11,706 research outputs found
Fringe Science: Defringing CCD Images with Neon Lamp Flat Fields
Fringing in CCD images is troublesome from the aspect of photometric quality
and image flatness in the final reduced product. Additionally, defringing
during calibration requires the inefficient use of time during the night to
collect and produce a "supersky" fringe frame. The fringe pattern observed in a
CCD image for a given near-IR filter is dominated by small thickness variations
across the detector with a second order effect caused by the wavelength extent
of the emission lines within the bandpass which produce the interference
pattern. We show that essentially any set of emission lines which generally
match the wavelength coverage of the night sky emission lines within a bandpass
will produce an identical fringe pattern. We present an easy, inexpensive, and
efficient method which uses a neon lamp as a flat field source and produces
high S/N fringe frames to use for defringing an image during the calibration
process.Comment: accepted to PAS
Women's experiences of pregnancy, childbirth, and the postnatal period in the Gambia: A qualitative study
Objective: In sub-Saharan African countries, there are unique cultural factors and adverse physical conditions that contribute to women's experiences of pregnancy and birth. The objective of this study was to qualitatively explore women's experiences of pregnancy, childbirth, the postnatal period, and maternal psychological distress in The Gambia.
Design and methods: Semi-structured interviews were carried out with 55 women who had given birth within the previous year.
Results: Thematic analysis identified five themes: (1) transition to adulthood, (2) physical difficulties, (3) value of children in relation to others, (4) children as a strain, and (5) going through it alone. The results suggest that having a child is a defining point in women's lives associated with happiness and joy. However, women also described situations which could lead to unhappiness and distress in the perinatal period. A child conceived out of wedlock or a baby girl can be sources of distress because of negative cultural perceptions. The strain of having a child, particularly the additional financial burden, and minimal support from men were also a concern for women. Finally, women recognized the danger associated with delivery and expressed recurrent worries of complications during childbirth which could result in the death of them or the baby.
Conclusions: Further research is needed to identify women vulnerable to psychological distress so that health services and target interventions can be developed accordingly
On some singularities of the correlation functions that determine neutrino opacities
Certain perturbation graphs in the calculation of the effects of the medium
on neutrino scattering in supernova matter have a nonintegrable singularity in
a physical region. A number of papers have addressed the apparent pathology
through an ansatz that invokes higher order (rescattering) effects. Taking the
Gamow-Teller terms as an example, we display an expression for the spin-spin
correlation function that determines the cross-sections. It is clear from the
form that there are no pathologies in the order by order perturbation
expansion. Explicit formulae are given for a simple case, leading to an answer
that is very different from one given by other authors.Comment: 8 page
Seasonal Activity, Population Characteristics, and Age Estimation in the Aquatic Salamander, Siren intermedia nettingi (Goin)
We conducted a study of the Western Lesser Siren (Siren intermedia nettinigi), at a locality termed the Airport Road site in Jonesboro (Craighead County, AR) from November 2004 until March 2007. This site consisted of a network of roadside ditches in cultivated lawns in an industrial park. Even though sirens are known to occur frequently in ditches, most studies of the genus Siren have taken place in natural wetlands. We compiled mark-recapture data at the Airport Road site for each season to determine if the seasonal activity pattern for sirens in northeast Arkansas varied from activity data previously published from other localities in the range of this species. Capture rates were higher in the fall and spring. The predicted overall population size was 110 sirens at a density of 0.81 sirens per linear m. This density was less than the densities (in sirens/m2 ) reported by previous studies. We found two prominent peaks in sirens per size class: the first at 161-170 mm, and the second at 201-210 mm. Other researchers have assumed that the two most abundant size classes in siren populations represent one-year-old and two-year-old cohorts. The sirens captured at the Airport Road site are smaller, on average, than those reported in previous population studies. We found no significant difference between the growth rates of sirens larger than 200 mm SVL and those smaller than 200 mm snout-vent length (= SVL; P = 0.957, confidence interval -1.945, 2.045, n = 16). Our mean growth rates did not significantly differ from growth rates reported for sirens elsewhere. We sectioned siren humeri to identify and quantify lines of arrested growth (LAGs) as part of a skeletochronological analysis. The use of SVL was a poor indicator of number of LAGs. The difference in the weather pattern history in each of the voucher sirens used likely resulted in broad ranges of LAGs for each SVL size class
