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Search Results: 1 - 10 of 138856 matches for " K. Niwa "
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New Alumina Substrates for Microelectronics
K. Niwa,K. Murakawa
Active and Passive Electronic Components , 1975, DOI: 10.1155/apec.2.115
Abstract:
Uncertainty in a Measurement of Density Dependence on Population Fluctuations  [PDF]
Hiro-Sato Niwa
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.58104
Abstract:

This article discusses the question of how elasticity of the system is intertwined with external stochastic disturbances. The speed at which a displaced system returns to its equilibrium is a measure of density dependence in population dynamics. Population dynamics in random environments, linearized around the equilibrium point, can be represented by a Langevin equation, where populations fluctuate under locally stable (not periodic or chaotic) dynamics. I consider a Langevin model in discrete time, driven by time-correlated random forces, and examine uncertainty in locating the population equilibrium. There exists a time scale such that for times shorter than this scale the dynamics can be approximately described by a random walk; it is difficult to know whether the system is heading toward the equilibrium point. Density dependence is a concept that emerges from a proper coarse-graining procedure applied for time-series analysis of population data. The analysis is illustrated using time-series data from fisheries in the North Atlantic, where fish populations are buffeted by stochastic harvesting in a random environment.

Genome-scale approaches for discovering novel nonconventional splicing substrates of the Ire1 nuclease
Maho Niwa, Christopher K Patil, Joe DeRisi, Peter Walter
Genome Biology , 2004, DOI: 10.1186/gb-2004-6-1-r3
Abstract: We developed methods to search for additional mRNA substrates of Ire1p in three independent lines of genome-wide analysis. These methods exploited the well characterized enzymology and genetics of the UPR and the yeast genome sequence in conjunction with microarray-based detection. Each method successfully identified HAC1 mRNA as a substrate according to three criteria: HAC1 mRNA is selectively cleaved in vitro by Ire1; the HAC1 mRNA sequence contains two predicted Ire1 cleavage sites; and HAC1 mRNA is selectively degraded in tRNA ligase mutant cells.Within the limits of detection, no other mRNA satisfies any of these criteria, suggesting that a unique nonconventional mRNA-processing mechanism has evolved solely for carrying out signal transduction between the ER and the nucleus. The approach described here, which combines biochemical and genetic 'fractionation' of mRNA with a novel application of cDNA microarrays, is generally applicable to the study of pathways in which RNA metabolism and alternative splicing have a regulatory role.The unfolded protein response (UPR) regulates the protein-folding and secretory capacity of eukaryotic cells by monitoring conditions within the endoplasmic reticulum (ER) and regulating a downstream gene-expression program (reviewed in [1-3]). In yeast, about 5% of the genome is under the transcriptional control of the UPR [4,5]. Induction of this vast set of genes is thought to lead to a restructuring of the secretory pathway to allow an increased protein flux to the cell surface and enable the cell to tolerate protein-folding stress. Hence, the UPR adjusts the secretory capacity of cells by feedback regulation.The identification and characterization of the UPR signaling components revealed a unique mechanism of signal transduction whose salient features are conserved among all eukaryotes. The UPR is initiated when the amino-terminal portion of the serine/threonine ER-transmembrane kinase Ire1 detects unfolded proteins within the ER l
Development of a new JMA flask sampling and trace gas measuring system for observation on a cargo aircraft C-130H
K. Tsuboi,H. Matsueda,Y. Sawa,Y. Niwa
Atmospheric Measurement Techniques Discussions , 2012, DOI: 10.5194/amtd-5-7067-2012
Abstract: We developed and evaluated a flask air sampling system for atmospheric trace gas observation on a cargo C-130H aircraft, as well as an automated analysis system for the flask samples, as part of a new operational monitoring program of the Japan Meteorological Agency (JMA). Air samples were collected during each flight, between Kanagawa Prefecture (near Tokyo) and Minamitorishima (an island located nearly 2000 km southeast of Tokyo), from the air-conditioning system on the aircraft. The quality assurance test of the flask sampling air was made by specially coordinated flights at a low altitude of 1000 ft over Minamitorishima and comparing the flask values with those obtained at the surface. Based on our storage tests, the flask samples remained stable until analyses. The concentration measuring system for the flask samples has, in addition to the conventional sensors, two laser-based analyzers using wavelength-scanned cavity ring-down spectroscopy (WS-CRDS) and off-axis integrated cavity output spectroscopy (ICOS). Laboratory tests of the measuring system indicated relatively high reproducibility with overall precisions of less than 0.06 ppm for CO2, 0.68 ppb for CH4, 0.36 ppb for CO, and 0.03 ppb for N2O. Inter-comparison experiments for ambient air measurements showed excellent agreements between the laser-based measurement techniques and the conventional methods currently in use. We also found that there are no significant influences of isotope effects for the laser-based analyzers.
