Showing papers by "Helsinki University of Technology published in 2002"

Frontal theta activity in humans increases with memory load in a working memory task.

Abstract: Recent theoretical work has suggested that brain oscillations in the theta band are involved in active maintenance and recall of working memory representations. To test this theoretical framework we recorded neuromagnetic responses from 10 subjects performing the Sternberg task. Subjects were required to retain a list of 1, 3, 5 or 7 visually presented digits during a 3-s retention period. During the retention period we observed ongoing frontal theta activity in the 7-8.5-Hz band recorded by sensors over frontal brain areas. The activity in the theta band increased parametrically with the number of items retained in working memory. A time-frequency analysis revealed that the task-dependent theta was present during the retention period and during memory scanning. Following the memory task the theta activity was reduced. These results suggest that theta oscillations generated in frontal brain regions play an active role in memory maintenance.

Oscillations in the Alpha Band (9–12 Hz) Increase with Memory Load during Retention in a Short-term Memory Task

Abstract: To study the role of brain oscillations in working memory, we recorded the scalp electroencephalogram (EEG) during the retention interval of a modified Sternberg task. A power spectral analysis of the EEG during the retention interval revealed a clear peak at 9−12 Hz, a frequency in the alpha band (8−13 Hz). In apparent conflict with previous ideas according to which alpha band oscillations represent brain ‘idling’, we found that the alpha peak systematically increased with the number of items held in working memory. The enhancement was prominent over the posterior and bilateral central regions. The enhancement over posterior regions is most likely explained by the well known alpha rhythm produced close to the parietal-occipital fissure, whereas the lateral enhancement could be explained by sources in somato-motor cortex. A time-frequency analysis revealed that the enhancement was present throughout the last 2.5 s of the 2.8 s retention interval and that alpha power rapidly diminished following the probe. The load dependence and the tight temporal regulation of alpha provide strong evidence that the alpha generating system is directly or indirectly linked to the circuits responsible for working memory. Although a clear peak in the theta band (5−8 Hz) was only detectable in one subject, other lines of evidence indicate that theta occurs and also has a role in working memory. Hypotheses concerning the role of alpha band activity in working memory are discussed.

Functional materials based on self-assembly of polymeric supramolecules

Abstract: Self-assembly of polymeric supramolecules is a powerful tool for producing functional materials that combine several properties and may respond to external conditions. We illustrate the concept using a comb-shaped architecture. Examples include the hexagonal self-organization of conjugated conducting polymers and the polarized luminance in solid-state films of rodlike polymers obtained by removing the hydrogen-bonded side chains from the aligned thermotropic smectic phase. Hierarchically structured materials obtained by applying different self-organization and recognition principles and directed assembly form a basis for tunable nanoporous materials, smart membranes, preparation of nano-objects, and anisotropic properties, such as proton conductivity.

Mercer kernel-based clustering in feature space

Abstract: The article presents a method for both the unsupervised partitioning of a sample of data and the estimation of the possible number of inherent clusters which generate the data. This work exploits the notion that performing a nonlinear data transformation into some high dimensional feature space increases the probability of the linear separability of the patterns within the transformed space and therefore simplifies the associated data structure. It is shown that the eigenvectors of a kernel matrix which defines the implicit mapping provides a means to estimate the number of clusters inherent within the data and a computationally simple iterative procedure is presented for the subsequent feature space partitioning of the data.

Non-negative sparse coding

Abstract: Non-negative sparse coding is a method for decomposing multivariate data into non-negative sparse components. We briefly describe the motivation behind this type of data representation and its relation to standard sparse coding and non-negative matrix factorization. We then give a simple yet efficient multiplicative algorithm for finding the optimal values of the hidden components. In addition, we show how the basis vectors can be learned from the observed data. Simulations demonstrate the effectiveness of the proposed method.

