Characterisation of Hybrid Pixel Detectors with capacitive charge division

In order to fully exploit the physics potential of the future high energy e+ e- linear collider, a Vertex Tracker providing high resolution track reconstruction is required. Hybrid pixel sensors are an attractive technology due to their fast read-out capabilities and radiation hardness. A novel pixel detector layout with interleaved cells between the readout nodes has been developed to improve the single point resolution. The results of the characterisation of the first processed prototypes are reported.Comment: 5 pages, 2 figures, presented at LCWS2000, Linear Collider Workshop, October 24-28 2000, Fermi National Accelerator Laboratory, Batavia, Illinois, U.S.A. Proceedings to be published by the American Institute of Physic

Performances of multi-gap timing RPCs for relativistic ions in the range Z=1-6

We present the performance of Multi-gap timing RPCs under irradiation by fully stripped relativistic ions (gamma*beta=2.7, Z=1-6). A time resolution of 80 ps at high efficiency has been obtained by just using standard `off the shelf' 4-gap timing RPCs from the new HADES ToF wall. The resolution worsened to 100 ps for ~ 1 kHz/cm2 proton flux and for ~ 100 Hz/cm2 Carbon flux. The chambers were operated at a standard field of E=100 kV/cm and showed a high stability during the experiment, supporting the fact that RPCs are a convenient choice when accommodating a very broad range of ionizing particles is needed. The data provides insight in the region of very highly ionizing particles (up to x 36 mips) and can be used to constrain the existing avalanche and Space-Charge models far from the usual `mip valley'. The implications of these results for the general case of detection based on secondary processes (n, gamma) resulting in highly ionizing particles with characteristic energy distributions will be discussed, together with the nature of the time-charge correlation curve.Comment: 31 pages, 19 figures, submitted to JINS

The Lambek calculus with iteration: two variants

Formulae of the Lambek calculus are constructed using three binary connectives, multiplication and two divisions. We extend it using a unary connective, positive Kleene iteration. For this new operation, following its natural interpretation, we present two lines of calculi. The first one is a fragment of infinitary action logic and includes an omega-rule for introducing iteration to the antecedent. We also consider a version with infinite (but finitely branching) derivations and prove equivalence of these two versions. In Kleene algebras, this line of calculi corresponds to the *-continuous case. For the second line, we restrict our infinite derivations to cyclic (regular) ones. We show that this system is equivalent to a variant of action logic that corresponds to general residuated Kleene algebras, not necessarily *-continuous. Finally, we show that, in contrast with the case without division operations (considered by Kozen), the first system is strictly stronger than the second one. To prove this, we use a complexity argument. Namely, we show, using methods of Buszkowski and Palka, that the first system is $\Pi_1^0$-hard, and therefore is not recursively enumerable and cannot be described by a calculus with finite derivations

The Straw Tube Trackers of the PANDA Experiment

The PANDA experiment will be built at the FAIR facility at Darmstadt (Germany) to perform accurate tests of the strong interaction through bar pp and bar pA annihilation's studies. To track charged particles, two systems consisting of a set of planar, closed-packed, self-supporting straw tube layers are under construction. The PANDA straw tubes will have also unique characteristics in term of material budget and performance. They consist of very thin mylar-aluminized cathodes which are made self-supporting by means of the operation gas-mixture over-pressure. This solution allows to reduce at maximum the weight of the mechanical support frame and hence the detector material budget. The PANDA straw tube central tracker will not only reconstruct charged particle trajectories, but also will help in low momentum (< 1 GeV) particle identification via dE/dx measurements. This is a quite new approach that PANDA tracking group has first tested with detailed Monte Carlo simulations, and then with experimental tests of detector prototypes. This paper addresses the design issues of the PANDA straw tube trackers and the performance obtained in prototype tests.Comment: 7 pages,16 figure

Revascularization of Chronic Hibernating Myocardium Stimulates Myocyte Proliferation and Partially Reverses Chronic Adaptations to Ischemia

