Double-cone Structure Research Articles

Absorptive characteristics of GaInAsSb tip-wedge nanopillar arrays structure for infrared detector

GaInAsSb has important application value in the field of infrared optoelectronics. In this paper, the optical properties of Ga0.84In0.16As0.14Sb0.86 nanopillar array with different tip-wedge structures are studied by using the method of finite-difference time-domain (FDTD). The simulation results show that a single tip-wedge structure cannot achieve the enhanced absorption with absorptance of more than 90 %, while the tip-wedge combination structure can effectively improve the absorptance of the nanostructure, and the absorptance of nanostructures reaches more than 97 % when the cone to column height ratio is 0.47 and the period is 500 nm. In addition, the double-cone structure can also effectively improve the absorption characteristics of the nanostructures. When the tip-wedge nanostructures have a high duty cycle, the absorption rate of the array structure can reach 93 %, which provides a theoretical basis for the preparation of high-density optical devices and reducing the difficulty of the preparation process.

A study on acoustically modulated bunsen flame and its impingement heat transfer

This study experimentally examines acoustic-field-flame-interaction by using a low-power loudspeaker to actuate the oscillation of a Bunsen flame. It is observed that under acoustic forcing, the flow dynamics are altered, different patterns of the flame front are triggered, and both flame temperature field and heat transfer characteristics are changed. Moreover, impingement heat transfer is found to be increased when the flame is under acoustic modulation, indicating that acoustics can be used to promote heat transfer for flame impingement heating applications. There is a threshold forcing frequency of 300 Hz, beyond which no interaction between the sound and flame exists. The response of the flame to acoustic excitation exhibits a double-cone structure to naked eyes, and is found to be convectively bubbling, wrinkling and shrinking flame front under high-speed photography. The oscillating flame front height has exactly the same frequency as the sound, but the waveform is non-sinusoidal. Both symmetric and asymmetric distorted flame fronts are observed, with the former occurring at low frequencies while the latter at relatively higher frequencies. The effect of acoustic field on the thermal field is to lower the high-temperature region of the flame. Therefore, the cool core in the centre is narrowed, leading to higher local heat transfer. A ten percent increase in total heat transfer rate is obtained when the optimum nozzle-to-plate distance is coupled with the most effective forcing frequency of 50 Hz. Therefore, acoustic modulation is a feasible technique for promoting heat transfer. • 1st study on promoting effect of acoustics on Bunsen flame heat transfer. • Both amplitude and frequency of the sound changes the shape of flame front. • Response of flame front to acoustics is similar to a turbulent one, broadening the space of heat release. • Broader space of higher temperature and heat release leads to higher heat transfer rate and efficiency.

Microstructure and energy dispersive diffraction reconstruction of 3D patterns of crystallographic texture in a shark centrum.

Purpose: Tomography using diffracted x-rays produces reconstructions mapping quantities such as crystal lattice parameter(s), crystallite size, and crystallographic texture, information quite different from that obtained with absorption or phase contrast. Diffraction tomography is used to map an entire blue shark centrum with its double cone structure (corpora calcerea) and intermedialia (four wedges). Approach: Energy dispersive diffraction (EDD) and polychromatic synchrotron x-radiation at 6-BM-B, the Advanced Photon Source, were used. Different, properly oriented Bragg planes diffract different x-ray energies; these intensities are measured by one of ten energy-sensitive detectors. A pencil beam defines the irradiated volume, and a collimator before each energy-sensitive detector selects which portion of the irradiated column is sampled at any one time. Translating the specimen along , and axes produces a 3D map. Results: We report 3D maps of the integrated intensity of several bioapatite reflections from the mineralized cartilage centrum of a blue shark. The axis reflection's integrated intensities and those of a reflection with no axis component reveal that the cone wall's bioapatite is oriented with its axes lateral, i.e., perpendicular to the backbone's axis, and that the wedges' bioapatite is oriented with its axes axial. Absorption microcomputed tomography (laboratory and synchrotron) and x-ray excited x-ray fluorescence maps provide higher resolution views. Conclusion: The bioapatite in the cone walls and wedges is oriented to resist lateral and axial deflections, respectively. Mineralized tissue samples can be mapped in 3D with EDD tomography and subsequently studied by destructive methods.

