Hajime Tamura
Tohoku University
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Featured researches published by Hajime Tamura.
Publications of the Astronomical Society of Japan | 2005
Yoshiaki Taniguchi; Masaru Ajiki; Tohru Nagao; Yasuhiro Shioya; Takashi Murayama; Nobunari Kashikawa; Keiichi Kodaira; Norio Kaifu; Hiroyasu Ando; Hiroshi Karoji; Masayuki Akiyama; Kentaro Aoki; Mamoru Doi; Shinobu S. Fujita; Hisanori Furusawa; Tomoki Hayashino; Fumihide Iwamuro; Masanori Iye; Naoto Kobayashi; Tadayuki Kodama; Yutaka Komiyama; Y. Matsuda; Satoshi Miyazaki; Yoshihiko Mizumoto; Kentaro Motohara; Kyoji Nariai; K. Ohta; Youichi Ohyama; Sadanori Okamura; Masami Ouchi
We present new results of a deep optical imaging survey using a narrow band filter (NB921) centered at λ = 9196 u A together with B, V, R, i � ,a ndzbroadband filters in the sky area of the Subaru Deep Field, which has been promoted as one of legacy programs of the 8.2m Subaru Telescope. We obtained a photometric sample of 58 Ly α emitter candidates at z ≈ 6.5-6.6 among ∼ 180 strong NB921-excess (z � −NB921 > 1.0) objects together with a color criterion of i � −z � > 1.3. We then obtained optical spectra of 20 objects in our NB921-excess sample, and identified at least nine Ly α emitters at z ∼ 6.5-6.6, including the two emitters reported by Kodaira et al. (2003, PASJ, 55, L17). Since our Ly α-emitter candidates are free from strong amplification of gravitational lensing, we are able to discuss their observational properties from a statistical point of view. Based on these new results, we obtained a lower limit of the star-formation rate density of ρSFR � 5.7 ×10 −4 h0.7 Myr −1 Mpc −3 at z ≈ 6.6, being
Annals of Nuclear Medicine | 2001
Hiroshi Ito; Iwao Kanno; Hidehiro Iida; Jun Hatazawa; Eku Shimosegawa; Hajime Tamura; Toshio Okudera
In quantitative functional neuroimaging with positron emission tomography (PET) and magnetic resonance imaging (MRI), cerebral blood volume (CBV) and its three components, arterial, capillary, and venous blood volumes are important factors. The arterial fraction for systemic circulation of the whole body has been reported to be 20–30%, but there is no report of this fraction in the brain. In the present study, we estimated the arterial fraction of CBV with PET in the living human brain. C15O and dynamic H215O PET studies were performed in each of seven, healthy subjects to determine the CBV and arterial blood volume (Va), respectively. A two-compartment model (influx: K1, efflux: k2) that takes Va into account was applied to describe the regional time-activity curve of dynamic H215O PET. K1, k2 and Va were calculated by a non-linear least squares fitting procedure. The Va and CBV values were 0.011±0.004 ml/ml and 0.031± 0.003 ml/ml (mean±SD), respectively, for cerebral cortices. The arterial fraction of CBV was 37%. Considering the limited first-pass extraction fraction of H215O, the true arterial fraction of CBV is estimated to be about 30%. The estimated arterial fraction of CBV was quite similar to that of the systemic circulation, whereas it was greater than that (16%) widely used for the measurement of cerebral metabolic rate of oxygen (CMRO2) using PET. The venous plus capillary fraction of CBV was 63–70% which is a important factor for the measurement of CMRO2 with MRI.
