Robust electric-field tunable opto-electrical behavior in Pt-NiO-Pt planar structures.

Capacitor-like metal-NiO-metal structures have attracted large interest in non-volatile memory applications based on electric field control of resistance, known as resistive switching (RS). Formation of conducting nanofilaments by the application of an electric field (electroformation) is considered an important pre-requisite for RS. Besides RS, due to the wide band gap and p-type semiconducting nature, NiO has been used to fabricate heterojunctions for photodetector applications. However, very little is known about the electrical and opto-electrical properties of NiO films in planar structure. Here, we demonstrate intriguing photoresponse and electrical behavior in electroformed Pt-NiO-Pt planar structures. While the pristine devices show ohmic electrical behavior and negligible photoresponse, the electroformed devices exhibit a nonlinear rectification behavior and a remarkable photoresponse at low voltage biases. More interestingly, the devices show a dramatic change of sign of rectification under light illumination at higher voltage biases. A polarity dependent and robust gain phenomenon is demonstrated in these devices. The large sensitivity, fast response, simple design and ease of preparation of these planar structures make them attractive for integration with current circuit technologies and various novel opto-electrical applications.

Implication of protein kinase C in IL-2-mediated proliferation and apoptosis in a murine T cell clone.

Several reports have suggested that protein kinase C plays an essential role in T cell activation and apoptosis. The recent synthesis of the selective protein kinase C inhibitor, GF109203X, has made it possible to test the relevance of protein kinase C in T cell proliferation and apoptosis. We report that the use of GF109203X, in concentrations that are below its toxicity limits, inhibits IL-2-dependent proliferation in murine T cells expressing intermediate or high-affinity IL-2R (TS1 beta and TS1 alpha beta). In addition, GF109203X reverts the suppression of apoptosis mediated by IL-2 or IL-2+ dexamethasone. The use of the phorbol ester PMA, a protein kinase C activator, allows a bypass of the IL-2/IL-2R interaction in the suppression of apoptosis mediated by dexamethasone or IL-2 withdrawal in TS1 beta cells but not in TS1 alpha beta cells. Taken together, our data indicate that activation of protein kinase C is an important step in IL-2-mediated proliferation and in suppression of apoptosis.

Increasing productivity in recent European oak trees?

As an attempt to analyze the role of the biosphere in the disturbed carbon cycle, as far as the standing biomass is concerned, a search for growth trends in tree ring series was started. A group of 27 cut oak trees from various locations in Europe and with ages between 25 and 262 years was analyzed in the following way: (1) A two-parameter smoothing function applied to each single tree cancelled out the year-to-year noise of ring widths; (2) this function containing the growth information over the whole life span of a tree was used to compute the (smoothed) width of the 40th and the 80th ring for each tree; (3) each ring width derived from a single tree in this way was plotted vs time, i.e., over the particular year of its formation. A statistical analysis of these plots shows that the variation of ring widths (delta r) in time (t) is best represented by an exponential function of the form delta rn(t) = delta r0n + aebt (n = 40; 80). The pre-industrial value, delta r0n (for t approximately less than 1,800), turns out to be identical with the 2,700 years average of European oak trees, as found by Hollstein (1979) in his dendrochronological work. Several possibilities are discussed what might have caused such growth trend.

Determination of zinc in sea-water by anodic stripping voltammetry.

The horizontal distribution of zinc in surface waters from Guanabara Bay has been studied by use of optimized voltammetric techniques and ultraclean working procedures. The non-linearity observed between the peak current for zinc and the electrolysis time, as well as the appearance of a peak at -1.16 V, are discussed. The values found for total zinc in the samples range between 0.3 and 22 mug/l.