Structure, reactivity and electronic properties of V-doped Co clusters

Structures, physical and chemical properties of V doped Co$_{13}$ clusters have been studied in detail using density functional theory based first-principles method. We have found anomalous variation in stability of the doped clusters with increasing V concentration, which has been nicely demonstrated in terms of energetics and electronic properties of the clusters. Our study explains the nonmonotonic variation in reactivity of Co$_{13-m}$V$_m$ clusters towards H$_2$ molecules as reported experimentally [J. Phys. Chem. {\bf 94}, 2744 (1990)]. Moreover, it provides useful insight into the cluster geometry and chemically active sites on the cluster surface, which can help to design better catalytic processes.Comment: 10 pages, 9 figures, 4 table

Engineering the magnetic properties of the Mn13_{13} cluster by doping

With a goal to produce giant magnetic moment in Mn$_{13}$ cluster which will be useful for practical applications, we have considered the structure and magnetic properties of pure Mn$_{13}$ cluster and substitutionally doped it with X = Ti, V, Cr, Fe, Co, Ni atom to produce Mn$_{12}$X clusters. We find that Ti and V substitutions in Mn$_{13}$ cluster are the most promising in terms of gaining substantial binding energy as well as achieving higher magnetic moment through ferromagnetic alignment of atom-centered magnetic moments. This has been demonstrated in terms of energetics and electronic properties of the clusters. For comparison, we have also studied the effect of N-capping of Mn$_{13}$ cluster, predicted in the earlier work [Phys. Rev. Lett. {\bf 89}, 185504 (2002)] as a means to produce stable giant magnetic moment in Mn clusters upto cluster size of 5 Mn atoms.Comment: 8 pages, 9 figures, 2 table

Ab initio study of structural stability of small 3dd late transition metal clusters : Interplay of magnetization and hybridization

Using first-principles density functional theory based calculations, we analyze the structural stability of small clusters of 3$d$ late transition metals. We consider the relative stability of the two structures - layer-like structure with hexagonal closed packed stacking and more compact structure of icosahedral symmetry. We find that the Co clusters show an unusual stability in hexagonal symmetry compared to the small clusters of other members which are found to stabilize in icosahedral symmetry based structure. Our study reveals that this is driven by the interplay between the magnetic energy gain and the gain in covalency through $s$-$d$ hybridization effect. Although we have focused our study primarily on clusters of size 19 atoms, we find that this behavior to be general for clusters having sizes between 15 and 20.Comment: 10 pages, 9 figures, work has been accepted in Phys. Rev. B (2011

Heterogeneity in criminal behavior after child birth: the role of ethnicity

This paper documents behavioral differences in parental criminality between majority and minority ethnic groups after child birth. The particular effect we exploit is that of the gender of the first-born child on fathers’ convictions rates. Based on detailed judicial and demographic data from New Zealand, we first show that the previously documented inverse relationship between having a son and father’s criminal behaviour holds across the average of the population. However, when splitting the fathers’ sample by ethnicity, the effect appears to be entirely driven by the white part of the population and that there is no effect on the native Māori. The strong ethnic divide is observed along many dimensions and challenges the implicitly made assumption in the economics of crime literature that findings are universally applicable across cultures and race

Structure, bonding and magnetism in cobalt clusters

The structural, electronic and magnetic properties of Co$_n$ clusters ($n=2-$20) have been investigated using density functional theory within the pseudopotential plane wave method. An unusual hexagonal growth pattern has been observed in the intermediate size range, $n=15-$20. The cobalt atoms are ferromagnetically ordered and the calculated magnetic moments are found to be higher than that of corresponding hcp bulk value, which are in good agreement with the recent Stern-Gerlach experiments. The average coordination number is found to dominate over the average bond length to determine the effective hybridization and consequently the cluster magnetic moment.Comment: 12 pages and 9 figure

Negotiating power relations, gender equality, and collective agency: are village health committees transformative social spaces in northern India?

BACKGROUND: Participatory health initiatives ideally support progressive social change and stronger collective agency for marginalized groups. However, this empowering potential is often limited by inequalities within communities and between communities and outside actors (i.e. government officials, policymakers). We examined how the participatory initiative of Village Health, Sanitation, and Nutrition Committees (VHSNCs) can enable and hinder the renegotiation of power in rural north India. METHODS: Over 18 months, we conducted 74 interviews and 18 focus groups with VHSNC members (including female community health workers and local government officials), non-VHSNC community members, NGO staff, and higherlevel functionaries. We observed 54 VHSNC-related events (such as trainings and meetings). Initial thematic network analysis supported further examination of power relations, gendered “social spaces,” and the “discourses of responsibility” that affected collective agency. RESULTS: VHSNCs supported some re-negotiation of intra-community inequalities, for example by enabling some women to speak in front of men and perform assertive public roles. However, the extent to which these new gender dynamics transformed relations beyond the VHSNC was limited. Furthermore, inequalities between the community and outside stakeholders were re-entrenched through a “discourse of responsibility”: The comparatively powerful outside stakeholders emphasized community responsibility for improving health without acknowledging or correcting barriers to effective VHSNC action. In response, some community members blamed peers for not taking up this responsibility, reinforcing a negative collective identity where participation was futile because no one would work for the greater good. Others resisted this discourse, arguing that the VHSNC alone was not responsible for taking action: Government must also intervene. This counter-narrative also positioned VHSNC participation as futile. CONCLUSIONS: Interventions to strengthen participation in health systems can engender social transformation. However they must consider how changing power relations can be sustained outside participatory spaces, and how discourse frames the rationale for community participation.ISIScopu

Sigma E Regulators Control Hemolytic Activity and Virulence in a Shrimp Pathogenic Vibrio harveyi

Members of the genus Vibrio are important marine and aquaculture pathogens. Hemolytic activity has been identified as a virulence factor in many pathogenic vibrios including V. cholerae, V. parahaemolyticus, V. alginolyticus, V. harveyi and V. vulnificus. We have used transposon mutagenesis to identify genes involved in the hemolytic activity of shrimp-pathogenic V. harveyi strain PSU3316. Out of 1,764 mutants screened, five mutants showed reduced hemolytic activity on sheep blood agar and exhibited virulence attenuation in shrimp (Litopenaeus vannamei). Mutants were identified by comparing transposon junction sequences to a draft of assembly of the PSU3316 genome. Surprisingly none of the disrupted open reading frames or gene neighborhoods contained genes annotated as hemolysins. The gene encoding RseB, a negative regulator of the sigma factor (σE), was interrupted in 2 out of 5 transposon mutants, in addition, the transcription factor CytR, a threonine synthetase, and an efflux-associated cytoplasmic protein were also identified. Knockout mutations introduced into the rpoE operon at the rseB gene exhibited low hemolytic activity in sheep blood agar, and were 3-to 7-fold attenuated for colonization in shrimp. Comparison of whole cell extracted proteins in the rseB mutant (PSU4030) to the wild-type by 2-D gel electrophoresis revealed 6 differentially expressed proteins, including two down-regulated porins (OmpC-like and OmpN) and an upregulated protease (DegQ) which have been associated with σE in other organisms. Our study is the first report linking hemolytic activity to the σE regulators in pathogenic Vibrio species and suggests expression of this virulence-linked phenotype is governed by multiple regulatory pathways within the V. harveyi