Investigation of an equity ethic in engineering and computing doctoral students

PEM fuel cells (PEMFCs) show great promise to increase the fuel efficiency for transportation applications; however, for this application, they must show performance and durability with the requirements for transportation. For transportation applications, the fuel cell will be subjected to frequent power cycling. For example, the DOE/Fuel Cell Tech Team (FCTT) protocol for durability includes load cycling from 0.02 A/cm2 to 1.2 A/cm2 every 0.5 min. The cathode catalyst and catalyst layer have been shown as susceptible to degradation causing loss of performance due to both loss of kinetics for the oxygen reduction reaction and loss of mass transport. Catalyst support-carbon corrosion can result in thinning of the catalyst layer contributing to degradation in performance. To examine the effect of power cycling in situ on carbon corrosion and electrode degradation, we directly measured the catalyst support degradation by measuring CO2 in the cathode outlet by NDIR (Non-Dispersive Infra-Red) while operating a single-cell fuel cell. CO2 present in air was removed by a lime bed prior to introduction to the fuel cell. We operated with a modified DOE/FCTT durability protocol using controlled voltage, and varied the potential limits to explore the effects of the upper potential limit, lower potential limit, the potential step size and time at potential. The upper potential limit was varied from 0.95 to 0.55V; the lower potential limit from 0.40V to 0.80V, with times ranging from 0.5 min to 5 min. The corrosion of three different types of carbon were explored, high surface area (E), vulcan (V), and graphitized (EA). The catalyst support carbon corrosion occurs under normal fuel cell operating conditions and is exacerbated by the voltage cycling inherent in these steps in potential. A series of carbon corrosion spikes during potential cycling is shown in Figure 1 for E-type carbon, varying the upper potential from 0.95 V to 0.60V while keeping the lower potential constant at 0.40V. Sharp spikes in the carbon corrosion rate are observed during a step increase in cell potential with the magnitude of the spikes decreasing as the high cell potential is reduced from 0.95 V to 0.6 V. The carbon corrosion rate at high cell potential (0.95V) decreases with time at potential, indicating formation of passivating carbon surface oxides. Carbon corrosion was measured during the drive cycle measurements for all three types of carbon, with the relative carbon corrosion rates of E>V>EA. The series of step potential carbon corrosion spikes where the potential was varied for the lower potential from 0.40 V to 0.60V while keeping the upper potential constant at 0.95V shows similar results in terms of the carbon corrosion. The magnitude of the spikes decrease as the lower cell potential is raised. These results indicate that the size of the step in potential has a more significant impact on the carbon corrosion rate than does the absolute value of the potential for normal cathode operating potentials. The peak in CO2 evolution occurs when the cell potential increases from high power operation to low power near open circuit. This correlates with when CO2 evolution is observed during cyclic voltammograms, which occurs during the positive sweep at ~ 0.55 to 0.60 V. The evolution of this CO2 peak suggests that oxygen is adsorbed onto the carbon and/or CO is formed on the Pt surface. During long-term operation, a reduction in catalyst layer thickness is observed during drive cycle operation, which can be due to the loss of carbon through carbon corrosion or possibly due to compaction; both effects likely lead to a loss of void volume. This reduction in thickness includes a sharp decrease in catalyst layer thickness within the first 100 hours of operation (30%), eventually reaching ~50% of its thickness after 1000 hours. Most of this reduction in electrode thickness does not appear to be directly due to carbon corrosion as there is little evidence for carbon corrosion from microscopic analysis, especially during the early stages of operation, where the thickness reduction is substantially more than what should be due to carbon corrosion. These results show that carbon corrosion occurs during normal potential operation, and is exacerbated by potential variations during operation. To minimize the carbon corrosion, the size of the steps in potential should be minimized. For a more stable catalyst, another requirement is for the Pt particles to be stabilized on graphitized carbon supports. Acknowledgments Funding for this work is from DOE EERE FCTO, Technology Development Manager Nancy Garland Figure 1

