Universal Relationship between Conductivity and Solvation-Site Connectivity in Ether-Based Polymer Electrolytes

We perform a joint experimental and computational study of ion transport properties in a systematic set of linear polyethers synthesized via acyclic diene metathesis (ADMET) polymerization. We measure ionic conductivity, σ, and glass transition temperature, T_g, in mixtures of polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. While T_g is known to be an important factor in the ionic conductivity of polymer electrolytes, recent work indicates that the number and proximity of lithium ion solvation sites in the polymer also play an important role, but this effect has yet to be systematically investigated. Here, adding aliphatic linkers to a poly(ethylene oxide) (PEO) backbone lowers T_g and dilutes the polar groups; both factors influence ionic conductivity. To isolate these effects, we introduce a two-step normalization scheme. In the first step, Vogel–Tammann–Fulcher (VTF) fits are used to calculate a temperature-dependent reduced conductivity, σ_r(T), which is defined as the conductivity of the electrolyte at a fixed value of T – T_g. In the second step, we compute a nondimensional parameter f_(exp), defined as the ratio of the reduced molar conductivity of the electrolyte of interest to that of a reference polymer (PEO) at a fixed salt concentration. We find that f_(exp) depends only on oxygen mole fraction, x_0, and is to a good approximation independent of temperature and salt concentration. Molecular dynamics simulations are performed on neat polymers to quantify the occurrences of motifs that are similar to those obtained in the vicinity of isolated lithium ions. We show that f_(exp) is a linear function of the simulation-derived metric of connectivity between solvation sites. From the relationship between σ_r and f_(exp) we derive a universal equation that can be used to predict the conductivity of ether-based polymer electrolytes at any salt concentration and temperature

Spending per Medicare Beneficiary Is Higher in Hospital‐Owned Small‐ and Medium‐Sized Physician Practices

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145215/1/hesr12765.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145215/2/hesr12765-sup-0001-AppendixSA1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145215/3/hesr12765_am.pd

Universal Relationship between Conductivity and Solvation-Site Connectivity in Ether-Based Polymer Electrolytes

We perform a joint experimental and computational study of ion transport properties in a systematic set of linear polyethers synthesized via acyclic diene metathesis (ADMET) polymerization. We measure ionic conductivity, σ, and glass transition temperature, T_g, in mixtures of polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. While T_g is known to be an important factor in the ionic conductivity of polymer electrolytes, recent work indicates that the number and proximity of lithium ion solvation sites in the polymer also play an important role, but this effect has yet to be systematically investigated. Here, adding aliphatic linkers to a poly(ethylene oxide) (PEO) backbone lowers T_g and dilutes the polar groups; both factors influence ionic conductivity. To isolate these effects, we introduce a two-step normalization scheme. In the first step, Vogel–Tammann–Fulcher (VTF) fits are used to calculate a temperature-dependent reduced conductivity, σ_r(T), which is defined as the conductivity of the electrolyte at a fixed value of T – T_g. In the second step, we compute a nondimensional parameter f_(exp), defined as the ratio of the reduced molar conductivity of the electrolyte of interest to that of a reference polymer (PEO) at a fixed salt concentration. We find that f_(exp) depends only on oxygen mole fraction, x_0, and is to a good approximation independent of temperature and salt concentration. Molecular dynamics simulations are performed on neat polymers to quantify the occurrences of motifs that are similar to those obtained in the vicinity of isolated lithium ions. We show that f_(exp) is a linear function of the simulation-derived metric of connectivity between solvation sites. From the relationship between σ_r and f_(exp) we derive a universal equation that can be used to predict the conductivity of ether-based polymer electrolytes at any salt concentration and temperature

