CiteULike: Tag delay

Phase synchronization in temperature and precipitation records

Diego Rybski — 2005-11-13T18:26:26-00:00

Physica A: Statistical Mechanics and its Applications, Vol. 320 (15 March 2003), pp. 601-610.

We study phase synchronization between atmospheric variables such as daily mean temperature and daily precipitation records. We find significant phase synchronization between records of Oxford and Vienna as well as between the records of precipitation and temperature in each city. To find the time delay in the synchronization between the records we study the time lag phase synchronization when the records are shifted by a variable time interval of days. We also compare the results of the method with the classical cross-correlation method and find that in certain cases the phase synchronization yields more significant results.

Estimation of time delay by coherence analysis

RB Govindan — 2005-11-13T18:21:31-00:00

Physica A: Statistical and Theoretical Physics, Vol. 350, No. 2-4. (15 May 2005), pp. 277-295.

Using coherence analysis (which is an extensively used method to study the correlations in frequency domain, between two simultaneously measured signals) we estimate the time delay between two signals. This method is suitable for time delay estimation of narrow band coherence signals for which the conventional methods cannot be reliably applied. We show, by analysing coupled Rossler attractors with a known delay, that the method yields satisfactory results. Then, we apply this method to human pathologic tremor. The delay between simultaneously measured traces of electroencephalogram (EEG) and electromyogram (EMG) data of subjects with essential hand tremor is calculated. We find that there is a delay of 11-27 milli-seconds (ms) between the tremor correlated parts (cortex) of the brain (EEG) and the trembling hand (EMG) which is in agreement with the experimentally observed delay value of 15 ms for the cortico-muscular conduction time. By surrogate analysis we calculate error bars of the estimated delay.

Role of Delays in Shaping Spatiotemporal Dynamics of Neuronal Activity in Large Networks

Alex Roxin — 2005-09-20T12:55:08-00:00

Physical Review Letters, Vol. 94, No. 23. (2005)

We study the effect of delays on the dynamics of large networks of neurons. We show that delays give rise to a wealth of bifurcations and to a rich phase diagram, which includes oscillatory bumps, traveling waves, lurching waves, standing waves arising via a period-doubling bifurcation, aperiodic regimes, and regimes of multistability. We study the existence and the stability of the various dynamical patterns analytically and numerically in a simplified rate model as a function of the interaction parameters. The results derived in that framework allow us to understand the origin of the diversity of dynamical states observed in large networks of spiking neurons.

Merging of alpha and slow beta relaxation in supercooled liquids

Takuya Fujima — 2005-09-25T09:54:46-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 66, No. 3. (2002)

Dielectric relaxation spectroscopy (1 Hz – 20 GHz) has been performed on supercooled glass-formers from the temperature of glass transition (Tg) up to that of melting. Precise measurements particularly in the frequencies of MHz order have revealed that the temperature dependences of secondary relaxation times in well above Tg deviate from the Arrhenius relation below Tg: the process does not merge with the process around the dynamical crossover temperature in contradiction to previously speculated extrapolations.

Outcomes analysis of delayed antibiotic treatment for hospital-acquired Staphylococcus aureus bacteremia.

TP Lodise — 2006-01-26T08:35:44-00:00

Clin Infect Dis, Vol. 36, No. 11. (1 June 2003), pp. 1418-1423.

The objective of this study was to determine the effect of delayed therapy on morbidity and mortality associated with nosocomial Staphylococcus aureus bacteremia. The study included all episodes of S. aureus bacteremia that developed >2 days after hospital admission during 1999 to 2001. Classification and regression tree analysis (CART) was used to select the mortality breakpoint between early and delayed treatment. During the 25-month study period, 167 patients met the inclusion criteria. The breakpoint between delayed and early treatment derived using CART was 44.75 hours. On multivariate analysis, delayed treatment was found to be an independent predictor of infection-related mortality (odds ratio, 3.8; 95% confidence interval, 1.3-11.0; P=.01) and was associated with a longer hospital stay than was early treatment (20.2 days versus 14.3 days; P=.05). These findings support the notion that delay of therapy has deleterious effects on clinical outcomes, and efforts should be made to ensure that appropriate therapy is initiated promptly.

Tolerance of temporal delay in virtual environments

RS Allison — 2008-05-22T14:04:01-00:00

Virtual Reality, 2001. Proceedings. IEEE (2001), pp. 247-254.

To enhance presence, facilitate sensory motor performance, and avoid disorientation or nausea, virtual-reality applications require the perception of a stable environment. End-end tracking latency (display lag) degrades this illusion of stability and has been identified as a major fault of existing virtual-environment systems. Oscillopsia refers to the perception that the visual world appears to swim about or oscillate in space and is a manifestation of this loss of perceptual stability of the environment. The effects of end-end latency and head velocity on perceptual stability in a virtual environment were investigated psychophysically. Subjects became significantly more likely to report oscillopsia during head movements when end-end latency or head velocity were increased. It is concluded that perceptual instability of the world arises with increased head motion and increased display lag. Oscillopsia is expected to be more apparent in tasks requiring real locomotion or rapid head movement.

Quantile sampling for practical delay monitoring in Internet backbone networks

Baek-Young Choi — 2007-12-20T21:33:13-00:00

Computer Networks, Vol. 51, No. 10. (11 July 2007), pp. 2701-2716.

