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Biomedical subjects

H Takagi

Publications and source records attributed to H Takagi.

At least 37 records · Page 2Linked to original sources
PubMed2005

Nodal quasiparticles and antinodal charge ordering in Ca2-xNaxCuO2Cl2.

Understanding the role of competing states in the cuprates is essential for developing a theory for high-temperature superconductivity. We report angle-resolved photoemission spectroscopy experiments which probe the 4a0 x 4a0 charge-ordered state discovered by scanning tunneling microscopy in the lightly doped cuprate superconductor Ca2-xNaxCuO2Cl2. Our measurements reveal a marked dichotomy between the real- and momentum-space probes, for which charge ordering is emphasized in the tunneling measurements and photoemission is most sensitive to excitations near the node of the d-wave superconducting gap. These results emphasize the importance of momentum anisotropy in determining the complex electronic properties of the cuprates and places strong constraints on theoretical models of the charge-ordered state.

Journal Article↗
PubMed2005

Texture in the superconducting order parameter of CeCoIn5 revealed by nuclear magnetic resonance.

We present a 115In NMR study of the quasi-two-dimensional heavy-fermion superconductor CeCoIn5 believed to host a Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state. In the vicinity of the upper critical field and with a magnetic field applied parallel to the ab plane, the NMR spectrum exhibits a dramatic change below T*(H) which well coincides with the position of reported anomalies in specific heat and ultrasound velocity. We argue that our results provide the first microscopic evidence for the occurrence of a spatially modulated superconducting order parameter expected in a FFLO state. The NMR spectrum also implies an anomalous electronic structure of vortex cores.

Journal Article↗
PubMed2005

Prevalence of atopic dermatitis in Japanese elementary schoolchildren.

BACKGROUND: Although there have been several reports on the prevalence of atopic dermatitis (AD) in Japanese schoolchildren based on questionnaires, there has been no nation-wide study of the frequency of this condition diagnosed by dermatologists in regular health check-ups of schoolchildren. OBJECTIVES: The objective of this work was to evaluate precisely the prevalence of AD in elementary schoolchildren in Japan based on regular health check-ups by dermatologists. METHODS: In 2001/2, elementary schoolchildren: first graders (age 6-7 years) and sixth graders (age 11-12 years) were examined by dermatologists in eight prefectures of Japan (Hokkaido, Iwate, Tokyo, Gifu, Osaka, Hiroshima, Kochi and Fukuoka). In each prefecture, public elementary schools were randomly selected from urban and rural districts. We planned to examine about 700 schoolchildren in each of urban first, urban sixth, rural first and rural sixth grades from the eight areas, a total of 22 400 children (700 x 4 x 8). AD was diagnosed by the dermatologists based on the Japanese Dermatological Association criteria for the disease. RESULTS: The point prevalence of AD was 11.2% overall (2664 of 23 719) ranging from 7.4% (Iwate) to 15.0% (Fukuoka) in the eight areas. Seventy-four per cent, 24%, 1.6% and 0.3% of those afflicted were in the mild, moderate, severe and very severe groups, respectively. Overall, the prevalence of first graders was slightly higher than that of sixth graders (11.8% vs. 10.5%, P < 0.01). There was no apparent difference in prevalence between urban and rural districts, or between boys and girls. CONCLUSIONS: The prevalence of AD in Japanese elementary schoolchildren was about 10%, three-quarters of those being mildly affected. This is the first nation-wide study made of Japanese elementary schoolchildren examined by dermatologists to evaluate the frequency of AD.

Child↗
PubMed2005

[Primary neurogenous sarcoma of the lung; report of a case].

We report a case of a 27-year-old woman with primary neurogenous sarcoma of the lung. She had no symptoms but an abnormal shadow of the right lower lung field on the chest X-ray. Chest computed tomography (CT) revealed a well defined round mass, 20 mm in maximum diameter, at the right S9. Pathological study of the specimen obtained by CT-guided percutaneous needle biopsy showed undefferentiated carcinoma. Positron emission tomography (PET) disclosed intensely increased uptake of fluoro-2-deoxy-D-glucose (FDG) at the lung lesion without other abnormal uptakes. The patient underwent right lower lobectomy of the lung and mediastinal lymph nodes dissection. Results from immunohistological study yielded a definitive diagnosis of neurogenous sarcoma. Postoperative course was uneventful, and there has been no evidence of recurrence and metastasis for more than a year after the surgery. Reported cases of primary neurogenous sarcoma of the lung are reviewed.

