52 research outputs found
DEVELOPMENT OF SELF-ASSEMBLED CONDUCTING POLYMER ULTRATHIN FILMS AND POLY(ANILINE) NANOWIRES/SOL-GEL COMPOSITE MATERIALS AS SUBSTRATES FOR PLANAR SUPPORTED BIOMIMETIC ARTIFICIAL PHOTOSYNTHETIC SYSTEMS by
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Broadband High Efficiency Power Amplifiersfor RF Front-Ends of Wireless Transmitters
No full textThis thesis explores Power Amplifier (PA) architectures for Radio Frequency (RF) front-ends of transmitters in Fifth Generation (5G) wireless communication systems. New PA operation classes and new efficiency enhanced architectures are presented with comprehensive analyses, well-designed state-of-art prototypes, and excellent experimental results. Firstly, a new class of PA, designated as Class-iF-1, is proposed, which utilizes input harmonics to achieve high efficiency with enhanced linearity performance beyond the conventional Class-F-1 PA. The Amplitude-to-Amplitude (AM/AM) profile of the conventional Class-F-1 PA is mathematically modeled as a function of input drive level. Theoretical derivation shows that the appropriate utilization of input nonlinearity poses a solution to rectify the double inflection characteristics of conventional Class-F-1 PA, which consequently, can be realized by proper manipulation of second harmonic source impedance. A broadened second harmonic design space over the open-circuit region is proposed. Secondly, a new solution for phase compensation in the Sequential Load Modulated Balanced Amplifier (SLMBA) architecture is presented. By using proper harmonic tuning in the control amplifier carrier branch, the load trajectory of the balanced amplifier can be made close to the real axis, which is beneficial to recovering peak output power and efficiency at both Output Power Back-Off (OPBO) and saturation of the SLMBA in wideband operation. Thirdly, a novel Waveform Engineered Sequential Load Modulated Balanced Amplifier (W-SLMBA) is proposed, which uses a continuous Class-F-1 Control Amplifier (CA) to manipulate the impedance trajectory of the Balanced Amplifier (BA). It is demonstrated that the use of the continuous Class-F-1 CA can trigger a unique impedance load modulation mechanism by which the fundamental impedance of the BA is shaped by the varying second harmonic load reactance of the CA. Theoretical derivations reveal that this special load modulation yields extended design space for the SLMBA, wherein high efficiency can be achieved over a wide bandwidth and OPBO. Fourthly, the design methodology of a broadband RF-input SLMBA is introduced, with extended high efficiency design space, by introducing the second harmonic load manipulation over an enlarged range for the CA. The extension of CA load design space not only can provide the time-domain varying drain current waveform inside the entire design continuum, but also allows maintaining high efficiency OPBO over an extended operation bandwidth. Last but not least, the impact of input nonlinearity in SLMBA architecture is investigated. The Class-F-1 operation is selected as the solution for CA branch due to its advantage of high OPBO performance, efficiency flatness and immunity versus second harmonic source phase ¿G2S, which leads to the adoption of Class-B/J operation for BA. While Class-F-1 CA is immune to the second harmonic source variation, the safe design space for BA lands in the region where ¿G2S is over (-90¿, 90¿)
The effect of wording on message propagation: Topic-and author-controlled natural experiments on twitter.
No full textAbstract Consider a person trying to spread an important message on a social network. He/she can spend hours trying to craft the message. Does it actually matter? While there has been extensive prior work looking into predicting popularity of socialmedia content, the effect of wording per se has rarely been studied since it is often confounded with the popularity of the author and the topic. To control for these confounding factors, we take advantage of the surprising fact that there are many pairs of tweets containing the same url and written by the same user but employing different wording. Given such pairs, we ask: which version attracts more retweets? This turns out to be a more difficult task than predicting popular topics. Still, humans can answer this question better than chance (but far from perfectly), and the computational methods we develop can do better than both an average human and a strong competing method trained on noncontrolled data
The effect of wording on message propagation: Topic-and author-controlled natural experiments on twitter.
