The first 1,3-disilabicyclo[1.1.0]butane with long-bridge silicon-silicon bond.
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Journal Article↗
Biomedical subjects
M Kira
Publications and source records attributed to M Kira.
Exciton formation in semiconductors and the influence of a photonic environment.
A fully microscopic theory is presented for interacting electrons, holes, photons, and phonons in semiconductor heterostructures. The formation dynamics and statistics of incoherent excitons are analyzed for different densities, lattice temperatures, and photonic environments. Luminescence experiments are shown to depend strongly on the photonic environment in contrast to suggested terahertz absorption measurements. Whereas luminescence in free space is dominated by plasma contributions, terahertz absorption should be able to directly measure excitonic populations.
Journal Article↗
The mechanism of 1,2-addition of disilene and silene. 1. Water and alcohol addition.
The mechanism of 1,2-addition reactions of water, methanol, and trifluoromethanol to Si=Si, Si=C, and C=C bonds has been investigated by ab initio quantum chemical methods. Geometries and relative energies of the stationary points and all the transition states were determined using the MP2/6-311++G(d,p), B3LYP/6-311++G(d,p), and CBS-Q levels of theory. The investigated reactions can be characterized by two main thermodynamical profiles. The type in which the reagent molecule attacks a carbon atom is moderately exothermic, with a high activation barrier. The second type, in which water or alcohol attacks a silicon, is strongly exothermic, with a small activation energy. At the early stage of all the reactions, a weakly bonded initial complex is found which determines the further mechanism of the reaction. On the basis of the HOMO, LUMO, and Laplacian of electron distribution of disilene and silene, several mechanisms have been assumed, depending on the substrate (disilene, substituted disilene, silene, or ethene) and the reagent (water, methanol, or trifluoromethanol). The reaction diagrams and proposed mechanisms explain the experimentally found regioselectivity and diastereoselectivity well.
Journal Article↗
A mechanistic study of reactions of stable disilenes with haloalkanes.
Mechanisms of the reactions of three tetrakis(trialkylsilyl)disilenes and a tetraaryldisilene with various haloalkanes such as carbon tetrachloride, chloroform, dichloromethane, which gave the corresponding 1-alkyl-2-chlorodisilanes and/or 1,2-dichlorodisilanes, were investigated in detail. As evidenced by an ESR observation of an intermediate radical, these reactions were quite unusual, forming neutral radical pairs from two closed shell molecules at the first step; no similar reactions have been observed between alkenes and haloalkanes. Low oxidation potentials of these disilenes, large negative activation entropies, and solvent effects for the rates are in good accord with the direct halogen abstraction of disilenes from haloalkanes instead of single-electron transfer at the rate-determining first step. The structure--reactivity relationship of the reactions and the Hammond postulate suggest that the transition state structures for the first step are similar to those for the halogen abstraction by silyl radicals, but more product-like.
Journal Article↗
Dimers of diaminosilylenes: doubly bonded or bridged? The dimers of (i-Pr(2)N)(2)Si:.
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Letter↗
Diagnostic accuracy of simultaneous acquisition of transmission and emission data with technetium-99m transmission source on thallium-201 myocardial SPECT.
PURPOSE: This study evaluates not only the clinical usefulness but also the problems in attenuation correction for thallium-201 (Tl-201) myocardial SPECT by means of simultaneous transmission and emission data acquisition in the detection of coronary artery disease (CAD). METHODS: A three-detector SPECT system equipped with a Tc-99m line source and fan-beam collimators was used for simultaneous transmission and emission data acquisition for Tl-201 myocardial SPECT in 73 patients (18 patients for normal database and 55 patients for the evaluation of diagnostic accuracy). Attenuation-corrected (AC) images and non-attenuation-corrected (NC) images were reconstructed with an iterative maximum-likelihood estimation-corrected (ML-EM) algorithm. Both sets of images were reoriented into the short axis. Normal database polar maps were constructed from the AC and NC images for quantitative analysis. RESULTS: There was a significant difference in specificity between NC and AC images in the RCA territory and those in specificity and accuracy in the LCX territory. There was no significant difference in sensitivity found between NC and AC images in either territory, but sensitivity in both territories tended to decrease with attenuation correction. In the LAD territory, there were various changes in sensitivity and specificity observed with attenuation correction in cases with each quantitative criterion. CONCLUSIONS: Diagnostic performance of significant stenosis in the RCA and LCX territories quantitatively improved with attenuation correction because of an increase in specificity, but no significant improvement in diagnostic performance was obtained in the LAD territory with attenuation correction. We recommend combined interpretation of AC and NC images and careful evaluation of any SPECT image by means of transmission computed tomography.