Point-to-point delay is an important network performance measure as it captures service degradations caused by various events. We study how to measure and report delay in a concise and meaningful way for an ISP, and how to monitor it efficiently. We analyze various measurement intervals and potential metric definitions. We find that reporting high quantiles (between 0.95 and 0.99) every 10-30 min as the most effective way to summarize the delay in an ISP. We then propose an active probing scheme to estimate a high quantile with bounded error. We show that only a small number of probes are sufficient to provide an accurate estimate. We validate the proposed delay monitoring technique on real data collected on the Sprint IP backbone network. To make our work complete, we lastly compare the overhead of our active probing technique with a passive sampling scheme and show that for delay measurement, active probing is more practical.

Packet delay and packet loss in the Internet

Jingping Bi — 2007-02-01T16:10:28-00:00

Computers and Communications, 2002. Proceedings. ISCC 2002. Seventh International Symposium on (2002), pp. 3-8.

The distribution characteristic of RTT (round-trip time) is an important part of Internet end-to-end behavior characteristics. People have made lots of studies of it, but many conclusions only adapt to the cases of small packet loss rate. We study the RTT characteristics on nearly 40 end-to-end paths in CSTNET and CERNET in China, and draw the following conclusions: (1) the distribution characteristics of RTT and loss rate are dependable; (2) when loss rate is small, RTT distribution is usually unimodal, but with the increase of loss rate, RTT distribution is no longer unimodal and it becomes more and more decentralized; (3) with the increase of loss rate, the occurring times of inherent RTT tend to decrease.

Delay Doppler characteristics of multipath propagation at 910 MHz in a suburban mobile radio environment

D Cox — 2007-09-17T14:28:37-00:00

Antennas and Propagation, IEEE Transactions on [legacy, pre - 1988], Vol. 20, No. 5. (1972), pp. 625-635.

Statistical descriptions of the time delays and Doppler shifts associated with multipath propagation in a suburban mobile radio environment obtained from bandpass impulse response measurements are presented. The measuring equipment which has<tex>0.1 mu</tex>s resolution in time delay and a data output bandwidth of less than 5 kHz is also described. For the first time small scale statistics of the multipath propagation for vehicle travel distances on the order of 30 m along streets are presented in the following forms: 1) average power-delay profiles made up of over 200 individual profiles, 2) cumulative distributions of signal amplitude at fixed delays, and 3) radio frequency Doppler spectra at fixed delays. Delay spreads for typical suburban streets are on the order of<tex>0.25 mu</tex>s. Extreme cases have paths with significant amplitudes at excess delays of 5 to<tex>7 mu</tex>s and the square root of the second central moment delay spreads up to about<tex>2 mu</tex>s. Often the signal at fixed delays has a Rayleigh distributed amplitude but large departures from the Rayleigh distribution also occur. RF Doppler spectra at fixed delays indicate that some of the multipath is from one relatively discrete scattering center while at other delays several scattering centers distributed widely in angle are involved. The observed RF Doppler spectra are consistent with the cumulative amplitude distributions at the same delays.

Depth in anticorrelated stereograms: Effects of spatial density and interocular delay

Alexander Cogan — 2008-05-29T10:20:18-00:00

Vision Research, Vol. 33, No. 14. (September 1993), pp. 1959-1975.

Disparity-based depth is not perceived in densely textured, anticorrelated random-dot stereograms (RDSs) whose elements carry opposite signs of brightness coatrast on corresponding loci, as extant data show. We observed global depth in anticorrelated RDSs flashed repetitively with an interocular delay. During the delay time, a dot array in one eye was paired with a gray frame hi the other eye and thus could interact with the negative afterimage of the contralateral dot array. A correlated RDS (e.g. 8 min arc dots, 50% density, 15-msec flash duration) lost depth with delays > 45 msec. An anticorrelated RDS, that was otherwise identical, showed robust depth when flashed with an interocular delay of some 60 msec. A delay was not always necessary to produce depth. At low dot density (1-2%), anticorrelated RDSs showed disparity-dependent local depth even when displayed continuously, or flashed simultaneously; as dot density alone was increased, depth was progressively lost. To make global depth visible in a dense RDS flashed with an interocular delay, the internal response had to be strongly biphasic. Our results support the generally held notion that cyclopean depth signals emerge exclusively from same-sign binocular cortical filters. However, the exclusionary rule may be invalid with respect to the processing of coarse local depth with figural stimuli. Relative depth between a pair of small dots was easily perceived when one of the dots was in opposite contrast, but the depth threshold was then about 0.5 log unit higher than with the same-contrast pair of dots indicating that the internal effects of contrast have not all lost their sign prior to binocular disparity processing. It remains to be determined whether depth can be perceived from edges of opposite contrast.

Competition in size-structured populations: mechanisms inducing cohort formation and population cycles

AM de Roos — 2004-12-28T15:39:16-00:00

Theoretical Population Biology, Vol. 63, No. 1. (February 2003), pp. 1-16.

Polychronization: Computation with Spikes

Eugene Izhikevich — 2005-12-11T22:46:39-00:00

Neural Computation, Vol. 18, No. 2. (February 2006), pp. 245-282.

Development of Affective Decision Making for Self and Other: Evidence for the Integration of First- and Third-Person Perspectives

Angela Prencipe — 2005-07-05T23:31:10-00:00

Psychological Science, Vol. 16, No. 7. (July 2005), pp. 501-505.

