Masashi Mizuguchi

The University of Tokyo, 白山, Tōkyō, Japan

Are you Masashi Mizuguchi?

Claim your profile

Publications (314)866.02 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We study the enhanced spin relaxation time of Au nanoparticles in nanopillar-shaped double-barrier junction devices with a stacked Fe/MgO/Au-nanoparticle/MgO/Fe structure. The size of Au nanoparticles located in a current path is deduced from a transmission electron micrograph and the Coulomb blockade behavior in the current-voltage characteristics of the devices. A finite tunnel magnetoresistance (TMR) is observed above a critical current and is attributable to spin accumulation in Au nanoparticles. Based on a simple model of TMR due to spin accumulation in a nanoparticle, the spin relaxation time τs is estimated from the magnitude of the critical current. The temperature and bias-voltage region where TMR appears are determined from systematic observations, showing that the appearance of TMR is not associated with the Coulomb blockade but with spin accumulation. We find that the obtained τs is anomalously extended (∼800 ns) at low temperatures and abruptly decreases above a critical temperature. Interestingly, the critical temperature strongly depends on the size of the Au nanoparticles and is much lower than the effective temperature corresponding to the discrete energy spacing. A theoretical analysis for the spin relaxation of electrons with discrete energy levels shows that not only the anomalously extended spin relaxation time, but also the strong temperature dependence of τs arise from the broadening of discrete energy levels due to coupling with phonons in the surrounding matrix. Numerical calculations using reasonable parameter values well reproduce the observed temperature and size dependence of the spin relaxation time in Au nanoparticles.
    No preview · Article · Feb 2016
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ellis-van Creveld syndrome (EvC) is a ciliopathy with cardiac anomalies, disproportionate short stature, polydactyly, dystrophic nails and oral defects. To obtain further insight into the genetics of EvC, we screened EVC/EVC2 mutations in 8 Vietnamese EvC patients. All the patients had a congenital heart defect with atypical oral and/or skeletal abnomalities. One had compound heterozygous EVC2 mutations: a novel mutation c.769G > T-p.E177X in exon 6 inherited from father and another previously reported c.2476C > T-p.R826X mutation in exon 14 inherited from mother. The EVC2 mRNA expression level was significantly lower in the patient and her parents compared to controls. Another case had a novel heterozygous EVC mutation (c.1717C > G-p.S572X) in exon 12, inherited from his father. Of note, the mother without any EVC mutation on Sanger sequencing showed a lower expression level of EVC mRNA compared with controls. SNP array analysis revealed that the patient and mother had a heterozygous 16.4 kb deletion in EVC. This patient also had a heterozygous novel variant in exon 9 of EFCAB7 (c.1171T > C-p.Y391H), inherited from his father. The atypical cardiac phenotype of this patient and the father suggested that EFCAB7 may modify the phenotype by interacting with EVC. In conclusion, we detected two novel nonsense mutations and a partial deletion of EVC/EVC2 in two Vietnamese families with EvC. Moreover, we found in one family a missense mutation of EFCAB7, a possible modifier gene in EvC and its related disorders. This article is protected by copyright. All rights reserved.
    No preview · Article · Jan 2016 · Congenital Anomalies
  • [Show abstract] [Hide abstract]
    ABSTRACT: Cosavirus is a recently established genus in the family Picornaviridae. The present study investigated the prevalence and genetic diversity of cosaviruses in stool samples collected from piglets and pigs with and without diarrhea in Thailand and Japan. It was observed that the cosavirus-positive rate in Thailand was higher than in Japan (55.4 % vs. 18.9 %). Phylogenetic analysis of a portion of the 5’ untranslated region showed that porcine cosavirus strains clustered together in the same branch with members of the species Cosavirus A. These strains showed 97.0 to 100 % nucleotide sequence identity to each other. The virus concentration of cosavirus was very low compared with that detected in a infant with diarrhea. These results demonstrated that cosaviruses were circulating in the swine populations of both countries during the study term; however, it remains unclear whether the virus causes diarrhea in piglets and pigs.
