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Biomedical subjects

T Yabuuchi

Publications and source records attributed to T Yabuuchi.

18 recordsLinked to original sources
PubMed2006

Surface acceleration of fast electrons with relativistic self-focusing in preformed plasma.

We report an observation of surface acceleration of fast electrons in intense laser-plasma interactions. When a preformed plasma is presented in front of a solid target with a higher laser intensity, the emission direction of fast electrons is changed to the target surface direction from the laser and specular directions. This feature could be caused by the formation of a strong static magnetic field along the target surface which traps and holds fast electrons on the surface. In our experiment, the increase in the laser intensity due to relativistic self-focusing in plasma plays an important role for the formation. The strength of the magnetic field is calculated from the bent angle of the electrons, resulting in tens of percent of laser magnetic field, which agrees well with a two-dimensional particle-in-cell calculation. The strong surface current explains the high conversion efficiency on the cone-guided fast ignitor experiments.

Journal Article↗
PubMed2006

Optimum hot electron production with low-density foams for laser fusion by fast ignition.

We propose a foam cone-in-shell target design aiming at optimum hot electron production for the fast ignition. A thin low-density foam is proposed to cover the inner tip of a gold cone inserted in a fuel shell. An intense laser is then focused on the foam to generate hot electrons for the fast ignition. Element experiments demonstrate increased laser energy coupling efficiency into hot electrons without increasing the electron temperature and beam divergence with foam coated targets in comparison with solid targets. This may enhance the laser energy deposition in the compressed fuel plasma.

Journal Article↗
PubMed2006

Transient electrostatic fields and related energetic proton generation with a plasma fiber.

We observe a hollow structure and a fine ring in the proton images from a petawatt scale laser interaction with a "cone-fiber" target. The protons related to the hollow structure are accelerated from the cone-tip surface and deflected later by a radial electric field surrounding the fiber. Those associated with the fine ring are accelerated from the fiber surface by this radial electric field. This field is found to decay exponentially within 3 ps from about 5 x 10(12) V/m. Two-dimensional particle-in-cell simulations produce similar proton angular distributions.

Journal Article↗
PubMed2006

Brain-derived neurotrophic factor-immunoreactive primary sensory neurons in the rat trigeminal ganglion and trigeminal sensory nuclei.

Immunohistochemistry for brain-derived neurotrophic factor (BDNF) was performed on the rat trigeminal ganglion (TG). The immunoreactivity (IR) was detected in 46% of TG neurons. These neurons were mostly small- or medium-sized (range, 149.7-1246.3 microm2; mean +/- SD = 373.4 +/- 151.6 microm2). A double immunofluorescence method also revealed that 54% of BDNF-immunoreactive (IR) neurons were immunoreactive for calcitonin-gene-related peptide. In addition, 93% of BDNF-IR TG neurons contained vanilloid receptor subtype 1. However, the co-expression of BDNF and vanilloid receptor 1-like receptor was very rare (less than 1%). In the trigeminal sensory nuclei, laminae II of the medullary dorsal horn was abundant in presumed BDNF-IR axon terminals. Such profiles were also detected in the dorsolateral part of the subnucleus oralis. The retrograde tracing and immunohistochemical methods demonstrated that BDNF-IR was common among cutaneous TG neurons (47%) but not tooth pulp TG neurons (13%). The present study indicates that BDNF-IR TG neurons have unmyelinated axons and project to the superficial medullary dorsal horn. It is likely that BDNF-containing neurons in both the trigeminal and spinal sensory systems have similarities in morphology and function. However, the content of BDNF in TG neurons probably depends on their peripheral targets. BDNF seems to convey nociceptive cutaneous input to the trigeminal sensory nuclei.

Animals↗
PubMed2006

Increase of galanin in trigeminal ganglion during tooth movement.

