Reentrant Localization Transition in a Quasiperiodic Chain.

Systems with quasiperiodic disorder are known to exhibit a localization transition in low dimensions. After a critical strength of disorder, all the states of the system become localized, thereby ceasing the particle motion in the system. However, in our analysis, we show that in a one-dimensional dimerized lattice with staggered quasiperiodic disorder, after the localization transition, some of the localized eigenstates become extended for a range of intermediate disorder strengths. Eventually, the system undergoes a second localization transition at a higher disorder strength, leading to all states being localized. We also show that the two localization transitions are associated with the mobility regions hosting the single-particle mobility edges. We establish this reentrant localization transition by analyzing the eigenspectra, participation ratios, and the density of states of the system.

Molecular Dynamics Simulations of Photo-Induced Free Radical Polymerization.

Curing kinetic models provide insight into how design parameters affect the kinetics of photopolymerization. However, they do not provide insight into how networks form or how they influence the process. This article describes a molecular dynamics simulation framework for simulating photoinitiated, chain growth, free radical polymerization. The framework was applied to simulate the photo-induced polymerization of bisphenol A (EO)10 diacrylate under varying conditions of curing light intensity and photoinitiator concentration. Results from the simulations agree very well with curing kinetic curves and gelation points derived from experiments. The simulations also reveal that: (1) gelation is highly correlated with the formation of giant molecules, (2) differences in the number of free radicals generated at the beginning of polymerization significantly affect polymer network formation at low to intermediate conversion, and thus affect the gelation point, and (3) increasing light intensity or photoinitiator concentration tends to delay the gelation point, but does not affect the ultimate polymer network structure near the latter stages of photopolymerization.

Second order topology in a band engineered Chern insulator.

Haldane model is a celebrated tight binding toy model of a Chern insulator in a 2D honeycomb lattice that exhibits quantized Hall conductance in the absence of an external magnetic field. In our work, we deform the bands of the Haldane model smoothly by varying one of its three nearest neighbour hopping amplitudes ([Formula: see text]), while keeping the other two (t) fixed. This breaks the [Formula: see text] symmetry of the Hamiltonian, while the [Formula: see text] symmetry is preserved. The symmetry breaking causes the Dirac cones to shift from the K and the K[Formula: see text] points in the Brillouin zone (BZ) to an intermediate M point. This is evident from the Berry curvature plots which show a similar shift in the corresponding values as a function of the deformation parameter, namely [Formula: see text]. We observe two different topological phases of which, one is a topological insulator (TI) and the other is a second order topological insulator (SOTI). The Chern number (C) remains perfectly quantized at a value of [Formula: see text] for the TI phase and it goes to zero in the SOTI phase. Furthermore, the evolution of the Wannier charge center (WCC) as the band is smoothly deformed shows a jump in the TI phase indicating the presence of conducting edge modes. We also study the SOTI phase and diagonalize the real space Hamiltonian on a rhombic supercell which shows the presence of in-gap zero energy corner modes. The polarization of the system, namely [Formula: see text] and [Formula: see text], are evaluated, along the x and the y directions, respectively. We see that both [Formula: see text] and [Formula: see text] are quantized in the SOTI phase owing to the presence of the inversion symmetry of the system. Finally we establish the SOTI phase as an example of a topological phase with zero Berry curvature and provide an analogy with the two dimensional Su-Schrieffer-Heeger model.

Parsing skin effect in a non-Hermitian spinless BHZ-like model.

This work comprehensively investigates the non-Hermitian skin effect (NHSE) in a spinless Bernevig-Hughes-Zhang -like model in one dimension. It is generally believed that a system with non-reciprocal hopping amplitudes demonstrates NHSE. However, we show that there are exceptions, and more in-depth analyses are required to decode the presence of NHSE or its variants in a system. The fascinating aspects of our findings, depending on the inclusion of non-reciprocity in the inter-orbital hopping terms, concede the existence of conventional NHSE or NHSE at both edges and even a surprising absence of NHSE. The topological properties and the (bi-orthogonal) bulk-boundary correspondence, enumerated via computation of the (complex) Berry phase and spatial localization of the edge modes, highlight the topological phase transitions occurring therein. Further, to facilitate a structured discussion of the non-Hermitian model, we split the results intoPTsymmetric and non-PTsymmetric cases with a view to comparing the two.

