Blue Symbols Research Articles

Towards a Deeper Understanding of Catalyst Degradation during Intermittent Operation at Different Operating Conditions of Proton Exchange Membrane Water Electrolyzers

Low-temperature water electrolysis with a proton exchange membrane (PEM) enables the production of green hydrogen without direct emissions of CO2. Besides the ability to generate hydrogen at elevated pressure and very high current densities, PEM water electrolyzers (PEMWEs) offer a high load flexibility [1]. This facilitates a coupling to renewable energy sources and opens pathways for the large-scale implementation of the PEM water electrolysis technology. Considering the limited supply of iridium, current efforts target reduced iridium loadings and even higher current densities while maintaining high performance, along with the implementation of iridium recycling loops [2]. To nevertheless ensure the durability of iridium-based catalysts over the desired >50,000 hours of PEMWE lifetime, it is crucial to fundamentally understand the various degradation mechanisms as well as lifetime-affecting operating parameters and conditions. Therefore, growing efforts are put into the development of accelerated stress tests (ASTs) to predict and understand the degradation of PEMWE components and materials within reasonably short experiments. While various anode catalyst materials have for example been screened by Alia et al. in galvanostatic and potentiostatic ASTs with intermittent operation or simulated start-stop cycles [3, 4], the underlying degradation mechanisms of iridium-based catalysts for the oxygen evolution reaction (OER) in PEMWE anodes are still not fully understood.The here presented work aims for a better understanding of anode catalyst degradation during intermittent operation of PEMWEs. Performance changes and catalyst durability of a TiO2 supported IrO2 anode catalyst are investigated in 5 cm2 single-cells at loadings of 1.7-1.8 mgIr cm-2 over the course of an AST, consisting of operation periods at 3 A cm-2 and 0.1 A cm-2 and of periods at open circuit voltage (OCV), which was previously developed by our group [5]. To mitigate the growing contact resistances between the Ti-based porous transport layer (PTL) and the anode electrode that was observed by Weiß et al. [5] and to focus on the performance changes resulting from catalyst layer degradation, a platinum-coated PTL is used here. While the catalyst activity and therefore the performance is increasing in the first cycles of the OCV-AST due to a transition of the IrO2-catalyst surface to a hydrous iridium oxide, a significant subsequent performance loss is observed upon further cycling (see blue symbols in Fig. 1). On the other hand, for an AST where the cell voltage during idle periods is held at 1.3 V to prevent the intermittent reduction of the iridium catalyst (caused by hydrogen crossover during OCV periods), the high-frequency resistance-corrected cell voltage at 0.1 A cm-2 initially remains at high values but increases by only ~5 mV over 660 cycles (see red symbols).Besides presenting factors that affect the initial performance improvement during the OCV-AST to better understand the performance gain, we will investigate the impact of different operating conditions such as maximum current density or operating temperature on the performance decay after prolonged cycling. With different in-situ characterization methods like electrochemical impedance spectroscopy or cyclic voltammetry, we will disentangle and elucidate possible reasons for the observed voltage losses to better understand catalyst degradation and critical lifetime-affecting operating parameters and conditions.

(Invited) The Impact ofin-Situ Activation of a C-Coated Catalyst on the Performance and Durability in Proton-Exchange Membrane Fuel Cells

