Thin Top Layer Research Articles

Spectrum formation in X-ray pulsars at very low mass accretion rate: Monte Carlo approach

ABSTRACT Recently, it has been discovered that the transition of X-ray pulsars to the low luminosity state ($L\lesssim 10^{35}\, {\rm erg\ \rm s^{-1}}$) is accompanied by a dramatic spectral change. That is, the typical power-law-like spectrum with high-energy cut-off transforms into a two-component structure with a possible cyclotron absorption feature on top of it. It was proposed that these spectral characteristics can be explained qualitatively by the emission of cyclotron photons in the atmosphere of the neutron star caused by collisional excitation of electrons to upper Landau levels and further Comptonization of the photons by electron gas. The electron gas are expected to be overheated in a thin top layer of the atmosphere. In this paper, we perform Monte Carlo simulations of the radiative transfer in the atmosphere of an accreting neutron star while accounting for a resonant scattering of polarized X-ray photons by thermally distributed electrons. The spectral shape is shown to be strongly polarization-dependent in soft X-rays ($\lesssim 10\, {\rm keV}$) and near the cyclotron scattering feature. The results of our numerical simulations are tested against the observational data of the X-ray pulsar A 0535+262 in the low-luminosity state. We show that the spectral shape of the pulsar can be reproduced by the proposed theoretical model. We discuss applications of the discovery to the observational studies of accreting neutron stars.

Extensive Evaluation of a Continental-Scale High-Resolution Hydrological Model Using Remote Sensing and Ground-Based Observations

Extreme hydrologic events are getting more frequent under a changing climate, and a reliable hydrological modeling framework is important to understand their mechanism. However, existing hydrological modeling frameworks are mostly constrained to a relatively coarse resolution, unrealistic input information, and insufficient evaluations, especially for the large domain, and they are, therefore, unable to address and reconstruct many of the water-related issues (e.g., flooding and drought). In this study, a 0.0625-degree (~6 km) resolution variable infiltration capacity (VIC) model developed for China from 1970 to 2016 was extensively evaluated against remote sensing and ground-based observations. A unique feature in this modeling framework is the incorporation of new remotely sensed vegetation and soil parameter dataset. To our knowledge, this constitutes the first application of VIC with such a long-term and fine resolution over a large domain, and more importantly, with a holistic system-evaluation leveraging the best available earth data. The evaluations using in-situ observations of streamflow, evapotranspiration (ET), and soil moisture (SM) indicate a great improvement. The simulations are also consistent with satellite remote sensing products of ET and SM, because the mean differences between the VIC ET and the remote sensing ET range from −2 to 2 mm/day, and the differences for SM of the top thin layer range from −2 to 3 mm. Therefore, this continental-scale hydrological modeling framework is reliable and accurate, which can be used for various applications including extreme hydrological event detections.

Mechanics of side-slipping in alpine skiing: theory of machining snow and ice

Side-slipping (or skidding) is a feature of several manoeuvres in alpine skiing, including a few types of skiing turns. On hard snow, side-slipping involves removal of a thin top layer of snow, that makes it similar to machining of materials in manufacturing. In this paper, we briefly review the theory of machining and then propose an approximate model that can be used to describe side-slipping in skiing. We test this model against published results of laboratory experiments in machining of ice and snow and find agreement.

Fe and S-isotope compositions of hydrothermal deposits from Kings Triple Junction, Lau Basin, southwest Pacific Ocean

