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The phonon dispersion spectrum, eigenvector and lattice vibration frequency of zincblende cadmium telluride (CdTe) are studied by density functional theory (DFT). The vertical or parallel relationship between the phonon propagating wave vector atomic vibration direction is analyzed, and the frequency of the CdTe transverse (TO)/longitudinal (LO) optical phonon is obtained. The Boltzmann transport equation clearly expresses the phonon scattering process, which is combined with the Huang Kun equation to obtain the three-phonon collision frequency (γ). The terahertz time-domain spectroscopy system is used to measure the reflectivity and dielectric constant of CdTe single crystal. The experimental results verify that the theoretical calculation based on DFT can give the correct terahertz band dielectric constant with frequency dependence characteristics completely independent of the experiment. [ABSTRACT FROM AUTHOR]

Zero-mean circular Gaussian statistics is a well-known model for coherent electromagnetic wave scattered by random media. Applying Kullback-Leibler Divergence to measure the deviation of the simulation scattering field probability distribution from this model, the formation of zero-mean circular Gaussian statistics is investigated quantitatively in two-dimensional random media based on finite element method. Increasing the scattering and randomness in the media, the transmission electric field gradually approaches zero-mean circular Gaussian statistics, however, the deviation from a perfect statistics distribution has a limit which is only determined by the number of random electric field variables used for estimates the probability distribution; besides, field amplitude forming stable statistics faster than field phase. [ABSTRACT FROM AUTHOR]

Spoof surface plasmons(SSP) is attractive to develop efficient THz radiation source owing to its strong localized electric field. In this work, a THz radiation source based on SSP modes on a layered metal-dielectric plasmonic metamaterial is proposed and investigated. The dispersion characteristics of SSP modes on the structure are solved analytically and numerically. Besides, the propagation of SSP mode which is tuned by the filled dielectric is also demonstrated. Following the studies, THz radiation source which is induced by injected electron beam in the system is studied by a FDTD simulation method. The outputs of THz source based on the interaction between SSP mode and electron beam with various kinds of filled dielectric are given and compared with the same injected beam energy. It is shown that maximum power is decreased in the structure compared with no dielectric situation and the frequency spectrum is lowered. The presented studies about the excitation of SSP modes by electron beam on the structure may provide a good candidate of enhanced and tunable THz radiation source. [ABSTRACT FROM AUTHOR]

We study the quantum phase transitions and the critical behavior of the quantum Rabi dimer model, where the two cavities are not equivalent. In our model the coupling strength in each cavity is individually tuned as what usually happens in experimental systems. In the frequency-ratio limit with an infinite ratio of the atomic transition frequency to the cavity frequency, the model is analytically solved so that we find a superradiant phase transition and the order parameter of the system is found to be the normal mode of the linear combination of the two cavity modes. Thus we can determine precisely the critical points and depict the associated phase diagram. We also extract the critical exponents through calculating the universal scaling function and thus conclude that the phase transition of the model belongs to the mean-field universality class. The von Neumann entropy and l 1 norm coherence are adopted to analyze the quantum phase transition and the associate critical phenomena. The critical points and critical exponents extracted from these information measures agree with ones distilled by the order parameter. We expect this work could stimulate the further study on the multi-cavity models with disorder, where a series of nonequivalent cavities are cascaded. [ABSTRACT FROM AUTHOR]

Abstract: We experimentally investigate the scaling probability distributions of various intrachain distances of granular chains in two-dimensional static packing, the chain length of which ranges from to 2048. With the scaling method proposed in the polymer theory, the scaled data from granular chains tend to cluster together so as to form a single experimental fitting curve. We find that the statistical distributions for all chains show a striking scaling behavior which can be described by Redner–des Cloizeaux formula in polymer theory. Finally, a crucial contact exponent is estimated from the fitting curve and compared with that from self-avoiding walk and compacted polymer models. [Copyright &y& Elsevier]

Abstract: A separated flow model of coiled adiabatic capillary tube for CO2 considering metastable flow region is presented. In the case of straight capillary, different friction factors are compared with each other, the model using Churchill and Lin correlations gives a deviation of −1.8% compared with the experimental data for CO2. Three different friction factor correlations (Schmidt, M&N and M&N modified) are discussed for coiled capillary tube. The results show that the M&N modified friction factor gives the best reasonable prediction with a deviation of 4% compared with the experimental data for R22. The discrepancy between the capillary tube length calculated with the separated flow model and that calculated with homogeneous flow model is about 2–7% for the chosen conditions. The mass flow rate for CO2 increases about 7% when the coiled diameter changes from 40 mm to 600 mm. [Copyright &y& Elsevier]

