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Search Results: 1 - 10 of 4312 matches for " Yoshiyuki Takahashi "
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The Effects of Trajectory and Endpoint Errors in a Reaching Movement on the Sense of Agency  [PDF]
Takuro Zama, Yoshiyuki Takahashi, Sotaro Shimada
Psychology (PSYCH) , 2017, DOI: 10.4236/psych.2017.814146
Abstract: The sense of agency (SoA) refers to the subjective feeling that an individual can control their own action with their own will. However, it is still unclear which aspects of the motor control process precisely affect the sense of agency. In this study, we investigated how the SoA is modulated by the online motor performance (trajectory error) and the outcome of the reaching movement (endpoint error). The results showed that the invalid priming and the visual feedback delay significantly increased both the trajectory and endpoint errors and that these errors significantly attenuated the SoA. The further correlation analyses showed that the decrease in SoA was significantly correlated with the trajectory error, but not with the endpoint error, when the error was explicitly noticed. We suggest that the deterioration in online motor performance, at least in a reaching movement, is the main cause of the attenuation in the SoA.
First eigenvalue/eigenvector in sparse random symmetric matrices: influences of degree fluctuation
Yoshiyuki Kabashima,Hisanao Takahashi
Physics , 2012, DOI: 10.1088/1751-8113/45/32/325001
Abstract: The properties of the first (largest) eigenvalue and its eigenvector (first eigenvector) are investigated for large sparse random symmetric matrices that are characterized by bimodal degree distributions. In principle, one should be able to accurately calculate them by solving a functional equation concerning auxiliary fields which come out in an analysis based on replica/cavity methods. However, the difficulty in analytically solving this equation makes an accurate calculation infeasible in practice. To overcome this problem, we develop approximation schemes on the basis of two exceptionally solvable examples. The schemes are reasonably consistent with numerical experiments when the statistical bias of positive matrix entries is sufficiently large, and they qualitatively explain why considerably large finite size effects of the first eigenvalue can be observed when the bias is relatively small.
The Jem-Euso Mission
Yoshiyuki Takahashi,the JEM-EUSO Collaboration
Physics , 2009, DOI: 10.1088/1367-2630/11/6/065009
Abstract: JEM-EUSO is a space science mission to explore extreme energies and physics of the Universe. Its instrument will watch the dark-side of the earth and will detect UV photons emitted from the extensive air shower caused by an Ultra-High Energy Cosmic Rays (UHECRs above 10^18 eV), or Extremely High Energy Cosmic Ray (EHECR) particle (e.g., above about 10^20 eV). Such a high-rigidity particles as the latter arrives almost in a straight-line from its origin through the magnetic fields of our Milky Way Galaxy and is expected to allow us to trace the source location by its arrival direction. This nature can open the door to the new astronomy with charged particles. In its five years operation including the tilted mode, JEM-EUSO will detect at least 1,000 events with E>7x10^19 eV with the GZK cutoff spectrum. It can determine the energy spectrum and source locations of GZK to super-GZK regions with a statistical accuracy of several percent. JEM-EUSO is planned to be deployed by H2 Transfer Vehicle (HTV) and will be attached to the Japanese Experiment Module/ Exposure Facility (JEM/EF) of International Space Station. JAXA has selected JEM-EUSO as one of the mission candidates of the second phase utilization of JEM/EF for the launch in early-to-mid 2010s.
Plasma Wakefield Acceleration for Ultrahigh Energy Cosmic Rays
Pisin Chen,Toshiki Tajima,Yoshiyuki Takahashi
Physics , 2002, DOI: 10.1103/PhysRevLett.89.161101
Abstract: A cosmic acceleration mechanism is introduced which is based on the wakefields excited by the Alfven shocks in a relativistically flowing plasma, where the energy gain per distance of a test particle is Lorentz invariant. We show that there exists a threshold condition for transparency below which the accelerating particle is collision-free and suffers little energy loss in the plasma medium. The stochastic encounters of the random accelerating-decelerating phases results in a power-law energy spectrum: f(e) 1/e^2. The environment suitable for such plasma wakefield acceleration can be cosmically abundant. As an example, we discuss the possible production of super-GZK ultra high energy cosmic rays (UHECR) through this mechanism in the atmosphere of gamma ray bursts. We show that the acceleration gradient can be as high as G ~ 10^16 eV/cm. The estimated event rate in our model agrees with that from UHECR observations.
