Spectral and spatial observations of microwave spikes and zebra structure in the short radio burst of May 29, 2003

The unusual radio burst of May 29, 2003 connected with the M1.5 flare in AR 10368 has been analyzed. It was observed by the Solar Broadband Radio Spectrometer (SBRS/Huairou station, Beijing) in the 5.2-7.6 GHz range. It proved to be only the third case of a neat zebra structure appearing among all observations at such high frequencies. Despite the short duration of the burst (25 s), it provided a wealth of data for studying the superfine structure with millisecond resolution (5 ms). We localize the site of emission sources in the flare region, estimate plasma parameters in the generation sites, and suggest applicable mechanisms for interpretating spikes and zebra-structure generation. Positions of radio bursts were obtained by the Siberian Solar Radio Telescope (SSRT) (5.7 GHz) and Nobeyama radioheliograph (NoRH) (17 GHz). The sources in intensity gravitated to tops of short loops at 17 GHz, and to long loops at 5.7 GHz. Short pulses at 17 GHz (with a temporal resolution of 100 ms) are registered in the R-polarized source over the N-magnetic polarity (extraordinary mode). Dynamic spectra show that all the emission comprised millisecond pulses (spikes) of 5-10 ms duration in the instantaneous band of 70 to 100 MHz, forming the superfine structure of different bursts, essentially in the form of fast or slow-drift fibers and various zebra-structure stripes. Five scales of zebra structures have been singled out. As the main mechanism for generating spikes (as the initial emission) we suggest the coalescence of plasma waves with whistlers in the pulse regime of interaction between whistlers and ion-sound waves. In this case one can explain the appearance of fibers and sporadic zebra-structure stripes exhibiting the frequency splitting.Comment: 11 pages, 5 figures, in press; A&A 201

The multifrequency Siberian Radioheliograph

The 10-antenna prototype of the multifrequency Siberian radioheliograph is described. The prototype consists of four parts: antennas with broadband front-ends, analog back-ends, digital receivers and a correlator. The prototype antennas are mounted on the outermost stations of the Siberian Solar Radio Telescope (SSRT) array. A signal from each antenna is transmitted to a workroom by an analog fiber optical link, laid in an underground tunnel. After mixing, all signals are digitized and processed by digital receivers before the data are transmitted to the correlator. The digital receivers and the correlator are accessible by the LAN. The frequency range of the prototype is from 4 to 8 GHz. Currently the frequency switching observing mode is used. The prototype data include both circular polarizations at a number of frequencies given by a list. This prototype is the first stage of the multifrequency Siberian radioheliograph development. It is assumed that the radioheliograph will consist of 96 antennas and will occupy stations of the West-East-South subarray of the SSRT. The radioheliograph will be fully constructed in autumn of 2012. We plan to reach the brightness temperature sensitivity about 100 K for the snapshot image, a spatial resolution up to 13 arcseconds at 8 GHz and polarization measurement accuracy about a few percent. First results with the 10-antenna prototype are presented of observations of solar microwave bursts. The prototype abilities to estimate source size and locations at different frequencies are discussed

The practice of going helps children to stop:The importance of context monitoring in inhibitory control

How do we stop ourselves during ongoing action? Recent work implies that stopping per se is easy given sufficient monitoring of contextual cues signaling the need to change action. We test key implications of this idea for improving inhibitory control. Seven- to 9-year old children practiced stopping an ongoing action, or monitoring for cues that signaled the need to go again. Both groups subsequently showed better response inhibition in a Stop-Signal task than active controls, and practice monitoring yielded a dose-response relationship. When monitoring practice was optimized to occur while children engaged in responding, the greatest benefits were observed – even greater than from practicing stopping itself. These findings demonstrate the importance of monitoring processes in developing response inhibition, and suggest promising new directions for interventions

Visual salience of the stop signal affects the neuronal dynamics of controlled inhibition

