Structural Stability In Terms Research Articles

Understanding the computational insights of spin-polarised density functional theory into the newly half-metallic f electron-based actinide perovskites SrMO3 (M = Pa, Np, Cm, Bk)

Here, we investigated the structural, mechanical, electronic, magnetic, thermodynamic and thermoelectric properties of Strontium based simple perovskites SrMO3 (M = Pa, Np, Cm, Bk) by using density functional theory. First and foremost, the ground state stability of these perovskites was initially evaluated by optimizing their total ground state energies in distinct ferromagnetic and non-magnetic configurations. The structural stability in terms of their ground state energies defines that these alloys stabilize in ferromagnetic rather than competing non-magnetic phase. From the understandings of mechanical parameters these alloys are characterized to be ductile in nature. After that, two approximation schemes namely Generalized Gradient approximation and Tran-Blaha modified Becke-Johnson potential have been used to find their intimate electronic structures which displays the half-metallic nature of these alloys. Further, we have verified temperature and pressure effect on these alloys. Finally, the transport properties have been evaluated within the selected temperature range of 150–900 K. In view of this, the different transport parameters along with half-metallic nature advocate their possible applications in thermoelectric and spintronics devices.

Probing the structural, mechanical, phonon, thermal, and transport properties of magnetic halide perovskites XTiBr3 (X = Rb, Cs) through ab-initio results

Herein, we have first reported the intrinsic properties, including structural, mechanical, electronic, magnetic, thermal, and transport properties of XTiBr3 (X = Rb, Cs) halide perovskites within the simulation scheme of density functional theory as integrated into Wien2k. First and foremost, the structural stability in terms of their ground state energies has been keenly evaluated from their corresponding structural optimizations, which advocate that XTiBr3 (X = Rb, Cs) has a stable ferromagnetic rather than the competing non-magnetic phase. Later on, the electronic properties have been computed within the mix of two applied potential schemes like Generalized Gradient Approximation (GGA) along with Trans-Bhala modified Becke Johnson (TB-mBJ), which thoroughly addresses the half-metallic behaviour with spin-up as metallic and in contrast to opposite spin-down channel signatures the semiconducting behaviour. Furthermore, the spin-splitting seen from their corresponding spin-polarised band structures offers a net magnetism of 2 µB which lends their opportunities to unlock the application branch of spintronics. In addition, these alloys have been characterised to show their mechanical stability describing the ductile feature. Moreover, phonon dispersions decisively certify the dynamical stability within the density functional perturbation theory (DFPT) context. Finally, the transport and thermal properties predicted within their specified packages have also been forwarded in this report.

Carbon Nanotube-Reinforced Dual Carbon Stress-Buffering for Highly Stable Silicon Anode Material in Lithium-Ion Battery.

Silicon (Si) anode suffers from huge volume expansion which causes poor structural stability in terms of electrode material, solid electrolyte interface, and electrode, limiting its practical application in high-energy-density lithium-ion batteries. Rationally designing architectures to optimize the stress distribution of Si/carbon (Si/C) composites has been proven to be effective in enhancing their structural stability and cycling stability, but this remains a big challenge. Here, metal-organic frameworks (ZIF-67)-derived carbon nanotube-reinforced carbon framework is employed as an outer protective layer to encapsulate the inner carbon-coated Si nanoparticles (Si@C@CNTs), which features dual carbon stress-buffering to enhance the structural stability of Si/C composite and prolong their cycling lifetime. Finite element simulation proves the structural advantage of dual carbon stress-buffering through significantly relieving stress concentration when Si lithiation. The outer carbon framework also accelerates the charge transfer efficiency during charging/discharging by the improvement of lithium-ion diffusion and electron transport. As a result, the Si@C@CNTs electrode exhibits excellent long-term lifetime and good rate capability, showing a specific capacity of 680 mAh g-1 even at a high rate of 1 A g-1 after 1000 cycles. This work provides insight into the design of robust architectures for Si/C composites by stress optimization.

Softening behaviors of 20Mn2SiCrMo bainitic steel under thermal cycling

20Mn2SiCrMo bainitic steel was subjected to tempering at 300 °C and 600 °C for 120 min, respectively, and following microstructure evolution and softening behaviors during thermal fatigue were studied. Experimental results show that 300 °C-tempered samples show a better strength and toughness match. However, a sharp hardness softening for 300 °C during the afterward thermal cycles demonstrates absolutely different hardness stability from the 600 °C. The phenomenon has been ascribed to retained austenite decomposition and carbide precipitation. The present study highlights the importance of structural stability in terms of service environment in pursuing higher thermal cycle softening resistance.

