2,588 research outputs found
The North Carolina A and T State University Student Space Shuttle Program
Inspired into being in 1979 by the late astronaut, Dr. Ronald McNair, the primary goal of this student centered program is to perform two experiments, Arthopod Development Study and Crystal Growth Study. Since 1979, 78 different students representing 12 majors have participated in every phase of development of the payload -- from coming up with the original ideas to final fabrication and testing. Students have also been involved in many extra activities such as presenting their results at annual meetings and hosting tours of our lab for local schools. The program has received extensive outside support in the form of funds, technical assistance and donated parts. The payload, made primarily out of aluminum, consists of a central column structure, a battery box, a crystal growth box, an arthropod development box, four control circuit boxes, and a thermograph box. The battery box contains 24, Eveready 6V, Alkaline batteries. The thermograph box contains 3 Ryan TempMentors. Fabrication of the payload is essentially complete and a complete testing program has been initiated
Complete spatial characterization of an optical wavefront using a variable-separation pinhole pair
We present a technique for measuring the transverse spatial properties of an
optical wavefront. Intensity and phase profiles are recovered by analysis of a
series of interference patterns produced by the combination of a scanning
X-shaped slit and a static horizontal slit; the spatial coherence may be found
from the same data. We demonstrate the technique by characterizing high
harmonic radiation generated in a gas cell, however the method could be
extended to a wide variety of light sources.Comment: 4 pages, 3 figures, 1 tabl
Drifter studies in warm core rings
The results of multiple deployments of surface drifters in warm core
rings of the Gulf Stream are presented. Four satellite drifters (tracked by
the Argos system) were deployed on nine separate occasions and two LORAN-C
drifters (operated by the University of Miami) were deployed three times.
Drifter studies were conducted during four cruises aboard the R/V Endeavor in
1982 in conjunction with the Warm Core Rings Experiment and one cruise of the
USNS Bartlett in January 1983 which was sponsored by the Office of Naval
Research. Translational velocities and periods of rotation are provided for
two rings: 82B and 82H.National Science Foundation
under grant OCE80-1698
Riccati type transformations for second-order linear difference equations
AbstractOscillation and comparison theorems for a linear homogeneous second-order difference equation are proved by employing various equivalent non-linear equations obtained by means of transformations analogous to the Riccati transformation for ordinary differential equations
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Emerg Infect Dis
Nucleophilic aromatic substitution (S<sub>N</sub>Ar) is widely used by organic chemists to functionalize aromatic molecules, and it is the most commonly used method to generate arenes that contain <sup>18</sup>F for use in positron-emission tomography (PET) imaging<sup>1</sup>. A wide range of nucleophiles exhibit S<sub>N</sub>Ar reactivity, and the operational simplicity of the reaction means that the transformation can be conducted reliably and on large scales<sup>2</sup>. During S<sub>N</sub>Ar, attack of a nucleophile at a carbon atom bearing a ‘leaving group’ leads to a negatively charged intermediate called a Meisenheimer complex. Only arenes with electron-withdrawing substituents can sufficiently stabilize the resulting build-up of negative charge during Meisenheimer complex formation, limiting the scope of S<sub>N</sub>Ar reactions: the most common S<sub>N</sub>Ar substrates contain strong π-acceptors in the ortho and/or para position(s)<sup>3</sup>. Here we present an unusual concerted nucleophilic aromatic substitution reaction (CS<sub>N</sub>Ar) that is not limited to electron-poor arenes, because it does not proceed via a Meisenheimer intermediate. We show a phenol deoxyfluorination reaction for which CS<sub>N</sub>Ar is favoured over a stepwise displacement. Mechanistic insights enabled us to develop a functional-group-tolerant <sup>18</sup>F−deoxyfluorination reaction of phenols, which can be used to synthesize <sup>18</sup>F-PET probes. Selective <sup>18</sup>F introduction, without the need for the common, but cumbersome, azeotropic drying of <sup>18</sup>F, can now be accomplished from phenols as starting materials, and provides access to <sup>18</sup>F-labelled compounds not accessible through conventional chemistry
