So-called Reversal Research Articles

Can metallic bipolar plates with low-cost Cr/a-C coating withstand cell reversal events in PEMFCs? Post-coated vs pre-coated BPs

The so-called cell reversal caused by H2 starvation during polymer electrolyte membrane fuel cell operation can lead to anode potentials >1.5 Vanode and thus to significant carbon corrosion in the anode catalyst layer. In this work, the influence of cell reversals on the electrochemical stability of low-cost Cr/a-C post- and pre-coating on metallic bipolar plates (BPs) was investigated in a vehicle application-oriented test cycle. While the electrical resistance of the BPs with the low-cost coatings increased after the tests, no impact on the H2/air polarization curves was detected in comparison to BPs coated with Au as reference. Nevertheless, surface changes of the carbon coatings were detected in regions of BP bends because of water accumulation. Further analyses showed that corrosion products from the chromium interlayer were detected. We therefore assume that the high electrochemical potential during the cell reversal events can only corrode the low-cost carbon coatings on the BP in the presence of water, while the overall degradation of the BPs regarding their electrical resistance was negligible compared to the performance loss due to anode catalyst layer corrosion. Furthermore, no significant difference of the degradation characteristics (metal ion leaching, anode catalyst layer thinning) was found regarding the coating sequence.

The Students–Professors Problem—The Reversal Error and Beyond

Abstract This paper first introduces and reviews the existing research on the well-known “students–professors (S/P) problem”, which was first formulated in 1979. Next, it presents an empirical study of Danish upper secondary students’ answers to two mathematical modeling versions of the S/P-problem; a mathematization version (296 students), and a de-mathematization version (658 students). Besides reproducing several previously reported findings, e.g., the so-called reversal error, the study identifies new error types not previously reported in the literature. The mathematical modeling perspective adopted, along with a mixed-methods design, give rise to new potential explanations of the reversal error as well as explanations of the new error types. Our study shows that interpreting the linguistic formulation of the S/P-problem statement is not only related to language but is intrinsically of a mathematical – and cognitive – nature as well. Altogether, there is still more to be said about the S/P-problem forty years after its emergence. The impact sheet to this article can be accessed at 10.6084/m9.figshare.16610104.

The proposal of a GSSP for the Berriasian Stage (Cretaceous System): Part 2

In part 1 of this work we discussed the possibilities for the selection of a GSSP for the Berriasian Stage of the Cretaceous System, based on prevailing practical methods for correlation in that J/K interval, traditional usage and the consensus over the best boundary markers that had developed in the last forty years. This consensus has developed further, based on the results of multidisciplinary studies on numerous sites over the last decade. Here in Part 2 we give an account of the application of those results by the Berriasian Working Group (ISCS), and present the stratigraphic evidence that justifies the selection of the locality of Tré Maroua (Hautes-Alpes, SE France) as the proposed GSSP. We describe a 45 m-thick section in the Calcaires Blancs vocontiens – that part of the formation covering the calpio­nellid Chitinoidella, Remanei. Intermedia, Colomi, Alpina, Ferasini, Elliptica and Simplex biozones. The stratigraphic data collected here has been compiled as part of a wider comparative study of complementary Vocontian Basin sites (with localities at Charens, St Bertrand, Belvedere and Le Chouet). Evidence from Tré Maroua thus sits in this substantial regional biostratigraphic and magnetostratigraphic context. For the purposes of the GSSP definition, here we particularly concentrate on the unbroken sequence and biotic markers in the interval immediately below the boundary, the Colomi Subzone (covering circa 675,000 years), and immediately above, the Alpina Subzone (covering circa 725,000 years). Particularly significant fossil datums identified in the Tré Maroua profile are the primary basal Berriasian marker, the base of the Alpina Subzone (a widespread event marked by dominance of small Calpionella alpina, with rare Crassicollaria parvula and Tintinopsella carpathica): the base of the Berriasian Stage is placed at the base of bed 14, which coincides with the base of the Alpina Subzone. Secondary markers bracketing the base of the Calpionella Zone are the FOs of the calcareous nannofossil species Nannoconus wintereri, close below the boundary, and the FO of Nannoconus steinmannii minor, close above. The Tithonian/Berriasian boundary level occurs within M19n.2n, in common with many documented sites, and is just below the distinctive reversed magnetic subzone M19n.1r (the so-called Brodno reversal). We present data which is congruent with magnetostratigraphic and biostratigraphic data from other key localities in France and in wider regions (Le Chouet, Saint Bertrand, Puerto Escaño, Rio Argos, Bosso, Brodno, Kurovice, Theodosia…), and thus the characteristics and datums identified at Tré Maroua are key for correlation and, in general, they typify the J/K boundary interval in Tethys and connected seas.

