We develop a dynamic control strategy for minimizing energy expenditure in a time-varying wireless network with adaptive transmission rates. The algorithm operates without knowledge of traffic rates ...or channel statistics, and yields average power that is arbitrarily close to the minimum possible value achieved by an algorithm optimized with complete knowledge of future events. Proximity to this optimal solution is shown to be inversely proportional to network delay. We then present a similar algorithm that solves the related problem of maximizing network throughput subject to peak and average power constraints. The techniques used in this paper are novel and establish a foundation for stochastic network optimization
We consider the throughput/delay tradeoffs for scheduling data transmissions in a mobile ad hoc network. To reduce delays in the network, each user sends redundant packets along multiple paths to the ...destination. Assuming the network has a cell partitioned structure and users move according to a simplified independent and identically distributed (i.i.d.) mobility model, we compute the exact network capacity and the exact end-to-end queueing delay when no redundancy is used. The capacity-achieving algorithm is a modified version of the Grossglauser-Tse two-hop relay algorithm and provides O(N) delay (where N is the number of users). We then show that redundancy cannot increase capacity, but can significantly improve delay. The following necessary tradeoff is established: delay/rate/spl ges/O(N). Two protocols that use redundancy and operate near the boundary of this curve are developed, with delays of O(/spl radic/N) and O(log(N)), respectively. Networks with non-i.i.d. mobility are also considered and shown through simulation to closely match the performance of i.i.d. systems in the O(/spl radic/N) delay regime.
We consider the fundamental delay tradeoffs for minimizing energy expenditure in a multiuser wireless downlink with randomly varying channels. First, we extend the Berry-Gallager bound to a multiuser ...context, demonstrating that any algorithm that yields average power within O (1/ V ) of the minimum power required for network stability must also have an average queueing delay greater than or equal to Omega(radic V ). We then develop a class of algorithms, parameterized by V , that come within a logarithmic factor of achieving this fundamental tradeoff. The algorithms overcome an exponential state-space explosion, and can be implemented in real time without a priori knowledge of traffic rates or channel statistics. Further, we discover a ldquosuperfastrdquo scheduling mode that beats the Berry-Gallager bound in the exceptional case when power functions are piecewise linear.
We consider optimal control for general networks with both wireless and wireline components and time varying channels. A dynamic strategy is developed to support all traffic whenever possible, and to ...make optimally fair decisions about which data to serve when inputs exceed network capacity. The strategy is decoupled into separate algorithms for flow control, routing, and resource allocation, and allows each user to make decisions independent of the actions of others. The combined strategy is shown to yield data rates that are arbitrarily close to the optimal operating point achieved when all network controllers are coordinated and have perfect knowledge of future events. The cost of approaching this fair operating point is an end-to-end delay increase for data that is served by the network.
Acute stress suppresses pain by activating brain pathways that engage opioid or non-opioid mechanisms. Here we show that an opioid-independent form of this phenomenon, termed stress-induced ...analgesia, is mediated by the release of endogenous marijuana-like (cannabinoid) compounds in the brain. Blockade of cannabinoid CB1 receptors in the periaqueductal grey matter of the midbrain prevents non-opioid stress-induced analgesia. In this region, stress elicits the rapid formation of two endogenous cannabinoids, the lipids 2-arachidonoylglycerol (2-AG) and anandamide. A newly developed inhibitor of the 2-AG-deactivating enzyme, monoacylglycerol lipase, selectively increases 2-AG concentrations and, when injected into the periaqueductal grey matter, enhances stress-induced analgesia in a CB1-dependent manner. Inhibitors of the anandamide-deactivating enzyme fatty-acid amide hydrolase, which selectively elevate anandamide concentrations, exert similar effects. Our results indicate that the coordinated release of 2-AG and anandamide in the periaqueductal grey matter might mediate opioid-independent stress-induced analgesia. These studies also identify monoacylglycerol lipase as a previously unrecognized therapeutic target.
Observations suggest that the optical depth of the stratospheric aerosol layer between 20 and 30 km has increased 4–10% per year since 2000, which is significant for Earth's climate. Contributions to ...this increase both from moderate volcanic eruptions and from enhanced coal burning in Asia have been suggested. Current observations are insufficient to attribute the contribution of the different sources. Here we use a global climate model coupled to an aerosol microphysical model to partition the contribution of each. We employ model runs that include the increases in anthropogenic sulfur dioxide (SO2) over Asia and the moderate volcanic explosive injections of SO2 observed from 2000 to 2010. Comparison of the model results to observations reveals that moderate volcanic eruptions, rather than anthropogenic influences, are the primary source of the observed increases in stratospheric aerosol.
Key Points
Observations do not rule out the anthropogenic impacts on stratospheric aerosol
Stratospheric aerosol is not impacted by the current Asian emissions
Recent trends in stratospheric aerosol are a natural radiative forcing
We consider a one-hop wireless network with independent time varying ON/OFF channels and N users, such as a multi-user uplink or downlink. We first show that general classes of scheduling algorithms ...that do not consider queue backlog must incur average delay that grows at least linearly with N . We then construct a dynamic queue-length aware algorithm that maximizes throughput and achieves an average delay that is independent of N . This is the first order-optimal delay result for opportunistic scheduling with asymmetric links. The delay bounds are achieved via a technique of queue grouping together with Lyapunov drift and statistical multiplexing concepts.
The English Lexicon Project Balota, David A; Yap, Melvin J; Cortese, Michael J ...
Behavior research methods,
08/2007, Letnik:
39, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The English Lexicon Project is a multiuniversity effort to provide a standardized behavioral and descriptive data set for 40,481 words and 40,481 nonwords. It is available via the Internet at ...elexicon.wustl.edu. Data from 816 participants across six universities were collected in a lexical decision task (approximately 3400 responses per participant), and data from 444 participants were collected in a speeded naming task (approximately 2500 responses per participant). The present paper describes the motivation for this project, the methods used to collect the data, and the search engine that affords access to the behavioral measures and descriptive lexical statistics for these stimuli.
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