On the elliptic nonabelian Fourier transform for unipotent representations of p-adic groups

In this paper, we consider the relation between two nonabelian Fourier transforms. The first one is defined in terms of the Langlands-Kazhdan-Lusztig parameters for unipotent elliptic representations of a split p-adic group and the second is defined in terms of the pseudocoefficients of these representations and Lusztig's nonabelian Fourier transform for characters of finite groups of Lie type. We exemplify this relation in the case of the p-adic group of type G_2.Comment: 17 pages; v2: several minor corrections, references added; v3: corrections in the table with unipotent discrete series of G

The structure of blocks with a Klein four defect group

We prove Erdmann’s conjecture [16] stating that every block with a Klein four defect group has a simple module with trivial source, and deduce from this that Puig’s finiteness conjecture holds for source algebras of blocks with a Klein four defect group. The proof uses the classification of finite simple groups

Adsorption and reaction of CO on (Pd–)Al2O3 and (Pd–)ZrO2: vibrational spectroscopy of carbonate formation

γ-Alumina is widely used as an oxide support in catalysis, and palladium nanoparticles supported by alumina represent one of the most frequently used dispersed metals. The surface sites of the catalysts are often probed via FTIR spectroscopy upon CO adsorption, which may result in the formation of surface carbonate species. We have examined this process in detail utilizing FTIR to monitor carbonate formation on γ-alumina and zirconia upon exposure to isotopically labelled and unlabelled CO and CO2. The same was carried out for well-defined Pd nanoparticles supported on Al2O3 or ZrO2. A water gas shift reaction of CO with surface hydroxyls was detected, which requires surface defect sites and adjacent OH groups. Furthermore, we have studied the effect of Cl synthesis residues, leading to strongly reduced carbonate formation and changes in the OH region (isolated OH groups were partly replaced or were even absent). To corroborate this finding, samples were deliberately poisoned with Cl to an extent comparable to that of synthesis residues, as confirmed by Auger electron spectroscopy. For catalysts prepared from Cl-containing precursors a new CO band at 2164 cm−1 was observed in the carbonyl region, which was ascribed to Pd interacting with Cl. Finally, the FTIR measurements were complemented by quantification of the amount of carbonates formed via chemisorption, which provides a tool to determine the concentration of reactive defect sites on the alumina surface

Determining adsorbate configuration on alumina surfaces with 13C nuclear magnetic resonance relaxation time analysis

Relative strengths of surface interaction for individual carbon atoms in acyclic and cyclic hydrocarbons adsorbed on alumina surfaces are determined using chemically resolved 13C nuclear magnetic resonance (NMR) T1 relaxation times. The ratio of relaxation times for the adsorbed atoms T1,ads to the bulk liquid relaxation time T1,bulk provides an indication of the mobility of the atom. Hence a low T1,ads/T1,bulk ratio indicates a stronger surface interaction. The carbon atoms associated with unsaturated bonds in the molecules are seen to exhibit a larger reduction in T1 on adsorption relative to the aliphatic carbons, consistent with adsorption occurring through the carbon-carbon multiple bonds. The relaxation data are interpreted in terms of proximity of individual carbon atoms to the alumina surface and adsorption conformations are inferred. Furthermore, variations of interaction strength and molecular configuration have been explored as a function of adsorbate coverage, temperature, surface pre-treatment, and in the presence of co-adsorbates. This relaxation time analysis is appropriate for studying the behaviour of hydrocarbons adsorbed on a wide range of catalyst support and supported-metal catalyst surfaces, and offers the potential to explore such systems under realistic operating conditions when multiple chemical components are present at the surface

Monitoring Hydrotreating Catalysts Synthesis and Deactivation using Raman Spectrometry

Raman spectrometry has become a popular characterization technique for hydrotreatment catalysts: it provides important information on chemical structures along all the synthesis cycle, from the impregnation solution to the sulfided catalyst. Aspects of physico-chemical processes taking place on the catalyst surface can be monitored using this technique. This article describes some examples where Raman spectrometry has been used to evaluate the impact of experimental parameters (choice of metallic precursors, presence of impurity, influence of calcination temperature, coke deposit) on the catalyst structure

DFT Study of the Interaction of a single Palladium Atomwith γ\gamma -Alumina Surfaces: the Role of Hydroxylation

International audienceConsidering the crucial role of the $\gamma$-alumina solid phase in heterogeneous catalysis as a support of numerous active phases, a revised and improved atomistic description of $\gamma$-alumina surfaces was mandatory to furnish new highlights in the field of $\gamma$-alumina supported catalysts. Two important scientific challenges in heterogeneous catalysis have recently been taken up by modern Density Functional Theory (DFT) simulations. The first challenge described in this paper is to show that DFT calculations combined with simple thermodynamic model provide an elegant way of determining the stable chemical species at the $\gamma$-alumina surface (such as hydroxyls or Lewis sites) as a function of reaction conditions. The (100) and (110) surfaces exposed mainly by the $\gamma$-alumina nanocrystallites exhibit two distinct behaviors regarding their hydroxylation states. The (110) surface maintains a high degree of hydroxyl coverage even at high temperature, whereas the (100) surface is dehydrated at low temperature. This first important step being achieved, a second challenge in heterogeneous catalysis is the interaction of the active phase with $\gamma$-alumina. In the second part of this paper, we present the adsorption of a single palladium atoms (Pd1) on the (100) and (110) $\gamma$-alumina surfaces. By determining the potential energy surface of Pd on $\gamma$-alumina, the relationship between structure and metal-oxide interaction energy at the interface is depicted. Furthermore, new insights are provided on the chemisorption and diffusion processes of Pd on the two surfaces. The adsorption energy and the hopping rate of Pd are strongly reduced when the hydroxyl coverage increases such as found on the (110) surface. As a consequence, the surface hydroxylation appears as a key parameter for understanding the active phase/support interaction and enables the interpretation of available experimental data

