Quasi-linear Phase Research Articles

Growth analysis of maize field crops under phosphorus deficiency. I. Leaf growth.

Biomass accumulation by crops depends both on light interception by leaves and on the efficiency with which the intercepted light is used to produce dry matter. Our aim was to identify which of these processes were affected for maize (Zea Mays L., cv Volga) field crops grown under phosphorus (P) deficiency, and assess their relative importance. In this paper, the effects of P deficiency on leaf appearance, leaf elongation rate, final individual leaf area and leaf senescence were studied. The experimental work was carried out in 1995–1977 on a long-term P fertilisation trial located on a sandy soil in the south-west of France. Three P fertilisation regimes have been applied since 1972: no-P (P0 treatment) and different rates of P fertiliser (P1.5:1.5 times the grain P export and P3:3 times the grain P export). These fertilisation regimes have led to contrasted levels of soil P supply, with the P0 treatment being limiting for growth. Very few differences were observed about leaf growth between the P1.5 and P3 treatments. Conversely, the leaf area index (LAI) was significantly reduced in the P0 treatment, especially during the first phases of the crop cycle (up to −60% between the 7- and 14-visible leaves). This effect gradually decreased over time. The lower LAI in P0 treatment was due to two main processes affecting the leaf growth. The final number of leaves per plant and leaf senescence were only slightly modified by P deficiency. Conversely, leaf appearance was delayed during the period between leaf 4 and leaf 9. The value of the phyllochron increased from 47 °C days in the P1.5 treatment to 65 °C days in the P0 treatment. Leaf elongation rates during the quasi-linear phase of leaf expansion were significantly reduced for lower leaves of P0 plants. The final size of leaves L2–L12 was reduced. On the opposite, leaf elongation duration was not greatly affected by P treatments. Before the emergence of leaf 9, the reduction of individual leaf size was the main factor responsible for the reduced LAI in the P0 treatment. After this stage, the delayed leaf appearance accounted for a great part of the reduced LAI in the P0 treatment.

Plant leaf area expansion and assimilate production in wheat (Triticum aestivum L.) growing under low phosphorus conditions.

Under phosphorus deficiency reductions in plant leaf area have been attributed to both direct effects of P on the individual leaf expansion rate and to a reduced availability of assimilates for leaf growth. In this work we use experimental and simulation techniques to identify and quantify these processes in wheat plants growing under P-deficient conditions. In a glasshouse experiment we studied the effects of soil P addition (0–138 kg P2O5 ha-1) on tillering, leaf emergence, leaf expansion, plant growth, and leaf photosynthesis of wheat plants (cv. INTA Oasis) that were not water stressed. Plants were grown in pots containing a P-deficient (3 mg P g-1 soil) sandy soil. Sowing and pots were arranged to simulate a crop stand of 173 plants m-2. Experimental results were integrated in a simulation model to study the relative importance of each process in determining the plant leaf area during vegetative stages of wheat. Phosphorus deficiency significantly reduced plant leaf area and dry weight production. Under P-deficient conditions the phyllochron (PHY) was increased up to a 32%, compared to that of high-P plants. In low-P plants the rate of individual leaf area expansion during the quasi-linear phase of leaf expansion (LER) was significantly reduced. The effect of P deficiency on LER was the main determinant of the final size of the individual leaves. In recently expanded leaves phosphorus deficiency reduced the photosynthesis rate per unit leaf area at high radiation (AMAX), up to 57%. Relative values of AMAX showed an hyperbolic relationship with leaf P% saturating at 0.27%. Relative values of the tillering rate showed an hyperbolic relationship with the shoot P% saturating at values above 0.38%. The value of LER was not related to the concentration of P in leaves or shoots. A morphogenetic model of leaf area development and growth was developed to quantify the effect of assimilate supply at canopy level on total leaf area expansion, and to study the sensitivity of different model variables to changes in model parameters. Simulation results indicated that under mild P stress conditions up to 80% of the observed reduction in plant leaf area was due to the effects of P deficiency on leaf emergence and tillering. Under extreme P-deficient conditions the simulation model failed to explain the experimental results indicating that other factors not taken into account by the model, i.e. direct effects of P on leaf expansion, must have been active. Possible mechanisms of action of the direct effects of P on individual leaf expansion are discussed in this work.

