1,627 research outputs found
Paper Session III-B - Space Station On-Orbit Assembly and Operation
The United States and its international partners are well on the way to developing Space Station Freedom which will be a very large orbiting facility with many capabilities for conducting space operations. Adjustments in the program content and station design have been implemented as a result of the recent restructure activity. This paper addresses the assembly and operations aspects of SSF. Assembly is achieved by sequential shuttle launches which carry portions of the station building the capability through the Manned Tended Capability and then on to Permanent Manned Capability. The pre-integrated truss segment resulting from the program restructure activity is shown and assembly techniques using the orbiter described. Both pay load and station operations are examined. The pay load operations include the conduct of materials processing and life science missions. These rely heavily on the microgravity capability of the Space Station. Station operations examined include EVA for assembly and maintenance and reboost techniques
Space Platform
The Space Platform (SP) will provide a cost effective long-term host vehicle for scientific and applications payloads beginning in the late 1980\u27s. SP will take advantage of STS capabilities for delivery to orbit, assembly, check-out, maintenance and servicing. Services provided to multiple payloads include electrical power, heat rejection, attitude control and high-rate data handling communications. The system includes self-contained altitude maintenance and is designed for indefinite orbital operation.
MDAC and TRW are currently studying Space Platform for NASA/MSFC to develop optimum configurations for the eventual development-phase competition. Included in the study is development of plans for evolution into an eventual Science and Applications Manned Space Platform (SAMSP)
Usefulness of a quantitative real-time PCR assay using serum samples to discriminate between inactive, serologically positive and active human brucellosis
AbstractDiagnosis of brucellosis can be difficult in certain scenarios where conventional microbiological techniques have important limitations. The aim of this study was to develop a LightCycler Quantitative PCR assay in serum samples to discriminate between active and past brucellosis. In total, 110 serum samples from 46 brucellosis patients and 64 controls, including persons who had recently been treated for brucellosis, asymptomatic persons exposed to brucellosis, and patients with febrile syndromes involving a differential diagnosis with brucellosis, were studied. Brucella spp.-specific sequences of the PCR primers and probe were selected from the gene encoding an immunogenic membrane protein of 31 kDa (BCSP31). The analytical sensitivity was 1 Ă 101 fg of Brucella DNA. The mean threshold cycles for brucellosis patients and controls were 31.8 ± 1.7 and 35.4 ± 1.1, respectively (p <0.001). The best cut-off for bacterial DNA load was 5 Ă 103 copies/mL. At this cut-off, the area under the receiver operating characteristic curves was 0.963 (95% CI 0.920â1.005), with a sensitivity of 93.5% and a specificity of 98.4%. Under the assay conditions, the LightCycler Quantitative PCR in serum samples seems to be highly reproducible, rapid, sensitive and specific. It is therefore a useful method for both the initial diagnosis and the differentiation between past and active brucellosis
Electrochemical performances and post-operational characterization of a segmented sofc operated under load for 15k hours
In the frame of the ENDURANCE FCH-JU-FP7 project (2014-2017) a segmented cell (20 segments regularly
distributed from fuel inlet to fuel outlet) was operated for 15k hours in co-flow at 750\ub0C (average temperature) in hydrogen under load.
Each segment was carefully monitored during operation by periodically acquiring the impedance spectra and constantly checking the voltage under current load.
After 15k hours of operation the test was stopped and the cell used for further investigations in order to compare the cell evolution with the segment degradation.
The overall observation in cross section of the cell has shown a good stability, however some differences were observed in the electrodes that might be related to the local operating conditions: temperature, H2
/H2O ratio in the fuel stream.
