208 research outputs found
Constraining the extra heating of the Diffuse Ionized Gas in the Milky Way
The detailed observations of the diffuse ionized gas through the emission
lines H, [NII], and [SII] in the Perseus Arm of our Galaxy by the
Wisconsin H Mapper (WHAM)--survey challenge photoionization models.
They have to explain the observed rise in the line ratios [NII]/H and
[SII]/H. The models described here consider for the first time the
detailed observational geometry toward the Perseus Arm. The models address the
vertical variation of the line ratios up to height of 2 kpc above the midplane.
The rising trends of the line ratios are matched. The increase in the line
ratios is reflected in a rise of the temperature of the gas layer. This is due
to the progressive hardening of the radiation going through the gas. However an
extra heating above photoionization is needed to explain the absolute values.
Two different extra heating rates are investigated which are proportional to
and . The models show that a combination of both are best to explain
the data, where the extra heating independent of density is dominant for z
0.8 kpc.Comment: accepted for publication in Ap
Practical Application of a One-Parameter Approach to Assess the Accuracy of Two Different Estimates of Diet Composition in Sheep
The composition of ingested herbage mixtures can be estimated using the alkane technique (Dove & Moore, 1995). Until now, the accuracy of the estimates is assessed by linear regression of estimated and actual proportions of the dietary components. The authors presented an approach to compare actual and estimated diet compositions using only one parameter named Distance (D; Elwert & Rodehutscord, 2005), thus enabling a statement regarding the similarity of estimated and known diet composition. In a feeding trial with sheep, diet composition was estimated using two different levels of information. The accuracy of the two estimates was assessed and compared using Distance
Theoretical Considerations on a One-Parameter Approach to Compare Actual and Estimated Compositions of Multi-Component Diets
The composition of ingested herbage mixtures can be estimated using the alkane technique (Dove & Moore, 1995), with the accuracy of the estimate assessed by linear regression of estimated and actual proportions of the dietary components (Dove, 1992). However, although the linear regression might not differ from the line of equality, large discrepancies may occur within individual components (Hoebee et al., 1998). This paper presents an approach to compare actual and estimated diet compositions using only one parameter
Generalized Regularization Techniques With Constraints For The Analysis Of Solar Bremsstrahlung X-Ray Spectra
Hard X-ray spectra in solar flares provide knowledge of the electron spectrum
that results from acceleration and propagation in the solar atmosphere.
However, the inference of the electron spectra from solar X-ray spectra is an
ill-posed inverse problem. Here we develop and apply an enhanced regularization
algorithm for this process making use of physical constraints on the form of
the electron spectrum. The algorithm incorporates various features not
heretofore employed in the solar flare context: Generalized Singular Value
Decomposition (GSVD) to deal with different orders of constraints; rectangular
form of the cross-section matrix to extend the solution energy range;
regularization with various forms of the smoothing operator; and
"preconditioning" of the problem. We show by simulations that this technique
yields electron spectra with considerably more information and higher quality
than previous algorithms.Comment: 21 pages, 8 fugures, accepted to Solar Physic
On the Dynamic Stability of Cool Supergiant Atmospheres
We have developed a new formalism to compute the thermodynamic coefficient
Gamma1 in the theory of stellar and atmospheric stability. We generalize the
classical derivation of the first adiabatic index, which is based on the
assumption of thermal ionization and equilibrium between gas and radiation
temperature, towards an expression which incorporates photo-ionization due to
radiation with a temperature T_rad different from the local kinetic gas
temperature.Our formalism considers the important non-LTE conditions in the
extended atmospheres of supergiant stars. An application to the Kurucz grid of
cool supergiant atmospheres demonstrates that models with T_rad =~ T_eff
between 6500 K and 7500 K become most unstable against dynamic perturbations,
according to Ledoux' stability integral . This results from Gamma1 and
acquiring very low values, below 4/3, throughout the entire stellar
atmosphere, which causes very high gas compression ratios around these
effective temperatures. Based on detailed NLTE-calculations, we discuss
atmospheric instability of pulsating massive yellow supergiants, like the
hypergiant rho Cas (Ia+), which exist in the extension of the Cepheid
instability strip, near the Eddington luminosity limit.Comment: 54 pages including figures and the Appendix, 7 figures, Accepted for
The Astrophysical Journal, Main Journal, 558, Sept. 200
X-Ray Polarization of Solar Flares Measured with Rhessi
The degree of linear polarization in solar flares has not yet been precisely
determined despite multiple attempts to measure it with different missions. The
high energy range in particular has very rarely been explored, due to its
