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Now showing items 1 - 16 of 45597

  • A Note on Campanato Spaces and Their Applications

    Wang, D. H.   Zhou, J.   Teng, Z. D.  

    In this paper, we obtain a version of the John-Nirenberg inequality suitable for Campanato spaces C (p,beta) with 0 < p < 1 and show that the spaces C (p,beta) are independent of the scale p a (0,a) in sense of norm when 0 < beta < 1. As an application, we characterize these spaces by the boundedness of the commutators [b,B (alpha) ] (j) (j =3D 1, 2) generated by bilinear fractional integral operators B (alpha) and the symbol b acting from L (p1) x L (p2) to L (q) for p1, p2 a (1,a), q a (0,a) and 1/q =3D 1/p1 + 1/p2 - (alpha + beta)/n.
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  • Extremely large magnetoresistance in the nonmagnetic semimetal YBi

    Qian, B.   Tang, F.   Ruan, Y. R.   Fang, Y.   Han, Z. D.   Jiang, X. F.   Zhang, J. -M.   Chen, S. Y.   Wang, D. H.  

    Extreme magnetoresistance in nonmagnetic compounds has received considerable attention because this phenomenon challenges the classical understanding of electron transport under a magnetic field. In this study, YBi, which crystallizes in a NaCl-type structure, was synthesized via self-flux method to study its magnetotransport properties and electronic structure. Under zero magnetic field, metallic behavior was observed in the whole temperature interval ranging from 2 to 300 K. Interestingly, extreme magnetoresistance and a resistivity plateau developed when the applied magnetic field was increased; the magnetoresistance reaches 0.8 x 10(5)% at 9 T and 2 K. Multiple bands including one electron pocket and two hole pockets revealed by Kohler's rule and first-principle calculations were responsible for the transport processes. Moreover, the hidden band inversion was also uncovered, which suggests the existence of a topological nature in this compound. The contribution of a single Fermi pocket and the combination thereof for magnetotransport indicate that electron-hole compensation plays an important role in determining the electric properties. All these results point towards YBi being a semimetal member of the RPn family (R =3D rare earth; Pn =3D Sb and Bi).
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  • Extremely large magnetoresistance in the antiferromagnetic semimetal GdSb

    Song, J. J.   Tang, F.   Zhou, W.   Fang, Y.   Yu, H. L.   Han, Z. D.   Qian, B.   Jiang, X. F.   Wang, D. H.   Du, Y. W.  

    Semimetals with extremely large magnetoresistance have attracted significant interest because of their possible nontrivial electronic structures, unusual transport properties, and also deep connections to high-energy physics. In this paper, we synthesize the GdSb single crystal and systematically characterize its crystal structure, magnetism, and electric transport properties. It is found that this compound crystallizes in the NaCl-type structure with a space group Fm (3) over barm and experiences an antiferromagnetic phase transition at 23.4 K. Electric transport measurements reveal that this compound is metallic, in which spin disorders induced a resistivity anomaly emerging around its magnetic transition temperature. Intriguingly, obvious resistivity plateaus are observed at low temperatures, when the compound is subjected to the external magnetic field, showing an extremely large magnetoresistance effect up to 12 100% at 2 K and 9 T. Through the Hall resistivity measurement and first-principles band structure calculations, GdSb is believed to be a multi-band and compensated semimetal, in which the total carrier concentrations of electrons and holes are almost comparable. The electron-hole compensation and ultrahigh mobility of GdSb can contribute to the large magnetoresistance in this compound.
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  • Sparsity-incorporated secure localisation for wireless sensor networks

    Zhang, Q.   Wan, J. W.   Wang, D. D.   Chen, J. Y.   Wang, D. H.  

