Biomedical subjects

Hirokazu Hasegawa

Publications and source records attributed to Hirokazu Hasegawa.

13 recordsLinked to original sources

PubMed2006

Interferometric autocorrelation of an attosecond pulse train in the single-cycle regime.

We report on the direct observation of the phase locking of the attosecond pulse train (APT) via interferometric autocorrelation in the extreme ultraviolet region. APT is formed with Fourier synthesis of high-order harmonic fields of a femtosecond laser pulse. Time-of-flight mass spectra of N+, resulting from the Coulomb explosion of N2 absorbing two photons of APT, efficiently yield correlated signals of APT. The measured autocorrelation trace exhibits that the duration of the pulse should be only 1.3 periods of the extreme ultraviolet carrier frequency. A few interference fringes within the short pulse duration clearly show two types of symmetry, which ensure the phase locking between pulses in APT.

Journal Article↗

PubMed2006

Conclusive evidence of an attosecond pulse train observed with the mode-resolved autocorrelation technique.

We report on the direct observation of an attosecond pulse train with a mode-resolved autocorrelation technique. The chirp among the three harmonic fields is specified by analyzing two-photon above-threshold ionization spectra of electrons, resulting in a pulse duration that should be shorter than 450 as, which is, to our knowledge, the first determination of the chirp in the attosecond pulse train with an autocorrelation technique. These results will open the way to full characterization of an attosecond pulse train with its envelope.

Journal Article↗

PubMed2006

Spatial arrangement of metal nanoparticles supported by porous polymer substrates studied by transmission electron microtomography.

Fine metal particles (nanoparticles) stabilized on porous (polymeric) substrates can be considered as a model system of a high-performance catalyst. In the present study, the substrate was made using the periodic microphase-separated structure of a block copolymer as the template, and the Pd nanoparticles were formed inside the porous material by reduction of the Pd2+ ions with 1-propanol as the reductant. The three-dimensional morphology of such a polymer-Pd hybrid material was studied by transmission electron microtomography. The characteristic structural parameters of the hybrid, e.g., the penetration of the Pd nanoparticles into the polymer substrate, number density of the Pd nanoparticles, and size distribution of the Pd nanoparticles, were measured for the first time.

Metal Nanoparticles↗

PubMed2006

[Practical procedure of totally implanted venous access system for outpatient cancer therapy].

Some outpatient cancer chemotherapy has been replacing inpatient chemotherapy. A totally implanted venous access system is now available for patients who undergo cancer chemotherapy on an outpatient basis. All eleven outpatients who underwent cancer chemotherapy with this system underwent placement of the port and administration of chemotherapy. Complications were observed in two of these eleven patients (18%). Because a subcutaneous abscess occurred in one patient between the placement of the port and her first chemotherapy session, we had to remove the port system once. Another patient developed fungemia, so we discontinued the system after 95 outpatient chemotherapy sessions. When the infection healed, we set up the system again, and no trouble was observed later in these two cases. According to the patients' survey, all patients were satisfied with outpatient chemotherapy using this system. Therefore, we concluded that this system contributes to enhanced quality of life among outpatients who undergo cancer chemotherapy.

Abscess↗

PubMed2005

Concerted and sequential Coulomb explosion processes of N2O in intense laser fields by coincidence momentum imaging.

The Coulomb explosion dynamics of N2O in intense laser fields (800 nm, 60 fs, approximately 0.16 PWcm2) is studied by the coincidence momentum imaging method. From the momentum correlation maps obtained for the three-body fragmentation pathway, N2O3+-->N++N++O+, the ultrafast structural deformation dynamics of N2O prior to the Coulomb explosion is extracted. It is revealed that the internuclear N-N and N-O distances stretch simultaneously as the bond angle less than approximately N-N-O decreases. In addition, two curved thin distributions are identified in the momentum correlation maps, and are interpreted well as those originating from the sequential dissociation pathway, N2O3+-->N++NO2+-->N++N++O+.

Journal Article↗

PubMed2005

Production of doubly charged helium ions by two-photon absorption of an intense sub-10-fs soft x-ray pulse at 42 eV photon energy.