    No preview · Article · Oct 2015 · Archives of Virology
  • [Show abstract] [Hide abstract]
    ABSTRACT: Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is the most common subtype of infectious pediatric encephalopathy in Japan. It is sometimes difficult to make an early diagnosis of AESD; excitotoxicity is postulated to be the pathogenesis based on elevated glutamine (Gln) and glutamate (Glu) complex (Glx = Glu + Gln) observed on MR spectroscopy. It is uncertain whether Gln or Glu contributes to the elevated Glx, or whether MR spectroscopy is useful for an early diagnosis. Five Japanese patients with AESD (three boys and two girls, 1 year of age) were enrolled in this study. MR spectroscopy was acquired from the frontal white matter (repetition time (TR) of 5000 ms, echo time (TE) of 30 ms) with a 1.5- or 3.0-T scanner. MR spectroscopy was performed four times for two patients, three times for one patient, and two times for two patients. Quantification of Glu and Gln was performed using LCModel. Glu was elevated in three of four studies on days 1-4 and became normal or low afterward. Gln was normal in three studies on days 1-2, elevated in all seven studies on days 4-12, and became normal or low afterward. These findings suggest that MR spectroscopy may be useful for an early diagnosis. Acute Glu elevation changes to subacute Gln elevation, suggesting that a disrupted Glu-Gln cycle may play an important role.
    No preview · Article · Aug 2015 · Neuroradiology
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) at onset manifests an early seizure (ES) usually lasting more than 30min. Following ES, some patients exhibit almost clear consciousness with no neurological symptoms, and no MRI abnormality for a few days, which may lead to an initial misdiagnosis of prolonged febrile seizures (PFS). To allow an early diagnosis of AESD, we retrospectively analyzed clinical manifestations, laboratory data, and radiologic and EEG findings in patients with AESD (n=62) having ES of over 30min, and ones with PFS (n=54), using logistic regression analyses. Multivariate logistic regression analysis revealed that an age below 1.5years and a Glasgow Coma Scale score of 14 or less than 14 (Japan Coma Scale score of 1 or higher) were high risk factors of developing AESD. We proposed an AESD prediction score system consisting of consciousness level, age, duration of convulsions, enforcement of mechanical intubation, and aspartate aminotransferase, blood glucose and creatinine levels (full score: 9), the mean scores in AESD and PFS being 5.9 and 1.8, which were significantly different (p<0.001). We herein propose a scoring system for differentiating patients with AESD and PFS around the time of ES (score of 4 or more than 4 suggesting AESD), which may contribute to early therapeutic intervention and an improved neurologic outcome. Copyright © 2015 Elsevier B.V. All rights reserved.
    Full-text · Article · Aug 2015 · Journal of the neurological sciences
  • [Show abstract] [Hide abstract]
    ABSTRACT: Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is a childhood encephalopathy following severe febrile seizures. The pathogenesis of AESD is considered to be fever-induced seizure susceptibility and excitotoxicity, which may be caused by sodium channel dysfunction in some cases. Here we studied whether mutations in genes encoding sodium channels, SCN1A and SCN2A, predispose children to AESD. We recruited 92 AESD patients in a nationwide survey of acute encephalopathy in Japan from 2008 to 2011. We collected their genomic DNA samples, and sequenced the entire coding region of SCN1A and SCN2A. Five out of 92 patients (5.4%) had missense mutations either in SCN1A or SCN2A. After a preceding infection with fever, all the patients showed status epilepticus at the onset. Hemiconvulsion-hemiplegia was recognized in three patients during the acute/subacute phase. One patient had taken theophylline for the treatment of bronchial asthma just before the onset of AESD. Familial history was not remarkable except one patient with a SCN1A mutation (G1647S) whose mother had a similar episode of AESD in her childhood. A different substitution (G1674R) at the same amino acid position, as well as two other SCN1A mutations found in this study, had previously been reported in Dravet syndrome. Another SCN1A mutation (R1575C) had been detected in other types of acute encephahlitis/encephalopathy. One patient had SCN2A mutation, F328V, which had previously been reported in Dravet syndrome. Another SCN2A mutation, I172V, was novel. None of the patients were diagnosed with Dravet syndrome or genetic (generalized) epilepsy with febrile seizure plus in the following-up period. Mutations in SCN1A and SCN2A are a predisposing factor of AESD. Altered channel activity caused by these mutations may provoke seizures and excitotoxic brain damage. Copyright © 2015 Elsevier B.V. All rights reserved.
