Multi c-BN Coatings by r.f Diode Sputtering and Investigation of Wear Behavior.

Cubic boron nitride (c-BN) films on tool substrates are tendency to delaminate. Therefore, many research groups have studied improvement of c-BN synthesis method and deposition processes due to many potential applications. In this paper, we show that the adhesion property of c-BN layer system can be improved by deposing multi c-BN layers. The multi c-BN layers were deposited by r.f (13.56 MHz) diode sputtering apparatus on cemented carbide tool substrates with a TiAlN adhesion layer. For industrial applications, we performed turning and milling experiments under dry and high speed cutting conditions. In this multi c-BN layer system, the lifetime of the tool is affected by the physical properties of the substrate and coated layers such as substrate grain size, thickness of the TiAlN and first c-BN layer and the total number of c-BN layers in this system. Mostly, fine grain size substrates showed longer lifetimes of over 4 times than raw one. In the turning performance, mono TiAlN layer systems were about two times lower lifetime than mono and multi c-BN layer system, moreover, we could be improved adhesion property for milling performance on tool substrates with binary multi c-BN layer systems under dry and high speed cutting conditions. The new application results of the multi c-BN layer system confirm that the high potential of c-BN coatings on cutting tools.

Energy from Waste--clean, efficient, renewable: transitions in combustion efficiency and NOx control.

Traditionally EfW (Energy from Waste) plants apply a reciprocating grate to combust waste fuel. An integrated steam generator recovers the heat of combustion and converts it to steam for use in a steam turbine/generator set. This is followed by an array of flue gas cleaning technologies to meet regulatory limitations. Modern combustion applies a two-step method using primary air to fuel the combustion process on the grate. This generates a complex mixture of pyrolysis gases, combustion gases and unused combustion air. The post-combustion step in the first pass of the boiler above the grate is intended to "clean up" this mixture by oxidizing unburned gases with secondary air. This paper describes modifications to the combustion process to minimize exhaust gas volumes and the generation of noxious gases and thus improving the overall thermal efficiency of the EfW plant. The resulting process can be coupled with an innovative SNCR (Selective Non-Catalytic Reduction) technology to form a clean and efficient solid waste combustion system. Measurements immediately above the grate show that gas compositions along the grate vary from 10% CO, 5% H(2) and 0% O(2) to essentially unused "pure" air, in good agreement with results from a mathematical model. Introducing these diverse gas compositions to the post combustion process will overwhelm its ability to process all these gas fractions in an optimal manner. Inserting an intermediate step aimed at homogenizing the mixture above the grate has shown to significantly improve the quality of combustion, allowing for optimized process parameters. These measures also resulted in reduced formation of NO(x) (nitrogenous oxides) due to a lower oxygen level at which the combustion process was run (2.6 vol% O(2,)(wet) instead of 6.0 vol% O(2,)(wet)). This reduction establishes optimal conditions for the DyNOR™ (Dynamic NO(x) Reduction) NO(x) reduction process. This innovative SNCR technology is adapted to situations typically encountered in solid fuel combustion. DyNOR™ measures temperature in small furnace segments and delivers the reducing reagent to the exact location where it is most effective. The DyNOR™ distributor reacts precisely and dynamically to rapid changes in combustion conditions, resulting in very low NO(x) emissions from the stack.

Gating models of the anomalous mole-fraction effect of single-channel current in Chara.

The dependence of single-channel current on the Tl+/K+ mole fraction exhibiting a minimum at [Tl+]/[K+] of about 1:15 is proportional to open probability in bursts. Five models are suggested to explain modulation of gating by the Tl+/K+ ratio. Three models start from a channel with 4 identical subunits, each with an allosteric binding site for K+ or Tl+. In the first model, ion binding is directly observable as a transition from one Markov state to another. This model can explain the dependence of the apparent single-channel current on Tl+ concentrations. However, the predicted linear dependence on ion concentrations of the apparent rate constants was not observed in measurements in 25 or 250 mM KNO3 and 250 mM Tl NO3. The second model can overcome this problem by introducing saturation kinetics for ion binding. In the third model, gating is caused by inherent vibrations of the protein, and the rate constants of the related transitions depend on the occupation of the allosteric sites. The fourth model is based on the foot-in-the-door approach with the essential feature that two K+ ions in the selectivity filter are necessary to keep the pore radius suitable for K+ ions. The fifth model is also a foot-in-the-door model, but non-Markovian because, similar to model 3, it is assumed that the conformation of the protein (and thus the rate constants of the Markov model of the time series) depends on the force exerted by the temporal average over the states of a Markov model of ion occupation. These ions may reside in the pore itself or outside.

A new level detector for ion channel analysis.

The algorithm proposed here for automatic level detection in noisy time series of patch-clamp current is based on the detection of jump-free sections in the time series. The detector moves along the time series and uses a chi(2) test for the detection of jumps. When a jump is detected, the mean value, the variance and the length of the preceding jump-free section are stored. A Student's t-test was employed for the assignment of detected jump-free sections to discrete levels of the Markov model and for rejection of all sections with multiple assignments. The choice of the two significance levels is based on a 3-D diagram displaying the average number of detected levels from several time series vs. the significance levels of jump detection and of level assignment. The correct one is selected out of several plateaus with integer number of levels by means of the criterion of minimum scatter or other plausibility considerations. The test has been applied to simulated data obtained from a 2-state model and a 5-state aggregated Markov model, and the influences of SNR and of gating frequency are shown. Finally, the performance of the level detector is compared with a fit-by-eye and with a fit of the amplitude histogram by a sum of gaussians. At high noise, the fit of amplitude histograms failed, whereas the other two approaches were about equal.