    To enable efficient and accurate secure localisation in wireless sensor networks, a sparsity-incorporated localisation algorithm is proposed. Unlike most of the existing schemes, the localisation problem is solved in an L1 minimisation framework which is based on the attack sparsity and the linearisation of a distance measurement model including the bogus data from malicious anchors. The localisation errors, speed and detection rates of the scheme are analysed in the simulations. Results demonstrate that the method can simultaneously achieve target localisation and malicious anchor identification in an efficient and accurate way.
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  • Magnetic manipulation of electric orders in Co4NbTaO9

    Liu, Y. Y.   Lu, Y. P.   Zhang, L.   Fang, Y.   Han, Z. D.   Qian, B.   Jiang, X. F.   Zhu, L. Y.   Wang, D. H.   Du, Y. W.  

    Magnetic, dielectric and magnetoelectric properties of the polycrystalline Co4NbTaO9 have been investigated in this paper. The antiferromagnetic phase transition of this compound is identified at the temperature of 23.6 K. Anomalies in the temperature-dependent dielectric constants and pyroelectric currents emerge around its magnetic transition point under magnetic field, and increase with the increasing external magnetic field. Antiferromagnetic fluctuation and domain effect are considered to be response for the phenomenon observed in this compound.
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  • Modulated multiferroic properties of MnWO4 via chemical doping

    Yang, J.   Chen, J.   Fang, Y.   Han, Z. D.   Yan, S. M.   Qian, B.   Jiang, X. F.   Wang, D. H.   Du, Y. W.  

    Here we prepare polycrystalline Mn1-xNixWO4 ceramics with x =3D 0, 0.02, 0.04, 0.06 for investigating their magnetic, ferroelectric, and multiferroic properties. The Ni2+-substitution gradually expands the lattice and modifies the magnetic performance with increasing x, resulting in a strong modulation of electric properties of those samples. For Mn0.96Ni0.04WO4, ferroelectric polarization is observed in the whole temperature regime below T-AF2, and is well modified by an external magnetic field, which is discussed under the framework of a spin-current model in this manuscript.
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  • A cardioid oscillator with asymmetric time ratio for establishing CPG models

    Fu, Q.   Wang, D. H.   Xu, L.   Yuan, G.  

    Nonlinear oscillators are usually utilized by bionic scientists for establishing central pattern generator models for imitating rhythmic motions by bionic scientists. In the natural word, many rhythmic motions possess asymmetric time ratios, which means that the forward and the backward motions of an oscillating process sustain different times within one period. In order to model rhythmic motions with asymmetric time ratios, nonlinear oscillators with asymmetric forward and backward trajectories within one period should be studied. In this paper, based on the property of the invariant set, a method to design the closed curve in the phase plane of a dynamic system as its limit cycle is proposed. Utilizing the proposed method and considering that a cardioid curve is a kind of asymmetrical closed curves, a cardioid oscillator with asymmetric time ratios is proposed and realized. Through making the derivation of the closed curve in the phase plane of a dynamic system equal to zero, the closed curve is designed as its limit cycle. Utilizing the proposed limit cycle design method and according to the global invariant set theory, a cardioid oscillator applying a cardioid curve as its limit cycle is achieved. On these bases, the numerical simulations are conducted for analyzing the behaviors of the cardioid oscillator. The example utilizing the established cardioid oscillator to simulate rhythmic motions of the hip joint of a human body in the sagittal plane is presented. The results of the numerical simulations indicate that, whatever the initial condition is and without any outside input, the proposed cardioid oscillator possesses the following properties: (1) The proposed cardioid oscillator is able to generate a series of periodic and anti-interference self-exciting trajectories, (2) the generated trajectories possess an asymmetric time ratio, and (3) the time ratio can be regulated by adjusting the oscillator's parameters. Furthermore, the comparison between the simulated trajectories by the established cardioid oscillator and the measured angle trajectories of the hip angle of a human body show that the proposed cardioid oscillator is fit for imitating the rhythmic motions of the hip of a human body with asymmetric time ratios.
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  • Magnetic, dielectric, and magnetoelectric properties in Sr2CoGe2O7

    Song, Y. Q.   Li, Q.   Zhang, Z. M.   Zhou, W. P.   Cao, Q. Q.   Xu, Q. Y.   Wang, D. H.   Du, Y. W.  

