Theory of nuclear quadrupole interactions in aluminum and copper metals in presence of muon

The electric field gradients at²⁷Al and⁶³Cu nuclei which are nearest neighbors to the muon in the face-centered cubic metals aluminum and copper, with muon at an octahedral interstitial site, are studied. The electron density fluctuations needed for the evaluation of the electronic, or valence, contributions to field gradients are taken from earlier investigations involving the spherical solid approximation. The enhancement factors a that have to be applied to the electric field-gradients obtained from these approximations, due to the departures of the electronic wave-functions from plane-wave character, and the incorporation of antishielding effects, have been obtained for both APW and OPW approaches to the conduction electron wave-functions and good agreement is found between the results by the two approaches. Size effects due to the lattice distortion associated with the presence of the muon are included through actual point ion summations using available calculated displacements of the ions surrounding the muon. The valence contributions are the dominant ones but the size effect contributions are also significant. The net field-gradient obtained for the²⁷Al site is significantly smaller than experiment while that for⁶³Cu is substantially larger than experiment. Possible sources that could lead to better agreement with experiment are discussed and it is concluded that major improvement is needed in the valence effect contributions in both metals.     

Theoretical Analysis of Viscous Coupling in Two-phase Flow through Porous Media

Theoretical analysis is presented to quantify the viscous coupling effect in two-phase flow through porous media. The analysis is based on the principle of potential difference equations as well as on the interfacial contact area and partition concept. The analysis shows that viscous coupling effect is negligible throughout the normalized saturation range. The expression, Xϕ ², was developed for the quantification of the parameter that controls the amount of viscous coupling, where X was theoretically found to have a maximum value of 2.     

Rapid,catalyst-free crosslinking of silicones using triazines

Silicone elastomers are a class of polymers that are typically cured with metal-based catalysts. There is a need to reduce the presence of metals in polymers for both cost and environmental reasons. We describe the preparation of amino-triazinyl silicone networks that are readily formed, without catalysts, from aminopropyl silicones and cyanuric chloride or, more practicably, a pre-modified dichlorotriazinyl silicone (a masterbatch). The amine groups serve both as nucleophiles leading to crosslinks and to neutralize the HCl byproduct of the reaction. Elastomer properties, ranging from very soft gels to rigid elastomers, could be controlled simply by choice of the telechelic or pendant aminopropylsilicones that were added to the masterbatch. The presence of amines and ammonium ions in the products do not significantly affect the high stability of the elastomers toward hydrolytic or thermal oxidative stress.     

Sequential α-Ketoacid-Hydroxylamine (KAHA) Ligations: Synthesis of C-Terminal Variants of the Modifier Protein UFM1

3 for 3: Sequential α-ketoacid-hydroxylamine (KAHA) ligations with 5-oxaproline allow access to the modifier protein UFM1 (Ubiquitin-fold modifier 1) with a C-terminal amide, carboxylic acid, or a masked thioester. Fmoc protection of an N-terminal 5-oxaproline permits the assembly of proteins of >80 residues in good yield by a two-pot process from three readily prepared medium-sized protein segments.     

Cheminformatic Characterization of Natural Antimicrobial Products for the Development of New Lead Compounds

The growing antimicrobial resistance (AMR) of pathogenic organisms to currently prescribed drugs has resulted in the failure to treat various infections caused by these superbugs. Therefore, to keep pace with the increasing drug resistance, there is a pressing need for novel antimicrobial agents, especially from non-conventional sources. Several natural products (NPs) have been shown to display promising in vitro activities against multidrug-resistant pathogens. Still, only a few of these compounds have been studied as prospective drug candidates. This may be due to the expensive and time-consuming process of conducting important studies on these compounds. The present review focuses on applying cheminformatics strategies to characterize, prioritize, and optimize NPs to develop new lead compounds against antimicrobial resistance pathogens. Moreover, case studies where these strategies have been used to identify potential drug candidates, including a few selected open-access tools commonly used for these studies, are briefly outlined.     

Numerical investigation of mid-infrared emission from Pr^{3+} doped GeAsGaSe fibre

The experimentally obtained luminescence characteristics of a praseodymium (Pr $^{3+})$ doped chalcogenide glass fiber are studied numerically using a rate equation approach. The numerical model includes both the radiative and non-radiative transition paths whilst it neglects the up-conversion processes. Photoluminescence spectra at mid-infrared wavelengths ranging from 3.5 to 6   ${\upmu }$ m were obtained by using two pump wavelengths: 1.55 and 1.94   ${\upmu }$ m. A good agreement between the experiment and theory is obtained for the photoluminescence decay profiles.