Geometry of catenoidal soap film collapse induced by boundary deformation.

Experimental and theoretical work reported here on the collapse of catenoidal soap films of various viscosities reveal the existence of a robust geometric feature that appears not to have been analyzed previously; prior to the ultimate pinchoff event on the central axis, which is associated with the formation of a well-studied local double-cone structure folded back on itself, the film transiently consists of two acute-angle cones connected to the supporting rings, joined by a central quasicylindrical region. As the cylindrical region becomes unstable and pinches, the opening angle of those cones is found to be universal, independent of film viscosity. Moreover, that same opening angle at pinching is found when the transition occurs in a hemicatenoid bounded by a surface. The approach to the conical structure is found to obey classical Keller-Miksis scaling of the minimum radius as a function of time, down to very small but finite radii. While there is a large body of work on the detailed structure of the singularities associated with ultimate pinchoff events, these large-scale features have not been addressed. Here we study these geometrical aspects of film collapse by several distinct approaches, including a systematic analysis of the linear and weakly nonlinear dynamics in the neighborhood of the saddle node bifurcation leading to collapse, both within mean curvature flow and the physically realistic Euler flow associated with the incompressible dynamics of the surrounding air. These analyses are used to show how much of the geometry of collapsing catenoids is accurately captured by a few active modes triggered by boundary deformation. A separate analysis based on a mathematical sequence of shapes progressing from the critical catenoid towards the Goldschmidt solution is shown to predict accurately the cone angle at pinching. We suggest that the approach to the conical structures can be viewed as passage close to an unstable fixed point of conical similarity solutions. The overall analysis provides the basis for the systematic study of more complex problems of surface instabilities triggered by deformations of the supporting boundaries.

Research on energy-absorption and failure of carbon fiber reinforced epoxy resins double cone structure

One of the research hotspot in strategic missile is to develop a multifunctional and lightweight composite launcher, which has a certain bearing capacity and anti-fragment penetration capability. On this basis, this paper designs the launcher’s wall by using carbon fiber reinforced epoxy resin composite double cone structure (CFREPDCS) as sandwich core layer. Due to obtain the high-speed impact energy-absorption and failure characteristic of the CFREPDCS, the quasi-static collapse experiment and the LS-DYNA finite element simulation were used. The experimental results and the scanning electron microscope show that the failure mode of the carbon fiber reinforced epoxy resin composite (CFREP) circular tube is progressive failure, which includes matrix fragmentation and fiber fracture. The CFREP circular tube with larger wall thickness has higher specific energy-absorption (SEA), approximately 58.6 J/g. The coupled relationship between SEA and mid-diameter height shows that the maximum SEA occurs while mid-diameter height reaches 8 mm. On the other hand, the change of the mid-diameter height also reflects the influence of loading direction on SEA. This study provides the significant guide to design and manufacture of sandwich carbon fiber composite launcher.

Emergence of Nontrivial Low-Energy Dirac Fermions in Antiferromagnetic EuCd2 As2.

