Enhancement of Omnidirectional Photonic Bandgaps in One-Dimensional Superconductor–Dielectric Photonic Crystals with a Staggered Structure

In this paper, the properties of the omnidirectional photonic bandgap (OBG) realized by one-dimensional (1D) photonic crystals with a staggered structure which is composed of superconductor and isotropic dielectric have been theoretically investigated by the transfer matrix method (TMM). From the numerical results, it has been shown that such OBG is insensitive to the incident angle and the polarization of electromagnetic wave (EM wave), and the frequency range and central frequency of OBG can be tuned by the ambient temperature of system, the average thickness of superconductor layer, the average thickness of dielectric layer, and staggered parameters, respectively. The bandwidth of OBG can be notably enlarged with increasing average thickness and staggered parameter of superconductor layer. Moreover, the frequency range of OBG can be narrowed with increasing the average thickness, staggered parameter of dielectric layer, and ambient temperature, respectively. The damping coefficient of superconductor layer has no effect on the bandwidth of OBG under low-temperature conditions. It is shown that 1D superconductor–dielectric photonic crystals (SDPCs) have a superior feature in the enhancement of frequency range of OBG. This kind of OBG has potential applications in filters, microcavities, and fibers, etc.     

Omnidirectional Photonic Band Gap in One-Dimensional Ternary Superconductor-Dielectric Photonic Crystals Based on a New Thue–Morse Aperiodic Structure

In this paper, an omnidirectional photonic band gap (OBG) of one-dimensional (1D) ternary superconductor-dielectric photonic crystals (SDPCs) based on a new Thue–Mores aperiodic structure is theoretically studied by the transfer matrix method (TMM) in detail. Compared to zero- $\bar{n}$ gap or single negative (negative permittivity or negative permeability) gap, such OBG originates from Bragg gap. From the numerical results, the bandwidth and central frequency of OBG can be notably enlarged by manipulating the thicknesses of superconductor and dielectric layers but cease to change with increasing the Thue–Mores order. The OBG also can be tuned by the ambient temperature of the system especially close to the critical temperature. However, the damping coefficient of the superconductor layer has no effects on the OBG. The relative bandwidth of OBG also is investigated by the parameters as mentioned above. It is clear that such 1D ternary SDPCs have a superior feature in the enhancement of the bandwidth of OBG compared to the conventional ternary SDPCs and conventional ternary Thue–Mores aperiodic SDPCs. These results may provide theoretical instructions to design the future SDPCs devices.     

Broadening of Photonic Band Gap in a One—Dimensional Superconductor Star Waveguide Structure

The present paper describes the theoretical investigation of enlarged reflection bands (photonic band gaps) in a 1D star waveguide (SWG) structure consists of superconductor and dielectric as its constituent materials. For the present study, we take the different combinations of superconductor and dielectric materials as a backbone and side branches of the SWG structure. In order to obtain the dispersion relation, Interface Response Theory (IRT) has been employed. Photonic band gaps of SWG structure having superconductor?Csuperconductor, superconductor?Cdielectric, and dielectric?Csuperconductor materials are compared with the band gaps of the conventional photonic crystal (PC) structure having superconductor?Csuperconductor and dielectric?Csuperconductor materials. Analysis of the dispersion characteristics shows that there exists no band gaps for conventional PC when both layers are made of the same superconducting materials (as the usual case) while the SWG structure shows forbidden bands of finite width even the backbone and side branches are made of same materials. Also, the SWG structure having superconductor?Cdielectric shows the wider reflection bands in comparison with the structure having dielectric?Csuperconductor as its constituent materials, while for the conventional PC structure it is same in both the cases. Further, the effect of temperature and the effect of variation of number of grafted branches on the photonic bands of SWG structure have been studied.     