We analyzed iron and sulfur isotopic compositions of polymetallic sulfides from an extinct hydrothermal mound near the Kings Triple Junction of the northern Lau basin belonging to a back-arc basin for understanding the origin and mineral zoning processes in this study. Sulfides from the hydrothermal mound's pedestal slab consisting of chalcopyrite and pyrite show enrichment of heavy S-isotope (δ34SV-CDT = +8.3 to +9.6‰). Sphalerite-dominated chimney on the mound's slope also has variable δ34S values between +5.5 and + 8.3‰ from central orifice to outer wall. These isotopic ratios indicate the substantial contribution of heavy isotope rich sulfate-S in seawater circulating within the mound. Low Δ33S values in these sulfides also indicate that the sulfate reduction is of thermal origin, with minimal or no role for microbes. Circulating seawater induced changes in fluid composition and post-depositional zone refinement of certain minerals can explain the variation in δ34S in different layers within the chimney and pedestal slab. The Fe-isotopic compositions (δ56FeIRMM-014) show a range from −1.1 to −0.3‰ in the pedestal slab while they vary between −1.7 and − 0.6‰ at different parts of the peripheral chimney section. We explain such changes are mostly due to redox processes and mineral zoning development during these sulfide deposit formation. The tree-like FeMn oxide growth structures in the vicinity of the hydrothermal mound having a thin birnessite top layer and amorphous iron oxide bottom part show distinct δ56Fe values of −3.0 and − 0.8‰, respectively.

Modeling and Optimization of Multi-functional Ammonia Slip Catalysts for Diesel Exhaust Aftertreatment

Ammonia slip catalysts (ASC) are used downstream of the NH3-selective catalytic NOx reduction (SCR) system, to minimize ammonia slip from transport sector SCR units. The ASC may consist of an SCR active layer for NOx control, a layer with oxidation functionality for ammonia conversion, or a combination thereof, either as individual layers or as a single mixed layer. Mathematical models of such systems involve flow and mass transfer in the monolithic channels as well as coupled reaction/diffusion processes in the catalytic layers. In this work, we develop a single-channel 1D-1D (pseudo 2D) steady-state tank-in-series mathematical model for monolithic ammonia slip catalysts with up to two layers. Kinetics of relevant reactions over the Cu-Beta zeolite and the Pt/TiO2 layer, including SCR, ammonia oxidation, and the formation of N2O, were derived based on an extensive flow reactor study. The model was validated based on experiments using four different small-scale ASC monoliths, showing good agreement between the model predictions and the experimental results. Comparison of ten ASC configurations for the oxidation of 200 ppm NH3 at 300 °C shows that configurations with a pure layer of NH3 oxidation catalyst generate undesirable high N2O and NOx levels. The best ASC configurations feature fast diffusion in the catalytic layers (a high effective diffusion coefficient), a thin top layer loading with some ammonia oxidation catalyst, and a mixed layer of ammonia oxidation catalyst and the SCR catalyst to limit the formation of N2O and NOx.

Effect of different structure of membrane support on polyamide formation and its performance in reverse osmosis

This work aims to investigate the polyamide (PA) morphology on polysulfone (PSf) membrane supports with different morphologies. It was achieved by systematically varying the N-Methyl-2-Pyrrolidone (NMP) and Dimethylformamide (DMF) solvent composition ratios in dope solution as adapted in Tiraferri et al. The PSf membrane support was firstly synthesized via phase separation technique. Next, the PA layer of the thin film composite (TFC) membrane was synthesized via consistent interfacial polymerization parameters on the PSf membrane support. The PA layer over the resulting array of membrane supports was investigated on their surface wettability, top and cross-sectional morphologies, and performances. Result shows that with more NMP content in the dope solution produces thin and dense sponge-like top skin layer with intense extended finger-like macrovoids sublayer. Meanwhile, more DMF content in the dope solution produces thicker and dense sponge-like morphology on the top skin with finger-like pores underneath. A layer of smaller and loosen ridge-and-valley PA structures is formed on the thicker and dense sponge-like morphology. TFC membrane over support made of NMP to DMF (40:60) was observed had the highest hydrophilicity with the lowest contact angle measurement of 61.9 ± 3.1°. It also performed the highest water permeability of 4.06 LMH/bar, moderate salt rejection of 95.65% with salt permeability of 1.9 gMH.

