3,095 research outputs found
Assessing Friction Characteristics of Liquid Lubricants
The decline of fossil fuel reserves and the increasing awareness of greenhouse gas emissions have been the primary driving forces behind the need to conserve energy. To improve fuel efficiency friction modifiers are commonly blended into lubricants. Reduction of friction will clearly lead to less energy requirements. However, an accurate evaluation of lubricant performance is not possible using existing test equipment. The main reason is that current test rigs require operating conditions that induce wear so that the measurement of friction in these rigs is not a real evaluation of friction. The paper will detail the design and commissioning of a purpose built test rig to measure frictional characteristics of various oils as well as the results of the tests performed
Collisions of low-energy electrons with isopropanol
We report measured and calculated cross sections for elastic scattering of low-energy electrons by isopropanol (propan-2-ol). The experimental data were obtained using the relative flow technique with helium as the standard gas and a thin aperture as the collimating target gas source, which permits use of this method without the restrictions imposed by the relative flow pressure conditions on helium and the unknown gas. The differential cross sections were measured at energies of 1.5, 2, 3, 5, 6, 8, 10, 15, 20, and 30 eV and for scattering angles from 10∘ to 130∘. The cross sections were computed over the same energy range employing the Schwinger multichannel method in the static-exchange plus polarization approximation. Agreement between theory and experiment is very good. The present data are compared with previously calculated and measured results for n-propanol, the other isomer of C_3H_7OH. Although the integral and momentum transfer cross sections for the isomers are very similar, the differential cross sections show a strong isomeric effect: In contrast to the f-wave behavior seen in scattering by n-propanol, d-wave behavior is observed in the cross sections of isopropanol. These results corroborate our previous observations in electron collisions with isomers of C_4H_9OH
Exploring Halo Substructure with Giant Stars IV: The Extended Structure of the Ursa Minor Dwarf Spheroidal
We present a large area photometric survey of the Ursa Minor dSph. We
identify UMi giant star candidates extending to ~3 deg from the center of the
dSph. Comparison to previous catalogues of stars within the tidal radius of UMi
suggests that our photometric luminosity classification is 100% accurate. Over
a large fraction of the survey area, blue horizontal branch stars associated
with UMi can also be identified. The spatial distribution of both the UMi giant
stars and the BHB stars are remarkably similar, and a large fraction of both
samples of stars are found outside the tidal radius of UMi. An isodensity
contour map of the stars within the tidal radius of UMi reveals two
morphological peculiarities: (1) The highest density of dSph stars is offset
from the center of symmetry of the outer isodensity contours. (2) The overall
shape of the outer contours appear S-shaped. We find that previously determined
King profiles with ~50' tidal radii do not fit well the distribution of our UMi
stars. A King profile with a larger tidal radius produces a reasonable fit,
however a power law with index -3 provides a better fit for radii > 20'. The
existence of UMi stars at large distances from the core of the galaxy, the
peculiar morphology of the dSph within its tidal radius, and the shape of its
surface density profile all suggest that UMi is evolving significantly due to
the tidal influence of the Milky Way. However, the photometric data on UMi
stars alone does not allow us to determine if the candidate extratidal stars
are now unbound or if they remain bound to the dSph within an extended dark
matter halo. (Abridged)Comment: accepted by AJ, 32 pages, 15 figures, emulateapj5 styl
A study of 15N14N isotopic exchange over cobalt molybdenum nitrides
The 14N/15N isotopic exchange pathways over Co3Mo3N, a material of interest as an ammonia synthesis catalyst and for the development of nitrogen transfer reactions, have been investigated. Both the homomolecular and heterolytic exchange processes have been studied, and it has been shown that lattice nitrogen species are exchangeable. The exchange behavior was found to be a strong function of pretreatment with ca. 25% of lattice N atoms being exchanged after 40 min at 600 °C after N2 pretreatment at 700 °C compared to only 6% following similar Ar pretreatment. This observation, for which the potential contribution of adsorbed N species can be discounted, is significant in terms of the application of this material. In the case of the Co6Mo6N phase, regeneration to Co3Mo3N under 15N2 at 600 °C occurs concurrently with 14N15N formation. These observations demonstrate the reactivity of nitrogen in the Co–Mo–N system to be a strong function of pretreatment and worthy of further consideration