Angle- and Thickness-Dependent Photonic Band Structure in?a?Superconducting Photonic Crystal

The angle- and thickness-dependent photonic band structures in a one-dimensional superconducting photonic crystal are theoretically investigated based on the transfer matrix method. The band structure is studied near and below the threshold frequency at which the superconducting material has a zero permittivity. The gap structure is analyzed as a function of the thicknesses of the two constituent superconducting and dielectric materials. In the angular dependence of the band structure, it is found that in the TM-polarization there exists a strongly localized superpolariton gap in the vicinity of the threshold frequency. This gap is shown to be enhanced as the angle increases.     

Large Increase of the Critical Field in a Magnet–Superconductor Nanowire Hybrid

We have fabricated two-dimensional periodic arrays of parallel magnetic and superconducting nanowires on a silicon substrate. Parallel magnetic (nickel) nanowires of cross section 90 nm by 300 nm form a periodic array with Pb₈₂Bi₁₈ superconducting nanowires of cross section 200 nm by 100 nm. These nanostructures were characterized with Scanning Electron Microscopy (SEM) and magnetic properties were studied with Magnetic Force Microscopy (MFM). The phase diagram was determined by electrical transport measurements. Depending on the temperature, the second critical field was 2 to 3 times larger than that of a homogeneous Pb₈₂Bi₁₈ superconducting control film. The superconducting phase diagram and transport properties exhibit strong hysteresis in a magnetic field. Results are explained on the basis of the theory of magnet–superconductor hybrids.     

On the Structure of the Superfluid State and Quasiparticle Spectrum in a Bose Liquid with a Suppressed Bose–Einstein Condensate

A self-consistent model of the superfluid (SF) state of a Bose liquid with strong interaction between bosons and a weak single-particle Bose–Einstein condensate (BEC) is considered. The ratio of the BEC density n ₀ to the total particle density n of the Bose liquid is used as a small parameter of the model, n ₀/n?1, unlike in the Bogolyubov theory of a quasi-ideal Bose gas, in which the small parameter is the ratio of the number of supracondensate excitations to the number of particles in an intensive BEC, (n?n ₀)/n ₀?1. A closed system of nonlinear integral equations for the normal ~Σ₁₁(p, ω) and anomalous ~Σ₁₂(p, ω) self-energy parts is obtained with account for terms of first order in the BEC density. A renormalized perturbation theory is used, which is built on combined hydrodynamic (at p→0) and field (at p≠0) variables with analytic functions ~Σ _ij (p, ε) at pε0 and ε→0 and a nonzero SF order parameter ~Σ₁₂(0, 0)≠0, proportional to the density ρ _s of the SF component. Various pair interaction potentials U(r) with inflection points in the radial dependence and with an oscillating sign-changing momentum dependence of the Fourier component V(p) are considered. Collective many-body effects of renormalization (“screening”) of the initial interaction, which are described by the bosonic polarization operator Π(p, ω), lead to a suppression of the repulsion [V(p)<0] and an enhancement of the effective attraction [V(p)<0] in the respective domains of nonzero momentum transfer, due to the negative sign of the real part of Π(p, ω) on the “mass shell” ω=E(p). In the framework of the “soft spheres” model with the single fitting parameter—the value of the repulsion potential at r=0—the quasiparticle spectrum E(p) is calculated, which is in good accordance with the experimental spectrum E _exp(p) of elementary excitations in superfluid ⁴He. It is shown that the roton minimum in the quasiparticle spectrum is directly associated with the first negative minimum of the Fourier component of the renormalized (“screened”) potential of pair interaction between bosons.     

Anomalous Resistivity and the Electron–Polaron Effect in the Two-Band Hubbard Model with One Narrow Band

We search for anomalous normal and superconductive behavior in the two-band Hubbard model with one narrow band. We analyze the influence of the electron?Cpolaron effect and the Altshuler?CAronov effect on effective mass enhancement and scattering times of heavy and light components in the clean case. We find anomalous behavior of resistivity at high temperatures $T > W_{h}^{*}$ both in 3D and 2D situations. The SC instability in the model is governed by an enhanced Kohn?CLuttinger effect for p-wave pairing of heavy electrons via polarization of light electrons.     

