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Biomedical subjects

Takayuki Kitamura

Publications and source records attributed to Takayuki Kitamura.

At least 19 recordsLinked to original sources
PubMed2006

Electron transport analysis for improvement of solid-state dye-sensitized solar cells using poly(3,4-ethylenedioxythiophene) as hole conductors.

Dye-sensitized solar cells (DSCs) using solid-state hole conductor, poly(3,4-ethylenedioxythiophene) (PEDOT), were fabricated using in-situ photoelectrochemical polymerization giving short-circuit photocurrent density of 3.20 mA cm-2, open-circuit voltage of 0.77 V, and fill factor of 0.50, and the resulting overall conversion efficiency of 1.25% on average under air mass 1.5 conditions. Furthermore, the electron transport properties of the DSCs based on PEDOT (PEDOT/DSCs) were analyzed using light intensity modulation induced photocurrent and photovoltage decay (SLIM-PCV) measurements and electrochemical impedance spectroscopy (EIS) measurements, and then compared to those of the DSCs based on organic liquid electrolyte containing I-/I3- as redox couple (liquid iodide/iodine electrolyte-DSCs, iodide/DSCs for short). The effective filling of PEDOT in the mesopores of dyed TiO2 layers is an important key to achieve the respectable conversion efficiency of PEDOT/DSCs that is comparable with iodide/DSCs.

Journal Article↗
PubMed2006

Averaged time evolution of rough surfaces.

We propose a method of extracting an approximated evolution equation of distribution of height fluctuations for a class of discrete growth models of rough surfaces where the behavior of local slopes can be described by a Markov process. Using the Markov property of the fluctuating field, the evolution equation is obtained as a map describing the time evolution averaged over possible growth paths. Applying the method to a -dimensional restricted solid-on-solid model, we obtain a map with finite degrees of freedom. The obtained map describes well the averaged evolution of surfaces.

Journal Article↗
PubMed2005

Dye-sensitized TiO2 nanotube solar cells: fabrication and electronic characterization.

TiO2 nanotubes (TNTs) with large aspect ratio and large specific surface area were prepared from P25 (Nippon Aerosil) and applied to dye-sensitized titanium dioxide solar cells (DSSCs). Optimization of fabrication conditions, i.e., pH of the starting paste, sintering temperature for the TiO2 electrodes, electrolyte compositions of DSSCs gave the high conversion efficiency with improved open circuit voltage (V(oc)) and fill factor (FF) when compared to DSSCs made of P25. The evaluation of dye adsorption and the photo-injected electron transport such as electron diffusion coefficient (D) and electron lifetime (tau) in TNTs electrodes revealed that the higher efficiency resulted from increase of electron density with keeping much longer tau in TNTs electrodes than in P25 electrodes.

Coloring Agents↗
PubMed2005

Origin of enhancement in open-circuit voltage by adding ZnO to nanocrystalline SnO2 in dye-sensitized solar cells.

SnO2 + ZnO working electrodes for dye-sensitized solar cells were made by mixing a nanocrystalline SnO2 colloidal dispersion with ZnO or Zn(CH3COO)2. Addition of ZnO or Zn(CH3COO)2 enhanced the open-circuit voltage (V(oc)) of the cells with respect to cells containing only SnO2. Dependence of the electron lifetime in the electrodes on short-circuit photocurrent density (J(sc)) gave evidence against the assumption that the suppression of back electron transfer to the electrolyte is the origin for the V(oc) enhancement by addition of Zn. V(oc) dependence on temperatures indicated a decrease in the combined capacitance of the mixed electrode. The slope of the V(oc) dependence versus the logarithm of J(sc) indicated that the contribution of unpinning of the band to the enhancement of V(oc) could be neglected. From the cyclic voltammograms of the electrodes, the combined capacitance of the mixed electrode was 1 order of magnitude smaller than that of SnO2. The decrease in the combined capacitance in the mixed electrode could be explained by the decrease in the chemical capacitance of SnO2, thus the shift of the conduction band position toward the vacuum level. X-ray photoelectron spectra of Sn 3d(5/2) peaks showed a shift toward lower binding energy with an increasing amount of added Zn. This was attributed to an increase in the surface potential toward the negative direction, which might have resulted from a dipole moment formed by Zn on the surface of SnO2.

