Comparative Monte Carlo Efficiency by Monte Carlo Analysis

We propose a modified power method for computing the subdominant eigenvalue $\lambda_2$ of a matrix or continuous operator. Here we focus on defining simple Monte Carlo methods for its application. The methods presented use random walkers of mixed signs to represent the subdominant eigenfuction. Accordingly, the methods must cancel these signs properly in order to sample this eigenfunction faithfully. We present a simple procedure to solve this sign problem and then test our Monte Carlo methods by computing the $\lambda_2$ of various Markov chain transition matrices. We first computed ${\lambda_2}$ for several one and two dimensional Ising models, which have a discrete phase space, and compared the relative efficiencies of the Metropolis and heat-bath algorithms as a function of temperature and applied magnetic field. Next, we computed $\lambda_2$ for a model of an interacting gas trapped by a harmonic potential, which has a mutidimensional continuous phase space, and studied the efficiency of the Metropolis algorithm as a function of temperature and the maximum allowable step size $\Delta$. Based on the $\lambda_2$ criterion, we found for the Ising models that small lattices appear to give an adequate picture of comparative efficiency and that the heat-bath algorithm is more efficient than the Metropolis algorithm only at low temperatures where both algorithms are inefficient. For the harmonic trap problem, we found that the traditional rule-of-thumb of adjusting $\Delta$ so the Metropolis acceptance rate is around 50% range is often sub-optimal. In general, as a function of temperature or $\Delta$, $\lambda_2$ for this model displayed trends defining optimal efficiency that the acceptance ratio does not. The cases studied also suggested that Monte Carlo simulations for a continuum model are likely more efficient than those for a discretized version of the model.Comment: 23 pages, 8 figure

Monte Carlo Determination of Multiple Extremal Eigenpairs

We present a Monte Carlo algorithm that allows the simultaneous determination of a few extremal eigenpairs of a very large matrix without the need to compute the inner product of two vectors or store all the components of any one vector. The new algorithm, a Monte Carlo implementation of a deterministic one we recently benchmarked, is an extension of the power method. In the implementation presented, we used a basic Monte Carlo splitting and termination method called the comb, incorporated the weight cancellation method of Arnow {\it et al.}, and exploited a new sampling method, the sewing method, that does a large state space sampling as a succession of small state space samplings. We illustrate the effectiveness of the algorithm by its determination of the two largest eigenvalues of the transfer matrices for variously-sized two-dimensional, zero field Ising models. While very likely useful for other transfer matrix problems, the algorithm is however quite general and should find application to a larger variety of problems requiring a few dominant eigenvalues of a matrix.Comment: 22 pages, no figure

Gene Therapy in Cellular Immunodeficiencies

The treatment of cellular primary immunodeficiencies has benefitted from significant advances in the field of allogeneic stem cell transplantation (alloHSCT). However, while this therapy is curative for many PIDs, the procedure requires a suitably matched donor and carries significant risks of morbidity and mortality from complications such as graft-versus-host disease (GVHD). Autologous gene therapy (GT) approaches using stem cells isolated from patients and modified ex vivo using viral vectors or gene editing techniques have the potential to offer curative therapy for PID without the immunological complications of alloHSCT. GT for PID has been developed over the last 30 years, and while several setbacks have been encountered along the way, there is now a licensed GT product for ADA-SCID, and promising results from phase I/II clinical trials have demonstrated that GT may offer clinical efficacy comparable to alloHSCT in several other PIDs. Developments in the field are broadening the application of GT, and we expect that this therapeutic modality may become standard of care for the management of several PIDs in the near future. This chapter explores the development of GT over the last 30 years and outlines its role in the management of cellular primary immunodeficiencies

Self-Adaptive Quadrature and Numerical Path Integration

In the present paper we explore the use of generalized Gaussian quadrature methods in the context of equilibrium path integral applications. Using moment techniques, we devise a compact, self-adaptive approach for use in conjunction with selected classes of interaction potentials. We demonstrate that, when applicable, the resulting approach reduces appreciably the number of potential energy evaluations required in equilibrium path integral simulations

How organisations can help their LGBTQI+ employees as they face divided experiences

LGBTQI+ people face divided experiences. They’re increasingly represented in media, and have more accessible information and wider access to legal marriage. At the same time, unprecedented criminalisation is excluding trans people from specific spaces and vital services. Jordana Moser, Jonathan E Booth and T Alexandra Beauregard describe the current state of play for LGBTQI+ inclusion and outline further steps that organisations can take to support their LGBTQI+ employees

