THz optical beat-note detection with a fast superconducting hot electron bolometer operating up to 31†GHz.

We study the performance of a hot-electron bolometer (HEB) operating at THz frequencies based on superconducting niobium nitride films. We report on the voltage response of the detector over a large electrical detection bandwidth carried out with different THz sources. We show that the impulse response of the fully packaged HEB at 7.5 K has a 3 dB cutoff around 2 GHz. Remarkably, detection capability is still observed above 30 GHz in an heterodyne beating experiment using a THz quantum cascade laser frequency comb. Additionally, the HEB sensitivity has been evaluated and an optical noise equivalent power NEP of 0.8 pW/√H z has been measured at 1 MHz.

Characterization of anomalous pair currents in Josephson junction networks.

Measurements performed on superconductive networks shaped in the form of planar graphs display anomalously large currents when specific branches are biased. The temperature dependences of these currents evidence that their origin is due to Cooper pair hopping through the Josephson junctions connecting the superconductive islands of the array. The experimental data are discussed in terms of theoretical models which predict, for the system under consideration, an inhomogeneous Cooper pair distribution on the superconductive islands of the network as a consequence of a Bose-Einstein condensation phenomenon.

Microwave-induced thermal escape in Josephson junctions.

We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multivalued in a temperature range far exceeding the classical to quantum crossover temperature. Plots of the switching currents traced as a function of the applied signal frequency show very good agreement with the functional forms expected from Josephson plasma frequency dependencies on the bias current. Throughout, numerical simulations of the corresponding thermally driven classical Josephson junction model show very good agreement with the experimental data.

Increasing the bandwidth of resonant gravitational antennas: the case of explorer.

Resonant gravitational wave detectors with an observation bandwidth of tens of hertz are a reality: the antenna Explorer, operated at CERN by the ROG Collaboration, has been upgraded with a new readout. In this new configuration, it exhibits an unprecedented useful bandwidth: in over 55 Hz about its center operating frequency of 919 Hz the spectral sensitivity is better than 10(-20) Hz(-1/2). We describe the detector and its sensitivity and discuss the foreseeable upgrades to even larger bandwidths.

A three year follow up of preterm infants after moderately early treatment with dexamethasone.

OBJECTIVE: To assess the effect of moderately early postnatal dexamethasone treatment on growth and neurodevelopmental outcome in preterm infants. METHODS: Thirty preterm infants enrolled in a randomised clinical trial to investigate the effectiveness of moderately early dexamethasone administration in the treatment of chronic lung disease were routinely followed up. Fifteen babies received a total dose of 4.75 mg/kg over 14 days from the 10th day of life, and 15 babies were untreated. Five infants in each group received open label steroids to facilitate extubation later in their clinical course. Growth and neurodevelopmental outcome are reported. RESULTS: The mean body weight, height, and head circumference as well as the number of babies with anthropometric measurements within normal range were similar in treated and untreated babies. There was no significant difference between treated and control groups with respect to incidence of cerebral palsy, major neurosensory impairment, mean intelligence quotient scores, and behavioural abnormalities. CONCLUSIONS: Postnatal dexamethasone treatment with the schedule used in this study did not impair growth and neurodevelopmental outcome in preterm infants. Data from larger trials have raised major concern that postnatal steroid treatment may increase neurodevelopmental impairment. The full extent of the risk will only be known when more trials have reported follow up data.

Further contribution to the description of phenotypes associated with partial 4q duplication.

We report on a 15-year-old girl with a previously undescribed de novo duplication of segment 4q13.1-->q22.2. The origin of the extrachromosomal material on 4q was unequivocally established by fluorescent in situ hybridization with a chromosome 4 painting probe. Clinical manifestations included moderate mental retardation, destructive behavior, and minor physical anomalies. An analysis of the literature on partial 4q trisomy led us to identify a region comprising bands 4q22-q23, which may be involved in the development of the acrorenal field.

Short-term brain 'plasticity' in humans: transient finger representation changes in sensory cortex somatotopy following ischemic anesthesia.

Transient rearrangements of finger representation in primary somatosensory cortex induced by an anesthetic block of the sensory information from adjacent fingers have been shown invasively in animals. Such a phenomenon has been now replicated in seven healthy human volunteers. Somatosensory Evoked Fields (SEFs) have been recorded during separate electrical stimulation of the 1st, 3rd, or 5th finger. Recordings were obtained in control conditions (stage A), following complete ischemic anesthesia of the 4 non-stimulated fingers (stage B), and after regaining sensation (stage C). SEFs were recorded using a 28-channel DC-SQUID magnetometer; a single position of the sensor was enough to identify the source of N20m, P30m and following components using the Equivalent Current Dipole (ECD) model. The amount of afferent input during stages A through C was monitored with surface electrodes placed on the nerve at wrist and elbow. No variation of the nerve compound potential was observed during stages A through C. In stage A, the localizing algorithm was able to discriminate the individual finger representation in accordance with the somatotopic organisation of the sensory homunculus. It was observed that the ECDs responsible for the cortical responses from the unanesthetized finger were significantly changing following a relatively brief period of sensory deprivation from the adjacent fingers. Such changes of the ECDs with respect to the control conditions were characterized by an increase in strength and deepening for the middle finger, and by a shift on the coronal plane for the thumb and the little finger (medial for the former, lateral for the latter). Such changes became progressively evident in stage B, but were persisting in stage C.

Surgical indication in children with congenital hemiparesis.

