Atomic oxygen studies on polymers

The purpose was to study the effects of atomic oxygen on the erosion of polymer based materials. The development of an atomic oxygen neutral beam facility using a SURFATRON surface wave launcher that can produce beam energies between 2 and 3 eV at flux levels as high as approx. 10 to the 17th power atoms/cm (2)-sec is described. Thin film dielectric materials were studied to determine recession rates and and reaction efficiencies as a function of incident beam energy and fluence. Accelerated testing was also accomplished and the values of reaction efficiency compared to available space flight data. Electron microscope photomicrographs of the samples' surface morphology were compared to flight test specimens

Lower limb biomechanics during drop jump landing in individuals with chronic ankle instability

ABSTRACT Context: Individuals with chronic ankle instability (CAI) exhibit impaired lower limb biomechanics during unilateral drop jump landing on a flat surface. However, lower limb biomechanical adaptations during unilateral drop jump landing on more challenging surfaces such as unstable or inclined are yet to be described. Objective: Determine how unilateral drop jump landing surfaces (flat, unstable and inclined) influence lower limb EMG, kinematics and kinetics in individuals with CAI. Design: Descriptive laboratory study. Setting: Biomechanics laboratory. Patients or Other Participants: Twenty-two young adults with CAI Interventions: Participants completed five trials of unilateral drop jump landing from a 46 cm height platform on flat (DROP), unstable (FOAM) and laterally inclined (WEDGE) surfaces. Main outcome measure(s): EMG of gluteus medius, vastus lateralis, gastrocnemius medialis, peroneus longus and tibialis anterior muscles were recorded. Knee and ankle angles and moments were calculated using a three-dimensional motion analysis system and a force plate. Biomechanical variables were compared between tasks using one-dimensional statistical nonparametric mapping. Results: During DROP, greater ankle dorsiflexion angles, knee extension moments and vastus lateralis muscle activity (FOAM only) were observed compared to FOAM and WEDGE. Greater ankle inversion angles were observed during FOAM and WEDGE compared to DROP. Peroneus longus muscle activity was greater during DROP compared to FOAM. During FOAM, greater ankle inversion and knee extension angles, ankle inversion and internal rotation moments as well as smaller peroneus longus muscle activity were observed compared to WEDGE. Conclusions: The greater ankle inversion and plantarflexion angles as well as the lack of increase in peroneus longus muscle activation during FOAM and WEDGE could increase the risk of recurrent LAS in individuals with CAI. The results of this study improve our understanding of lower limb biomechanics changes when landing on more challenging surfaces and will help clinicians better targeting deficits associated with CAI during rehabilitation

Lower limb biomechanics in individuals with chronic ankle instability during gait: a case-control study

Individuals with chronic ankle instability (CAI) exhibit many biomechanical changes to lower limbs during walking. However, only a few studies have investigated the differences in lower limb biomechanics of individuals with CAI compared to healthy controls using a comprehensive approach including kinematic, kinetic and electromyography (EMG) measures. Consequently, the theoretical framework explaining the biomechanical adaptations in individuals with CAI is mostly based on the results of studies including heterogenous methods and participants’ specificities (e.g., level of disability). More studies using a comprehensive approach are needed to better understand the biomechanical adaptations associated with CAI. The objective of this case-control study was to identify the kinematic, kinetic and EMG differences between individuals with CAI and healthy controls during walking

Tuning a Schottky barrier in a photoexcited topological insulator with transient Dirac cone electron-hole asymmetry

The advent of Dirac materials has made it possible to realize two dimensional gases of relativistic fermions with unprecedented transport properties in condensed matter. Their photoconductive control with ultrafast light pulses is opening new perspectives for the transmission of current and information. Here we show that the interplay of surface and bulk transient carrier dynamics in a photoexcited topological insulator can control an essential parameter for photoconductivity - the balance between excess electrons and holes in the Dirac cone. This can result in a strongly out of equilibrium gas of hot relativistic fermions, characterized by a surprisingly long lifetime of more than 50 ps, and a simultaneous transient shift of chemical potential by as much as 100 meV. The unique properties of this transient Dirac cone make it possible to tune with ultrafast light pulses a relativistic nanoscale Schottky barrier, in a way that is impossible with conventional optoelectronic materials.Comment: Nature Communications, in press (12 pages, 6 figures

The impact of lake shape and size on lake breezes and air-lake exchanges on Titan

