8,846 research outputs found
Evaluation of a series hybird thrust bearing at DN values to three million. 1: Analysis and design
The analysis and design are presented of a hybrid bearing consisting of a 150-mm ball bearing and a centrifugally actuated, conical, fluid film bearing fitting an envelope with an outer radius of 86.4 mm (3.4 in.) and an inner radius of 71 mm (2.8 in.). The bearing analysis, combined with available torque data on ball bearings, indicates that an effective speed split between the ball and fluid-film bearings of 50 percent may be expected during operation at 20,000 rpm and under an axial load of 17,800 newtons (4000 lbs.). This speed split can result in a ten-fold increase in the life of the ball bearing when compared to a simple ball bearing system operating under similar conditions
Line-profile tomography of exoplanet transits I: The Doppler shadow of HD 189733b
We present a direct method for isolating the component of the starlight
blocked by a planet as it transits its host star, and apply it to spectra of
the bright transiting planet HD 189733b. We model the global shape of the
stellar cross-correlation function as the convolution of a limb-darkened
rotation profile and a gaussian representing the Doppler core of the average
photospheric line profile. The light blocked by the planet during the transit
is a gaussian of the same intrinsic width, whose trajectory across the line
profile yields a precise measure of the misalignment angle and an independent
measure of v sin I. We show that even when v sin I is less than the width of
the intrinsic line profile, the travelling Doppler "shadow" cast by the planet
creates an identifiable distortion in the line profiles which is amenable to
direct modelling. Direct measurement of the trajectory of the missing starlight
yields self-consistent measures of the projected stellar rotation rate, the
intrinsic width of the mean local photospheric line profile, the projected
spin-orbit misalignment angle, and the system's centre-of-mass velocity.
Combined with the photometric rotation period, the results give a geometrical
measure of the stellar radius which agrees closely with values obtained from
high-precision transit photometry if a small amount of differential rotation is
present in the stellar photosphere.Comment: 8 pages, 5 figures, 2 tables; accepted by MNRA
The association of shift work and coronary heart disease risk factors among male factory workers in Kota Bharu, Kelantan
Shift work is one of the work hour systems in which a relay of employees extends the period of production beyond the conventional 8-hour working day. It has been found to be associated with various health problems and there is concern that shift workers are at higher risk to develop risk factors for coronary heart disease (CHD). The study was undertaken to examine relationships between shift work and CHD risk factors, namely hypertension, dyslipidaemia (either hypercholesterolaemia, hyper-low density lipoprotein-cholesterolaemia, hypo-high density lipoprotein-cholesterolaemia or hypertriglyceridaemia), high body mass index (BMI), hyperglycemia and physical inactivity among male factory workers in a factory in Kota Bharu, Kelantan. METHODS: This study was a contrived cross-sectional study of 76 shift and 72 day workers from one ofthe factories in Kota Bharu, Kelantan. Data was collected through a questionnaire on psychosocial and life-style factors, anthropometric and blood pressure measurement, fasting blood sugar and fasting lipid proJiles analyses. RESULTS: The prevalence of hypertension, hypercholesterolaemia, hypertriglyceridaemia and high body mass index (BMO were significantly higher among shift workers compared to day workers. There was no difference in the prevalence of hyperg[ycemia, hypo-high-density lipoprotein-cholesterolaemia, hyper-high-density lipoprotein-cholesterolaemia and physical inactivity. When the shiji workers were compared with the day workers, the aajusted odds ratio (OR) for hypertension, high BMI andphysical inactivity were 9.1 (95% CI 1.4-56.8), 2.9 (95% CI 1.3-6.1) and 7.7 (95% CI 2.1-27.5) respectively. There was neither association of shift work with dyslipidaemia, nor with hyperglycemia. CONCLUSIONS: There were positive association between shiji work and hypertension, high BMI andphysical inactivity which denotes a higher risk of CHD risk factors among shift workers compared to day workers
Small, high-speed bearing technology for cryogenic turbo-pumps
The design of 20-mm bore ball bearings is described for cryogenic turbo-machinery applications, operating up to speeds of 120,000 rpm. A special section is included on the design of hybrid bearings. Each hybrid bearing is composed of a ball bearing in series with a conventional pressurized fluid-film journal bearing. Full details are presented on the design of a test vehicle which possesses the capability of testing the above named bearings within the given speed range under externally applied radial and axial loads
The spin-orbit angle of the transiting hot jupiter CoRoT-1b
We measure the angle between the planetary orbit and the stellar rotation
axis in the transiting planetary system CoRoT-1, with new HIRES/Keck and
FORS/VLT high-accuracy photometry. The data indicate a highly tilted system,
with a projected spin-orbit angle lambda = 77 +- 11 degrees. Systematic
uncertainties in the radial velocity data could cause the actual errors to be
larger by an unknown amount, and this result needs to be confirmed with further
high-accuracy spectroscopic transit measurements.
