A Study of Neural Networks for the Quantum Many-Body Problem

One of the fundamental problems in analytically approaching the quantum many-body problem is that the amount of information needed to describe a quantum state. As the number of particles in a system grows, the amount of information needed for a full description of the system increases exponentially. A great deal of work then has gone into finding efficient approximate representations of these systems. Among the most popular techniques are Tensor Networks and Quantum Monte Carlo methods. However, one new method with a number of promising theoretical guarantees is the Neural Quantum State. This method is an adaptation of the Restricted Boltzmann machine(RBM). Unlike the traditional RBM, Neural Quantum States act as a feedforward network, calculating a single complex value of the wave function for every spin configuration. We examine this method, and compare its performance to a feedforward network for a similar problem. Another recent application includes the use of neural networks for detecting phase transitions. We examine the claims made about this technique and propose a new method for solving this problem. We report results for both experiments

The 2014 Operational Management Procedure for the South African horse mackerel resource

This document specifies the 2014 Operational Management Procedure (OMP) to provide Precautionary Upper Catch Limit (PUCL) recommendations for horse mackerel bycatches in the South African pelagic fishery and Total Allowable Catch (TAC) recommendations for targeted horse mackerel catches in the South African midwater trawl fishery. The basis for the associated computations for each fishery are set out in separate sections below. Appendix A gives the details for the GLM procedure used to produce a horse mackerel CPUE series for the midwater fishery, and Appendix B describes Exceptional Circumstances (ECs) that could lead to deviations from OMP recommendations

Message-Layer Encryption in Ricochet

My intention for this project was to implement encryption and authentication on Ricochet\u27s message layer. This provides two major benefits. The first is a higher level of encryption in the event that a flaw is found in the existing channel-layer encryption, or if increases in computing power make attacks on that encryption feasible. Tor is used by the military, journalists, law enforcement, researchers, and activists, whose communications may be interesting to state-level adversaries and criminal organizations with access to great amount of computing resources. Additionally, message-layer encryption would allow users to specify relay nodes that can temporarily store messages and forward them once the recipient comes online. Because the channel-layer encryption in hidden services only encrypts data between end users, the addition of authentication and encryption within messages would enable the application to conceal communication data from relay nodes

Inverse opal ceria–zirconia: architectural engineering for heterogeneous catalysis

The application of inverse opal structured materials is extended to the ceria–zirconia (Ce_(0.5)Zr_(0.5)O_2) system and the significance of material architecture on heterogeneous catalysis, specifically, chemical oxidation, is examined

An alternative synthesis of cycloalkyl-substituted CPA catalysts and application in asymmetric protonation reactions

LAM thanks the EPSRC (grant number EP/S027165/1) for postdoctoral funding.An alternative synthesis of cycloalkyl-substituted CPA catalysts is reported. A Negishi coupling offers improved yields and purity of the necessary 1,3,5-tri(cycloalkyl)benzenes. Limitations in the use of commercial organozinc reagents have been identified and a robust procedure for the preparation of these reagents is detailed. Similarly, a robust procedure for the key Kumada coupling is also provided. The route is demonstrated by preparation of three different tri(cycloalkyl)aryl-substituted CPAs and the utility of these catalysts in asymmetric protonation reactions is shown.Publisher PDFPeer reviewe

A preliminary evaluation of the potential use of pelagic survey data in setting the horse mackerel PUCL

The existing population model for the horse-mackerel resource is extended to take commercial catch-at-length information from the mid-water trawl fishery and demersal surveys into account to allow the estimation of recruitment variations, which are correlated with the results for horse-mackerel abundance (considered to primarily reflect recruits) from the November pelagic surveys. Correlation is better with results for the West coast only from these surveys, rather than with those for the assessment area as a whole. At this stage the conclusion is either that these November survey estimates are (for whatever reason) a relatively weak predictor of incoming horse-mackerel recruitment strength, or that there are problems with the modelling of the demersal/midwater data which require further attention

Nernst quantum oscillations in bulk semi-metals

With a widely available magnetic field of 10 T, one can attain the quantum limit in bismuth and graphite. At zero magnetic field, these two elemental semi-metals host a dilute liquid of carriers of both signs. When the quantum limit is attained, all quasi-particles are confined to a few Landau tubes. Each time a Landau tube is squeezed before definitely leaving the Fermi surface, the Nernst response sharply peaks. In bismuth, additional Nernst peaks, unexpected in the non-interacting picture, are resolved beyond the quantum limit. The amplitude of these unexpected Nernst peaks is larger in the samples with the longest electron mean-free-path.Comment: Accepted for publication in Journal of Physics: Condensed Matter's special issue on Strongly Correlated Electron Systems(SCES

A model for drift velocity mediated scalar eddy diffusivity in homogeneous turbulent flows

Low Stokes number particles at dilute concentrations in turbulent flows can reasonably be approximated as passive scalars. The added presence of a drift velocity due to buoyancy or gravity when considering the transport of such passive scalars can reduce the turbulent dispersion of the scalar via a diminution of the eddy diffusivity. In this work, we propose a model to describe this decay and use a recently developed technique to accurately and efficiently measure the eddy diffusivity using Eulerian fields and quantities. We then show a correspondence between this method and standard Lagrangian definitions of diffusivity and collect data across a range of drift velocities and Reynolds numbers. The proposed model agrees with data from these direct numerical simulations, offers some improvement to previous models in describing other computational and experimental data, and satisfies theoretical constraints that are independent of Reynolds number