We studied the three-dimensional Thirring model in the limit of an infinite number of flavors at finite temperature and density. We calculated the number density as a function of temperature and the ...density at zero temperature serves as a relevant parameter. A three-dimensional free fermion gas behavior as the density at zero temperature approaches zero smoothly crosses over to a two-dimensional free fermion gas behavior as the density at zero temperature approaches infinity.
Easy to prepare solid materials based on fumed silica impregnated with polyethylenimine (PEI) were found to be superior adsorbents for the capture of carbon dioxide directly from air. During the ...initial hours of the experiments, these adsorbents effectively scrubbed all the CO2 from the air despite its very low concentration. The effect of moisture on the adsorption characteristics and capacity was studied at room temperature. Regenerative ability was also determined in a short series of adsorption/desorption cycles.
The electrochemical behavior of titanium has been investigated in chloride electrolyte of different pH values (2.1, 5.2 and 7.4). Potentiodynamic polarization studies showed wide passive behavior ...irrespective of change in pH. Passive films were grown by applying different passive potentials (0.2 to 0.6V (vs SCE)) by recording chronoamperometric curves for duration of 8h. Electrochemical impedance spectroscopy (EIS) measurements showed higher impedance values for the oxide layer grown in neutral pH condition and for oxides formed at higher formation potentials. Emphasis is made mainly on the properties of titanium oxide estimated by Mott-Schottky analysis, which shows that passive film formed, is of n-type semiconducting film and the donor concentration is in the order of 1020cm−3. The calculated diffusivity of point defects is in the range of (0.5 to 2.5) × 10˗16 cm2s−1 and tends to decrease with increase in electrolyte pH. Surface morphology of the passive films was examined using scanning electron microscope and surface roughness was characterized using confocal microscope. Ex- situ ellipsometry measurements were performed to analyze the optical constants of the oxide layer and to determine the oxide thickness. The thickness is in the range of 3.5 to 5.8nm and comparable to the calculated values.
•Thin passive film was grown potentiostatically on titanium at various pH conditions•Passive films formed on titanium are of n-type semiconducting nature.•Diffusivity of point defects decreases with increase in pH.
Conspectus Increasing levels of carbon dioxide in the atmosphere and the growing need for energy necessitate a shift toward reliance on renewable energy sources and the utilization of carbon dioxide. ...Thus, producing carbonaceous fuel by the electrochemical reduction of carbon dioxide has been very appealing. We have focused on addressing the principal challenges of poor selectivity and poor energy efficiency in the electrochemical reduction of carbon dioxide. We have demonstrated here a viable pathway for the efficient and continuous electrochemical reduction of CO2 to formate using the metal-independent enzyme type of formate dehydrogenase (FDH) derived from Candida boidinii yeast. This type of FDH is attractive because it is commercially produced. In natural metabolic processes, this type of metal-independent FDH oxidizes formate to carbon dioxide using NAD+ as a cofactor. We show that FDH can catalyze the reverse process to generate formate when the natural cofactor NADH is replaced with an artificial cofactor, the methyl viologen radical cation. The methyl viologen radical cation is generated in situ, electrochemically. Our approach relies on the special properties of methyl viologen as a “unidirectional” redox cofactor for the conversion of CO2 to formate. Methyl viologen (in the oxidized form) does not catalyze formate oxidation, while the methyl viologen radical cation is an effective cofactor for the reduction of carbon dioxide. Thus, although the thermodynamic driving force is favorable for the oxidized form of methyl viologen to oxidize formate to carbon dioxide, the kinetic factors are not favorable. Only the reverse reaction of carbon dioxide reduction to formate is kinetically viable with the cofactor, methyl viologen radical cation. Binding free energy calculated from atomistic molecular dynamics (MD) simulations consolidate our understanding of these special binding properties of the methyl viologen radical cation and its ability to facilitate the two-electron reduction of carbon dioxide to formate in metal-independent FDH. By carrying out the reactions in a novel three-compartment cell, we have demonstrated the continuous production of formate at high energy efficiency and yield. This cell configuration uses judiciously selected ion-exchange membranes to separate the reaction compartments to preserve the yields of the methyl viologen radical cation and formate. By the electroregeneration of the methyl viologen radical cation at −0.44 V versus the normal hydrogen electrode, we could produce formate at 20 mV negative to the reversible electrode potential for carbon dioxide reduction to formate. Our results are in sharp contrast to the large overpotentials of −800 to −1000 mV required on metal catalysts, vindicating the selectivity and kinetic facility provided by FDH. Formate yields as high as 97% ± 1% could be realized by avoiding the adventitious reoxidation of the methyl viologen radical cation by molecular oxygen. We anticipate that the insights from the electrochemical studies and the MD simulations to be useful in redesigning the metal-independent FDH and alternate artificial cofactors to achieve even higher rates of conversion.
