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Biomass cookstoves have been studied extensively for several decades. The Water Boiling Test (WBT) has been a widely adopted protocol for obtaining measurements needed to quantify biomass cookstove performance metrics. WBT metrics have been commonly used to evaluate cookstove effectiveness and serve as a basis for comparing biomass cookstoves. This paper demonstrates the influence of variations in testing parameters on measured or calculated metrics, especially since changes in multiple testing parameters may have competing effects on a given metric. In controlled experiments, this study assessed the effects of variations in the presence or absence of a pot lid, firepower, pot size, the initial mass of water, and presence or absence of boiling on the performance metrics of overall thermal efficiency (η), thermal efficiency associated with heating water (η heat), specific consumption (SC), and the time to reach 90 °C. η was not greatly affected by variations in any of the testing parameters (i.e. no effect was greater than 6% of the base case). SC and η heat , which are interrelated metrics, can provide additional insights on cookstove efficiency. Although these latter metrics showed a wide range of values due to variations in testing parameters, the use of a lid greatly reduced variations in both η heat and SC metrics even when there were significant variations in the other testing parameters. Thus, the use of a lid would provide better consistency for cookstove comparisons when using these metrics. The time to reach 90 °C varied widely among changes in testing parameters. Therefore, this metric is difficult to use for cookstove comparison without strict control of testing protocols. • Overall efficiency is not greatly affected by several testing parameters. • Specific consumption (SC) and η heat are related metrics for cookstove comparison. • A lid greatly reduced variation in both η heat and SC metrics. [ABSTRACT FROM AUTHOR]

We revisit the puzzle of | V u s | values obtained from the conventional implementation of hadronic- τ - decay-based flavor-breaking finite-energy sum rules lying > 3 σ below the expectations of three-family unitarity. Significant unphysical dependences of | V u s | on the choice of weight, w , and upper limit, s 0 , of the experimental spectral integrals entering the analysis are confirmed, and a breakdown of assumptions made in estimating higher dimension, D > 4 , OPE contributions identified as the main source of these problems. A combination of continuum and lattice results is shown to suggest a new implementation of the flavor-breaking sum rule approach in which not only | V u s | , but also D > 4 effective condensates, are fit to data. Lattice results are also used to clarify how to reliably treat the slowly converging D = 2 OPE series. The new sum rule implementation is shown to cure the problems of the unphysical w - and s 0 -dependence of | V u s | and to produce results ∼0.0020 higher than those of the conventional implementation employing the same data. With B-factory input, and using, in addition, dispersively constrained results for the Kπ branching fractions, we find | V u s | = 0.2231 ( 27 ) e x p ( 4 ) t h , in excellent agreement with the result from K ℓ 3 , and compatible within errors with the expectations of three-family unitarity, thus resolving the long-standing inclusive τ | V u s | puzzle. [ABSTRACT FROM AUTHOR]

Many individuals in developing areas use biomass cookstoves for cooking although there are many inherent health hazards. Judging which improved cookstove to use and distinguishing the best one for a given cooking style to mitigate these hazards is challenging. Thermal efficiency ( η th ) is one assessment parameter of cookstoves that is often used. To compare η th between cookstoves or to assess the effects of a design change on η th , it is important to understand how the uncertainty in η th depends on measurements, input data (equipment uncertainties, literature values, etc.), and test conditions. In this work, measurement and input data uncertainties are quantified with a propagation of uncertainty analysis for a basic brick channel cookstove used in many Peruvian households. This method can be used in any study by using reasonable uncertainty values for that study. Results showed that the four main parameters contributing to 93% of the η th uncertainty were the lower heating values (LHV) of wood and char, the moisture content, and the change in temperature of the water in the pot. Reducing the uncertainty of LHV of unprocessed fuels is the most difficult. If such fuels are used, reporting the LHV value and its associated uncertainty is highly valuable. [ABSTRACT FROM AUTHOR]

