Analyzing Cell Designs by Conputer for Optimum Performance

Plant cell biology (2nd edition) Edited by C. R. Hawes & B. Satiat-Jeunemaitre. 338 pages. Oxford, UK: Oxford University Press, 2001. £70.00 hours/b. ISBN 0 19 963866 7 In Plant cell biology (2nd edition) a practical approach, an attempt has been made to do the impossible. Editors Chris Hawes and Béatrice Satiat-Jeunemaitre have attempted to collect into a single, reasonably priced volume descriptions of, and protocols for, most of the techniques used by plant cell biologists. A wide range of methodologies are presented, including light and electron microscopy, immunocytochemistry and in situ hybridization, transient expression of genes in plant cells, and use of the green fluorescent protein (GFP) as a reporter molecule. Each chapter is written by researchers who share with the reader insights that have come from their own experience, and protocols from their own laboratories. The editors, perhaps deliberately, have done little to impose a uniform writing style. Although this is slightly off putting when liberties are taken with standard English, it reinforces the impression that what is presented is based on the experience of individuals and on the success they have had with particular cell types, tissues and plant species. Of note are excellent, thorough chapters on optical microscopy, fluorescent probes for live cells, in situ hybridization, and organelle isolation. The chapter ‘Plant histology’ provides a brief introduction to the subject, and will be useful to those needing a set of standard protocols. There is a wealth of information in the chapter ‘Electron microscopy’, though at times the inclusion of so much material obscures the organization of the chapter and is confusing. Likewise ‘Immunocytochemistry for light microscopy’ lacks the focus that would make it most useful to novices. Coverage of transient expression seems, at first glance, to be extremely limited since only electroporation is described in any detail. Fortunately, protocols for plant transformation using polyethylene glycol, Agrobacterium, Potato Virus X and biolistics are included in the chapter ‘The green fluorescent protein (GFP) as reporter in plant cells’. The chapter on microinjection scarcely mentions transformation via microinjection, but does discuss in detail the unique challenges posed by various cell types. Perhaps least useful to most readers, except as a description of the methodology, is ‘Micromanipulation by laser microbeams and optical tweezers’. The chapter on electrophysiological methods, surprisingly, is restricted to capacitance measurements as an assay for exo- and endocytosis. More basic voltage clamp and patch clamp techniques have been extremely useful tools for plant cell biologists during the past two decades. It is unfortunate that explicit protocols were not included for making measurements of, for example, voltage difference across the plasma membrane or whole cell currents. Flow cytometry is a powerful technique that is rarely used by plant biologists, but commonly used by other cell biologists. It is disappointing therefore that the chapter on flow cytometry covers only the quantification of DNA in nuclei in any depth. Illustrating a wider range of applications would have been beneficial to the plant science community. This book will be an excellent resource for anyone who needs more than a cursory introduction to an unfamiliar methodology. Those that will find it useful are scientists who want to use a new technique for their own research, and instructors trying to develop contemporary laboratory exercises. Plant cell biology (2nd edition) a practical approach, does not accomplish the impossible. Yet it is a remarkably good attempt, and exceptionally good value. I highly recommend it.