Pressure dependence of the thermal stability in LiMn2O4

Structural stability in terms of the decomposition temperature in LiMn2O4 was systematically investigated by a series of high-temperature and high-pressure experiments. LiMn2O4 was found to have structural stability up to 5 GPa at room temperature. Under ambient pressure, the compound decomposed at 1300 °C. The decomposition temperature decreased with increasing pressure, yielding more complex decomposed products, Below the decomposition temperature, the crystal structure of LiMn2O4 varied with pressure. The presented results in this study offer new insights into the thermal and pressure stability of LiMn2O4 materials as a cathode for lithium-ion batteries that can operate under extreme conditions. Therefore, these findings may serve as a useful guide for future work for improving lithium-ion batteries.

Nano-encapsulated solvent via pickering emulsion in NaOH aqueous solution for indoor CO2 capture

Considering the limitations of indoor ventilation owing to air pollution, CO2 concentration rises rapidly to 3000 ppm, which is a level that can affect human health. It is essential to develop materials to reduce naturally occurring CO2 in the buildings. Herein, a nano-encapsulated solvent (NES) via Pickering emulsion is proposed for indoor CO2 capture. NaOH aqueous solution is wrapped with hydrophobic surface-functionalized SiO2 (HS-SiO2) nanoparticles, and the corrosiveness of NaOH is not caused by HS-SiO2 wall. CO2 capture capacity of NES-NaOH is evaluated as 7.57 mmol-CO2/g-solvent which is the highest compared to other solvents including metal-organic frameworks (MOFs); it exhibits excellent structural stability in terms of temperature, time, moisture, and CO2 reaction. NES-NaOH presents high selectivity toward CO2 molecules due to the characteristics of NaOH with high gas permeability of macroporous silica wall and it is dispersed in a silicone oil harmless to human body. It is concluded that NES-NaOH can be successfully applied to air purifier filter to control the CO2 concentration in buildings.

8-16-4 graphyne: Square-lattice two-dimensional nodal line semimetal with a nontrivial topological Zak index

An unprecedented graphyne allotrope with square symmetry and nodal line semimetallic behavior has been proposed in the two-dimensional (2D) realm. The emergence of the Dirac loop around the high-symmetry points in the presence of both the inversion and time-reversal symmetries is a predominant feature of the electronic band structure of this system. Besides, the structural stability in terms of the dynamic, thermal, and mechanical properties has been critically established for the system. Following the exact analytical model based on the real-space renormalization group scheme and tight-binding approach, we have inferred that the family of 2D nodal line semimetals with square symmetry can be reduced to a universal four-level system in the low-energy limit. This renormalized lattice indeed explains the underlying mechanism responsible for the fascinating emergence of 2D square nodal line semimetals. Besides, the analytical form of the generic dispersion relation of these systems is well supported by our density-functional theory results. Finally, the nontrivial topological properties have been explored for the predicted system without breaking the inversion and time-reversal symmetry of the lattice. We have obtained that the edge states are protected by the nonvanishing topological index, i.e., Zak phase.

Improved Dynamic Characteristics for Machine Tools Structure Using Filler Materials

Simplified filler approach has been developed to enhance structural stability of existing cast iron columns and beds. The motivation for this research was to develop a machine tool structural material having characteristics such as, improved dynamic stability, ease in production, cost-effectiveness, and sustainability. A methodology has been developed to predict dynamic behaviour of prototype column structure using simplified reduced odd-scale model. A combination of formulae based similitude model, FE based structural analysis and statistics based Taguchi design analysis has been used to achieve enhanced structural dynamic performance of a VMC column. Similitude principles have been developed to correlate simplified odd-scale column model with existing complex prototype column through FE based 1:5 scaled column structure. Prototype column has been replaced by simplified odd-scale column for filler optimization experiments using Taguchi design and scaling factors. Simplified odd-scale column models were filled with a number of combinational designs of unique composite filler material. VMC column structural stability in terms of excitation decay time, dynamic stress and displacement has been analyzed for present hollow cast iron structures as well as filled structures. Present methodology combination reduces efforts to develop dynamically improved machine tool structures through simplified odd-scale models, avoiding complexity involved in implementation of traditional scaling approach. As a result, dynamic characteristics have been improved by 20-30 times with introduction of composite filler material as compared to unfilled structures. This composite filler technology has been applied for patent.

