130,610 research outputs found
Silicon photomultipliers in Very High Energy gamma-ray astrophysics
No full textIn the last ten years silicon photomultipliers (SiPMs) have gained terrain in experiments and applications in which photomultiplier tubes have been the dominant photosensors during decades. Imaging Atmospheric Cherenkov Telescopes (IACTs) for very high energy (VHE, E>50 GeV) gamma-ray astronomy are experiencing the same process. Until now FACT was the only IACT using SiPMs. In the Cherenkov Telescope Array (CTA), the next-generation VHE gamma-ray observatory, at least 70 telescopes equipped with SiPMs are planned to be built. The first prototypes have already been constructed and are now being commissioned. Here we discuss some of the advantages and drawbacks of using SiPMs in VHE gamma-ray astronomy and provide a brief overview of different developments related to the use of SiPMs in IACTs. © 2020 IOP Publishing Ltd and Sissa Medialab
Large-Area SiPM Pixels (LASiPs): A cost-effective solution towards compact large SPECT cameras
No full textSingle Photon Emission Computed Tomography (SPECT) scanners based on photomultiplier tubes (PMTs) are still largely employed in the clinical environment. A standard camera for full-body SPECT employs - 50-100 PMTs of 4?8 cm diameter and is shielded by a thick layer of lead, becoming a heavy and bulky system that can weight a few hundred kilograms. The volume, weight and cost of a camera can be significantly reduced if the PMTs are replaced by silicon photomultipliers (SiPMs). The main obstacle to use SiPMs in full-body SPECT is the limited size of their sensitive area. A few thousand channels would be needed to fill a camera if using the largest commercially-available SiPMs of 6 x 6 mm2. As a solution, we propose to use Large-Area SiPM Pixels (LASiPs), built by summing individual currents of several SiPMs into a single output. We developed a LASiP prototype that has a sensitive area 8 times larger than a 6 x 6 mm2 SiPM. We built a proof-of-concept micro-camera consisting of a 40 x 40 x 8 mm3 NaI(Tl) crystal coupled to 4 LASiPs. We evaluated its performance in a central region of 15 x 15 mm2, where we were able to reconstruct images of a 99mTc capillary with an intrinsic spatial resolution of - 2 mm and an energy resolution of - 11.6% at 140 keV. We used these measurements to validate Geant4 simulations of the system. This can be extended to simulate a larger camera with more and larger pixels, which could be used to optimize the implementation of LASiPs in large SPECT cameras. We provide some guidelines towards this implementation
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Photo-Trap: A low-cost and low-noise large-area SiPM-based pixel
No full textThe small sensitive area of commercial silicon photomultipliers (SiPMs) is often the main limitation for their use in experiments and applications that require large detection areas. Since capacitance, dark count rate and cost increase with the SiPM size, they are rarely found in sizes larger than 6 × 6 mm2. Photo-Trap combines a wavelength-shifter plastic, a dichroic filter and a standard commercial SiPM to build pixels of a few cm2. With this approach it can collect light over an area that can be ∼10–100 times larger than the area of a commercial SiPM, while keeping the noise, single-photoelectron resolution, power consumption and likely the cost of a single small SiPM. We developed four different proof-of concept pixels sensitive in the near UV band, the largest one being of 40 × 40 mm2. We characterized them through laboratory measurements and Geant4 simulations. The optical gain we measured with the prototypes went from ∼5 to ∼15, while the single-photon time resolution was of ∼3–5 ns FWHM. With the achieved performance Photo-Trap could be a competitive low-cost alternative for applications that require photosensors with large collection areas and low noise, such as dark matter experiments and optical wireless communication
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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