Selective Cancellation Research Articles

Selective cancellation of reactive or anticipated movements: Differences in speed of action reprogramming, but not stopping

The ability to inhibit movements is an essential component of a healthy executive control system. Two distinct but commonly used tasks to assess motor inhibition are the stop signal task (SST) and the anticipated response inhibition (ARI) task. The SST and ARI tasks are similar in that they both require cancelation of a prepotent movement; however, the SST involves cancelation of a speeded reaction to a temporally unpredictable signal, while the ARI task involves cancelation of an anticipated response that the participant has prepared to enact at a wholly predictable time.33 participants (mean age = 33.3 years, range = 18–55 years) completed variants of the SST and ARI task. In each task, the majority of trials required bimanual button presses, while on a subset of trials a stop signal indicated that one of the presses should be cancelled (i.e., motor selective inhibition). Additional variants of the tasks also included trials featuring signals which were to be ignored, allowing for insights into the attentional component of the inhibitory response. Electromyographic (EMG) recordings allowed detailed comparison of the characteristics of voluntary action and cancellation.The speed of the inhibitory process was not influenced by whether the enacted movement was reactive (SST) or anticipated (ARI task). However, the ongoing (non-cancelled) component of anticipated movements was more efficient than reactive movements, as a result of faster action reprogramming (i.e., faster ongoing actions following successful motor selective inhibition). Older age was associated with both slower inhibition and slower action reprogramming across all reactive and anticipated tasks.

Sum-frequency generation at interfaces: A Fresnel story. I. Designing high contrast in two interface systems.

When a homogeneous film of finite thickness is optically probed, interference due to multiple reflections modulates in amplitude the electric field of light. For optical processes located only at the interfaces between two media, as is common for Sum-Frequency Generation (SFG), interference also modulates the contrast between signals generated at the entrance and exit planes of the film. We introduce a universal formalism for Fresnel factors, which bear all the information about interference, valid at any point in a three-layer system and for the three beams involved in the SFG process. Their analysis provides general rules for obtaining a high contrast. In particular, we define four configurations leading to the cancellation of the SFG response from the entrance side of the film when its thickness or the angles of incidence are tuned. Cancellation conditions depend on the polarization of light and follow simple analytical rules, leading to a straightforward experimental implementation. Such a selective cancellation makes it possible to independently measure single components of the nonlinear susceptibility, for example, in a ppp experiment and to separate surface from bulk response by combining a few measurements.

A Frequency-Domain Output-Constrained Active Noise Control Algorithm Based on an Intuitive Circulant Convolutional Penalty Factor

Due to their computational efficiency, least mean square (LMS)–based algorithms are still widely utilized to achieve optimal control in active noise control (ANC) applications. Real-world implementation of advanced ANC functionalities, such as selective cancellation of frequencies, is nonetheless hampered by complexity trade-offs, especially with computationally-expensive frequency-domain approaches. Prevailing time-domain adaptive algorithms – proposed to alleviate complexities from transformation – continue to incur increased complexities while constraining the magnitude of frequency bins in the time-domain filters. To address existing complexities in time-domain approaches, this paper proposes a circulant convolutional penalty factor that assists the extended leaky filtered-reference LMS (FxLMS) algorithm in achieving frequency constraint without any frequency-domain transform. This circulant convolutional penalty factor is readily determined by methods for designing finite response filters, such as frequency sampling. Additionally, the coordinate descent method is adopted to further reduce the proposed algorithm's computations, significantly increasing its feasibility for implementation on conventional real-time processors. Finally, the numerical simulations performed on the measured primary and secondary paths demonstrate the effectiveness of the proposed algorithm.

Selective active noise cancellation based on directional reference signals

Active noise control (ANC) technologies have been successfully applied in headphones to cancel the sound that propagates into one’s ear canal from outside. However, the standard ANC systems would attenuate the sound from all the sound sources blindly ignoring that a listener may prefer to listen to some of them. This paper proposes a feed-forward ANC system for ear-level applications, which is capable of preserving the sound of a source in any given direction relative to a listener while attenuating the sound in other directions. The selective cancellation is achieved based on the creation of appropriate reference signals from the output of a microphone array wore on user’s head. Theoretical analysis and simulation results will be presented to demonstrate the potential benefit and limitations of such a system.

