Time-domain terahertz compressive imaging.

We present an implementation of the single-pixel imaging approach into a terahertz (THz) time-domain spectroscopy (TDS) system. We demonstrate the indirect coherent reconstruction of THz temporal waveforms at each spatial position of an object, without the need of mechanical raster-scanning. First, we exploit such temporal information to realize (far-field) time-of-flight images. In addition, as a proof of concept, we apply a typical compressive sensing algorithm to demonstrate image reconstruction with less than 50% of the total required measurements. Finally, the access to frequency domain is also demonstrated by reconstructing spectral images of an object featuring an absorption line in the THz range. The combination of single-pixel imaging with compressive sensing algorithms allows to reduce both complexity and acquisition time of current THz-TDS imaging systems.

First operation in SPIDER and the path to complete MITICA.

The requirements of ITER neutral beam injectors (1 MeV, 40 A negative deuterium ion current for 1 h) have never been simultaneously attained; therefore, a dedicated Neutral Beam Test Facility (NBTF) was set up at Consorzio RFX (Padova, Italy). The NBTF includes two experiments: SPIDER (Source for the Production of Ions of Deuterium Extracted from Rf plasma), the full-scale prototype of the source of ITER injectors, with a 100 keV accelerator, to investigate and optimize the properties of the ion source; and MITICA, the full-scale prototype of the entire injector, devoted to the issues related to the accelerator, including voltage holding at low gas pressure. The present paper gives an account of the status of the procurements, of the timeline, and of the voltage holding tests and experiments for MITICA. As for SPIDER, the first year of operation is described, regarding the solution of some issues connected with the radiofrequency power, the source operation, and the characterization of the first negative ion beam.

Ion collector design for an energy recovery test proposal with the negative ion source NIO1.

Commercial viability of thermonuclear fusion power plants depends also on minimizing the recirculation power used to operate the reactor. The neutral beam injector (NBI) remains one of the most important method for plasma heating and control. For the future fusion power plant project DEMO, a NBI wall plug efficiency at least of 0.45 is required, while efficiency of present NBI project is about 0.25. The D(-) beam from a negative ion source is partially neutralized by a gas cell, which leaves more than 40% of energy in residual beams (D(-) and D(+)), so that an ion beam energy recovery system can significantly contribute to optimize efficiency. Recently, the test negative ion source NIO1 (60 keV, 9 beamlets with 15 mA H(-) each) has been designed and built at RFX (Padua) for negative ion production efficiency and the beam quality optimization. In this paper, a study proposal to use the NIO1 source also for a beam energy recovery test experiment is presented and a preliminary design of a negative ion beam collector with simulations of beam energy recovery is discussed.

First experiments with the negative ion source NIO1.

Neutral Beam Injectors (NBIs), which need to be strongly optimized in the perspective of DEMO reactor, request a thorough understanding of the negative ion source used and of the multi-beamlet optics. A relatively compact radio frequency (rf) ion source, named NIO1 (Negative Ion Optimization 1), with 9 beam apertures for a total H(-) current of 130 mA, 60 kV acceleration voltage, was installed at Consorzio RFX, including a high voltage deck and an X-ray shield, to provide a test bench for source optimizations for activities in support to the ITER NBI test facility. NIO1 status and plasma experiments both with air and with hydrogen as filling gas are described. Transition from a weak plasma to an inductively coupled plasma is clearly evident for the former gas and may be triggered by rising the rf power (over 0.5 kW) at low pressure (equal or below 2 Pa). Transition in hydrogen plasma requires more rf power (over 1.5 kW).

Active-feedback control of the magnetic boundary for magnetohydrodynamic stabilization of a fusion plasma.

Stable operation with control on magnetohydrodynamic modes has been obtained in the modified reversed field experiment employing a set of 192 feedback controlled saddle coils. Improvements of plasma temperature, confinement (twofold), and pulse length (threefold) and, as a consequence of the magnetic fluctuation reduction, strong mitigation of plasma-wall interaction and mode locking are reported.

[Usefulness of ambulatory EEG in detecting critical and intercritical events in patients with epilepsy or with suspected epilepsy]. / Utilità dell'EEG dinamico nel riconoscimento di eventi critici e intercritici in pazienti epilettici o con sospetta epilessia.