    No preview · Article · Aug 2015 · Epilepsy research
  • M. Mizuguchi · M. Inoue · S. Mizukami · K. Takanashi
    [Show abstract] [Hide abstract]
    ABSTRACT: L10 type MnGa alloy is attracting attention as materials to be applied to spintronic devices since they generally show large magnetic anisotropy, small saturation magnetization, and small Gilbert damping constant. It is known that an L10 type MnGa alloy thin film keeps large magnetic anisot-ropy with the increase of the Mn-composition even though saturation magnetization decreases[1]. Thus, it is interesting to investigate various magnetic properties of this alloy-system. On the other hand, 'spin-caloritronics', which deals with a relationship between spin current and heat current, is getting an attracting research field[2]. Previously, we studied a thermomagnetic phenomenon, that is, anomalous Nernst effect (ANE), of L10 type FePt alloy thin films, and evaluated anomalous Nernst coefficient and anomalous Nernst angle of the FePt thin film[3]. Besides, a new-type of thermopile device using ANE was proposed to show a potential of ANE-based thermoelectric applications[4]. In this paper, ANE of epitaxial Mnx-Ga1-x thin films with varied Mn-compositions (x) within the L10 composition range was systematically studied to explore their thermomagnetic characteristics. Moreover, anomalous Hall effects (AHE) of the films were investigated to understand the correlation of the two effects in L1 type Mn-Ga thin films.
    No preview · Article · Jul 2015
  • K. Takanashi · M. Mizuguchi · T. Kojima · T. Tashiro
    [Show abstract] [Hide abstract]
    ABSTRACT: L10-FeNi, showing uniaxial magnetic anisotropy (Ku) of 1.3×107 erg/cm3 in a bulk sample[1], is promising as a 'rare metal-free' high Ku material. It is known that iron meteorites contain the L10-FeNi phase, what is called 'tetrataenite', which reveals unique magnetic properties different from usual Fe-Ni alloys[2]. However, the artificial fabrication of L10-FeNi is difficult because the order-disorder transformation temperature is low (∼320C), and below this temperature the atomic diffusion is extremely slow. In this study, we have tried to fabricate L10-FeNi thin films with high Ku by two methods: molecular beam epitaxy (MBE) and sputtering.
    No preview · Article · Jul 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: Information about viral acute respiratory infections (ARIs) is essential for prevention, diagnosis and treatment, but it is limited in tropical developing countries. This study described the clinical and epidemiological characteristics of ARIs in children hospitalized in Vietnam. Nasopharyngeal samples were collected from children with ARIs at Ho Chi Minh City Children's Hospital 2 between April 2010 and May 2011 in order to detect respiratory viruses by polymerase chain reaction. Viruses were found in 64% of 1082 patients, with 12% being co-infections. The leading detected viruses were human rhinovirus (HRV; 30%), respiratory syncytial virus (RSV; 23·8%), and human bocavirus (HBoV; 7·2%). HRV was detected all year round, while RSV epidemics occurred mainly in the rainy season. Influenza A (FluA) was found in both seasons. The other viruses were predominant in the dry season. HRV was identified in children of all age groups. RSV, parainfluenza virus (PIV) 1, PIV3 and HBoV, and FluA were detected predominantly in children aged <6 months, 6–12 months, 12–24 months, and >24 months, respectively. Significant associations were found between PIV1 with croup ( P < 0·005) and RSV with bronchiolitis ( P < 0·005). HBoV and HRV were associated with hypoxia ( P < 0·05) and RSV with retraction ( P < 0·05). HRV, RSV, and HBoV were detected most frequently and they may increase the severity of ARIs in children.
