Unraveling quantum Hall breakdown in bilayer graphene with scanning gate microscopy.

Investigating the structure of quantized plateaus in the Hall conductance of graphene is a powerful way of probing its crystalline and electronic structure and will also help to establish whether graphene can be used as a robust standard of resistance for quantum metrology. We use low-temperature scanning gate microscopy to image the interplateau breakdown of the quantum Hall effect in an exfoliated bilayer graphene flake. Scanning gate images captured during breakdown exhibit intricate patterns where the conductance is strongly affected by the presence of the scanning probe tip. The maximum density and intensity of the tip-induced conductance perturbations occur at half-integer filling factors, midway between consecutive quantum Hall plateau, while the intensity of individual sites shows a strong dependence on tip-voltage. Our results are well-described by a model based on quantum percolation which relates the points of high responsivity to tip-induced scattering in a network of saddle points separating localized states.

Note: Improvement of the 3ω thermal conductivity measurement technique for its application at the nanoscale.

Conventional techniques for thermal conductivity measurements can lead to unreliable results when applied to nanostructures because heaters and temperature sensors needed for the measurement cannot have a negligible size and therefore perturb the result. In this paper, we focus on the 3ω technique, applied to the evaluation of the thermal conductivity of suspended silicon nanoribbons. We introduce a numerical approach based on the finite element solution of the electrical and thermal transport equations and compare its results with those of conventional methods. We show that with our approach we achieve an excellent fit of the experimental data, in particular, for nanostructured materials.

Monitoring of somatosensory evoked potentials during carotid endarterectomy.

Somatosensory evoked potentials (SEPs) were monitored in the course of 368 carotid endarterectomies (CEAs) carried out in 312 patients. In an initial group of 26 patients the shunt was used routinely while in a second group, involving 342 CEAs, it was applied selectively on the basis of modifications which the SEP underwent during clamping. The criterion for shunting was the progressive reduction, up to 50%, of the N20-P25 amplitude. New postoperative neurological deficits appeared in 6 patients, all of whom displayed a transitory SEP flattening. The SEPs of 2 of these returned to normal by the time they awoke and both showed a clinical deficit homolateral to the operated side. In only 2 cases did the deficit fail to regress completely and their postoperative CT scans revealed ischaemic lesions. A positive relationship emerged between SEP changes and back pressure values; nonetheless, as many as 75% of the patients with low residual back pressure values (less than 25 mmHg) tolerated the clamping. SEP monitoring appears to provide a reliable basis for selectively applying a shunt when there is a high risk of haemodynamic ischaemia during clamping.

Remote effects of cortical dysgenesis on the primary motor cortex: evidence from the silent period following transcranial magnetic stimulation.

OBJECTIVE: In cortical dysgenesis (CD), animal studies suggested abnormal cortico-cortical connections. Cerebral areas projecting to the primary motor cortex (M1) modulate the cortical silent period (CSP) following transcranial magnetic stimulation (TMS). Therefore, we used the CSP to investigate remote effects of CD on the M1. METHODS: A detailed investigation, including single-pulse TMS and electrical nerve stimulation, was performed in 3 consecutive adults with focal CD located outside the M1 and in 18 controls. Two patients with unilateral CD were epileptic and treated with anti-epileptic drugs. One patient with focal CD on both sides had no history of seizures. Neurological examination was normal in all patients. Recordings were made from both first dorsal interosseous muscles. RESULTS: In CD patients, the CSP was significantly lengthened contralaterally to the affected hemispheres. In treated patients with unilateral CD, the interside difference of the CSP duration was also significantly increased. In contrast, excitability threshold, peripheral and corticospinal motor conduction studies, and peripheral as well as ipsilateral silent periods were not significantly modified. CONCLUSIONS: Our findings indicate that focal CD outside the M1 may produce CSP modifications, which are likely due to changes of afferent control.

