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Search Results: 1 - 10 of 31118 matches for " Than Tun Thein;Choi Look Law;Kai Fu "
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250 MHz to 30 GHz, Unilateral Circuitmodel for Ingap/GaAs Hbt
Than Tun Thein;Choi Look Law;Kai Fu
PIER C , 2012, DOI: 10.2528/PIERC11101702
Abstract: A unilateral circuit model, which precisely predicts small signal response over a wide range of frequencies and bias points, is quantitatively analyzed and presented. The shortfall of current unilateral assumption and transformation technique is presented. A complete and explicit analysis is provided to develop a compact unilateral circuit model. The model is intended to predict input reflection, forward transmission and output reflection coefficients over wide range of frequencies. The technique is validated by transforming bilateral a small signal model of 3 x 3 μm x 40 μm, InGaP/GaAs HBT into its unilateral equivalent over the frequency range of 250 MHz to 30 GHz. The accuracy of the technique is corroborated at various bias conditions; collector current from 3 mA to 150 mA and collector-emitter voltage from 1 V to 5 V. Simulated results show very good agreement between small signal responses of transformed unilateral and bilateral circuit models.
Frequency Domain Dynamic Thermal Analysis in GaAs Hbt for Power Amplifier Applications
Than Tun Thein;Choi Look Law;Kai Fu
PIER , 2011, DOI: 10.2528/PIER11050301
Abstract: Dynamic temperature distributions in GaAs HBT are numerically analyzed in frequency domain as a function of power dissipation, frequency and space. Complete thermal characteristics, including frequency-dependent thermal impedance and phase lag behavior, are presented. The analysis is also extended for arbitrary periodic or aperiodic pulse heating operation to predict junction temperature of a Power Amplifier (PA) with non-constant envelope input signal. Dynamic junction temperatures of a single finger 2 μm x 20 μm GaAs HBT are predicted for square pulse envelope signal input with power levels varying with up to 10 dB above a nominal average level of 40 mW and with pulse widths ranging from 10 ns to 100 μs. With the input envelope signal amplitude of 10 dB above the average, the analytical results show that junction temperature rises from room temperature of 27C to 39C when heated by 10 ns pulse, increase to 36C by 100ns pulse, 105C by 1μs pulse and to 198C by 100 μs pulse. A novel setup is developed for nano-second pulsed measurements, and the analysis is validated through time domain on wafer pulsed measurements at three different power levels: 0 dB, 3 dB, and 6 dB above the average level. Results show that analytical results track well with measured junction temperature within the accuracy of ±5C over the entire measurement set.
5.8-GHz Suppressed UWB Bandpass Filter Employing Modified CRLH-Tl of Two and Three Unit Cells
Yizhu Shen;Choi Look Law
PIER Letters , 2012, DOI: 10.2528/PIERL11120206
Abstract: This paper presents a novel modified composite right/left-handed (CRLH) unit cell to achieve sharp rejection at 5.8 GHz. Design formulas are theoretically derived and numerically verified. Based on this unit cell, ultra-wideband (UWB) bandpass filters with two and three cells are designed, fabricated, and on-wafer measured. The measurement results show that the CRLH bandpass filter has a rejection of >60 dB at 5.8 GHz, a minimum insertion loss of 1.1 dB, and 3-dB bandwidths of 3.09-4.79 GHz and 3.22-4.61 GHz for the two and three unit cells, respectively.
A Two-Port Antenna for Wireless-Powered UWB-RFID Tags
Yizhu Shen;Choi Look Law
PIER C , 2012, DOI: 10.2528/PIERC12011004
Abstract: This paper presents a two-port antenna including a receiving port and a transmitting one in the same volume. These two antennas are physically integrated and electrically isolated. The receiving antenna is a linearly polarized narrowband slot for energy harvesting, whereas the transmitting one is a circularly-polarized ultrawideband (UWB) quasi-spiral for signal radiation. The measurement results show that, the slot resonates at 5.8 GHz, and the quasi-spiral has a 10-dB return loss bandwidth of 2.85-5.16 GHz and a 3-dB axial ratio bandwidth of 3.05-4.43 GHz. The electrical isolation between these two antennas is more than 20 dB covering 1-8 GHz. This two-port antenna is a good candidate for wireless-powered UWB-RFID tags.
Synthesis, Design and Implementation of Ultra-Wideband Impulse Radio Active Mmic Matched Filters
Jingjing Xia;Choi Look Law;Yuan Zhou
PIER C , 2012, DOI: 10.2528/PIERC11100101
Abstract: In this paper, we present a comprehensive framework from synthesis to implementation of active matched filters for UWB Impulse Radio. The method delays and sums UWB pulses coherently to strengthen the signal over white Gaussian noise. Theoretical analysis shows that the signal peak is maximized against noise, and an arbitrary transfer function could be realized by adjusting filter parameters. To verify the concept, a four-stage matched filter operating in 3-5 GHz with 360 degrees phase delay is demonstrated first. It is implemented in a commercial 2-μm GaAs HBT process and achieves a power gain of 13.8 dB with a 10 dB bandwidth of 1.3 GHz. Based on a similar architecture, another design is presented but with only half of the delay. It has a power gain of 15.9 dB at the center frequency of 4 GHz and a 10 dB bandwidth of 2.3 GHz. An advantage of the proposed method is a precise control of the impulse response that can be matched to either symmetrical or asymmetrical UWB pulses by taking a time domain design approach.