Zero-emission electricity production for stationary or mobile applications can be realized by PEM fuel cells (PEMFCs), making it an important constituent for a renewable energy transition. Especially relevant in heavy-duty applications, a high power output at low current densities (related to a high mass activity, MA) under dry conditions is necessary to meet the efficiency targets.[1] In general, mass activity of a Pt/C catalyst can be negatively affected by ionomer poisoning, which describes the adsorption of ionomer endgroups onto the active Pt surface. This effect is especially pronounced for platinum supported on so-called solid carbon supports (e.g., Vulcan – Pt/V)[2] and by operating a fuel cell at low relative humidity (RH).[3] In order to minimize performance losses due to ionomer poisoning, concepts exist to shield the Pt particle from the ionomer, e.g., by alkanethiol masking[4] or by Pt-overlayers of porous SiO2 [5] and carbon derived from dopamine coatings.[6] In the latter case, the authors observed that it was possible to decrease ionomer poisoning and increase MEA performance under dry conditions. However, the transport of reactants to the Pt active sites is hindered by the carbon-overlayer, resulting in inferior high current density (HCD) performance.In this work, we developed multiple in-situ activation strategies for a carbon-coated Pt/V cathode catalyst, synthesized following an adapted protocol from Yamada et al.[6] Our results show that apart from a significantly improved MA, high current density performance is retained for an activated carbon-coated Pt/V (C-Pt/Vactivated, solid orange symbols in Figure 1). Compared to the Pt/V baseline catalyst (blue symbols), the MA can be increased by a factor of ~2 (C-Pt/Vactivated with im 0.9V = 248±9 A gPt -1 and Pt/V with im 0.9V = 110±13 A gPt -1) while simultaneously maintaining comparable high current density performance at 90% RH. However, as we will show, the beneficial effect of the activated carbon-coated Pt/V is particularly pronounced at operation under dry conditions, where C-Pt/Vactivated outperformed the Pt/V baseline over the entire current density range (e.g., by 80 mV at 1.7 A cm-2).Furthermore, possible limitations in terms of durability of the C-overlayer used in this work will be discussed. Figure 1: Differential-flow H2/Air performance at 80 °C/90% RH and 145 kPaabs for different cathode catalysts: baseline catalyst (Pt/V), C-coated Pt/V catalyst before activation (C-Pt/Vb efore activation), and activated C-coated Pt/V catalyst (C-Pt/Va ctivated). In the 5 cm2 active area single-cell, the catalyst loadings were 0.25 mgPt cm-2 and 0.05 mgPt cm-2 on cathode and anode, respectively; a 15 µm reinforced low-EW PFSA membrane was used.

Do Visual Cues Aid Comprehension of a Dialogue?

Do Visual Cues Aid Comprehension of a Dialogue?

Busting the Silos of “Global” Scholarship

Busting the Silos of “Global” Scholarship

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis: A Strategy for Ammonia Synthesis under Mild Conditions

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis: A Strategy for Ammonia Synthesis under Mild Conditions

Bariatric surgery on obese walking: mass(ive) changes akin to load carrying and hypogravity for normal-weight adults.

Bariatric surgery on obese walking: mass(ive) changes akin to load carrying and hypogravity for normal-weight adults.

Revisiting the limitation to with ageing: is mitochondrial (dys)function the key?

Revisiting the limitation to with ageing: is mitochondrial (dys)function the key?

A Comparative Study of Structural Changes during Long-Term Cycling of NCM-811 at Ambient and Elevated Temperatures