The voluntary control of movement is often tested by using the countermanding, or stop-signal task that sporadically requires the suppression of a movement in response to an incoming stop-signal. Neurophysiological recordings in monkeys engaged in the countermanding task have shown that dorsal premotor cortex (PMd) is implicated in movement control. An open question is whether and how the perceptual demands inherent the stop-signal affects inhibitory performance and their underlying neuronal correlates. To this aim we recorded multi-unit activity (MUA) from the PMd of two male monkeys performing a countermanding task in which the salience of the stop-signals was modulated. Consistently to what has been observed in humans, we found that less salient stimuli worsened the inhibitory performance. At the neuronal level, these behavioral results were subtended by the following modulations: when the stop-signal was not noticeable compared to the salient condition the preparatory neuronal activity in PMd started to be affected later and with a less sharp dynamic. This neuronal pattern is probably the consequence of a less efficient inhibitory command useful to interrupt the neural dynamic that supports movement generation in PMd

Acting without being in control: Exploring volition in Parkinson's disease with impulsive compulsive behaviours.

BACKGROUND: Several aspects of volitional control of action may be relevant in the pathophysiology of impulsive-compulsive behaviours (ICB) in Parkinson's disease (PD). We aimed to explore multiple aspects of action control, assessing reward-related behaviour, inhibition (externally and internally triggered) and sense of agency in PD patients, with and without ICB compared to healthy subjects. METHODS: Nineteen PD patients with ICB (PD-ICB), 19 PD without ICB (PD-no-ICB) and 19 healthy controls (HC) underwent a battery of tests including: Intentional Binding task which measures sense of agency; Stop Signal Reaction Time (SSRT) measuring capacity for reactive inhibition; the Marble task, assessing intentional inhibition; Balloon Analog Risk Task for reward sensitivity. RESULTS: One-way ANOVA showed significant main effect of group for action binding (p = 0.004, F = 6.27). Post hoc analysis revealed that PD-ICB had significantly stronger action binding than HC (p = 0.004), and PD-no-ICB (p = 0.04). There was no difference between PD-no-ICB and HC. SSRT did not differ between PD groups, whereas a significant difference between PD-no-ICB and HC was detected (p = 0.01). No other differences were found among groups in the other tasks. CONCLUSIONS: PD patients with ICB have abnormal performance on a psychophysical task assessing sense of agency, which might be related to a deficit in action representation at cognitive/experiential level. Yet, they have no deficit on tasks evaluating externally and internally triggered inhibitory control, or in reward-based decision-making. We conclude that impaired sense of agency may be a factor contributing to ICB in PD patients

Flare SOL2012-07-06: on the origin of the circular polarization reversal between 17 GHz and 34 GHz

The new generations of multiwavelength radioheliographs with high spatial resolution will employ microwave imaging spectropolarimetry to recover flare topology and plasma parameters in the flare sources and along the wave propagation paths. The recorded polarization depends on the emission mechanism and emission regime (optically thick or thin), the emitting particle properties, and propagation effects. Here, we report an unusual flare, SOL2012-07-06T01:37, whose optically thin gyrosynchrotron emission of the main source displays an apparently ordinary mode sense of polarization in contrast to the classical theory that favors the extraordinary mode. This flare produced copious nonthermal emission in hard X-rays and in high-frequency microwaves up to 80 GHz. It is found that the main flare source corresponds to an interaction site of two loops with greatly different sizes. We have investigated the three possible known reasons of the circular polarization sense reversal - mode coupling, positron contribution, and the effect of beamed angular distribution. We excluded polarization reversal due to contribution of positrons because there was no relevant response in the X-ray emission. We find that a beam-like electron distribution can produce the observed polarization behavior, but the source thermal density must be much higher than the estimate from to the X-ray data. We conclude that the apparent ordinary wave emission in the optically thin mode is due to radio wave propagation across the quasi-transverse (QT) layer. The abnormally high transition frequency (above 35 GHz) can be achieved reasonably low in the corona where the magnetic field value is high and transverse to the line of sight. This places the microwave source below this QT layer, i.e. very low in the corona.Comment: 15 pages, 7 figure