169,901 research outputs found
A double stub impedance tuner with SiC diode varactors
No full textDesign and characterization of a double-stub impedance tuner at 1.4 GHz, based on SiC varactors, fabricated at the Chalmers University, is presented. Preliminary studies are carried out to evaluate the capacitance range required to reach the desired impedance coverage, extending from 15 to 80Ω. Accurate optimization is then completed through RF CAD simulation adopting a reliable nonlinear varactor model. The circuit, that to the authors' knowledge is the first example of a generic tuner based on SiC varactors, represents a good compromise between coverage range and losses, the most important figures of merit of a tuner, that besides will be shown to exhibit very good agreement between measurements and simulations. Tuner performances, layout compactness and simplicity, together with the high voltage that can be handled by SiC varactors make it a viable solution for the tunable output networks required in reconfigurable RF power amplifiers
Kit Preparation with Cobot-Supported Sorting in Mixed Model Assembly
No full textKitting is a common approach of materials supply with mixed-model assembly, by which components are supplied to the assembly process in pre-sorted kits. With kitting, the kit preparation is a labour intensive process and order batching is often applied to enhance efficiency. Here, improved quality and efficiency by means of automation is desirable, but knowledge of the potential of collaborative robots to support kit preparation with order batching is lacking. The purpose of this paper is to identify the potential of cobots to support time-efficient kit preparation with order batching, when the pick task is performed manually and a cobot carries out the sort task. A modelling approach is applied with experimental data from laboratory experiments to compare the cycle time between fully manual and cobot-supported kit preparation with order batching. The findings suggest that a cobot-supported sort task leads to a comparable average cycle time, with less variability of the cycle time, when compared to the fully manual setup. The paper contributes several insights on the application of cobots to support kit preparation, and the model developed in the paper can be used by practitioners to assess the potential of cobots to support their processes for kit preparation. (C) 2019, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Design and characterization of SiC varactor-based phase shifters
No full textDesign and realization of two continuously tunable phase shifters for 1.4 GHz band is presented. Both circuits are based on SiC varactors, conceived to enable high-voltage, high-power operation, and suitable for application in the transmitter chain of reconfigurable radios. Experimental characterization shows, for the loaded line phase shifter, 74° maximum phase shift with insertion loss lower than 1 dB, and, for the reflective phase shifter, 90° maximum phase shift and insertion loss lower than 0.6 d
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Design method for quasi-optimal multiband branch-line couplers
No full textIn this article, the design approach, the implementation, and experimental results of multiband branch-line couplers operating at arbitrary frequencies are presented.
The conventional branch-line coupler structure is adapted to multiband operation by shunting its four ports with multiband reactive networks. The performance of the proposed multiband couplers is theoretically analyzed and optimized through the even-odd mode circuit analysis. Dual-band (2.4–3.5 GHz), triple-band (1.5–2.4–4.2 GHz), and quad-band (1.5–2.4–3.5 GHz) microstrip branch-line couplers have been realized and tested to verify the design method. The good experimental results (input return loss greater than 15 dB and amplitude imbalance lower than 0.7 dB) show excellent agreement with theoretical and simulated ones, thus validating the proposed approach
Design of a concurrent dual-band 1.8-2.4-GHz GaN-HEMT doherty power amplifier
No full textIn this paper, the design, implementation and experimental
results of a high efficiency dual-band GaN-HEMT
Doherty power amplifier (DPA) are presented. An extensive
discussion about the design of the passive structures is presented
showing different possible topologies of the dual-band DPA. One
of the proposed topologies is used to design a dual-band DPA in
hybrid technology for the frequency bands 1.8GHz and 2.4GHz
with the second efficiency peak at 6 dB output power backoff
(OBO). For a continuous wave output power of 20W, the
measured power added efficiency is 64% and 54% at 1.8GHz
and 2.4GHz, respectively. At 6 dB OBO, the resulting measured
Power-Added Efficiency (PAE) were 60% and 44% in the two
frequency bands. Linearized concurrent modulated measurement
using 10MHz LTE signal with 7 dB Peak-to-Average-Ratio (PAR)
at 1.8GHz and 10MHz WiMAX signal with 8.5 dB PAR at
2.4GHz shows an average PAE of 34%, at an adjacent channel
leakage ratio of -48 dBc and -46 dBc at 1.8GHz and 2.4GHz,
respectively
Efficiency optimization for phase controlled multi-source microwave oven
No full textA solid-state microwave generators system is considered as an alternative to the magnetron, in order to inject electromagnetic energy into the cavity of a microwave oven for domestic use. Over current devices, the use of solid state technology allows one to control the frequency and phase of the electromagnetic field generated.
Considering a simplified cavity with 2 solid state sources, the influence of the electrical parameters on maximum efficiency obtainable in the process of microwave heating is investigated. By varying the frequency, different values of optimal phases and different values of maximum efficiency are detected.
Moreover, the procedure is repeated with varying the position of one source port and the influence of geometry on the system performance is evaluated.
Our results demonstrate that the ability to control the electrical quantities of a microwave heating process makes it possible to obtain better results in terms of energy efficiency over the current poorly controllable systems
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