The Astrophysical Journal | 2006
Nobunari Kashikawa; Makiko Yoshida; Kazuhiro Shimasaku; Masahiro Nagashima; Hideki Yahagi; Masami Ouchi; Y. Matsuda; Matthew A. Malkan; Mamoru Doi; Masanori Iye; Masaru Ajiki; Masayuki Akiyama; Hiroyasu Ando; Kentaro Aoki; Hisanori Furusawa; Tomoki Hayashino; Fumihide Iwamuro; Hiroshi Karoji; Naoto Kobayashi; Keiichi Kodaira; Tadayuki Kodama; Yutaka Komiyama; Satoshi Miyazaki; Yoshihiko Mizumoto; Kentaro Motohara; Takashi Murayama; Tohru Nagao; Kyoji Nariai; Kouji Ohta; Sadanori Okamura
We explored the clustering properties of Lyman break galaxies at z = 4 and 5 with an angular two-point correlation function on the basis of the very deep and wide Subaru Deep Field data. We confirmed the previous result that the clustering strength of LBGs depends on the UV luminosity in the sense that brighter LBGs are more strongly clustered. In addition, we found an apparent dependence of the correlation function slope on UV luminosity for LBGs at both z = 4 and 5. More luminous LBGs have a steeper correlation function. The bias parameter was found to be a scale-dependent function for bright LBGs, whereas it appears to be almost scale-independent for faint LBGs. Luminous LBGs have a higher bias at smaller angular scales, which decreases as the scale increases. To compare these observational results, we constructed numerical mock LBG catalogs based on a semianalytic model of hierarchical clustering combined with high-resolution N-body simulation, carefully mimicking the observational selection effects. The luminosity functions and the overall correlation functions for LBGs at z = 4 and 5 predicted by this mock catalog were found to be almost consistent with the observation. The observed dependence of the clustering on UV luminosity was not reproduced by the model, unless subsamples of distinct halo mass were considered. That is, LBGs belonging to more massive dark halos had steeper and larger amplitude correlation functions. With this model, we found that LBG multiplicity in massive dark halos amplifies the clustering strength at small scales, which steepens the correlation function. The hierarchical clustering model could therefore be reconciled with the observed luminosity dependence of the correlation function if there is a tight correlation between UV luminosity and halo mass. Our finding that the slope of the correlation function depends on luminosity could be an indication that massive dark halos hosted multiple bright LBGs.
Neuroreport | 1998
Laxmi N. Singh; Shuichi Higano; Shoki Takahashi; Noriko Kurihara; Susumu Furuta; Hajime Tamura; Yoshihisa Shimanuki; Shunji Mugikura; Toshikatsu Fujii; Atsushi Yamadori; Maya Sakamoto; Shogo Yamada
WE used fMRI to compare the ipsilateral activation in the sensorimotor region (SMR) during dominant and non-dominant hand motor tasks between right and left handers. In right handers, the ipsilateral activation was significantly greater during non-dominant (left) hand task than dominant (right) hand task, while in left handers, it showed no significant difference. The ipsilateral activation was most pronounced in the precentral subregion (presumably corresponding to the premotor area) during either hand task in both groups. We conclude that the different patterns of ipsilateral activation might be mainly explained by the hemispheric dominance. The skill of the hand and complexity of tasks may be related to the predominant activation of the premotor area.
American Journal of Neuroradiology | 2009
Y. Kato; Shuichi Higano; Hajime Tamura; Shunji Mugikura; A. Umetsu; Takaki Murata; Shoki Takahashi
BACKGROUND AND PURPOSE: Early accurate diagnosis of brain metastases is crucial for a patients prognosis. This study aimed to compare the conspicuity and detectability of small brain metastases between contrast-enhanced 3D fast spin-echo (sampling perfection with application-optimized contrasts by using different flip angle evolutions [SPACE]) and 3D gradient-echo (GE) T1-weighted (magnetization-prepared rapid acquisition of GE [MPRAGE]) images at 3T. MATERIALS AND METHODS: Sixty-nine consecutive patients with suspected brain metastases were evaluated prospectively by using SPACE and MPRAGE on a 3T MR imaging system. After careful evaluation by 2 experienced neuroradiologists, 92 lesions from 16 patients were selected as brain metastases. We compared the shorter diameter, contrast rate (CR), and contrast-to-noise ratio (CNR) of each lesion. Diagnostic ability was compared by using receiver operating characteristic (ROC) analysis. Ten radiologists (5 neuroradiologists and 5 residents) participated in the reading. RESULTS: The mean diameter was significantly larger by using SPACE than MPRAGE (mean, 4.5 ± 3.7 versus 4.3 ± 3.7 mm, P = .0014). The CR and CNR of SPACE (mean, 57.3 ± 47.4%, 3.0 ± 1.9, respectively) were significantly higher than those of MPRAGE (mean, 37.9 ± 41.2%, 2.6 ± 2.2; P < .0001, P = .04). The mean area under the ROC curve was significantly larger with SPACE than with MPRAGE (neuroradiologists, 0.99 versus 0.88, P = .013; residents, 0.99 versus 0.78, P = .0001). CONCLUSIONS: Lesion detectability was significantly higher on SPACE than on MPRAGE, irrespective of the experience of the reader in neuroradiology. SPACE should be a promising diagnostic technique for assessing brain metastases.