Life cycle of the dung beetle Onthophagus cervus (Fabricius, 1798) (Coleoptera: Scarabaeidae: Scarabaeinae) in moist belts of south India

Biology, nesting behaviour, and the factors favouring the high abundance of prominent dung beetle species, Onthophagus cervus (Fabricius, 1798) in an open agricultural field in North Kerala were studied. Short life cycle with high fecundity, low egg mortality, shorter larval duration, shorter developmental period, short generation time, female-biased sex ratio, and longer survivability of females were recorded. Female-biased sex ratio in O. cervus indicates that mating competition takes place between male offsprings and the high cost of producing males led to their reduction. Broad categorization of Onthophagus species is provided based on the comparison of data of brood mass production, fecundity, duration of egg, larval, pupal, adult stages, adult mortality and life span of various Onthophagus species. Higher abundance of O. cervus in the region is attributed to traits that are characterize of r-selection such as high fecundity, small body size, low egg mortality, shorter larval duration, early onset of maturity, and shorter developmental period. Short generation time which enables attaining maturity earlier together with female biased sex ratio, longer duration of females favouring high egg production and shallow tunnels which enable easy and fast tunnelling process and development in thin soil top soil layer are the other factors that contributed to the higher abundance of O. cervus. Present study showed that geographic region wise knowledge on the life history traits of prominent dung beetles are necessary for interpretation of the exact mechanism behind their seasonality and abundance in specific regions and the generated data will be useful for the conservation of species in natural habitats.

Metal organic framework enhanced SPEEK/SPSF heterogeneous membrane for ion transport and energy conversion

Abstract Bioinspired nanofluidic devices have drawn increasing global interest due to their giant applicable potential in a wide range of fields. By mimicking biological prototype, it is expected to achieve high energy conversion efficiency and tunable ion transport. However, the low osmotic conversion efficiency, weak ion transport capability and poor mechanical performance limit practical application. We designed a class of heterogeneous membrane consisting of a support layer and a thin top layer to meet fundamental requirements. To achieve higher power generation, we incorporated metal organic framework (MOF) nanosheets (dispersed phase) into polymer matrix (continuous phase) to afford a mixed matrix top layer. This unique structure addressed the geometric restriction associated with the polymeric specie due to their limited pore accessibility. As a result, the presented membranes produced high power density of ca. 7 W m−2 and a high energy conversion efficiency of ca. 40% under a salinity gradient of 50 (0.5 M|0.01 M, NaCl). This work thus offers an insight into a new methodology in the development of a novel membrane technology for highly efficient energy conversion.

Self-supporting covalent organic framework membranes synthesized through two different processes: solvothermal annealing and solvent vapor annealing

Rigid, freestanding covalent organic framework (COF-1) membranes have been synthesized from 1,4-benzenediboronic acid (BDBA) precursors using two different approaches: room temperature solvent-vapour annealing (SVA) and solvothermal annealing (SA). Characterization of films using Fourier-transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), and various microscopies shows that the films obtained through the two different routes vary in their retained BDBA proportion, crystal size and macroscale morphology. Gas adsorption measurements give specific surface areas of 579 ± 7 m2 g−1 and 739 ± 11 m2 g−1 respectively, suggesting that the average porosity of these films is competitive with bulk-synthesized COF-1 particles. The films have a stratified structure, with a dense, thin top layer and a thicker, sponge-like base layer. Using nanoindentation, we measured the Young’s modulus at the top surface of the SVA and SA films to be 3.64 ± 1.20 GPa and 3.33 ± 0.12 GPa respectively, with the smaller uncertainty for the SA film attributed to a more uniform morphology. These measurements provide useful experimental data pertaining to COF-1 mechanical properties, furnishing information relevant to the use of these free-standing membranes in applications such as gas filtration or storage.

Evidence for different behaviors of atmospheric glass alteration as a function of glass composition

The glass composition is a determining parameter that influences the glass chemical durability, particularly in atmospheric conditions (defined by the relative humidity, RH, < 100%). This is obvious in the field of the cultural heritage (CH), where some glass compositions qualified as unstable show advanced signs of degradation under atmosphere, while others seem, on the contrary, stable. This study investigates the differences between stable and unstable glass compositions regarding the phenomenology of the atmospheric glass alteration, by means of accelerated ageing of three glass replicas followed by the characterization of their alteration layers at different scales. Over the same ageing period and experimental conditions, the two glass compositions qualified as unstable develop thick hydrated layers and a thin top layer of carbonate precipitates. Their hydrated layers are depolymerized, and they remarkably retain alkalis and non-bridging oxygens in a dense network of hydrogen bonds, as demonstrated by 29Si and 1H MAS NMR. On the contrary, the stable glass composition shows a considerably thinner hydrated layer and, relatively, a higher amount of carbonates on the surface. In unstable glasses, the retention of a significant proportion of alkalis and NBOs, probably by maintaining a basic character to the hydrated layer, seems comparatively a destabilizing factor sustaining hydration by fast network hydrolysis.

