University of Akron

The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of -80 millivolts and a current density of 4.1 milliamps per square centimeter at -0.22 volts, compared with -85 millivolts and 1.1 milliamps per square centimeter at -0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.

Electrospinning uses electrical forces to produce polymer fibres with nanometre-scale diameters. Electrospinning occurs when the electrical forces at the surface of a polymer solution or melt overcome the surface tension and cause an electrically charged jet to be ejected. When the jet dries or solidifies, an electrically charged fibre remains. This charged fibre can be directed or accelerated by electrical forces and then collected in sheets or other useful geometrical forms.

A considerable amount of research has examined trust since our 1995 publication. We revisit some of the critical issues that we addressed and provide clarifications and extensions of the topics of levels of analysis, time, control systems, reciprocity, and measurement. We also recognize recent research in new areas of trust, such as affect, emotion, violation and repair, distrust, international and cross-cultural issues, and context-specific models, and we identify promising avenues for future research.

Problem-based learning (PBL) is an instructional approach that has been used successfully for over 30 years and continues to gain acceptance in multiple disciplines. It is an instructional (and curricular) learner-centered approach that empowers learners to conduct research, integrate theory and practice, and apply knowledge and skills to develop a viable solution to a defined problem. This overview presents a brief history, followed by a discussion of the similarities and differences between PBL and other experiential approaches to teaching, and identifies some of the challenges that lie ahead for PBL.

Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal stress caused by the external electric field acting on the charge carried by the jet stabilized the straight jet for some distance. Then a lateral perturbation grew in response to the repulsive forces between adjacent elements of charge carried by the jet. The motion of segments of the jet grew rapidly into an electrically driven bending instability. The three-dimensional paths of continuous jets were calculated, both in the nearly straight region where the instability grew slowly and in the region where the bending dominated the path of the jet. The mathematical model provides a reasonable representation of the experimental data, particularly of the jet paths determined from high speed videographic observations.

In electrospinning, polymer nanofibers are formed by the creation and elongation of an electrified fluid jet. The path of the jet is from a fluid surface that is often, but not necessarily constrained by an orifice, through a straight segment of a tapering cone, then through a series of successively smaller electrically driven bending coils, with each bending coil having turns of increasing radius, and finally solidifying into a continuous thin fiber. Control of the process produces fibers with nanometer scale diameters, along with various cross-sectional shapes, beads, branches and buckling coils or zigzags. Additions to the fluid being spun, such as chemical reagents, other polymers, dispersed particles, proteins, and viable cells, resulted in the inclusion of the added material along the nanofibers. Post-treatments of nanofibers, by conglutination, by vapor coating, by chemical treatment of the surfaces, and by thermal processing, broaden the usefulness of nanofibers.

Surface resistance to nonspecific protein adsorption, cell/bacterial adhesion, and biofilm formation is critical for the development and performance of biomedical and analytical devices. Significant needs and efforts have been made in the development of biocompatible and bioactive materials for antifouling surfaces, but much of the work retains an empirical flavor due to the complexity of experiments and the lack of robust theoretical models. In this review, two major classes of nonfouling materials (i.e. hydrophilic and zwitterionic materials) and associated basic nonfouling mechanisms and practical examples are discussed. Highly hydrated chemical groups with optimized physical properties of the surface, along with appropriate surface coating methods, are the keys to developing effective and stable nonfouling materials for long-term biomedical applications. The zwitterionic polymers are promising nonfouling biomaterials due to the simplicity of synthesis, ease of applicability, abundance of raw materials, and availability of functional groups.

De<plt » past entreaties to organizational theorists and reseontchars to address levels issues more carefully, levels issues continue to arouse confusion and controversy within &e organizational literature. We highlight three alternative assumptions that underlie the specifica-tion of levels of theory throuj^out mganizational behavior: (a) homo-geneity within higher level units, (b) independence from higher Uvel tinits. and (c) heterogeneity within higher level ludts. These assump-tions influence the nature of theoretical constructs and propositions and should, ideally, also influence data collection, analysis, and in-terpretation. Greater attention to levels issues will strengthen orga-nizational theory development and research. Consider a levels-of-analysis issue arising in contemporary Ameri-can politics: How should electoral college votes be allocated In the pres-idential election? Currently, electoral college votes are allocated at the state level in all but two states (Maine and Nebraska). Thus, in 48 states,