It is known that nerve fibers containing neuropeptides such as galanin increase in the periodontal ligament during experimental tooth movement. However, the origin of galanin-containing nerve fibers in the periodontal ligament remains unclear. This study was conducted to examine our hypothesis that the increased galanin nerve fibers have a sensory neuronal origin, and that the peptide is associated with pain transmission and/or periodontal ligament remodeling during experimental tooth movement. In control rats, galanin-immunoreactive trigeminal ganglion cells were very rare and were observed predominantly in small ganglion cells. After 3 days of experimental tooth movement, galanin-immunoreactive trigeminal ganglion cells significantly increased, and the most marked increase was observed at 5 days after experimental tooth movement. Furthermore, their cell size spectrum also significantly changed after 3 and 5 days of movement: Medium-sized and large trigeminal ganglion cells began expressing, and continued to express, galanin until 14 days after experimental tooth movement. These findings suggest that the increase of galanin in the periodontal ligament during experimental tooth movement at least partially originates from trigeminal ganglion neurons and may play a role in pain transmission and/or periodontal remodeling.

Animals↗
PubMed2005

Demonstration of bulk acceleration of ions in ultraintense laser interactions with low-density foams.

Ion acceleration inside low-density foams irradiated by ultraintense laser pulses has been studied experimentally and theoretically. It is found that the ion generation is closely correlated with the suppressed hot electron transport inside the foams. Particle-in-cell simulations suggest that localized electrostatic fields with multi peaks around the surfaces of lamellar layers inside the foams are induced. These fields inhibit hot electron transport and meanwhile accelerate ions inside the foams, forming a bulk acceleration in contrast to the surface acceleration at the front and rear sides of a thin solid target.

Journal Article↗
PubMed2005

Enhancement of energetic electrons and protons by cone guiding of laser light.

Energetic electrons and protons are observed when a target consisting of a reentrant cone with a disk at the tip is irradiated by a petawatt (PW) laser at an intensity of approximately 10(19) W cm(-2). The angular distribution of the electrons and protons, dependent on the open angle of the reentrant cone, is found to differ from that in the case when a target with planar geometry is used. Two jet beams are observed, in directions parallel to the cone axis and normal to the cone-shaped wall. The number and cutoff energies of the generated protons are also related to the open angle of the cone. The efficiency of the generation of energetic electrons from the cone target is 2-3 times higher than that from a simple plane target. These results indicate a guiding of the PW laser beam in the cone geometry.

Journal Article↗
PubMed2004

Plasma devices to guide and collimate a high density of MeV electrons.

The development of ultra-intense lasers has facilitated new studies in laboratory astrophysics and high-density nuclear science, including laser fusion. Such research relies on the efficient generation of enormous numbers of high-energy charged particles. For example, laser-matter interactions at petawatt (10(15) W) power levels can create pulses of MeV electrons with current densities as large as 10(12) A cm(-2). However, the divergence of these particle beams usually reduces the current density to a few times 10(6) A cm(-2) at distances of the order of centimetres from the source. The invention of devices that can direct such intense, pulsed energetic beams will revolutionize their applications. Here we report high-conductivity devices consisting of transient plasmas that increase the energy density of MeV electrons generated in laser-matter interactions by more than one order of magnitude. A plasma fibre created on a hollow-cone target guides and collimates electrons in a manner akin to the control of light by an optical fibre and collimator. Such plasma devices hold promise for applications using high energy-density particles and should trigger growth in charged particle optics.

Journal Article↗
PubMed2004

Study of hot electrons by measurement of optical emission from the rear surface of a metallic foil irradiated with ultraintense laser pulse.

Hot electrons and optical emission are measured from the rear surface of a metallic foil. The spectra of the optical emission in the near infrared region have a sharp spike around the wavelength of the incident laser pulse. The optical emission is ascribed to coherent transition radiation due to microbunching in the hot electron beam. It is found that the optical emission closely correlates with the hot electrons accelerated in resonance absorption.

Journal Article↗
PubMed2004

High-energy electrons produced in subpicosecond laser-plasma interactions from subrelativistic laser intensities to relativistic intensities.