Optimizing Ion Transport in Polyether-Based Electrolytes for Lithium Batteries

We report on the synthesis of poly(diethylene oxide-alt-oxymethylene), P(2EO-MO), via cationic ring-opening polymerization of the cyclic ether monomer, 1,3,6-trioxocane. We use a combined experimental and computational approach to study ion transport in electrolytes comprising mixtures of P(2EO-MO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt. Mixtures of poly(ethylene oxide) (PEO) and LiTFSI are used as a baseline. The maximum ionic conductivities, σ, of P(2EO-MO) and PEO electrolytes at 90 °C are 1.1 × 10^(–3) and 1.5 × 10^(–3) S/cm, respectively. This difference is attributed to the T_g of P(2EO-MO)/LiTFSI (−12 °C), which is significantly higher than that of PEO/LiTFSI (−44 °C) at the same salt concentration. Self-diffusion coefficients measured using pulsed-field gradient NMR (PFG-NMR) show that both Li+ and TFSI– ions diffuse more rapidly in PEO than in P(2EO-MO). However, the NMR-based cation transference number in P(2EO-MO) (0.36) is approximately twice that in PEO (0.19). The transference number measured by the steady-state current technique, t_(+,ss), in P(2EO-MO) (0.20) is higher than in PEO (0.08) by a similar factor. We find that the product σt_(+,ss) is greater in P(2-EO-MO) electrolytes; thus, P(2EO-MO) is expected to sustain higher steady-state currents under dc polarization, making it a more efficacious electrolyte for battery applications. Molecular-level insight into the factors that govern ion transport in our electrolytes was obtained using MD simulations. These simulations show that the solvation structures around Li+ are similar in both polymers. The same is true for TFSI–. However, the density of Li+ solvation sites in P(2EO-MO) is double that in PEO. We posit that this is responsible for the observed differences in the experimentally determined transport properties of P(2EO-MO) and PEO electrolytes

Rainfall and sentinel chicken seroconversions predict human cases of Murray Valley encephalitis in the north of Western Australia

Background Murray Valley encephalitis virus (MVEV) is a flavivirus that occurs in Australia and New Guinea. While clinical cases are uncommon, MVEV can cause severe encephalitis with high mortality. Sentinel chicken surveillance is used at many sites around Australia to provide an early warning system for risk of human infection in areas that have low population density and geographical remoteness. MVEV in Western Australia occurs in areas of low population density and geographical remoteness, resulting in logistical challenges with surveillance systems and few human cases. While epidemiological data has suggested an association between rainfall and MVEV activity in outbreak years, it has not been quantified, and the association between rainfall and sporadic cases is less clear. In this study we analysed 22 years of sentinel chicken and human case data from Western Australia in order to evaluate the effectiveness of sentinel chicken surveillance for MVEV and assess the association between rainfall and MVEV activity. Methods Sentinel chicken seroconversion, human case and rainfall data from the Kimberley and Pilbara regions of Western Australia from 1990 to 2011 were analysed using negative binomial regression. Sentinel chicken seroconversion and human cases were used as dependent variables in the model. The model was then tested against sentinel chicken and rainfall data from 2012 and 2013.Results Sentinel chicken seroconversion preceded all human cases except two in March 1993. Rainfall in the prior three months was significantly associated with both sentinel chicken seroconversion and human cases across the regions of interest. Sentinel chicken seroconversion was also predictive of human cases in the models. The model predicted sentinel chicken seroconversion in the Kimberley but not in the Pilbara, where seroconversions early in 2012 were not predicted. The latter may be due to localised MVEV activity in isolated foci at dams, which do not reflect broader virus activity in the region. Conclusions We showed that rainfall and sentinel chickens provide a useful early warning of MVEV risk to humans across endemic and epidemic areas, and that a combination of the two indicators improves the ability to assess MVEV risk and inform risk management measures

Foregut caustic injuries: Results of the world society of emergency surgery consensus conference

Introduction: Lesions of the upper digestive tract due to ingestion of caustic agents still represent a major medical and surgical emergency worldwide. The work-up of these patients is poorly defined and no clear therapeutic guidelines are available. Purpose of the study: The aim of this study was to provide an evidence-based international consensus on primary and secondary prevention, diagnosis, staging, and treatment of this life-threatening and potentially disabling condition. Methods: An extensive literature search was performed by an international panel of experts under the auspices of the World Society of Emergency Surgery (WSES). The level of evidence of the screened publications was graded using the Oxford 2011 criteria. The level of evidence of the literature and the main topics regarding foregut caustic injuries were discussed during a dedicated meeting in Milan, Italy (April 2015), and during the 3rd Annual Congress of the World Society of Emergency Surgery in Jerusalem, Israel (July 2015). Results: One-hundred-forty-seven full papers which addressed the relevant clinical questions of the research were admitted to the consensus conference. There was an unanimous consensus on the fact that the current literature on foregut caustic injuries lacks homogeneous classification systems and prospective methodology. Moreover, the non-standardized definition of technical and clinical success precludes any accurate comparison of therapeutic modalities. Key recommendations and algorithms based on expert opinions, retrospective studies and literature reviews were proposed and approved during the final consensus conference. The clinical practice guidelines resulting from the consensus conference were approved by the WSES council. Conclusions: The recommendations emerging from this consensus conference, although based on a low level of evidence, have important clinical implications. A world registry of foregut caustic injuries could be useful to collect a homogeneous data-base for prospective clinical studies that may help improving the current clinical practice guidelines