Cavity approach to the first eigenvalue problem in a family of symmetric random sparse matrices
Yoshiyuki Kabashima,Hisanao Takahashi,Osamu Watanabe
Mathematics , 2010, DOI: 10.1088/1742-6596/233/1/012001
Abstract: A methodology to analyze the properties of the first (largest) eigenvalue and its eigenvector is developed for large symmetric random sparse matrices utilizing the cavity method of statistical mechanics. Under a tree approximation, which is plausible for infinitely large systems, in conjunction with the introduction of a Lagrange multiplier for constraining the length of the eigenvector, the eigenvalue problem is reduced to a bunch of optimization problems of a quadratic function of a single variable, and the coefficients of the first and the second order terms of the functions act as cavity fields that are handled in cavity analysis. We show that the first eigenvalue is determined in such a way that the distribution of the cavity fields has a finite value for the second order moment with respect to the cavity fields of the first order coefficient. The validity and utility of the developed methodology are examined by applying it to two analytically solvable and one simple but non-trivial examples in conjunction with numerical justification.
Phylogenetic Relationships and Evolutionary Patterns of the Order Collodaria (Radiolaria)
Yoshiyuki Ishitani, Yurika Ujiié, Colomban de Vargas, Fabrice Not, Kozo Takahashi
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0035775
Abstract: Collodaria are the only group of Radiolaria that has a colonial lifestyle. This group is potentially the most important plankton in the oligotrophic ocean because of its large biomass and the high primary productivity associated with the numerous symbionts inside a cell or colony. The evolution of Collodaria could thus be related to the changes in paleo-productivity that have affected organic carbon fixation in the oligotrophic ocean. However, the fossil record of Collodaria is insufficient to trace their abundance through geological time, because most collodarians do not have silicified shells. Recently, molecular phylogeny based on nuclear small sub-unit ribosomal DNA (SSU rDNA) confirmed Collodaria to be one of five orders of Radiolaria, though the relationship among collodarians is still unresolved because of inadequate taxonomic sampling. Our phylogenetic analysis has revealed four novel collodarian sequences, on the basis of which collodarians can be divided into four clades that correspond to taxonomic grouping at the family level: Thalassicollidae, Collozoidae, Collosphaeridae, and Collophidae. Comparison of the results of our phylogenetic analyses with the morphological characteristics of each collodarian family suggests that the first ancestral collodarians had a solitary lifestyle and left no silica deposits. The timing of events estimated from molecular divergence calculations indicates that naked collodarian lineages first appeared around 45.6 million years (Ma) ago, coincident with the diversification of diatoms in the pelagic oceans. Colonial collodarians appeared after the formation of the present ocean circulation system and the development of oligotrophic conditions in the equatorial Pacific (ca. 33.4 Ma ago). The divergence of colonial collodarians probably caused a shift in the efficiency of primary production during this period.