The proposal of a GSSP for the Berriasian Stage (Cretaceous System): Part 1

Here in the first part of this publication we discuss the possibilities for the selection of a GSSP for the Berriasian Stage of the Cretaceous System, based on the established methods for correlation in the Tithonian/Berriasian interval. This will be followed, in the second part, by an account of the stratigraphic evidence that justifies the locality of Tre Maroua (Hautes-Alpes, SE France) as the proposed GSSP. Here we discuss the possibilities for correlation in the historical J/K boundary interval, and the evolution of thinking on the positioning of the boundary over recent generations, and in relation to research in the last ten years. The Tithonian/Berriasian boundary level is accepted as occurring within magnetosubzone M19n.2n. The detailed distribution of calpionellids has been recorded at numerous sites, tied to magnetostratigraphy, and the base of the calpionellid Alpina Zone is taken to define the base of the Berriasian Stage. This is at a level just below the distinctive reversed magnetic subzone M19n.1r (the so-called Brodno reversal). We discuss a wide range of magneto­stratigraphic and biostratigraphic data from key localities globally, in the type Berriasian areas of France and wider regions (Le Chouet, Saint Bertrand, Puerto Escano, Rio Argos, Bosso, Brodno, Kurovice, Theodosia etc.). The characteristic datums that typify the J/K boun­dary interval in Tethys and its extensions are detailed, and the correlative viability of various fossil groups is discussed. The boundary level is correlated to well-known J/K sections globally, and a series of secondary markers and proxies are indicated which assist wider correlation. Particularly significant are the primary basal Berriasian marker, the base of the Alpina Subzone (marked by dominance of small Calpionella alpina, Crassicollaria parvula and Tintinopsella carpathica) and secondary markers bracketing the base of the Calpio­nella Zone, notably the FOs of the calcareous nannofossil species Nannoconus wintereri (just below the boundary) and the FO of Nannoconus steinmannii minor (just above). Notable proxies for the boundary are: 1) the base of the Arctoteuthis tehamaensis Zone in boreal and subboreal regions, 2) the dated base of the Alpina Subzone at 140.22 ±0.14 Ma, which also gives a precise age estimate for the system boundary; and 3) the base of radiolarian “unitary zone” 14, which is situated just above the base of the Alpina Subzone.

Liver Transplant From a Donor With Situs Inversus Totalis Using Orthotopic and Retroversus Technique: A Case Report

Situs inversus totalis is an infrequent genetic malformation affecting 0.01% of the population and consists of the total rotation of the organs 180 degrees, generating the so-called mirror-image reversal. For many years donors with this pathology were discouraged from organ donation. We present a case of hepatic and renal transplantation using the 2 techniques described, orthotopic and retroversus. The recipient was a 69-year-old man with end-stage liver and kidney disease due to alcoholism and diabetes, respectively, and a Model for End-Stage Liver Disease score of 32. There was no mismatch between recipient and donor. The implant started with the piggy-back technique using the retroversus technique, generating a tense portal vein anastomosis due to the superior situation of the elements of the hepatic hilum, so it was decided to undo suprahepatic anastomosis with the orthotopic technique, rotating the liver on its axis, without complications. Roux-en-Y hepaticojejunoanastomosis was carried out. The patient was discharged 15 days after surgery with normalization of renal function. Although both techniques must be taken into account, the one that fits best for a particular recipient should be used, given the particularities of size and shape of the liver graft. This can take some art and creativity from the surgical team.

Responsibility, Libertarians, and the “Facts as We Know Them”: A Concern-Based Construal of Strawson’s Reversal

Here, I put forth a construal of P. F. Strawson’s so-called reversal, his view that what it means to be morally responsible is determined (in some way) by our practices of holding responsible. The ...

