1,720,983 research outputs found
Polarization-insensitive wavelength conversion in a lithium niobate waveguide by the cascading technique
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Waveguide photodetector in germanium on silicon
No full textIt is described a photodetector structure (1,1′,1"), comprising a silicon-based waveguide (2) in which optical signals to be detected travel in a given direction (X) and are confined therein; a germanium-based layer (4) disposed on a portion of the silicon-based waveguide (2), the germanium layer (4) including a first mesa (10) defining an active region having a length (L) along the signal propagating direction (X) and a width (W) in a direction (Z) substantially perpendicular to the propagating direction (X) so that an evanescent tail of the propagating optical signal in the waveguide (2) is coupled into the active region, and a second mesa (30; 40) separated by a distance d from the first mesa (10) in said direction (Z) substantially perpendicular to the signal propagating direction. The photodetector further includes a first (7) and a second metallic contact (9a,9b) having opposite polarities, the first metallic contact (7) being located on the active region of the first mesa (10) and the second metallic contact (9a, 9b) being located on said second mesa (30), said first and second contact being used to collect electrons generated by light absorption to obtain an output electric signal
Coaxially driven microwave electrodeless UV lamp
No full textThe construction and operating characteristics of a microwave (MW) electrodeless UV lamp are described. Instead of using a MW oven or a MW cavity to excite a plasma discharge in a glass bulb, in this work the optical radiation emitted by the gaseous plasma discharge is produced by the near field of a coaxial cable dipole antenna placed inside the recess of the quartz bulb. Experimental results are reported, which were obtained by applying MW power up to 700 W in continuous wave regime to an Ar-Hg filled cylindrical bulb, and 160 W to a XeBr2 filled spherical bulb at 2.45 GHz. The UV emission from a 6 W Ar-Hg lamp is compared with a commercial lamp, demonstrating the advantages of the new method in terms of efficiency. When the lamp is excited at high MW levels, the MW coaxial antenna is cooled using forced air or water flowing into the glass recess. The physical modeling of the electromagnetic field distribution in the near-field region of the antenna and its interaction with the gaseous discharge are in good agreement with experimental results. The article focuses on the advantages of the non-cavity activation method of the UV lamp, taking into account industrial applications. In fact, the coaxial antenna excitation method is characterized by extreme simplicity, due to the absence of resonant metal enclosures. Thus, the ordinary MW cavity can be replaced by a number of independent MW UV emitters, placed inside a reaction vessel of arbitrary size and material.The construction and operating characteristics of a microwave (MW) electrodeless
UV lamp are described. Instead of using a MW oven or a MW cavity to excite a
plasma discharge in a glass bulb, in this work the optical radiation emitted by the
gaseous plasma discharge is produced by the near field of a coaxial cable dipole
antenna placed inside the recess of the quartz bulb. Experimental results are
reported, which were obtained by applying MW power up to 700W in continuous
wave regime to an Ar–Hg filled cylindrical bulb, and 160W to a XeBr2 filled
spherical bulb at 2.45 GHz. The UV emission from a 6W Ar–Hg lamp is compared
with a commercial lamp, demonstrating the advantages of the new method in terms
of efficiency. When the lamp is excited at high MW levels, the MW coaxial antenna
is cooled using forced air or water flowing into the glass recess. The physical
modeling of the electromagnetic field distribution in the near-field region of the
antenna and its interaction with the gaseous discharge are in good agreement with
experimental results. The article focuses on the advantages of the non-cavity
activation method of the UV lamp, taking into account industrial applications. In
fact, the coaxial antenna excitation method is characterized by extreme simplicity,
due to the absence of resonant metal enclosures. Thus, the ordinary MW cavity can
be replaced by a number of independent MW UV emitters, placed inside a reaction
vessel of arbitrary size and materia
Computational Patient-Specific Models Based on 3D Ultrasound Data to Quantify Uterine Arterial Flow during Pregnancy.
No full textInformation on uterine blood flow rate during pregnancy would widely improve our knowledge on feto-placental patho-physiology. Ultrasonographic flow rate evaluation requires the knowledge of the spatial velocity profiles throughout the investigated vessel; these data may be obtained from hemodynamic simulations with accurate computational models. Recently, computational models of superficial vessels have been created using 3-D ultrasound data; unfortunately, common reconstruction methods are unsuitable for the uterine arteries due to the low quality achievable of imaged deep vessels. In this paper a simplified spline-based technique was applied to create computational models for patient-specific simulations of uterine arterial heamodynamics. Moreover, a novel method to quantify the uterine flow rates was developed based on echo-Doppler measurements and computational data. Preliminary results obtained for four patients indicated a quite narrow range for the blood flow rate through the main uterine artery with large variability in the flow split between corporal and cervical branches. Furthermore, parabolic-like velocity profiles were obtained in the branching region of the different patients, suggesting a clinical use of averaged, not patient-specific, spatial velocity distribution coefficients for the blood flow rate calculation. The developed reconstruction method based on 3-D ultrasound imaging is efficient for creating realistic custom models of the uterine arteries. The results of the fluid dynamic simulations allowed us to quantify the uterine arterial flow and its repartition in normal pregnancies
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
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