Screw dislocation in a Rashba spin-orbit coupled α - T 3 Aharonov-Bohm quantum ring.

In this paper we investigate the effect of a topological defect, such as a screw dislocation in an α - T 3 Aharonov-Bohm quantum ring and scrutinized the effects of an external transverse magnetic field and Rashba spin-orbit coupling therein. The screw dislocation yields an effective flux which reshape the periodic oscillations in the persistent current in both charge and spin sectors, with a period equal to one flux quantum. Moreover, they suffer a phase shift proportional to the degree of dislocation, and include scattering effects due to the dislocation present in the system. Such tunable oscillation of the spin persistent current highlights applications of our system as potential spintronic devices. Further, the behaviour of the current induced by the Burgers vector ( b z ) which denotes the strength of the dislocation is investigated in the absence and presence of an external magnetic field. In both the scenarios, an almost linear decrease in the current profile as a function of the Burgers vector is observed. Notably, without the external magnetic field, the Burgers current suffers a back flow for α = 1 (dice lattice), while in the presence of the external magnetic field, for other values of α (e.g., α = 0.5 ) this back flow occurs for a specific value of b z . Additionally, the presence of the distortion induces a chirality effect, giving rise to an additional chiral current even in the absence of an external field. Furthermore, in the absence of field, the Burgers spin current initially rises, attains a maximum before diminishing as b z is enhance for all values of α . However, such a non-monotonicity in the Burgers spin current is conspicuously non-existent in the presence of an external field. The chiral current discussed above may hold important applications to spintronics.

Spin and charge persistent currents in a Kane Meleα-T3quantum ring.

We conduct a thorough study of different persistent currents in a spin-orbit coupledα-T3(pseudospin-1) fermionic quantum ring (QR) that smoothly interpolates between graphene (α = 0, pseudospin-1/2) and a dice lattice (α = 1, pseudospin-1) in presence of an external perpendicular magnetic field. In particular, we have considered effects of intrinsic (ISOC) and Rashba spin-orbit couplings (RSOC) that are both inherent to two dimensional quantum structures and yield interesting consequences. The energy levels of the system comprise of the conduction bands, valence bands, and flat bands which show non-monotonic dependencies on the radius,Rof the QR, in the sense that, for smallR, the energy levels vary as1/R, while the variation is linear for largeR. The dispersion spectra corresponding to zero magnetic field are benchmarked with those for finite fields to enumerate the role played by the spin-orbit coupling terms therein. Further, it is noted that the flat bands demonstrate dispersive behavior, and hence is able to contribute to the transport properties only for finite ISOC. Moreover, RSOC yields spin-split bands, thereby contributing to the spin-resolved currents. The charge and the spin-polarized persistent currents are hence computed in presence of these spin-orbit couplings. The persistent currents in both the charge and spin sectors oscillate as a function of the magnetic field with a period equal to the flux quantum, as they should be; although they now depend upon the spin-orbit coupling parameters. Interestingly, the ISOC distorts the current profiles, owing to the distribution of the flat band caused by it, whereas RSOC alone preserves the flat band and hence a perfect periodicity of the current characteristic is maintained. Further, we have explored the role played by the parameterαin our entire analysis to enable studies while interpolating from graphene to a dice lattice.

Higher order topology in a Creutz ladder.

A Creutz ladder, is a quasi one dimensional system hosting robust topological phases with localized edge modes protected by different symmetries such as inversion, chiral and particle-hole symmetries. Non-trivial topology is observed in a large region of the parameter space defined by the horizontal, diagonal and vertical hopping amplitudes and a transverse magnetic flux that threads through the ladder. In this work, we investigate higher order topology in a two dimensional extrapolated version of the Creutz ladder. To explore the topological phases, we consider two different configurations, namely a torus (periodic boundary) and a ribbon (open boundary) to look for hints of gap closing phase transitions. We also associate suitable topological invariants to characterize the non-trivial sectors. Further, we find that the resultant phase diagram hosts two different topological phases, one where the higher order topological excitations are realized in the form of robust corner modes, along with (usual) first order excitations demonstrated via the presence of edge modes in a finite lattice, for the other.

Properties of the non-Hermitian SSH model: role ofPTsymmetry.