Adult↗
PubMed2005

Looped reconstruction of the internal and external iliac arteries in repair of abdominal aortic or iliac artery aneurysm with a bifurcated graft.

AIM: The aim of our study is to describe an original technique of distal anastomosis of a bifurcated graft, coining looped reconstruction, and our preliminary clinical experience. METHODS: This technique has been applied in 16 of 24 distal anastomoses of 12 patients with abdominal aortic aneurysm (AAA) and/or iliac artery aneurysm. Both the internal (IIA) and external iliac arteries (EIA) are transected and anastomosed with end-to-end fashion to reconstruct their continuity, and the limb of a bifurcated graft is anastomosed to the EIA with end-to-side fashion. RESULTS: Operative and in-hospital death, ischemic colitis, or ischemia of the lower extremities including blue toe syndrome has never occurred. All the 28 reconstructed IIAs and EIAs have been patent in 11 patients who could undergo early postoperative computed tomography scans with contrast medium. CONCLUSIONS: The looped reconstruction of the IIA and the EIA in repair of an AAA and/or an iliac artery aneurysm with a bifurcated graft is an anatomically easy and technically simple method.

Aged↗
PubMed2005

Stent placement for severe stenosis in the deep femoral artery with the occluded superficial femoral and popliteal arteries.

In both superficial and deep femoral artery involvement, where angioplasty of the former is not suitable or feasible, angioplasty of the latter seems to be the method of choice and is a less invasive and efficient treatment particularly for limb threatening ischemia, an appropriate obstruction morphology provided. The authors describe a case of a 73-year-old man, with a rest pain of the foot and intermittent cyanosis of the toe, who underwent stent placement with transluminal angioplasty for severe stenosis in the deep femoral artery with the occluded superficial femoral and popliteal artery. The patient's ankle brachial index was remarkably increased from 0.25 to 0.61, and the preoperative symptoms were improved.

Aged↗
PubMed2005

Preoperative measurement of the intrathrombotic pressure of a thrombosed popliteal artery aneurysm for decision of surgical indication.

To evaluate the risk of rupture of a 77 mm thrombosed popliteal artery aneurysm (PAA) in an 82-year-old woman, the aneurysm was percutaneously punctured and the intrathrombotic pressure (ITP) was measured preoperatively. The percentage of the mean ITP to the mean brachial artery pressure was 80%. The aneurysm was judged to have the risk of rupture, and replacement with a prosthetic graft was performed. The percentages of the mean ITP to the mean radial artery pressure and to the mean femoral artery pressure measured intraoperatively were 83% and 71%, respectively, which approximated to the percentage measured preoperatively. PAA may have the risk of rupture even though thrombosed, and preoperative measurement of the ITP might be useful to decide surgical indication.

Aged, 80 and over↗
PubMed2004

Missing quasiparticles and the chemical potential puzzle in the doping evolution of the cuprate superconductors.

The evolution of Ca2-xNaxCuO2Cl2 from Mott insulator to superconductor was studied using angle-resolved photoemission spectroscopy. By measuring both the excitations near the Fermi energy as well as nonbonding states, we tracked the doping dependence of the electronic structure and the chemical potential with unprecedented precision. Our work reveals failures in the standard weakly interacting quasiparticle scenario, including the broad line shapes of the insulator and the apparently paradoxical shift of the chemical potential within the Mott gap. To resolve this, we develop a model where the quasiparticle is vanishingly small at half filling and grows upon doping, allowing us to unify properties such as the dispersion and Fermi wave vector with the chemical potential.

Journal Article↗
PubMed2004

Dispersive excitations in the high-temperature superconductor La2-xSrxCuO4.

High-resolution neutron scattering experiments on optimally doped La2-xSrxCuO4 (x=0.16) reveal that the magnetic excitations are dispersive. The dispersion is the same as in YBa2Cu3O6.85, and is quantitatively related to that observed with charge sensitive probes. The associated velocity in La2-xSrxCuO4 is only weakly dependent on doping with a value close to the spin-wave velocity of the insulating (x=0) parent compound. In contrast with the insulator, the excitations broaden rapidly with increasing energy, forming a continuum at higher energy and bear a remarkable resemblance to multiparticle excitations observed in 1D S=1/2 antiferromagnets. The magnetic correlations are 2D, and so rule out the simplest scenarios where the copper oxide planes are subdivided into weakly interacting 1D magnets.