Get PDFAbstract Consider a person trying to spread an important message on a social network. He/she can spend hours trying to craft the message. Does it actually matter? While there has been extensive prior work looking into predicting popularity of socialmedia content, the effect of wording per se has rarely been studied since it is often confounded with the popularity of the author and the topic. To control for these confounding factors, we take advantage of the surprising fact that there are many pairs of tweets containing the same url and written by the same user but employing different wording. Given such pairs, we ask: which version attracts more retweets? This turns out to be a more difficult task than predicting popular topics. Still, humans can answer this question better than chance (but far from perfectly), and the computational methods we develop can do better than both an average human and a strong competing method trained on noncontrolled data
in soil and their fixation effect to reduce lead translocation in two rice cultivars
No full textThe fate of nanoparticles in the ecological chain of agriculture has been concerned as their potential pollution and biological effect to humans with rapid development and massive emission of nanomaterials. Here, we found that two rice cultivars (Oryza sativa L) have different heavy metal accumulation results in the roots and shoots after 15 days growth. Two rice cultivars (Oryza sativa L), grown in soil containing magnetite (Fe3O4@NH2) nanoparticles and heavy metal simultaneous, showed less Pb uptake in the roots and shoots, compared with that without Fe3O4@NH2 added. The shape and magnetic properties of Fe3O4@NH2 have no obvious change; however, the transmission electron microscope (TEM) results showed the shell of Fe3O4@NH2 could be broken in the process of interaction with soil. These results suggested that magnetite nanoparticles, such as Fe3O4@NH2, could potentially be used as the recyclable heavy metal fixation materials for alleviating heavy metal poisoning to plant
Dual Active Bridge Converter with PWM Control In Solid State Transformer Application
Get PDFabstract: For the solid-state transformer (SST) application, a three-stage configuration consisting of a PWM rectifier based AC/DC stage, a dual active bridge (DAB) converter based DC/DC stage and a PWM inverter based DC/AC stage offers several advantages. For single-phase SST, the instantaneous input and load power seen by the DC/DC stage varies from zero to twice the load average power at double the line frequency. Traditionally, with phase-shift control, large DAB DC link capacitors are used to handle the instantaneous power variation of the load, with the DAB converter processing only the load average power resulting in better soft-switching range and consequently high efficiency. However, the large electrolytic capacitors required adversely affect the power density and the reliability of SST. In this thesis, a PWM control is used for the DAB converter in SST, which extends the ZVS range of DAB and allows the DAB converter to handle the pulsating power while maintaining/improving efficiency. The impact of the output capacitance of switches with PWM control is discussed for practical implementation. A 40kHz, 500W DAB converter is designed and built, and the experimental results proves that the DAB converter with PWM control in SST can achieve comparable efficiency while the DC link capacitors of SST can be reduced to a value that electrolytic capacitors are not required.Dissertation/ThesisM.S. Electrical Engineering 201
The effect of wording on message propagation: Topic- and author-controlled natural experiments on Twitter
No full text
: Linearity Enhanced High Efficiency Power Amplifier
Get PDFThis paper presents a new class of power amplifier (PA) - Class-iF- 1 - resolving the highly nonlinear double inflection characteristics in the conventional Class-F- 1 PA. It is illustrated that, by properly terminating the second harmonic source impedance Z 2S from conventional short-circuit to open-circuit, the double inflection nonlinear gain profile can be mitigated in the proposed Class-iF- 1 PA, wherein the same saturation output power is achieved with less gain compression without drain efficiency trade-off. The idea was validated with source/load-pull and a broadband prototype operating from 2.0 to 2.6 GHz was designed using a commercial 10-W Gallium Nitride (GaN) transistor. Under continuous wave (CW) signal test, the proposed Class-iF- 1 PA can achieve 40.1-40.8-dBm output power, 71.2%-77.3% drain efficiency (DE) and 67.4%-74.1 % power added efficiency (PAE) at 3-dB gain compression level over 2.0-2.6 GHz.Science Foundation Irelan
28/38 GHz Dual-band Dual-polarized Highly Isolated Antenna for 5G Phased Array Applications
Get PDFIEEE IWS 2019: Sixth IEEE MTT-S International Wireless Symposium, Guangzhou, China, 19-22 May 2019This paper proposed a new dual-band dual-polarized array antenna operating at 28 GHz and 38 GHz for 5G communication applications. Three stacked patches are adopted to achieve the dual-band operation. The lower band from 27.48 to 28.50 GHz is achieved by using the lower large patch, which is couple-fed by the middle patch. While the upper band from 36.94 to 40.43 GHz is achieved by using the middle and upper patches. The two patches resonant at 38 and 40 GHz respectively and the two resonant modes coupled together, which greatly enhances the upper band. To increase the polarization isolation in the lower band, a shorting pin connecting the lower patch and ground is utilized. Taking advantages of the multi-layer technology, the position of the vertical feeding probe between the middle patch and lower patch is slightly shifted to ensure the good impedance matching in both lower band and upper band. For the antenna element, the simulated -12 dB bandwidths are 27.48-28.50 GHz and 36.94-40.43 GHz for the two bands, respectively. The in-band gains are over 6 dBi in the lower band, and over 4 dBi in the upper band. For the 2×2 antenna array, the isolations are better than 20 dB in both bands.Science Foundation IrelandGuangdong Innovative and Entrepreneurial Research Tea
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