Cubic potential models for cluster radioactivity

Cluster radioactivity is a process by which nuclei equal and heavier than the α-particle is emitted spontaneously. The clusters usually emitted in this process are the α-particle, carbon, oxygen, neon, magnesium, silicon etc. When the mass of the cluster becomes comparable with the mass of the daughter, symmetric fission takes place. Thus the cluster radioactivity is an intermediate process between the well known α-decay and the spontaneous fission. In earlier years such cluster radioactivity was found mostly in actinide nuclei like radium, uranium etc. Very recently it has been predicted that such decays are possible in a new region around ¹¹¹Ba. There has been an exciting experimental detection of the emission of ¹²C from ¹¹¹Ba leading to ¹⁰²Sn, which is attracting a lot of attention recently. To study the phenomenon of cluster radioactivity there are various theoretical models in vogue. The existing models generally fall under two categories: the unified fission model (UFM) and the preformed cluster model (PCM). The physics of the UFM and the PCM are completely different. The UFM considers cluster radioactivity simply as a barrier penetration phenomenon in between the fission and the α-decay without worrying about the cluster being or not being preformed in the parent nucleus. In the PCM clusters are assumed to be preborn in a parent nucleus before they could penetrate the potential barrier with a given Q-value. The basic assumption of the UFM is that heavy clusters as well as the α-particle have equal probability of being preformed. In PCM, clusters of different sizes have different probabilities of their being preformed in the parent nucleus. We have developed three fission models during the last decade using the cubic potential for the pre-scission region. The use of these models in the study of cluster radioactivity in both the actinide and barium regions will be discussed in this talk in comparison with the other existing theories.     

Helium implanted CuHf as studied by TDPAC and positron lifetime measurements

¹⁸¹Ta time differential perturbed angular correlation (TDPAC) and positron lifetime measurements were carried out on homogeneously α-implanted CuHf samples. TDPAC measurements indicate the trapping of vacancy clusters and helium associated defect complexes by Hf atoms. The presence of helium-vacancy complexes and helium stabilised voids has been identified by positron lifetime measurements. Further the nucleation and growth stages of helium bubbles have been identified. TDPAC and positron lifetime measurements indicate that Hf atoms act as heterogeneous nucleating centers for helium bubbles. Hf atoms are found to suppress the bubble growth in CuHf as indicated by the results of positron lifetime measurements.     

Interventional Fairness with Indirect Knowledge of Unobserved Protected Attributes

The deployment of machine learning (ML) systems in applications with societal impact has motivated the study of fairness for marginalized groups. Often, the protected attribute is absent from the training dataset for legal reasons. However, datasets still contain proxy attributes that capture protected information and can inject unfairness in the ML model. Some deployed systems allow auditors, decision makers, or affected users to report issues or seek recourse by flagging individual samples. In this work, we examine such systems and consider a feedback-based framework where the protected attribute is unavailable and the flagged samples are indirect knowledge. The reported samples are used as guidance to identify the proxy attributes that are causally dependent on the (unknown) protected attribute. We work under the causal interventional fairness paradigm. Without requiring the underlying structural causal model a priori, we propose an approach that performs conditional independence tests on observed data to identify such proxy attributes. We theoretically prove the optimality of our algorithm, bound its complexity, and complement it with an empirical evaluation demonstrating its efficacy on various real-world and synthetic datasets.     

Crystal structure and DFT analyses of a pentacoordinated PCP pincer nickel(II) complex

The reaction of NiCl₂ with 1,3‐bis[(diphenylphosphanyl)methyl]hexahydropyrimidine in the presence of 2,6‐dimethylphenyl isocyanide and KPF₆ afforded a new pentacoordinated PCP pincer Ni^II complex, namely {1,3‐bis[(diphenylphosphanyl)methyl]hexahydropyrimidin‐2‐yl‐κN²}(2,6‐dimethylphenyl isocyanide‐κC)nickel(II) hexafluoridophosphate 0.70‐hydrate, [Ni(C₉H₉N)(C₃₀H₃₀ClN₂P₂)]PF₆·0.7H₂O or [NiCl{C(NCH₂PPh₂)₂(CH₂)₃‐κ³P,C,P′}(Xylyl‐NC)]PF₆·0.7H₂O, in very good yield. Its X‐ray structure showed a distorted square‐pyramidal geometry and the compound does not undergo dissociation in solution, as shown by variable‐temperature NMR and UV–Vis studies. Density functional theory (DFT) calculations provided an insight into the bonding; the nickel dsp²‐hybridized orbitals form the basal plane and the nearly pure p orbital forms the axial bond. This is consistent with the NBO (natural bond orbital) analysis of analogous nickel(II) complexes.     