Parity-time symmetry plays an essential role for the formation of Dirac states in Dirac semimetals. So far, all of the experimentally identified topologically nontrivial Dirac semimetals (DSMs) possess both parity and time reversal symmetry. The realization of magnetic topological DSMs remains a major issue in topological material research. Here, combining angle-resolved photoemission spectroscopy with density functional theory calculations, it is ascertained that band inversion induces a topologically nontrivial ground state in EuCd2 As2 . As a result, ideal magnetic Dirac fermions with simplest double cone structure near the Fermi level emerge in the antiferromagnetic (AFM) phase. The magnetic order breaks time reversal symmetry, but preserves inversion symmetry. The double degeneracy of the Dirac bands is protected by a combination of inversion, time-reversal, and an additional translation operation. Moreover, the calculations show that a deviation of the magnetic moments from the c-axis leads to the breaking of C3 rotation symmetry, and thus, a small bandgap opens at the Dirac point in the bulk. In this case, the system hosts a novel state containing three different types of topological insulator: axion insulator, AFM topological crystalline insulator (TCI), and higher order topological insulator. The results provide an enlarged platform for the quest of topological Dirac fermions in a magnetic system.

Phononic band structure and figure of merit of three-dimensional anisotropic asymmetric double-cone pentamode metamaterials

<sec> Pentamode metamaterial (PM) is a kind of artificial microstructure extremum material with solid morphology and fluid properties proposed by Milton and Cherkaey. By decoupling the compression and the shear waves, the periodic structure is difficult to be compressed, but the shear deformation occurs easily. Theoretically, acoustic metamaterials consisting of such periodic arrangement of structural units can achieve complete matching with water. Therefore, the characteristics of adjustable modulus anisotropy, small stuffing rate and broadband endow the PMs with excellent acoustic control ability, which has attracted more attention of researchers.</sec><sec> In this paper, the narrow-diameter intersection point <i>P</i> (0.25<i>a</i>, 0.25<i>a</i>, 0.25<i>a</i>) of an isotropic three-dimensional PM selected as the reference point in four different directions (X-axis, Y-axis, Z-axis and body diagonal). When the <i>P</i>-point moves, the farther the <i>P</i>-point is, the greater the degree of anisotropy is. The introduction of anisotropy will cause the structural bifurcation of the three-dimensional PM to change structural parameters, and the structural parameters are important factors affecting the band characteristics of the three-dimensional PM of Bragg scattering. In order to study the influence of anisotropy on the band structure and pentamode properties of three-dimensional asymmetric double-cone PMs, we use the finite element simulation software COMSOL to calculate the primitive-cell of three-dimensional anisotropic PMs under Bloch boundary conditions. </sec><sec> By adjusting the position of <i>P</i> point, four different types of three-dimensional anisotropic asymmetric double-cone PMs are constructed. Since the anisotropy changes in different directions have different effects on the parameters of the asymmetric double-cone structure, the band characteristics and the pentamode characteristics will also receive different degrees of influence. In this paper, the relationship between the degree of anisotropy and the band gap characteristics, single-mode region and figure of merit (FOM) are given, and the result can provide guidance for the design of asymmetric double-cone PM acoustic device. Compared with the isotropic double-cone PMs, the relative bandwidth of the first band gap of the anisotropic double-cone PMs can be broadened to 123%, and the FOM can be increased to 6.9 times. Due to the introduction of anisotropy, Due to the introduction of anisotropy, the structure of three-dimensional asymmetric double-cone PMs are more complex, the demand for sample fabrication is further improved, and the stability of PMs also reduced. Therefore, PMs with high stability and easy to be fabricated still needs further research and exploration.</sec>

Design of Prussian blue analogue-derived double-cone structure Ce–Fe catalysts and their enhanced performance for the selective catalytic reduction of NOx with NH3

Prussian blue (PB) and its analogues (PBA) with different structures and adjustable compositions have been recognized as promising materials for catalysis, energy storage, and biological applications.

Functional and Basis Set Dependence for Time-Dependent Density Functional Theory Trajectory Surface Hopping Molecular Dynamics: Cis-Azobenzene Photoisomerization.