Biomass cookstoves are used by many people throughout the developing world for daily cooking, which unfortunately brings inherent risks to individuals and the environment. During the past several decades, extensive efforts have been made to mitigate the harm by developing clean burning, high efficiency biomass cookstoves. However, comparison and selection of cookstoves has proven to be difficult. Generally, cookstoves are characterized using the Water Boiling Test (WBT) or a variant thereof. The WBT protocol identifies several metrics used to assess cookstoves, such as average thermal efficiency ( η avg ), turn-down ratio, time to boil, and several pollutant-based metrics. Unfortunately, the results of lab tests often are not replicated by actual users in the field. Additionally, results may vary from lab to lab and sometimes within the same lab. To provide an additional tool for assessment, this study demonstrates how to predict a cookstove's average thermal efficiency with time ( η t ) which enables analyses and comparisons not possible using η avg obtained at the end of the WBT. Model predictions were validated with several experiments. Insights and benefits of time-dependent η t analysis include reduced testing times, identification of the reasons η avg varies in repeated experiments, comparison of η t at specified times even when the length of tests differ, identification of η t characteristics between cold and hot starts, and determination as to if and when η avg has reached steady state. The only required modification of the current WBT protocol to obtain η t is to record water temperature with time. [ABSTRACT FROM AUTHOR]

A root cause failure investigation was performed on anomalous (early) MIM capacitor failures on an HBT MMIC process. These failures were only observed on capacitors in the actual MMICs; process control monitor (PCM) capacitors were nominal. Multiple failure analysis techniques were employed to determine the most probable root cause of the early failures. The root cause was determined to be etching of the capacitor dielectric by a chemical used in the MMIC fabrication process, at a step after the capacitors themselves were fully built. It was determined that only CAD layouts with certain features were susceptible to the etching. These features were not present on the PCM capacitors. A design based corrective action was recommended to eliminate the failure mechanism. The effectiveness of the corrective actions was verified with several designed processing experiments. These experiments also demonstrated that the failure rate of the faulty parts increased with the time (even if the parts were not in operation). Finally, the experiments showed that the reliability of a nominal capacitor with a BCB layer on top was better than that of an identical capacitor without the BCB layer. Capacitor reliability model For the sake of completeness, the following discussion on ramped voltage TDDB testing of capacitors is included. In this work, ramped voltage data was not used to predict capacitor lifetimes, but it was used to quantitatively compare capacitor reliability by plotting percent cumulative failure versus failure voltage. Normally, destructive ramped voltage testing and the linear field model are employed in order to estimate the lifetime of capacitors. This method has been described in detail elsewhere for intrinsic capacitors (Cramer et al. [1,2,3] ). It is generally assumed that defects on or in the capacitor bottom plate or in dielectric itself causes a localized thinning of the dielectric which shortens the intrinsic lifetime of the capacitor, as illustrated in Fig. 2. Extrinsic capacitors require a refinement of the Nominal Thickness Method to the Effective Thickness Method. Typically, plots of percent cumulative failure versus failure voltage will be transformed into plots of percent cumulative failure versus lifetime via the above equations. The shapes of these two plots are nearly identical, only the values on the abscissa are changed from (linear) voltage to (logarithmic) lifetime. Since, in this work, the effort was directed at root cause determination of anomalous failures rather than predictions of expected lifetimes, the linear field model was never employed and the data was always plotted as a function of failure voltage. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogenase activity plays an important role in the fermentation of biomass-generated syngas (containing CO, CO2, and H2) to obtain ethanol and other biofuels. One process efficiency issue for producing biofuels from syngas fermentation is the ability of key cellular enzymes to produce reducing equivalents from syngas. For microbes using the Wood–Ljungdahl pathway, inhibition of the hydrogenase enzyme would decrease reducing equivalent production from H2, thus potentially reducing carbon conversion efficiency and biofuel production. During biomass gasification to produce syngas, several impurities are generated. These impurities, such as ammonia (NH3), can potentially impact the fermentation process. In this work, it was shown that NH3 rapidly converts to ammonium ion (NH4 +) following exposure of fermentation media to NH3. The accumulated NH4 + also inhibited hydrogenase activity and cell growth. A kinetic model for hydrogenase activity that included inhibition effects from NH4 + was developed. Model parameters included (Michaelis–Menten constant) and (the inhibition constant for NH4 +). Experimental results showed that NH4 + is a non-competitive inhibitor for hydrogenase activity with of (649 ± 35) mol m−3. As part of the work to distinguish the unique aspect of NH4 + inhibition, additional work showed that potassium and phosphate ions had no effect on hydrogenase activity. Since NH4 + can easily be accumulated in fermentation media and transport across the cell membrane, it is necessary to remove NH3 impurity from raw syngas to minimize the reduction in hydrogenase activity. [Copyright &y& Elsevier]

