To wet or not to wet: that is the question

Wetting transitions have been predicted and observed to occur for various combinations of fluids and surfaces. This paper describes the origin of such transitions, for liquid films on solid surfaces, in terms of the gas-surface interaction potentials V(r), which depend on the specific adsorption system. The transitions of light inert gases and H2 molecules on alkali metal surfaces have been explored extensively and are relatively well understood in terms of the least attractive adsorption interactions in nature. Much less thoroughly investigated are wetting transitions of Hg, water, heavy inert gases and other molecular films. The basic idea is that nonwetting occurs, for energetic reasons, if the adsorption potential's well-depth D is smaller than, or comparable to, the well-depth of the adsorbate-adsorbate mutual interaction. At the wetting temperature, Tw, the transition to wetting occurs, for entropic reasons, when the liquid's surface tension is sufficiently small that the free energy cost in forming a thick film is sufficiently compensated by the fluid- surface interaction energy. Guidelines useful for exploring wetting transitions of other systems are analyzed, in terms of generic criteria involving the "simple model", which yields results in terms of gas-surface interaction parameters and thermodynamic properties of the bulk adsorbate.Comment: Article accepted for publication in J. Low Temp. Phy

The Cholecystectomy As A Day Case (CAAD) Score: A Validated Score of Preoperative Predictors of Successful Day-Case Cholecystectomy Using the CholeS Data Set

Background Day-case surgery is associated with significant patient and cost benefits. However, only 43% of cholecystectomy patients are discharged home the same day. One hypothesis is day-case cholecystectomy rates, defined as patients discharged the same day as their operation, may be improved by better assessment of patients using standard preoperative variables. Methods Data were extracted from a prospectively collected data set of cholecystectomy patients from 166 UK and Irish hospitals (CholeS). Cholecystectomies performed as elective procedures were divided into main (75%) and validation (25%) data sets. Preoperative predictors were identified, and a risk score of failed day case was devised using multivariate logistic regression. Receiver operating curve analysis was used to validate the score in the validation data set. Results Of the 7426 elective cholecystectomies performed, 49% of these were discharged home the same day. Same-day discharge following cholecystectomy was less likely with older patients (OR 0.18, 95% CI 0.15–0.23), higher ASA scores (OR 0.19, 95% CI 0.15–0.23), complicated cholelithiasis (OR 0.38, 95% CI 0.31 to 0.48), male gender (OR 0.66, 95% CI 0.58–0.74), previous acute gallstone-related admissions (OR 0.54, 95% CI 0.48–0.60) and preoperative endoscopic intervention (OR 0.40, 95% CI 0.34–0.47). The CAAD score was developed using these variables. When applied to the validation subgroup, a CAAD score of ≤5 was associated with 80.8% successful day-case cholecystectomy compared with 19.2% associated with a CAAD score >5 (p < 0.001). Conclusions The CAAD score which utilises data readily available from clinic letters and electronic sources can predict same-day discharges following cholecystectomy

Characteristics of the 7-GeV advanced photon source: A guide for users

In this document we present the characteristics of the electromagnetic radiation from various types of sources on the 7-GeV Advanced Photon Source (APS) storage ring. The sources include bending magnets, undulators, and wigglers. The characteristics are compared with those of other synchrotron sources when operated at their design specifications. The influence of positron beam size on the on-axis brilliance is discussed, along with the power distribution from these sources. The goal of this document is to provide users with enough information on the characteristics of radiation from the APS storage ring so that experiments can be efficiently planned. 23 refs., 20 figs., 8 tabs

ELECTRONIC AND STRUCTURAL STUDIES OF THE HYDRIDES OF ErFe2 FROM 57Fe AND 166Er MÖSSBAUER SPECTROSCOPY

On étudie deux hydrures du composé intermétallique ErFe2 qui présente une phase de Laves C15. Les analyses par rayons X de ErFe2H3,65 révèlent la présence d'une phase cubique C15 dilatée et d'une phase de symétrie inférieure. Le champ hyperfin moyen à saturation pour 57Fe est 20% plus élevé que dans ErFe2 tandis que le champ hyperfin de 166Er est inférieur de 15%. Ces résultats, combinés aux mesures antérieures du moment total, impliquent que le couplage Er-Fe n'est pas anti-parallèle dans l'hydrure. Dans ErFe2H4,12 on ne détecte qu'une phase qui est compatible avec une structure trigonale. Les résultats Mössbauer suggèrent une température de transition magnétique entre 1,7 et 4,2 K et une réduction importante du moment du fer dans cet hydrure.Two different hydrides of the C15 Laves phase intermetallic ErFe2 are considered. For ErFe2H3.65, X-ray analyses showed the présence of an expanded C15 cubic phase and a lower symmetry phase. The 57Fe mean saturated hyperfine field is 20% larger than in ErFe2 and the 166Er hyperfine field is 15% smaller. Thèse results coupled with previous measurements of the net moment imply that the Er-Fe coupling is not antiparallel in this hydride. For ErFe2H4.12, the only phase detected was rhombobedral. The Mössbauer results indicate a magnetic transition temperature between 1.7 K and 4.2 K and a drastic reduction of the Fe moment in this hydride

57MÖSSBAUER STUDY OF Th7Fe3 AND THE HYDRIDE Th7Fe3H14.2

Th7Fe3 est un système paramagnétique de Pauli et est supraconducteur au-dessous de 1.86 K. Par contre, l'hydrure saturé Th7Fe3H30 présente un ordre magnétique. Pour l'hydrure stable de concentration intermédiaire Th7Fe3H14.2 que nous considérons ici, le champ hyperfin à saturation au site de 57Fe est d'environ 20 kG. Un déplacement isomérique positif de 0,30 ± 0,02 mm/s à 300 K par rapport à Th7Fe3 serait en accord avec une augmentation du caractère d au site de Fe causé par la présence d'hydrogène.Th7Fe3 is known to be a Pauli paramagnet and to undergo a superconducting transition at 1.86 K. In contrast, its saturated hydride Th7Fe3H30 shows magnetic ordering. For the stable hydride considered here of intermediate concentration Th7Fe3H14.2, the 57Fe saturated hyperfine field to estimate to be approximately 20 kG. A positive isomer shift of 0.30 ± 0.02 mm/s at 300 K relative to Th7Fe3 would be consistent with an increase of d character at the Fe site induced by hydrogen