Hot Wind Research Articles

On the dynamics and survival of fractal clouds in galactic winds

Abstract Recent observations suggest that dense gas clouds can survive even in hot galactic winds. Here we show that the inclusion of turbulent densities with different statistical properties has significant effects on the evolution of wind-swept clouds. We investigate how the initial standard deviation of the lognormal density field influences the dynamics of quasi-isothermal clouds embedded in supersonic winds. We compare uniform, fractal solenoidal, and fractal compressive cloud models in both 3D and 2D hydrodynamical simulations. We find that the processes of cloud disruption and dense gas entrainment are functions of the initial density distribution in the cloud. Fractal clouds accelerate, mix, and are disrupted earlier than uniform clouds. Within the fractal cloud sample, compressive clouds retain high-density nuclei, so they are more confined, less accelerated, and have lower velocity dispersions than their solenoidal counterparts. Compressive clouds are also less prone to Kelvin–Helmholtz and Rayleigh–Taylor instabilities, so they survive longer than solenoidal clouds. By comparing the cloud properties at the destruction time, we find that dense gas entrainment is more effective in uniform clouds than in either of the fractal clouds, and it is more effective in solenoidal than in compressive models. In contrast, mass loading into the wind is more efficient in compressive cloud models than in uniform or solenoidal models. Overall, wide density distributions lead to inefficient entrainment, but they facilitate mass loading and favour the survival of very dense gas in hot galactic winds.

Strip technology of corn and soy-bean cultivation for grain - a new stage in the development of soy-bean sowing on irrigated lands of the Volga region

Soy-bean plants develop more intensively and by the time of harvesting exceed the crops by means of the ordinary technology by 37-52 cm. Beans of the lower tiers are formed at an height of 18-20 cm (2-5 cm higher than in ordinary sowing), which is very important for mechanized harvesting, more beans with large seeds are formed. Ultimately, the grain yield with the new technology increases by 0.33-0.58 t/ha. Production tests of strip technology of soy-bean cultivation confirm its prospects in the conditions of irrigation of Zavolzhye. Especially it is perspective for the drought-resistant regions of a dry-steppe zone of the Volga region where during vegetation of crops air temperature rises till 35-40 degrees, but the relative humidity decreases to 12-8%. In these severe weather conditions existence of corn strips will reliably protect crops of soy-bean from hot winds and will be a reliable guarantor of increasing its harvest.

CHEERS Results from NGC 3393. III. Chandra X-Ray Spectroscopy of the Narrow Line Region

Abstract We present spatially resolved Chandra narrow-band imaging and imaging spectroscopy of NGC 3393. This galaxy hosts a Compton-thick Seyfert 2 active galactic nucleus (AGN) with sub-kpc bipolar outflows that are strongly interacting with the circumnuclear gas. We identify narrow-band excess emission associated with the Ne ix 0.905 keV transition (with likely contributions due to intermediate-state iron emission) that points to strong shocks driven by AGN feedback. Imaging spectroscopy resolves outflow-interstellar medium (ISM) interaction sites and the surrounding ISM at ∼100 pc scales, and suggests the presence of a hot AGN wind above the plane at radii beyond the shock sites. The cross-cone shows evidence for reprocessing of photoionization that has passed through gaps in the torus, and also for collisionally excited plasma that may be powered by a shock-confined equatorial outflow. Deep X-ray observations at subarcsecond resolution (such as may be performed very efficiently by Lynx, which would also energetically resolve the complex line emission) are necessary to eliminate model degeneracies and reduce uncertainties in local feedback properties.

A Satellite Observation-based Analysis of Aerosol-cloud-precipitation Interaction during the February 2016 Unseasonal Heatwave Episode over Indian Region

