Construction of the B88 exchange-energy functional in two dimensions

We construct a generalized-gradient approximation for the exchange-energy density of finite two-dimensional systems. Guided by non-empirical principles, we include the proper small-gradient limit and the proper tail for the exchange-hole potential. The observed performance is superior to that of the two-dimensional local-density approximation, which underlines the usefulness of the approach in practical applications

On the violation of a local form of the Lieb-Oxford bound

In the framework of density-functional theory, several popular density functionals for exchange and correlation have been constructed to satisfy a local form of the Lieb-Oxford bound. In its original global expression, the bound represents a rigorous lower limit for the indirect Coulomb interaction energy. Here we employ exact-exchange calculations for the G2 test set to show that the local form of the bound is violated in an extensive range of both the dimensionless gradient and the average electron density. Hence, the results demonstrate the severity in the usage of the local form of the bound in functional development. On the other hand, our results suggest alternative ways to construct accurate density functionals for the exchange energy.Comment: (Submitted on 27 April 2012

A Case Study of the Integration of Mine water into Smart Cooling and Heating Network systems

Minewater presents a significant opportunity as an energy source and store in the UK and elsewhere. This research investigates the feasibility and factors necessary to successfully integrate minewater into smart cooling and heating network systems that can support acceleration towards the UK’s net zero target. Heat recovery from minewater offers a lowcarbon source of energy for either heating or cooling and can provide thermal storage, potentially valuable for inter-seasonal demand. The work builds on a feasibility study in Barnsley, Yorkshire, which explored the design of a heat network that integrates heat, power, and mobility and uses waste heat from a glass factory. This work focusses on analyzing the subsurface factors including flowrate, yield, mine void volume, and interconnectivity, which affect the flow and consequently thermal behavior of the available minewater. A 3D model using Petrel and Groundhog have been created combining data from the available boreholes and Coal Authority maps to characterise the subsurface conditions

Mine water utilization as a secondary heat source and heat storage in a smart local heating and cooling distribution system

Mine water has been gaining increasing attention in recent years as a potential source for heat recovery and storage. This is due to its unique properties that make it an ideal medium for capturing and storing large amounts of thermal energy. Mine water is naturally heated by the earth's geothermal energy and typically has a constant temperature throughout the year, making it an excellent source of renewable energy. Additionally, the water's high thermal conductivity and large volumes provide an effective means for storing and transferring heat. With the increasing demand for sustainable energy sources and the need to reduce greenhouse gas emissions, the utilization of mine water for heat recovery and storage has become an attractive option for many industries and communities. In this project, we will explore the benefits of using mine water for heat recovery and storage, as well as some of the risks and challenges that need to be overcome to fully realize its potential as a renewable energy source

Density-based mixing parameter for hybrid functionals

A very popular ab-initio scheme to calculate electronic properties in solids is the use of hybrid functionals in density functional theory (DFT) that mixes a portion of Fock exchange with DFT functionals. In spite of their success, a major problem still remains, related to the use of one single mixing parameter for all materials. Guided by physical arguments that connect the mixing parameter to the dielectric properties of the solid, and ultimately to its band gap, we propose a method to calculate this parameter from the electronic density alone. This method is able to cut significantly the error of traditional hybrid functionals for large and small gap materials, while retaining a good description of structural properties. Moreover, its implementation is simple and leads to a negligible increase of the computational time.Comment: submitte

R-symmetric Gauge Mediation and the MRSSM

This is an invited summary of a seminar talk given at various institutions in the United States and Canada. After a brief introduction, a review of the minimal R-symmetric supersymmetric standard model is given, and the benefits to the flavor sector are discussed. R-symmetric gauge mediation is an attempt to realize this model using metastable supersymmetry breaking techniques. Sample low energy spectra are presented and tuning is discussed. Various other phenomenological results are summarized.Comment: 14 pages, invited Brief Review, submitted to Modern Physics Letters A; v2: replaced Figure 1, updated acknowledgments, fixed typo

Tuning hole mobility in InP nanowires

Transport properties of holes in InP nanowires were calculated considering electron-phonon interaction via deformation potentials, the effect of temperature and strain fields. Using molecular dynamics, we simulate nanowire structures, LO-phonon energy renormalization and lifetime. The valence band ground state changes between light- and heavy-hole character, as the strain fields and the nanowire size are changed. Drastic changes in the mobility arise with the onset of resonance between the LO-phonons and the separation between valence subbands.Comment: 4 pages, 4 figure

Orientational phase transitions in the hexagonal phase of a diblock copolymer melt under shear flow

We generalize the earlier theory by Fredrickson [J. Rheol. v.38, 1045 (1994)] to study the orientational behaviour of the hexagonal phase of diblock copolymer melt subjected to steady shear flow. We use symmetry arguments to show that the orientational ordering in the hexagonal phase is a much weaker effect than in the lamellae. We predict the parallel orientation to be stable at low and the perpendicular orientation at high shear rates. Our analysis reproduces the experimental results by Tepe et al. [Macromolecules v.28, 3008 (1995)] and explains the difficulties in experimental observation of the different orientations in the hexagonal phase.Comment: 21 pages, 6 eps figures, submitted to Physical Review

The Ultrasensitivity of Living Polymers

Synthetic and biological living polymers are self-assembling chains whose chain length distributions (CLDs) are dynamic. We show these dynamics are ultrasensitive: even a small perturbation (e.g. temperature jump) non-linearly distorts the CLD, eliminating or massively augmenting short chains. The origin is fast relaxation of mass variables (mean chain length, monomer concentration) which perturbs CLD shape variables before these can relax via slow chain growth rate fluctuations. Viscosity relaxation predictions agree with experiments on the best-studied synthetic system, alpha-methylstyrene.Comment: 4 pages, submitted to Phys. Rev. Let