This contribution describes the PICOSEC-Micromegas detector which achieves a time resolution below 25ps. In this device the passage of a charged particle produces Cherenkov photons in a radiator, ...which then generate electrons in a photocathode and these photoelectrons enter a two-stage Micromegas with a reduced drift region and a typical anode region. The results from single-channel prototypes (demonstrating a time resolution of 24ps for minimum ionizing particles, and 76ps for single photoelectrons), the understanding of the detector in terms of detailed simulations and a phenomenological model, the issues of robustness and how they are tackled, and preliminary results from a multi-channel prototype are presented (demonstrating that a timing resolution similar to that of the single-channel device is feasible for all points across the area covered by a multi-channel device).
The PICOSEC-Micromegas detector was developed for precise timing of the arrival of charged particles with a resolution bellow 30 ps. This contribution, after a brief introduction presents results ...concerning the PICOSEC-Micromegas response to single photoelectrons, estimation of the photoelectron yield of various photocathode types, as well as its performance to time the arrival of test beam muons. In addition, results based on detailed simulation studies and a stochastic model developed for the understanding of the detector are presented. Finally, results of studies related to the development of large scale PICOSEC-Micromegas detector for practical applications are also presented, in particular, the timing performance of a multi-channel PICOSEC prototype.
This paper describes the use of weighted Monte Carlo events to accurately approximate integrals of functions of the experimentally measured kinematical vectors and their dependence on physical ...parameters. This technique is demonstrated in estimating the evolution of cross-sections, efficiencies, measured kinematical distributions and mean values as functions of the Trilinear Gauge Couplings.
The optical module for the NESTOR neutrino telescope Anassontzis, E.G.; Ioannou, P.; Katsanevas, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2002, Volume:
479, Issue:
2
Journal Article
Peer reviewed
NESTOR is a deep-sea water Cherenkov neutrino detector now under construction for deployment in the Mediterranean off Greece. Its key component is an optical module employing a photomultiplier tube ...with a 15
in. hemispherical photocathode in a transparent glass pressure housing. Extensive tests have been made on the sensitivity, uniformity, time resolution, noise rates and mechanical properties of the module: several test deployments have been made at sea.
The death receptor Fas is present in thyroid carcinomas, yet fails to trigger apoptosis. Interestingly, Fas has been reported to be actually overexpressed in papillary thyroid carcinomas, suggesting ...that it may confer a survival advantage.
We investigated the expression and activation status of Fas pathway mediators in thyroid carcinoma cell lines and tumor specimens.
All cell lines tested express Fas-associated death domain, procaspase-8, procaspase-9, and procaspase-3; resistance to Fas-mediated apoptosis could not be attributed to lack of any of these apoptosis mediators. Moreover, Fas death domain mutations were not found in our study. The proteasome inhibitors MG132 and PS-341 (bortezomib, Velcade), which lead to accumulation of the nuclear factor kappaB (NF-kappaB) inhibitor IkappaB, did not sensitize SW579 cells to Fas-mediated apoptosis, suggesting that resistance to Fas-mediated apoptosis is not due to proteasome or NF-kappaB activity. Cross-linking of Fas in vitro induced recruitment of Fas-associated death domain-like interleukin-1beta-converting enzyme inhibitory protein (FLIP) instead of procaspase-8. Inhibition of FLIP expression with a FLIP antisense oligonucleotide resulted in significant sensitization to Fas-mediated apoptosis. Fas cross-linking promoted BrdUrd incorporation; activated the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase, NF-kappaB, and activator protein-1 pathways in thyroid carcinoma cells in vitro; and protected cells from tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis. We also found that good prognosis papillary thyroid carcinoma specimens exhibited higher immunoreactivity for cleaved (activated) caspase-8 than poor prognosis tumors.
In thyroid carcinomas, the proteolytic cleavage and activation of caspase-8 depends on the balance between expression levels for procaspase-8 and FLIP and correlates with favorable clinical prognosis. Fas may actually stimulate proliferation and confer a survival advantage to thyroid cancer cells.
Histone deacetylases (HDAC) and histone acetyltransferases exert opposing enzymatic activities that modulate the degree of acetylation of histones and other intracellular molecular targets, thereby ...regulating gene expression, cellular differentiation, and survival. HDAC inhibition results in accumulation of acetylated histones and induces differentiation and/or apoptosis in transformed cells. In this study, we characterized the effect of two HDAC inhibitors, suberoylanilide hydroxamic acid (SAHA) and m-carboxycinnamic acid bis-hydroxamide, on thyroid carcinoma cell lines, including lines originating from anaplastic and medullary carcinomas. In these models, both SAHA and m-carboxycinnamic acid bis-hydroxamide induced growth arrest and caspase-mediated apoptosis and increased p21 protein levels, retinoblastoma hypophosphorylation, BH3-interacting domain death agonist cleavage, Bax up-regulation, down-regulation of Bcl-2, A1, and Bcl-x(L) expression, and cleavage of poly(ADP-ribose) polymerase and caspase-8, -9, -3, -7, and -2. Transfection of Bcl-2 cDNA partially suppressed SAHA-induced cell death. SAHA down-regulated the expression of the apoptosis inhibitors FLIP and cIAP-2 and sensitized tumor cells to cytotoxic chemotherapy and death receptor activation. Our studies provide insight into the tumor type-specific mechanisms of antitumor effects of HDAC inhibitors and a framework for future clinical applications of HDAC inhibitors in patients with thyroid cancer, including histologic subtypes (e.g., anaplastic and medullary thyroid carcinomas) for which limited, if any, therapeutic options are available.
EPR studies of neutron-irradiated n-type FZ silicon doped with tin Mitrikas, G; Kordas, G; Fanourakis, G ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
2002, 2002-1-00, Volume:
186, Issue:
1
Journal Article
Peer reviewed
N-type float zone (FZ) silicon doped with tin (
2–10×10
18
cm
−3
) was irradiated by neutrons in a nuclear reactor (fluence of
1×10
17
cm
−2
for 2 h). The irradiation-induced paramagnetic defects ...were studied by continuous wave (cw) and pulsed electron paramagnetic resonance (EPR) spectroscopy. The EPR measurements were carried out between liquid helium and room temperature. The two- and three-pulse electron spin echo envelope modulation (ESEEM) experiments were performed in order to inspect the hyperfine couplings between the electron spin and its surrounding nuclei. This study also revealed the existence of a weak coupling between the paramagnetic centre and nearby protons.
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