Engineering Adaptive Digital Investigations using Forensics Requirements
Liliana Pasquale. Yijun Yu,Luca Cavallaro,Mazeiar Salehie,Thein Than Tun,Bashar Nuseibeh
Computer Science , 2014,
Abstract: A digital forensic investigation aims to collect and analyse the evidence necessary to demonstrate a potential hypothesis of a digital crime. Despite the availability of several digital forensics tools, investigators still approach each crime case from scratch, postulating potential hypotheses and analysing large volumes of data. This paper proposes to explicitly model forensic requirements in order to engineer software systems that are forensic-ready and guide the activities of a digital investigation. Forensic requirements relate some speculative hypotheses of a crime to the evidence that should be collected and analysed in a crime scene. In contrast to existing approaches, we propose to perform proactive activities to preserve important - potentially ephemeral - evidence, depending on the risk of a crime to take place. Once an investigation starts, the evidence collected proactively is analysed to assess if some of the speculative hypotheses of a crime hold and what further evidence is necessary to support them. For each hypothesis that is satisfied, a structured argument is generated to demonstrate how the evidence collected supports that hypothesis. Our evaluation results suggest that the approach provides correct investigative findings and reduces significantly the amount of evidence to be collected and the hypotheses to be analysed.
Design and Analysis of High-Voltage High-Efficiency Ultra-Wideband Pulse Synthesizer
Chao Fang;Choi Look Law;James C. M. Hwang;Jingjing Xia
PIER C , 2011, DOI: 10.2528/PIERC11020509
Abstract: A novel ultra-wideband (UWB) pulse synthesizer is proposed, which uses a distributed amplifier to combine Gaussian pulses of different polarities, amplitudes and delays. The center frequency and bandwidth of the synthesized pulse can be adjusted by varying the number of the Gaussian pulses and the delays between them. Compared to other UWB pulse generators, the present synthesizer is capable of higher voltages and higher efficiencies. Using 0.25-μm pHEMTs, a prototype synthesizer has been designed and fabricated with a center frequency of 4.0 GHz and a bandwidth of 1.9 GHz. Under a Gaussian input pulse of 1.5 V and 100 ps, the synthesizer outputs into 50 Ω a pulse of 4.5 V and 1 ns. At a pulse-repetition frequency of 10 MHz, the synthesizer consumes 1 mA at 3 V with 17% efficiency. Approaches to maintain high efficiency by scaling the supply voltage for different input amplitudes and pulse-repetition frequencies have also been verified experimentally.
Melting and Solidification Heat Transfer Characteristics of a Phase-Change Material in a Latent Heat Storage Vessel: Effects of a Perforated Partition Plate and Metal Fiber  [PDF]
Than Tun Naing, Akihiko Horibe, Naoto Haruki, Yutaka Yamada
Journal of Power and Energy Engineering (JPEE) , 2017, DOI: 10.4236/jpee.2017.58002
Abstract: Today, latent heat storage technology has advanced to allow reuse of waste heat in the middle-temperature range. This paper describes an approach to develop a latent heat storage system using middle-temperature waste heat (~100oC - 200oC) from factories. Direct contact melting and solidification behavior between a heat-transfer fluid (oil) and a latent heat storage material mixture were observed. The mixture consisted of mannitol and erythritol (Cm = 70 mass %, Ce = 30 mass %) as a phase-change material (PCM). The weight of the PCM was 3.0 kg and the flow rate of the oil, foil, was 1.0, 1.5, or 2.0 kg/min. To decrease the solidified height of the PCM mixture during the solidification process, a perforated partition plate was installed in the PCM region in the heat storage vessel. PCM coated oil droplets were broken by the perforated partition plate, preventing the solidified height of the PCM from increasing. The solidification and melting processes were repeated using metal fiber. It was found that installing the metal fiber was more effective than installing the perforated partition plate to prevent the flow out problem of the PCM.
Utilities and Limitations of the World Health Organization 2009 Warning Signs for Adult Dengue Severity
Tun-Linn Thein equal contributor ,Victor C. Gan equal contributor,David C. Lye,Chee-Fu Yung,Yee-Sin Leo
PLOS Neglected Tropical Diseases , 2013, DOI: 10.1371/journal.pntd.0002023
Abstract: Background In 2009, the World Health Organization (WHO) proposed seven warning signs (WS) as criteria for hospitalization and predictors of severe dengue (SD). We assessed their performance for predicting dengue hemorrhagic fever (DHF) and SD in adult dengue. Method DHF, WS and SD were defined according to the WHO 1997 and 2009 dengue guidelines. We analyzed the prevalence, sensitivity (Sn), specificity (Sp), positive predictive value (PPV) and negative predictive value (NPV) of WS before DHF and SD onset. Results Of 1507 cases, median age was 35 years (5th–95th percentile, 17–60), illness duration on admission 4 days (5th–95th percentile, 2–6) and length of hospitalization 5 days (5th–95th percentile, 3–7). DHF occurred in 298 (19.5%) and SD in 248 (16.5%). Of these, WS occurred before DHF in 124 and SD in 65 at median of two days before DHF or SD. Three commonest warning signs were lethargy, abdominal pain/tenderness and mucosal bleeding. No single WS alone or combined had Sn >64% in predicting severe disease. Specificity was >90% for both DHF and SD with persistent vomiting, hepatomegaly, hematocrit rise and rapid platelet drop, clinical fluid accumulation, and any 3 or 4 WS. Any one of seven WS had 96% Sn but only 18% Sp for SD. Conclusions No WS was highly sensitive in predicting subsequent DHF or SD in our confirmed adult dengue cohort. Persistent vomiting, hepatomegaly, hematocrit rise and rapid platelet drop, and clinical fluid accumulation, as well as any 3 or 4 WS were highly specific for DHF or SD.
Prevention and Treatment of Venous Thromboembolism with New Oral Anticoagulants: A Practical Update for Clinicians
Nay Min Tun,Thein Hlaing Oo
Thrombosis , 2013, DOI: 10.1155/2013/183616
Abstract:
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