Increasing the Entrapment of Protein-Loaded Liposomes with a Modified Freeze–Thaw Technique: A Preliminary Experimental Study

The objective of this study was to investigate the possibility of increasing the entrapment of protein-loaded liposomes with a modified freeze–thaw technique. Blank liposomes were prepared by ethanol injection method. Then recombinant human growth hormone (rhGH) was added to blank liposome suspension. rhGH encapsulation efficiency was enhanced by modified freeze–thaw technique. We separated each step and studied the effect of each parameter on encapsulation: incubation temperature (water bath from 0 to 15°C), incubation duration (from 5 to 90 min), number of freeze–thaw (from 0 to 4 cycle), and the ratio between rhGH and phospholipids (from 1:5 to 1:10). The effect of cryoprotectants on the encapsulation and particle size distribution was finally examined. rhGH encapsulation efficiency was determined by Bradford's dye-binding assay. Morphology and size distribution of rhGH liposomes were also observed. The optimum parameters for rhGH encapsulation were incubation temperature of 5°C, incubation duration of 40 min, and three to four cycles of freeze–thaw. The ratio between rhGH and phospholipids did not affect the encapsulation percentage. Trehalose exhibited the highest integrated value among the cryoprotectants investigated. From the results, this study demonstrates the suitability of the modified freeze–thaw technique for obtaining rhGH liposomes with high entrapment.     

Development of a Model for the Formation of Materials with a Hierarchical Pore Structure Produced under Sol–Gel Processing Conditions

We have developed a model for the formation of silica-containing synthetic functional materials with a hierarchical pore structure and a large specific surface area under self-assembly conditions of sol–gel processes. The model includes the formation of a three-dimensional core (of a cristobalite type) of sol particles consisting of joined polymorphoids in the form of n-membered rings and a continuous transition between fractal aggregate growth mechanisms, from diffusion-limited to cluster–cluster aggregation, followed by evolution culminating in spinodal decomposition. Hierarchical structures have been studied using three-dimensional simulation with Autodesk 3ds Max software.     

Dielectric resonators with complex crystal structures in the La2O3–Al2O3–TiO2 system for microwave applications

LaTi₂Al₉O₁₉ and La₃Ti₅Al₁₅O₃₇ ceramics in the La₂O₃–Al₂O₃–TiO₂ system have been prepared by conventional solid state ceramic route. The structure and microstructure of the compositions have been studied using powder X-ray diffraction and scanning electron microscopic techniques. Laser Raman studies have been employed to understand the complex crystal structure of these compositions in molecular level. The microwave dielectric properties of the sintered ceramic compacts were measured by Hakki and Colemann post resonator and TE_01δ cavity techniques using a vector network analyzer. LaTi₂Al₉O₁₉ and La₃Ti₅Al₁₅O₃₇ ceramics possess excellent microwave dielectric properties such as relatively high unloaded quality factors 7,762 and 7,415, low dielectric constant 15.7 and 22.1 and low temperature coefficient of resonant frequency values ?22 and +18.9 ppm/°C, respectively.     

Improving the push–pull strategy in a serial supply chain by a hybrid push–pull control with multiple pulling points

Because of its benefits – from lowered inventory costs to greater flexibility in adapting to shifting market forces – the push–pull strategy is being widely used in today's competitive supply-chain designs. The push–pull strategy also brings potential supply-chain risks related to order fulfilment capability and robustness against external variability. More specifically, the use of this strategy often results in an inability to minimise the impact of lead-time variability. We present a new, hybrid push–pull strategy that incorporates additional stock points after the push–pull boundary as the pulling points in a serial supply chain, which can mitigate the risks and improve the robustness of the push–pull strategy without sacrificing its benefits in inventory cost reduction. For the evaluation and comparison of different supply-chain strategies, a nonlinear, mixed-integer programming model with a cost-minimisation objective function is developed and implemented in the numerical experimentation, with simulated annealing as the search algorithm. Results from the experiments demonstrate the potential improvement by our proposed strategy in terms of the robustness and cost-effectiveness against external variability. The results also verify the risks and limitations of the conventional push–pull strategy and provide some managerial implications regarding the use of push–pull supply chains.     

