1,534 research outputs found

    Antisite Disorder-induced Exchange Bias Effect in Multiferroic Y2CoMnO6

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    Exchange bias effect in the ferromagnetic double perovskite compound Y2_2CoMnO6_6, which is also a multiferroic, is reported. The exchange bias, observed below 8~K, is explained as arising due to the interface effect between the ferromagnetic and antiferromagnetic clusters created by {\it antisite} disorder in this material. Below 8~K, prominent ferromagnetic hysteresis with metamagnetic "steps" and significant coercive field, HcH_c \approx 10~kOe are observed in this compound which has a TcT_c \approx 75~K. A model based on growth of ferromagnetic domains overcoming the elastic energy of structurally pinned magnetic interfaces, which closely resembles martensitic-like transitions, is adapted to explain the observed effects. The role of {\it antisite} disorder in creating the domain structure leading to exchange bias effect is highlighted in the present work.Comment: 4 pages two-column, 4 figures, accepted to Appl. Phys. Let

    Supersolid and solitonic phases in one-dimensional Extended Bose-Hubbard model

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    We report our findings on quantum phase transitions in cold bosonic atoms in a one dimensional optical lattice using the finite size density matrix renormalization group method in the framework of the extended Bose-Hubbard model. We consider wide ranges of values for the filling factors and the nearest neighbor interactions. At commensurate fillings, we obtain two different types of charge density wave phases and a Mott insulator phase. However, departure from commensurate fillings yield the exotic supersolid phase where both the crystalline and the superfluid orders coexist. In addition, we obtain signatures for solitary waves and also superfluidity.Comment: 7 pages, 11 figure

    Geometric dimensioning and tolerancing a tool for concurrent engineering

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    The concept of Concurrent Engineering recognizes an immediate need for a new design environment and technology and so requires extensive interdisciplinary cooperation and integration of diverse functions of a manufacturing organization such as marketing, design, manufacturing and finance. One of the key factors to achieve successful integration among the departments is better communication and it becomes imperative in cases of varying levels of communication needs, especially in interdepartmental cases. Concurrent Engineering is a philosophy which provides certain benefits. There are various tools and methods available for implementation of Concurrent Engineering concepts. One of the tools is Geometric Dimensioning & Tolerancing (GD & T), which can be used for indespensible communication of exact part design and its proper execution. Unlike other tools, GD & T concepts emphasize on the integration of various functions in a manufacturing organization. This thesis discusses the applicability of Geometric Dimensioning and Tol-erancing as an integrating tool for related functional departments in the concurrent environment. It also establishes the synchronization between the objectives of the two concepts. Also, it discusses the effect of using GD & T on vendor lead time and manufacturing lead time. The effect on the product quality, the cost economics and the learning curve is also investigated. Lastly, the thesis concludes that the implementation of GD & T concepts automatically attains the objectives of concurrent engineering. The use of GD & T in industries may lead to widespread implementation of the concurrent engineering concepts globally. Therefore, it can be considered as a medium or tool for Concurrent Engineering

    Many-body approach to low-lying collective excitations in a BEC approaching collapse

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    An approximate many-body theory incorporating two-body correlations has been employed to calculate low-lying collective multipole frequencies in a Bose-Einstein condensate containing AA bosons, for different values of the interaction parameter λ=Aasaho\lambda=\frac{Aa_{s}}{a_{ho}}. Significant difference from the variational estimate of the Gross-Pitaevskii equation has been found near the collapse region. This is attributed to two-body correlations and finite range attraction of the realistic interatomic interaction. A large deviation from the hydrodynamic model is also seen for the second monopole breathing mode and the quadrupole mode for large positive λ\lambda.Comment: 8 pages, 2 figure

    Magnetic ordering in double perovskites R2_2CoMnO6_6 (R= Y,Tb) investigated by high resolution neutron spectroscopy

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    We have investigated low energy nuclear spin excitations in double perovskite compounds R2_2CoMnO6_6 (R = Y,Tb) by inelastic neutron scattering with a high-resolution back-scattering spectrometer. We observed inelastic signals at about 2.1 μ\mueV for Y2_2CoMnO6_6 and also for Tb2_2CoMnO6_6 at T = 2 K in both energy loss and energy gain sides. We interpret these inelastic peaks to be due to the transitions between the hyperfine split nuclear levels of 59^{59}Co nucleus. The inelastic peaks move towards the central elastic peak and finally merge with it at the magnetic ordering temperature TCT_C. The energy of the low energy excitations decreases continuously and becomes zero at TC75T_C \approx 75 K for Y2_2CoMnO6_6 and TC100T_C \approx 100 K for Tb2_2CoMnO6_6. For Tb2_2CoMnO6_6, which contains magnetic rare-earth ions, additional quasielastic scattering due presumably to the fluctuations of large Tb magnetic moments was observed. The present study reveals the magnetic ordering of the Co sublattice. The results of this investigation along with that obtained by us for other compounds indicate the presence of unquenched orbital moments in some of the Co compounds

