ABSTRACT
The Tunka Advanced Instrument for Gamma- and cosmic-ray Astronomy (TAIGA) is a multicomponent experiment for the measurement of TeV to PeV gamma- and cosmic rays. Our goal is to establish a ...novel hybrid direct air shower technique, sufficient to access the energy domain of the long-sought Pevatrons. The hybrid air Cherenkov light detection technique combines the strengths of the HiSCORE shower front sampling array, and two ∼4 m class, ∼9.6° field of view Imaging Air Cherenkov Telescopes (IACTs). The HiSCORE array provides good angular and shower core position resolution, while the IACTs provide the image shape and orientation for gamma-hadron separation. In future, an additional muon detector will be used for hadron tagging at ≥100 TeV energies. Here, only data from the first IACT of the TAIGA experiment are used. A randomforest algorithm was trained using Monte Carlo (MC) simulations and real data, and applied to $85\, \mathrm{h}$ of selected observational data tracking the Crab Nebula at a mean zenith angle of 33.5°, resulting in a threshold energy of 6 TeV for this data set. The analysis was performed using the gammapy package. A total of 163.5 excess events were detected, with a statistical significance of 8.5 σ. The observed spectrum of the Crab Nebula is best fit with a power law above 6 TeV with a flux normalization of (3.20 ± 0.42) · 10−10 TeV−1 cm−2 s−1at a reference energy of $13\, \mathrm{TeV}$ and a spectral index of −2.74 ± 0.16.
The current generation of ground-based imaging atmospheric Cherenkov telescopes (IACTs) operate in the very-high-energy (VHE) domain from ~100 GeV to ~100 TeV. They use electronic digital trigger ...systems to discern the Cherenkov light flashes emitted by extensive air showers (EASs), from the overwhelming light of the night sky (LoNS) background. Near the telescope energy threshold, the number of emitted Cherenkov photons by gamma-ray-induced EASs is comparable to the fluctuations of the LoNS and the photon distribution at the Cherenkov-imaging camera plane becomes patchy. This results in a severe loss of effectiveness of the digital triggers based on combinatorial logic of thresholded signals. A stereoscopic analog trigger system has been developed for improving the detection capabilities of the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes at the lowest energies. It is based on the analog sum of the photosensor electrical signals. In this article, the architectural design, technical performances, and configuration of this stereoscopic analog trigger, dubbed " Sum-Trigger-II ," are described.
Abstract
Imaging Atmospheric Cherenkov Telescopes (IACTs) currently in operation feature large mirrors and order of 1 ns time response to signals of a few photo-electrons produced by optical photons. ...This means that they are ideally suited for optical interferometry observations. Thanks to their sensitivity to visible wavelengths and long baselines optical intensity interferometry with IACTs allows reaching angular resolutions of tens to microarcsec. We have installed a simple optical setup on top of the cameras of the two 17 m diameter MAGIC IACTs and observed coherent fluctuations in the photon intensity measured at the two telescopes for three different stars. The sensitivity is roughly 10 times better than that achieved in the 1970’s with the Narrabri interferometer.
Context
. We are operating an elastic light detecting and ranging system (LIDAR) for the monitoring of atmospheric conditions during regular observations of the MAGIC telescopes.
Aims
. We present ...and evaluate methods for converting aerosol extinction profiles, obtained with the LIDAR, into corrections of the reconstructed gamma-ray event energy and instrument response functions of Imaging Atmospheric Cherenkov Telescopes.
Methods
. We assess the performance of these correction schemes with almost seven years of Crab Nebula data obtained with the MAGIC telescopes under various zenith angles and different aerosol extinction scenarios of Cherenkov light.
Results
. The methods enable the reconstruction of data taken under nonoptimal atmospheric conditions with aerosol transmissions down to ~0.65 with systematic uncertainties comparable to those for data taken under optimal conditions. For the first time, the correction of data affected by clouds has been included in the assessment. The data can also be corrected when the transmission is lower than 0.65, but the results are less accurate and suffer from larger systematics.
The two MAGIC imaging atmospheric Cherenkov telescopes (IACTs) are located on the Canary island of La Palma. Their cameras are currently equipped with more than 1000 photomultiplier tubes (PMTs). We ...developed a silicon photomultiplier (SiPM) based detector module to evaluate the feasibility of a camera upgrade using only solid state detectors. We combined SiPMs to a composite matrix in order to achieve the same active area as the 1inch PMTs currently in use. This first prototype was installed in 2015 and is operated alongside the PMTs. Utilizing the collected data, we developed two more SiPM based detector modules. They are equipped with SiPMs from two different suppliers. These three different SiPM based detector modules will enable us to compare three different manufacturers of SiPMs under real observational conditions. Most important is the comparison to the neighbouring PMT modules.
•The performance expectations at high levels of background light are IACTs described.•The operational stability of DC and temperature is presented.•A calibration procedure for gain and cross talk is demonstrated.•A comparison to PMTs is shown utilizing the described calibration method.