The characteristics of the forward hot electrons produced by subpicosecond laser-plasma interactions are studied for different laser polarizations at laser intensities from subrelativistic to relativistic. The peak of the hot electron beam produced by p-polarized laser beam shifts to the laser propagation direction from the target normal direction as the laser intensity reaches the relativistic. For s-polarized laser pulse, hot electrons are mainly directed to the laser axis direction. The temperature and the maximum energy of hot electrons are much higher than that expected by the empirical scaling law. The energy spectra of the hot electrons evolve to be a single-temperature structure at relativistic laser intensities from the two-temperature structure at subrelativistic intensities. For relativistic laser intensities, the forward hot electrons are less dependent on the laser polarization under the laser conditions. The existing of a preplasma formed by the laser amplified spontaneous emission pedestal plays an important role in the interaction. One-dimensional particle-in-cell simulations reproduce the most characteristics observed in the experiment.

Journal Article↗
PubMed2001

Sesquiterpenes and monoterpenes from the bark of Inula macrophylla.

Eleven new sesquiterpenes (1--11) and two thymol derivatives (12, 13), along with 12 known sesquiterpenes and monoterpenes, were isolated from the bark of Inula macrophylla. Their structures were determined on the basis of spectral evidence (especially by HREIMS and 2D NMR) as well as chemical transformations. The structure of macrophyllic acid A (1) was confirmed by X-ray analysis, and the absolute configuration of 1 was determined on the basis of the appropriate chemical conversions and the application of a modified Mosher's method.

Crystallography, X-Ray↗
PubMed2000

Phenylglycine methyl ester, a useful tool for absolute configuration determination of various chiral carboxylic acids

A new chiral anisotropic reagent, phenylglycine methyl ester (PGME), developed for the elucidation of the absolute configuration of chiral alpha,alpha-disubstituted acetic acids, has turned out to be applicable to other substituted carboxylic acids, such as chiral alpha-hydroxy-, alpha-alkoxy-, and alpha-acyloxy-alpha, alpha-disubstituted acetic acids, as well as to chiral beta, beta-disubstituted propionic acids. Because a carboxylic moiety is convertible from other functional groups, e.g., ozonolysis of an olefin and oxidative cleavage of a glycol, the present findings can expand the utility of the PGME method to the absolute configuration determination of various types of organic compounds, even those which initially lack oxygen functions. Several examples of the combination of chemical reactions and the PGME method are described.

Journal Article↗
PubMed2000

Effectiveness of interferon therapy for reducing the incidence of hepatocellular carcinoma among patients with type C chronic hepatitis.

STUDY PURPOSE: To evaluate the effect of interferon treatment for reducing the incidence of hepatocellular carcinoma among patients with type C chronic hepatitis. METHODS: Retrospective cohort study was conducted on 923 patients with type C chronic hepatitis, who were identified through databases of Osaka Medical Center for Cancer and Cardiovascular Diseases. Two hundred and twenty-four of those had undergone interferon treatment, while the other 699 patients had not. Kaplan-Meier method and the proportional hazards model were used for statistical analysis. RESULTS: Five-years' cumulative incidence of hepatocellular carcinoma was 2.2% among the interferon treated patients, while 9.5% among the interferon untreated. Difference between the 2 curves of the cumulative incidence was statistically significant (p=0.0015). After adjustment for possible confounders, hazard rate ratio of hepatocellular carcinoma was 0.31 in the interferon treated group, significantly lower than that in the untreated (p=0.015). Hazard rate ratio for death from causes other than hepatocellular carcinoma and liver diseases was also lower among the interferon treated group than that among the untreated, although not significant. CONCLUSIONS: Interferon treatment is suggested to reduce the risk of hepatocellular carcinoma among patients with type C chronic hepatitis, and not to increase the risk for death from causes other than hepatocellular carcinoma and liver diseases.

