The metallicity of gamma-ray burst environments from high energy observations

Gamma-ray bursts (GRBs) and their early afterglows ionise their circumburst material. Only high-energy spectroscopy therefore, allows examination of the matter close to the burst itself. Soft X-ray absorption allows an estimate to be made of the total column density in metals. The detection of the X-ray afterglow can also be used to place a limit on the total gas column along the line of sight based on the Compton scattering opacity. Such a limit would enable, for the first time, the determination of lower limits on the metallicity in the circumburst environments of GRBs. In this paper, we determine the limits that can be placed on the total gas column density in the vicinities of GRBs based on the Compton scattering. We simulate the effects of Compton scattering on a collimated beam of high energy photons passing through a shell of high column density material to determine the expected lightcurves, luminosities, and spectra. We compare these predictions to observations, and determine what limits can realistically be placed on the total gas column density. The smearing out of pulses in the lightcurve from Compton scattering is not likely to be observable, and its absence does not place strong constraints on the Compton depth for GRBs. However, the distribution of observed luminosities of bursts allows us to place statistical, model-dependent limits that are typically <~1e25 cm^{-2} for less luminous bursts, and as low as ~1e24 cm$^{-2} for the most luminous. Using the shape of the high-energy broadband spectrum, however, in some favourable cases, limits as low as ~5e24 cm^{-2} can placed on individual bursts, implying metallicity lower limits from X- and gamma-rays alone from 0 up to 0.01 Z/Zsun. At extremely high redshifts, this limit would be at least 0.02 Z/Z_sun, enough to discriminate population III from non-primordial GRBs.Comment: 4 pages, 4 figures, submitted to A&A letter

Grid of Lya radiation transfer models for the interpretation of distant galaxies

Lya is a key diagnostic for numerous observations of distant star-forming galaxies. It's interpretation requires, however, detailed radiation transfer models. We provide an extensive grid of 3D radiation transfer models simulating the Lya and UV continuum radiation transfer in the interstellar medium of star-forming galaxies. We have improved our Monte Carlo MCLya code, and have used it to compute a grid of 6240 radiation transfer models for homogeneous spherical shells containing HI and dust surrounding a central source. The simulations cover a wide range of parameter space. We present the detailed predictions from our models including in particular the Lya escape fraction fesc, the continuum attenuation, and detailed Lya line profiles. The Lya escape fraction is shown to depend strongly on dust content, but also on other parameters (HI column density and radial velocity). The predicted line profiles show a great diversity of morphologies ranging from broad absorption lines to emission lines with complex features. The results from our simulations are distributed in electronic format. Our models should be of use for the interpretation of observations from distant galaxies, for other simulations, and should also serve as an important base for comparison for future, more refined, radiation transfer models.Comment: Accepted for publication in Astronomy & Astrophysics. Results from simulations available at http://obswww.unige.ch/sf

Stabilizing the surface morphology of Si1–x–yGexCy/Si heterostructures grown by molecular beam epitaxy through the use of a silicon-carbide source

Si1–x–yGexCy/Si superlattices were grown by solid-source molecular beam epitaxy using silicon carbide as a source of C. Samples consisting of alternating layers of nominally 25 nm Si1–x–yGexCy and 35 nm Si for 10 periods were characterized by high-resolution x-ray diffraction, transmission electron microscopy (TEM), and Rutherford backscattering spectrometry to determine strain, thickness, and composition. C resonance backscattering and secondary ion mass spectrometries were used to measure the total C concentration in the Si1–x–yGexCy layers, allowing for an accurate determination of the substitutional C fraction to be made as a function of growth rate for fixed Ge and substitutional C compositions. For C concentrations close to 1%, high-quality layers were obtained without the use of Sb-surfactant mediation. These samples were found to be structurally perfect to a level consistent with cross-sectional TEM (< 10^7 defects/cm^2) and showed considerably improved homogeneity as compared with similar structures grown using graphite as the source for C. For higher Ge and C concentrations, Sb-surfactant mediation was found to be required to stabilize the surface morphology. The maximum value of substitutional C concentration, above which excessive generation of stacking fault defects caused polycrystalline and/or amorphous growth, was found to be approximately 2.4% in samples containing between 25 and 30% Ge. The fraction of substitutional C was found to decrease from roughly 60% by a factor of 0.86 as the Si1–x–yGexCy growth rate increased from 0.1 to 1.0 nm/s

Determining the Authenticity of the Concerto for Two Horns, Woo 19, Attributed to Ferdinand Ries

Ferdinand Ries is credited as the composer of the Concerto for Two Horns, WoO. 19 preserved in the Berlin State Library. Dated 1811, ostensibly Ries wrote it in the same year as his Horn Sonata, Op. 34, yet the writing for the horns in the Concerto is significantly more demanding. Furthermore, Ries added to the mystery by not claiming the Concerto in his personal catalog of works or mentioning it in any surviving correspondence. The purpose of this dissertation is to study the authorship of the Concerto for Two Horns and offer possible explanations for the variance in horn writing. Biographical information of Ries is given followed by a stylistic analysis of Ries’s known works. A stylistic analysis of the Concerto for Two Horns, WoO. 19 is offered, including a handwriting comparison between the Concerto for Two Horns and Ries’s Horn Sonata. Finally, possible explanations are proposed that rationalize the variance in horn writing between the Concerto for Two Horns, WoO. 19 and Ries’s other compositions that include the horn

A Study on Optimization and Evaluation of the Visualization of Complex Algorithm Results in Remote Monitoring of COPD

