A subtype of alpha 1 adrenoceptor mediates depression of conduction in Purkinje fibers exposed to halothane

BACKGROUND: An action of epinephrine at alpha adrenoceptors has been reported to slow conduction in Purkinje fibers exposed to halothane. In Purkinje fibers one pharmacologically distinguishable alpha 1-adrenoceptor subtype (alpha 1B) sensitive to the noncompetitive antagonist chloroethylcholinidine mediates decreases in automaticity. Another alpha 1 subtype (alpha 1A), sensitive to the competitive antagonist WB4101, increases spontaneous rate and action potential duration by a mechanism thought to involve hydrolysis of membrane phosphoinositides by phospholipase C. This study examined the dose-response relation and receptor-effector mechanisms underlying depression of conduction in canine Purkinje fibers by epinephrine with halothane. METHODS: Conduction velocity was determined in vitro by measuring the conduction time between action potentials recorded from two Purkinje fibers located about 6 mm apart along the length of free running portions of the ventricular conduction system, the false tendons. Velocity was evaluated at 1-min intervals during trials of rapid exposure to different agonists in groups of 6-12 preparations. RESULTS: Epinephrine (0.2-5.0 microM) transiently decreased Purkinje conduction velocity in a dose-related manner by as much as 33% (at 5 microM epinephrine with 0.86 mM (2.8%) halothane). Velocity decreased by 5% (P < or = 0.01) at an epinephrine concentration similar to "just-threshold" dysrhythmogenic plasma epinephrine concentrations (0.2 microM epinephrine with 0.46 mM halothane) reported in halothane-anesthetized dogs. The decreases of conduction velocity were blocked by prazosin but not by metoprolol, were produced by phenylephrine but not by clonidine, and were antagonized by equimolar (0.5 microM) concentrations of WB4101 more so (P < or = 0.01) than by chloroethylclonidine. WB4101 (0.1 microM) produced 87% inhibition of the response to 0.2 microM epinephrine after chloroethylclonidine pretreatment, indicating mediation by the alpha 1A subtype. Other agonists linked to cardiac phospholipase C activation, including endothelin 1 (40 nM) and the muscarinic agonist carbamylcholine (1 mM), also decreased conduction velocity in fibers exposed to halothane. CONCLUSIONS: Clinically relevant concentrations of epinephrine transiently depress conduction in Purkinje fibers exposed to halothane by activating cardiac alpha 1 adrenoceptors, largely but not exclusively the WB4101-sensitive alpha 1A subtype, reportedly coupled to stimulation of phospholipase C and generation of the second messengers diacylglycerol and inositol trisphosphate. Anesthetic potentiation of cardiac alpha 1-adrenoceptor effects may contribute to the generation of halothane-epinephrine dysrhythmias by abnormally slowing conduction and facilitating reentry.     

Autocorrelation study of quasiparticle relaxation in a YBa2Cu3O7-δ film

Using an autocorrelation method we studied the voltage photoresponse of a current-carrying superconducting YBa₂Cu₃O_7– film excited by femtosecond near infrared radiation pulses. Near the transition temperature we found a picosecond response time consistent with the energy relaxation of nonequilibrium quasiparticles. We also observed a subpicosecond component of the voltage response which we attributed to the current redistribution between excited quasiparticles and the superconducting condensate.     

Hierarchical Bucket Queuing for Fine‐Grained Priority Scheduling on the GPU

While the modern graphics processing unit (GPU) offers massive parallel compute power, the ability to influence the scheduling of these immense resources is severely limited. Therefore, the GPU is widely considered to be only suitable as an externally controlled co‐processor for homogeneous workloads which greatly restricts the potential applications of GPU computing. To address this issue, we present a new method to achieve fine‐grained priority scheduling on the GPU: hierarchical bucket queuing. By carefully distributing the workload among multiple queues and efficiently deciding which queue to draw work from next, we enable a variety of scheduling strategies. These strategies include fair‐scheduling, earliest‐deadline‐first scheduling and user‐defined dynamic priority scheduling. In a comparison with a sorting‐based approach, we reveal the advantages of hierarchical bucket queuing over previous work. Finally, we demonstrate the benefits of using priority scheduling in real‐world applications by example of path tracing and foveated micropolygon rendering.     

Of Embodied Action and Sensors: Knowledge and Expertise Sharing in Industrial Set-Up

Knowledge and expertise sharing has long been an important theme in CSCW and, importantly, one that has frequently challenged a prevailing view concerning knowledge management. This critique focused, initially, on the practical problems associated with issues of Organisational Memory (OM), and in particular the difficulties inherent in an oversimplified ‘repository’ model. Attention then turned to issues of contextuality and communication for expertise sharing, drawing on concepts such as communities of practice and social capital to understand, again, the sharing of knowledge and expertise in practice. Here, we report on how particular kinds of ‘embodied action’ can be identified in relation to the potential of cyber-physical infrastructures for knowledge sharing in an industrial context. We argue that, in a complex industrial domain, both the recording of physical movement – ‘showing’ – and the representation of local knowledge – ‘telling’ – are potentially relevant. Our proposal is that the evolution of cyber-physical infrastructures now offers a way of changing some early assumptions about how knowledge might be captured and displayed. We argue that we are entering a third generation of knowledge and expertise sharing research, where the use of augmented reality (AR) and sensor technology will result in significant new methodological innovations, including the capture and sharing of knowledge, embedded in embodied action.     

