放射性废物概述

全世界许多国家都在着手于核废物的管理任务．目前，还不能认为这个极其困难的问题在任何国家中真正得到了解答，然而又必须得出解答．本文中概括地说明了有关核废物各方面的常识     

The reaction pattern of norbornene with excited state carbonyl compounds: Photochemical preparations of norbornene derivatives

We established that acetylacetone and acetone photolytically sensitize norbornene to undergo an efficient radical addition of solvent (ranging from hexane, cyclic ethers, haloalkanes, acetone, alcohols and acetonitrile) across the double bond. In view of its synthetic applicability, sensitized photoreactions of norbornene were reviewed and their mechanisms were compared. Photolysis of acetylacetone in the presence of norbornene in hexane induced i) acetylacetone to cycloadd to norbornene giving the expected 1,5-diketone, and ii) sensitization by triplet excited acetylacetone to generate reactive norbornene, which underwent dimerization as well as the addition of a solvent molecule by radical chain processes. In other solvents, the radical chain addition of solvent dominated the photoreaction, and superseded the cycloaddition, to give excellent to good yields of adducts to norbornene. While the excited species of acetylacetone for the sensitization was deduced to be its spectroscopic triplet excited state, that for the cycloaddition should involve a different one which may be a twisted triplet acetylacetone; sensitization experiments showed that the cycloaddition did not occur from the spectroscopic triplet state. Triplet excited acetone sensitized norbornene to undergo the same solvent addition more efficiently and cleanly than acetylacetone did. In view of various conflicts existing in the proposed energy transfer mechanism, the sensitized norbornene reactions were rationalized with electron transfer and a cation radical chain mechanism.     

Experimental study of a plasma-filled backward wave oscillator

Experimental studies of a plasma-filled X-band backward-wave oscillator (BWO) are presented. Depending on the background gas pressure, microwave frequency upshifts of up to 1 GHz appeared along with an enhancement by a factor of 7 in the total microwave power emission. The bandwidth of the microwave emission increased from ⩽0.5 GHz to 2 GHz when the BWO was working at the RF power enhancement pressure region. The RF power enhancement appeared over a much wider pressure range in a high beam current case (10-100 mT for 3 kA) than in a lower beam case (80-115 mT for 1.6 kA). The plasma-filled BWO has higher power output than the vacuum BWO over a broader region of magnetic guide field strength. Trivelpiece-Gould modes (T-G modes) are observed with frequencies up to the background plasma frequency in a plasma-filled BWO. Mode competition between the T-G modes and the X-band Tm₀₁ mode prevailed when the background plasma density was below 6×10¹¹ cm^-3 . At a critical background plasma density of ≃8×10¹¹ cm^-3 power enhancement appeared in both X-band and the T-G modes. Power enhancement of the S-band in this mode collaboration region reached up to 8 dB. Electric fields measured by the Stark-effect method were as high as 34 kV/cm while the BWO power level was 80 MW. These electric fields lasted throughout the high-power microwave pulse     

The standard model on non-commutative space-time

We consider the standard model on a non-commutative space and expand the action in the non-commutativity parameter . No new particles are introduced; the structure group is . We derive the leading order action. At zeroth order the action coincides with the ordinary standard model. At leading order in we find new vertices which are absent in the standard model on commutative space-time. The most striking features are couplings between quarks, gluons and electroweak bosons and many new vertices in the charged and neutral currents. We find that parity is violated in non-commutative QCD. The Higgs mechanism can be applied. QED is not deformed in the minimal version of the NCSM to the order considered. Received: 29 November 2001 / Published online: 25 January 2002     

线状锗等离子体X射线线谱的时间分辨测量

用自行研制的X射线条纹晶体谱仪首次测量了线状锗等离子体的X射线时间分辨谱。给出了类Ne-锗L线共振线的时间演化过程,并用类Ne-锗L线共振线与其双电子俘获伴线的相对强度比粗估了锗等离子体的电子温度及其随时间的变化,实验给出了X光激光增益区介质的电子温度为400～760eV,同时给出了电子温度保持相对恒定的时间不小于90ps(电子温度变化小于2％)。     

Determination of the portfolio selection for a property-liability insurance company

This paper presents an analysis of a portfolio model which can be used to assist a property-liability insurance company in determining the optimal composition of the insurance and investment portfolios. By introducing insurer's threshold risk and relaxing some non-realistic assumptions made in traditional chance constraint insurance and investment portfolio models, we propose a method for an insurer to maximize his return threshold for a given threshold risk level. This proposed model can be used to optimize the composition of underwriting and investment portfolios regarding the insurer's threshold risk level, as well as to generate the efficient frontier by adjusting insurer's threshold risk levels. A numerical example is given based on the industry's aggregated data for a sixteen year period.     

Observation of spontaneous pattern with six-fold symmetry in disk-shaped ZnO complex microstructures

Using a simple vapor phase transport technique, we have fabricated unique complex disk-shaped ZnO microstructures comprising a small disk coaxially grown on a large one and observed spatially perfect six-fold symmetric patterns. The observed results can be explained based on the spontaneous nanoindentation (NI) effect under the geometric constraints and the explanation can be extended to fathom the growth mechanism of other highly symmetrical ZnO nanostructures. Our results indicate that NI not only can elucidate the mechanical properties of surfaces and thin films but also is an effective approach to fabricate ordered nanostructures with high precision on the location of the building blocks. PACS 81.16.Rf; 81.07.-b; 81.05.Dz     

Effect of nitrogen surface doping on the work function and field emission of hydrogenated amorphous carbon films

The effect of nitrogen surface doping on the electron field emission characteristics of hydrogenated amorphous carbon films was studied. It was found that the emission threshold electric field decreased after nitrogen surface doping which indicated the reduction of the emission barrier at the film surface. It was demonstrated that this improvement arose from the decrease of the effective work function due to the formation of a dipole layer induced by chemical termination and chemical structural change on the film surface. PACS 52.75.Xx; 73.30 +y; 73.61.Jc