Unraveling Excited-Singlet-State Aromaticity via Vibrational Analysis

Summary The concept of excited-state aromaticity is receiving much attention in that completely reversed aromaticity in the excited state (so-called aromaticity reversal) provides crucial insight into photostability, photoreactivity, and its application to the photosynthetic mechanism and photoactive materials. Despite this significance, experimental elucidation of excited-state aromaticity is still unsolved, particularly for the excited singlet state. Here, as an unconventional approach, time-resolved IR (TRIR) spectroscopy on aromatic and anti-aromatic hexaphyrin congeners shed light on excited-singlet-state aromaticity. The contrasting spectral features between the Fourier transform IR and TRIR spectra reveal the aromaticity-driven structural changes, corroborating aromaticity reversal in the excited singlet states. Our paradigm for excited-state aromaticity, the correlation of IR spectral features with aromaticity reversal, provides another fundamental key to understanding the role of (anti)aromaticity in the stability, dynamics, and reactivity in the excited singlet state of π-conjugated molecular systems.

Young Children's Transfer of Series Completion in a Dynamic Test Setting: Does Cognitive Flexibility Play a Role?

Dynamic testing aims to assess potential for learning by measuring how much a child can profit from a training procedure during the testing process. These procedures often include transfer tasks as a measure of the potential for learning, as the ability to transfer learned skills and knowledge is considered essential in successful learning. The aim of the current study was to investigate whether including a specific type of transfer task in a dynamic testing context, a so-called reversal procedure, would provide extra information on 6-7-year-old children’s potential for learning. Moreover, it was investigated whether children’s ability to transfer newly learned skills was dependent on their level of cognitive flexibility, as this executive function has previously been argued to be of significant importance in the transfer of academic skills. The results revealed that children’s transfer abilities were indeed related to another measure of potential for learning, i.e. children’s learner status. In addition, children’s cognitive flexibility predicted greater transfer abilities and appeared to play a greater role for children who did not receive training or did not profit much from the training procedure. The results underline the importance of supporting children’s cognitive flexibility when teaching for transfer.

Weibull Wind-Speed Distribution Parameters Derived from a Combination of Wind-Lidar and Tall-Mast Measurements Over Land, Coastal and Marine Sites

Wind-speed observations from tall towers are used in combination with observations up to 600 m in altitude from a Doppler wind lidar to study the long-term conditions over suburban (Hamburg), rural coastal (Hovsore) and marine (FINO3) sites. The variability in the wind field among the sites is expressed in terms of mean wind speed and Weibull distribution shape-parameter profiles. The consequences of the carrier-to-noise-ratio (CNR) threshold-value choice on the wind-lidar observations are revealed as follows. When the wind-lidar CNR is lower than a prescribed threshold value, the observations are often filtered out as the uncertainty in the wind-speed measurements increases. For a pulsed heterodyne Doppler lidar, use of the traditional –22 dB CNR threshold value at all measuring levels up to 600 m results in a $$\approx $$ 7 % overestimation in the long-term mean wind speed over land, and a $$\approx $$ 12 % overestimation in coastal and marine environments. In addition, the height of the profile maximum of the shape parameter of the Weibull distribution (so-called reversal height) is found to depend on the applied CNR threshold; it is found to be lower at small CNR threshold values. The reversal height is greater in the suburban (high roughness) than in the rural (low roughness) area. In coastal areas the reversal height is lower than that over land and relates to the internal boundary layer that develops downwind from the coastline. Over the sea the shape parameter increases towards the sea surface. A parametrization of the vertical profile of the shape parameter fits well with observations over land, coastal regions and over the sea. An applied model for the dependence of the reversal height on the surface roughness is in good agreement with the observations over land.

Dynamically Adaptive Control System for Bioanodes in Serially Stacked Bioelectrochemical Systems

Microbial bioelectrochemical systems (BESs) use microorganisms as catalysts for electrode reactions. They have emerging applications in bioenergy, bioproduction, and bioremediation. BESs can be scaled up as a linked series of units or cells; however, this may lead to so-called cell reversal. Here, we demonstrate a cell balance system (CBS) that controls individual BES cells connected electrically in series by dynamically adapting the applied potential in the kilohertz frequency range relative to the performance of the bioanode. The CBS maintains the cell voltage of individual BES cells at or below a maximum set point by bypassing a portion of applied current with a high-frequency metal oxide semiconductor field-effect transistor switch control system. We demonstrate (i) multiple serially connected BES cells started simultaneously and rapidly from a single power source, as the CBS imparts no current limitation, (ii) continuous, stable, and independent performance of each stacked BES cell, and (iii) stable BES cell and stack performance under excessive applied currents. This control system has applications for not only serially stacked BESs in scaled-up stacks but also rapidly starting individual- and/or lab-scale BESs.

