Thermal conductivity of amorphous polymers and its dependence on molecular weight

Thermal conductivity is an important transport property governing the performance of polymers in non-isothermal conditions. Nevertheless, its dependence on molecular weight M has not been the subject of as much attention as other properties of polymeric materials. We determine the thermal conductivity of polystyrene and polyisobutylene for a wide range of molecular weight by measuring the density, heat capacity and thermal diffusivity. Using coarse-graining and reverse mapping methods, we were able to produce molecular melts to study the thermal conductivity of polystyrene using molecular dynamics simulations over a similar range of molecular weight. We find satisfactory agreement between the experimental and simulation results. However, all of our results show that thermal conductivity depends only slightly on molecular weight up the entanglement limit and it is independent thereafter. Our results put into question the few previous experimental studies on this topic by showing that the previously accepted proportionality to $\sqrt{M}$ does not hold. Our findings could have significant implications for the understanding of complex phenomena such as anisotropic thermal conductivity in polymers subjected to flow.Marie Skłodowska-Curie IF MTCIATTP 750985

Fine-time energetic electron behavior observed by Cluster/RAPID in the magnetotail associated with X-line formation and subsequent current disruption

Energetic electrons with 90deg pitch angle have been observed in the magnetotail at ~19 <i>R<sub>E</sub></i> near local midnight during the recovery phase of a substorm event on 27 August 2001 (Baker et al., 2002). Based on auroral images Baker et al. (2002) placed the substorm expansion phase between ~04:06:16 and ~04:08:19 UT. The electron enhancements perpendicular to the ambient magnetic field occurred while the Cluster spacecraft were on closed field lines in the central plasma sheet approaching the neutral sheet. Magnetic field and energetic particle measurements have been employed from a number of satellites, in order to determine the source and the subsequent appearance of these electrons at the Cluster location. It is found that ~7.5 min after an X-line formation observed by Cluster (Baker et al., 2002) a current disruption event took place inside geosynchronous orbit and subsequently expanded both in local time and tailward, giving rise to field-aligned currents and the formation of a current wedge. A synthesis of tail reconnection and the cross-tail current disruption scenario is proposed for the substorm global initiation process: When a fast flow with northward magnetic field, produced by magnetic reconnection in the midtail, abruptly decelerates at the inner edge of the plasma sheet, it compresses the plasma populations earthward of the front, altering dynamically the B<sub>z</sub> magnetic component in the current sheet. This provides the necessary and sufficient conditions for the kinetic cross-field streaming/current (KCSI/CFCI) instability (Lui et al., 1990, 1991) to initiate. As soon as the ionospheric conductance increases over a threshold level, the auroral electrojet is greatly intensified (see Fig. 2 in Baker et al., 2002), which leads to the formation of the substorm current wedge and dipolarization of the magnetic field. This substorm scenario combines the near-Earth neutral line and the current disruption for the initiation of substorms, at least during steady southward IMF. One can conclude the following: The observations suggest that the anisotropic electron increases observed by Cluster are not related to an acceleration mechanism associated with the X-line formation in the midtail, but rather these particles are generated in the dusk magnetospheric sector due to the longitudinal and tailward expansion of a current disruption region and subsequently observed at the Cluster location with no apparent energy dispersion.<br><br> <b>Keywords.</b> Magnetospheric physics (Magnetotail; Plasma convection; Storms and substorms

Obesity and iron deficiency anemia as risk factors for asymptomatic bacteriur

Background: Few studies examined the risk factors of asymptomatic bacteriuria, showing contradictory results. Our study aimed to examine the association between different clinical and laboratory parameters and asymptomatic bacteriuria in internal medicine patients. Materials and methods: 330 consecutive hospitalized subjects, asymptomatic for urinary tract infections (UTIs), underwent to microscopic examination of urine specimens. 100 subjects were positive for microscopic bacteriuria and were recruited into the study. At the quantitative urine culture 31 subjects of study population were positive while 69 subjects were negative for bacteriuria. Results: The analysis of clinical characteristics showed that the two groups of subjects (positive and negative urine culture for bacteriuria) were significant different (p b 0.05) about obesity (76.7% vs 42% respectively), metabolic syndrome (80.6% vs 44,9%), cholelithiasis (35.5% vs 13,2%) and iron deficiency anemia (80.6% vs 53,6%). The univariate analysis showed that only obesity, cholelithiasis and iron deficiency anemia were positively associated with positive urine culture for bacteriuria (Odds Ratios [OR] = 3.79, p = 0.0003; OR = 2,65, p =0.0091; OR = 2.63, p = 0.0097; respectively). However, the multivariate analysis by logistic regression showed that only obesity and iron deficiency anemia, independently associated with positive urine culture for bacteriuria (OR = 3.9695, p = 0.0075; OR = 3.1569, p = 0.03420 respectively). Conclusions: This study shows that obesity and iron deficiency anemia are independent risk factors for asymptomatic bacteriuria

