20,838 research outputs found
Characterization of Si/Si_(1-y)C_y superlattices grown by surfactant assisted molecular beam epitaxy
Si/Si_(0.97)C_(0.03) superlattices grown on Si(001) substrates by Sb surfactant assisted molecular beam epitaxy are characterized by in situ reflection high energy electron diffraction (RHEED), atomic force microscopy, transmission electron microscopy (TEM), and high resolution xâray diffraction. The RHEED shows that, in the absence of Sb, the growth front roughens during Si_(0.97)C_(0.03) growth and smooths during subsequent Si growth. In contrast, when Sb is present, the growth front remains smooth throughout the growth. This observation is confirmed by crossâsectional TEM, which reveals that for samples grown without the use of Sb, the Si/Si_(0.97)C_(0.03) interfaces (Si_(0.97)C_(0.03) on Si) are much more abrupt than the Si_(0.97)C_(0.03)/Si interfaces. In the case of Sb assisted growth, there is no observable difference in abruptness between the two types of interfaces. Atomic force microscopy micrographs of the Si_(0.97)C_(0.03) surface reveal features that could be the source of the roughness observed by RHEED and TEM
Sb-surfactant-mediated growth of Si/Si1âyCy superlattices by molecular-beam epitaxy
Si/Si0.97C0.03 superlattices were grown on Si(001) substrates by molecular beam epitaxy (MBE) to study the use of Sb as a surfactant during Si1âyCy growth. In situ reflection high energy electron diffraction (RHEED) shows that while carbon easily disrupts the two-dimensional growth of homoepitaxial Si, such disruption is suppressed for layers grown on Sb-terminated Si(001) surfaces. Cross-sectional transmission electron microscopy (TEM) reveals that for samples grown without the use of Sb, the Si/Si0.97C0.03 interfaces (Si0.97C0.03 on Si) were much more abrupt than Si0.97C0.03/Si interfaces. In the case of Sb-mediated growth, differences in abruptness between the two types of interfaces were not readily observable
Portable dynamic fundus instrument
A portable diagnostic image analysis instrument is disclosed for retinal funduscopy in which an eye fundus image is optically processed by a lens system to a charge coupled device (CCD) which produces recordable and viewable output data and is simultaneously viewable on an electronic view finder. The fundus image is processed to develop a representation of the vessel or vessels from the output data
Submillimeter Array multiline observations of the massive star-forming region IRAS 18089-1732
Submillimeter Array (SMA) observations of the high-mass star-forming region
IRAS 18089-1732 in the 1 mm and 850 m band with 1 GHz bandwidth reveal a
wealth of information. We present the observations of 34 lines from 16
different molecular species. Most molecular line maps show significant
contributions from the outflow, and only few molecules are confined to the
inner core. We present and discuss the molecular line observations and outline
the unique capabilities of the SMA for future imaging line surveys at high
spatial resolution.Comment: Accepted for ApJ Letters, SMA special volum
SMA outflow/disk studies in the massive star-forming region IRAS18089-1732
SMA observations of the massive star-forming region IRAS 18089-1732 in the
1mm and 850mu band reveal outflow and disk signatures in different molecular
lines. The SiO(5--4) data show a collimated outflow in the northern direction.
In contrast, the HCOOCH3(20--19) line, which traces high-density gas, is
confined to the very center of the region and shows a velocity gradient across
the core. The HCOOCH3 velocity gradient is not exactly perpendicular to the
outflow axis but between an assumed disk plane and the outflow axis. We
interpret these HCOOCH3 features as originating from a rotating disk that is
influenced by the outflow and infall. Based on the (sub-)mm continuum emission,
the mass of the central core is estimated to be around 38M_sun. The dynamical
mass derived from the HCOOCH3 data is 22Msun, of about the same order as the
core mass. Thus, the mass of the protostar/disk/envelope system is dominated by
its disk and envelope. The two frequency continuum data of the core indicate a
low dust opacity index beta ~ 1.2 in the outer part, decreasing to beta ~ 0.5
on shorter spatial scales.Comment: 7 pages of text, 1 table, 3 figures, accepted for ApJ Letter
Myoporum montanum R. Br.
