Bragg reflection from space charge waves in a semiconductor waveguide

A dispersion relation for the space charge waves (SCWs) in a thin semiconductor layer with symmetric dielectric surrounding is obtained. The collinear waveguide SCW-optic interaction is analyzed for the zero-order (homogeneous) and first-order SCW modes. It is shown that effective Bragg reflection is possible on the SCW-optic TE and TM modes of various orders.     

Perfect tunneling of a structure containing a left-handed material layer

Tunneling of monochromatic radiation obliquely incident on a plane-layered structure is investigated. In the structure, a left-handed material layer (with a negative refractive index) is surrounded by layers with positive refractive indexes. Conditions for resonance amplification of evanescent waves that occurs simultaneously with perfect tunneling, i.e., reflection-free transmission of radiation through the plane-layered structure, are revealed.     

Negative effective refractive index in superconductor-ferromagnet superlattice

Tensors of the effective material parameters in a long-wavelength approximation are constructed and dispersion relations for the intrinsic TE and TM modes are obtained for a superlattice that comprises alternating layers of a high temperature superconductor and a ferromagnet. The control magnetic field is perpendicular to the direction of wave propagation and to the axis of periodicity of the superlattice. Based on the results of a numerical analysis performed for YBaCuO/U₃Fe₅O₁₂ superlattices, intervals of the frequency and field strength are found in which the effective refractive index for the intrinsic waves becomes negative. It is shown that high selective reflection or transmission of TE modes in a superlattice can be achieved by properly selecting the working frequency, external magnetic field, and relative thicknesses of layers in the system.     

Changes in the duodenal mucosa in Whipple's disease

A case of Whipple's disease is described in a male patient of 43 who has been previously examined in different hospitals for six years. The diagnosis was established after surgery and histological examination of the duodenum biopsy. Infiltration of the tunica propria of the duodenum with PAS-positive macrophages was observed. Therapy with rondomycin in combination with GUMET-P produced a response but the recurrence took place after therapy. A new operation was followed by peritonitis and pneumonia which terminated in the patient's death.     

The effect of a linear mode coupling dispersionon the wave packet dynamics in an optical waveguide with Kerr nonlinearity

The influence of a dispersion of the linear mode coupling coefficient of an optical waveguide (OWG) with Kerr nonlinearity on the dispersion parameters and dynamics of an optical pulse propagating in such a system is studied. In OWGs with a strong linear mode coupling, the presence of a dispersion of the mode coupling may lead to a significant decrease in the energy threshold for nonlinear self-compression of pulses as compared to the case of a single-mode OWG.     

Velocity regimes of a Gaussian pulse in an inhomogeneous nonlinear amplifying fiber-optic waveguide

The possibility of propagation of the maximum envelope of a narrowband frequency-modulated pulse at a supraluminal velocity in a nonlinear amplifying fiber-optic waveguide with parameters distributed along its length is analyzed. It is shown that Gaussian pulses can be accelerated to supraluminal velocities in the presence or absence of initial frequency modulation. Supraluminal-velocity regimes are considered in the case of a Lorentz amplification line for various types of the irregularity of the fiber-optic waveguide.     

Influence of the medium nonlinearity on the reflection of monochromatic and pulsed radiation

The features of Gaussian pulse reflection from a nonlinear medium with the resonance frequency dependence of permittivity are investigated. The results of numerical analysis of the equations describing the light-field distribution in reflected pulses with s and p polarizations are presented. The influence of the intensity, incidence angle, carrier frequency, and incident-pulse duration on the reflected pulse envelope shape is discussed.     

Strength improvement of iPP/MWCNT nanocomposites

The mechanisms of microhardness increase in thermoplastic polypropylene/multi‐walled carbon nanotubes (MWCNT) nanocomposites during electron irradiation (E_e = 1.8 MeV) with different absorption doses are investigated. The crystal structure of the nanocomposites, Raman scattering, and microhardness in a MWCNT concentration range between 0.1 and 5.0 wt% is studied in detail. During irradiation, changes in the degree of crystallinity of the polymer matrix, lattice parameters of the topologically ordered phase, Raman scattering, and microhardness show a complex conjugation process between the composite components. Their interaction is accomplished as the result of the formation of new bonds, which appeared with the radiation damages. Furthermore, the crosslinking of the internal MWCNT layers also contributes to an increase in the strength properties of the polymer nanocomposites. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

The refractive index sign chosen for amplifying and lossy metamaterials

Three definitions of a refractive index that differ in the meaning of its real part are considered for a homogeneous isotropic medium. The signs of wave characteristics (a refractive index and an impedance) are determined for sixteen possible combinations of the signs of the real and imaginary parts of the permittivity and permeability of a medium.