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Search Results: 1 - 10 of 1127 matches for " Masato Ohmi "
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Dynamic imaging of a small artery underneath skin surface of a human finger by optical coherence tomography  [PDF]
Masato Ohmi, Mitsuo Kuwabara, Masamitsu Haruna
Journal of Biomedical Science and Engineering (JBiSE) , 2013, DOI: 10.4236/jbise.2013.63030

OCT is a powerful tool for detection of physiological functions of micro organs underneath the human skin surface, besides the clinical application to ophthalmology, as recently demonstrated by the authors’ group. In particular, dynamics of peripheral vessels can be observed clearly in the time-sequential OCT images. Among the vascular system, only the small artery has two physiological functions both for the elastic artery and for muscle-controlled one. It, therefore, is important for dynamic analysis of blood flow and circulation. In the time-sequential OCT images obtained with 25 frames/sec, it is found that the small artery makes a sharp response to sound stress for contraction and expansion while it continues pulsation in synchronization with the heartbeats. This result indicates that the small artery exhibits clearly the two physiological functions for blood flow and circulation. In response to sound stress, blood flow is controlled effectively by thickness change of the tunica media which consists of five to six layers of smooth muscles. It is thus found that the thickness of the tunica media changes remarkably in response to external stress, which shows the activity of the sympathetic nerve. The dynamic analysis of the small artery presented here will allow us not only to understand the mechanism of blood flow control and also to detect abnormal physiological functions in the whole vascular system.

Dynamic Analysis of Mental Sweating by the Time-Sequential Piled-Up En-Face OCT Images  [PDF]
Masato Ohmi, Yuki Wada, Motomu Tanigawa
Optics and Photonics Journal (OPJ) , 2013, DOI: 10.4236/opj.2013.37A004

In this paper, the dynamic analysis of mental sweating for sound stimulus of a few tens of eccrine sweat glands is performed by the time-sequential piled-up en-face optical coherence tomography (OCT) images with the frame spacing of 3.3 sec. In the experiment, the amount of excess sweat can be evaluated simultaneously for a few tens of sweat glands by piling up of all the en-face OCT images. Strong non-uniformity is observed in mental sweating where the amount of sweat in response to sound stimulus is different for each sweat gland. Furthermore, the amount of sweat is significantly increased in proportion to the strength of the stimulus.

Development of Optical Coherence Tomography Using KTN Optical Probe  [PDF]
Eunjoo Choi, Masato Ohmi, Takayuki Komatsu, Shogo Yagi, Kazuo Fujiura
Optics and Photonics Journal (OPJ) , 2017, DOI: 10.4236/opj.2017.75008
Abstract: We have developed optical coherence tomography system with KTN optical probe for a diagnosis in the orthopedic surgery fields. The present system demonstrates that biological image was measured by using KTN optical scanner for having degree of freedom in sample arm as optical coherence tomography. In addition, the developed optical coherence tomography (OCT) system has shown feasibility for imaging biological tissue in orthopedics. The system was shown to have a resolution 14.2 μm for biological tissue in few mm depths. The sensitivity to be measured is 92.3 dB.
High-Speed Time-Domain En Face Optical Coherence Tomography System Using KTN Optical Beam Deflector  [PDF]
Masato Ohmi, Yusuke Shinya, Jun Miyazu, Seiji Toyoda, Tadashi Sakamoto
Optics and Photonics Journal (OPJ) , 2019, DOI: 10.4236/opj.2019.95006
Abstract: We developed high-speed time-domain (TD) en face optical coherence tomography (OCT) system using KTN optical beam deflector. The KTN optical beam deflector operates at a high repetition rate of 200 kHz with a fairly large beam deflection angle. We proposed a high-speed en face OCT system that used a KTN optical deflector as the sample beam scanning. In the experiment, we obtained en face OCT images of human fingerprint with a frame rate of 800 fps, which is the fastest speed obtained by a TD-OCT imaging. Furthermore, a 3D-OCT image was also obtained at 0.2 s (=5 volumes/s) by our imaging system.
High-Speed Optical Coherence Tomography System Using a 200-kHz Swept Light Source with a KTN Deflector  [PDF]
Yuichi Okabe, Yuzo Sasaki, Masahiro Ueno, Takashi Sakamoto, Seiji Toyoda, Junya Kobayashi, Masato Ohmi
Optics and Photonics Journal (OPJ) , 2013, DOI: 10.4236/opj.2013.32031