A resource-based view of manufacturing strategy and the relationship to manufacturing performance

Abstract: This paper examines manufacturing strategy from the perspective of the resource-based view of the firm. It explores the role of resources and capabilities in manufacturing plants that cannot be easily duplicated, and for which ready substitutes are not available. Such resources and capabilities are formed by employees' internal learning based on cross-training and suggestion systems, external learning from customers and suppliers, and proprietary processes and equipment developed by the firm. Based on data from 164 manufacturing plants, the paper empirically demonstrates that competitive advantage in manufacturing (as measured by superior plant performance) results from proprietary processes and equipment which, in turn, is driven by external and internal learning. The implication is that resources such as standard equipment and employees with generic skills obtainable in factor markets are not as effective in achieving high levels of plant performance, since they are freely available to competitors. The paper also demonstrates the important role of internal and external learning in developing resources that are imperfectly imitable and difficult to duplicate. Copyright © 2002 John Wiley & Sons, Ltd.

Vacancy and interstitial defects in hafnia

Abstract: We have performed plane wave density functional theory calculations of atomic and molecular interstitial defects and oxygen vacancies in monoclinic hafnia $({\mathrm{HfO}}_{2})$ The atomic structures of singly and doubly positively charged oxygen vacancies, and singly and doubly negatively charged interstitial oxygen atoms and molecules are investigated We also consider hafnium vacancies, substitutional zirconium, and an oxygen vacancy paired with substitutional zirconium in hafnia Our results predict that atomic oxygen incorporation is energetically favored over molecular incorporation, and that charged defect species are more stable than neutral species when electrons are available from the hafnia conduction band The calculated positions of defect levels with respect to the bottom of the silicon conduction band demonstrate that interstitial oxygen atoms and molecules and positively charged oxygen vacancies can trap electrons from silicon

Resonator-based analysis of the combination of mobile handset antenna and chassis

Abstract: The performance of the mobile phone handset antenna-chassis combination is analyzed based on an approximate decomposition of the waves on the structure into two resonant wavemodes: the antenna-element wavemode and the chassis wavemode. A double resonator equivalent circuit model is presented and used to estimate the impedance bandwidth and the respective distributions of radiation losses with typical parameter values at 900 and 1800 MHz. It is noticed that at 900 MHz, the radiation losses of the antenna element wavemode represent typically less than 10% of the total power. Thus, the antenna element works mainly as a matching element, which couples to the low-Q resonant wavemode of the chassis. At 1800 MHz, the contribution of the antenna element wavemode is larger. By enhancing the coupling and by tuning the chassis resonance, it is possible to obtain an impedance bandwidth of over 50% (6 dB return loss) at both at 900 and 1800 MHz. The results given by the equivalent circuit study are fully supported by those of three-dimensional phone-model simulations, including calculation of the SAR and efficiency values. In prototyping, the 6 dB bandwidth of 5.5% was obtained at 980 MHz with a nonradiating coupling element with a volume of 1.6 cm/sup 3/ on a 120 mm long chassis.

A review of cardiac image registration methods

Abstract: In this paper, the current status of cardiac image registration methods is reviewed. The combination of information from multiple cardiac image modalities, such as magnetic resonance imaging, computed tomography, positron emission tomography, single-photon emission computed tomography, and ultrasound, is of increasing interest in the medical community for physiologic understanding and diagnostic purposes. Registration of cardiac images is a more complex problem than brain image registration because the heart is a nonrigid moving organ inside a moving body. Moreover, as compared to the registration of brain images, the heart exhibits much fewer accurate anatomical landmarks. In a clinical context, physicians often mentally integrate image information from different modalities. Automatic registration, based on computer programs, might, however, offer better accuracy and repeatability and save time.

Unsupervised Discovery of Morphemes

Abstract: We present two methods for unsupervised segmentation of words into morpheme-like units. The model utilized is especially suited for languages with a rich morphology, such as Finnish. The first method is based on the Minimum Description Length (MDL) principle and works online. In the second method, Maximum Likelihood (ML) optimization is used. The quality of the segmentations is measured using an evaluation method that compares the segmentations produced to an existing morphological analysis. Experiments on both Finnish and English corpora show that the presented methods perform well compared to a current state-of-the-art system.