Gravitational Radiation Instability in Hot Young Neutron Stars
We show that gravitational radiation drives an instability in hot young
rapidly rotating neutron stars. This instability occurs primarily in the l=2
r-mode and will carry away most of the angular momentum of a rapidly rotating
star by gravitational radiation. On the timescale needed to cool a young
neutron star to about T=10^9 K (about one year) this instability can reduce the
rotation rate of a rapidly rotating star to about 0.076\Omega_K, where \Omega_K
is the Keplerian angular velocity where mass shedding occurs. In older colder
neutron stars this instability is suppressed by viscous effects, allowing older
stars to be spun up by accretion to larger angular velocities.Comment: 4 Pages, 2 Figure
A flight investigation with a STOL airplane flying curved, descending instrument approach paths
A flight investigation using a De Havilland Twin Otter airplane was conducted to determine the configurations of curved, 6 deg descending approach paths which would provide minimum airspace usage within the requirements for acceptable commercial STOL airplane operations. Path configurations with turns of 90 deg, 135 deg, and 180 deg were studied; the approach airspeed was 75 knots. The length of the segment prior to turn, the turn radius, and the length of the final approach segment were varied. The relationship of the acceptable path configurations to the proposed microwave landing system azimuth coverage requirements was examined
Assessing the UK policies for broadband adoption
Broadband technology has been introduced to the business community and the public as a rapid way of exploiting the Internet. The benefits of its use (fast reliable connections, and always on) have been widely realised and broadband diffusion is one of the items at the top of the agenda for technology related polices of governments worldwide. In this paper an examination of the impact of the UK governmentâs polices upon broadband adoption is undertaken. Based on institutional theory a consideration of the manipulation of supply push and demand pull forces in the diffusion of broadband is offered. Using primary and secondary data sources, an analysis of the specific institutional actions related to IT diffusion as pursued by the UK government in the case of broadband is provided. Bringing the time dimension into consideration it is revealed that the UK government has shifted its attention from supply push-only strategies to more interventional ones where the demand pull forces are also mobilised. It is believed that this research will assist in the extraction of the âsuccess factorsâ in government intervention that support the diffusion of technology with a view to render favourable results if applied to other national settings
Observation of Quantum Effects in sub Kelvin Cold Reactions
There has been a long-standing quest to observe chemical reactions at low
temperatures where reaction rates and pathways are governed by quantum
mechanical effects. So far this field of Quantum Chemistry has been dominated
by theory. The difficulty has been to realize in the laboratory low enough
collisional velocities between neutral reactants, so that the quantum wave
nature could be observed. We report here the first realization of merged
neutral supersonic beams, and the observation of clear quantum effects in the
resulting reactions. We observe orbiting resonances in the Penning ionization
reaction of argon and molecular hydrogen with metastable helium leading to a
sharp increase in the absolute reaction rate in the energy range corresponding
to a few degrees kelvin down to 10 mK. Our method is widely applicable to many
canonical chemical reactions, and will enable a breakthrough in the
experimental study of Quantum Chemistry
Spin susceptibility of neutron matter at zero temperature
The Auxiliary Field Diffusion Monte Carlo method is applied to compute the
spin susceptibility and the compressibility of neutron matter at zero
temperature. Results are given for realistic interactions which include both a
two-body potential of the Argonne type and the Urbana IX three-body potential.
Simulations have been carried out for about 60 neutrons. We find an overall
reduction of the spin susceptibilty by about a factor 3 with respect to the
Pauli susceptibility for a wide range of densities. Results for the
compressibility of neutron matter are also presented and compared with other
available estimates obtained for semirealistic nucleon-nucleon interactions by
using other techniques
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