The gathered results will contribute to increase the understanding the evolution of a SOFC in real operating
conditions. Evidences of the effect of temperature, time and fuel pollutants were found
Rapid diagnosis of human brucellosis by SYBR Green I-based real-time PCR assay and melting curve analysis in serum samples
SUMMARYThe aim of this study was to develop a LightCycler-based real-time PCR (LC-PCR) assay and to evaluate its diagnostic use for the detection of Brucella DNA in serum samples. Following amplification of a 223-bp gene sequence encoding an immunogenetic membrane protein (BCSP31) specific for the Brucella genus, melting curve and DNA sequencing analysis was performed to verify the specificity of the PCR products. The intra- and inter-assay variation coefficients were 1.3% and 6.4%, respectively, and the detection limit was 5 fg of Brucella DNA (one genome equivalent). After optimisation of the PCR assay conditions, a standard curve was obtained with a linear range (correlation coefficient = 0.99) over seven orders of magnitude from 107 to 10 fg of Brucella DNA. The LC-PCR assay was found to be 91.9% sensitive and 95.4% specific when tested with 65 negative control samples and 62 serum samples from 60 consecutive patients with active brucellosis. The assay is reproducible, easily standardised, minimises the risk of infection in laboratory workers, and has a total processing time of < 2 h. It could therefore form a promising and practical approach for the rapid diagnosis of human brucellosis
Diagnosis of recent and relapsed cases of human brucellosis by PCR assay
BACKGROUND: Brucellosis affects human populations in many developing countries including the Middle East, and Latin America where it is still endemic. It has been prevalent in Jordan for years, where 7842 cases of human brucellosis were registered at the Ministry of Health during 10 year-period. This study was initiated by the recent increase in the number of human cases diagnosed in a rural area in the Northern Jordan to help assess the status of the disease in that area. For this purpose blood specimens from brucellosis suspected cases were tested by serology, culture and PCR. METHODS: Peripheral blood specimens from 50 healthy control subjects and 165 seropositive patients having compatible signs and symptoms that were clinically diagnosed to have brucellosis were tested by blood culture, and by PCR. The PCR assay used genus-specific primers from the conserved region of the 16S rRNA sequence, which showed high specificity for the Brucella spp. RESULTS: Diagnosis of Brucella was established by PCR in 120 cases (72.7%). All of them were seropositive and 20 were positive by culture. Forty-eight of 58 (82.8%) of the relapsed cases two months after completing the treatment with an increase in the previous serological titers were positive by PCR. The assay has 85.7% positive predicative value, 100% sensitivity and specificity since it correctly identified all cases that were positive by blood cultures, 95.8% by serology and none of the control group was positive. CONCLUSIONS: Results showed that PCR assay can be applied with serology for the diagnosis of brucellosis suspected cases and relapses regardless of the duration or type of the disease without relying on the blood cultures, especially in chronic cases
Observing a column-dependent zeta in dense interstellar sources: the case of the Horsehead Nebula
Context: Observations of small carbon-bearing molecules such as CCH, C4H,
c-C3H2, and HCO in the Horsehead Nebula have shown these species to have higher
abundances towards the edge of the source than towards the center.
Aims: Given the determination of a wide range of values for zeta (s-1), the
total ionization rate of hydrogen atoms, and the proposal of a column-dependent
zeta(N_H), where N_H is the total column of hydrogen nuclei, we desire to
determine if the effects of zeta(N_H) in a single object with spatial variation
can be observable. We chose the Horsehead Nebula because of its geometry and
high density.
Method: We model the Horsehead Nebula as a near edge-on photon dominated
region (PDR), using several choices for zeta, both constant and as a function
of column. The column-dependent zeta functions are determined by a Monte Carlo
model of cosmic ray penetration, using a steep power-law spectrum and
accounting for ionization and magnetic field effects. We consider a case with
low-metal elemental abundances as well as a sulfur-rich case.
Results: We show that use of a column-dependent zeta(N_H) of 5(-15) s-1 at
the surface and 7.5(-16) s-1 at Av = 10 on balance improves agreement between
measured and theoretical molecular abundances, compared with constant values of
zeta.Comment: 12 pages, 6 figures, 5 tables, accepted in A&
Young starless cores embedded in the magnetically dominated Pipe Nebula
The Pipe Nebula is a massive, nearby dark molecular cloud with a low
star-formation efficiency which makes it a good laboratory to study the very
early stages of the star formation process. The Pipe Nebula is largely
filamentary, and appears to be threaded by a uniform magnetic field at scales
of few parsecs, perpendicular to its main axis. The field is only locally
perturbed in a few regions, such as the only active cluster forming core B59.
The aim of this study is to investigate primordial conditions in low-mass
pre-stellar cores and how they relate to the local magnetic field in the cloud.
We used the IRAM 30-m telescope to carry out a continuum and molecular survey
at 3 and 1 mm of early- and late-time molecules toward four selected starless
cores inside the Pipe Nebula. We found that the dust continuum emission maps
trace better the densest regions than previous 2MASS extinction maps, while
2MASS extinction maps trace better the diffuse gas. The properties of the cores
derived from dust emission show average radii of ~0.09 pc, densities of
~1.3x10^5 cm^-3, and core masses of ~2.5 M_sun. Our results confirm that the
Pipe Nebula starless cores studied are in a very early evolutionary stage, and
present a very young chemistry with different properties that allow us to
propose an evolutionary sequence. All of the cores present early-time molecular
emission, with CS detections toward all the sample. Two of them, Cores 40 and
109, present strong late-time molecular emission. There seems to be a
correlation between the chemical evolutionary stage of the cores and the local
magnetic properties that suggests that the evolution of the cores is ruled by a
local competition between the magnetic energy and other mechanisms, such as
turbulence.Comment: Accepted for publication in ApJ. 15 pages, 5 figures, 9 table
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