Determining whether seed production is pollen limited has been an area of intensive empirical study over the last two decades. Yet current evidence does not allow satisfactory assessment of the causes or consequences of pollen limitation. Here, we critically evaluate existing theory and issues concerning pollen limitation. Our main conclusion is that a change in approach is needed to determine whether pollen limitation reflects random fluctuations around a pollen–resource equilibrium, an adaptation to stochastic pollination environments, or a chronic syndrome caused by an environmental perturbation. We formalize and extend D. Haig and M. Westoby's conceptual model, and illustrate its use in guiding research on the evolutionary consequences of pollen limitation, i.e., whether plants evolve or have evolved to ameliorate pollen limitation. This synthesis also reveals that we are only beginning to understand when and how pollen limitation at the plant level translates into effects on plant population dynamics. We highlight the need for both theoretical and empirical approaches to gain a deeper understanding of the importance of life-history characters, Allee effects, and environmental perturbations in population declines mediated by pollen limitation. Lastly, our synthesis identifies a critical need for research on potential effects of pollen limitation at the community and ecosystem levels.

Graphene and its derivatives are attractive for electrocatalytical application in fuel cells because of their unique structures and electronic properties. The electrocatalytical mechanism of nitrogen doped graphene in acidic environment was studied by using density functional theory (DFT). The simulations demonstrate that the oxygen reduction reaction (ORR) on N-doped graphene is a direct four-electron pathway, which is consistent with the experimental observations. The energy calculated for each ORR step shows that the ORR can spontaneously occur on the N-graphene. The active catalytical sites on single nitrogen doped graphene are identified, which have either high positive spin density or high positive atomic charge density. The nitrogen doping introduces asymmetry spin density and atomic charge density, making it possible for N-graphene to show high electroncatalytic activities for the ORR.

This calculus-based book presents a blend of theory and application. It focuses on inference making as the goal of studying probability and statistics, and features an emphasis on real-life applications of the mathematically divided techniques. Exercises based on documented data sets and other realistic experimental situations motivate the theoretical foundation. Updated and expanded coverage includes: the negative binomial probability distribution (optional); and explicit models for the analysis of variance of completely randomized block designs.

A facile approach has been developed to prepare B,N co-doped graphene with tuneable composition simply by thermal annealing graphene oxide in the presence of boric acid and ammonia. The resultant BCN graphene (see picture; C gray, H white, B pink, N blue) has superior electrocatalytic activity over commercial Pt/C electrocatalysts for the oxygen reduction reaction in alkaline media. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

This study investigated the relationships of the in-role performance and organizational citizenship behavior (OCB) of the employees in an organization with their trust in their plant managers and top management team. The study indicated that trust in these two managerial referents related to employees' ability to focus attention on value-producing activities and that this focus related to OCB.

Unilateral ureteral obstruction (UUO) is a well-characterized murine model of renal inflammation leading to fibrosis. Renal dendritic cells (DCs) constitute a significant portion of kidney leukocytes and may participate in local inflammation and have critical roles in antigen presentation. The heterogeneity in renal DC populations and surface marker overlap with monocytes/macrophages has made studying renal DCs difficult. These studies used CD11c-promoter driven reporter/depletion mice to study DCs in vivo. Studying early local inflammatory events (day 3 of UUO), in vivo multiphoton imaging of the intact kidney of CD11c reporter mice revealed more dendrite extensions and increased activity of renal DCs in real time. Phenotypic analysis suggested resident DC maturation in obstructed kidneys with increased CD11b and less F4/80 expressed. CD11b(hi) Gr-1(+) inflammatory DCs were also present in obstructed kidneys. T-cell receptor transgenic mice revealed enhanced antigen-presenting capacity of renal DCs after UUO, with increased antigen-specific T-cell proliferation in vivo and ex vivo. However, conditional DC ablation at days 0, 2, or 4 did not attenuate fibrosis or apoptosis 7 days after UUO, and depletion at 7 days did not alter outcomes at day 14. Therefore, after UUO, renal DCs exhibit inflammatory morphological and functional characteristics and are more effective antigen-presenting cells, but they do not directly contribute to tubulointerstitial damage and fibrosis.

Re-examen de la relation entre des traits de personnalite issus de theories actuelles de la perception sociale et les perceptions du leadership ou l'etendue de l'emergence d'un leader

Molecular dynamics and Monte Carlo simulations often rely on Lennard-Jones (LJ) potentials for nonbond interactions. We present 12−6 and 9−6 LJ parameters for several face-centered cubic metals (Ag, Al, Au, Cu, Ni, Pb, Pd, Pt) which reproduce densities, surface tensions, interface properties with water and (bio)organic molecules, as well as mechanical properties in quantitative (<0.1%) to good qualitative (25%) agreement with experiment under ambient conditions. Deviations associated with earlier LJ models have been reduced by 1 order of magnitude due to the precise fit of the new models to densities and surface tensions under standard conditions, which also leads to significantly improved results for surface energy anisotropies, interface tensions, and mechanical properties. The performance is comparable to tight-binding and embedded atom models at up to a million times lower computational cost. The models extend classical simulation methods to metals and a variety of interfaces with biopolymers, surfactants, and other nanostructured materials through compatibility with widely used force fields, including AMBER, CHARMM, COMPASS, CVFF, OPLS-AA, and PCFF. Limitations include the neglect of electronic structure effects and the restriction to noncovalent interactions with the metals.