Finite size scaling of the de Almeida-Thouless instability in random sparse networks
Hisanao Takahashi,Federico Ricci-Tersenghi,Yoshiyuki Kabashima
Physics , 2010, DOI: 10.1103/PhysRevB.81.174407
Abstract: We study, in random sparse networks, finite size scaling of the spin glass susceptibility $\chi_{\rm SG}$, which is a proper measure of the de Almeida-Thouless (AT) instability of spin glass systems. Using a phenomenological argument regarding the band edge behavior of the Hessian eigenvalue distribution, we discuss how $\chi_{\rm SG}$ is evaluated in infinitely large random sparse networks, which are usually identified with Bethe trees, and how it should be corrected in finite systems. In the high temperature region, data of extensive numerical experiments are generally in good agreement with the theoretical values of $\chi_{\rm SG}$ determined from the Bethe tree. In the absence of external fields, the data also show a scaling relation $\chi_{\rm SG}=N^{1/3}F(N^{1/3}|T-T_c|/T_c)$, which has been conjectured in the literature, where $T_c$ is the critical temperature. In the presence of external fields, on the other hand, the numerical data are not consistent with this scaling relation. A numerical analysis of Hessian eigenvalues implies that strong finite size corrections of the lower band edge of the eigenvalue distribution, which seem relevant only in the presence of the fields, are a major source of inconsistency. This may be related to the known difficulty in using only numerical methods to detect the AT instability.
Gamma-Ray Bursts are precise distance indicators similar to Type Ia Supernovae?
Ryo Tsutsui,Takashi Nakamura,Daisuke Yonetoku,Keitaro Takahashi,Yoshiyuki Morihara
Physics , 2012,
Abstract: We estimate the distance modulus to long gamma-ray bursts (LGRBs) using the Type I Fundamental Plane, a correlation between the spectral peak energy $E_{\rm p}$, the peak luminosity $L_{\rm p}$, and the luminosity time $T_{\rm L}$ ($\equiv E_{\rm iso}/L_{\rm p}$ where $E_{\rm iso}$ is isotropic energy) for small Absolute Deviation from Constant Luminosity(ADCL). The Type I Fundamental Plane of LGRBs is calibrated using 8 LGRBs with redshift $z<1.4$. To avoid any assumption on the cosmological model, we use the distance modulus of 557 Type Ia supernovae (SNeIa) from the Union 2 sample. This calibrated Type I Fundamental Plane is used to measure the distance moduli to 9 high-redshift LGRBs with the mean error $\bar \sigma_{\mu}=0.31$, which is comparable with that of SNe Ia $\bar \sigma_{\mu}=0.26$ where $\mu$ stands for the distance modulus. The Type I Fundamental Plane is so tight that our distance moduli have very small uncertainties. From those distance moduli, we obtained the constraint $\Omega_{\rm M}=0.22\pm0.04$ for flat $\Lambda$CDM universe. Adding 9 LGRBs distance moduli ($z>1.4$) to 557 SNeIa distance moduli ($z<1.4$) significantly improves the constraint for non-flat $\Lambda$CDM universe from ($\Omega_{\rm M}, \Omega_{\rm \Lambda}$)=($0.29\pm0.10$, $0.76\pm0.13$) for SNeIa only to ($\Omega_{\rm M}, \Omega_{\rm \Lambda}$)=($0.23\pm0.06$, $0.68\pm0.08$) for SNeIa and 9 LGRBs.
Identifying Subclasses of Long Gamma-Ray Bursts with Cumulative Light Curve Morphology of Prompt Emissions
Ryo Tsutsui,Takashi Nakamura,Daisuke Yonetoku,Keitaro Takahashi,Yoshiyuki Morihara
Physics , 2012, DOI: 10.1093/pasj/65.1.3
Abstract: We argue a new classification scheme of long gamma-ray bursts (LGRBs) using the morphology of the cumulative light curve of the prompt emission. We parametrize the morphology by the absolute deviation from their constant luminosity ($ADCL$) and derive the value for 36 LGRBs which have spectropic redshifts, spectral parameters determined by the Band model, 1-second peak fluxes, fluences, and 64-msec resolution light curves whose peak counts are 10 times larger than background fluctuations. Then we devide the sample according to the value of ADCL into two groups ($ADCL < 0.17$ and $ADCL > 0.17$) and, for each group, derive the spectral peak energy $E_{\rm p}$ - peak luminosity $L_{\rm p}$ correlation and the Fundamental Plane of LGRBs, which is a correlation between the spectral peak energy $E_{\rm p}$, the luminosity time $T_{\rm L}$ ($\equiv E_{\rm iso}/L_{\rm p}$ where $E_{\rm iso}$ is isotropic energy) and the peak luminosity $L_{\rm p}$. We find that both of the correlations for both groups are statistically more significant compared with ones derived from all samples. The Fundamental Planes with small and large ADCL are given by $L_{\rm p}=10^{52.53\pm 0.01}(E_{\rm p}/10^{2.71}{\rm keV})^{1.84\pm 0.03} (T_{\rm L}/10^{0.86}{\rm sec})^{0.29\pm0.08}$ with $\chi^2_{\nu}=10.93/14$ and $L_{\rm p}=10^{52.98\pm0.08}(E_{\rm p}/10^{2.71}{\rm keV})^{1.82\pm 0.09} (T_{\rm L}/10^{0.86}{\rm sec})^{0.85\pm 0.27}$ with $\chi^2_{\nu}=7.58/8$, respectively. This fact implies the existence of subclasses of LGRBs characterized by the value of $ADCL$. Also there is a hint for the existence of the intermediate-$ADCL$ class which deviates from both fundamental planes. Both relations are so tight that our result provides a new accurate distance measurement scheme up to the high redshift universe.