Ventilation and health in non-industrial indoor environments: report from a European multidisciplinary scientific consensus meeting (EUROVEN).

Abstract: Scientific literature on the effects of ventilation on health, comfort, and productivity in non-industrial indoor environments (offices, schools, homes, etc.) has been reviewed by a multidisciplinary group of European scientists, called EUROVEN, with expertise in medicine, epidemiology, toxicology, and engineering. The group reviewed 105 papers published in peer-reviewed scientific journals and judged 30 as conclusive, providing sufficient information on ventilation, health effects, data processing, and reporting, 14 as providing relevant background information on the issue, 43 as relevant but non-informative or inconclusive, and 18 as irrelevant for the issue discussed. Based on the data in papers judged conclusive, the group agreed that ventilation is strongly associated with comfort (perceived air quality) and health [Sick Building Syndrome (SBS) symptoms, inflammation, infections, asthma, allergy, short-term sick leave], and that an association between ventilation and productivity (performance of office work) is indicated. The group also concluded that increasing outdoor air supply rates in non-industrial environments improves perceived air quality; that outdoor air supply rates below 25 l/s per person increase the risk of SBS symptoms, increase short-term sick leave, and decrease productivity among occupants of office buildings; and that ventilation rates above 0.5 air changes per hour (h-1) in homes reduce infestation of house dust mites in Nordic countries. The group concluded additionally that the literature indicates that in buildings with air-conditioning systems there may be an increased risk of SBS symptoms compared with naturally or mechanically ventilated buildings, and that improper maintenance, design, and functioning of air-conditioning systems contributes to increased prevalence of SBS symptoms.

Waves and energy in chiral nihility

Abstract: A model for a chiral material in which both the permittivity and permeability are equal to zero is discussed. Such a material is referred by us as a ``chiral nihility". It is shown that this exotic material can be realized as a mixture of small helical inclusions. Wave solutions and energy in such a medium are analyzed. It is shown that an extraordinary wave in chiral nihility is a backward wave. Wave reflection and refraction on a chiral nihility interface is also considered. It is shown that a linearly polarized wave normally incident onto this interface produces the wave of "standing phase" and the same wave in the case of oblique incidence causes two refracted waves, one of them with an anomalous refraction.

Altered central sensorimotor processing in patients with complex regional pain syndrome

Abstract: Alterations in tactile sensitivity are common in patients with chronic pain. Recent brain imaging studies have indicated that brain areas activated by acute experimental pain partly overlap with areas processing innocuous tactile stimuli. However, the possible effect of chronic pain on central tactile processing has remained unclear. We have examined, both clinically and with whole-head magnetoencephalography, six patients suffering from complex regional pain syndrome (CRPS) of the upper limb. The cortical somatosensory responses were elicited by tactile stimuli applied to the fingertips and the reactivity of spontaneous brain oscillations was monitored as well. Tactile stimulation of the index finger elicited an initial activation at 65 ms in the contralateral SI cortex, followed by activation of the ipsi- and contralateral SII cortices at about 130 ms. The SI responses were 25-55% stronger to stimulation of the painful than the healthy side. The distance between SI representations of thumb and little finger was significantly shorter in the hemisphere contralateral than ipsilateral to the painful upper limb. In addition, reactivity of the 20-Hz motor cortex rhythm to tactile stimuli was altered in the CRPS patients, suggesting modified inhibition of the motor cortex. These results imply that chronic pain may alter central tactile and motor processing.

Implementing strategies successfully

Abstract: The paper presents the key findings of a study on strategy implementation. A qualitative study of 298 interviews was conducted in 12 service organizations. In the paper, the key findings are introduced, and the challenges of strategic communication and action, the identification of and support for strategic actors, and structure and systems aligned with strategy, are discussed.

