Threshold Configuration Research Articles

Exact Results for a Toy Model Exhibiting Dynamic Criticality

We discuss a one-dimensional, periodic charge density wave model, and a toy model introduced in Kaspar and Mungan (EPL 103:46002, 2013) which is intended to approximate the former in the case of strong pinning. For both systems an external force may be applied, driving it in one of two (±) directions, and we describe an avalanche algorithm producing an ordered sequence of static configurations leading to the depinning thresholds. For the toy model these threshold configurations are explicit functions of the underlying quenched disorder, as is the threshold-to-threshold evolution via iteration of the algorithm. These explicit descriptions are used to study the law of the random polarization P for the toy model in two cases. Evolving from a macroscopically flat initial state to threshold, we give a scaling limit characterization determines the final value of P. Evolving from (−)-threshold to (+)-threshold, we use an identification with record sequences to study P as a function of the difference between the current force F and the threshold force F th. The results presented are rigorous and give strong evidence that the depinning transition in the toy model is a dynamic critical phenomenon.

Measurement threshold configuration scheme based on the traffic load

This study proposes a performance analysis of the measurements mechanism applicable to the terminal controlled cell reselection algorithm in a mobile cellular communication system. The cell reselection mechanism decides on which cell, a user equipment (UE) is camped on, when it is in the idle mode. The analysis demonstrates the impact of the neighbour cells measurement threshold setting during the reselection on the serving cell pilot channel quality and a measurement effort in the UE, in terms of the time spent measuring neighbour cells. The authors demonstrate that there is a trade-off between the cell reselection performance, in terms of the signal quality during the mobility and the battery life in the mobile terminal with different system configurations. Furthermore, a novel approach and enhanced load based measurement threshold configuration scheme is proposed, in order to improve this trade-off and also the overall system performance and the user experience. Performance analysis results are given in different scenarios to demonstrate the efficacy of the proposed scheme.

Optimal Threshold Configuration Methods for Flow Admission Control with Cooperative Users

We have proposed a novel call admission control (CAC) method for maximizing total user satisfaction in a heterogeneous traffic network and showed their effectiveness by using the optimal threshold from numerical analysis [1],[2]. With these CAC methods, it is assumed that only selfish users exist in a network. However, we need to consider the possibility that some cooperative users exist who would agree to reduce their requested bandwidth to improve another user's Quality of Service (QoS). Under this assumption, conventional CAC may not be optimal. If there are cooperative users in the network, we need control methods that encourage such user cooperation. However, such “encourage” control methods have not yet been proposed. Therefore, in this paper, we propose novel CAC methods for cooperative users by using queueing theory. Numerical analyses show their effectiveness. We also analyze the characteristics of the optimal control parameter of the threshold.

A multi-objective genetic optimization for spectrum sensing in cognitive radio

Cognitive radio (CR) has emerged as a promising solution to the problem of spectrum underutilization. In CR, spectrum sensing is a key feature. It enables the cognitive user or secondary user (SU) to detect spectrum holes and ensure non-interference to primary communication. Spectrum sensing has its own challenges, such as discovery of opportunities for transmission and sensing overhead. High sensing overhead may impair spectral efficiency as the radio is mostly used for detecting primary users (PUs), rather than transmitting data. On the other hand, a less frequent sensing may result in interference to PU, due to the delay in the detection of the PÚs reappearance and can lead to loss of transmission opportunities. Thus, it is of paramount importance to optimize the sensing periods for each primary channel in order to maximize the number of transmission opportunities and reduce the sensing overhead incurred. This paper extends our previous letter (Balieiro, Yoshioka, Dias, Cavalcanti, & Cordeiro, 2013) and presents a detailed description of our adaptive sensing optimization scheme for CR Networks based on a multi-objective genetic algorithm (GA) formulation. Our scheme aims at maximizing the spectrum opportunities as well as keeping the sensing overhead always within a user-defined maximum value. The simulation results show that the proposed scheme outperforms the schemes described in the literature, while keeping the sensing overhead within a target value. In addition, it provides different levels of protection to PU communication through the configuration of threshold for sensing overhead.

