Biodegradation of poly(lactic acid) powders proposed as the reference test materials for the international standard of biodegradation evaluation methods

The methods for producing reference test materials for biodegradation evaluation tests have been studied. Mechanical crushing at low temperature of polymer pellets using dry ice was selected for the method of producing polymer powder of poly(lactic acid) (PLA). The powders were fractionated using 60 mesh (250 μm) and 120 mesh (125 μm) sieves. The size distributions were then measured. The average diameter of the PLA particles obtained by this method was 214.2 μm. The biodegradation speeds of these PLA polymer powders were evaluated by two methods based on the international standard and one in vitro method based on the enzymatic degradation. First, the degree of biodegradation for this PLA powder was 91% for 35 days in a controlled compost determined by a method based on ISO 14855-1 (JIS K6953) at 58 °C managed by the Mitsui Chemical Analysis and Consulting Service, Inc. (Japan). Second, these polymer powders were measured for biodegradation by the Microbial Oxidative Degradation Analyzer (MODA) in a controlled compost at 58 °C and 70 °C based on ISO/DIS 14855-2 under many conditions. The degree of biodegradation for this PLA powder was approximately 80% for 50 days. In addition, the polymer powders were biodegraded by Proteinase K which is a PLA degradation enzyme. This polymer powder was suitable as a reference material for the evaluation methods of biodegradation.     

Microwave spectrum,centrifugal distortion,internal rotation and excited torsional states of isobutene

The microwave spectrum of isobutene has been recorded from 10 to 35 GHz. From the analysis of the ground and first two excited torsional state splittings, the following internal rotation parameters were calculated: V₃ = 2170 cal mol.^?1, V'₁₂ = ?210 cal. mol.^?1, I_α = 3.18amu Ų and angle (methyl-top to b-axis) 58.21°. Centrifugal distortion parameters were also obtained for the ground state.     

The present situation of Japanese certified reference materials registered in the COMAR database

 In the field of reference materials, COMAR (Code d'Indexation des Matériaux de Référence) is now internationally known as a reliable directory. In order to improve the quality of COMAR, a document which covers general requirements for the registration of reference material has recently been adopted by the Japanese coding centre, NITE. This paper describes the general requirements for reference materials and the current status of the COMAR database coded by the National Institute of Technology and Evaluation (NITE), Japan. The concept of the requirements is fundamentally based on the ISO Guides 30, 31, 33, 34 and 35. Certifications of reference materials are divided into the following three categories in the newly adopted document. 1. Certifications based on the results of interlaboratory comparisons 2. Certifications in accordance with the Measurement Law 3. Certifications in accordance with the measurement results of national institutions An example of an uncertainty evaluation is also presented in the paper. Received: 14 October 1996 Accepted: 3 December 1996     

Solid-state NMR study of metastable immiscibility in alkali borosilicate glasses

In several series of lithium, sodium, and potassium borosilicate glasses whose compositions traverse known regions of liquid-liquid phase separation, we have applied triple-quantum magic-angle spinning (3QMAS) ¹¹B and ¹⁷O NMR to obtain high-resolution information about short-range structure and connections among various network structural units, and their variation with composition and thermal history. Oxygen-17 3QMAS spectra reveal changes in connectivities between silicate and BO₃ (^[3]B) and BO₄ (^[4]B) units, by quantifying populations of bridging oxygens such as B-O-B, Si-O-B and Si-O-Si, and of non-bridging oxygens. ^[3]B-O-Si and ^[4]B-O-Si as well as ^[3]B-O-^[3]B and ^[4]B-O-^[3]B linkages can be distinguished. ¹¹B MAS and 3QMAS at a magnetic field of 14.1 T allow proportions of several borate units to be determined, including ^[3]B in boroxol ring and non-ring sites and ^[4]B with 3 versus 4 Si neighbors. By combining the ¹¹B and ¹⁷O NMR results, detailed information on Si/B mixing in sodium borosilicates can be derived, showing, for example, that ^[4]B and non-ring ^[3]B tend to mix with silicate units, while ring ^[3]B is mainly connected to borate groups. In a preliminary study of the effects of varying alkali cation, potassium-containing glasses are similar to those in the sodium borosilicate system, but a lithium borosilicate seems to exhibit considerably greater chemical heterogeneity. In annealing experiments that converted an optically clear to obviously phase-separated glasses, the ratio of ^[3]B to ^[4]B does not change significantly, but part of the non-ring ^[3]B converts to ring ^[3]B as the degree of unmixing increases.     

