Microwave scattering diagrams of three-layered SiC-metamaterial/gyrotropic ferrite-SiC cylinders

We present here for the first time the rigorous solution of the boundary diffraction problem of microwave scattering by a multilayered 2D cylinder. The cylinder layers may be made of isotropic, uniaxial anisotropic, electrically and (or) magnetically gyrotropic materials. The number and thickness of the layers may have arbitrary values in our solution. We calculated scattering diagrams (a radial component of real part of the Poynting vector) inside and outside of cylinder using the solution. Here we present scattering diagrams from a three-layered cylinder made of SiC and metamaterial or saturate magnetized ferrite. Diagrams were computed for wave incidence angles θ=π/2,π/3,π/6 inside of metamaterial/ferrite layer at a distance of 1 mm and outside of cylinder at a distance of 2.5 mm from the cylinder axis.     

Scattering characteristics of structures of lossy metamaterial–semiconductor cylinders

Here, we present for the first time the rigorous boundary problem solution of the Maxwell’s equations for the determination of scattering characteristics of a structure. The structure consists of a finite set of infinite parallel circular cylinders that can be made of different lossy isotropic materials. We numerically analyzed two structures that differ only in the symmetrical arrangement of semiconductor cylinders in relation to a central metamaterial cylinder. The electrical radii of cylinders can be arbitrary. Both polarizations of the incident microwave are considered in this work. The Poynting vector of the plane microwave that reflected from and transmitted through the structures analyzed here. We investigated dependency on the radius of an arc where are placed the semiconductor cylinders, the semiconductor-specific resistivity, the operating frequency at two radii of the metamaterial cylinder. We discovered that the structure can have features of a band gap photonic crystal dependent on the topology and the polarization of the incident microwave. We have found that the structure can operate as a microwave reflector at the certain radius of the arc on which are located thirteen n-Si cylinders. The Poynting vector is very sensitive to the change of semiconductor-specific resistivity when the incident microwave has the parallel polarization.     

Phase interactions in TiN<Subscript>x</Subscript>(TiB<Subscript>x</Subscript>)-<Emphasis Type="Italic">n</Emphasis>-Si-<Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript>-Si contacts and their thermal degradation due to rapid thermal annealing

The temperature stability of TiN_x(TiB_x)-n-Si-n ⁺-Si, Au-TiN_x(TiB_x)-n-Si-n ⁺-Si, and Au-Ti(Mo)-TiN_x(TiB_x)-n-Si-n ⁺-Si Schottky-barrier contacts subjected to rapid thermal annealing in hydrogen at temperatures T=400, 600, and 800°C is studied. It is shown that structural and morphological transformations and the related degradation of electrophysical characteristics in interstitial alloys (titanium nitrides and borides) start at 600°C. Reasons for the degradation of the barrier properties of titanium borides and nitrides are discussed.     

The thermal–optical effect due to varying the angle of incidence used for designing a tunable filter in photonic crystals

Tunable devices based on photonic-crystal (PhC) structures are employed in optical sources, detectors, and filters. We present the design and optimization of a wavelength-selective tunable filter with potential applications to the wavelength-division-multiplexing (WDM) systems. We analyze the design of a 1D tunable photonic-crystal filter, where tunability is achieved either by changing the temperature or the angle of incidence. The device is designed in a multilayered structure of silicon/silica (Si/SiO₂) with a defect in the middle. Based on the induced variation of optical parameters introduced by an external change of temperature, we analyze the effects of these changes in temperature on the transmission of the optical filter at different angles of incidence. We show that the position of the resonance peak has a linear dependence on temperature and the square of the angle of incidence. A linear regression provides a slope of d??/dT?=?+0.06?nm/°C and d??/d?? ²?=??0.104?nm/degree² around the transmission wavelength ???=?1.55???m. We obtain the corresponding field patterns and the transmission spectra using the transfer-matrix-method (TMM) simulations. We show the ability to tune the optical properties of the photonic-crystal filter elaborated by changing two parameters: the angle of incidence for selecting the wavelength and the temperature for fine tuning of the wavelength, which can be applied in integrated optics.     

Properties of magnesium silicate doped with chromium in porous silicon

Forsterite doped with Cr⁴⁺ ions is prepared in silicon-based structures according to a simple technique. These structures are of interest due to the characteristic luminescence in the near-IR range. Forsterite is synthesized by impregnation of porous silicon layers on n⁺-Si and p⁺-Si substrates with subsequent annealing in air. A photoluminescence response at a wavelength of 1.15 μm is observed at room temperature in porous silicon layers doped with magnesium and chromium for which the optimum annealing temperature is close to 700°C. The photoluminescence spectrum of porous silicon on the p⁺-Si substrate contains a broad band at a wavelength of approximately 1.2 μm. This band does not depend on the annealing temperature and the magnesium and chromium content and is most likely associated with the presence of dislocations in silicon. The experimental EPR data and eletrical properties of the structures are discussed. It is found that layers of pure porous silicon and chromium-doped porous silicon on n⁺-Si subtructures exhibit indications of discrete electron tunneling.     