The role of perspective taking in affective decision making was studied in children at two ages (3 and 4 years) using a delay-of-gratification paradigm in which children chose between an immediate reward of lower value and a delayed reward of higher value. Half the children chose for themselves (self condition), and half chose for the experimenter (other condition). Three-year-olds chose delayed rewards in the other condition but made impulsive choices in the self condition. Compared with 3-year-olds, 4-year-olds performed better in the self condition and worse in the other condition. Results suggest that 3-year-olds took either a subjective, first-person perspective (for self) or an objective, third-person perspective (for other). Four-year-olds integrated these perspectives, considering a third-person perspective in the self condition and the experimenter's subjective perspective in the other condition (i.e., her desire for immediate gratification). This integration allowed reason to be tempered by emotion, and vice versa.

Delayed Internet routing convergence

Craig Labovitz — 2006-06-20T01:35:21-00:00

Vol. 30, No. 4. (October 2000), pp. 175-187.

Delayed Internet routing convergence

Craig Labovitz — 2006-06-20T01:32:37-00:00

IEEE/ACM Trans. Netw., Vol. 9, No. 3. (June 2001), pp. 293-306.

Delayed Internet routing convergence

C Labovitz — 2006-06-20T01:15:31-00:00

Networking, IEEE/ACM Transactions on, Vol. 9, No. 3. (2001), pp. 293-306.

This paper examines the latency in Internet path failure, failover, and repair due to the convergence properties of interdomain routing. Unlike circuit-switched paths which exhibit failover on the order of milliseconds, our experimental measurements show that interdomain routers in the packet-switched Internet may take tens of minutes to reach a consistent view of the network topology after a fault. These delays stem from temporary routing table fluctuations formed during the operation of the border gateway protocol (BGP) path selection process on the Internet backbone routers. During these periods of delayed convergence, we show that end-to-end Internet paths will experience intermittent loss of connectivity, as well as increased packet loss and latency. We present a two-year study of Internet routing convergence through the experimental instrumentation of key portions of the Internet infrastructure, including both passive data collection and fault-injection machines at major Internet exchange points. Based on data from the injection and measurement of several hundred thousand interdomain routing faults, we describe several unexpected properties of convergence and show that the measured upper bound on Internet interdomain routing convergence delay is an order of magnitude slower than previously thought. Our analysis also shows that the upper theoretic computational bound on the number of router states and control messages exchanged during the process of BGP convergence is factorial with respect to the number of autonomous systems in the Internet. Finally, we demonstrate that much of the observed convergence delay stems from specific router vendor implementation decisions and ambiguity in the BGP specification

An empirical evaluation of internet latency expansion

Hui Zhang — 2006-05-20T07:50:46-00:00

SIGCOMM Comput. Commun. Rev., Vol. 35, No. 1. (January 2005), pp. 93-97.

Analysis of point-to-point packet delay in an operational network

BK Choi — 2006-05-09T06:12:50-00:00

INFOCOM 2004. Twenty-third AnnualJoint Conference of the IEEE Computer and Communications Societies, Vol. 3 (2004), pp. 1797-1807 vol.3.

We perform a detailed analysis of point-to-point packet delay in an operational tier-1 network. The point-to-point delay is the time between a packet entering a router in one PoP (an ingress point) and its leaving a router in another PoP (an egress point). It measures the one-way delay experienced by packets from an ingress point to an egress point across an ISP's network and provides the most basic information regarding the delay performance of the ISP's network. Using packet traces captured in the operational network, we obtain precise point-to-point packet delay measurements and analyze the various factors affecting them. Through a simple, step-by-step, systematic methodology and careful data analysis, we identify the major network factors that contribute to point-to-point packet delay and characterize their effect on the network delay performance. Our findings are: 1) delay distributions vary greatly in shape, depending on the path and link utilization; 2) after constant factors dependent only on the path and packet size are removed, the 99th percentile variable delay remains under 1 ms over several hops and under link utilization below 90% on a bottleneck; 3) a very small number of packets experience very large delay in short bursts.

Nicholson's blowflies revisited

WSC Gurney — 2008-06-06T19:43:32-00:00

Nature, Vol. 287, No. 5777. (1980), pp. 17-21.

A simple time-delay model of laboratory insect populations which postulates a 'humped' relationship between future adult recruitment and current adult population gives good quantitative agreement with Nicholson's classic blowfly data and explains the appearance of narrow 'discrete' generations in cycling populations.

Nonoptimal Component Placement, but Short Processing Paths, due to Long-Distance Projections in Neural Systems

Marcus Kaiser — 2006-08-07T10:48:26-00:00

PLoS Computational Biology, Vol. 2, No. 7. (1 July 2006), e95.

It has been suggested that neural systems across several scales of organization show optimal component placement, in which any spatial rearrangement of the components would lead to an increase of total wiring. Using extensive connectivity datasets for diverse neural networks combined with spatial coordinates for network nodes, we applied an optimization algorithm to the network layouts, in order to search for wire-saving component rearrangements. We found that optimized component rearrangements could substantially reduce total wiring length in all tested neural networks. Specifically, total wiring among 95 primate (Macaque) cortical areas could be decreased by 32%, and wiring of neuronal networks in the nematode Caenorhabditis elegans could be reduced by 48% on the global level, and by 49% for neurons within frontal ganglia. Wiring length reductions were possible due to the existence of long-distance projections in neural networks. We explored the role of these projections by comparing the original networks with minimally rewired networks of the same size, which possessed only the shortest possible connections. In the minimally rewired networks, the number of processing steps along the shortest paths between components was significantly increased compared to the original networks. Additional benchmark comparisons also indicated that neural networks are more similar to network layouts that minimize the length of processing paths, rather than wiring length. These findings suggest that neural systems are not exclusively optimized for minimal global wiring, but for a variety of factors including the minimization of processing steps.

