Impact of water vapor diffusion and latent heat on the effective thermal conductivity of snow

Heat transport in snowpacks is understood to occur through the two processes of heat conduction and latent heat transport carried by water vapor, which are generally treated as decoupled from one another. This paper investigates the coupling between both these processes in snow, with an emphasis on the impacts of the kinetics of the sublimation and deposition of water vapor onto ice. In the case when kinetics is fast, latent heat exchanges at ice surfaces modify their temperature and therefore the thermal gradient within ice crystals and the heat conduction through the entire microstructure. Furthermore, in this case, the effective thermal conductivity of snow can be expressed by a purely conductive term complemented by a term directly proportional to the effective diffusion coefficient of water vapor in snow, which illustrates the inextricable coupling between heat conduction and water vapor transport. Numerical simulations on measured three-dimensional snow microstructures reveal that the effective thermal conductivity of snow can be significantly larger, by up to about 50 % for low-density snow, than if water vapor transport is neglected. A comparison of our numerical simulations with literature data suggests that the fast kinetics hypothesis could be a reasonable assumption for modeling heat and mass transport in snow. Lastly, we demonstrate that under the fast kinetics hypothesis the effective diffusion coefficient of water vapor is related to the effective thermal conductivity by a simple linear relationship. Under such a condition, the effective diffusion coefficient of water vapor is expected to lie in the narrow 100 % to about 80 % range of the value of the diffusion coefficient of water vapor in air for most seasonal snows. This may greatly facilitate the parameterization of water vapor diffusion of snow in models.</p

A simple evaluation tool (ET-CET) indicates increase of diagnostic skills from Small bowel capsule endoscopy training courses: A prospective observational european multicenter study

Small bowel capsule endoscopy (SBCE) has become a first line diagnostic tool. Several training courses with a similar format have been established in Europe; however, data on learning curve and training in SBCE remain sparse. Between 2008 and 2011, different basic SBCE training courses were organized internationally in UK (n=2), Italy (n= 2), Germany (n=2), Finland (n=1), and nationally in Germany (n=10), applying similar 8-hour curricula with 50% lectures and 50% hands-on training. The Given PillCam System was used in 12 courses, the Olympus EndoCapsule system in 5, respectively. A simple evaluation tool for capsule endoscopy training (ET-CET) was developed using 10 short SBCE videos including relevant lesions and normal or irrelevant findings. For each video, delegates were required to record a diagnosis (achievable total score from 0 to 10) and the clinical relevance (achievable total score 0 to 10). ET-CET was performed at baseline before the course and repeated, with videos in altered order, after the course. Two hundred ninety-four delegates (79.3% physicians, 16.3% nurses, 4.4% others) were included for baseline analysis, 268 completed the final evaluation. Forty percent had no previous experience in SBCE, 33% had performed 10 or less procedures. Median scores for correct diagnosis improved from 4.0 (IQR 3) to 7.0 (IQR 3) during the courses (P&lt;0.001, Wilcoxon), and for correct classification of relevance of the lesions from 5.0 (IQR 3) to 7.0 (IQR 3) (P&lt;0.001), respectively. Improvement was not dependent on experience, profession, SBCE system, or course setting. Previous experience in SBCE was associated with higher baseline scores for correct diagnosis (P&lt; 0.001; Kruskal-Wallis). Additionally, independent nonparametric partial correlation with experience in gastroscopy (rho 0.33) and colonoscopy (rho 0.27) was observed (P&lt;0.001). A simple ET-CET demonstrated significant improvement of diagnostic skills on completion of formal basic SBCE courses with hands-on training, regardless of preexisting experience, profession, and course setting. Baseline scores for correct diagnoses show a plateau after interpretation of 25 SBCE before courses, supporting this number as a compromise for credentialing. Experience in flexible endoscopy may be useful before attending an SBCE course

Structure and Ionic Conductivity in the Mixed-Network Former Chalcogenide Glass System [Na2S]2/3[(B2S3)x(P2S5)1–x]1/3

