2,450 research outputs found
Radioactive method enables determination of surface areas rapidly and accurately
Radioactive krypton adsorption technique is used to determine the surface area of more than one sample of material simultaneously
VETA x ray data acquisition and control system
We describe the X-ray Data Acquisition and Control System (XDACS) used together with the X-ray Detection System (XDS) to characterize the X-ray image during testing of the AXAF P1/H1 mirror pair at the MSFC X-ray Calibration Facility. A variety of X-ray data were acquired, analyzed and archived during the testing including: mirror alignment, encircled energy, effective area, point spread function, system housekeeping and proportional counter window uniformity data. The system architecture is presented with emphasis placed on key features that include a layered UNIX tool approach, dedicated subsystem controllers, real-time X-window displays, flexibility in combining tools, network connectivity and system extensibility. The VETA test data archive is also described
Temperature dependence of the energy dissipation in dynamic force microscopy
The dissipation of energy in dynamic force microscopy is usually described in
terms of an adhesion hysteresis mechanism. This mechanism should become less
efficient with increasing temperature. To verify this prediction we have
measured topography and dissipation data with dynamic force microscopy in the
temperature range from 100 K up to 300 K. We used
3,4,9,10-perylenetetracarboxylic-dianhydride (PTCDA) grown on KBr(001), both
materials exhibiting a strong dissipation signal at large frequency shifts. At
room temperature, the energy dissipated into the sample (or tip) is 1.9
eV/cycle for PTCDA and 2.7 eV/cycle for KBr, respectively, and is in good
agreement with an adhesion hysteresis mechanism. The energy dissipation over
the PTCDA surface decreases with increasing temperature yielding a negative
temperature coefficient. For the KBr substrate, we find the opposite behaviour:
an increase of dissipated energy with increasing temperature. While the
negative temperature coefficient in case of PTCDA agrees rather well with the
adhesion hysteresis model, the positive slope found for KBr points to a
hitherto unknown dissipation mechanism
Screening of COPD patients for abdominal aortic aneurysm
Purpose: Screening for abdominal aortic aneurysm (AAA) in “men aged over 65
years who have ever smoked” is a recommended policy. To reduce the number of
screenings, it may be of value to define subgroups with a higher prevalence of
AAA. Since chronic obstructive pulmonary disease (COPD) and AAA are associated
with several common risk factors, this study investigates the prevalence of
AAA in COPD patients. Patients and methods: Patients with COPD were identified
via the hospital information system. Inclusion criteria were: COPD stage I–IV,
ability to give full consent, and age >18 years; exclusion criteria were:
patient too obese for an ultrasound check, previously diagnosed AAA, prior
surgery for AAA, or ethical grounds such as concomitant advanced malignant or
end-stage disease. The primary endpoint of the study was an aortic diameter
measured by ultrasound of ≥30 mm. Defined secondary endpoints were evaluated
on the basis of medical records and interviews. Results: Of the 1,180
identified COPD patients, 589 were included in this prospective study. In 22
patients (3.70%), the aortic diameter was ≥30 mm, representing an AAA
prevalence of 6.72% among males aged >65 years. The risk of AAA increased with
the following comorbidities/risk factors: male sex (odds ratio [OR] 2.98),
coronary heart disease (OR 2.81), peripheral arterial occlusive disease (OR
2.47), hyperlipoproteinemia (OR 2.77), AAA in the family history (OR 3.95),
and COPD stage I/II versus IV (OR 1.81). Conclusion: The overall AAA
prevalence of 3.7% in our group of COPD patients is similar to that of the
general population aged >65 years. However, the frequency of AAA in male COPD
patients aged >65 years is considerably higher (6.72%) and increased further
still in those individuals with additional comorbidities/risk factors.
Defining subgroups with a higher risk of AAA may increase the efficiency of
screening
Surveying the Inner Halo of the Galaxy with 2MASS-Selected Horizontal Branch Candidates
We use 2MASS photometry to select blue horizontal branch (BHB) candidates
covering the sky |b|>15 deg. A 12.5<J<15.5 sample of BHB stars traces the thick
disk and inner halo to d<9 kpc, with a density comparable to that of M giant
stars. We base our sample selection strategy on the Century Survey Galactic
Halo Project, a survey that provides a complete, spectroscopically-identified
sample of blue stars to a similar depth as the 2MASS catalog. We show that a
-0.20<(J-H)_0<0.10, -0.10<(H-K)_0<0.10 color-selected sample of stars is 65%
complete for BHB stars, and is composed of 47% BHB stars. We apply this
photometric selection to the full 2MASS catalog, and see no spatial
overdensities of BHB candidates at high Galactic latitude |b|>50 deg. We insert
simulated star streams into the data and conclude that the high Galactic
latitude BHB candidates are consistent with having no ~5 deg wide star stream
with density greater than 0.33 objects deg^-2 at the 95% confidence level. The
absence of structure suggests there have been no major accretion events in the
inner halo in the last few Gyr. However, at low Galactic latitudes a two-point
angular correlation analysis reveals structure on angular scales <1 deg. This
structure is apparently associated with stars in the thick disk, and has a
physical scale of 10-100 pc. Interestingly, such structures are expected by
cosmological simulations that predict the majority of the thick disk may arise
from accretion and disruption of satellite mergers.Comment: 11 pages, including figures. Accepted by AJ with minor revision
VETA x ray data acquisition and control system
We describe the X-ray Data Acquisition and Control System (XDACS) used together with the X-ray Detection System (XDS) to characterize the x-ray image during testing of the AXAF P1/H1 mirror pair at the MSFC X-ray Calibration Facility. A variety of x-ray data were acquired, analyzed, and archived during the testing including: mirror alignment, encircled energy, effective area, point spread function, system housekeeping, and proportional counter window uniformity data. The system architecture will be presented with emphasis placed on key features that include a layered UNIX tool approach, dedicated subsystem controllers, real-time X-window displays, flexibility in combining tools, network connectivity, and system extensibility. The VETA test data archive are also described
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Beagle 2: Mission to Mars — current status
Beagle 2, developed in the UK, was launched on June 2, 2003. It landed on Mars on December 25th, 2003 in Isidis Planitia, a large sedimentary basin. To date, the team is awaiting signals from the Beagle 2 lander. Current status of the mission will be reported
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