Abstract: The fermentation of syngas (CO, CO2, and H2) produced from biomass gasification for the production of ethanol has received increased attention due to the low cost and abundance of cellulosic feedstocks. Since CO plays a critical role in the available reducing equivalents and carbon conversion, this work assessed the effects of constant CO partial pressure (P CO), ranging from 0.35 to 2.0atm, on cell growth, acetic acid production, and ethanol production using Clostridium carboxidivorans P7T. Several key findings included: (a) the maximum cell concentration increased with increasing P CO, increasing 440% with a P CO increase from 0.35 to 2.0atm, (b) ethanol production changed from non-growth-associated to growth-associated with increasing P CO, (c) acetic acid production (gram acetic acid per gram cells) decreased for P CO ≥1.05atm relative to P CO ≤0.70atm, and (d) acetic acid appeared to be converted in the latter growth stages for P CO of 1.35 and 2.0atm. Several explanations point to the potential importance of P CO and the P CO to ratio on electron and ATP production. Since gasification processes that generate syngas could result in differing gas partial pressures, process variations could significantly change growth and product formation as evidenced by metabolic changes observed in this work due to changing P CO and/or the P CO to ratio. [Copyright &y& Elsevier]

Abstract: Polyethylene terephthalate (PET) was functionalized to introduce carboxyl groups onto its surface by a carboxylation technique. Surface and bulk properties, such as possible surface deterioration, surface roughness and the mechanical strength of the carboxylated polymers, were studied and compared with those of aminolyzed and hydrolyzed PET. Atomic force microscopy studies showed that unlike aminolysis and hydrolysis, which increased the surface roughness significantly due to cracking and pitting, the surface roughness of unmodified and carboxylated PET were comparable. While hydrolysis and aminolysis of PET resulted in significant loss of strength, tensile testing revealed that unmodified and carboxylated polymers had similar strength. The development of mechanically stable, functionalized PET would vastly improve the biomedical applications of this polymer. To understand the potential for improving biomedical applications, biologically active molecules, namely nucleoside triphosphate diphosphohydrolase (NTPDase) and cysteine, were immobilized on the carboxylated PET using amide bonds. NTPDase was also immobilized to aminolyzed PET using imine bonds, while cysteine was immobilized on aminolyzed PET using both imine and amide bonds. Attachment of NTPDase and cysteine was verified by analyzing the NTPDase activity and the cysteine surface concentration. The stability of these immobilizations was also studied. [Copyright &y& Elsevier]

Abstract: Thiol groups were attached to polyethylene terephthalate (PET) to promote the transfer of a known platelet inhibitor, nitric oxide (NO), from nitrosated thiols naturally found in the body to PET, followed by the release of NO from PET to prevent platelet adhesion. In order to immobilize the most thiols on the modified polymer, the processing parameters used to attach the following three thiol containing groups were assessed: l-cysteine, 2-iminothiolane, and a cysteine polypeptide. When comparing the immobilized concentrations of thiol groups from each of the optimized processes the amount of immobilized thiol groups increased in order with the following groups: cysteine polypeptide <2-iminothiolane

