Biomedical subjects

M Nohara

Publications and source records attributed to M Nohara.

At least 19 recordsLinked to original sources

PubMed2006

Fulde-Ferrell-Larkin-Ovchinnikov state in a perpendicular field of quasi-two-dimensional CeCoIn5.

A Fulde-Ferrell-Larkin-Ovchinnkov (FFLO) state was previously reported in the quasi-2D heavy fermion CeCoIn5 when a magnetic field was applied parallel to the ab plane. Here, we conduct 115In NMR studies of this material in a perpendicular field, and provide strong evidence for FFLO in this case as well. Although the topology of the phase transition lines in the H-T phase diagram is identical for both configurations, there are several remarkable differences between them. Compared to H parallelab, the FFLO phase for H perpendicularab is confined in a much narrower region at the low-T-high-H corner in the H-T plane, and the critical field separating the FFLO and non-FFLO superconducting states almost ceases to have a temperature dependence. Moreover, directing H perpendicularab results in a notable change in the quasiparticle excitation spectrum within the planar node associated with the FFLO transition.

Journal Article↗

PubMed2006

A cross sectional study of the respiratory health of workers handling printing toner dust.

BACKGROUND: Although recent case reports have suggested possible respiratory effects of solid toner dust inhalation, this hypothesis has not been verified by epidemiological studies. OBJECTIVES: To conduct a cross sectional study to evaluate the association between the biological indices of lung fibrosis and toner dust exposure in an occupational cohort handling solid toner dust in their work life. METHODS: A total of 600 male toner workers and 212 control subjects were surveyed in terms of their subjective respiratory symptoms, pulmonary functions, and chest radiographic findings. In addition to the exposure history, the current working conditions and personal exposure levels to toner dust were also examined. RESULTS: Although subjects handling toner for more than 20 years tended to show a higher prevalence of respiratory symptoms and minimal chest x ray abnormalities, there was no consistent relation between the exposure to toner dust and the biological responses of the respiratory system. CONCLUSION: Deterioration of respiratory health related to toner dust exposure is less likely to occur in current well controlled work environments, especially if the powdered toner is handled carefully. Nonetheless, it is important to collect further epidemiological evidence on the biological effects of toner dust inhalation, preferably using a longitudinal study design.

Adult↗

PubMed2005

Three-dimensionality of field-induced magnetism in a high-temperature superconductor.

Many physical properties of high-temperature superconductors are two-dimensional phenomena derived from their square-planar CuO2 building blocks. This is especially true of the magnetism from the copper ions. As mobile charge carriers enter the CuO2 layers, the antiferromagnetism of the parent insulators, where each copper spin is antiparallel to its nearest neighbours, evolves into a fluctuating state where the spins show tendencies towards magnetic order of a longer periodicity. For certain charge-carrier densities, quantum fluctuations are sufficiently suppressed to yield static long-period order, and external magnetic fields also induce such order. Here we show that, in contrast to the chemically controlled order in superconducting samples, the field-induced order in these same samples is actually three-dimensional, implying significant magnetic linkage between the CuO2 planes. The results are important because they show that there are three-dimensional magnetic couplings that survive into the superconducting state, and coexist with the crucial inter-layer couplings responsible for three-dimensional superconductivity. Both types of coupling will straighten the vortex lines, implying that we have finally established a direct link between technical superconductivity, which requires zero electrical resistance in an applied magnetic field and depends on vortex dynamics, and the underlying antiferromagnetism of the cuprates.

Copper↗

PubMed2005

Nonequilibrium quasiparticle relaxation in the vortex state of La2-xSrxCuO4.

We have measured the charge dynamics in the vortex state of La(2-x)Sr(x)CuO(4) by femtosecond time-resolved reflectance, which we demonstrate to be a direct probe of low-energy quasiparticle states. Application of a c-axis magnetic field induces regions surrounding vortex cores that display pseudogap charge dynamics. We determine the characteristic width approximately 130 A in optimally doped material and we show that it increases with decreasing doping. These results confirm a new experimental method of probing the microscopic properties of vortices in the cuprates.

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↗

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↗

PubMed2003

Field-induced thermal metal-to-insulator transition in underdoped La(2-x)Sr(x)CuO(4+delta).

The transport of heat and charge in cuprates was measured in single crystals of La(2-x)Sr(x)CuO(4+delta) (LSCO) across the doping phase diagram at low temperatures. In underdoped LSCO, the thermal conductivity is found to decrease with increasing magnetic field in the T-->0 limit, in striking contrast to the increase observed in all superconductors, including cuprates at higher doping. In heavily underdoped LSCO, where superconductivity can be entirely suppressed with an applied magnetic field, we show that a novel thermal metal-to-insulator transition takes place upon going from the superconducting state to the field-induced normal state.

