1,720,988 research outputs found
Superheated emulsions for the detection of special nuclear material
No full textA novel solution for the detection and smuggling interdiction of special nuclear materials is presented here consisting of large detector modules which contain superheated emulsions and which are readout with an optical approach. The detectors can be produced to be fully sensitive to prompt fission neutrons and totally insensitive to the interrogation beam, whether X-rays or neutrons below a chosen energy threshold. Therefore, the detectors are able to operate while the selected interrogation beam is on and they will only pick up the signal from fission neutrons. A position-sensitive readout mechanism is used in our design, relying on the scattering of light by neutron-induced bubbles. A beam of coherent light crosses the active area of the detector, and local variations in scattered light due to the presence of bubbles are detected in real time by arrays of silicon planar photodiodes affixed along the whole length of the detector. The system may offer a variety of advantages compared to current approaches, such as the possibility of simultaneous irradiation and detection, i.e. a 100% duty cycle, without requiring complex signal analysis, and high signal-to-noise ratio, minimizing costly nuisance alarms, thanks to its inherent insensitivity to photons
Advanced readout methods for superheated emulsion detectors
No full textSuperheated emulsions develop visible vapor bubbles when exposed to ionizing radiation. They consist in droplets of a metastable liquid, emulsified in an inert matrix. The formation of a bubble cavity is accompanied by sound waves. Evaporated bubbles also exhibit a lower refractive index, compared to the inert gel matrix. These two physical phenomena have been exploited to count the number of evaporated bubbles and thus measure the interacting radiation flux. Systems based on piezoelectric transducers have been traditionally used to acquire the acoustic (pressure) signals generated by bubble evaporation. Such systems can operate at ambient noise levels exceeding 100 dB; however, they are affected by a significant dead time (>10 ms). An optical readout technique relying on the scattering of light by neutron-induced bubbles has been recently improved in order to minimize measurement dead time and ambient noise sensitivity. Beams of infra-red light from light-emitting diode (LED) sources cross the active area of the detector and are deflected by evaporated bubbles. The scattered light correlates with bubble density. Planar photodiodes are affixed along the detector length in optimized positions, allowing the detection of scattered light from the bubbles and minimizing the detection of direct light from the LEDs. A low-noise signal-conditioning stage has been designed and realized to amplify the current induced in the photodiodes by scattered light and to subtract the background signal due to intrinsic scattering within the detector matrix. The proposed amplification architecture maximizes the measurement signal-to-noise ratio, yielding a readout uncertainty of 6% (±1 SD), with 1000 evaporated bubbles in a detector active volume of 150 ml (6 cm detector diameter). In this work, we prove that the intensity of scattered light also relates to the bubble size, which can be controlled by applying an external pressure to the detector emulsion. This effect can be exploited during the readout procedure to minimize shadowing effects between bubbles, which become severe when the latter are several thousands. The detector we used in this work is based on superheated C-318 (octafluorocyclobutane), emulsified in 100 μm ± 10% (1 SD) diameter drops in an inert matrix of approximately 150 ml. The detector was operated at room temperature and ambient pressure
Taratura del sistema di controllo e regolazione del rivelatore per neutroni a emulsioni surriscaldate
No full textI rivelatori a emulsioni surriscaldate, costituiti da fiale contenenti gel SDD 1000, trovano uno dei loro impieghi preferenziali nella spettrometria di campi neutronici di energia compresa tra le centinaia di keV e circa 10 MeV. La variazione della temperatura operativa del gel consente infatti di variare la soglia energetica di rivelazione
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
La ricerca dell’antigene fecale dell’Helicobacter Pylori come test non invasivo in confronto al 13C-urea Breath-Test. Esperienza personale
Full text linkScopo dello studio è stato quello di confrontare l’utilizzo di due
test non invasivi per la ricerca dell’infezione da Helicobacter Pylori:
il 13C-urea Breath-Test, considerato il “gold standard”, e l’HpSa che
ricerca l’antigene dell’Helicobacter Pylori nelle feci.
Gli Autori hanno studiato 30 pazienti che presentavano sinto -
matologia dispeptica e mai sottoposti a terapia antibiotica eradicante
l’Helicobacter Pylori, concludendo che a tutt’oggi il 13C-urea
B r e a t h -Test è il metodo con maggiore sensibilità e specificità per lo
screening pre-endoscopico dei pazienti dispeptici, che comunque
l’HpSA è una metodica da migliorar
Moderni orientamenti nel trattamento medico della malattia diverticolare sintomatica
Full text linkGli Autori riportano la loro esperienza sull'uso di un antibiotico e di un antinfiammatorio per il trattamento della malattia diverticolare sintomatica.
Si conferma l'osservazione di altri Autori della maggiore efficacia di questo nuovo approccio terapeutico rispetto al tradizionale trattamento con antibiotici.
English version: Authors refer about their experience on treatment of symptomatic diverticular disease both with antibiotic and antinflammatory drugs.
They confirm the observation of other Authors on effectiveness of this new therapeutic approach versus traditional antibiotic therapy
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
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