18,817 research outputs found
A Search for Intrinsic Polarization in O Stars with Variable Winds
New observations of 9 of the brightest northern O stars have been made with
the Breger polarimeter on the 0.9~m telescope at McDonald Observatory and the
AnyPol polarimeter on the 0.4~m telescope at Limber Observatory, using the
Johnson-Cousins UBVRI broadband filter system. Comparison with earlier
measurements shows no clearly defined long-term polarization variability. For
all 9 stars the wavelength dependence of the degree of polarization in the
optical range can be fit by a normal interstellar polarization law. The
polarization position angles are practically constant with wavelength and are
consistent with those of neighboring stars. Thus the simplest conclusion is
that the polarization of all the program stars is primarily interstellar.
The O stars chosen for this study are generally known from ultraviolet and
optical spectroscopy to have substantial mass loss rates and variable winds, as
well as occasional circumstellar emission. Their lack of intrinsic polarization
in comparison with the similar Be stars may be explained by the dominance of
radiation as a wind driving force due to higher luminosity, which results in
lower density and less rotational flattening in the electron scattering inner
envelopes where the polarization is produced. However, time series of
polarization measurements taken simultaneously with H-alpha and UV spectroscopy
during several coordinated multiwavelength campaigns suggest two cases of
possible small-amplitude, periodic short-term polarization variability, and
therefore intrinsic polarization, which may be correlated with the more widely
recognized spectroscopic variations.Comment: LaTeX2e, 22 pages including 11 tables; 12 separate gif figures; uses
aastex.cls preprint package; accepted by The Astronomical Journa
Investigation of fast initialization of spacecraft bubble memory systems
Bubble domain technology offers significant improvement in reliability and functionality for spacecraft onboard memory applications. In considering potential memory systems organizations, minimization of power in high capacity bubble memory systems necessitates the activation of only the desired portions of the memory. In power strobing arbitrary memory segments, a capability of fast turn on is required. Bubble device architectures, which provide redundant loop coding in the bubble devices, limit the initialization speed. Alternate initialization techniques are investigated to overcome this design limitation. An initialization technique using a small amount of external storage is demonstrated
Loss-tolerant operations in parity-code linear optics quantum computing
A heavy focus for optical quantum computing is the introduction of
error-correction, and the minimisation of resource requirements. We detail a
complete encoding and manipulation scheme designed for linear optics quantum
computing, incorporating scalable operations and loss-tolerant architecture.Comment: 8 pages, 6 figure
Electron-scattering form factors for 6Li in the ab initio symmetry-guided framework
We present an ab initio symmetry-adapted no-core shell-model description for
Li. We study the structure of the ground state of Li and the impact
of the symmetry-guided space selection on the charge density components for
this state in momentum space, including the effect of higher shells. We
accomplish this by investigating the electron scattering charge form factor for
momentum transfers up to fm. We demonstrate that this
symmetry-adapted framework can achieve significantly reduced dimensions for
equivalent large shell-model spaces while retaining the accuracy of the form
factor for any momentum transfer. These new results confirm the previous
outcomes for selected spectroscopy observables in light nuclei, such as binding
energies, excitation energies, electromagnetic moments, E2 and M1 reduced
transition probabilities, as well as point-nucleon matter rms radii.Comment: 10 pages, 7 figures; accepted to Physical Review
Perceptions and Attitudes Are Primary Contributors to Insulin Delivery System Satisfaction in People with Type 2 Diabetes
Abstract Background: This study identifies factors that influence satisfaction with an insulin delivery system (IDS). Knowledge of such factors could help identify individuals who would benefit from innovative IDS. Methods: Individuals with type 2 diabetes who use insulin, recruited from a general and chronic illness panel, participated in a web-based survey that included questions about demographics, self-reported diagnoses and hemoglobin A1c (HbA1c), current IDS used, insulin therapy attitudes, current IDS features, and satisfaction with IDS. Univariate analyses identified variables associated with IDS satisfaction (P<0.05); those variables were entered into stepwise linear regression analyses with IDS satisfaction as the dependent variable. Results: Six hundred sixty-seven individuals with type 2 diabetes participated (mean age, 57 years; 52% female; 88% Caucasian; 73% vial/syringe users, 27% insulin pen users). IDS satisfaction was associated (P<0.05) with gender, health status, HbA1c, self-reported comorbidity, insulin therapy attitudes, IDS type, and evaluation of IDS features. Among individuals who reported their HbA1c (n=438), the best predictors of IDS satisfaction were perceived effectiveness and value of insulin therapy, evaluation of IDS activity interference, and commitment to insulin therapy (R2=0.49, P<0.001). Among all participants (n=667), a second regression analysis that employed a variable representing report of HbA1c found the best predictors of IDS satisfaction included those in the first analysis with the addition of gender, report of HbA1c, and evaluation of IDS ease of use. These variables provided additional variance (R2=0.56, P<0.001). Conclusions: In people with type 2 diabetes, positive perceptions and attitudes about insulin therapy have greater influence than the type of IDS used on IDS satisfaction.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78124/1/dia.2008.0123.pd
The phase transition in the localized ferromagnet EuO probed by muSR
We report results of muon spin rotation measurements performed on the
ferromagnetic semiconductor EuO, which is one of the best approximations to a
localized ferromagnet. We argue that implanted muons are sensitive to the
internal field primarily through a combination of hyperfine and Lorentz fields.
The temperature dependences of the internal field and the relaxation rate have
been measured and are compared with previous theoretical predictions.Comment: 4 pages, 4 figure
Anomalous temperature evolution of the internal magnetic field distribution in the charge-ordered triangular antiferromagnet AgNiO2
Zero-field muon-spin relaxation measurements of the frustrated triangular
quantum magnet AgNiO2 are consistent with a model of charge disproportionation
that has been advanced to explain the structural and magnetic properties of
this compound. Below an ordering temperature of T_N=19.9(2) K we observe six
distinct muon precession frequencies, due to the magnetic order, which can be
accounted for with a model describing the probable muon sites. The precession
frequencies show an unusual temperature evolution which is suggestive of the
separate evolution of two opposing magnetic sublattices.Comment: 4 pages, 3 figure
Thermodynamic and magnetic properties of the layered triangular magnet NaNiO2
We report muon-spin rotation, heat capacity, magnetization, and ac magnetic
susceptibility measurements of the layered spin-1/2 antiferromagnet NaNiO2.
These show the onset of long-range magnetic order below T_N = 19.5K. Rapid muon
depolarization persisting to about 5K above T_N is consistent with the presence
of short-range magnetic order. The temperature and frequency dependence of the
ac susceptibility suggests that magnetic clusters persist above 25K in the
paramagnetic state and that their volume fraction decreases with increasing
temperature. A frequency dependent peak in the ac magnetic susceptibility at
T_sf = 3K is observed, consistent with a slowing of spin fluctuations at this
temperature. A partial magnetic phase diagram is deduced.Comment: 4 pages, 4 figure
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