Visualizing plant cell biology

Introduction Lead acid batteries have been widely used for more than 100 years. They are used for vehicles and backup power supplies. However, when overdischarged, lead acid battery cannot be recharged and its performance is greatly declined. Recently, Iwai et al. had revealed that the cause of not being able to be recharged is the nucleation of α-PbO2 on cathode material, β-PbO2, and that, when gold or platinum is used as the current collector, formation of α-PbO2 is prevented due to local cell reaction, then that lead acid battery can be recharged even after overdischarge [1,2]. In this study, we investigated the possibility of realizing the lead acid battery with high resistance to overdischarge using graphite materials, such as natural expanded graphite sheet as a current collector. We think that graphite materials will be advantageous for cost reduction, weight reduction and improvement of processability for lead acid batteries. Experiment We developed graphite based composite material as a current collector which was prepared by the following procedure, in order to improve water repellency. Resin materials such as polyethylene, polypropylene (PP), ethylene propylene copolymer and fluororesin were dispersed with graphite sheet, preheated in air at 100 degrees for 10 minutes, and then heated at 160 degrees to 200 degrees for 10 minutes. Then, the graphite-based composite material was immersed in sulfuric acid (H2SO4) and the weight variation was measured. Also, the surface electric resistance of the graphite composite material was measured by four-terminal method. We decided to use PP as resin for graphite based composite materials, because graphite based composite material using PP have a low electric resistance and PP is easily dispersed in graphite sheet. Then, we chose PP contents of 5% from the viewpoint of water resistance. We used two-electrode glass cell for charge-discharge experiments. The cathode paste was prepared by mixing purchased β-PbO2 powder as an active material, acetylene black as a conducting additive and PTFE as a binder at the ratio of 80:15:5 in weight. The cathode was fabricated by pressing the paste on a current collector. In this study, we tested three kinds of current collectors, Pb plate, graphite sheet and graphite-based composite material. Each current collectors were used in 35 wt% H2SO4. Lead plate and 35 wt% H2SO4 were employed as anode and electrolyte, respectively. Firstly, we discharged the cell at 9 mAg-1 for 30 min and charged at 180 mAg-1 for 20 min. We repeated this cycle 20 times in order to stabilize the charge-discharge reaction. Secondly, we deeply discharged the cell down to 0 V at 9 mAg-1 and opened the circuit for 48 h. Finally, we once again charged the cell at 180 mAg-1 for 60 min, then we discharged the cell at 9 mAg-1 for 30 min and charged at 180 mAg-1 for 20 min and repeated the cycle to study the cell performance. Results and discussion Figure 1 (A) and (B) show the charge-discharge curves for the lead acid battery using Pb plate and graphite sheet as a current collector, respectively. In the case of Pb plate, the lead acid battery cannot be recharged after the open circuit. On the other hand, in the case of graphite sheet, it can be recharged even after the open circuit. Electrode potential does not come out for carbon, so it is thought that carbon has a role of stopping the local cell reaction. From this reason, it can be explained that the formation of α-PbO2 is prevented on cathode β-PbO2 then that the similar performance was shown when using gold or platinum as a current collector. In figure 2, performance of lead acid battery using graphite based composite as cathode current collector is shown. We discharged the cell at 9 mAg-1 to 0 volt and charged at 180 mAg-1 for 60 min and repeated the cycle between 0 volt and 2 volt. Between 1.9 V and 1.3 V, potential flat area is clearly observed. Just only inserting a thin graphite based composite, lead acid battery repeating charge / discharge cycles between 0 volt and 2 volt so many times without decay was realized. This result may be caused by improvement of water repellency of current collector by impregnate with PP into graphite sheet.

Optimal charging of stand-alone lead-acid and lithium-ion batteries is studied in this paper. The objective is to maximize the charging efficiency. In the lithium-ion case two scenarios are studied. First only electronic resistance is considered and in the next step the effect of polarization resistance is also included. By considering constant model parameters for the lithium-ion battery analytical solutions exists for both scenarios using Pontryagins minimum principle. In lead-acid chemistry the variation of total internal resistance with state of charge (SOC) is considerable and the optimal charging problem results in a set of two nonlinear differential equations with one initial and a final condition to be satisfied. This so called two point boundary value problem is solved numerically.

