Filling the void in confined polymer nematics: phase transitions in a minimal model of dsDNA packing

Inspired to understand the complex spectrum of space-filling organizations the dsDNA genome within the capsid of bacterial viruses, we study a minimal, coarse-grained model of single chains densely-packed into a finite spherical volume. We build the three basic elements of the model--i) the absence of chain ends ii) the tendency of parallel-strand alignment and iii) a preference of uniform areal density of chain segments--into a polymer nematic theory for confined chains. Given the geometric constraints of the problem, we show that axially symmetric packings fall into one of three topologies: the coaxial spool; the simple solenoid; and the twisted-solenoid. Among these, only the twisted-solenoid fills the volume without the presence of line-like disclinations, or voids, and are therefore generically preferred in the incompressible limit. An analysis of the thermodynamics behavior of this simple model reveals a rich behavior, a generic sequence of phases from the empty state for small container sizes, to the coaxial spool configuration at intermediate sizes, ultimately giving way, via a second-order, symmetry-breaking transition, to the twisted-solenoid structure above a critical sphere size.Comment: 7 pages; 3 figure

The Milky Way Galaxy as a Strong Gravitational Lens

We study the gravitational lensing effects of spiral galaxies by taking a model of the Milky Way and computing its lensing properties. The model is composed of a spherical Hernquist bulge, a Miyamoto-Nagai disc and an isothermal halo. As a strong lens, a spiral galaxy like the Milky Way can give rise to four different imaging geometries. They are (i) three images on one side of the galaxy centre (`disc triplets'), (ii) three images with one close to the centre (`core triplets'), (iii) five images and (iv) seven images. Neglecting magnification bias, we show that the core triplets, disc triplets and fivefold imaging are roughly equally likely. Even though our models contain edge-on discs, their image multiplicities are not dominated by disc triplets. The halo has a small effect on the caustic structure, the time delays and brightnesses of the images. The Milky Way model has a maximum disc (i.e., the halo is not dynamically important in the inner parts). Strong lensing by nearly edge-on disc galaxies breaks the degeneracy between the relative contribution of the disc and halo to the overall rotation curve. If a spiral galaxy has a sub-maximum disc, then the astroid caustic shrinks dramatically in size, whilst the radial caustic shrinks more modestly. This causes changes in the relative likelihood of the image geometries, specifically (i) core triplets are now 9/2 times more likely than disc triplets, (ii) the cross section for threefold imaging is reduced by a factor of 2/3, whilst (iii) the cross section for fivefold imaging is reduced by 1/2. Although multiple imaging is less likely (the cross sections are smaller), the average total magnification is greater.Comment: MNRAS, in pres

Thermal And Mechanical Analysis of High-power Light-emitting Diodes with Ceramic Packages

In this paper we present the thermal and mechanical analysis of high-power light-emitting diodes (LEDs) with ceramic packages. Transient thermal measurements and thermo-mechanical simulation were performed to study the thermal and mechanical characteristics of ceramic packages. Thermal resistance from the junction to the ambient was decreased from 76.1 oC/W to 45.3 oC/W by replacing plastic mould to ceramic mould for LED packages. Higher level of thermo-mechanical stresses in the chip were found for LEDs with ceramic packages despite of less mismatching coefficients of thermal expansion comparing with plastic packages. The results suggest that the thermal performance of LEDs can be improved by using ceramic packages, but the mounting process of the high power LEDs with ceramic packages is critically important and should be in charge of delaminating interface layers in the packages.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Transfer and Development Length of Prestressing Tendons in Full-Scale AASHTO Prestressed Concrete Girders Using Self-Consolidating Concrete

Self-consolidating concrete (SCC) is a highly workable concrete that flows through densely reinforced or complex structural elements under its own weight. The benefits of using SCC include: a) Reducing labor costs by eliminating the need for mechanical vibration, b) Improving constructability, c) Providing a virtually flawless finish, d) Providing uniform and homogenous concrete, and e) Easily filling a complex shape formwork. Even though SCC is comparable to conventional concrete in terms of strength, the comparability of its bond to steel is less well-defined. This disparity of knowledge becomes more critical when using SCC in prestressed members due to the impact that bond strength has on the transfer and development lengths of prestressing tendons. The increasing interest among Illinois precasters in using SCC in bridge girders has motivated the Illinois Department of Transportation (IDOT) and the Illinois Center for Transportation (ICT) to sponsor this synthesis study, which reviews and combines information from literature discussing the impact of using SCC on the transfer and development lengths of prestressing tendons in AASHTO bridge girders. The primary objectives of this study include: (1) Utilizing the results of previous research to evaluate the effect of using SCC on the transfer and development lengths of prestressing tendons and evaluate how SCC compares with conventional concrete, (2) Investigating the feasibility of using SCC in AASHTO bridge girders without the need for changing current design provisions recommended by the ACI and AASHTO, and (3) Providing IDOT with recommendations regarding the application of SCC in prestressed bridge girders. 17. KeyICT-R27-36published or submitted for publicationis peer reviewe

Development of Streams Classification System for Nutrient Criteria in Illinois

USEPApublished or submitted for publicationis peer reviewe