Resistive plate chambers for time-of-flight measurements

The applications of Resistive Plate Chambers (RPCs) have recently been extended by the development of counters with time resolution below 100 ps sigma for minimum ionising particles. Applications to HEP experiments have already taken place and many further applications are under study. In this work we address the operating principles of such counters along with some present challenges, with emphasis on counter aging.Comment: Presented at "PSD6 - 6th International Conference on Position Sensitive Detectors", 9-13 September 2002, Leicester, UK. Submitted to Nuclear Instruments and Methods

Infrared spectra of crystalline and glassy silicates and application to interstellar dust

The infrared spectra of crystalline minerals predicted in theoretical condensation sequences do not match the astronomical observations. Since the astronomical spectra are a closer match to glassy silicates, the authors undertook a study to measure the infrared spectra of glassy silicates that have compositions similar to silicate minerals predicted in theoretical condensation sequences. The data should support observations aimed at elucidating condensation chemistry in dust forming regions. The authors measured the mass absorption coefficients, from 2.5 to 25 microns, of ground samples of olivine, diopside, and serpentine and also smoke samples that were prepared from these minerals. The smoke samples prepared in this way are predominantly glassy with nearly the same composition as the parent minerals. The crystalline samples consisted of pure olivine ((Fe(0.1)Mg(0.9))(2)SiO(4)), serpentine, diopside. Sample purity was confirmed by x ray diffraction. Each mineral was ground for 10 hours and a measured mass of the powder was mixed with KBr powder for absorption measurements using the method of Borghesi et a. (1985). The smoke samples were prepared from the same samples used for grinding by vaporizing the minerals using pulsed laser radiation in air. The smoke samples formed by condensation of the resulting vapor. The smoke settled onto infrared transparent KRS-5 substrates and onto a quartz crystal microbalance used to obtain mass measurements. A description of the preparation method is given in Stephens (1980). The glassy diopside showed only diffuse electron diffraction peaks and hence was nearly amorphous, while the serpentine smoke showed a weak diffraction pattern corresponding to MgO. The smoke from olivine showed a weak diffraction pattern corresponding to Fe2O3 and/or Fe3O4. The mass absorption coefficients, from 2.5 to 25 microns, of crystalline diopside, olivine, and serpentine and their corresponding smoke samples are shown in figures

Spectroscopic search for binaries among EHB stars in globular clusters

We performed a spectroscopic search for binaries among hot Horizontal Branch stars in globular clusters. We present final results for a sample of 51 stars in NGC6752, and preliminary results for the first 15 stars analyzed in M80. The observed stars are distributed along all the HBs in the range 8000 < Teff < 32000 K, and have been observed during four nights. Radial velocity variations have been measured with the cross-correlation technique. We carefully analyzed the statistical and systematic errors associated with the measurements in order to evaluate the statistical significance of the observed variations. No close binary system has been detected, neither among cooler stars nor among the sample of hot EHB stars (18 stars with Teff > 22000 K in NGC6752). The data corrected for instrumental effects indicate that the radial velocity variations are always below the 3sigma level of ~15 km/s. These results are in sharp contrast with those found for field hot subdwarfs, and open new questions about the formation of EHB stars in globular clusters, and possibly of the field subdwarfs.Comment: To appear in Baltic Astronomy. Proceedings of the 2nd meeting on Hot Subdwarf Stars, La Palma, June 2005. 4 pages, 2 figure

Progression from ocular hypertension to visual field loss in the English hospital eye service

Background There are more than one million National Health Service visits in England and Wales each year for patients with glaucoma or ocular hypertension (OHT). With the ageing population and an increase in optometric testing, the economic burden of glaucoma-related visits is predicted to increase. We examined the conversion rates of OHT to primary open-angle glaucoma (POAG) in England and assessed factors associated with risk of conversion. Methods Electronic medical records of 45 309 patients from five regionally different glaucoma clinics in England were retrospectively examined. Conversion to POAG from OHT was defined by deterioration in visual field (two consecutive tests classified as stage 1 or worse as per the glaucoma staging system 2). Cox proportional hazards models were used to examine factors (age, sex, treatment status and baseline intraocular pressure (IOP)) associated with conversion. Results The cumulative risk of conversion to POAG was 17.5% (95% CI 15.4% to 19.6%) at 5 years. Older age (HR 1.35 per decade, 95% CI 1.22 to 1.50, p<0.001) was associated with a higher risk of conversion. IOP-lowering therapy (HR 0.45, 95% CI 0.35 to 0.57, p<0.001) was associated with a lower risk of conversion. Predicted 5-year conversion rates for treated and untreated groups were 14.0% and 26.9%, respectively. Conclusion Less than one-fifth of OHT patients managed in glaucoma clinics in the UK converted to POAG over a 5-year period, suggesting many patients may require less intensive follow-up. Our study provides real-world evidence for the efficacy of current management (including IOP-lowering treatment) at reducing risk of conversion