ABSTRACT Aerosol-cloud-precipitation (ACP) interaction during the February 2016 unseasonal heatwave episode over India is analyzed and presented. Moderate Resolution Imaging Spectroradiometer (MODIS) datasets from the Aqua satellite are used to examine the relationship between aerosol and cloud parameters, viz., the aerosol optical depth (AOD), Angstrom exponent (AE), cloud fraction, ice and liquid cloud effective radius, cloud optical depth, cloud top temperature, and ice and liquid cloud water path. Furthermore, the Tropical Rainfall Measuring Mission (TRMM) dataset is used to analyze the rainfall during the dissipating phase of the heatwave episode. The prevailing meteorological conditions during the pre-mature, mature, and dissipating phases of the episode are identified by analyzing the near-surface temperature, relative humidity, and vertically integrated moisture flux convergence via 0.25°-resolution ERA-Interim datasets. Back-trajectory analysis is conducted to determine the origin of air masses and transported aerosols. Hot and dry westerly winds dominate during the pre-mature and mature phases, and consequently, significant aerosol transport is observed. The AOD reaches a maximum of 1.6 during the three phases, with the AE being in the range of 0.8–1.7, indicating the presence of both fine- and coarse-mode aerosols. Due to microphysical processes, clouds respond fairly strongly to aerosols in the presence of favorable dynamic and thermodynamic atmospheric conditions. The suppression of precipitation during the pre-mature and mature phases is primarily attributable to weak aerosol-cloud interaction. A major rainfall event in the region comprising northern Odisha, eastern Jharkhand, and most parts of West Bengal, which is situated north of the minimum vertically integrated moisture flux zone, occurs during the dissipating phase. This rainfall event results from the unseasonal transport of moisture from the neighboring Bay of Bengal, the presence of appreciable aerosol loading, and the consequent ACP interaction.

Our breathing sounds like a blanket

Our breathing sounds like a blanket A. G. Pettet (bio) Hot winds bring trouble.but the tunnels are cool,algae water runningankle-deep,slippery,down the middle. If a storm catches us herewe'll drown. But the sky issharp autumn blue.The tunnel opening atiny circle of white. They won't find us here,we are far from the light. Beyond where teenagersscrawl names andcrude suggestionsacross the walls. We'll stay here,in this between place. A tunnel vision view. Where our words echoour words echoand our laughtersounds frightening. You speak of musesand demons,poetry and visions,children in pain. [End Page 423] Things you can only sayin the dark.Where our facesare smudgesand our breathingsounds like a blanket. The water runs sluggish here,where the tunnel turnsfurther into the earthand the darkness becomesabsolute.Spots of silver and gold flickerlike peacock featherdifficult to tellif the eyesare open or closed. We are in the bellyof the serpent.You say. Can you smell it?That scent of decay,the stagnation of thought. The death of tomorrow. I begin to worry aboutyour sanity,my sanity,that tiny circle of lightin the distance,extinguished. [End Page 424] A. G. Pettet A. G. Pettet is a poet, short-fiction writer, academic, literary critic, publisher, and editor. His poems and other writings have been published in Australia, the United Kingdom, the United States, Canada, New Zealand, and India, including in Oxford Poetry, Australian Poetry Anthology, Island Magazine, Going Down Swinging, World Literature Today, Dazed and Confused Magazine (International) Broadsheet, and the Cortland Review. He has performed, chaired panels, and been a panel member at various festivals, including the Brisbane Writers Festival, Queensland Poetry Festival, and the National Young Writers Festival. This is his first appearance in Antipodes. Copyright © 2021 Wayne State University Press

Защитные лесные полосы вдоль автомобильных дорог

Despite the economic transformation in Russia, and the decline in the development of certain industries, the stability of the existence and development of social and economic relations depends on the freight and passenger turnover of the country. Shipping and passengers on public roads tends to increase, which leads to an increase in the proportion of all types of road transport on the road network. Transport, in addition to the positive aspects for the social and economic sphere, also has negative sides, in the form of a large number of traffic accidents, congestion situations and environmental pollution. At the present stage of the study of these negative aspects, ecology plays a special, important role, protecting the environment from the negative impact of transport. There is a need to protect the roadside area, which is able to provide cut-off of emissions of polluted substances into the air and a kind of noise and vibration protection near the road. This problem can be solved by creating protective plantings, since green plantings are the best are the best natural (inartificial) means of protection against air pollution, snow and sand drifts, noise and vibration, they provide architectural and artistic design along the roads. And, in addition to performing their main function - protection, they are of great practical importance along the regional and federal highways, since they have a beneficial effect on the growth conditions of agricultural crops, blocking the way for hot dry winds.