Observational evidence for the accretion-disk origin for a radio jet in an active galaxy

Abstract: Accretion of gas onto black holes is thought to power the relativistic jets of material ejected from active galactic nuclei (AGN) and the ‘microquasars’ located in our Galaxy1,2,3. In microquasars, superluminal radio-emitting features appear and propagate along the jet shortly after sudden decreases in the X-ray fluxes1. This establishes a direct observational link between the black hole and the jet: the X-ray dip is probably caused by the disappearance of a section of the inner accretion disk4 as it falls past the event horizon, while the remainder of the disk section is ejected into the jet, creating the appearance of a superluminal bright spot5. No such connection has hitherto been established for AGN, because of insufficient multi-frequency data. Here we report the results of three years of monitoring the X-ray and radio emission of the galaxy 3C120. As has been observed for microquasars, we find that dips in the X-ray emission are followed by ejections of bright superluminal knots in the radio jet. The mean time between X-ray dips appears to scale roughly with the mass of the black hole, although there are at present only a few data points.

Continuous GPS measurements of postglacial adjustment in Fennoscandia 1. Geodetic results

Abstract: [1] Data collected under the auspices of the BIFROST GPS project yield a geographically dense suite of estimates of present-day, three-dimensional (3-D) crustal deformation rates in Fennoscandia [Johansson et al., 2002]. A preliminary forward analysis of these estimates [Milne et al., 2001] has indicated that models of ongoing glacial isostatic adjustment (GIA) in response to the final deglaciation event of the current ice age are able to provide an excellent fit to the observed 3-D velocity field. In this study we revisit our previous GIA analysis by considering a more extensive suite of forward calculations and by performing the first formal joint inversion of the BIFROST rate estimates. To establish insight into the physics of the GIA response in the region, we begin by decomposing a forward prediction into the three contributions associated with the ice, ocean, and rotational forcings. From this analysis we demonstrate that recent advances in postglacial sea level theory, in particular the inclusion of rotational effects and improvements in the treatment of the ocean load in the vicinity of an evolving continental margin, involve peak signals that are larger than the observational uncertainties in the BIFROST network. The forward analysis is completed by presenting predictions for a pair of Fennoscandian ice histories and an extensive suite of viscoelastic Earth models. The former indicates that the BIFROST data set provides a powerful discriminant of such histories. The latter yields bounds on the ( assumed constant) upper and lower mantle viscosity (nu(UM), nu(LM)); specifically, we derive a 95% confidence interval of 5 x 10(20) less than or equal to nu(UM) less than or equal to 10(21) Pa s and 5 x 10(21) less than or equal to nu(LM) less than or equal to 5 x 10(22) Pa s, with some preference for (elastic) lithospheric thickness in excess of 100 km. The main goal of the ( Bayesian) inverse analysis is to estimate the radial resolving power of the BIFROST GPS data as a function of depth in the mantle. Assuming a reasonably accurate ice history, we demonstrate that this resolving power varies from similar to 200 km near the base of the upper mantle to similar to 700 km in the top portion of the lower mantle. We conclude that the BIFROST data are able to resolve structure on radial length scale significantly smaller than a single upper mantle layer. However, these data provide little constraint on viscosity in the bottom half of the mantle. Finally, elements of both the forward and inverse analyses indicate that radial and horizontal velocity estimates provide distinct constraints on mantle viscosity.

Normalized amplitude quotient for parametrization of the glottal flow

Abstract: Normalized amplitude quotient (NAQ) is presented as a method to parametrize the glottal closing phase using two amplitude-domain measurements from waveforms estimated by inverse filtering. In this technique, the ratio between the amplitude of the ac flow and the negative peak amplitude of the flow derivative is first computed using the concept of equivalent rectangular pulse, a hypothetical signal located at the instant of the main excitation of the vocal tract. This ratio is then normalized with respect to the length of the fundamental period. Comparison between NAQ and its counterpart among the conventional time-domain parameters, the closing quotient, shows that the proposed parameter is more robust against distortion such as measurement noise that make the extraction of conventional time-based parameters of the glottal flow problematic. Experiments with breathy, normal, and pressed vowels indicate that NAQ is also able to separate the type of phonation effectively.

Association of ventilation system type with SBS symptoms in office workers.

