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T Sasagawa

Publications and source records attributed to T Sasagawa.

At least 19 recordsLinked to original sources
PubMed2006

Strong and complex electron-lattice correlation in optimally doped Bi2Sr2CaCu2O8+delta.

We discuss the nature of electron-lattice interaction in optimally doped Bi_{2}Sr_{2}CaCu_{2}O_{8+delta} samples, using the isotope effect (IE) in angle resolved photoemission spectroscopy (ARPES) data. The IE in the ARPES linewidth and the IE in the ARPES dispersion are both quite large, implying a strong electron-lattice correlation. The strength of the electron-lattice interaction is "intermediate," i.e., stronger than the Migdal-Eliashberg regime but weaker than the small polaron regime, requiring a more general picture of the ARPES kink than the commonly used Migdal-Eliashberg picture. The two IEs also imply a complex interaction, due to their strong momentum dependence and their differing sign behaviors. In sum, we propose an intermediate-strength coupling of electrons to localized lattice vibrations via charge density fluctuations.

Journal Article↗
PubMed2006

Elastic scattering susceptibility of the high temperature superconductor Bi2Sr2CaCu2O(8+delta): a comparison between real and momentum space photoemission spectroscopies.

The joint density of states of Bi2Sr2CaCu2O(8+delta) is calculated by evaluating the autocorrelation of the single particle spectral function A(k, omega) measured from angle resolved photoemission spectroscopy (ARPES). These results are compared with Fourier transformed (FT) conductance modulations measured by scanning tunneling microscopy (STM). Good agreement between the two experimental probes is found for two different doping values examined. In addition, by comparing the FT-STM results to the autocorrelated ARPES spectra with different photon polarization, new insight on the form of the STM matrix elements is obtained. This shines new light on unsolved mysteries in the tunneling data.

Journal Article↗
PubMed2005

Polaronic behavior of undoped high-T(c) cuprate superconductors from angle-resolved photoemission spectra.

We present angle-resolved photoemission spectroscopy (ARPES) data on undoped La2CuO4, indicating polaronic coupling between bosons and charge carriers. Using a shell model, we calculate the electron-phonon coupling and find that it is strong enough to give self-trapped polarons. We develop an efficient method for calculating ARPES spectra in undoped systems. Using the calculated couplings, we find the width of the phonon sideband in good agreement with experiment. We analyze reasons for the observed dependence of the width on the binding energy.

Journal Article↗
PubMed2005

Multiple bosonic mode coupling in the electron self-energy of (La2-xSrx)CuO4.

High resolution angle-resolved photoemission spectroscopy data along the (0,0)-(pi,pi) nodal direction with significantly improved statistics reveal fine structure in the electron self-energy of the underdoped (La2-xSrx)CuO4 samples in the normal state. Fine structure at energies of (40-46) meV and (58-63) meV, and possible fine structure at energies of (23-29) meV and (75-85) meV, have been identified. These observations indicate that, in (La2-xSrx)CuO4, more than one bosonic modes are involved in the coupling with electrons.

Journal Article↗
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↗
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

Dichotomy between nodal and antinodal quasiparticles in underdoped (La2-xSrx)CuO4 superconductors.

High resolution angle-resolved photoemission measurements on an underdoped (La(2-x)Srx)CuO4 system show that, at energies below 70 meV, the quasiparticle peak is well defined around the (pi/2,pi/2) nodal region and disappears rather abruptly when the momentum is changed from the nodal point to the (pi,0) antinodal point along the underlying "Fermi surface." It indicates that there is an extra low energy scattering mechanism acting upon the antinodal quasiparticles. We propose that this mechanism is the scattering of quasiparticles across the nearly parallel segments of the Fermi surface near the antinodes.

Journal Article↗
PubMed2004

Delivery of all trans-retinoic acid (RA) to hepatocyte cell line from RA/galactosyl alpha-cyclodextrin inclusion complex.

All trans-retinoic acid (RA) plays a role in regulation of P450RAI gene expression. In this study, hepatocyte cell line (HepG2) was used to study an effect of RA released from RA/galactosyl alpha-cyclodextrin (GCD) inclusion complex on regulation of P450RAI gene expression. A delivery system composed of RA/GCD inclusion complex was applied because RA is poorly water soluble, and organic solvents used to dissolve it often interfere with cytotoxicity. Solubility of RA in water was increased by forming complex with GCD. Inclusion complex between GCD and RA was checked by (1)H-nuclear magnetic resonance, Fourier transformation infrared (FT-IR) spectroscopy and X-ray diffraction (XRD). The chemical shifts of the interior and exterior GCD protons in the presence of RA indicated that the RA was included within the GCD macrocycle cavity. The carbonyl band of RA and crystalline peak of RA in RA/GCD inclusion complex disappeared from FT-IR and XRD measurements, respectively, indication of inclusion complex between RA and GCD. From the observation of fluorescence micrograph of hepatocytes and flow cytometry measurement of HepG2, the internalization of fluorescein isothiocyanate-GCD by the hepatocyte occurred. Gene expression of P450RAI in HepG2 by delivery of RA from RA/GCD complex was observed.

