Variational model for one-dimensional quantum magnets

A new variational technique for investigation of the ground state and correlation functions in 1D quantum magnets is proposed. A spin Hamiltonian is reduced to a fermionic representation by the Jordan–Wigner transformation. The ground state is described by a new non-local trial wave function, and the total energy is calculated in an analytic form as a function of two variational parameters. This approach is demonstrated with an example of the XXZ-chain of spin-1/2 under a staggered magnetic field. Generalizations and applications of the variational technique for low-dimensional magnetic systems are discussed.     

Separability criterion for quantum effects

Entanglement of quantum states is absolutely essential for modern quantum sciences and technologies. It is natural to extend the notion of entanglement to quantum observables dual to quantum states. For quantum states, various separability criteria have been proposed to determine whether a given state is entangled. In this Letter, we propose a separability criterion for specific quantum effects (binary observables) that can be regarded as a dual version of the Bell–Clauser–Horne–Shimony–Holt (Bell–CHSH) inequality for quantum states. The violation of the dual version of the Bell–CHSH inequality is confirmed by using IBM's cloud quantum computer. As a consequence, the violation of our inequality rules out the maximal tensor product state space, that satisfies information causality and local tomography. As an application, we show that an entangled observable which violates our inequality is useful for quantum teleportation.     

Review of recent UV–Vis and infrared spectroscopy researches on wine detection and discrimination

Wine has become a commodity of significant commercial value, and the demand for high quality wine by consumers has been increasing. Suitable analytical techniques are needed for its quality control. Ultraviolet, Visible, Near-infrared and infrared spectroscopy is by far one of the most important techniques for determining the wine quality, including its components and characterization. This review will overview the available most recent applications of spectroscopic techniques in the past decade for wine quality prediction and discrimination both quantitatively and qualitatively. The fundamental principles of these techniques will be introduced briefly, and some innovative setups/instrumentations will also be illustrated. At last the limitations and prospects of spectroscopic techniques for wine industry will be discussed.     

Comment on ‘Ab initio study: the potential energy curves and rovibrational spectrum of low-lying excited states of HCl+ cation’ (Molecular Physics, 114:19, 2817–2823)

In a recent article, Y. Liu, X. Cheng, H. Cheng, J. Cheng and X. Song [Mol. Phys., 114:19, 2817–2823] report on the calculation of potential energy curves and the derivation of spectroscopic constants and line intensities for the lowest energy electronic states of HCl⁺. There are several shortcomings in the article; the most notable being the incorrect ordering of the ²П_3/2 and ²П_1/2 state energies, erroneous selection rules, which lead to the absence of a Q-branch in their predicted spectra, incorrect Höln–London factors, and a missing appendix.     

Stabilities,electronic and magnetic properties of Cu-doped nickel clusters: a DFT investigation

In this paper, we investigate the electronic and magnetic properties of Cu-doped nickel clusters by means of density functional theory. The stabilities of these clusters have also been studied in terms of the binding energies, second-order difference of energies, fragmentation energies and HOMO–LUMO energy gaps. The obtained results reveal that the N₄Cu, N₅Cu and Ni₇Cu clusters are found to be more stable that than all other clusters. Higher HOMO–LUMO gap was observed for Ni₅Cu cluster (2.265 eV), indicating its higher chemical stability. A half-metallic behaviour has also been observed for the Ni_nCu clusters, which suggests that these clusters can be employed as nanocatalysts for several catalytic processes, particularly for hydrogenation and dehydrogenation reactions. The magnetism calculations show that the magnetic moment is mostly located on the Ni atoms, and the contribution of the Cu atom to the total magnetic moment in the Ni_nCu clusters is very small. Furthermore, partial density of states analysis indicates that the 3d orbitals in Ni atoms are mostly responsible for the magnetic behaviour of these clusters, and the s orbitals have a very little contribution to the total magnetic moment.     