Subthreshold behavior and avalanches in an exactly solvable charge density wave system

We present a toy charge density wave (CDW) model in 1d exhibiting a depinning transition with threshold force and configurations that are explicit. Due to the periodic boundary conditions imposed, the threshold configuration has a set of topological defects whose location and number depend on the realization of the random phases. Approaching the threshold, these defects are relocated by avalanches whose size dependence on the external driving force F is described by a record-breaking process. We find that the depinning transition in this model is a critical phenomenon, with the cumulative avalanche size diverging near the threshold as . The exact avalanche size distributions and their dependence on the control parameter are obtained. Remarkably, the scaling exponents associated with the critical behavior depend on 1) the initial conditions and 2) the relationship between the system size and the pinning strength.

Analyzing uncertainties of probabilistic rough set regions with game-theoretic rough sets

Probabilistic rough set approach defines the positive, negative and boundary regions, each associated with a certain level of uncertainty. A pair of threshold values determines the uncertainty levels in these regions. A critical issue in the community is the determination of optimal values of these thresholds. This problem may be investigated by considering a possible relationship between changes in probabilistic thresholds and their impacts on uncertainty levels of different regions. We investigate the use of game-theoretic rough set (GTRS) model in exploring such a relationship. A threshold configuration mechanism is defined with the GTRS model in order to minimize the overall uncertainty level of rough set based classification. By realizing probabilistic regions as players in a game, a mechanism is introduced that repeatedly tunes the parameters in order to calculate effective threshold parameter values. Experimental results on text categorization suggest that the overall uncertainty of probabilistic regions may be reduced with the threshold configuration mechanism.

Automated Anomaly Detector Adaptation using Adaptive Threshold Tuning

Real-time network- and host-based Anomaly Detection Systems (ADSs) transform a continuous stream of input data into meaningful and quantifiable anomaly scores. These scores are subsequently compared to a fixed detection threshold and classified as either benign or malicious. We argue that a real-time ADS’ input changes considerably over time and a fixed threshold value cannot guarantee good anomaly detection accuracy for such a time-varying input. In this article, we propose a simple and generic technique to adaptively tune the detection threshold of any ADS that works on threshold method. To this end, we first perform statistical and information-theoretic analysis of network- and host-based ADSs’ anomaly scores to reveal a consistent time correlation structure during benign activity periods. We model the observed correlation structure using Markov chains, which are in turn used in a stochastic target tracking framework to adapt an ADS’ detection threshold in accordance with real-time measurements. We also use statistical techniques to make the proposed algorithm resilient to sporadic changes and evasion attacks. In order to evaluate the proposed approach, we incorporate the proposed adaptive thresholding module into multiple ADSs and evaluate those ADSs over comprehensive and independently collected network and host attack datasets. We show that, while reducing the need of human threshold configuration, the proposed technique provides considerable and consistent accuracy improvements for all evaluated ADSs.

Analytical Modelling and Optimization of Congestion Control for Prioritized Multi-Class Self-Similar Traffic

Traffic congestion in communication networks can dramatically deteriorate user-perceived Quality-of-Service (QoS). The integration of the Random Early Detection (RED) and priority scheduling mechanisms is a promising scheme for congestion control and provisioning of differentiated QoS required by multimedia applications. Although analytical modelling of RED congestion control has received significant research efforts, the performance models reported in the current literature were primarily restricted to the RED algorithm only without consideration of traffic scheduling scheme for QoS differentiation. Moreover, for analytical tractability, these models were developed under the simplified assumption that the traffic follows Short-Range-Dependent (SRD) arrival processes (e.g., Poisson or Markov processes), which are unable to capture the self-similar nature (i.e., scale-invariant burstiness) of multimedia traffic in modern communication networks. To fill these gaps, this paper presents a new analytical model of RED congestion control for prioritized multi-class self-similar traffic. The closed-form expressions for the loss probability of individual traffic classes are derived. The effectiveness and accuracy of the model are validated through extensive comparison between analytical and simulation results. To illustrate its application, the model is adopted as a cost-effective tool to investigate the optimal threshold configuration and minimize the required buffer space with congestion control.