We report on the observation of doubly charged helium ions produced by a nonlinear interaction between a helium atom and photons with a photon energy of 42 eV which are generated with the 27th harmonic of a femtosecond pulse from a Ti:sapphire laser. The number of ions is proportional to the square of the intensity of the 27th harmonic pulse, and thus two-photon double ionization should be dominantly induced as compared with other nonlinear processes accompanying sequential ionization via a singly charged ion. This phenomenon is utilized to measure the pulse duration of the 27th harmonic pulse by using an autocorrelation technique, for the first time to our knowledge, and as a result a duration of 8 fs is found.

Journal Article↗

PubMed2005

MDCT of hypervascular hepatocellular carcinomas: a prospective study using contrast materials with different iodine concentrations.

OBJECTIVE: The objective of our study was to investigate the effect of different iodine concentrations in contrast materials on the depiction of hypervascular hepatocellular carcinomas (HCCs) by MDCT. SUBJECTS AND METHODS: This prospective study involved 100 consecutive patients with chronic liver disease, including 27 patients with hypervascular HCCs. The first 50 patients received 100 mL of iopamidol at a concentration of 370 mg I/mL (group A) and the subsequent 50, 100 mL at 300 mg I/mL (group B); in both groups, the contrast material was administered at a rate of 3.0 mL/sec. Unenhanced scanning and four-phase enhanced scanning at 25, 40, 60, and 180 sec after the start of contrast injection were performed. The enhancement of the aorta, liver, and portal vein was measured during each phase. In addition, tumor-to-liver contrast was calculated for the 27 patients with hypervascular HCCs. Of the 27 patients with hypervascular HCCs, 15 were in group A and 12 were in group B. RESULTS: During all phases, aortic enhancement was significantly greater in group A than group B (p < 0.01). Hepatic enhancement was significantly greater in group A than group B at 60 and 180 sec (both p < 0.01). There was no significant difference in hepatic enhancement between the two groups at 25 and 40 sec. Tumor-to-liver contrast was significantly greater in group A than group B during the late arterial phase (40 sec, p = 0.02), although there was no significant difference at 25, 60, and 180 sec. CONCLUSION: Contrast materials with higher iodine concentration are more effective for depicting hypervascular HCCs on MDCT during the late arterial phase.

Adult↗

PubMed2004

Comparative study between DNA copy number aberrations determined by quantitative microsatellite analysis and clinical outcome in patients with stomach cancer.

PURPOSE: We detected the relative DNA copy numbers (RCNs) at target loci in patients with stomach cancer with quantitative microsatellite analysis. We additionally clarified the relationship between DNA copy number aberrations and the clinical outcome of the patients. EXPERIMENTAL DESIGN: Fresh frozen samples were obtained from 30 patients who had undergone surgery for stomach cancer. Seven microsatellite loci in chromosomes 8q, 16q, and 20q and one gene-specific locus (ZNF217) were selected as the target loci. The DNA copy number was obtained relatively to a pooled reference consisting of six microsatellite primer sets selected from the regions where few aberrations have been reported in comparative genomic hybridization analysis. On the basis of the TaqMan PCR system, the internal probes used were carrying donor (6-carboxyfluorescein) and acceptor (6-carboxytetramethylrhodamine) fluorescent molecules complementary to CA repeats in the microsatellite markers and to one gene-specific oligomer in the gene-specific marker. RESULTS: Chromosome 8q gain, 20q gain, and 16q loss were detected in 18 (60.0%), 8 (26.7%), and 13 (43.3%) cases, respectively. Gains in the RCNs of D8S1801 and D8S1724 were most frequently found (36.7%). There was a significant correlation between the loss of D16S3026 and reduced survival duration (P = 0.0158), and the simultaneous aberrations of D8S1801 gain and D16S3026 loss (double marker positive) was significantly associated with reduced survival duration (P = 0.0008). According to Cox proportional hazards model, the double marker positive was a significant and independent factor indicating an unfavorable prognostic factor (relative risk, 17.176; 95% confidence interval, 2.782-106.026; P = 0.0022). CONCLUSION: RCN aberrations in tumor tissues determined by quantitative microsatellite analysis enable identification of the prognostic factors that correlate with clinical outcome of the patients with stomach cancer.

Aged↗

PubMed2004

High-throughput, high-damage-threshold broadband beam splitter for high-order harmonics in the extreme-ultraviolet region.

