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Search Results: 1 - 10 of 3168 matches for " Kodai Yamamoto "
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Simplified Bernoulli Formula to Diagnose Ischemia-Causing Stenosis at Coronary CT Angiography: Comparison with SPECT  [PDF]
Nobuo Tomizawa, Hiroaki Arakawa, Kodai Yamamoto, Shinichi Inoh, Takeshi Nojo, Sunao Nakamura
Advances in Computed Tomography (ACT) , 2019, DOI: 10.4236/act.2019.82002
Abstract: Purpose: To compare the diagnostic performance of estimated energy loss (EEL) calculated using a simplified Bernoulli formula at coronary computed tomography (CT) and single photon emission computed tomography (SPECT) to diagnose ischemia-causing stenosis by invasive fractional flow reserve (FFR). Methods: We retrospectively included 43 patients who underwent coronary CT, SPECT, and FFR measurement by catheter within 3 months. When an intermediate stenosis (40% - 70%) was present at CT, EEL was calculated using the following parameters: lesion length, diameter stenosis, minimal lumen area, and the myocardial volume. An EEL > 1.17 or diameter stenosis > 70% was determined ischemic. Stress-induced ischemia by SPECT was determined when a perfusion defect at stress was accompanied with a fill-in at rest. An FFR ≤ 0.80 or diameter stenosis >70 % was determined as ischemic by catheter. Results: A total of 26 vessels were determined as ischemic by catheter exam. The per-vessel sensitivity and specificity of EEL and SPECT were 81% vs 42% and 92% vs 91%, respectively. The accuracy of EEL to diagnose stenosis causing ischemia was significantly higher than SPECT (90% vs 81%, p = 0.04). The area under the curve of the receiver operating characteristics curve was also significantly higher for EEL than SPECT (0.86 vs 0.67, p < 0.005). Conclusions: EEL showed higher accuracy than SPECT to diagnose ischemia-causing stenosis by improving the sensitivity.
Study of infrared excess from circumstellar disks in binaries with Spitzer/IRAC
Yusuke Itoh,Misato Fukagawa,Hiroshi Shibai,Takahiro Sumi,Kodai Yamamoto
Physics , 2015, DOI: 10.1093/pasj/psv071
Abstract: The presence of excess emission at 3.6--8.0 $\mu$m was investigated in a sample of 27 binary systems located in two nearby star-forming regions, Taurus and Ophiuchus, by using Spitzer/Infrared Array Camera (IRAC) archival data. Angular (Projected) separations for the binaries are greater than 2"($\sim$280 AU), which allowed us to perform spatially resolved photometry of individual primary and secondary sources. The measured occurrence of infrared excess suggests that binarity plays a role in the evolution of circumstellar disks, even at such wide binary separations. Most of the binaries have excess emission from both the circumprimary and circumsecondary disks, or show photospheric levels for both components at all four wavelengths of IRAC. On the other hand, four systems ($17^{+11}_{-8}$%, designated by "mixed" systems) exhibit excess emission from a single binary component. This ratio is significantly smaller than that predicted by the random pairing of single stars, suggesting that circumprimary and circumsecondary disks are synchronously dispersed. In addition, the excess frequencies (EFs) of primary and secondary sources with a projected distance of $a_{\rm p}$$\simeq$280--450 AU are $100^{+0}_{-17}$% and $91^{+8}_{-18}$%, respectively, and significantly higher than that of single stars ($70 \pm 5$%). We made a simple model describing the EF distribution as a function of the disk outer radius, $R_{\rm out}$. Comparisons with observations using the Kolmogorov-Smirnov test show that the observational data are consistent with the model when the $\rm{EF} \simeq 1$ region is found at $R_{\rm out}$$\sim$30--100 AU. This disk radius is smaller than that typically estimated for single stars. The high EF of circumstellar disks with these radii may indicate a prolonged lifetime of dust in binary systems possibly because smaller disks counteract mass loss by photoevaporation.