First textbook in vascular surgery

First textbook in vascular surgery

Molecular Simulation of Ompf Channel in Salts of Divalent Cations: Molecular Insight on Charge Inversion

Extensive recent experimental and theoretical work has shown that the interaction of biologically relevant divalent cations (such as Mg2+, Ca2+) has surprising properties. One of the most fascinating and unexpected effect is the so-called charge inversion or charge reversal phenomenon: cations accumulate at the interface in excess of its own bare charge, thus inverting the effective charge of the interface. Recently, charge inversion has been reported in the bacterial channel OmpF, in the presence of salts of divalent cations [Alcaraz et al. Biophys. J. 96 (2009) 56]. Aiming to get an insight on the atomistic mechanism of the cation interaction with the protein, we have performed extensive MD simulations of a realistic model of the OmpF WT protein in a POPC membrane in MgCl2 and explicit water. The simulations were computationally highly demanding, with half million atoms in a simulation box and production runs around 25 nsec.The simulations were performed employing the NAMD simulation package running in 128 processor at the CESGA Supercomputing Center. Our main result is that we have observed charge inversion of certain important acidic groups. The observed charge inversion is accompanied by a change in the transport mechanism of ions inside the channel and a reversal in the selectivity of the channel. Overall, our simulations give an accurate microscopic image of this unexpected effect with potentially important biological and nanotechnological implications.

Erythema nodosum–like lesions in treated Whipple's disease: Signs of immune reconstitution inflammatory syndrome

Treatment of systemic infections due to mycobacteria and HIV infection can lead to paradoxical worsening, the immune reconstitution inflammatory syndrome, in a minority of patients. Herein we describe a patient with Whipple's disease, a chronic systemic inflammatory disease caused by Tropheryma whipplei, who developed cutaneous and later ocular disease after initiation of antibiotic therapy. A 42-year-old man with a 12-year history of arthralgias presented with deteriorating health, including weight loss, diarrhea, fever, and acral hyperkeratosis. Whipple's disease was suspected and subsequently confirmed by finding periodic acid-Schiff (PAS)-positive foamy macrophages and T whipplei DNA by polymerase chain reaction (PCR) assays in duodenal biopsy specimens. After 5 weeks of antibiotic treatment with ceftriaxone, erythema nodosum (EN)-like lesions developed on the legs and trunk. Notably, lesional and nonlesional skin harbored intracellular and extracellular degenerated bacteria that were associated with a neutrophilic and granulomatous inflammatory response in lesional skin. Continued antibiotic therapy was associated with recurring EN-like skin nodules, orbital swelling, and facial herpes simplex virus 1 infection. Corticosteroid therapy controlled the duration and severity of the EN-like nodules and orbital swelling. Apart from cutaneous hyperpigmentation, skin disease in Whipple's disease is infrequent and can be categorized as disorders due to malnutrition from malabsorption or so-called reversal reactions consisting of reactive erythemas, and neutrophilic and granulomatous responses to T whipplei, the latter of which can represent an immune reconstitution inflammatory reaction after initiation of antibiotic therapy. Finally, based on the presence of T whipplei in normal skin, skin biopsy may serve as another site for diagnostic testing in patients suspected of having Whipple's disease.

Geomagnetic reversals in the paleozoic: A transitional field, polarity bias, and mantle convection

The paper analyzes previously published results of studies of detailed records of geomagnetic reversals in sedimentary and volcanic sequences of the Paleozoic in the Siberian and Eastern European platforms. It is shown that the processes of geomagnetic reversals, both in the Early Paleozoic and at the end of this era, are well described by a model in which the transitional field is controlled by an equatorial dipole. During a reversal, this dipole maintained a magnetic field at the Earth’s surface whose intensity amounted to about 20% of the intensity before and after the reversal. The equatorial dipole existed before and during the reversal and was responsible for the deviation from antipodality of paleomagnetic poles of adjacent polarity chrons (the so-called reversal bias). The position of the equatorial dipole axis during the Paleozoic correlates with the supposed geometry of convective motions in the mantle at that time.