Radiation Conditions near Exoplanets of the TRAPPIST-1 System

Stellar and galactic cosmic rays (SCR and GCR) are the primary factors influencing the radiation conditions near exoplanets. The GCR spectrum and its time variations are shaped by modulation processes in the astrosphere (the parameters of stellar wind and the local interstellar medium). The estimation of the velocity and density of hot stellar wind in the Parker model demonstrates that their values may change several fold, while the observations reveal that the stellar magnetic fields (and, consequently, the magnetic field of stellar wind) vary by one or two orders of magnitude. Galactic CR may be virtually non-existent near exoplanets of stars with strong magnetic field as a result of the modulation. The radiation conditions are then determined by SCR: the stellar activity, the energy of stellar flares, and the parameters of exoplanet orbits. The estimates of GCR and SCR fluxes near the exoplanets in the habitable zone of the TRAPPIST-1 system, which were obtained using the Parker model and the available data on the stellar magnetic field and activity, are presented below.

Wind inhibition by X-ray irradiation in HMXBs: the influence of clumping and the final X-ray luminosity

Context. In wind-powered X-ray binaries, the radiatively driven stellar wind from the primary may be inhibited by the X-ray irradiation. This creates the feedback that limits the X-ray luminosity of the compact secondary. Wind inhibition might be weakened by the effect of small-scale wind inhomogeneities (clumping) possibly affecting the limiting X-ray luminosity. Aims. We study the influence of X-ray irradiation on the stellar wind for different radial distributions of clumping. Methods. We calculate hot star wind models with external irradiation and clumping using our global wind code. The models are calculated for different parameters of the binary. We determine the parameters for which the X-ray wind ionization is so strong that it leads to a decrease of the radiative force. This causes a decrease of the wind velocity and even of the mass-loss rate in the case of extreme X-ray irradiation. Results. Clumping weakens the effect of X-ray irradiation because it favours recombination and leads to an increase of the wind mass-loss rate. The best match between the models and observed properties of high-mass X-ray binaries (HMXBs) is derived with radially variable clumping. We describe the influence of X-ray irradiation on the terminal velocity and on the mass-loss rate in a parametric way. The X-ray luminosities predicted within the Bondi-Hoyle-Lyttleton theory agree nicely with observations when accounting for X-ray irradiation. Conclusions. The ionizing feedback regulates the accretion onto the compact companion resulting in a relatively stable X-ray source. The wind-powered accretion model can account for large luminosities in HMXBs only when introducing the ionizing feedback. There are two possible states following from the dependence of X-ray luminosity on the wind terminal velocity and mass-loss rate. One state has low X-ray luminosity and a nearly undisturbed wind, and the second state has high X-ray luminosity and exhibits a strong influence of X-rays on the flow.

Farmers’ Knowledge, Perception and Practices in Apple Pest Management and Climate Change in the Fes-Meknes Region, Morocco

Apple production in the Fes-Meknes region of Morocco is highly affected by pests and adverse weather conditions. A survey of apple farmers’ knowledge, perceptions and practices (KPP) in pest management and climate change was conducted in spring 2018 in two major apple-producing provinces of the region. Each farmer reported three insect pests and two diseases on average affecting their orchards. Pest management was performed by a combination of cultural and chemical methods. All farmers used dormant chemical sprays. About 60% of the respondents adopted pest surveillance based on visual inspection and 41.9% chose their pesticides on the basis of the information received from pesticide sellers. An average of 20 treatments per year was applied in each orchard. Regression analysis showed that neither the age of apple trees nor the number of pesticide applications influenced yield. Adverse weather conditions affected all apple plantations and the most frequent problems perceived were frosts, hailstorms, hot winds and water shortage. Of the orchards reported, 51.3% were protected with anti-hail nets. In order to reduce the rate of pesticide applications, better information on integrated pest management is required. Introduction of organic farming is necessary as 40.5% of the farmers agreed to convert to this practice in the future provided that market facilitation is established.

Influence of flat endwall simplification in gas turbines on cooling performance

In most investigations on the film cooling performance of turbine endwalls, real annular endwalls were usually simplified into flat endwalls. However, up to now, the influence of flat endwall simplification on cooling performance is seldom considered. In present work, a film cooling experiment was conducted in the hot gas wind tunnel at the University of Science and Technology of China (USTC), in order to validate the conjugate heat transfer algorithm and SST k-ω turbulence model used in the following numerical simulations. Then a series of numerical simulations was conducted by two endwall models: one is a real annular endwall, and the other is a flat endwall simplified from the first. The cooling performances of the two endwalls were analyzed and compared, and the numerical results reveal the following interesting and important phenomena: (1) Under real conditions, the adiabatic film effectiveness of the annular endwall is generally higher than that of the flat endwall, but at our experimental environment, the overall cooling effectiveness of the annular endwall is lower than that of the flat endwall. (2) Under the real conditions of gas turbine operation, the annular endwall exhibits a “Matthew effect”, i.e., better overall cooling performance appear in good film-covered region, but worse overall cooling performance appear in poorly film-covered region. (3) Under the real conditions, the temperature differences between the two endwalls can be larger than 25 K, and the temperature gradient in annular endwall is much higher. With other words, using flat endwall simplification may cause a high risk of endwall lifespan. This is very important for the designers of turbine endwall and users of the experimental data obtained by flat endwalls.