Antiviral Agents↗
PubMed1996

Crystallization and preliminary X-ray analysis of salicylate hydroxylase from Pseudomonas putida S-1.

Apo-salicylate hydroxylase from Pseudomonas putida S-1 has been crystallized by the dialysis method, using ammonium sulfate as the precipitant. The crystals belong to hexagonal space group P6(2) or P6(4) with unit cell dimensions of a = b = 142.8 A and c = 63.8 A, and diffract X-rays at higher than 3.5 A resolution. A heavy-atom derivative has been prepared by soaking a crystal in an ammonium sulfate solution containing p-chloromercuriphenylsulfonate.

Crystallization↗
PubMed1993

Risk factors for hepatocellular carcinoma among patients with chronic liver disease.

BACKGROUND AND METHODS: To detect potentially curable cases of hepatocellular carcinoma, outpatients with chronic hepatitis or compensated liver cirrhosis who were seen at the Center for Adult Diseases (Osaka, Japan) were examined periodically by means of ultrasonography and measurement of serum alpha-fetoprotein. Risk factors for hepatocellular carcinoma were identified with a Cox proportional-hazards model. RESULTS: A total of 917 patients, 40 to 69 years old, were registered from May 1987 to March 1991. By the end of September 1991, liver cancer had developed in 54. The three-year cumulative risk of liver cancer was 12.5 percent for 240 patients with liver cirrhosis at enrollment and 3.8 percent for 677 patients with chronic hepatitis. Cox regression analysis showed that the risk of liver cancer was increased almost sevenfold in patients with hepatitis B surface antigen (rate ratio, 6.92; 95 percent confidence interval, 2.92 to 16.39) and fourfold in patients with hepatitis C antibody (rate ratio, 4.09; 95 percent confidence interval, 1.30 to 12.85). A high alpha-fetoprotein value at enrollment was also a risk marker for liver cancer. CONCLUSIONS: Patients with hepatitis C virus infection have a greatly increased risk of liver cancer. Further studies are required to clarify the roles of other risk factors, including drinking and smoking habits.

Adult↗
PubMed1993

[Risk factors of hepatitis C virus infection].

In order to clarify the risk factors of hepatitis C virus (HCV) infection, past medical histories, family histories of liver disease, and lifestyle factors (smoking and drinking habits) were compared between anti-HCV positive cases and anti-HCV negative controls. Studies were 433 anti-HCV positive cases and 298 negative controls, all of whom were out-patients with chronic hepatitis or liver cirrhosis. The findings were contrasted with the risk factors of hepatitis B virus (HBV) chronic infection. Multiple logistic regression analysis revealed the following findings. Prevalence of anti-HCV among patients with chronic hepatitis or liver cirrhosis increased with age, while prevalence of HBsAg decreased with age. Histories of blood transfusion were closely associated with the risk of HCV infection. Adjusted relative risk for patients with a history of blood transfusion was estimated to be 2.97 (95% confidence intervals: 1.88-4.71) in comparison with the risk for patients without it. Any family history of liver disease was not related with the risk of HCV infection, while mother's history of liver disease was significantly associated with the risk of chronic HBV infection (adjusted relative risk was 2.96 with 95% confidence intervals: 1.32-6.62).

Adult↗
PubMed1990

Syntheses, antiinflammatory, and analgesic activities of arylbiurets.

A number of arylbiurets were prepared and evaluated as antiinflammatory and analgesic agents by using the carrageenan paw edema and acetic acid stretching tests. Among them, the antiinflammatory activity of 1,3-dimethyl-5-phenylbiuret (7), 1-ethyl-3-methyl-5-phenylbiuret (11), and 1,1,3-trimethyl-5-phenylbiuret (13) were found to be more potent than phenylbutazone. The analgesic activity of 7 and of 5-(4-chlorophenyl)-1,1,3-trimethylphenylbiuret (16) is higher than that of aminopyrine.

Animals↗