▪ Abstract Quantifying the extent to which seed production is limited by the availability of pollen has been an area of intensive empirical study over the past few decades. Whereas theory predicts that pollen augmentation should not increase seed production, numerous empirical studies report significant and strong pollen limitation. Here, we use a variety of approaches to examine the correlates of pollen limitation in an effort to understand its occurrence and importance in plant evolutionary ecology. In particular, we examine the role of recent ecological perturbations in influencing pollen limitation and discuss the relation between pollen limitation and plant traits. We find that the magnitude of pollen limitation observed in natural populations depends on both historical constraints and contemporary ecological factors.

Exploring efficient and inexpensive oxygen evolution reaction (OER) electrocatalysts is of great importance for various electrochemical energy storage and conversion technologies. Ni-based electrocatalysts have been actively pursued because of their promising activity and earth abundance. However, the OER efficiency for most of the developed Ni-based electrocatalysts has been intrinsically limited due to their low electrical conductivity and poor active site exposure yield. Herein, we report metallic Ni3N nanosheets as an efficient OER electrocatalyst for the first time. The first-principles calculations and electrical transport property measurements unravel that the Ni3N is intrinsically metallic, and the carrier concentration can be remarkably improved with dimensional confinement. The EXAFS spectra provide solid evidence that the Ni3N nanosheets have disordered structure resultant of dimensional reduction, which then could provide more active sites for OER. Benefiting from enhanced electrical conductivity with metallic behavior and atomically disordered structure, the Ni3N nanosheets realize intrinsically improved OER activity compared with bulk Ni3N and NiO nanosheets. Our finding suggests that metallic nitride nanosheets could serve as a new group of OER electrocatalysts with excellent property.