Ni-rich layered oxides, like NCM-811 (Li1+δ[Ni0.8Co0.1Mn0.1]1-δO2), are promising cathode active materials for lithium-ion-batteries used in applications such as portable devices and battery electric vehicles. An increased Ni-content typically allows for a higher reversible lithium usage at a given cell potential, thereby improving the specific capacity. However, pronounced capacity fading, especially at high voltages and elevated temperatures, still leads to a limited cycle life.1 The underlying degradation mechanisms and whether they are due to detrimental reactions in the bulk or at the surface, are still controversially discussed in the literature.2,3 We will show a comparison of two studies investigating the capacity fading of NCM-811/graphite full-cells over several hundreds of cycles at ambient and elevated temperatures. In order to focus on the NCM-811 material, we excluded Li loss at the anode by pre-lithiating the graphite anode. The first study was conducted in-situ with two cells cycled at ambient temperature (≈22°C) over 1000 cycles,4 while in the follow-up study a number of pouch-cells were analyzed after cycling at 45°C for up to 700 cycles. As shown in Figure 1a, all cells were cycled at a C-rate of C/2 in a potential window between 3.0 and 4.5 V vs. a Li reference electrode at both 22°C (black line in Fig. 1a) and at 45°C (blue line in Fig. 1a), with two additional C/10 cycles every 50 cycles in case of the 45°C study (blue dots in Fig. 1a). One cell was disassembled every 150 cycles to conduct ex-situ experiments, such as X-ray powder diffraction (XPD) and impedance spectroscopy. A quantitative correlation between the NCM-811 lattice parameters and the Li amount, xLi, allows for monitoring the different contributions to the capacity loss by XPD.4 In the 22°C study, it was shown that the continuous growth of a resistive surface around the NCM-811 primary particles results in (i) an irreversible capacity loss due to the material lost for its formation, and (ii) in a significant impedance growth. The former is compared for both studies according to our XPD analysis in Figure 1b, showing a clear difference in the progression and in the absolute values, suggesting a more detrimental process to kick-in after ≈550 cycles at 45°C. In contrast to the time consuming XPD analysis, the material loss was also quantified by slow C/50 cycling, a rate which is slow enough to not lead to overpotential induced capacity losses due to the gradual resistance build-up over cycling. Hence, this approach could be verified to be a far more practical method to determine the material loss during cycle-life tests. In addition, the bulk material stability in terms of the Li-Ni mixing was analyzed by Rietveld refinement of the XPD data. In contrast to the study conducted at ambient temperature, where the extent of Ni disorder was observed to remain at an essentially constant value over 1000 cycles, it was found to clearly increase when cycling the cells at 45°C over 700 cycles (see Figure 1c).In conclusion, we can state that at both temperatures a resistive surface layer is formed, suggesting that future research should focus on stabilizing the surface of Ni-rich materials. In addition to this surface process, the bulk stability of NCM-811 is altered at elevated temperatures, which is manifesting itself in an increasing Ni disorder.Figure 1:Comparison of data obtained from NCM-811/graphite pouch-cells cycled at ≈22°C (black symbols) and at 45°C (blue symbols) between 3.0 and 4.5 V vs. Li+/Li (controlled vs. Li reference electrode) at the indicated C-rates. (a) Discharge capacity of two exemplary cells, (b) relative material loss of the NCM-811 calculated from XPD analysis, (c) Ni disorder determined via XPD of harvested electrodes after cycling to the indicated cycle number at 45°C (error from calculating the average of two independent measurements).Acknowledgement:This work is financially supported by the BASF SE Network on Electrochemistry and Battery Research.

Visibility of color symbology in head-up and head-mounted displays in daylight environments

Color-coded symbology has the potential to enhance the performance of people using head-up and head-mounted displays, as well as head-worn, optical see-through, augmented-reality displays. The distinguishing feature of these displays is the optical combiner that presents symbology overlaid upon the forward natural scene. The presence of high-ambient daylight can desaturate the symbol colors, making them difficult to identify. This is especially true for blue symbols that become faint and colorless in even moderate daylight. We defined a set of colors for testing based on color coding conventions, color symbology research, and results from our previous testing. Included in this set was blue-prime, a color that lies between blue and cyan. We then conducted an experiment to test the visibility of color symbols, the naming of symbol colors, and the legibility of color text mixed with daylight. Results were statistically analyzed and modeled using color-difference formulae. Additional experiments were conducted to test the effects of increasing the luminance of blue symbols and shifting primary colors to increase the luminance. Specific attention was given to the symbol color blue, where the alternative color blue-prime was shown to always outperform the color blue while retaining the color name blue.

Dual function hollow structured mesoporous Prussian blue mesocrystals for glucose biosensors

Dual function hollow structured mesoporous Prussian blue mesocrystals (HMPB) serve both as a scaffold carrier matrix to load the enzyme glucose oxidase and as a redox mediator of H2O2, the by-product of glucose oxidase catalyzed glucose reaction. The red and blue symbols represent glucose oxidase and HMPB, respectively.