We demonstrate a high-throughput and high-damage-threshold beam splitter for high-order harmonics in the soft-x-ray region that uses Si and (or) SiC plates set at Brewster's angle with respect to the pump wavelength. The beam splitters are guaranteed to have a damage threshold of at least 0.8 TW/cm2 (average power density, 0.25 W/cm2) and an attenuation rate of 10(-4)-10(-5) for a 30-fs pump pulse. The measured reflection efficiency at the 27th harmonic (29.6 nm) was 0.56 for Si and 0.45 for SiC. These beam splitters are useful not only for high harmonics but also for longitudinally pumped x-ray lasers.

Journal Article↗

PubMed2003

Solid-state variation of troglitazone drug substance by using a different recrystallization method.

Rapid and slow crystallization methods (A and B) were applied for troglitazone, an equal mixture of four stereoisomers. Differences in the powder x-ray diffractometry patterns and hygroscopic patterns were observed among the samples crystallized by these methods, suggesting that troglitazone has solid-state variation. In this article, troglitazone recrystallized by method A was evaluated to clarify its structural characteristics and physical property. The crystal structure of predried troglitazone recrystallized by method A was proved to be a dihydrate. By drying, it changed reversibly to an anhydrate, which is the same structure as the RS/SR form, keeping the same enantiomer ratio. The solubility of the troglitazone by method A higher than that by method B at all enantiomer levels. But making the troglitazone amorphous equalized the enantiomeric solubilities of the substances by both methods as well as increased the intrinsic solubilities. Troglitazone by both methods was proved to be stable and retained the ratio of the stereoisomers.

Adsorption↗

PubMed2002

Physical property of troglitazone, an equal mixture of four stereoisomers.

Troglitazone, an oral antidiabetic agent, is an equal mixture of four stereoisomers involving two chiral centers. In the present study, the physical property of troglitazone were investigated. The solid state of troglitazone drug substance is characterized as a simple physical mixture of two diastereomers, as shown by the two endothermic peaks caused by the melting of the RR/SS and the RS/SR forms by differential scanning calorimetry (DSC). In addition, the powder X-ray diffraction pattern includes peaks resulting from both the RR/SS and the RS/SR forms. The water adsorption of troglitazone drug substance is due to the presence of the RR/SS diastereomer, which adsorbs water as a monohydrate. The solubility of troglitazone and the diastereomers were increased and the solubility ratios of the stereoisomers were changed by quenching. Troglitazone was proved to be stable against heat and humidity by the ratio of the stereoisomers and from the solid state form indicated by the DSC results.

Chemistry, Pharmaceutical↗

PubMed2002

Viscoelastic effects in relaxation processes of concentration fluctuations in dynamically asymmetric polymer blends.

Relaxation processes of the concentration fluctuations induced by a rapid pressure change were investigated for a dynamically asymmetric polymer blend [deuterated polybutadiene (DPB)/polyisoprene (PI)] with a composition of 50-50 by weight by using time-resolved small-angle neutron scattering. The pressure change was carried out inside the single-phase of the blend with the cell designed for polymeric systems under high pressure and temperature. Time change in the scattered intensity distribution with wave number (q) during the relaxation processes was found to be approximated by Cahn-Hilliard-Cook linearized theory. The theoretical analysis yielded the q dependence of Onsager kinetic coefficient that is characterized by the q(-2) dependence at q(xi)(ve)>1 with the characteristic length xi(ve) (with xi(ve) being the viscoelastic length) being much larger than radius of gyration of DPB or PI. The estimated xi(ve) agrees well with that calculated using the Doi and Onuki theory that takes into account the viscoelastic effects arising from the dynamical asymmetry between the component polymers in the relaxation of concentration fluctuations.

Journal Article↗

PubMed2002

[Endoscopic hemorrhoidal ligation from the rectum].

Endoscopic hemorrhoidal ligation with a rubber band was carried out on 40 patients with internal hemorrhoids. All the patients were treated in the outpatient ward. Seven patients complained of mild to moderate aches in the early postoperative days, which were easily controlled by medication. One week after the treatment, no patient complained of pain. None of the patients had any postoperative bleeding. The results of this treatment were classified as good (no complaint or symptoms after the treatment), fair (at least some improvement), or poor (no change or worse than before the treatment). Twenty-nine of the 40 patients were classified as good, and the remaining 11 patients were fair. No patients were classified as poor. EHL is a harmless and painless procedure and is easily performed in the outpatient ward. When internal hemorrhoids of operative indication are detected by colonoscopy, EHL can be easily and simultaneously carried out.

Adult↗