Coronary Disease↗
Quantum correlations in the nonperturbative regime of semiconductor microcavities.
The nonlinear optical response of semiconductor microcavities in the nonpertubative regime is studied in resonant single-beam-transmission and pump-probe experiments. In both cases a pronounced third transmission peak lying spectrally between the two normal modes is observed. A fully quantized theory is essential for the agreement with the experimental observations, demonstrating that quantum fluctuations leading to intraband polarizations are responsible for this effect.
Journal Article↗
Two distinct signaling pathways in hair cycle induction: Stat3-dependent and -independent pathways.
The hair follicle is an epidermal derivative that undergoes cycles of growth, involution, and rest. The hair cycle has well-orchestrated kinetics regulated by interactions between mesenchymal and epithelial cells, although the intracellular signals remain unclear. We previously established keratinocyte-specific Stat3-disrupted mice, by which we demonstrated that signal transducer and activator of transcription 3 (Stat3) is required for wound healing and anagen progression in the hair cycle. Growth factor-dependent migration of Stat3-disrupted keratinocytes was severely impaired, suggesting that not only wound healing but also telogen-to-anagen progression required organized keratinocyte migration in response to mesenchymal stimuli. In the present study, to examine whether Stat3 activation in keratinocytes is a prerequisite for hair cycle progression, we applied methods for experimental anagen induction to Stat3-disrupted mice. It was demonstrated that anagen was successfully induced in Stat3-disrupted as well as wild-type mice by chemical or mechanical stimulation, i.e. , by topical application of phorbol 12-myristate 13-acetate (PMA) or by hair plucking, respectively. This result indicated that anagen in these methods occurred in the absence of Stat3. Furthermore, PMA stimulated the migration of Stat3-disrupted keratinocytes in vitro, supporting a hypothesis that the protein kinase C (PKC) and Stat3 pathways occur independently in the postnatal anagen induction. Both Stat3-dependent and -independent migration of keratinocytes was inhibited by a phosphoinositide 3-kinase (PI3K) inhibitor, wortmannin. Therefore, we infer that entry into anagen is mediated by at least two distinct signaling pathways: Stat3-dependent pathway for spontaneous hair cycling and Stat3-independent (probably PKC-dependent) pathway for exogenously induced hair cycling, whereas both pathways require PI3K activation.
Animals↗
A stable bicyclic compound with two Si=Si double bonds.
In contrast to carbon, silicon does not readily form double bonds, and compounds containing silicon-silicon double bonds can usually be stabilized only by protection with bulky substituents. We have isolated a silicon analog of spiropentadiene 1, a carbon double-ring compound that has not been isolated to date. In the crystal structure of tetrakis[tri(t-butyldimethylsilyl)silyl]spiropentasiladiene 2, a substantial deviation from the perpendicular arrangement of the two rings is observed, and the silicon-silicon double bonds are shown to be distorted. Spectroscopic data indicate pronounced interaction between two remote silicon-silicon double bonds in the molecule. Silicon-silicon bonds may be more accessible to synthesis than previously assumed.
Journal Article↗
Quantitative planar imaging method for measurement of renal activity by using a conjugate-emission image and transmission data.
We are proposing a method to accurately measure renal activity in renography using Tc-99m labeled tracers. This method uses a conjugate-view image and transmission data for attenuation correction, the triple energy window (TEW) method for scatter correction, and background correction techniques that consider the source volume for accurate background activity correction. To examine this method in planar imaging, we performed two renal phantom studies with various uniform background activity concentrations. One study used two ideal box-shaped kidney phantoms with a thickness of 2 or 4 cm in a water tank and the other study employed two real kidney-shaped phantoms in a fillable abdominal cavity. For these studies the kidney phantom-to-background activity concentration ratio (S) was changed from 5 to infinity. The transmission data were obtained with an external Tc-99m line array source. The anterior- and posterior-view emission images were acquired with a dual-headed gamma camera simultaneously and the TEW method was used to correct scatter for the emission and transmission images. The results showed that this method with both the accurate background correction and scatter correction could give depth-independent count rates and could estimate the true count rate with errors of less than 5% for all S values. However, if either accurate background correction or scatter correction was performed alone, the absolute error increased to about 50% for the smaller S values. Our proposed method allows one to accurately and simply measure the renal radioactivity by planar imaging using the conjugate-emission image and transmission data.
