Trapped Bose–Einstein condensates with quadrupole–quadrupole interactions

We numerically investigate the ground-state properties of a trapped Bose–Einstein condensate with quadrupole–quadrupole interaction.We quantitatively characterize the deformations of the condensate induced by the quadrupolar interaction.We also map out the stability diagram of the condensates and explore the trap geometry dependence of the stability.     

Flame capturing with an advection–reaction–diffusion model

We conduct several verification tests of the advection–reaction–diffusion flame-capturing model, developed by Khokhlov in 1995 for subsonic nuclear burning fronts in supernova simulations. We find that energy conservation is satisfied, but there is systematic error in the computed flame speed due to thermal expansion, which was neglected in the original model. We decouple the model from the full system, determine the necessary corrections for thermal expansion, and then demonstrate that these corrections produce the correct flame speed. The flame-capturing model is an alternative to other popular interface tracking techniques, and might be useful for applications beyond astrophysics.     

Dye-sensitized solar cells with PVA–KI–EC–PC gel electrolytes

Gel polymer electrolytes consisting of PVA–EC–PC–KI have been studied in this work. The highest room temperature (298 K) conductivity of 12.92 mS cm $^{-1}$ is obtained for PVA-based gel polymer electrolyte (GPE) with composition 14.5 PVA-21.7 EC-28.7 PC-30.4 KI-4.7 $\text{ I }_{2}$ (in wt%). The high conductivity is due to the highest number density of mobile ions in the electrolyte. The conductivity–temperature dependence follows the Vogel–Tamman–Fulcher (VTF) relationship. The trend of pseudoactivation energy $(E_{a})$ with salt concentration is contrary to that of conductivity. PVA-based GPEs with 5 to 35 wt% KI were used as a medium in ruthenium 535 (N719) dye-sensitized solar cells. The efficiency ( $\eta $ ) of the solar cells increased as the composition of KI salt in the electrolyte increased. The highest power conversion efficiency of 2.74 % is obtained for solar cells fabricated with electrolyte containing 35 wt% KI. The variation of efficiency follows the same trend as short circuit current density $(J_{sc})$ . The increase in $J_{sc}$ is influenced by the increase in iodide ion concentration in the electrolyte that assists the redox process and helps electron to shuttle between ionized dye and counter electrode.     

Hydrogen interaction with GaN metal–insulator–semiconductor diodes

Interaction mechanism of hydrogen with GaN metal–insulator–semiconductor (MIS) diodes is investigated, focusing on the metal/semiconductor interfaces. For MIS Pt-GaN diodes with a SiO₂ dielectric, the current–voltage (I–V) characteristics reveal that hydrogen changes the conduction mechanisms from Fowler–Nordheim tunneling to Poole–Frenkel emission. In sharp contrast, Pt-Si_xN_y-GaN diodes exhibit Poole–Frenkel emission in nitrogen and do not show any change in the conduction mechanism upon exposure to hydrogen. The capacitance–voltage (C–V) study suggests that the work function change of the Schottky metal is not responsible mechanism for the hydrogen sensitivity.     

Einstein energy associated with the Friedmann–Robertson–Walker metric

Following Einstein’s definition of Lagrangian density and gravitational field energy density (Einstein in Ann Phys Lpz 49:806, 1916, Einstein in Phys Z 19:115, 1918, Pauli in Theory of Relativity, B.I. Publications, Mumbai, 1963), Tolman derived a general formula for the total matter plus gravitational field energy (P ₀) of an arbitrary system (Tolman in Phys Rev 35:875, 1930, Tolman in Relativity, Thermodynamics &; Cosmology, Clarendon Press, Oxford, 1962, Xulu in hep-th/0308070, 2003). For a static isolated system, in quasi-Cartesian coordinates, this formula leads to the well known result \({P_0 = \int \sqrt{-g} (T_0^0 - T_1^1 - T_2^2 - T_3^3) d^3 x,}\) where g is the determinant of the metric tensor and \({T^a_b}\) is the energy momentum tensor of the matter. Though in the literature, this is known as “Tolman Mass”, it must be realized that this is essentially “Einstein Mass” because the underlying pseudo-tensor here is due to Einstein. In fact, Landau–Lifshitz obtained the same expression for the “inertial mass” of a static isolated system without using any pseudo-tensor at all and which points to physical significance and correctness of Einstein Mass (Landau, Lifshitz in The Classical Theory of Fields, Pergamon Press, Oxford, 1962)! For the first time we apply this general formula to find an expression for P ₀ for the Friedmann–Robertson–Walker (FRW) metric by using the same quasi-Cartesian basis. As we analyze this new result, it transpires that, physically, a spatially flat model having no cosmological constant is preferred. Eventually, it is seen that conservation of P ₀ is honoured only in the static limit.     