Journal Article↗
PubMed2005

Volatile solvent-free solid-state polymer-sensitized TiO2 solar cells with poly(3,4-ethylenedioxythiophene) as a hole-transporting medium.

Novel, volatile solvent free, solid-state solar cells were fabricated with mesoporous TiO2 electrodes sensitized using thiophene derivatives containing carboxyl groups and in situ electropolymerized poly(3,4-ethylenedioxythiophene) as a hole-transporting material together with the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide and lithium bis(trifluoromethanesulfone)imide as additives for charge transport promotion.

Journal Article↗
PubMed2005

Roles of electrolytes on charge recombination in dye-sensitized TiO(2) solar cells (2): the case of solar cells using cobalt complex redox couples.

Dye-sensitized solar cells (DSC) were prepared from nanoporous TiO(2) electrodes with two different cobalt complex redox couples, propylene-1,2-bis(o-iminobenzylideneaminato)cobalt(II) {Co(II)(abpn)} and tris(4,4'-di-tert-buthyl-2,2'-bipyridine)cobalt(II) diperchlorate {Co(II)(dtb-bpy)(3)(ClO(4))(2)}. The performances of the DSCs were examined with varying the concentrations of the redox couples and Li cations in methoxyacetonitrile. Under 1 sun conditions, short-circuit currents (J(sc)) increased with the increase of the redox couple concentration, and the maximum J(sc) was found at the Li(+) concentration of 100 mM. To rationalize the observed trends of J(sc), electron diffusion coefficients and lifetimes in the DSCs were measured. Electron diffusion coefficients in the DSCs using cobalt complexes were comparable to the previously reported values of nanoporous TiO(2). Electron lifetime was independent of the concentration of the redox couples when the concentration ratio of Co(II)(L) and Co(III)(L) was fixed. With the increase of Li(+) concentration, the electron lifetime increased. These results were interpreted as due to their slow charge-transfer kinetics and the cationic nature of Co complex redox couples, in contrast to the anionic redox couple of I(-)/I(3)(-). The increase of the lifetimes with Li(+) was interpreted with the decrease of the local concentration of Co(III) near the surface of TiO(2). The addition of 4-tert-butylpyridine (tBP) with the presence of Li(+) increased J(sc) significantly. The observed increase of the electron lifetime by tBP could not explain the large increase of J(sc), implying that tBP facilitates the charge transfer from Co(II)(L) to dye cation, with the association of the change of the reorganization energy between Co(II) and Co(III).

Journal Article↗
PubMed2005

Role of electrolytes on charge recombination in dye-sensitized TiO(2) solar cell (1): the case of solar cells using the I(-)/I(3)(-) redox couple.

Performance of dye-sensitized solar cells (DSCs) was investigated depending on the compositions of the electrolyte, i.e., the electrolyte with a different cation such as Li(+), tetra-n-butylammonium (TBA(+)), or 1,2-dimethyl-3-propylimidazolium (DMPIm(+)) in various concentrations, with and without 4-tert-butylpyridine (tBP), and with various concentrations of the I(-)/I(3)(-) redox couple. Current-voltage characteristics, electron lifetime, and electron diffusion coefficient were measured to clarify the effects of the constituents in the electrolyte on the charge recombination kinetics in the DSCs. Shorter lifetimes were found for the DSCs employing adsorptive cations of Li(+) and DMPIm(+) than for a less-adsorptive cation of TBA(+). On the other hand, the lifetimes were not influenced by the concentrations of the cations in the solutions. Under light irradiation, open-circuit voltages of DSCs decreased in the order of TBA(+)> DMPIm(+) > Li(+), and also decreased with the increase of [Li(+)]. The decreases of open-circuit voltage (V(oc)) were attributed to the positive shift of the TiO(2) conduction band potential (CBP) by the surface adsorption of DMPIm(+) and Li(+). These results suggest that the difference of the free energies between that of the electrons in the TiO(2) and of I(3)(-) has little influence on the electron lifetimes in the DSCs. The shorter lifetime with the adsorptive cations was interpreted with the thickness of the electrical double layer formed by the cations, and the concentration of I(3)(-) in the layer, i.e., TBA(+) formed thicker double layer resulting in lower concentration of I(3)(-) on the surface of the TiO(2). The addition of 4-tert-butylpyridine (tBP) in the presence of Li(+) or TBA(+) showed no significant influence on the lifetime. The increase of V(oc) by the addition of tBP into the electrolyte containing Li(+) and the I(-)/I(3)(-) redox couple was mainly attributed to the shift of the CBP back to the negative potential by reducing the amount of adsorbed Li cations.