Ambulatory EEGs (EEGAs) were recorded in 251 patients. In 91 of these patients there was a suspicion of having epileptic seizures, in 117 a diagnosis of epilepsy was already established, in 43 the withdrawal of antiepileptic drugs was envisaged being apparently free from seizures for years. The EEGA showed epileptogenic abnormalities in 31% of patients of the first group. This percentage was not far from the one obtained with standard EEG (EEGS) recordings. In the second group, a divergence was found, as for the classification of seizures, between the ictal events actually recorded on the EEGA and the definition of seizures based on clinical information. Furthermore ictal events recorded by the EEGA were less frequent than one would have anticipated according to the seizure frequency asserted by the patients. In the third group the EEGA disclosed the persistence of epileptic seizures, mostly represented by diffuse spike and wave discharges, in about 30% of the patients. Finally, comparison of the results obtained by the EEGA with those obtained by the EEGS in all patients suggested that the two recording techniques are complementary.

Ethosuximide alters intrathalamic and thalamocortical synchronizing mechanisms: a possible explanation of its antiabsence effect.

Effects of systemic administration of a single dose (50 mg/kg) of ethosuximide (ESM) on extracellularly recorded thalamic (nucleus centralis lateralis, CL; nucleus reticularis, RE) and cortical neurons and on cortical EEG activity of acute cats, have been studied. In intact animals ESM led to: (a) desynchronization of cortical EEG activity; (b) reduction of cortical recruiting responses to 6 Hz stimulation of nucleus centralis medialis (CeM); (c) increased firing rate of CL units; and (d) reduction of incremental responses (IRs) of CL neurons to CeM stimulation. In midbrain reticular formation (MRF)-lesioned animals, ESM induced: (a) reduction of cortical spindle waves; (b) increment of their intraburst frequency; (c) reduction of the IR of CL neurons to 3 and 6 Hz CeM stimulation; (d) shortening of the inhibitory period following each response; and (e) no increment of spontaneous firing rate of CL units. Moreover, ESM led to important changes in the spontaneous activity of RE neurons: spike barrages, typical of these neurons in MRF-lesioned animals, became less frequent and of longer duration, being also constituted by longer interspike intervals. However, responses of RE neurons to low frequency CeM stimulation, when present, did not show any incremental phenomenon and appeared unchanged after ESM. Responses of cortical neurons to paired stimuli, applied with different interstimulus intervals, to nucleus ventralis posterolateralis or in animals with isolated cortex, to subcortical white matter, disclosed a reduction of the cortical inhibitory period following the response to the conditioning stimulus. These data suggest that ESM exerts a moderate diffuse anti-inhibitory action at both cortical and thalamic levels and an activating effect on MRF, which could also be accomplished through disinhibition. The reduction of the inhibitory phases in thalamic nuclei would alter spontaneous intrathalamic synchronizing mechanisms, leading to a decreased effectiveness of thalamocortical volleys, which are believed to be fundamental for the appearance of cortical spike and wave discharges. This hypothesis would therefore explain the specific efficacy of ESM against absence seizures.

On the intracortical activity during recruiting responses: an analysis of laminar profiles before and after topical application of GABA to the cortex.

Intracortical activity during recruiting responses (RRs) has been studied by recording laminar profiles of intracortical field potentials during repetitive stimulation, at 6 Hz, of nucleus centralis lateralis (CL) and nucleus centralis medialis (NCM) in lightly anesthetized cats, before and after topical application to the cortex of 1% GABA solution. The data obtained underwent current source density analysis (CSD) which disclosed that in the pre-GABA condition, there are two almost simultaneous sinks, one in the most superficial layer and the other in mid-cortical layers. After GABA application, a single large sink was present in mid-cortical layers. Extracellular single cortical unit activity was recorded in different animals, through a microelectrode tangentially inserted into the cortex, during repetitive stimulation of CL or NCM, both before and after GABA application. In 75% of these units there was, after GABA, a mean reduction of about 50% of firing probability while in the remaining 25% there was an increased activity. Topical application of 1% Manganese sulfate to the cortical surface appeared to completely inactivate the whole thickness of the cortex where it was applied, making evident the contribution to RRs of the potentials generated in the cortex buried in the adjacent sulci. Finally, a reciprocal facilitating effect of RRs and augmenting responses (ARs), which was studied by combined stimulation of nucleus ventralis posterolateralis (VPL) and NCM, appeared to be dependent upon an intracortical mechanism. All these data suggest that: RRs are the result of a simultaneous activation of superficial and mid-cortical layers; RRs are contaminated by a volume conducted potential arising from the cortex buried in the sulci; a superficial inhibition following the initial excitation seems to be an usual component of the response; ARs and RRs probably share a similar intracortical mechanism for incrementing the response.

