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Event-related functional magnetic resonance imaging was used to compare activity in the human parietal cortex in two attention-switching paradigms. On each trial of the visual switching (VS) paradigm, subjects attended to one of two visual stimuli on the basis of either their color or shape. Trials were presented in blocks interleaved with cues instructing subjects to either continue attending to the currently relevant dimension or to switch to the other stimulus dimension. In the response switching (RS) paradigm, subjects made one of two manual responses to the single stimulus presented on each trial. The rules for stimulus-response mapping were reversed on different trials. Trials were presented in blocks interleaved with cues that instructed subjects to either switch stimulus-response mapping rules or to continue with the current rule. Brain activity at "switch" and "stay" events was compared. The results revealed distinct parietal areas concerned with visual attentional set shifts (VS) and visuomotor intentional set shifts (RS). In VS, activity was recorded in the lateral part of the intraparietal region. In RS, activity was recorded in the posterior medial intraparietal region and adjacent posterior superior and dorsomedial parietal cortex. The results also suggest that the basic functional organization of the intraparietal sulcus and surrounding regions is similar in both macaque and human species.

著者人数：48名, Accepted: 2002-12-31, 資料番号: SA1002070000

Using multichannel electroencephalography (EEG), we investigated temporal dynamics of the cortical response to transcranial magnetic stimulation (TMS). TMS was applied over the left primary motor cortex (M1) of healthy volunteers, intermixing single suprathreshold pulses with pairs of sub- and suprathreshold pulses and simultaneously recording EEG from 60 scalp electrodes. Averaging of EEG data time locked to the onset of TMS pulses yielded a waveform consisting of a positive peak (30 ms after the pulse P30), followed by two negative peaks [at 45 (N45) and 100 ms]. Peak-to-peak amplitude of the P30–N45 waveform was high, ranging from 12 to 70 μV; in most subjects, the N45 potential could be identified in single EEG traces. Spectral analysis revealed that single-pulse TMS induced a brief period of synchronized activity in the beta range (15–30 Hz) in the vicinity of the stimulation site; again, this oscillatory response was apparent not only in the EEG averages but also in single traces. Both the N45 and the oscillatory response were lower in amplitude in the 12-ms (but not 3-ms) paired-pulse trials, compared with the single-pulse trials. These findings are consistent with the possibility that TMS applied to M1 induces transient synchronization of spontaneous activity of cortical neurons within the 15- to 30-Hz frequency range. As such, they corroborate previous studies of cortical oscillations in the motor cortex and point to the potential of the combined TMS/EEG approach for further investigations of cortical rhythms in the human brain.

Event-related functional magnetic resonance imaging was used to compare activity in the human parietal cortex in two attention-switching paradigms. On each trial of the visual switching (VS) paradigm, subjects attended to one of two visual stimuli on the basis of either their color or shape. Trials were presented in blocks interleaved with cues instructing subjects to either continue attending to the currently relevant dimension or to switch to the other stimulus dimension. In the response switching (RS) paradigm, subjects made one of two manual responses to the single stimulus presented on each trial. The rules for stimulus–response mapping were reversed on different trials. Trials were presented in blocks interleaved with cues that instructed subjects to either switch stimulus–response mapping rules or to continue with the current rule. Brain activity at “switch” and “stay” events was compared. The results revealed distinct parietal areas concerned with visual attentional set shifts (VS) and visuomotor intentional set shifts (RS). In VS, activity was recorded in the lateral part of the intraparietal region. In RS, activity was recorded in the posterior medial intraparietal region and adjacent posterior superior and dorsomedial parietal cortex. The results also suggest that the basic functional organization of the intraparietal sulcus and surrounding regions is similar in both macaque and human species.

A new model is presented for predicting the field strength inside buildings for microcell and small macrocell base stations. The field strength is calculated by an outdoor/spl rarr/indoor model, which uses the field estimates in the points just outside the boundary line of the building at same height, calculated by a three dimensional, ray-based outdoor model. The predictions by the new model are compared with measurements.

The third-generation cellular systems will offer services with higher bit rates compared to today's networks and therefore for an operator it is of the utmost importance to exploit all possible resources to improve the capacity of the radio network. One attractive possibility, already used in most of the second-generation networks, is to increase the sectorisation at the base stations, i.e., using 3 or even up to 6 sectors per site. In this paper we demonstrate with simulations and some theoretical derivation how the sectorisation of the base stations influences the performance (capacity and quality of service) of a WCDMA radio network. In addition the simulator and the modelling of the third generation's fast power control and soft handover are presented.

A diversity handover simulator using measured propagation data is introduced. Furthermore, three different diversity handover algorithms are compared and the comparison results are introduced in this paper. The algorithms used in the study were the basic cdmaOne algorithm, modified cdmaOne algorithm and an algorithm with a threshold relative to the strongest received pilot channel Ec/Io. The most stable performance in terms of diversity handover (DHO) probability can be achieved with the slope algorithm. The basic cdmaOne algorithm tends to be very sensitive to the interference situation. The algorithm, which makes the decision based on the relative differences of the received pilot Ec/Io levels, rather than on absolute thresholds, shows moderate change in both the active set update period and in the DHO probability in changing interference conditions.

The third-generation cellular systems will offer services well beyond the capabilities of today's networks. For an operator to provide the maximum capacity of the network supporting multiple traffic mixes more advanced analysis methods are required. The scope of this paper is to demonstrate with simulations how the subscriber profile (mobile station speed and the used service) impact on the network capacity and quality of service. Furthermore, the simulator used in the study is described, the uplink and downlink iterations and the fast power control and soft handover modeling are briefly introduced.