greater instrumental difficulties. We approached the subject using the Reuven
Ramaty High Energy Spectroscopic Imager (RHESSI) satellite to study 6 X-class
and 1 M-class flares in the energy range between 100 keV and 350 keV. Using
RHESSI as a polarimeter requires the application of strict cuts to the event
list in order to extract those photons that are Compton scattered between two
detectors. Our measurements show polarization values between 2% and 54%, with
errors ranging from 10% to 26% in 1 sigma level. In view of the large
uncertainties in both the magnitude and direction of the polarization vector,
the results can only reject source models with extreme properties.Comment: 26 pages, 11 figures, accepted for publication by Solar Physic
Widowhood and Mortality: A Meta-Analysis
While the "widowhood effect" is well known, there is substantial heterogeneity in the magnitude of effects reported in different studies. We conducted a meta-analysis of widowhood and mortality, focusing on longitudinal studies with follow-up from the time of bereavement.A random-effects meta-analysis was conducted to calculate the overall relative risk (RR) for subsequent mortality among 2,263,888 subjects from 15 prospective cohort studies. We found a statistically significant positive association between widowhood and mortality, but the widowhood effect was stronger in the period earlier than six months since bereavement (overall RRâ=â1.41, 95% CI: 1.26, 1.57) compared to the effect after six months (overall RRâ=â1.14, 95% CI: 1.10, 1.18). Meta-regression showed that the widowhood effect was not different for those aged younger than 65 years compared to those older than 65 (Pâ=â0.25). There was, however, a difference in the magnitude of the widowhood effect by gender; for women the RR was not statistically significantly different from the null (overall RRâ=â1.04, 95% CI: 1.00, 1.08), while it was for men (overall RRâ=â1.23, 95% CI: 1.18, 1.28).The results suggest that further studies should focus more on the mechanisms that generate this association especially among men
Adaptive model-driven user interface development systems
Adaptive user interfaces (UIs) were introduced to address some of the usability problems that plague many software applications. Model-driven engineering formed the basis for most of the systems targeting the development of such UIs. An overview of these systems is presented and a set of criteria is established to evaluate the strengths and shortcomings of the state-of-the-art, which is categorized under architectures, techniques, and tools. A summary of the evaluation is presented in tables that visually illustrate the fulfillment of each criterion by each system. The evaluation identified several gaps in the existing art and highlighted the areas of promising improvement
Using plant wax markers to estimate the diet composition of grazing Holstein dairy cows
The objective of this study was to test whether diet selection of dairy cows under grazing conditions could be estimated using plant wax markers. Furthermore, differences between 2 cow strains and the effect of concentrate supplementation on plant species selection were investigated. The experiment was a study with a crossover design performed on an organic farm with 12 Swiss Holstein cows and 12 New Zealand Holstein cows. Both experimental periods consisted of a 21-d adaptation and a 7-d measurement period. All cows grazed full time in a rotational stocking system and received either no concentrate or 6 kg/d of a commercial cereal-grain mix. Representative herbage samples of each grazed paddock were taken and botanical composition of subsamples was manually determined. The average proportions of the plant species were 27.8% Lolium perenne, 6.1% Dactylis glomerata, 10.4% Trifolium repens, and 9.0% Taraxacum officinale. Other grass species were merged as "other grass" (38.2%) and other forb species as "other forbs" (8.5%). n-Alkanes, long-chain fatty acids, and long-chain alcohols (LCOH) were analyzed in the samples of plant species, concentrate, and feces from each cow. A linear discriminant analysis indicated that diet components were differentiated best with LCOH (96%) and worst with the combination of all marker groups together (12%). For each marker, the fecal marker recovery (FR) relative to dosed ytterbium was determined in 2 ways. Estimation of diet composition was performed with the software "EatWhat," and results were compared with botanical composition with the Aitchison distance. The results indicate that the diet composition of grazing dairy cows can be estimated using plant wax markers. Additionally, the calculation of FR led to mostly reliable results, yet this approach needs further validation. The most accurate estimation was achieved with the marker combination of n-alkanes and LCOH with a correction for FR. Less accurate estimations were achieved with long-chain fatty acids alone or in combination with n-alkanes. No difference relating to diet selection between the 2 cow strains was recorded, but supplemented cows apparently ingested higher proportions of T. repens than nonsupplemented cows. Awareness that supplementation influences selection behavior of grazing dairy cows may lead to adaptations in botanical composition of the pasture according to the demand of the animals
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