Synaptic delay learning in pulse-coupled neurons.

H Hüning — 2005-04-04T16:03:52-00:00

Neural Computation, Vol. 10, No. 3. (1 April 1998), pp. 555-565.

We present rules for the unsupervised learning of coincidence between excitatory postsynaptic potentials (EPSPs) by the adjustment of postsynaptic delays between the transmitter binding and the opening of ion channels. Starting from a gradient descent scheme, we develop a robust and more biological threshold rule by which EPSPs from different synapses can be gradually pulled into coincidence. The synaptic delay changes are determined from the summed potential--at the site where the coincidence is to be established--and from postulated synaptic learning functions that accompany the individual EPSPs. According to our scheme, templates for the detection of spatiotemporal patterns of synaptic activation can be learned, which is demonstrated by computer simulation. Finally, we discuss possible relations to biological mechanisms.

Asset Price Dynamics in a Financial Market with Heterogeneous Trading Strategies and Time Delays

G Garofalo — 2007-04-01T15:14:06-00:00

ArXiv Physics e-prints (July 2006)

In this paper we present a continuous time dynamical model of heterogeneous agents interacting in a financial market where transactions are cleared by a market maker. The market is composed of fundamentalist, trend following and contrarian agents who process information from the market with different time delays. Each class of investor is characterized by path dependent risk aversion. We also allow for the possibility of evolutionary switching between trend following and contrarian strategies. We find that the system shows periodic, quasi-periodic and chaotic dynamics as well as synchronization between technical traders. Furthermore, the model is able to generate time series of returns that exhibit statistical properties similar to those of the S&P500 index, which is characterized by excess kurtosis, volatility clustering and long memory

Mechanism Equivalence in Enzyme-Substrate Reactions: Distributed Differential Delay in Enzyme Kinetics

R Hinch — 2006-10-26T03:48:43-00:00

Journal of Chemistry, Vol. V35, No. 3. (21 March 2004), pp. 253-264.

Persistent neural activity during the maintenance of spatial position in working memory

Riju Srimal — 2007-11-20T19:33:08-00:00

NeuroImage, Vol. 39, No. 1. (1 January 2008), pp. 455-468.

The mechanism for the short-term maintenance of information involves persistent neural activity during the retention interval, which forms a bridge between the cued memoranda and its later contingent response. Here, we used event-related functional magnetic resonance imaging to identify cortical areas with activity that persists throughout working memory delays with the goal of testing if such activity represents visuospatial attention or prospective saccade goals. We did so by comparing two spatial working memory tasks. During a memory-guided saccade (MGS) task, a location was maintained during a delay after which a saccade was generated to the remembered location. During a spatial item recognition (SIR) task identical to MGS until after the delay, a button press indicated whether a newly cued location matched the remembered location. Activity in frontal and parietal areas persisted above baseline and was greater in the hemisphere contralateral to the cued visual field. However, delay-period activity did not differ between the tasks. Notably, in the putative frontal eye field (FEF), delay period activity did not differ despite that the precise metrics of the memory-guided saccade were known during the MGS delay and saccades were never made in SIR. Persistent FEF activity may therefore represent a prioritized attentional map of space, rather than the metrics for saccades.

The time course of off-line motor sequence learning.

DZ Press — 2005-10-08T22:26:55-00:00

Brain Res Cogn Brain Res, Vol. 25, No. 1. (September 2005), pp. 375-378.

The acquisition of motor skill occurs with practice, but skill can also increase between sessions, a process termed "off-line learning". Here, we investigated the amount of time required for the off-line development of skills. Participants were tested on an implicit version of the Serial Reaction Time Task and re-tested 1, 4 or 12 h later. Only those re-tested 4 h or 12 h after initial testing showed off-line improvements. This demonstrates that implicitly acquired skills can increase between sessions and the process occurs over hours.

The effects of landmarks on the performance of delayed and real-time pointing movements.

Sukhvinder Obhi — 2005-10-08T21:29:51-00:00

Exp Brain Res (22 July 2005), pp. 1-10.

Converging lines of evidence suggest that the presence of non-target landmarks affects the performance of delayed target-directed movements (e.g., Diedrichsen et al. 2004; Sheth and Shimojo 2004). In the present experiment, we examined the effects of non-target landmarks on the accuracy and precision of delayed and immediate target-directed pointing movements. In our experiment, the landmarks were present just prior to and during the presentation of the target; they were never present during the execution of the movement. Absolute errors were significantly reduced when the landmarks were available during target presentation for both delayed and immediate action conditions. In contrast, the presence of landmarks improved the precision of delayed but not immediate movements (as indexed by the variable error). The locus of this "landmark benefit" appears to be in the encoding of target position since landmarks were never available after target offset. We suggest that, when available, information provided by landmarks is used to improve the accuracy of the estimation of target location. Since the targets were presented for only 100 ms, it is apparent that the spatial information available from landmarks can be quite rapidly used to estimate target position. Further, with respect to the precision of movements, we suggest that the presence of landmarks serves to improve the stability of the estimation of target position. This particular reliance on landmark information becomes more critical as the movement is delayed.