Possible existence of Ep-Lp and Ep-Eiso correlations for Short Gamma-Ray Bursts with a factor 5 to 100 dimmer than those for Long Gamma-Ray Bursts
Ryo Tsutsui,Daisuke Yonetoku Takashi Nakamura,Keitaro Takahashi,Yoshiyuki Morihara
Physics , 2012, DOI: 10.1093/mnras/stt262
Abstract: We analyzed correlations among the rest frame spectral peak energy $E_{\rm p}$, the observed frame 64ms peak isotropic luminosity $L_{\rm p}$ and the isotropic energy $E_{\rm iso}$ for 13 Short Gamma Ray Burst (SGRB) candidates having the measured redshift $z$, $T_{\rm 90}^{\rm obs}/(1+z)<2$ sec and well determined spectral parameters. A SGRB candidate is regarded as a misguided SGRB if it is located in the 3-$\sigma_{\rm int}$ dispersion region from the best-fit function of the $E_{\rm p}$--$E_{\rm iso}$ correlation for Long GRBs (LGRBs) while the others are regarded as secure SGRBs possibly from compact star mergers. Using 8 secure SGRBs out of 13 SGRB candidates, we tested whether $E_{\rm p}$--$E_{\rm iso}$ and $E_{\rm p}$--$L_{\rm p}$ correlations exist for SGRBs. We found that $E_{\rm p}$--$E_{\rm iso}$ correlation for SGRBs($E_{\rm iso} =10^{51.42 \pm 0.15}{\rm erg s^{-1}} ({E_{\rm p}}/{\rm 774.5 keV})^{1.58 \pm 0.28}$) seems to exist with the correlation coefficeint $r=0.91$ and chance probability $p=1.5\times10^{-3}$. We found also that the $E_{\rm p}$--$L_{\rm p}$ correlation for SGRBs($L_{\rm p} = 10^{52.29 \pm 0.066}{\rm erg s^{-1}} ({E_{\rm p}}/{\rm 774.5 keV})^{1.59 \pm 0.11}$) is tighter than $E_{\rm p}$--$E_{\rm iso}$ correlation since $r=0.98$ and $p=1.5\times10^{-5}$. Both correlations for SGRBs are dimmer than those of LGRBs for the same $E_{\rm p}$ by factors $\sim$100 ($E_{\rm p}$--$E_{\rm iso}$) and $\sim$ 5($E_{\rm p}$--$L_{\rm p}$). Applying the tighter $E_{\rm p}$--$L_{\rm p}$ correlation for SGRBs to 71 bright BATSE SGRBs, we found that pseudo redshift $z$ ranges from 0.097 to 2.258 with the mean $$ of 1.05. The redshifts of SGRBs apparently cluster at lower redshift than those of LGRBs ($\sim 2.2 $), which supports the merger scenario of SGRBs.
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