Titan, the largest moon of Saturn, has many lakes on its surface, formed mainly of liquid methane. Like water lakes on Earth, these methane lakes on Titan likely profoundly affect the local climate. Previous studies (Rafkin and Soto 2020, Chatain et al 2022) showed that Titan's lakes create lake breeze circulations with characteristic dimensions similar to the ones observed on Earth. However, such studies used a model in two dimensions; this work investigates the consequences of the addition of a third dimension to the model. Our results show that 2D simulations tend to overestimate the extension of the lake breeze over the land, and underestimate the strength of the subsidence over the lake, due to divergence/convergence geometrical effects in the mass conservation equations. In addition, 3D simulations including a large scale background wind show the formation of a pocket of accelerated wind behind the lake, which did not form in 2D simulations. An investigation of the effect of shoreline concavity on the resulting air circulation shows the formation of wind currents over peninsulas. Simulations with several lakes can either result in the formation of several individual lake breeze cells (during the day), or the emergence of a large merged cell with internal wind currents between lakes (during the night). Simulations of several real-shaped lakes located at a latitude of 74{\deg}N on Titan at the spring equinox show that larger lakes trigger stronger winds, and that some sections of lakes might accumulate enough methane vapor to form a thin fog. The addition of a third dimension, along with adjustments in the parametrizations of turbulence and subsurface land temperature, results in a reduction in the magnitude of the average lake evaporate rate, namely to ~6 cm/Earth year.Comment: Submitted to Icarus on 2023-07-21. Dataset available at the DOI: 10.5281/zenodo.817227

Trading in Complex Networks

Global supply networks in agriculture, manufacturing and services are a defining feature of the modern world. The efficiency and the distribution of surpluses across different parts of these networks depend on choices of intermediaries. This paper conducts price formation experiments with human subjects located in large complex networks to develop a better understanding of the principles governing behavior. Our first finding is that prices are larger and that trade is significantly less efficient in small world networks as compared to random networks. Our second finding is that location within a network is not an important determinant of pricing. An examination of the price dynamics suggests that traders on cheapest - and hence active - paths raise prices while those off these paths lower them. We construct an agent based model (ABM) that embodies this rule of thumb. Simulations of this ABM yield macroscopic patterns consistent with the experimental findings. Finally, we extrapolate the ABM on to significantly larger random and small world networks and find that network topology remains a key determinant of pricing and efficiency

Influence of Neutron Enrichment on Disintegration Modes of Compound Nuclei

Cross sections, kinetic energy and angular distributions of fragments with charge 6$\le$Z$\le$28 emitted in 78,82Kr+40C at 5.5 MeV/A reactions were measured at the GANIL facility using the INDRA apparatus. This experiment aims to investigate the influence of the neutron enrichment on the decay mechanism of excited nuclei. Data are discussed in comparison with predictions of transition state and Hauser-Feshbach models.Comment: 8 pages, 1 figure, paper presented at the First Workshop on "State of the Art in Nuclear Cluster Physics" 13-16 May, 2008, at Strasbourg, France (SOTANCP2008) and accepted for publication at International Journal of Modern Physics E (Special Issue), Proceedings of SOTANCP2008 (to be published

Associations with 5 CFTR Mutations in »Grande Brière«, an Isolate Located in Southern Brittany

The variability at three microsatellites in the Cystic Fibrosis Transmembrane Conductance Regulator Gene (CFTR) locus has been studied for frequent mutations encountered in an isolated population of »Grande Brière«, a small region located in Southern Brittany. Fluorescent multiplex PCR of these microsatellites were assayed in 16 Cystic Fibrosis (CF) families carrying 5 different mutations. The four most frequent haplotypes on df508 chromosomes were the same as those found in Northern France and Europe but the distribution of these haplotypes provides new enlightenment on the population origin of this insular community

Fragment properties of fragmenting heavy nuclei produced in central and semi-peripheral collisions

Fragment properties of hot fragmenting sources of similar sizes produced in central and semi-peripheral collisions are compared in the excitation energy range 5-10 AMeV. For semi-peripheral collisions a method for selecting compact quasi-projectiles sources in velocity space similar to those of fused systems (central collisions) is proposed. The two major results are related to collective energy. The weak radial collective energy observed for quasi-projectile sources is shown to originate from thermal pressure only. The larger fragment multiplicity observed for fused systems and their more symmetric fragmentation are related to the extra radial collective energy due to expansion following a compression phase during central collisions. A first attempt to locate where the different sources break in the phase diagram is proposed.Comment: 23 pages submitted to NP

Diet, body size and menarche in a multiethnic cohort

A multiethnic cohort of 1378 Southern California school girls aged 8–13 years was followed for 4 years to evaluate factors predicting age at menarche, a risk factor for breast cancer. Height and weight were measured and dietary intake was assessed using a semi-quantitative food frequency questionnaire. Of 939 girls providing data on menarcheal status, 767 were premenarcheal at the start of the study; 679 girls provided acceptable dietary data and were included in the analyses. Cox proportional hazards models were used to assess the relationship between diet, body size, ethnicity and age at menarche. Hispanic, Asian/Pacific Island and African-American girls were more likely to experience early menarche than non-Hispanic white girls. Tall (> 148.6 cm) versus short (< 135.9 cm) girls experienced earlier menarche (relative hazard (RH) = 2.9, 95% confidence interval (CI) 2.1–4.1) as did those with high Quetelet's index (QI, kg m−2) (> 20.7) versus low QI (< 16.1) (RH = 2.2, 95% CI 1.7–2.9). Of all the dietary variables analysed, only energy intake was related to age at menarche. High versus low energy intake (> 12013 kJ vs < 7004 kJ) was associated with a delay in menarche (RH = 0.7, 95% CI 0.5–0.9); this finding was limited to a subset of heavy Hispanic girls who appeared to underreport their dietary intake. © 1999 Cancer Research Campaig