In the present study, synthesis of monophasic Sr-HAp nanocrystals using a single step Solution Combustion Synthesis (SCS) process is reported. Effects of important process parameters on the formation ...of monophasic Sr-HAp nanocrystals were investigated to optimize the process for cost effective synthesis. X-ray Diffraction (XRD) and transmission electron microscopy (TEM) studies of as-synthesized powders (Sr ranging from 0 to 30%) revealed close packed hexagonal structure, with individual primary particle sizes ranging from 15 to 70nm length and 5±1nm diameter. Scanning Electron Microscopy (SEM) studies showed that Sr substitution in HAp increased the aspect (L/D) ratio of primary nanorod and reduced the secondary agglomerate coarsening. Fourier Transform-Infrared (FTIR) and Energy Dispersive Spectroscopy (EDS) studies confirmed the presence of appropriate concentrations of phosphates and hydroxyl groups along with small amounts of carbonates in the as-synthesized Sr-HAp. Differential Scanning Calorimetry (DSC) studies up to 400°C and XRD patterns of powders calcined at 1100°C proved that Sr addition in HAp enhances the stability by suppressing the phase transformation during further consolidation. In effect, nano Sr-HAp powders synthesized using SCS process resembled the structural and chemical nature of bone mineral and could be used as a possible candidate material for hard tissue replacement and drug delivery systems.
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•Nanosized Strontium and carbonate co-substituted Hydroxyapatite was synthesized.•A single step Solution Combustion synthesis was used to produce nano Sr-HAp.•Low cost and environment friendly precursors were used.•Sr addition increased the L/D ratio of nanorods and lattice parameters of HAp.•Sr addition suppressed phase transformation and crystal growth at high temperatures.
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Biofilms are self-assembling structures consisting of rigid microbial cells embedded in a soft biopolymeric extracellular matrix (ECM), and have been commonly viewed as being detrimental to health ...and equipment. In this work, we show that biofilms formed by a non-pathogenic fungus
Neurospora discreta
, are fungal bio-composites (FBCs) that can be directed to self-organize through active stresses to achieve specific properties. We induced active stresses by systematically varying the agitation rate during the growth of FBCs. By growing FBCs that are strong enough to be conventionally tensile loaded, we find that as agitation rate increases, the elongation strain at which the FBCs break, increases linearly, and their elastic modulus correspondingly decreases. Using results from microstructural imaging and thermogravimetry, we rationalize that agitation increases the production of ECM, which concomitantly increases the water content of agitated FBCs up to 250% more than un-agitated FBCs. Water held in the nanopores of the ECM acts a plasticizer and controls the ductility of FBCs in close analogy with polyelectrolyte complexes. This paradigm shift in viewing biofilms as bio-composites opens up the possibility for their use as sustainable, biodegradable, low-modulus structural materials.
Graphical abstract
This review describes the ion implantation methods used to improve the mechanical, chemical and biological properties of biomedical titanium alloys. They give excellent adhesion of the coating. ...Although the process is expensive and useful for high-value products, it is extremely controllable and can be tailored to implant different ions to form ultra-high purity coating layers. Calcium and phosphorus implantation are useful in improvement of the biocompatibility of titanium. Sections cover calcium phosphate ceramics (dicalcium phosphate dihydrate, tricalcium phosphate and hydroxyapatite) and properties and biological activity of ion-implanted HA coatings.
Owing to the low conductivity of pure water, using an electrolyte is common for achieving efficient water electrolysis. In this paper, we have fundamentally broken through this common sense by using ...deep-sub-Debye-length nanogap electrochemical cells to achieve efficient electrolysis of pure water (without any added electrolyte) at room temperature. A field-assisted effect resulted from overlapped electrical double layers can greatly enhance water molecules ionization and mass transport, leading to electron-transfer limited reactions. We have named this process “virtual breakdown mechanism” (which is completely different from traditional mechanisms) that couples the two half-reactions together, greatly reducing the energy losses arising from ion transport. This fundamental discovery has been theoretically discussed in this paper and experimentally demonstrated in a group of electrochemical cells with nanogaps between two electrodes down to 37 nm. On the basis of our nanogap electrochemical cells, the electrolysis current density from pure water can be significantly larger than that from 1 mol/L sodium hydroxide solution, indicating the much better performance of pure water splitting as a potential for on-demand clean hydrogen production.
•Honeycomb core sandwich sheets made by FSSW with disc insert and adhesive bonding.•Modeling attempted using homogenized core and equivalent cohesive layer.•Cohesive zone modeling attempted using ...actual core and adhesive layer.•Hybrid joint (FSSW with disc insert + adhesive bonding) performed better in peel test.•Peel test numerical predictions agreed well with experimental values.
The present work examines the fabrication and numerical modelling of honeycomb core sandwich sheets utilizing Friction Stir Spot Welding (FSSW) techniques as prospective substitutes for adhesive-bonded structures. Here, the sandwich sheet contains AA5052-H32 skins and AA3003 honeycomb core. Two strategies, FSSW with disc insert (FSSW_D) and FSSW with disc insert and adhesive bonding (FSSW_D_AB), were evaluated against traditional adhesive-bonded sandwiches using peel test performance and finite element (FE) simulation with cohesive zone modelling (CZM). In the CZM, a homogenized core with an equivalent cohesive layer was substituted for the honeycomb core and cohesive layer. The utilization of FSSW_D and FSSW_D_AB methods resulted in substantial improvements in maximum load capacity, with enhancements in the hybrid sandwich specimen ranging from 254 % to 399 % compared to adhesive-bonded connections. The maximum load of hybrid joints (FSSW_D_AB) was 15 %–23 % higher than that of ordinary spot-welded joints (FSSW_D). An approach to model the hybrid sandwich specimen using both the homogenized core and equivalent cohesive zone model accurately was proposed. FE analysis, including peel tests of adhesive-bonded, spot-welded, and hybrid joints, was performed, and the numerical predictions agreed satisfactorily with the experimental values for all the joint types.
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