1,721,094 research outputs found
Spectral broadening and shaping of nanosecond pulses: toward shaping of single photons from quantum emitters
No full textWe experimentally demonstrate spectral broadening and shaping of exponentially-decaying nanosecond pulses via nonlinear mixing with a phase-modulated pump in a periodically poled lithium niobate (PPLN) waveguide. 1550 nm pump light is imprinted with a temporal phase and used to upconvert a weak 980 nm pulse to 600 nm while simultaneously broadening the spectrum to that of a Lorentzian pulse up to 10 times shorter. While the current experimental demonstration is for spectral shaping, we also provide a numerical study showing the feasibility of subsequent spectral phase correction to achieve temporal compression and reshaping of a 1 ns mono-exponentially decaying pulse to a 250 ps Lorentzian, which would constitute a complete spectrotemporal waveform shaping protocol. This method, which uses quantum frequency conversion in PPLN with > 100 ∶ 1 signal-to-noise ratio, is compatible with single photon states of light
Bright Single-Photon Emission From a Quantum Dot in a Circular Bragg Grating Microcavity
No full textBright single-photon emission from single quantum dots (QDs) in suspended circular Bragg grating microcavities is demonstrated. This geometry has been designed to achieve efficient (>50%) single-photon extraction into a near-Gaussian-shaped far-field pattern, modest (≈10×) Purcell enhancement of the radiative rate, and a spectral bandwidth of a few nanometers. Measurements of fabricated devices show progress toward these goals, with collection efficiencies as high as ≈10% demonstrated with moderate spectral bandwidth and rate enhancement. Photon correlation measurements are performed under above-bandgap excitation (pump wavelength = 780 to 820 nm) and confirm the single-photon character of the collected emission. While the measured sources are all antibunched and dominantly composed of single photons, the multiphoton probability varies significantly. Devices exhibiting tradeoffs among collection efficiency, Purcell enhancement, and multiphoton probability are explored and the results are interpreted with the help of finite-difference time-domain simulations. Below-bandgap excitation resonant with higher states of the QD and/or cavity (pump wavelength = 860 to 900 nm) shows a near-complete suppression of multiphoton events and may circumvent some of the aforementioned tradeoffs
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Rangeland rehabilitation in the southern part of the Mediterranean basin
No full textRangelands of the southern part of the Mediterranean basin have for centuries provided forage for livestock and wildlife. Now their role as providers of ecosystem services and goods is being widely recognized by local governments and international organizations. But the widespread degraded ecological status of rangelands is causing increasing concern. Over-exploitation of rangeland resources, land tenure issues, conversion of rangelands into rainfed cropping systems, and climate change including drought are the main drivers for this degradation. Several governments are becoming increasingly aware of the magnitude of the problem and have begun to address the root causes through holistic approaches. However, there are major challenges in tackling the issue: the importance of rangelands is generally marginalized, conservation measures are incomplete and often ineffective for the sustainable restoration of degraded rangeland resources. In addition, given the low and slow return on investment, governments are not able to finance large-scale projects to effectively restore and develop rangeland natural resources. Nonetheless, there are ways to improve the situation. In this paper, we propose how to go about this. Not least, we outline how understanding and managing the constraints to widespread adoption of sustainable practices is key to the successful out-scaling of interventions with known potential
Data Collection, Experimental Design Data Analysis in Forage Trials Training Course
No full textTraining course on Data Collection, Experimental Design & Data Analysis in Forage Trials was Conducted in Kabul, Afghanistan 16 – 18 April 2018 where 16 professionals from Agricultural Research Institute of Afghanistan (ARIA). The objective of the workshop was to share knowledge on statistical concepts and methodologies for designing field experiments and biometrical techniques applied in agricultural (forage trial) research, and to provide an opportunity to ARIA staff/researchers to carry out statistical analysis of their data, and prepare a draft research manuscript for publication
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