Flow-Admission Control Based on Equality of Heterogeneous Traffic (Two-Type Flow Model)

Multimedia applications such as video and audio have recently come into much wider use. Because this heterogeneous traffic consumes most of the network's resources, call admission control (CAC) is required to maintain high-quality services. User satisfaction depends on CAC's success in accommodating application flows. Conventional CACs do not take into consideration user satisfaction because their main purpose is to improve the utilization of resources. Moreover, if we assume a service where an ISP provides a “flat-based charging,” each user may receive same user satisfaction as a result of users being accommodated in a network, even if each has a different bandwidth. Therefore, we propose a novel CAC to maximize total user satisfaction based on a new philosophy where heterog eneous traffic is treated equally in networks. Theoretical analysis is used to derive optimal thresholds for various traffic configurations with a full search system. We also carried out theoretical numerical analysis to demonstrate the effectiveness of our new CAC. Moreover, we propose a sub-optimal threshold configuration obtained by using an approximation formula to develop practical CAC from these observations. We tested and confirmed that performance could be improved by using sub-optimal parameters.

Imaging performance of the hybrid pixel detectors XPAD3-S

Hybrid pixel detectors, originally developed for tracking particles in high-energy physics experiments, have recently been used in material sciences and macromolecular crystallography. Their capability to count single photons and to apply a threshold on the photon energy suggests that they could be optimal digital x-ray detectors in low energy beams such as for small animal computed tomography (CT). To investigate this issue, we have studied the imaging performance of photon counting hybrid pixel detectors based on the XPAD3-S chip. Two detectors are considered, connected either to a Si or to a CdTe sensor, the latter being of interest for its higher efficiency. Both a standard ‘International Electrotechnical Commission’ (IEC) mammography beam and a beam used for mouse CT results published in the literature are employed. The detector stability, linearity and noise are investigated as a function of the dose for several imaging exposures (∼0.1–400 µGy). The perfect linearity of both detectors is confirmed, but an increase in internal noise for counting statistics higher than ∼5000 photons has been found, corresponding to exposures above ∼110 µGy and ∼50 µGy for the Si and CdTe sensors, respectively. The noise power spectrum (NPS), the modulation transfer function (MTF) and the detective quantum efficiency (DQE) are then measured for two energy threshold configurations (5 keV and 18 keV) and three doses (∼3, 30 and 300 µGy), in order to obtain a complete estimation of the detector performances. In general, the CdTe sensor shows a clear superiority with a maximal DQE(0) of ∼1, thanks to its high efficiency (∼100%). The DQE of the Si sensor is more dependent on the radiation quality, due to the energy dependence of its efficiency its maximum is ∼0.4 with respect to the softer radiation. Finally, we compare the XPAD3-S DQE with published curves of other digital devices in a similar radiation condition. The XPAD3-S/CdTe detector appears to be the best with the highest DQE at low frequency, although some improvements are expected to reduce the increase of noise with the counts statistics and to guarantee a better stability of the detector response.

Threshold configuration and routing optimization for PCN-based resilient admission control

Pre-Congestion Notification (PCN) in IP networks uses packet metering and marking within a PCN domain to notify its egress nodes whether link-specific admissible or supportable rate thresholds have been exceeded by high-priority traffic. Based on this information simple admission control and flow termination is implemented. The latter is a new flow control function and useful in case of overload through high priority traffic which can occur in spite of admission control, e.g., when traffic is rerouted in failure cases. Resilient admission control admits only so much traffic that admitted traffic can be rerouted without causing congestion on backup paths in case of a likely failures, e.g., single link failures. We propose algorithms to configure the link-specific PCN rate thresholds such that resources are utilized efficiently and fairly by competing traffic aggregates while meeting resilience constraints. This is done for the single and dual marking PCN architecture whereby the single marking case is more demanding since it requires that the supportable rate is a fixed multiple of the admissible rate on all links within a single PCN domain. Furthermore, we derive objective functions to optimize the underlying routing system for both cases. Our performance results for various network types show that the dual marking PCN architecture leads to significantly better resource efficiency than the single marking PCN architecture.