Impact of Microporous Layer Properties for High Current Density Operation

A microporous layer (MPL) is conventionally applied to the gas diffusion layer (GDL) in order to improve liquid water transport and to provide a smooth contact between GDL and electrode. It typically consists of carbon components (e.g., carbon black, graphite) and a hydrophobic binder (e.g., PTFE).1 The small hydrophobic pores prevent condensed water from accumulating inside the layer or at the interface between MPL and electrode, which allows an efficient oxygen transport to the cathode.2,3 Figure 1 shows polarization curves at standard and humid conditions for 3 different GDL materials. At standard conditions (full symbols) where little amounts of liquid water are expected inside the MEA and GDL, the fuel cell performances of the GDL substrate without MPL and with different MPLs are very similar. On the other hand, the polarization curves at humid conditions (open symbols) are very different: the substrate without MPL reveals an early voltage drop at 2.5 A cm-2 caused by flooding of the cathode/GDL interface, while the addition of an MPL clearly improves the performance, with the MPL based on carbon fibers exhibiting the highest current densities. To characterize the oxygen transport, we determine the total oxygen transport resistance (R T,O2) from limiting current density measurements with diluted oxygen.4 The bar graph in Figure 1 illustrates R T,O2 at the two conditions. While all materials behave very similar at standard conditions, at humid conditions the application of the carbon fiber MPL decreases R T,O2 by 50%. This shows that MPL structural differences as indicated by the SEM images significantly impact the liquid water transport. In our study we will show to how MPL properties influence the oxygen transport for (1) various operating conditions, (2) various oxygen concentrations, and (3) different GDL substrates. With this work, we aim to illustrate under which operating conditions and for which materials (e.g., type of GDL substrate, fuel cell operating strategy) advanced MPLs help to improve the overall fuel cell performance at high current densities. Literature M. F. Mathias, J. Roth, J. Fleming and W. Lehnert, in Handbook of Fuel Cells, W. Vielstich, H. A. Gasteiger and A. Lamm (Editors), John Wiley and Sons, Ltd (2010).J. T. Gostick, M. A. Ioannidis, M. W. Fowler and M. D. Pritzker, Electrochem. Commun., 11, 576 (2009).J. P. Owejan, J. E. Owejan, W. B. Gu, T. A. Trabold, T. W. Tighe and M. F. Mathias, J. Electrochem. Soc., 157, B1456 (2010).D. A. Caulk and D. R. Baker, J. Electrochem. Soc., 157, B1237 (2010). Acknowledgments The authors gratefully acknowledge the financial support by the German Federal Ministry for Economic Affairs and Energy (BMWi), Freudenberg Performance Materials SE & Co. KG, and Daimler AG under agreement number 03ET6015E (“Optigaa 2” project). Figure 1 : Polarization curves for three different GDL materials on the cathode (also see SEM images in the figure): GDL substrate (Freudenberg H1410 I4) without MPL (green symbols), with carbon black based MPL (blue symbols), and with carbon fiber based MPL (red symbols). Measurements are performed with differential gas flow rates (2 nlm H2 and 5 nlm air for active area of 5 cm²) at standard conditions (full symbols; T cell = 80 °C, p abs = 170 kPa, RH = 100%) and at humid conditions (open symbols; T cell = 50 °C, p abs = 300 kPa, RH = 120%). The bar graph in the figure illustrates the total oxygen transport resistance (R T,O2) at standard and humid conditions determined from the limiting current density at a dry oxygen content of 2%. Figure 1

A portable knowledge-based system for car breakdown evaluation

Modern cars have many dashboard lights and not all drivers recognize or know the importance of all of them. Red symbols usually indicate a safety issue or a serious problem, meanwhile yellow symbols use to indicate a not so urgent problem. Green and blue symbols usually provide information about the systems connected. But not all the red icons require of the same action, and the user manuals of most modern cars, with their sophisticated electronic systems, have hundreds of pages. Meanwhile, smart devices have become popular and have an outstanding computing power plus Internet connection. Consequently, the conditions for developing a knowledge-based system that helped the unaware driver in case a dashboard light went on, exist. The application should evaluate the situation and recommend the best actions to be carried out by the driver (regarding the possible repair on site or at a workshop, its urgency or even the need to immobilize the vehicle immediately). We have designed such a knowledge-based system and have developed a simplified one as example. A friendly Graphical User Interface has been developed in order to ease the communication with the application and its use in remote using any smart device with Internet connection.

