Designing polymer metamaterial for protective armor: a coarse-grained formulation

Meccanica - Designing protective armors is important for varied civil and defense applications. Ceramic-polymer composite armors are particularly interesting for their high strength and light...     

Investigation of carbon steel anodic dissolution in ammonium chloride solutions using electrochemical impedance spectroscopy

The anodic dissolution of carbon steel in ammonium chloride (NH₄Cl) solutions (5, 10, and 20 wt%) is investigated via various electrochemical techniques and other complementary techniques. The polarization measurements reveals that the carbon steel is susceptible to general corrosion. The impedance data taken at various overpotentials shows multiple loops, corresponding to capacitance, inductance, and negative capacitance, and the number of time constants observed is also not the same for various NH₄Cl concentrations. From reaction mechanism analysis, a multi-step reaction mechanism with three adsorbed intermediates and three dissolution paths (one chemical path and two electrochemical paths) is proposed to describe the observed patterns in impedance measurements. The surface coverage of intermediate species and the contribution of chemical reaction and electrochemical reaction to the overall corrosion rate are also estimated from the proposed model. The results obtained from field emission scanning electron microscopy and Raman spectroscopy measurements are also reported.     

Kinetics of carbon steel dissolution in ammonium chloride solution containing sodium thiosulfate

The dissolution behavior of carbon steel in ammonium chloride (NH₄Cl) solution containing sodium thiosulfate (Na₂S₂O₃) of various concentrations (0.01 and 0.1 M) was investigated using electrochemical impedance spectroscopy (EIS) and other nonelectrochemical techniques. The weight loss and polarization measurements indicate a significant increase in the NH₄Cl corrosion rate of carbon steel on addition of Na₂S₂O_3. The EIS measurements exhibited two capacitive loops at multiple direct current (dc) potentials for both the concentrations. Electrical equivalent circuit (EEC) and reaction mechanism analysis (RMA) were employed to analyze the impedance data. A four-step mechanism with two intermediate adsorbate species of same charge was proposed to explain the dissolution behavior of carbon steel in the given system. The surface coverage values enumerated that the surface was entirely covered with adsorbed species unlike in the pure NH₄Cl system. Charge transfer resistance and polarization resistance values estimated from RMA parameters indicate the increase in a dissolution rate with dc potential. The surface morphology was inspected via field emission scanning electron microscopy, and the corrosion products including surface state of carbon steel electrode were analyzed using energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.     

Food safety measurement issues: way forward

Ensuring food safety (FS) is a persistent concern frequently faced by many countries. Safeguarding the quality of food that is fit for human consumption is the primary responsibility of the governmental regulatory agencies. For most part, agro-industries and food processors assume voluntary leadership for producing safe food. However, in the event of FS breach, the regulatory responsibility kicks into identify and rectify the situation. Notwithstanding whether it is the regulator or the industry that institutes the remedial action (e.g. improved hygiene and refined agricultural and manufacturing practices), the role of laboratory measurements is central in safeguarding the integrity of a functioning FS system. There are many analytical tools available to implement this task, such as validated analytical methods, natural matrix reference materials, field tested monitoring systems (proactive assessment) and effective surveillance systems (constant vigilance to prevent repeat safety violations). Way forward: existing FS tools are insufficient and should be strengthened with innovative approaches. Examples are: assembling swift intervention logistics to face FS breaches; rapid response systems including communication; robust metrology based measurement systems located at strategic locations in the country; and inter-disciplinary human resource to match the need for capacity development. These issues are discussed.     

A Short New Synthesis of Ethyl trans-Chrysanthemate

The discovery of synthetic pyrethroids with increased insecticidal activity and low mammalian toxicity led to abundance of new synthetic results in the chemistry of pyrethroids¹ . Many of these methods adopted on an industrial scale make use of sigmatropic rearrangement, radical addition and nucleophilic ring closer with carbanions. Herein we report a simple and stereospecific route for the synthesis of ethyl trans-chrysanthernate (1) by utilizing carbonyl stabilized sulphuranes. Although the use of Sulphurane was demonstrated at a much earlier stage for the synthesis of methyl trans-chrysanthe-mate², the present approach makes use of simple reagents and offers some operational advantages.     

Cohomology of arithmetic groups and periods of automorphic forms

We recall some unusual features of the cohomology of arithmetic groups, and propose that they are explained by a hidden action of certain motivic cohomology groups.     

Purification, cloning and expression of an Aspergillus niger lipase for degradation of poly(lactic acid) and poly(ε-caprolactone)

A lipase from Aspergillus niger MTCC 2594 was purified 53.8-fold to homogeneity by hydrophobic interaction chromatography using octyl sepharose and the enzyme showed two protein bands with apparent molecular mass of 35 and 37 kDa respectively. The lipase exhibited maximum activity at pH 7.0 and 37 °C and was stable between pH 4.0 and 10.0 and temperatures up to 50 °C. The values of K_m and V_max were 3.83 mM and 32.21 μmol/min/mg respectively, using olive oil as substrate. Lipase encoding gene, lipA, coded for 297 amino acid residues with conserved pentapeptide sequence, G-H-S-L-G, was cloned and expressed in Pichia pastoris. Although lipA showed high homology with the known Aspergillus lipases, it exhibited differences in putative lid domain. Both native and recombinant lipases have potential for degradation of poly(lactic acid) and poly(ε-caprolactone), and the present study will serve as a baseline of initial studies for its exploitation in polymer degradation.     

Effect of Solvents and pH on <Emphasis Type="Italic">β</Emphasis>-Cyclodextrin Inclusion Complexation of 2,4-Dihydroxyazobenzene and 4-Hydroxyazobenzene

The spectral characteristics of 2,4-dihydroxyazobenzene (DHAB, sudan orange G) and 4-hydroxyazobenzene (HAB) have been studied in various solvents, different hydrogen ion and β-cyclodextrin (β-CD) concentrations, and are compared with azobenzene (AB). The inclusion complexes of the above molecules with β-CD were analyzed by UV-vis spectrometry, flourometry, FT-IR, ¹H NMR, SEM and DFT methods. The solvent study shows that only the azo form is present in DHAB and HAB molecules. The unusually large red shift observed in acidic solutions indicates both molecules exhibit azo-hydrazo tautomerization. In the β-CD solutions, the increase in fluorescence intensity and large bathochromic shift in the S₁ state indicates that DHAB and HAB form 2:2 inclusion complexes, whereas AB forms a 1:1 inclusion complex.