https://thekeep.eiu.edu/herbarium_specimens_byname/21548/thumbnail.jp
Large Magnetic Fields and Motions of OH Masers in W75 N
We report on a second epoch of VLBA observations of the 1665 and 1667 MHz OH
masers in the massive star-forming region W75 N. We find evidence to confirm
the existence of very strong (~40 mG) magnetic fields near source VLA 2. The
masers near VLA 2 are dynamically distinct and include a very bright spot
apparently moving at 50 km/s relative to those around VLA 1. This fast-moving
spot may be an example of a rare class of OH masers seen in outflows in
star-forming regions. Due to the variability of these masers and the rapidity
of their motions, tracking these motions will require multiple observations
over a significantly shorter time baseline than obtained here. Proper motions
of the masers near VLA 1 are more suggestive of streaming along magnetized
shocks rather than Keplerian rotation in a disk. The motions of the easternmost
cluster of masers in W75 N (B) may be tracing slow expansion around an unseen
exciting source.Comment: 7 pages including 4 figures (2 color) & 3 tables, to appear in Ap
Polycyclic aromatic hydrocarbons in the dwarf galaxy IC 10
Infrared observations from the Spitzer Space Telescope archive are used to
study the dust component of the interstellar medium in the IC~10 irregular
galaxy. Dust distribution in the galaxy is compared to the distributions of
H and [SII] emission, neutral hydrogen and CO clouds, and ionizing
radiation sources. The distribution of polycyclic aromatic hydrocarbons (PAH)
in the galaxy is shown to be highly non-uniform with the mass fraction of these
particles in the total dust mass reaching 4%. PAHs tend to avoid bright HII
regions and correlate well with atomic and molecular gas. This pattern suggests
that PAHs form in the dense interstellar gas. We propose that the significant
decrease of the PAH abundance at low metallicity is observed not only globally
(at the level of entire galaxies), but also locally (at least, at the level of
individual HII regions). We compare the distribution of the PAH mass fraction
to the distribution of high-velocity features, that we have detected earlier in
wings of H and SII lines, over the entire available galaxy area. No
conclusive evidence for shock destruction of PAHs in the IC~10 galaxy could be
found.Comment: Accepted for publication in Astronomy Report
Colloidal stabilization via nanoparticle haloing
We present a detailed numerical study of effective interactions between
micron-sized silica spheres, induced by highly charged zirconia nanoparticles.
It is demonstrated that the effective interactions are consistent with a
recently discovered mechanism for colloidal stabilization. In accordance with
the experimental observations, small nanoparticle concentrations induce an
effective repulsion that counteracts the intrinsic van der Waals attraction
between the colloids and thus stabilizes the suspension. At higher nanoparticle
concentrations an attractive potential is recovered, resulting in reentrant
gelation. Monte Carlo simulations of this highly size-asymmetric mixture are
made possible by means of a geometric cluster Monte Carlo algorithm. A
comparison is made to results obtained from the Ornstein-Zernike equations with
the hypernetted-chain closure
Place matters: but does local leadership?
The arrival of New Labour into Government witnessed the prominent re-emergence of place onto the policy agenda. This heralded a range of area-based-initiatives designed to both tackle neighbourhood forms of deprivation and to re-establish a sense of identity and connection between individuals and their local community. In terms of place-making, effective and inclusive participation, representation and leadership were all identified as prerequisites for the creation of sustainable communities . But how important is local leadership and strategic vision within local public service organisations in achieving the desired place-making outcomes? This paper examines the extent to which local leadership and strategic vision represents a significant factor in promoting higher levels of satisfaction, belonging, cohesion and participation across single tier councils in England. The ensuing empirical evidence raises significant questions not only about the importance of local leadership in place-making, but also the environmental and organizational factors that shape local places
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