Mechanical Behaviors of Alloys From First Principles

Several mesoscale models have been developed to considera number of mechanical properties and microstructuresof Ti-V approximants to Gum Metal and steels from the atomistic scale.In Gum Metal, the relationships between phonon properties and phase stabilities are studied. Our results show thatit is possible to design a BCC (&beta-phase) alloy that deforms near the ideal strength, while maintaining structural stability with respect to the formation of the &omegaand &alpha'' phases. Theoretical diffraction patterns revealthe role of the soft N-point phonon and the BCC-to-HCP transformationpath in post-deformation samples. The total energiesof the path explain the formation of the giant faultsand nano shearbands in Gum Metal.In the study of steels, we focus on the carbon-solute dislocationinteractions. The analysis covers the Eshelby's model of point defectsand first principles calculations. It is argued that the effectsof chemistry and magnetism, omitted in the elasticity model,do not make major contributions to the segregation energy. The predicted solute atmospheres are in good agreementwith atom probe measurements

Thermal fluctuations of biological membranes

At physiological temperatures, most biological membranes noticeably fluctuate and these thermal fluctuations appear to govern an astounding array of biological functions: cell adhesion, membrane fusion, self-assembly, binding–unbinding transition among others. In this discussion, I will: (i) critically re-examine the entropic repulsive force between two fluctuating membranes and attempt to resolve a recent controversy on this issue, (ii) discuss the effect of curvature on thermal fluctuations and, (iii) discuss the connection between thermal fluctuations and electromechanical coupling in membranes –including implications for the minimum electric field that can be -detected by a cell

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Quantum capacitance is a fundamental quantity that can directly reveal many-body interactions among electrons and is expected to play a critical role in nanoelectronics. One of the many tantalizing recent physical revelations about quantum capacitance is that it can possess a negative value, hence allowing for the possibility of enhancing the overall capacitance in some particular material systems beyond the scaling predicted by classical electrostatics. Using detailed quantum mechanical simulations, we found an intriguing result that mechanical strains can tune both signs and values of quantum capacitance. We used a small coaxially gated carbon nanotube as a paradigmatical capacitor system and showed that, for the range of mechanical strain considered, quantum capacitance can be adjusted from very large positive to very large negative values (in the order of plus/minus hundreds of attofarads), compared to the corresponding classical geometric value (0.31035 aF). This finding opens novel avenues in designing quantum capacitance for applications in nanosensors, energy storage, and nanoelectronics. The behavior of nanoscale capacitors is remarkably rich and exhibits features unanticipated by conventional electrostatic theory. Despite having been identified for nearly three decades, 5 quantum capacitance (C Q ) has gained much interest only in recent years. 6-9 Quantum capacitance arises from the finiteness of the density of states and the many-body interactions among electrons. It relates to the change in electron density with the chemical potential of the metallic gate. For a two-dimensional system, this relation is written as where contributions to dm/dn stem from density of states and exchange/correlation energy functional of the gates. A is the area of the two-dimensional system. Since the appearance of C Q requires only a finite dm/dn, it is ubiquitous. Considering different energetic contributions to the electron chemical potential m, the quantum capacitance can then be separated into two components as The capacitance C DOS arises from the limiting density of states, given by C DOS = Ae 2 r(E F ) or C DOS = Le 2 r(E F ) in two-and onedimensional systems, respectively. The symbol r(E F ) represents the density of states (DOS) at the fermi level E F . e is the electron charge. The many-body effects are lumped together as 1/C XC , in which both the exchange and correlation energy functionals are included. As discussed in ref. 4, the capacitance C XC is negative. Luryi has also reported that quantum capacitance depends on the electrical screening behaviors of the metallic gates

Effects of Re on Vacancy Mobility in a Ni-Re System: An Atomistic Study

The performance of modern Ni-based superalloys depends critically on the kinetic transport of point defects around solutes such as rhenium. Here, we use atomistic calculations to study the diffusion of vacancy in the low-concentration limit, using the crystalline fcc-framework nickel as a model. On-the-fly kinetic Monte Carlo is combined with an efficient energy-valley search to find energies of saddle points, based on energetics from the embedded atom method. With this technique, we compute the local energy barriers to vacancy hopping, tracer diffusivities, and migration energies of the low-concentration limit of Ni-Re alloys. It was estimated that the computed diffusion rates are comparable to the reported rates. The presence of Re atoms affects the difference between the energy of the saddle point and the initial energy of point defect hopping. In pure Ni, this difference is about 1 eV, while at 9.66 mol% Re, the value is raised to about 1.5 eV. The vacancy migration energy of vacancy in the 9.66 mol % Re sample is raised above that of pure Ni. Our findings demonstrate that even in the low-concentration limit, Re solute atoms continue to play a crucial role in the mobility of the vacancies.</jats:p