A novel method for improving the haemocompatibility of biomedical materials through endogenous nitric oxide (NO) is presented. l-cysteine was covalently immobilized onto two biomedical polymers: polyurethane (PU) and polyethylene terephthalate (PET). The l-cysteine content on the polymers was approximately 5–8 nmol/cm2 as quantified via a chemiluminescence-based assay. The haemocompatibility of the modified polymers was evaluated in terms of the number of adhered platelets when exposed to a platelet suspension labeled with Cr51. Platelet adherence on the l-cysteine-modified polymers was reduced more than 50% as compared to the control (glycine-modified polymers) when the platelet suspension contained plasma constituents. No difference in platelet adhesion was observed in the absence of plasma constituents. Further experiments demonstrated that NO was easily transferred to the l-cysteine-modified polymers from S-nitroso-albumin in PBS buffer. The NO was then released from the polymer. NO transfer or release was not observed for the control. The results suggest that l-cysteine-modified polymers are effective in reducing platelet adhesion via the transfer of NO from endogenous S-nitrosoproteins in plasma to the polymer followed by the subsequent release of NO. Thus, exploiting endogenous NO is a viable option for improving the haemocompatibility of biomaterials. [Copyright &y& Elsevier]

Abstract: Currently, syngas fermentation is being developed as one option towards the production of biofuels from biomass. This process utilizes the acetyl-CoA (Wood–Ljungdahl) metabolic pathway. Along the pathway, CO and CO2 are used as carbon sources. Electrons required for the metabolic process are generated from H2 and/or from CO. This study showed that electron production from CO is always more thermodynamically favorable compared to electron production from H2 and this finding is independent of pH, ionic strength, gas partial pressure, and electron carrier pairs. Additionally, electron production from H2 may be thermodynamically unfavorable in some experimental conditions. Thus, it is unlikely that H2 can be utilized for electron production in favor of CO when both species are present. Therefore, CO conversion efficiency will be sacrificed during syngas fermentation since some of the CO will provide electrons at the expense of product and cell mass formation. [Copyright &y& Elsevier]

Abstract: Biomass gasification to generate raw syngas used in anaerobic fermentation processes is one of several emerging technologies for the production of biofuels from biomass. The gasification-fermentation process can utilize a wide variety of lignocellulosic biomass such as prairie grasses, wood chips, and paper wastes, in addition to non-lignocellulosic biomass such as solid municipal wastes. Although the primary components of raw syngas used in the fermentation process are CO, H2, and CO2, several impurities can also be present. Some of these impurities may interfere with the fermentation process. Since the impurities will depend upon the feedstock, the gasifier type, and cleanup conditions, an understanding of the positive or adverse effects of the impurities on raw syngas fermentation is critical to understand the need for efficient gas cleaning processes required for commercialization. This work describes the impurities generated during gasification and discusses the potential accumulation of impurities in the fermentation media and the associated potential effects on the microbial fermentation process (e.g. cell toxicity, enzymatic inhibition and end product distribution). A wide distribution of impurity solubilities in the media shows that certain impurities, such as ammonia, are more likely to accumulate in the media. Additionally, entrained tar particulates greater than 0.025 μm, nitric oxide greater than 0.004 mol%, and ammonia in general have an adverse effect on the fermentation process. Therefore, a cleanup system suitable for raw syngas fermentation processes is evident although the degree of cleanup would likely depend upon the feedstock and the associated gasification process. [Copyright &y& Elsevier]

A recently discovered clostridial bacteria converts components of synthesis gas (CO, CO2, H2) into liquid products such as ethanol, butanol and acetic acid. Isolated from an agricultural lagoon, the stability and productivity characteristics of the bacteria were studied in a continuous 4.5 l bubble column bioreactor at 37°C using artificial blends of CO, CO2, and N2. Preliminary results on the rates of cell growth, substrate utilization, product formation, and yields of products and cells from CO are discussed. At steady state, apparent yields (mole C in products per mole CO consumed) of ethanol, butanol, and acetic acid were 0.15, 0.075 and 0.025, respectively, and the cell yield was 0.25 g/mol CO. The theoretical yield of ethanol is 0.33 if CO is only utilized for the production of ethanol. The experimental yield of CO2 from CO was approximately 60% compared to the theoretical yield of 67% with ethanol as the sole product. As a comparison with another ethanol-producing bacteria, the results of a similar fermentation study using batch-grown Clostridium ljungdahlii showed yields of 0.062 for ethanol and 0.094 for acetic acid and a cell yield of 1.378 g/mol. [Copyright &y& Elsevier]

