Molecular dynamics simulation studies of the structure and the differential capacitance (DC) for the ionic liquid (IL) N-methyl-N-propylpyrrolidinium bis(trifluoromethane)sulfonyl imide (pyr13TFSI) ...near a graphite electrode have been performed as a function temperature and electrode potential. The IL exhibits a multilayer structure that extends 20−30 Å from the electrode surface. The composition and ion orientation in the innermost layer were found to be strongly dependent on the electrode potential. While at potentials near the potential of zero charge (PZC), both cations and anions adjacent to the surface are oriented primarily perpendicular to the surface, the counterions in first layer orient increasingly parallel to the surface with increasing electrode potential. A minimum in DC observed around −1 VRPZC (potential relative to the PZC) corresponds to the point of highest density of perpendicularly aligned TFSI near the electrode. Maxima in the DC observed around +1.5 and −2.5 VRPZC are associated with the onset of “saturation”, or crowding, of the interfacial layer. The asymmetry of DC versus electrode polarity is the result of strong interactions between the fluorine of TFSI and the surface, the relatively large footprint of TFSI compared to pyr13, and the tendency of the propyl tails of pyr13 to remain adsorbed on the surface even at high positive potentials. Finally, an observed decreased DC and the disappearance of the minimum in DC near the PZC with increasing temperature are likely due to the increasing importance of entropic/excluded volume effects (interfacial crowding) with increasing temperature.
Bayesian parameter estimation is fast becoming the language of gravitational-wave astronomy. It is the method by which gravitational-wave data is used to infer the sources' astrophysical properties. ...We introduce a user-friendly Bayesian inference library for gravitational-wave astronomy, Bilby. This Python code provides expert-level parameter estimation infrastructure with straightforward syntax and tools that facilitate use by beginners. It allows users to perform accurate and reliable gravitational-wave parameter estimation on both real, freely available data from LIGO/Virgo and simulated data. We provide a suite of examples for the analysis of compact binary mergers and other types of signal models, including supernovae and the remnants of binary neutron star mergers. These examples illustrate how to change the signal model, implement new likelihood functions, and add new detectors. Bilby has additional functionality to do population studies using hierarchical Bayesian modeling. We provide an example in which we infer the shape of the black hole mass distribution from an ensemble of observations of binary black hole mergers.
Molecular dynamics (MD) simulations of an electrolyte comprised of ethylene carbonate (EC), dimethyl carbonate (DMC), and LiPF6 salt near the basal face of graphite electrodes have been performed as ...a function of electrode potential. Upon charging of the electrodes, the less polar DMC molecule is partially replaced in the interfacial electrolyte layer by the more polar EC. At negative potentials, the carbonyl groups from the carbonate molecules are repelled from the surface, while at positive potentials, we find a substantial enrichment of the surface with carbonyl groups. PF6 – rapidly accumulates at the positive electrode with increasing potential and vacates the negative electrode with increasing negative potential. In contrast, Li+ concentration in the interfacial layer is found to be only weakly dependent on potential except at very large negative potentials. Hence, both composition of the electrolyte at the electrode surface and solvent environment around Li+ are observed to vary dramatically with the applied potential with important implications for oxidation/reduction of the electrolyte and the process of Li+ intercalation/deintercation.
Molecular dynamics simulations of N-methyl-N-propylpyrrolidinium (pyr13) bis(trifluoromethanesulfonyl)imide (Ntf2) ionic liquid pyr13Ntf2 mixed with LiNtf2 salt have been conducted using a ...polarizable force field. Mixture simulations with lithium salt mole fractions between 0% and 33% at 363 and 423 K yield densities, ion self-diffusion coefficients, and ionic conductivities in very good agreement with available experimental data. In all investigated electrolytes, each Li+ cation was found to be coordinated, on average, by 4.1 oxygen atoms from surrounding anions. At lower concentrations (x ≤ 0.20), the Li+ cation was found to be, on average, coordinated by slightly more than three Ntf2 anions with two anions contributing a single oxygen atom and one anion contributing two oxygen atoms to Li+ coordination. At the highest LiNtf2 concentration, however, there were, on average, 3.5 anions coordinating each Li+ cation, corresponding to fewer bidendate and more monodentate anions in the Li+ coordination sphere. This trend is due to increased sharing of anions by Li+ at higher salt concentrations. In the pyr13Ntf2/LiNtf2 electrolytes, the ion diffusivity is significantly smaller than that in organic liquid electrolytes due to not only the greater viscosity of the solvent but also the formation of clusters resulting from sharing of anions by Li+ cations. The ionic conductivity of the electrolytes was found to decrease with increasing salt concentration, with the effect being greater at the higher temperature. Finally, we found that the contribution of Li+ to ionic conductivity does not increase proportionally to Li+ concentration but saturates at higher doping levels.