Journal Article↗
PubMed2004

Imaging nanoscale electronic inhomogeneity in the lightly doped Mott insulator Ca(2-x)NaxCuO2Cl2.

The spatial variation of electronic states was imaged in the lightly doped Mott insulator Ca(2-x)NaxCuO2Cl2 using scanning tunneling microscopy or spectroscopy. We observed nanoscale domains with a high local density of states within an insulating background. The observed domains have a characteristic length scale of 2 nm (approximately 4-5a, a: lattice constant) with preferred orientations along the tetragonal [100] direction. We argue that such spatially inhomogeneous electronic states are inherent to slightly doped Mott insulators and play an important role for the insulator to metal transition.

Journal Article↗
PubMed2004

A 'checkerboard' electronic crystal state in lightly hole-doped Ca2-xNaxCuO2Cl2.

The phase diagram of hole-doped copper oxides shows four different electronic phases existing at zero temperature. Familiar among these are the Mott insulator, high-transition-temperature superconductor and metallic phases. A fourth phase, of unknown identity, occurs at light doping along the zero-temperature bound of the 'pseudogap' regime. This regime is rich in peculiar electronic phenomena, prompting numerous proposals that it contains some form of hidden electronic order. Here we present low-temperature electronic structure imaging studies of a lightly hole-doped copper oxide: Ca2-xNaxCuO2Cl2. Tunnelling spectroscopy (at energies |E| > 100 meV) reveals electron extraction probabilities greatly exceeding those for injection, as anticipated for a doped Mott insulator. However, for |E| < 100 meV, the spectrum exhibits a V-shaped energy gap centred on E = 0. States within this gap undergo intense spatial modulations, with the spatial correlations of a four CuO2-unit-cell square 'checkerboard', independent of energy. Intricate atomic-scale electronic structure variations also exist within the checkerboard. These data are consistent with an unanticipated crystalline electronic state, possibly the hidden electronic order, existing in the zero-temperature pseudogap regime of Ca2-xNaxCuO2Cl2.

Journal Article↗
PubMed2004

Spinons in the strongly correlated copper oxide chains in SrCuO2.

We have investigated the spin dynamics in the strongly correlated chain copper oxide SrCuO2 for energies up to greater, similar 0.6 eV using inelastic neutron scattering. We observe a gapless continuum of magnetic excitations, which is well described by the "Müller ansatz" for the two-spinon continuum in the S=1/2 antiferromagnetic Heisenberg spin chain. The lower boundary of the continuum extends up to approximately 360 meV, which corresponds to an exchange constant J=226(12) meV.

Journal Article↗
PubMed2004

An unusual isotope effect in a high-transition-temperature superconductor.

In conventional superconductors, the electron pairing that allows superconductivity is caused by exchange of virtual phonons, which are quanta of lattice vibration. For high-transition-temperature (high-T(c)) superconductors, it is far from clear that phonons are involved in the pairing at all. For example, the negligible change in T(c) of optimally doped Bi2Sr2CaCu2O8+delta (Bi2212; ref. 1) upon oxygen isotope substitution (16O --> 18O leads to T(c) decreasing from 92 to 91 K) has often been taken to mean that phonons play an insignificant role in this material. Here we provide a detailed comparison of the electron dynamics of Bi2212 samples containing different oxygen isotopes, using angle-resolved photoemission spectroscopy. Our data show definite and strong isotope effects. Surprisingly, the effects mainly appear in broad high-energy humps, commonly referred to as 'incoherent peaks'. As a function of temperature and electron momentum, the magnitude of the isotope effect closely correlates with the superconducting gap--that is, the pair binding energy. We suggest that these results can be explained in a dynamic spin-Peierls picture, where the singlet pairing of electrons and the electron-lattice coupling mutually enhance each other.

Journal Article↗
PubMed2004

Clinical success of Neoral absorption profile.