Effects of Re on Vacancy Mobility in a Ni-Re System: An Atomistic Study

The performance of modern Ni-based superalloys depends critically on the kinetic transport of point defects around solutes such as rhenium. Here, we use atomistic calculations to study the diffusion of vacancy in the low-concentration limit, using the crystalline fcc-framework nickel as a model. On-the-fly kinetic Monte Carlo is combined with an efficient energy-valley search to find energies of saddle points, based on energetics from the embedded atom method. With this technique, we compute the local energy barriers to vacancy hopping, tracer diffusivities, and migration energies of the low-concentration limit of Ni-Re alloys. It was estimated that the computed diffusion rates are comparable to the reported rates. The presence of Re atoms affects the difference between the energy of the saddle point and the initial energy of point defect hopping. In pure Ni, this difference is about 1 eV, while at 9.66 mol% Re, the value is raised to about 1.5 eV. The vacancy migration energy of vacancy in the 9.66 mol % Re sample is raised above that of pure Ni. Our findings demonstrate that even in the low-concentration limit, Re solute atoms continue to play a crucial role in the mobility of the vacancies

Novel Dihydro-1,3,2H-benzoxazine Derived from Furfurylamine: Crystal Structure, Hirshfeld Surface Analysis, Photophysical Property, and Computational Study

Dihydro-1,3,2H-benzoxazines (or benzoxazine monomers) are a class of compounds that have been widely utilized in many areas such as the production of the functional polymers and optoelectronic materials. The structure variety of the benzoxazines plays a vital role in their desired properties. The effort of synthesizing functionalized benzoxazines from bioresources is of interest for sustainable development. Herein, we report the synthesis of the novel benzoxazine monomer referred to as 3-(furan-2-ylmethyl)-6-methyl-3,4-dihydro-2H-benzo[e][1,3]oxazine or benzoxazine (I) from a one-pot Mannich reaction using p-cresol, paraformaldehyde, and furfurylamine (a bio-derived amine). An X-ray crystallographic study was performed at low temperature (100 K) to obtain the structural characteristics of the benzoxazine (I). The result reveals that the oxazine ring adopts a half chair conformation to locate all the members of the benzoxazine ring as planar as possible by employing the expansion of the bond angles within the ring. Apart from the structural parameters, the intermolecular interactions were also examined. It was found that the significant interactions within the crystal are C–H···N, C–H···O, and the C–H···π interactions. The C–H···N interactions link the benzoxazine (I) molecules into an infinite molecular chain, propagating along the [100] direction. Hirshfeld surfaces and their corresponding fingerprint plots were comprehensively analyzed to confirm and quantify the significance of these interactions. Moreover, the photophysical properties of the benzoxazine (I) were investigated in solvents with various polarities. The corresponding relations between the structural features, frontier molecular orbitals, and absorption-and-emission characteristics were proposed and explained according to the DFT and TD-DFT calculations.</jats:p

Crystallographic and Spectroscopic Investigations on Oxidative Coordination in the Heteroleptic Mononuclear Complex of Cerium and Benzoxazine Dimer

Among lanthanide-based compounds, cerium compounds exhibit a significant role in a variety of research fields due to their distinct tetravalency, high economic feasibility, and high stability of Ce(IV) complexes. Herein, a systematic investigation of crystallographic information, chemical properties, and mechanistic formation of the novel Ce(IV) complex synthesized from cerium(III) nitrate hexahydrate and 2,2′-(methylazanediyl)bis(methylene)bis(4-methylphenol) (MMD) ligand has been explored. According to the analysis of the crystallographic information, the obtained complex crystal consists of the Ce(IV) center coordinated with two nitrate ligands and two bidentate coordinated (N-protonated and O,O-deprotonated) MMD ligands. The fingerprint plots and the Hirshfeld surface analyses suggest that the C–H⋯O and C–H⋯π interactions significantly contribute to the crystal packing. The C–H⋯O and C–H⋯π contacts link the molecules into infinite molecular chains propagating along the [100] and [010] directions. Synchrotron powder X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) techniques have been employed to gain an understanding of the oxidative complexation of Ce(IV)-MMD complex in detail. This finding would provide the possibility to systematically control the synthetic parameters and wisely design the precursor components in order to achieve the desired properties of novel materials for specific applications.</jats:p