No description available.

Two aspects of cognitive control were investigated using the item-recognition task and the verb generation task. The item-recognition task had two conditions, high and low interference. The verb generation task was manipulated in three ways, for different levels of interference and time interval. The intention was to more deeply investigate one aspect of the item-recognition task, comparing response times for different trial types in different conditions, and to investigate a fatigue effect between the item-recognition and verb generation task. Thirty-two participants were tested at two occasions, in a within-subjects design. Results for the verb generation task revealed effects for levels of interference and time interval, although there was no difference in the manipulation. Results for the item-recognition task revealed effects for condition and trial type, as well as an interaction effect between these. The non-familiar trials in the high interference condition resulted in faster response times compared to the same kind of trials in the low condition. The result from the item-recognition task extends those from previous studies, revealing details for differences between trial types. This finding demonstrates a carry-over facilitation effect.

With the increasing system clock, a clock circuit will cause an amount of electromagnetic interference. To reduce EMI of the products, various EMI strategies have been developed. In the thesis, we study the suppression of electromagnetic interference of a clock circuit by using the spread spectrum technique. The basic idea of the spread spectrum is to slightly modulate the frequency of the clock signal and the energy of the signal will be dispersed to a controllable range to reduce the peak energy of each harmonic wave in the spectrum, and the products can pass the electromagnetic compatibility test more easily. We obtain the attenuation factor of spread spectrum from the theoretical derivation, including modulation index and modulation profiles. From the numerical simulation, we verify that spread spectrum technique can suppress the peak energy. We propose the attenuation formulas which can control the attenuation of every frequency point. To verify our findings, we use a spread spectrum clock generator from market to perform measurement. The trapezoidal waveform can be used to represent a clock circuit. Its waveform includes rise time and duty cycle. We will discuss the influence of rise time and duty cycle on the spread spectrum technique. Shorter rise time will cause high order harmonics in the high speed clock circuit. We verify that spread spectrum technique can suppress high order harmonics from both the simulation and experiment. Because every harmonic can be suppressed, the spread spectrum technique has the good suppression effect for the whole system.

The purpose of this work is to study the interference between the coherent nonresonant four-wave-mixing (FWM) background and the Raman-resonant signal in the coherent anti-Stokes Raman spectroscopy (CARS). The nonresonant background is usually considered as a detriment to CARS. We prove that the background can be exploited in a controllable way, through the heterodyne detection due to the interference, to amplify the signal and optimize the spectral shape of the detected Raman signal, and hence enhance the measurement sensitivity. Our work is based on an optimized CARS technique which combines instantaneous coherent excitation of multiple characteristic molecular vibrations with subsequent probing of these vibrations by an optimally shaped, time-delayed, narrowband laser pulse. This pulse configuration mitigates the nonresonant background while maximizing the resonant signal, and allows rapid and highly specific detection even in the presence of multiple scattering. We investigate the possibility of applying this CARS technique to non-invasive monitoring of blood glucose levels. Under certain conditions we find that the measured signal is linearly proportional to the glucose concentration due to optical interference with the residual background light instead of a quadratic dependence, which allows reliable detection of spectral signatures down to medically-relevant glucose levels. With the goal of making the fullest use of the background, we study the interference between an external local oscillator (nonresonant FWM field) and the CARS signal field by controlling their relative phase and amplitude. Our experiment shows that this control allows direct observation of the real and imaginary components of the third-order nonlinear susceptibility (χ(3)) of the Raman sample. In addition, this method can be used to amplify the signal significantly. Furthermore, we develop an approach by femtosecond laser pulse shaping to precisely control the interference between the Raman-resonant signal and its intrinsic nonresonant background generated within the same sample volume. This technique is similar to the heterodyne detection with the coherent background playing the role of the local oscillator field. By making fine adjustments to the probe field shape, we vary the relative phase between the resonant signal and the nonresonant background, and observe the varying spectral interference pattern. These controlled variations of the measured pattern reveal the phase information within the Raman spectrum, akin to holographic detection revealing the phase structure of a source.

