In-situ monitoring of UF5 nanoparticle growth in a plug-flow reactor by a low-pressure differential mobility analyzer

The dependence of UF₅ nanoparticle size distribution on growth time was investigated for various initial concentrations of UF₅ monomers. UF₅ nanoparticles prepared by photodissociation of UF₆ in a mixed-flow reactor were allowed to pass through a plug-flow reactor (PFR), and their size distribution was measured by an in-situ size-monitoring system, namely a low-pressure differential mobility analyzer. By changing the length of the PFR, the growth time in the PFR was controlled from 0 to 30 s. An analysis using Lee’s coagulation model revealed that the growth mechanism of the UF₅ nanoparticles involved a Brownian coagulation process and that the sticking probability of the nanoparticles was approximately unity. Received: 27 August 2001 / Accepted: 6 September 2001 / Published online: 20 December 2001     

A Mathematical Model of Intermittent Androgen Suppression for Prostate Cancer

For several decades, androgen suppression has been the principal modality for treatment of advanced prostate cancer. Although the androgen deprivation is initially effective, most patients experience a relapse within several years due to the proliferation of so-called androgen-independent tumor cells. Bruchovsky et al. suggested in animal models that intermittent androgen suppression (IAS) can prolong the time to relapse when compared with continuous androgen suppression (CAS). Therefore, IAS has been expected to enhance clinical efficacy in conjunction with reduction in adverse effects and improvement in quality of life of patients during off-treatment periods. This paper presents a mathematical model that describes the growth of a prostate tumor under IAS therapy based on monitoring of the serum prostate-specific antigen (PSA). By treating the cancer tumor as a mixed assembly of androgen-dependent and androgen-independent cells, we investigate the difference between CAS and IAS with respect to factors affecting an androgen-independent relapse. Numerical and bifurcation analyses show how the tumor growth and the relapse time are influenced by the net growth rate of the androgen-independent cells, a protocol of the IAS therapy, and the mutation rate from androgen-dependent cells to androgen-independent ones.

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The High-Resolution ν5 Band of Jet-Cooled Si2F6

Vibration-rotation spectra of the parallel ν₅ band of hexafluorodisilane have been measured in a supersonic free jet with 0.001 cm⁻¹ resolution. Three isotopic species, ^28,28Si₂F₆, ^28,29Si₂F₆, and ^28,30Si₂F₆, have been studied. The effect of internal rotation is not observed, indicating that the splitting is smaller than our spectral resolution. A very weak parallel band observed with a slight red shift from the ν₅ fundamental band has been assigned tentatively to the (ν₄ + ν₅)-ν₄ hot band.     

Triton with N---N potential from a quark model

The properties of the three-nucleon bound state are studied employing a nucleon-nucleon potential deduced from the quark cluster model in a five-channel Faddeev calculation. The triton is bound about 0.2–0.3 MeV more than would be expected from conventional meson-exchange models.     

Pyrolysis and mass spectra of trimethylsilyl derivatives of monosaccharides

The pyrolysis of trimethylsilyl derivatives of saccharides (1) was investigated by DTA-TG, MS, GC/MS and TG-GC/MS. The DTA-TG/DTG curves showed that the pyrolysis of 1 occurred in one stage. The exothermic peaks were due to sublimation or thermal decomposition by vaporization. The cleavage mechanism by electron impact of 1 was classified into four categories: 1) stepwise elimination of the side-chain, 2) cleavage of the side-chain, 3) cleavage of the pyranose ring, and 4) cleavage of the pyranose ring and side-chain at the same time. The mass-spectrum for 1 revealed the main common four fragment ions, such asm/z 73, 191, 204 and 217, with cleavage of the pyranose ring. These fragment ions were detected with a similar retention time in the gas cromatogram by GC/MS or TG-GC/MS. The retention time for 1 increased in the sequence aldopentose相似文献   

Design of unique titanium oxide photocatalysts by an advanced metal ion-implantation method and photocatalytic reactions under visible light irradiation

The metal ion-implantation of titanium oxide with various transition metal ions was carried out by applying by high voltage acceleration. The subsequent calcination of the implanted TiO₂ in oxygen at around 723 K resulted in a large shift in the absorption spectra of the TiO₂ toward visible light regions, its extent being dependent on the amount and the kind of metal ions implanted. Such metal ion-implanted titanium oxide catalysts were active in carrying out various photocatalytic reactions such as the decomposition of NO into N₂, O₂ and N₂O at 275 K under irradiation with visible light longer than 450 nm. The application of this advanced, high energy metal ion-implantation method enables the novel design of titanium oxide photocatalysts which can absorb and initiate vital reactions under visible light and will contribute to the development of catalytic systems utilizing solar energy.     

Iridium complex-catalyzed method for the construction of a quaternary carbon center α to allene

[Ir(cod)Cl]₂/dppe-catalyzed allylic alkylation of 1,1-disubstituted-2,3-butadienyl acetates gives a product bearing a quaternary carbon center α to allene in high yield.     

Indirect photometric detection of monovalent cations via postsuppressor ion replacement in microcolumn ion chromatography

Summary Monovalent cations were indirectly detected via postcolumn suppressor ion replacement in microcolumn ion chromatography. The ion-repalcement column loaded by chromophoric ions was connected to the suppressor column. The eluent, nitric acid, was converted to water through the suppressor and anion-replacement columns, while the analyte cations were coeluted with the chromophoric anions. The analyte cations were indirectly detected by measuring UV absorptions of the chromophoric anions.     

Cross section of supercooled238UF6 in multiphoton absorption induced by 16 micrometer Raman-laser radiation

Measurements of multiphoton absorption of 16 µm Raman-laser radiation in supercooled²³⁸UF₆ at 90 K were performed by using a pulsed Laval nozzle with an optical path length of 50 cm. The laser fluence was varied between 50 and 500 mJ/cm² for four frequencies in the range from 625 to 629 cm^–1. The energy absorbed by²³⁸UF₆ molecules was investigated as a function of laser frequency or fluence, and highly accurate results were obtained with the use of the nozzle whose optical path length is much greater than that of nozzles used before. The results indicated that the absorption cross section at the peak absorption frequency (627.8cm^–1) was proportional to the –1/3 power of the fluence.