Abstract: Submitted to Indoor Air. Association of Ventilation System Type with SBS symptoms in Office Workers Olli Seppanen 1 and William J. Fisk 2, Helsinki University of Technology Laboratory of Heating, Ventilating and Air Conditioning Helsinki, Finland Lawrence Berkeley National Laboratory Indoor Environment Department Berkeley, CA USA February 6, 2001 Communications should be addressed to Olli Seppanen Abstract This paper provides a review and synthesis of current knowledge about the associations of ventilation system types in office buildings with sick building syndrome symptoms and discusses potential explanations for the associations. Relative to natural ventilation, air conditioning, with or without humidification, was consistently associated with a statistically significant increase in the prevalence of one or more SBS symptoms. Prevalences were typically higher by approximately 30% to 200% in the air conditioned buildings. In two of three assessments from a single study, symptom prevalences were also significantly higher in air conditioned buildings than in buildings with simple mechanical ventilation and no humidification. In approximately half of assessments, SBS symptom prevalences were significantly higher in buildings with simple mechanical ventilation than in buildings with natural ventilation. Insufficient information was available for conclusions about the potential increased risk of SBS symptoms with humidification. The statistically significant associations of mechanical ventilation and air conditioning with SBS symptoms are much more frequent than expected from chance and also not likely to be a consequence of confounding by several potential personal, job, or building- related confounders. The reasons for the increases in symptom prevalences with mechanical ventilation and particularly with air conditioning remain unclear. Multiple deficiencies in HVAC system design, construction, operation, or maintenance, including some which cause pollutant emissions from HVAC systems, may contribute to the increases in symptom prevalences. Practical Implications Because the causes of increases in SBS symptom prevalences in mechanically ventilated buildings are uncertain, the implications for building professionals are also uncertain. The available evidence suggests, but does not prove, that multiple preventative and corrective measures are needed to substantially reduce the SBS symptoms associated with HVAC systems. Commissioning, operational checks, training of operators, and maintenance may be particularly important for reducing the risks of health effects associated with HVAC systems.

Degree of polarization for optical near fields.

Abstract: We investigate an extension to the concept of degree of polarization that applies to arbitrary electromagnetic fields, i.e., fields whose wave fronts are not necessarily planar. The approach makes use of generalized spectral Stokes parameters that appear as coefficients, when the full 3 x 3 spectral coherence matrix is expanded in terms of the Gell-Mann matrices. By defining the degree of polarization in terms of these parameters in a manner analogous to the conventional planar-field case, we are led to a formula that consists of scalar invariants of the spectral coherence matrix only. We show that attractive physical insight is gained by expressing the three-dimensional degree of polarization explicitly with the help of the correlations between the three orthogonal spectral components of the electric field. Furthermore, we discuss the fundamental differences in characterizing the polarization state of a field by employing either the two- or the three-dimensional coherence-matrix formalism. The extension of the concept of the degree of polarization to include electromagnetic fields having structures of arbitrary form is expected to be particularly useful, for example, in near-field optics.

Investigation of Mass-Transport Limitations in the Solid Polymer Fuel Cell Cathode I. Mathematical Model

Abstract: In this paper, a one-dimensional, steady-state agglomerate model was used to describe the functioning and the mass transport limitations of the cathode in the solid polymer fuel cell (SPFC). This mathematical model is then compared to experimental results obtained on cathodes in an SPFC. The following processes were considered: Tafel kinetics of the oxygen reduction reaction, proton migration, oxygen diffusion in the agglomerates, and diffusion of a ternary gas mixture vapor in the pores of the active layer and of the gas backing. The model shows that limitation by proton migration in the active layer or by oxygen diffusion in the agglomerates leads to a doubling of the Tafel slope at higher current densities. For those two types of transport limitations, the dependence of the reaction rate on the active-layer thickness, oxygen partial pressure, and relative humidity of the gas were simulated. When additional limitation due to slow gas phase diffusion appears, the double Tafel slope is distorted. A mathematical expression for the limiting current density due to this process is presented. By using this expression, it is possible to correct the polarization curves for slow gas phase diffusion. © 2002 The Electrochemical Society. All rights reserved.