Incommensurate smectic phase in close proximity to the high-Tc superconductor FeSe/SrTiO3

Superconductivity is significantly enhanced in monolayer FeSe grown on SrTiO3, but not for multilayer films, in which large strength of nematicity develops. However, the link between the high-transition temperature superconductivity in monolayer and the correlation related nematicity in multilayer FeSe films is not well understood. Here, we use low-temperature scanning tunneling microscopy to study few-layer FeSe thin films grown by molecular beam epitaxy. We observe an incommensurate long-range smectic phase, which solely appears in bilayer FeSe films. The smectic order still locally exists and gradually fades away with increasing film thickness, while it suddenly vanishes in monolayer FeSe, indicative of an abrupt smectic phase transition. Surface alkali-metal doping can suppress the smectic phase and induce high-Tc superconductivity in bilayer FeSe. Our observations provide evidence that the monolayer FeSe is in close proximity to the smectic phase, and its superconductivity is likely enhanced by this electronic instability as well.

pH-Dependent Formation of Oriented Zinc Oxide Nanostructures in the Presence of Tannic Acid

To crucially comprehend the relaying factors behind the growth mechanism of ZnO nanostructures, the needs to understand the cause of preferences in the enhancement of desired physicochemical properties are essential. The particular oriented attachment (OA) is believed to become the cause of the classical growth pattern of ZnO nanostructures which is mainly controlled by the Ostwald ripening (OR) process. In the present work, the concerns over the systematic changes in size and the morphological surface of ZnO nanostructures upon exposure to tannic acid (TA) prepared by drop-wise method turns the particles to different surface adjustment state. Here, we assessed the TA capping ability and its tendency to influence the OA process of the ZnO nanostructures. The detailed process of the growth-based TA system via transmission electron microscopy (TEM), scanning electron microscopy (SEM), and FFT autocorrelation revealed the pH effect on their physical properties which proved the transition surface properties state of the particles from rough to smooth states due to oriented attachment. For pure ZnO nanostructures, the surface is almost smooth owing to the strong bonding particles which are then changed to coarsened surface structures upon the introduction of TA. Strong surface adsorption of Zn cations and phenol ligands mediated the agglomerated nanocrystals, surprisingly with smaller nanostructures dimension.

Synthesis,Surface Morphology, Optical Properties and Photocatalyst Activities of TiO2/ZnO/Fe2O3 Nanocomposites.

The photocatalytic degradation of methylene blue in aqueous solutions is enhanced significantly by formulating multiphase TiO2/ZnO/Fe2O3 nanocomposites. The photocatalytic activity of unary TiO2, binary TiO2/ZnO, and ternary TiO2/ZnO/Fe2O3 compounds are compared and reported. Using TiO2/ZnO/Fe2O3, methylene blue degradation became rapid and the reaction followed first-order kinetics. The consequences of the phase transition, surface features, and optical properties are compared and elucidated. The reduced photoluminescence intensity and decreased optical band gap energy in tertiary compounds impose higher degradation of methylene blue under irradiation.

Theoretical and Experimental Study on Contact Characteristics of Spiral Bevel Gears under Quasi-Static and Large Loading Conditions

The precise mathematical model for the tooth surface and transition surface of spiral bevel gears is derived. Taking a pair of spiral bevel gears of a heavy vehicle as an example of calculation and analysis, a finite element model of spiral bevel gears transmission system is established. Through the finite element tooth contact analysis under quasi-static loading and high loading condition, the influences of torque on the root stress distribution, contact stress, and transmission error are discussed, and the results are compared with the empirical formula results. Finally, a contact performance test bench of spiral bevel gear pair is developed, then the root bending stress, contact pattern, and transmission error tests are carried out. These experiment results are compared with analyzed ones, which showed a good agreement.