Cell Line↗
PubMed2003

Metallic behavior of lightly doped La2-xSrxCuO4 with a Fermi surface forming an arc.

Lightly doped La2-xSrxCuO4 in the so-called "insulating" spin-glass phase has been studied by angle-resolved photoemission spectroscopy. We have observed that a "quasiparticle" (QP) peak crosses the Fermi level in the node direction of the d-wave superconducting gap, forming an "arc" of Fermi surface, which explains the metallic behavior at high temperatures of the lightly doped materials. The QP spectral weight of the arc smoothly increases with hole doping, which we attribute to the n approximately x behavior of the carrier number in the underdoped and lightly doped regions.

Journal Article↗
PubMed2003

Enhanced immunogenicity of human papillomavirus 16 L1 genetic vaccines fused to an ER-targeting secretory signal peptide and RANTES.

To increase the potency of human papillomavirus (HPV) DNA vaccines, we constructed a series of HPV16 L1 vaccines genetically fused with a secretion signal and/or immune cell-recruiting RANTES. The DNA vaccines encoding secretory HPV L1 were constructed by inserting HPV L1 gene into a vector with an ER-targeting secretory signal sequence. The expression plasmid encoding secretory HPV L1 (pER/L1) was fused with cDNA of RANTES, generating pER/L1/R. For comparison, HPV L1 genes were cloned into pVAX1 vector with no signal sequence (pL1), and further linked to the N-terminus (pL1/R) or C-terminus of RANTES (pR/L1). The secretion of L1 proteins was observed in the pER/L1, pER/L1/R, and pR/L1-transfected cells, except the pL1/R-transfected group. Cytoplasmic localization of L1 protein was observed in the cells transfected with pL1/R, but not with pER/L1/R at 48 h after transfection. In mice, RANTES-fused vaccines more effectively elicited the levels of HPV16 L1-specific IgG and IgG2a antibodies than pL1. Of RANTES-fused vaccines, pER/L1/R encoding the secreted fusion protein induced the highest humoral and CD8(+) T-cell-stimulating responses. These results suggest that the immunogenicity of HPV L1 DNA vaccines could be enhanced by genetic fusion to a chemokine and secretory signal peptide sequences.

Antibodies, Viral↗
PubMed2003

Pilot study of S-1 in patients with disseminated gastric cancer.

The prognosis for patients with advanced gastric cancer remains poor. Peritoneal metastasis is the most frequent cause of death in patients with gastric cancer, but the most appropriate treatment for patients with disseminated gastric cancer remains uncertain. S-1 is a newly developed oral fluoropyrimidine derivative with unusually high activity against several tumor types. The aim of this study was to evaluate the feasibility and efficacy of S-1 for the treatment of patients with disseminated gastric cancer. A total of 31 patients with primary or recurrent gastric cancer with peritoneal dissemination were entered into this study. One course of this single-drug therapy consisted of S-1 (80-120 mg) twice daily for 28 days, followed by a 2-week period of no treatment. These treatments were repeated until disease progression or patient refusal. With a median follow-up period in survivors of 293 days, the median survival time was 357 days. Toxicities were mild and no patient withdrew from treatment before disease progression. Grade 3 hematotoxicity was observed in only one patient. S-1 showed promising activity against gastric cancer with peritoneal dissemination and acceptable toxicity. Further evaluation of S-1 treatment is warranted in this disease.

Administration, Oral↗
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↗
PubMed2002

CD8+ T cells from feline immunodeficiency virus (FIV) infected cats suppress exogenous FIV replication of their peripheral blood mononuclear cells in vitro.