A linear relationship has been found under certain conditions between the 1st order flotation rate constant, k, and Sb, the bubble surface area flux produced in a flotation cell. Sb is the total surface area of bubbles moving up through a unit cell cross-sectional area per unit time and gives a measure of the hydrodynamic and gas dispersion properties in the cell. This relationship has been found to be independent of the size of the cell and, in mechanical cells, independent of the type of impeller used ie. method of Sb production, which allows scale-up possibilities. These findings are, however, only related to metalliferous flotation in conventional mechanical cells and to date no work has been carried out to study this effect in coal or non-conventional cells. The aims of this thesis were to firstly determine whether the k-Sb relationship, which has found to be an effective scale-up tool for base metal flotation, is evident in coal flotation and secondly, to determine whether it exists for non-conventional flotation technologies, commonly used in coal flotation. Testwork was performed at two industrial sites and consisted of: . • Site measurements of bubble size, superficial air velocity and air hold-up to determine the value of Sb in operating plant scale cells. This characterised the particular cell under investigation and identified the existing hydrodynamic conditions. The measurements were combined with conventional sampling of feed and products followed by analysis and mass balancing to reveal the prevailing rate constant k. . • Simultaneous operation of the JKMRC 60 litre conventional flotation cell or pilot scale Jameson cell (depending on plant cell being used) in parallel with the site cell under investigation. It was possible to make major changes to the operating conditions of the test cell (as opposed to the site cell) in order to determine the k-Sb relationship for the coal under investigation. . • Measurement of froth recovery in site cells. The effect of froth residence time and other parameters on froth recovery was determined in the 60-litre conventional cell or pilot Jameson cell. • Keeping the cell hydrodynamic conditions (as specified by the Sb value) fixed, and independently evaluating the effect of other parameters such as reagent regime and froth depth, using the 60-litre cell. Results for conventional flotation (and, it is assumed, all coal flotation) showed that particle size and feed composition effects are significant and can override the effect a change in Sb has on cell performance. Decoupling these effects indicated a distinct relationship between Sb and flotation rate. Also, the range of Sb values under which linearity is maintained was found to be limited. Further work to investigate these effects in more detail was unsuccessful, therefore additional testwork is recommended to enable firm conclusions to be made. Feed changes made analysis of the effect of the froth phase inconclusive for the conventional cell, however, the froth phase was found to be a significant factor in the performance of the plant scale Microcel. It was found that conditions inside the downcomer of the Jameson cell appear to be most significant in terms of the k-Sb relationship, indicating that, in line with popular opinion, collection occurs solely within the downcomer of the Jameson cell. Conditions in the pilot scale Jameson cell rig exhibited perfect mixing behaviour with mixing conditions in the plant cell inconclusive but most likely perfect mixing or axial dispersion with large amounts of dispersion. Improvements in gas dispersion measurement techniques in the plant cells, in particular bubble size, need to be developed for specific application to coal flotation to allow further investigation into the findings of this work.

Heat generation in a lead acid battery during energy conversion was studied. The temperature effects which are to be expected were evaluated using the fundamental laws of heat dissipation, and a computer program was established to predict the heat balance of a battery. The results are compared with overcharge experiments carried out with valve regulated block-batteries of the type Vsb 6905 T (6 Volt; K/sub 10/=85 Ah, Microglas absorbent version) including gas measurements and gas analysis. It is suggested that valve regulated lead acid batteries, especially when designed for short bridging periods, should be equipped with a monitoring system to avoid critical situations in case the voltage controlling system fails. The temperature of the battery is one of the parameters suited for this kind of monitoring.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Phytochelatins (PCs), (gamma-Glu-Cys)n Gly polymers that were formerly considered to be restricted to plants and some fungal systems, are now known to play a critical role in heavy metal (notably Cd2+) detoxification in Caenorhabditis elegans. In view of the functional equivalence of the gene encoding C. elegans PC synthase 1, ce-pcs-1, to its homologs from plant and fungal sources, we have gone on to explore processes downstream of PC fabrication in this organism. Here we describe the identification of a half-molecule ATP-binding cassette transporter, CeHMT-1, from C. elegans with an equivalent topology to that of the putative PC transporter SpHMT-1 from Schizosaccharomyces pombe. At one level, CeHMT-1 satisfies the requirements of a Cd2+ tolerance factor involved in the sequestration and/or elimination of Cd x PC complexes. Heterologous expression of cehmt-1 in S. pombe alleviates the Cd2+-hypersensitivity of hmt- mutants concomitant with the localization of CeHMT-1 to the vacuolar membrane. Suppression of the expression of ce-hmt-1 in intact worms by RNA interference (RNAi) confers a Cd2+-hypersensitive phenotype similar to but more pronounced than that exhibited by ce-pcs-1 RNAi worms. At another level, it is evident from comparisons of the cell morphology of ce-hmt-1 and cepcs-1 single and double RNAi mutants that CeHMT-1 also contributes to Cd2+ tolerance in other ways. Whereas the intestinal epithelial cells of ce-pcs-1 RNAi worms undergo necrosis upon exposure to toxic levels of Cd2+, the corresponding cells of ce-hmt-1 RNAi worms instead elaborate punctate refractive inclusions within the vicinity of the nucleus. Moreover, a deficiency in CeHMT-1 does not interfere with the phenotype associated with CePCS-1 deficiency and vice versa. Double ce-hmt-1; ce-pcs-1 RNAi mutants exhibit both cell morphologies when exposed to Cd2+. These results and those from our previous investigations of the requirement for PC synthase for heavy metal tolerance in C. elegans demonstrate PC-dependent, HMT-1-mediated heavy metal detoxification not only in S. pombe but also in some invertebrates while at the same time indicating that the action of CeHMT-1 does not depend exclusively on PC synthesis.