Susceptibility to CD8 T-Cell–Mediated Killing Influences the Reservoir of Latently HIV-1–Infected CD4 T Cells

HIV-1 establishes a lifelong infection in the human body, but host factors that influence viral persistence remain poorly understood. Cell-intrinsic characteristics of CD4 T cells, the main target cells for HIV-1, may affect the composition of the latent viral reservoir by altering the susceptibility to CD8 T-cell-mediated killing. We observed that susceptibilities of CD4 T cells to CD8 T-cell-mediated killing, as determined in direct ex vivo assays, were significantly higher in persons with natural control of HIV-1 (elite controllers) than in individuals effectively treated with antiretroviral therapy. These differences were most pronounced in naive and in terminally differentiated CD4 T cells and corresponded to a reduced viral reservoir size in elite controllers. Interestingly, the highest susceptibility to CD8 T-cell-mediated killing and lowest reservoirs of cell-associated HIV-1 DNA was consistently observed in elite controllers expressing the protective HLA class I allele B57. These data suggest that the functional responsiveness of host CD4 T cells to cytotoxic effects of HIV-1-specific CD8 T cells can contribute to shaping the structure and composition of the latently infected CD4 T-cell pool.

Bin Packing via Discrepancy of Permutations

A well-studied special case of bin packing is the 3-partition problem , where n items of size > 1/4 have to be packed in a minimum number of bins of capacity one. The famous Karmarkar-Karp algorithm transforms a fractional solution of a suitable LP relaxation for this problem into an integral solution that requires at most O (log n ) additional bins. The three-permutations-problem of Beck is the following. Given any three permutations on n symbols, color the symbols red and blue, such that in any interval of any of those permutations, the number of red and blue symbols is roughly the same. The necessary difference is called the discrepancy . We establish a surprising connection between bin packing and Beck’s problem: The additive integrality gap of the 3-partition linear programming relaxation can be bounded by the discrepancy of three permutations. This connection yields an alternative method to establish an O (log n ) bound on the additive integrality gap of the 3-partition. Conversely, making use of a recent example of three permutations, for which a discrepancy of Ω(log n ) is necessary, we prove the following: The O (log 2 n ) upper bound on the additive gap for bin packing with arbitrary item sizes cannot be improved by any technique that is based on rounding up items. This lower bound holds for a large class of algorithms including the Karmarkar-Karp procedure.

Corrigendum

Correction of British Journal of Haematology 2010: 151, 106–109. doi 10.1111/j.1365-2141.2010.08306.x. Epub 2010 July 16. EPO-mediated reduction in Hamp expression in vivo corrects iron deficiency anemia in tmprss6 deficiency. I would like to sincerely apologize to everyone, but especially to Gael Nicolas and colleagues, for a mistake in my laboratory caused by mismanagement of the Tmprss6Msk/Msk mice used in the experiments described in BJH 151:106–9, 2010 (Peng et al, 2010). The reported Tmprss6Msk/Msk were not Tmprss6Msk/Msk mice but were mice of mixed Tmprss6 genotypes. The Hjv−/− Tmprss6Msk/Msk double mutant were of the correct genotype and the original data are correct. We have repeated the experiments with Tmprss6Msk/Msk mice and the results of these experiments are consistent with those reported by Nicolas et al (Nicolas et al, 2011). We found that Tmprss6Msk/Msk exhibited reticulocytosis in response to erythropoietin (EPO) treatment (50 U or 100 U/day for 4 days) as indicated by an increase in spleen weight and reticulocyte percent (Fig 1A,B). Treatment of Tmprss6Msk/Msk with EPO was not sufficient to correct anemia and microcytosis in the absence of supplemental iron (Fig. 1D,E). Hamp expression was only modestly repressed by erythropoietin treatment as compared to wildtype C57BL6 mice (Fig 1C). Resistance to exogenous erythropoietin is consistent with high endogenous expression of erythropoietin in Tmprss6Msk/Msk mice (Fig 1F). Nevertheless, the original Hjv−/− Tmprss6Msk/Msk double mutant were of the correct genotype, and exhibited effective repression of Hamp in response to EPO demonstrating that tmprss6 and hemojuvelin are not required for repression of Hamp by EPO. Effect of in vivo erythropoietin (EPO) treatment of C57BL6 and Tmprss6Msk/Msk mutant mice. Mice (males are indicated with blue symbols, females with red symbols) were untreated or treated with human recombinant EPO (Cell Sciences, Canton, MA, USA) 50 or 100 U/day for 4 days with or without supplemental high iron diet (2 × 104 ppm) started on Day 1. Mouse blood and tissues were harvested on Day 5. Reticulocyte percent was determined by flow cytometry using thiazole orange Retic-Count reagent (BD Biosciences, San Diego, CA, USA) according to manufacturers’ instructions. Hemoglobin and mean corpuscular volume (MCV) were determined with a Hemavet 950 chemistry analyzer (Drew Scientific, Oxford, CT, USA). Murine erythropoietin levels were determined using Quantikine Mouse/Rat Erythropoietin ELISA (R&D Systems, Minneapolis, MN, USA) for male and female mice (n = 4/group) as indicated. Hamp and Rps18 expression were performed as previously described (Truksa et al, 2009) Means and standard errors are shown. Statistical analyses were performed with GRAPHPAD PRISM 5 (Graphpad Software Inc., La Jolla, CA, USA) software using Mann–Whitney non-parametric two-tailed t-test. This is manuscript 21565-MEM from the Scripps Research Institute. This work was supported by a grant from the National Institutes of Health DK53505-12, and The Beutler Foundation.