Experiences of refugees and asylum seekers in general practice: a qualitative study
Background: There has been much debate regarding the refugee health situation in the UK. However most of the existing literature fails to take account of the opinions of refugees themselves. This study was established to determine the views of asylum seekers and refugees on their overall experiences in primary care and to suggest improvements to their care. Methods: Qualitative study of adult asylum seekers and refugees who had entered the UK in the last 10 years. The study was set in Barnet Refugee Walk in Service, London. 11 Semi structured interviews were conducted and analysed using framework analysis. Results: Access to GPs may be more difficult for failed asylum seekers and those without support from refugee agencies or family. There may be concerns amongst some in the refugee community regarding the access to and confidentiality of professional interpreters. Most participants stated their preference for GPs who offered advice rather than prescriptions. The stigma associated with refugee status in the UK may have led to some refugees altering their help seeking behaviour. Conclusion: The problem of poor access for those with inadequate support may be improved by better education and support for GPs in how to provide for refugees. Primary Care Trusts could also supply information to newly arrived refugees on how to access services. GPs should be aware that, in some situations, professional interpreters may not always be desired and that instead, it may be advisable to reach a consensus as to who should be used as an interpreter. A better doctor-patient experience resulting from improvements in access and communication may help to reduce the stigma associated with refugee status and lead to more appropriate help seeking behaviour. Given the small nature of our investigation, larger studies need to be conducted to confirm and to quantify these results
Temperature and Kinematics of CIV Absorption Systems
We use Keck HIRES spectra of three intermediate redshift QSOs to study the
physical state and kinematics of the individual components of CIV selected
heavy element absorption systems. Fewer than 8 % of all CIV lines with column
densities greater than 10^{12.5} cm^{-2} have Doppler parameters b < 6 km/s. A
formal decomposition into thermal and non-thermal motion using the simultaneous
presence of SiIV gives a mean thermal Doppler parameter b_{therm}(CIV) = 7.2
km/s, corresponding to a temperature of 38,000 K although temperatures possibly
in excess of 300,000 K occur occasionally. We also find tentative evidence for
a mild increase of temperature with HI column density. Non-thermal motions
within components are typically small (< 10 km/s) for most systems, indicative
of a quiescent environment. The two-point correlation function (TPCF) of CIV
systems on scales up to 500 km/s suggests that there is more than one source of
velocity dispersion. The shape of the TPCF can be understood if the CIV systems
are caused by ensembles of objects with the kinematics of dwarf galaxies on a
small scale, while following the Hubble flow on a larger scale. Individual high
redshift CIV components may be the building blocks of future normal galaxies in
a hierarchical structure formation scenario.Comment: submitted to the ApJ Letters, March 16, 1996 (in press); (13 Latex
pages, 4 Postscript figures, and psfig.sty included
An Expansion Term In Hamilton's Equations
For any given spacetime the choice of time coordinate is undetermined. A
particular choice is the absolute time associated with a preferred vector
field. Using the absolute time Hamilton's equations are
+ (\delta H_{c})/(\delta \pi)=\dot{q}\Theta = V^{a}_{.;a}N\equiv exp(-\int\Theta d \ta)\pi^{N}\pi^N$. Briefly the possibility of a non-standard sympletic form
and the further possibility of there being a non-zero Finsler curvature
corresponding to this are looked at.Comment: 10 page
Local Surface Density of the Galactic Disk from a 3-D Stellar Velocity Sample
We have re-estimated the surface density of the Galactic disk in the solar
neighborhood within 0.4 kpc of the Sun using parallaxes and proper
motions of a kinematically and spatially unbiased sample of 1476 old bright red
giant stars from the Hipparcos catalog with measured radial velocities from
Barbier-Brossat & Figon (2000). We determine the vertical distribution of the
red giants as well as the vertical velocity dispersion of the sample, (14.4
0.26 km/sec), and combine these to derive the surface density of
gravitating matter in the Galactic disk as a function of the galactic
coordinate . The surface density of the disk increases from 10.5 0.5
/ pc within 50 pc to 42 6 / pc
within 350 pc. The estimated volume density of the galactic disk within
50 pc is about 0.1 / pc which is close to the volume
density estimates of the observed baryonic matter in the solar neighborhood.Comment: 24 pages, 15 figures, AJ in pres
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