Nine children with perinatal occlusion of the middle cerebral artery, resulting in unilateral enlargement of one lateral cerebral ventricle associated with cortical atrophy and subcortical cavity formation, were operated on because of intractable epilepsy. All subjects exhibited mild to severe hemiparesis, localized in the right side of the body in six instances and in the left side in the three cases. All but one patient presented with some degree of psychomotor retardation. The surgical treatment consisted of the removal of the atrophic cerebral cortex. One child died after surgery because of disseminated intravascular coagulation. All the remaining eight children benefited from the operation, with a decrease in the hypertonia of the affected limbs and an improvement in dexterity and gait as well as in intellectual performance. Five patients could be considered seizure-free following the surgical treatment, and the remaining three experienced a significant reduction in the frequency of the seizures.

Neuromagnetic somatosensory homunculus: a non-invasive approach in humans.

The somatosensory homunculus has been identified during stimulation of median (at wrist and elbow), femoral, tibial and pudendal nerves of the left hemibody via the neuromagnetic imaging technique. The somatic representations of different body districts have been localized in the somatosensory cortex, by means of an equivalent dipole localization algorhythm. Dipole locations agree with the well-known somatotopic organization obtained with invasive techniques. The proposed method is, therefore, an important investigating tool for studies on normal and diseased subjects.

Multichannel hybrid system for neuromagnetic measurements.

This paper describes progress toward the development of a 28-multichannel system for neuromagnetic measurements. A novel 'hybrid' design consisting of 16 first-order axial gradiometers and 12 first-order planar gradiometers was chosen, which optimises the use of the available cylindrical volume of the dewar tail. This configuration maintains the symmetry of the detected pattern with respect to rotation of a biomagnetic source located under the centre of the array and features a localisation power considerably better than an array of all first-order planar gradiometers. The detecting array permits simultaneous magnetic measurements over a circular scalp region of 16 cm diameter. The magnetic sensors used are Nb/PbAuIn DC SQUIDs fabricated at the IBM. The devices incorporate resonant damping resistors shunting the inductance, resulting in smooth flux-voltage characteristics and, consequently, very low noise figures in a flux-locked loop configuration. A simple and low cost electronic system has been designed and fabricated for the DC SQUID sensors.

Evoked alpha- and mu-rhythm in humans: a neuromagnetic study.

We present the results of a neuromagnetic study on the spatial structure of brain rhythms enhanced by photic and somatosensory stimulation, as measured on the occipital, rolandic and frontorolandic regions in humans. It emerges that, while it is always possible to drive the cerebral activity during sustained stimulation at any given frequency, only certain specific frequencies can produce prolonged synchronization (i.e. the oscillating activity elicited by the repetitive stimulation continues well beyond its termination). In both studied modalities we were able to localize equivalent sources for the synchronized responses; their relationship with the known evoked responses is discussed. In the visual modality the synchronization was characterized by a potentiation of the subjects' alpha-rhythm. In the somatosensory modality synchronization was reflecting two different activities: one probably related to the rolandic mu-rhythm, the second suggesting the presence of two widely separated and time correlated sources possibly driven by a unique, deep clock. Possible implications for other studies of the dominant brain rhythms, or experimental checks on specific brain models, as well as of the visual and somatosensory evoked responses are discussed.

Neuromagnetic topography of photoconvulsive response in man.

The neuromagnetic method was applied to the study of photoconvulsive responses. The identification of specific magnetic field distributions over the scalp was achieved by; (a) a stimulation paradigm consisting of series of trains of flicker stimuli randomly presented to the epileptic patient, after eye closure, to get epileptic responses while avoiding seizures; (b) a novel procedure for data analysis, to select consistent responses. These patterns, when sufficiently stable in time and dipolar in shape, were used for source localization in the usual biomagnetic framework of the equivalent current dipole source representation. The results of this approach suggest that different specific cortical areas are repeatedly and randomly activated, involving mainly the frontal, occipital and temporal areas, often with a hemispheric prevalence.

Simultaneous motor output and sensory input: cortical interference site resolved in humans via neuromagnetic measurements.

Neuromagnetic measurements were carried out during median nerve stimulation at the wrist in complete relaxation (a) and during active contraction of the hand muscles (b). Firstly, activity of the generator source responsible for the major component of the sensory evoked magnetic fields (SEFs) was mapped and localized during condition (a) and (b). Then the subtraction maps ((a)-(b)) were obtained and the virtual 'dipole' responsible for the 'interference' (less than or equal to SEFs amplitude) between the afferent input and the motor output was tridimensionally localized in a position compatible with the knee and the convexity of the postcentral gyrus.

Study of focal epilepsy by multichannel neuromagnetic measurements.

A systematic investigation of several cases of focal epilepsy has been performed in an unshielded environment using a 4-channel neuromagnetic sensor. The localizations provided by the magnetic measurements have been compared with clinical evidence and confirmed by X-ray findings, and in one case also by intracranial surgery. The results show the importance of simultaneous detection of magnetic fields at different sites of the scalp in order to get a dynamic view of the epileptic activity and to detect multifocal activity unsuspected on the basis of the EEG investigation.

Neuromagnetic characterization of the cortical response to median nerve stimulation in the steady state paradigm.

Magnetic methods for localizing evoked neural activity in the human brain have been used to search for evidence of a functional organization in primary somatosensory cortex. We have found that in response to median nerve stimulation the deduced source for the evoked component with a latency of 45 ms lies at a depth in the central sulcus that depends on stimulus repetition rate, whereas the sources of the 20 ms and 24 ms components lie at a fixed depth. Moreover we have identified this 45 ms component with the dominant sinusoidal feature characteristic of steady state response.