Learning Contrast-Invariant Cancellation of Redundant Signals in Neural Systems

Cancellation of redundant information is a highly desirable feature of sensory systems, since it would potentially lead to a more efficient detection of novel information. However, biologically plausible mechanisms responsible for such selective cancellation, and especially those robust to realistic variations in the intensity of the redundant signals, are mostly unknown. In this work, we study, via in vivo experimental recordings and computational models, the behavior of a cerebellar-like circuit in the weakly electric fish which is known to perform cancellation of redundant stimuli. We experimentally observe contrast invariance in the cancellation of spatially and temporally redundant stimuli in such a system. Our model, which incorporates heterogeneously-delayed feedback, bursting dynamics and burst-induced STDP, is in agreement with our in vivo observations. In addition, the model gives insight on the activity of granule cells and parallel fibers involved in the feedback pathway, and provides a strong prediction on the parallel fiber potentiation time scale. Finally, our model predicts the existence of an optimal learning contrast around 15% contrast levels, which are commonly experienced by interacting fish.

Selective Host-Interference Cancellation: A New Informed Embedding Strategy for Spread Spectrum Watermarking

Selective Host-Interference Cancellation: A New Informed Embedding Strategy for Spread Spectrum Watermarking

Frequency-Tuned Cerebellar Channels and Burst-Induced LTD Lead to the Cancellation of Redundant Sensory Inputs

For optimal sensory processing, neural circuits must extract novel, unpredictable signals from the redundant sensory input in which they are embedded, but the detailed cellular and network mechanisms that implement such selective cancellation are presently unknown. Using a combination of modeling and experiment, we characterize in detail a cerebellar circuit in weakly electric fish, showing how it can carry out this computation. We use a model incorporating the wide range of experimentally estimated parallel fiber feedback delays and a burst-induced LTD rule derived from in vitro experiments to explain the precise cancellation of redundant signals observed in vivo. Our model demonstrates how the backpropagation-dependent burst dynamics adjusts the temporal pairing width of the plasticity mechanism to precisely match the frequency of the redundant signal. The model also makes the prediction that this cerebellar feedback pathway must be composed of frequency-tuned channels; this prediction is subsequently verified in vivo, highlighting a novel and general capability of cerebellar circuitry.

Three-Phase PLLs With Fast Postfault Retracking and Steady-State Rejection of Voltage Unbalance and Harmonics by Means of Lead Compensation

This paper proposes an advanced controller suitable for three-phase phase-locked loops (PLLs), which are employed in grid-connected power converters. This controller is formed of one or more lead compensators cascaded to the main proportional integral regulator. The proposed lead compensators are second order with pure imaginary roots: they have both a notch peak and a resonant peak (the notch frequency is lower than the resonant frequency). Hence, their phase versus frequency response exhibits phase wraps of ± 180°. Consequently, the parameters of each lead compensator are tuned with two objectives: to eliminate a specific frequency in the synchronous reference frame (SRF) and to enhance stability by a phase lead (phase boost). Through this technique, three-phase PLLs achieve both high bandwidth (fast transient response) and selective cancellation (filtering of unbalance and harmonics ripple in the SRF). The proposed controllers are suitable for simpler three-phase PLL schemes, such as the SRF-PLL. Therefore, big improvement is achieved without adding extra blocks and signals to basic PLL structures. Simulation and real-time implementation (dSpace DS1103) tests, emulating very demanding realistic conditions, have been performed. Key figures from these tests are shown, which prove the high performance and robustness of the proposal.