Quantum chemistry studies of ethylene carbonate (EC) and dimethyl carbonate (DMC) complexes with Li+ and LiPF6 have been conducted. We found that Li+ complexation significantly stabilizes the highly ...polar cis−trans DMC conformation relative to the nearly nonpolar gas-phase low energy cis−cis conformer. As a consequence, the binding of Li+ to EC in the gas phase is not as favorable relative to binding to DMC as previously reported. Furthermore, quantum chemistry studies reveal that, when complexation of LiPF6 ion pairs is considered, the DMC/LiPF6 complex is about 1 kcal/mol more stable than the EC/LiPF6 complex. The EC3DMC(cis−cis)/Li+ complex was found to be the most energetically stable among EC n DMC m /Li+ (n + m = 4) investigated complexes followed by EC4/Li+. Results of the quantum chemistry studies of these complexes were utilized in the development of a many-body polarizable force field for EC:DMC/LiPF6 electrolytes. Molecular dynamics (MD) simulations of EC/LiPF6, DMC/LiPF6, and mixed solvent EC:DMC/LiPF6 electrolytes utilizing this force field were performed at 1 M salt concentration for temperatures from 298 to 363 K. Good agreement was found between MD simulation predictions and experiments for thermodynamic and transport properties of both pure solvents and the electrolytes. We find increased ion pairing with increasing DMC content; however, both EC and DMC were found to participate in Li+ solvation in mixed EC:DMC electrolytes despite a huge difference in their dielectric constants. In contrast to previous NMR studies, where dominance of EC in cation solvation was reported, we find a slight preference for DMC in the cation solvation shell for EC:DMC (1 wt:1 wt) electrolytes and show that reanalyzed Raman spectroscopy experiments are in good agreement with results of MD simulations. Finally, analysis of solvent residence times reveals that cation transport is dominated by motion with solvating DMC and approximately equal contributions from vehicular motions with the first solvation shell and solvent exchange with respect to solvating EC.
Molecular dynamics simulations were performed on N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (pyr13FSI) room temperature ionic liquid (RTIL) confined between graphite electrodes as a ...function of applied potential at 393 and 453 K using an accurate force field developed in this work. The electric double layer (EDL) structure and differential capacitance (DC) of pyr13FSI was compared with the results of the previous study of a similar RTIL pyr13bis(trifluoromethanesulfonyl)imide (pyr13TFSI) with a significantly larger anion Vatamanu J. ; Borodin O. ; Smith G. D. J. Am. Chem. Soc. 2010, 132, 14825 . Intriguingly, the smaller size of the FSI anion compared to TFSI did not result in a significant increase of the DC on the positive electrode. Instead, a 30% higher DC was observed on the negative electrode for pyr13FSI compared to pyr13TFSI. The larger DC observed on the negative electrode for pyr13FSI compared to pyr13TFSI was associated with two structural features of the EDL: (a) a closer approach of FSI compared to TFSI to the electrode surface and (b) a faster rate (vs potential decrease) of anion desorption from the electrode surface for FSI compared to TFSI. Additionally, the limiting behavior of DC at large applied potentials was investigated. Finally, we show that constant potential simulations indicate time scales of hundreds of picoseconds required for electrode charge/discharge and EDL formation.
