The “direct detection” of neuronal activity by MRI could offer improved spatial and temporal resolution compared to the blood oxygenation level-dependent (BOLD) effect. Here we describe initial attempts to use MRI to detect directly the neuronal currents resulting from spontaneous alpha wave activity, which have previously been shown to generate the largest extracranial magnetic fields. Experiments were successfully carried out on four subjects at 3 T. A single slice was imaged at a rate of 25 images per second under two conditions. The first (in darkness with eyes-closed) was chosen to promote alpha wave activity, while the second (eyes-open viewing a visual stimulus) was chosen to suppress it. The fluctuations of the phase and magnitude of the resulting MR image data were frequency analysed, and tested for the signature of both alpha wave activity and neuronal activity evoked by the visual stimulus.
Regions were found that consistently showed elevated power in fluctuations of the phase of the MR signal, in the frequency range of alpha waves, during the eyes-closed condition. It was conservatively assumed that if oscillations occurred at the same frequency in the magnitude signal from the same region or at the same frequency in the phase or magnitude signal from other regions overlying large vessels or cerebrospinal fluid (CSF), then the phase changes were not due to neuronal activity related to alpha waves. Using these criteria the data obtained were consistent with direct detection of alpha wave activity in three of the four volunteers. No significant MR signal fluctuations due to evoked activity were identified. 相似文献
Using the quasiregular model, some characteristics of the phase diagram with a minimum point were studied for a binary system. We obtained the inequalities which must be satisfied by these parametera WS,WL,VS and VL in various models. 相似文献
A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer
processes in collisions of 60–120 MeV Siq+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization,
electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated.
The data reported on the present collision system result from a direct measurement in the considered impact energy for the
first time. The total ionization cross-sections for the recoil ions are shown to scale as q1.7/Ep0.5
, where Ep is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing
recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j2 upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing
cross-sections σqq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow
our data for different ionization processes is reviewed and discussed. 相似文献
Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies.
Coupled channel calculations incorporating couplings to 2+ and 3− states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements
had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer
were carried out for 46,48Ti+61Ni systems. The present paper gives the results of these studies. 相似文献
A two-dimensional (horizontal plane) coastal and estuarine region model, capable of predicting the combined effects of gravity surface shallow- water waves (shoaling, refraction, diffraction, reflection and breaking), and steady currents, is described and numerical results are compared with those obtained experimentally. Two series of observations within a wave flume and a combined wave-current facility were developed. In the first case, the wave was generated via a hinged paddle located within a deepened section at one end of the channel, as, in the second case, the wave propagating with or against the current was generated by a plunger-type wavemaker; the re-circulating current was introduced via one passing tank connected to a centrifugal pump. Several comparisons for a number of 1D situations and one 2D horizontal plane case are presented. 相似文献
It is known that the problem of minimizing total weighted completion time on a series-batching machine is NP-hard. We consider a series-batching bicriteria scheduling problem of minimizing makespan and total weighted completion time with equal length job simultaneously. A batching machine can handle up to b jobs in a batch, where b is called the batch capacity of the machine. We study the unbounded model with b≥n, where n denotes the number of jobs. A dynamic programming algorithm is proposed to solve the unbounded model, which can find all Pareto optimal schedules in O(n3) time. 相似文献
The Mekong River (MR) is the major water source in Southeast Asia, sharedby six countries. There is a rush, by riparian states, to acquire sources of alternative energy and other benefits to meet growing demands for water and energy. China and Myanmar have refused to cooperate fully in the MR Forum, leading to increase risks within the region. Development of the water resources of the MR Basin is the subject of intense debate both within the Mekong region and internationally. This paper investigates the concept of issue linkage to resolve unidirectional externalities in the MR. Using linked games, the paper shows that the downstream nations can consider the use of linkage as a form of side payment in achieving a basin‐wide agreement. While this approach supports the Integrated Water Resource Management‐based Basin Development Strategy adopted by the Mekong River Commission in April 2011 for managing the region's sustainability development, facts on the ground suggest that traditional issues to be linked may not be sufficient. The paper addresses this observation and suggests a cadre of issues, including nontraditional ones, to be analyzed in a future work. 相似文献