Stratified flow over a backward‐facing step: hybrid solution by integral transforms

The generalized integral transform technique (GITT) is employed in the hybrid numerical–analytical solution of the stratified backward‐facing step flow problem, with automatic global accuracy control towards a user‐prescribed accuracy target. The present paper is aimed at extending the available database on benchmark results in heat and fluid flow, which were progressively obtained through integral transforms, for the co‐validation of more flexible fully discrete approaches. Numerical results are presented for the situations more frequently encountered in the literature Copyright © 2001 John Wiley & Sons, Ltd.     

A new partitioning scheme for molecular interacting systems within a multiconfigurational or monoconfigurational Hartree–Fock formalism

A new method, based on the spatial decomposition of the reduced‐density and pair‐density matrices and the indistinguishable integrals formalism, is introduced to partition the molecular and stabilization energies into meaningful fragments. These are defined as entirely flexible variable‐size entities, for example, atoms, group of atoms, ions, and interacting monomers. This new partitioning scheme is especially appropriated to study systems in which a directly bonded group‐transfer process occurs. In these cases, the stabilization energies are partitioned into an intrafragment component, associated with the difference of intrinsic affinity to the transferred group between the involved fragments, and an interfragment component, associated with the difference of the magnitude of the interaction between the fragments in the initial and final binding complexes. This method was applied to the study of the arginine–carboxylate interactions, allowing us to have insight into what really happens in this system. Two (zwitterionic and neutral) binding complexes can be considered. The main effects accountable for the preferential stabilizations of the binding complexes are determined to be basis‐set independent. The zwitterionic complex is favored by the interfragment component, while the neutral complex is favored by the larger intrinsic proton affinity of the acetate relatively to the methylguanidium. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 157–176, 1999     

Isobaric volume and enthalpy recovery of glasses. II. A transparent multiparameter theory

A multiordering parameter model for glass-transition phenomena has been developed on the basis of nonequilibrium thermodynamics. In this treatment the state of the glass is determined by the values of N ordering parameters in addition to T and P; the departure from equilibrium is partitioned among the various ordering parameters, each of which is associated with a unique retardation time. These times are assumed to depend on T, P, and on the instantaneous state of the system characterized by its overall departure from equilibrium, giving rise to the well-known nonlinear effects observed in volume and enthalpy recovery. The contribution of each ordering parameter to the departure and the associated retardation times define the fundamental distribution function (the structural retardation spectrum) of the system or, equivalently, its fundamental material response function. These, together with a few experimentally measurable material constants, completely define the recovery behavior of the system when subjected to any thermal treatment. The behavior of the model is explored for various classes of thermal histories of increasing complexity, in order to simulate real experimental situations. The relevant calculations are based on a discrete retardation spectrum, extending over four time decades, and on reasonable values of the relevant material constants in order to imitate the behavior of polymer glasses. The model clearly separates the contribution of the retardation spectrum from the temperature-structure dependence of the retardation times which controls its shifts along the experimental time scale. This is achieved by using the natural time scale of the system which eliminates all the nonlinear effects, thus reducing the response function to the Boltzmann superposition equation, similar to that encountered in the linear viscoelasticity. As a consequence, the system obeys a rate (time) -temperature reduction rule which provides for generalization within each class of thermal treatment. Thus the model establishes a rational basis for comparing theory with experiment, and also various kinds of experiments between themselves. The analysis further predicts interesting features, some of which have often been overlooked. Among these are the impossibility of extraction of the spectrum (or response function) from experiments involving cooling from high temperatures at finite rate; and the appearance of two peaks in the expansion coefficient, or heat capacity, during the heating state of three-step thermal cycles starting at high temperatures. Finally, the theory also provides a rationale for interpreting the time dependence of mechanical or other structure-sensitive properties of glasses as well as for predicting their long-range behavior.     

