Velocity Distribution in Smooth Rectangular Open Channels-Closure

Abstract is not available.

Rotational cut-off and anharmonicity effects on thermodynamic properties of gases at high temperatures

The exact expressions for the partition function (Q) and the coefficient of specific heat at constant volume (Cv) for a rotating-anharmonic oscillator molecule, including coupling and rotational cut-off, have been formulated and values of Q and Cv have been computed in the temperature range of 100 to 100,000 K for O2, N2 and H2 gases. The exact Q and Cv values are also compared with the corresponding rigid-rotator harmonic-oscillator (infinite rotational and vibrational levels) and rigid-rotator anharmonic-oscillator (infinite rotational levels) values. The rigid-rotator harmonic-oscillator approximation can be accepted for temperatures up to about 5000 K for O2 and N2. Beyond these temperatures the error in Cv will be significant, because of anharmonicity and rotational cut-off effects. For H2, the rigid-rotator harmonic-oscillator approximation becomes unacceptable even for temperatures as low as 2000 K.

Is there an athermal region of plastic flow in metals at intermediate temperatures?

The question of the existence or otherwise of an athermal temperature region of plastic flow in metals is examined. It is suggested that the athermal region is absent in metals with large dislocation densities. Such an explanation is provoked by a fairly recent proposition that the unzipping of attractive junctions is a plausible rate-controlling mechanism at high temperatures.

Plant guard cell anion channel SLAC1 regulates stomatal closure

Plants are rooted to their growth place; therefore it is important that they react adequately to changes in environmental conditions. Stomatal pores, which are formed of a pair of guard cells in leaf epidermis, regulate plant gas-exchange. Importantly, guard cells protect the plant from desiccation in drought conditions by reducing the aperture of the stomatal pore. They serve also as the first barrier against the major air pollutant ozone, but the behaviour of guard cells during ozone exposure has not been sufficiently addressed. Aperture of the stomatal pore is regulated by the influx and efflux of osmotically active ions via ion channels and transporters across the guard cell membrane, however the molecular identity of guard cell plasma membrane anion channel has remained unknown. In the frame of this study, guard cell behaviour during ozone exposure was studied using the newly constructed Arabidopsis whole-rosette gas-exchange system. Ozone induced a Rapid Transient Decrease (RTD) in stomatal conductance within 10 min from the start of exposure, which was followed by a recovery in the conductance within the next 40 min. The decrease in stomatal conductance was dependent on the applied ozone concentration. Three minutes of ozone exposure was sufficient to induce RTD and further ozone application during the closure-recovery process had no effect on RTD, demonstrating that the whole process is programmed within the first three minutes. To address the molecular components responsible for RTD, the ozone response was measured in 59 different Arabidopsis mutants involved in guard cell signalling. Four of the tested mutants slac1 (originally rcd3), ost1, abi1-1 and abi2-1 lacked RTD completely. As the ozone sensitive mutant slac1 lacked RTD, the next aim of this study was to identify and characterize SLAC1. SLAC1 was shown to be a central regulator in response to all major factors regulating guard cell aperture: CO2, light/darkness transitions, ozone, relative air humidity, ABA, NO, H2O2, and extracellular Ca2+. It encodes the first guard cell plasma membrane slow type anion channel to be identified at the molecular level. Interestingly, the rapid type anion conductance was intact in slac1 mutant plants. For activation, SLAC1 needs to be phosphorylated. Protein kinase OST1 was shown to phosphorylate several amino acids in the N-terminal tail of SLAC1, Ser120 was one of its main targets, which led to SLAC1 activation. The lack of RTD in type 2C protein phosphatase mutants abi1-1 and abi2-1, suggests that these proteins have a regulatory role in ozoneinduced activation of the slow type anion channel.

Polarization switching in near-stoichiometric Zn:LiNbO3 at high temperatures

The effect of temperature and stoichiometry on the polarization switching rate in lithium niobate is presented. An increased polarization switching rate in congruent and near-stoichiometric lithium niobate (CLN and SLN) and SLN doped with 1.6 mol% Zn (SLN:Zn(1.6)) is observed using a pulsed field switching technique near the transition temperature (TO. Compared to CLN, the observed switching rate and domain wall mobility for SLN and SLN:Zn(1.6) are higher. The extra charge flow was observed during switching at high temperatures,and is attributed to the creation of defect dipoles and increase in ionic conductivity. Forward domain motion is expected to be the mechanism involved in switching. (C) 2010 Elsevier Ltd. All rights reserved.

A two-dimensional model for crack closure effect in plates under bending

A two-dimensional model is proposed for taking into account the establishment of contact on the compression side of crack faces in plates under bending. An approximate but simple method is developed for evaluating reduction of stress intensity factor due to such ‘crack closure’. Analysis is first carried out permitting interference of the crack faces. Contact forces are then introduced on the crack faces and their magnitudes determined from the consideration that the interference is just eliminated. The method is based partly on finite element analysis and partly on a continuum analysis using Irwin's solution for point loads on the crack line.

Study of the random vibration of nonlinear systems by the Gaussian closure technique

A technique is developed to study random vibration of nonlinear systems. The method is based on the assumption that the joint probability density function of the response variables and input variables is Gaussian. It is shown that this method is more general than the statistical linearization technique in that it can handle non-Gaussian excitations and amplitude-limited responses. As an example a bilinear hysteretic system under white noise excitation is analyzed. The prediction of various response statistics by this technique is in good agreement with other available results.

A lock-type cell for NMR studies at high hydrostatic pressures and low temperatures

Details of a simple and convenient high-pressure cell for continuous-wave, wide-line nuclear magnetic resonance investigation at high pressures and low temperatures are described. Experimental results obtained with the cell at 14*108 Pa and 77K for ammonium iodide are presented briefly.

Observation of crack closure using a crack mouth opening displacement gauge

A crack mouth opening displacement (CMOD) gauge has been designed to estimate the crack length as well as the crack opening stress level in an automated fatigue crack propagation test programme. The CMOD gauge accurately predicts crack tip opening levels in K-controlled tests with constant K, K increasing or K decreasing. In all three K-controlled tests with a single 100% overload cycle, the CMOD gauge does not measure the crack tip opening stress level over a large range of crack lengths after the application of the overload. The CMOD gauge measures the stress level at which the overload plastic zone site opens. Caution should thus be exercised in using the crack opening stress level, estimated by the CMOD gauge, to explain fatigue crack propagation under arbitrary load sequences from the viewpoint of crack closure phenomena.

Effect of Storage Temperatures on the Mechanical Properties of the Composite Solid Propellants

Accelerated ageing studies for three composite propellant formulations, namely polystyrene (PS)/ ammonium perchlorate (AP), polymethylmethacrylate (PMMA)/AP and poly phenol formaldehyde (PPF)/AP have been carried out in the temperature range of 55-125°C. Measurements of the ultimate compression strength (Uc) and isothermal decomposition rate (TD rate) were monitored as a function of storage time and temperature. The change in Uc was found to be linearly dependent on the change in TD rate irrespective of the propellant systems. Analysis of the results further revealed that the cause of ageing for both Uc and burning rate (r) is the thermal decomposition of the propellant. The safe-life for the change in mechanical properties was found to be higher compared to the change in r for PS and PMMA based propellants.