Connections on Lie algebroids and on derivation-based noncommutative geometry

In this paper, we show how connections and their generalizations on transitive Lie algebroids are related to the notion of connections in the framework of the derivation-based noncommutative geometry. In order to compare the two constructions, we emphasize the algebraic approach of connections on Lie algebroids, using a suitable differential calculus. Two examples allow this comparison: on the one hand, the Atiyah Lie algebroid of a principal fiber bundle and, on the other hand, the space of derivations of the algebra of endomorphisms of an SL(n,C)-vector bundle. Gauge transformations are also considered in this comparison.     

Electrical and optical analyses of Er-doped silicon grown by liquid-phase epitaxy

We have studied the deep levels present in Er-doped silicon epilayers grown by the liquid-phase epitaxy method by deep level transient spectroscopy (DLTS) and optical DLTS, in order to identify the majority and minority carrier traps and a possible correlation between these traps and the observed photoluminescence (PL) and cathodoluminescence (CL) spectra. Capacitance–voltage analyses have been performed to analyze uniformity and depth distribution of the existing traps and marked differences have been observed between the luminescent and non-luminescent materials.The PL and depth resolved CL revealed the presence of dislocation-related emission lines which can possibly be correlated to the broadened peaks observed in DLTS analyses of luminescent material.     

Nuclide distributions for Fe-like fragments in the 136Xe + 56Fe reaction

The nuclide distributions of Fe-like reaction products from the reaction 5.9 MeV/u ¹³⁶Xe on. ⁵⁶Fe were measured as a function of total kinetic energy loss at a laboratory angle of 55°. The first and second moments of N, Z and A were obtained in addition to the correlation coefficients and the isobaric variances. We compare these results for the Fe-like fragment to those implied by previous measurements of the secondary distribution of the Xe-like fragment. We incorporate the effects of particle evaporation on both the light and heavy complementary primary distributions. There is overall qualitative agreement, but the variances are somewhat smaller than those obtained previously even after correction for particle evaporation. Evaporation calculations are also performed on the primary distributions predicted by a nucleon exchange model, and yield distributions in good agreement with the present experimental data.     

Polarization field effects on the recombination dynamics in low-In-content InGaN multi-quantum wells

The interplay of polarization fields and free carrier screening in In_xGa_1−xN/GaN (0.03<x<0.07) multiple quantum wells is studied by combining photoluminescence (time-integrated and time-resolved) and cathodoluminescence studies, in an excitation density range from 10⁸ to 10¹² cm⁻² of generated e–h pairs. For such low In content, the quantum-confined Stark effect is verified to rule the recombination dynamics, while effects of carrier localization in potential fluctuations have a minor role. Efficient field screening is demonstrated in CL steady-state high-injection conditions and in PL time-resolved experiments at the maximum excitation density. Under recovered nearly flat band conditions, quantum confinement effects are revealed and a high and possibly composition-dependent bowing parameter is extrapolated. Information on radiative and non-radiative rates for carrier recombination in the wells is obtained, both from steady-state and from time-resolved experiments, modelling the carrier dynamics in the framework of a theoretical rate equation model, which calculates electronic states and recombination rates in the nanostructure by coupling complete self-consistent solutions of Schrödinger and Poisson equations.     

Interaction-free, automatic, on-chip fluid routing by surface acoustic waves

By exploiting the resonant coupling between a travelling wave and the stationary modes of a cavity, we present the first scheme for integrated automatic interaction-free surface acoustic wave routing of fluids. Our scheme opens the way to the implementation of logic gates based on instantaneous liquid distribution.     

Kronecker’s limit formula and the height of Euclidean lattices

The height \({h(\Lambda)}\) of a Euclidean lattice \({\Lambda}\) is defined as the derivative at the point 0 of the spectral zeta function of the associated flat torus \({{\bf R}^n /\Lambda}\). The quest of the lattices which realise a minimum of h is an open problem in dimension higher than 3. In this paper, we show that a lattice which realises a local minimum of the height is irreducible, i.e. it cannot be decomposed into the orthogonal sum of two non-zero sublattices. The proof is based on a formula found by Terras, which generalises Kronecker’s limit formula for the Epstein zeta function.     

Determining the structure and mode of action of microbisporicin, a potent lantibiotic active against multiresistant pathogens

Antibiotics blocking bacterial cell wall assembly (beta-lactams and glycopeptides) are facing a challenge from the progressive spread of resistant pathogens. Lantibiotics are promising candidates to alleviate this problem. Microbisporicin, the most potent antibacterial among known comparable lantibiotics, was discovered during a screening applied to uncommon actinomycetes. It is produced by Microbispora sp. as two similarly active and structurally related polypeptides (A1, 2246-Da and A2, 2230-Da) of 24 amino acids linked by 5 intramolecular thioether bridges. Microbisporicin contains two posttranslational modifications that have never been reported previously in lantibiotics: 5-chloro-trypthopan and mono- (in A2) or bis-hydroxylated (in A1) proline. Consistent with screening criteria, microbisporicin selectively blocks peptidoglycan biosynthesis, causing cytoplasmic UDP-linked precursor accumulation. Considering its spectrum of activity and its efficacy in vivo, microbisporicin represents a promising antibiotic to treat emerging infections.