The physics of multiphase gas flows: fragmentation of a radiatively cooling gas cloud in a hot wind

Galactic winds exhibit a multiphase structure that consists of hot-diffuse and cold-dense phases. Here we present high-resolution idealised simulations of the interaction of a hot supersonic wind with a cold cloud with the moving-mesh code arepo in setups with and without radiative cooling. We demonstrate that cooling causes clouds with sizes larger than the cooling length to fragment in two- and three-dimensional simulations (2D and 3D). We confirm earlier 2D simulations by McCourt et al. 2018 and highlight differences of the shattering processes of 3D clouds that are exposed to a hot wind. The fragmentation process is quantified with a friends-of-friends analysis of shattered cloudlets and density power spectra. Those show that radiative cooling causes the power spectral index to gradually increase when the initial cloud radius is larger than the cooling length and with increasing time until the cloud is fully dissolved in the hot wind. A resolution of around 1 pc is required to reveal the effect of cooling-induced fragmentation of a 100 pc outflowing cloud. Thus, state-of-the-art cosmological zoom simulations of the circumgalactic medium (CGM) fall short by orders of magnitudes from resolving this fragmentation process. This physics is, however, necessary to reliably model observed column densities and covering fractions of Lyman-$\alpha$ haloes, high-velocity clouds, and broad-line regions of active galactic nuclei.

Unravelling the baffling mystery of the ultrahot wind phenomenon in white dwarfs

ABSTRACT The presence of ultrahigh excitation (UHE) absorption lines (e.g. O VIII) in the optical spectra of several of the hottest white dwarfs poses a decades-long mystery and is something that has never been observed in any other astrophysical object. The occurrence of such features requires a dense environment with temperatures near 106 K, by far exceeding the stellar effective temperature. Here we report the discovery of a new hot wind white dwarf, GALEX J014636.8+323615. Astonishingly, we found for the first time rapid changes of the equivalent widths of the UHE features, which are correlated to the rotational period of the star (P = 0.242035 d). We explain this with the presence of a wind-fed circumstellar magnetosphere in which magnetically confined wind shocks heat up the material to the high temperatures required for the creation of the UHE lines. The photometric and spectroscopic variability of GALEX J014636.8+323615 can then be understood as consequence of the obliquity of the magnetic axis with respect to the rotation axis of the white dwarf. This is the first time a wind-fed circumstellar magnetosphere around an apparently isolated white dwarf has been discovered and finally offers a plausible explanation of the ultrahot wind phenomenon.

Slingshot prominences: nature’s wind gauges

Mass loss rates for the tenuous, hot winds of cool stars are extremely difficult to measure, yet they are a crucial ingredient in the stars' rotational evolution. We present a new method for measuring these mass loss rates in young, rapidly-rotating stars. These stars are known to support systems of "slingshot prominences" fed by hot wind material flowing up from the stellar surface into the summits of closed magnetic loop structures. The material gathers and cools near the co-rotation radius until its density becomes large enough that it is visible as a transient absorption feature in the hydrogen Balmer lines and strong resonance lines such as Ca II H \&\ K. Here we present the key insight that the sonic point usually lies well below the condensation region. The flow at the wind base is therefore unaffected by the presence of an overlying prominence, so we can use the observed masses and recurrence times of the condensations to estimate the mass flux in the wind. These measurements extend the relationship between mass loss rate per unit surface area and X-ray flux to span 5 orders of magnitude. They demonstrate no evidence of the suspected weakening of stellar mass loss rates at high X-ray flux levels.