• High numerical aperture and large focusing efficiency metalenses in the microwave spectrum are studied. • Numerical and experimental results demonstrate a high NA metalens in the order of 0.8 and the large focusing efficiency around 40% based on four-layer high transmission gradient element. • Besides, the NA of proposed metalens can be further improved from 0.8 to 0.9 by increasing dielectric thickness and/or the focusing efficiency can be enhanced to above 50% by adding the layer number of the stacked meta-atoms. High numerical aperture (NA) metalenses with large focusing efficiency are crucial for various applications in modern optics and photonics, particularly in high resolution imaging, high directivity lasing process and so on. Recent progresses have been achieved in designing high NA metalenses which can surpass conventional ones but mainly in the visible and infrared regimes by using all-dielectric metasurfaces. Here, multilayer phase gradient metallic metasurfaces sandwiched by filling dielectrics are employed to design high NA and large efficiency metalenses in the low spectrums. Benefiting from its high transmission amplitude and the full phase control to the incident waves of the proposed gradient meta-atoms with a double split ring resonator, the designed ultra-thin and small footprint four-layer metalens (5λ × 5λ × 0.23λ, λ is wavelength) demonstrates a high NA in the order of 0.8 and the large focusing efficiency around 40% according to the full-wave simulations and experimental measurements. Furthermore, the influences of the dielectric thickness and the layer number of stacked meta-atoms on the presented high NA metalens are investigated. The results reveal that the NA of proposed metalens can be surprisingly further improved from 0.8 to 0.9 by increasing dielectric thickness and/or the focusing efficiency can be enhanced to above 50% by adding the layer number of the stacked meta-atoms. These findings also imply that our high NA metalens in low spectrum can be compatible to the standard printed circuit board fabrication and also posses of good robustness to the metasurface layer number. The presented work provides new vistas to develop high NA and large efficiency metalens in low microwave or Terahertz (THz) spectrum, where the metallic metasurfaces are commonly used. Besides, it can benefit to the development of various novel metadevices such as miniaturized high-gain lens antenna, compact cloaks and many others in modern microwave engineering and/or THz optics. [ABSTRACT FROM AUTHOR]

A series of Co–Al layered double hydroxide (Co–Al LDHs)@reduced graphene oxide (rGO) nanocomposite are successfully synthesized through a hydrothermal method and applied as novel cathode additives for nickel-based secondary batteries for the first time. The obtained Co–Al LDHs@rGO nanocomposite is composed of many thin nanosheets, displaying laminated structure. The effects of various Co–Al LDHs@rGO on the properties of nickel cathodes were compared and its action mechanism was further investigated. Interestingly, the Ni(OH) 2 electrode added with Co–Al LDHs@rGO(10%) delivers best high-rate performances and more stable cycling stability as comparison with the pure Ni(OH) 2 and Ni(OH) 2 +CoO electrodes. Owing to its soft and flexible structure, Co–Al LDHs@rGO(10%) is conducive to modify the electronic conductivity, proton diffusion and electrochemical reversibility of the electrode by forming a more effective and stable conductive network. Especially, Co–Al LDHs@rGO(10%) with high electrochemical activity can contribute much higher discharge capacity than the commercial CoO. Owing to its high efficiency and low cobalt content, Co–Al LDHs@rGO(10%) can be applied as an effective, cheap, and promising cathode additive for nickel-based rechargeable batteries. [ABSTRACT FROM AUTHOR]

A series of Co–Al layered double hydroxide nanosheets-coated spherical nickel hydroxide with improved high-rate and cycling performance are successfully synthesized through a hydrothermal method. Scanning electron microscopy images show that Co–Al layered double hydroxide is uniformly anchored on the surface of nickel hydroxide. As cathode material for nickel-based battery, the Ni(OH) 2 @Co–Al layered double hydroxide(10%) displays a highest high-rate properties and cycling performance. The discharge capacities of the as-obtained Ni(OH) 2 @Co–Al LDH(10%) reach up to 299.7, 276.6, 247.5 and 223.2 mA h g−1 at 0.2, 1.0, 5.0 and 10.0C, respectively. After 500 cycles at 1C/1C, the Ni(OH) 2 @Co–Al LDH (10 wt %) delivers a high capacity retention of 87.3%. These performance improvements are ascribed to the fact that Co–Al layered double hydroxide not only forms a stable high conductive layer of β-CoOOH and γ-CoOOH, but also provides many capacity through a reversible conversion between and γ-CoOOH and CoAl LDHs, eventually leading to the improvement of the reversible property, proton diffusion and conductivity of the Ni(OH) 2 cathode. Consequently, the spherical Ni(OH) 2 @Co–Al layered double hydroxide(10%) is a promising cathodes material for advanced nickel-based secondary batteries. [ABSTRACT FROM AUTHOR]