Radio-frequency control of spontaneous emission from a coherently driven multilevel atom

The spontaneous emission properties of radio-frequency(RF)-driven multilevel atomic systems with three different configurations are investigated in details. It is demonstrated that, due to the presence of the RF-induced coherence in the multilevel system, a few interesting phenomena such as spectral-line narrowing, spectral-line enhancement, spectral-line suppression, and fluorescence-quenching can be realized under realistic experimental conditions. By inspecting single-RF-driven, double-RF-driven, and triple-RF-driven atomic systems, we find that (i) when only one RF-driven field is applied, there are two fluorescence-quenching points and four spectral lines; (ii) in the case of applying two RF-driven fields, there are three fluorescence-quenching points and five spectral lines; (iii) when applying three RF-driven fields, there are four fluorescence-quenching points and six spectral lines; and (iv) as expected, when the atomic system coupled by N RF-driven fields, there will be N + 1 fluorescence-quenching points and N + 3 spectral lines. Interestingly enough, the spectral-line enhancement, the spectral-line suppression, and the selective cancellation of fluorescence-quenching can be well controlled just by appropriately modulating the intensities and frequencies of the applied RF fields, respectively. The proposed schemes can be achieved by use of RF-driven fields into hyperfine levels in rubidium atomic systems. These investigations may find applications in high-precision spectroscopy.

Density measurements of dentin by dual-energy radiography

The aim of this study was to apply the dual-energy radiographic technique to teeth and to soft tissue simulated with Lucite and report the visual and quantitative results. High- and low-energy image pairs were exposed of aluminum and Lucite calibration wedges and human teeth sections. Reconstructed images of the calibration wedges and teeth sections were viewed and measured. The aluminum reconstruction images accentuated the aluminum wedge and the teeth, whereas the Lucite reconstruction images minimized them. Correlations between the nominal direct and dual-energy measurements of the wedges and teeth thicknesses were found to be very good. The root-mean-square deviation of the dual-energy reconstructions from the measured nominal thicknesses was found to be no greater than 0.6 mm. These results demonstrate the feasibility of using dual energy as a means of selective cancellation of unwanted tissues and the measurement of posterior tooth density.

Selective Compensation in Four-Wire Electric Systems Based on a New Equivalent Conductance Approach

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a new calculation method to obtain the reference currents for a selective shunt active power compensator (APC) with the capability of distinguishing between selective and global operating modes. This selective compensation operation is done through an identification of the current terms related to the physical phenomena that exist in electrical systems following a new equivalent conductance concept. Through this identification, this paper proposes the adequate set of reference currents that, used by a shunt APC (SAPC), achieve the selective cancellation of a desired nonefficient phenomenon. Furthermore, by combining the different current terms, it is possible to derive the sets of reference currents that allow the cancellation of a desired combination of nonefficient phenomena. By using these reference currents, a selective compensation feature is added to the SAPC control. An SAPC based on a three-phase three-leg inverter with a split dc bus has been implemented. The neutral wire of the electrical installation is connected to the midpoint of the dc bus, so the selective SAPC is able to work in four-wire electrical systems. The experimental results obtained demonstrate that the proposed selective compensation properly works in three-phase electrical systems with load-current unbalances, voltage asymmetries, and harmonic components. The electric quality is improved with the use of the proposed selective control based on this new equivalent conductance approach. </para>

Cancellation of EEG and MEG signals generated by extended and distributed sources.

Extracranial patterns of scalp potentials and magnetic fields, as measured with electro- and magnetoencephalography (EEG, MEG), are spatially widespread even when the underlying source in the brain is focal. Therefore, loss in signal magnitude due to cancellation is expected when multiple brain regions are simultaneously active. We characterized these cancellation effects in EEG and MEG using a forward model with sources constrained on an anatomically accurate reconstruction of the cortical surface. Prominent cancellation was found for both EEG and MEG in the case of multiple randomly distributed source dipoles, even when the number of simultaneous dipoles was small. Substantial cancellation occurred also for locally extended patches of simulated activity, when the patches extended to opposite walls of sulci and gyri. For large patches, a difference between EEG and MEG cancellation was seen, presumably due to selective cancellation of tangentially vs. radially oriented sources. Cancellation effects can be of importance when electrophysiological data are related to hemodynamic measures. Furthermore, the selective cancellation may be used to explain some observed differences between EEG and MEG in terms of focal vs. widespread cortical activity.

