Mechanisms of Diffusional Nucleation of Nanocrystals and Their Self-Assembly into Uniform Colloids

We survey our research on modeling the mechanisms of control of uniformity in growth of nanosize and colloid particles. The former are produced as nanocrystals, by burst-nucleation from solution. The latter, colloid-size particles, are formed by self-assembly (aggregation) of the nanocrystals. In the colloid particle synthesis, the two dynamical processes are coupled, and both are governed by diffusional transport of the respective building blocks (monomers). The interrelation of the two processes allows for synthesis of narrow size distribution colloid dispersions which are of importance in many applications. We first review a mathematical model of diffusive cluster growth by capture of monomer "singlets." Burst nucleation of nanoparticles in solution is then analyzed. Finally, we couple it to the secondary process of aggregation of nanoparticles to form colloids, and we discuss various aspects of the modeling of particle size distribution, as well as other features of the processes considered.Comment: 26 pages in PDF, including 5 figure

Tests of concrete flanged beams reinforced with CFRP bars.

yesTests results of three flanged and two rectangular cross-section concrete beams reinforced with carbon fibre reinforced polymer (CFRP) bars are reported. In addition, a companion concrete flanged beam reinforced with steel bars is tested for comparison purposes. The amount of CFRP reinforcement used and flange thickness were the main parameters investigated in the test specimens. One CFRP reinforced concrete rectangular beam exhibited concrete crushing failure mode, whereas the other four CFRP reinforced concrete beams failed due to tensile rupture of CFRP bars. The ACI 440 design guide for FRP reinforced concrete members underestimated the moment capacity of beams failed due to CFRP tensile rupture and reasonably predicted deflections of the beams tested. A simplified theoretical analysis for estimating the moment capacity of concrete flanged beams reinforced with FRP bars was developed. The experimental moment capacity of the CFRP reinforced concrete beams tested compared favourably with that predicted by the theoretical analysis developed

Fresh look at randomly branched polymers

We develop a new, dynamical field theory of isotropic randomly branched polymers, and we use this model in conjunction with the renormalization group (RG) to study several prominent problems in the physics of these polymers. Our model provides an alternative vantage point to understand the swollen phase via dimensional reduction. We reveal a hidden Becchi-Rouet-Stora (BRS) symmetry of the model that describes the collapse ($\theta$-)transition to compact polymer-conformations, and calculate the critical exponents to 2-loop order. It turns out that the long-standing 1-loop results for these exponents are not entirely correct. A runaway of the RG flow indicates that the so-called $\theta^\prime$-transition could be a fluctuation induced first order transition.Comment: 4 page

Mechanism of Formation of Monodispersed Colloids by Aggregation of Nanosize Precursors

It has been experimentally established in numerous cases that precipitation of monodispersed colloids from homogeneous solutions is a complex process. Specifically, it was found that in many systems nuclei, produced rapidly in a supersaturated solution, grow to nanosize primary particles (singlets), which then coagulate to form much larger final colloids in a process dominated by irreversible capture of these singlets. This paper describes a kinetic model that explains the formation of dispersions of narrow size distribution in such systems. Numerical simulations of the kinetic equations, with experimental model parameter values, are reported. The model was tested for a system involving formation of uniform spherical gold particles by reduction of auric chloride in aqueous solutions. The calculated average size, the width of the particle size distribution, and the time scale of the process, agreed reasonably well with the experimental values.Comment: 38 pages in plain TeX and 7 JPG figure

Scaling behaviour of lattice animals at the upper critical dimension

We perform numerical simulations of the lattice-animal problem at the upper critical dimension d=8 on hypercubic lattices in order to investigate logarithmic corrections to scaling there. Our stochastic sampling method is based on the pruned-enriched Rosenbluth method (PERM), appropriate to linear polymers, and yields high statistics with animals comprised of up to 8000 sites. We estimate both the partition sums (number of different animals) and the radii of gyration. We re-verify the Parisi-Sourlas prediction for the leading exponents and compare the logarithmic-correction exponents to two partially differing sets of predictions from the literature. Finally, we propose, and test, a new Parisi-Sourlas-type scaling relation appropriate for the logarithmic-correction exponents.Comment: 10 pages, 5 figure

Tracing shadows: How gendered power relations shape the impacts of maternal death on living children in Sub-Saharan Africa

Driven by the need to better understand the full and intergenerational toll of maternal mortality (MM), a mixed-methods study was conducted in four countries in sub-Saharan Africa to investigate the impacts of maternal death on families and children. The present analysis identifies gender as a fundamental driver not only of maternal, but also child health, through manifestations of gender inequity in house- hold decision making, labor and caregiving, and social norms dictating the status of women. Focus group discussions were conducted with community members, and in depth qualitative interviews with key- informants and stakeholders, in Tanzania, Ethiopia, Malawi, and South Africa between April 2012 and October 2013. Findings highlight that socially constructed gender roles, which define mothers as care- givers and fathers as wage earners, and which limit women's agency regarding childcare decisions, among other things, create considerable gaps when it comes to meeting child nutrition, education, and health care needs following a maternal death. Additionally, our findings show that maternal deaths have differential effects on boy and girl children, and exacerbate specific risks for girl children, including early marriage, early pregnancy, and school drop-out. To combat both MM, and to mitigate impacts on children, investment in health services interventions should be complemented by broader interventions regarding social protection, as well as aimed at shifting social norms and opportunity structures regarding gendered divisions of labor and power at household, community, and society levels.Web of Scienc

Assessment of polygenic architecture and risk prediction based on common variants across fourteen cancers

Abstract: Genome-wide association studies (GWAS) have led to the identification of hundreds of susceptibility loci across cancers, but the impact of further studies remains uncertain. Here we analyse summary-level data from GWAS of European ancestry across fourteen cancer sites to estimate the number of common susceptibility variants (polygenicity) and underlying effect-size distribution. All cancers show a high degree of polygenicity, involving at a minimum of thousands of loci. We project that sample sizes required to explain 80% of GWAS heritability vary from 60,000 cases for testicular to over 1,000,000 cases for lung cancer. The maximum relative risk achievable for subjects at the 99th risk percentile of underlying polygenic risk scores (PRS), compared to average risk, ranges from 12 for testicular to 2.5 for ovarian cancer. We show that PRS have potential for risk stratification for cancers of breast, colon and prostate, but less so for others because of modest heritability and lower incidence