Processing and Creep Resistance of Nickel/Yttria Composites

In this study, pure nickel and yttria (Y2O3) were selected as a model system to investigate the feasibility of processing metal matrix composites (MMCs) through a powder metallurgy approach for the in-situ formation of a continuous three-dimensional reinforcement network or the in-situ formation of discrete reinforcements with certain degrees of interconnected clusters. Composites with a volume fraction of Y2O3 ranging from 20 to 50 % were prepared through hot pressing. The density, microstructure and creep resistance of these composites were evaluated as a function of the yttria volume fraction. It was found that a continuous Y2O3 network was formed in composites with 40 and 50 vol % Y2O3, while yttria was discrete with some degrees of interconnected clusters in composites with 20 and 30 vol % Y2O3. The creep rate was reduced by two to three orders of magnitude with the addition of 20 to 30 vol % Y2O3, and it continued to decrease with increasing the volume fraction of yttria to 50%. The analysis indicated that the load transfer to isolated yttria particles could not account for the improved creep resistance of composites with 20 and 30 vol % Y2O3, while the load transfer to a continuous yttria network in composites with 40 and 50 vol % Y2O3 could not be approximated by the model of the load transfer to continuous fibres. The discrepancies are believed to be related to the presence of interconnected yttria clusters, the low relative density of the yttria phase in the composite, and the low load-carrying capability through a three-dimensional network in comparison with the load-carrying capability through continuous fibres. It is suggested that the density of the yttria phase and hence the creep resistance of the composite can be further improved over what have been obtained in this study by densifying the composite at high temperatures and pressures.     

Multiple sclerosis: basic immunology

A 24-year-old male presented with a 4 year history of a crusted erythematous papular eruption of the scalp and external auditory meati and a 12 month history of painful perianal ulceration. A diagnosis of Langerhans cell histiocytosis was made and confirmed by skin histology. Extensive investigation revealed no systemic involvement. Rapid improvement occurred after intravenous 2-chlorodeoxyadenosine but relapse of perianal lesions occurred within 5 months. Local radiotherapy to the perianal region resulted in a complete remission sustained over 12 months.     

Diffusion in mercury cadmium telluride—an update

The various diffusion coefficients (self-diffusivity, chemical self-diffusivity compositional diffusivity, impurity diffusivity) are defined. The conditions required for the observation of a Kirkendall effect are described. There is good agreement in the results for Hg and for Cd self-diffusion. The evidence suggests that the self-diffusivity is largely independent of P_Hg above ~300°C but shows an increase as Hg saturation is approached (for both Hg and Cd). Good agreement is also found in the Arrhenius parameters describing the movement of the p to n conversion boundary. Modeling of this diffusion boundary does, however, raise problems which are discussed. The situation in compositional interdiffusion is more complex: above ~400°C, reasonable agreement exists between various workers for large x_Hg but not for small values; below 400°C, substantial disagreement is evident. In impurity diffusion exhibits both erfc and non-erfc profiles for reasons which are unclear. Good agreement is found between In diffusivity measurements at high In concentrations: at low concentrations, the diffusivity decreases dramatically. As diffusion yields erfc profiles with good agreement again being found: a notable feature is the P_Hg dependence of the As diffusivity. Where appropriate, diffusion models are discussed.     

Polarisation-independent 20 Gbit/s soliton data transmission over12500 km using amplitude and phase modulation soliton transmissioncontrol

Polarisation-independent error-free 20 Gbit/s soliton data transmission over 12500 km with flat system Q dependence on distance, has been demonstrated using static filtering and a semiconductor polarisation-independent amplitude and phase modulator for soliton transmission control     