Journal Article↗
PubMed2005

Ionic liquid crystal as a hole transport layer of dye-sensitized solar cells.

Use of a new ionic liquid crystal, 1-dodecyl-3-methylimidazolium iodide, and iodine as an electrolyte of dye-sensitized solar cells leads to a high short circuit photocurrent density and a high light-to-electricity conversion efficiency, due to a self-assembled structure of the imidazolium cations, resulting in high conductivity of the electrolyte.

Journal Article↗
PubMed2005

[Headache attributed neurosurgical diseases].

When we see headache patients, it is most important thing that we rule out patients with intracranial diseases. Intracranial diseases with headache are so many. I'd like to emphasize some intracranial diseases with headache not to miss. Especially subarachnoid hemorrhage due to ruptured cerebral aneurysm is a serious disease not to miss. Recently the cases of dissecting cerebral aneurysm (vertebral artery) and venous/sinus thrombosis are increasing with spreading MRI/MRA examination. And brain tumors and chronic subdural hematoma is a serious disease not to miss in recent Japanese aging society. I'd like to mention these important diseases with headache.

Brain Diseases↗
PubMed2004

Radio-guided brain tumorectomy using a gamma detecting probe and a mobile solid-state gamma camera.

BACKGROUND: We herein report a technique to distinguish brain tumors from normal brain tissue during surgery using a gamma probe and a solid-state mobile gamma camera after (99m)Tc-hexakis-2-methoxy-isobutyl-isonitrile ((99m)Tc-MIBI) is administered to patients immediately before operation. METHODS: We examined 13 patients with brain tumors. Before the operation, (99m)Tc-MIBI single photon emission computed tomography (SPECT) was performed to assess accumulation in the tumors. On the day of the operation, (99m)Tc-MIBI was administered intravenously and craniotomy for tumor resection was performed. During the operation, the tumor was localized with a gamma probe and preremoval scintigraphy images were taken with a mobile gamma camera. After tumor resection was completed, residual tumors were confirmed using it again. We compared accumulation found in the preoperative SPECT images and intraoperative scintigraphy images, performed a histologic examination of adjacent tissues, and measured the dose the personnel was exposed to per operation. RESULTS: In all patients, tumors were confirmed by a gamma probe and scintigraphy during the operation. Intraoperative accumulation in tumors was significantly related to accumulation found in the preoperative (99m)Tc-MIBI SPECT images. In 9 out of 13 patients, accumulation disappeared in the postremoval scintigraphy images, and no tumor tissue was found by histologic examination. Residual tumor tissue was found in 4 patients. Average exposure of the personnel per operation was 22.9 +/- 4.0 microSv. CONCLUSION: Resection of brain tumors with a gamma probe and a mobile gamma camera was very useful since the area to be removed was easily identified and residual tumors could be detected.

Adult↗
PubMed2004

Change in bispectral index during epileptiform electrical activity under sevoflurane anesthesia in a patient with epilepsy.

UNLABELLED: We observed abnormal fluctuation in Bispectral Index (BIS) caused by repeated alternations between two electroencephalographic (EEG) waveform patterns in a patient with a recent history of epileptic seizure under sevoflurane anesthesia. The repetitive development of the abnormal EEG changes (slow delta with or without spike) and the fluctuation in BIS disappeared almost immediately after administration of anticonvulsants. BIS may give useful information not only on the sedative-hypnotic state, but also on the development of and recovery from abnormal epileptiform EEG activity. IMPLICATIONS: During epileptiform electroencephalographic activity (EEG), the Bispectral Index shows an abnormal fluctuation caused by repeated abrupt alterations between normal EEG and abnormal epileptiform EEG patterns.