The mechanisms of lithium cation (Li+) and bis(trifluoromethane)sulfonamide anion (TFSI-) transport in poly(ethylene oxide) (PEO, M w = 2380) melts were examined using molecular dynamics (MD) ...simulations over a wide range of salt concentrations and temperatures. MD simulations using a quantum-chemistry-based many-body polarizable force field yielded ion self-diffusion coefficients, electrolyte conductivity, ion aggregation, and the coordination environment of Li+ in good agreement with experiment. Lithium transport was found to arise from a combination of the subdiffusive Li+ motion along PEO chains, motion together with PEO segments and intersegmental Li+ hops from one PEO segment to another. The rate of intersegmental hops was found to correlate well with times at which Li+ motion crosses over from subdiffusive to diffusive behavior. The contribution of Li+ motion along PEO chains to the total Li+ transport was found to be approximately equal to the contribution from Li+ moving together with PEO segments. Diffusion of both Li+ and TFSI- was found to be strongly coupled to PEO ether oxygen atom displacements and PEO conformational dynamics.
The oxidative decomposition mechanism of the lithium battery electrolyte solvent propylene carbonate (PC) with and without PF6 – and ClO4 – anions has been investigated using the density functional ...theory at the B3LYP/6-311++G(d) level. Calculations were performed in the gas phase (dielectric constant ε = 1) and employing the polarized continuum model with a dielectric constant ε = 20.5 to implicitly account for solvent effects. It has been found that the presence of PF6 – and ClO4 – anions significantly reduces PC oxidation stability, stabilizes the PC–anion oxidation decomposition products, and changes the order of the oxidation decomposition paths. The primary oxidative decomposition products of PC–PF6 – and PC–ClO4 – were CO2 and acetone radical. Formation of HF and PF5 was observed upon the initial step of PC–PF6 – oxidation while HClO4 formed during initial oxidation of PC–ClO4 –. The products from the less likely reaction paths included propanal, a polymer with fluorine and fluoro-alkanols for PC–PF6 – decomposition, while acetic acid, carboxylic acid anhydrides, and Cl– were found among the decomposition products of PC–ClO4 –. The decomposition pathways with the lowest barrier for the oxidized PC–PF6 – and PC–ClO4 – complexes did not result in the incorporation of the fluorine from PF6 – or ClO4 – into the most probable reaction products despite anions and HF being involved in the decomposition mechanism; however, the pathway with the second lowest barrier for the PC–PF6 – oxidative ring-opening resulted in a formation of fluoro-organic compounds, suggesting that these toxic compounds could form at elevated temperatures under oxidizing conditions.
Epidemiology and screening for renal cancer Rossi, Sabrina H.; Klatte, Tobias; Usher-Smith, Juliet ...
World journal of urology,
09/2018, Letnik:
36, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Purpose
The widespread use of abdominal imaging has affected the epidemiology of renal cell carcinoma (RCC). Despite this, over 25% of individuals with RCC have evidence of metastases at ...presentation. Screening for RCC has the potential to downstage the disease.
Methods
We performed a literature review on the epidemiology of RCC and evidence base regarding screening. Furthermore, contemporary RCC epidemiology data was obtained for the United Kingdom and trends in age-standardised rates of incidence and mortality were analysed by annual percentage change statistics and joinpoint regression.
Results
The incidence of RCC in the UK increased by 3.1% annually from 1993 through 2014. Urinary dipstick is an inadequate screening tool due to low sensitivity and specificity. It is unlikely that CT would be recommended for population screening due to cost, radiation dose and increased potential for other incidental findings. Screening ultrasound has a sensitivity and specificity of 82–83% and 98–99%, respectively; however, accuracy is dependent on tumour size. No clinically validated urinary nor serum biomarkers have been identified. Major barriers to population screening include the relatively low prevalence of the disease, the potential for false positives and over-diagnosis of slow-growing RCCs. Individual patient risk-stratification based on a combination of risk factors may improve screening efficiency and minimise harms by identifying a group at high risk of RCC.
Conclusion
The incidence of RCC is increasing. The optimal screening modality and target population remain to be elucidated. An analysis of the benefits and harms of screening for patients and society is warranted.
Dispersing nanoparticles in a polymer matrix is intrinsically challenging because of unfavorable entropic interactions between the matrix and the nanoparticle. Similar to suspensions of larger ...colloidal particles, it has been found that thermodynamically stable dispersions of nanoparticles can be achieved in polymer matrices when the nanoparticles are decorated with dense layers of polymer tethers whose molecular weight is comparable to or greater than that of the matrix. Utilizing molecular dynamics simulations, we demonstrate that, in contrast to larger colloidal particles, repulsive interactions between nanoparticles can be achieved with tethered polymers much shorter than the polymer matrix when relatively sparse grafting is employed.
PDF