The present work addresses the distinction between the topological properties ofPTsymmetric and non-PTsymmetric scenarios for the non-Hermitian Su-Schrieffer-Heeger model. The non-PTsymmetric case is represented by non-reciprocity in both the inter- and the intra-cell hopping amplitudes, while the one withPTsymmetry is modeled by a complex on-site staggered potential. In particular, we study the loci of the exceptional points, the winding numbers, band structures, and explore the breakdown of bulk-boundary correspondence (BBC). We further study the interplay of the dimerization strengths on the observables for these cases. The non-PTsymmetric case denotes a more familiar situation, where the winding number abruptly changes by half-integer through tuning of the non-reciprocity parameters, and demonstrates a complete breakdown of BBC, thereby showing non-Hermitian skin effect. The topological nature of thePTsymmetric case appears to follow closely to its Hermitian analogue, except that it shows unbroken (broken) regions with complex (purely real) energy spectra, while another variant of the winding number exhibits a continuous behavior as a function of the strength of the potential, while the conventional BBC is preserved.

Detection of Newcastle disease virus and assessment of associated relative risk in backyard and commercial poultry in Kerala, India.

BACKGROUND: Newcastle disease (ND) is an economically important viral disease affecting the poultry industry. In Kerala, a state in South India, incidences of ND in commercial and backyard poultry have been reported. But a systematic statewide study on the prevalence of the disease has not been carried out. OBJECTIVES: A cross-sectional survey was performed to detect the presence of Newcastle disease virus (NDV) in suspect cases and among apparently healthy commercial flocks and backyard poultry, in the state and to identify risk factors for NDV infection. METHODS: Real-time reverse transcription-PCR (RT-PCR) was used to detect the M gene of NDV in choanal swabs and tissue samples collected from live and dead birds, respectively and the results were statistically analysed. RESULTS: The predominant clinical signs of the examined birds included mild respiratory signs, huddling together and greenish diarrhoea. Nervous signs in the form of torticollis were noticed in birds in some of the affected flocks. On necropsy, many birds had haemorrhages in the proventriculus and caecal tonsils which were suggestive of ND. Of the 2079 samples tested, 167 (8.0%) were positive for the NDV M-gene by RT-PCR. Among 893 samples collected from diseased flocks, 129 (14.5%), were positive for M gene with pairwise relative risk (RR) of 15.6 as compared to apparently healthy flocks where 6 out of 650 (0.9%) samples were positive. All positive samples were from poultry; none of the ducks, pigeons, turkey and wild birds were positive. Commercial broilers were at higher risk of infection than commercial layers (RR: 4.5) and backyard poultry (RR: 4.9). Similarly, birds reared under intensive housing conditions were at a higher risk of being infected as compared to those reared under semi-intensive (RR: 6.7) or backyard housing (RR: 2.1). Multivariable analysis indicated that significantly higher risk of infection exists during migratory season and during ND outbreaks occurring nearby. Further, lower risk was observed with flock vaccination and backyard or semi-intensive housing when compared to intensive housing. When the M gene positive samples were tested by RT-PCR to determine whether the detected NDV were mesogenic/velogenic, 7 (4.2%) were positive. CONCLUSIONS: In Kerala, NDV is endemic in poultry with birds reared commercially under intensive rearing systems being affected the most. The outcome of this study also provides a link between epidemiologic knowledge and the development of successful disease control measures. Statistical analysis suggests that wild bird migration season and presence of migratory birds influences the prevalence of the virus in the State. Further studies are needed to genotype and sub-genotype the detected viruses and to generate baseline data on the prevalence of NDV strains, design better detection strategies, and determine patterns of NDV transmission across domestic poultry and wild bird populations in Kerala.

Image-based data on strain fields of microstructures with porosity defects.

The present article provides a compilation of microstructures and respective strain fields expressed by them during elastic loading. These microstructures were synthesized in Abaqus Standard software and their strain fields were modelled using Abaqus based static implicit analysis. The Python Development Environment (PDE) in Abaqus was used. These microstructures were subjected to uniform displacement boundary condition to obtain strain fields in the plane-strain mode. The purpose of the generating this data was to test the efficacy of convolutional neural networks (CNNs) in predicting strain fields. This raw data consisting of microstructure and their strain fields was converted to images using MATLAB as two dimensional arrays with each pixel denoting value to be used as input for training the CNN. This processed data in the form of images can be potentially used in deep learning or data science methodologies to perform finite element simulations.

Topological phase transition induced by band structure modulation in a Chern insulator.

