Increase In Initial Slope Research Articles

Comparison of the dynamic magnetomechanical properties of Tb0.27Dy0.73Fe2 and Tb0.30Dy0.70Fe2

Comparison is made between the magnetomechanical properties of Tb0.27Dy0.73Fe2 (27 Tb) and Tb0.30Dy0.70Fe2 (30 Tb), two commercially available compositions of the giant magnetostrictive alloy Terfenol-D. The quasi-static magnetostriction (as a function of bias field) and the dynamic strain coefficient (as a function of bias field and frequency) are shown for the two compositions at room temperature, using stress bias values of 0 and 9 MPa. The energy loss per cycle as a function of frequency is also given. The data for the static magnetostriction versus bias field shows 30 Tb to exhibit a significantly greater increase in initial slope and saturation strain when stress bias is applied compared to that seen for 27 Tb, which possesses superior magnetostriction at zero stress bias. A similar trend is observed in the data for the dynamic strain coefficient with 30 Tb again performing better under stress bias. The widening of the static strain hysteresis loop observed for stressed 30 Tb is seen to manifest itself in the low frequency energy loss per cycle; however 27 Tb is observed to possess the higher eddy current loss at 1 kHz. Data for the ratio d/χ, a quantity which is dependent only on magnetization processes and material constants, are shown which suggests that the application of a stress bias affects the magnetization processes, but differently for the two compositions.

Effects of nitrogen on the response of loblolly pine to water stress I. Photosynthesis and stomatal conductance

summaryPhotosynthetic and stomatal response of loblolly pine (Pinus taeda L.) to water stress were determined for seedlings grown under 4 different nitrogen levels. Photosynthetic rate of well–watered seedlings was linearly related to foliar N. There was no observed N effect on the relative reduction of photosynthesis due to water stress. N did not influence stomatal conductance before or during the water stress period. Therefore, instantaneous water use efficiency of well–watered seedlings was significantly increased with increased N. Significantly reduced internal CO2 concentration (Ci) associated with increased N in well–watered seedlings may be indicative of greater relative stomatal contribution to overall limitation of photosynthesis. Water stress caused an increase in Ci, the slope of the increase being related to N treatment. Stomatal conductance and photosynthesis correlated strongly within each N treatment, and increased N caused an increase in initial slope of the function. Therefore, stomatal control was uncoupled from photosynthetic capacity by N treatment in loblolly pine. These data fail to support the proposition that improved stomatal response to water stress can explain reported gains in water status of nitrogen–fertilized conifers in the field.

Lithium and phorbol ester modify the activating capacity of ascidian spermatozoa

In this paper we have shown, using the whole-cell voltage clamp technique, that two parameters of the fertilization current in ascidian eggs may be modified by exposing spermatozoa to lithium or to phorbol ester. When spermatozoa were pre-treated in 250 mM lithium sea water for up to 30 min there was a significant increase in the mean initial slope of the fertilization current, from 116±90 to 169±84 pA/s (p 0.05). Pre-treatment in 200–600 nM phorbol 12-myristate 13-acetate also increased the activating capacity of ascidian sperm, as monitored by a significant increase in the initial slope current in control eggs; however, there was no increase in peak current. Furthermore, we have shown, using NH4Cl, that an increase in intracellular pH alone is insufficient to change the activating capacity of spermatozoa. This is the first report showing that the kinetics of an egg activation event depend upon the physiological status of the spermatozoon.

Photosynthesis of tropical tree seedlings in relation to light and nutrient supply

The photosynthetic performances of two tropical tree species, a pioneer Nauclea diderrichii (De Wilde.) Merrill, and a climax species Entandrophragma angolense (Welw.) C. DC., both from West Africa, were compared. Young plants were grown in controlled environments where photon flux density and nutrient supply were varied. A/C1 curves of the two species were very similar, both showing an increased initial slope and maximal rate of photosynthesis when the leaves had been grown at high photon flux density. Nutrient supply had a similar, but smaller, influence. However, the pioneer Nauclea showed a greater increase in initial slope in relation to both light and nutrient supply. It also showed greater anatomical response to light, developing a second layer of palisade mesophyll when grown at high photon flux density. Light response curves of photosynthesis were also determined. The apparent quantum efficiency was insensitive to growing conditions, but the carboxylation rate, dark respiration and tight-saturated photosynthetic rate were sensitive to the light climate of growth. The pioneer Nauclea displayed an increase in assimilation rate as the photosynthetic photon flux density was increased beyond 300 μmol m-2 s-1 , but Entandrophragma did not, and often showed a decline.

Effect of the nootropic drug oxiracetam on field potentials of rat hippocampal slices

1. The effect of the nootropic drug oxiracetam on hippocampal neurotransmission was investigated in the CA1 region of the rat hippocampal slice in vitro by use of extracellular recordings. 2. Superfusion of oxiracetam (0.1-100 microM) produced a concentration-dependent, wash-resistant (greater than 90 min), increase in initial slope and amplitude of the dendritic field excitatory postsynaptic potential (e.p.s.p.). This increase was maximal at a concentration of 1 microM (70%). 3. Input-output curves relating the initial slope to the amplitude of the afferent volley were significantly (P less than 0.05) steeper and showed a greater maximal response in the presence of 1 microM oxiracetam than in control conditions. 4. Two trains of high frequency stimulation (100 Hz, 0.4 s, 5 min apart) delivered in the stratum radiatum 30 min after washout of oxiracetam (1 microM) still elicited a long-term potentiation (LTP) of the field e.p.s.p. However, the absolute magnitude of the LTP produced did not differ from that obtained in untreated slices. 5. After induction and establishment of LTP, oxiracetam (1 microM) had a smaller (27%) and reversible effect on the evoked field e.p.s.p. 6. D-2-Amino-5-phosphonopentanoic acid (AP-5), at the same concentration (50 microM) which in our conditions prevented the induction of LTP, blocked the action of 1 microM oxiracetam and strongly depressed the effect of higher concentrations of the nootropic drug. 7. It is concluded that oxiracetam provokes an enduring increase of neurotransmission in the CA1 rat hippocampal region. This action appears to share some features with LTP as indicated by its persistence, sensitivity to AP-5 and lack of additivity with electrically-induced LTP.