Search results for: Keiichi Yamaguchi

Items from 1 to 20 out of 20 results

article

Impact of moderate‐intensity aerobic exercise in combined hypoxic and hot conditions on endothelial function

Takuma Morishima, Keiichi Yamaguchi, Kazushige Goto

Clinical Physiology and Functional Imaging > 44 > 6 > 415 - 425

There is no study that has investigated the impact of exercise in a combined hypoxic and hot environment on endothelial function. Therefore, we tested whether aerobic exercise in a combined hypoxic and hot conditions induces further enhancement of endothelial function. Twelve healthy males cycled at a constant workload (50% of their maximal oxygen uptake under normoxic/thermoneutral conditions) for...

article

The residual structure of acid‐denatured β₂‐microglobulin is relevant to an ordered fibril morphology

Ryosuke Tomiyama, Masatomo So, Keiichi Yamaguchi, Yohei Miyanoiri, more

Protein Science > 32 > 1 > n/a - n/a

β₂‐Microglobulin (β2m) forms amyloid fibrils in vitro under acidic conditions. Under these conditions, the residual structure of acid‐denatured β2m is relevant to seeding and fibril extension processes. Disulfide (SS) bond‐oxidized β2m has been shown to form rigid, ordered fibrils, whereas SS bond‐reduced β2m forms curvy, less‐ordered fibrils. These findings suggest that the presence of an SS bond...

article

Polyphenol‐solubility alters amyloid fibril formation of α‐synuclein

Masatomo So, Yuto Kimura, Keiichi Yamaguchi, Toshihiko Sugiki, more

Protein Science > 30 > 8 > 1701 - 1713

Amyloid fibril formation is associated with various amyloidoses, including neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Amyloid fibrils form above the solubility of amyloidogenic proteins or peptides upon breaking supersaturation, followed by a nucleation and elongation mechanism, which is similar to the crystallization of solutes. Many additives, including salts, detergents,...

article

Daidzein reductase of Eggerthella sp. YY7918, its octameric subunit structure containing FMN/FAD/4Fe-4S, and its enantioselective production of R-dihydroisoflavones

Yuika Kawada, Tomoko Goshima, Rie Sawamura, Shin-ichiro Yokoyama, more

Journal of Bioscience and Bioengineering > 2018 > 126 > 3 > 301-309

S-Equol is a metabolite of daidzein, a type of soy isoflavone, and three reductases are involved in the conversion of daidzein by specific intestinal bacteria. S-Equol is thought to prevent hormone-dependent diseases. We previously identified the equol producing gene cluster (eqlABC) of Eggerthella sp. YY7918. Daidzein reductase (DZNR), encoded by eqlA, catalyzes the reduction of daidzein to dihydrodaidzein...

chapter

Output harmonic optimisation of dynamically load modulated power amplifiers

Konstantinos Mimis, Gavin T. Watkins, Atsushi Yamaoka, Keiichi Yamaguchi

2016 46th European Microwave Conference (EuMC) > 1071 - 1074

2016 46th European Microwave Conference (EuMC)

In this work, efficiency improvements of dynamically load modulated amplifiers through output harmonic manipulation are explored. A probability density function (PDF) conscious design approach is proposed, according to which the harmonic output terminations are optimised based on the PDF of the intended input signal. The approach is investigated through load-pull measurements of two GaN HEMT devices...

article

Logical design of anti-prion agents using NAGARA

Biao Ma, Keiichi Yamaguchi, Mayuko Fukuoka, Kazuo Kuwata

Biochemical and Biophysical Research Communications > 2016 > 469 > 4 > 930-935

To accelerate the logical drug design procedure, we created the program “NAGARA,” a plugin for PyMOL, and applied it to the discovery of small compounds called medical chaperones (MCs) that stabilize the cellular form of a prion protein (PrP^C). In NAGARA, we constructed a single platform to unify the docking simulation (DS), free energy calculation by molecular dynamics (MD) simulation, and interfragment...

article

Improved Reactance-Compensation Technique for the Design of Wideband Suboptimum Class-E Power Amplifiers

