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Search Results: 1 - 10 of 118014 matches for " T. Ochiai "
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Relativistic electron energy loss and induced radiation emission in two-dimensional metallic photonic crystals I: formalism and surface plasmon polariton
T. Ochiai,K. Ohtaka
Physics , 2003, DOI: 10.1103/PhysRevB.69.125106
Abstract: A fully relativistic description of the electron energy loss and the induced radiation emission in arbitrary arrays of non-overlapping metallic cylinders is presented in terms of the multiple scattering method on the basis of vector cylindrical waves. Numerical analysis is given for dilute and dense arrays of Aluminum cylinders with a nanoscale diameter. The results of the electron energy loss spectrum are well correlated with the dispersion relation of coupled surface plasmon polaritons, and can be interpreted with an effective medium approximation when the electron runs inside the arrays. In addition, the cavity modes localized in the grooves between the cylinders can affect strongly the electron energy loss spectrum.
Theory of unconventional Smith-Purcell radiation in finite-size photonic crystals
T. Ochiai,K. Ohtaka
Physics , 2006, DOI: 10.1364/OE.14.007378
Abstract: Unusual emission of light, called the unconventional Smith-Purcell radiation (uSPR) in this paper, was demonstrated from an electron traveling near a finite photonic crystal (PhC) at an ultra-relativistic velocity. This phenomenon is not related to the accepted mechanism of the conventional SPR and arises because the evanescent light from the electron has such a small decay constant in the ultra-relativistic regime that it works practically as a plane-wave probe entering the PhC from one end. We analyze the dependence of the SPR spectrum on the velocity of electron and on the parity of excited photonic bands and show, for PhCs made up of a finite number of cylinders, that uSPR probes the photonic band structure very faithfully.
Errata for Geometric Function Theory in Several Complex Variables
J. Noguchi,T. Ochiai
Mathematics , 1996,
Abstract: This is a list of corrections for the book: J. Noguchi and T. Ochiai, Geometric Function Theory in Several Complex Variables, xi + 282 pp., Math.\ Monographs Vol.\ {\bf 80}, Amer.\ Math.\ Soc., Providence, 1990. The authors hope that this distribution will be helpful for readers to avoid unnecessary confusions.
Carpet cloaking and Laplace transformation
T. Ochiai,J. C. Nacher
Physics , 2012,
Abstract: Recently, researchers have proposed several carpet cloaking designs that are able to hide a real object under a bump in a way that it is perceived as a flat ground plane. Here, we present a method to design two-dimensional isotropic carpet cloaking devices using Laplace transformation. We show that each functional form of a Laplace transformation corresponds to a different carpet cloaking design. Therefore, our approach allows us to systematically design a rich variety of cloaking devices. Our analysis includes several examples containing different bump geometries that illustrate the proposed methodology.
Plus-minus construction leads to perfect invisibility
J. C. Nacher,T. Ochiai
Physics , 2010, DOI: 10.1063/1.3533937
Abstract: Recent theoretical advances applied to metamaterials have opened new avenues to design a coating that hides objects from electromagnetic radiation and even the sight. Here, we propose a new design of cloaking devices that creates perfect invisibility in isotropic media. A combination of positive and negative refractive indices, called plus-minus construction, is essential to achieve perfect invisibility (i.e., no time delay and total absence of reflection). Contrary to the common understanding that between two isotropic materials having different refractive indices the electromagnetic reflection is unavoidable, our method shows that surprisingly the reflection phenomena can be completely eliminated. The invented method, different from the classical impedance matching, may also find electromagnetic applications outside of cloaking devices, wherever distortions are present arising from reflections.
Reflection-less device allows electromagnetic warp drive
T. Ochiai,J. C. Nacher
Physics , 2010,
Abstract: One of the striking properties of artificially structured materials is the negative refraction, an optical feature that known natural materials do not exhibit. Here, we propose a simple design, composed of two parallel layers of materials with different refraction indices $n_1=-n_2$, that constructs perfect reflection-less devices. The electromagnetic waves can tunnel from one layer to the other, a feature that resembles a truncation of the physical space leading to an electromagnetic warp drive. Since the refractive indices do not require any large values, this method demonstrates for the first time the practical feasibility of guiding electromagnetic fields in complete absence of reflection phenomena and without degradation of transmission efficiency at all.
