Young’s double-slit interference pattern from a twisted beam

A wide range of diffractive elements have been used to evaluate the topological charge of Laguerre–Gaussian beams. Here, we show theoretically and experimentally that this charge can be simply and readily measured from the interference pattern in Young’s double-slit experiment. It can be evaluated from the twisting order of the interference. The results are confronted with previously published studies. The potentialities of the method are then compared with existing techniques.     

Large-eddy simulation of low-frequency unsteadiness in a turbulent shock-induced separation bubble

The need for better understanding of the low-frequency unsteadiness observed in shock wave/turbulent boundary layer interactions has been driving research in this area for several decades. We present here a large-eddy simulation investigation of the interaction between an impinging oblique shock and a Mach 2.3 turbulent boundary layer. Contrary to past large-eddy simulation investigations on shock/turbulent boundary layer interactions, we have used an inflow technique which does not introduce any energetically significant low frequencies into the domain, hence avoiding possible interference with the shock/boundary layer interaction system. The large-eddy simulation has been run for much longer times than previous computational studies making a Fourier analysis of the low frequency possible. The broadband and energetic low-frequency component found in the interaction is in excellent agreement with the experimental findings. Furthermore, a linear stability analysis of the mean flow was performed and a stationary unstable global mode was found. The long-run large-eddy simulation data were analyzed and a phase change in the wall pressure fluctuations was related to the global-mode structure, leading to a possible driving mechanism for the observed low-frequency motions.      

Beta-turn modified gramicidin S analogues containing arylated sugar amino acids display antimicrobial and hemolytic activity comparable to the natural product

This paper describes the design and synthesis of gramicidin S (GS) analogues 10a-c containing arylated sugar amino acids (SAAs) as a replacement of one of the two (D)Phe-Pro beta-turn regions. The cyclic, amphiphilic peptides adopt a beta-sheet conformation featuring an unusual reverse turn induced by the SAAs. The altered turn region induces a slight distortion of the antiparallel beta-sheet, as compared to GS; the overall geometry however closely resembles that of the nonarylated GS analogue 1. GS analogues 10a-c proved to be as active as the parent GS itself as antibacterial agents and are equally efficient in lysing red blood cells. These properties are in sharp contrast to the diminished biological activity displayed by 1. We conclude that the presence of aromaticity in the turn regions of GS derivatives is required for biological activity, whereas the native conformation of the beta-hairpin is not. Our findings may guide future research toward efficient and nonhemolytic GS analogues for combating bacterial infections.     

Comparing column dynamics in the liquid and vapor phase adsorption of biobutanol on an activated carbon monolith

Adsorption - Adsorbent monoliths are gaining increasing interest in gas phase separation processes, but have rarely been studied for liquid phase separations. In this work, we investigate an...     

Synthesis of s-triazolo[4,3-b]pyridazine C-nucleosides

A one step synthesis of s-triazolo[4,3-b]pyridazine using 3-chloro-6-hydrazinopyridazine and an appropriate thioformimidate is described. Applying this procedure to 5-O-benzoyl-1-benzylthio-1-formimidate-D-ribofuranose, 5′ benzoyl-6-chloro-3β-D-ribofuranosyl-s-triazolo[4,3-b]pyridazine was obtained. Substitutions of chlorine by nucleophilic reagents afforded some derivatives of a new series of C-nucleo-sides. Structural determination including anomeric configuration assignment is discussed based mainly on ¹H nmr spectroscopy.     

An Adamantyl Amino Acid Containing Gramicidin S Analogue with Broad Spectrum Antibacterial Activity and Reduced Hemolytic Activity

The cyclic cationic antimicrobial peptide gramicidin S (GS) is an effective topical antibacterial agent that is toxic for human red blood cells (hemolysis). Herein, we present a series of amphiphilic derivatives of GS with either two or four positive charges and characteristics ranging between very polar and very hydrophobic. Screening of this series of peptide derivatives identified a compound that combines effective antibacterial activity with virtually no toxicity within the same concentration range. This peptide acts against both Gram‐negative and Gram‐positive bacteria, including several MRSA strains, and represents an interesting lead for the development of a broadly applicable antibiotic.     

Imidazo[1,5-g][1,4]diazepines, TIBO analogues lacking the phenyl ring: synthesis and evaluation as anti-HIV agents.

The imidazo[1,5-g][1,4]diazepine derivatives 7a and 7b, analogues of TIBO lacking the aromatic ring, were prepared as part of a research program to find compounds displaying antiviral activity against HIV-2 and resistant strains of HIV-1. Condensation of N-trityl and N-tosyl 4-(2-chloroethyl)-imidazole with the appropriate amino alcohols gave compounds 10a-c and 16a-e. The hydroxyl group in these intermediates was activated toward closure of the [1,4]diazepine ring by either conversion to the corresponding chloro derivative, or by N → O transfer of the tosyl group. However, only cyclization to compounds 13a and 13b proved efficient. These products were converted to the target molecules 7 by reaction of their C-2 anion with S₈. In vitro evaluation of compounds 7a,b and 13,a,b in cell culture (CEM SS/HIV-1-LAI and CEM SS/HIV 1 nevirapine resistant cells) revealed that only 13b displayed minimal activity.     

Book Reviews

Linear Algebra, 2nd edition by Serge Lang (1971). Addison-Wesley Publishing Company.

Linear Algebra with Applications by Hugh G. Campbell. Appleton-Century-Crofts, New York, 1971. xiii + 396 pp. + A45.An Engineering Approach to Linear Algebra, by W. W. Sawyer. Cambridge University Press, Cambridge, 1972. 304 pp. ($11.50)

An Engineering Approach to Linear Algebra, By W. W. Sawyer. Cambridge University Press, Cambridge, 1972. 304 pp. ($11.50) Sparse Matrices, by R. P. Tewarson. ($11.95)

Sparse Matrices, by R. P. Tewarson. ($11.95)