Adding Policy-based Control to Mobile Hosts Switching between Streaming Proxies

We add a simple policy-based control component to mobile hosts that enables them to control the continuous reception of live multimedia content (e.g. a TV broadcast) while they switch between different distributors of that content. Policy-based control provides a flexible means to automate the switching behavior of mobile hosts. The policies react to changes in the mobile host's environment (e.g. when a hotspot network appears) and determine when and how to invoke an earlier developed application-level protocol to discover the capabilities (e.g. supported encodings) of the content distributors and to execute the switches. The design of the control component is based on the IETF policy model, but extended and applied at the application-level instead of at the network-level. We implemented the system and deployed it in a small-scale test bed

Designing online audiovisual heritage services: an empirical study of two comparable online video services

The purpose of this study is to seek input for a new online audiovisual heritage service. In doing so, we assess comparable online video services to gain insights into the motivations and perceptual innovation characteristics of the video services. The research is based on data from a Dutch survey held among 1,939 online video service users. The results show that online video service held overlapping antecedents but does show differences in motivations and in perceived innovation characteristics. Hence, in general, one can state that in comparison, online video services comply with different needs and have differences in perceived innovation characteristics. This implies that one can design online video services for different needs. In addition to scientific implications, the outcomes also provide guidance for practitioners in implementing new online video service

Preconditioning in globally ischemic isolated rat hearts: effect on function and metabolic indices of myocardial damage

We assessed the effects of ischemic preconditioning on heart recovery and metabolic indices of damage following global ischemia and reperfusion, in relationship to post-ischemic lactate release. Three groups of Langendorff rat hearts were studied: (1) A control group of 40 min global ischemia and 45 min reperfusion; (2) preconditioning by 5 min global ischemia and 15 min reperfusion prior to sustained ischemia and reperfusion; (3) Preconditioning by three episodes of brief ischemia-re

Delivering Live Multimedia Streams to Mobile Hosts in a Wireless Internet with Multiple Content Aggregators

We consider the distribution of channels of live multimedia content (e.g., radio or TV broadcasts) via multiple content aggregators. In our work, an aggregator receives channels from content sources and redistributes them to a potentially large number of mobile hosts. Each aggregator can offer a channel in various configurations to cater for different wireless links, mobile hosts, and user preferences. As a result, a mobile host can generally choose from different configurations of the same channel offered by multiple alternative aggregators, which may be available through different interfaces (e.g., in a hotspot). A mobile host may need to handoff to another aggregator once it receives a channel. To prevent service disruption, a mobile host may for instance need to handoff to another aggregator when it leaves the subnets that make up its current aggregator�s service area (e.g., a hotspot or a cellular network).\ud In this paper, we present the design of a system that enables (multi-homed) mobile hosts to seamlessly handoff from one aggregator to another so that they can continue to receive a channel wherever they go. We concentrate on handoffs between aggregators as a result of a mobile host crossing a subnet boundary. As part of the system, we discuss a lightweight application-level protocol that enables mobile hosts to select the aggregator that provides the �best� configuration of a channel. The protocol comes into play when a mobile host begins to receive a channel and when it crosses a subnet boundary while receiving the channel. We show how our protocol can be implemented using the standard IETF session control and description protocols SIP and SDP. The implementation combines SIP and SDP�s offer-answer model in a novel way

Ischemic nucleotide breakdown increases during cardiac development due to drop in adenosine anabolism/catabolism ratio

Abstract Our earlier work on reperfusion showed that adult rat hearts released almost twice as much purine nucleosides and oxypurines as newborn hearts did [Am J Physiol 254 (1988) H1091]. A change in the ratio anabolism/catabolism of adenosine could be responsible for this effect. We therefore measured the activity of adenosine kinase, adenosine deaminase, nucleoside phosphorylase and xanthine oxidoreductase in homogenates of hearts and myocytes from neonatal and adult rats. In hearts the activity of adenosine deaminase and nucleoside phosphorylase (10–20 U/g protein) changed relatively little. However, adenosine kinase activity decreased from 1.3 to 0.6 U/g (P < 0.025), and xanthine oxidoreductase activity increased from 0.02 to 0.85 U/g (P < 0.005). Thus the ratio in activity of these rate-limiting enzymes for anabolism and catabolism dropped from 68 to 0.68 during cardiac development. In contrast, the ratio in myocytes remained unchanged (about 23). The large difference in adenosine anabolism/catabolism ratio, observed in heart homogenates, could explain why ATP breakdown due to hypoxia is lower in neonatal than in adult heart. Because this change is absent in myocytes, we speculate that mainly endothelial activities of adenosine kinase and xanthine oxidoreductase are responsible for this shift in purine metabolism during development

Urate production by human heart

Xanthine oxidoreductase has been demonstrated in the heart of various species. However, its presence in human heart is still debated. In the literature, high to undetectable levels have been reported. We studied the arterial-venous urate difference across the heart of patients undergoing both routine cardiac catheterization and percutaneous transluminal coronary angioplasty. Urate is the end product of the reaction catalysed by xanthine oxidoreductase. In 10 patients, studied before angioplasty, the plasma urate level in the great cardiac vein exceeded the arterial one by 26 +/- 10 nmol/ml (P = 0.028). In a further 13 patients, urate production was maximal immediately after the last of four consecutive occlusions (23 +/- 8 nmol/ml, P = 0.018) and concomitant with increased coronary sinus hypoxanthine levels. We conclude that xanthine oxidoreductase is probably present in the heart of patients, suffering from ischemic heart disease, and responsible for the increase in urate production during transient myocardial ischemia