Glasses in the system [Na2S]2/3[(B2S3)x(P2S5)1–x]1/3 (0.0 ≤ x ≤ 1.0) were prepared by the melt quenching technique, and their properties were characterized by thermal analysis and impedance spectroscopy. Their atomic-level structures were comprehensively characterized by Raman spectroscopy and 11B, 31P, and 23Na high resolution solid state magic-angle spinning (MAS) NMR techniques. 31P MAS NMR peak assignments were made by the presence or absence of homonuclear indirect 31P–31P spin–spin interactions as detected using homonuclear J-resolved and refocused INADEQUATE techniques. The extent of B–S–P connectivity in the glassy network was quantified by 31P{11B} and 11B{31P} rotational echo double resonance spectroscopy. The results clearly illustrate that the network modifier alkali sulfide, Na2S, is not proportionally shared between the two network former components, B and P. Rather, the thiophosphate (P) component tends to attract a larger concentration of network modifier species than predicted by the bulk composition, and this results in the conversion of P2S74–, pyrothiophosphate, Na/P = 2:1, units into PS43–, orthothiophosphate, Na/P = 3:1, groups. Charge balance is maintained by increasing the net degree of polymerization of the thioborate (B) units through the formation of covalent bridging sulfur (BS) units, B–S–B. Detailed inspection of the 11B MAS NMR spectra reveals that multiple thioborate units are formed, ranging from neutral BS3/2 groups all the way to the fully depolymerized orthothioborate (BS33–) species. On the basis of these results, a comprehensive and quantitative structural model is developed for these glasses, on the basis of which the compositional trends in the glass transition temperatures (Tg) and ionic conductivities can be rationalized. Up to x = 0.4, the dominant process can be described in a simplified way by the net reaction equation P1 + B1 P0 + B4, where the superscripts denote the number of BS atoms for the respective network former species. Above x = 0.4, all of the thiophosphate units are of the P0 type and both pyro- (B1) and orthothioborate (B0) species make increasing contributions to the network structure with increasing x. In sharp contrast to the situation in sodium borophosphate glasses, four-coordinated thioborate species are generally less abundant and heteroatomic B–S–P linkages appear to not exist. On the basis of this structural information, compositional trends in the ionic conductivities are discussed in relation to the nature of the charge-compensating anionic species and the spatial distribution of the charge carriers

Medical Imaging Gastroenterology And Hepatology

viii.229 hal;23 c

ERCP -Key for diagnosis in the cholestasis syndrome

In presence of a choleslasis syndrome there exists a diagnostic necessity of success since the elimination of an extrahepatic cause avoids invalidism. With some experience the ERCP is a nearly riskless examination with high efficacy which is but little inconvenient for the patient and which is in an optimum way suited for differentiation of an obstructive jaundice. In single cases therapeutic interventions can immediately follow the diagnostic. The ERCP shall therefore be the first different intervention for etiological clearing of a cholestasis

Determination of the loudness dependence of auditory evoked potentials: single-electrode estimation versus dipole source analysis

Objective: The loudness dependence of auditory evoked potentials (LDAEP) has been described as a measure of central serotonergic activity. Single-electrode estimation and dipole source analysis (DSA) are the most utilized methods for the estimation of LDAEP. To date, it is assumed that both methods are equally reliable. Nevertheless, according to our knowledge, the advantage of either method has not yet been shown directly. The aim of our study was to compare single-electrode estimation and dipole source analysis in the determination of the LDAEP. Methods: Tones of five different intensities were presented binaurally to 10 healthy volunteers. Amplitudes of N1/P2 and LDAEP were determined at the central electrode site referenced to average and to linked mastoids and with DSA in the left and the right hemispheres. Scores were normalized (z-scores), compared, and correlated. Results: Contrary to our expectations, we found a significant difference between scores obtained with single-electrode estimation and with DSA. Conclusion: The difference may be caused by confounding activation of a frontal source in the single-electrode method. The single-electrode approach cannot be equated with DSA in the determination of the LDAEP. This should be considered when comparing the results of different LDAEP studies using only one of these methods

Medical Imaging in Gastroenterology and Hepatology

x. 235 hlm.; ill.; 24 c

La neige en tant que matériau granulaire : évaluation d'un nouvel algorithme de segmentation en grains

International audienceRapid deformations in snow are mainly con- trolled by particle rearrangements and contact interactions. To study this deformation regime, the description of the snow microstructure in terms of grains, which could eventually be handled by discrete element models, is relevant. In practice, microtomography has become a standard method to image the three-dimensional distribution of ice and pores, as a set of binary voxels. Here, we propose a new method to directly identify individual snow grains defined as zones separated by regions of potential mechanical weakness, in the microtomo- graphic images. In general, these grains are not well sepa- rated but rather sintered together. Our new method, based on local geometrical criteria, is shown to detect contacts directly inferred from an explicit numerical mechanical experiment. The developed algorithm is tested on snow but is generic and applicable to various geomaterials with a granular-like microstructure