    We investigate the magnetoelectric effect in Sr2CoGe2O7, which has a two-dimensional magnetic interaction between Co ions in the ab plane. This compound shows a weak magnetism and field-induced magnetic transition below the temperature of 7 K. It does not exhibit electric polarization under zero magnetic field. However, by applying an external magnetic field, the electric polarization is induced around its Neel temperature and increases with increasing magnetic field. The induced electric polarization in Sr2CoGe2O7 is almost two orders of magnitude smaller than that of Ba2CoGe2O7. This result suggests that the different ionic radius of the strontium and the barium anion plays a key role in determining the property of electric polarization. The origins of electric polarization and magnetoelectric effect are discussed. (C) 2015 AIP Publishing LLC.
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  • Brilliant GeV gamma-ray flash from inverse Compton scattering in the QED regime

    Gong, Z.   Hu, R. H.   Lu, H. Y.   Yu, J. Q.   Wang, D. H.   Fu, E. G.   Chen, C. E.   He, X. T.   Yan, X. Q.  

    An all-optical scheme is proposed for studying laser plasma based incoherent photon emission from inverse Compton scattering in the quantum electrodynamic regime. A theoretical model is presented to explain the coupling effects among radiation reaction trapping, the self-generated magnetic field and the spiral attractor in phase space, which guarantees the transfer of energy and angular momentum from electromagnetic fields to particles. Taking advantage of a prospective similar to 10(23) W cm(-2) laser facility, 3D particle-in-cell simulations show a gamma-ray flash with unprecedented multi-petawatt power and brightness of 1.7 x 10(23) photons s(-1) mm(-2) mrad(-2)/0.1% bandwidth (at 1 GeV). These results bode well for new research directions in particle physics and laboratory astrophysics exploring laser plasma interactions.
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  • Cost Estimates of Cellulosic Ethanol Production: A Review

    Zhang, P. F.   Zhang, Q.   Pei, Z. J.   Wang, D. H.  

    Increasing demands and concerns for reliable supply of liquid transportation fuels make it important to find alternatives to petroleum-based fuels. One such alternative is ethanol made from cellulosic biomass. Considerable investigations have been conducted to evaluate the viability of cellulosic ethanol production in several aspects (including cost competitiveness). Cost estimates of cellulosic ethanol production have been reported by many researchers in order to evaluate the economic viability of cellulosic ethanol production. However, the reported cost estimates in the literature have a large variation. The current literature contains limited reviews on the cost estimates of cellulosic ethanol production and mostly focused on some individual processes. This paper presents a literature review on the cost estimates of entire cellulosic ethanol production. It reviews the estimated costs for both the entire cycle (from planting to conversion) and individual processes for cellulosic ethanol production. It also covers factors that lead to variations among reported cost estimates.
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  • Magnetostructural transition and magnetocaloric effect in MnCoGe-NiCoGe system

    Zhang, C. L.   Shi, H. F.   Ye, E. J.   Nie, Y. G.   Han, Z. D.   Wang, D. H.  

    Magnetostructural transition and magnetocaloric effect were investigated for MnCoGe-NiCoGe system. Chemically alloying NiCoGe with the parent compound MnCoGe stabilizes the high-temperature hexagonal structure relative to the low-temperature orthorhombic structure and keeps their Curie temperatures nearly constants, establishing a Curie temperature window in which the magnetic and structural transitions coincide. As a result, magnetostructural transitions occur between ferromagnetic and paramagnetic states with sharp jumps in magnetization around room temperature. Large magnetocaloric effects with tunable phase transition temperatures were observed in the MnCoGe-NiCoGe system. (C) 2015 Elsevier B.V. All rights reserved.
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  • Magnetoresistance in magnetite film:A theoretical and experimental investigation

    Zhang, Z. M.   Zhou, W. P.   Li, Q.   Wang, D. H.   Cao, Q. Q.   Du, Y. W.  