Spin Density Wave Ordering in CeIrSi3

Pressure induced superconductivity discovered in CeRhSi3 and CeIrSi3 has attracted much attention due to their being heavy fermion superconductors without inversion symmetry. It is also pointed out that both of them lie close to the quantum critical point, and interestingly Ce 4f electrons are itinerant even in their antiferromagnetic phase in sharp contrast to CeRhIn5 in which Ce 4f electrons are localized in the antiferromagnetic phase. The itinerant character of the Ce 4f electron in CeRhSi3 was pointed out by de Haas–van Alphen (dHvA) measurements. When Ce 4f electrons are localized, the Fermi surfaces (FSs) in CeRhSi3 will be very similar to those in LaRhSi3. On the other hand, the observed dHvA frequencies and then FSs in CeRhSi3 are totally different to those in LaRhSi3, and these results are interpreted as a strong indication of the itinerant character of Ce 4f electrons in CeRhSi3. The angle-resolved photoemission study in CeIrSi3 indicates that the Ce 4f electrons in CeIrSi3 are also itinerant. The observed FSs in CeIrSi3 are substantially larger than those in LaIrSi3 and they contact each other at Brillouin zone boundaries. The ground states of Ce ions in CeIrSi3 and CeRhSi3 are determined to be 7 doublets through the susceptibility studies, and their magnetic moments order antiferromagnetically at low temperatures. A neutron diffraction study of those magnetic structures may provide important information on the possible itinerant character of Ce 4f electrons in CeIrSi3 and CeRhSi3. The magnetic structure of CeRhSi3 was determined by our previous study. CeRhSi3 shows an antiferromagnetic phase below TN 1⁄4 1:6K with the magnetic moment of ord 1⁄4 0:13 B/Ce. The magnetic moments lie in the c plane and form a longitudinal spin-density wave with a propagation vector 1⁄4 ð0:215; 0; 1=2Þ, being consistent with a picture that the Ce 4f electrons are itinerant. Recently, we also succeeded in observing magnetic peaks in CeIrSi3 by neutron diffraction. The magnetic peaks appear below TN 1⁄4 5:0K at Q 1⁄4 G 1 and at Q 1⁄4 G 2 with 1 1⁄4 ð0:265; 0; 0:43Þ and 2 1⁄4 ð 0:265; 0; 0:43Þ, and G denotes the fundamental reciprocal vector for the BaNiSn3-type structure. In contrast to the magnetic structure of CeRhSi3, the observed magnetic structure is incommensurate both along the a and c directions. The single crystal sample used in the present study was grown by Czochralsky pulling method in a tetra-arc furnace at Tohoku university. The X-ray powder diffraction measurements at room temperature confirmed only the Bragg peak lines expected for the BaNiSn3-type structure. The size of the crystal was 3mm in diameter and 35mm long whose weight was 1.1 g. Neutron diffraction measurements were carried out with the GPTAS triple-axis spectrometer installed at 4G in the JRR-3 research reactor at Japan Atomic Energy Agency. The incident momentum of ki 1⁄4 3:83 A 1 was adopted to avoid large absorption of Ir atoms with a set of collimators of 400-800-400. To reduce the higher order contaminations, two PG filters were utilized. The one was placed at the position before the monochromator and the other just before the analyzer. The crystal was mounted to the He gas closed cycle refrigerator whose base temperature is 0.75K, and it was aligned with the (0 1 0) axis vertical so that the (h0l) zone can be observed. The lattice parameters at 1 K was a 1⁄4 1:487 A , and c 1⁄4 0:642 A . The (h0l) reciprocal plane in CeIrSi3 is shown in Fig. 1 in which the fundamental reflections for the BaNiSn3-type structure are denoted by open circles, while observed magnetic satellites are denoted by yellow filled circles (for the propagation vector 1) and star-shape blue symbols (for the propagation vector 2). The dashed circles indicate the position at which the aluminum powder lines are observed. In order to find the magnetic peaks in CeIrSi3, we carried out a two-dimensional survey scans around the Q 1⁄4 ð0:215; 0; 2:5Þ at which the magnetic peak was observed in CeRhSi3. The scans were carried out for the range with h: 0.10–0.30 and l: 2.34–2.48 which is indicated by a gray hatch in Fig. 1, and the observed intensity distribution is depicted as a contour map in Fig. 2. We discovered a weak peak at Q 1⁄4 ð0:265; 0; 2:43Þ. We noted that the peak is actually a single peak and dips of intensity around Q 1⁄4 Magnetic Bragg Nuclear Bragg 111 200 ( h 0 l ) zone CeIrSi3

