Potentials and challenges of peer-to-peer based content distribution

Multimedia content currently accounts for over three quarters of all Internet traffic. This increase in traffic volume and content availability derives from a paradigm shift from the traditional text and picture based Web, to more resource demanding audio and video content. A controversial driver for this development is content distribution systems based on peer-to-peer overlay networks. Flooding the Internet with often illegal content, these networks now pose challenges to all actors in the value chain. However, if viewed as surmountable challenges in an evolutionary path, peer-to-peer technology has the potential of increasing efficiency in content distribution and unleashing resources to form scalable and resilient overlay networks of unprecedented dimensions.

In this paper we examine the potentials and challenges of peer-to-peer technology in content distribution, and analyse how, and under which circumstances, peer-to-peer technology can be used to increase the efficiency of multimedia services. The paper provides an up-to-date overview of the development of peer-to-peer networks as well as describing the economics laws governing their use. To conclude the study, the paper analyses Skype, a well known telecommunications service utilising the peer-to-peer technology, as well as demonstrating the benefits of peer-to-peer based content distribution using empirical data from the Danish Broadcasting Corporation.     

Dynamic behavior of balanced NV-trees

In recent years, some approximate high-dimensional indexing techniques have shown promising results by trading off quality guarantees for improved query performance. While the query performance and quality of these methods has been well studied, however, the performance of index maintenance has not yet been reported in any detail. Here, we focus on the dynamic behavior of the balanced NV-tree, which is a disk-based approximate index for very large collections. We report on an initial study of the effects of several implementation choices for the balanced NV-tree, and show that with appropriate implementation, significant performance improvements are possible. Overall, the proposed techniques not only reduce maintenance cost, but can also improve search performance significantly with minimal loss of search quality.     

Analysis of tracer test data, and injection-induced cooling, in the Laugaland geothermal field, N-Iceland

The Laugaland geothermal system in N-Iceland is hosted by low-permeability fractured basalt and its productivity is limited by insufficient recharge, even though substantial thermal energy is in-place in the 90–100 °C hot rocks of the system. The purpose of a 2-year reinjection experiment, completed in late 1999, was to demonstrate that some of this energy could be extracted economically through long-term reinjection. A comprehensive monitoring program was implemented as part of the project, including three detailed tracer tests. More than 1400 tracer samples were collected during the tests. Tracer return data indicate that the injected water travels through the area bedrock by two modes: first, along direct, small volume flow-paths, such as fractures or interbeds; second, by dispersion and mixing throughout a large volume of the reservoir. Based on the tracer test results, and assuming 15 l/s average future reinjection, the temperature of water produced is predicted to decline by 1–3 °C in 10 years. It can be asserted, in spite of measurement uncertainties, that the 2-year reinjection experiment did not cause a temperature decline greater than about 0.5 °C, conforming to predictions. It is estimated that future reinjection at 15 l/s will enable an increase in energy production amounting to about 24 GWh_th/year, which equals roughly of the average yearly energy production at Laugaland during the last decade. Reinjection has continued after the experiment and is already an important part of the management of the Laugaland geothermal system.     

Fatty acid selectivity of microbial lipase and lipolytic enzymes from salmonid fish intestines toward astaxanthin diesters

The objective of the work described in this paper was to study a possible FA selectivity of digestive lipolytic enzymes isolated from salmon and trout intestines toward astaxanthin diesters of various FA composition and compare it with the FA selectivity of microbial lipase. Astaxanthin diesters of varying FA composition were prepared in excellent yields (>90%) by chemical esterification using a carbodiimide coupling aget. The astaxanthin diesters were screened in a hydrolysis reaction by various commercially available lipases. The highest conversion rates were observed with the Candida rugosa lipase, which discriminated against n−3 PUFA. The rate of hydrolysis was determined by HPLC. Digestive lipolytic enzymes isolated from salmon and rainbow trout intestines displayed reversed FA selectivity. Thus, astaxanthin diesters highly enriched with n−3 PUFA including EPA and DHA were observed to be hydrolyzed at a considerably higher rate than the more saturated esters. Similar trends in FA selectivity were observed in the hydrolysis of fish oil TAG by the digestive lipolytic enzyme mixtures.     

