8 results on '"Yurie Tamura"'
Search Results
2. Asymptotic Theory of Test Statistic for Sphericity of High-Dimensional Time Series
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Yurie Tamura, Masanobu Taniguchi, and Yan Liu
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Statistics and Probability ,Independent and identically distributed random variables ,Asymptotic analysis ,Series (mathematics) ,Applied Mathematics ,05 social sciences ,Mauchly's sphericity test ,01 natural sciences ,Sphericity ,Normal distribution ,010104 statistics & probability ,0502 economics and business ,Test statistic ,Null distribution ,Applied mathematics ,0101 mathematics ,Statistics, Probability and Uncertainty ,050205 econometrics ,Mathematics - Abstract
We consider the testing problem for the sphericity hypothesis regarding the covariance matrix based on high-dimensional time series, under the assumption that the sample size n and the dimension p satisfy limn,p→∞p/n=c∈(0,∞). Recently, several studies on test statistics for sphericity of independent and identically distributed p-dimensional random variables have been carried out under the assumption that both n and p diverge to infinity. A test statistic for sphericity has been proved to be well behaved even when p>n. We investigate the test statistic under situations of high-dimensional time series. The asymptotic null distribution of the test statistic is shown to be standard normal distribution when the observations come from Gaussian stationary processes. In the simulation study, we illustrate the properties of the test statistic for several time series models. We apply the test to a problem of portfolio selection in our empirical study.
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- 2018
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3. Neuroprotective effects of propofol on ER stress-mediated apoptosis in neuroblastoma SH-SY5Y cells
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Manami Inagaki, Mayumi Tsuji, Ai Nakajima, Yuki Usui, Akifumi Niiya, Yurie Tamura, Masumi Kato, and Katsuji Oguchi
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Thapsigargin ,SH-SY5Y ,Eukaryotic Initiation Factor-2 ,Intracellular Space ,Apoptosis ,Pharmacology ,Neuroprotection ,Neuroblastoma ,chemistry.chemical_compound ,Cell Line, Tumor ,Humans ,Medicine ,Phosphorylation ,Propofol ,biology ,Calpain ,business.industry ,Endoplasmic reticulum ,Endoplasmic Reticulum Stress ,medicine.disease ,Caspases, Initiator ,Neuroprotective Agents ,Gene Expression Regulation ,chemistry ,Unfolded protein response ,biology.protein ,Calcium ,business ,Reperfusion injury - Abstract
Anesthetic treatment has been associated with widespread apoptotic neurodegeneration in the neonatal rodent brain. It has recently been suggested that propofol, a short-acting intravenous anesthetic agent, may have a potential as a neuroprotective agent. An apoptotic pathway mediated through endoplasmic reticulum (ER) stress has been attracting attention. ER stress is associated with accumulation of unfolded or misfolded proteins in ER, and ER stress-induced apoptosis is implicated in a wide range of diseases, including ischemia/reperfusion injury, neurodegeneration, and diabetes. We investigated whether thapsigargin-induced ER stress is prevented by propofol in human neuroblastoma SH-SY5Y cells. SH-SY5Y cells were pretreated with various concentrations of propofol (1-10 μM) for 3h before co-treatment with 0.5 μM thapsigargin and propofol for 20 h. Levels of ssDNA, specific evidence of apoptosis, and biomarkers of ER stress (mRNA expression of Chop and sXbp-1) were determined. We also assayed calpain and caspase-4 activities and intracellular Ca(2+) ([Ca(2+)]i) levels. Thapsigargin-induced increases in ssDNA levels, expressions of ER stress biomarkers, activities of caspase-4 and calpain, and level of [Ca(2+)]i were suppressed by co-incubation with propofol. Our data indicate the possibility that propofol inhibits the Ca(2+) release from ER at clinically employed dose levels. These results demonstrate that propofol suppresses the ER stress-induced apoptosis in this cell system, and may have the neuroprotective potency. It may also be a promising agent for preventing damage from cerebral ischemia or edema.