One area of exploration for renewable energy is the development of fuel cells, including carbohydrate fuel cells that can extract energy from carbohydrates. Viologen electron mediators have been shown to enhance energy extraction and improve carbohydrate conversion efficiencies, although the limiting step appears to be the homogeneous rate at which electrons are first transferred from the carbohydrate to the viologen. In this work, electron transfer rates for various monosaccharides in the presence of methyl viologen were studied in the absence of a fuel cell to isolate the homogeneous rate. Using glucose as the model carbohydrate, a rigorous mechanistic model of the homogeneous electron transfer rate was developed and showed a first-order dependence on OH− concentration, a first-order dependence on carbohydrate concentration, a zero-order dependence when the methyl viologen concentration was ≫ 0.4 mM, and an increasing rate with incubation time when glucose was incubated in a buffer solution prior to exposure to methyl viologen. The incubation effect had a strong dependence on pH and was consistent with interconversion between glucose and fructose. The mechanistic model, which agreed well with experimental data, can be useful for identifying process improvements to carbohydrate fuel cells, especially when the homogenous rate is a limiting step. • Viologen-mediated carbohydrate electron transfer rates were evaluated. • Electron transfer rates generally increased with decreasing number of carbons. • A rigorous mechanistic electron transfer model for glucose was developed. • Electron transfer model is first order in pH and carbohydrate concentration. • Incubation time of glucose increases electron transfer rate and is pH dependent. [ABSTRACT FROM AUTHOR]

Highlights • New technique to measure H 2 and CO mass transfer coefficients (k i a) in HFR using GC. • k i a increased with an increase in liquid flow rate in the HFR. • Largest measured k i a for H 2 and CO were 840 and 420 h−1, respectively. • Model predictions of k i a for O 2 , CO and H 2 agreed well with experimental values. • HFRs can potentially support high cell densities due to their high mass transfer. Abstract Syngas fermentation for producing biofuels and other products suffers from mass transfer limitations due to low CO and H 2 solubility in liquid medium. Therefore, it is critical to characterize mass transfer rates of these gases to guide bioreactor design and optimization. This work presents a novel technique to measure the volumetric mass transfer coefficients (k i a) for H 2 and CO using gas chromatography in a non-porous hollow fiber reactor (HFR). The largest measured k i a for H 2 and CO were 840 and 420 h−1, respectively. A model was developed to predict k i a for H 2 and CO that agreed well with experimental data. This study is the first to measure, compare, and model both H 2 and CO mass transfer coefficients in an HFR. Based on model predictions, HFRs have the potential to be a reactor of choice for syngas fermentation as a result of high mass transfer that can support high cell densities. [ABSTRACT FROM AUTHOR]

An efficient syngas fermentation bioreactor provides a mass transfer capability that matches the intrinsic kinetics of the microorganism to obtain high gas conversion efficiency and productivity. In this study, mass transfer and gas utilization efficiencies of a trickle bed reactor during syngas fermentation by Clostridium ragsdalei were evaluated at various gas and liquid flow rates. Fermentations were performed using a syngas mixture of 38% CO, 28.5% CO 2 , 28.5% H 2 and 5% N 2 , by volume. Results showed that increasing the gas flow rate from 2.3 to 4.6 sccm increased the CO uptake rate by 76% and decreased the H 2 uptake rate by 51% up to Run R6. Biofilm formation after R6 increased cells activity with over threefold increase in H 2 uptake rate. At 1662 h, the final ethanol and acetic acid concentrations were 5.7 and 12.3 g/L, respectively, at 200 ml/min of liquid flow rate and 4.6 sccm gas flow rate. [ABSTRACT FROM AUTHOR]