Leaf area expansion and assimilate production in sunflower (Helianthus annuus L.) growing under low phosphorus conditions

Reductions in leaf area and plant growth as a consequence of phosphorus (P) limitations have been attributed both to direct effects of P shortage on leaf expansion rate and to a reduced production of assimilates required for growth. Canopy assimilation and leaf area expansion are closely interrelated processes. In this work we used experimental and simulation techniques to identify and study their importance in determining leaf area on sunflower (Helianthus annuus L.) growing under P-deficient conditions. Experiment 1 was done outdoors, in Buenos Aires, Argentina, and Experiment 2 in a glasshouse in Wageningen, The Netherlands. In both experiments we studied the effects of soil P addition on leaf appearance, leaf expansion, dry matter accumulation, and leaf photosynthesis of non-water stressed plants grown in pots containing a P-deficient soil. Before sowing the equivalent amounts of 0–600 kg of super phosphate ha-1 were added to the pots. Phosphorus deficiency delayed leaf appearance increasing the value of the phyllochron (PHY) up to 76%, the rate of leaf area expansion during the quasi-linear phase of leaf expansion (LER) was reduced by up to 74%, with respect to high P plants. Phosphorus deficiency reduced by up to 50% the rate of light saturated photosynthesis per unit of leaf area (AMAX) in recently expanded leaves, while at low levels of leaf insertion in the canopy, AMAX was reduced by up to 85%, when compared to that in high P plants. Phosphorus deficiency also reduced the duration of the quasi-linear phase of leaf expansion by up to eight days. The values of LER were related (r = 0.56, P < 0.05) to the mean concentration of P in all the leaves (Leaves P%) and not to the concentration of P in the individual leaf where LER was determined (r = 0.22, P < 0.4) suggesting that under P deficiency individual leaf expansion was not likely to be regulated by the total P concentration at leaf level. The values of AMAX of individual leaves were related (r = 0.79, P < 0.01) to the concentration of total P in the corresponding leaf (Leaf P%). LER showed a hyperbolic relationship with Leaves P% (R2 = 0.94, P < 0.01, n = 13) that saturate at 0.14%. AMAX showed a hyperbolic relationship with Leaf P% (R2 = 0.73, P < 0.01, n = 53) that saturated with values of Leaf P% higher than 0.22. A morphogenetic model of leaf area development and growth was developed to quantify the effect of assimilate supply at canopy level on total leaf area expansion, and to study the effects of model parameters on the growth of sunflower plants under P-deficient conditions. With this model we identified the existence of direct effects of P deficiency on individual leaf area expansion. However, we calculated that under mild P stress conditions up to 83% of the reduction in the observed leaf area was explained by the particular effects of P% on the rate of leaf appearance, on the duration of the linear period of leaf expansion, and on the value of AMAX. We also calculated that the effects of P deficiency on the value of AMAX alone, explained up to 41% of the observed reductions in total leaf area between the highest and the intermediate P level in Experiment 2. Possible mechanisms of action of the direct effects of P on individual leaf expansion are discussed in this paper.

The low-frequency transport in the Santa Barbara Channel: description and forcing

Current meter, wind and adjusted sea level (ASL) data from January to July 1984 are used to (a) isolate the currents inside the channel that are associated with low-frequency (6–18 day band) transport fluctuations which dominate the record of the eastern mouth transport and (b) find the forcing mechanism(s) and its(their) dynamical role(s) in the low-frequency transport. The dominant mode of the currents is highly coherent with the eastern mouth transport in the 6–18 day band. About 62% of the total variance of the eastern mouth transport can be hindcast by both wind stress and remote adjusted sea level (ASL). The comparison of the amplitudes, and phases of the regression coefficients of a multiple regression analysis, to the amplitudes and phases expected from momentum conservation suggests that both the alongshore remote pressure gradient and the local wind stress forcing are balanced at the eastern mouth of the channel by the local acceleration of the transport there. The ASL data analysis suggests evidence of low mode coastally trapped wave propagation from San Quintin in Mexico to Port San Luis in central California. A quasi-linear phase vs longshore distance implies a propagation speed of about 70 km day −1 (period of 13.6 days), which compares well with the theoretical value of 75 km day −1 (period of 13.3 days) for the Southern California Bight.

