Influence of surfactants on the structure of titanium oxide gels : experiments and simulations

We report here on experimental and numerical studies of the influence of surfactants on mineral gel synthesis. The modification of the gel structure when the ratios water-precursor and water-surfactant vary is brought to the fore by fractal dimension measures. A property of {\em polydispersity of the initial hydrolysis} is proposed to explain these results, and is successfuly tested through numerical experiments of three dimensional chemically limited aggregation.Comment: 12 pages, 4 Postscript figures, uses RevTe

Energy- and charge-state-resolved spectrometry of tin laser-produced plasma using a retarding field energy analyzer

We present a method to obtain the individual charge-state-dependent kinetic-energy distributions of tin ions emanating from a laser-produced plasma from their joint overlapping energy distributions measured by means of a retarding field energy analyzer (RFA). The method of extracting charge state specific parameters from the ion signals is described mathematically, and reinforced with experimental results. The absolute charge-state-resolved ion energy distributions is obtained from ns-pulse Nd:YAG-laser-produced microdroplet tin plasmas in a setting relevant for state-of-the-art extreme ultraviolet nanolithography

A Silicon, Carbon and Deuterium NMR Investigation of Molecular Templating in Amorphous Silicas

The precise pore sizes defined by crystalline zeolite lattices have led to intensive research on zeolite membranes. Unfortunately zeolites have proven to be extremely difficult to prepare in a defect-free thin film form needed for membrane flux and selectivity. We introduce tetrapropylammonium TPA (a structure directing agent for zeolite ZSM-5) into a silica sol and exploit the development of high solvation stresses to create templated amorphous silicas with pore apertures comparable in size to those of ZSM-5. {sup 29}Si and {sup 2}H NMR experiments were performed to evaluate the efficacy of our templating approach. The {sup 29}Si NMR spectrum of the silica matrix was observed by an intermolecular cross-polarization experiment between the {sup 1}H nuclei of TPA and the {sup 29}Si nuclei in the silica matrix. The efficiency of the cross-polarization interaction was used to investigate the degree to which the matrix formed a tight cage surrounding the template molecule. Normally prepared xerogel materials exhibited only weak interactions between the two sets of nuclei. Drying under reduced pressure, where solvation stresses are maximized, resulted in significantly increased interactions. Analogous materials were prepared using fully deuterated TPA. The {sup 2}H NMR wideline spectra consisted of a partially narrowed resonance, corresponding to template molecules which were undergoing restricted rotational motion, and an isotropically narrowed resonance, corresponding to molecules which were undergoing rapid rotational motion. The number of isotropically rotating template molecules decreased for specimens dried under reduced pressure, consistent with improved templating of amorphous silica by TPA

Trauma mechanism and patient reported outcome in tibial plateau fractures with posterior involvement

Introduction: Posterior tibial plateau fractures (PTPF) have a high impact on functional outcome and the optimal treatment strategy is not well established. The goal of this study was to assess the relationship between trauma mechanism, fracture morphology and functional outcome in a large multicenter cohort and define possible strategies to improve the outcome. Methods: An international retrospective cohort study was conducted in five level-1 trauma centers. All consecutive operatively treated PTPF were evaluated. Preoperative imaging was reviewed to determine the trauma mechanism. Patient reported outcome was scored using the Knee injury and Osteoarthritis Outcome Score (KOOS). Results: A total of 145 tibial plateau fractures with posterior involvement were selected with a median follow-up of 32.2 months (IQR 24.1-43.2). Nine patients (6%) sustained an isolated posterior fracture. Seventy-two patients (49%) sustained a two-column fracture and three-column fractures were diagnosed in 64 (44%) patients. Varus trauma was associated with poorer outcome on the 'symptoms' (p = 0.004) and 'pain' subscales (p = 0.039). Delayed-staged surgery was associated with worse outcome scores for all subscales except 'pain'. In total, 27 patients (18%) were treated with posterior plate osteosynthesis without any significant difference in outcome. Conclusions: Fracture morphology, varus trauma mechanism and delayed-staged surgery (i.e. extensive soft-tissue injury) were identified as important prognostic factors on postoperative outcome in PTPF. In order to assess possible improvement of outcome, future studies with routine preoperative MRI to assess associated ligamentous injury in tibial plateau fractures (especially for varus trauma) are needed. (c) 2021 Elsevier B.V. All rights reserved

