11,990 research outputs found
Fluorescence visualization of a convective instability which modulates the spreading of volatile surface films
The spontaneous spreading of a thin liquid film along the surface of a deep liquid layer of higher surface tension is a ubiquitous process which provides rapid and efficient surface transport of organic or biological material. For a source of constant concentration, the leading edge of a nonvolatile, immiscible film driven to spread by gradients in surface tension is known to advance as t^3/4 in time. Recent experiments using laser shadowgraphy to detect the advancing front of spreading films indicate, however, that immiscible but volatile sources of constant concentration spread with a reduced exponent according to t^1/2. Using a novel technique whereby fluorescent lines are inscribed in water, we have detected the evolution of a thermal instability beneath the leading edge of volatile films which strongly resembles a Rayleigh-BĂ©nard roll. We propose that the increased dissipation from this rotational flow structure is likely responsible for the reduction in spreading exponent. This observation suggests a conceptual framework for coupling the effects of evaporation to the dynamics of spreading
A 6-12 GHz Analogue Lag-Correlator for Radio Interferometry
Aims: We describe a 6-12 GHz analogue correlator that has been developed for
use in radio interferometers. Methods: We use a lag-correlator technique to
synthesis eight complex spectral channels. Two schemes were considered for
sampling the cross-correlation function, using either real or complex
correlations, and we developed prototypes for both of them. We opted for the
``add and square'' detection scheme using Schottky diodes over the more
commonly used active multipliers because the stability of the device is less
critical. Results: We encountered an unexpected problem, in that there were
errors in the lag spacings of up to ten percent of the unit spacing. To
overcome this, we developed a calibration method using astronomical sources
which corrects the effects of the non-uniform sampling as well as gain error
and dispersion in the correlator.Comment: 14 pages, 21 figures, accepted for publication in A&
A 6-12 GHz Analogue Lag-Correlator for Radio Interferometry
Aims: We describe a 6-12 GHz analogue correlator that has been developed for
use in radio interferometers. Methods: We use a lag-correlator technique to
synthesis eight complex spectral channels. Two schemes were considered for
sampling the cross-correlation function, using either real or complex
correlations, and we developed prototypes for both of them. We opted for the
``add and square'' detection scheme using Schottky diodes over the more
commonly used active multipliers because the stability of the device is less
critical. Results: We encountered an unexpected problem, in that there were
errors in the lag spacings of up to ten percent of the unit spacing. To
overcome this, we developed a calibration method using astronomical sources
which corrects the effects of the non-uniform sampling as well as gain error
and dispersion in the correlator.Comment: 14 pages, 21 figures, accepted for publication in A&
Cryogenic microstripline-on-Kapton microwave interconnects
Simple broadband microwave interconnects are needed for increasing the size
of focal plane heterodyne radiometer arrays. We have measured loss and
cross-talk for arrays of microstrip transmission lines in flex circuit
technology at 297 and 77 K, finding good performance to at least 20 GHz. The
dielectric constant of Kapton substrates changes very little from 297 to 77 K,
and the electrical loss drops. The small cross-sectional area of metal in a
printed circuit structure yields overall thermal conductivities similar to
stainless steel coaxial cable. Operationally, the main performance tradeoffs
are between crosstalk and thermal conductivity. We tested a patterned ground
plane to reduce heat flux.Comment: 3 pages, 3 figures, submitted to The Review of Scientific Instrument
A Deep ROSAT HRI Observation of NGC 1313
We describe a series of observations of NGC 1313 using the ROSAT HRI with a
combined exposure time of 183.5 ksec. The observations span an interval between
1992 and 1998; the purpose of observations since 1994 was to monitor the X-ray
flux of SN1978K, one of several luminous sources in the galaxy. No diffuse
emission is detected in the galaxy to a level of ~1-2x10^37 ergs/s/arcmin^-2. A
total of eight sources are detected in the summed image within the D_25
diameter of the galaxy. The luminosities of five of the eight range from
\~6x10^37 to ~6x10^38 erg/s; these sources are most likely accreting X-ray
binaries, similar to sources obseved in M31 and M33. The remaining three
sources all emit above 10^39 erg/s. We present light curves of the five
brightest sources. Variability is detected at the 99.9% level from four of
these. We identify one of the sources as an NGC 1313 counterpart of a Galactic
