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Biomedical subjects

Y Maeno

Publications and source records attributed to Y Maeno.

At least 37 records · Page 2Linked to original sources
PubMed2004

de Haas-van Alphen effect across the metamagnetic transition in Sr3Ru2O7.

We report a study of the de Haas-van Alphen (dHvA) effect on the itinerant metamagnet Sr3Ru2O7. Extremely high sample purity allows the observation of dHvA oscillations both above and below the metamagnetic transition field of 7.9 T. The quasiparticle masses are fairly large away from the transition, and are enhanced by up to an extra factor of 3 as the transition is approached, but the Fermi surface topography change is quite small. The results are qualitatively consistent with a field-induced Stoner transition in which the mass enhancement is the result of critical fluctuations.

Journal Article↗
PubMed2004

Multiple first-order metamagnetic transitions and quantum oscillations in ultrapure Sr3Ru2O7.

We present measurements on ultraclean single crystals of the bilayered ruthenate metal Sr3Ru2O7, which has a magnetic-field-tuned quantum critical point. Quantum oscillations of differing frequencies can be seen in the resistivity both below and above its metamagnetic transition. This frequency shift corresponds to a small change in the Fermi surface volume that is qualitatively consistent with the small moment change in the magnetization across the metamagnetic transition. Very near the metamagnetic field, unusual behavior is seen. There is a strong enhancement of the resistivity in a narrow field window, with a minimum in the resistivity as a function of temperature below 1 K that becomes more pronounced as the disorder level decreases. The region of anomalous behavior is bounded at low temperatures by two first-order phase transitions. The implications of the results are discussed.

Journal Article↗
PubMed2004

Anisotropy of the incommensurate fluctuations in Sr2RuO4: a study with polarized neutrons.

The anisotropy of the magnetic incommensurate fluctuations in Sr2RuO4 has been studied by inelastic neutron scattering with polarized neutrons. We find a sizable enhancement of the out-of-plane component by a factor of 2 for intermediate energy transfer, which appears to decrease for higher energies. Our results qualitatively confirm calculations of the spin-orbit coupling, but the experimental anisotropy and its energy dependence are weaker than predicted.

Journal Article↗
PubMed2004

Gap structure of the spin-triplet superconductor Sr2RuO4 determined from the field-orientation dependence of the specific heat.

We report the field-orientation dependent specific heat of the spin-triplet superconductor Sr2RuO4 under the magnetic field aligned parallel to the RuO2 planes with high accuracy. Below about 0.3 K, striking fourfold oscillations of the density of states reflecting the superconducting gap structure have been resolved for the first time. We also obtained strong evidence of multiband superconductivity and concluded that the superconducting gap in the active band, responsible for the superconducting instability, is modulated with a minimum along the [100] direction.

Journal Article↗
PubMed2004

An angiogenesis inhibitor TNP-470 (AGM-1470) suppresses vascular smooth muscle cell proliferation in experimental rat aortotomy models.

AIM: Vascular intimal hyperplasia is an important clinical concern in vascular diseases, such as anastomotic stricture as a possible complication of cardiovascular surgery. We recently suggested that a rat aortotomy model could be substituted for a vascular anastomotic stricture around a suture line. TNP-470 is known as an angiogenesis inhibitor and has demonstrated abilities to inhibit DNA synthesis of smooth muscle cells (SMCs) and SMCs proliferation. The aim of this study was to investigate the effect of TNP-470 on SMC proliferation using rat aortotomy models. METHODS: Longitudinal aortotomy was performed in the abdominal aorta of rats. Rats received a subcutaneous injection of materials (TNP-470, 20 mg/kg) or vehicle 3 times a week (n=10 in each group). The aorta was harvested 2 weeks after aortotomy. Serial sections from tissues were stained with hematoxylin and eosin, and the ratio of intimal to medial cross-sectional areas (I/M ratio) was determined. Values are expressed as the mean +/- the standard deviation. Results. Thickening of the intimal layer 2 weeks following aortotomy was observed in the control group however, intimal thickening was inhibited in the TNP-treated group. The I/M ratio was significantly (p = 0.0376) lower in the TNP-treated group than in the control group (8.3 +/- 4.8 vs 15.6 +/- 9.6%). Conclusion. TNP-470 significantly suppressed intimal thickening in experimental rat aortotomy models. TNP-470 might inhibit the development of anastomotic stricture after cardiovascular surgery.

Angiogenesis Inhibitors↗
PubMed2003

Occurrence, histopathology and experimental transmission of hepatopancreatic parvovirus infection in Penaeus monodon postlarvae.

