Mass flow through solid 4He induced by the fountain effect

Using an apparatus that allows superfluid liquid 4He to be in contact with hcp solid \4he at pressures greater than the bulk melting pressure of the solid, we have performed experiments that show evidence for 4He mass flux through the solid and the likely presence of superfluid inside the solid. We present results that show that a thermomechanical equilibrium in quantitative agreement with the fountain effect exists between two liquid reservoirs connected to each other through two superfluid-filled Vycor rods in series with a chamber filled with solid 4He. We use the thermomechanical effect to induce flow through the solid and measure the flow rate. On cooling, mass flux appears near T = 600 mK and rises smoothly as the temperature is lowered. Near T = 75 mK a sharp drop in the flux is present. The flux increases as the temperature is reduced below 75 mK. We comment on possible causes of this flux minimum.Comment: 20 pages, 22 figures, 7 table

A Degenerate Bose-Fermi Mixture of Metastable Atoms

We report the observation of simultaneous quantum degeneracy in a dilute gaseous Bose-Fermi mixture of metastable atoms. Sympathetic cooling of helium-3 (fermion) by helium-4 (boson), both in the lowest triplet state, allows us to produce ensembles containing more than 10^6 atoms of each isotope at temperatures below 1 micro-Kelvin, and achieve a fermionic degeneracy parameter of T/Tf=0.45. Due to their high internal energy, the detection of individual metastable atoms with sub-nanosecond time resolution is possible, permitting the study of bosonic and fermionic quantum gases with unprecedented precision. This may lead to metastable helium becoming the mainstay of quantum atom optics.Comment: 4 pages, 3 figures submitted to PR

Estimations of electron-positron pair production at high-intensity laser interaction with high-Z targets

Electron-positron pairs' generation occuring in the interaction of $10^{18}$-$10^{20}$~W/cm$^2$ laser radiation with high-Z targets are examined. Computational results are presented for the pair production and the positron yield from the target with allowance for the contribution of pair production processes due to electrons and bremsstrahlung photons. Monte-Carlo simulations using the PRIZMA code confirm the estimates obtained. The possible positron yield from high-Z targets irradiated by picosecond lasers of power $10^2$-$10^3$~TW is estimated to be $10^9$-$10^{11}$

Resistance of legionella pneumophila and helicobacter pylori to chlorination in drinking water biofilms

The disintegration of concrete structures made of ordinary Portland cement (OPC) is a worrying topic of increasing significance. The development of new binders with longer durability is therefore needed. Alkali-activated binders have emerged as an alternative to OPC binders, which seems to have superior durability and environmental impact. This paper reviews current knowledge about alkali-activated binders. The subjects of Part 1 in this paper are historical background, terminology and hydration products. The proper terminology to designate these new binders will be discussed. The influence of the prime materials and the type of alkaline activator on the reaction mechanisms and on the nature of the reaction products will be described

Community interactions promote Legionella pneumophila survival in drinking water biofilms

Legionella pneumophila is a waterborne pathogen that can cause Pontiac Fever or Legionnaires’ disease, a type of pneumonia that can be fatal. Although L. pneumophila is not able to replicate in low nutrient environments, such as drinking water, it is known that heterotrophic biofilms have a crucial role in the survival of this pathogen in drinking water distribution systems. The aim of this work is to study the community interactions that influence the survival of L. pneumophila in biofilms. For that, mono and dual-species biofilms of L. pneumophila and the predominant biofilm isolates Variovorax paradoxus, Mycobacterium chelonae, Acidovorax spp., Sphingomonas spp., were formed on PVC surfaces and sessile cells quantified for total cells, viable and cultivable L. pneumophila and cultivable non-Legionellae. Results demonstrated that Acidovorax spp. and Sphingomonas spp. appear to have an antagonistic effect on L. pneumophila cultivability but not in the viability, leading to the formation of viable but noncultivable (VBNC) cells, while M. chelonae increased the cultivability of this pathogen. M. chelonae is one of the microorganisms commonly found in drinking water and this work demonstrates that this strain is able to promote L. pneumophila survival in these systems. It is also demonstrated that other species might stimulate this pathogen to enter a VBNC state and consequently be underestimated in the drinking water quality control, as drinking water safety assessment still relies on standard culture techniques. It is essential for future work to study other biofilm community members to understand their ecological interactions with L. pneumophila

Influence of physico-chemical parameters on the survival of Helicobacter pylori in drinking water biofilms

The route of transmission for Helicobacter pylori is not well-known, but one of the suggested possibilities is via drinking water and associated biofilms. As such, the aim of this work is to study the influence of several physico-chemical parameters, including temperature, shear-stress and carbon concentration, on the prevalence and survival of H. pylori in drinking water biofilms. The biofilm studies were carried out using a two-stage chemostat system. The outflow culture of the first vessel fed three secondary chemostats in parallel and under different conditions of shear stress and carbon concentration. After 10 days the chemostats reached steady conditions, and the second stage chemostats were spiked with an inoculum of H. pylori NCTC 11637 (of approximately 106 cells ml-1) and PVC coupons were then immersed to allow biofilm formation. The coupons were removed at different times (up to 32 days) and biofilms detached with sterile glass beads. Planktonic and sessile cells were quantified by standard cultivation techniques (R2A and HPSPA) and SYTO9 staining. Remarkably, H. pylori lost cultivability under all conditions in less than 1 h which compares with 24-75 h that the pathogen usually takes to lose cultivability in pure culture at these temperatures. This suggests that H. pylori is negatively affected by the presence of heterotrophic microbial consortium; alternatively, overgrowth of other species might hinder colony development of H. pylori. Current studies are tracking the uncultivable H. pylori in the biofilms using peptide nucleic acid probes in a high performance fluorescence in situ hybridisation assay

A New Technique for Finding Needles in Haystacks: A Geometric Approach to Distinguishing Between a New Source and Random Fluctuations

We propose a new test statistic based on a score process for determining the statistical significance of a putative signal that may be a small perturbation to a noisy experimental background. We derive the reference distribution for this score test statistic; it has an elegant geometrical interpretation as well as broad applicability. We illustrate the technique in the context of a model problem from high-energy particle physics. Monte Carlo experimental results confirm that the score test results in a significantly improved rate of signal detection.Comment: 5 pages, 4 figure

Testing linear hypotheses in high-dimensional regressions

For a multivariate linear model, Wilk's likelihood ratio test (LRT) constitutes one of the cornerstone tools. However, the computation of its quantiles under the null or the alternative requires complex analytic approximations and more importantly, these distributional approximations are feasible only for moderate dimension of the dependent variable, say $p\le 20$. On the other hand, assuming that the data dimension $p$ as well as the number $q$ of regression variables are fixed while the sample size $n$ grows, several asymptotic approximations are proposed in the literature for Wilk's \bLa including the widely used chi-square approximation. In this paper, we consider necessary modifications to Wilk's test in a high-dimensional context, specifically assuming a high data dimension $p$ and a large sample size $n$. Based on recent random matrix theory, the correction we propose to Wilk's test is asymptotically Gaussian under the null and simulations demonstrate that the corrected LRT has very satisfactory size and power, surely in the large $p$ and large $n$ context, but also for moderately large data dimensions like $p=30$ or $p=50$. As a byproduct, we give a reason explaining why the standard chi-square approximation fails for high-dimensional data. We also introduce a new procedure for the classical multiple sample significance test in MANOVA which is valid for high-dimensional data.Comment: Accepted 02/2012 for publication in "Statistics". 20 pages, 2 pages and 2 table