Interfacial p-n heterojunction of polyaniline-nickel ferrite nanocomposite as room temperature liquefied petroleum gas sensor

In this work, we introduce polyaniline–nickel ferrite (PANI-NF) nanostructured composite to detect liquefied petroleum gas (LPG) at room temperature. The composite synthesized by relatively simple method of in-situ chemical polymerization was structurally characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The presence of characteristic absorption bands of both PANI and NF in the FTIR spectrum of the composite with small shifts confirmed interfacial interaction of PANI with NF. The XRD studies also confirmed interfacial interaction between PANI and NF in the composite and its crystalline nature with an average crystallite size of 20 nm. Highly agglomerated granular porous morphology favourable for LPG adsorption was revealed by SEM image of the composite. The TEM image of the composite clearly showed nanosized NF particles embedded in PANI matrix. The LPG sensing performance of the composite at room temperature was tested using a film prepared by depositing the composite on an ordinary glass substrate by cost-effective spin coating technique. The maximum sensing response of the composite was found to be 57% at 700 ppm of LPG, with a response time of 50 s and a recovery time of 200 s. The composite was found to be stable for a period of one month. The sensing mechanism has been discussed on the basis of formation of interfacial p–n heterojunction barrier.     

Experimental and LES investigation of premixed methane/air flame propagating in a tube with a thin obstacle

In this paper, an experimental and numerical investigation of premixed methane/air flame dynamics in a closed combustion vessel with a thin obstacle is described. In the experiment, high-speed video photography and a pressure transducer are used to study the flame shape changes and pressure dynamics. In the numerical simulation, four sub-grid scale viscosity models and three sub-grid scale combustion models are evaluated for their individual prediction compared with the experimental data. High-speed photographs show that the flame propagation process can be divided into five stages: spherical flame, finger-shaped flame, jet flame, mushroom-shaped flame and bidirectional propagation flame. Compared with the other sub-grid scale viscosity models and sub-grid scale combustion models, the dynamic Smagorinsky–Lilly model and the power-law flame wrinkling model are better able to predict the flame behaviour, respectively. Thus, coupling the dynamic Smagorinsky–Lilly model and the power-law flame wrinkling model, the numerical results demonstrate that flame shape change is a purely hydrodynamic phenomenon, and the mushroom-shaped flame and bidirectional propagation flame are the result of flame–vortex interaction. In addition, the transition from “corrugated flamelets” to “thin reaction zones” is observed in the simulation.     

Turbulent structures in an optimal Taylor–Couette flow between concentric counter-rotating cylinders

The turbulent structures formed in a Taylor–Couette (TC) flow established between two concentric counter-rotating cylinders were explored numerically. The shear Reynolds number was set to Re_shear = 8000 and the radius ratio was set to r_i/r_o = 0.5. An optimal flow corresponding to the maximal angular velocity transport between the cylinders was selected for the TC flow. The mean velocity profile reached its steepest value near the cylinders in the optimal TC flow. The streamwise velocity correlations at the outer cylinder in the gap exceeded those at the inner cylinder. The large convective transport of angular velocity in the gap generated a maximal angular velocity flux to achieve the optimal flow. The angular velocity flux generated by the momentum source exceeded that generated by the momentum sink. The vorticity dispersion was larger near the inner cylinder than near the outer cylinder, but vorticity stretching near the outer cylinder exceeded than that near the inner cylinder. The skin friction coefficient budgets were plotted using the velocity–vorticity correlation. The vortex stretching contributions dominated the skin friction budgets. The area near the inner cylinder was populated by stronger vortices, but their population density was smaller than the population density of the vortices near the outer cylinder. The probability density functions of the wall-normal and streamwise velocity fluctuations delineated the presence of the large wall-normal velocity fluctuations near the outer cylinder.     

Flocking dynamics for a multiagent system involving task strategy

Collective behavior sometimes requires forming a particular formation or reaching a certain velocity to accomplish a specific task, such as bird migration. In this paper, we investigate the collective migration model, which consists of two parts: Cucker–Smale type interaction and target velocity. Each agent has a strategy to allocate limited energy to group interaction and velocity tracking. In this case, if the system achieves monocluster flocking then the final velocity is equal to target velocity. When the strategy is invariant, we show that 1/2 is a critical threshold which is consistent with the classical Cucker–Smale model. When the strategy is time varying, we provide a time-varying strategy named threshold strategy to ensure that for any initial state the system achieves monocluster flocking and the final velocity reaches target velocity. In addition, the case of multiple target velocities is considered. According to the theory of bicluster flocking, we obtain a sufficient framework to guarantee that the system achieves bicluster flocking and two groups would reach their target velocities, respectively.     

Products of two 1ϕ1 series and implications

An expansion formula into bivariate formal power series is established that implies, as consequences, three remarkable identities of partial theta functions due to Warnaar (2003), Schilling–Warnaar (2002) and Andrews–Warnaar (2007).