Introduction: The aim of the study was to compare the neuroprotective and cerebrovascular effects of bioactive, endogenous lipid – N-arachidonoyl-GABA (AA-GABA) and GABA conjugate with prostaglandin ...E2 (PGE2-GABA) by evaluation of a morphological state of rat brain tissue and lipofuscin levels under the condition of permanent focal brain ischemia, as well as cerebral circulation under the condition of global transient ischemia.
Materials and methods: The study has been implemented using the models of the left middle cerebral artery occlusion (MCAO) and global transient ischemia of the brain. A morphological examination of the brain tissue, a registration of local blood flow by laser flowmeter, and quantitative measurement of lipofuscin by fluorescence spectroscopy were used.
Results and discussion: AA-GABA and the putative COX-2 metabolite PGE2-GABA showed significant neuroprotective and cerebrovascular effects in rat models of global and focal cerebral ischemia. In the MCAOmodel, AA-GABA and PGE2-GABA at a dose of 2 mg/kg/day administered i.p. for 6 or 12 days led to: 1) significant restoration of neurons and glial cells with intracellular regeneration of cytoplasmic and nuclear structures, 2) decrease in brain tissue edema; 3) attenuated thrombosis and stasis, and 4) absence of large necrotic foci in rat brain tissue. AA-GABA and PGE2-GABA at the same dose prevented excessive accumulation of lipofuscin in both brain hemispheres in rats with MCAO. All the studied compounds increase cerebral blood circulation in rats subjected to global transient ischemia. However, the cerebrovascular effect of PGE2-GABA was superior to the activity of AA-GABA and all other tested compounds. AA-GABA and PGE2-GABA, unlike PGE2 and nimodipine, increase the cerebral blood flow in rats with global transient brain ischemia and have no influence on the intact animals. Apparently, the GABAergic vascular system of the brain is involved in the mechanisms of the neuroprotective action of AA-GABA and PGE2-GABA.
Conclusion: For the first time, we demonstrated the ability of AA-GABAand its putative metabolite COX-2 PGE2-GABA to improve cerebral circulation, attenuate structural damage and lipofuscin accumulation during cerebral ischemia. The natural origin of AA-GABA, which possesses neuroprotective and cerebrovascular activity, as well as anti-aggregatory activity, allows considering AA-GABA as one of the endogenous protective factors in ischemic brain lesions.
A test of silicon photomultipliers as readout for PET Otte, A.N.; Barral, J.; Dolgoshein, B. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2005, Letnik:
545, Številka:
3
Journal Article
Recenzirano
The silicon photomultiplier (SiPM) is a novel photon detector based on Geiger mode operating avalanche photodiodes. In this paper, we present results from a test, demonstrating the feasibility of ...SiPM as readout elements in scintillator-based positron emission tomography (PET). As scintillator we use the newly developed LYSO crystals having similar characteristics as LSO. With our setup we measure an energy resolution of about 22% and a time resolution of a single crystal element of
(
1.51
±
0.07
)
ns
, both full-width at half-maximum. A significant improvement in time resolution could be achieved by triggering on the first photoelectron in the signal. We also present the coincidence rate of two detector channels vs. the position of a small point-like
22Na positron source.
Migraine pharmacology and brain ischemia Mirzoyan, Ruben S.; Gan’shina, Tamara S.; Kurdyumov, Ilya N. ...
Research results in pharmacology (English ed.),
06/2021, Letnik:
7, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Introduction: The aim of this review article was to analyze in details the mechanism of drugs’ effects in the treatment and prevention of a migraine attack, as well as to discuss the hypotheses of ...migraine pathogenesis.
Migraine attack treatment agents: The main agents for migraine attack treatment have an anti-nociceptive activity.
Agents for migraine preventive treatment: β-blocker propranolol also has anti-serotonin and analgesic activities, and most drugs used for the prophylactic treatment of migraine have a vasodilating activity.
Vascular hypothesis of migraine pathogenesis: Despite numerous studies that have expanded our understanding of migraine pathogenesis, the importance of the vascular component in the pathogenesis of this disease has not questioned yet.
Neurogenic hypotheses of cortical spreading depression: It is necessary to take into account the points of this hypothesis in the context of the pathophysiology of migraine.
Neurochemical serotonin hypotheses of migraine pathogenesis: Serotonin plays an important role in the pathogenesis of migraine.
Trigemino-vascular hypotheses of migraine pathogenesis: The trigemino-vascular hypothesis claims to solve the problem of migraine pain.
Migraine and ischemic brain damage: Migraine is a risk factor for ischemic stroke and cognitive disorders.
Search for the new anti-ischemic anti-migraine preparations: A methodology for the search for new anti-ischemic anti-serotonin drugs for the treatment of migraine is proposed.
Conclusion: Belonging of a drug to one or another pharmacological group does not always correspond to its therapeutic effect on the pathogenetic processes of migraine. Migraine with its variety of forms cannot fit only one of the proposed hypotheses on the pathogenesis of this disease.
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