Spatially Resolved Spin-Injection Probability for Gallium Arsenide

We report a large spin-polarized current injection from a ferromagnetic metal into a nonferromagnetic semiconductor, at a temperature of 100 Kelvin. The modification of the spin-injection process by a nanoscale step edge was observed. On flat gallium arsenide [GaAs(110)] terraces, the injection efficiency was 92%, whereas in a 10-nanometer-wide region around a [111]-oriented step the injection efficiency is reduced by a factor of 6. Alternatively, the spin-relaxation lifetime was reduced by a factor of 12. This reduction is associated with the metallic nature of the step edge. This study advances the realization of using both the charge and spin of the electron in future semiconductor devices.

Economic analysis of adjuvant therapy with interferon alpha-2a in stage II malignant melanoma

Using the trial demonstrating that interferonalpha-2a (IFNalpha-2a) is efficacious as adjuvant therapy in stage II melanoma, we evaluate its outcomes and economic consequences. Using rates observed in the 5-year trial and published figures, survival and Q-TWIST (Time Without Symptoms and Toxicity) were extrapolated to a 10-year and lifetime horizon. Cost analysis was performed using the trial's data, published literature and experts' opinions from the perspective of the French Sickness Funds. Patients in the IFNalpha-2a-group have an additional 0.26 years in life-expectancy over a 5-year time period (P=0.046), 0.67 years over a 10-year period and 2.59 years over a lifetime. Cost per life-year-gained was estimated at approximately 14400 after 5 years, 6635 after 10 years and 1716 over a lifetime. Assuming that there is an improvement in disease-free survival only, cost is 26147 per Q-TWIST. Cost-effectiveness of IFNalpha-2a in stage II melanoma compares favourably with estimates for widely used therapies in the oncological field.

Creutzfeldt-Jakob disease guidelines: a regional approach

Creutzfeldt-Jakob Disease (CJD) is an infectious, progressive, degenerative neurological disorder. Unique CJD Precautions must be adhered to as the infectious agent is difficult to destroy. A regional group in Hamilton-Burlington Ontario developed CJD guidelines based on critical review of the current evidence of transmission in a Canadian healthcare environment, current published standards of practice in North America, the United Kingdom and Australia; and principles of laboratory and patient care safety as well as expert opinion.

Microscopic view of a two-dimensional lattice-Gas ising system within the grand canonical ensemble

A reversible 2D critical transition is observed on the GaAs(001) surface and modeled as a lattice-gas Ising system. Without depositing any material, 2D GaAs islands spontaneously form. The order parameter, four critical exponents, and coupling energies are measured from scanning tunneling microscope images of the microscopic domain structure and correlation functions as a function of temperature and pressure. Unprecedented insight into the domain structure of a 2D Ising system through the critical point and a complete Hamiltonian for modeling the GaAs(001) surface are presented.

Guidance for the performance evaluation of three-dimensional air quality modeling systems for particulate matter and visibility

Guidance for the performance evaluation of three-dimensional air quality modeling systems for particulate matter and visibility is presented. Four levels are considered: operational, diagnostic, mechanistic, and probabilistic evaluations. First, a comprehensive model evaluation should be conducted in at least two distinct geographical locations and for several meteorological episodes. Next, streamlined evaluations can be conducted for other similar applications if the comprehensive evaluation is deemed satisfactory. In all cases, the operational evaluation alone is insufficient, and some diagnostic evaluation must always be carried out. Recommendations are provided for designing field measurement programs that can provide the data needed for such model performance evaluations.

Electrophysiological changes in hippocampal slices isolated from rats embedded with depleted uranium fragments

Although nephrotoxicity is considered to be the most serious consequence of uranium exposure, several studies have previously suggested the potential for neurotoxicity. In Operation Desert Storm, U.S. military personnel were wounded by fragments of depleted uranium (DU). This study was initiated to test the potential for DU fragments to cause electrophysiological changes in the central nervous system. Rats were surgically implanted with pellets of DU or tantalum (Ta) as a control metal. After 6, 12 and 18 months rats were euthanized, hippocampi removed and electrophysiological potentials analyzed by extracellular field potential recordings. Six months after implantation, synaptic potentials in DU-exposed tissue were less capable of eliciting spikes (E/S coupling). At 12 months, amplitudes of synaptic potentials were significantly increased in tissue from DU treated rats compared to Ta controls. E/S coupling was reduced. The differences between the electrophysiological measurements in DU-treated and control tissue were no longer evident at the 18 month time point. An analysis of the changes in the synaptic potentials and E/S coupling over the three time points suggests that by 18 months, the effects of aging and DU exposure converge, thereby obscuring the effects of the metal. Since kidney toxicity was not evident in these animals, effects secondary to nephrotoxicity are unlikely. This study raises the possibility that physiological changes occur in the brain with chronic exposure to DU fragments, which could contribute to neurological deficits.

