Hall effect in the accumulation layers on the surface of organic semiconductors.

We have observed the Hall effect in the field-induced accumulation layer on the surface of single-crystal samples of a small-molecule organic semiconductor rubrene. The Hall mobility muH increases with decreasing temperature in both the intrinsic (high-temperature) and trap-dominated (low-temperature) conduction regimes. In the intrinsic regime, the density of mobile field-induced charge carriers extracted from the Hall measurements, nH, coincides with the density n calculated using the gate-channel capacitance and becomes smaller than n in the trap-dominated regime. The Hall data are consistent with the diffusive bandlike motion of field-induced charge carriers between trapping events.

Intrinsic charge transport on the surface of organic semiconductors.

The air-gap field-effect technique enabled realization of the intrinsic (not limited by static disorder) polaronic transport on the surface of rubrene (C42H28) crystals over a wide temperature range. The signatures of this intrinsic transport are the anisotropy of the carrier mobility, mu, and the growth of mu with cooling. Anisotropy of mu vanishes in the activation regime at low temperatures, where the transport is dominated by shallow traps. The deep traps, introduced by x-ray radiation, increase the field-effect threshold without affecting mu, an indication that the filled traps do not scatter polarons.

Local and global processing of music in high-functioning persons with autism: beyond central coherence?

A multi-modal abnormality in the integration of parts and whole has been proposed to account for a bias toward local stimuli in individuals with autism (Frith, 1989; Mottron & Belleville, 1993). In the current experiment, we examined the utility of hierarchical models in characterising musical information processing in autistic individuals. Participants were 13 high-functioning individuals with autism and 13 individuals of normal intelligence matched on chronological age, nonverbal IQ, and laterality, and without musical experience. The task consisted of same-different judgements of pairs of melodies. Differential local and global processing was assessed by manipulating the level, local or global, at which modifications occurred. No deficit was found in the two measures of global processing. In contrast, the clinical group performed better than the comparison group in the detection of change in nontransposed, contour-preserved melodies that tap local processing. These findings confirm the existence of a "local bias" in music perception in individuals with autism, but challenge the notion that it is accounted for by a deficit in global music processing. The present study suggests that enhanced processing of elementary physical properties of incoming stimuli, as found previously in the visual modality, may also exist in the auditory modality.

Clinical and MRI long term evolution of intracavernous and carotid ophtalmic artery aneurysms, treated by common carotid ligation.

In four large, 15-25 mm, internal carotid artery aneurysms (3 intracavernous and 1 carotid ophthalmic), treatment by common carotid ligation was preferred. Pre- and postoperative MRI were obtained, at a delay between 5 to 9 years. Recovery of the ocular and visual symptomatology was a function of the role played by mechanical and/or ischaemic factors. No early or late consequences, ascribable to the common carotid ligation, were observed. Aneurysmal thrombosis occurred in the first postoperative week, but retraction of the thrombosed aneurysms was only obvious and maximal after several months. For this reason, rapid clinical recovery could be due, in the first instance, to the loss of aneurysmal pulsatility. Complete disappearance of the aneurysm was observed in two cases. In the other two, a small remnant of the initial lesion, without any unfavourable consequences, was revealed, respectively 6 and 9 years after the intervention, by current, modern-days, MRA.

Local bias in autistic subjects as evidenced by graphic tasks: perceptual hierarchization or working memory deficit?

In the present study, copying tasks were used to assess hierarchical aspects of visual perception in a group of 10 nonsavant autistic individuals with normal intelligence. In Experiment 1, the hierarchical order of graphic construction and the constancy of this order were measured for the copying of objects and nonobjects. In comparison to control participants, autistic individuals produced more local features at the start of the copying. However, they did not differ from controls with respect to graphic constancy. Experiment 2 measured the effect of geometrical impossibility on the copying of figures. Results revealed that autistic individuals were less affected by figure impossibility than were controls. Therefore, these experiments seem to support the notion of a local bias for visual information processing in individuals with autism. Two interpretations are proposed to account for this effect. According to the hierarchical deficit hypothesis, individuals with autism do not manifest the normal global bias in perceiving scenes and objects. Alternatively, the executive function hypothesis suggests that autism brings about limitations in the complexity of information that can be manipulated in short-term visual memory during graphic planning.

The changing face of children's health: a positive state perspective.

In the midst of health care cutbacks, imposed or increasing copays, and managed care crises, the face of children's health care is undergoing significant changes. These, quite fortunately for the children of Texas, are positive changes, including the establishment of the Texas Healthy Kids Corporation and utilization of the newly implemented Children's Health Insurance Plan.

The influence of desmopressin on blood loss during spinal fusion surgery in neuromuscular patients.