Hepatopancreatic parvovirus (HPV) was detected in samples of Penaeus monodon post-larvae (PL-13, PL-18, PL-19, PL-26) from 2 hatcheries in 2 provinces (Samar and Iloilo) in the Philippines. The percentage of infection was 20 to 100% in postlarvae obtained from the hatchery in Samar in August 2001. Postlarvae from the hatchery in Iloilo, sampled in October and November 2001, had 70 to 99% HPV infection. Wet mounts of squashed hepatopancreatic tissue stained with malachite green (wet-mount technique) and histopathology revealed the presence of large, usually single, basophilic intranuclear inclusion bodies in the distal tubules, which led to displacement of the nucleoli. Light microscopy showed ovoid to spherical inclusion bodies, 5 to 11 mmicrom in diameter. Transmission electron microscopy revealed that the inclusion bodies were composed of electron-dense granular material and virions. The virions appeared roughly spherical and averaged 18 to 22 nm in diameter. An experiment was undertaken to induce HPV infection by feeding P. monodon postlarvae with virus-infected postlarvae. P. monodon postlarvae (PL-16), initially determined as free from HPV, were found HPV-positive 24 h after being fed with infected material. The percentage of infection ranged from 30% at Day 1 post-infection (p.i.) to 100% at Day 7 p.i. determined by the wet-mount technique and by histopathology. This is the first report of a successful horizontal transmission of HPV in P. monodon postlarvae.

Animals↗
PubMed2003

Heavy-mass fermi liquid near a ferromagnetic instability in layered ruthenates.

Low temperature magnetic, thermal, and transport measurements in Ca2-xSrxRuO4 clarify the appearance of a cluster glass phase, after the evolution of a nearly ferromagnetic heavy-mass Fermi liquid from the spin-triplet superconductor Sr2RuO4. As the Mott transition is approached across a 2nd-order structural transition, both the magnetization and specific heat decrease considerably while the transport scattering rate diverges. A metamagnetic transition to a highly spin polarized state, with a local moment S=1/2, is observed. We argue that an orbital rearrangement with Ca substitution changes itinerant ferromagnetism to antiferromagnetism of localized moments.

Journal Article↗
PubMed2003

Prenatal diagnosis of sustained bradycardia with 1 : 1 atrioventricular conduction.

OBJECTIVES: The aims of this study were to elucidate the clinical course of fetal bradycardia with 1 : 1 atrioventricular conduction, and to discuss the optimal management of affected fetuses in the second and third trimesters of pregnancy. METHODS: The hospital records of five fetuses with the diagnosis of bradycardia (100 bpm) with 1 : 1 atrioventricular conduction between 1981 and 2000 in our institution were reviewed. Atrioventricular conduction was evaluated by simultaneous M-mode echocardiographic tracing of the atria and the ventricles. RESULTS: The gestational ages at referral ranged from 19 to 36 (median, 25) weeks, and fetal heart rates ranged from 60 to 80 (median, 80) bpm. Postnatal electrocardiography revealed sinus bradycardia in four (two of which were siblings) of the five cases, and junctional rhythm in the remaining case. Two fetuses with congenital heart defects (CHDs) were delivered by Cesarean section but died postnatally. The three fetuses without CHDs were delivered vaginally and have survived to date for 6, 8 and 15 years. CONCLUSIONS: Fetal bradycardia with 1 : 1 atrioventricular conduction caused by sustained sinus bradycardia or wandering pacemaker is an important type of fetal arrhythmia. Further investigations with a larger number of cases are required to determine the risk factors for predicting the outcome of affected fetuses.

Bradycardia↗
PubMed2002

Electron and orbital correlations in Ca2-xSrxRuO4 probed by optical spectroscopy.

The optical conductivity spectra of the quasi-two-dimensional Ca2-xSrxRuO4 (0.0< or =x< or =2.0) system were investigated. In the Mott insulating state, two electron correlation-induced peaks were observed about 1.0 and 1.9 eV, which could be explained using the 3-orbital Hubbard model. The low frequency peak showed a shift toward higher frequency as temperature was lowered, indicating that electron-phonon interactions play an important role in the orbital arrangements. From the systematic analysis, it was suggested that the antiferro-orbital and the ferro-orbital ordering states could coexist.

Journal Article↗
PubMed2002

Pressure-tuned collapse of the Mott-like state in Ca(n+1)Ru(n)O(3n+1) (n=1,2): Raman spectroscopic studies.

We report a Raman scattering study of the pressure-induced collapse of the Mott-like phases of Ca3Ru2O7 (T(N)=56 K) and Ca2RuO4 (T(N)=110 K). The pressure dependence of the phonon and two-magnon excitations in these materials indicate (i) a T approximately 0 pressure-induced collapse of the antiferromagnetic (AF) insulating phase above P(*) approximately 55 kbar in Ca3Ru2O7 and P(*) approximately 5-10 kbar in Ca2RuO4, (ii) a remarkable insensitivity of the exchange interaction to pressure in both systems, and (iii) evidence for persistent AF correlations above the critical pressure of Ca2RuO4, suggestive of phase separation involving AF insulator and ferromagnetic metal phases.

Journal Article↗
PubMed2002

Enlarged bronchial arteries in a fetus with transposition of the great arteries and intact ventricular septum.