The crop performance dependence of the winter soft wheat from hot wind in southern Uzbekistan

The crop performance dependence of the winter soft wheat from hot wind in southern Uzbekistan

GRAVITY chromatic imaging of η Car’s core

Context. η Car is one of the most intriguing luminous blue variables in the Galaxy. Observations and models of the X-ray, ultraviolet, optical, and infrared emission suggest a central binary in a highly eccentric orbit with a 5.54 yr period residing in its core. 2D and 3D radiative transfer and hydrodynamic simulations predict a primary with a dense and slow stellar wind that interacts with the faster and lower density wind of the secondary. The wind-wind collision scenario suggests that the secondary’s wind penetrates the primary’s wind creating a low-density cavity in it, with dense walls where the two winds interact. However, the morphology of the cavity and its physical properties are not yet fully constrained. Aims. We aim to trace the inner ∼5–50 au structure of η Car’s wind-wind interaction, as seen through Brγ and, for the first time, through the He I 2s-2p line. Methods. We have used spectro-interferometric observations with the K-band beam-combiner GRAVITY at the VLTI. The analyses of the data include (i) parametrical model-fitting to the interferometric observables, (ii) a CMFGEN model of the source’s spectrum, and (iii) interferometric image reconstruction. Results. Our geometrical modeling of the continuum data allows us to estimate its FWHM angular size close to 2 mas and an elongation ratio ϵ = 1.06 ± 0.05 over a PA = 130° ± 20°. Our CMFGEN modeling of the spectrum helped us to confirm that the role of the secondary should be taken into account to properly reproduce the observed Brγ and He I lines. Chromatic images across the Brγ line reveal a southeast arc-like feature, possibly associated to the hot post-shocked winds flowing along the cavity wall. The images of the He I 2s-2p line served to constrain the 20 mas (∼50 au) structure of the line-emitting region. The observed morphology of He I suggests that the secondary is responsible for the ionized material that produces the line profile. Both the Brγ and the He I 2s-2p maps are consistent with previous hydrodynamical models of the colliding wind scenario. Future dedicated simulations together with an extensive interferometric campaign are necessary to refine our constraints on the wind and stellar parameters of the binary, which finally will help us predict the evolutionary path of η Car.

The Close AGN Reference Survey (CARS)

Aims. We probe the radiatively-efficient, hot wind feedback mode in two nearby luminous unobscured (type 1) AGN from the Close AGN Reference Survey (CARS), which show intriguing kpc-scale arc-like features of extended [O III]ionized gas as mapped with VLT-MUSE. We aimed to detect hot gas bubbles that would indicate the existence of powerful, galaxy-scale outflows in our targets, HE 0227–0931 and HE 0351+0240, from deep (200 ks) Chandra observations. Methods. By measuring the spatial and spectral properties of the extended X-ray emission and comparing with the sub kpc-scale IFU data, we are able to constrain feedback scenarios and directly test if the ionized gas is due to a shocked wind. Results. No extended hot gas emission on kpc-scales was detected. Unless the ambient medium density is low (n H ∼ 1 cm−3 at 100 pc), the inferred upper limits on the extended X-ray luminosities are well below what is expected from theoretical models at matching AGN luminosities. Conclusions. We conclude that the highly-ionized gas structures on kpc scales are not inflated by a hot outflow in either target, and instead are likely caused by photoionization of pre-existing gas streams of different origins. Our nondetections suggest that extended X-ray emission from an AGN-driven wind is not universal, and may lead to conflicts with current theoretical predictions.

Fast winds drive slow shells: a model for the circumgalactic medium as galactic wind-driven bubbles

Successful models of the low redshift circumgalactic medium (CGM) must account for (1) a large amount of gas, (2) relatively slow gas velocities, (3) a high degree of metal enrichment, (4) the similar absorption properties around both star-forming and passive galaxies, and (5) the observationally inferred temperature and densities of the CGM gas. We show that galactic wind-driven bubbles can account for these observed properties. We develop a model describing the motion of bubbles driven by a hot, fast galactic wind characteristic of supernova energy injection. The bubble size grows slowly to hundreds of kiloparsecs over $5-10$ Gyr. For high star formation rates or high wind mass loading $\dot M_w/\dot M_\star$, the free-flowing hot wind, the shocked hot wind in the interior of the bubble, and the swept-up halo gas within the bubble shell can all radiatively cool and contribute to low-ionization state metal line absorption. We verify that if the free-flowing wind cools, the shocked wind does as well. We find effective mass loading factors of $(M_w+M_\mathrm{swept})/M_\star\sim5-12$ as the bubbles sweep into the CGM. We predict cool gas masses, velocities, column densities, metal content, and absorption line velocities and linewidths of the bubble for a range of parameter choices. This picture can reproduce many of the COS-Halos and Keeney et al. (2017) observations of low-ionization state metal absorption lines around both star-forming and passive galaxies.