Engineering Escherichia coli for Fermentative Dihydrogen Production: Potential Role of NADH-Ferredoxin Oxidoreductase from the Hydrogenosome of Anaerobic Protozoa

Trichomonas vaginalis generates reduced ferredoxin within a unique subcellular organelle, hydrogenosome that is used as a reductant for H₂ production. Pyruvate ferredoxin oxidoreductase and NADH dehydrogenase (NADH-DH) are the two enzymes catalyzing the production of reduced ferredoxin. The genes encoding the two subunits of NADH-DH were cloned and expressed in Escherichia coli. Kinetic properties of the recombinant heterodimer were similar to that of the native enzyme from the hydrogenosome. The recombinant holoenzyme contained 2.15 non-heme iron and 1.95 acid-labile sulfur atoms per heterodimer. The EPR spectrum of the dithionite-reduced protein revealed a [2Fe–2S] cluster with a rhombic symmetry of g _xyz?=?1.917, 1.951, and 2.009 corresponding to cluster N1a of the respiratory complex I. Based on the Fe content, absorption spectrum, and the EPR spectrum of the purified small subunit, the [2Fe–2S] cluster was located in the small subunit of the holoenzyme. This recombinant NADH-DH oxidized NADH and reduced low redox potential electron carriers, such as viologen dyes as well as Clostridium ferredoxin that can couple to hydrogenase for H₂ production from NADH. These results show that this unique hydrogenosome NADH dehydrogenase with a critical role in H₂ evolution in the hydrogenosome can be produced with near-native properties in E. coli for metabolic engineering of the bacterium towards developing a dark fermentation process for conversion of biomass-derived sugars to H₂ as an energy source.     

N-functionalized cyclam based trinuclear copper(II) complexes: electrochemical,magnetic, catalytic and antimicrobial studies

A series of trinuclear Cu(II) complexes have been prepared by Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclotetradecane and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane with aromatic and aliphatic diamines, Cu(II) perchlorate and triethylamine. The complexes were characterized by elemental and spectroscopic analysis. Electrochemical studies of the complexes in DMF solution show three irreversible one-electron reduction processes around E_pc ¹ = −0.73 to −0.98 V, E_pc ² = −0.91 to −1.20 V and E_pc ³ = −1.21 to −1.33 V. ESR spectra and magnetic moments of the trinuclear Cu(II) complexes show the presence of antiferromagnetic coupling. The rate constants for hydrolysis of 4-nitrophenylphosphate by the Cu(II) complexes are in the range of 3.33 × 10⁻² to 7.58 × 10⁻² min⁻¹. The rate constants for the catecholase activity of the complexes fall in the range of 2.67 × 10⁻² to 7.56 × 10⁻² min⁻¹. All the complexes were screened for antifungal and antibacterial activity.     

Peripheral Hexabromination,Hexaphenylation, and Hexaethynylation of meso‐Aryl‐Substituted Subporphyrins

Effective peripheral fabrication methods of meso‐aryl‐substituted subporphyrins were explored for the first time. Hexabrominated subporphyrins 2 were prepared quantitatively from the bromination of subporphyrins 1 with bromine. Hexaphenylated subporphyrins 3 and hexaethynylated subporphyrins 4 and 5 were synthesized by Suzuki–Miyaura coupling and Stille coupling, respectively, in good yields. X‐ray crystal structures of 2 b , 3 b , 4 b , and 5 a revealed preservation of the bowl‐shaped bent structures with bowl depths similar to that of 1 . Hexaethynylated subporphyrins exhibit large two‐photon‐absorption cross‐sections due to effective delocalization of the conjugated network to the ethynyl substituents.     