Surfactant-controlled shape change of organic droplets using polypyrrole

Control of the shape and position of organic droplets has been investigated using polypyrrole doped with the surfactant dodecylbenzenesulfonate (PPy.DBS). Ex-situ contact angle measurements of electrochemically-reduced PPy.DBS revealed a dramatic increase in wettability compared to the oxidised polymer, attributable to dopant reorientation and cation incorporation during the reduction process. In-situ studies showed that droplets of dichloromethane resting upon PPy.DBS electrodes and immersed in an aqueous electrolyte changed shape dramatically upon electrochemical reduction of the polymer. A mechanism for the unusual and unexpected changes in drop shape is presented. Controlled release of the surfactant dopant into the electrolyte upon reduction of PPy.DBS and subsequent doping of the polymer upon oxidation were found to affect the droplet shape.     

Chemoenzymatic synthesis of structured triacylglycerols containing eicosapentaenoic and docosahexaenoic acids

There are indications in the recent literature that the location of polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), in triacylglycerols (TAG) may influence their oxidative stability. To address that question, two types of structured lipids were designed and synthesized: firstly, a TAG molecule possessing pure EPA or DHA at the mid-position with stearic acid at the outer positions; and secondly, a TAG molecule possessing pure EPA or DHA located at one of the outer positions with stearic acid at the mid-position and the remaining end position. The former adduct was synthesized in two steps by a chemoenzymatic approach. In the first step 1,3-distearolyglycerol was afforded in good yield (74%) by esterifying glycerol with two equivalents of stearic acid in ether in the presence of silica gel using Lipozyme^TM as a biocatalyst. This was followed by a subsequent chemical esterification with pure EPA or DHA using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide as a coupling agent in the presence of 4-dimethylaminopyridine in dichloromethane in excellent yields (94 and 91, respectively). The latter adduct was synthesized in two enzymatic steps. In the first step tristearoylglycerol was prepared in very high yield (88%) by esterifying glycerol with a stoichiometric amount of stearic acid under vacuum at 70–75°C using an immobilized Candida antarctica lipase without a solvent. That adduct was subsequently treated in an acidolysis reaction with two equivalents of EPA or DHA without solvent at 70–75°C or in toluene at 40°C in the presence of Lipozyme to afford the desired product in moderate yields (44 and 29%, respectively). This work was presented at the Biocatalysis Symposium in April 2000, held at the 91st Annual Meeting and Expo of the American Oil Chemists’ Society, San Diego, CA.     

Mechanism of alpha-2 adrenergic modulation of canine cardiac Purkinje action potential

We reported recently that stimulation of postjunctional alpha-2 adrenergic receptors prolongs the action potential durations (APD) of isolated canine Purkinje fibers. With standard microelectrode techniques, we examined the ionic mechanism through which alpha-2 adrenergic stimulation prolonged Purkinje APD, by measuring the effects of inhibitors of the various plateau currents on the alpha-2-mediated prolongation of APD. The alpha-2-specific agonist UK 14,304 (0.1 microM) prolonged the Purkinje APD at 50% repolarization and the APD at 90% repolarization, and these effects were inhibited by yohimbine (0.1 microM). The Purkinje APD at 50% repolarization and the APD at 90% repolarization were prolonged significantly with the transient outward potassium current inhibitor 4-aminopyridine (1 mM), the rapid component of delayed rectifier potassium current inhibitor d-sotalol (10 microM), the slow component of delayed rectifier potassium current inhibitor indapamide (0.1 microM) and the chloride current inhibitor mefenamic acid (10 nM) and were shortened significantly with the calcium current inhibitor nifedipine (0.3 microM). Prolongation of Purkinje APD at 50% repolarization and APD at 90% repolarization by UK 14,304 remained intact in the presence of d-sotalol, indapamide, mefenamic acid and nifedipine. All of these UK 14,304 effects were significantly reversed by yohimbine. Only in the presence of 4-aminopyridine did UK 14,304 fail to prolong Purkinje APD. The phase 1 magnitudes of Purkinje action potentials were also significantly inhibited by UK 14,304. This effect was completely abolished only in the presence of 4-aminopyridine. These results suggest that inhibition of the 4-aminopyridine-sensitive transient outward potassium current is the major ionic mechanism by which alpha-2 adrenergic stimulation prolongs Purkinje APD.