Spin-orbit alignment has now been measured in a dozen extra-solar planetary
systems, and several show strong misalignment. The first three misaligned
planets were all much more massive than Jupiter and followed eccentric orbits.
CoRoT-1, however, is a jovian-mass close-in planet on a circular orbit. If its
strong misalignment is confirmed, it would break this pattern. The high
occurence of misaligned systems for several types of planets and orbits favours
planet-planet scattering as a mechanism to bring gas giants on very close
orbits.Comment: to appear in in MNRAS letters [5 pages
The cosmic ray spectrum above 10(17) eV
The final analysis of the data obtained by the Sydney University Giant Airshower Recorder (SUGAR) is presented. The data has been reanalysed to take into account the effects of afterpulsing in the photomultiplier tubes. Event data was used to produce a spectrum of equivalent vertical muon number and from this a model dependent primary energy spectrum was obtained. These spectra show good evidence for the Ankle: a flattening at 10(19) eV. There is no sign of the cut-off which would be expected from the effects of the universal black body radiation
A Tentative Detection of a Starspot During Consecutive Transits of an Extrasolar Planet from the Ground: No Evidence of a Double Transiting Planet System Around TrES-1
There have been numerous reports of anomalies during transits of the planet
TrES-1b. Recently, Rabus and coworkers' analysis of HST observations lead them
to claim brightening anomalies during transit might be caused by either a
second transiting planet or a cool starspot. Observations of two consecutive
transits are presented here from the University of Arizona's 61-inch Kuiper
Telescope on May 12 and May 15, 2008 UT. A 5.4 +/- 1.7 mmag (0.54 +/- 0.17%)
brightening anomaly was detected during the first half of the transit on May 12
and again in the second half of the transit on May 15th. We conclude that this
is a tentative detection of a r greater than or equal to 6 earth radii starspot
rotating on the surface of the star. We suggest that all evidence to date
suggest TrES-1 has a spotty surface and there is no need to introduce a second
transiting planet in this system to explain these anomalies. We are only able
to constrain the rotational period of the star to 40.2 +22.9 -14.6 days, due to
previous errors in measuring the alignment of the stellar spin axis with the
planetary orbital axis. This is consistent with the previously observed P_obs =
33.2 +22.3 -14.3 day period. We note that this technique could be applied to
other transiting systems for which starspots exist on the star in the transit
path of the planet in order to constrain the rotation rate of the star.
(abridged)Comment: 21 pages, 3 tables, 6 figures, Accepted to Ap
Neutron scattering study of spin ordering and stripe pinning in superconducting LaSrCuO
The relationships among charge order, spin fluctuations, and
superconductivity in underdoped cuprates remain controversial. We use neutron
scattering techniques to study these phenomena in
LaSrCuO, a superconductor with a transition temperature
of ~K. At , we find incommensurate spin fluctuations with a
quasielastic energy spectrum and no sign of a gap within the energy range from
0.2 to 15 meV. A weak elastic magnetic component grows below ~K,
consistent with results from local probes. Regarding the atomic lattice, we
have discovered unexpectedly strong fluctuations of the CuO octahedra about
Cu-O bonds, which are associated with inequivalent O sites within the CuO
planes. Furthermore, we observed a weak elastic superlattice peak
that implies a reduced lattice symmetry. The presence of inequivalent O sites
rationalizes various pieces of evidence for charge stripe order in underdoped
\lsco. The coexistence of superconductivity with quasi-static spin-stripe order
suggests the presence of intertwined orders; however, the rotation of the
stripe orientation away from the Cu-O bonds might be connected with evidence
for a finite gap at the nodal points of the superconducting gap function.Comment: 13 pages, 11 figures; accepted versio
Gas Absorption in the KH 15D System: Further Evidence for Dust Settling in the Circumbinary Disk
Na I D lines in the spectrum of the young binary KH 15D have been analyzed in
detail. We find an excess absorption component that may be attributed to
foreground interstellar absorption, and to gas possibly associated with the
solids in the circumbinary disk. The derived column density is log N_NaI = 12.5
cm^-2, centered on a radial velocity that is consistent with the systemic
velocity. Subtracting the likely contribution of the ISM leaves log N_NaI ~
12.3 cm^-2. There is no detectable change in the gas column density across the
"knife edge" formed by the opaque grain disk, indicating that the gas and
solids have very different scale heights, with the solids being highly settled.
Our data support a picture of this circumbinary disk as being composed of a
very thin particulate grain layer composed of millimeter-sized or larger
objects that are settled within whatever remaining gas may be present. This
phase of disk evolution has been hypothesized to exist as a prelude to the
formation of planetesimals through gravitational fragmentation, and is expected
to be short-lived if much gas were still present in such a disk. Our analysis
also reveals the presence of excess Na I emission relative to the comparison
spectrum at the radial velocity of the currently visible star that plausibly
arises within the magnetosphere of this still-accreting young star.Comment: Accepted for publication in ApJ, 23 pages, 6 figure
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