Journal Article↗

PubMed2003

Charge ordering and spin frustration in AlV2-x CrxO4.

The relationship between charge and spin degrees of freedom in a geometrically frustrated system, AlV2-xCrxO4 spinel, is investigated. Upon Cr doping, the charge-ordered phase of AlV2O4 is rapidly suppressed and a charge-disordered phase grows up instead. It is found that the magnetic ground state is a spin-glass state dominated by geometrical frustration for both phases, but larger spin entropy remains down to low temperatures in the charge-ordered phase, possibly owing to its two-dimensional character.

Journal Article↗

PubMed2002

Gap function with point nodes in borocarbide superconductor YNi2B2C.

To determine the superconducting gap function of YNi2B2C, the c-axis thermal conductivity kappa(zz) was measured in H rotated in various directions. The angular variation of kappa(zz) in H rotated within the ab plane shows a peculiar fourfold oscillation with narrow cusps. The amplitude of this fourfold oscillation becomes very small when H is rotated conically around the c axis with a tilt angle of 45 degrees. These results provide the first compelling evidence that the gap function has point nodes located along the a and b axes. This unprecedented gap structure challenges the current view on the pairing mechanism.

Journal Article↗

PubMed2002

Antiferromagnetic order induced by an applied magnetic field in a high-temperature superconductor.

One view of the high-transition-temperature (high-Tc) copper oxide superconductors is that they are conventional superconductors where the pairing occurs between weakly interacting quasiparticles (corresponding to the electrons in ordinary metals), although the theory has to be pushed to its limit. An alternative view is that the electrons organize into collective textures (for example, charge and spin stripes) which cannot be 'mapped' onto the electrons in ordinary metals. Understanding the properties of the material would then need quantum field theories of objects such as textures and strings, rather than point-like electrons. In an external magnetic field, magnetic flux penetrates type II superconductors via vortices, each carrying one flux quantum. The vortices form lattices of resistive material embedded in the non-resistive superconductor, and can reveal the nature of the ground state-for example, a conventional metal or an ordered, striped phase-which would have appeared had superconductivity not intervened, and which provides the best starting point for a pairing theory. Here we report that for one high-Tc superconductor, the applied field that imposes the vortex lattice also induces 'striped' antiferromagnetic order. Ordinary quasiparticle models can account for neither the strength of the order nor the nearly field-independent antiferromagnetic transition temperature observed in our measurements.

Journal Article↗

PubMed2001

Fermi surface sheet-dependent superconductivity in 2H-NbSe2.

High-resolution angle-resolved photoemission spectroscopy was used to study the superconducting energy gap and changes in the spectral function across the superconducting transition in the quasi-two-dimensional superconductor 2H-NbSe2. The momentum dependence of the superconducting gap was determined on different Fermi surface sheets. The results indicate Fermi surface sheet-dependent superconductivity in this low-transition temperature multiband system and provide a description consistent with thermodynamic measurements and the anomalous de Haas-van Alphen oscillations observed in the superconducting phase. The present data suggest the importance of Fermi surface sheet-dependent superconductivity in explaining exotic superconductivity in other multiband systems with complex Fermi surface topology, such as the borides and f-electron superconductors.

Journal Article↗

PubMed2001

Spins in the vortices of a high-temperature superconductor.

Neutron scattering is used to characterize the magnetism of the vortices for the optimally doped high-temperature superconductor La(2-x)Sr(x)CuO4 (x = 0.163) in an applied magnetic field. As temperature is reduced, low-frequency spin fluctuations first disappear with the loss of vortex mobility, but then reappear. We find that the vortex state can be regarded as an inhomogeneous mixture of a superconducting spin fluid and a material containing a nearly ordered antiferromagnet. These experiments show that as for many other properties of cuprate superconductors, the important underlying microscopic forces are magnetic.

Journal Article↗

PubMed2001

[The relationships between the prevalence of asthmatic symptoms and environmental factors].

