3,919 research outputs found
A scanning tunneling microscopy based potentiometry technique and its application to the local sensing of the spin Hall effect
A scanning tunneling microscopy based potentiometry technique for the
measurements of the local surface electric potential is presented and
illustrated by experiments performed on current-carrying thin tungsten films.
The obtained results demonstrate a sub-millivolt resolution in the measured
surface potential. The application of this potentiometry technique to the local
sensing of the spin Hall effect is outlined and some experimental results are
reported.Comment: 9 pages and 4 figure
Si and Mn Abundances in Damped Lya Systems with Low Dust Content
We have measured the abundances of Zn, Si, Mn, Cr, Fe, and Ni in three damped
Lyman alpha systems at redshifts z < 1 from high resolution echelle spectra of
QSOs recorded with the Keck I telescope. In all three cases the abundances of
Cr, Fe, and Ni relative to Zn indicate low levels of dust depletions. We
propose that when the proportion of refractory elements locked up in dust
grains is less than about 50 percent, it is plausible to assume an
approximately uniform level of depletion for all grain constituents and, by
applying a small dust correction, recover the intrisic abundances of Si and Mn.
We use this approach on a small sample of damped systems for which it is
appropriate, with the aim of comparing the metallicity dependence of the ratios
[Si/Fe] and [Mn/Fe] with analogous measurements in Milky Way stars. The main
conclusion is that the relative abundances of both elements in distant galaxies
are broadly in line with expectations based on Galactic data. Si displays a
mild enhancement at low metallicities, as expected for an alpha-capture
element, but there are also examples of near-solar [Si/Fe] at [Fe/H] < -1. The
underabundance of Mn at low metallicities is possibly even more pronounced than
that in metal-poor stars, and no absorption system has yet been found where
[Mn/Fe] is solar. The heterogeneous chemical properties of damped Lyman alpha
systems, evident even from this limited set of measurements, provide further
support for the conclusion from imaging studies that a varied population of
galaxies gives rise to this class of QSO absorbers.Comment: 29 pages, LaTex, 7 Postscript Figures. Accepted for Publication in
the Astrophysical Journa
Squeezing in the audio gravitational wave detection band
We demonstrate the generation of broad-band continuous-wave optical squeezing
down to 200Hz using a below threshold optical parametric oscillator (OPO). The
squeezed state phase was controlled using a noise locking technique. We show
that low frequency noise sources, such as seed noise, pump noise and detuning
fluctuations, present in optical parametric amplifiers have negligible effect
on squeezing produced by a below threshold OPO. This low frequency squeezing is
ideal for improving the sensitivity of audio frequency measuring devices such
as gravitational wave detectors.Comment: 5 pages, 6 figure
Interstellar and Circumstellar Optical & Ultraviolet Lines Towards SN1998S
We have observed SN1998S which exploded in NGC3877, with the UES at the WHT
and with the E230M echelle of STIS aboard HST. Both data sets were obtained at
two seperate epochs. From our own Galaxy we detect interstellar absorption
lines of CaII, FeII, MgI, and probably MnII from the edge of the HVC Complex M.
We derive gas-phase abundances which are very similar to warm disk clouds in
the local ISM, which we believe argues against the HVC material having an
extragalactic origin. At the velocity of NGC3877 we detect interstellar MgI,
MgII, MnII, CaII, & NaI. Surprisingly, one component is seen to increase by a
factor of ~1 dex in N(NaI) and N(MgI) between the two epochs over which the
data were taken. Unusually, our data also show narrow Balmer, HeI, and
metastable FeII P-Cygni profiles, with a narrow absorption component
superimposed on the bottom of the profile's absorption trough. Both the broad
and narrow components of the optical lines are seen to increase substantially
in strength between the two epochs. Most of the low-ionization absorption can
be understood in terms of gas co-rotating with the disk of NGC 3877, providing
the SN is at the back of an HI disk with a similar thickness to that of our own
Galaxy. However, the variable absorption components, and the classic P-Cygni
emission profiles, most likely arise in slow-moving circumstellar outflows
originating from the red supergiant progenitor of SN1998S. [Abridged.]Comment: Accepted by ApJ, 26 pages including 9 figure
Assessment of non-contacting optical methods to measure wear and surface roughness in ceramic total disc replacements
This study presents a method for measuring the low volumetric wear expected in ceramic total disc replacements, which can be used to replace intervertebral discs in the spine, using non-contacting optical methods. Alumina-on-alumina ball-on-disc tests were conducted with test conditions approximating those of cervical (neck region of the spine) total disc replacement wear tests. The samples were then scanned using a three-dimensional non-contacting optical profilometer and the data used to measure surface roughness and develop a method for measuring the wear volume. The results showed that the magnification of the optical lens affected the accuracy of both the surface roughness and wear volume measurements. The method was able to successfully measure wear volumes of 0.0001mm3, which corresponds to a mass of 0.0001 mg, which would have been undetectable using the gravimetric method. A further advantage of this method is that with one scan the user can measure changes in surface topography, volumetric wear and the location of the wear on the implant surface. This method could also be applied to more severe wear, other types of orthopaedic implants and different materials
A Near-Solar Metallicity, Nitrogen-Deficient Lyman Limit Absorber Associated with two S0 Galaxies
From UV spectra of the bright quasar PHL 1811 recorded by FUSE and the E140M
configuration on STIS, we have determined the abundances of various atomic
species in a Lyman limit system at z = 0.0809 with log N(H I) = 17.98.
Considerably more hydrogen may be in ionized form, since the abundances of C
II, Si II, S II and Fe II are very large compared to that of O I, when compared
to their respective solar abundance ratios. Our determination [O/H] = -0.19 in
the H I-bearing gas indicates that the chemical enrichment of the gas is
unusually high for an extragalactic QSO absorption system. However, this same
material has an unusually low abundance of nitrogen, [N/O] < -0.59, indicating
that there may not have been enough time during this enrichment for secondary
nitrogen to arise from low and intermediate mass stars. In an earlier
investigation we found two galaxies at nearly the same redshift as this
absorption system and displaced by 34 and 87 kpc from the line of sight. An
r-band image recorded by the ACS on HST indicates these are S0 galaxies. One or
both of these galaxies may be the source of the gas, which might have been
expelled in a fast wind, by tidal stripping, or by ram-pressure stripping.
Subtraction of the ACS point-spread function from the image of the QSO reveals
the presence of a face-on spiral galaxy under the glare of the quasar; although
it is possible that this galaxy may be responsible for the Lyman limit
absorption, the exact alignment of the QSO with the center of the galaxy
suggests that the spiral is the quasar host.Comment: 74 pages, 14 figures; to be published in the Astrophysical Journal
(Part 1) May 1, 2005 issue. A version of the paper with figures of better
quality may be found at http://www.astro.princeton.edu/~ebj/PHL1811_paper.ps
(postscript) or http://www.astro.princeton.edu/~ebj/PHL1811_paper.pdf (pdf
- …