Product variety strategies for vertically differentiated products in a two-stage supply chain

In this paper, we study how the presence of coordination, competition and cost structures affect the product variety and pricing decisions in a two-stage supply chain. We consider vertically differentiated industries. Products reach the end customers via assembly companies positioned in the middle-tier between the producers and end customers. The assembly operations incur bill-of-materials (BOM) cost, which includes the cost of raw materials and components as well as the cost of producing, managing and synchronising supply, storage and distribution of these materials and components. We consider three coordination scenarios in the supply chain, and compare an uncoordinated supply chain with a horizontal and a vertical coordination scenario using the Nash equilibria of a multi-leader Stackelberg game between the producers and assembly companies. For exogenously given quality levels, we show that producers and assembly companies should either differentiate their product offering, or offer the high-end product only depending on the BOM cost. In addition, the uncoordinated scenario helps reduce the intensity of competition in the supply chain. For endogenous quality levels, partial product-differentiation equilibrium can emerge. Numerical experiments are performed to illustrate the impacts of BOM cost and quality levels on the equilibrium.     

Glassomer—Processing Fused Silica Glass Like a Polymer

Fused silica glass is one of the most important high‐performance materials for scientific research, industry, and society. However due to its high chemical and thermal resistance as well as high hardness, fused silica glass is notoriously difficult to structure. This work introduces Glassomer, a solid nanocomposite, which can be structured using polymer molding and subtractive technologies at submicrometer resolution. After polymer processing Glassomer is turned into optical grade fused silica glass during a final heat treatment. The resulting glass has the same optical transparency as commercial fused silica and a smooth surface with a roughness of a few nanometers. This work makes high‐performance fused silica glass components accessible to high‐throughput fabrication technologies and will enable numerous optical, photonic and medical applications in science and industry.     

Why different trust relationships matter for information systems users

Technology acceptance research has shown that trust is an important factor fostering use of information systems (IS). As a result, numerous IS researchers have studied factors that build trust in IS. However, IS research on trust has mainly focused on the trust relationship between the user and the IS itself, largely neglecting that other targets of trust might also drive IS use from a user’s point of view. Accordingly, we investigate the importance of different targets of trust in IS use. Therefore, we use the concept of a network of trust and identify four different targets of trust that are prevalent from a user’s point of view. Afterwards, we develop our research model and evaluate it using a free simulation experiment. The results show that multiple targets of trust are important in the context of IS use. In particular, we highlight the importance of a second target – trust in the provider – which is equally important as trust in the IS itself. Consequently, IS providers should focus not only on fostering users’ trust in their IS but also on positioning themselves as trustworthy providers. In addition, we show that a third target – trust in the Internet – has significant indirect effects on multiple constructs that impact IS use.     

Experiences with software-based soft-error mitigation using AN codes

Arithmetic error coding schemes are a well-known and effective technique for soft-error mitigation. Although the underlying coding theory is generally a complex area of mathematics, its practical implementation is comparatively simple in general. However, compliance with the theory can be lost easily while moving toward an actual implementation, which finally jeopardizes the aspired fault-tolerance characteristics and effectiveness. In this paper, we present our experiences and lessons learned from implementing arithmetic error coding schemes (AN codes) in the context of our Combined Redundancy fault-tolerance approach. We focus on the challenges and pitfalls in the transition from maths to machine code for a binary computer from a systems perspective. Our results show that practical misconceptions (such as the use of prime numbers) and architecture-dependent implementation glitches occur at every stage of this transition. We identify typical pitfalls and describe practical measures to find and resolve them. This allowed us to eliminate all remaining silent data corruptions in the Combined Redundancy framework, which we validated by an extensive fault-injection campaign covering the entire fault space of 1-bit and 2-bit errors.     

A new version of transfer matrix method for multibody systems

In order to avoid the global dynamics equations and increase the computational efficiency for multibody system dynamics (MSD), the transfer matrix method of multibody system (MSTMM) has been developed and applied very widely in research and engineering in recent 20 years. It differs from ordinary methods in multibody system dynamics with respect to the feature that there is no need for a global dynamics equation, and it uses low-order matrices for high computational efficiency. For linear systems, MSTMM is exact even if continuous elements like beams are involved. The discrete time MSTMM, however, has to use local linearization. In order to release the method from such approximations, a new version of MSTMM is presented in this paper where translational and angular accelerations, on the one hand, and internal forces and moments, on the other hand, are used as state variables. Already linear relationships among these quantities are utilized, which results in new element transfer matrices and algorithms making the study of multibody systems as simple as the study of single bodies. The proposed approach also allows combining MSTMM with any general numerical integration procedure. Some numerical examples of MSD are given to demonstrate the proposed method.     

Using Science Gateways for Bridging the Differences between Research Infrastructures

Researchers can perform large-scale analyses on diverse computing and data infrastructures such as NGIs (National Grid Infrastructures), XSEDE (Extreme Science and Engineering Discovery Environment) and PRACE (Partnership for Advanced Computing in Europe). Some are national like NGIs and XSEDE, some are international like PRACE and all of them require a more or less restrictive application process to get access to resources. Science gateways integrating diverse infrastructures provide the possibility to re-use methods independent of such underlying infrastructures and thus potentially deliver the technical prerequisite for creating reproducible science. To achieve this goal, science gateways have to be integrated seamlessly with security mechanisms and job, data as well as workflow management of the targeted resources. This paper gives an overview on general findings for porting science gateways as well as the challenges faced for porting the German MoSGrid science gateway (Molecular Simulation Grid) to exploit XSEDE and PRACE infrastructures.