The relationships between the prevalence of asthmatic symptoms and environmental factors were evaluated using a modified version of the Japanese ATS-DLD children's questionnaire. The questionnaire was distributed to 13,306 students in 3 areas of Yokohama City; in 1986 (4705), 1988 (4440), and 1991 (4161). The results indicate: 1. The prevalence of asthmatic symptoms among boys increased slightly from 1986 (9.2%) to 1991 (9.6%), but no increase was observed that among girls (5.7%). The overall prevalence among boys was 1.7 times higher than that among girls. 2. On the whole, the air pollution level was Tsurumi-ku > Naka-ku > Midori-ku. But the prevalence of asthmatic symptoms among boys was Naka-ku > Tsurumi-ku > Midori-ku in 1986, 1988 and 1991. The prevalence among girls was the same result in 1986, but in 1988 and 1991, it was Tsurumi-ku > Naka-ku > Midori-ku. 3. In the longitudinal study of the same group, the prevalence of asthmatic symptoms among boys decreased between 5th and 6th grade. In contrast, remission of asthma increased between 5th and 6th grade. And the prevalence of asthmatic symptoms among girls decreased between 3rd and 6th grade. In contrast, remission of asthma increased between 3rd and 6th grade. 4. Children who had a personal or family history of allergic diseases, allergic disposition, respiratory diseases before 2 years old, wheezing or difficulty in breathing, or allergies against foods or medicines, showed a statistically significant Odds ratio (p < 0.01) for asthmatic symptoms.

Air Pollution↗

PubMed2001

[Changes in the prevalence of asthma-like symptoms and risk factors in school children in Yokohama from 1986 to 1991].

We conducted a questionnaire survey of first graders from six elementary schools in three areas of Yokohama annually from 1986 to 1991 (about 700 children each year) to investigate the changes in prevalence of asthma-like symptoms and association with potential risk factors. The prevalence rate of asthma-like symptoms increased from 7.6% to 11.0% in boys and from 6.5% to 8.8% in girls from 1986 to 1991. The ratio of affected boys was consistently higher than that in girls, but there were no significant regional differences. We found statistically significant odds ratios for the effect of a previous history of allergies, respiratory disease before age two, wheezing or difficulty in breath before age two and cough without respiratory tract infections on the prevalence of asthma-like symptoms.

Asthma↗

PubMed2000

Ultrahigh-resolution photoemission spectroscopy of Ni borocarbides: direct observation of the superconducting gap and a change in gap anisotropy by impurity

We have performed ultrahigh-resolution photoemission spectroscopy of Y(Ni1-xPtx)2B2C ( x = 0.0 and 0.2) in order to study the changes in the density of states across the superconducting transition. Because of a drastic increase in energy resolution, we clearly observe the opening of superconducting gaps across T(c) in both compounds. Furthermore, we find a small but significant difference in the superconducting-state spectral shape. This can be explained in terms of reduction in gap anisotropy by introducing impurities and provides spectroscopic evidence for an anisotropic s-wave gap in YNi2B2C.

Journal Article↗

PubMed2000

LiV2O4 spinel as a heavy-mass fermi liquid: anomalous transport and role of geometrical frustration

Transport and specific heat measurements on hydrothermally grown single crystals reveal the formation of a heavy-mass Fermi liquid in the LiV2O4 spinel, below a coherence temperature of T* = 20-30 K. A few observations which illustrate the uniqueness of this spinel are discussed in connection with the origin of the heavy mass, such as the anomalous absence of resistivity saturation above T* and the close proximity to a spin glass phase where the influence of the magnetic frustration is evident.

Journal Article↗

PubMed2000

The health care system for female workers and its current status in Japan.

In this paper we describe female workers' health care, the women's and maternal protection system within the Japanese legal system, the current status of female workers in Japan, and problems regarding methods of advancing health care and the women's or maternal protection system. Motherhood is respected in the workplace in Japan, and in order to provide an environment in which women can work and still bear and rear children with a sense of security, laws concerning maternal protection of female workers, and revisions in terms of the system have been made, and a new system has been in effect since the fiscal year of 1998. Nevertheless, gender discrimination against women and the disparagement of women, rooted in gender role stereotypes concerning the division of labor, remain firmly planted in the social environment and in long-established custom.

Adolescent↗

PubMed2000

[A case of giant sebaceous gland carcinoma without adequate treatment].

BACKGROUND: A patient with a sebaceous gland carcinoma without adequate treatment is reported. CASE: A 67-year-old man underwent an operation on his left upper eyelid after a diagnosis of chalazion in 1981. Two years after the initial operation, he noticed a tumor in the left upper eyelid. In 1987, he visited another hospital and was diagnosed with sebaceous gland carcinoma by a tissue biopsy. He left it untreated against medical advice. When he visited our hospital in 1996, the tumor was as large as 80 x 75 x 40 mm and the left upper and lower eyelids stuck together. After admission, he died of myocardial infarction 23 days after his visit to our hospital. Autopsy revealed that the tumor had extended into the orbital cavity, paranasal sinus, and base of the skull, with metastasis to the preauricular, submandibular, and cervical lymph nodes and both lungs. The pathology of the tumor was a moderately differentiated sebaceous gland carcinoma. CONCLUSION: This case showed the natural course of extension and metastasis of a sebaceous gland carcinoma.

Aged↗