Performance analysis of multi-homed transport protocols with network failure tolerance

The performance of multi-homed transport protocols tolerant of network failure is studied. It evaluates the performance of different retransmission policies combined with path failure detection thresholds, infinite or finite receive buffers for various path bandwidths, delays and loss rate conditions through stream control transmission protocol simulation. The results show that retransmission policies perform differently with different path failure detection threshold configurations. It identifies that retransmission of all data on an alternate path with the path failure detection threshold set to zero performs the best in symmetric path conditions but its performance degrades acutely in asymmetric path conditions even when the alternate path delay is shorter than the primary path delay. It illustrates that retransmission of all data on the same path with the path failure detection threshold set to one or zero gives the most stable performance in all path configurations.

Threshold position control of arm movement with anticipatory increase in grip force

The grip force holding an object between fingers usually increases before or simultaneously with arm movement thus preventing the object from sliding. We experimentally analyzed and simulated this anticipatory behavior based on the following notions. (1) To move the arm to a new position, the nervous system shifts the threshold position at which arm muscles begin to be recruited. Deviated from their activation thresholds, arm muscles generate activity and forces that tend to minimize this deviation by bringing the arm to a new position. (2) To produce a grip force, with or without arm motion, the nervous system changes the threshold configuration of the hand. This process defines a threshold (referent) aperture (R(a)) of appropriate fingers. The actual aperture (Q(a)) is constrained by the size of the object held between the fingers whereas, in referent position R(a), the fingers virtually penetrate the object. Deviated by the object from their thresholds of activation, hand muscles generate activity and grip forces in proportion to the gap between the Q(a) and R(a). Thus, grip force emerges since the object prevents the fingers from reaching the referent position. (3) From previous experiences, the system knows that objects tend to slide off the fingers when arm movements are made and, to prevent sliding, it starts narrowing the referent aperture simultaneously with or somewhat before the onset of changes in the referent arm position. (4) The interaction between the fingers and the object is accomplished via the elastic pads on the tips of fingers. The pads are compressed not only due to the grip force but also due to the tangential inertial force ("load") acting from the object on the pads along the arm trajectory. Compressed by the load force, the pads move back and forth in the gap between the finger bones and object, thus inevitably changing the normal component of the grip force, in synchrony with and in proportion to the load force. Based on these notions, we simulated experimental elbow movements and grip forces when subjects rapidly changed the elbow angle while holding an object between the index finger and the thumb. It is concluded that the anticipatory increase in the grip force with or without correlation with the tangential load during arm motion can be explained in neurophysiological and biomechanical terms without relying on programming of grip force based on an internal model.

MFTPM: Maximum Frequent Traversal Pattern Mining with Bidirectional Constraints

An important application of sequential mining technique is maximal frequent traversal pattern mining, since users' traversal pattern and motivation are latent in session sequence at some time segment. In this paper, a Frequent Traversal Pattern Tree structure with dwell time (FTP-Tree) is designed to store, compress the session database, and simplify the configuration of dwell time thresholds during mining. A novel algorithm based on bidirectional constraints, called Maximal Frequent Traversal Pattern Mining (MFTPM) is presented, which traverses quickly FTP-Tree and discovers maximal frequent traversal patterns from the session sequences. Experimental results show that MFTPM can significantly reduce the average execution time and the storage space for mining maximal frequent traversal patterns. Our performance study shows that MFTPM performs muth better than previous approaches in the time constraint environment.

Inner-valence states of N2+ and the dissociation dynamics studied by threshold photoelectron spectroscopy and configuration interaction calculation

The N2(+) states lying in the ionization region of 26-45 eV and the dissociation dynamics are investigated by high-resolution threshold photoelectron spectroscopy and threshold photoelectron-photoion coincidence spectroscopy. The threshold photoelectron spectrum exhibits several broad bands as well as sharp peaks. The band features are assigned to the N2(+) states associated with the removal of an inner-valence electron, by a comparison with a configuration interaction calculation. In contrast, most of the sharp peaks on the threshold photoelectron spectrum are allocated to ionic Rydberg states converging to N2(2+). Dissociation products formed from the inner-valence N2(+) states are determined by threshold photoelectron-photoion coincidence spectroscopy. The dissociation dynamics of the inner-valence ionic states is discussed with reference to the potential energy curves calculated.