Potentials with Convergent Schwinger–DeWitt Expansion

Convergence of the Schwinger–DeWittexpansion for the evolution operator kernel for specialclass of potentials is studied. It is shown that thisexpansion, which is in the general case asymptotic,converges for the potentials considered (widely used, inparticular, in one-dimensional many-body problems), andthat convergence takes place only for definite discretevalues of the coupling constant. For other values of the charge, a divergent expansiondetermines the kernels having essential singularity atthe origin (beyond the usual -function). If oneconsiders only this class of potentials, then one can avoid many problems connected withasymptotic expansions, and one gets a theory withdiscrete values of the coupling constant that is incorrespondence with the discreteness of charge innature. This approach can be applied to quantum fieldtheory.     

Morris–Thorne wormhole with Karmarkar condition

In this paper, we construct a wormhole shape function by using Karmarkar condition. We observe that our proposed shape function connects two asymptotically flat regions, which shows the existence of Morris–Thorne traversable wormhole. Moreover, we also represent the embedding diagram in three-dimensional Euclidean space which can be extended from throat to infinity. Further, the Null and Weak energy conditions are discussed in detail. With this shape function, the anisotropic factor exhibits a repulsive nature at the throat. We support all the analysis of this work through graphical representation. It is concluded that our proposed model fulfills all the necessary conditions and shows the existence of exotic matter in the formulism of wormhole geometry in the context of General Relativity.     

Confronting Finsler space–time with experiment

Within all approaches to quantum gravity small violations of the Einstein Equivalence Principle are expected. This includes violations of Lorentz invariance. While usually violations of Lorentz invariance are introduced through the coupling to additional tensor fields, here a Finslerian approach is employed where violations of Lorentz invariance are incorporated as an integral part of the space–time metrics. Within such a Finslerian framework a modified dispersion relation is derived which is confronted with current high precision experiments. As a result, Finsler type deviations from the Minkowskian metric are excluded with an accuracy of 10⁻¹⁶.     

Solitons in magneto–optic waveguides with quadratic–cubic nonlinearity

This paper implements unified Riccati equation expansion scheme as well as extended auxiliary equation method to obtain bright, dark and singular solitons in magneto–optic waveguides. The quadratic–cubic form of nonlinear refractive index is the focus of the paper. These solitons emerge after a limiting value when the modulus of ellipticity approaches unity.     

Improving Einstein–Podolsky–Rosen steering inequalities with state information

We discuss the relationship between entropic Einstein–Podolsky–Rosen (EPR)-steering inequalities and their underlying uncertainty relations along with the hypothesis that improved uncertainty relations lead to tighter EPR-steering inequalities. In particular, we discuss how using information about the state of a quantum system affects one?s ability to witness EPR-steering. As an example, we consider the recent improvement to the entropic uncertainty relation between pairs of discrete observables (Berta et al., 2010 [10]). By considering the assumptions that enter into the development of a steering inequality, we derive correct steering inequalities from these improved uncertainty relations and find that they are identical to ones already developed (Schneeloch et al., 2013 [9]). In addition, we consider how one can use state information to improve our ability to witness EPR-steering, and develop a new continuous variable symmetric EPR-steering inequality as a result.     

Spin–orbit coupled Bose–Einstein condensates with Rydberg-dressing interaction

Interaction between Rydberg atoms can be used to control the properties of interatomic interaction in ultracold gases by weakly dressing the atoms with a Rydberg state. Here we investigate the effect of the Rydberg-dressing interaction on the ground-state properties of a Bose–Einstein condensate imposed by Raman-induced spin–orbit coupling. We find that,in the case of SU(2)-invariant s-wave interactions, the gas is only in the plane-wave phase and the zero-momentum phase is absent. In particular, we also predict an unexpected magnetic stripe phase composed of two plane-wave components with unequal weight when s-wave interactions are non-symmetric, which originates from the Rydberg-dressing interaction.     

Einstein–Maxwell gravity with additional corrections

Motivated by the E ₈×E ₈ heterotic string theory, we obtain topological black hole solutions of Einstein–Maxwell gravity with additional corrections. We consider the Gauss–Bonnet (GB) and (F _μν F ^μν )² terms as an effective quartic order Lagrangian of gauge–gravity coupling and investigate geometric and thermodynamic properties of the black hole solutions. We also analyze the effects of the GB term as well as the correction of Maxwell field on the properties of the solutions.     

Coercivity mechanism of La–Nd–Fe–B films with Y spacer layer

The effect of the Y spacer layer on the phase composition, coercivity, and magnetization reversal processes of La–Nd–Fe–B films has been investigated. The addition of a 10 nm Y spacer layer increases the coercivity of the film to 1.36 T at 300 K and remains 0.938 T at 380 K. As the thickness of the Y spacer layer increases, Y participates in the formation of the main phase in the film, and further regulates the formation of La–B phases. The results of the first-order reversal curve(FORC) and mic...