Three-dimensional variations of atmospheric CO2: aircraft measurements and multi-transport model simulations
Y. Niwa,P. K. Patra,Y. Sawa,T. Machida
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011, DOI: 10.5194/acp-11-13359-2011
Abstract: Numerical simulation and validation of three-dimensional structure of atmospheric carbon dioxide (CO2) is necessary for quantification of transport model uncertainty and its role on surface flux estimation by inverse modeling. Simulations of atmospheric CO2 were performed using four transport models and two sets of surface fluxes compared with an aircraft measurement dataset of Comprehensive Observation Network for Trace gases by AIrLiner (CONTRAIL), covering various latitudes, longitudes, and heights. Under this transport model intercomparison project, spatiotemporal variations of CO2 concentration for 2006–2007 were analyzed with a three-dimensional perspective. Results show that the models reasonably simulated vertical profiles and seasonal variations not only over northern latitude areas but also over the tropics and southern latitudes. From CONTRAIL measurements and model simulations, intrusion of northern CO2 in to the Southern Hemisphere, through the upper troposphere, was confirmed. Furthermore, models well simulated the vertical propagation of seasonal variation in the northern free troposphere. However, significant model-observation discrepancies were found in Asian regions, which are attributable to uncertainty of the surface CO2 flux data. In summer season, differences in latitudinal gradients by the fluxes are comparable to or greater than model-model differences even in the free troposphere. This result suggests that active summer vertical transport sufficiently ventilates flux signals up to the free troposphere and the models could use those for inferring surface CO2 fluxes.
The Fruit Fly Drosophila melanogaster as a Model System to Study Cholesterol Metabolism and Homeostasis
Ryusuke Niwa,Yuko S. Niwa
Cholesterol , 2011, DOI: 10.1155/2011/176802
Abstract: Cholesterol has long been recognized for its versatile roles in influencing the biophysical properties of cell membranes and for serving as a precursor of steroid hormones. While many aspects of cholesterol biosynthesis are well understood, little is currently known about the molecular mechanisms of cholesterol metabolism and homeostasis. Recently, genetic approaches in the fruit fly, Drosophila melanogaster, have been successfully used for the analysis of molecular mechanisms that regulate cholesterol metabolism and homeostasis. This paper summarizes the recent studies on genes that regulate cholesterol metabolism and homeostasis, including neverland, Niemann Pick type C(NPC) disease genes, and DHR96.
The Fruit Fly Drosophila melanogaster as a Model System to Study Cholesterol Metabolism and Homeostasis
Ryusuke Niwa,Yuko S. Niwa
Cholesterol , 2011, DOI: 10.1155/2011/176802
Abstract: Cholesterol has long been recognized for its versatile roles in influencing the biophysical properties of cell membranes and for serving as a precursor of steroid hormones. While many aspects of cholesterol biosynthesis are well understood, little is currently known about the molecular mechanisms of cholesterol metabolism and homeostasis. Recently, genetic approaches in the fruit fly, Drosophila melanogaster, have been successfully used for the analysis of molecular mechanisms that regulate cholesterol metabolism and homeostasis. This paper summarizes the recent studies on genes that regulate cholesterol metabolism and homeostasis, including neverland, Niemann Pick type C(NPC) disease genes, and DHR96. 1. Introduction Cholesterol is essential for many biological processes; it plays critical roles in influencing the permeability and fluidity of cell membranes as well as in modulating the activity of intracellular signal transduction pathways through its covalent attachment to proteins such as Hedgehog [1]. Importantly, cholesterol also serves as a precursor in the synthesis of steroid hormones. Cholesterol levels are tightly controlled by the body; an overabundance of cholesterol is accompanied by a variety of prevalent diseases in humans including cardiac infarction, stroke, and neurodegenerative disorders such as Alzheimer’s disease [2, 3]. Thus, the importance of cholesterol in eukaryotes and human disease pathogenesis has been intensively investigated using vertebrate model systems, and the mechanisms of cholesterol biosynthesis have been characterized in great detail. Nevertheless, our knowledge of cholesterol metabolism and homeostasis has not been fully elucidated. In particular, our knowledge of the