Enlarged bronchial arteries are associated in some patients with transposition of the great arteries and intact ventricular septum. The etiology of these enlarged bronchial arteries is not yet known. In this report, we describe a case of TGA/IVS in which enlarged bronchial arteries were demonstrated from the prenatal period. The arteriogram at one year after arterial switch repair demonstrated enlarged bronchial arteries. This prenatal information may be useful for deciding on a strategy for postnatal treatment and counseling the family members.

Angiography↗
PubMed2002

Evolution of Fermi-liquid interactions in Sr2RuO4 under pressure.

We have measured the temperature and field dependence of the resistivity of the unconventional superconductor Sr2RuO4 at pressures up to 3.3 GPa. Using the Shubnikov-de Haas effect, we find that the Fermi surface sheet believed to be primarily responsible for superconductivity becomes more two-dimensional with increasing pressure, a surprising result that is, however, consistent with a recent model of orbital-dependent superconductivity in this system. Many-body enhancements and the superconducting transition temperature all fall gradually with increasing pressure, contrary to previous suggestions of a ferromagnetic quantum critical point at approximately 3 GPa.

Journal Article↗
PubMed2002

Increased angiogenic growth factor in cyanotic congenital heart disease.

To examine the relationship between the plasma levels of angiogenic growth factors and the severity of cyanosis, 80 patients with cyanotic heart disease (CHD) and 81 healthy controls were studied. Median age and mean arterial blood oxygen saturation respectively were 4.2 years and 81% in CHD subjects and 4.8 years and 98% in controls. Vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) were measured in plasma using enzyme-linked immunoassay. Plasma VEGF levels in controls depended negatively on age (p < 0.0001) until 3 months, when VEGF was no longer elevated. No such age dependence was found for HGF. Although VEGF levels did not differ between CHD and control subjects up to the age of 3 months, VEGF was significantly elevated in CHD patients older than 3 months compared to controls of similar age (149 +/- 106 vs 65 +/- 23 pg/ml, p < 0.0001). Moreover, the VEGF levels were negatively correlated with oxygen saturation (p = 0.03) and positively correlated with hemoglobin (p = 0.004) in CHD patients aged between 3 months and 10 years. Although the physiologic elevation of VEGF in the neonatal period decreases rapidly if oxygen saturation is normal, VEGF elevations persist if systemic hypoxia is present.

Adolescent↗
PubMed2002

Anomalous spin-density distribution on oxygen and Ru in Ca(1.5)Sr(0.5)RuO(4): polarized neutron diffraction study.

By means of polarized neutron diffraction in a magnetic field of 7.0 T at 1.6 K an anomalously large magnetization density is observed on the in-plane oxygen in Ca(1.5)Sr(0.5)RuO(4). Field-induced moments of different ions are determined by refinement on the flipping ratios, yielding micro(Ru)=0.346(11)micro(B), micro(O1)=0.076(6)micro(B), and micro(O2)=0.009(6)micro(B). The moment on the oxygen arises from the strong hybridization between the Ru-4d and O-2p orbitals. The maximum entropy magnetization density reconstruction reveals a strongly anisotropic density at the Ru site, consistent with the distribution of the xy (t(2g) band) d orbitals.

Journal Article↗
PubMed2002

Universal heat transport in Sr2RuO4.

We present the temperature dependence of the thermal conductivity kappa(T) of the unconventional superconductor Sr2RuO4 down to low temperatures ( approximately 100 mK). In the T-->0 K limit we found a finite residual term in kappa/T, providing clear evidence for the superconducting state with an unconventional pairing. The residual term remains unchanged for samples with different T(c), demonstrating the universal character of heat transport in this spin-triplet superconductor. The low-temperature behavior of kappa suggests the strong impurity scattering with a phase shift close to pi/2. A criterion for the observation of universality is experimentally deduced.

Journal Article↗
PubMed2002

Incommensurate magnetic ordering in Sr2Ru(1-x)TixO4.

In Sr2RuO4 the spin excitation spectrum is dominated by incommensurate fluctuations at q = (0.3 0.3q(z)), which arise from Fermi-surface nesting. We show that upon Ti substitution, known to suppress superconductivity, a short range magnetic order develops with a propagation vector (0.307 0.307 1). In Sr2Ru0.91Ti0.09O4, the ordered moment points along the c direction. This finding shows that superconducting Sr2RuO4 is extremely close to an incommensurate spin density wave instability.

Journal Article↗
PubMed2002

Sensitivity to disorder of the metallic state in the ruthenates.

We report the results of transport measurements on SrRuO3, Sr3Ru2O7, and CaRuO3. In SrRuO3 and Sr3Ru2O7, our findings are consistent with the predictions of Fermi liquid theory, in contrast to previous reports based on samples with much shorter mean free paths. In CaRuO3, however, a T1.5 power law is seen in the resistivity in the high purity samples studied here. Our work gives concrete evidence that even the metallic state of the ruthenates is highly sensitive to disorder.

Journal Article↗