STUDY DESIGN: A double-blind study comparing the effects of desmopressin and a placebo (normal saline) on blood loss during spinal instrumentation for neuromuscular scoliosis. OBJECTIVE: To determine the effectiveness of desmopressin acetate (DDAVP) in reducing operative blood loss in hemostatically normal patients undergoing spinal fusion surgery for neuromuscular scoliosis. SUMMARY OF BACKGROUND DATA: Desmopressin acetate has been shown to improve bleeding times and to provide surgical hemostasis in patients with platelet disorders. Its effect in reducing bleeding times in normal patients has been the subject of debate in several surgical specialties. Recent observations that DDAVP seems to reduce bleeding times and blood loss in patients undergoing spinal surgery for neuromuscular scoliosis warranted a more focused analysis on its role in this surgical procedure. METHODS: Patients undergoing surgery for neuromuscular scoliosis were randomly assigned to receive DDAVP or placebo. Bleeding times and plasma clotting factors were measured before the administration of the DDAVP or placebo and 60 minutes after. Operative blood loss was carefully measured. RESULTS: Although the administration of DDAVP decreased overall blood loss by an average of 19% compared with blood loss in the placebo group and blood loss per vertebra fused by an average of 15%, these results were not statistically significant. CONCLUSIONS: Bleeding time and blood loss seem to respond better to DDAVP in some patients, in whom significant decreases were observed, than they do in others. The problem is in identifying those patients in whom a decrease in bleeding time will be elicited after administration of DDAVP. Preoperative administration of DDAVP to such patients should significantly decrease operative blood loss.

The association of tranexamic acid and nimodipine in the pre-operative treatment of ruptured intracranial aneurysms.

In the scope of a late intervention policy on ruptured intracranial aneurysms, on D.+12 on an average, we first used tranexamic acid, at moderate doses: 3 g orally or 1.5 g intravenously per day. We, subsequently, added nimodipine, usually 240 mg orally per day or 2 mg intravenously per hour. The medical treatment consisted of amply sufficient hydration, and in systematic and regular administration of analgesics and sedatives. Hypotension was absolutely avoided; if necessary, an antihypertensive treatment was prescribed very cautiously. Phenytoin was regularly given. In the present study, we try to answer the following questions: (1) Can we confirm that the preventive action of tranexamic acid remains as effective, when doses, markedly lower than usually recommended, are used? (2) Does nimodipine prevent the increase of pre-operative ischaemic complications, which should be expected when tranexamic acid is administered? Amongst 101 patients with SAH of proven aneurysmal origin, 84 were treated with tranexamic acid and nimodipine. In 25 patients, an aneurysm was not visualised; 21 received this treatment. For several reasons, only a retrospective study was possible, to evaluate the results of our antifibrinolytic and calcium-blocking therapies, on rebleeding and pre-operative delayed ischaemia. We compared, therefore, similar cases from the literature, with our own cases, taking into consideration the clinical grades, the days of admission and of intervention, the moment of rebleeding and of delayed pre-operative ischaemia, etc. The following impressions emerge: (1) same effectiveness of moderate doses of tranexamic acid; (2) no increase of pre-operative delayed ischaemic complications, in comparison with patients not receiving antifibrinolytics but nimodipine; (3) important role of a devastating initial bleed and of operative complications; (4) difficulty of avoiding rebleeding at D.0, whatever the therapeutic measures, medical and/or surgical.

Midazolam reduces vomiting after tonsillectomy in children.

The purpose of this study was to assess the effect of midazolam on vomiting after tonsillectomy in children. We compared 215 children aged 1.5-14 yr undergoing tonsillectomy or adenotonsillectomy under general anaesthesia with nitrous oxide and halothane. In a double-blind fashion the subjects were administered either placebo or midazolam 75 micrograms.kg-1 iv after induction of anaesthesia. After the operation, the number of emetic episodes and the length of stay in hospital were recorded. The groups were similar with respect to age, weight, sex, mode of induction, duration of anaesthesia, surgical procedure, opioid administration and length of stay in the PAR and the Day Care Surgical Unit. The 108 midazolam-treated children had a lower incidence (42% vs 57%) of vomiting than the placebo group, P < 0.02. The placebo group had a higher incidence (9% vs 2%) of unscheduled admissions to hospital due to nausea and vomiting, P < 0.05. It is concluded that midazolam administered intravenously to children intraoperatively reduces vomiting after tonsillectomy.

Pathogenetic factors in chronic subdural haematoma and causes of recurrence after drainage.

The radiological aspect, pathology, treatment and results of 132 subdural haematomas observed in 100 patients, are discussed. The majority of these cases were characterized by a nonhomogenous CT scan picture, resulting from repeated bleeding in a previous subdural haematoma evolving to chronicity, or in a pre-existent subdural hygroma. Taking aspirin may have constituted a predisposing factor in 16% of our patients, whilst coagulation disturbances, including anticoagulant treatment, were observed in another 6%; ethylism was present in 11%. A traumatic origin was ascertained in 80% of the patients. The treatment consisted of burr hole evacuation and drainage in 91.5% of the haematomas, corresponding to 92% of the patients; it was eventually repeated once or twice in some cases. In 6% of the patients, a subduro-peritoneal drainage had to be placed ultimately and in 2%, a membranectomy had to be performed because the haematoma had become nearly completely fibrous. The necessity for repeated evacuation and eventual subduro-peritoneal drainage seems to depend mainly on a slow brain re-expansion in some elderly people, who are actually more frequently referred. Two patients died; one was deeply comatose and another in poor general condition. Morbidity in the 96 remaining patients, 2 being lost to follow-up, was 11%: 5% related to the haematoma or to the causal trauma, and 6% from other concomitant neurological disease. The functional result was satisfactory in 85%.