    No preview · Article · Jul 2015 · Epidemiology and Infection
  • [Show abstract] [Hide abstract]
    ABSTRACT: Material dependence of the anomalous Nernst effect (ANE) in perpendicularly magnetized ordered-alloy thin films is systematically investigated. The ANE was found to have a tendency to increase simply as uniaxial magnetic anisotropy increased at room temperature. The ANE increases as temperature increases from 10 to 300 K for all the materials. However, the signs of the ANE in Fe-based ordered-alloys (L10-FePt and L10-FePd) and in a Co/Ni multilayer are opposite to those in Mn-based ordered-alloys (L10-MnGa and D022-Mn2Ga). Ordered-alloys with larger uniaxial magnetic anisotropies reveal larger ANE and might be desirable for thermoelectric applications.
    No preview · Article · Jul 2015 · Applied Physics Letters
  • [Show abstract] [Hide abstract]
    ABSTRACT: Molecular epidemiology and clinical impact of human rhinovirus (HRV) are not well documented in tropical regions. This study compared the clinical characteristics of HRV to other common viral infections and investigated the molecular epidemiology of HRV in hospitalized children with acute respiratory infections (ARIs) in Vietnam. From April 2010 to May 2011, 1082 nasopharyngeal swabs were screened for respiratory viruses by PCR. VP4/VP2 sequences of HRV were further characterized. HRV was the most commonly detected virus (30%), in which 70% were diagnosed as either pneumonia or bronchiolitis. Children with single HRV infections presented with significantly higher rate of hypoxia than those infected with respiratory syncytial virus or parainfluenza virus (PIV)-3 (12·4% vs. 3·8% and 0%, respectively, P < 0·05), higher rate of chest retraction than PIV-1 (57·3% vs. 34·5%, P = 0·028), higher rate of wheezing than influenza A (63·2% vs. 42·3%, P = 0·038). HRV-C did not differ to HRV-A clinically. The genetic diversity and changes of types over time were observed and may explain the year-round circulation of HRV. One novel HRV-A type was discovered which circulated locally for several years. In conclusion, HRV showed high genetic diversity and was associated with significant morbidity and severe ARIs in hospitalized children.
    No preview · Article · Jun 2015 · Epidemiology and Infection
  • Source
    K Mibu · T Kojima · M Mizuguchi · K Takanashi
    [Show abstract] [Hide abstract]
    ABSTRACT: The local structure and magnetism of FeNi alloy films prepared by alternate deposition of Fe and Ni monatomic layers, where perpendicular magnetic anisotropy has been observed, were investigated through 57Fe nuclear probes using Mössbauer spectroscopy. It was confirmed that the films are composed of L10-type ordered FeNi phase and A1-type disordered FeNi phase. For the films grown at 40-70 °C, which have no perpendicular anisotropy, the A1-disordered phase is dominant, whereas for the films grown at 100-190 °C, which have a stronger perpendicular anisotropy, the relative amount of the L10-ordered phase reaches 40% or more. It was clearly shown that the magnetic anisotropy of these films is strongly correlated with the local environments of Fe in the films. The results imply that if a further increase in the ratio of the L10-ordered phase is successfully achieved, one would obtain films with a stronger magnetic anisotropy applicable to perpendicular magnetic recording.
    Full-text · Article · May 2015 · Journal of Physics D Applied Physics
  • [Show abstract] [Hide abstract]
    ABSTRACT: FeNi films were fabricated by sputtering and rapid thermal annealing on thermally amorphous substrates to realize the formation of an L10-FeNi phase by a simple method. Structural and magnetic properties of FeNi films were investigated by varying the annealing temperature. L10-FeNi superlattice peaks were not observed in X-ray diffraction patterns, indicating no formation of L10-ordered phase, however, the surface structure systematically changed with the annealing temperature. Magnetization curves also revealed a drastic change depending on the annealing temperature, which indicates the close relation between the morphology and magnetic properties of FeNi films fabricated on amorphous substrates.