Multi-robot systems have the potential to improve performance through parallelism. Unfortunately, interference often diminishes those returns. Starting from the earliest multi-robot research, a variety of arbitration mechanisms have been proposed to maximize speed-up. Vaughan and his collaborators demonstrated the effectiveness of an arbitration mechanism inspired by biological signalling where the level of aggression displayed by each agent effectively prioritizes the limited resources. But most often these arbitration mechanisms did not do any principled consideration of environmental constraints or task structure, signalling cost and precision of the outcome. These factors have been taken into consideration in this research and a taxonomy of the arbitration mechanisms have been presented. The taxonomy organizes prior techniques and newly introduced novel techniques. The latter include theoretical and practical mechanisms (from minimalist to especially efficient). Practicable mechanisms were evaluated on physical robots for which both data and models are presented. The arbitration mechanisms described span a whole gamut from implicit (in case of robotics, entirely without representation) to deliberately coordinated (via an established Biological model, reformulated from a Bayesian perspective). Another significant result of this thesis is a systematic characterization of system performance across parameters that describe the task structure: patterns of interference are related to a set of strings that can be expressed exactly. This analysis of the domain has the important (and rare) property of completeness, i.e., all possible abstract variations of the task are understood. This research presents efficiency results showing that a characterization for any given instance can be obtained in sub-linear time. It has been shown, by construction, that: (1) Even an ideal arbitration mechanism can perform arbitrarily poorly; (2) Agents may manipulate task-structure for individual and collective good; (3) Task variations affect the influence that initial conditions have on long-term behaviour; (4) The most complex interference dynamics possible for the scenario is a limit cycle behaviour.

Executive control allows us to ignore distraction and switch between tasks in a flexible, yet organized fashion. While a hallmark of controlled behavior, distinctions among executive control processes are not thoroughly agreed upon. The present work explored the organization of two of these executive control processes, inhibition and shifting, and their relationship to each other. There were two primary goals. The first goal was to investigate the distinction among inhibitory control processes, as “inhibition” has oftentimes been considered a unitary construct. For example, there is evidence that response-distractor inhibition, which involves resolving interference from dominant responses or distractors in the external environment, is different from resistance to proactive interference (PI), which involves overcoming interference from previously relevant representations in memory. Using aging, neuropsychology, and individual differences methodologies, I investigated the unity and diversity of inhibitory control mechanisms. The healthy aging and neuropsychological evidence supported a distinction between response-distractor inhibition and resistance to proactive interference. However, when controlling for processing speed, the individual differences work suggested a need for further specification, as only a subset of these tasks emerged in the single factor model that provided the best fit to the data. The second goal was to explore how inhibitory control processes interact with task switching, as some theoretical accounts of task switching have suggested that switch costs result from the need to overcome interference from the previously relevant task. Inconsistent with these theories, I found little relation between inhibitory control and measures of global and local task switching, and instead, working memory served as the best predictor of these shifting measures. In contrast, inhibitory control was related to the backward inhibition abilities of older adults. These findings are discussed within a theory of working memory that accounts for the patterns of results found across the different methodologies.

Executive control allows us to ignore distraction and switch between tasks in a flexible, yet organized fashion. While a hallmark of controlled behavior, distinctions among executive control processes are not thoroughly agreed upon. The present work explored the organization of two of these executive control processes, inhibition and shifting, and their relationship to each other. There were two primary goals. The first goal was to investigate the distinction among inhibitory control processes, as “inhibition” has oftentimes been considered a unitary construct. For example, there is evidence that response-distractor inhibition, which involves resolving interference from dominant responses or distractors in the external environment, is different from resistance to proactive interference (PI), which involves overcoming interference from previously relevant representations in memory. Using aging, neuropsychology, and individual differences methodologies, I investigated the unity and diversity of inhibitory control mechanisms. The healthy aging and neuropsychological evidence supported a distinction between response-distractor inhibition and resistance to proactive interference. However, when controlling for processing speed, the individual differences work suggested a need for further specification, as only a subset of these tasks emerged in the single factor model that provided the best fit to the data. The second goal was to explore how inhibitory control processes interact with task switching, as some theoretical accounts of task switching have suggested that switch costs result from the need to overcome interference from the previously relevant task. Inconsistent with these theories, I found little relation between inhibitory control and measures of global and local task switching, and instead, working memory served as the best predictor of these shifting measures. In contrast, inhibitory control was related to the backward inhibition abilities of older adults. These findings are discussed within a theory of working memory that accounts for the patterns of results found across the different methodologies.