Pulmonary hypertension, family and environment

The focus of interest on pulmonary hypertension (PH) has come through recent therapeutic advances which prolong and improve quality of life. From this interest, recent observations form family studies indicate that a gene located on chromosome 2 is associated with PH. Environmental factors, the use of an anorectic agent, dexfenfluramine, has been associated with a risk of developing primary PH. A link with hypoxic induced PH has emerged in that a strain of rat, the fawn-hooded rat (FHR) which has a susceptibility to developing PH with mild hypoxia has an inherited storage defect to serotonin. Dexfenfluramine, by inhibiting the serotonin transporter, produces a similar pattern of disturbance of biogenic amine metabolism. This observation provides some insight into potential mechanisms for this complex disorder.

External cervical resorption: a case study using orthodontic extrusion

A case is presented of external cervical resorption detected on routine 6-monthly examination. Following root canal therapy orthodontic extrusion and pericision, the tooth was restored using a radicular retained post and core supporting a porcelain bonded to gold full coverage crown.

The determinants of treatment duration for congenital muscular torticollis

BACKGROUND AND PURPOSE

Although the success of conservative management of congenital muscular torticollis has been well documented, relatively little is known about the determinants of response to treatment, such as treatment duration. The purpose of this study was to determine how factors such as severity of restriction of range of motion, age at initiation of treatment, and presence of a palpable intramuscular fibrotic sternocleidomastoid muscle mass affect treatment duration.

SUBJECTS

One hundred one children (mean age = 4 months, SD = 2.87, range = 0.5-15.5) who were diagnosed with congenital muscular torticollis and referred to physical therapy at British Columbia's Children's Hospital (Vancouver, British Columbia, Canada) prior to 2 years of age were included in the study.

METHODS

Following a standardized initial assessment, parents were taught the home treatment program, which included passive stretches of the affected sternocleidomastoid muscle and strengthening exercises for the contralateral side, and positioning and handling skills. Evaluation at 2-week intervals included measurement of passive neck rotation and lateral flexion using an adapted standard goniometer. Treatment duration was defined as the time between initiation of treatment and achievement of full passive neck range of motion.

RESULTS

Complete recovery (full passive range of motion) was achieved in all but one of the children in this sample. The mean treatment duration was 4.7 months (SD = 5.06, range = 1-36). Correlations were noted between severity of restriction and treatment duration (r = .31) as well as between presence of a mass and treatment duration (r = .26). Multiple regression analysis revealed that severity of restriction was the strongest predictor of treatment duration.

CONCLUSION AND DISCUSSION

The results of this study will make it possible for therapists to better predict treatment duration at the time of the initial assessment. By providing parents with more precise information about the length of treatment, parents may be more willing to adhere to the exercise program. [Emery C. The determinants of treatment duration for congenital muscular torticollis.

Wegener's granulomatosis: a case study in general dental practice

Wegener's granulomatosis is a disease involving renal, lung and vascular tissue, but patients also present to the general dental practitioner with intra-oral manifestations. This case study describes the early onset, progression and treatment of the presenting intra-oral manifestations and the periodontal and endodontic implications of Wegener's granulomatosis.

Endothelial control of the pulmonary circulation in normal and chronically hypoxic rats

1. The effect of blockade of nitric oxide synthesis in pulmonary endothelium by two L-arginine analogues was tested in isolated blood-perfused lungs of normal rats and rats exposed chronically to 10% O2. 2. In both groups of rats the analogues (N-monomethyl-L-arginine (L-NMMA) and N-nitro-L-arginine methyl ester (L-NAME)) enhanced hypoxic vasoconstriction. In normal rats, with rare exceptions, these analogues had little or no effect on pulmonary artery pressure (Ppa) at constant blood flow during normoxia. However, chronically hypoxic rats have pulmonary hypertension and in these rats the analogues always raised Ppa; the rise in Ppa after L-NMMA but not L-NAME could be partially reversed by L-arginine. L-NAME was more potent than L-NMMA. 3. To see whether the difference between rat groups was due to the high Ppa in chronically hypoxic rats, in control rats we raised Ppa passively by lung inflation to values higher than found in chronically hypoxic rats. L-NAME did not alter the effects of lung inflation on Ppa. 4. Ppa was also raised passively by plotting pressure-flow lines up to high flow rates; the lines were changed minimally by both analogues in control rats but in chronically hypoxic rats the lines were raised to higher pressures and steepened substantially. 5. In control rats, during vasoconstriction caused by hypoxia, endothelin 1 and almitrine, L-NAME caused further rises in pressure. We conclude that a stimulus for nitric oxide release in control rats is the narrowing of vessels caused by vasoconstriction rather than passive increases in intravascular pressure. 6. In chronically hypoxic rats arterioles are narrowed by growth of new muscle and there is some muscle tone even in normoxia. Thus narrowing of the vascular lumen is the stimulus common to both groups of rats which leads to nitric oxide synthesis and attenuation of Ppa by a negative feedback process. Narrowing is associated with a large increase in shear stress due to two factors; the pressure drop along a vessel segment is increased and the surface area of the lining of the affected segment is decreased. 7. Atrial natriuretic peptide caused dose-dependent pulmonary vasodilation in both rat groups but had a greater effect in chronically hypoxic rats. The action persisted and was enhanced after blockade of NO synthesis.