Blood flow in free muscle flaps measured by color Doppler ultrasonography

Color Doppler ultrasonography, a noninvasive method for studying changes in blood flow, has been used to monitor 18 patients with free microvascular lower limb muscle flaps. The peak, mean, and minimum velocities, resistance indices, and diameters of the flap pedicle arteries and also of the limb recipient arteries proximal to the microvascular anastomoses were measured at 2 and 6 weeks and 3, 6, and 9 months after surgery. The peak velocities did not significantly differ from each other, but the mean velocity in the flap pedicle arteries was 12.5% higher than that in the recipient arteries throughout the study period. End diastolic velocity in the pedicle was positive (toward the ultrasound probe) at 2 weeks (mean, 2 cm/sec, SD 10), 6 weeks (mean, 5 cm/sec, SD 16), and 3 months (mean, 3 cm/sec, SD 13) after surgery and significantly higher (P < 0.05) than at 6 months (mean, 7 cm/sec, SD 11), when the pattern of blood flow was normal forward/backward flow during systole/diastole. The resistance indices of the pedicle at 2 weeks (Ri = 0.978), 6 weeks (Ri = 0.936), and 3 months (Ri = 1.001) were significantly lower (P < 0.05) than at 6 months (Ri = 1.108), when the pedicle and recipient artery indices were the same. The diameter of the pedicle arteries was 14% smaller than those of the recipient arteries, but did not change during follow-up. This prospective clinical study shows that blood flow in the pedicle of a free microvascular muscle flap is increased until 6 months after surgery, mainly due to the increased minimum velocity of the pedicle in diastole and decreased resistance index. These findings can be attributed to the loss of vessel tone after denervation and are in accordance with earlier studies showing that denervated muscles lose their autoregulation and that blood flow increases, but that these phenomena subside with time. Increased blood flow in free muscle flaps can explain the high success rate of microanastomoses and positive effect on wound healing.     

MRI evaluation of the brain in infantile neuronal ceroid-lipofuscinosis. Part 2: MRI findings in 21 patients

The purpose of this study was to demonstrate the course of infantile neuronal ceroid-lipofuscinosis with brain magnetic resonance imaging (MRI) in children aged 3 months to 11 years. Twenty-one patients and 46 neurologically normal controls of the same age were examined. The images were evaluated visually; then signal intensities were measured and related to those of references. MRI abnormalities were detectable before clinical symptoms. The radiologic picture of the brain varied with the duration of the disease. Pathognomonic MRI findings in the early stage of the disease were generalized cerebral atrophy, strong thalamic hypointensity to the white matter and to the basal ganglia, and thin periventricular high-signal rims from 13 months onward on T2-weighted images. In patients over 4 years old, cerebral atrophy was extreme, and the signal intensity of the entire white matter was higher than that of the gray matter, which is the reverse of normal. This study showed that the abnormalities seen on MRI progress rapidly during the first 4 years of life, then stabilize, in conformity with the clinical and histopathologic pictures of infantile neuronal ceroid-lipofuscinosis.     

Endocrine and behavioural responses to noise stress: comparison of virgin and lactating female rats during non-disrupted maternal activity

The behavioural and endocrine responses to a 10 min white noise stress have been characterized in female virgin and undisturbed lactating Sprague-Dawley rats. Animals were continuously video-taped and frequent blood samples were collected using an automated sampling system. Noise stress caused hypothalamo-pituitary-adrenal (HPA) activation, as indicated by a rapid increase in plasma corticosterone and ACTH in the virgins: corticosterone concentrations peaked 20 min after initiation of the stress before declining rapidly back to basal concentrations. In contrast, noise stress had no significant effect on either plasma corticosterone or ACTH concentrations in the lactating animals. However, 72 h after weaning the corticosterone response of the ex-lactating rats was of comparable magnitude, but longer duration to that seen in the virgins. Plasma prolactin concentrations were significantly higher in the lactating animals and declined in response to the noise whereas, a transient but reproducible increase was seen in the virgin group. In situ hybridization revealed a significantly lower basal expression of CRF mRNA in the paraventricular nucleus of lactating rats as compared to the virgins, but noise stress had no further effect. Virgin animals showed behavioural responses to the stress, including an increase in the total activity, exploratory behaviours (rearing) and displacement behaviours (grooming). Lactating animals also showed behavioural responses to the noise, but their activities were principally directed towards the pups. These data show that although lactating rats showed normal behavioural reactivity to a psychological stress they showed no statistically significant activation of the HPA axis, suggesting a dissociation of behavioural and neuroendocrine responses to this mild stress.