We demonstrate a high-speed swept-source optical coherence tomography (SS-OCT) system, which is based on a high-speed swept light source and a Mach-Zehnder interferometer with a high-speed photodetector. The light source is an external-cavity laser tuned by a KTN electro-optic deflector, which exhibits a very fast response and large deflection. The scanning wavelength range is almost 80 nm up to 200 kHz with a ±400-V deflector driving voltage. The system acquires 1 mm × 1 mm images consisting of 200 × 200 pixels within few milliseconds. We present preliminary SS-OCT images of an in-vitro human nail and an in-vivo finger pad.

Electron cloud effects: codes and simulations at KEK
K. Ohmi
Physics , 2013, DOI: 10.5170/CERN-2013-002.219
Abstract: Electron cloud effects had been studied at KEK-Photon Factory since 1995. e-p instability had been studied in proton rings since 1965 in BINP, ISR and PSR. Study of electron cloud effects with the present style, which was based on numerical simulations, started at 1995 in positron storage rings. The instability observed in KEKPF gave a strong impact to B factories, KEKB and PEPII, which were final stage of their design in those days. History of cure for electron cloud instability overlapped the progress of luminosity performance in KEKB. The studies on electron cloud codes and simulations in KEK are presented.
Beam-beam effects under the influence of external noise
K. Ohmi
Physics , 2014, DOI: 10.5170/CERN-2014-004.69
Abstract: Fast external noise, which gives fluctuation into the beam orbit, is discussed in connection with beam-beam effects. Phase noise from crab cavities and detection devices (position monitor) and kicker noise from the bunch by bunch feedback system are the sources. Beam-beam collisions with fast orbit fluctuations with turn by turn or multi-turn correlations, cause emittance growth and luminosity degradation. We discuss the tolerance of the noise amplitude for LHC and HL-LHC.
The Effect of the Pressure for the Formation of YBa2Cu3O7–d Bulk Ceramics with Domestic Microwave Oven  [PDF]
Masato Ohmukai
Engineering (ENG) , 2011, DOI: 10.4236/eng.2011.311136
Abstract: We fabricated YBa2Cu3O7–d bulk ceramics with a domestic microwave oven and investigated the effect of pressure at the press procedure. If the pressure was not high enough, the ratio of BaCuO2 phase became large, estimated from x-ray diffraction (XRD) measurements. We found that the pressure should be 700 kgf/cm2 at least in order to suppress the BaCuO2 phase.
Topological Quantum Computing with p-Wave Superfluid Vortices
Tetsuo Ohmi,Mikio Nakahara
Physics , 2009, DOI: 10.1143/JPSJ.79.104602
Abstract: It is shown that Majorana fermions trapped in three vortices in a p-wave superfluid form a qubit in a topological quantum computing (TQC). Several similar ideas have already been proposed: Ivanov [Phys. Rev. Lett. {\bf 86}, 268 (2001)] and Zhang {\it et al.} [Phys. Rev. Lett. {\bf 99}, 220502 (2007)] have proposed schemes in which a qubit is implemented with two and four Majorana fermions, respectively, where a qubit operation is performed by exchanging the positions of Majorana fermions. The set of gates thus obtained is a discrete subset of the relevant unitary group. We propose, in this paper, a new scheme, where three Majorana fermions form a qubit. We show that continuous 1-qubit gate operations are possible by exchanging the positions of Majorana fermions complemented with dynamical phase change. 2-qubit gates are realized through the use of the coupling between Majorana fermions of different qubits.
Stability of Magnetically Trapped Bose-Einstein Condensates
Yuki Kawaguchi,Tetsuo Ohmi
Physics , 2002, DOI: 10.1143/JPSJ.72.1118
Abstract: According to the adiabatic approximation atoms moving in a magnetic trap keep their magnetic states. We investigate the validity of this approximation for quantum condensates, where a change of field's direction generates effective interactions between hyperfine angular momentum states. Condensates in general traps are found to be stable because they are confined in the vicinity of the trap center. A decay of a condensate is observable in a trap with extremely large field gradient.
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