Within three functionals (TD-B3LYP, TD-BHandHLYP, and TD-CAM-B3LYP) in combination with four basis sets (3-21g, 6-31g, 6-31g(d), and cc-pvdz), global switching (GS) trajectory surface hopping molecular dynamics has been performed for cis-to-trans azobenzene photoisomerization up to the S1 (nπ*) excitation. Although all the combinations show artificial double-cone structure of conical intersection between ground and first excited states, simulated quantum yields and lifetimes are in good agreement with one another; 0.6 (±5%) and 40.5 fs (±10%) by TD-B3LYP, 0.5 (±10%) and 35.5 fs (±4%) by TD-BHandHLYP, and 0.44 (±9%) and 35.2 fs (±10%) by TD-CAM-B3LYP. By analyzing distributions of excited-state population decays, hopping spots, and typical trajectories with performance of 12 functional/basis set combinations, it has been concluded that functional dependence for given basis set is slightly more sensitive than basis set dependence for given functional. The present GS on-the-fly time-dependent density functional theory (TDDFT) trajectory surface hopping simulation can provide practical benchmark guidelines for conical intersection driven excited-state molecular dynamics simulation involving in large complex system within ordinary TDDFT framework. © 2019 Wiley Periodicals, Inc.

QX factorization of centrosymmetric matrices

We show how the factorization A=QX, introduced in Burnik (2015) [2], of a real centrosymmetric m×n matrix A into a centrosymmetric orthogonal m×m matrix Q and a centrosymmetric m×n matrix X with a double-cone structure can be directly obtained via standard QR factorizations of two matrices about half the size of A. Examples and a Matlab code are included.

Performance of TDDFT with and without spin-flip in trajectory surface hopping dynamics: cis–trans azobenzene photoisomerization

Time-dependent density functional theory (TDDFT) with and without a spin-flip scheme is extensively compared in on-the-fly trajectory surface hopping molecular dynamics with a global switching (GS) algorithm. The simulation is performed for cis-trans azobenzene photoisomerization following the excitation to the S1(nπ*) state that is involved in a conical intersection (CI) between ground and first excited states. This CI is found correctly to be a single-cone (artificial double-cone) structure computed by the TDDFT method with (and without) spin-flip. Nevertheless, simulated quantum yields and lifetimes are in very good agreement; 0.43 and 63 fs (0.34 and 62 fs) for cis-to-trans isomerization, and 0.11 and 2200 fs (0.13 and 1040 fs) for trans-to-cis isomerization, by TDDFT with (and without) a spin-flip scheme. Distributions of excited-state decay, hopping spots and products, as well as typical trajectories have similar patterns and behaviors with and without spin-flip. The global switching trajectory surface hopping method is demonstrated to be well suited to TDDFT on-the-fly dynamic simulation with and without spin-flip. For comparison, previous simulations with the CASSCF method and Tully's fewest-switches trajectory surface hopping method are also addressed.

Microwave Synthesis and Photoluminescence Properties of BaWO<sub>4</sub> of Homogeneous Double Cone Structure

Barium tungstate of homogeneous double cone structure was synthesized by microwave synthesis method with sodium tungstate, barium nitrate as raw materials, polyethylene glycol (PEG2000) as surfactant. The as-prepared sample was characterized by X-ray diffraction (XRD), scanning electron micrograph (SEM) and photoluminescence spectrum (PL). The XRD Pattern showed that the samples are scheelite structure of BaWO4. The SEM image showed that the majority of as-prepared sample is a double cone structure, and some particles are attached to it. The length of most of the double cone is 10 μm. PL spectra showed that as-prepared sample had strong luminescence properties, and it had purity green emission at 495 nm and 521 nm. The effects of different surface active agent on the luminescence properties were studied. The results showed that when PEG2000 is as surfactant, the luminescence intensity of as-prepared sample was maximum.