    Type I singularities and the Phantom Menace

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    We consider the future dynamics of a transient phantom dominated phase of the universe in LQC and in the RS braneworld, which both have a non-standard Friedmann equation. We find that for a certain class of potentials, the Hubble parameter oscillates with simple harmonic motion in the LQC case and therefore avoids any future singularity. For more general potentials we find that damping effects eventually lead to the Hubble parameter becoming constant. On the other hand in the braneworld case we find that although the type I singularity can be avoided, the scale factor still diverges at late times.Comment: More references added. Final PRD versio

    Live Soap: Order, Fluctuations and Instabilities in Active Smectics

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    We construct a hydrodynamic theory of noisy, apolar active smectics, in bulk suspension or on a substrate. Our predictions include: quasi-long-ranged smectic order in dimension d = 2, and long- ranged in d = 3, extending previously published results to all dynamical regimes; Kosterlitz-Thouless melting to an active nematic at high and low concentrations in d = 2; nonzero second-sound speed parallel to the layers; the suppression of giant number fluctuations by smectic elasticity; instability to spontaneous undulation and flow in bulk contractile smectics; a layer spacing instability, possibly oscillatory, for large enough extensile active stresses.Comment: 5 pages, 1 figure, submitted to Phys Rev Let

    Photonuclear reactions of actinides in the giant dipole resonance region

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    Photonuclear reactions at energies covering the giant dipole resonance (GDR) region are analyzed with an approach based on nuclear photoabsorption followed by the process of competition between light particle evaporation and fission for the excited nucleus. The photoabsorption cross section at energies covering the GDR region is contributed by both the Lorentz type GDR cross section and the quasideuteron cross section. The evaporation-fission process of the compound nucleus is simulated in a Monte-Carlo framework. Photofission reaction cross sections are analyzed in a systematic manner in the energy range of \sim 10-20 MeV for the actinides 232^{232}Th, 238^{238}U and 237^{237}Np. Photonuclear cross sections for the medium-mass nuclei 63^{63}Cu and 64^{64}Zn, for which there are no fission events, are also presented. The study reproduces satisfactorily the available experimental data of photofission cross sections at GDR energy region and the increasing trend of nuclear fissility with the fissility parameter Z2/AZ^2/A for the actinides.Comment: 4 pages including 2 tables and 1 figur

    Multiphysics modelling of a hybrid magnetic bearing (HMB) for calculating power loss and temperature with different loss minimization strategies

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    This paper represents a multiphysics modelling for calculating loss and temperature of a hybrid magnetic bearing (HMB) using finite element method (FEM). It also addresses the different loss minimization strategies for the HMB. The main sources of losses are identified as eddy current loss in permanent magnets, flywheel and copper loss in electromagnet. Due to these losses, the temperature distribution in different portions of HMB is computed using coupled field analysis. To minimize the eddy current loss, slits are fabricated in flywheel plate instead of a solid flywheel. The improvement of the control current is investigated by providing a coating of different metal, like copper, brass and stainless steel on the flywheel. A zero bias current (ZBC) scheme has been introduced where no bias current is required to levitate the rotor or to avoid singularity due to external disturbances, thus reducing the copper loss

    A new HPTLC method for estimation of Bamifylline: Development and validation consideration

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    A new and rapid high-performance thin-layer chromatographic (HPTLC) method was developed and validated for quantitative determination of Bamifylline. The HPTLC separation was achieved on an aluminum-backed layer of silica gel 60F 254 using methanol : toluene (2.5 + 7.5 v/v) as mobile phase. Quantitation was achieved by densitometric analysis at 277 nm over the concentration range of 100600 ng/spot. The method was found to give compact spot for the drug ( R f = 0.51 0.01). The linear regression analysis data for the calibration plots showed good linear relationship with r 2 = 0.9995. The method was validated for precision, recovery, repeatability, and robustness as per the International Conference on Harmonization guidelines. The minimum detectable amount was found to be 7.65 ng/spot, whereas the limit of quantitation was found to be 23.19 ng/spot. Statistical analysis of the data showed that the method is precise, accurate, reproducible, sensitive and selective for the analysis of Bamifylline. The method was successfully employed for the estimation of Bamifylline as a bulk drug and in commercially available tablet formulation
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