Characterization of polyxylylenes with solid state {sup 13}C nuclear magnetic resonance spectroscopy

Polyxylylenes are thermoplastics used as encapsulants for electronic devices. Five polyxylylenes were prepared by pyrolysis of [2.2]paracyclophanes and characterized by solid state {sup 13}C NMR spectroscopy. The chemical shift data, in combination with interrupted decoupling experiments, allowed assignment of resonances to their carbon sources in the polymers. This confirmed the integrity of the xylylene building block in the polymers and is consistent with linear polymers. No crosslinking could be detected within the NMR sensitivity limits. Residual paracyclophane was detected by {sup 13}C CP MAS NMR spectroscopy in the polyxylylene samples prepared at room temperature; however discrete {sup 13}C resonances due to amorphous and crystalline phases in the polymers were not resolved

Current-induced highly dissipative domains in high Tc thin films

We have investigated the resistive response of high Tc thin films submitted to a high density of current. For this purpose, current pulses were applied into bridges made of Nd(1.15)Ba(1.85)Cu3O7 and Bi2Sr2CaCu2O8. By recording the time dependent voltage, we observe that at a certain critical current j*, a highly dissipative domain develops somewhere along the bridge. The successive formation of these domains produces stepped I-V characteristics. We present evidences that these domains are not regions with a temperature above Tc, as for hot spots. In fact this phenomenon appears to be analog to the nucleation of phase-slip centers observed in conventional superconductors near Tc, but here in contrast they appear in a wide temperature range. Under some conditions, these domains will propagate and destroy the superconductivity within the whole sample. We have measured the temperature dependence of j* and found a similar behavior in the two investigated compounds. This temperature dependence is just the one expected for the depairing current, but the amplitude is about 100 times smaller.Comment: 9 pages, 9 figures, Revtex, to appear in Phys. Rev.

Comparison of co-located independent ground-based middle atmospheric wind and temperature measurements with numerical weather prediction models

High-resolution, ground-based and independent observations including co-located windradiometer, lidar stations, and infrasound instruments are used to evaluate the accuracy of general circulationmodels and data-constrained assimilation systems in the middle atmosphere at northern hemispheremidlatitudes. Systematic comparisons between observations, the European Centre for Medium-Range WeatherForecasts (ECMWF) operational analyses including the recent Integrated Forecast System cycles 38r1 and 38r2,the NASA’s Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalyses, and thefree-running climate Max Planck Institute–Earth System Model–Low Resolution (MPI-ESM-LR) are carried out inboth temporal and spectral dom ains. We find that ECMWF and MERRA are broadly consistent with lidar and windradiometer measurements up to ~40 km. For both temperature and horizontal wind components, deviationsincrease with altitude as the assimilated observations become sparser. Between 40 and 60 km altitude, thestandard deviation of the mean difference exceeds 5 K for the temperature and 20 m/s for the zonal wind. Thelargest deviations are observed in winter when the variability from large-scale planetary waves dominates.Between lidar data and MPI-ESM-LR, there is an overall agreement in spectral amplitude down to 15–20 days. Atshorter time scales, the variability is lacking in the model by ~10 dB. Infrasound observations indicate a generalgood agreement with ECWMF wind and temperature products. As such, this study demonstrates the potentialof the infrastructure of the Atmospheric Dynamics Research Infrastructure in Europe project that integratesvarious measurements and provides a quantitative understanding of stratosphere-troposphere dynamicalcoupling for numerical weather prediction applications

Fullerene-based materials research and development. LDRD final report

The chemistry and physical properties of fullerenes, the third, molecular allotrope of carbon, have been studied using both experimental and computational techniques. Early computational work investigated the stability of fullerene isomers and oxides, which was followed by extensive work on hydrogenated fullerenes. Our work led to the first synthesis of a polymer containing C{sub 60} and the synthesis of the simplest hydrocarbon derivatives of C{sub 60} and C{sub 70}. The excellent agreement between theory and experiment ({plus_minus} 0.1 kcal/mol in the relative stability of isomers) has provided insight into the chemical nature of fullerenes and has yielded a sound basis for prediction of the structure of derivatized fullerenes. Such derivatives are the key to the preparation of fullerene-based materials