Control of the spontaneous emission spectrum in a driven N-type atom by dynamically induced quantum interference

The modification of the spontaneous emission spectrum has been studied in this paper in a four-level doubly driven N-type atomic system. In the presence of two coherent fields, emphasis has been given to studying the spectral distribution of spontaneous emission in the relaxation process of the initially prepared excited level. The phenomenon of quantum interference dynamically induced in the system by these fields can significantly change the spontaneous emission spectrum. We have shown the emergence of a two-peak spectrum where two widely separated symmetric peaks are associated with a sharp dark line at their mid-position. At different dynamic conditions, we have also shown that two symmetric peaks may appear in the spectrum with an extended dark zone between them. Depending on the values of the Rabi frequencies and the detunings of the external fields, one can achieve a large enhancement of very narrow spectral components within the spontaneous emission line shape under different conditions. The phenomenon of suppression of spectral line and the selective cancellation of spontaneous emission have also been discussed. The results shown in various cases are analysed by considering all possible dressed states corresponding to the bare state model. The influence of collision-induced effects on the spontaneous emission spectrum is investigated as a conditional case.

From angle-resolved ellipsometry of light scattering to imaging in random media

A procedure is described to allow selective cancellation of polarized scattering within optical substrates and multilayers. It is shown how bulk scattering (respectively surface) can be directly eliminated while the remaining roughness (respectively bulk) signal is still measurable. The same procedure can be applied to isolate a single interface or bulk within a stack or to detect slight departure from perfect correlation within multilayers. Experiments and a procedure for selective imaging in random media are described.

An Improved Adaptive Detection Method for Power Quality Improvement

A new adaptive harmonic selective detection method is proposed in this paper. This adaptive method has better convergence properties compared to previous adaptive or neuron detection methods. The adaptive gains of this method can be relatively large to obtain faster convergence. The stability of the proposed method is guaranteed and its properties are analyzed when compared to its predecessors. This proposed adaptive method is simple and effective in extracting fundamental and harmonic current information from nonlinear load currents. The extracted fundamental or harmonic currents therefore can be used as the reference signals for power quality improvement, harmonic selective cancellation or reactive power compensation. The method is also phase-independent and can thus be easily applied to single- or three-phase unbalanced systems. Simulation and experimental results verify the good performance of this improved adaptive detection method. Moreover, two application cases are built and tested to demonstrate its effectiveness in harmonic selective cancellation and reactive power compensation.

Robust Multiuser Interference Cancellation for OFDM Systems With Frequency Offset

In orthogonal frequency division multiple access systems clusters of subcarriers are assigned to different users for parallel data transmissions. The subcarriers are overlapped, but orthogonal to each other such that there is no intercarrier interference (ICI). However, synchronization errors among users cause the loss of the orthogonality and introduce ICI resulting in multiple-access interference. Synchronization between users is particularly difficult in the uplink channel where the user signals are potentially asynchronous and affected by different frequency offsets due to misalignment in carrier frequencies and Doppler shifts. This paper proposes a method to lower the effects of different frequency offsets among user signals in an OFDMA uplink system. The multiple access interference due to the user frequency misalignments is reduced by reconstructing and removing the interfering signals in the frequency domain. An approach based on the selective cancellation method, is proposed and its performance is analyzed by means of theoretical analysis and computer simulations. The effectiveness of the proposed system has been evaluated in the case of ideal and no-ideal frequency offset estimation and has been compared with that of the classical successive and parallel cancellation schemes. Simulation results show that the proposed approach allows performance close to the ideal case, i.e., with ideal frequency synchronization among users, with a low increase of the implementation complexity. Moreover, it is also highlighted here, that the successive cancellation method slightly outperforms the selective scheme, at the expense of a higher computational complexity and processing delay

An improved density matrix functional by physically motivated repulsive corrections