Analysis of the Structural Stability Among Cyclotide Members Through Cystine Knot Fold that Underpins Its Potential Use as a Drug Scaffold

Recent emergence of plant derived peptide cyclotides, characterized with a cyclized head-to-tail backbone and three disulfide bonds forming cyclic cystine knot, has advanced the field of biopharmaceutics to next level. This conserved structural feature of cyclotides holds responsible for its outstanding resistance towards thermal, chemical and enzymatic degradation. Besides, the cyclotides are preferred widely in current research to develop them as potent peptide therapeutics, where the improvement of structural stability is a demanding task in pharmaceutical firm. Hence, in this work, the structural stability of six cyclotides of kalata family (kalata B1, kalata B2, kalata B5, kalata B7, kalata B8 and kalata B12) was investigated. Among all, maximum number of intra-molecular interactions was observed only in kalata B1 (kB1). In addition, geometrical observables using conformational sampling of six kalata cyclotides also revealed that kB1 exhibited statistically significant structural stability in terms of contours of root mean square fluctuation, gyration radius, ovality and surface area (polar and non-polar). Furthermore, the distance of disulfide bridges (S–S within 2.2 A) also confirmed that kB1 achieved maximum strength in terms of structural stability and accomplished remarkable functionality in terms of ovality as compared to other five kalata cyclotides. Accordingly, kB1 could be demonstrated as a stable template for the advancement of peptide therapeutics.

Mechanics of Confined Thin-Walled Cylinders Subjected to External Pressure

Motivated by practical engineering applications, the present paper examines the mechanical response of thin-walled cylinders surrounded by a rigid or deformable medium, subjected to uniform external pressure. Emphasis is given to structural stability in terms of buckling, postbuckling, and imperfection sensitivity. The present investigation is computational and employs a two-dimensional model, where the cylinder and the surrounding medium are simulated with nonlinear finite elements. The behavior of cylinders made of elastic material is examined first, and a successful comparison of the numerical results is conducted with available closed-form analytical solutions for rigidly confined cylinders. Subsequently, the response of confined thin-walled steel cylinders is examined. The numerical results show an unstable postbuckling response beyond the point of maximum pressure and indicate severe imperfection sensitivity on the value of the maximum pressure. A good comparison with limited available test data is also shown. Furthermore, the effects of the deformability of the surrounding medium are examined. In particular, soil embedment conditions are examined, with direct reference to the case of buried thin-walled steel pipelines. Finally, based on the numerical results, a comparison is attempted between the present buckling problem and the problem of “shrink buckling.” The differences between those two problems of confined cylinder buckling are pinpointed, emphasizing the issue of imperfection sensitivity.

Electronic origin of structural trends across early transition-metal disilicides: Anomalous behavior ofCrSi2

We have investigated the structural stability of the early transition-metal disilicides $({\mathrm{TMSi}}_{2})$ using a hierarchy of electronic structure methods from the accurate ab initio to a simple $\mathrm{pd}$ tight-binding model. First, ab initio density-functional theory calculations provided excellent heats of formation and structural coordinates for the ${C11}_{b}$ ground state of ${\mathrm{MoSi}}_{2}.$ However, the $C40$ structure of ${\mathrm{CrSi}}_{2}$ was predicted to be less stable than ${C11}_{b}$ at absolute zero, indicating that the lattice entropy might stabilize the observed $C40$ phase. Second, less precise frozen-potential calculations allowed a Jones-type analysis of the structural stability in terms of the relative behavior of the densities of states. A $C5\stackrel{\ensuremath{\rightarrow}}{4}C4\stackrel{\ensuremath{\rightarrow}}{0}{C11}_{b}$ structure trend with increasing electron occupancy was found in good agreement with experiment. Finally, a very simple $\mathrm{pd}$ tight-binding model demonstrated that the structural trends were driven primarily by the $\mathrm{pd}\ensuremath{\pi}$ bond between the nearest-neighbor Si and TM atoms, reflecting the sensitivity of the $\ensuremath{\pi}$ bond order to dihedral angles.

Surface effects in GaN growth

By means of plane wave pseudopotential periodic supercell density functional theory calculations, we investigated the energetics of several GaN(0 0 0 1) surfaces containing atomic and molecular adsorbates. The surface structures were selected in order to get insight into GaN epitaxial growth, in situations where NH 3 molecules are employed as the nitrogen precursor and H 2 molecules as the carrier gas, typical of standard vapor phase growth techniques. Therefore, we considered NH 2 complexes and H atoms as molecular and atomic adsorbates, respectively, assuming they derive from molecular dissociation from the gas flows in the growth chambers. We took into account different adsorption stoichiometries, varying the relative proportion of NH 2 and H adsorbates, and different degrees of clusterization of the ad-atoms and ad-complexes. For each structure, we obtained the relaxed atomic configuration and the corresponding total energy. Hence, we describe here the relative structural stability in terms of a phase diagram that identifies the optimal growth conditions to attain at intermediate stages the most favorable equilibrium surfaces.

Dissociation and unfolding of cold-active alkaline phosphatase from atlantic cod in the presence of guanidinium chloride.