Double transverse wave-vector correlations in photon pairs generated by spontaneous parametric down-conversion pumped by Bessel-Gauss beams

We present an experimental and theoretical study of type I, frequency-degenerate spontaneous parametric down-conversion (SPDC) with a Bessel-Gauss pump in which we include both paraxial and nonparaxial pump beam configurations. We present measurements of the SPDC angular spectrum (AS), of the conditional angular spectrum (CAS) of signal-mode single photons as heralded by the detection of an idler photon, and of the transverse wave-vector signal-idler correlations (TWC). We show that as the pump is made increasingly nonparaxial, the AS acquires a nonconcentric double-cone structure, with the CAS shape depending on the azimuthal location of the heralding detector, while the signal-idler wave-vector correlation region splits into characteristic doublet stripes, representing as yet unexplored nontrivial, nonlocal quantum correlations between the signal and idler photons. Our work provides further understanding of SPDC with a particular class of structured pump beams, and we believe that the controlled presence of double wave-vector correlations represents an interesting resource for photon-pair quantum-state engineering.

Laser-driven high-energy-density deuterium and tritium ions for neutron production in a double-cone configuration

By using two-dimensional particle-in-cell simulations, we investigate laser-driven ion acceleration and compression from a thin DT foil in a double-cone configuration. By using two counterpropagating laser pulses, it is shown that a double-cone structure can effectively guide, focus, and strengthen the incident laser pulses, resulting in the enhanced acceleration and compression of D+ and T+. Due to the ion Coulomb repulsion and the effective screening from the external laser electric fields, the transverse diffusion of ions is significantly suppressed. Finally, the peak energy density of the compressed ions exceeds 2.73 × 1016 J/m3, which is about five orders of magnitude higher than the threshold for high energy density physics, 1011 J/m3. Under this condition, DT fusion reactions are initiated and the neutron production rate per volume is estimated to be as high as 7.473 × 1035/m3 s according to Monte Carlo simulations. It is much higher than that of the traditional large neutron sources, which may facilitate many potential applications.

Large and bistable Goos–Hänchen shifts from the Kretschmann configuration with a nonlinear negative–zero–positive index metamaterial

Motivated by the realization of the Dirac point (DP) with a double-cone structure for the optical field in a negative–zero–positive index metamaterial (NZPIM), we perform a theoretical investigation on the reflected light beam from the Kretschmann configuration containing an NZPIM with Kerr-type nonlinearity. Near the DP and the optimal thickness, it is found that the peak values of the Goos–Hänchen (GH) shifts can vary from negative to positive. The peak value and position are strongly dependent on the incident angle, frequency, and the thickness of the metal film. It is also found that the peak values can be greatly enhanced near the optimal thickness and the DP. We further demonstrate that there exist large and bistable shifts, which are more sensitive to variations of the incident angle and the thickness of the metal film. These results may lead to potential applications in integrated optics and optical-based devices, and also suggest analogous optical phenomena of valence electrons in graphene.

Capillary instability of a viscous liquid thread in a cylindrical tube

We study axisymmetric breakup and drop formation of a liquid thread confined in a cylindrical tube by using a long wave model. The limit with large viscosity contrast is investigated, consisting of a highly viscous core and a less viscous annulus. Satellite drop formation near pinching is found to be dependent on the location of the tube wall, while inertia is found to have little effect. It is also shown that main drops tend to form so called “plug with collar” structures when the tube wall is close to the thread interface so that rings of fluid are trapped inside the plugs. Finally, our numerical simulations show that a double cone structure occurs on the breakup and the cone angles are fixed, even though self-similar solutions may not exist.

Lateral shifts and photon tunneling in a frustrated total internal reflection structure with a negative-zero-positive index metamaterial

Motivated by the realization of the Dirac point (DP) with a double-cone structure for optical field in the negative-zero-positive index metamaterial (NZPIM), the lateral shift and tunneling time of photon tunneling through a frustrated total internal reflection structure containing a NZPIM barrier are investigated by employing Artman's stationary phase method. Near the DP, the lateral shift can vary from positive to negative and the photon tunneling displays a superluminal dynamic. Because of the Hartman effect, both lateral shift and tunneling time tend to a saturation value when the barrier thickness increases. These results may lead to potential applications in integral optics and optical-based devices and also suggest analogous phenomena of valance electron in single-layered carbon graphene.