BACKGROUND: Artificial intelligence (AI) can potentially increase the quality of telemonitoring in chronic obstructive pulmonary disease (COPD). However, the output from AI is often difficult for clinicians to understand due to the complexity. This challenge may be accommodated by visualizing the AI results, however it hasn't been studied how this could be done specifically, i.e., considering which visual elements to include.AIM: To investigate how complex results from a predictive algorithm for patients with COPD can be translated into easily understandable data for the clinicians.METHODS: Semi-structured interviews were conducted to explore clinicians' needs when visualizing the results of a predictive algorithm. This formed a basis for creating a prototype of an updated user interface. The user interface was evaluated using usability tests through the "Think aloud" method.RESULTS: The clinicians pointed out the need for visualization of exacerbation alerts and the development in patients' data. Furthermore, they wanted the system to provide more information about what caused exacerbation alerts. Elements such as color and icons were described as particularly useful. The usability of the prototype was primarily assessed as easily understandable and advantageous in connection to the functions of the predictive algorithm.CONCLUSION: Predictive algorithm use in telemonitoring of COPD can be optimized by clearly visualizing the algorithm's alerts, clarifying the reasons for algorithm output, and by providing a clear overview of the development in the patient's data. This can contribute to clarity when the clinicians should act and why they should act on alerts from predictive algorithms.</p

Selecting and Testing Cryptogam Species for Use in Wetland Delineation in Alaska

To support the determination of hydrophytic vegetation in wetland delineations in Alaska, USA, a series of tests were conducted to develop a group of “test positive” species to be used in a “cryptogam indicator.” In 2004, non-vascular cryptogam species (bryophytes, lichens, and fungi) from Interior and South-Central Alaska in the vicinities of Fairbanks and Anchorage were collected at a series of ten 50 × 50 cm plots along two 30 m transects in each of six upland and five wetland sites. Nineteen moss and liverwort species were selected from 86 species surveyed to test for wetland fidelity. In 2005, a plot-based analysis of frequency and cover data yielded a revised list of 17 bryophyte species that were specific to wetland communities dominated by black spruce, Picea mariana (P. Mill.) B.S.P. Fungi and lichens were found to be inadequate wetland indicators in the sampled locations because the lichen species were sparsely distributed and the fungi were too ephemeral. The cryptogam indicator was thus restricted to bryophytes. Also in 2005, bryophytes were analyzed for their presence on microtopographic positions within the landscape, including tops of hummocks and hollows at the bases of hummocks. Upland bryophyte species were found on hummock tops inside the wetland boundary, but were not abundant in the hollows (p &lt; 0.05). The fidelity of the species selected for use in the cryptogam indicator was tested. It was determined that if more than 50% of all bryophyte cover present in hollows is composed of one or more of the 17 wetland bryophytes tested in 2005, then vascular vegetation can be considered to be hydrophytic (p &lt; 0.001).Afin d’étayer la présence de végétation hydrophytique dans les délimitations de zones humides de l’Alaska, aux États-Unis, une série de tests a été effectuée dans le but d’aboutir à un groupe d’espèces « de test positives » à utiliser avec un « indicateur de sporophyte ». En 2004, des espèces de sporophytes non vasculaires (bryophytes, lichens et champignons) de l’intérieur et du centre-sud de l’Alaska, aux environs de Fairbanks et d’Anchorage, ont été recueillies à une série de dix parcelles de 50 sur 50 cm le long de deux transects de 30 m dans chacun de six sites montagnards et de cinq sites humides. Dix-neuf espèces de mousse et d’hépatiques ont été choisies à partir de 86 espèces prélevées dans le but d’en déterminer la fidélité aux zones humides. En 2005, une analyse de fréquence de parcelles et des données de couverture ont permis d’obtenir la liste révisée de 17 espèces de bryophytes propres aux zones humides dominées par l’épinette noire, Picea mariana (P. Mill.) B.S.P. Nous avons constaté que les champignons et les lichens étaient des indicateurs de zones humides inadéquats aux sites échantillonnés parce que les espèces de lichen étaient réparties maigrement et que les champignons étaient trop éphémères. Par conséquent, l’indicateur de sporophytes a été restreint aux bryophytes. Également en 2005, nous avons analysé les bryophytes afin d’en déterminer la présence à des positions microtopographiques du paysage, ce qui comprenait le sommet de hummocks et les creux à la base de hummocks. Des espèces de bryophytes montagnardes ont été décelées aux sommets de hummocks à l’intérieur de la limite des zones humides, mais celles-ci n’abondaient pas dans les creux (p &lt; 0.05). La fidélité des espèces choisies afin d’être utilisées dans l’indicateur de sporophytes a été testée. Nous avons déterminé que si plus de 50 % de toute la couverture de bryophyte présente dans les creux est composée de l’une ou plusieurs des 17 bryophytes de zones humides testées en 2005, la végétation vasculaire peut alors être considérée comme hydrophytique (p &lt; 0,001)

Cooling and the SU(2) Instanton Vaccuum

We present results of an investigation into the nature of instantons in 4-dimensional pure gauge lattice $SU(2)$\ obtained from configurations which have been cooled using an under-relaxed cooling algorithm. We discuss ways of calibrating the cooling and the effects of different degrees of cooling, and compare our data for the shapes, sizes and locations of instantons with continuum results. In this paper we extend the ideas and techniques developed by us for use in $O(3)$, and compare the results with those obtained by other groups.Comment: 22 pages, LaTeX, uuencoded compressed tarfile of figures sent separately. Full (compressed) postscript version (118k)available from ftp://rock.helsinki.fi/pub/preprints/tft/Year1995/HU-TFT-95-21/paper.ps.