1,720,983 research outputs found
Quantifying distortion in time-correlated single photon counting: a universal parameter
No full textOne major drawback of the classic time-correlated single photon counting (TCSPC) technique is pileup-related distortion. To keep it under a reasonable level, the maximum count rate has to be reduced, posing a serious limitation to the overall measurement speed. This means that there is an intrinsic trade-off between speed and distortion: either count rate is raised, but distortion is worsened, or distortion is minimized at the expense of speed. In both cases, it is impossible to precisely evaluate the degree of distortion introduced. Here comes our new, to the best of our knowledge, figure of merit, which is able to provide a numerical estimate of the distortion whatever the signal shape is, marking a real turning point in the way of doing TCSPC. In this article, this new parameter will be defined and its effectiveness will be demonstrated by means of mathematical computations
Fully digital routing logic for single-photon avalanche diode arrays in highly efficient time-resolved imaging
No full textTime-correlated single-photon counting (TCSPC) is a powerful optical technique, which permits recording fast luminous signals with picosecond precision. Unfortunately, given its repetitive nature, TCSPC is recognized as a relatively slow technique, especially when a large time-resolved image has to be recorded. In recent years, there has been a fast trend toward the development of TCPSC imagers. Unfortunately, present systems still suffer from a trade-off between number of channels and performance. Even worse, the overall measurement speed is still limited well below the saturation of the transfer bandwidth toward the external processor. We present a routing algorithm that enables a smart connection between a 32×32 detector array and five shared high-performance converters able to provide an overall conversion rate up to 10 Gbit/s. The proposed solution exploits a fully digital logic circuit distributed in a tree structure to limit the number and length of interconnections, which is a major issue in densely integrated circuits. The behavior of the logic has been validated by means of a field-programmable gate array, while a fully integrated prototype has been designed in 180-nm technology and analyzed by means of postlayout simulations
TCSPC 2.0: a new constraint-less methodology to avoid distortion at any speed
No full textTime Correlated Single Photon Counting (TCSPC) has been historically subject to the count-rate vs distortion tradeoff. Several attempts to work around this limitation have been reported in the literature, either based on multichannel systems or on post-processing correction algorithms. In this work, we’ll show how distortion can be avoided by exploiting additional information on the system status acquired during the whole experiment. We’ll provide evidence that a new research line can finally combine all the advantages of TCSPC with very high speed. Starting from on-field results, we’ll present the novel technique providing design guidelines for next-generation ultrafast TCSPC acquisition systems
Toward Constraintless Time-Correlated Single-Photon Counting Measurements: A New Method to Remove Pile-up Distortion
Get PDFTime-Correlated Single-Photon Counting (TCSPC) is a well-renowned technique allowing to reconstruct light signals with high sensitivity and resolution. Nevertheless, to this day, its use in applications requiring a fast analysis of the sample is limited due to its long acquisition time. The reason is twofold: on one hand, it is based on a statistical method thus requiring the collection of a large number of events to properly reconstruct the signal waveform; on the other hand, the average number of photons impinging on the sensor has to be kept particularly low to avoid artifacts. Indeed, the existence of dead time of both single-photon detectors and electronics can lead to distortion in the reconstructed waveform, which can be mitigated only if the count rate is kept below few percent of the excitation frequency. Recently, it has been demonstrated that an appropriate tuning of detector dead time allows to remove such power restriction, but, unfortunately, this constraint also sets a limit to the maximum count rate of the detector. In this paper, we present a novel method for TCSPC measurements, which ensures negligible distortion at unprecedented rates without requiring any constraint on either illumination power or detector dead time. We will show that this is possible thanks to the acquisition of additional information on the status of TCSPC system. The theoretical analysis reported in this paper is supported by analytical computation and numerical simulation, taking into account also potential non idealities of a real implementation
High-efficiency integrated readout circuit for single photon avalanche diode arrays in fluorescence lifetime imaging
Get PDFIn recent years, lifetime measurements by means of the Time Correlated Single Photon Counting (TCSPC) technique have led to a significant breakthrough in medical and biological fields. Unfortunately, the many advantages of TCSPC-based approaches come along with the major drawback of a relatively long acquisition time. The exploitation of multiple channels in parallel could in principle mitigate this issue, and at the same time it opens the way to a multi-parameter analysis of the optical signals, e.g., as a function of wavelength or spatial coordinates. The TCSPC multichannel solutions proposed so far, though, suffer from a tradeoff between number of channels and performance, and the overall measurement speed has not been increased according to the number of channels, thus reducing the advantages of having a multichannel system. In this paper, we present a novel readout architecture for bi-dimensional, high-density Single Photon Avalanche Diode (SPAD) arrays, specifically designed to maximize the throughput of the whole system and able to guarantee an efficient use of resources. The core of the system is a routing logic that can provide a dynamic connection between a large number of SPAD detectors and a much lower number of high-performance acquisition channels. A key feature of our smart router is its ability to guarantee high efficiency under any operating condition
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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