Density dependent potentials: structure and thermodynamics

Local density dependent potentials constitute a family of many body potentials which have been recently introduced in mesoscopic modeling of simple and complex fluids. We construct a field theory for these potentials and calculate the structure factor of the fluid through a saddle point expansion. We propose also an integral equation for local density potentials which shows quantitative agreement both for the correlation functions and thermodynamic properties of such potentials, even close to binodals where the simpler saddle point approximation fails. Contrary to the limitations of global density dependent potentials, there is no ambiguity in the expression of thermodynamics quantities such as the pressure.     

Respiratory protection against airborne nanoparticles: a review

As a precautionary measure, it is often recommended that workers take steps to reduce their exposure to airborne nanoparticles through the use of respiratory protective devices. The purpose of this study was to provide a review and analysis of the research literature and current recommendations on respirators used for protection against nanoparticles. Key research findings were that studies with particles as small as 4 nm have shown that conventional single-fiber filtration theory can be used to describe the filtration performance of respirators and that the most penetrating particle size for respirators equipped with commonly used electrostatic filter media is in the range of 30–100 nm. Future research needs include human laboratory and workplace protection factor studies to measure the respirator total inward leakage of nanoparticles. Industrial hygienists and safety professionals should continue to use traditional respirator selection guidance for workers exposed to nanoparticles.     

Heterogeneous dynamics, ageing, and rejuvenating in van der Waals liquids

It has been shown over the past ten years that the dynamics close to the glass transition is strongly heterogeneous: fast domains coexist with domains three or four decades slower, the size of these regions being about 3 nm at T(g). The authors extend here a model that has been proposed recently for the glass transition in van der Waals liquids. The authors describe in more details the mechanisms of the alpha relaxation in such liquids. It allows then to interpret physical ageing in van der Waals liquids as the evolution of the density fluctuation distribution towards the equilibrium one. The authors derive the expression of macroscopic quantities (volume, compliance, etc.). Numerical results are compared with experimental data (shape, times to reach equilibrium) for simple thermal histories (quenches, annealings). The authors explain the existence of a "Kovacs memory effect" and the temporal asymmetry between down jump and up jump temperatures experiments, even for systems for which there is no energy barriers. Their model allows also for calculating the evolution of small probe diffusion coefficients during ageing.     

Thermodynamics of interactions of vancomycin and synthetic surrogates of bacterial cell wall

Glycopeptide antibiotics, including vancomycin, form complexes via a set of five hydrogen bonds with the acyl-l-Lys-d-Ala-d-Ala portion of the peptidyl stems of the bacterial cell wall peptidoglycan. This complexation deprives the organism from the ability to cross-link peptidyl stems of the peptidoglycan, leading to bacterial cell death. Four synthetic fragments as surrogates of the components of the bacterial cell wall have been prepared in our lab in multistep syntheses. These synthetic samples were used in investigations of the thermodynamics properties (DeltaG degrees , DeltaH degrees , and TDeltaS degrees ) for the complexation with vancomycin by isothermal titration calorimetry (ITC). Complexation with the glycopeptide analogues is largely enthalpy-driven (formation of five hydrogen bonds), and in the analogues with a single peptidyl stem, the complexation is 1:1. The complexation is more complicated with an approximately 2 kDa cell wall surrogate (compound 4), which possesses two peptidyl stems. The data were suggestive of interactions between the two vancomycin molecules, with an entropic penalty attributable to restriction of molecular movements within the complex due to restriction of motion of the highly mobile acyl-d-Ala-d-Ala moiety of the peptidyl stems. These data were reconciled with the recently determined NMR solution structure for the peptidoglycan fragment 4 and its implications for the larger cell wall.     

MALDI-TOF/TOF de novo sequence analysis of 2-D PAGE-separated proteins from Halorhodospira halophila, a bacterium with unsequenced genome

Because protein identifications rely on matches with sequence databases, high-throughput proteomics is currently largely restricted to those species for which comprehensive sequence databases are available. The identification of proteins derived from organisms with unsequenced genomes mainly depends on homology searching. Here, we report the use of a simplified, gel-based, chemical derivatization strategy for de novo sequence analysis using a MALDI-TOF/TOF mass spectrometer. This approach allows the determination of de novo peptide sequences of up to 20 amino acid residues in length. The protocol was applied on a proteomic study of 2-D PAGE-separated proteins from Halorhodospira halophila, an extremophilic eubacterium with yet unsequenced genome. Using three different homology-based search algorithms, we were able to identify more than 30 proteins from this organism using subpicomole quantities of protein.     

