Effect of iron compounds (oxide,salt, or complexes) on poly(vinyl chloride) thermal and photochemical stability

The color requirements for vinyl siding have drastically evolved over the last decade and have moved toward medium to dark colors. Therefore, manufacturers are exploring new ways to modify their formulations in order to improve weather-ability of these challenging colors. Examination of some of the PVC additives typically used in these formulations has led to some interesting revelations about the performance of iron-containing pigments, which are extensively used in darker colors. A quick weathering test was designed to evaluate the effect of iron in PVC formulations, and this test clearly demonstrates the correlation between iron content and PVC photodegradation.     

Water levels in the Amazon basin derived from the ERS 2 and ENVISAT radar altimetry missions

This study sets out to analyze the stages of water bodies in the Amazon basin derived from the processing of ERS-2 and ENVISAT satellite altimetry data. For ENVISAT, GDR measurements for both Ice-1 and Ice-2 tracking algorithms were tested. For ERS-2, the Ice-2 data produced by the OSCAR project was used. Water level time series over river segments of very different width, from several kilometers to less than a hundred of meters, were studied. The water level time series that can be derived from narrow riverbeds are enhanced by off-nadir detections. Conversely, the off-nadir effect may degrade the series over large bodies if not properly accounted for. Comparison at crossovers and with in situ gauges shows that the quality of the series can be highly variable, from 12 cm in the best cases and 40 cm in most cases to several meters in the worse cases. Cautious data selection is clearly a key point to achieve high quality series. Indeed, low quality series mostly result from inclusion of outliers in the data set finally retained for the computation of the series. Ice-2 and Ice-1 tracking algorithms in the ENVISAT data perform almost equally well. ENVISAT altimetry is clearly an improvement on ERS-2 altimetry.     

在加强型学习系统中用伪熵进行不确定性估计

加强型学习系统是一种与没有约束的，未知的环境相互作用的系统，学习系统的目标在大最大可能地获取累积奖励信号，这个奖励信号在有限，未知的生命周期由系统所处的环境中得到，对于一个加强型学习系统，困难之一在于奖励信号非常稀疏，尤其是对于只有时延信号的系统，已有的加强型学习方法以价值函数的形式贮存奖励信号，例如著名的Ｑ－学习。本文提出了一个基于状态的不生估计模型的方法，这个算法对有利用存贮于价值函数中的奖励     

Call-by-Value {lambda}-calculus and LJQ

LJQ is a focused sequent calculus for intuitionistic logic,with a simple restriction on the first premiss of the usualleft introduction rule for implication. In a previous paperwe discussed its history (going back to about 1950, or beyond)and presented its basic theory and some applications; here wediscuss in detail its relation to call-by-value reduction inlambda calculus, establishing a connection between LJQ and theCBV calculus _C of Moggi. In particular, we present an equationalcorrespondence between these two calculi forming a bijectionbetween the two sets of normal terms, and allowing reductionsin each to be simulated by reductions in the other.     

Protocol considerations for a prefix-caching proxy for multimedia streams

The increasing popularity of multimedia streaming applications introduces new challenges in content distribution. Web-initiated multimedia streams typically experience high start-up delay, due to large protocol overheads and the poor delay, throughput, and loss properties of the Internet. Internet service providers can improve performance by caching the initial segment (the prefix) of popular streams at proxies near the requesting clients. The proxy can initiate transmission to the client while simultaneously requesting the remainder of the stream from the server. This paper analyzes the challenges of realizing a prefix-caching service in the context of the IETF's Real-Time Streaming Protocol (RTSP), a multimedia streaming protocol that derives from HTTP. We describe how to exploit existing RTSP features, such as the Range header, and how to avoid several round-trip delays by caching protocol information at the proxy. Based on our experiences, we propose extensions to RTSP that would ease the development of new multimedia proxy services. In addition, we discuss how caching the partial contents of multimedia streams introduces new challenges in cache coherency and feedback control. Then, we briefly present our preliminary implementation of prefix caching on a Linux-based PC, and describe how the proxy interoperates with the RealNetworks server and client.     

Mobile agents and intellectual property protection

Technical enforcemment of intellectual property (IP) rights often conflicts with the ability to use the IP. This is especially true when the IP is data, which may eaisly be copied while it is being accessed. As electronic commerce of data becomes more widespread, traditional approaches will prove increasingly problematic. In this paper, we show that the mobile agent architecture is an ideal solution to this dilemma: by providing full access to the data but charging for the transmission of results back to the user-reslts-based billing-we resulve the access versus protection conflict. We define new requirements for agent frameworks to implement results-based billing: data-aware accounting and data-tight sandboxing, which, along with the common requirements such as authentication, authorisation, agen self-monitoring, and efficiency, provide the mechanisms by which database owners can effectively grant users access to their intellectual property.     

Comparative study between computational and experimental results for binary rarefied gas flows through long microchannels

A comparative study between computational and experimental results for pressure-driven binary gas flows through long microchannels is performed. The theoretical formulation is based on the McCormack kinetic model and the computational results are valid in the whole range of the Knudsen number. Diffusion effects are taken into consideration. The experimental work is based on the Constant Volume Method, and the results are in the slip and transition regime. Using both approaches, the molar flow rates of the He–Ar gas mixture flowing through a rectangular microchannel are estimated for a wide range of pressure drops between the upstream and downstream reservoirs and several mixture concentrations varying from pure He to pure Ar. In all cases, a very good agreement is found, within the margins of the introduced modeling and measurement uncertainties. In addition, computational results for the pressure and concentration distributions along the channel are provided. As far as the authors are aware of, this is the first detailed and complete comparative study between theory and experiment for gaseous flows through long microchannels in the case of binary mixtures.     

A parallel algorithm for constrained two-staged two-dimensional cutting problems

In this paper, we solve the two-staged two-dimensional cutting problem using a parallel algorithm. The proposed approach combines two main features: beam search (BS) and strip generation solution procedures (SGSP). BS employs a truncated tree-search, where a selected subset of generated nodes are retuned for further search. SGSP, a constructive procedure, combines a (sub)set of strips for providing both partial lower and complementary upper bounds. The algorithm explores in parallel a subset of selected nodes following the master-slave paradigm. The master processor serves to guide the search-resolution and each slave processor develops its proper way, trying a global convergence. The aim of such an approach is to show how the parallelism is able to efficiently solve large-scale instances, by providing new solutions within a consistently reduced runtime. Extensive computational testing on instances, taken from the literature, shows the effectiveness of the proposed approach.     

The origin of N2O formation in the selective catalytic reduction of NOx by NH3 in O2 rich atmosphere on Cu-faujasite catalysts

The selective catalytic reduction (SCR) of NO_x (NO + NO₂) by NH₃ in O₂ rich atmosphere has been studied on Cu-FAU catalysts with Cu nominal exchange degree from 25 to 195%. NO₂ promotes the NO conversion at NO/NO₂ = 1 and low Cu content. This is in agreement with next-nearest-neighbor (NNN) Cu ions as the most active sites and with N_xO_y adsorbed species formed between NO and NO₂ as a key intermediate. Special attention was paid to the origin of N₂O formation. CuO aggregates form 40–50% of N₂O at ca. 550 K and become inactive for the SCR above 650 K. NNN Cu ions located within the sodalite cages are active for N₂O formation above 600 K. This formation is greatly enhanced when NO₂ is present in the feed, and originated from the interaction between NO (or NO₂) and NH₃. The introduction of selected co-cations, e.g. Ba, reduces very significantly this N₂O formation.