EXAFS study of mechanical-milling-induced solid-state amorphization of Se

Complete solid-state amorphization has been realized in elemental selenium by means of mechanical milling of crystalline Se powder. Extended X-ray-absorption fine-structure measurements (EXAFS) indicated that the amorphization process of crystalline Se was accompanied with a decrease of the nearest neighboring coordination number and the bond length, and the increase of the Debye-Waller factor. Combined with the previous study, we conclude that the mechanical milling results in the strengthening of intra-chain and weakening of inter-chain interactions of Se during amorphization. Compared to the structure of the as-quenched amorphous Se, the first nearest neighbor coordination number of the as-milled amorphous Se becomes smaller, while the Debye-Waller factor is larger, which is caused by the milling process.     

Structural investigation of sodium borate glasses and melts by Raman spectroscopy.: I. Quantitative evaluation of structural units

Short-range and intermediate range structures of the sodium borate glass system were investigated using Raman spectroscopy to quantify their dependence on Na₂O concentration. High-resolution spectra were collected by Raman spectroscopy using the Q-switched, second-harmonic pulse of a Nd:YAG laser as an excitation source. The system was designed for measurement of the spectra of glasses and melts up to temperatures over 1000 °C with high signal to noise ratio. Use of polarized light and the simultaneous analysis of HH and VH spectra allowed deconvolution of Raman spectra into appropriate bands with high reproducibility. The deconvoluted bands in the high-frequency region of 1100-1600 cm⁻¹ could be assigned to the vibration modes due to the short-range structures of BO₃ and BO₂O⁻ units in the glasses. The band intensity ratios showed a simple linear relationship with the molar ratio, symmetric BO₃ triangle unit, N_3s, to asymmetric BO₂O⁻ triangle unit, N_3a, obtained from ¹¹B-NMR results. These results allowed a quantitative measure for normalizing the spectra leading to a direct comparison of the band intensities. The ring-structures of intermediate range order, boroxol, pentaborate, tetraborate and diborate groups, could be quantified from the spectra in the middle-frequency region. Their trends with Na₂O concentration showed a good consistency with ¹⁰B-NMR results and also Krogh-Moe’s model.     

Observation of a new photoluminescence band at 320 nm under 270 nm excitation in Ge-doped silica glass

We investigate the influence of temperature on photoluminescence (PL) in Ge-doped silica glass. Under 270 nm excitation, we observe only one PL band at 424 nm at room temperature (RT). This band shifts to 436 nm with cooling (4 K), and a new PL band is recorded at 320 nm. We assign these PL bands to triplet-to-singlet and singlet-to-singlet transitions of a same Ge-related defect, whose structure is still unknown. The shift of the PL band (from 424 nm at RT to 436 nm at 4 K) is explained by the decrease of the overlap between PLs from different centers.     

Management review checklist for ISO/IEC 17025 and ISO 15189 quality-management systems

Management reviews are key processes in many quality-management systems, including laboratory-management systems, in accordance with ISO/IEC 17025 and ISO 15189. These reviews are fine opportunities to understand and manage all the inputs and outputs of a quality-management system. Laboratories often meet some difficulties fully exploiting the management-review process because either they do not realize the importance of this process or they do not have the experience to run this process in a way producing the intended results. This work presents a management review checklist which helps laboratories carry out an effective management review going through all the important aspects of the quality-management system.     

符合ISO/IEC指南25-1990的实验室质量体系向ISO/IEC 17025-1999标准过渡的文件修改

按照ISO／IEC指南25－1990建立起较完善的质量体系的实验室,可通过对质量体系文件进行适当增补或少量删减,以实现向ISO／IEC 17025－1999标准的过渡。对质量手册,按照ISO／IEC指南25－1990的13个要素逐个讨论了具体的增删内容;对程序文件,则按ISO／IEC 17025－1999要求逐个列出了应有的程序。     

The (γ,p) reaction in Au

Proton energy spectra of the ¹⁹⁷Au(e,p) reaction were measured in the region between 17 and 30 MeV at three angles: 40°, 90° and 140°. Two prominent bumps were observed in the (γ,p) spectra converted using virtual photon theory. The higher-energy bump shifts with photon energies and the lower-energy one stays at 10.5 MeV. The higher-energy bump is much larger at 40° than at 140°; on the contrary the angular dependence of the lower-energy bump is small. Neither bump can be described by a statistical calculation. A calculation of a microscopic shell model shows that the lower-energy bump is attributed to the decay of proton-particle–neutron-hole pairs in the T_> states, leaving a neutron hole around the Fermi surface. The higher-energy bump can be ascribed to the direct–semidirect mechanism. This paper gives the solution to a part of the long-standing question about the origin of photo-proton emission in heavy nuclei.