Interferometric measurements of femtosecond group delay in optical components

WH Knox — 2007-07-26T02:47:57-00:00

Optics Letters, Vol. 13 (July 1988), pp. 574-576.

Not Available

Measurement of group delay dispersion of high numerical aperture objective lenses using two-photon excited fluorescence

JB Guild — 2007-08-24T13:26:18-00:00

Appl. Opt., Vol. 36 (January 1997), pp. 397-401.

Not Available

Reconfigurable Resource Scheduling with Variable Delay Bounds

CG Plaxton — 2008-07-14T07:43:43-00:00

Parallel and Distributed Processing Symposium, 2007. IPDPS 2007. IEEE International (2007), pp. 1-10.

Certain emerging network applications involve dynamically allocating shared resources to a variety of services to provide QoS guarantees for each service. Motivated by such applications, we address the following online scheduling problem belonging to the recently introduced class of reconfigurable resource scheduling problems: unit jobs of different categories arrive over time and need to be completed within category-specific delay bounds, or else they are dropped at a unit drop cost; processors can be reconfigured to process jobs of a certain category at a fixed reconfiguration cost; the goal is to minimize the total cost. We study this problem in the framework of competitive analysis. Through a novel combination of the EDF and LRU scheduling principles, we obtain an online algorithm that is constant competitive when given a constant factor resource advantage over an optimal offline algorithm.

C.P.M. Scheduling with Small Communication Delays and Task Duplication

JY Colin — 2008-07-09T04:51:11-00:00

Operations Research, Vol. 39, No. 4. (1991), pp. 680-684.

This paper addresses a machine scheduling problem that arises in the case of scheduling tasks over an idealized distributed multiprocessor. Precedence constraints with small communication delays have to be taken into account and task duplication is allowed. A critical path-like algorithm is presented, which is shown to construct an optimal schedule in polynomial time.

A delay stochastic process with applications in molecular biology

Robert Schlicht — 2008-05-05T23:42:19-00:00

Journal of Mathematical Biology

Abstract Molecular processes of cell differentiation often involve reactions with delays. We develop a mathematical model that provides a basis for a rigorous theoretical analysis of these processes as well as for direct simulation. A discrete, stochastic approach is adopted because several molecules appear in small numbers only. Our model is a non-Markovian stochastic process. The main theoretical results include a constructive proof of the existence of the process and a derivation of the rates for initiation and completion of reactions with delays. These results guarantee that the stochastic process is a consistent and realistic description of the molecular system. They also serve as a theoretical justification of recent work on delay stochastic simulation. We apply our model to an important process in developmental biology, the formation of somites in the vertebrate embryo. Simulation of the molecular oscillator controlling this process reveals major differences between stochastic and deterministic models.

Low-delay peer-to-peer streaming using scalable video coding

Pierpaolo Baccichet — 2008-05-09T20:50:52-00:00

Packet Video 2007 (2007), pp. 173-181.

Peer-to-peer (P2P) networks represent a valuable architecture for streaming video over the Internet. In these systems, users contribute their resources to relay the media to others and no dedicated infrastructure is required. In order to ensure a low end-to-end delay, P2P overlay networks are often organized as a set of complementary multicast trees. The source of the stream multiplexes the data on top of these trees and the routing of packets is statically defined. In this scenario, the reliability of the overlay links is critical for the performance of the system since temporary link failure or network congestion can cause a significant disruption of the end-user quality. The novel Scalable Video Coding (SVC) standard enables efficient usage of the network capacity by allowing intermediate high capacity nodes in the overlay network to dynamically extract layers from the scalable bit stream to serve less capable peers. On the other hand, SVC incurs a certain loss in terms of coding efficiency with respect to H.264/AVC single-layer coding. We propose a simple model that allows to evaluate the trade-off of using a scalable codec with respect to single-layer coding, given the distribution of the receivers’ capacities in an error-free network. We also report experimental results obtained by using SVC on top of a real-time implementation of the Stanford Peer-to-Peer Multicast (SPPM) protocol that clearly show the benefits of a prioritization mechanism to react to network congestion.

Second Derivative Algorithms for Minimum Delay Distributed Routing in Networks

D Bertsekas — 2006-07-15T20:46:09-00:00

IEEE Transactions on Communications, Vol. 32, No. 8. (1984), pp. 911-919.

We propose a class of algorithms for finding an optimal quasi-static routing in a communication network. The algorithms are based on Gallager's method [1] and provide methods for iteratively updating the routing table entries of each node in a manner that guarantees convergence to a minimum delay routing. Their main feature is that they utilize second derivatives of the objective function and may be viewed as approximations to a constrained version of Newton's method. The use of second derivatives results in improved speed of convergence and automatic stepsize scaling with respect to level of traffic input. These advantages are of crucial importance for the practical implementation of the algorithm using distributed computation in an environment where input traffic statistics gradually change.

A Minimum Delay Routing Algorithm Using Distributed Computation

R Gallager — 2006-07-15T20:42:38-00:00

IEEE Transactions on Communications, Vol. 25, No. 1. (1977), pp. 73-85.