Fruit set, fruit retention and yield of chilli genotypes under hot and dry condition of western terai of Nepal

Thirteen selected chilli genotypes were evaluated in randomized completely block design with three replications to study the flowering, fruit set and yield potential during spring-summer of 2005 at Khajura, Banke (Western terai district of Nepal). High temperature, long drought period and hot wind blow during flowering and fruiting period severely affected the fruit set and fruit size. Only 18.81% flowers set fruits while 72.41% of set fruits reached to marketable size (harvesting). Wide variations observed in yield potential of the genotypes ranging total fruit number per plant from 6 to 71 and in total fruit yield 7.97 to 95.33 q/ha. The genotype Mr. Lee No. 3 Selex produced maximum marketable fresh fruit yield (90.69 q/ha) which was 234.5% higher than that of Jwala (standard check) with 50.57% fruit set and 74.93% fruit retention. One fruit per plant was 0.63 and 0.52 coefficient of fruit set (%) and fruit retention (%) respectively. Highly significant coefficient of determination (R2=0.86) of the product of fruit number per plant and 100 fruit weight (g) against fresh fruit yield (q/ha) showed that chilli genotypes yield can be predicted considering fruit number per plant and fruit weight in hot and dry summer condition.Journal of the Institute of Agriculture and Animal Science.Vol. 33-34, 2015, page: 229-236

Hydrothermal Treatments of Fe/N/C Based Oxygen Reduction Catalyst for High Durability in NH4F Solution

Introduction N-doped carbon materials (e.g., Fe/N/C and carbon alloy catalysts) with high oxygen reduction reaction (ORR) activity are promising alternatives to conventional Pt-based catalysts for polymer electrolyte fuel cells (PEFCs). However, their durability is insufficient compared with Pt based catalysts. Hence, in this study, a Fe/N/C-type oxygen reduction catalyst was hydrothermally-treated with fluoride ions to improve its durability. The electrochemical properties and the deterioration behavior of the catalysts were examined by a rotating ring disk electrode (RRDE) method and an accelerated durability test (ADT). Experimental Ketjenblack (KB, ECP600JD), 1,10-phenanthroline (phen) methanol solution and iron acetate aqueous solution were added to zinc acetate methanol/water solution, and the obtained suspension was heated at 75°C for 24 h followed by drying and grounding with a mortar to obtain a catalyst precursor. The precursor was heat-treated in a tube furnace at 1050°C for 60 min under Ar flow and at 950°C for 15 min under ammonia gas to obtain a catalyst (denoted as Fe-phen-Zn/KB). The catalyst was dispersed in 100 mM NH4F aqueous solution in a sealed PTFE container, and heated from 20°C to 120°C at a heating rate of ca. 3.3°C min-1 and kept 120°C for 30 min to obtain a catalyst hydrothermally-treated with fluoride ions (denoted as “Fe-phen-Zn/KB(F)”). A catalyst hydrothermally-treated without fluoride ions was also prepared for the comparison (denoted as “Fe-phen-Zn/KB(HyT)”). The catalysts-modified electrode was prepared by casting 2.0 mg mL-1 catalyst / 0.1 wt% Nafion® 2-PrOH ink to a glassy carbon (GC) disk for a Pt ring-GC disk electrode and dried under hot wind. Electrochemical measurements were carried out in 0.1 M HClO4 with the modified working electrode, a reversible hydrogen reference electrode and a GC rod counter electrode. ADTs were carried out for different periods of “ADTs time (t ADT)” using a start/stop protocol, consisting of a triangular waveform (1.0 V to 1.5 V vs. RHE at 500 mVs-1), as proposed for carbon corrosion by the Fuel Cell Commercialization Conference of Japan (FCCJ). X-ray photoelectron spectroscopy (XPS) experiments were carried out using a PHI X-tool (ULVAC-PHI, Inc.) using Al-Kα X-rays. The binding energies were calibrated based on the peak energy positions of Au7/2 (84.0 eV). Results and discussion Fig. 1 shows the dependence of ORR current at 0.7 V vs. RHE on t ADT / min of each catalyst. Whereas the initial ORR currents of the three catalysts were almost the same, the current values of the catalyst after 6 h of ADT is in the order: Fe-phen-Zn/KB(F) > Fe-phen-Zn/KB(HyT) > Fe-phen-Zn/KB, suggesting that the hydrothermal treatments with NH4F are effective for the improvement of durability for Fe/N/C catalysts. The peak energy positions of F1s XPS for Fe-phen-Zn/KB(F) before and after ADTs were ca. 684 eV (fluoride ion environment) and ca. 689 eV (C-F bonding environment), respectively, suggesting that fluoride ions , which adsorbed on and/or intercalated to the catalyst during the hydrothermal treatment with NH4F, formed bond with carbons during ADTs. Based on the N1s XPS spectra, Fe-phen-Zn/KB(F) before ADT involved pyridinic N, Fe-N, graphitic N, NO3 and NO, whereas the catalyst after ADTs only involved pyridonic N, which is probably derived from pyridinic N. Figure 1