Bundle sheath cells of small veins in maize leaves are the location of uptake from the xylem.

Rb(+) as a tracer for K(+) was used to test the hypothesis that uptake of K(+) from xylem vessels of small veins into the symplast of maize leaves occurs at the xylem/bundle sheath cell interface. 22.5 min after immersing cut leaves into 20 mM RbCl+1 mM KCl, Rb(+) appeared in the cells of the leaves. Sections of these leaves were freeze-dried. In cryo-thin sections (5 microm), (85)Rb(+) and (41)K(+) content was determined by laser microprobe mass analysis with a large resolution of about 1 microm. Determining the ratio of (85)Rb(+) to (41)K(+) in the cell walls and cytosols of bundle sheath cells, mesophyll cells, and in the cells between the xylem elements resulted in the following picture: In small veins, Rb(+) entered the symplast directly at the xylem/bundle sheath cell interface.

The anomalous mole fraction effect in Chara: gating at the edge of temporal resolution.

The anomalous mole fraction effect (AMFE) of the K(+) channel in excised patches of the tonoplast of Chara showed a minimum of apparent open-channel current at 20 mM Tl(+) and 230 mM K(+). Time series obtained at a sampling rate of 100 kHz (filter 25 kHz) were analyzed by three methods to find out whether the AMFE results from an effect on gating or on the conductivity of the open state. Fitting the amplitude histograms by a superposition of gaussians showed a broadening in the presence of Tl(+). Dwell-time analysis based on an O-O-C-C-C model failed to evaluate rate constants above the filter frequency. Thus, the absence of any reduction of apparent open-channel current in time series simulated with the evaluated rate constants could not be taken as evidence against the hypothesis of gating. Finally, a direct fit of the measured time series using five different 5-state Hidden Markov models revealed that the presence of Tl(+) changed the rate constants in such a way that the number of transitions into the short-lived open state (30 micros) increased strongly compared to those in the absence of Tl(+). These models explain 25% reduction of apparent single-channel current amplitude through a rapid gating mechanism.

Different pH-dependences of K+ channel activity in bundle sheath and mesophyll cells of maize leaves.

The isolation of bundle sheath protoplasts from leaves of Zea mays L. for patch clamp whole-cell experiments presents special problems caused by the suberin layer surrounding these cells. These problems were overcome by the isolation technique described here. Two different types of whole-cell response were found: a small response caused by MB-1 (maize bundle sheath conductance type 1) which was instantaneously activated, and another caused by MB-2 (maize bundle sheath conductance type 2) consisting of an instantaneous response (maize bundle sheath K+ instantaneous current type 2; MB-KI2) similar to but stronger than the current through MB-1 plus a small time-dependent outward rectifying component (maize bundle sheath activated outward rectifying current; MB-AOR) with voltage-dependent delayed activation. The occurrence of MB-AOR was often accompanied by a smaller contribution from an inward rectifying channel at negative potentials. Activation of MB-2 required ATP. It is suggested that MB-1 and MB-2 are related to bundle sheath cells with and without direct contact with the xylem vessels. In mesophyll cells, only one type of response caused by MM-2 (maize mesophyll conductance type 2) was found with an instantaneous (maize mesophyll K+ instantaneous current type 2, MM-KI2) and a voltage-dependent delayed component (maize mesophyll activated outward rectifying current, MM-AOR). The most striking difference between bundle sheath and mesophyll cells was the pH dependence of K+ uptake. At pH 7.2, uptake of K+ by MB-2 was identical to that by MM-2 over the whole voltage range. However, acidification stimulated K+ conductance in bundle sheath cells, whereas a decrease was found for MM-2. At pH 6.15, the bundle sheath channel MB-2 had more than a 10-fold higher K+ uptake at positive and negative potentials than MM-2. The channel MB-1, too, was stimulated by low pH. This seems to indicate a putative role for MB-1 and MB-2 in charge balance during uptake of nutrients via cotransport from the xylem into the symplasm.

Gating and permeation models of plant channels.

Models of different level are applied to plant membrane transport. For the evaluation of I/V curves, models based on enzyme kinetics, limitation by diffusion and the ion well are described. Physical models of ion-ion interaction deal with the Woodhull model, the multi-site single-file ion pore, the ion-ion ion-water interaction model and the effect of screening. The discussion of channel gating starts with pre-patch evidence of gating and the biological importance of gating. State models play a dominant role in the analysis of patch clamp records. Gating may strongly interfere with permeation models. With respect to this, the limits of temporal resolution are of great importance. The effects of Na(+) and Tl(+) are examples of the influence of fast gating on modelling and the problems of its detection. The highest level of modelling is achieved when the knowledge about the structure of channels is employed for the modelling of gating. Major topics in this field are blockade by ions and phosphorylation.