Morphology dependent field emission of acid-spun carbon nanotube fibers.

Acid spun carbon nanotube (CNT) fibers were investigated for their field emission properties and performance was determined to be dependent on fiber morphology. The fibers were fabricated by wet-spinning of pre-made CNTs. Fiber morphology was controlled by a fabrication method and processing conditions, as well as purity, size, and type of the CNT starting material. The internal fiber structure consisted of CNT fibrils held together by van der Waals forces. Alignment and packing density of the CNTs affects the fiber's electrical and thermal conductivity. Fibers with similar diameters and differing morphology were compared, and those composed of the most densely packed and well aligned CNTs were the best field emitters as exhibited by a lower turn-on voltage and a larger field enhancement factor. Fibers with higher electrical and thermal conductivity demonstrated higher maximum current before failure and longer lifetimes. A stable emission current at 3 mA was obtained for 10 h at a field strength of <1 V µm(-1). This stable high current operation makes these CNT fibers excellent candidates for use as low voltage electron sources for vacuum electronic devices.

Transmission mode affects the population genetic structure of Daphnia parasites.

Parasite life cycle variation can shape parasite evolution, by predisposing them towards different population genetic structures. We compared the population genetic structure of two co-occurring parasite species of Daphnia, to collect evidence for their expected transmission modes. The ichthyosporean Caullerya mesnili has a direct life cycle, whereas the microsporidian Berwaldia schaefernai is hypothesized to require passage through a secondary host. The parasites were collected from three geographically isolated Daphnia populations. The nucleotide variation in the internal transcribed spacer (ITS) region was assessed at the within-individual, within-population and among-population levels, using amova. We detected significant partitioning at all levels, except for a lack of among-population variation in Berwaldia. This was confirmed by neighbour-joining and principal component analyses; Caullerya populations were distinct from each other, while there was much overlap among parasite isolates representing different populations of Berwaldia. This all implies a higher amount of gene flow for Berwaldia, consistent with the hypothesized transmission mode.

The effects of TNF deficiency on age-related cognitive performance.

Growing evidence suggests that 'pro-inflammatory' cytokines such as TNF play a role in cognitive processes and in aging. To test the effects of TNF on cognitive function throughout aging, we used transgenic mice which were TNF deficient. We then tested these mice along with wild-type mice, at 3, 6 and 12 months of age, using the Barnes maze. Wild-type controls showed better memory than TNF knock-out mice at 3 months of age, but not at 6 and 12 months of age. Results of our experiment show that endogenous TNF plays an important role in cognitive processes throughout aging processes. The implications of these findings are far-reaching and include a possible role for cytokines in the molecular and cellular mechanisms subserving age-related changes in learning, memory and cognition.

Ethics in reproductive medicine in the German Democratic Republic.

The paper discusses the practice of genetic counseling and elective abortion in the German Democratic Republic.

Effects of nonischemic hypoxia on jejunal mucosal structure and function: study of an experimental model in dogs.

A model of nonischemic hypoxia of the jejunum was designed in dogs, by shunting of blood from the inferior vena cava directly into the regional mesenteric arterial supply, thereby lowering the PaO2 of the blood that reached the jejunal wall from 98.6 +/- 3 to 62 +/- 5 mm Hg. Absorption rates of sodium, glucose, fructose, glycine, and the dibasic aminoacid lysine were studied by in situ luminal perfusion of a 30-cm proximal jejunal segment with a bicarbonate buffer solution containing phenol red as a nonabsorbable marker for determination of water fluxes. During periods of control, hypoxia, and after discontinuation of the venoarterial admixture (recovery), effluent perfusate was collected and mucosal biopsies were obtained for assay of lactase, maltase and sucrase activity, mucosal ATPase activity and ATP content, and for light- and electron microscopic examination. Mesenteric supply with hypoxic blood was associated with a significant inhibition of Na+,K+-ATPase activity (p less than 0.001) and a rise in mucosal ATP content (p less than 0.05). There was a significant reduction in the absorption rates of sodium (p less than 0.001), glucose, and glycine (p less than 0.01), but no change in the transport of fructose and of lysine. Brush border enzymes were unaltered. The histological appearance of the mucosa remained normal throughout the experiment, but on electron microscopy a distinct swelling of the enterocyte mitochondria was noted during the hypoxia period.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulbactam/ampicillin versus cefoxitin in the treatment of obstetric and gynaecological infections.

Preliminary results of a randomised trial comparing parenteral sulbactam 1g plus ampicillin 2g every 8 hours and cefoxitin 2g every 8 hours in 75 patients with gynaecological infection are reported. Clinical and bacteriological cure were achieved in 87% and 91% of patients treated with sulbactam/ampicillin compared with 83% and 59% treated with cefoxitin. Both treatments were well tolerated.