1,720,995 research outputs found
Discretely tunable comb spacing of a frequency comb by multilevel phase modulation of a periodic pulse train
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Tapered two-wire waveguide for time-domain integration of broadband terahertz pulses
No full textWe show the time-domain integration of terahertz pulses achieved in a sub-wavelength, tapered two-wire waveguide. Both simulation and experimental results prove the time integration functionality of this waveguide topology
Towards on-chip photonic-assisted radio-frequency spectral measurement and monitoring
Get PDFPrecise detection and monitoring of the frequency spectrum of microwave signals are essential to myriad scientific and technological disciplines, including both civil and defense areas, such as telecommunications, radar, biomedical instrumentation, radio astronomy, etc. Historically, microwave engineering has provided solutions for these tasks. However, current radio-frequency (RF) technologies suffer from inherent shortcomings that limit their capability to provide agile (e.g., real-time) measurements over a large operation bandwidth in energy-efficient and compact (e.g., integrated) formats. Overcoming these limitations is key to fulfilling pressing performance requirements in the above-mentioned application fields, as well as for compatibility with platforms that require chip-scale integration and/or low weight and dimensions, such as satellites and drones. Integrated microwave photonics is an emerging field that leverages the advantages of optical technologies for realization of microwave operations with high bandwidth, low power consumption, and increased agility and flexibility in on-chip platforms, offering an alternative path for integration of advanced RF processing and analysis methods in mature semiconductor technologies. This mini review surveys some of the latest advances in microwave spectral measurement and monitoring techniques realized through photonic approaches, with a special focus on methods suitable for on-chip integration
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
Time-Domain Integration of Broadband Terahertz Pulses via Tapered Two-Wire Waveguide
No full textIn this work, we report on the implementation of a time-domain integrator device operating on arbitrary broadband Terahertz (THz) pulses. This analog signal-processing functionality is implemented by employing a two-wire waveguide (TWWG) variant, based on a tapered configuration. A conventional TWWG is made of two copper wires separated by an air gap between them. Here, we show here that, if the gap between the wires is much smaller than the THz wavelength and the wire radius, the propagating THz field undergoes a field enhancement factor that is inversely proportional to the THz frequency, thus matching with the spectral behavior of a time-domain integrator. Both simulation and experimental results here demonstrate that the tapered TWWG (briefly, TTWWG) is indeed able to perform the time-domain integration functionality
Spectrum to distance mapping via nonlinear Airy pulses
No full textWe theoretically and experimentally study the phenomena related to self-phase modulation of Airy pulses in fibers. During nonlinear evolution, most spectral components of the Airy pulses concentrate into one or two peaks for normal and anomalous dispersion, respectively. The resulting peaks self-shift along the propagation, effectively mapping the longitudinal coordinate into the frequency domain. The frequency shift can be precisely controlled by simply acting on the spectral cubic phase structure without the need to alter the fiber length. (C) 2013 Optical Society of Americ
Time-Domain Integration of Terahertz pulses
No full textWe report on the time-domain integration of terahertz pulses obtained via the tight confinement of the radiation in a tapered two-wire waveguide. Both simulation and experimental results prove the time integration capability of this structure
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
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