Effects of ligustrazine on the pressure/flow relationship in isolated perfused rat lungs

Ligustrazine, the synthesized principle of a Chinese herbal remedy shown previously to be a pulmonary vasodilator, was tested in chronically hypoxic and normal rats. Pressure/flow, (P/Q), relations were measured in isolated perfused lungs during normoxia, hypoxia and after reversal of hypoxic vasoconstriction by increasing doses of ligustrazine. P/Q lines were linear over a wide range and extrapolation to the pressure axis gave an intercept which was the effective downstream pressure for flow. In chronically hypoxic rats the slope of the line was steeper and the intercept greater than in control rats, which we attributed to newly muscularized arterioles with tone. Hypoxia caused an increase in slope and intercept in both groups but the intercept increase was greater in chronically hypoxic rats. In both groups of rats increasing doses of ligustrazine given during continued hypoxia caused a fan of lines which moved progressively towards the control normoxic line. In chronically hypoxic rats it required only 2 mg of ligustrazine to bring the line back to the normoxic position, whereas in controls it required 4 mg. In chronically hypoxic rats the change in intercept with every dose was greater than in control rats; this suggests that ligustrazine mainly relaxes the muscle of small collapsible vessels. The action of ligustrazine remained in both control and chronically hypoxic rats after administration of an arginine analogue which blocks synthesis of the endothelial relaxant factor nitric oxide. This and previous evidence suggest that ligustrazine is a non-endothelial-dependent pulmonary vasodilator.

Effects of ligustrazine on the pressure/flow relationship in isolated perfused rat lungs

Ligustrazine, the synthesized principle of a Chinese herbal remedy shown previously to be a pulmonary vasodilator, was tested in chronically hypoxic and normal rats. Pressure/flow, (P/Q), relations were measured in isolated perfused lungs during normoxia, hypoxia and after reversal of hypoxic vasoconstriction by increasing doses of ligustrazine. P/Q lines were linear over a wide range and extrapolation to the pressure axis gave an intercept which was the effective downstream pressure for flow. In chronically hypoxic rats the slope of the line was steeper and the intercept greater than in control rats, which we attributed to newly muscularized arterioles with tone. Hypoxia caused an increase in slope and intercept in both groups but the intercept increase was greater in chronically hypoxic rats. In both groups of rats increasing doses of ligustrazine given during continued hypoxia caused a fan of lines which moved progressively towards the control normoxic line. In chronically hypoxic rats it required only 2 mg of ligustrazine to bring the line back to the normoxic position, whereas in controls it required 4 mg. In chronically hypoxic rats the change in intercept with every dose was greater than in control rats; this suggests that ligustrazine mainly relaxes the muscle of small collapsible vessels. The action of ligustrazine remained in both control and chronically hypoxic rats after administration of an arginine analogue which blocks synthesis of the endothelial relaxant factor nitric oxide. This and previous evidence suggest that ligustrazine is a non-endothelial-dependent pulmonary vasodilator.

Structure and function of the carotid body in New Zealand genetically hypertensive rats

Morphology of the carotid body and the ventilatory response to hypoxia were compared in New Zealand genetically hypertensive rats and 'normotensive' control rats from the same genetic stock. Hypertensive rats grew more slowly, had higher blood pressure from 6 weeks of age and developed left ventricular hypertrophy. Carotid bodies of both groups were similar in size but larger than those of a common Wistar strain. Intimal damage and proliferation were seen in 1st- and 2nd-order branches of the carotid body artery in hypertensive rats and point-counting showed that the volume proportion of Type 1 cell nuclei and vascular lumen was reduced and vascular wall increased. In age-matched anaesthetized rats, minute ventilation per 100 g was greater in hypertensives than 'normotensive' when inspiring O2 concentrations of 30, 21, 18, 15, 12, 10 and 8%. However, at each inspired O2 concentration, arterial Pa.O2 was higher and Pa.CO2 lower in hypertensive than in 'normotensive' rats. Hypertensive rats were hyperventilating. The shape of the ventilation/O2 tension curve was similar in hypertensive and 'normotensive' rats; thus carotid body sensitivity to hypoxia was probably unchanged. Possible causes of hyperventilation and the relation of carotid body morphology to hypertension are discussed.