Mesoscopic simulations of crosslinked polymer networks

Institut für Theoretische Physik, Georg-August Universität, Göttingen, Germany E-mail: [email protected] Abstract. A new methodology and the corresponding C++ code for mesoscopic simulations of elastomers are presented. The test system, crosslinked cis-1,4-polyisoprene, is simulated with a Brownian Dynamics/kinetic Monte Carlo algorithm as a dense liquid of soft, coarse-grained beads, each representing 5-10 Kuhn segments. From the thermodynamic point of view, the system is described by a Helmholtz free-energy containing contributions from entropic springs between successive beads along a chain, slip-springs representing entanglements between beads on different chains, and non-bonded interactions. The methodology is employed for the calculation of the stress relaxation function from simulations of several microseconds at equilibrium, as well as for the prediction of stress-strain curves of crosslinked polymer networks under deformation. Introduction Atomistic and mesoscopic simulations are widely employed for the study of polymer systems, since they provide insights that are complementary to the information derived from experiments. Although the full-atom or united-atom representations provide an accurate description of polymers, their long relaxation time constitutes a severe obstacle to such approaches, and thus the development of mesoscopic (or coarse-grained) models is needed to cover longer time and length scales. One of the main characteristics of polymer melts and polymer networks is the entanglement effect, arising due to the uncrossability of polymer chains, which gives rise to complicated topological constraints [1]-[4]. The tube model, which considers a single chain in a mean field, is one of the most significant models for the description of entangled polymer

Validity of physical activity monitors during daily life in patients with COPD.

Symptoms during physical activity (PA) and physical inactivity are COPD. Our aim was to evaluate the validity and usability of six activity in patients with COPD against the doubly labelled water (DLW) indirect calorimetry method.Eighty COPD patients (age 68+/-6 years, FEV1 57+/-19% predicted) recruited in four centres each wore simultaneously three or six commercially available monitors validated in chronic conditions for consecutive days. A priori validity criteria were defined. These ability to explain total energy expenditure (TEE) variance through regression analysis, using TEE as the dependent variable with total body (TBW) plus several PA monitors outputs as independent variables; and with DLW measured activity energy expenditure (AEE).The Actigraph GT3X DynaPort MoveMonitor best explained the majority of the TEE variance not explained by TBW (53% and 70% respectively) and showed the most correlations with AEE (r=0.71 p<0.001, r=0.70 p<0.0001, of this study should guide users in choosing valid activity monitors for or for clinical use in patients with chronic diseases such as COPD

Comparative study of corrosion performance of HVOF-sprayed coatings produced using conventional and suspension WC-Co feedstock.

Corrosion properties of nanostructured coatings deposited by suspension high-velocity oxy-fuel (S-HVOF) via an aqueous suspension of milled WC-Co powder were compared with conventional HVOF-sprayed coatings. Microstructural evaluations of these coatings included x-ray diffraction and scanning electron microscopy equipped with an energy-dispersive x-ray spectroscopy. The corrosion performance of AISI440C stainless steel substrate and the coatings was evaluated in a 3.5 wt.% NaCl aqueous solution at ~25 °C. The electrochemical properties of the samples were assessed experimentally, employing potentiodynamic polarization and electrochemical impedance spectroscopy. The potentiodynamic polarization results indicated that coatings produced by S-HVOF technique show lower corrosion resistance compared with the coatings produced by HVOF-JK (HVOF Jet Kote) and HVOF-JP (HVOF JP5000) techniques. Results are discussed in terms of corrosion mechanism, Bode and Nyquist plots, as well as equivalent circuit models of the coating–substrate system