Abstract: Producing biofuels from gasified biomass (synthesis gas) via microbial fermentation is currently being pursued as one alternative in biofuels development. In synthesis gas fermentation, reducing equivalents from H2 oxidation via hydrogenase is important towards directing more carbon towards product formation. In this work, kinetic studies of H2 utilization via the Clostridium P11 hydrogenase enzyme were performed to determine the most appropriate model to predict hydrogenase activity as a function of H2 partial pressure. An important aspect of this work included the proper analysis of electron acceptors used in the kinetic studies. The model parameter governing the effect of H2 partial pressure on activity was ∼30 kPa (absolute), independent of the type and concentration of electron acceptor. The value indicates that H2 partial pressures typically associated with syngas fermentation will result in compromised efficiency of the hydrogenase activity. [Copyright &y& Elsevier]

Abstract: Trickle-bed reactor (TBR), hollow fiber membrane reactor (HFR) and stirred tank reactor (STR) can be used in fermentation of sparingly soluble gasses such as CO and H2 to produce biofuels and bio-based chemicals. Gas fermenting reactors must provide high mass transfer capabilities that match the kinetic requirements of the microorganisms used. The present study compared the volumetric mass transfer coefficient (KtotA/VL ) of three reactor types; the TBR with 3mm and 6mm beads, five different modules of HFRs, and the STR. The analysis was performed using O2 as the gaseous mass transfer agent. The non-porous polydimethylsiloxane (PDMS) HFR provided the highest KtotA/VL (1062h−1), followed by the TBR with 6mm beads (421h−1), and then the STR (114h−1). The mass transfer characteristics in each reactor were affected by agitation speed, and gas and liquid flow rates. Furthermore, issues regarding the comparison of mass transfer coefficients are discussed. [Copyright &y& Elsevier]

Abstract: In our previous work, we demonstrated that biomass-generated producer gas can be converted to ethanol and acetic acid using a microbial catalyst Clostridium carboxidivorans P7T. Results showed that the producer gas (1) induced cell dormancy, (2) inhibited H2 consumption, and (3) affected the acetic acid/ethanol product distribution. Results of this work showed that tars were the likely cause of cell dormancy and product redistribution and that the addition of a 0.025μm filter in the gas cleanup negated the effects of tars. C. carboxidivorans P7T can adapt to the tars (i.e. grow) only after prolonged exposure. Nitric oxide, present in the producer gas at 150ppm, is an inhibitor of the hydrogenase enzyme involved in H2 consumption. We conclude that significant conditioning of the producer gas will be required for the successful coupling of biomass-generated producer gas with fermentation to produce ethanol and acetic acid. [Copyright &y& Elsevier]

• Viologen-mediated glucose oxidation was measured in an electrochemical cell. • Faster rates of the mediator electrochemical reoxidation improved the efficiency. • The presence of oxygen changed the glucose oxidation pathway and efficiency. • Viologen-mediated oxidation efficiency was 3 times that observed with noble metals. Glucose is a potential source of energy for fuel cell applications. However, its complete oxidation has been a challenge. Dimethyl viologen, as an electron mediator, has been shown to promote high levels of glucose oxidation under aerobic conditions. Nevertheless, the efficiency of viologen-mediated glucose oxidation has been low in electrochemical experiments. In this study, viologen-mediated oxidation of glucose was investigated under anaerobic electrochemical conditions to understand the factors that impact the oxidation efficiency. Of particular interest was the improvement of electrochemical oxidation for glucose fuel cell applications. An experimental cell was developed to electrochemically reoxidize the mediator as it was homogeneously reduced by glucose under anaerobic conditions. In contrast, the mediator was reoxidized by direct reaction with oxygen under aerobic conditions. The aerobic oxidation efficiency was 75%, three times larger than the maximum efficiency in the electrochemical cell. 13C-NMR results show that the main product formed under aerobic conditions was formic acid, whereas glycolic acid was the principal product formed in the electrochemical cell. Carbonate was only formed under aerobic conditions. Therefore, the use of oxygen to reoxidize the mediator also directly influenced the glucose oxidation pathway. In the electrochemical cell, the oxidation efficiency depended on the electrochemical reaction rate of the mediator and was higher at faster rates. The efficiency also depended on the initial molar ratio of the mediator to glucose. The maximum oxidation efficiency of glucose in the electrochemical cell was approximately 22%, which is about three times larger than the maximum efficiency for precious-metal-based anodes. [ABSTRACT FROM AUTHOR]