The 14-22 μm absorption spectrum of nitrous acid studied by high-resolution Fourier-transform spectroscopy: New analysis of the ν5 and ν6 interacting bands of trans-HONO and first analysis of the ν6 band of cis-HONO

High-resolution Fourier-transform absorption spectra of nitrous acid (HONO) were recorded in the 400-700 cm⁻¹ spectral region. For the trans-HONO isomer a very extensive analysis of the ν₅ (ONO bend) and ν₆ (torsion) interacting fundamental bands of trans-HONO located near 595.620 and 543.879 cm⁻¹, respectively, was performed starting from the results of a previous study [C.M. Deeley, I.M. Mills, L.O. Halonen, J. Kauppinen, Can. J. Phys. 63 (1985) 962-965]. In addition, for the less abundant cis-HONO isomer, the first high-resolution study of the ν₆ band located at 639.7432 cm⁻¹ was achieved, the ν₅ band is presumed to be located near 609.2 cm⁻¹. For both isomers the strong A-type and B-type Coriolis interactions linking the {5¹, 6¹} interacting energy levels were accounted for during the energy level calculations. Finally, using these results a list of positions and of realistic relative line intensities has been generated for both isomers, and a comparison with some ab initio predictions was performed.     

Use of fluorobenzoyl protective groups in synthesis of glycopeptides: beta-elimination of O-linked carbohydrates is suppressed

Fluorobenzoyl groups have been investigated as alternatives to acetyl and benzoyl protective groups in carbohydrate and glycopeptide synthesis. D-Glucose and lactose were protected with different fluorobenzoyl groups and then converted into glycosyl bromides in high yields (>80% over two steps). Glycosylation of protected derivatives of serine with these donors gave 1,2-trans glycosides in good yields (approximately 60--70%) and excellent stereoselectivity without formation of ortho esters. The resulting glycosylated amino acid building blocks were then used in solid-phase synthesis of two model O-linked glycopeptides known to be unusually sensitive to beta-elimination on base-catalyzed deacylation. When either a 3-fluoro- or a 2,5-difluorobenzoyl group was used for protection of each of the two model glycopeptides the extent of beta-elimination decreased from 80% to 10% and from 50% to 0%, respectively, as compared to when using the ordinary benzoyl group. Fluorobenzoyl groups thus combine the advantages of the benzoyl group in formation of glycosidic bonds (i.e., high stereoselectivity and low levels of ortho ester formation) with the ease of removal characteristic of the acetyl group.     

Credit risk—A structural model with jumps and correlations

We set up a structural model to study credit risk for a portfolio containing several or many credit contracts. The model is based on a jump-diffusion process for the risk factors, i.e. for the company assets. We also include correlations between the companies. We discuss that models of this type have much in common with other problems in statistical physics and in the theory of complex systems. We study a simplified version of our model analytically. Furthermore, we perform extensive numerical simulations for the full model. The observables are the loss distribution of the credit portfolio, its moments and other quantities derived thereof. We compile detailed information about the parameter dependence of these observables. In the course of setting up and analyzing our model, we also give a review of credit risk modeling for a physics audience.     

Triple-point wetting on rough substrates

The influence of substrate roughness on the wetting scenario of adsorbed van der Waals films is investigated by theory and experiment. Calculating the bending free energy penalty of a solid sheet picking up the substrate roughness, we show that a finite roughness always leads to triple-point wetting reducing the widths of the adsorbed solid films considerably as compared to that of smooth substrates. Testing the theory against our experimental data for molecular hydrogen adsorbed on gold, we find quantitative agreement.     

实时测量飞秒激光脉冲的二次谐波相关技术研究

本文介绍了一种具有飞秒分辨率实时监测激光脉宽的二次谐波自相关技术。该技术既可进行强度自相关测量,又可进行自标定的干涉自相关测量。干涉自相关测量精度达1fs,强度自相关测量相对误差为3.6%。     

统计不变测度及其维数性质

研究了Graf定义的统计自相似集的结构，提出了统计不变测度的概念，并得到了统计不变测量的支撑，以及它的维数和维数分布。     

改进的静止图像小波零树编码

在深入研究尺度小波变换和嵌入式小波零树压缩编码算法的基础上，探讨了一种改进的小波零树编码算法。通过采用基于嵌入式零树预测扫描算法的改进小波变换编码方法，对小波分解的低频子带图像采用DPCM预测编码，高频子带图像采用了改进的取消重要系数排序的零树预测扫描算法进行压缩编码，使之既具有原零树算法良好的压缩品质，同时也简化了的压缩算法，提高了该算法 的适应性，与JPEG压缩相比，它消除了JPEG图像在高压缩比下的方块效应，取得了令人满意的实验效果。     

在局部区域上的奇摄动非线性方程Robin边值问题

本文是讨论一类在局部区域上的奇摄动非线性Robin边值问题。利用算子理论和不动点原理，得到了相应问题解的存在性和唯一性。     

Analysis of the dryout incident in the Oskarshamn 2 boiling water reactor

Early in 1988 dryout of fuel rods occurred in the Oskarshamn 2 boiling water reactor. During refuelling it was observed that one corner rod was damaged in each of four fuel assemblies. These were of the SVEA design, SVEA being the trade name of the ABB Atom water cross fuel. The damaged zone covered about 180° of the rod periphery facing the corner sub-channel, over a stretch of about 30 cm with the upper end just below the last downstream spacer.

The dominating cause of the dryout was re-use of fuel channels for ordinary 64-rod fuel, which were located in neighbouring positions to the SVEA fuel. The re-used channels showed excessive bowing because of irradiation. This bow increased the water gap between the fuel assemblies, thus increasing the neutron moderation and the local power around one corner of the SVEA fuel. This and some other factors caused the local peaking factor for the corner rod to increase from 1.04 to 1.38.

The flow and power conditions in the damaged fuel assemblies were calculated by means of the POLCA, PHOENIX, CASMO and CONDOR computer programs. The results of these calculations were used as a base for dryout predictions, which were carried out employing eight correlations, which are available in the open literature. The Barnett, the Becker and the Bezrukow correlations predicted the dryout power within 1%. Also the Condie & Bengston, the EPRI and the XN-1 correlations yielded very good results with accuracies of, respectively, −5.1, −2.3 and 7.3%. The Becker, the XN-1, the Bezrukow and the Condie & Bengston correlations predicted dryout to occur inside of the observed dryout zone of 30 cm length.

It is concluded that the dryout in the Oskarshamn 2 nuclear power plant was not caused by any faults in the design or manufacture of the SVEA fuel, and that the re-use of fuel channels should not be permitted.