关于中国放射源管理的建议

1　放射性废物管理方面( 1 )应当建立一个国家级的废放射源管理战略。此战略应包括过去、现在和将来产生的所有放射性废物。此废物管理战略可以由国家指定的委员会来制订。该委员会可以包括来自主要废物的产生单位、废物管理机构和相应的审管部门的代表。此战略应当涵盖技术选择 (处理和处置 )和基础架构 (废物管理机构和基金 )。( 2 )放射性废物管理 ,包括废密封源管理。要求有专门的技术设施和特别训练的人员。为避免基础结构和人力资源重复设置 ,可以考虑单一的废物管理机构。该机构可设有区域性的分支机构 ,也可以设有专门的部门管理来…     

Natural Occurrence of Undecaenes in Some Fruits and Vegetables

1-(E,Z)-3,5-undecatriene and 1-(E,Z,Z)-3,5,8-undecatetraene were isolated under enzyme inhibition from edible parts of peach, passion fruit, and kiwi; the triene only was found in celery, parsley, mandarine, apple and pear. Capillary gas chromatography, sniffing-capillary gas chromatography, and combined “live”-capillary gas chromatography-mass spectrometry of the concentrated liquid-liquid extracts were used to establish their identity. Owing to their ultra-low odor detection thresholds and the proposed biogenesis, these trace compounds may be “character impacts” in a wide variety of food flavors of plant origin.     

Thermochemistry of MgAl2O4-Al8/3O4 Defect Spinels

Solution calorimetry of MgAl₂O₄-Al_8/3O₄ solid solutions was performed in a molten 2PbO · B₂O₃ solvent at 975 K. The results indicate small negative heats of mixing, relative to spinel standard states for both end-members. These data were combined with information on the energetics of the α-γ transition in Al₂O₃ and on the MgAl₂O₄-Al_8/3O₄ (MgO-Al₂O₃) subsolidus phase relations to estimate the partial molar entropy of mixing of γ-Al_8/3O₄ in the solid solution. This entropy is much less positive than that calculated from several models for the configurational entropy of mixing of magnesium, aluminum, and vacancies on octahedral and/or tetrahedral sites. The data suggest a good deal of local order to be present in the solid solutions, consistent with negative enthalpies of mixing and entropies of mixing far less than ideal configurational values.     

COMPUTER AIDED DESIGN OF HORN RADIATORS FOR SATELLITE COMMUNICATION BY LEAST SQUARES OPTIMIZATION

Computer aided design optimization of corrugated horns became a powerful tool to reduce development costs on the one hand and to improve performance of space antennas on the other. In this paper the physical model is outlined, based on Maxwell's equations, and it is shown how a complete numerical simulation of a circular corrugated horn can be achieved, assuming that the interior geometry of the horn is known. In order to compute the electromagnetic properties of a horn, the so-called scattering matrix is assembled. This matrix is needed to relate mode amplitudes of reflected and transmitted waves in horn sections with different diameters. Envelope functions, determined by a few geometric design parameters, are used to describe the inner geometry of a horn. These parameters are applied to formulate a least squares optimization problem. As a starting point, an amplitude spectrum in the aperture has to be determined which radiates a given far field. The differences between those amplitudes and the amplitudes predicted by the model are to become as small as possible by adapting the design variables. Moreover, the return loss is to be minimized. The resulting least squares optimization problem can be solved by a standard sequential quadratic programming (SQP) code after a suitable transformation into a nonlinear programming problem, by which typical features of Gauss-Newton methods are retained. Some numerical results are included to show the successful application of the introduced advance to design a circular corrugated horn which radiates a given far field.     

AUTOMATIC EXTRACTING AS AN INTERACTIVE PROCESS

In our study we have tried to evaluate most of the existing methods of automatic extracting and to combine them into one single system for text reduction. Hitherto, all existing automatic extracting systems have produced only extracts of documents: they select certain sentences from the full text and list them in text order.

Despite the result that statistical methods can be used for extracting German language texts (and that similar methods show best results for German and English texts) the main outcome of this study was that computer-based methods for text extracting can alter the whole extracting and abstracting process as such and lead to completely new and as yet unknown aspects of text reduction: the tailormade extract and extracting as an interactive process.     

Mechanical Properties of Hot-Pressed Silicon Nitride with Different Grain Structures

During hot-pressing of α-Si₃N₄ powders, the equiaxed α micro-structure gradually transforms into a β structure characterized by needle-shaped prismatic grains which are closely entangled and linked together. With increasing amounts of the β fraction, the bend strength, fracture toughness, and work of fracture increase significantly, then decrease as grain growth occurs. The K _lc, improves by a factor of >2 and the change in γ_F by a factor of >4. The crack resistance to achieve the same crack velocity in materials of different β contents shows a similar trend. The dependence of the mechanical properties on the microstructure is explained by linking and pullout of the β crystals and by grain coarsening.     

Phosphorus detection in vitrified bacteria by cryo‐STEM annular dark‐field analysis

Bacterial cells often contain dense granules. Among these, polyphosphate bodies (PPBs) store inorganic phosphate for a variety of essential functions. Identification of PPBs has until now been accomplished by analytical methods that required drying or chemically fixing the cells. These methods entail large electron doses that are incompatible with low‐dose imaging of cryogenic specimens. We show here that Scanning Transmission Electron Microscopy (STEM) of fully hydrated, intact, vitrified bacteria provides a simple means for mapping of phosphorus‐containing dense granules based on quantitative sensitivity of the electron scattering to atomic number. A coarse resolution of the scattering angles distinguishes phosphorus from the abundant lighter atoms: carbon, nitrogen and oxygen. The theoretical basis is similar to Z contrast of materials science. EDX provides a positive identification of phosphorus, but importantly, the method need not involve a more severe electron dose than that required for imaging. The approach should prove useful in general for mapping of heavy elements in cryopreserved specimens when the element identity is known from the biological context.     

DIFFUSION of LOW-MOLECULAR COMPOUNDS IN FOOD MODEL SYSTEMS

The diffusion of NaCl and isopropanol was studied in a matrix of pure gel and one containing either carbohydrates, proteins or fat using the concentration-distance method. Concentrations of NaCl were measured by conductivity, those of isopropanol by gas chromatography. Diffusion experiments have shown that the temperature dependence of the diffusion coefficient is in accordance with an Arrhenius approach.
Experimental and predicted diffusion coefficients didnot agree satisfactorily when only models of mere obstruction were considered. Including the effect of hydration by values obtained from pure gels, experimental diffusion coefficients range throughout between the calculated values of mere obstruction and those obtained from a mathematical combination of obstruction and maximum hydration.