Micro-reactors for characterization of nanostructure-based sensors.

Fabrication and testing of micro-reactors for the characterization of nanosensors is presented in this work. The reactors have a small volume (100 µl) and are equipped with gas input/output channels. They were machined from a single piece of kovar in order to avoid leaks in the system due to additional welding. The contact pins were electrically insulated from the body of the reactor using a borosilicate sealing glass and the reactor was hermetically sealed using a lid and an elastomeric o-ring. One of the advantages of the reactor lies in its simple assembly and ease of use with any vacuum/gas system, allowing the connection of more than one device. Moreover, the lid can be modified in order to fit a window for in situ optical characterization. In order to prove its versatility, carbon nanotube-based sensors were tested using this micro-reactor. The devices were fabricated by depositing carbon nanotubes over 1 µm thick gold electrodes patterned onto Si/SiO(2) substrates. The sensors were tested using oxygen and nitrogen atmospheres, in the pressure range between 10(-5) and 10(-1) mbar. The small chamber volume allowed the measurement of fast sensor characteristic times, with the sensors showing good sensitivity towards gas and pressure as well as high reproducibility.

Electrical characterization of multi-walled carbon nanotubes.

Electrical characteristics of multi-walled carbon nanotubes (MWNTs) grown by chemical vapor deposition have been investigated as a function of the bias voltage, nanotubes length and temperature, in 2 and 4 terminal configurations. Nanotubes were deposited over metal electrodes using ac dielectrophoresis method. For better contacts between the nanotubes and electrodes, Ni and Pd films were deposited by an electroless deposition technique. Differential conductance was found to rise considerably with bias, and this effect was more pronounced for Ni. Using 2 and 4 terminal configurations, electrical resistance measurements for individual MWNTs were performed, and the results were interpreted using the model of nanotube as a resistive transmission line, where current at low bias flows mainly through the two outermost shells.

Solitary fibrous tumor of the thoracic spine.

Intraspinal solitary fibrous tumors are rare: to our knowledge, the literature reports only 27 cases. We present a histologically and immunohistochemically confirmed solitary fibrous tumor involving the intradural extramedullary compartment of the thoracic spine. Microsurgical gross-total resection was achieved. A definitive role for adjuvant treatments in this type of tumor has not been established and therefore, they were not used. The patient was well, without clinical or radiological recurrence, 18 months after surgery.

[Atypical meningioma]. / Meningeomas invulgares.

One case of intradiploic meningioma, causing partial occlusion of the superior longitudinal sinus, with subsequent visual trouble and another of lipomatous meningioma with great fat content and very calcified, that was found in a LCR fistula study of the cranial anterior stage, are described by the authors as atypical meningiomas.

[Dementia as a result of dural vascular malformation]. / Demência resultante de malformação vascular dural.

A case of dementia can result from encephalopathy caused by venous hypertension, produced by a dural vascular malformation (DVM). The authors describe one tentorial DVM with sinusal venous drainage and retrograde reflux to the cerebral veins (type II), that originated a leukoencephalopathy, and a progressive demential symptomatology. This demential status partially regressed after surgical treatment.

Antibody avidity as a surrogate marker of successful priming by Haemophilus influenzae type b conjugate vaccines following infant immunization.

Evaluation of the new generation of conjugate vaccines is hampered by the absence of reliable surrogate markers of immunologic memory. Memory responses are characterized by rapid production of relatively high-avidity antibody; thus, a solid-phase ELISA was adapted for the measurement of anti-Haemophilus influenzae type b (Hib) IgG avidity. In a cohort of infants vaccinated at 2, 3, and 4 months of age with Hib conjugate vaccines, avidity increased in the period following vaccination, while antibody titer fell. After a booster dose at 1 year of age, both antibody titer and avidity increased. In a cohort with anti-Hib IgG <1.0 microg/mL following primary immunization, antibody avidity after booster was low, indicating an absence of priming. Antibody avidity may help distinguish, in persons with low antibody titers, between those who are primed for memory and those who are not.

Migraine and intracranial vascular malformations.

The relationships between migraine and A-V Malformations is a subject of controversy and the arguments are mainly based on case reports and retrospective data. To clarify this subject a structured inquiry and classification of headaches in large samples of patients with intracranial vascular malformations (IVM) is essential. The authors studied the prevalence of headaches in 51 patients with IVM admitted to our Department, between 1984 and 1992. The methods used were a review of medical records followed by a self-administered headache questionnaire and clinical interview using the IHS criteria for the diagnostic classification of headaches. The relative frequency of the different types of headaches was calculated and compared with the general population data. A correlative study of the headache characteristics with the type and location of the IVM was made. A high prevalence (47%) of migraine type headaches and a strong positive correlation (88.8%) between the site of AVM and side of the pain was found. This is highly suggestive but not conclusive of a pathophysiologic relationship between these entities. The conclusion drawn is that a prospective study of headaches by questionnaire or semi-structured clinical interview in patients with IVM is essential to discover the effective prevalence and characteristics of headaches associated with IVM and their relationships.

Posttraumatic epilepsy in civilians: clinical and electroencephalographic studies.

Posttraumatic epilepsy (PTE) is a known consequence of head trauma. The factors involved in posttraumatic seizures generation and the relationship between acute seizures and posttraumatic epilepsy are not without controversy. This also applies to the evolution of the electroencephalographic characteristics. The study here reported was performed analysing data from patients with posttraumatic epilepsy (N = 205) and data from patients followed-up since trauma and considered as a high risk population for the development of PTE (patients with acute seizures and/or patients with focal lesions--contusion, haematomas or penetrating head injury) (N = 152). Seizure type was associated with age and trauma severity (children, elderly and worst trauma cases present with a higher proportion of partial seizures). Neurological deficit and lesion location were associated with the seizure occurrence. The increased incidence of seizures was found when the most diffused brain dysfunction was combined with neurological deficits. The analysis of sequential EEGs performed at first, at 6th and 12 months post trauma revealed a non-stationary pattern throughout these time periods with EEG focal abnormalities remaining frequent for more than two years after the trauma. Children and old people have a higher proportion of EEG abnormalities with more frequent abnormal generalized activity in children and more frequent abnormal focal EEG activity in the elderly.

Controversies in posttraumatic epilepsy.

In civilian accidents the factors involved in the origin of posttraumatic epilepsy are controversial. In this study of 506 consecutive head trauma patients and 101 epileptic patients developing seizures after head trauma, we have examined the importance of the duration of coma, type of seizure and drug therapy, time to first seizure, age and focal lesions and compared our results with the literature. The importance is stressed of focal lesions and of neurological deficits for the origin of posttraumatic seizures.