Study of Desorption Process of Nitrogen Poisoning Species Generated during Ammonia Oxidation on Pt/C

A hydrogen society are one of the solution to alleviate the current global warming. However, since the energy density of hydrogen is low in the gas state, hydrogen must be transported under high pressure or liquid state, which causes energy loss. Ammonia is a promising hydrogen carrier because of its low production cost and ease in liquefaction and transport. A low temperature direct ammonia type fuel cell (DAmFC) is a device for directly extracting energy from ammonia. However, even Pt and Ir do not have enough catalytic activity for ammonia oxidation at low temperatures, which is disturbing practical application. The reason is that an inert surface poisoning by strongly adsorbed nitrogen (Nad) takes place competitively with a reaction generating nitrogen molecules. We investigated the desorption process of Nad on an Ir disk electrode and multiwalled carbon nanotube supported Ir nanoparticles (Ir/MWCNT) by normal pulse voltammetry (NPV). The purpose of this study is to analyze the desorption process of Nad generated during ammonia oxidation on Pt/C. To prepare catalyst modified electrode, 2 mg of 20 % Pt/XC-72 (E-TEK) was dispersed in 0.1 wt%Nafion-2-PrOH solution, and 10 μL of the dispersion was cast on a glassy carbon disk electrode (6 mm) and dried by hot wind. A three-electrode cell configuration was adopted using the modified electrode as the working electrode, a Pt wire as the counter electrode and RHE as the reference electrode. Electrochemical measurements were performed in 0.1 M NH3– 0.1 M KOH aqueous solution in nitrogen atmosphere. All potentials shown in this abstract are quoted with respect to the RHE. To analyze the desorption process of Nad, a waveform used in the NPV was shown in Fig. 1. First, Nad was generated by applying a potential step to 0.6 V, where ammonia oxidation occurs, for 180 s to generate Nad. After that, Nad was attempted to be desorbed by applying potential step to E recover [V] (0.4 V – 0.1 V) for a certain time (t recover, 1 s – 180 s). Finally, ammonia oxidation current with non-Faradaic current was obtained by reapplying potential step to 0.6 V. The ammonia oxidation current was determined by subtracting the current value considering the change in solution resistance and charging capacity in 0.1 M KOH. Assuming that desorption process consists of two independent pseudo first-order reactions, the oxidation current is expressed by the following equation: i (0.6V,0.5s)= I max Γ [p{1-exp(-k1 t recover) }+ (1-p){1-exp(-k 2 t recover)}] (1) where I max[μAcm-2 ECSA] is the maximum ammonia oxidation current normalized by electrochemically active surface area (ECSA), Γ is the relative coverage of the ammonia, p is the rate of the fast reaction, and k 1 [s-1] and k 2 [s-1] are the pseudo-first order reaction rate constants, and each parameter was determined by the nonlinear least square method. Fig. 1 shows the t recover dependence of the ammonia oxidation current after applying various E recover. The current reached almost a plateau after 60 s of applying E recover, suggesting that the Nad dissociation reaction reached equilibrium at the potentials. The current increased with decreasing E recover. Nad dissociation was promoted at the hydrogen adsorption/desorption potential region. Thus, it is predicted that hydrogen atoms adsorbed on the Pt atoms react with Nad, followed by desorption of N x H y . Figure 1