Molecular Dynamics Study of Self-Diffusion in Zr

We employed a recently developed semi-empirical Zr potential to determine the diffusivities in the hcp and bcc Zr via molecular dynamics simulation. The point defect concentration was determined directly from MD simulation rather than from theoretical methods using T=0 calculations. We found that the diffusion proceeds via the interstitial mechanism in the hcp Zr and both the vacancy and interstitial mechanisms give contribution in diffusivity in the bcc Zr. The agreement with the experimental data is excellent for the hcp Zr and for the bcc Zr it is rather good at high temperatures but there is a considerable disagreement at low temperatures

Neron models of intermediate Jacobians associated to moduli spaces

Let $\pi_1:\mathcal{X} \to \Delta$ be a flat family of smooth, projective curves of genus $g \ge 2$, degenerating to an irreducible nodal curve $X_0$ with exactly one node. Fix an invertible sheaf $\mathcal{L}$ on $\mathcal{X}$ of relative odd degree. Let $\pi_2:\mathcal{G}(2,\mathcal{L}) \to \Delta$ be the relative Gieseker moduli space of rank $2$ semi-stable vector bundles with determinant $\mathcal{L}$ over $\mathcal{X}$. Since $\pi_2$ is smooth over $\Delta^*$, there exists a canonical family $\widetilde{\rho}_i:\mathbf{J}^i_{\mathcal{G}(2, \mathcal{L})_{\Delta^*}} \to \Delta^{*}$ of $i$-th intermediate Jacobians i.e., for all $t \in \Delta^*$, $(\widetilde{\rho}_i)^{-1}(t)$ is the $i$-th intermediate Jacobian of $\pi_2^{-1}(t)$. There exist different N\'{e}ron models $\overline{\rho}_i:\overline{\mathbf{J}}_{\mathcal{G}(2, \mathcal{L})}^i \to \Delta$ extending $\widetilde{\rho}_i$ to the entire disc $\Delta$, constructed by Clemens, Saito, Schnell, Zucker and Green-Griffiths-Kerr. In this article, we prove that in our setup, the Neron model $\overline{\rho}_i$ is canonical in the sense that the different Neron models coincide and is an analytic fiber space which graphs admissible normal functions. We also show that for $1 \le i \le \max\{2,g-1\}$, the central fiber of $\overline{\rho}_i$ is a fibration over product of copies of $J^k(\mathrm{Jac}(\widetilde{X}_0))$ for certain values of $k$, where $\widetilde{X}_0$ is the normalization of $X_0$. In particular, for $g \ge 5$ and $i=2, 3, 4$, the central fiber of $\overline{\rho}_i$ is a semi-abelian variety. Furthermore, we prove that the $i$-th generalized intermediate Jacobian of the (singular) central fibre of $\pi_2$ is a fibration over the central fibre of the N\'{e}ron model $\overline{\mathbf{J}}^i_{\mathcal{G}(2, \mathcal{L})}$. In fact, for $i=2$ the fibration is an isomorphism

Strategies for Large-scale Production of Polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible intracellular polyesters that are accumulated as energy and carbon reserves by bacterial species, under nutrient limiting conditions. Successful large-scale production of PHAs is dependent on three crucial factors, which include the cost of substrate, downstream processing cost, and process development. In this respect, design and implementation of bioprocess strategies for efficient PHA bioconversions enable high PHA concentrations, yields and productivities. Additionally, development of PHA fermentation processes using inexpensive substrates, such as agro-industrial wastes, facilitates further cost reduction, thus benefitting large-scale PHA production. Thus, the aim of this review is to highlight various bioprocess strategies for high production of PHAs and their novel copolymers in relatively large quantities. This review also discusses the application of kinetic analysis and mathematical modelling as important tools for process optimization and thus improvement of the overall process economics for large-scale production of PHAs

A specialization property of index

In [Kol13] Kollár defined $i$-th index of a proper scheme over a field. In this note we study how index behaves under specialization, in any characteristic

Examples of varieties with index one on C1 fields

Let K be the fraction field of a Henselian discrete valuation ring with algebraically closed residue field k. In this article we give a sufficient criterion for a projective variety over such a field to have index 1

A note on the determinant map

Classically, there exists a determinant map from the moduli space of semi-stable sheaves on a smooth, projective variety to the Picard scheme. Unfortunately, if the underlying variety is singular, then such a map does not exist. In the case the underlying variety is a nodal curve, a similar map was produced by Bhosle on a stratification of the moduli space of semi-stable sheaves. In this note, we generalize this result to the higher dimension case

Stability and Aggregation Kinetics of Titania Nanomaterials under Environmentally Realistic Conditions.

Nanoparticle morphology is expected to play a significant role in the stability, aggregation behaviour and ultimate fate of engineered nanomaterials in natural aquatic environments. The aggregation kinetics of ellipsoidal and spherical titanium dioxide (TiO2) nanoparticles (NPs) under different surfactant loadings, pH values and ionic strengths were investigated in this study. The stability results revealed that alteration of surface charge was the stability determining factor. Among five different surfactants investigated, sodium citrate and Suwannee river fulvic acid (SRFA) were the most effective stabilizers. It was observed that both types of NPs were more stable in monovalent salts (NaCl and NaNO3) as compared with divalent salts (Ca(NO3)2 and CaCl2). The aggregation of spherical TiO2 NPs demonstrated a strong dependency on the ionic strength regardless of the presence of mono or divalent salts; while the ellipsoids exhibited a lower dependency on the ionic strength but was more stable. This work acts as a benchmark study towards understanding the ultimate fate of stabilized NPs in natural environments that are rich in Ca(CO3)2, NaNO3, NaCl and CaCl2 along with natural organic matters

Scientific discovery and topological transitions in collaboration networks

We analyze the advent and development of eight scientific fields from their inception to maturity and map the evolution of their networks of collaboration over time, measured in terms of co-authorship of scientific papers. We show that as a field develops it undergoes a topological transition in its collaboration structure between a small disconnected graph to a much larger network where a giant connected component of collaboration appears. As a result, the number of edges and nodes in the largest component undergoes a transition between a small fraction of the total to a majority of all occurrences. These results relate to many qualitative observations of the evolution of technology and discussions of the “structure of scientific revolutions”. We analyze this qualitative change in network topology in terms of several quantitative graph theoretical measures, such as density, diameter, and relative size of the network's largest component. To analyze examples of scientific discovery we built databases of scientific publications based on keyword and citation searches, for eight fields, spanning experimental and theoretical science, across areas as diverse as physics, biomedical sciences, and materials science. Each of the databases was vetted by field experts and is the result of a bibliometric search constructed to maximize coverage, while minimizing the occurrence of spurious records. In this way we built databases of publications and authors for superstring theory, cosmic strings and other topological defects, cosmological inflation, carbon nanotubes, quantum computing and computation, prions and scrapie, and H5N1 influenza. We also built a database for a classical example of “pathological” science, namely cold fusion. All these fields also vary in size and in their temporal patterns of development, with some showing explosive growth from an original identifiable discovery (e.g. carbon nanotubes) while others are characterized by a slow process of development (e.g. quantum computers and computation). We show that regardless of the detailed nature of their developmental paths, the process of scientific discovery and the rearrangement of the collaboration structure of emergent fields is characterized by a number of universal features, suggesting that the process of discovery and initial formation of a scientific field, characterized by the moments of discovery, invention and subsequent transition into “normal science” may be understood in general terms, as a process of cognitive and social unification out of many initially separate efforts. Pathological fields, seemingly, never undergo this transition, despite hundreds of publications and the involvement of many authors