Mechanical and High-Temperature Tribological Properties of Cr3C2-NiCr/TiN Duplex Coating

Preparation of duplex coating is an innovative way to improve components surface in terms of mechanical and tribological properties by the combination of high velocity oxy-fuel (HVOF) and physical vapor deposition (PVD) technologies. The present work focused on the construction, mechanical properties and high temperature tribological behaviors of the duplex coating consisting of a thick HVOF Cr3C2-NiCr interlayer and a thin PVD TiN top layer, as well as compared it with the Cr3C2-NiCr coating and the single TiN film. The results showed that the Cr3C2-NiCr/TiN duplex coating exhibited higher hardness, elastic modulus, H/E and H3/E2 ratios and superior load-bearing capacity than the single TiN film. The introduction of Cr3C2-NiCr intermediate layer did not affect the microstructure of TiN film but significantly improved the adhesion strength between TiN film and substrate, as well as the wear resistance sliding against WC ball at different temperatures. In addition, the friction and wear mechanism of the Cr3C2-NiCr coating, TiN film and Cr3C2-NiCr/TiN duplex coating was revealed by investigating the friction-induced morphological and structural evolutions of the sliding surface at elevated temperature.

Experimental Investigation on Two Lift Cement Concrete Pavement

Rigid pavement construction is promoting now a days due to its durablilitycriteria.Cost of fresh aggregate is 30-35% more than recycled aggregate which causes increase of overall cost of pavementthustwo lift pavement has great potential as a sustainable paving solution.The main objective of this study is to use recycled aggregate in concrete pavement which reduced overall cost of the pavement.Sincenatural aggregate scarcity is increasing day by day.Generally homogenous layer of concrete is commonly used in our country. As maximum stress induced at top of the pavement and it decreases along the depth.So using of recycled material in the thick bottom layer and natural aggregate in thin top layer is a good solution of shortage of natural aggregate or disposal of recycled material.In this rigid pavement two layer of slab with different thickness of upper and lower lift such as varying the thickness of bottomlayer50%.60%.70%, 80% & 90% of overall thickness of concrete sample. Quality aggregate is provided in upper lift& recycled aggregate in bottom lift.Physical and mechanical properties of materials evaluated which satisfy the standard criteria.Mix proportioning is carried out to evaluate the mechanical propertis and performance of the prototype model.Result shows best agreement. It is found that two lift concrete pavement of 200mm with top lift thickness 60mm and bottom lift thickness 140mm made of M40 and M20 respectively may be the sustainable solution. Keywords: Two lift pavement, Compressive strength,Flexuralstrength,Rebound hammer, Stiffness modulus

CZTSSe Formation Mechanism Using a Cu/Zn/SnS Stacked Precursor: Origin of Triple CZTSSe Layer Formation.

In this study, to control the formation of non-uniformly distributed large voids and Cu-Sn alloy agglomeration, which leads to local compositional misfit and secondary phase formation, a SnS compound precursor was applied instead of metal Sn to avoid compositional non-uniformity. Using a Cu/Zn/SnS stacked precursor, a temperature tracking experiment was conducted to confirm the formation controllability of the void and the secondary phase. According to the results of this temperature-profile tracking experiment, it was confirmed that the large void was successfully controlled; however, an additional ZnSSe secondary phase layer was formed in the middle of the CZTSSe upper layer and small voids were distributed relatively uniformly in the bottom CZTSSe layer. An efficiency of approximately 8% was obtained when the Cu/Zn/SnS stacked precursor was used. The origins of the low short-circuit current and fill factor are posited to be caused by the increase of the energy bandgap of the CZTSSe layer due to the SnS precursor, the thin top CZTSSe layer (around 600 nm) of the triple CZTSSe layer, and the diffusion length extension of the minor carriers caused by bypassing the ZnSSe phase.

