5,471 research outputs found
Magnetic Field Effects on the 1083 nm Atomic Line of Helium. Optical Pumping of Helium and Optical Polarisation Measurement in High Magnetic Field
The structure of the excited S and P triplet states of He
and He in an applied magnetic field B is studied using different
approximations of the atomic Hamiltonian. All optical transitions (line
positions and intensities) of the 1083 nm S-P transition are
computed as a function of B. The effect of metastability exchange collisions
between atoms in the ground state and in the S metastable state is
studied, and rate equations are derived, for the populations these states in
the general case of an isotopic mixture in an arbitrary field B. It is shown
that the usual spin-temperature description remains valid. A simple optical
pumping model based on these rate equations is used to study the B-dependence
of the population couplings which result from the exchange collisions. Simple
spectroscopy measurements are performed using a single-frequency laser diode on
the 1083 nm transition. The accuracy of frequency scans and of measurements of
transition intensities is studied. Systematic experimental verifications are
made for B=0 to 1.5 T. Optical pumping effects resulting from hyperfine
decoupling in high field are observed to be in good agreement with the
predictions of the simple model. Based on adequately chosen absorption
measurements at 1083 nm, a general optical method to measure the nuclear
polarisation of the atoms in the ground state in an arbitrary field is
described. It is demonstrated at 0.1 T, a field for which the usual
optical methods could not operate.Comment: 33 pages, 31 figures, 17 tables, 61 references. Revised version
(typos corrected, figure 11 replaced by the proper one) Accepted for
publication in EPJ
4-H club circular ; 025
Prepared by Miss Marion K. White, Extension Specialist in Nutrition, in collaboration with Miss Jane Hinote, Miss Margaret C. Huston and Miss Sara Chiles, Assistant State Club Agents, as a revision of the original material prepared by Miss Marion E. Dunshee, Extension Specialist in Nutrition."April, 1928" (Reprinted, January, 1930
Near-IR studies of recurrent nova V745 Scorpii during its 2014 outburst
The recurrent nova (RN) V745 Scorpii underwent its third known outburst on
2014 February 6. Infrared monitoring of the eruption on an almost daily basis,
starting from 1.3d after discovery, shows the emergence of a powerful blast
wave generated by the high velocity nova ejecta exceeding 4000 kms
plowing into its surrounding environment. The temperature of the shocked gas is
raised to a high value exceeding 10K immediately after outburst
commencement. The energetics of the outburst clearly surpass those of similar
symbiotic systems like RS Oph and V407 Cyg which have giant secondaries. The
shock does not show a free-expansion stage but rather shows a decelerative
Sedov-Taylor phase from the beginning. Such strong shockfronts are known to be
sites for ray generation. V745 Sco is the latest nova, apart from five
other known novae, to show ray emission. It may be an important
testbed to resolve the crucial question whether all novae are generically
ray emitters by virtue of having a circumbinary reservoir of material
that is shocked by the ejecta rather than ray generation being
restricted to only symbiotic systems with a shocked red giant (RG) wind. The
lack of a free-expansion stage favors V745 Sco to have a density enhancement
around the white dwarf (WD), above that contributed by a RG wind. Our analysis
also suggests that the WD in V745 Sco is very massive and a potential
progenitor for a future SN Ia explosion.Comment: To appear in ApJ (Letters
Measuring ^{12}C(&alpha,&gamma)^{16}O from White Dwarf Asteroseismology
During helium burning in the core of a red giant, the relative rates of the
3&alpha and ^{12}C(&alpha,&gamma)^{16}O reactions largely determine the final
ratio of carbon to oxygen in the resulting white dwarf star. The uncertainty in
the 3&alpha reaction at stellar energies due to the extrapolation from
high-energy laboratory measurements is relatively small, but this is not the
case for the ^{12}C(&alpha,&gamma)^{16}O reaction. Recent advances in the
analysis of asteroseismological data on pulsating white dwarf stars now make it
possible to obtain precise measurements of the central ratio of carbon to
oxygen, providing a more direct way to measure the ^{12}C(&alpha,&gamma)^{16}O
reaction rate at stellar energies. We assess the systematic uncertainties of
this approach and quantify small shifts in the measured central oxygen
abundance originating from the observations and from model settings that are
kept fixed during the optimization. Using new calculations of white dwarf
internal chemical profiles, we find a rate for the ^{12}C(&alpha,&gamma)^{16}O
reaction that is significantly higher than most published values. The accuracy
of this method may improve as we modify some of the details of our description
of white dwarf interiors that were not accessible through previous
model-fitting methods.Comment: 8 pages, 4 figures, 3 tables, uses emulateapj5.sty, Accepted for
publication in the Astrophysical Journa
Mental health promotion for young people - the case for yoga in schools
Peer reviewedPublisher PD
Coherent Bayesian inference on compact binary inspirals using a network of interferometric gravitational wave detectors
Presented in this paper is a Markov chain Monte Carlo (MCMC) routine for
conducting coherent parameter estimation for interferometric gravitational wave
observations of an inspiral of binary compact objects using data from multiple
detectors. The MCMC technique uses data from several interferometers and infers
all nine of the parameters (ignoring spin) associated with the binary system,
including the distance to the source, the masses, and the location on the sky.
The Metropolis-algorithm utilises advanced MCMC techniques, such as importance
resampling and parallel tempering. The data is compared with time-domain
inspiral templates that are 2.5 post-Newtonian (PN) in phase and 2.0 PN in
amplitude. Our routine could be implemented as part of an inspiral detection
pipeline for a world wide network of detectors. Examples are given for
simulated signals and data as seen by the LIGO and Virgo detectors operating at
their design sensitivity.Comment: 10 pages, 4 figure
Older Adolescents’ Understanding of Participant Rights in the BlackBerry Project, a Longitudinal Ambulatory Assessment Study
For a long‐term, longitudinal study that used BlackBerry smartphones for passive ambulatory assessment among older adolescents, this study focused on three areas of ethical concern: (1) adolescents’ competence to give assent; (2) understanding of confidentiality, the protection of information, and project goals; and (3) awareness of procedures and benefits, and comfort with the research design. One hundred and seventy‐eight participants were 17 and 18 years old (84 girls). Results suggested that participants freely gave consent and understood most, but not all of the informed consent information. Participants reported a high level of satisfaction. Participants showed less understanding of when their confidentiality would be broken and how data would be protected
How Adolescents Use Text Messaging Through their High School Years
Co‐construction theory suggests adolescents use digital communication to address developmental challenges. For a sample of 214 ethnically diverse adolescents, this research used direct observation to investigate the frequency, content, and timing of texting with parents, peers, and romantic partners through grades 9–12. Analyses showed that texting frequency follows a curvilinear trajectory, peaking in eleventh grade. Adolescents discussed a range of topics, predominantly with peers. Communication with parents was less frequent, but consistent over time. Approximately 45‐65% of adolescents communicated with romantic partners, texting heavily and about topics similar to those discussed with peers. Texting may help adolescents navigate key developmental challenges of adolescence—the establishment of autonomy, intimate peer relationships, romantic relationships, and self‐identity
Clinical stakeholders' opinions on the use of selective decontamination of the digestive tract in critically ill patients in intensive care units : an international Delphi study
Peer reviewedPublisher PD
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