“Polyaniline”: Formation reaction and structure

Restoration of the high-potential form of cytochrome b-559 by electron transport reactions through Photosystem II in Tris-treated Photosystem II membranes

Importance: Diagnosis of small choroidal melanoma is based upon clinical features and presence of factors predictive of local malignant growth. Prognostic biopsy quantifies risk of metastasis. Objective: The aim of this study is to explore relationship between clinical characteristics and metastatic potential of a small choroidal melanoma. Design: Retrospective review of 53 patients with small choroidal melanoma treated in a tertiary oncology clinic. Patients were derived from 3 cohorts, with pathologic confirmation, with growth confirmation, and those treated only on clinical basis. Based upon prognostic biopsy outcomes, each case was classified into low or high metastatic potential groups. Distribution of clinical characteristics such as age, laterality, symptoms, tumor dimensions, tumor distance from optic nerve and fovea, presence of surface orange pigment, drusen, retinal pigment epithelial atrophy, and subretinal fluid was analyzed between metastatic groups. Main Outcome Measures: Distribution of clinical characteristics between low or high metastatic potential groups was analyzed. Results: A total of 53 patients [mean age, 61 years (range, 27–81 years); 32 (60%) men and 21 (40%) women] were classified into pathology confirmed group (n = 13), growth confirmed group (n = 26), and with clinical group (n = 14). Prognostic biopsy in the growth, pathology, and clinical groups revealed low metastatic potential in 23, 10, and 11 patients, respectively, and high metastatic potential in 3 patients in each group. Distribution of clinical characteristics between low or high metastatic potential groups was not statistically significantly different. Conclusion: Clinical characteristics do not identify metastatic potential of a small choroidal melanoma.

: The accessible potential region in a conventional electrochemical experiment is limited by the oxidation or reduction of the solvent or supporting electrolyte. It is impossible to study the redox reactions of species with very low electron affinities or high ionization potentials by ordinary electrochemical methods. It has been demonstrated recently, however, that by reducing the electrode dimensions to very small values, however, the quantity of supporting electrolyte necessary to develop the electrical double layer can be reduced to low levels. It has thus been possible to study electrode reactions in highly resistive media; these include the oxidation of ferrocene in acetonitrile without purposely added supporting electrolyte, oxidation of chromium hexacarbonyl in pure dichloromethane, oxidation of aromatic hydrocarbons in pure benzene, oxidation ferrocene in pure acetone down to 95 C.

Spectator ionic species in electrolyte solutions affect the rate and mechanism of electro-catalytic reactions. For example, it is well known that many anions, including (bi)sulfate and organic sulfonate can specifically adsorb to a platinum electrode at high potentials and affect the rate of the oxygen reduction reaction, important to fuel cell performance. If organic anions can specifically adsorb at high potentials and effect reaction rates, it should be determined if the organic cations proposed for use in new anion exchange membrane (AEM) fuel cells could specifically adsorb to platinum at low potentials and affect the rate of the hydrogen oxidation reaction. Recent evidence has shown that alkali metal cations can affect a variety of electro-catalytic reactions on platinum, including methanol oxidation, hydrogen oxidation, and oxygen reduction, but direct experimental evidence for their specific adsorption is lacking. Previously, we have used density functional theory (DFT), an ab initio quantum mechanics based technique to show that alkali metal cations can specifically adsorb to platinum and palladium electrodes at low potentials and compete with hydrogen adsorption in high pH electrolytes. We have found experimentally that the rate of the hydrogen oxidation reaction is dependent on the cation present in an alkaline electrolyte solution. We proposed and evaluated a mechanism for this effect using DFT to show alkali metal cations can specifically adsorb to the most active low index platinum facet for hydrogen oxidation, Pt(110), and can promote the adsorption of hydroxide, an important reaction intermediate. We have extended both our computational and experimental work to find that quaternary ammonium cations can also specifically adsorb to low index platinum electrode surfaces. The development of the mechanism for the effect of alkali metal cations on the rate of the hydrogen oxidation reaction and the DFT methods for simulating alkali metal cation and organic cation specific adsorption will be discussed.

