Can correlations drive a band insulator metallic?

We analyze the effects of the on-site Coulomb repulsion U on a band insulator using dynamical mean field theory (DMFT). We find the surprising result that the gap is suppressed to zero at a critical Uc1 and remains zero within a metallic phase. At a larger Uc2 there is a second transition from the metal to a Mott insulator, in which the gap increases with increasing U. These results are qualitatively different from Hartree-Fock theory which gives a monotonically decreasing but nonzero insulating gap for all finite U.     

Evaluation of mixed mode stress intensity factors for interface cracks using EFGM

This paper presents the implementation of element free Galerkin method for the stress analysis of structures having cracks at the interface of two dissimilar materials. The material discontinuity at the interface has been modeled using a jump function with a jump parameter that governs its strength. The jump function enriches the approximation by the addition of special shape function that contains discontinuities in the derivative. The trial and test functions of the weak form are constructed using moving least-square interpolants in each material domain. An intrinsic enrichment criterion with enriched basis has been used to model the crack tip stress fields. The mixed mode (complex) stress intensity factors for bi-material interface cracks are numerically evaluated using the modified domain form of interaction integral. The numerical results are obtained for edge and center cracks lying at the bi-material interface, and are found to be in good agreement with the reference solutions for the interfacial crack problems.     

Explicit convex and concave envelopes through polyhedral subdivisions

In this paper, we derive explicit characterizations of convex and concave envelopes of several nonlinear functions over various subsets of a hyper-rectangle. These envelopes are obtained by identifying polyhedral subdivisions of the hyper-rectangle over which the envelopes can be constructed easily. In particular, we use these techniques to derive, in closed-form, the concave envelopes of concave-extendable supermodular functions and the convex envelopes of disjunctive convex functions.     

Fermions in 3D optical lattices: cooling protocol to obtain antiferromagnetism

A major challenge in realizing antiferromagnetic and superfluid phases in optical lattices is the ability to cool fermions. We determine the equation of state for the 3D repulsive Fermi-Hubbard model as a function of the chemical potential, temperature, and repulsion using unbiased determinantal quantum Monte Carlo methods, and we then use the local density approximation to model a harmonic trap. We show that increasing repulsion leads to cooling but only in a trap, due to the redistribution of entropy from the center to the metallic wings. Thus, even when the average entropy per particle is larger than that required for antiferromagnetism in the homogeneous system, the trap enables the formation of an antiferromagnetic Mott phase.     

Electron impact total cross section calculations for CH3SH (methanethiol) from threshold to 5 keV

We report calculated total elastic cross sections Q_el, total ionisation cross sections, Q_ion, summed total excitation cross sections ∑Q_exc and total cross sections Q_T for CH₃SH upon electron impact for energies from ionisation threshold to 5 keV. We have employed Spherical Complex Optical Potential (SCOP) formalism to calculate total elastic cross section Q_el, and total inelastic cross section Q_inel and used Complex Scattering Potential – the ionisation contribution (CSP-ic) method to extract the ionisation cross sections, Q_ion, from the calculated Q_inel. The calculated total cross sections are examined as functions of incident electron energy and are compared with available data wherever possible and overall good agreement is observed. In this work Q_el, Q_ion, and ∑Q_exc are reported for the first time for CH₃SH in this energy range.     

Self-Assembly Propensity Dictates Lifetimes in Transient Naphthalimide–Dipeptide Nanofibers

Transient self-assembly of dipeptide nanofibers with lifetimes that are predictably variable through dipeptide sequence design are presented. This was achieved using 1,8-naphthalimide ( NI ) amino acid methyl-esters (Phe, Tyr, Leu) that are biocatalytically coupled to amino acid-amides (Phe, Tyr, Leu, Val, Ala, Ser) to form self-assembling NI -dipeptides. However, competing hydrolysis of the dipeptides results in disassembly. It was demonstrated that the kinetic parameters like lifetimes of these nanofibers can be predictably regulated by the thermodynamic parameter, namely the self-assembly propensity of the constituent dipeptide sequence. These lifetimes could vary from minutes, to hours, to permanent gels that do not degrade. Moreover, the in-built NI fluorophore was utilized to image the transient nanostructures in solution with stimulated emission depletion (STED) based super-resolution fluorescence microscopy.     

Condensation of plasmid DNA by benzyl hydraphiles and lariat ethers: dependence on pH and chain length

Lariat ethers and hydraphiles have been studied by the use of gel electrophoresis to evaluate the complexation of a 10 kilobase plasmid DNA. Both receptor systems show behaviour that reflects differences in side or spacer chain lengths. In addition, the formation of complexes or aggregates (identified by transmission electron microscopy, TEM) is pH dependent. Some detergents and polyamines can affect the formation and/or deaggregation of the complexes which TEM shows form particles of a relatively uniform size (~100–150 nm) and density for a specific receptor.