Jiafeng Zhou, Kevin A. Morris, Gavin T. Watkins, Keiichi Yamaguchi

IEEE Transactions on Microwave Theory and Techniques > 2015 > 63 > 9 > 2793 - 2801

A reactance-compensation technique has been introduced recently for the design of wideband class-E power amplifiers (PAs). With this technique, the load resistance can be transformed to an optimal complex drain impedance in a broad frequency band. One potential problem of this technique is that an additional network is often needed to transform 50 $\Omega$ to the optimum load resistance, which is typically...

article

Uncertainty of Out-of-Band Distortion Measurement With a Spectrum Analyzer

Makoto Tanahashi, Keiichi Yamaguchi

IEEE Transactions on Broadcasting > 2015 > 61 > 3 > 532 - 540

In broadcasting and wireless communications, modulated signals are deformed by nonlinear radio frequency components, of which power amplifiers are the most significant example. The resulting distortion can leak outside the main signal band, and this leak, called out-of-band (OOB) distortion, can be directly measured with a spectrum analyzer (SA). Little attention has been paid to this measurement...

chapter

A study on the frequency response compensation for Envelope Amplifiers in EER Power Amplifiers

Atsushi Yamaoka, Keiichi Yamaguchi

2014 Asia-Pacific Microwave Conference > 1092 - 1094

2014 Asia-Pacific Microwave Conference (APMC)

The Envelope Elimination and Restoration Power Amplifier (EER-PA) and the Envelope Tracking Power Amplifier (ET-PA) have attracted significant attention because of their capability of high efficiency under back-off operation. In EER-PAs or ET-PAs, the performance of Digital Pre-Distortion (DPD) is degraded due to their tendency towards high nonlinear behavior including frequency response of the envelope...

chapter

On the Detection Mode of Spectrum Analyzers in the Measurement of OFDM Out-of-Band Distortion

Makoto Tanahashi, Yoshimasa Egashira, Keiichi Yamaguchi, Yasuhiko Tanabe

2013 IEEE 78th Vehicular Technology Conference (VTC Fall) > 1 - 5

2013 IEEE 78th Vehicular Technology Conference (VTC Fall)

In wireless industry, the out-of-band (OOB) leakage power of transmit signals is widely used as a simple yet important metric to evaluate the interference to the signals communicated in adjacent frequency bands. A common way of measuring the OOB emission is via a spectrum analyzer (SA) that allows us to directly read the OOB level from the displayed trace of the signal spectra. Although this task,...

chapter

Wideband class-E power amplifier covering the whole UHF broadcast band

Jiafeng Zhou, Kevin Morris, Gavin Watkins, Keiichi Yamaguchi

2013 European Microwave Integrated Circuit Conference > 336 - 339

2013 European Microwave Integrated Circuit Conference (EuMIC)

Design and experimental results of a wideband and highly efficient class-E power amplifier are reported in this paper. The amplifier can cover the whole UHF broadcast band from 470MHz to 860MHz with an output power of 10W. The PA can achieve better than 70% power added efficiency (PAE) in a fractional bandwidth of 41% or better than 60% PAE in a bandwidth of 54% with 10W output power. To test the...

chapter

Wideband class-E power amplifier covering the whole UHF broadcast band

Jiafeng Zhou, Kevin Morris, Gavin Watkins, Keiichi Yamaguchi

2013 European Microwave Conference > 1307 - 1310

2013 European Microwave Conference (EuMC)

article

High‐efficiency wideband class‐E PA with reduced circuit elements

Jiafeng Zhou, Kevin Morris, Gavin Watkins, Keiichi Yamaguchi

Microwave and Optical Technology Letters > 55 > 2 > 323 - 325

This letter proposes a method to design wideband class‐E amplifiers.Traditionally, wideband class‐E operation can be achieved by cascading a wideband filter and a wideband matching network. In this letter, an output network is designed as both the filter and the matching network. The circuit is thus significantly simplified. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:323–325, 2012;...