Versatile Photophysical Properties of meso‐Aryl‐Substituted Subporphyrins: Dipolar and Octupolar Charge‐Transfer Interactions

Donor–acceptor systems based on subporphyrins with nitro and amino substituents at meta and para positions of the meso‐phenyl groups were synthesized and their photophysical properties have been systematically investigated. These molecules show two types of charge‐transfer interactions, that is, from center to periphery and periphery to center depending on the peripheral substitution, in which the subporphyrin moiety plays a dual role as both donor and acceptor. Based on the solvent‐polarity‐dependent photophysical properties, we have shown that the fluorescence emission of para isomers originates from the solvatochromic, dipolar, symmetry‐broken, and relaxed excited states, whereas the non‐solvatochromic fluorescence of meta isomers is of the octupolar type with false symmetry breaking. The restricted meso‐(4‐aminophenyl) rotation at low temperature prevents the intramolecular charge‐transfer (ICT)‐forming process. The two‐photon absorption (TPA) cross‐section values were determined by photoexcitation at 800 nm in nonpolar toluene and polar acetonitrile solvents to see the effect of ICT on the TPA processes. The large enhancement in the TPA cross‐section value of approximately 3200 GM (1 GM=10^?50 cm⁴ s photon^?1) with donor–acceptor substitution has been attributed to the octupolar effect and ICT interactions. A correlation was found between the electron‐donating/‐withdrawing abilities of the peripheral groups and the TPA cross‐section values, that is, p‐aminophenyl>m‐aminophenyl>nitrophenyl. The increased stability of octupolar ICT interactions in highly polar solvents enhances the TPA cross‐section value by a factor of approximately 2 and 4, respectively, for p‐amino‐ and m‐nitrophenyl‐substituted subporphyrins. On the other hand, the stabilization of the symmetry‐broken, dipolar ICT state gives rise to a negligible impact on the TPA processes.     

Characterization of Thermostable Serine Alkaline Protease from an Alkaliphilic Strain Bacillus pumilus MCAS8 and Its Applications

This study describes the characterization and optimization of medium components for an extracellular detergent, surfactant, organic solvent and thermostable serine alkaline protease produced by alkaliphilic Bacillus pumilus MCAS8 strain isolated from Pulicat lake sediments, Tamil Nadu, India. The strain yielded maximum protease (2,214?U/ml) under optimized conditions: carbon source, citric acid??1.5?% (w/w); inducer, soyabean meal??2?% (w/w); pH?11.0; shaking condition 37?°C for 48?h. The enzyme had pH and temperature optima of 9.0 and 60?°C, respectively. The enzyme displayed the molecular mass of 36?kDa in sodium dodecyl sulphate?Cpolyacrylamide gel electrophoresis study and exhibited activity at a wide range of pH (6.0?C11.0) and thermostability (20?C70?°C). More than 70?% residual activity was observed when the enzyme was incubated with dithiothreitol, ethylenediaminetetraacetic acid, ethylene glycol tetraacetic acid and H₂O₂ for 30?min. The protease activity was also enhanced by divalent cations such as Ba²⁺, Ca²⁺ and Mg²⁺ and was strongly inhibited by Fe²⁺, Zn²⁺, Sr²⁺, Hg²⁺ and urea. The enzyme retained more than 50?% of its initial activity after pre-incubation for 1?h in the presence of 5?% (v/v) organic solvents such as dimethyl sulphoxide and acetone. The protease could hydrolyse various native proteinaceous substrates (1?%?w/v) such as bovine serum albumin, casein, skim milk, gelatine, azocasein and haemoglobin. Wash performance analysis of enzyme revealed that it could effectively remove blood stains from the cotton fabric, thus making it suitable to use as an effective detergent additive. The protease enzyme also exhibited promising result in the dehairing of goat skin. The potency of the eco-friendly enzyme without using any chemicals against washing and dehairing showed that the enzyme could be used for various industrial applications.