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Kishida M.,Japan National Institute of Information and Communications Technology
IEEE Transactions on Automatic Control | Year: 2017

This technical note considers the problem of maximizing the volume of a box of parameters that satisfy polytopic output constraints for linear fractional models using the structured singular value μ. In particular, four kinds of boxes are considered: 1) a hypercube centered at a specified location; 2) a freely located hypercube; 3) a freely located box of free shape; and 4) a freely located box of free shape and rotation. It is found that the problem for 1) can be solved by computing μ for the number of scalar constraints, while problems for 2)-4) can be reformulated as a constant-matrix μ-synthesis problem, which can be approached by D,G-K iteration. © 1963-2012 IEEE.

Matsumoto A.,Japan National Institute of Information and Communications Technology | Kakigi R.,National Institute for Physiological science
Journal of Cognitive Neuroscience | Year: 2014

Recent neuroimaging experiments have revealed that subliminal priming of a target stimulus leads to the reduction of neural activity in specific regions concerned with processing the target. Such findings lead to questions about the degree to which the subliminal priming effect is based only on decreased activity in specific local brain regions, as opposed to the influence of neural mechanisms that regulate communication between brain regions. To address this question, this study recorded EEG during performance of a subliminal semantic priming task. We adopted an information-based approach that used independent component analysis and multivariate autoregressive modeling. Results indicated that subliminal semantic priming caused significant modulation of alpha band activity in the left inferior frontal cortex and modulation of gamma band activity in the left inferior temporal regions. The multivariate autoregressive approach confirmed significant increases in information flow from the inferior frontal cortex to inferior temporal regions in the early time window that was induced by subliminal priming. In the later time window, significant enhancement of bidirectional causal flow between these two regions underlying subliminal priming was observed. Results suggest that unconscious processing of words influences not only local activity of individual brain regions but also the dynamics of neural communication between those regions. © 2013 Massachusetts Institute of Technology.

Kishida M.,Japan National Institute of Information and Communications Technology
IEEE Transactions on Automatic Control | Year: 2017

This technical note considers problems that involve eigenvalues of uncertain matrices expressed in linear fractional form using the structured singular value $\mu$ and the skewed structured singular value $\nu$. In particular, positive definiteness conditions, maximum and minimum eigenvalues and generalized eigenvalues of uncertain matrices are expressed using $\mu$ and $\nu$. The obtained results allow us to acquire information of an uncertain matrix efficiently by the existing computational tools that provide practically useful approximations to the values of $\mu$ and $\nu$. IEEE

Cukur T.,University of California at Berkeley | Nishimoto S.,University of California at Berkeley | Nishimoto S.,Japan National Institute of Information and Communications Technology | Huth A.G.,University of California at Berkeley | Gallant J.L.,University of California at Berkeley
Nature Neuroscience | Year: 2013

Little is known about how attention changes the cortical representation of sensory information in humans. On the basis of neurophysiological evidence, we hypothesized that attention causes tuning changes to expand the representation of attended stimuli at the cost of unattended stimuli. To investigate this issue, we used functional magnetic resonance imaging to measure how semantic representation changed during visual search for different object categories in natural movies. We found that many voxels across occipitooral and fronto-parietal cortex shifted their tuning toward the attended category. These tuning shifts expanded the representation of the attended category and of semantically related, but unattended, categories, and compressed the representation of categories that were semantically dissimilar to the target. Attentional warping of semantic representation occurred even when the attended category was not present in the movie; thus, the effect was not a target-detection artifact. These results suggest that attention dynamically alters visual representation to optimize processing of behaviorally relevant objects during natural vision. © 2013 Nature America, Inc. All rights reserved.