Modeling of the worm cutter in the process of cutting the gears

This work offers a new approach to graphical modeling of worm cutter parameters, based on analyses and synthesis of simple kinematic movements, causing its cutting elements a single move and displacement when placing metal into a hollow between spikes of the gear, which is being cut. It is one of the most difficult cutting and shaping processes, combining four kinematic movements – rotation of the cutters, their axial feed, rotation of the billet and a constructive move – displacement of cutting elements, located on the principle worm helix along the cutter axis. The modeling difficulty is that the cutting surface constantly changes its location and form in relation to the spikes. This surface is formed on the billet as a kind of a transition surface between the untreated surface, the partly treated surface and the partly treated hollow between the spikes of the gear, which is being cut. Its formation is participated by all the spikes, which have performed the cutting during all the time before a certain moment. Continuous change of the transition surface shape and size determines the shape and size of the shavings and the cross-sectional parameters of the spikes slices and the tool blades, and its reproduction is a base for a correct quantitative assessment of the cutting parameters of individual blades and spikes of the cutter. In its turn, complete and authentic information about the cross-sections and the shape and size of metal layers cut during the spike milling is a base for calculating and analysis of the cutting power, the friction force, the thermal processes, fluctuations and vibrations. The algorithm of an instant surface formation between the gear spikes and the shavings 3D geometry on all of the active spikes of the tool are realized in AutoCAD graphic system. Here are given the results of computer modeling of the shavings when using the Archimedean cutter with counter feed. Complete information about geometrical structure of the cut off layers creates the base for a detailed and system modeling of this process abreast the separate warm cutter rails, the spikes and the blades. In combination with intensity of the plastic deformation data, the tension and the temperature received in Deform system for a certain spike milling condition, the parameters of the cut layers data referred in this work, create the condition for thermo prognostication and the cutting elements waste, their power load, strength protective coatings, cutting force and temperature transition processes, optimum technological processes of spike milling projecting and its managing.

Extended enthalpy formulations in the ice flow model ISSM version 4.17: discontinuous conductivity and anisotropic SUPG

The thermal state of an ice sheet is an important control on its past and future evolution. Some parts of the ice sheets may be polythermal, leading to discontinuous properties at the cold–temperate transition surface (CTS). These discontinuities require a careful treatment in ice sheet models (ISMs). Additionally, the highly anisotropic geometry of the 3D elements in ice sheet modelling poses a problem for stabilization approaches in advection dominated problems. Here, we present extended enthalpy formulations within the finite-element Ice Sheet System Model (ISSM) that show a better performance to earlier implementations. In a first polythermal-slab experiment, we found that the treatment of the discontinuous conductivities at the CTS with a geometric mean produce more accurate results compared to the arithmetic or harmonic mean. This improvement is particularly efficient when applied to coarse vertical resolutions. In a second ice dome experiment, we find that the numerical solution is sensitive to the choice of stabilization parameters in the well-established Streamline Upwind Petrov–Galerkin (SUPG) method. As standard literature values for the SUPG stabilization parameter are not accounting for the highly anisotropic geometry of the 3D elements in ice sheet modelling, we propose a novel Anisotropic SUPG (ASUPG) formulation. This formulation circumvents the problem of high aspect-ratio by treating the horizontal and vertical directions separately in the stabilization coefficients. The ASUPG method provides accurate results for the thermodynamic equation on geometries with very small aspect ratios like ice sheets.

Temporal and Spatial Variations in Abundance and Diversity of Zooplankton Fauna of Opa Reservoir, Obafemi Awolowo University, Ile-Ife, Southwest Nigeria

The present study investigated the ecological status of Opa reservoir, Obafemi Awolowo University, Ile Ife, Nigeria, based on the spatial and temporal variations in abundance and distribution of zooplankton. 72 samples were collected monthly with a quantitative net zooplankton from both the surface and bottom levels in three stations established at the dam site (Lacustrine), mid-lake (Transition) and inflow (Riverine) over a period of an annual cycle. A total of fifty-four (54) species were recorded from the reservoir comprising Rotifera (57.41%) > Arthropoda (33.33%) > Protozoa (5.56%) > Ciliophora (1.85%) = Cnidaria (1.85%), in the order of abundance. The least number of species (47) was recorded at the Transition station, while the highest number of species (49) occurred at the Lacustrine zone. Of all the zooplankton recorded, four species had significant spatial variation, while nine displayed seasonal variations during the study period (p ≤ 0.05). The highest species richness was observed in Transition surface station (4.18), followed by Lacustrine surface station (3.80) and Riverine surface station (3.23). Shannon’s index showed that zooplankton species were more diverse during the rainy season than dry season. The highest Trophic State Index (TSICR) with respect to Rotifer abundance occurred in Transition surface, followed by Riverine surface and the least occurred in Transition bottom portion. The mean TSICR value obtained was 65.20, indicative of hyper-eutrophic, while the mean TSICL value with respect to cyclopoida-calanoida obtained was 58.07 also revealing eutrophic status of the study area. Opa reservoir comprises mainly Rotifers and its TSICR showed the lake as eutrophic, tending towards becoming hyper-eutrophic, which could speed up the aging of the lake.