A simple and efficient approach to the optimization of correlated wave functions

We present a simple and efficient method to optimize within energy minimization the determinantal component of the many-body wave functions commonly used in quantum Monte Carlo calculations. The approach obtains the optimal wave function as an approximate perturbative solution of an effective Hamiltonian iteratively constructed via Monte Carlo sampling. The effectiveness of the method as well as its ability to substantially improve the accuracy of quantum Monte Carlo calculations is demonstrated by optimizing a large number of parameters for the ground state of acetone and the difficult case of the $1{}^1{B}_{1u}$ state of hexatriene.Comment: 5 pages, 1 figur

Fugitive Testimonies

This research thesis takes the form of a longitudinal fieldwork study (2009–16) to question what is ‘fugitive’ from the family photographic archive. The research borrows the term from Roland Barthes: ‘the Photograph is a certain but fugitive testimony’.1 The research project relates this idea to what goes missing from family albums and posits that discarded materials from family albums, as found in flea markets, can constitute the ‘fugitive memories’ of family life. As a result, collecting these materials can be used to construct new ‘archives’, named in this project as the Fugitive Testimonies Archive. This archive acts as a repository for examining fugitive memories. The ‘sample’ of discarded photographs has been gathered in the practical fieldwork at a regional flea market, located in the southwest of England (specifically at the Royal Bath and West Showground in Shepton Mallet, Somerset) from 2009 to 2016. The fieldwork method was developed in two phases. The first is collecting and mapping the found materials in fieldwork notebooks (organised as a photoarchive) to form a timeline and survey of encounters, and the annotation of photographs and materials with critical notes on the transactions and encounters. All these notes give extra insight into the flea market as a site of enquiry and fugitive discourse. This work is inspired by the historical traditions of such methods as bricolage (Claude Lévi-Strauss) and objective chance (e.g. in André Breton and Surrealism).2 Examples of contemporary artists also drawing on these tactics and methods of practice are Tacita Dean and Taryn Simon.3 Phase two of the project represents the critical intervention of reconfiguring the ‘outtakes’ curated (by me) from selected material prints in the Fugitive Testimonies Archive. The subsequent grouping of these ‘outtakes’ constructs the conceptual assemblages, to reveal and expose from this discarded material what has been censored by families. By presenting and rereading these found discarded photographs the thesis produces new perspectives on family album photography, by engaging in theoretical discussion of the direct relationships between personal and social memory, and between personal and family identity vested in what is discarded from the family photographic archive. In a supplementary argument, the thesis argues that the analogue era of photography is what enabled and created - through its material form - the very possibility of this fugitive discarding of ‘family material’. The potential for new scholarship about the re-configuration of the photograph within this bricolage mode is in direct relation to the material process of analogue photography. The fugitive testimonies of family held on analogue paper substrates offer specific visual image memories whose insistent capture are likely to evaporate, deteriorate, change, fade or disappear. In consequence, the contribution of this research to new knowledge concerns the importance of this documentation of private life, a documentation, which has a disruptive urgency through questioning and investigating affective visual narratives of ‘the family’ in fugitive prints. Equally significant for this research are the intricate forms of the photographic records, the unconscious escapes from contracts of compatibility (the fugitive stories of family) to inform the tactics of a practice

Energy loss mechanism for suspended micro- and nanoresonators due to the Casimir force

A so far not considered energy loss mechanism in suspended micro- and nanoresonators due to noncontact acoustical energy loss is investigated theoretically. The mechanism consists on the conversion of the mechanical energy from the vibratory motion of the resonator into acoustic waves on large nearby structures, such as the substrate, due to the coupling between the resonator and those structures resulting from the Casimir force acting over the separation gaps. Analytical expressions for the resulting quality factor Q for cantilever and bridge micro- and nanoresonators in close proximity to an underlying substrate are derived and the relevance of the mechanism is investigated, demonstrating its importance when nanometric gaps are involved

Simulations of Time-Resolved X-Ray Diffraction in Laue Geometry

A method of computer simulation of Time-Resolved X-ray Diffraction (TRXD) in asymmetric Laue (transmission) geometry with an arbitrary propagating strain perpendicular to the crystal surface is presented. We present two case studies for possible strain generation by short-pulse laser irradiation: (i) a thermoelastic-like analytic model; (ii) a numerical model including effects of electron-hole diffusion, Auger recombination, deformation potential and thermal diffusion. A comparison with recent experimental results is also presented.Comment: 9 pages, 11 figure

First-principles calculation of P-type alloy scattering in Si1-xGex

The p-type carrier scattering rate due to alloy disorder in Si1-xGex alloys is obtained from first principles. The required alloy scattering matrix elements are calculated from the energy splitting of the valence bands, which arise when one average host atom is replaced by a Ge or Si atom in supercells containing up to 128 atoms. Alloy scattering within the valence bands is found to be characterized by a single scattering parameter. The hole mobility is calculated from the scattering rate using the Boltzmann transport equation in the relaxation time approximation. The results are in good agreement with experiments on bulk, unstrained alloys.

Growth and Survivorship of Scleractinian Coral Transplants and the Effectiveness of Plugging Core Holes in Transplant Donor Colonies

Replicate scleractinian coral transplants were obtained from the species Meandrina meandrites and Montastrea cavernosa on a natural reef, off Dania Beach, Florida, using a hydraulic drill fitted with a 4 in. (~10 cm) core barrel. The transplants were fixed to Reef Ball™ substrates using an adhesive marine epoxy. Drill holes in the donor corals (core holes) were filled with concrete plugs. Control corals, of comparable size to both donor colonies and transplant corals, were monitored for comparison. Transplant corals, donor corals, and controls on the natural reef were monitored for growth and survivorship. Core holes were monitored for tissue regrowth over the surface of concrete plugs. Growth during the transplantation project was defined as an increase in surface area of tissue and skeleton. Growth was monitored on a quarterly basis using photographic techniques. Meandrina meandrites transplants experienced greater mortality and significantly less growth than M. cavernosa transplants. No significant difference in the change in percent tissue coverage between both species of donor corals or between their respective controls was determined. The process of filling core holes in donor colonies with concrete plugs was effective, however, tissue did not completely regenerate over the surface of plugs in either species over the relatively short 15-month observation period. Results of this study indicate that species selection is an important factor in the success of coral transplantation