mechanisms that regulate absorption and trafficking of dietary cholesterol is far from complete. For many years, the fruit fly, Drosophila melanogaster, has served as an excellent model system for studying the mechanisms regulating essential biological processes and has had a major role in unraveling the molecular mechanisms of development and physiology [4]. The availability of genome sequences, the ease of genetic manipulation, and the large collection of available mutants make Drosophila an attractive system that has enabled a better understanding of human diseases at the molecular level [5]. More recently, in the past five years, studies on cholesterol homeostasis and metabolism have also been performed in this excellent genetic model organism. Similar to vertebrates, Drosophila requires cholesterol as a precursor for steroid hormones and as a
Carbon balance of South Asia constrained by passenger aircraft CO2 measurements
P. K. Patra,Y. Niwa,T. J. Schuck,C. A. M. Brenninkmeijer
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011, DOI: 10.5194/acp-11-4163-2011
Abstract: Quantifying the fluxes of carbon dioxide (CO2) between the atmosphere and terrestrial ecosystems in all their diversity, across the continents, is important and urgent for implementing effective mitigating policies. Whereas much is known for Europe and North America for instance, in comparison, South Asia, with 1.6 billion inhabitants and considerable CO2 fluxes, remained terra incognita in this respect. We use regional measurements of atmospheric CO2 aboard a Lufthansa passenger aircraft between Frankfurt (Germany) and Chennai (India) at cruise altitude, in addition to the existing network sites for 2008, to estimate monthly fluxes for 64-regions using Bayesian inversion and transport model simulations. The applicability of the model's transport parameterization is confirmed using SF6, CH4 and N2O simulations for the CARIBIC datasets. The annual amplitude of carbon flux obtained by including the aircraft data is twice as large as the fluxes simulated by a terrestrial ecosystem model that was applied to prescribe the fluxes used in the inversions. It is shown that South Asia sequestered carbon at a rate of 0.37 ± 0.20 Pg C yr 1 (1 Pg C = 1015 g of carbon in CO2) for the years 2007 and 2008. The seasonality and the strength of the calculated monthly fluxes are successfully validated using independent measurements of vertical CO2 profiles over Delhi and spatial variations at cruising altitude over Asia aboard Japan Airlines passenger aircraft.
Longitudinal magnetic excitation in KCuCl3 studied by Raman scattering under hydrostatic pressures
H. Kuroe,N. Takami,N. Niwa,T. Sekine,M. Matsumoto,F. Yamada,H. Tanaka,K. Takemura
Physics , 2012, DOI: 10.1088/1742-6596/400/3/032042
Abstract: We measure Raman scattering in an interacting spin-dimer system KCuCl3 under hydrostatic pressures up to 5 GPa mediated by He gas. In the pressure-induced quantum phase, we observe a one-magnon Raman peak, which originates from the longitudinal magnetic excitationand is observable through the second-order exchange interaction Raman process. We report the pressure dependence of the frequency, halfwidth and Raman intensity of this mode.
A Novel Serum-Free Monolayer Culture for Orderly Hematopoietic Differentiation of Human Pluripotent Cells via Mesodermal Progenitors
Akira Niwa, Toshio Heike, Katsutsugu Umeda, Koichi Oshima, Itaru Kato, Hiromi Sakai, Hirofumi Suemori, Tatsutoshi Nakahata, Megumu K. Saito
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0022261
Abstract: Elucidating the in vitro differentiation of human embryonic stem (ES) and induced pluripotent stem (iPS) cells is important for understanding both normal and pathological hematopoietic development in vivo. For this purpose, a robust and simple hematopoietic differentiation system that can faithfully trace in vivo hematopoiesis is necessary. In this study, we established a novel serum-free monolayer culture that can trace the in vivo hematopoietic pathway from ES/iPS cells to functional definitive blood cells via mesodermal progenitors. Stepwise tuning of exogenous cytokine cocktails induced the hematopoietic mesodermal progenitors via primitive streak cells. These progenitors were then differentiated into various cell lineages depending on the hematopoietic cytokines present. Moreover, single cell deposition assay revealed that common bipotential hemoangiogenic progenitors were induced in our culture. Our system provides a new, robust, and simple method for investigating the mechanisms of mesodermal and hematopoietic differentiation.
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