedly reduced CD4+ counts, exhibit a normal cloning efficiency, and proliferative capacity. This result is in contrast to two prior reports of a low cloning efficiency in CD4+ T cells from HIV-1-infected patients. Second, when we added high doses of exogenous HIV-1 to T cell clones from control subjects, we observed infection but not cytotoxity or loss of CD4+ cells, following addition of virus stocks at days 0, 3, and/or 7 of clonal growth. The same HIV-1 isolates markedly reduced CD4+ T cells in bulk mononuclear cultures. When tested at day 11, HIV-1 mRNA was expressed in some cells of exogenously infected clones by in situ hybridization; when tested at day 18, several clones could transactivate a TAT-sensitive cell line. These findings suggest that the loss of CD4+ T cells in infected individuals is not the inevitable result of the activation of latent infection, or spread of a productive infection, during clonal growth
Proximity effect in Nb-Mo layered films: Transition temperature and critical current dependence on period
The behavior of the transition temperature and critical current density for a
Mo/Nb repeated bilayer system as a function of the number of periods was
explored. The measured values of the transition temperature are compared to the
theoretical predictions for the proximity effect in the dirty limit. We find
that the transition temperature does not decrease as the number of periods
increase. In addition, inductive critical current density measurements also
show a scaling that indicates the superconductivity properties are not
dependent on the number of bilayers.Comment: 13 pages, 6 figures, to be published Journal of Applied Physic
Latent HIV-1 infection in enriched populations of blood monocytes and T cells from seropositive patients
The extent of latent HIV-1 infection in blood T cells and monocytes of 23 seropositive individuals was examined using DNA amplification (PCR) of HIV-1 sequences. Amplified DNA was found in at least one cell type in all seropositives tested, including 13 asymptomatic, 5 ARC, and 5 AIDS patients. Amplification with two or more primer sets from the gag, env, LTR occurred in 21 (91%) patients\u27 T cells and 17 (74%) patients\u27 monocytes. However, amplification with the LTR primers n monocytes was uncommon. Among four patients tested, amplified DNA continued to be detected after a greater than one thousand-fold dilution (\u3c 500 cells) of both T cell and monocyte lysates. Repeat analysis after 7-9 mo in five seropositives yielded similar findings in T cells and monocytes, but some variation in the efficacy of amplification with individual primers occurred. There was no difference in those 10 patients who were taking AZT, compared to those who were untreated. Our results indicate that a fraction (\u3c 1%) of both T cells and monocytes in blood carry a latent infection in all stages of HIV-1 disease and can serve as reservoirs throughout AZT therapy
Drug Treatment Program Ownership, Medicaid Acceptance, and Service Provision.
The Institute of Medicine noted that effective substance abuse treatment (SAT) programs integrate individual therapeutic approaches with transitional/ancillary services. In addition, research suggests that type of ownership impacts SAT services offered and that Medicaid plays a key role in SAT access. Data from the National Survey of Substance Abuse Treatment Services for the years 2000 and 2002–2006 were used to examine relationships among SAT program Medicaid acceptance, program ownership, and transitional/ancillary service accessibility. Multivariate logistic regression models controlling for state- and program-level contextual factors were used to analyze the data. Nonprofit SAT programs were significantly more likely to offer transitional/ancillary services than for-profit programs. However, programs that accepted Medicaid, regardless of ownership, were significantly more likely to offer most transitional/ancillary services. The data suggest that Medicaid may play a significant role in offering key transitional/ancillary services related to successful treatment outcome, regardless of program ownership type
The Higgs Sector in a Extension of the MSSM
We consider the Higgs sector in an extension of the MSSM with extra SM
singlets, involving an extra gauge symmetry, in which the
domain-wall problem is avoided and the effective parameter is decoupled
from the new gauge boson mass. The model involves a rich Higgs
structure very different from that of the MSSM. In particular, there are large
mixings between Higgs doublets and the SM singlets, significantly affecting the
Higgs spectrum, production cross sections, decay modes, existing exclusion
limits, and allowed parameter range. Scalars considerably lighter than the LEP2
bound (114 GeV) are allowed, and the range is both allowed
and theoretically favored. Phenomenologically, we concentrate our study on the
lighter (least model-dependent, yet characteristic) Higgs particles with
significant SU(2)-doublet components to their wave functions, for the case of
no explicit CP violation in the Higgs sector. We consider their spectra,
including the dominant radiative corrections to their masses from the top/stop
loop. We computed their production cross sections and reexamine the existing
exclusion limits at LEP2. We outline the searching strategy for some
representative scenarios at a future linear collider. We emphasize that
gaugino, Higgsino, and singlino decay modes are indicative of extended models
and have been given little attention. We present a comprehensive list of model
scenarios in the Appendices.Comment: 49 pages, 17 figure
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