Sodium Carbazolide and Derivatives as Solid-State Electrolytes for Sodium-Ion Batteries

Replacing widely used organic liquid electrolytes with solid-state electrolytes (SSEs) could effectively solve the safety issues in sodium-ion batteries. Efforts on seeking novel solid-state electrolytes have been continued for decades. However, issues about SSEs still exist, such as low ionic conductivity at ambient temperature, difficulty in manufacturing, low electrochemical stability, poor compatibility with electrodes, etc. Here, sodium carbazolide (Na-CZ) and its THF-coordinated derivatives are rationally fabricated as Na⁺ conductors, and two of their crystal structures are successfully solved. Among these materials, THF-coordinated complexes exhibit fast Na⁺ conductivities, i.e., 1.20×10⁻⁴ S cm⁻¹ and 1.95×10⁻³ S cm⁻¹ at 90 °C for Na-CZ-1THF and Na-CZ-2THF, respectively, which are among the top Na⁺ conductors under the same condition. Furthermore, stable Na plating/stripping is observed even over 400 h cycling, showing outstanding interfacial stability and compatibility against Na electrode. More advantages such as ease of synthesis, low-cost, and cold pressing for molding can be obtained. In situ NMR results revealed that the evaporation of THF may play an essential role in the Na⁺ migration, where the movement of THF creates defects/vacancies and facilitates the migration of Na⁺.     

Nematic polymer mechanics: flow-induced anisotropy

In this paper, we model and compute flow-induced mechanical properties of nematic polymer nano-composites, consisting of transversely isotropic rigid spheroids in an isotropic matrix. Our goal is to fill a gap in the theoretical literature between random and perfectly aligned spheroidal composites (Odegard et al. in Compos. Sci. Technol. 63, 1671–1687, 2003; Gusev et al. in Adv. Eng. Mater. 4(12), 927–931 2002; Torquato in Random heterogeneous materials. Springer, Berlin Heidelberg New York, 2002; Milton in The Theory of Composites. Cambridge University Press, Cambridge, 2002) by modeling the influence of nano-particle volume fraction, flow type and flow rate on nano-composite elasticity tensors. As these influences vary, we predict the degree of elastic anisotropy, determining the number of independent moduli, and compute their values relative to the nano-particle and matrix moduli. We restrict here to monodomains, addressing features associated with orientational configurations of the rod or platelet ensemble. The key modeling advance is the transfer of symmetries (Forest et al. in Phys. Fluids 12(3), 490–498, 2000) and numerical databases (Forest et al. in Rheol. Acta 43(1), 17–37, 2004a, Rheol. Acta 44(1), 80–93, 2004b) for the orientational probability distribution function of the nematic polymer ensemble into the classical Mori–Tanaka effective elasticity tensor formalism. Isotropic, transversely isotropic, orthotropic, monoclinic, and maximally anisotropic elasticity tensors are realized as volume fraction, imposed flow type and flow strength are varied, with 2, 5, 9, 13 or 21 independent moduli for the various symmetries.     

Rapid quantitative measurements of proteomes by Fourier transform ion cyclotron resonance mass spectrometry.

The patterns of gene expression, post-translational modifications, protein/biomolecular interactions, and how these may be affected by changes in the environment, cannot be accurately predicted from DNA sequences. Approaches for proteome characterization are generally based upon mass spectrometric analysis of in-gel digested two dimensional polyacrylamide gel electrophoresis (2-D PAGE) separated proteins, allowing relatively rapid protein identification compared to conventional approaches. This technique, however, is constrained by the speed of the 2-D PAGE separations, the sensitivity limits intrinsic to staining necessary for protein visualization, the speed and sensitivity of subsequent mass spectrometric analyses for identification, and the limited ability for accurate quantitative measurements based on differences in spot intensity. We are presently developing alternative approaches for proteomics based upon the combination of fast capillary electrophoresis, or other suitable chromatographic separations, and the high mass accuracy and sensitivity obtainable with unique Fourier transform ion cyclotron resonance (FTICR) mass spectrometers available at our laboratory. Several approaches are presently being pursued; one based upon the analysis of intact proteins and the second upon approaches for global protein digestion and accurate peptide mass analysis. Quantitation of protein/peptide levels are based on using two or more stable-isotope labeled versions of proteomes which are combined to obtain precise quantitation of relative protein abundances. We describe the status of our efforts towards the development of a high-throughput proteomics capability and present initial results for application to several microorganisms and discuss our efforts for extending the developed capability to mammalian proteomes.     