[Clinical evaluation in the early diagnosis of tuberculous meningoencephalitis]. / La valutazione clinica nella diagnosi precoce di meningoencefalite tubercolare.

In this short review, the Author evaluates the most important diagnostic problems about tuberculous meningoencephalitis. Any inadequate therapy can alternate the clinical picture and the results of the cerebrospinal fluid examination, and the clinical evaluation may become very difficult. The neuroradiological findings (CT and MRI), even when correlated to the typical neuropathological features of the disease, could be very sensitive but not specific. An accurate evaluation of the clinical context and, above all, of the clinical history, is the best way to avoid a tardive diagnosis and inappropriate therapies, and to choose which diagnostic procedures must be performed. In the latest years, the immunodeficiency status related to HIV infection, and the mobility of many persons from geographic areas endemic for TBC stressed the importance of this diagnosis. The extreme variability of the clinical picture is discussed, and the author describes the common manifestations as well as the rare syndromes associated with this disorder. The review indicates also the diseases with which the neurologist must challenge for a differential diagnosis. Some practical suggestions indicate how to minimize a diagnostic and therapeutic delay, for a disorder that in many cases is still lethal or leading to serious neurological complications or sequelae.

Improvement of the accuracy of noise measurements by the two-amplifier correlation method.

We present a novel method for device noise measurement, based on a two-channel cross-correlation technique and a direct "in situ" measurement of the transimpedance of the device under test (DUT), which allows improved accuracy with respect to what is available in the literature, in particular when the DUT is a nonlinear device. Detailed analytical expressions for the total residual noise are derived, and an experimental investigation of the increased accuracy provided by the method is performed.

Huge conductance peak caused by symmetry in double quantum dots.

We predict a huge interference effect contributing to the conductance through large ultraclean quantum dots of chaotic shape. When a double-dot structure is made such that the dots are the mirror image of each other, constructive interference can make a tunnel barrier located on the symmetry axis effectively transparent. We show (via theoretical analysis and numerical simulation) that this effect can be orders of magnitude larger than the well-known universal conductance fluctuations and weak localization (both less than a conductance quantum). A small magnetic field destroys the effect, massively reducing the double-dot conductance; thus a magnetic field detector is obtained, with a similar sensitivity to a SQUID, but requiring no superconductors.

Simultaneous femoral nerve palsy due to hemorrhage in both iliac muscles.

A man aged 65 receiving low-dose anticoagulant therapy for a previous myocardial infarction suddenly developed a bilateral femoral nerve palsy. An abdominal CT scan showed small hemorrhages in both iliac muscles with consequent compression of the femoral nerves. The case is reported for its exceptional bilaterality.

The cerebrospinal fluid in the diagnosis of tuberculous meningoencephalitis: review of the literature.

We review the literature on the biochemical, cytological and immunological changes in the cerebrospinal fluid (CSF) in tuberculous meningoencephalitis, emphasizing the inconsistency and low specificity of the CSF findings described in classic accounts of this disease. We consider separately the possible causes of yellow or bloody fluid. The development of accurate techniques of analysis does not diminish the importance of the clinical findings and history in the early diagnosis of this disease.

The relevance of transcranial Doppler to ischemic stroke outcome.

To assess the value of transcranial Doppler examination for the early prognosis of ischemic stroke, we examined 24 patients (15 males and 9 females, mean age 66.8 +/- 9.3 years) with hemispheric cerebral infarction, within 6 hours of stroke onset. Of these 24 patients, 22 were evaluated on the Canadian Neurological Scale, the Toronto Stroke Scale, and the Barthel Index on days 60 and 120. Mean flow velocity in the middle cerebral artery on the lesion side was measured and values outside the range 30 to 80 cm/sec were rated abnormal. Two of nine patients with normal flow velocity died compared to five of the 13 patients with abnormal values. Four of the seven remaining patients in the former group made a full recovery compared with none of the remaining eight patients in the latter group (P less than 0.05). Neurological and functional status measured on the scales used on days 60 and 120 were also significantly better in the group with normal flow velocity. Early transcranial Doppler may prove useful in predicting the outcome of hemispheric infarction in the acute phase of cerebral ischemia.