Is there a significant transmural gradient in repolarization time in the intact heart?

Is there a significant transmural gradient in repolarization time in the intact heart?

Young Children Do Not Integrate Visual and Haptic Form Information

Several studies have shown that adults integrate visual and haptic information (and information from other modalities) in a statistically optimal fashion, weighting each sense according to its reliability [1, 2]. When does this capacity for crossmodal integration develop? Here, we show that prior to 8 years of age, integration of visual and haptic spatial information is far from optimal, with either vision or touch dominating totally, even in conditions in which the dominant sense is far less precise than the other (assessed by discrimination thresholds). For size discrimination, haptic information dominates in determining both perceived size and discrimination thresholds, whereas for orientation discrimination, vision dominates. By 8-10 years, the integration becomes statistically optimal, like adults. We suggest that during development, perceptual systems require constant recalibration, for which cross-sensory comparison is important. Using one sense to calibrate the other precludes useful combination of the two sources.

Feature Article: Hot phonons in GaN channels for HEMTs

In the Feature Article [1] a fluctuation technique is used to obtain the hot electron energy relaxation time (blue symbols in the cover picture) and the hot phonon lifetime (red) for a biased two-dimensional channel in an AlGaN/AlN/GaN heterostructure as a function of the supplied electric power. The close proximity of red and blue symbols illustrates that the relaxation is mainly determined by the phonon conversion into other vibrational modes being able to drain the Joule heat out of the channel. The red inset shows the momenta of hot phonons launched by hot electrons. The green line presents the electron energy relaxation time obtained by Monte Carlo simulation for lightly doped GaN under the assumption that hot phonons are absent. A strong effect of hot phonons on the electron energy relaxation is evident. The author Arvydas Matulionis is Professor of Physics and head of the Fluctuation Research Laboratory of the Vilnius Semiconductor Physics Institute. He investigates hot electron fluctuations and other high electric field effects in semiconductor heterostructures for microwave electronics. The Editor's Choice “Anomalous charge relaxation in channels of pentacene-based organic field-effect transistors: a charge transient spectroscopy study” by I. Thurzo et al. [2] is also part of the present issue.

Corrigenda

Corrigenda