Feline immunodeficiency virus (FIV) isolates from domestic cats have been classified into five subtypes, designated A, B, C, D and E. Although many FIV-infected cats may have frequent contact with multiple strains of FIV, they usually become infected with a single FIV subtype. In the present study, we demonstrate that peripheral blood mononuclear cells (PBMC) of FIV infected cats were resistant to exogenous FIV (second virus) replication in vitro and that the resistance of these PBMC was mediated by CD8+ T cells. In cats with a low anti-FIV activity of CD8+ T cells, the proviral DNA of the second virus inoculated into PBMC was detected intracellularly, and both the second and the originally infecting strain (original virus) were produced in the culture supernatant. In contrast, in cats with a high anti-FIV activity of CD8+ T cells, both the proviral DNA of the second virus and the original virus were detected in PBMC intracellularly, but neither virus was produced in the culture supernatant. However, when PBMCs from these cats were depleted of CD8+ T cells, the RNA of both viruses was detected in the culture supernatant. These results suggest that CD8+ T cells inhibit the late phase of FIV replication after viral integration. Moreover, the inhibition was also effective against FIV strains of different subtypes from that of the original strain. It appears that the CD8+ T cell-mediated immune response plays important roles in the maintenance of an asymptomatic state in FIV-infected cats and their resistance to superinfection.

Animals↗
PubMed2002

Influences of a dietary fatty acid composition on the emergence of glutathione S-transferase-P (GST-P) positive foci in the liver of carcinogen-treated rats.

The rats treated with a single i.p. injection of diethylnitrosoamine (DEN) and percial hepatectomy were fed for 11 weeks with a high fat diet mixed with 10% lard, eicosapentaenoic-acid-rich oil (EPA-oil) or arachidonic-acid-rich oil (AA-oil) and the emergence of glutathione S-transferase placental form (GST-P) in the liver was evaluated. There were no significant differences in the serum aminotransferase activities. The molar ratio of n-6 and n-3 fatty acid in the liver phospholipids was significantly low in the EPA-oil group compared with the other groups. In the EPA-oil group, the area percent and the unit area of GST-P positive foci were significantly smaller than the other groups. In the AA-oil group, no significant differences were recognized in the quantitative values for GST-P positive foci compared with the control and lard groups. In conclusion, a hepatic neoplasmic lesion induced by DEN was suppressed with EPA-rich fish oil, and arachidonic-acid-rich oil showed no effect of suppression or acceleration.

Administration, Oral↗
PubMed2001

Pyridoxal 5'-phosphate inhibits DNA binding of HNF1.

An efficient Escherichia coli expression system was constructed for the production of a variant form of HNF1 protein having the additional five amino acid residues (Asp-Arg-Trp-Gly-Ser) at the NH(2)-terminal. The cDNA encoding HNF1 was ligated to 6 x His tag and inserted into an inducible bacterial expression vector pRSET A. After expression in E. coli, the recombinant product was purified by Ni-NTA affinity column chromatography. The purified product showed expected NH(2)-terminal sequence and specific binding to the HNF1 site. The effect of pyridoxal 5'-phosphate and its analogues on the binding activity of recombinant HNF1 was examined and found that only pyridoxal 5'-phosphate effectively inhibited the DNA binding. The concentration of pyridoxal 5'-phosphate that inhibited 50% of DNA binding was around 100 microM. Furthermore, we identified Lys197 of HNF1 molecule as the essential residue of DNA binding. These observations suggest that pyridoxal 5'-phosphate directly interacts with tissue-specific transcription factor HNF1 and modulates the binding to DNA.

Amino Acid Sequence↗
PubMed2001

Receptor-mediated delivery of all trans-retinoic acid to hepatocyte using poly(L-lactic acid) nanoparticles coated with galactose-carrying polystyrene.

All trans-retinoic acid (RA)-loaded poly(L-lactic acid) (PLA) nanoparticles coated with galactose-carrying polymer, as hepatocyte-specific targeting material using galactose ligands as recognition signals to asialoglycoprotein receptors were prepared by the diafiltration method. Effects of released RA from its loaded nanoparticles on morphology and DNA synthesis of hepatocytes were studied. Receptor-mediated endocytosis of the nanoparticles was checked by fluorescence and confocal laser microscopy. It was found that the shapes of most hepatocytes attached onto polystyrene dish precoated with collagen solution were flat and spreading at low concentration of RA for the RA-loaded nanoparticles, whereas their shapes were round at even low concentration of RA when RA was mixed with the nanoparticles. From the fluorescence and confocal laser microscopic studies, it was suggested that the nanoparticles coated with galactose-carrying polymers were internalized by the hepatocytes through the receptor-mediated mechanism. The RA-loaded nanoparticles were more potent stimulators of hepatocyte DNA synthesis than the free RA system in the presence of epidermal growth factor (EGF) owing to the controlled release of RA from the RA-loaded nanoparticles.

Animals↗