The role of cadmium(II) bridges in the self-assembly with lanthanide(III) and thiacalix[4]arene (TCAS) to selectively form a luminescent ternary CdII2·TbIII2·TCAS2 complex

The ability of metal ions to self-assemble to form luminescent ternary complexes with TbIII and thiacalix[4]arene-p-tetrasulfonate (TCAS) was investigated, as exemplified by AgI in AgI2·TbIII2·TCAS2 and AgI2·TbIII·TCAS2 at pH 6.5 and 10, respectively. Among FeIII, NiII, ZnII, PdII, CdII, HgII, TlI, and PbII metals, only CdII resulted in more intense luminescence than a TbIII–TCAS binary system, which occurs at pH values of ∼6.5 and suggests the formation of a ternary complex. Determination of the molar ratio and electrospray-ionization mass spectrometry results revealed that the species formed at pH 6.5 was CdII2·TbIII2·TCAS2. Analogous to the solid-state structure of AgI2·TbIII2·TCAS2, CdII2·TbIII2·TCAS2 should also adopt a double-cone structure with the cyclic tetrametal CdII–CdII–TbIII–TbIII core sandwiched by two cone-shaped TCAS ligands that are connected by two S–CdII–S linkages at the two adjacent S atoms in TCAS. However, the CdII system did not form a ternary complex like AgI2·TbIII·TCAS2 at higher pH values; this is because the S–CdII–S linkages are shorter than S–AgI–S, which brings the two TCAS ligands closer together and ejects TbIII. In aqueous solutions CdII2·TbIII2·TCAS2 exhibited the following photophysical properties: a luminescence quantum yield (Φ) of 0.15 and lifetime (τ) of 1.12ms; these values are very close to those obtained for AgI2·TbIII2·TCAS2. The number of water molecules coordinated to TbIII was determined to be 2.2, which is identical to the number coordinated to TbIII in AgI2·TbIII2·TCAS2. Together, these results elucidate the structural similarities of CdII2·TbIII2·TCAS2 and AgI2·TbIII2·TCAS2. Other LnIII species (i.e., NdIII and YbIII) also afforded ternary complexes with the same stoichiometry, which shows that it is the CdII bridges that restrict the self-assembly to CdII2·LnIII2·TCAS2.

2A2-F08 海底に設置する地震津波センサ用潮流発電機の開発 : 流速増大効果を持つ二重円錐形シュラウドの提案(水中ロボット・メカトロニクス(1))

It is required to construct network of monitoring equipment which measures seismic waves and tsunami to coastal sea area around Japan. In this study, it is proposed to supply electricity to the equipment by tidal power generator. The tidal power generator is moored and suspended in water current like a "streamer" and it generates electricity by rotation of propeller. In order to accelerate current around propeller, a broadened cylinder called "Shroud" is attached to the generator. A new type of shroud "double-cone structure" is designed according to the result of fluid analysis and it achieves high current acceleration. The validity of those propositions is verified by experiment in water.

Nonlinear surface waves near the Dirac point in negative–zero–positive indexmetamaterial

Motivated by the realization of the Dirac point (DP) with a double-cone structure for theoptical field in a negative–zero–positive index metamaterial (NZPIM), we study thenonlinear surface waves localized at the single interface separating a nonlinearconventional dielectric medium and a NZPIM. It is found that, near the DP, thereis a forbidden band for the nonlinear surface waves and the nonlinear surfacewaves also have a frequency threshold. In contrast to the negative permeability ofNZPIM in some frequency regions, we show that the nonlinear surface waves arealways forward with positive power fluxes. The frequency property, the groupvelocity and the power flux of the surface waves are also discussed in detail. Theseresults may have potential applications in guided wave optics and optical devices.