Robust photonic entanglement distribution via state-independent encoding onto decoherence-free subspace
Takashi Yamamoto,Kodai Hayashi,Sahin Kaya Ozdemir,Masato Koashi,Nobuyuki Imoto
Physics , 2008, DOI: 10.1038/nphoton.2008.130
Abstract: Efficient and faithful implementation of quantum information tasks, e.g., quantum computing, quantum communication and quantum metrology, requires robust and state-independent decoherence-suppressing measures to protect quantum information carriers. Here we present an experimental demonstration of a robust distribution scheme in which one photon of an entangled photon pair is successfully encoded into and decoded from a decoherence-free subspace (DFS) by a state-independent scheme. We achieved a high-fidelity distribution of the entangled state over fibre communication channel, and also demonstrated that the scheme is robust against fragility of the reference frame. The scheme, thanks to its state-independence, is also applicable to multipartite case where the photon to be distributed is entangled with many other photons. Such a universal scheme opens the possibility of robust distribution of quantum information among quantum communication and computing networks.
Milnor invariants and edge-homotopy classification of clover links
Kodai Wada
Mathematics , 2015,
Abstract: Given a clover link, we construct a bottom tangle by using a disk/band surface of the clover link. Since the Milnor number is already defined for a bottom tangle, we define the Milnor number for the clover link to be the Milnor number for the bottom tangle and show that for a clover link, if Milnor numbers of length k or less vanish, then Milnor numbers of length 2k+1 or less are well-defined. Moreover we prove that two clover links whose Milnor numbers of length k or less vanish are equivalent up to edge-homotopy and $C_{2k+1}$-equivalence if and only if those Milnor numbers of length 2k+1 or less are equal. In particular, we give an edge-homotopy classification of 3-clover links by their Milnor numbers of length 3 or less.
Two Types of Well Followed Users in the Followership Networks of Twitter
Kodai Saito, Naoki Masuda
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0084265
Abstract: In the Twitter blogosphere, the number of followers is probably the most basic and succinct quantity for measuring popularity of users. However, the number of followers can be manipulated in various ways; we can even buy follows. Therefore, alternative popularity measures for Twitter users on the basis of, for example, users' tweets and retweets, have been developed. In the present work, we take a purely network approach to this fundamental question. First, we find that two relatively distinct types of users possessing a large number of followers exist, in particular for Japanese, Russian, and Korean users among the seven language groups that we examined. A first type of user follows a small number of other users. A second type of user follows approximately the same number of other users as the number of follows that the user receives. Then, we compare local (i.e., egocentric) followership networks around the two types of users with many followers. We show that the second type, which is presumably uninfluential users despite its large number of followers, is characterized by high link reciprocity, a large number of friends (i.e., those whom a user follows) for the followers, followers' high link reciprocity, large clustering coefficient, large fraction of the second type of users among the followers, and a small PageRank. Our network-based results support that the number of followers used alone is a misleading measure of user's popularity. We propose that the number of friends, which is simple to measure, also helps us to assess the popularity of Twitter users.
The Milnor invariants of clover links
Kodai Wada,Akira Yasuhara
Mathematics , 2015,
Abstract: J.P. Levine introduced a clover link to investigate the indeterminacy of the Milnor invariants of a link. It is shown that for a clover link, the Milnor numbers of length at most $2k+1$ are well-defined if those of length at most $k$ vanish, and that the Milnor numbers of length at least $2k+2$ are not well-defined if those of length $k+1$ survive. For a clover link $c$ with the Milnor numbers of length at most $k$ vanishing, we show that the Milnor number $\mu_c(I)$ for a sequence $I$ is well-defined up to the greatest common devisor of $\mu_{c}(J)'s$, where $J$ is a subsequence of $I$ obtained by removing at least $k+1$ indices. Moreover, if $I$ is a non-repeated sequence with length $2k+2$, the possible range of $\mu_c(I)$ is given explicitly. As an application, we give an edge-homotopy classification of $4$-clover links.