Magnetoresistivity in a tilted magnetic field in p-Si/SiGe/Si heterostructures with an anisotropic g-factor. Part II

The magnetoresistance components ??xx and ??xy are measured in two p-Si/SiGe/Si quantum wells that have an anisotropic g-factor in a tilted magnetic field as a function of the temperature, field, and tilt angle. Activation energy measurements demonstrate the existence of a ferromagnetic-paramagnetic (F-P) transition for the sample with the hole density p = 2 × 10¹¹ cm^?2. This transition is due to the crossing of the 0?? and 1?? Landau levels. However, in another sample with p = 7.2 × 10¹⁰ cm^?2, the 0?? and 1?? Landau levels coincide for angles ?? = 0?C70°. Only for ?? > 70° do the levels start to diverge which, in turn, results in the energy gap opening.     

Electrically stimulated movement of edge dislocations in silicon in the temperature range 300–450 K

The movement of edge dislocations and the related acoustic emission of Si (111) carrying a direct current of density 0.5?5×10⁵ A/m² in the [110] direction are studied in the temperature range T=300–450 K. It is shown that the basic mechanism of dislocation movement is the electric wind determining the magnitude of the effective charge (per atom of the dislocation line) Z _eff=0.06 (n-Si) and ?0.01 (p-Si). Matching theory with experimental data has made it possible to determine the main contribution of edge dislocations to the acoustic-emission response of the silicon samples under investigation. The characteristic transition frequencies of dislocations in n-and p-Si from one metastable state into another are found to be f _max=0.1–0.5 Hz. The numerical values of the diffusion coefficient for atoms in the dislocation impurity atmosphere are estimated as 3.2×10^?18 m²/s (n-Si) and 1.5×10^?18 m²/s (p-Si).     

Phase constant peculiarities of cylindrical zero-index anisotropic metamaterial waveguide

Here, we present the phase constant dependencies of propagating eigenmodes of an open cylindrical anisotropic metamaterial waveguide when the metamaterial permittivity and permeability tensor components may accept values close or equal to zero. Dispersion characteristics of rod and hollow-core waveguides with the radii 0.5, 2.5, and 5 mm at the left-handed polarization of the microwave are shown here. There are unusual shapes of eigenmode dispersion characteristics and anomalous sectors of the characteristics at certain frequencies. The first eigenmode of the rod waveguide with the lowest cutoff frequency is a particularly important mode because it is a single one in the frequency range 1.0?C1.9 GHz, and some small variations on the frequency produce large changes in the phase constant. We can observe packages of dispersion characteristic branches when their cutoff frequencies closed to the metamaterial electric and magnetic plasma frequencies between 1.9 and 3.5 GHz. There are only three modes in the hollow core anisotropic metamaterial waveguide at the frequency range 1.4?C2.8 GHz.     

Microwave response of octagon-shaped parallel plates: Low-loss metamaterial

A very low-loss metamaterial formed by a pair of homogeneous octagon-shaped parallel plates separated by a dielectric substrate is presented to achieve simultaneous negative permittivity and permeability in the microwave region. The double-negative behavior with a high figure of merit (FOM=|Re(n)/Im(n)|=80 at 24.7 GHz) leads to reduced losses in this proposed metamaterial. The high quality feature of the structure can make the applications of the negative refractive index metamaterial more efficient and applicable, such as perfect- or super-lenses at microwave frequencies since FOM≈64.5, where the real part of the refractive index ≈?1 at 25.3 GHz.     

New approach to analyzing and evaluating cross sections for partial photoneutron reactions