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- 2014
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4. Intermittently-visual Tracking Experiments Reveal the Roles of Error-correction and Predictive Mechanisms in the Human Visual-motor Control System
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Yoshikatsu Hayashi, Yurie Tamura, Ken Sugawara, Yasuji Sawada, and Kazuya Sase
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Mechanism (engineering) ,Rhythm ,Computer science ,business.industry ,Control system ,Eye tracking ,Computer vision ,Circular orbit ,Artificial intelligence ,Tracking (particle physics) ,business ,Reset (computing) ,Motion (physics) - Abstract
Prediction mechanism is necessary for human visual motion to compensate a delay of sensory-motor system. In a previous study, “proactive control” was discussed as one example of predictive function of human beings, in which motion of hands preceded the virtual moving target in visual tracking experiments. To study the roles of the positional-error correction mechanism and the prediction mechanism, we carried out an intermittently-visual tracking experiment where a circular orbit is segmented into the target-visible regions and the target-invisible regions. Main results found in this research were following. A rhythmic component appeared in the tracer velocity when the target velocity was relatively high. The period of the rhythm in the brain obtained from environmental stimuli is shortened more than 10%. The shortening of the period of rhythm in the brain accelerates the hand motion as soon as the visual information is cut-off, and causes the precedence of hand motion to the target motion. Although the precedence of the hand in the blind region is reset by the environmental information when the target enters the visible region, the hand motion precedes the target in average when the predictive mechanism dominates the error-corrective mechanism.
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- 2010
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5. Roll of the rhythmic component in the proactive control of a human hand
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Ken Sugawara, Yurie Tamura, Yasuji Sawada, and Yoshikatsu Hayashi
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Mechanism (engineering) ,Rhythm ,Artificial Intelligence ,Computer science ,Position (vector) ,Control theory ,Control system ,Component (UML) ,Constant (mathematics) ,Cursor (databases) ,General Biochemistry, Genetics and Molecular Biology ,Motion (physics) - Abstract
In terms of evolution, the strategy of catching prey would have been an important part of survival in a constantly changing environment. A prediction mechanism would have developed to compensate for any delay in the sensory-motor system. In a previous study, “proactive control” was found, in which the motion of the hands preceded the virtual moving target. These results implied that the positive phase shift of the hand motion represents the proactive nature of the visual-motor control system, which attempts to minimize the brief error in the hand motion when the target changes position unexpectedly. In our study, a visual target moves in circle (13 cm diameter) on a computer screen, and each subject is asked to keep track of the target’s motion by the motion of a cursor. As the frequency of the target increases, a rhythmic component was found in the velocity of the cursor in spite of the fact that the velocity of the target was constant. The generation of a rhythmic component cannot be explained simply as a feedback mechanism for the phase shifts of the target and cursor in a sensory-motor system. Therefore, it implies that the rhythmic component was generated to predict the velocity of the target, which is a feed-forward mechanism in the sensory-motor system. Here, we discuss the generation of the rhythmic component and its roll in the feed-forward mechanism.
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- 2009
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6. Virtual needle pain stimuli activates cortical representation of emotions in normal volunteers
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Shigeki Tanaka, Tatsunori Ikemoto, Shinichirou Taniguchi, Yoriko Murata, Takahiro Ushida, Matthew McLaughlin, Yurie Tamura, Young-Chang P. Arai, and Jun Shinozaki
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Adult ,Male ,media_common.quotation_subject ,Emotions ,Pain ,Posterior parietal cortex ,Inferior frontal gyrus ,Empathy ,behavioral disciplines and activities ,Brain mapping ,Cortex (anatomy) ,Image Processing, Computer-Assisted ,Reaction Time ,medicine ,Humans ,media_common ,Cerebral Cortex ,Brain Mapping ,General Neuroscience ,Chronic pain ,Precentral gyrus ,medicine.disease ,Magnetic Resonance Imaging ,Oxygen ,Emotional lateralization ,medicine.anatomical_structure ,nervous system ,Visual Perception ,Female ,Psychology ,Neuroscience ,Photic Stimulation - Abstract
Psychological factors are known to play an extremely important role in the maintenance and development of chronic pain conditions. However, it is unclear how such factors relate to the central neural processing of nociceptive transmission in healthy individuals. To investigate this issue, the activation of the brain was studied in 30 healthy volunteers responding to virtual pain stimuli by fMRI. In the first series of the study (non-preconditioned study), 15 participants were shown a digital video demonstrating an injection needle puncturing the right palm. In the second series of the study (pre-conditioned study), same-task paradigms were used for another 15 participants. Prior to the fMRI session, real needle punctuate stimuli were applied to the right palm of participants for pre-conditioning. fMRI analysis revealed that bilateral activations in anterior insula (BA45), parietal operculum (S2: BA40), premotor area, medial globus pallidus, inferior occipital gyrus (BA18), left temporal association cortex, right fusiform gyrus, right parietal association cortex and cerebellum occurred due to the task in the preconditioned group. On the other hand, right parietal operculum (S2: BA40), premotor area, parietal association cortex, left inferior frontal gyrus and bilateral temporal association cortex were activated in the non-preconditioned group. In addition, activation of anterior insula, inferior frontal gyrus, precentral gyrus and cerebellum significantly increased in the preconditioned group compared with the non-preconditioned group. These results suggest that the virtual needle puncture task caused memory retrieval of unpleasant experiences which is possibly related to empathy for pain, resulting in the activation of specific brain areas.