    Functional dependence of magnetoresistance on external magnetic field is of great importance for not only discovering the origin of electrical transport but also tailoring materials for advanced properties in magnetic-field-controlled devices. By utilizing the magnetic domain-rotation model combined with antiphase boundary and charge carrier hopping theories, the formular description of magnetoresistance in magnetite (Fe3O4) film has been studied systematically. The calculation shows that the magnetoresistance depends linearly and quadratically on the external magnetic field when the fields are applied parallel and perpendicular to the Fe3O4 film plane, respectively. We give the experimental MR data to verify these theoretical results. (C) 2017 Elsevier B.V. All rights reserved.
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  • Parameter constrain in neutron star by twin kHz QPOs

    Wang, D. H.   Chen, L.  

    We use data on twin kHz QPOs and measured neutron star (NS) masses to test the relation between the lower (ν1) and upper (ν2) peak frequencies predicted with the MHD Alfvén wave oscillation model (AWOM) and the general relativistic precession model (GRPM). In the context of AWOM, the NS radius can be constrained from kHz QPO data and a measured NS mass.
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  • Distribution of twin kHz QPOs in LMXBs

    Wang, D. H.   Chen, L.  

    With kilohertz quasi-periodic oscillation (kHz QPO) sources in neutron star low mass X-ray binaries (NS-LMXBs) published up to now, we analyze the centroid frequency (ν) distribution of twin kHz QPOs. We find that Atoll and Z sources show the similar distributions of ν1 and ν2, which indicate that twin kHz QPOs may be the common property of NS-LXMBs and have the similar physical origins. The mean values of ν1 and ν2 in Atoll sources are higher than those in Z sources, and we consider that this may because the QPO signals are sheltered by the thicken accretion disk or corona in Z sources. The maximums of ν2 in both Atoll and Z sources are the same order as the Keplerian orbital frequency of the NS surface, so kHz QPOs could occur near the NS surface.
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  • Morphological analysis on the coherence of kHz QPOs

    Wang, J.   Chang, H. K.   Zhang, C. M.   Wang, D. H.   Chen, L.   Qu, J. L.   Song, L. M.  

    We take the recently published data of twin kHz quasi-period oscillations (QPOs) in neutron star (NS) low-mass X-ray binaries (LMXBs) as the samples, and investigate the morphology of the samples, which focuses on the quality factor, peak frequency of kHz QPOs, and try to infer their physical mechanism. We notice that: (1) The quality factors of upper kHz QPOs are low (2 similar to 20 in general) and increase with the kHz QPO peak frequencies for both Z and Atoll sources. (2) The distribution of quality factor versus frequency for the lower kHz QPOs are quite different between Z and Atoll sources. For most Z source samples, the quality factors of lower kHz QPOs are low (usually lower than 15) and rise steadily with the peak frequencies except for Sco X-1, which drop abruptly at the frequency of about 750 Hz. While for most Atoll sources, the quality factors of lower kHz QPOs are very high (from 2 to 200) and usually have a rising part, a maximum and an abrupt drop. (3) There are three Atoll sources (4U 1728-34, 4U 1636-53 and 4U 1608-52) of displaying very high quality factors for lower kHz QPOs. These three sources have been detected with the spin frequencies and sidebands, in which the source with higher spin frequency presents higher quality factor of lower kHz QPOs and lower difference between sideband frequency and lower kHz QPO frequency.
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  • Statistical analysis for the Q-factor of twin kHz QPOs

    Wang, J.   Chang, H. K.   Zhang, C. M.   Wang, D. H.   Chen, L.  

    Using the recently published data of twin kHz quasi-period oscillations (QPOs) in neutron stars of low-mass X-ray binaries (LMXBs), we study the different profiles between bright Z sources and less luminous Atoll sources. The quality factors of upper kHz QPOs show a narrow distribution both for Z sources and Atoll sources, which concentrate at 7.98 and 9.75, respectively. The quality factors of lower kHz QPOs show a narrow distribution for Z sources and a broader distribution for Atoll sources, which concentrate at 5.25 and 86.22, respectively. In order to investigate the relation between the quality factor and the peak frequency of kHz QPOs, we fit the data with power-law, linear, and exponential functions, respectively. There is an obvious trend that the quality factors increase with the peak frequencies both for upper and lower QPOs. The implications of our results are discussed ((c) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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