Modelling the long-term fate of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) in the Grenland Fjords, Norway

The development and application of a predictive fate model (DIG--Dioxins in Grenland) for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in the marine environment of the Norwegian Grenland Fjords are described. The objective of the modelling study was to predict long-term future changes in PCDD/F concentrations in the fjord following the cessation of point source emissions. To assess the reliability of the model, the model performance was evaluated by comparing model results to field measurements collected between 1989 and 2001. Model bias (defined as the ratio of median predicted concentration and median observed concentration) for prediction of concentrations for three different PCDD/F congeners (2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 1,2,3,6,7,8-hexadibenzofuran (HxCDF) and octachlorodibenzofuran (OCDF)) in the fjord was between 0.53 and 24, which was deemed a satisfactory result for models of this type. The model was run to determine the dynamic change in concentrations between 1950 and 2050 and to examine the key fluxes of PCDD/Fs in the fjord. Between 1990 and 2050 sediment concentrations of TCDD, HxCDF and OCDF were predicted to fall at fairly constant but gradually slowing rates to concentrations 52, 98 and 88 times lower, respectively, of their 1990 values. Losses of PCDD/Fs from the bottom sediments in the Frierfjord were predicted to be a combination of sediment burial and net resuspension to the water column. Sediment burial was shown to be relatively more important in the fjord's deep-water sediments, whereas resuspension was relatively more important in the shallow sediments. For the shallower sediments, a net water-to-sediment flux was predicted for all three congeners up until the mid-1970s, when emission reductions were initiated, and thereafter a net sediment-to-water flux was predicted. The shallow sediments acted as net sources to the deeper sediments and to the fishing areas in the outer fjord.     

The influence of freezing and duration of storage on Campylobacter and indicator bacteria in broiler carcasses

In total, 215 commercially processed broiler carcasses were examined to determine optimum cultural enumeration, the effects of freezing, method of thawing, and duration of frozen storage on levels of Campylobacter spp. and fecal coliforms. Enumeration studies compared MPN procedures to direct plating onto selective mCCDA agar and indicated equivalency for quantitation of Campylobacter spp. Levels of Campylobacter and fecal coliforms were subsequently estimated by direct plating of carcass rinses. Freezing of naturally contaminated carcasses followed by storage at -20 degrees C for 31, 73, 122 and 220 days showed statistically significant (P< or =0.05) reductions in Campylobacter counts initially as compared with counts found on fresh product. Among 5 lots of broilers, levels of Campylobacter on carcasses were reduced by log mean values ranging from 0.65 to 2.87 after freezing and 31 days of storage. Similar reductions due to freezing were not observed for fecal coliforms counts. The level of Campylobacter was reduced by approximately one log immediately after freezing, and remained relatively constant during the 31-220 days of frozen storage. The levels were constant during 7 days of refrigerated storage. After 31 days of frozen storage there was a reduced rate in reduction of counts among broilers thawed at 7 degrees C as compared to thawing at 22 degrees C with either cultural method (MPN and mCCDA). These findings warrant consideration of the public health benefits related to freezing contaminated poultry prior to commercial distribution to reduce Campylobacter exposure levels associated with contaminated carcasses.     

Sharing Tacit Knowledge Online: A Case Study of e-Learning in Cisco's Network of System Integrator Partner Firms

This paper contributes to an ongoing debate about the impact of information and communication technologies (ICTs) on the interpersonal sharing of tacit knowledge. Drawing upon the philosophical writings of Michael Polanyi and an original case study of e-learning in Cisco Systems, the paper challenges the widespread argument that ICT-mediated communication is inadequate for the sharing of tacit knowledge. The main conclusion is that advanced e-learning systems—particularly remote laboratories—make possible efficient sharing of tacit knowledge between internationally dispersed technicians. However, successful knowledge-sharing depends crucially on the degree to which the users are motivated to acquire new knowledge online. Motivation can be facilitated through the participation in online networks of practice, but in order to access and benefit from these networks people require a certain threshold level of technical relevant knowledge, which is the most easily generated in local communities of practice.     