    No preview · Article · Apr 2015 · Journal of Applied Physics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated comparative experiments for spin injection into semiconductor in an ordered L10-FePt/MgO/n-GaAs hybrid structure using electrical and optical detection methods. Spatial-resolved Kerr rotation microscope image clearly demonstrates accumulation of perpendicularly oriented spins in an n-GaAs channel at zero magnetic field. On the other hand, electrical three-terminal Hanle measurement shows shorter spin lifetime than that of the optical measurement. It suggests that the spin lifetime obtained from three-terminal Hanle method originates from spins at the MgO/GaAs interface but not in the bulk GaAs channel.
    Full-text · Article · Apr 2015 · Journal of Physics D Applied Physics
  • [Show abstract] [Hide abstract]
    ABSTRACT: Acute gastroenteritis continues to be a major public health problem worldwide. A wide variety of viruses associated with diarrhea disease is being reported continually. This study investigated the epidemiological situation of viruses that cause diarrhea in Japanese pediatric patients. This study enrolled a total of 2,381 fecal specimens collected between 2009 and 2013 from Japanese children with acute gastroenteritis. There is currently a 70.4% prevalence of viruses causing diarrhea among these Japanese pediatric outpatients. Norovirus was detected in 39.3% of the patients, whereas the prevalence of rotavirus, human parechovirus, enterovirus, adenovirus, sapovirus, astrovirus, and Aichi virus was 20.1, 6.6, 6.1, 5.6, 4.8, 2.3, and 0.1%, respectively. Co-infections were observed at the prevalence rates of 13.4 and 0.5% for double infections and triple infections, respectively. Mixed viral infections were found commonly in Japanese outpatients, and the norovirus seemed to play a major role in co-infections. Viral diarrhea cases were detected mostly in children younger than 3 years of age. The norovirus and rotavirus can be detected throughout the year, with a peak during the cold and dry seasons, whereas other common viruses are found during no specific season. Surveillance data revealed that a wide variety of viruses has caused diarrhea to circulate currently in Japanese pediatric outpatients, with very high detection rates; and norovirus and rotavirus are the most important pathogens. The data obtained from this study are valuable for compiling the overall picture of several viruses that causes diarrhea and associates with acute gastroenteritis in the Japanese pediatric population. J. Med. Virol. 2015. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
    No preview · Article · Apr 2015 · Journal of Medical Virology
  • A Sato · Y Takamatsu · Y Kasai · S Kobayashi · T Hino · K Ikeda · M Mizuguchi

    No preview · Article · Apr 2015 · Nihon shinkei seishin yakurigaku zasshi = Japanese journal of psychopharmacology
  • [Show abstract] [Hide abstract]
    ABSTRACT: The symptoms of attention-deficit/hyperactivity disorder (ADHD) are characterized by inattention and hyperactivity-impulsivity. It is a common childhood neurodevelopmental disorder that often persists into adulthood. Improvements in ADHD symptoms using psychostimulants have been recognized as a paradoxical calming effect. The psychostimulant methylphenidate (MPH) is currently used as the first-line medication for the management of ADHD. Recent studies have drawn attention to altered dopamine-mediated neurotransmission in ADHD, particularly reuptake by the dopamine transporter (DAT). This hypothesis is supported by the observation that DAT knockout mice exhibit marked hyperactivity that is responsive to acute MPH treatment. However, other behaviors relevant to ADHD have not been fully clarified. In the present study, we observed learning impairment in shuttle-box avoidance behavior together with hyperactivity in a novel environment in DAT knockout mice. Methylphenidate normalized these behaviors and enhanced escape activity in the tail suspension test. Interestingly, the effective dose of MPH increased extracellular dopamine in the prefrontal cortex but not striatum, suggesting an important role for changes in prefrontal dopamine in ADHD. Research that uses rodent models such as DAT knockout mice may be useful for elucidating the pathophysiology of ADHD.