Combined visible and near-infrared OPA for wavelength scaling experiments in strong-field physics
We report the operation of an optical parametric amplifier (OPA) capable of
producing gigawatt peak-power laser pulses with tunable wavelength in either
the visible or near-infrared spectrum. The OPA has two distinct operation modes
(i) generation of >350 uJ, sub 100 fs pulses, tunable between 1250 - 1550 nm;
(ii) generation of >190 uJ, sub 150 fs pulses tunable between 490 - 530 nm. We
have recorded high-order harmonic spectra over a wide range of driving
wavelengths. This flexible source of femtosecond pulses presents a useful tool
for exploring the wavelength-dependence of strong-field phenomena, in both the
multi-photon and tunnel ionization regimes.Comment: 14 pages, 9 figures, This paper was published in Proceedings of SPIE
10088, Nonlinear Frequency Generation and Conversion: Materials and Devices
XVI, doi 10.1117/12.225077
Perinatal outcomes of frequent attendance in midwifery care in the Netherlands: a retrospective cohort study
Background Over the last decade, a trend towards high utilisation of primary maternity care was observed in high-income countries. There is limited research with contradictory results regarding frequent attendance (FA) and perinatal outcomes in midwifery care. Therefore, this study examined possible associations between FA in midwifery care and obstetric interventions and perinatal outcomes. Methods A retrospective cohort study was performed in a medium-sized midwifery-led care practice in an urban region in the Netherlands. Frequent attenders (FAs) were categorised using the Kotelchuck-Index Revised. Regression analyses were executed to examine the relationship between FAs and perinatal outcomes, stratified by antenatal referral to an obstetrician. Main outcomes of interest were Apgar score ≤ 7 and perinatal death, birth weight, mode of delivery, haemorrhage, place of birth, transfer during labour, and a requirement for pain relief. Results The study included 1015 women, 239 (24%) FAs and 776 (76%) non-FAs, 538 (53%) were not referred and 447 (47%) were referred to an obstetrician. In the non-referred group, FA was significantly associated with a requirement for pain relief (OR 1.98, 95% CI 1.24–3.17) and duration of dilatation (OR 1.20, 95% CI 1.04–1.38). In the referred group, FA was significantly associated with induction of labour (OR 1.86, 95% CI 1.17–2.95), ruptured perineum (OR 0.50, 95% CI 0.27–0.95) and episiotomy (OR 0.48, 95% CI 0.24–0.95). In the non-referred and the referred group, FA was not associated with the other obstetric and neonatal outcomes. Due to small numbers, we could not measure possible associations of FA with an Apgar score ≤ 7 and perinatal death. Conclusion In our study, perinatal outcomes differed by FA and antenatal referral to an obstetrician. In the non-referred group, FA was significantly associated with medical pain relief and duration of dilatation. In the referred group, FA was significantly associated with induction of labour, ruptured perineum, and episiotomy. Further research with a larger study population is needed to look for a possible association between FA and primary adverse birth outcomes such as perinatal mortality
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Amygdala Response to Facial Expressions Reflects Emotional Learning
The functional role of the human amygdala in the evaluation of emotional facial expressions is unclear. Previous animal and human research shows that the amygdala participates in processing positive and negative reinforcement as well as in learning predictive associations between stimuli and subsequent reinforcement. Thus, amygdala response to facial expressions could reflect the processing of primary reinforcement or emotional learning. Here, using functional magnetic resonance imaging, we tested the hypothesis that amygdala response to facial expressions is driven by emotional association learning. We show that the amygdala is more responsive to learning object-emotion associations from happy and fearful facial expressions than it is to the presentation of happy and fearful facial expressions alone. The results provide evidence that the amygdala uses social signals to rapidly and flexibly learn threatening and rewarding associations that ultimately serve to enhance survival.Psycholog
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