We study a systematic evolution of the topological properties of a Chern insulator upon smooth variation of a hopping parameter (t1) of the electrons among a pair of nearest neighbour sites on a honeycomb lattice, while keeping the other two hopping terms (t) fixed. In the absence of a Haldane flux, the tuning oft1results in gradual shifting of the Dirac cones which eventually merge into one at theMpoint in the Brillouin zone (BZ) att1= 2twith a gapless semi-Dirac dispersion at low energies. In the presence of a Haldane flux, the system becomes a Chern insulator fort1< 2t, but turns gapless att1= 2twith the semi-Dirac dispersion being transformed to an anisotropic Dirac one. The spectrum eventually gaps out and transforms into a trivial insulator fort1> 2t. The Chern number phase diagram obtained via integrating the Berry curvature over the BZ shows a gradual shrinking of the 'topological' lobes, and vanishes just beyondt1= 2t, where a small but a finite Berry curvature still exists. Thus, there is a phase transition from a topological phase to a trivial phase across the semi-Dirac point (t1= 2t). The vanishing of the anomalous Hall conductivity plateau and the merger of the chiral edge states with the bulk bands near theMpoint provide robust support of the observed phase transition.

Veering the motion of a magnetic chemical locomotive in a liquid.

The motion of micron-sized catalytic polymer beads coated with thin film or nanoparticle form of Ni in aqueous H(2)O(2) is reported herein. In the absence of any magnetic field, the beads moved vertically upward in the medium, owing to sufficient bubbles deposited on them following catalytic decomposition of H(2)O(2) by Ni. However, in the presence of an external magnetic field (perpendicular to the direction of motion), angular deviation in the motion is observed, with the deviations increasing with the strength of the field. The results are explained based on a model involving interaction of the beads with the external magnetic field.

Deformation heterogeneity and texture in surface severe plastic deformation of copper.

Comprehensive understanding of thermomechanical response and microstructure evolution during surface severe plastic deformation (S2PD) is important towards establishing controllable processing frameworks. In this study, the evolution of crystallographic textures during directional surface mechanical attrition treatment on copper was studied and modelled using the visco-plastic self-consistent framework. In situ high-speed imaging and digital image correlation of surface deformation in circular indentation were employed to elucidate mechanics occurring in a unit process deformation and to calibrate texture model parameters. Material response during directional surface mechanical attrition was simulated using a finite-element model coupled with the calibrated texture model. The crystallographic textures developed during S2PD were observed to be similar to those resultant from uniaxial compression. The implications of these results towards facilitating a processing-based framework to predict deformation mechanics and resulting crystallographic texture in S2PD configurations are briefly discussed.

Catalytic gold nanoparticle driven pH specific chemical locomotion.

Gold nanoparticle (Au NP) catalyzed decomposition of alkaline hydrogen peroxide has been utilized in driving chemical locomotives in a liquid. Au NPs deposited on spherical micron sized polymer resin beads catalyzed the decomposition of H(2)O(2) in the pH range 9.1-10.8. The O(2) gas bubbles produced in the decomposition moved the beads upward with average velocities that depended on the pH of the solution. The measured average velocity of the bead increased with the increase in pH in the range 9.1-10.8. Above this pH, the self-decomposition of H(2)O(2) produced sufficient bubbles in the medium that made the motion haphazard and thus prevented a clear measurement of the velocity. The observed accelerated motion of the locomotive has been explained by considering the time-dependent growth of O(2) gas bubbles on the polymer, while taking into consideration desorption and other factors.

Some clues in the investigation of the FFLO phase in superconductors.

The Fulde-Ferrell-Larkin-Ovichinnikov (FFLO) phase is investigated in a two-dimensional superconductor described by a negative- U Hubbard model in the presence of a magnetic field. The parameter space defined by interparticle attraction and band filling is investigated and a search is performed for the FFLO phase therein, so as to provide clues to experiments designed to confirm the existence of a nonuniform spatial nature of the superconducting state. Our results convincingly demonstrate periodic modulation of the local pairing gap in real space. Heavy fermions, considered as a probable candidate that hosts the FFLO phase, are found in a metallurgically clean state and shows extreme type-II behaviour. In our calculations both these conditions are satisfied for a certain magnetic field range and the range expands for large interacting strengths and particle densities. The cleanliness condition is met as the coherence length becomes very small (compared to the mean free path) and the extreme type-II behaviour shows up via a large Ginzburg-Landau parameter.