TiO2 microring resonators with high Q and compact footprint fabricated by a bottom-up method.

Titanium dioxide (TiO2) microring resonators (MRRs) with high quality factors (Qs) are demonstrated by using a new, to the best of our knowledge, bottom-up fabrication method. Pattern platforms with a T-shaped cross section are first defined by etching a thin top layer of silicon nitride and a thick bottom layer of silica and partially undercutting the silica. Then, TiO2 is deposited on the platforms to form the TiO2 waveguides and devices. TiO2 MRRs with different bending radii, waveguide widths, and gaps in the bus waveguide are fabricated and measured. The intrinsic Q(Qint) is achieved to be ∼1.1×105 at the telecommunication wavelengths, corresponding to a bend waveguide loss of 3.9 dB/cm while the compact MRR with a radius of 10 µm can still sustain a Qint of ∼105. These results not only unfold the feasibilities of the proposed bottom-up method for fabricating TiO2 waveguides and MRRs with high Qs and compact footprints but also suggest a new approach for fabricating waveguides in other materials, of which direct etching is not easily accessible.

High-performance MFI zeolite hollow fiber membranes synthesized by double-layer seeding with variable temperature secondary growth

Hydrophobic MFI zeolite membranes are perm-selective to organic compounds over water and offer applications for organic/water separations. However, reproducible synthesis of MFI zeolite membranes with high organic selectivity remains a challenge. This paper reports a new synthesis method consisting of dual-layer seeding and varying-temperature secondary growth for the synthesis of hydrophobic MFI zeolite membranes on alumina hollow fiber supports. The effects of seeding method, seed particle size, seed size ratio, and variable temperature/time profile on the microstructure, hydrophobicity and gas perm-selectivity of the membranes are investigated leading to the identification of optimum seed structure and secondary growth conditions for synthesis of MFI zeolite membranes with high ethanol/water separation performance. The high-performance MFI zeolite membrane has a microstructure consisting of a thin, fully inter-grown, and dense top zeolite layer responsible for high selectivity, and a porous low inter-grown bottom zeolite layer minimizing resistance and retarding aluminum transfer from the support to zeolite. The best hollow fiber supported MFI zeolite membrane with a Si/Al ratio of 187 exhibits ethanol/water pervaporation separation factor of 160 with a total flux of 3 kg m−2 h−1.

Performance of plasma-sprayed MoSi2-based coating as a heating element

Rollers covered with a thermally sprayed heater coating are an alternative to conventional stream heated and electromagnetic induction heated rollers. In this study, a heater coating was developed using a combination of a thermally sprayed NiAl bonding layer, an MgAl2O4 insulating layer, and an MoSi2-based conductive layer; for comparison, an optional thin MgAl2O4 top layer was applied to provide corrosion and wear protection. The microstructures and characteristics, particularly the electrical-thermal performance, were systematically investigated. The MgAl2O4 layer was found to provide excellent high-temperature insulation performance. Thermo-cycling tests indicate the MoSi2-based coating can be heated to 320 °C with a relatively uniform temperature distribution at the roller surface. The addition of the top layer as a protective mask is beneficial to the heating stability, and NiCr added as a bonding phase in the conductive layer significantly improves the electrical-thermal performance.

Development of Design Chart for Jute Geotextiles Reinforced Low Volume Road Section by Finite Element Analysis

A 3D finite element (FE) analysis has been carried out to propose a design chart for Sand-Jute geotextiles-Sand (SJS) reinforced low volume road section on soft subgrade foundation. The SJS (Jute geotextile with a thin layer of sand on each side of it) layer has been placed in between the subgrade soil and the top granular layer. In the present FE analysis, nonlinear behaviour of low volume road materials has been considered. The rutting behaviour of a low volume road section with jute geotextiles reinforcement layer has been investigated. Results of the FE analysis reveal that the improvement due to jute geotextiles is more pronounced in road sections with thin top granular layer than in other sections. An attempt has also been made to study the mobilization of tensile strength of jute geotextiles under small and large rut depths. In the case of large rut depth (75 mm), it has been found that a minimum thickness of the top granular layer of 0.2 m is adequate for woven jute geotextiles with stiffness of 20 kN/m. For benefit of the practising engineers dealing with designing jute geotextiles reinforced low volume road section, a design chart has been proposed for 50-mm rut depth.

