Reduced Peak Height Research Articles

Signalling in guard cells and regulation of ion channel activity

A review is presented of the properties of ion channels in plasmalemma and tonoplast of stomatal guard cells, their regulation, with particular reference to Ca(2+) and protein phosphorylation/dephosphorylation, and of the evidence for ABA-induced changes in specific ion channels, with an attempt to identify the signalling chains involved in each such change. A key question is whether a local increase in Ca(2+), close to cell membranes and capable of triggering Ca(2+)-dependent changes in a variety of ion channels, is a universal feature of the ABA-reponse. If this is so, then there exist Ca(2+)-coupled mechanisms for most of the observed changes, including inhibition of the inward K(+) channel and activation of the slow anion channel in the plasmalemma, and activation of two channels in the tonoplast, the K(+)-selective (VK) channel and the slow vacuolar (SV) channel, initiating efflux of both anions and cations from the vacuole. The detailed signalling chains are not complete, and the role of protein phosphorylation/dephosphorylation is not clearly defined, nor linked to ABA. Control of the outward K(+) channel is Ca(2+)-independent; its activation by ABA may be mediated by cytoplasmic alkalinization, but the role of protein dephosphorylation in the signalling chain has still to be clarified. If Ca(2+) is not available as second messenger, then the signalling chains involved have hardly begun to be understood. Detailed comparison of the efflux transients in different conditions provides evidence that ABA changes the 'set-point' of a stretch-activated channel, initiating loss of vacuolar K(+). The inclusion of Ba(2+) in the bathing solution has effects similar to those of reduced ABA concentration, a delay in initiating the vacuolar transient, and a slower rise to a reduced peak height. It is suggested that this could be the result of inhibition of the process of Ca(2+) release from internal stores, by blocking a charge-balancing K(+) flux.

Plastics wood substitute

The objective of this study is to evaluate effect of various machining techniques on the surface roughness of beech (Fagus orientalis) and aspen (Populus tremula) lumber. Surface characteristics of sawn, planed, and sanded samples of both species were determined employing a stylus type profilometer. Average roughness (Ra), mean peak-to-valley height (Rz), core roughness depth (Rk), reduced peak height (Rpk), and reduced valley depth (Rvk) roughness parameters were used to determine surface characteristics of the samples. Based on the results of statistical analysis, measurements taken from the surface in tangential and radial directions of both species did not result in significant difference at a 95% confidence level. However, significant statistical difference was found between surface characteristics of aspen and beech samples, machined with four different ways in both grain orientations. This study suggests that stylus method can be successfully used to evaluate and distinguish variations on the surface of wood, due to grain orientation and planning and sanding. Data generated in this study can be used as a quality control tool for further processes such as finishing or gluing of wood from two species.

Determination of copper in concentrated matrices by flow injection with inductively coupled plasma atomic emission spectrometry

Determination of copper in solutions containing various sulphate compounds, such as H2SO4, Na2SO4, K2SO4, MgSO4 and ZnSO4 at concentrations up to 200 g l–1 are reported. The chosen technique was flow injection inductively coupled plasma atomic emission spectrometry. Of the materials mentioned above, ZnSO4 has a particularly strong influence on the copper emission. At slow carrier flow-rates, increased solution viscosity leads to peak broadening and reduced peak height. As carrier flow is increased, peaks sharpen and these viscosity effects are overcome. Thus, at a flow-rate of 13.2 ml min–1, copper peaks in either aqueous or high salt matrices are not significantly different in height.The method developed has been applied to the determination of copper in a Burt filtrate taken from a zinc plant, a solution high in sulphate salts. Flow injection using both a standard calibration plot and the standard additions method has been applied to the filtrate. The procedure has been shown to offer advantages in speed over an existing xanthate technique, which relies on copper precipitation to separate it from interferences, with re-dissolution prior to analysis. The precision of the method is generally better than 8% RSD, with copper recoveries of 90–115%.

Adverse Effects of Lag Filters Used for Detector Baseline Noise Suppression in High Performance Liquid Chromatography

Abstract Most detectors used for High Performance Liquid Chromatography employ a lag filter for suppression of baseline noise. This filter is characterised by its time constant, τ. At high values of τ (in excess of 0.5 sec), the lag filter seriously distorts the shape of a chromatographic peak, causing reduced peak heights, altered retention times and increased peak width. These changes result in significantly decreased resolution and decreased plate counts. These effects are investigated quantitatively.

A Digital Mass Spectrometer

A mass spectrometer control and recording system has been built which utilizes synchronous incremental stepping of the magnet current during the scanning of the mass spectrum with time-locked digitizing of the output, producing successive scans as similar time series and preserving the frequency spectral content of each scan. The digital output is recorded on magnetic tape and processed later on a computer. A new method of fitting polynomials to the reduced peak heights is described, which yields a measuring precision of about 0.06% at one standard deviation on 10–20 scans of the spectrum.Some studies of fractionation are described which illustrate the large errors which may occur from this effect.

The use of a new potential barrier model in the Fowler-Nordheim theory of field emission

It is well known that for fields ⩽ 10 7 V/cm the observed field emitted current density is in agreement with the Fowler-Nordheim theory using the classical image-force barrier for the model of the surface potential. However, for fields ⩾ 5 × 10 7 V/cm, the measured current densities deviate from the linear log j versus 1/ F curve, becoming progressively less than predicted values as the field increases. It was suggested that the departures from theory were due to space-charge distortions of the cathode field by high current densities. There are, however, other effects that occur at high fields which may also produce significant departures from the Fowler-Nordheim Law. One such possibility is the inaccuracy of the classical image-force barrier at small distances (several ångströms) from the surface. We have examined the effect of a modified surface potential barrier on the emitted current and energy distributions in the field emission region. The new potential represents quantum modifications to the classical image-force and is based on quantum-mechanical calculations of the electronic potential in the surface region of a metal. The result for the current density is obtained in analytic form. Deviations from the linear Powler-Nordheim plot begin about 5 × 10 7 V/cm and decrease progressively to a value about 4 % lower at the highest fields. Energy distributions of the field emitted electrons have been calculated for the normal and total energy cases. These are given for the zero temperature limit and the T-F region. For the normal energy case differences with the image-force results are evidenced in the narrower half-widths and reduced peak heights obtained with the modified potential model. Improved agreement with the experimentally measured total energy distributions is obtained in a) location and height of the maxima and b) half-widths.