Design of active phase shifters based on multichannel heterojunction field effect transistors (MCHFET's)

Design criteria of active phase shifters based on GaAs/AlGaAs multichannel (MC) HFET in the frequency range 4-60 GHz are presented. The phase characteristics of MCHFET devices were studied using the computer aided design program TOUCHSTONE. The dependence of transmission phase on various intrinsic elements in the equivalent circuit model as a function of control gate bias was also studied. There are limited gate bias ranges which correspond to the active regions of the two conducting wells for which a quasi-linear continuous phase shift for analog applications was achieved. Continuously varying the gate bias from V/sub gs/=-1.9 V to V/sub gs/=-0.6 V results in a quasilinear phase shift of 10/spl deg/, 15/spl deg/, 21/spl deg/, and 29/spl deg/ at f=12, 20, 30, and 60 GHz, respectively. Similarly, varying the gate bias from V/sub gs/=-0.4 V to V/sub gs/=0.7 V a quasi-linear phase shift of 21/spl deg/, 26/spl deg/, 27/spl deg/, and 23/spl deg/ at f=12, 20, 30, and 60 GHz, respectively, was achieved. The gain variation was less than 3 dB in these bias regions. With digital applications in mind, a maximum differential phase shift of around 50/spl deg/ was obtained by switching the gate bias discretely. The transmission phase of single gate MCHFET mostly depends on variation of gate source capacitance with gate bias rather than on other intrinsic elements. The dependence of phase shift on various geometrical and structural parameters is also presented. To test the practicality of the device, other scattering parameters (e.g., S/sub 11/, S/sub 22/, S/sub 12/) and the noise figure (NF) were finally studied.

Tubulin in sea urchin embryonic cilia: post-translational modifications during regeneration.

Tubulin is the major protein found in the membrane/periaxonemal matrix fraction of mature sea urchin embryonic cilia but its distribution and possible function during ciliary assembly are unknown. Hypertonic salt may be used to deciliate the embryos, allowing synchronous regrowth of cilia and subsequent deciliation of the regenerating embryos at various times. During the earliest stages of regeneration, the amounts of tubulin in the axoneme and membrane/matrix fractions are nearly equal, but the proportion of tubulin in the axoneme fraction increases coincident with the quasi-linear growth phase while the membrane/matrix tubulin remains constant. Antibodies to tyrosinated and detyrosinated alpha-tubulin show that both the membrane/matrix and axonemal tubulin fractions are primarily unmodified (i.e. tyrosinated) at the earliest stages of regeneration but are progressively and equally detyrosinated coincident with regeneration, approaching a final level of 50% C-terminal Glu. A monoclonal antibody to acetylated alpha-tubulin reveals that both tubulin fractions are equally and maximally acetylated at relatively early stages of regeneration. In contrast, three-times-repolymerized tubulin from either unfertilized eggs or midgastrula embryos is primarily tyrosinated (greater than 97%) and not detectably acetylated. These data suggest that membrane/matrix tubulin is a precursor to axonemal tubulin and that acetylation and detyrosination may be involved in partitioning tubulin among cytoplasmic, ciliary membrane/matrix, and 9 + 2 compartments.

Light adaptation and responses to contrast flashes in cones of the walleye retina.