An algorithm is defined for establishing routing tables in the individual nodes of a data network. The routing table at a node<tex>i</tex>specifies, for each other node<tex>j</tex>, what fraction of the traffic destined for node<tex>j</tex>should leave node<tex>i</tex>on each of the links emanating from node<tex>i</tex>. The algorithm is applied independently at each node and successively updates the routing table at that node based on information communicated between adjacent nodes about the marginal delay to each destination. For stationary input traffic statistics, the average delay per message through the network converges, with successive updates of the routing tables, to the minimum average delay over all routing assignments. The algorithm has the additional property that the traffic to each destination is guaranteed to be loop free at each iteration of the algorithm. In addition, a new global convergence theorem for noncontinuous iteration algorithms is developed.

End-to-end delay analysis of videoconferencing over packet-switched networks

M Baldi — 2008-05-22T04:19:00-00:00

Networking, IEEE/ACM Transactions on, Vol. 8, No. 4. (2000), pp. 479-492.

Videoconferencing is an important global application-it enables people around the globe to interact when distance separates them. In order for the participants in a videoconference call to interact naturally, the end-to-end delay should be below human perception; even though an objective and unique figure cannot be set, 100 ms is widely recognized as the desired one-way delay requirement for interaction. Since the global propagation delay can be about 100 ms, the actual end-to-end delay budget available to the system designer (excluding propagation delay) can be no more than 10 ms. We identify the components of the end-to-end delay in various configurations with the objective of understanding how it can be kept below the desired 10-ms bound. We analyze these components step-by-step through six system configurations obtained by combining three generic network architectures with two video encoding schemes. We study the transmission of raw video and variable bit rate (VBR) MPEG video encoding over (1) circuit switching; (2) synchronous packet switching; and (3) asynchronous packet switching. In addition, we show that constant bit rate (CBR) MPEG encoding delivers unacceptable delay-on the order of the group of pictures (GOP) time interval-when maximizing the quality for static scenes. This study aims at showing that having a global common time reference, together with time-driven priority (TDP) and VBR MPEG video encoding, provides adequate end-to-end delay, which is (1) below 10 ms; (2) independent of the network instant load; and (3) independent of the connection rate. The resulting end-to-end delay (excluding propagation delay) can be smaller than the video frame period, which is better than what can be obtained with circuit switching

Japan's nuclear energy policy: from firm commitment to difficult dilemma addressing growing stocks of plutonium, program delays, domestic opposition and international pressure

Susan Pickett — 2008-04-18T00:15:42-00:00

Energy Policy, Vol. 30, No. 15. (December 2002), pp. 1337-1355.

Since 1956, Japan has been on a path to reduce its dependence on foreign energy sources through the development of nuclear power. This paper examines the origins of this commitment, the changing social issues and the current dilemma Japan faces regarding the future of its nuclear energy policy and its efforts to overcome the domestic and international pressures to ensure safety and security. Galvanized by international initiatives and further motivated by the oil crises in the 1970s, Japan's commitment to develop a closed nuclear fuel cycle, one which reprocesses fuel from thermal reactors for use in advanced fast breeder reactors, has remained resolute. However, program delays, international security concerns over the plutonium, a weapons-grade nuclear material and one of the products of reprocessing, and increasing public opposition to various components of the Atomic Energy Commissions' Long-Term Program for Development and Utilization of Nuclear Energy, have put pressure on the government to resolve these issues. The commitment to develop the technology on one hand is commendable however it has contributed to the dilemma the Japanese nuclear industry now faces: a growing stockpile of plutonium and no readily available means of reducing it. With growing public involvement, finding a straightforward technology solution is increasingly difficult. In 1995, an accident at Monju, one of the first prototype fast breeder reactors in Japan, prompted the Commission to initiate the first Roundtable Conference. The purpose of the Conference was to open the policy making process in an effort to determine a "national consensus" on nuclear energy. Further accidents and on-going opposition further slowed the implementation of the Program, however, in the latest Program, released in 2000, the Commission attempts to address these issues while building in a new style of flexibility in order to allow for greater options in the future.

Multicarrier delay diversity modulation for MIMO systems

Jun Tan — 2007-02-16T03:47:37-00:00

Wireless Communications, IEEE Transactions on, Vol. 3, No. 5. (2004), pp. 1756-1763.

Multicarrier delay diversity modulation (MDDM) is a scheme that uses orthogonal frequency division multiplexing (OFDM) on a "multipath" channel that is generated by using delay diversity. The full diversity criterion for MDDM is proven and illustrative examples of full-diversity codes are obtained based on the established criterion. Coding gains and interleaver designs are also considered and analyzed. Simulation results for MDDM on quasi-static flat and frequency-selective fading channels are discussed. MDDM is established as a strong competitive technique to existing space-time block codes and space-time tellis codes techniques for multiple input multiple output systems.

Prefrontal neuronal activity in rhesus monkeys performing a delayed anti-saccade task

Shintaro Funahashi — 2007-03-07T03:31:34-00:00

Nature, Vol. 365, No. 6448. (21 October 1993), pp. 753-756.

Effects of inductance on the propagation delay and repeater insertion in VLSI circuits

YI Ismail — 2005-09-15T17:37:55-00:00

Very Large Scale Integration (VLSI) Systems, IEEE Transactions on, Vol. 8, No. 2. (2000), pp. 195-206.