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- 2008
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7. Low-Grade Inflammation Is a Risk Factor for Clinical Stroke Events in Addition to Silent Cerebral Infarcts in Japanese Older Hypertensives
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Joji Ishikawa, Kazuyuki Shimada, Shizukiyo Ishikawa, Satoshi Hoshide, Yurie Tamura, Kazuomi Kario, and Kazuo Eguchi
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Male ,medicine.medical_specialty ,Monitoring, Ambulatory ,Central nervous system disease ,Asian People ,Risk Factors ,Internal medicine ,Humans ,Medicine ,cardiovascular diseases ,Risk factor ,Stroke ,Aged ,Aged, 80 and over ,Inflammation ,Advanced and Specialized Nursing ,biology ,business.industry ,Vascular disease ,Cerebral infarction ,Incidence (epidemiology) ,C-reactive protein ,Cerebral Infarction ,Middle Aged ,medicine.disease ,Magnetic Resonance Imaging ,C-Reactive Protein ,Blood pressure ,Hypertension ,Physical therapy ,Cardiology ,biology.protein ,Female ,Neurology (clinical) ,Cardiology and Cardiovascular Medicine ,business ,Follow-Up Studies - Abstract
Background and Purpose— High-sensitivity C-reactive protein (hsCRP), a marker of inflammation, is associated with atherosclerosis, hypertensive target organ damage, and cardiovascular events. In the general Japanese population, the level of hsCRP is reported to be lower than that in Western countries, and the relationships among hsCRP, silent cerebral infarcts (SCIs), and clinical stroke events in older Japanese hypertensives remain unclear. Methods— We conducted brain MRI and measured hsCRP at baseline in 514 older Japanese hypertensives (clinic blood pressure ≥140/90 mm Hg, age ≥50 years old) who were enrolled in the Jichi Medical School ABPM Study, wave 1. They were followed up for an average of 41 months (range: 1 to 68 months, 1751 person-years) and the incidence of subsequent clinical stroke events was evaluated. Results— The subjects with SCIs at baseline (n=257) had a higher hsCRP level than those without SCIs (geometric mean hsCRP [SD range]; 0.19 [0.18 to 0.21] versus 0.14 [0.13 to 0.16] mg/L, P =0.007) after adjustment for confounding factors, and the OR for the presence of SCIs was increased with the quartile of hsCRP levels. In Cox regression analysis, the patients with above median hsCRP level (≥0.21 mg/L) (hazard ratio [HR]: 2.50, 95% CI: 1.24 to 5.00, P =0.01) and those with SCIs (HR: 4.60, 95% CI: 1.91 to 11.03, P =0.001) at baseline had independently higher risks for clinical stroke events after adjustment for age, smoking status, antihypertensive medication use, and 24-hour systolic blood pressure level. Compared with the patients with below median hsCRP level without SCIs, those with above median hsCRP level and SCIs at baseline had a higher risk for clinical stroke events (HR: 7.32, 95% CI: 2.17 to 24.76, P =0.001), although those with below median hsCRP level and SCIs (HR: 2.46, 95% CI: 0.64 to 9.47, P =0.19) and those with above median hsCRP level without SCIs (HR: 1.11, 95% CI: 0.22 to 5.55, P =0.90) did not have significant risks. Conclusion— High-sensitivity C-reactive protein is a risk factor for clinical stroke events in addition to silent cerebral infarcts in Japanese older hypertensives, indicating that the risk for clinical stroke events increases with preexisting hypertensive target organ damage in the brain and additionally with ongoing low-grade inflammation.
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- 2007
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8. The current state of the translation of the role language by comparison between Japanese manga and Korean translation
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Yurie Tamura
- Subjects
Political science ,State (computer science) ,Current (fluid) ,Translation (geometry) ,Linguistics - Published
- 2015
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