Effect of Shutoff Sequence of Hydrogen and Air on Performance Degradation in PEFC

The objective of this research is to characterize the performance degradation attributable to the shutdown operations of polymer electrolyte fuel cells and to explore possible methods of reducing such degradation. As a result, it was made clear that a sequence of shutting off the air supply prior to stopping the hydrogen supply was effective in mitigating such performance degradation. Diagnostic technology revealed that the performance degradation was mainly observed at the cathode catalyst and that it was caused by so-called reversal current, which was triggered by air that crossed leak from the cathode to the anode.

Drug Interactions Casebook: The Cytochrome P450 System and Beyond

Drug Interactions Casebook: The Cytochrome P450 System and Beyond

Presentation of a test system in terms of generated pulsatile flow characteristics

A complete test system associative with the measurement and data acquisition components was designed and constructed for an experimental investigation on pulsatile pipe flows. The basics of the test system and conducted experiments directed towards the determination of pulsatile flow characteristics at the measurement site in passage from laminar to turbulent regime are presented in this paper. Pulsatile flow was produced by superimposing a purely sinusoidal oscillation on steady axial flow in a rigid circular cross-sectional pipe. The flow nature at the measurement site was determined via cross-sectional velocity and wall pressure gradient measurements in the range of time-averaged Reynolds number; Re ta 1800≤ Re ta≤60,000. The covered ranges for the dominant oscillation parameters; dimensionless frequency parameter ω′ and the oscillation velocity amplitude ratio; A 1 were 5≤ ω′ ≤28 and 0.0035≤ A 1≤0.7113 respectively. The so-called flow reversal observed for the cases with ω′ =7 and ω′ =12.5 was represented in terms of correlations between Re ta, oscillating Reynolds number; Re os and A 1 to describe the flow behaviour in the critical stage prior to the flow reversal.

Numerical calculation of fully developed turbulent flow in curved channels: An extended algebraic Reynolds-stress model

The primary objective of the paper is to extend an algebraic Reynolds-stress model including a new expression for the turbulent shear stress, in order to describe the negative production of turbulent kinetic energy appearing in curved channel flows in a region between the points of maximum velocity and vanishing shear stress. This so-called energy reversal cannot be captured by the majority of turbulence models with conventional eddy-viscosity formulation. Computations are made for fully developed flows in channels of rectangular cross section and large aspect ratio with mild and strong curvature. The results are compared with different model predictions and experimental data reported in the literature. In the cases considered, the accuracy of present model predictions is comparable to that of a Reynolds-stress model. The latter, however, requires much more computing time and is thus more costly than the model here proposed.

An enhanced adsorption cycle operated by periodic reversal forced convection

A different cycle configuration is suggested in this work. Interesting improvement in performances is envisaged by applying the fixed bed adsorbers with the forced unsteady-state operation of periodic flow reversal to convective thermal wave cycle, which results in the so-called Periodic Reversal Forced Convective cycle. To describe process behavior for this kind of cycle with seven possible operating modes of flow reversal, a two-phase, one-dimensional model for the zeolite 13X-water pair is developed. Some important phenomena, such as the heat pipe effect, internal and external thermal regeneration etc., are discussed. The results of numerical simulations show that among all possible operating modes of flow reversal, only the mode of CCAA (switching the flow directions each phase duration) could improve the global performances of non-reversed flow operation, but others could not. Under the current conditions of cycle, the proposed CCAA cycle with heat exchanger regenerator could offer significant improvements in coefficient of performance ( COP) over both the conventional cycle without flow reversal operation and existing convective thermal wave cycle with inert packed bed regenerator. The results of calculation also show that more than 1.7 of COP h, 0.9 of COP c and 125 W/kg adsorbent of specific cooling power ( SCP) within this system could be possible. Analysis gives satisfactory explanation of these results.

Incentives and preference reversals: escape moves and community decisions in experimental economics

This article examines the debate on the influence of incentives on the occurrence of the so-called preference reversal phenomenon. Firstly, the participants’ views on the issue and the main shifts in the debate are identified. Secondly, the statements of views and the shifts in the debate are analyzed within the framework of ‘escape moves (Kitcher 1993). In this analysis the focus is on attempts to resolve particular inconsistencies in the statements and on the ability of proposed solutions to induce a community decision to alter more or less permanently a portion of its established practices. The analysis brings to light the negotiation process in which the significance and meaning of the contested issue is not settled by adopting certain rules in a mechanical way but is worked out by context-dependent interpretations of the community of specialists.