Dft Studies of Fluid-Minerals Interactions At the Molecular Level: Examples and Perspectives

The scope of applications of first-principle theoretical chemistry methods has been vastly expanded over the past years due to the combination of improved methods and algorithms for solving the polyelectronic Schrödinger equation with exponential growth of computer power available at constant cost (the so-called Moore law). In particular, atomistic studies of solid-fluid interfaces are now routinely producing new qualitative and quantitative insights into adsorption, surface speciation as a function of the prevailing chemical potentials, and reactivity of surface species. This approach is currently widely exploited in the fields of heterogeneous catalysis and surface physics, and so far to a lesser extent for geochemical purposes, although the situation is rapidly evolving. Many fundamental issues of fluid-minerals interaction phenomena can indeed be addressed ab initio with atomistic 3D periodic models of fluid-solid interfaces involving up to 200-300 unequivalent atoms. We illustrate this proposal with recent IFP results, some of which are of primary interest with respect to the manufacture of catalysts supports, but which also show some relevance for inorganic geochemical issues in the context of the sequestration of acid gases in subsurface porous rocks: - reactive wetting of boehmite AlOOH and morphology prediction; - acido-basic surface properties of a transition alumina; - hydroxylation and sulfhydrylation of anatase TiO2 surfaces. Through these examples, the performances of DFT and a variety of up-to-date modeling techniques and strategies are discussed

Use of DFT to achieve a rational understanding of acid?basic properties of ?-alumina surfaces

International audienc

Establishing a COVID-secure site for elective surgery during the COVID pandemic: An observational study.

INTRODUCTION Maintaining timely and safe delivery of major elective surgery during the COVID-19 pandemic is essential to manage cancer and time-critical surgical conditions. Our NHS Trust established a COVID-secure elective site with a level 2 Post Anaesthetic Care Unit (PACU) facility. Patients requiring level 3 Intensive Care Unit admission were transferred to a non-COVID-secure site. We investigated the relationship between perioperative anaesthetic care and outcomes. MATERIALS AND METHODS All consecutive patients undergoing major surgery at the COVID-secure site between June and November 2020 were included. Patient demographics, operative interventions and 30-day outcomes were recorded. Multivariate logistic regression was used to determine the odds ratio of outcomes according to PACU length of stay and the use of spinal or epidural anaesthesia, with age, sex, malignancy status and American Society of Anesthesiologists grade as independent co-variables. RESULTS There were 280 patients. PACU length of stay >23h was associated with increased 30-day complications. Epidural anaesthesia was associated with PACU length of stay >23h, increased total length of stay, increase hospital transfer and 30-day complications. Two patients acquired nosocomial COVID-19 following hospital transfer. DISCUSSION Establishing a separate COVID-secure site has facilitated delivery of major elective surgery during the COVID-19 pandemic. Choice of perioperative anaesthesia and utilisation of PACU appear likely to affect the risk of adverse outcomes

A rational interpretation of improved catalytic performances of additive-impregnated dried CoMo hydrotreating catalysts: a combined theoretical and experimental study

RAFFINAGE:SURFACES+JKR:CGECoMo additive-impregnated dried catalysts are studied, exploring the "CoMoS" active phase features by combining X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and catalytic tests. Starting from different polyoxomolybdate precursors, additive-impregnated dried, additive-free dried and calcined catalyst performances are compared. TEM reveals that the mean particle sizes are about 3.1 nm and do not depend on the catalytic precursors except for the additive-free dried catalysts exhibiting higher lengths: 3.7 nm. XPS quantification of the Mo species shows that 75 mol% of the Mo species are present in the MoS2 phase whatever the preparation route. This value is slightly enhanced (ca. 85%) with additive impregnation. The molybdenum to aluminium surface coverage ratio (Mo/Al) ranking is found to be as follows: additive-free dried < additive-impregnated dried < calcined. However, this ranking is not significantly modified by the impregnating solution used, and the behaviour is similar for the cobalt to aluminium ratio (Co/Al). A geometrical model combining XPS quantification of the crystallite's Co/Mo ratio and DFT calculations is used to establish a correlation with the catalytic results obtained in toluene hydrogenation. It is shown that the catalytic performances of additive-free dried, additive-impregnated dried and calcined catalysts directly correlate the number of mixed Co-Mo sites present at the MoS2 edges. DFT calculations highlight that the adsorption step of toluene is thermodynamically favored on the mixed Co-Mo site located at the M-edge. As a consequence, this study suggests that the various routes of preparation leading to different catalytic performances would not lead to new types of active sites or morphology but rather to a different number of mixed sites present at the edges