The study involves tests on the perception by speakers of Finnish of vowel sounds in natural speech in four important varieties of standard Swedish and as produced by an OVE III synthesizer.The contrastive analysis takes the form of experiments to reveal the divisions of the vowel space in Swedish and Finnish. Perceptually optimal areas and the diffuse zones in the vowel space are contrasted. On the basis of these tests predictions are made concerning second language perceptual problems.The contrastive relations of the vowel sounds in Swedish and Finnish are further illuminated by perceptual tests to study the inherent tendency of speakers of Finnish to confuse certain Swedish vowels. The distribution of the phonemic reactions of speakers of Finnish not knowing Swedish are taken as material for an error analysis relevant to the time of starting to learn Swedish. A number of phonemically long vowel sounds were discovered to cause problems of identification for Finnish listeners. These are / y:/, /in:/, /e:/, / e :/, /#:/, and /o:/. A comparison of the predictions and actual confusions shows a high degree of correlation.Finnish vowel harmony was found to be a factor influencing the responses of Finns to Swedish vowels. The responses to combinations of vowels not complying with the vowel harmony rules contained an increased proportion of confusions leading to harmony-compatible or neutral vowels. Also the vowel qualities which were in an intermediate position in the vowel space in relation to the Finnish vowels tended to be influenced by assimilation or sequential contrast.The perceptual interference properties of the mother tongue in the perception of the vowel qualities as illuminated by the results of the perceptual test are discussed.Certain didactic conclusions are drawn concerning the problems experienced by speakers of Finnish in the identification and also the production of the Swedish vowels. Gestures of lip position and its contrastive perceptual effects are noted to be of especial importance in the learning of the vowel qualities of Swedish by Finns. / digitalisering@umu

This thesis is concerned with the channel assignment (CA) problem in multi-channel multi-interface wireless mesh networks (M2WNs). First, for M2WNs with general topologies, we rigorously demonstrate using the combinatorial principle of inclusion/exclusion that the CA solution space can be quantified, indicating that its cardinality is greatly influenced by the number of radio interfaces installed on each router. Based on this analysis, a novel scheme is developed to construct a new reduced search space, represented by a lattice structure, that is searched more efficiently for a CA solution. The elements in the reduced lattice-based space, labeled Solution Structures (SS), represent groupings of feasible CA solutions satisfying the radio constraints at each node. Two algorithms are presented for searching the lattice structure. The first is a greedy algorithm that finds a good SS in polynomial time, while the second provides a user-controlled depthfirst search for the optimal SS. The obtained SS is used to construct an unconstrained weighted graph coloring problem which is then solved to satisfy the soft interference constraints. For the special class of full M2WNs (fM2WNs), we show that an optimal CA solution can only be achieved with a certain number of channels; we denote this number as the characteristic channel number and derive upper and lower bounds for that number as a function of the number of radios per router. Furthermore, exact values for the required channels for minimum interference are obtained when certain relations between the number of routers and the radio interfaces in a given fM2WN are satisfied. These bounds are then employed to develop closed-form expressions for the minimum channel interference that achieves the maximum throughput for uniform traffic on all communication links. Accordingly, a polynomial-time algorithm to find a near-optimal solution for the channel assignment problem in fM2WN is developed. Experimental results confirm the obtained theoretical results and demonstrate the performance of the proposed schemes.

Interference is a key limiting factor in modern communication systems. In a wireless cellular network, the performance of cell-edge users is severely limited by the intercell interference. This thesis studies the use of interference-channel and relay-channel techniques to mitigate intercell interference and to improve the throughput and coverage of cellular networks. The aim of this thesis is to demonstrate the benefit of the proposed interference mitigation schemes through both information theoretical studies and applications in the cellular network. There are three mains results in this thesis: First, it is shown that for the $K$-user cyclic Gaussian interference channel, where the $k$th user interferes with only the ($k -1$)th user (mod $K$) in the network, the Etkin-Tse Wang power splitting strategy achieves the capacity region to within 2 bits in the weak interference regime. For the special 3-user case, this gap can be sharpened to $1\frac{1}{2}$ bits by the time-sharing technique. Second, it is shown that for a two-user Gaussian interference channel with an in-band-reception and out-of-band transmission relay, generalized hash-and-forward together with Han-Kobayashi information splitting can achieve the capacity region of this channel to within a constant number of bits in a certain weak-relay regime. A generalized-degrees-of-freedom analysis in the high signal-to-noise ratio regime reveals that in the symmetric channel setting, each common relay bit improves the sum rate up to two bits. The third part of this thesis studies an uplink multicell joint processing model in which the base stations are connected to a centralized processing server via rate-limited digital backhaul links. This thesis proposes a suboptimal achievability scheme employing the Wyner-Ziv compress-and-forward relaying technique and successive-interference-cancellation decoding. The main advantage of the proposed approach is that it results in achievable rate regions that are easily computable, in contrast to previous schemes in which the rate regions can only be characterized by exponential number of rate constraints.