On the Cauchy problem for a nonlinearly dispersive wave equation

We establish the local well-posedness for a new nonlinearly dispersive wave equation and we show that the equation has solutions that exist for indefinite times as well as solutions which blowup in finite times. Furthermore, we derive an explosion criterion for the equation and we give a sharp estimate from below for the existence time of solutions with smooth initial data.Comment: arxiv version is already officia

Chiral Superconducting Membranes

We develop the dynamics of the chiral superconducting membranes (with null current) in an alternative geometric approach either making a Lagrangian description and a Hamiltonian point of view. Besides of this, we show the equivalence of the resulting descriptions to the one known Dirac-Nambu-Goto (DNG) case. Integrability for chiral string model is obtained using a proposed light-cone gauge. In a similar way, domain walls are integrated by means of a simple ansatz. We compare the results with recently works appeared in the literature.Comment: Latex file, 17 pages, no figures. Improved version, typos corrected, Comments and references adde

Optics studies of a Muon Accumulator Ring based on FFA cells

The production of an intense, high energy and low emittance muon beam is interesting for a possible muon collider. The Low EMittance Muon Accelerator (LEMMA) team at the Istituto Nazionale di Fisica Nucleare (INFN), in Italy, is studying the production of a 22.5 GeV low emittance muon beam from a high energy positron beam at twice the muon energy impinging on a fixed thin target. The LEMMA scheme proposes to perform the muon accumulation from multiple ($10^2$ to $10^3$) positron bunches to increase the population of a single muon bunch that is recirculated through the target using two small accumulator rings, one per muon species. The three beams ($\mu^+$ and $\mu^-$ at 22.5 GeV and $e^+$ at twice the muon energy) share the same phase space at the target on every positron bunch interaction, producing new muons inside the preserved beam emittance. We study the requirements and optics design of the accumulator to recirculate the muons over the target using a Fixed Field Alternating Gradient (FFA) arc. As a result, we achieve a compact 230 m long accumulator with two Interaction Points, energy acceptance of $\pm5$ %, low twiss beta function at the target $\beta^*_\mu=20$ cm, and a drift space 2$L^*$ of 20 cm enough to accommodate 1 % of a radiation length $X_0$ for several material options. These optics parameters are obtained with magnets similar to those foreseen for new colliders like FCC or CLIC, and could be extended further with new magnet designs. The current muon accumulation results will serve as input for beam combination studies.Comment: Low emittance muon accumulation studie

Nanometric muon beam emittance from e + annihilation on multiple thin targets

The production of a low emittance muon beam is interesting for muon collider projects. In such context we study the production of positive and negative muon beams at 22 GeV, from ${e}^{+}$ beam-vs-fixed target collisions, with a very small transverse and longitudinal emittance of 25\text{ }\text{ }\ensuremath{\pi}\text{ }\mathrm{nm}\text{ }\mathrm{rad} and 3\ifmmode\times\else\texttimes\fi{}1\text{ }\text{ }\ensuremath{\pi}\text{ }\mathrm{mm}\text{ }\mathrm{GeV}, respectively. In order to cope with the small conversion efficiency of positrons into muon pairs and the divergence of the beams, we connect thin targets by a quadrupole-only transport line common to three beams ({\ensuremath{\mu}}^{+}, {\ensuremath{\mu}}^{\ensuremath{-}}, and ${e}^{+}$) at two different energies (\ensuremath{\mu} at 22 GeV and ${e}^{+}$ at 44 GeV), where the line is specially designed to match the muon beam phase space over \ifmmode\pm\else\textpm\fi{}5% energy spread and to mitigate the effect of multiple scattering with the targets on all beams. The transport line allows us to use a larger fraction of target material, increasing the muon population by a factor of 10 per positron bunch and splitting the power deposition over 20 to 40 targets, while keeping the muon beam emittance equal or similar to one from a single thin target of 1% of a radiation length. It might be possible to integrate this line into an accumulator ring in order to increase the muon bunch population over hundreds of positron bunches

Significant differences in incubation times in sheep infected with bovine spongiform encephalopathy result from variation at codon 141 in the PRNP gene

The susceptibility of sheep to prion infection is linked to variation in the PRNP gene, which encodes the prion protein. Common polymorphisms occur at codons 136, 154 and 171. Sheep which are homozygous for the A&lt;sub&gt;136&lt;/sub&gt;R&lt;sub&gt;154&lt;/sub&gt;Q&lt;sub&gt;171&lt;/sub&gt; allele are the most susceptible to bovine spongiform encephalopathy (BSE). The effect of other polymorphisms on BSE susceptibility is unknown. We orally infected ARQ/ARQ Cheviot sheep with equal amounts of BSE brain homogenate and a range of incubation periods was observed. When we segregated sheep according to the amino acid (L or F) encoded at codon 141 of the PRNP gene, the shortest incubation period was observed in LL141 sheep, whilst incubation periods in FF&lt;sub&gt;141&lt;/sub&gt; and LF&lt;sub&gt;141&lt;/sub&gt; sheep were significantly longer. No statistically significant differences existed in the expression of total prion protein or the disease-associated isoform in BSE-infected sheep within each genotype subgroup. This suggested that the amino acid encoded at codon 141 probably affects incubation times through direct effects on protein misfolding rates