The effects of light adaptation on the intracellular responses of cones to incremental and decremental light flashes were investigated in the superfused walleye retina. The time course of light adaptation was relatively slow, some 10-20 min being required to reach steady-state conditions. Under steady-state conditions: (1) both dark-adapted and light-adapted amplitude/intensity data were well described by the Michaelis-Menten relation, (2) the incremental response did not saturate on intense backgrounds and (3) the cone sensitivity conformed closely to Weber's law. Effects of the polarity and magnitude of the flash contrast were analyzed by deriving "equivalent contrast" relations for cones and comparing the results to those of recent psychophysical experiments. Results based on the response amplitude suggest that responses to negative contrast flashes may be enhanced by post-receptor mechanisms. Results based on cone latency suggest that equivalent contrast relations for visual latency may be largely shaped in the very early, quasi-linear phase of the cone response.

Functional properties of twin and single cones

The effects of light adaptation on the intracellular responses of cones to incremental and decrementai light flashes were investigated in the superfused walleye retina. The time course of light adaptation was relatively slow, some 10–20 min being required to reach steady-state conditions. Under steady-state conditions:(1)both dark-adapted and light-adapted amplitude/intensity data were well described by the Michaelis-Menten relation,(2)the incremental response did not saturate on intense backgrounds and(3)the cone sensitivity conformed closely to Weber's law. Effects of the polarity and magnitude of the flash contrast were analyzed by deriving “equivalent contrast” relations for cones and camparing the results to those of recent psychophysical experiments. Results based on the response amplitude suggest that responses to negative contrast flashes may be enhanced by post-receptor mechanisms. Results based on cone latency suggest that equivalent contrast relations for visual latency may be largely shaped in the very early, quasi-linear phase of the cone response.

RE Pulse Shapes for Selective Excitation in NMR Imaging

It is shown that the requirements of an RF pulse needed to produce a slice for use in NMR imaging approximate the requirements of the windows used for calculating the discrete Fourier transform (DFT). This approach gives an interesting insight into the physical background of pulse shape tailoring. One of the more successful DFT windows is the 3 term Blackman-Harris window, which is tailored to produce minimum sidelobes. The results of applying radio frequency (RF) pulses modulated to give this window shape is given. The pulse shape produces a uniform magnetization over a range of frequencies with a quasi-linear phase shift making it suitable for producing a slice for NMR imaging when an echo is produced via an inverse magnetic field gradient.

Quasi-linear model for heat flow and diffusion in a micro-unstable tokamak

A formulation of transport theory, including cross-field thermal conductivity, is presented and applied to transport in tokamak due to trapped-particle instabilities,in the quasi-linear stage. Ratios of ion heat conduction, convection, and turbulent heating to electron heat conduction, and ratios of electron heat convection and turbulent heating to electron heat conduction are presented in the quasi-linear phase of trapped-electron and trapped-ion modes, along with general techniques for obtaining these ratios for other modes in a quasi-static micro-unstable plasma.

Motion reversal invariance in tape recorders

Under certain circumstances, when replaying prerecorded tapes, a reversal of head-tape motion causes a simple time reversal of the output. The occurrence of this phenomenon depends entirely upon the characteristics of the reproduce channel. Motion reversal invariance occurs when the time dependent part of the reproduce channel impulse response displays either of two types of symmetry;in the frequency domain this is equivalent to a quasi-linear phase response.

The design of linear-phase low-pass filters

The general principles underlying the design of low-pass filters with quasi-linear phase characteristics are considered, and a method suitable for the design of certain low-pass filters required in television transmission equipment is described. Adequate linearity of phase response can be obtained over the whole pass band only by limiting the discrimination which is required in the attenuation region of the insertion-loss characteristic. If the phase linearity demands are relaxed at the lower part of the pass band of the low-pass filter, much higher discrimination can be obtained in the region above cut-off. These principles are illustrated by two examples. The first is a set of low-pass filters having linear phase characteristics from zero frequency to the region of cut-off frequency, with discriminations of 15 db or more above the transition interval. There are six independent filters in the set, having cut-off frequencies of 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 Mc/s. The second example is an asymmetric-sideband filter having a cut-off frequency of 6.12 Mc/s with an insertion-phase characteristic linear between 3 and 7 Mc/s; the discrimination exceeds 30 db above 7 Mc/s.