Stroke | 2002
Hajime Tamura; Jun Hatazawa; Hideto Toyoshima; Eku Shimosegawa; Toshio Okudera
Background and Purpose— Acute decreases in the MR T2*-weighted signal have been reported in experimental models of middle cerebral artery occlusion. This has been attributed to blood deoxygenation in association with an increased brain oxygen extraction fraction. The aim of this study was to detect this signal by susceptibility-weighted MR imaging in acute ischemic stroke patients. Methods— Dynamic susceptibility contrast-enhanced MR (DSC-MR) imaging was performed within 4 hours of stroke onset in 6 patients with unilateral cerebral artery occlusion (middle cerebral artery, n=5; internal carotid artery, n=1). Cerebral blood volume was estimated on a pixel-by-pixel basis. DSC-MR images taken before arrival of the contrast medium were examined visually to identify hypointense areas. Bilateral regions of interest were set in the middle cerebral artery territory for comparison of the mean signal intensity. A semilogarithmic plot of signal intensity versus cerebral blood volume for every pixel in the region of interest was also analyzed. Results— The side on which the hypointense area was seen was significantly correlated with the side of arterial occlusion. The mean signal intensity was significantly smaller on the affected side than on the contralateral side. The semilogarithmic plot of signal intensity versus cerebral blood volume indicated greater deoxyhemoglobin concentrations for the ipsilateral than for the contralateral region of interest. Conclusions— DSC-MR images allow detection of hypointensity in the affected cerebral hemisphere in acute ischemic stroke patients. Such hypointensity may indicate increased oxygen extraction fraction (misery perfusion) and may provide information valuable to patient care.
Publications of the Astronomical Society of Japan | 2003
Keiichi Kodaira; Yoshiaki Taniguchi; Nobunari Kashikawa; Norio Kaifu; Hiroyasu Ando; Hiroshi Karoji; Masaru Ajiki; Masayuki Akiyama; Kentaro Aoki; Mamoru Doi; Shinobu S. Fujita; Hisanori Furusawa; Tomoki Hayashino; Masatoshi Imanishi; Fumihide Iwamuro; Masanori Iye; Koji S. Kawabata; Naoto Kobayashi; Tadayuki Kodama; Yutaka Komiyama; George Kosugi; Y. Matsuda; Satoshi Miyazaki; Yoshihiko Mizumoto; Kentaro Motohara; Takashi Murayama; Tohru Nagao; Kyoji Nariai; Kouji Ohta; Youichi Ohyama
We performed a deep optical imaging survey using a narrow-band filter (NB921) centered at λ=9196 u A together
The Astronomical Journal | 2003
Shinobu S. Fujita; Masaru Ajiki; Yasuhiro Shioya; Tohru Nagao; Takashi Murayama; Yoshiaki Taniguchi; Sadanori Okamura; Masami Ouchi; Kazuhiro Shimasaku; Mamoru Doi; Hisanori Furusawa; Masaru Hamabe; Masahiko Kimura; Yutaka Komiyama; Masayuki Miyazaki; Satoshi Miyazaki; Fumiaki Nakata; Maki Sekiguchi; Masafumi Yagi; Naoki Yasuda; Yuichi Matsuda; Hajime Tamura; Tomoki Hayashino; Keiichi Kodaira; Hiroshi Karoji; Toru Yamada; Kouji Ohta; Masayuki Umemura
We present the results of a survey for emission-line objects based on optical intermediate-band (
European Radiology | 1998
Noriko Kurihara; Shinji Takahashi; Shuichi Higano; H. Ikeda; Shunji Mugikura; L. N. Singh; Susumu Furuta; Hajime Tamura; Tadashi Ishibashi; Shin Maruoka; Shogo Yamada
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arXiv: Astrophysics | 2002
Shinobu S. Fujita; Masaru Ajiki; Yasuhiro Shioya; Tohru Nagao; Takashi Murayama; Yoshiaki Taniguchi; Sadanori Okamura; Masami Ouchi; Kazuhiro Shimasaku; Mamoru Doi; Hisanori Furusawa; Masaru Hamabe; Masahiko Kimura; Yutaka Komiyama; Masayuki Miyazaki; Satoshi Miyazaki; Fumiaki Nakata; Maki Sekiguchi; Masafumi Yagi; Naoki Yasuda; Yuichi Matsuda; Hajime Tamura; Tomoki Hayashino; Keiichi Kodaira; Hiroshi Karoji; Toru Yamada; Kouji Ohta; Masayuki Umemura
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