1,721,020 research outputs found
Interfacing a SiPM to a Current-mode Front-end: Effects of the Coupling Inductance
No full textThe design of front-end electronics for SiPM detectors poses some peculiar constraints which call for dedicated architectures that may remarkably differ from the commonly used ones for other solid state detectors. In particular, present day SiPM’s may have a number of microcells as high as 90,000. This may pose serious problems in terms of dynamic range of the output signal, especially when low voltage technologies are employed to implement the FE. Besides that, SiPM’s are inherently high speed devices characterized by large equivalent capacitance CDET. All the above characteristics indicate a current mode architecture as the most suitable one to interface this kind of devices. In the past several different topologies have been proposed in the literature most of them aiming at realizing the lowest possible value of input resistance, Rin, in the perspective of limiting the time constant in = RinCDET associated to the input node of the amplifier, which is usually deemed to be the dominant parameter affecting the dynamic performance of the FE. In this contribution we show that this is not the case in real situations and that there is an optimum range of values for the input resistance in dependence of the particular SiPM and of the interconnection parasitics, thus avoiding the need of realizing arbitrarily low values of input resistance that would also imply unnecessary high power dissipation and additional electronic noise, due to the high bias currents required in the input stage of the preamplifier. The results of the study, performed on a handly 2nd order SiPM model, are confirmed by both circuit simulations on a more accurate 4th order model and by lab experiments on commercially available devices
Origin of informational polymers: Differential stability of 3′-and 5′-phosphoester bonds in deoxy monomers and oligomers
No full textTo survive, an informational macromolecule must solve the major problem set by its very polymeric nature: instability. This is especially true in prebiotic terms because of the presumed initial absence of protective structures (proteins, lipids, etc.). We have analyzed the stability of the β-glycosidic and of the 3′- and 5′-phosphoester bonds in both deoxy monomers and deoxy oligomers under a large set of conditions. The results show a strong dependence of the relative stability of these bonds on the physico-chemical environment. A set of conditions has been identified in which the stability of polymers becomes comparable with that of the precursor monomers. In certain instances the stability of the 5′-phosphoester bond is even higher in the polymer than in the mononucleotide. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Time performance of voltage-mode vs current-mode readouts for SiPM's
No full textA comparison among different architectures of front-end preamplifiers for SiPM detectors is useful when relevant performance in terms of timing accuracy is required in single photon detection applications. Many different solutions have been proposed in the past, which can be grouped into three main approaches: charge sensitive amplifiers, voltage-mode amplifiers and current-mode buffers. Here these architectures have been discussed and their limitations and advantages have been highlighted. The comparison has been carried out considering a simplified model of the detector and the classical expression of the time jitter. The influence of parasitic effects associated to the interconnections between the SiPM and the front-end electronics has also been analyzed and the corresponding limitations to the achievable timing performance of the different front-end styles have been considered, in order to find out more about the most suitable approach. To support the analysis, simulations of simple circuit implementations of the compared architectures have been carried out, under equal conditions. The results of the study show that the charge sensitive amplifier configuration results to be inefficient, due to bandwidth limitations, and that the best timing accuracy performance can be achieved by a current-mode approach, especially when the interconnection parasitics become relevant
Assessing the time resolution of an integrated front-end for solid state radiation detectors
No full textMany factors influence the timing accuracy and precision of a TOF-PET system. In particular, the light yield and the decay time constant of the scintillating crystal used, the depth of interaction of the γ-photon within the crystal, the statistical fluctuations of the photon emission process and the light propagation within the crystal appear to be the most relevant ones connected to the detector. When the overall timing performance of the system has to be assessed, it is important also to estimate the influence of the front-end (FE) electronics on it, to find out suitable criteria for the correct choice of the main specifications which affect the timing accuracy. In this contribution Monte Carlo simulations have preventively been employed to evaluate a number of realistic sets of arrival times for the first scintillating photons on a Silicon Photo Multiplier (SiPM), once the geometrical and physical characteristics of the system are known and taking into account the statistical dispersion of the photon emission process of the scintillator and the light propagation mechanisms within the crystal. Then, the elementary current pulses produced by the SiPM coupled with the FE electronics in response to each incident low energy photon have been summed up, according to the respective arrival times, resulting in a realistic set of waveforms for the overall output current pulse in response to a scintillation event. Preliminary lab experiments have been used to validate the equivalent circuit model of the photo-detector coupled to the FE electronics which has been exploited to evaluate its response to a single photon excitation. When the overall output current pulse, is applied to a leading edge current discriminator, the described procedure allows estimating how the performance parameters of the FE electronics affect the timing accuracy of the detection syste
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Phosphaditylserine liposomes as a possible candidate for the therapeutic management of Mycobacterium abscessus infection in CF patients
No full textIntroduction: we have previously reported that phosphatidylserine liposome (PS-L) were capable to induce a significant antimycobacterial response in mycobacterium tuberculosis (MTB)-infected and MTB/HIV-1-coinfected macrophages by simultaneously limiting inflammatory response and HIV replication. Here, we have assessed the therapeutic value of PS-L on human macrophages in vitro infected with M. abscessus (Mab), a non-tubercular mycobacterium which represents a relevant cause of morbidity and mortality in vulnerable patients such as those with cystic fibrosis (CF).
Materials and methods: Differentiated THP-1 cells (dTHP-1), used as a model of human macrophages, and primary macrophages derived from CF patients, were in vitro infected with Mab and then stimulated or not PS-L. the therapeutic value of the treatment was assessed in terms of intracellular mycobacterial viability, by CFU assay, and NF-kB activation (calculated as the ratio between total NF-κB and phosphorylated NF-κB) by NFκB p65 (Total/Phospho) Human InstantOneTM ELISA Kit (Invitrogen)
results: results show that in vitro stimulation with PS-L of dTHP-1 cells in vitro infected with mab significantly reduces intracellular mycobacterial viability and was associated with a significant drop in NF-κB activation. Importantly, such pro-mycobacteriocidal effect was also observed on macrophages from cystic fibrosis patients in vitro infected with Mab.
discussion and conclusions: altogether, these results extend our previously reported results obtained on MTB-infected and MTB/HIV-coinfected cells, also against a relevant difficult-to-treat non tubercular mycobacterium, such as Mab, and support the therapeutic exploitation of PS-L as host-directed therapy to simultaneously limit potentially pathogenetic proinflammatory response and intracellular Mab viability in vulnerable patients, such as CF patients
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