Configuration of Traffic-Responsive Plan Selection System Parameters and Thresholds: Robust Bayesian Approach

Traffic-responsive plan selection (TRPS) is one of the two major closed-loop system modes of operation. The TRPS mode is more beneficial than its competitor (time-of-day mode) because of its ability to accommodate abnormal traffic conditions such as incidents, special events, and holiday traffic. However, no guidelines are available for optimal setup of TRPS systems. Improper configuration of a TRPS system can result in inefficient system performance or unstable operation in which the closed-loop system operates in a perpetual transitioning state. The TRPS mechanism implemented in current traffic signal controllers is described, and a Bayesian-based methodology for selecting an optimal set of TRPS factors, parameters, and thresholds is proposed. The proposed methodology was tested with data from a closed-loop system in Texas and resulted in 100% classification accuracy.

Threshold configurations in the presence of Lorentz violating dispersion relations

A general characterization of lower and upper threshold configurations for two particle reactions is determined under the assumptions that the single particle dispersion relations E(p) are rotationally invariant and monotonic in p, and that energy and momentum are conserved and additive for multiple particles. It is found that at a threshold the final particle momenta are always parallel and the initial momenta are always anti-parallel. The occurrence of new phenomena not occurring in a Lorentz invariant setting, such as upper thresholds and asymmetric pair production thresholds, is explained, and an illustrative example is given.

An analysis of noise enhanced information transmission in an array of comparators

An array of N comparators subject to the same input signal and independent additive noise, with the outputs from each comparator summed, is a useful noise model for a range of systems including flash analog-to-digital converters, Digital Multibeam Steering sonar arrays and parallel neurons. It has previously been shown that for certain threshold configurations the transmitted information through such an array is maximised for non-zero noise. This behaviour has been termed Suprathreshold Stochastic Resonance (SSR) [1] and in this paper we show that SSR occurs for a number of different signal and noise distributions. Also presented is an analysis of the variance of the quantisation error incurred when all thresholds are set equal to the signal mean, for Gaussian and uniform distributions. It is shown that the minimum error variance is given by a non-zero value of noise.

TeV astrophysics constraints on Planck scale Lorentz violation

We analyze observational constraints from TeV astrophysics on Lorentz violating nonlinear dispersion for photons and electrons without assuming any a priori equality between the photon and electron parameters. The constraints arise from thresholds for vacuum Cerenkov radiation, photon decay and photo-production of electron-positron pairs. We show that the parameter plane for cubic momentum terms in the dispersion relations is constrained to an order unity region in Planck units. We find that the threshold configuration can occur with an asymmetric distribution of momentum for pair creation, and with a hard photon for vacuum Cerenkov radiation.

Implantation of retina stimulation electrodes and recording of electrical stimulation responses in the visual cortex of the cat.

Simple basic visual perception may be restored by epiretinal electrical stimulation in patients that are blind due to photoreceptor loss. To stimulate ganglion cells, epiretinally flat platinum microelectrodes embedded in thin polyimide film were developed and tested in the cat. After removal of the lens and the vitreous body a thin microfilm electrode array was implanted through a corneoscleral incision in the cat eye (n = 4). In two eyes no further attempt was made to fixate the tip of the electrode, which was pressed onto the retinal surface due to the tension of the curved polyimide film. In two eyes the tip of the electrode was fixed with cyanoacrylate adhesive. The exterior part of the microelectrode film was directed under the skin towards the forehead which allowed fixation of the microplug to a head fixation bolt. Retinal stimulation experiments were performed within 1 week after implantation. Success of stimulation was assessed by recording neuronal activities from areas 17 and 18. Retinal microelectrodes were removed 2 weeks or longer after implantation. Intraocular inflammation or retinal detachment were not observed after implantation of the microelectrode film. In two eyes the tip of the microelectrodes dislocated spontaneously within the first few days. The lowest threshold of electrical stimulation was 35 microA, corresponding to a charge transfer of 14 nC per phase. These values were ten times higher than those obtained by needle electrodes used in prior experiments. Intraocular implanted flat microelectrodes made of platinum and polyimide were well tolerated. Because of the flat configuration of the microelectrodes higher stimulation thresholds than for needle electrodes were found, indicating insufficient contact to the retinal surface. An alternative shape and fixation technique is required to minimise electrodes' threshold of stimulation.