    No preview · Article · Mar 2015 · Current Molecular Medicine
  • [Show abstract] [Hide abstract]
    ABSTRACT: Acute encephalopathy is classified into multiple syndromes, such as acute encephalopathy with biphasic seizures and late reduced diffusion (AESD), clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) and acute necrotizing encephalopathy (ANE), characterized radiologically by lesions in the cerebral subcortical white matter, splenium of the corpus callosum and bilateral thalami, respectively. We described a previously healthy 8-year-old boy who had febrile and biphasic seizures, and encephalopathy. MRI showed abnormal signal intensity in the corpus callosum on day 2 and cerebral subcortical white matter and bilateral thalamic lesions on day 8. This is the first case of acute encephalopathy in which callosal, subcortical and thalamic lesions co-existed. The clinical course of this case was typical for AESD, atypical for MERS, and different from that of ANE.
    No preview · Article · Mar 2015 · Neurology Asia
  • [Show abstract] [Hide abstract]
    ABSTRACT: Genetic variability makes influenza virus to escape the immunity and causes yearly epidemics. Monitoring those changes is necessary for vaccine selection. In addition, H3N2 viruses were considered to be seeded from Southeast Asia before spreading globally. This study described the molecular epidemiology of influenza A during the post-pandemic season 2010-2011 in Vietnam. Nasopharyngeal samples were collected from children with respiratory infections at Children's Hospital 2, Ho Chi Minh City. The HA, NA, M genes were amplified, sequenced and analyzed. Thirty-five of 1,082 (3.2%) patients were positive for influenza A, including 14 pandemic H1N1 2009 (H1N1pdm09) and 21 H3N2 infections. H3N2 was dominant in the rainy season (May-October 2010) while H1N1pdm09 was dominant in the dry season (November 2010-April 2011). Phylogenetic analysis showed that Vietnamese H1N1pdm09 sequences in 2010-2011 formed the distinct cluster, with other contemporary Asian and 2012-American sequences, suggesting a possible common ancestor. All were oseltamivir-sensitive except two strains carrying S247N and D199N in NA which reduced the neuraminidase inhibitor susceptibility. The Vietnamese H3N2 viruses in mid-2010 belonged to the emerging subclade Perth10/2010, which then spread worldwide in 2011. The Vietnamese influenza viruses were well matched with the Southern Hemisphere vaccine formulation. Mutations at antigenic sites were also identified in these viruses. Surveillance of influenza viruses in tropical countries is important not only for development of their prevention and control strategies but also for earlier identification of the newly emerged strains that may be selected for future vaccine. J. Med. Virol. 00: 1-9, 2015. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
    No preview · Article · Feb 2015 · Journal of Medical Virology
  • Source

    Full-text · Dataset · Dec 2014

Publication Stats

5k Citations
866.02 Total Impact Points


  • 1993-2016
    • The University of Tokyo
      • • Department of International Health
      • • Department of Pediatrics
      • • Department of Applied Chemistry
      白山, Tōkyō, Japan
  • 2015
    • Japan Science and Technology Agency (JST)
      Edo, Tokyo, Japan
  • 2010-2015
    • Tohoku University
      • Institute for Materials Research
      Miyagi, Japan
    • Chiang Mai University
      • Department of Microbiology
      Amphoe Muang Chiang Mai, Chiang Mai, Thailand
  • 2009-2010
    • Aino University
      Takatuki, Ōsaka, Japan
    • Tampa General Hospital
      Tampa, Florida, United States
  • 1996-2008
    • Jichi Medical University
      • Department of Pediatrics
      Totigi, Tochigi, Japan
  • 2004
    • National Institute of Advanced Industrial Science and Technology
      Tsukuba, Ibaraki, Japan
  • 1995-2000
    • National Center of Neurology and Psychiatry
      • Department of Mental Retardation and Birth Defect Research
      Кодаиры, Tōkyō, Japan
  • 1999
    • Niigata University
      • Brain Research Institute
      Niahi-niigata, Niigata, Japan
    • imec Belgium
      • Smart Systems and Energy Technology
      Louvain, Flemish, Belgium
  • 1991-1992
    • University of British Columbia - Vancouver
      • Division of Neurology
      Vancouver, British Columbia, Canada