AbstractBackgroundThe time course and extent of recovery after revascularization of viable dysfunctional myocardium are variable. Although fibrosis is a major determinant, myocyte structural and molecular remodeling may also play important roles.ObjectivesThis study sought to determine whether persistent myocyte loss and/or irreversibility of protein changes that develop in hibernating myocardium have an impact on functional recovery in the absence of infarction.MethodsSwine implanted with a chronic left anterior descending artery (LAD) stenosis to produce hibernating myocardium underwent percutaneous revascularization, with serial functional recovery evaluated for 1 month (n = 12). Myocardial tissue was evaluated to assess myocyte size, nuclear density, and proliferation indexes in comparison with those of normal animals and nonrevascularized controls. Proteomic analysis by 2-dimensional differential in-gel electrophoresis was used to determine the reversibility of molecular adaptations of hibernating myocytes.ResultsAt 3 months, physiological features of hibernating myocardium were confirmed, with depressed LAD wall thickening and no significant infarction. Revascularization normalized LAD flow reserve, with no immediate change in LAD wall thickening. Regional LAD wall thickening slowly improved but remained depressed 1 month post–percutaneous coronary intervention. Surprisingly, revascularization was associated with histological evidence of myocytes re-entering the growth phase of the cell cycle and increases in the number of c-Kit+ cells. Myocyte nuclear density returned to normal, whereas regional myocyte hypertrophy regressed. Proteomic analysis demonstrated heterogeneous effects of revascularization. Up-regulated stress and cytoskeletal proteins normalized, whereas reduced contractile and metabolic proteins persisted.ConclusionsDelayed recovery of hibernating myocardium in the absence of scar may reflect persistent reductions in the amounts of contractile and metabolic proteins. Although revascularization appeared to stimulate myocyte proliferation, the persistence of small immature myocytes may have contributed to delayed functional recovery

Time resolution of the plastic scintillator strips with matrix photomultiplier readout for J-PET tomograph

Recent tests of a single module of the Jagiellonian Positron Emission Tomography system (J-PET) consisting of 30 cm long plastic scintillator strips have proven its applicability for the detection of annihilation quanta (0.511 MeV) with a coincidence resolving time (CRT) of 0.266 ns. The achieved resolution is almost by a factor of two better with respect to the current TOF-PET detectors and it can still be improved since, as it is shown in this article, the intrinsic limit of time resolution for the determination of time of the interaction of 0.511 MeV gamma quanta in plastic scintillators is much lower. As the major point of the article, a method allowing to record timestamps of several photons, at two ends of the scintillator strip, by means of matrix of silicon photomultipliers (SiPM) is introduced. As a result of simulations, conducted with the number of SiPM varying from 4 to 42, it is shown that the improvement of timing resolution saturates with the growing number of photomultipliers, and that the 2 x 5 configuration at two ends allowing to read twenty timestamps, constitutes an optimal solution. The conducted simulations accounted for the emission time distribution, photon transport and absorption inside the scintillator, as well as quantum efficiency and transit time spread of photosensors, and were checked based on the experimental results. Application of the 2 x 5 matrix of SiPM allows for achieving the coincidence resolving time in positron emission tomography of $\approx$ 0.170 ns for 15 cm axial field-of-view (AFOV) and $\approx$ 0.365 ns for 100 cm AFOV. The results open perspectives for construction of a cost-effective TOF-PET scanner with significantly better TOF resolution and larger AFOV with respect to the current TOF-PET modalities.Comment: To be published in Phys. Med. Biol. (26 pages, 17 figures

Classification of singular Q-homology planes. I. Structure and singularities

A Q-homology plane is a normal complex algebraic surface having trivial rational homology. We obtain a structure theorem for Q-homology planes with smooth locus of non-general type. We show that if a Q-homology plane contains a non-quotient singularity then it is a quotient of an affine cone over a projective curve by an action of a finite group respecting the set of lines through the vertex. In particular, it is contractible, has negative Kodaira dimension and only one singular point. We describe minimal normal completions of such planes.Comment: improved results from Ph.D. thesis (University of Warsaw, 2009), 25 pages, to appear in Israel J. Mat

Determination of the b quark mass at the M_Z scale with the DELPHI detector at LEP

An experimental study of the normalized three-jet rate of b quark events with respect to light quarks events (light= \ell \equiv u,d,s) has been performed using the CAMBRIDGE and DURHAM jet algorithms. The data used were collected by the DELPHI experiment at LEP on the Z peak from 1994 to 2000. The results are found to agree with theoretical predictions treating mass corrections at next-to-leading order. Measurements of the b quark mass have also been performed for both the b pole mass: M_b and the b running mass: m_b(M_Z). Data are found to be better described when using the running mass. The measurement yields: m_b(M_Z) = 2.85 +/- 0.18 (stat) +/- 0.13 (exp) +/- 0.19 (had) +/- 0.12 (theo) GeV/c^2 for the CAMBRIDGE algorithm. This result is the most precise measurement of the b mass derived from a high energy process. When compared to other b mass determinations by experiments at lower energy scales, this value agrees with the prediction of Quantum Chromodynamics for the energy evolution of the running mass. The mass measurement is equivalent to a test of the flavour independence of the strong coupling constant with an accuracy of 7 permil.Comment: 24 pages, 10 figures, Accepted by Eur. Phys. J.