Di‐N‐Methylation of Anti‐Gram‐Positive Aminoglycoside‐Derived Membrane Disruptors Improves Antimicrobial Potency and Broadens Spectrum to Gram‐Negative Bacteria

The effect of di‐N‐methylation of bacterial membrane disruptors derived from aminoglycosides (AGs) on antimicrobial activity is reported. Di‐N‐methylation of cationic amphiphiles derived from several diversely structured AGs resulted in a significant increase in hydrophobicity compared to the parent compounds that improved their interactions with membrane lipids. The modification led to an enhancement in antibacterial activity and a broader antimicrobial spectrum. While the parent compounds were either modestly active or inactive against Gram‐negative pathogens, the corresponding di‐N‐methylated compounds were potent against the tested Gram‐negative as well as Gram‐positive bacterial strains. The reported modification offers a robust strategy for the development of broad‐spectrum membrane‐disrupting antibiotics for topical use.     

Ultrafast Structural Fluctuations of Myoglobin‐Bound Thiocyanate and Selenocyanate Ions Measured with Two‐Dimensional Infrared Photon Echo Spectroscopy

Structural dynamics within the distal cavity of myoglobin protein is investigated using 2D‐IR and IR pump–probe spectroscopy of the N≡C stretch modes of heme‐bound thiocyanate and selenocyanate ions. Although myoglobin‐bound thiocyanate group shows a doublet in its IR absorption spectrum, no cross peaks originating from chemical exchange between the two components are observed in the time‐resolved 2D IR spectra within the experimental time window. Frequency–frequency correlation functions of the two studied anionic ligands are obtained by means of a few different analysis approaches; these functions were then used to elucidate the differences in structural fluctuation around ligand, ligand–protein interactions, and the degree of structural heterogeneity within the hydrophobic pocket of these myoglobin complexes.     

3D Velocimetry and droplet sizing in the Ranque–Hilsch vortex tube

The Ranque–Hilsch vortex tube (RHVT) is a device currently used to generate local cooling. In general, the fluid that is injected into the RHVT is a single-phase gas. In this study, however, we have added a dispersed phase (water droplets) to the gas (nitrogen). By means of phase Doppler particle analysis, three velocity components, their higher order moments, and sizes of droplets were measured, showing high intensity velocity fluctuations in the core region of the main vortex. The frequency spectrum of the velocity is presented and reveals that wobbling of the vortex axis is the cause of the high intensity fluctuations. The wobbling motion reduces the influence of the droplet size on the radial droplet velocity.     

Coupled-cluster calculation of dispersion contributions to interaction energies and polarizabilities

 The induced dipole dispersion-type contributions to the two-body and nonadditive three-body energies and electric dipole polarizabilities are studied for long-range interactions involving the He, Ne, Ar and Kr atoms and the H₂ and N₂ molecules. The coupled-cluster singles and doubles model and large basis sets are used. Comparison of the energy contributions with data derived from experiment shows in most cases the deviations to be less than 1%; therefore, it may be expected that the calculated polarizability increments are accurately determined and can be used to estimate the accuracy of approximate methods. Received: 20 March 2001 / Accepted: 5 April 2001 / Published online: 27 June 2001     

Single bubble deformation and breakup in simple shear flow

Experiments in a parallel band apparatus and a transparent concentric cylinder device allow the observation of bubble deformation (shape and orientation) and breakup as a function of the viscosity ratio λ and the Capillary number Ca. For viscosity ratios between 3.1 × 10⁻⁷ and 6.7 × 10⁻⁸, critical Capillary numbers Ca _c for bubble breakup between 29 and 45 are found. It is furthermore shown that in the given parameter space no clear distinction between tip breakup and fracture can be made for bubbles. An erratum to this article can be found at     

An innovative silicon photomultiplier digitizing camera for gamma-ray astronomy

The single-mirror small-size telescope (SST-1M) is one of the three proposed designs for the small-size telescopes (SSTs) of the Cherenkov Telescope Array (CTA) project. The SST-1M will be equipped with a 4 m-diameter segmented reflector dish and an innovative fully digital camera based on silicon photo-multipliers. Since the SST sub-array will consist of up to 70 telescopes, the challenge is not only to build telescopes with excellent performance, but also to design them so that their components can be commissioned, assembled and tested by industry. In this paper we review the basic steps that led to the design concepts for the SST-1M camera and the ongoing realization of the first prototype, with focus on the innovative solutions adopted for the photodetector plane and the readout and trigger parts of the camera. In addition, we report on results of laboratory measurements on real scale elements that validate the camera design and show that it is capable of matching the CTA requirements of operating up to high moonlight background conditions.     

Bosonic preheating in left-right-symmetric SUSY GUTs

We investigate the possibility of a bosonic preheating in the simplest model of supersymmetric Hybrid Inflation (F-term inflation), where the inflationary superpotential is of the O'Raifertaigh-Witten type. The end of inflation is related to a spontaneous symmetry breaking, which in the context of left-right symmetric models lowers the rank of the gauge group. Our results indicate that the possibility for bosonic preheating in this model is limited. Received: 4 August 1999 / Published online: 14 April 2000     

Shakedown theorems and asymptotic behaviour of solids in non-smooth mechanics

Non-smooth mechanics is concerned with systems for which constraints are imposed on the physical quantities or their time derivatives. This article addresses the asymptotic behaviour (i.e. as time tends towards infinity) of such systems when they are submitted to a given loading history. A special emphasis is laid on shape-memory alloys structures, which are a typical example of systems for which an analysis in non-smooth mechanics is required. Extending the approach introduced by Koiter in plasticity, we state sufficient conditions for the energy dissipation to remain bounded in time, independently on the initial state. Concerning the asymptotic behaviour in the particular case of cyclic loadings, we also point out the fundamental differences that exist between the framework of plasticity and that of non-smooth mechanics.     

Synthesis of Poly[(R,S)-3-hydroxybutyrate- block-ethylene glycol-block-(R,S)-3-hydroxybutyrate] via Anionic ROP

Summary: New synthetic pathway of a-PHB/PEG/a-PHB triblock amphiphilic copolymers is presented. The copolymers are obtained via racemic BL polymerization initiated with respective PEG macroinitiators. The structure of resulting block copolymers has been proved by SEC and NMR spectroscopy.     

Concentrated aqueous MgCl2 solutions. A computer simulation study of the solution structure and excess electron localisation

Molecular Dynamics simulations of aqueous solutions of magnesium chloride were performed. The concentration of the solutions ranged from 0.2 to 4.9 M. The structures of hydration shells of the ions and the topological properties of the ionic structures were analysed using RDFs, Voronoi tessellations, coordination numbers, etc. The regions of crystalline order were found in concentrated MgCl₂ solutions. Cation-centered clusters were selected to study the electron localisation. Quantum calculations were performed on the DFT level using 6-31++G** basis set. The absorption spectra of the excess electron in MgCl₂ solutions were calculated by two different methods: histograms of the LUMO-HOMO energies and the excited states energies obtained from the time-dependent DFT.