The treatment of Lemna gibba plants with the weak acids (trimethylacetic acid and butyric acid), used as tools to decrease intracellular pH, induced a hyperpolarization of membrane potential, dependent on the concentration of the undissociated permeant form of the weak acid and on the value of the resting potential. Measurements were carried out both with ;high potential' and ;low potential' plants and the maximum values af acid induced hyperpolarizations were about 35 and 71 millivolts, respectively. Weak acids influenced also the transient light-dark membrane potential changes, typical for photosynthesizing material, suggesting a dependence of these changes on an acidification of cytoplasm. In the presence of the weak acids, the membrane depolarization induced by the cotransport of alanine and phosphate with protons was reduced; the maximum reduction (about 90%) was obtained with alanine during 2 millimolar trimethylacetic acid perfusion at pH 5. A strong inhibition of the uptake rates (up to 48% for [(14)C]alanine and 68% for (32)P-phosphate) was obtained in the presence of the weak acids, both by decreasing the pH of the medium and by increasing the concentration of the acid. In these experimental conditions, the ATP level and O(2) uptake rates did not change significantly. These results constitute good evidence that H(+)/solute cotransport in Lemna, already known to be dependent on the electrochemical potential difference for protons, is also strongly regulated by the cytoplasmic pH value.

Antimicrobial and cytotoxic potential of seeds and flowers crude extracts of sunflower

Beta type titanium alloys are developed as metallic biomaterials due to their low elastic modulus compared to well-known Ti-6Al-4V alloy. Since Mo is known to be an efficient beta phase stabilizer, Ti-Mo binary alloy have been extensively studied on their microstructural characteristics, mechanical properties and corrosion resistance. The stability of the beta phase can be expressed using the “molybdenum equivalent” which has minimum critical value of 10-11 .wt%. Niobium is well known to be very good to resist against corrosion in simulated body fluid and presents an excellent biocompatibility. Mn was selected as an alloying element due to its beta stabilizing effect, low cytotoxicity, high availability and lower cost when compared to other popular alloying elements. Cr-induced passive layer has been proven to be strong and solid. Ti-Cr based alloys also have been widely used for dental applications. In this study, the amount of alloying additions were calculated as a function of 10 .wt% Mo equivalence in order to evaluate the corrosion performance of each alloy. Potentiodynamic polarization test and time-based electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior in Ringer’s solution. It was found that the corrosion parameters obtained from potentiodynamic polarization test were not significantly different to those of Ti-10Mo alloy. Substituting Mo to the other studied elements simply shifts the corrosion potential into less-noble zone. However, the overall corrosion current density were lower compared to those of Ti-10Mo alloy. The lowest corrosion current density observed in Ti-6Mn alloy with the value of 7.742 nA/cm2, which 8 times lower than those of Ti-10Mo with the value of 48.81 nA/cm2. Impedance responses increase with increasing immersion time. There is little difference in the profiles in the high- and medium-frequency regions, but at lower frequencies the difference becomes substantial. The solution-film resistance element remains low for different immersion times at lower potentials, while film-substrate resistance increases with time. At higher potentials, both resistance have comparable values, pointing to the increased protectiveness, or less defective structure, of the outer porous layer at higher potentials. This result agrees with XPS evaluation on the passive film which formed on their most stable formation within the working potential range. At OCP, the capacitance values increase with the time. While at higher potentials, the capacitance values remain constant with time.