Effective Excitation of Magnetoelectric Voltage Harmonics in a Ferromagnet–Piezoelectric Structure by Current Passing through the Magnetic Layer

Technical Physics Letters - The magnetoelectric (ME) effect in a planar amorphous ferromagnet–piezoelectric lead zirconate titanate (PZT) composite structure can be effectively excited by...     

Modulating Electronic Structure with Copper Doping to Promote the Electrocatalytic Performance of Cobalt Disulfide in Li–O2 Batteries

Introducing heteroatom into catalyst lattice to modulate its intrinsic electronic structure is an efficient strategy to improve the electrocatalytic performance in Li–O₂ batteries. Herein, Cu-doped CoS₂ (Cu–CoS₂) nanoparticles are fabricated by a solvothermal method and evaluated as promising cathode catalysts for Li–O₂ batteries. Based on physicochemical analysis as well as density functional theory calculations, it is revealed that doping Cu heteroatom in CoS₂ lattice can increase the covalency of the Co S bond with more electron transfer from Co 3d to S 3p orbitals, thereby resulting in less electron transfer from Co 3d to O 2p orbitals of Li–O species, which can weaken the adsorption strength toward Li–O intermediates, decrease the reaction barrier, and thus improve the catalytic performance in Li–O₂ batteries. As a result, the battery using Cu–CoS₂ nanoparticles in the cathode exhibits superior kinetics, reversibility, capacity, and cycling performance, as compared to the battery based on CoS₂ catalyst. This work provides an atomic-level insight into the rational design of transition-metal dichalcogenide catalysts via regulating the electronic structure for high-performance Li–O₂ batteries.     

A microwave chaos generator with a flat envelope of the power spectrum in the range of 3–8 GHz

A promising type of ultrawideband (UWB) signals for communications and radar techniques operating in an unlicensed frequency range of 3.1–10.6 GHz, which has been actively developed in recent years, is offered by chaotic oscillations. We have designed and studied a chaotic oscillator with a uniform distribution of spectral power density in the range of 3–8 GHz. The possibility of using these oscillators in multiband UWB communication systems and noise generators for radio-engineering measurements is discussed.     

Structure of Mo2.0 – x Ni1.0 + x P (x = 0.2) and Some Crystal-Chemical Features of Ternary Phases in the Mo–Ni–P System

The crystal structure of Mo_{2.0 – x} Ni_{1.0 + x} P (x= 0.2) is determined by powder x-ray diffraction (monoclinic symmetry, new structure type, sp. gr. Im, a = 1.04036(5) nm, b= 0.84055(4) nm, c= 0.47357(2) nm, = 91.538(3)°; R _int = 0.094, R _prof = 0.197). The 850°C section of the Mo–Ni–P phase diagram is studied in detail, and the crystal-chemical features of molybdenum nickel phosphides are discussed.     

Structure and dielectric properties of a new series of pyrochlores in the Ca–Sm–Ti–M–O (M = Nb and Ta) system

The present work investigates the dielectric properties of pyrochlore type oxides, Ca–Sm–Ti–M–O (M = Nb and Ta) in the low frequency region (100 Hz–1 MHz) over the temperature range 30–100 °C. The 1 MHz dielectric constants (K) of these oxides are in the range 23–108 and show low variation with frequency (1 kHz–1 MHz). The temperature coefficient of dielectric constant (TCK) over the temperature range varies from positive to negative values in the range 48 to −107 ppm/°C. Rietveld analysis of the X-ray diffraction data establishes a cubic pyrochlore-type phase in the space group Fd3 m (no. 227).The grain morphology observation by scanning electron microscope shows well sintered grains.