Health promotion interventions for increasing stroke awareness in ethnic minorities: a systematic review of the literature

Abstract Background: Stroke places a significant burden to all affected individuals, but it is perhaps more significant amongst members of black, minority and ethnic communities, who may experience poorer awareness of stroke symptoms than the general population. Recently, several initiatives tried to improve public awareness that symptoms of stroke need to be treated as a medical emergency. However, ethnic communities present cultural barriers, requiring tailored health promotion interventions, whose effectiveness remains uncertain. Our systematic review aimed to identify relevant published evidence, synthesize the main study components and identify evidence of the effectiveness of the interventions. Methods: MEDLINE, EMBASE, CINAHL, and PsycInfo were searched for journal articles on health promotion interventions for increasing stroke awareness in ethnic minorities, published in English between 1995 and 2012. Search results were collaboratively assessed by the authors; included studies were analysed to identify their main characteristics, and a thematic analysis of their content was conducted. No meta-analysis was performed, due to the heterogeneity of results. Results: Eighteen studies were included, reporting 15 interventions conducted in the US, for African-Americans or Hispanics; populations sizes differed between interventions. Interventions were mostly carried out in community settings with different educational techniques, focussing on experiential methods. Health professionals usually organized the programs, delivered by nurses, other health professionals or volunteers. The few theory-based interventions focussed on individual-level behavioural change. Practical cultural adaptation strategies were not linked to specific theoretical frameworks. Interventions widely differed as for target populations, settings, delivery methods, contents and professional roles involved. All study designs were quantitative, and the emerging evidence of effectiveness was inconclusive. Such interventions operate in very complex scenarios, and several variables may influence their effectiveness. Therefore, qualitative or mixed-methods study designs may shed light on barriers and facilitators, experiential education strategies and community involvement. Network- and community-level theories may help improving design and evaluation of interventions. Conclusions: Eleven case reports and four RCTs provide evidence about stroke awareness interventions organized in the US. The studies provide only partial and inconclusive evidence about the effectiveness of the interventions. Hence, further research is needed on different countries and ethnic minorities

The kinetics of fluoride uptake by synthetic hydroxyapatite

The kinetics of fluoride uptake by synthetic hydroxyapatite from aqueous solution has been studied. Experiments involved exposing 0.1 g of synthetic hydroxyapatite to 5 cm3 of sodium fluoride solution in the concentration range 100-1000 ppm fluoride and determining fluoride concentration at regular time intervals with a fluoride ion-selective electrode. In all cases, uptake was found to follow pseudo-second order kinetics with correlation coefficients of at least 0.998; all systems equilibrated by 24 hours with equilibrium uptake values that varied with the initial fluoride concentration. The kinetic results differ from those previously reported for much lower concentrations of fluoride, but in the present case, the concentrations were of clinical relevance, as they are those used in fluoride-containing dental products. Further work is necessary to determine how well these findings model uptake by natural hydroxyapatite and hence the extent to which they might apply in vivo

Fundamental properties and applications of quasi-local black hole horizons

The traditional description of black holes in terms of event horizons is inadequate for many physical applications, especially when studying black holes in non-stationary spacetimes. In these cases, it is often more useful to use the quasi-local notions of trapped and marginally trapped surfaces, which lead naturally to the framework of trapping, isolated, and dynamical horizons. This framework allows us to analyze diverse facets of black holes in a unified manner and to significantly generalize several results in black hole physics. It also leads to a number of applications in mathematical general relativity, numerical relativity, astrophysics, and quantum gravity. In this review, I will discuss the basic ideas and recent developments in this framework, and summarize some of its applications with an emphasis on numerical relativity.Comment: 14 pages, 2 figures. Based on a talk presented at the 18th International Conference on General Relativity and Gravitation, 8-13 July 2007, Sydney, Australi

Probing 5f-state configurations in URu2Si2 with U L3-edge resonant x-ray emission spectroscopy

Resonant x-ray emission spectroscopy (RXES) was employed at the U L3 absorption edge and the La1 emission line to explore the 5f occupancy, nf, and the degree of 5f orbital delocalization in the hidden order compound URu2Si2. By comparing to suitable reference materials such as UF4, UCd11, and alpha-U, we conclude that the 5f orbital in URu2Si2 is at least partially delocalized with nf = 2.87 +/- 0.08, and does not change with temperature down to 10 K within the estimated error. These results place further constraints on theoretical explanations of the hidden order, especially those requiring a localized f2 ground state.Comment: 11 pages,7 figure