Naruse M.,Japan National Institute of Information and Communications Technology
Reports on progress in physics. Physical Society (Great Britain) | Year: 2013

Nanophotonics has been extensively studied with the aim of unveiling and exploiting light-matter interactions that occur at a scale below the diffraction limit of light, and recent progress made in experimental technologies--both in nanomaterial fabrication and characterization--is driving further advancements in the field. From the viewpoint of information, on the other hand, novel architectures, design and analysis principles, and even novel computing paradigms should be considered so that we can fully benefit from the potential of nanophotonics. This paper examines the information physics aspects of nanophotonics. More specifically, we present some fundamental and emergent information properties that stem from optical excitation transfer mediated by optical near-field interactions and the hierarchical properties inherent in optical near-fields. We theoretically and experimentally investigate aspects such as unidirectional signal transfer, energy efficiency and networking effects, among others, and we present their basic theoretical formalisms and describe demonstrations of practical applications. A stochastic analysis of light-assisted material formation is also presented, where an information-based approach provides a deeper understanding of the phenomena involved, such as self-organization. Furthermore, the spatio-temporal dynamics of optical excitation transfer and its inherent stochastic attributes are utilized for solution searching, paving the way to a novel computing paradigm that exploits coherent and dissipative processes in nanophotonics.

Sasaki K.,Japan National Institute of Information and Communications Technology
Physics in medicine and biology | Year: 2013

The free space method using a pair of lens antennas was modified for the complex permittivity measurement of biological samples from 20 to 110 GHz. Two methodologies were used to obtain the complex permittivities by the free space method, which were based on the reflection and transmission coefficients. The measurement results obtained with the two methodologies were compared with each other. The measured complex permittivities of the biological samples from the free space method were then compared with those measured using the coaxial probe method. Finally, the measurement data were also compared with those from measurement methods developed in past literatures.

Hayasaka K.,Japan National Institute of Information and Communications Technology
Applied Physics B: Lasers and Optics | Year: 2012

Ion chains consisting of different species play an important role in new applications in quantum information processing as well as in optical frequency standards. We demonstrate generation and stabilization of ion chains consisting of Ca+ and In+. The Ca+ chains with In + located at specified positions are synthesized using resonant photoionization, real-time imaging and trap field control techniques. A specific configuration of an ion chain is stabilized by destabilizing other configurations via selective excitation of vibrational modes using amplitude modulation on the cooling laser beam. New approaches to an indium ionoptical clock are proposed using the ions chains. © Springer-Verlag 2012.

Hayasaka K.,Japan National Institute of Information and Communications Technology
Optics Letters | Year: 2011

Optical locking to a filter cavity is an effective method to eliminate the limitations of an external-cavity diode laser, such as broad spontaneous emission backgrounds and frequency jitters. Stable operation of the optical locking requires simultaneous control of the feedback phase and the diode-laser frequency. Frequency dither is usually used to extract the two error signals, but this causes extra frequency modulation in the output beam. A modulation- free method for deriving the error signals by modulating the laser-cavity coupling strength is demonstrated with a violet diode laser. A modulation-free linewidth upper limit of about 7 kHz for a 1 s measurement is realized by the method. © 2011 Optical Society of America.

Kajita M.,Japan National Institute of Information and Communications Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

The vibrational transition frequencies of a N2+ molecular ion are advantageous for precise measurement because the Stark shift is much smaller than that of heteronuclear diatomic molecules. The 14N2+ S(0) transition has been observed by a group in Basel. For most transitions, the Zeeman shift limits the attainable accuracy. This paper reports the quadrupole transitions (observed with simpler apparatus than that required for the Raman transition) for which the Zeeman shift is less than 100 Hz at a magnetic field of 1 G. QN transitions (N: even) of the molecular ion with I=0 are advantageous for measurement within an uncertainty of 10-16. The transition frequencies of molecular ions with I≠0 are difficult to measure within an uncertainty of 10-12 because J-mixing makes the linear Zeeman coefficient in the Q transitions large and narrow hyperfine splitting makes the quadratic Zeeman coefficient large. © 2015 American Physical Society.

Han T.S.,Japan National Institute of Information and Communications Technology
IEEE Transactions on Information Theory | Year: 2011

The problem of network coding for multicasting a single source to multiple sinks has first been studied by Ahlswede, Cai, Li, and Yeung in 2000, in which they have established the celebrated max-flow min-cut theorem on nonphysical information flow over a network of independent channels. On the other hand, in 1980, Han has studied the case with multiple correlated sources and a single sink from the viewpoint of polymatroidal functions in which a necessary and sufficient condition has been demonstrated for reliable transmission over the network. This paper presents an attempt to unify both cases, which leads to establish a necessary and sufficient condition for reliable transmission over a network for multicasting multiple correlated sources to multiple sinks. Here, the problem of separation of source coding and network coding is also discussed. © 2006 IEEE.