Cold-adaptation of enzymes involves improvements in catalytic efficiency. This paper describes studies on the conformational stability of a cold-active alkaline phosphatase (AP) from Atlantic cod, with the aim of understanding more clearly its structural stability in terms of subunit dissociation and unfolding of monomers. AP is a homodimeric enzyme that is only active in the dimeric state. Tryptophan fluorescence, size-exclusion chromatography and enzyme activity were used to monitor alterations in conformational state induced by guanidinium chloride or urea. In cod AP, a clear distinction could be made between dissociation of dimers into monomers and subsequent unfolding of monomers (fits a three-state model). In contrast, dimer dissociation of calf AP coincided with the monophasic unfolding curve observed by tryptophan fluorescence (fits a two-state model). The DeltaG for dimer dissociation of cod AP was 8.3 kcal.mol-1, and the monomer stabilization free energy was 2.2 kcal.mol-1, giving a total of 12.7 kcal.mol-1, whereas the total free energy of calf intestinal AP was 17.3 kcal.mol-1. Thus, dimer formation provided a major contribution to the overall stability of the cod enzyme. Phosphate, the reaction product, had the effect of promoting dimer dissociation and stabilizing the monomers. Cod AP has reduced affinity for inorganic phosphate, the release of which is the rate-limiting step of the reaction mechanism. More flexible links at the interface between the dimer subunits may ease structural rearrangements that facilitate more rapid release of phosphate, and thus catalytic turnover.

Solution structures of a duplex containing an adenine opposite a gap (absence of one nucleotide). An NMR study and molecular dynamic simulations with explicit water molecules.

We investigated the behaviour of a 15mer DNA duplex, [5'd(CAGAGTCACTGGCTC)3']. [5'd(GAGCCAG)3' + 5'd(GACTCTG)3'] which contained an adenine opposite the gap. Analysis of the NMR data showed the existence of one major species, which was in equilibrium with two minor species. Their relative concentrations varied as a function of pH with a pKa of approximately 4.5. For the major species, the duplex was globally in B conformation with the central adenine stacked in the helix. The two G.C base pairs adjacent to the central adenine were well formed and a gap was present in front of this adenine. For the minor species, major structural perturbations occurred in the centre of the duplex. At neutral pH, the central adenine was involved in a G.A mismatch with G23 adjacent to the gap. Cytosine C7 was then extrahelical and no gap was observed. Under these conditions, the major neutral species corresponded to 70% of the total and the minor species to 30%. At acidic pH, the central adenine of the minor species was protonated and was involved in a G(syn).A+(anti) mismatch. The difference is that C9 is now extrahelical and G22 is implicated in the mispair. Three-dimensional models were built to initiate molecular dynamic simulations, which were in good agreement with the NMR data. Their structural stability in terms of hydrogen bonding and their flexibility are discussed and the biological significance for the interaction with DNA polymerase is evoked.

Calculation of the average properties of atoms in molecules. II

AbstractThis article describes an algorithm for the calculation of the average properties of an atom in a molecule. The atom is defined within the topological theory of molecular structure, a theory which defines atoms, bonds, structure, and structural stability in terms of the topological properties of a system's charge distribution. The average properties of the atom so defined are uniquely determined by quantum mechanics. Results for a number of hydrocarbon molecules, obtained by the program PROAIM (properties of atoms in molecules) which implements this algorithm, are given. In general, this program enables one to calculate the average energy of an atom in a molecule to an accuracy of ±1 kcal/mol.

Inductive Functions of the Nervous System

In addition to their responsibility for the minute to minute control of behavior and homeostasis, nerve cells are important in maintaining the long term stability of structure and function of the nervous system and the cells it innervates. The trophic action of motor nerve cells on skeletal muscles is a well known example of such activity. Miledi (270) defined trophic actions as due to an influence of the nerve not mediated by impulses, but it has recently been suggested that only some of the classical trophic effects on skeletal muscle are exerted independently of nerve im­ pulses and/or muscle contraction. For example, direct electrical stimulation of a denervated muscle may reverse the development of denervation hypersensitivity (83, 241). The presence and the function of muscie innervation have a variety of in de pen­ dentiy exerted long term effects on the motoneurone itself, and on the physiological and anatomical state of the muscle. For example, botulinus toxin affects most of the trophic actions of the nerve except the maintenance of end plate cholinesterase (82), preganglionic cholinergic nerves form functional synapses on frog skeletal muscle but do not induce endpiate cholinesterase (223), and adrenergic nerves can prevent denervation fibrillation without forming functional synapses (265). Similarly com­ plex sets of interactions have been described elsewhere in the peripheral and auto­ nomic nervous systems, and within the brain as well.