The scope of this paper is to demonstrate the impact of the soft handover on the WCDMA network performance. The gains from the selection combining and increased diversity in uplink soft handover of a WCDMA system have been studied with the help of link level simulations. Two base stations have been included in the simulation model. The average required transmitted and received E/sub b//I/sub 0/ ensuring the desired quality has been measured as a function of the level difference between the two base stations. This has been done for two multipath propagation channels and several mobile station (MS) speeds. In addition, the paper discusses how the soft handover reduces the required power control headroom near the cell edge.

A static radio network simulator for studying various topics of 3rd generation WCDMA radio network planning is presented. The simulator allows analyzing coverage, capacity and quality of service related issues. Input to the simulator is the network scenario and the user information as a mobile station map. The uplink and downlink are separately analyzed and the outputs are presented in form of maps of best server, number of users, served traffic, SHO areas, AS size, SHO statistics for the area and for the users, Perch C/I plots. In the analysis, impact of the 3rd generations fast power control and soft(er) handover (SHO) possibility are taken into account by importing link level simulations into the analyses. The whole simulator is entirely based on Matlab(R) software.

This paper studies the WCDMA mobile transmission power and its variations due to fast power control with theoretical calculations, simulations, laboratory measurements and field measurements. The effect of mobile speed, multipath profile and base station reception antenna diversity is studied. The results show that a mobile speed of 120 km/h requires less transmission power than low mobile speeds because of the time diversity provided by interleaving. With little multipath diversity and without antenna diversity the difference in terms of transmitted power is up to 2 dB. The measurements and simulations show that the multipath diversity gain of the ITU Vehicular A channel compared to ITU Pedestrian A channel is 3 dB without antenna diversity and 1 dB with antenna diversity at 3 km/h. At higher mobile speeds the multipath diversity gains are smaller. The base station antenna diversity gain is shown to be 3-4 dB in ITU Vehicular A channel and 4-6 dB in ITU Pedestrian A channel. The results show good agreement between simulations and measurements. The results also showed inaccuracies in the implementation of the SIR estimation in the experimental WCDMA base station receiver.

A simple method is derived for estimating the downlink capacity and required base station transmission power in a WCDMA system. This is based on a downlink pole equation which is mostly similar with the well known CDMA uplink pole equation. It is shown that the total downlink transmission power is composed of two terms. The first term is equal to what would be needed in the absence of interference and the second one shows the increase due to multiple access interference which is inversely proportional to 1-/spl eta//sub DL/ where /spl eta//sub DL/ is called the downlink loading. The method can be used in radio network dimensioning where extensive simulations can not be run. Usage of the method is demonstrated by some examples.

The third generation cellular systems will offer services well beyond the capabilities of today's networks. For an operator to optimise their business cases accurate methods are required for the capacity and coverage estimation. The scope of this paper is to concentrate on the first phase of the radio network planning process: radio network dimensioning. Dimensioning is providing the first rough estimate of the radio network's capabilities in terms of capacity, coverage and quality. In this work the radio network dimensioning rules and methods are introduced. Furthermore, the proposed methods are verified with radio network simulations. It has been demonstrated that the proposed methods work reasonable well even with relatively high bit rates. In addition to that it is shown that in case of WCDMA macrocell dimensioning it is not adequate to base the results on uplink only.

We used event-related functional magnetic resonance imaging (fMRI) to measure brain activity when subjects were performing identical tasks in the context of either a task-set switch or a continuation of earlier performance. The context, i.e., switching or staying with the current task, influenced medial frontal cortical activation; the medial frontal cortex is transiently activated at the time that subjects switch from one way of performing a task to another. Two types of task-set-switching paradigms were investigated. In the response-switching (RS) paradigm, subjects switched between different rules for response selection and had to choose between competing responses. In the visual-switching (VS) paradigm, subjects switched between different rules for stimulus selection and had to choose between competing visual stimuli. The type of conflict, sensory (VS) or motor (RS), involved in switching was critical in determining medial frontal activation. Switching in the RS paradigm was associated with clear blood-oxygenation-level-dependent signal increases (“activations”) in three medial frontal areas: the rostral cingulate zone, the caudal cingulate zone, and the presupplementary motor area (pre-SMA). Switching in the VS task was associated with definite activation in just one medial frontal area, a region on the border between the pre-SMA and the SMA. Subsequent to the fMRI session, we used MRI-guided frameless stereotaxic procedures and repetitive transcranial magnetic stimulation (rTMS) to test the importance of the medial frontal activations for task switching. Applying rTMS over the pre-SMA disrupted subsequent RS performance but only when it was applied in the context of a switch. This result shows, first, that the pre-SMA is essential for task switching and second that its essential role is transient and limited to just the time of behavioral switching. The results are consistent with a role for the pre-SMA in selecting between response sets at a superordinate level rather than in selecting individual responses. The effect of the rTMS was not simply due to the tactile and auditory artifacts associated with each pulse; rTMS over several control regions did not selectively disrupt switching. Applying rTMS over the SMA/pre-SMA area activated in the VS paradigm did not disrupt switching. This result, first, confirms the limited importance of the medial frontal cortex for sensory attentional switching. Second, the VS rTMS results suggest that just because an area is activated in two paradigms does not mean that it plays the same essentialrole in both cases.

One key application for biomass is in combined heat and power (CHP) production where it could cut the use of fossil fuels drastically. A specific example can be found in Finland where regional small-scale district heating plants are being converted to CHP to increase its CHP production. To assess the potential of small-scale CHP plant, a team from VTT Energy attempted to find the most profitable way to boost plant efficiencies. The team developed a so-called optimization model to assess the impact of a range of production process changes. It was found that adding a feedwater preheater, steam reheater and a two-stage district heat exchanger were the most promising alternatives for increasing the power production in all small-scale plant, between 1 to 20 MWe.