Laminar field potentials and unit activity in the cortex during visual evoked potentials in feline generalized penicillin epilepsy.

Modifications of the visual evoked potential during generalized epilepsy were investigated in feline generalized penicillin epilepsy. Visual evoked potentials and their intracortical profiles were averaged during intraburst periods and during the wave of the spike and wave complex to a fixed latency from the preceding spike. During interburst periods, the evoked potentials showed an increase in the amplitude of the early positive peak and the appearance after a variable latency period of a second consistent peak during the late phase of the evoked potential. Laminar profiles of visual evoked potentials and their current source density analysis compared with the activity of single cortical units suggested an early excitation of neuronal populations at layers II, III and IV, as seen before penicillin, followed by a variable inhibitory period and by a subsequent rebounded excitation at those same levels. In evoked potentials recorded during the wave of the spike and wave complex, the early phase was unchanged and the late positive peak and the corresponding deep sink were greatly reduced or nonexistent, although the rebounded activation of cortical units was still evident. These data support the conclusion that during feline generalized penicillin epilepsy a larger number of cortical neurons are activated and a sequence of excitation-inhibition-excitation, probably involving also subcortical structures, is brought about. Moreover, the inhibitory phase of the spike and wave complex is soon disrupted whenever a consistent sensory stimulus arrives at the cortex.

Aspartate and glutamate induced reductions in extracellular free calcium and sodium concentration in area CA1 of 'in vitro' hippocampal slices of rats.

Extracellular Ca2+ and Na+ were simultaneously measured with ion selective electrodes in the CA1 pyramidal cell layer of rat hippocampal slices. Repetitive stimulation of the Schaffer collateral/commissural fiber system led to decreases in [Ca2+] omicron and [Na+] omicron (delta Ca, delta Na) by up to 0.5 mM and 13 mM, respectively. Iontophoretic application of glutamate or aspartate caused dose-dependent delta Ca of more than 1 mM and delta Na of more than 45 mM. Such ionic alterations were smaller in the presence of GABA or of the Ca2+ antagonists Ni2+ and Mg2+. Ca2+ signals were diminished when evoked in low-Na+ bathing medium and Na+ signals were reduced in Ca2+-free solutions. Thus glutamate- and aspartate-dependent decreases in [Na+] omicron and [Ca2+] omicron appear to be caused by 3 different mechanisms: Na+ movement through amino acid-activated ionophores; Ca2+ movement through selective channels, and Ca2+-dependent Na+ movement.

Feline generalized epilepsy induced by tranexamic acid (AMCA).

Epileptic activities induced by topical application of tranexamic acid (AMCA) and penicillin to the cortex of 12 cats in acute experiments were compared. Both substances when diffusely applied on a wide cortical area of both hemispheres at very low concentration produced an EEG pattern consisting of spike-wave bursts similar to the electrographic manifestations seen in feline generalized epilepsy induced by large parenteral doses of sodium penicillin. These epileptic bursts could be triggered by repetitive stimulation of nucleus centralis medialis. Increased concentrations of both AMCA and penicillin led to the appearance of bilaterally synchronous spikes and poly-spikes which were not further excited by NCM stimulation. Two factors seem to play an important role in eliciting spike-wave bursts in both models: (1) the area of the cortex exposed to the epileptogenic agent and (2) the concentration of the epileptogenic agent used. The similar effects observed in 5 chronic animals either by intravenous injection of high doses of AMCA or by intramuscular injection of sodium penicillin confirm the results obtained in acute experiments and suggest a new way of inducing feline generalized epilepsy.

[EEG in transient ischemic attacks (author's transl)]. / Aspetti elettroencefalografici negli episodi ischemici cerebrali transitori.

60 patients under 65 years of age with one or more episodes of reversible ischemic attacks lasting less or more than 24 hours (T.I.A. or R.I.N.D.) were studied. Each patient had a complete clinical assessment and an EEG, followed by an arteriogram. 35 patients had an EEG activation with digital carotid compression. EEG abnormalities were present in 26 cases while 34 patients had normal records. No correlation was found between EEG abnormalities and arteriographic alterations. EEG activation by digital carotid compression is a valuable hemodynamic test but cannot necessarily indicate a controlateral carotid artery occlusion.