Photochemotherapy--psoralen + UV-A (PUVA)--increased risk of cancer?

Photochemotherapy with psoralens + ultraviolet (UV)-A light (PUVA) has been used for about 16 years to treat psoriasis. Some reports have indicated a higher frequency of cutaneous squamous cell carcinoma among treated patients. The results are not consistent, however, and are not generally conceded. Our material from Ullev?l Hospital comprises 585 patients who have been treated with PUVA from 1977 until 1991. Three patients developed cutaneous squamous cell carcinoma, but in one of them the tumour developed before start of PUVA treatment. The two others had received only very small doses. One of them had an intraepithelial cancer of the penis. In addition we registered various internal cancers in 25 patients. The Norwegian Cancer Registry compared our patient materiel with a matched control group as regards sex, age and age-specific incidence rate. There was no statistically significant difference in incidence between the patient and the control group.     

Communication efficient matrix multiplication on hypercubes

In a recent paper Fox, Otto and Hey consider matrix algorithms for hypercubes. For hypercubes allowing pipelined broadcast of messages they present a communication efficient algorithm. We present in this paper a similar algorithm that uses only nearest neighbour communication. This algorithm will therefore by very communication efficient also on hypercubes not allowing pipelined broadcast. We introduce a new algorithm that reduces the asymptotic communication cost from . This is achieved by regarding the hypercube as a set of subcubes and by using the cascade sum algorithm.     

The resolved history of galaxy evolution

We briefly review the study of the evolution of galaxies from an observational point of view, with particular emphasis on the role of the Hubble Space Telescope in probing the evolution of the different morphological types of galaxy. We show how using the stellar mass of galaxies as a tracer of evolution can improve our understanding of the physical process taking place before turning our eyes towards the future and giving an overview of what we can expect from future advances in technology.     

等离子弧焊熔敷Ti-6Al-4V合金原位拉伸过程中显微组织及应变响应的电子背散射衍射表征

航天级钛合金的新型叠层制造技术（ALM）的优势体现在较低的制造成本等方面,并可替代传统加工成型工艺。由等离子弧焊熔敷叠层制造技术制备Ti-6Al-4V合金的显微组织由定向凝固生长的β柱状晶及在其晶内生长的细小的α片层组织构成。在原位拉伸过程中结合应用高速离线电子背散射衍射表征（Offline EBSD）可快速获取试样显微组织和形变特征之间的关系。揭示出不均匀变形的发生取决于柱状晶界间的应变响应。柱状滑移和基面滑移系统被激活进而导致最后出现形变滑移线,即在某些柱状晶中滑移扩展至整个晶粒;而在另一些晶粒中表现为存在应变梯度和应力集中的地方发生形变失配。形变的扩展习性受制于定向凝固生长的柱状晶生长方向及其之间的界面取向关系。在垂直于柱状晶方向的拉伸试验揭示存在剧烈的变形局域化。基于原位拉伸观测及高速的离线电子背散射衍射表征结果,本文作者提出从微观到宏观形变扩展的控制机制。     

Robust multigrid solvers for the biharmonic problem in isogeometric analysis

In this paper, we develop multigrid solvers for the biharmonic problem in the framework of isogeometric analysis (IgA). In this framework, one typically sets up B-splines on the unit square or cube and transforms them to the domain of interest by a global smooth geometry function. With this approach, it is feasible to set up $H^2$-conforming discretizations. We propose two multigrid methods for such a discretization, one based on Gauss–Seidel smoothing and one based on mass smoothing. We prove that both are robust in the grid size, the latter is also robust in the spline degree. Numerical experiments illustrate the convergence theory and indicate the efficiency of the proposed multigrid approaches, particularly of a hybrid approach combining both smoothers.