Nano-scale Flexible Interphase in a Glass Fiber/Epoxy Resin System Obtained by Admicellar Polymerization

Organosilane coupling agents are widely used in the composites industry to improve the wetting of inorganic reinforcements by low surface energy resins. An increased wettability is often a harbinger of better mechanical properties in a structural composite. Silane coatings effectively increase the spreading of liquid matrixes over glass reinforcement by altering the surface energetics of glass, not by extensive coverage, but by eradication of the high-energy sites present in the oxide surface. Commercial sizings often applied to glass fibers contain up to 10% of the active silane agent, while the remaining 90% is a mixture of lubricants, surfactants, anti-stats, and film formers. Recent investigations have demonstrated that non-reactive components tend to remain in high concentrations within the interphase, thus weakening the resin network crosslink density and increasing the potential for water ingress. Further, sizing formulations are proprietary and designed for specific resin system, which make them expensive, consequently limiting their widespread use. In this paper, admicellar polymerization, a versatile technique to prepare elastomeric thin films of styrene-isoprene copolymer and polystyrene on the surface of random glass-fiber mats is presented. This hydrophobic coating of monolayer thickness applied to the glass fibers is not expected to disrupt the matrix cross-linking reaction; and due to its higher elastic modulus, is believed to cause a change in the stress distribution along the fiber length. Admicellar-modified reinforcements were impregnated with an epoxy resin system: EPON 815C/EPICURE 3232, and molded by Resin Transfer Molding (RTM) into disk shaped parts. Tensile strength, stiffness and interlaminar shear strength (ILSS) were measured for the flexible interphase composites, and compared to parts containing commercially sized and bare fibers. Void fraction, void size and shape distributions, as well as water diffusivity were investigated for each system.YesPeer reviewed and presented at the 18th International Conference of the Polymer processing Society

Functional determinants for general Sturm-Liouville problems

Simple and analytically tractable expressions for functional determinants are known to exist for many cases of interest. We extend the range of situations for which these hold to cover systems of self-adjoint operators of the Sturm-Liouville type with arbitrary linear boundary conditions. The results hold whether or not the operators have negative eigenvalues. The physically important case of functional determinants of operators with a zero mode, but where that mode has been extracted, is studied in detail for the same range of situations as when no zero mode exists. The method of proof uses the properties of generalised zeta-functions. The general form of the final results are the same for the entire range of problems considered.Comment: 28 pages, LaTe

Design and fabrication of densely integrated silicon quantum dots using a VLSI compatible hydrogen silsesquioxane electron beam lithography process

Hydrogen silsesquioxane (HSQ) is a high resolution negative-tone electron beam resist allowing for direct transfer of nanostructures into silicon-on-insulator. Using this resist for electron beam lithography, we fabricate high density lithographically defined Silicon double quantum dot (QD) transistors. We show that our approach is compatible with very large scale integration, allowing for parallel fabrication of up to 144 scalable devices. HSQ process optimisation allowed for realisation of reproducible QD dimensions of 50 nm and tunnel junction down to 25 nm. We observed that 80% of the fabricated devices had dimensional variations of less than 5 nm. These are the smallest high density double QD transistors achieved to date. Single electron simulations combined with preliminary electrical characterisations justify the reliability of our device and process

Behavior of multitemporal and multisensor passive microwave indices in Southern Hemisphere ecosystems

©2014. American Geophysical Union. All Rights Reserved. This study focused on the time series analysis of passive microwave and optical satellite data collected from six Southern Hemisphere ecosystems in Australia and Argentina. The selected ecosystems represent a wide range of land cover types, including deciduous open forest, temperate forest, tropical and semiarid savannas, and grasslands. We used two microwave indices, the frequency index (FI) and polarization index (PI), to assess the relative contributions of soil and vegetation properties (moisture and structure) to the observations. Optical-based satellite vegetation products from the Moderate Resolution Imaging Spectroradiometer were also included to aid in the analysis. We studied the X and Ka bands of the Advanced Microwave Scanning Radiometer-EOS and Wind Satellite, resulting in up to four observations per day (1:30, 6:00, 13:30, and 18:00-h). Both the seasonal and hourly variations of each of the indices were examined. Environmental drivers (precipitation and temperature) and eddy covariance measurements (gross ecosystem productivity and latent energy) were also analyzed. It was found that in moderately dense forests, FI was dependent on canopy properties (leaf area index and vegetation moisture). In tropical woody savannas, a significant regression (R2) was found between FI and PI with precipitation (R2->-0.5) and soil moisture (R2->-0.6). In the areas of semiarid savanna and grassland ecosystems, FI variations found to be significantly related to soil moisture (R2->-0.7) and evapotranspiration (R2->-0.5), while PI varied with vegetation phenology. Significant differences (p-<-0.01) were found among FI values calculated at the four local times. Key Points Passive microwave indices can be used to estimate vegetation moisture Microwave observations were supported by flux data Passive microwave indices could be used to estimate evapotranspiratio