Free Damage Propagation with Memory

We introduce a simple model for free damage propagation based on non-local potentials. The model is developed using a state based peridynamic formulation. The resulting evolution is shown to be well posed. At each instant of the evolution we identify the damage set. On this set the local strain has exceeded critical values either for tensile or hydrostatic strain and damage has occurred. For this model the damage set is nondecreasing with time and associated with damage variables defined at each point in the body. We show that energy balance holds for this evolution. For differentiable displacements away from the damage set we show that the nonlocal model converges to the linear elastic model.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

A saddle-point theorem with application to structural optimization

The relaxation for optimal complicance design is independent of whether the underlying elastic problem is formulated in terms of displacements or strains. For the purposes of numerical experimentation and computation, it may be advantageous to formulate optimal design problems in terms of displacements as is done in Ref. 1. The relaxed problem delivered by the displacement-based formulation is of min-min-max type. Because of this, efficient numerical implementation is hampered by the order of the last two min-max operations. We show here that the last two min-max operations may be exchanged, facilitating an efficient numerical algorithm. We remark that the rigorous results given here corroborate the numerical methods and experiments given in Ref. 1.This work was supported by NSF Grant DMS-92-05158.     

On the Fourier spectrum of symmetric Boolean functions

We study the following questionWhat is the smallest t such that every symmetric boolean function on κ variables (which is not a constant or a parity function), has a non-zero Fourier coefficient of order at least 1 and at most t?We exclude the constant functions for which there is no such t and the parity functions for which t has to be κ. Let τ (κ) be the smallest such t. Our main result is that for large κ, τ (κ)≤4κ/logκ.The motivation for our work is to understand the complexity of learning symmetric juntas. A κ-junta is a boolean function of n variables that depends only on an unknown subset of κ variables. A symmetric κ-junta is a junta that is symmetric in the variables it depends on. Our result implies an algorithm to learn the class of symmetric κ-juntas, in the uniform PAC learning model, in time n ^o(κ) . This improves on a result of Mossel, O’Donnell and Servedio in [16], who show that symmetric κ-juntas can be learned in time n ^2κ/3.     

PRESSURE-VELOCITY EQUILIBRIUM HYDRODYNAMIC MODELS

This article describes mathematical models for phase separated mixtures of materials that are in pressure and velocity equilibrium but not necessarily temperature equilibrium. General conditions for constitutive models for such mixtures that exhibit a single mixture sound speed are discussed and specific examples are described.     

Molecular structure and dynamics in the low temperature (orthorhombic) phase of NH3BH3

Variable temperature 2H NMR experiments on the orthorhombic phase of selectively deuterated NH3BH3 spanning the static to fast exchange limits of the borane and amine motions are reported. New values of the electric field gradient (EFG) tensor parameters have been obtained from the static 2H spectra of V(zz) = 1.652 (+/-0.082) x 10(21) V/m(2) and eta = 0.00 +/- 0.05 for the borane hydrogens and V(zz) = 2.883 (+/-0.144) x 10(21) V/m(2) and eta = 0.00 +/- 0.05 for the amine hydrogens. The molecular symmetry inferred from the observation of equal EFG tensors for the three borane hydrogens and likewise for the three amine hydrogens is in sharp contrast with the C(s) symmetry derived from diffraction studies. The origin of the apparent discrepancy has been investigated using molecular dynamics methods in combination with electronic structure calculations of NMR parameters, bond lengths, and bond angles. The computation of parameters from a statistical ensemble rather than from a single set of atomic Cartesian coordinates gives values that are in close quantitative agreement with the 2H NMR electric field gradient tensor measurements and are more consistent with the molecular symmetry revealed by the NMR spectra.