[Loss of psychic autoactivation syndrome: bilateral lacunae of the neostriatum. Clinico-radiological study of 2 cases]. / Athymormia syndrome: lacune bilaterali del neostriato. Studio clinico-radiologico di due casi.

In two patients with lack of spontaneous activity and emotionality, without dementia or depression and in absence of other neurologic signs, the "athymormia syndrome" has been diagnosed. CT scan and MRI showed bilateral symmetrical lesions in basal ganglia. We discuss the possible pathophysiological basis of the syndrome and the recent data about the functional connections among basal ganglia, frontal cortex and limbic system.

Electric and CO2 laser SEPs in a patient with asymptomatic syringomyelia.

We recorded electrically stimulated somatosensory evoked potentials (electric SEPs) and pain-related SEPs following CO2 laser stimulation (CO2 laser SEPs) from a 17-year-old patient affected by myotonic dystrophy whose MRI disclosed a large syrinx extending from spinal level C2 to S3. Careful clinical and electromyographic examinations revealed no motor or sensory disturbances, apart from myotonia. The only abnormality noted in median and ulnar nerve short-latency electric SEPs (recorded with a non-cephalic reference electrode) was the absence of cervical component N13, the other SEP responses (N9, N10, N11, P14, N20) being normal. The cutaneous pain threshold and CO2 laser SEPs (both obtained by a CO2 laser beam applied to the back of the hand) were normal. Thus cervical component N13 appears to be highly sensitive to the effects of central cord lesions, even when these are asymptomatic.

Primary antiphospholipid syndrome: two case reports, one with histological examination of skin, peripheral nerve and muscle.

Two cases of primary antiphospholipid antibody syndrome are reported. One patient presented multiple abortions and epilepsy. The second patient was affected by a brain vascular accident, with a residual hemiparesis. Both cases showed livedo reticularis in arms, NMR evidence of diffuse lesions of the white matter, high serum levels of anticardiolipin antibodies and cardiopathy. Lupus anticoagulant was also found in the serum of the first patient, and cortisone and antiaggregants enabled her to reach term in a fifth pregnancy after four miscarriages. In the other case histological examination of specimens of skin, peripheral nerve and skeletal muscle revealed occlusive, non arteriosclerotic vasculopathy and an absence of inflammatory lesions. Histological study has rarely been performed in primary antiphospholipid syndrome but suggests that the mechanism of thrombosis is not vascular; in our subjects it revealed findings similar to those in Sneddon syndrome.

Familial AL-amyloidosis in three Italian siblings.

BACKGROUND AND METHODS: Familial occurrence of immunoglobulin-related (AL) amyloidosis has occasionally been reported. In this work we describe the concomitance of systemic amyloidosis and monoclonal gammopathy (one case of Waldenström's macroglobulinemia and two cases without multiple myeloma or related diseases) in three Italian siblings, two males and one female. RESULTS AND CONCLUSIONS: All of them showed a common pattern of polyneuropathy to different degrees; two presented a sicca syndrome and one also suffered from nephropathy. Two of them showed the same HLA typing with the same light chain type (k), but had different presenting symptoms. Polyneuropathy and a history of peptic disease in two cases was suggestive of type III familial amyloidotic polyneuropathy (FAP) occurring in the setting of a familial monoclonal component. However, immunohistochemical studies on different tissue specimens using anti-apolipoprotein A1 and anti-transthyretin antibodies were negative. Further screening of DNA samples for transthyretin (TTR) gene mutations was also negative. Clinical and laboratory investigations ruled out reactive or senile amyloidosis and immunohistochemical studies with anti-light chain antibodies on amyloidotic tissue specimens were positive. As a consequence, this family represents a new case of familial AL-amyloidosis.