Flexural,impact, rheological and physical characterizations of POM reinforced by carbon nanotubes and paraffin oil

The paraffin oil dispersion technique innovated in the recent years to synthesize bulk polymer nanocomposite materials has a uniform dispersion. This research work aims to study the effect of added carbon nanotubes (CNTs) on flexural, impact and rheology behaviors of polyoxymethylene (POM) reinforced by 0–0.03 wt% of CNT using paraffin oil dispersion technique. The wettability and lamellar thickness were measured and rheological performance investigated using a parallel plate rheometer. The flexural and impact mechanical properties were also evaluated. The fracture surfaces were then examined by microscopy. The results showed that the energy to break, flexural strength and modulus increased proportionally with the addition of the amount of CNT in the matrix. For the rheology behavior, the viscosity decreased at the low percentage of CNT and then increased with increase in the percentage weight ratio of CNT in the POM matrix. It was also noted that the water contact angle rose with the increase the CNT percentages. Copyright © 2016 John Wiley & Sons, Ltd.     

UV/Vis,IR and 1H NMR spectroscopic studies of bisazo-dianil compounds based on 5-(2-carboxyphenyl azo)-salicylaldehyde and primary diamines

The electronic absorption and emission spectra of the titled biazo-dianils are studied in organic solvents of different polarity as well as in aqueous buffer solutions of varying pH. The important bands in the IR spectra as well as the main signals of the 1H NMR spectra are assigned. The observed UV/Vis absorption bands are assigned to the corresponding electronic transitions. The fluorescence quantum yield and pK(a)(-) values in the ground and excited states are determined.     

Shear flow effect on phase behavior and morphology in polymer blends

The effect of simple shear flow on the phase behavior and morphology was investigated for both polystyrene/poly(vinyl methyl ether) (PS/PVME) and poly(methyl methacrylate)/poly(styrene‐co‐acrylonitrile) (PMMA /SAN‐29.5) blends, which have LCST (lower critical solution temperature)‐type phase diagram. The measurements were carried out using a special shear apparatus of two parallel glass plates type. The PS/PVME blends showed shear‐induced demixing and shear‐induced mixing at low and high shear rate values, respectively. In addition, the rotation speed and the sample thickness were found to have a pronounced effect on the phase behavior under shear flow. On the‐other hand, PMMA/SAN blend showed only shear‐induced mixing and the magnitudes of the elevation of the cloud points were found to be composition and molecular weight dependent. The morphology of the PMMA/SAN=75/25 blend indicated that shear‐induced mixing occurred at a critical shear rate value, below which the two phases were highly oriented and elongated in the flow direction.     

Enrichment of Zinc and Iron Micronutrients in Lentil (Lens culinaris Medik.) through Biofortification

Biofortification of pulse crops with Zn and Fe is a viable approach to combat their widespread deficiencies in humans. Lentil (Lens culinaris Medik.) is a widely consumed edible crop possessing a high level of Zn and Fe micronutrients. Thus, the present study was conducted to examine the influence of foliar application of Zn and Fe on productivity, concentration, uptake and the economics of lentil cultivation (LL 931). For this, different treatment combinations of ZnSO₄·7H₂O (0.5%) and FeSO₄·7H₂O (0.5%), along with the recommended dose of fertilizer (RDF), were applied to the lentil. The results of study reported that the combined foliar application of ZnSO₄·7H₂O (0.5%) + FeSO₄·7H₂O (0.5%) at pre-flowering (S1) and pod formation (S2) stages was most effective in enhancing grain and straw yield, Zn and Fe concentration, and uptake. However, the outcome of this treatment was statistically on par with the results obtained under the treatment ZnSO₄·7H₂O (0.5%) + FeSO₄·7H₂O (0.5%) at S1 stage. A single spray of ZnSO₄·7H₂O (0.5%) + FeSO₄·7H₂O (0.5%) at S1 stage enhanced the grain and straw yield up to 39.6% and 51.8%, respectively. Similarly, Zn and Fe concentrations showed enhancement in grain (10.9% and 20.4%, respectively) and straw (27.5% and 27.6% respectively) of the lentil. The increase in Zn and Fe uptake by grain was 54.8% and 68.0%, respectively, whereas uptake by straw was 93.6% and 93.7%, respectively. Also the benefit:cost was the highest (1.96) with application of ZnSO₄·7H₂O (0.5%) + FeSO₄·7H₂O (0.5%) at S1 stage. Conclusively, the combined use of ZnSO₄·7H₂O (0.5%) + FeSO₄·7H₂O (0.5%) at S1 stage can contribute significantly towards yield, Zn and Fe concentration, as well as uptake and the economic returns of lentil to remediate the Zn and Fe deficiency.     

On countable completions of quotient ordered semigroups

A poset is said to be ω-chain complete if every countable chain in it has a least upper bound. It is known that every partially ordered set has a natural ω-completion. In this paper we study the ω-completion of partially ordered semigroups, and the topological action of such a semigroup on its ω-completion. We show that, for partially ordered semigroups, ω-completion and quotient with respect to congruences are two operations that commute with each other. This contrasts with the case of general partially ordered sets.