A closed-form expression for the propagation delay of a CMOS gate driving a distributed RLC line is introduced that is within 5% of dynamic circuit simulations for a wide range of RLC loads. It is shown that the error in the propagation delay if inductance is neglected and the interconnect is treated as a distributed RC line can be over 35% for current on-chip interconnect. It is also shown that the traditional quadratic dependence of the propagation delay on the length of the interconnect for RC lines approaches a linear dependence as inductance effects increase. On-chip inductance is therefore expected to have a profound effect on traditional high-performance integrated circuit (IC) design methodologies. The closed-form delay model is applied to the problem of repeater insertion in RLC interconnect. Closed-form solutions are presented for inserting repeaters into RLC lines that are highly accurate with respect to numerical solutions. RC models can create errors of up to 30% in the total propagation delay of a repeater system as compared to the optimal delay if inductance is considered. The error between the RC and RLC models increases as the gate parasitic impedances decrease with technology scaling. Thus, the importance of inductance in high-performance very large scale integration (VLSI) design methodologies will increase as technologies scale

A universal tool for determining the time delay and the frequency shift of light: Synge's world function

Pierre Teyssandier — 2007-11-19T08:10:06-00:00

(31 Oct 2007)

In almost all of the studies devoted to the time delay and the frequency shift of light, the calculations are based on the integration of the null geodesic equations. However, the above-mentioned effects can be calculated without integrating the geodesic equations if one is able to determine the bifunction $Ω(x_A, x_B)$ giving half the squared geodesic distance between two points $x_A$ and $x_B$ (this bifunction may be called Synge's world function). In this lecture, $Ω(x_A, x_B)$ is determined up to the order $1/c^3$ within the framework of the PPN formalism. The case of a stationary gravitational field generated by an isolated, slowly rotating axisymmetric body is studied in detail. The calculation of the time delay and the frequency shift is carried out up to the order $1/c^4$. Explicit formulae are obtained for the contributions of the mass, of the quadrupole moment and of the internal angular momentum when the only post-Newtonian parameters different from zero are $β$ and $γ$. It is shown that the frequency shift induced by the mass quadrupole moment of the Earth at the order $1/c^3$ will amount to $10^-16$ in spatial experiments like the ESA's Atomic Clock Ensemble in Space mission. Other contributions are briefly discussed.

Differentiated TCP User Perception over Downlink Packet Data Cellular Systems

Aimin Sang — 2008-02-20T06:27:29-00:00

IEEE Transactions on Mobile Computing, Vol. 6, No. 3. (March 2007), pp. 252-263.

Current downlink scheduling algorithms in the (enhanced) third-generation (3G) cellular packet systems exploit instantaneous channel status of multiple users, but most of them are blind to traffic information. To improve TCP users' perception of quality-of-services (QoSs), characterized by response delay, goodput, and always-on connectivity, we propose a cross-layer hierarchical scheduler with traffic awareness and channel dependence to properly prioritize buffer and radio resource allocation among different TCP classes. The scheduler has two tiers: at the IP layer, an intrauser scheduler enhances a common practice, i.e., the DiffServ-based buffer management, by dequeuing same-user TCP packets according to per-class specified and measured responsiveness; at the MAC layer, an interuser scheduler transmits the dequeued packets by considering the opportunistic channel states, mean throughput, and class ID of all users. Both tiers consider the online measured throughput, a cross-layer metric, to achieve resource and performance fairness and TCP classification. Experiments show that, compared with (variations of) proportional fairness (PF) and other schemes, our scheduler can notably speed up time-critical interactive TCP services (HTTP and TELNET) or TCP slow-starts with minor cost to bulk file transfer (FTP) or long-lived flows. It offers scalable and low-cost TCP performance enhancement over the emerging cellular systems

An Adaptive Media-Aware Retransmission Timeout Estimation Method for Low-Delay Packet Video

Ali Begen — 2008-02-20T07:00:53-00:00

IEEE Transactions on Multimedia, Vol. 9, No. 2. (February 2007), pp. 332-347.

Time-constrained error recovery is an integral component of reliable low-delay video applications. Regardless of the error-control method adopted by the application, unacknowledged or missing packets must be quickly identified as lost or delayed, so that necessary actions can be taken by the server/client on time. Historically, this problem has been referred to as retransmission timeout (RTO) estimation. Earlier studies show that existing RTO estimators suffer from either long loss detection times or a large number of spurious timeouts. The goal of this study is to address these problems by developing an RTO estimation method specifically tailored for low-delay video applications. In the media-unaware mode, this method exploits the temporal dependence in packet delay to optimally manage the tradeoff between the amount of overwaiting and redundant retransmission rate. As opposed to existing methods, our approach is completely adaptive to the source video characteristics and time-varying network conditions, and does not use any preset parameters. In the media-aware mode, on the other hand, the timeout estimates are jointly optimized based on the importance and urgency of the video packets such that the rendering quality is maximized under the given rate constraints. With a comprehensive set of simulation and experimental results, we show that both the media-unaware and media-aware RTO estimators detect lost packets faster and more accurately than their rivals. Furthermore, our results also substantiate the fact that the media-aware RTO estimator outperforms all other RTO estimators in terms of video quality

Recovering Periodically Spaced Missing Samples

Andor Bariska — 2008-02-14T12:42:17-00:00

IEEE Signal Processing Magazine, Vol. 24, No. 6. (November 2007), pp. 127-129.

We presented a novel method to recover periodically missing samples from appropriately bandlimited signals. We used filterbanks with fractional delay filters as building blocks, and described a windowed-sine method to approximate the fractional delays with FIR subfilters. Because the implementation of filterbanks and the approximation of fractional delay filters are well-studied problems, this makes the proposed recovery method flexible and easy to implement.