The presence of substantial systematic discrepancies between the results of different experiments devoted to determining cross sections for partial photoneutron reactions??first of all, (??, n), (??, 2n), and (??, 3n) reactions??is a strong motivation for studying the reliability and authenticity of these data and for developing methods for taking into account and removing the discrepancies in question. In order to solve the first problem, we introduce objective absolute criteria involving transitional photoneutron-multiplicity functions F ₁, F ₂, F ₃, ??; by definition, their values cannot exceed 1.0, 0.5, 0.33, ??, respectively. With the aim of solving the second problem, we propose a new experimental-theoretical approach. In this approach, reaction cross sections are evaluated by simultaneously employing experimental data on the cross section for the total photoneutron yield, ?? ^expt(??, xn) = ?? ^expt(??, n) + 2?? ^expt(??, 2n) + 3?? ^expt(??, 3n) + ??, which are free from drawbacks plaguing experimental methods for sorting neutrons in multiplicity, and the results obtained by calculating the functions F _theor ¹ , F _theor ² , F _theor ³ , ?? on the basis of the modern model of photonuclear reactions. The reliability and authenticity of data on the cross sections for (??, n), (??, 2n), and (??, 3n) partial reactions???? ^eval(??, in) = F _i ^theor ?? ^expt(??, xn)??were evaluated for the ⁹⁰Zr, ¹¹⁵In, ^{112,114,116,117,118,119,120,122,124}Sn, ¹⁵⁹Tb, and ¹⁹⁷Au nuclei.     

Resistive high-impedance surfaces (RHIS) as absorbers for oblique incidence electromagnetic waves

This paper presents a lightweight microwave absorber suitable for space applications. The absorber is based on a resistive high-impedance surface (RHIS) optimized to achieve reflection under ?15 dB in the band (2–2.3 GHz) at oblique incidence for transverse electric (TE) and transverse magnetic (TM) polarizations. A first classical isotropic RHIS structure is shown to be limited to angles of incidence up to 40° for TE polarized waves and up to 35° for TM polarized waves. So the objective of this contribution is to present a second solution based on an anisotropic RHIS structure which presents good absorption of incident waves in TE and TM polarizations for larger angles of incidence. An example is presented for an incidence angle of 65°.     

Pseudo volume plasmon in arrays of doped and un-doped semiconductors

We present a theoretical work which shows that for a metamaterial consisting of a periodic array of doped and un-doped semiconductors it is possible to define a frequency ?? _t corresponding to a pseudo volume plasmon. ?? _t?depends on the thicknesses and on the dielectric constants of the components of the metamaterial and on the plasma frequency of the doped semiconductor. As its homologue in noble metal, the pseudo volume plasmon is the collective oscillation of charges present in the metallic part of the metamaterial leading to a pure longitudinal electric wave. We show that ?? _t is the degeneracy frequency between the anti-symmetric mode in a transverse magnetic field and the mode in a transverse electric field. We demonstrate that this degeneracy is due to the periodicity of the structure, which transforms the imaginary solution of a metal?Cdielectric interface into a real solution in the case of the periodic metamaterial.     

Experimental Study of Space Star Anomaly in pd Breakup Around 10?MeV/A

Cross section of pd breakup at Star configuration (equilateral triangle) was systematically measured at E?=?9.5 and 13?MeV/A with varying an angle ?? between the Star plane and the beam axis. At 13?MeV/A, Star anomaly appears only around Space Star (?? =?90°) configuration. At 9.5?MeV/A, same feature was found in our experimental data at ?? =?0°?105°, but large difference of about ?25% at ???=?124°?180° was reported by K?ln group.     

Measurement of 232Th(n, γ) and 232Th({n}, {2n}) cross-sections at neutron energies of 13.5, 15.5 and 17.28?MeV using neutron activation techniques

The ²³²Th(n, ??) reaction cross-section at average neutron energies of 13.5, 15.5 and 17.28?MeV from the ⁷Li(p, n) reaction has been determined for the first time using activation and off-line ??-ray spectrometric technique. The ²³²Th(n, 2n) cross-section at 17.28?MeV neutron energy has also been determined using the same technique. The experimentally determined ²³²Th(n, ??) and ²³²Th(n, 2n) reaction cross-sections from the present work were compared with the evaluated data of ENDF/BVII and JENDL-4.0 and were found to be in good agreement. The present data, along with literature data in a wide range of neutron energies, were interpreted in terms of competition between ²³²Th(n, ??), (n, f), (n, nf) and (n, xn) reaction channels. The ²³²Th(n, ??) and ²³²Th(n, 2n) reaction cross-sections were also calculated theoretically using the TALYS 1.2 computer code and were found to be in good agreement with the experimental data from the present work but were slightly higher than the literature data at lower neutron energies.     

The structure of a stepped copper (410) surface determined by ion scattering spectroscopy

Ion Scattering Spectroscopy applied in the multiple scattering mode is used to determine the structure of a stepped Cu(410) surface. The energy of singly scattered ions is influenced by the presence of neighbour surface atoms. This effect can be used to determine interatomic distances up to about 10Å, as is shown by the results of 8 keV Ar⁺ and 11 keV Ne⁺ scattered through θ = 50°. The edge-edge distance of the stepped copper surface appears to be in accordance with the results of LEED experiments obtained by other investigators. The experiments show a good agreement with the results of the analytical 3-atom model of Poelsema. The energy of the so-called “plateau collision” appears to depend on the effective plateau length l as measured in the plane of incidence. Lengths l between 15 and 60 Å can be determined with an accuracy of 5 Å. Results are shown for 8 and 12 keV Ar⁺, θ = 40° and 60°, and 8 keV Kr⁺ θ = 40°. The experimental dependence of the energy on lis described correctly by a phenomenological model.     

