Studies on the constituents of Catalpa species. IX. Iridoids from the fallen leaves of Catalpa ovata G. Don

Two new iridoids, 6-O-trans-p-coumaroyl-7-deoxyrehmaglutin A (1) and 6-O-cis-p-coumaroyl-7-deoxyrehmaglutin A (2), were isolated from the fallen leaves of Catalpa ovata G. DON. together with six artifact iridoids (3-8). Their structures were established by spectral analysis. In addition, the scavenging effects of the principal compounds isolated from this plant on 1,1-diphenyl-2-picrylhydrazyl radical-scavenging activity were examined.     

Metal-induced gap states at well defined alkali-halide/metal interfaces

In order to search for states specific to insulator/metal interfaces, we have studied epitaxially grown interfaces with element-selective near edge x-ray absorption fine structure. An extra peak is observed below the bulk edge onset for LiCl films on Cu and Ag substrates. The nature of chemical bonds as probed by x-ray photoemission spectroscopy and Auger electron spectroscopy remains unchanged, so we regard this as evidence for metal-induced gap states (MIGS) formed by the proximity to a metal, rather than local bonds at the interface. The dependence on the film thickness shows that the MIGS are as thin as one monolayer. An ab initio electronic structure calculation supports the existence of the MIGS that are strongly localized at the interface.     

Measurement of bidirectional reflectance distribution function with a linear light source

This paper proposes a practical measurement system for bidirectional reflectance distribution functions (BRDFs) of a three-dimensional (3D) object with a linear light source. Using the linear light source, the proposed system can reduce the number of image acquisitions which are necessary for an estimation of the spatially-varying BRDFs of the object. Furthermore, the size of the proposed system is much smaller than a conventional system which uses a parallel light. In this proposed system, the light field of the linear light source is previously measured to determine direction and radiance of incident rays to each point of the object, because the direction and radiance are not constant at each point. Using the proposed system, the BRDF of a point of flat objects was experimentally measured, and results showed validation of the estimation accuracy of the proposed system. Measurement efficiency of the proposed system was also evaluated by comparing reflectance model parameters estimated by the conventional and proposed systems. For the estimation, the reflectance function of a 3D object was measured by both systems. The estimation accuracy of the proposed method was also evaluated by comparing among a real image and rendered 3D objects of the conventional and proposed methods.     

On formation of thin SiO2/a-Si:H interface when biased oxidized semiconductor surface interacts with plasma or liquid solution

In this paper we present the results of research into a relation(s) between the bias voltage of an oxide/a-Si:H/c-Si sample during formation of very-thin and thin oxides and the resulting distribution of oxide/semiconductor interface states in the a-Si:H band gap. Two oxygen plasma sources were used for the first time in our laboratories for formation of oxide layers on a-Si:H: i) inductively coupled plasma in connection with its application at plasma anodic oxidation; ii) rf plasma as the source of positive oxygen ions for the plasma immersion ion implantation process. The oxide growth on a-Si:H during plasma anodization is also simply described theoretically. Properties of plasmatic structures are compared to ones treated by chemical oxidation that uses 68 wt% nitric acid aqueous solutions. We have confirmed that three parameters of the oxide growth process — kinetic energy of interacting particles, UV-VIS-NIR light emitted by plasma sources, and bias of the samples — determine the distribution of defect states at both the oxide/a-Si:H interface and the volume of the a-Si:H layer, respectively. Additionally, a bias of the sample applied during the oxide growth process has a similar impact on the distribution of defect states as it can be observed during the bias-annealing of similar MOS structure outside of the plasma reactor. Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia     

Decay asymmetry in non-mesonic weak decay of light Λ -hypernuclei

The proton decay asymmetry, α^NM _p , of the polarized Λ -hypernuclei, ⁵ _ΛHe , ¹² _ΛC and ¹¹ _ΛB , has been investigated to understand the reaction mechanism of the non-mesonic weak-decay process. These Λ -hypernuclei were produced in the highest statistics ever via the (π⁺, K ⁺) reaction at 1.05GeV/c by using the SKS spectrometer at KEK 12GeV PS. The results show that the α^NM _p are very small for these s -shell and p -shell hypernuclei.     

On interface properties of ultra-thin and very-thin oxide/a-Si:H structures prepared by oxygen based plasmas and chemical oxidation

Amorphous hydrogenated silicon (a-Si:H) belongs still to most promising types of semiconductors for its utilization in fabrication of TFTs and thin film solar cell technology due to corresponding cheap a-Si:H-based device production in comparison with, e.g. crystalline silicon (c-Si) technologies. The contribution deals with both two important modes of preparation of very-thin and ultra-thin silicon dioxide films in the surface region of a-Si:H semiconductor (oxygen plasma sources and liquid chemical methods) and electrical, optical and structural properties of produced oxide/semiconductor structures, respectively. Dominant aim is focused on investigation of oxide/semiconductor interface properties and their comparison and evaluation from view of utilization of used technological modes in the nanotechnological industry. Following three basic types of oxygen plasma sources were used for the first time in our laboratories for treatments of surfaces of a-Si:H substrates: (i) inductively coupled plasma in connection with its applying at plasma anodic oxidation; (ii) rf plasma as the source of positive oxygen ions for plasma immersion ion implantation process; (iii) dielectric barrier discharge ignited at high pressures.The liquid chemical manner of formation SiO₂/a-Si:H structures uses 68 wt% nitric acid aqueous solutions (i.e., azeotropic mixture with water). Their application in crystalline Si technologies has been presented with excellent results in the formation of ultra-thin SiO₂/c-Si structures [H. Kobayashi, M. Asuha, H.I. Takahashi, J. Appl. Phys. 94 (2003) 7328].Passivation of surface and interface states by liquid cyanide treatment is additional original technique applied after (or before) formation of almost all formed thin film/a-Si:H structures. Passivation process should be used if high-quality electronical parameters of devices can be reached.     

An inequality for finite permutation groups

An inequality which has a combinatorial theoretical flavor is proved for finite permutation groups.     

Explanation for the 3.4-power law for viscosity of polymeric liquids on the basis of the tube model

The viscosity η₀(M) of polymeric liquids of molecular weight M is calculated on the basis of the tube model formulated by Doi and Edwards (ref. 3). The contour length fluctuation of polymers along the tube, which was neglected in ref. 3, is now explicitly taken into account. The result is where M_c = 2M_e, and M_e is the molecular weight between the entanglement points. This result is numerically close to the empirical 3.4-power law, η₀(M) = η₀(M_c)(M/M_c)^3.4, for 10M_c ? M ? 100M_c but approaches the result in ref. 3 for very high molecular weight. We thus conclude that the 3.4-power law is actually an approximate expression for the real curve which slowly approaches the asymptotic form calculated in ref. 3.     

Stereocontrolled syntheses of chiral intermediates of thienamycin from threonines

Both stereospecific and stereoselective syntheses of thienamycin intermediates which have the correct configurations at the three contiguous chiral centers are reported.