X-ray source. The light curve, though crudely sampled, most closely resembles
that of a Galactic black hole candidate such as GX339-4, but with considerably
higher peak X-ray luminosity. An additional seven sources lie outside of the
D_25 diameter and are either foreground stars or background AGN.Comment: 18 pages, 9 figures; accepted AJ, scheduled for November 200
Women Talking about Water: Feminist Subjectivities and Intersectional Understandings
In this study based on discussions held by women\u27s groups across Canada on water challenges and interests, we recognized that in the current context in Canada, women are truly connected with peoples, humans or any other form of life. They recognize that water is socially embedded, integrating issues of social, ecological and intergenerational justice in relation to complex changes in riparian landscapes. Clearly their talk is from a gender perspective, but we also found movement beyond gender that nuanced cross-sectoral understanding, critical links between gender, class and ethnicity are frequently mentioned
Make Art Real
The Make Art Real project aims to introduce new audiences to the arts. It supports Theme II of VCU’s Quest for Distinction by promoting and fostering creative expression through innovative collaborations. The project involves displaying existing connections between art and non-art disciplines, as well as making new connections. These unusual pairings are then placed on exhibition through a lunch-time lecture series named “Unexpected_Connections,” which allow faculty, staff, and students to lead and participate in discussions about the reality of art. The lecture series is the first sustainable and reoccurring program to be held in the Depot building, a multidisciplinary facility which is intended to foster interdisciplinary collaborations. The targeted audience includes faculty, staff, students, and members of the greater VCU community
Degenerate dispersive equations arising in the study of magma dynamics
An outstanding problem in Earth science is understanding the method of
transport of magma in the Earth's mantle. Models for this process, transport in
a viscously deformable porous media, give rise to scalar degenerate,
dispersive, nonlinear wave equations. We establish a general local
well-posedness for a physical class of data (roughly ) via fixed point
methods. The strategy requires positive lower bounds on the solution. This is
extended to global existence for a subset of possible nonlinearities by making
use of certain conservation laws associated with the equations. Furthermore, we
construct a Lyapunov energy functional, which is locally convex about the
uniform state, and prove (global in time) nonlinear dynamic stability of the
uniform state for any choice of nonlinearity. We compare the dynamics to that
of other problems and discuss open questions concerning a larger range of
nonlinearities, for which we conjecture global existence.Comment: 27 Pages, 7 figures are not present in this version. See
http://www.columbia.edu/~grs2103/ for a PDF with figures. Submitted to
Nonlinearit
Prevalence and severity of abscesses and cellulitis, and their associations with other health outcomes, in a community-based study of people who inject drugs in London, UK.
BACKGROUND: Skin and soft tissue infections (SSTI) are a common but preventable cause of morbidity and mortality among people who inject drugs (PWID). They can be severe, and hospitalisations of PWID with SSTI are rising. The most common SSTI presentations are abscesses and cellulitis. METHODS: We used data from Care & Prevent, a cross-sectional community survey of PWID in London. We reported the lifetime prevalence of SSTI, severity of infections, key risk factors, and associated sequelae. Pictorial questions were used to assess SSTI severity. RESULTS: We recruited 455 PWID. SSTI lifetime prevalence was high: 64% reported an abscess and/or cellulitis. Over one-third (37%) reported a severe infection, 137 (47%) reported hospitalisation. SSTIrisk factors were: aged 35+ years, injecting once or more times a day, subcutaneous or intra-muscular injections, and making four or more attempts to achieve an injection. Those who reported having other health conditions were at higher odds of having an abscess or cellulitis, with risk tending to increase with number of reported conditions. Half (46%) employed self-care for their worst SSTI, and 43% waited for ten or more days before seeking medical care or not seeking medical care at all. CONCLUSIONS: Abscess and cellulitis are very common among PWID in London. We corroborate findings indicating SSTIs are associated with risks, e.g. venous access problems, as well as other co-morbid conditions: septicaemia, endocarditis, DVT, and kidney disease. These co-morbidities may impact SSTIs severity and outcomes. Delayed healthcare seeking potentially exacerbates infection severity, which in turn increases poorer health outcomes and complications
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