Quantum Study of Information Delay in Electromagnetically Induced Transparency

MTL Hsu — 2006-11-03T12:11:36-00:00

Physical Review Letters, Vol. 97, No. 18. (2006)

Using electromagnetically induced transparency (EIT), it is possible to delay and store light in atomic ensembles. Theoretical modeling and recent experiments have suggested that the EIT storage mechanism can be used as a memory for quantum information. We present experiments that quantify the noise performance of an EIT system for conjugate amplitude and phase quadratures. It is shown that our EIT system adds excess noise to the delayed light that has not hitherto been predicted by published theoretical modeling. In analogy with other continuous-variable quantum information systems, the performance of our EIT system is characterized in terms of conditional variance and signal transfer.

Electromagnetically Induced Transparency in optically trapped rubidium atoms

Bernd Kaltenhäuser — 2007-01-10T16:50:09-00:00

(9 Jan 2007)

We demonstrate electromagnetically induced transparency (EIT) in a sample of rubidium atoms, trapped in an optical dipole trap. Mixing a small amount of $σ^-$-polarized light to the weak $σ^+$-polarized probe pulses, we are able to measure the absorptive and dispersive properties of the atomic medium at the same time. Features as small as 4 kHz have been detected on an absorption line with 20 MHz line width.

Delay analysis of IEEE 802.11 in single-hop networks

MM Carvalho — 2007-01-19T01:11:02-00:00

Network Protocols, 2003. Proceedings. 11th IEEE International Conference on (2003), pp. 146-155.

This paper presents an analytical model to compute the average service time and jitter experienced by a packet when transmitted in a saturated IEEE 802.11 ad hoc network. In contrast to traditional work in the literature, in which a distribution is usually fitted or assumed, we use a bottom-up approach and build the first two moments of the service time based on the IEEE 802.11 binary exponential backoff algorithm and the events underneath its operation. Our model is general enough to be applied to any type of IEEE 802.11 wireless ad hoc network where the channel state probabilities driving a node's backoff operation are known. We apply our model to saturated single-hop ad hoc networks under ideal channel conditions. We validate our model through extensive simulations and conduct a performance evaluation of a node's average service time and jitter for both direct sequence and frequency-hopping spread spectrum physical layers.

Steady-state stabilization due to random delays in maps with self-feedback loops and in globally delayed-coupled maps

Arturo Marti — 2007-07-11T19:40:08-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 72, No. 6. (2005)

We study the stability of the fixed-point solution of an array of mutually coupled logistic maps, focusing on the influence of the delay times, ij, of the interaction between the ith and jth maps. Two of us recently reported [Phys. Rev. Lett. 94, 134102 (2005)] that if ij are random enough, the array synchronizes in a spatially homogeneous steady state. Here we study this behavior by comparing the dynamics of a map of an array of N delayed-coupled maps with the dynamics of a map with N self-feedback delayed loops. If N is sufficiently large, the dynamics of a map of the array is similar to the dynamics of a map with self-feedback loops with the same delay times. Several delayed loops stabilize the fixed point, when the delays are not the same; however, the distribution of delays plays a key role; if the delays are all odd a periodic orbit (and not the fixed point) is stabilized. We present a linear stability analysis and apply some mathematical theorems that explain the numerical results.

Anticipated synchronization in coupled chaotic maps with delays

Cristina Masoller — 2006-07-10T18:27:23-00:00

Physica A: Statistical Mechanics and its Applications, Vol. 300, No. 3-4. (15 November 2001), pp. 359-366.

We study the synchronization of two chaotic maps with unidirectional (master-slave) coupling. Both maps have an intrinsic delay n1, and coupling acts with a delay n2. Depending on the sign of the difference n1-n2, the slave map can synchronize to a future or a past state of the master system. The stability properties of the synchronized state are studied analytically, and we find that they are independent of the coupling delay n2. These results are compared with numerical simulations of a delayed map that arises from discretization of the Ikeda delay-differential equation. We show that the critical value of the coupling strength above which synchronization is stable becomes independent of the delay n1 for large delays.

Synchronization of coupled time-delay systems: Analytical estimations

K Pyragas — 2006-07-07T20:43:53-00:00

Physical Review E, Vol. 58, No. 3. (1998), 3067.

The synchronization threshold of coupled time-delay chaotic systems is estimated by two different analytical approaches. One of them is based on the Krasovskii-Lyapunov theory that represents an extension of the second Lyapunov method for delay differential equations. Another approach uses a perturbation theory of large delay time. The analytical expression relating synchronization threshold to the maximal Lyapunov exponent of uncoupled driving and response subsystems is derived. The analytical results are compared with the numerical simulations for two coupled Mackey-Glass systems.

Synchronization of time-delay systems

Martin Bünner — 2006-07-10T20:37:21-00:00

Physical Review E, Vol. 58, No. 4. (October 1998), R4072.

We present the linear stability analysis of synchronized states in coupled time-delay systems. There exists a synchronization threshold; for which we derive upper bounds; which does not depend on the delay time. We prove that at least for scalar time-delay systems; synchronization is achieved by transmitting a single scalar signal; even if the synchronized solution is given by a high-dimensional chaotic state with a large number of positive Lyapunov exponents. The analytical results are compared with numerical simulations of two coupled Mackey-Glass equations.