Transcription and noise in negative feedback loops
J. C. Nacher,T. Ochiai
Quantitative Biology , 2007,
Abstract: Recently, several studies have investigated the transcription process associated to specific genetic regulatory networks. In this work, we present a stochastic approach for analyzing the dynamics and effect of negative feedback loops (FBL) on the transcriptional noise. First, our analysis allows us to identify a bimodal activity depending of the strength of self-repression coupling D. In the strong coupling region D>>1, the variance of the transcriptional noise is found to be reduced a 28 % more than described earlier. Secondly, the contribution of the noise effect to the abundance of regulating protein becomes manifest when the coefficient of variation is computed. In the strong coupling region, this coefficient is found to be independent of all parameters and in fair agreement with the experimentally observed values. Finally, our analysis reveals that the regulating protein is significantly induced by the intrinsic and external noise in the strong coupling region. In short, it indicates that the existence of inherent noise in FBL makes it possible to produce a basal amount of proteins even though the repression level D is very strong.
A Constructive Approach to Gene Expression Dynamics
T. Ochiai,J. C. Nacher,T. Akutsu
Quantitative Biology , 2004, DOI: 10.1016/j.physleta.2004.07.045
Abstract: The advent of new experimental genomic technologies and the massive increase of DNA sequence information is helping researchers better understand how our genes work. Recently, experiments on mRNA abundance (gene expression) have revealed that gene expression shows a stationary organization described by a power-law distribution (scale-free organization) (i.e., gene expression $k$ decays as $k^{-\gamma}$), which is highly conserved in all the major five kingdoms of life, from Bacteria to Human. An underlying gene expression dynamics "rich-travel-more" was suggested to recover that evolutional conservation of transcriptional organization. Here we propose a constructive approach to gene expression dynamics with larger scope. Our gene expression construction restores the stationary state, predicts the power-law exponent for different organisms with natural explanation for small correction at high and low expression levels, describes the intermediate state dynamics (time finite) and elucidates the gene expression stability. This approach requires only one assumption: Markov property.
A stochastic approach to multi-gene expression dynamics
T. Ochiai,J. C. Nacher,T. Akutsu
Quantitative Biology , 2005, DOI: 10.1016/j.physleta.2005.02.066
Abstract: In the last years, tens of thousands gene expression profiles for cells of several organisms have been monitored. Gene expression is a complex transcriptional process where mRNA molecules are translated into proteins, which control most of the cell functions. In this process, the correlation among genes is crucial to determine the specific functions of genes. Here, we propose a novel multi-dimensional stochastic approach to deal with the gene correlation phenomena. Interestingly, our stochastic framework suggests that the study of the gene correlation requires only one theoretical assumption -Markov property- and the experimental transition probability, which characterizes the gene correlation system. Finally, a gene expression experiment is proposed for future applications of the model.
Symmetry and Dynamics in living organisms: The self-similarity principle governs gene expression dynamics
T. Ochiai,J. C. Nacher,T. Akutsu
Quantitative Biology , 2005,
Abstract: The ambitious and ultimate research purpose in Systems Biology is the understanding and modelling of the cell's system. Although a vast number of models have been developed in order to extract biological knowledge from complex systems composed of basic elements as proteins, genes and chemical compounds, a need remains for improving our understanding of dynamical features of the systems (i.e., temporal-dependence). In this article, we analyze the gene expression dynamics (i.e., how the genes expression fluctuates in time) by using a new constructive approach. This approach is based on only two fundamental ingredients: symmetry and the Markov property of dynamics. First, by using experimental data of human and yeast gene expression time series, we found a symmetry in short-time transition probability from time $t$ to time $t+1$. We call it self-similarity symmetry (i.e., surprisingly, the gene expression short-time fluctuations contain a repeating pattern of smaller and smaller parts that are like the whole, but different in size). Secondly, the Markov property of dynamics reflects that the short-time fluctuation governs the full-time behaviour of the system. Here, we succeed in reconstructing naturally the global behavior of the observed distribution of gene expression (i.e., scaling-law) and the local behaviour of the power-law tail of this distribution, by using only these two ingredients: symmetry and the Markov property of dynamics. This approach may represent a step forward toward an integrated image of the basic elements of the whole cell.
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