On Multiple Scattering of Radiation by an Infinite Grating of Dielectric Circular Cylinders at Oblique Incidence

A rigorous analytical representation for the multiple scattering coefficients of the fields radiated by an infinite grating of dielectric circular cylinders excited by an obliquely incident plane electromagnetic wave is derived in terms of the “well-known scattering coefficients of an isolated dielectric cylinder at oblique incidence” and “Schl?milch series”. In addition, a generalized sum-integral grating equation is acquired for the multiple scattered amplitude of a cylinder at oblique incidence in the grating in terms of the scattering coefficients of the insulating dielectric circular cylinder at oblique incidence.      

9 Be Low-Lying Spectrum Within a Three-Cluster Model

The energy spectrum of ⁹Be is studied within the cluster model ???+ ???+?n. Configuration space Faddeev equations are applied to calculate energies of the bound state and resonances. LS coupling is used for partial wave analysis. The ⁹Be low-lying levels are classified as members of spin-flip doublets, in compliance with the total orbital momentum of the ???+????+?n system. The ⁹Be spectral data are well reproduced by the proposed model.     

Messung der Neutronenpolarisation bei der Reaktion12C(d,n 0)13N mit Hilfe der Mott-Schwinger-Streuung

The polarization of neutrons produced in the reaction¹²C(d, n ⁰)¹³N was measured. Deuterons from the Karlsruhe isochronous cyclotron were used to induce this reaction at 51,5 MeV laboratory energy. The degree of polarization was determined by using the special features of Mott-Schwinger scattering. With an uranium scatterer analysing efficiencies of up to 0.92 can be obtained at very small angles (0.23°). The analysing efficiency can be calculated if the differential cross section at 0° and the total cross section is known. These quantities were experimentally determined. The differential cross section for 49.4 MeV neutrons, scattered by uranium, was measured between 0.88° and 2.10°. By an extrapolation the value 43.4±2.6 b/sr was found for the nuclear differential cross section at zero degree. A total cross section ofσ _t=4.80±0.22 b was obtained. The neutron polarization was measured at a reaction angle of 24.5° and the result isP=?0.45±0.07. This value is fairly above the semiclassical 1/3 limit and can be only explained, if spin orbit forces are taken into account. For (d, n) reactions this is the first neutron-polarization measurement above an energy of 20 MeV.     

Glauber Dynamics for the Mean-Field Potts Model

We study Glauber dynamics for the mean-field (Curie-Weiss) Potts model with q??3 states and show that it undergoes a critical slowdown at an inverse-temperature ?? _s (q) strictly lower than the critical ?? _c (q) for uniqueness of the thermodynamic limit. The dynamical critical ?? _s (q) is the spinodal point marking the onset of metastability. We prove that when ??<?? _s (q) the mixing time is asymptotically C(??,q)nlogn and the dynamics exhibits the cutoff phenomena, a sharp transition in mixing, with a window of order n. At ??=?? _s (q) the dynamics no longer exhibits cutoff and its mixing obeys a power-law of order n ^4/3. For ??>?? _s (q) the mixing time is exponentially large in n. Furthermore, as ?????? _s with n, the mixing time interpolates smoothly from subcritical to critical behavior, with the latter reached at a scaling window of O(n ^?2/3) around ?? _s . These results form the first complete analysis of mixing around the critical dynamical temperature??including the critical power law??for a model with a first order phase transition.     

Experimental proof of mirror instabilities in the Isar I theta pinch

In the Isar I linear theta pinchm=0 instabilities were observed and experimentally investigated. The variation of the plasma parameters over a wide range (τ _ii =10^?2... 10²μsec) showed that them=0 instabilities only occurred in sufficiently hot and thin plasmas, and so they are most probably due to the anisotropic pressure of the ions and should be mirror instabilities. Perturbations of the plasma limited in space and time were observed by measuring the continuum radiation, by 90 ° laser scattering measurements and by measuring the magnetic field and the local neutron rate. All measurements showed distinct, correlated, local perturbations of the plasma cylinder. These perturbations were accompanied by bulging of the plasma cylinder and increasing density. The extent in the axial direction was of the order of the plasma diameter. It may be assumed that the observed instabilities contribute appreciably to relaxation of the anisotropic ion pressure and increase the end losses.