An improved density matrix functional [correction to Buijse and Baerends functional (BBC)] is proposed, in which a hierarchy of physically motivated repulsive corrections is employed to the strongly overbinding functional of Buijse and Baerends (BB). The first correction C1 restores the repulsive exchange-correlation (xc) interaction between electrons in weakly occupied natural orbitals (NOs) as it appears in the exact electron pair density rho(2) for the limiting two-electron case. The second correction C2 reduces the xc interaction of the BB functional between electrons in strongly occupied NOs to an exchange-type interaction. The third correction C3 employs a similar reduction for the interaction of the antibonding orbital of a dissociating molecular bond. In addition, C3 applies a selective cancellation of diagonal terms in the Coulomb and xc energies (not for the frontier orbitals). With these corrections, BBC still retains a correct description of strong nondynamical correlation for the dissociating electron pair bond. BBC greatly improves the quality of the BB potential energy curves for the prototype few-electron molecules and in several cases BBC reproduces very well the benchmark ab initio potential curves. The average error of the self-consistent correlation energies obtained with BBC3 for prototype atomic systems and molecular systems at the equilibrium geometry is only ca. 6%.

Detecting effects of donepezil on visual selective attention using signal detection parameters in Alzheimer's disease

Attentional function is impaired in Alzheimer's disease (AD). Moreover, attention is mediated by acetylcholine. But, despite the widespread use of acetylcholinesterase inhibitors (AChE-I) to augment available acetylcholine in AD, measures of attentional function have not been used to assess the drug response. We hypothesized that as cholinergic augmentation impacts directly on the attentional system, higher-order measures of visual selective attention would be sensitive to effects of treatment using an AChE-I (donepezil hydrochloride). We also sought to determine whether these attentional measures were more sensitive to treatment than other measures of cognitive function. Seventeen patients with AD (8 untreated, 9 treated with donepezil) were contrasted on performance of a selective cancellation task. Two signal detection parameters were used as outcome measures: decision strategy (beta, beta) and discriminability (d-prime, d'). Standard screening and cognitive domain measures of vigilance, language, memory, and executive function were also contrasted. Treated patients judged stimuli more conservatively (p = 0.29) by correctly endorsing targets and rejecting false alarms. They also discriminated targets from distractors more easily (p = 0.58). The screening and neuropsychological measures failed to differentiate the groups. Higher-order attentional measures captured the effects of donepezil treatment in small groups of patients with AD. The results suggest that cholinergic availability may directly affect the attentional system, and that these selective attention measures are sensitive markers to detect treatment response.

Selective signal cancellation for multiple-listener audio applications using eigenfilters

Selectively canceling signals at specific locations within an acoustical environment with multiple listeners is of significant importance for home theater, automobile, teleconferencing, office, industrial, and other applications. The traditional noise cancellation approach is impractical for such applications because it requires secondary sources to "anti-phase" the primary source, or sensors to be placed on the listeners. In this paper we propose an alternative method for signal cancellation by pre-processing the acoustical signal with a filter known as the eigenfilter , . We examine the theoretical properties of such filters, and investigate the performance (gain) and tradeoff issues such as, spectral distortion. Sensitivity of the performance as a function of the room impulse response duration (reverberation) modeled in the eigenfilter is also investigated.

Pilot-aided data detection in DS-CDMA communication systems

The paper deals with the performance evaluation of a pilot-aided channel parameter estimation method suitable for applications in direct-sequence code-division multiple-access (DS-CDMA) communication systems. Differently from previous approaches, a suitable selective interference cancellation algorithm is used in order to reduce multipath interference on the channel parameter estimation and the detection of the information-bearing signals due to pilot signal replicas. Simulation results demonstrate the good channel parameter estimation capability of the proposed method in the case of uplink communications and different types of receiving schemes. In order to highlight the good behavior of the proposed approach, performance comparisons are shown with the ideal case of perfect knowledge of the channel parameter values, as well as with the classical implementation of the considered channel parameter estimation algorithm.