Search for ideal sulfinyl dienophile and dipolarophile

By analysis, the advantages and drawbacks of the differently substituted vinyl sulfoxides so far reported, (Z)‐3‐p‐tolylsulfinyl acrylonitriles are proposed as the best sulfinyl dienophiles. The stereoselective synthesis of these compounds was optimized by hydrocyanation of sulfinyl alkynes with Et₂AlCN. Their behavior as chiral dienophiles and dipolarophiles is responsible for the high stereocontrol of Diels–Alder and 1,3‐dipolar reactions, respectively. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:453–462, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10066     

Investigation of the Second Harmonic Generation at the Water–Vacuum Interface by Using Multi‐Scale Modeling Methods

Invited for this month′s cover picture are Dr. Tárcius N. Ramos and Prof. Benoît Champagne at the University of Namur (Belgium). The cover picture shows the interfacial selectivity of second harmonic generation at the water‐vacuum interface, which is targeted in this work. In more details, the molecular first hyperpolarizability responses have been calculated by combining classical molecular dynamics and quantum chemistry simulations, and our model was able to distinguish between the bulk and the interfacial contributions. Read the full text of their Research Article at 10.1002/open.202200045.

“… The orientation of the polarization induced by the explicit surrounding water molecules is essential for describing interfacial second harmonic generation studies….” Find out more about the story behind the front cover research at 10.1002/open.202200045.     

Strategies for the Biofunctionalization of Straining Flow Spinning Regenerated Bombyx mori Fibers

High-performance regenerated silkworm (Bombyx mori) silk fibers can be produced efficiently through the straining flow spinning (SFS) technique. In addition to an enhanced biocompatibility that results from the removal of contaminants during the processing of the material, regenerated silk fibers may be functionalized conveniently by using a range of different strategies. In this work, the possibility of implementing various functionalization techniques is explored, including the production of fluorescent fibers that may be tracked when implanted, the combination of the fibers with enzymes to yield fibers with catalytic properties, and the functionalization of the fibers with cell-adhesion motifs to modulate the adherence of different cell lineages to the material. When considered globally, all these techniques are a strong indication not only of the high versatility offered by the functionalization of regenerated fibers in terms of the different chemistries that can be employed, but also on the wide range of applications that can be covered with these functionalized fibers.     

Synthesis and Antimycobacterial Evaluation of N-(4-(Benzyloxy)benzyl)-4-aminoquinolines

Tuberculosis remains a global health problem that affects millions of people around the world. Despite recent efforts in drug development, new alternatives are required. Herein, a series of 27 N-(4-(benzyloxy)benzyl)-4-aminoquinolines were synthesized and evaluated for their ability to inhibit the M. tuberculosis H37Rv strain. Two of these compounds exhibited minimal inhibitory concentrations (MICs) similar to the first-line drug isoniazid. In addition, these hit compounds were selective for the bacillus with no significant change in viability of Vero and HepG2 cells. Finally, chemical stability, permeability and metabolic stability were also evaluated. The obtained data show that the molecular hits can be optimized aiming at the development of drug candidates for tuberculosis treatment.     

Development of an FI-ICP Method for On-Line Preconcentration and Determination of Platinum

This paper presents a new simple and rapid procedure for the preconcentration and determination of platinum. It is based on the adsorption of the metal ion and preconcentration on a micro-column (3cm×3mm) placed in the injection valve of a flow injection (FI) manifold and packed with 1,5-bis[(2-pyridyl)-3-sulphophenyl-methylene]thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex 1X8-200). The metal was eluted from the column using a solution of 2M HNO₃. Various parameters and chemical variables affecting the preconcentration and determination of this metal by ICP-AES were evaluated. Five variables (sample flow rate, eluent flow rate, nebulizer flow rate, buffer concentration and mixing coil length) were considered as factors in the optimisation process. Interactions between analytical factors, and their optimal levels were investigated using two level factorial and central matrix designs. The optimum conditions established were applied to the determination of platinum by flow injection inductively coupled plasma atomic emission spectrometry (FI-ICP-AES). The method has a linear calibration range of 25 to at least 200ngmL^–1 with a detection limit of 7.4ngmL^–1 (S/N=3) and a throughput of 10 samples h^–1 using 5min. preconcentration time. The precision of the method (RSD) was 3.06% ngmL^–1 at the 50ngmL^–1 level of Pt(IV) and 2.93% at the 150ngmL^–1 level. The accuracy of the method was examined by determining the analyte content in spiked waters and by analysing an automobile catalyst standard reference material. The results show good agreement with the certified value and sufficiently high recoveries.