The arrival directions of extremely high energy cosmic rays (EHECR) above 4×10
19 eV, observed by four surface array experiments in the northern hemisphere, are examined for coincidences from similar ...directions in the sky. The total number of cosmic rays is 92. A significant number of double coincidences (doublet) and triple coincidences (triplet) is observed on the supergalactic plane within the experimental angular resolution. The chance probability of such multiplets from a uniform distribution is less than 1% if we consider a restricted region within ±10° of the supergalactic plane. Though there is still a possibility of chance coincidence, the present results on small angle clustering along the supergalactic plane may be important in interpreting EHECR enigma. An independent set of data is required to check our claims.
Distribution of tropical rainforests in Southeastern Asia has changed over geo‐logical time scale, due to movement of tectonic plates and/or global climatic changes. Shorea parvifolia is one of the ...most common tropical lowland rainforest tree species in Southeastern Asia. To infer population structure and demographic history of S. parvifolia, as indicators of temporal changes in the distribution and extent of tropical rainforest in this region, we studied levels and patterns of nucleotide polymorphism in the following five nuclear gene regions: GapC, GBSSI, PgiC, SBE2, and SODH. Seven populations from peninsular Malaysia, Sumatra, and eastern Borneo were included in the analyses. STRUCTURE analysis revealed that the investigated populations are divided into two groups: Sumatra‐Malay and Borneo. Furthermore, each group contained one admixed population. Under isolation with migration model, divergence of the two groups was estimated to occur between late Pliocene (2.6 MYA) and middle Pleistocene (0.7 MYA). The log‐likelihood ratio tests of several demographic models strongly supported model with population expansion and low level of migration after divergence of the Sumatra‐Malay and Borneo groups. The inferred demographic history of S. parvifolia suggested the presence of a scarcely forested land bridge on the Sunda Shelf during glacial periods in the Pleistocene and predominance of tropical lowland rainforest at least in Sumatra and eastern Borneo.
The inferred demographic history of Shorea parvifolia suggested the presence of a scarcely forested land bridge on the Sunda Shelf during the glacial periods in the Pleistocene and a predominance of tropical lowland rainforest at least in Sumatra and eastern Borneo. We also found low level of migration after divergence of the Sumatra‐Malay and Borneo groups.
In this study we reviewed the use of genetic information in the Ecologically or Biologically Significant Marine Areas (EBSA) of Convention on Biological Diversity (CBD). We also evaluated genetic ...indicators for each criterion of important marine areas. We proposed five genetic indices, mainly based on microsatellite analysis (e.g., private allele frequency and number of cryptic species), then selected EBSAs in tropical and temperate zones of Japan based on eight coral species as a case study. Finally, we compared the results with the findings from conventional species-based EBSAs. In the EBSAs genetic information was mainly used in the Northern Hemisphere, particularly in the Baltic Sea; it was rarely applied in the Southern Hemisphere and Asian regions. Although typically applied to large organisms, genetic information is used to various organisms, including benthic and bacterial communities. Genetic data are used as indicators of diversity and endemism. Genetic indices were available for all seven EBSA criteria, but only five indices of three criteria were used. Examination of important areas of corals in the temperate zone using these indices showed that the indices without genetic indicators extracted a large number of important areas in the tropics; however, the use of genetic indicators identified important locations, including in temperate zones. Comparison with conventional, mainly species-based non-genetic methods showed less than 50% agreement, although particularly important sites in marine protected areas were identified by both methods. While there is still more work to be done, such as consideration of the number of survey sites or target species, one reason is that species-based methods tend to evaluate tropical areas higher. Therefore, these genetic indices are useful for examining important regions, particularly in temperate zones; they revealed cryptic lineages, indicating that many unknown marine taxa should be considered in vulnerable marine areas. Some indicators could be extracted with additional effort, such as population size estimation, immigration, or the use of next-generation sequencing, thus guiding future studies. Because limited genetic information was available in the early stages of EBSA selection, there is a need for systematic surveys and evaluations, particularly in the Southern hemisphere, Asian region, and in small organisms.