Anesthetics, Inhalation↗
PubMed2004

Paramedian suboccipital mini-craniectomy for evacuation of spontaneous cerebellar hemorrhage.

Patients with spontaneous cerebellar hemorrhage are usually treated by large suboccipital craniectomy for hematoma evacuation or by computed tomography-guided stereotactic aspiration of the hematoma. The present study evaluated the outcome and complications in 25 patients with spontaneous cerebellar hemorrhage treated by paramedian suboccipital mini-craniectomy and 21 patients treated by large suboccipital craniectomy. There were no significant differences between the two groups with respect to age, clinical grade, hematoma volume, hematoma location, hydrocephalus, and mean interval from admission to operation. There was also no significant difference in postoperative outcome between the two groups. However, patients treated by paramedian suboccipital mini-craniectomy were less likely to require blood transfusion, had a shorter operating time, and had less postoperative liquorrhea compared with those undergoing extensive suboccipital craniectomy. Paramedian suboccipital mini-craniectomy is a simple and effective method for hematoma evacuation that causes fewer complications.

Adult↗
PubMed2003

High-affinity autoantibodies specifically eliminate granulocyte-macrophage colony-stimulating factor activity in the lungs of patients with idiopathic pulmonary alveolar proteinosis.

Deficiency of granulocyte-macrophage colony-stimulating factor (GM-CSF) in mice results in pulmonary alveolar proteinosis (PAP) from impaired surfactant catabolism by alveolar macrophages (AMs). Recently, we have shown that neutralizing anti-GM-CSF autoantibodies develop specifically in patients with idiopathic pulmonary alveolar proteinosis (iPAP). Analogous to murine PAP models, it is plausible that the autoantibodies reduce GM-CSF activity, resulting in AM dysfunction and surfactant accumulation. To examine this hypothesis, we estimated the neutralizing activity of the autoantibodies in the lungs of patients and characterized their biologic properties. GM-CSF bioactivity was completely abrogated in the bronchoalveolar lavage fluid (BALF) of patients with iPAP but not in healthy subjects. Autoantibodies were present in the alveoli in high concentrations and colocalized with GM-CSF. They recognized human GM-CSF with high avidity (K(AV) = 20.0 +/- 7.5 pM) and high specificity, reacting with its superstructure and neutralizing GM-CSF activity to a level 4000 to 58 000 times the levels of GM-CSF normally present in the lung. Although target epitopes varied among patients, GM-CSF amino acids 78 to 94 were consistently recognized. Thus, autoantibodies bind GM-CSF with high specificity and high affinity, exist abundantly in the lung, and effectively block GM-CSF binding to its receptor, inhibiting AM differentiation and function. Our data strengthen the evidence associating anti-GM-CSF autoantibodies with the pathogenesis of this disease.

Adult↗
PubMed2003

Tetra-n-butylammonium tetrakis(pentafluorobenzenethiolato-kappaS)aurate(III).

The title compound, (C(16)H(36)N)[Au(C(6)F(5)S)(4)], is the first example of a structurally characterized gold(III) complex with monodentate benzenethiolate ligands. The Au atom lies on a fourfold axis and the AuS(4) group has square-planar geometry. The anion shows a two-dimensional linkage through pi-pi and C-F...pi intermolecular interactions.

Journal Article↗
PubMed2003

Central neurocytoma expressing characteristics of ependymal differentiation: electron microscopic findings of two cases.

We describe two cases of central neurocytoma in the lateral ventricle. Ultrastructural examination showed occasional cilia mixed in with sparse dense core vesicles and thin tumor cell processes containing parallel microtubules. These central neurocytomas revealed evidence of ependymal differentiation. We propose that central neurocytoma originates from multiple differentiation from the germinal matrix cell layer.

Adult↗