Dynamic modeling and performance of the first cell of a multi-effect distillation plant

The electrical conductivity of the negative active material in lead-acid batteries has been found to significantly influence the properties of the electrode. Though several publications have addressed this subject, essential information on the conductivity evolution during cycling as well as the influence of additives could yet not be elucidated, even though specific knowledge could support the enhancement of existing lead-acid battery technology. In this study, a novel measurement setup is presented which enables the in-situ and operando measurement of the electrical resistance of bulk electrodes during operation based on the implementation of a four-point probe setup into a laboratory electrode. A comprehensive evaluation of the measurement setup is conducted using the negative electrode of a lead-acid battery as a test material. The experimental results are supported by numerical simulations in order to reflect and include all relevant geometrical and electrical influences from the measurement setup. A direct correlation between active material resistance and conductivity can be established, including the influence of the vertical position of the four-point probes. Finally, the evolution of the discharge capacity, electrical resistance and electrical conductivity of the negative electrode is studied over ten C 5 cycles and correlated to well-known structural developments within the active material.

A study on the influence of sulphuric acid (H2SO4) concentration on the electrochemical activity, phase composition, structure and morphology of the lead dioxide (PbO2) particle thereby its impact on performance of battery was carried out. For the formation process, cells made up of two positive and two negative plates with graphite powder/acetylene carbon and H2SO4 with different concentrations (1.05, 1.15 and 1.25 specific gravity (SG) are used. During the soaking period, lead oxide (PbO) and basic lead sulphate (PbO.PbSO4) react with H2SO4, and sulfation of the plate starts. These processes changes the structure and morphology of the crystals in the cured paste. The results showed that the concentration of H2SO4 decreases gradually during soaking indicating that H2SO4 is reacting with PbO present in the paste. After the formation process the phase composition and morphology of active material are characterized using X-ray powder diffraction (XRD) and Scanning Electron Microscope (SEM) studies respectively. After formation, the concentration of H2SO4 is altered to 1.24 SG. The simulated 2 V lead-acid cells are subjected to capacity and service life measurement. The results proved indeed the acid SG in formation alters the structure of active material and life of battery.

Technical and economic survey of low enthalpy solar installations for heating sanitary water

The objective of this work is to examine the effects of the flow channel area ratio (40%, 50%, and 60%) on the reactant gas transport and the cell performance of proton exchange membrane fuel cells (PEMFCs) with parallel and interdigitated flow channel designs. The effects of liquid water formation on the reactant gas transport are taken into account in the present study. Higher flow area ratios are expected to provide more area for fuel diffusion into the gas diffusion layer to enhance the electrochemical reaction rate and improve cell performance. Numerical predictions show that the cell performance for parallel flow channel design can be enhanced by increasing the flow channel area ratio and the best overall cell performance occurs for a flow channel area ratio of 60%. For the interdigitated flow channel design, because the fuel transport is by forced convection rather than diffusion, the flow channel area ratio has less effect on cell performance. Taking into account liquid water removal and pressure losses, the optimal cell performance occurs for a flow channel area ratio of 50% for the interdigitated flow channel design. The results also show that the flow channel area ratio and liquid water distribution significantly influence cell performance at lower voltages.