Refinement Type Inference via Horn Constraint Optimization
Kodai Hashimoto,Hiroshi Unno
Computer Science , 2015,
Abstract: We propose a novel method for inferring refinement types of higher-order functional programs. The main advantage of the proposed method is that it can infer maximally preferred (i.e., Pareto optimal) refinement types with respect to a user-specified preference order. The flexible optimization of refinement types enabled by the proposed method paves the way for interesting applications, such as inferring most-general characterization of inputs for which a given program satisfies (or violates) a given safety (or termination) property. Our method reduces such a type optimization problem to a Horn constraint optimization problem by using a new refinement type system that can flexibly reason about non-determinism in programs. Our method then solves the constraint optimization problem by repeatedly improving a current solution until convergence via template-based invariant generation. We have implemented a prototype inference system based on our method, and obtained promising results in preliminary experiments.
FPGA Implementation of a Scalable and Highly Parallel Architecture for Restricted Boltzmann Machines  [PDF]
Kodai Ueyoshi, Takao Marukame, Tetsuya Asai, Masato Motomura, Alexandre Schmid
Circuits and Systems (CS) , 2016, DOI: 10.4236/cs.2016.79185
Abstract: Restricted Boltzmann Machines (RBMs) are an effective model for machine learning; however, they require a significant amount of processing time. In this study, we propose a highly parallel, highly flexible architecture that combines small and completely parallel RBMs. This proposal addresses problems associated with calculation speed and exponential increases in circuit scale. We show that this architecture can optionally respond to the trade-offs between these two problems. Furthermore, our FPGA implementation performs at a 134 times processing speed up factor with respect to a conventional CPU.
Dilemmas Faced by Nurses Regarding the Physical Restraint of Elderly Patients with Dementia in Japan  [PDF]
Miwa Yamamoto
International Journal of Clinical Medicine (IJCM) , 2011, DOI: 10.4236/ijcm.2011.25099
Abstract: This study aimed to clarify the dilemma of nurses working in general wards who face the ethical dilemma of restraining older people with dementia in Midwestern Japan. The study used the questionnaire method with an independently prepared questionnaire. The questionnaire was designed to ensure privacy and anonymity. The privacy and anonymity of study participants was assured. Of the 340 survey questionnaires distributed, 291 (85.6%) completed surveys were eligible number (12 additional surveys were returned without answers). An explanatory factor analysis revealed four dilemma factors among 15 items investigated (KMO value 0.84). These were: factor 1: “Execution of treatment and security,” α = 0.91; factor 2: “approach in the nursing of older people with dementia,” α = 0.93; factor 3: “A cooperative relationship in nursing of older people with dementia,” α = 0.87; and factor 4: “Priorities in nursing,” α = 0.81. The cumulative contribution ratio was 79.1%. We suggest that the program would enable nurses to cope with these dilemmas.
The effects of ethical dilemmas regarding the use of physical restraints in eldercare on female nurses who care for their relatives in Japan  [PDF]
Miwa Yamamoto
Open Journal of Nursing (OJN) , 2012, DOI: 10.4236/ojn.2012.22006
Abstract: Purpose: This study sought to clarify the relationship between a nurse’s exposure to elderly relatives and their perspective in using restraints on the elderly in health care situations. Methods: We approached nursing staff supervisors at 17 general hospital wards and explained the objectives of the study. Supervisors at 14 hospitals agreed to participate, giving us a sampling pool of 1929 nurses. We used a chi square test to compare nurses who had spent time with elderly relatives and those who had not on several variables related to using restraints on elderly patients. Results and Conclusion: This study found that nurses who live with elderly family members were significantly more likely to believe that restraints cause diseases (including chronic diseases) based on a chi square test (p < 0.05). Therefore it would be important that essential was the experiences of individuals with elderly family members when making programs of decreasing nurse’s dilemma to restraining the elderly.
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