9R47. Extended Surface Heat Transfer. - AD Kraus (Dept of Mech Eng, Univ of Akron, Akron OH), A Aziz (Dept of Mech Eng, Gonzaga Univ, Spokane WA), and J Welty (Dept of Mech Eng, Oregon State Univ, Corvallis OR). Wiley, New York. 2001. 1105 pp. ISBN 0-471-39550-1. $175.00.Reviewed by DP Sekulic (Col of Eng, Univ of Kentucky, 425 CRMS Bldg, Lexington KY 40506-0108).This book undoubtedly represents a most thorough compilation of the knowledge related to design and performance of fins and finned surfaces for heat transfer applications. In addition, a very detailed review of the work devoted to various aspects of extended surface convective heat transfer is provided. For those familiar with the first edition of Extended Surface Heat Transfer, by Donald Q Kern and Allan D Krauss (1972), the most striking difference, as indicated by the authors of this new edition, is a substantially increased volume of the work done in the field over the last 30 years. This book should be considered neither as a textbook nor as a monograph focused on a single topic. It rather represents an almost encyclopedic effort of the authors to collect a variety of information about the subject and present this in a user-friendly manner. The authors were not reluctant to include a number of examples to demonstrate the use of various concepts, procedures, and calculation routines. Moreover, the approach to mathematical modeling and corresponding solution findings is very transparent and may assist a reader in developing the skills needed to analyze similar problems. Hence, the book may be recommended not only to the engineers who in their daily practice have to deal with an extended surface design, but also to students at senior and post graduate levels who are familiar with basic heat transfer concepts and are capable of using advanced applied mathematics tools. The book consists of 20 chapters, which may be conveniently split into two groups. The first set of chapters (Chs 1–3, 5–9, and 13–17) is devoted to steady-state and transient conduction-convection-radiation studies of 2D and some 3D fin configurations and fined surfaces, while the second set of chapters (Chs 4, 10–12, and 18–20) provides information about convective heat transfer characteristics (notably heat transfer coefficients) associated with finned surfaces for single-phase and two-phase conditions, including presentation of extended surface heat exchangers design topics. Clearly, the main contribution of this book is located in the first set of chapters. In the existing literature, there are some more elaborate and very detailed reference sources devoted to determination of heat transfer coefficients in single- and two-phase flows. Also, design of heat exchangers has been a topic of a number of specialized sources devoted to heat exchangers. However, as a guide to designs of fins, finned surfaces, and/or finned array assemblies and their analysis, this book should be considered as a premier source.Chapter 1, Convection with simplified constraints, introduces the basic concept of fin efficiency and treats basic configurations such as longitudinal fins, radial fins and spines assuming the validity of the traditional Murray-Gardner idealizations. This material is extended in Chapter 2, entitled Convection with real constraints, following an effort to relax some of the Murray-Gardner idealizations related to geometry, boundary conditions, and presence of internal thermal energy generation. Chapter 3, Convective optimizations, considers optimizations of individual fins of rectangular, trapezoidal, triangular, concave parabolic, convex parabolic, and hyperbolic profiles. Chapter 4, Convection coefficients, provides a rather basic compilation of information related to heat transfer coefficient determination. The very detailed closure of this chapter provides a balance to this limited set of information through an extensive literature review. Chapters 5 through 8, ie, Linear transformations, Elements of linear transformations, Algorithms for finned array assembly, and Advanced Array methods and array optimization, are devoted to linear transformations for fins and finned array assemblies and some advanced methods for arrays with loops. Based on the argument that the fin efficiency definition does not use a uniform standard for comparing different fins (ie, “two fins of different dimensions in the same environment may have the same efficiency but they may transmit different quantities of heat”), an alternative approach (developed over the years by the first author) has been suggested in particular for finned arrays. This approach is based on the realization that there is a linear transformation that leads to mapping of the conditions from the fin base to conditions at the fin tip and vice versa. This approach introduces instead of fin efficiency the so-called thermal transmission ratio (ie, the input admittance). Chapter 9, Finned passages, is devoted to the application of methods for evaluation of the input admittance and fin efficiency of single, double, triple, and quadruple stacks of compact heat transfer cores for different conditions of heat loading. The following three chapters (Chs 10–12) provide information about traditional design methods for Compact heat exchangers, Longitudinal fin double-pipe exchangers, and Transverse high-fin exchangers (ie, air-fin coolers), respectively. Both the effectiveness-number of transfer units and logarithmic mean temperature difference methods were used. Chapter 13, Fins with radiation, explores the analysis and design of fins with thermal radiation as the sole heat transfer mode, while Chapter 14, Optimum design of radiating and convective-radiating fins, deals with optimum dimensions of the fins exposed to both types of conditions. Chapters 15 through 17 are adding new dimensions to the study of various fin configurations, ie, focused on additional spatial and temporal dependences. Chapter 15 is devoted to “Multidimensional heat transfer in fins and fin assemblies, Chapter 16 presents the intricacies of Transient heat transfer in extended surfaces, and Chapter 17 deals with Periodic heat flows in fins. Phase change phenomena associated with extended surfaces is summarized in Chapters 18 and 19, ie, Boiling from finned surfaces and Condensation on finned surfaces. The book concludes with Chapter 20, Augmentation and additional studies, that addresses a variety of issues related to heat transfer augmentation and performance characteristic of some compact heat transfer surfaces, including heat transfer in electronic equipment, heat pipes, solar collectors, and finned regenerators. For the convenience of the reader, the book is equipped with fairly detailed author and subject indexes. Nomenclatures are listed for each chapter separately, which may be the only plausible solution in a book covering such a vast number of sources. Two detailed appendices, one devoted to gamma and Bessel functions and the other to matrices and determinants, are helpful summaries for those less familiar with the mathematical background information needed to follow the material exposition. The list of references takes more than three-dozen pages and should be considered as the most comprehensive on the subject. In conclusion, it should be pointed out that in spite of a relatively high price, Extended Surface Heat Transfer should find its place in a library of a specialist dealing with extended surface heat transfer, and is a must for libraries supporting various thermal design fields.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAg(I) N-Heterocyclic Carbene Complexes: Synthesis, Structure, and ApplicationJered C. Garrison and Wiley J. YoungsView Author Information Department of Chemistry, The University of Akron, Akron, Ohio 44325-3601 Cite this: Chem. Rev. 2005, 105, 11, 3978–4008Publication Date (Web):November 9, 2005Publication History Received1 March 2005Published online9 November 2005Published inissue 1 November 2005https://pubs.acs.org/doi/10.1021/cr050004shttps://doi.org/10.1021/cr050004sresearch-articleACS PublicationsCopyright © 2005 American Chemical SocietyRequest reuse permissionsArticle Views12970Altmetric-Citations970LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Anions,Carbene compounds,Ligands,Salts,Silver Get e-Alerts