Kidney↗
Quantitative evaluation of the hepatic functional reserve using technetium-99m DTPA-galactosyl human serum albumin before and after transjugular intrahepatic portosystemic shunt.
Transjugular intrahepatic portosystemic shunt (TIPS), a new therapeutic method, has been performed widely for the treatment of portal hypertension. TIPS produces a decrease in the portal blood flow to the hepatic parenchyma, which is considered to cause a reduction in hepatic functional reserve. To evaluate the changes in hepatic functional reserve after TIPS, we performed technetium-99m DTPA-galactosyl human serum algumin (99mTc-GSA) hepatic scintigraphy before and after TIPS in eight male patients, ranging in age from 54 to 72 years (mean 62.2 years). Two quantitative indices - blood clearance index (uptake ratio of the heart at 15 min to that at 3 min, HH15) and hepatic accumulation index (uptake ratio of the liver to the liver plus heart at 15 min, LHL15) - were calculated from the time-activity curves of the heart and liver. Early and late uptake constant indices (early and late KU) were also calculated from the time-activity curves of the heart and liver by means of Patlak plot. The values of HH15, LHL15 and late KU deteriorated after TIPS in all patients. Early KU (1-3 min) decreased by more than 55% in two patients who showed a poor prognosis and corresponded well with the status of the portosystemic shunt. It is concluded that 99mTc-GSA hepatic scintigraphy is a useful means of evaluating the degree to which hepatic function is compromised following TIPS. The post-TIPS alterations in HH15, LHL15 and late KU (5-10 min) reflect the changes in hepatic functional reserve, and early KU is a useful index for evaluating the degree of portosystemic shunt.
Humans↗
[Energy spectral analysis in a photopeak region of 201Hg X-rays for 201Tl imaging].
For thallium-201 (201Tl) imaging, a photopeak of X-ray region of mercury-201 (201Hg) around 70 keV is usually employed. In such a low energy region, scatter and attenuation in the body become serious problems for quantitative scintigraphic imaging. We measured energy spectra around 201Hg X-ray region by a 201Tl line source with scattering materials and a gamma camera, and analyzed them to investigate the amount of scattered photons in 201Tl imaging window. Furthermore, Monte Carlo calculations were performed to distinguish primary photons from scattered photons. The results of analysis of energy spectra showed that the 201Hg X-ray photopeak consists of four different X-rays and do not have a perfect Gaussian shape. It was also found that not only forward scatter but also much backward scatter are included in this region. These scattered photons were reduced by using an off-peak window moved toward the higher energy region. We conclude that the data obtained from the analysis of scattered photons in 201Tl imaging window are very useful to develop a new scatter correction method and evaluate the scatter rejection methods proposed.
Gamma Cameras↗
[Scatter correction with an off-peak triple energy window method in thallium-201 imaging].
For scatter correction using the triple energy window (TEW) acquisition in 201Tl imaging, we propose an off-peak TEW (OFPTEW) method. This OFPTEW method employs a wide main energy window of 34 keV centered at 73 keV and two 5.1 keV sub-energy windows and uses the scatter correction factor of 0.55. To assess scatter correction using the OFPTEW method in 201Tl imaging, phantom studies for planar and SPECT imaging were performed and the data with the OFPTEW method were compared with those by the conventional TEW method using the trapezoidal formula with the 20% main energy window centered at 70 keV and two 4.9 keV sub-energy windows. The planar images corrected by both methods were visually similar. The OFPTEW method, however, estimated the true primary counts and the contrast value in the cold lesion accurately, while the conventional TEW method underestimated the primary counts by 30% and gave wrong contrast values. For the myocardial SPECT imaging, the short-axis images by both methods were very similar, but the images by the OFPTEW method had 1.46 times more counts than those corrected by the conventional TEW method. In conclusion, the OFPTEW method can correct scatter in 201Tl imaging accurately and increase the primary counts effectively compared with the conventional TEW method.