We investigated the clinical benefits of cyclosporine microemulsion preconcentrate (CyA-MEPC; Neoral) in 16 de novo renal transplant recipients. The dose of CyA-MEPC was managed from AUC(0-4h), with serial target values of AUC(0-4h) at 5000-->4000-->3000-->2000 ng. hr/mL. The frequency of acute rejection episodes was 25%. The decreased renal function reached a low value of 12.5%, and creatinine was stable. Therefore, setting the target AUC(0-4h) value in the early phase at 5000 ng.hr/mL is an effective strategy to prevent acute rejection episodes. The single dose of Neoral given immediately after the renal transplant was 6 mg/kg (making a daily dose of 12 mg/kg). Thereafter, the dose-normalized AUC(0-4h) was set at a constant value to 4 weeks posttransplant. At week 4, the single dose was decreased to 4 mg/kg twice daily (a daily dose of 8 mg/kg). From these studies a daily dose of 12 mg/kg is suggested to be the appropriate amount for the first dose immediately after transplant. The renal biopsy performed at 6 months posttransplant showed neither cyclosporine-induced renal impairments, nor findings of chronic rejection, suggesting that 2000 ng.hr/mL is an appropriate target AUC(0-4h) value in the maintenance phase. These results suggest that it is possible to set the target value of C2 monitoring in the maintenance phase to a value slightly lower than that proposed from other studies.

Adult↗
PubMed2004

Sequential analysis of testicular lesions and serum hormone levels in rats treated with a Psoralea corylifolia extract.

In order to clarify pathogenetic targets for the testicular toxicity of a extract of Psoralea corylifolia (P. corylifolia), F344 rats were fed diet containing 3% P. corylifolia extract for up to 12 weeks and subjected to hormone assays and histopathological examination on the testis and epididymis at weeks 1, 2, 4, 8 and 12 (Exp 1). Similar analyses were performed on 1, 3, 7 and 14 days after a single gavage administration of the P. corylifolia extract at a dose of 10 g/kg b.w. (Exp 2). In Exp 1, increase in the numbers of degenerated and exfoliated germ cells and loss of elongated spermatids beyond steps 7 or 8 were initially observed in the seminiferous tubules at week 1, followed by more pronounced degeneration of germ cells with depletion of post-meiotic populations from week 2. The tubular degeneration was associated with Leydig cell atrophy and persistent reduction of serum testosterone and FSH levels throughout the treatment period and a slight reduction of serum LH in later stages. In Exp 2, reduction of serum testosterone and FSH levels preceded degeneration of germ cells in stage VII and VIII tubules at 3 and 7 days after the administration. The results suggest that rapid androgen deprivation reflecting direct interference with Leydig cell function and simultaneous disturbance of the pituitary-testicular axis play pivotal roles in P. corylifolia extract-induced germ cell injury in seminiferous tubules.

Animals↗
PubMed2003

Expression of a novel yeast gene that detoxifies the proline analog azetidine-2-carboxylate confers resistance during tobacco seed germination, callus and shoot formation.

A novel acetyltransferase (Mpr1) found in Saccharomyces cerevisiae (strain Sigma1278b) has been shown to specifically detoxify a proline analog, l-azetidine-2-carboxylic acid (A2C) in yeast cells [M. Shichiri et al. (2001) J Biol Chem 276: 41998-42002]. We investigated whether the yeast MPR1 gene would function similarly in a plant system and if its expression could confer resistance to proline analogs. The MPR1 gene coding sequence driven by two different constitutive promoters, with or without the 5'- and 3'-noncoding sequence from the MPR1 gene adjacent to the conventional NOS terminator, was transformed into tobacco ( Nicotiana tabacum L. cv. Xanthi) plants via Agrobacterium tumefaciens infection. The presence of the yeast 5'- and 3'-noncoding sequences appeared to increase the likelihood of MPR1 gene expression in the transgenic plants. The kanamycin-selected transgenic plants with a high level of Mpr1 activity grew normally, and their progeny expressed acetyltransferase activity that could utilize A2C, azetidine-3-carboxylic acid and 4-hydroxy- l-proline as substrates. Resistance to A2C, but not to the other two analogs, was exhibited during leaf tissue culture and seed germination. The A2C toxicity to the wild-type plants was reversed by the addition of proline, suggesting that A2C acts as a proline analog. Our studies confirm that MPR1 can function in a similar fashion in tobacco as in yeast to detoxify the toxic proline analog A2C, so it could potentially be used as a new selectable marker for plant transformation. However, our attempts to utilize MPR1 as an efficient selectable marker gene for the A. tumefaciens-mediated transformation of tobacco were unsuccessful.

Azetidinecarboxylic Acid↗