As lower catalyst loading is required to maintain cost efficiency for PEMFCs, O2 transport becomes pivotal due to the spontaneously increased pressure-independent transport resistance. While O2 transport occurs from nanoscale to macroscale, emerging evidence suggests that the interfacial region at atomistic level near catalyst surface dominates the total transport resistance. Extensive experimental efforts have been taken to understand the transport resistance contributions from each level. However, due to the complexity of the multiscale porous structure and the triple-phase interfaces in catalyst layer, coupled with the limited laboratory techniques for probing the interface at nanoscale in MEA, no conclusive correlation has been established across the scales. Mathematical modelling is a promising approach to connect nanoscale interactions with macroscopic phenomena in a computationally efficient manner. In this work, a multiscale modeling study is presented to understand the effect of platinum interfacial transport resistance on cell performance. The Pt interfaces are separately considered as exterior and interior to represent solid carbon and porous carbon situations. Ionomer and SO3 - coverage are considered for the exterior Pt interfaces, and interior Pt is correlated with pore water uptake in terms of Pt utilization, O2 transport, and proton transport. The interface-dependent properties are up-scaled to a 2D MEA cell-level model through a modified agglomerate model framework. The model reasonably predicts the MEA measurements using Pt/Vulcan and Pt/KB with varying interior Pt loading. The ionomer poisoning not only attributes to the site blocking from SO3 - (reducing ECSA) but also from the low O2 solubility at Pt-ionomer interface compared to the water-covered exterior Pt interface. As for the Pt loaded inside the high surface area carbon (HSC) pores, we found a similar O2 interfacial permeability with the Pt-ionomer interface. Possible explanation includes ionomer penetration, confined water structure inside nanopore that hinders the O2 diffusion, or the long diffusion pathway because of the tortuous pore network. We also performed parametric studies to understand how transport at different scales—interface, ionomer film, and agglomerate—affect the total transport resistance. Lastly, a HSC pore water uptake model was integrated into the cell-level model to address the effect of RH and pore size distribution. We examined the optimal HSC pore size distribution that can balance the Pt utilization, proton transport, and oxygen transport at given operation conditions. The model offers guidance for catalyst design by optimizing ink interaction and CL multiscale porous structure.

Although lead-acid batteries contain about 11 to 30% by weight of electrolyte, the reuse of sulphuric acid solutions raises many questions concerning the advantages of this process, mainly due to the influence of these solutions on performance of batteries. The electrolyte may have critical amounts of dissolved metal ions that can decrease the hydrogen production overvoltage, increasing water loss and decreasing its electrical performance. In the present work, the influence of Cu2+, Mn2+ and Fe3+ ions present in reused electrolytic solutions on the hydrogen evolution potential in the negative electrode was investigated. An assumption of the physicochemical action of these contaminants was investigated by cyclic voltammetry and electrochemical impedance. The results showed that all the metal ions displace the potential of hydrogen evolution to less cathodic values, indicating that these species must have their concentrations minimized to allow acid solution reuse in lead-acid batteries without significant loss of performance.

The worldwide effort to decarbonize the electricity grid has made battery energy storage system (BESS) an essential technology. A promising technology for long duration storage on the grid is Vanadium Redox Flow Batteries (VRFBs), which can support the grid by regulating peak load, reducing intermittency of large-scale renewables, and as emergency power supply. There are two primary methods of integrating a BESS to the grid. Frist, the BESS is directly connected to the DC-link of a DC-AC converter that interfaces with the grid. Second, the BESS is connected to a DC-DC converter that in turn interfaces with the DC-link of a DC-AC converter. These converters all have a characteristic ripple voltage and current during operation. The magnitude and frequency of the ripples depend on topology and switching frequency of a converter, controller design and protocol, type of connection to the grid, voltage magnitude and load characteristics. Currently, studies on the impact of ripples have been limited to Lithium-ion and Lead-Acid batteries. The impact of ripple current and voltage has not been studied in VRFBs. In a VRFB, potential impact includes excessive gassing of hydrogen and carbon corrosion of the bipolar plate and porous electrode and cell heating. To better integrate and operate VRFBs to the electricity grid, the impact of ripples needs to be studied in detail.Using a novel experimental platform, where both magnitude and frequency of ripples will be incorporated, we will emulate the performance of different power electronic converter configurations. It will comprise standard 5cm2 VRFB cells with a carbon felt electrode and Nafion ion exchange membrane. The various converter ripples in an electricity grid setting will be emulated by superimposing the signals from a potentiostat (constant current) and a high frequency transformer (modulated ripples), which will be connected to the cathode of the cells.The experimental testbed will be used to cycle the VRFB cells at various states of charge with ripples that emulate the performance of power electronic converters during grid operations and disturbances. Varied parameters will include ripple amplitude, ripple frequency, electrolyte flow rate, applied current density and state of charge. Measurement data from monitoring voltage of each electrode, cell voltage and current, gas generation, electrolyte crossover and electrolyte loss will be analyzed to determine the impact of ripples on VRFB cells. Finally, the cells will be monitored for signs of gas generation and postmortem signs of carbon corrosion.Our analysis will determine the impact of various ripple magnitude and frequencies on VRFBs in a simulated grid integration environment. This work will facilitate the development of design standards for power electronic converters that are intended for battery applications, while also informing future efforts to optimize VRFB cell and stack performance.