Phantoms, Imaging↗
[Experimental study on the location of energy windows for scatter correction by the TEW method in 201Tl imaging].
To investigate validity of scatter correction by the TEW method in 201Tl imaging, we performed an experimental study using the gamma camera with the capability to perform the TEW method and a plate source with a defect. Images were acquired with the triple energy window which is recommended by the gamma camera manufacturer. The result of the energy spectrum showed that backscattered photons were included within the lower sub-energy window and main energy window, and the spectral shapes in the upper half region of the photopeak (70 keV) were not changed greatly by the source shape and the thickness of scattering materials. The scatter fraction calculated using energy spectra and, visual observation and the contrast values measured at the defect using planar images also showed that substantial primary photons were included in the upper sub-energy window. In TEW method (for scatter correction), two sub-energy windows are expected to be defined on the part of energy region in which total counts mainly consist of scattered photons. Therefore, it is necessary to investigate the use of the upper sub-energy window on scatter correction by the TEW method in 201Tl imaging.
Phantoms, Imaging↗
Excitonic Nonlinearities of Semiconductor Microcavities in the Nonperturbative Regime.
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Journal Article↗
Microscopic model for a quantum cascade laser.
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Journal Article↗
Quantitative renography with the organ volume method and interporative background subtraction technique.
When quantification of renal activity is performed by planar imaging, many correction factors must be considered. To obtain quantitative renal images and renogram, we have examined our proposed method by using the organ volume for scatter, attenuation, and background activity, and the interporative background subtraction (IBS) technique in phantom and clinical studies. A renal phantom study was performed by varying the renal depth from 3 to 11 cm and the kidney-to-background activity concentration ratio from 5 to 80. Planar images were properly corrected for scatter, attenuation and background activity by our method and the corrected images were compared with the images obtained by the conventional method for the estimation of true renal activity. Clinical Tc-99m DTPA dynamic data for both a good and a poor renal function were also corrected by our method and volume-corrected renograms were obtained. For the phantom study, depth-independent images were obtained and these images gave a good estimation of the true count rate. In the clinical study, the conventional renogram was especially modified to allow for oversubtraction of background counts in the early phase (0-4 min). In conclusion, our proposed correction method can assess renal function qualitatively and quantitatively in both static and dynamic planar renal imaging.
Evaluation Studies as Topic↗
[Evaluation of simultaneous acquisition of transmission and emission data on thallium-201 myocardial SPECT].
This study evaluates the usefulness of attenuation correction on regional myocardial tracer distributions defined by Thallium-201 myocardial SPECT images obtained from cardiac phantoms and patients with or without coronary heart disease. A three-detector SPECT system equipped with a Technetium-99m line source and a fan-beam collimator was used for simultaneous transmission and emission data acquisition. All three detectors were equipped with fan-beam collimators. Thallium-201 myocardial scintigraphy was performed on phantom study and 19 patients. Transmission images, uncorrected and corrected emission images were iteratively reconstructed with a EM-ML algorithm. Attenuation map computed from the transmission data was utilized for the attenuation correction. For the phantom study, circumferential profile analysis was applied to both datasets of horizontal long-axis slices through the center of the phantom. The maximum profile value in the circumferential profile set to 100% in the normalized uncorrected and corrected profiles. The uncorrected circumferential profiles from cardiac insert model 7070 and RH-2 cardiophantom showed decrease in activity in basal regions which appeared improvement in the attenuation corrected profiles. In clinical study, the inferior-to-anterior activity ratio, changed from 0.78 +/- 0.10 to 0.97 +/- 0.11 on stress images in patients with inferior ischemia and from 0.96 +/- 0.12 to 1.15 +/- 0.13 on 4 hour delayed or rest images in normal cases. The anteroapical wall of the attenuation corrected images, however, showed a decrease in activity relative to the inferior wall in normal cases. The increase in activity in inferior wall on attenuation corrected images was observed frequently in clinical study but not in phantom study. A presence of scatter from the liver or bowels may cause the increase in activity in the inferior wall in clinical study. In conclusion, transmission scan is one of the useful methods for the attenuation correction. Scatter correction, however, is also necessary to make an accurate attenuation corrected images.
Heart↗