chapter

Three-band high-efficiency modulator for envelope tracking power amplifier using class-B push-pull amplifiers

Jiafeng Zhou, Kevin Morris, Gavin Watkins, Keiichi Yamaguchi

2012 42nd European Microwave Conference > 124 - 127

2012 European Microwave Conference (EuMC)

Envelope modulators for wideband and high- power envelope tracking or envelope elimination and restoration amplifiers are usually realized by combing a switching stage and a linear stage. The efficiency and bandwidth of the modulator is mainly limited by the linear stage. This paper proposes a method to improve the performance of the linear stage by adding another stage. The third stage is a push-pull...

chapter

Simplified Temperature Compensation Technique for Digital Predistorter Using Fixed Coefficients

Toshihiro Tango, Atsushi Yamaoka, Keiichi Yamaguchi, Yasuhiko Tanabe

2010 IEEE 72nd Vehicular Technology Conference - Fall > 1 - 5

2010 IEEE 72nd Vehicular Technology Conference Fall

An adaptive digital predistorter (ADPD) promises accurate nonlinear compensation and can automatically follow the change of output power of PA, a gain of transmitter consisting of DAC, mixer, PA, etc., and nonlinearity of PA by temperature fluctuation. However, an ADPD needs costly, large-power-consuming, and bulky equipment for calibration-loop. To overcome these drawbacks, we propose a simplified...

chapter

Experimental performance evaluation of IQ imbalance and DC offset estimation and compensation technique for 3GPP LTE base station

Atsushi Yamaoka, Keiichi Yamaguchi, Takayuki Kato, Yasuhiko Tanabe

2010 IEEE MTT-S International Microwave Symposium > 1

2010 IEEE/MTT-S International Microwave Symposium - MTT 2010

In the case of recent wireless communication systems, the need to achieve high performance means that impairments in analog circuits cannot be disregarded. In view of the need for highly accurate compensation, many error compensation techniques using digital signal processing have been studied recently. Digital predistorter (DPD), which can eliminate odd-order distortion caused by PA nonlinearity,...

chapter

Experimental performance evaluation of IQ imbalance and DC offset estimation and compensation technique for 3GPP LTE base station

Atsushi Yamaoka, Keiichi Yamaguchi, Takayuki Kato, Yasuhiko Tanabe

2010 IEEE MTT-S International Microwave Symposium > 268 - 271

2010 IEEE/MTT-S International Microwave Symposium - MTT 2010

chapter

A Novel Error Separation Technique for Quadrature Modulators and Demodulators

Atsushi Yamaoka, Keiichi Yamaguchi

2007 IEEE Radio and Wireless Symposium > 563 - 566

2007 IEEE Radio and Wireless Symposium

In recent mobile communication systems, impairments in analog circuits cannot be disregarded due to achieving high performance. Errors in analog circuits consist of a distortion of a power amplifier(PA), gain and phase imbalance in a quadrature modulator (QMOD) and a quadrature demodulator (QDEMOD), dc offset, frequency offset, and so on. Because of high accuracy of compensation, many techniques of...

article

Direct Observation of Amyloid Fibril Growth, Propagation, and Adaptation

Tadato Ban, Keiichi Yamaguchi, Yuji Goto

Accounts of Chemical Research > 2006 > 39 > 9 > 663 - 670

article

Association of thin filaments into thick filaments revealing the structural hierarchy of amyloid fibrils

Takashi Kanno, Keiichi Yamaguchi, Hironobu Naiki, Yuji Goto, more

Journal of Structural Biology > 2005 > 149 > 2 > 213-218

β ₂ -Microglobulin (β2-m) is a major structural component of dialysis-related amyloid fibrils. Kozhukh et al. [J. Biol. Chem. 277 (2002) 1310] prepared a series of peptide fragments of β2-m by the protease digestion and examined their ability to form amyloid fibrils in citrate buffer at pH 2.5. Among various peptides, a 22-residue K3 peptide corresponding to Ser20-Lys41 spontaneously formed...

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POWER AMPLIFIER (5)
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