Two-level ablation and damage morphology of Ru films under femtosecond extreme UV irradiation

The dynamics of a thin ruthenium film irradiated by femtosecond extreme UV laser pulses is studied with a hybrid computational approach, which includes Monte Carlo, two-temperature hydrodynamics and molecular dynamics models. This approach is capable of accurate simulations of all stages of material evolution induced by extreme UV or X-ray photons: from nonequilibrium electron kinetics till complete lattice relaxation. We found that fast energy deposition in a subsurface layer leads to a two-level ablation: the top thin layer is ablated as a gas–liquid mixture due to expansion of overheated material at near and above critical conditions, whereas a thicker liquid layer below is ablated via a cavitation process. The latter occurs due to a thermo-mechanically induced tensile pressure wave. The liquid ablating layer exhibits unstable behaviour and disintegrates into droplets soon after detachment from the rest of the target. Our simulations reveal basic processes leading to formation of specific surface morphologies outside and inside the damage craters. The calculated ablation threshold, crater depth and morphological features are in quantitative agreement with the experimental data, which justifies the applicability of our hybrid model to study laser-induced material damage.

Recent Development in Composite Membranes for Flow Batteries.

Flow batteries (FBs) are one of the most attractive candidates for stationary energy storage and vital in realizing the wide application of renewable energies. Membranes play an important role in isolating redox couples while transporting ions to close the internal electrical circuit. Therefore, membranes with high selectivity and conductivity are highly important. Among different membranes, a composite membrane with independent design of support layer and thin selective top layer becomes one of the most promising candidates to break the trade-off between selectivity and conductivity. In this Review, recent studies on composite membranes for FBs and the principles of membrane design in different systems are discussed and summarized. Finally, the future direction on membrane design for different FBs is presented, which will provide an extensive, comprehensive reference to design and construct high-performance composite membranes for FBs.

The suitability of Ulva fasciata, Ulva compressa, and Hypnea musciformis for production in an outdoor spray cultivation system, with respect to biomass yield and protein content

Land-based seaweed ponds can produce 500–700 t of fresh weight (FW) ha−1 year−1, but their profitability can be cut by the cost of pond construction, including ground leveling, infrastructure cost, and water agitation. A potentially cost-effective, land-based seaweed culture approach where seaweed grow on substrates by spray culture has been examined. We measured the yield and biomass quality of three intertidal cultivable seaweeds, Ulva fasciata, Ulva compressa, and Hypnea musciformis, in spray (known elsewhere also as film or drip culture) and pond culture approaches, varying surface inclination and nutrient loading. These technical details are necessary for the evaluation of the approach and for upscaling. The best yield (up to 84 g FW m−2 day−1, 44–84% of yield in ponds) and quality (protein content and additional parameters) of spray-grown U. fasciata was obtained on 6°-inclined trays with highly fertilized water. The highest protein content (24.5%), but with reduced yield, was obtained on 80°-inclined trays. H. musciformis and U. compressa, apparently thanks to their stringy morphologies, yielded in spray culture up to 286 g FW m−2 day−1 and 172 g FW m−2 day−1, respectively. The overall quality and resilience of spray-grown algae profited from nutrient enrichment, and the best yields were achieved with enrichment of 10 g N and 1 g P m−2 day−1 in H. musciformis and 15 g N and 1.5 g P m−2 day−1 in both Ulva species. Biomass growth occurred in layers, which visibly differed in color and consistency. A thin bleached top thalli layer protected the biomass below from dehydration and bleaching and allowed there a high photosynthetic rate. A spray culture of Ulva sp. on seawater-sprayed cement tiles, with minimal maintenance, yielded up to 50 g FW m−2 of tile day−1. Economically, spray culture appears to be particularly suitable to the stringy algae.