Laccases are copper-containing enzymes belonging to the family of multicopper oxidases (MCOs). All MCOs use molecular oxygen to oxidize a wide range of organic compounds by radical catalysis. One of the key fundamental properties of laccases is having high or low redox potentials depending on the active site organization. Several experimental studies have been done to rationalize the high and low redox potential laccases (LRPL), however, molecular understanding is still lacking. In this work, we explored the proteomic profile of laccases produced in the fungal cultures, specifically induced with lignocellulosic biomass such as rice straw. This study was undertaken to explain the differences in the high redox and low redox potential values of different laccases using in-silico approaches. Proteomic profiling and structural and sequence analysis revealed a low level of similarity among them. Docking analyses and molecular dynamics simulation analysis revealed that high redox potential laccases (HRPL) are having good binding affinity compared to low or medium redox potential laccases (MRPL). The stability of these complexes was further analyzed based on reactive distances, active site volume comparison and a number of tunnel formations that were observed to be significantly higher for HRPL. Our results indicate that the number of tunnel formations calculated from the simulation’s trajectories and available water molecules at the T3 site directly correlates with the laccases’ redox potentials. This study will be helpful and provide valuable inputs for the designing of new laccases to improve lignin degradation. Communicated by Ramaswamy H. Sarma

In vacuo XPS investigation of surface engineering for lithium metal anodes with plasma treatment

On the capacity of nitroheterocyclic compounds to elicit an unusual axial asymmetry in cultured rat embryos

The electrochemical oxidation of CuFeS2 in various acid solutions was studied using electrodes made from massive samples. The primary techniques employed were potentiodynamic polarization and constant potential experiments supplemented by capacitance measurements. It was the purpose of this study to investigate the behavior of: (1) several sources of CuFeS2 in H2SO4 electrolytes, and (2) a single source of CuFeS2 in various dilute acids. Electrochemical characterization of CuFeS2 from various locations was performed in 1 M H2SO4 which showed significant differences in their behavior. All samples exhibited passive-like response during anodic polarization. The current density in this passive region was reproducible and showed differences of up to two orders of magnitude between samples from different sources which has been attributed mainly to the presence of impurities in some of the samples. During anodic polarization CuFeS2 was found to be sensitive to pH at higher potential, but insensitive at low potential in sulfate solution. In addition, current decay measurements at constant potential in the low potential-passive region were found to follow the Sato-Cohen (logarithmic) model for solid film formation. Based on current and mass balance measurements, two intermediate sulfide phases appeared to form in the sequence CuFeS2 → S, → S2. At higher potentials, in the transpassive region, the observed increase in current is compatible with the decomposition of water to form chemisorbed oxygen which releases copper and forms sulfate ions.

Anodic oxidation of UO2 Part-II. Electrochemical and X-Ray photoelectron spectroscopic studies in alkaline solutions

The electrochemical oxidation of CuFeS2 in various acid solutions was studied using electrodes made from massive samples. The primary techniques employed were potentiodynamic polarization and constant potential experiments supplemented by capacitance measurements. It was the purpose of this study to investigate the behavior of: (1) several sources of CuFeS2 in H2SO4 electrolytes, and (2) a single source of CuFeS2 in various dilute acids. Electrochemical characterization of CuFeS2 from various locations was performed in 1 M H2SO4 which showed significant differences in their behavior. All samples exhibited passive-like response during anodic polarization. The current density in this passive region was reproducible and showed differences of up to two orders of magnitude between samples from different sources which has been attributed mainly to the presence of impurities in some of the samples. During anodic polarization CuFeS2 was found to be sensitive to pH at higher potential, but insensitive at low potential in sulfate solution. In addition, current decay measurements at constant potential in the low potential-passive region were found to follow the Sato-Cohen (logarithmic) model for solid film formation. Based on current and mass balance measurements, two intermediate sulfide phases appeared to form in the sequence CuFeS2→S1→S2. At higher potentials, in the transpassive region, the observed increase in current is compatible with the decomposition of water to form chemisorbed oxygen which releases copper and forms sulfate ions.