This paper presents a detailed study on superdense wavelength-division multiplexing (WDM) transmission of spectrum-sliced incoherent light used for a wide-area access network. The transmission ...performance possible with this approach is evaluated numerically with regard to the following items: the transmission limit due to the chromatic dispersion, optimized signal-to-noise ratio design for the optical spectral width taking into account the adjacent-channel crosstalk, and the nonlinear effect generated by four-wave mixing at around the zero-dispersion wavelength. Superdense WDM transmission is also performed experimentally using 25-GHz channel-spaced, 15-GHz wide, up-to 156-Mb/s signals through up to 120 km of dispersion-shifted fiber.
The peak photon detection efficiency (PDE) of silicon photomultipliers (SiPMs) can be as good or better than the PDE of photomultiplier tubes (PMTs). There are experiments where the signal is ...measured in the presence of a strong, steady background light emission. In these, one needs to accurately evaluate the signal-to-noise ratio. Imaging Atmospheric Cherenkov Telescopes (IACT) observe in the presence of strong noise induced by the light of the night sky. It is certainly interesting to investigate the SiPM performance under operational conditions of IACTs and to compare it with that of the PMTs.
For that purpose, we built a SiPM-based detector module, which was installed in one of the imaging cameras of the two Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes in 2015. The experience gained from that module was used to design the second generation of modules of improved performance. Two such modules were installed in 2017.
MAGIC is a system of two IACTs located on the Canary Island of La Palma. The mechanical structure of the MAGIC imaging cameras offers the possibility to install up to 6 additional detector modules of 7 pixels each into the open vertices of the hexagonal-shaped camera. This allows us to directly, without making any assumption, compare the performance of the PMT-based modules with that of the SiPM-based prototype modules, where SiPMs from three different manufacturers are used.
Ground-based Atmospheric Air Cherenkov Telescopes (ACTs) are successfully used to observe very high energy (VHE) gamma rays from celestial objects. The light of the night sky (LONS) is a strong ...background for these telescopes. The gamma ray pulses being very short, an ultra-fast read-out of an ACT can minimize the influence of the LONS. This allows one to lower the so-called tail cuts of the shower image and the analysis energy threshold. It could also help to suppress other unwanted backgrounds.
Fast ‘flash’ analog-to-digital converters (FADCs) with GSamples/s are available commercially; they are, however, very expensive and power consuming. Here we present a novel technique of Fiber-Optic Multiplexing which uses a single 2 GSamples/s FADC to digitize 16 read-out channels consecutively. The analog signals are delayed by using optical fibers. The multiplexed (MUX) FADC read-out reduces the cost by about 85% compared to using one ultra-fast FADC per read-out channel.
Two prototype multiplexers, each digitizing data from 16 channels, were built and tested. The ultra-fast read-out system will be described and the test results will be reported. The new system will be implemented for the read-out of the 17
m diameter MAGIC telescope camera.
Selection of photomultipliers for the Cherenkov Telescope Array facility Shayduk, M.; Mirzoyan, R.; Zimmer, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2010, Letnik:
617, Številka:
1
Journal Article
Recenzirano
The future ground-based gamma-ray facility—Cherenkov Telescope Array (CTA)—is aiming for a sensitivity of 1
mCrab at energies above 20
GeV. This goal in sensitivity is aiming for an order of ...magnitude increase compared to currently operating instruments H.E.S.S., MAGIC, CANGAROO III and VERITAS. In order to provide high sensitivity and low energy threshold the photosensors should have highest possible photon detection efficiency (PDE), low after-pulsing rate and good single photoelectron resolution. Photosensors of Cherenkov telescopes are permanently exposed to the background light of the night sky, therefore a long life time and low fatigue are also necessary conditions.
Various photomultipliers (PMT) of 1–2
in. size from PHOTONIS and HAMAMATSU were tested in MPI for Physics in Munich. Comparative measurements of quantum efficiency, timing, after-pulsing and single photoelectron resolution will be presented here. An evaluation of Electron Tubes photomultipliers is ongoing
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