Progress of the APS high heat load x-ray beam position monitor development

Several novel design developments have been established for the Advanced Photon Source (APS) insertion device (ID) X-ray beam position monitor (XBPM) to improve its performance: (1) optimized geometric configuration of the monitor`s sensory blades; (2) smart XBPM system with an intelligent digital signal processor, which provides a self-learning and calibration function; and (3) transmitting XBPM with prefiltering in the commissioning windows for the front end. In this write-up, the authors summarize the recent progress on the XBPM development for the APS ID front ends

A Molecular Platinum Cluster Junction: A Single-Molecule Switch

We present a theoretical study of the electronic transport through single-molecule junctions incorporating a Pt6 metal cluster bound within an organic framework. We show that the insertion of this molecule between a pair of electrodes leads to a fully atomically engineered nano-metallic device with high conductance at the Fermi level and two sequential high on/off switching states. The origin of this property can be traced back to the existence of a HOMO which consists of two degenerate and asymmetric orbitals, lying close in energy to the Fermi level of the metallic leads. Their degeneracy is broken when the molecule is contacted to the leads, giving rise to two resonances which become pinned close to the Fermi level and display destructive interference.Comment: 4 pages, 4 figures. Reprinted (adapted) with permission from J. Am. Chem. Soc., 2013, 135 (6), 2052. Copyright 2013 American Chemical Societ

Gastrointestinal endoscopy during the coronavirus pandemic in the New York area: results from a multi-institutional survey.

Background and study aims  The coronavirus disease 2019 (COVID-19), and measures taken to mitigate its impact, have profoundly affected the clinical care of gastroenterology patients and the work of endoscopy units. We aimed to describe the clinical care delivered by gastroenterologists and the type of procedures performed during the early to peak period of the pandemic. Methods  Endoscopy leaders in the New York region were invited to participate in an electronic survey describing operations and clinical service. Surveys were distributed on April 7, 2020 and responses were collected over the following week. A follow-up survey was distributed on April 20, 2020. Participants were asked to report procedure volumes and patient characteristics, as well protocols for staffing and testing for COVID-19. Results  Eleven large academic endoscopy units in the New York City region responded to the survey, representing every major hospital system. COVID patients occupied an average of 54.5 % (18 - 84 %) of hospital beds at the time of survey completion, with 14.5 % (2 %-23 %) of COVID patients requiring intensive care. Endoscopy procedure volume and the number of physicians performing procedures declined by 90 % (66 %-98 %) and 84.5 % (50 %-97 %) respectively following introduction of restricted practice. During this period the most common procedures were EGDs (7.9/unit/week; 88 % for bleeding; the remainder for foreign body and feeding tube placement); ERCPs (5/unit/week; for cholangitis in 67 % and obstructive jaundice in 20 %); Colonoscopies (4/unit/week for bleeding in 77 % or colitis in 23 %) and least common were EUS (3/unit/week for tumor biopsies). Of the sites, 44 % performed pre-procedure COVID testing and the proportion of COVID-positive patients undergoing procedures was 4.6 % in the first 2 weeks and up to 19.6 % in the subsequent 2 weeks. The majority of COVID-positive patients undergoing procedures underwent EGD (30.6 % COVID +) and ERCP (10.2 % COVID +). Conclusions  COVID-19 has profoundly impacted the operation of endoscopy units in the New York region. Our data show the impact of a restricted emergency practice on endoscopy volumes and the proportion of expected COVID positive cases during the peak time of the pandemic