Effect of the open roof on low frequency acoustic propagation in street canyons

This paper presents an experimental, numerical and analytical study of the open roof effect on acoustic propagation along a 3D urban canyon. The experimental study is led by means of a street scale model. The numerical results are performed with a 2D-Finite Difference in Time Domain approach adapted to take into account the acoustic radiation losses due to the street open roof. An analytical model, based on the modal decomposition of the pressure field in the street width mixed with a 2D image sources model including the reflection by the open roof, is also presented. Results are given for several frequencies in the low frequency domain. The comparison of these approaches shows a quite good agreement until f = 100 Hz at full scale. For higher frequency, experimental results show that the leakage, due to the street open roof, is not anymore uniformly distributed on all modes of the street. The notion of leaky modes must be introduced to model the acoustic propagation in a street canyon.     

Comparative study between dispersive and non-dispersive dielectric permittivity in spectral remittances of chiral sculptured zirconia thin films

The transmission and reflection spectra from a right-handed chiral sculptured zirconia thin film are calculated using the piecewise homogeneity approximation method and the Bruggeman homogenization formalism using both dispersive and non-dispersive functions for axial and non-axial states. The comparison of spectral results shows that the dispersion of the dielectric function has a considerable effect on the results. In axial excitation of cross-polarized reflectances and co-polarized transmittances the dispersion effect becomes more pronounced at wavelengths further away from the homogenization wavelength. This is also true in the case of non-axial excitation of circular transmittances, while there are considerable differences for cross-polarized reflectances where (wavelength) the first Bragg peak occurs. At wavelengths in the vicinity of the homogenization wavelength the dispersion effect of the dielectric function in R_RR becomes more significant.     

The physical parameterization of the top-of-atmosphere reflection function for a cloudy atmosphere—underlying surface system: the oxygen A-band case study

The paper is devoted to the physical parameterization of the top-of-atmosphere reflection function. The accuracy of the parameterization is checked against exact radiative transfer calculations in a cloudy atmosphere for various cloud-top-heights, cloud optical and geometrical thicknesses, solar illumination and surface reflection conditions. It was found that the error of approximation is smaller than 5% for most cases studied at the wavelength interval , which corresponds to the oxygen A-band. This band is routinely used in cloud-top-height retrievals. The model proposed can be used for cloud-top-height and cloud geometrical thickness retrievals. This allows to avoid a standard look-up-table retrieval scheme, involving complex numerical procedures.     

Solution of the equation of radiative transfer for interlocked doublets by double interval spherical harmonic method

The double-ordinate spherical harmonic method presented by Wilson and Sen (Publ. Astron. Soc. Jpn. 15 (1963) 351) has been used to solve the equation of radiative transfer in the Milne-Eddington model for interlocked doublets. Solutions have been obtained in the first and second approximation in a particular case η₁=1; .     

Corrections to the classical continuity boundary conditions at the interface of a composite medium

Using the multiple-scales homogenization method, we derive generalized sheet transition conditions (GSTCs) for electromagnetic fields at the interface between two media, one of which is free-space and the other a certain type of composite material. The parameters in these new boundary conditions are interpreted as effective electric and magnetic surface susceptibilities, which themselves are related to the geometry of the scatterers that constitute the composite. We show that the effective tangential E and H fields are not continuous across the interface except in the limit when the lattice constant (the spacing between the scatterers—atoms, molecules or inclusions in the case of a composite material) of the composite medium is very small compared to a wavelength. We derive first-order corrections to the classical continuity conditions. For naturally occurring materials whose lattice constants are on an atomic scale, these effects are shown to be negligible for waves at optical frequencies or lower. However, once the lattice constant becomes a significant fraction of a wavelength (which is the case for many artificial dielectrics and metamaterials), the corrections can be important. In previous work we have alluded to the fact that such a GSTC is needed to correctly account for the surface effects when extracting the effective material properties of a metamaterial. The results of this current paper justify the assumptions made in that previous work. In general, these GSTCs will result in corrections to the classical Fresnel reflection and transmission coefficients (which are themselves merely zeroth-order approximations to the actual reflection and transmission coefficients), and in a separate publication we will use these GSTCs to address this issue.     

Investigation of the decay η′ → 3 π 0 with the GAMS-4π spectrometer

An experiment performed with the GAMS-4π spectrometer resulted in observing 235 ± 45 events of the decay η′ → 3π ⁰. The respective charge-exchange reaction at a momentum of 32.5 GeV/c was used as a source of η′ mesons. The decay branching ratio was found to be Br(η′ → 3π ⁰) = (1.8 ± 0.4) × 10^?3. The slope parameter of the square of the respective matrix element in the linear approximation proved to be β = ?0.59 ± 0.18.     

Controlling subluminal to superluminal behavior of group velocity in an f-deformed Bose-Einstein condensate beyond the rotating wave approximation

In this paper, we investigate tunable control of the group velocity of a weak probe field propagating through an f-deformed Bose-Einstein condensate of Λ-type three-level atoms beyond the rotating wave approximation. For this purpose, we use an f-deformed generalization of an effective two-level quantum model of the three-level Λ-configuration without the rotating wave approximation in which the Gardiner’s phonon operators for Bose-Einstein condensate are deformed by an operator-valued function, , of the particle-number operator . We consider the collisions between the atoms as a special kind of f-deformation where the collision rate κ is regarded as the deformation parameter. We demonstrate the enhanced effect of subluminal and superluminal propagation based on electromagnetically induced transparency and electromagnetically induced absorption, respectively. In particular, we find that (i) the absorptive and dispersive properties of the deformed condensate can be controlled effectively in the absence of the rotating wave approximation by changing the deformation parameter κ, the total number of atoms and the counter-rotating terms parameter λ, (ii) by increasing the values of λ, κ and η = 1/N, the group velocity of the probe pulse changes, from subluminal to superluminal and (iii) beyond the rotating wave approximation, the subluminal and superluminal behaviors of the probe field are enhanced.     

A tunable infrared plasmonic polarization filter with asymmetrical cross resonator

A tunable infrared plasmonic polarization filter is proposed and investigated in this paper. The filter is based on the sandwich absorption structure which consists of three layers. The top layer is an array of asymmetrical cross resonator.The middle and bottom layers are dielectric spacer and metal film respectively. By absorbing specific wavelength of the incident light perfectly, the reflection spectrum of the structure shows filter performance. The calculated results show that the absorption wavelength is strongly dependent on the length of branch of the asymmetrical cross resonator which is parallel to the light polarization and independent of the length of the vertical one. Therefore, the asymmetrical cross resonator filter structure opens the way for freely tuning the filtering wavelength for a different light polarization. We can fix a resonant wavelength(absorption wavelength) corresponding to one polarization and change the resonant wavelength for the other polarization by adjusting the corresponding branch length of the asymmetrical cross resonator, or change the two resonant wavelengths of both two polarizations at the same time.     

Second-Order Absorbing Boundary Conditions for TLM Analysis of Open Region Scattering Problems

A set of second-order absorbing boundary conditions is derived for the three-dimensional finite-difference TLM analysis of open region scattering problems. These boundary conditions are implemented into a computer code using a two-level discretization scheme. A simulation experiment using a 4-term Blackman-Harris pulse excitation with very low sidelobes is used to examine the efficiency of the boundary conditions. It is observed that the absorbing boundaries are perfectly transparent to waves impinging upon them at angles between 0 and 45 degrees, and the normal incidence reflection coefficient is less than -35 dB.     

The far-infrared laser magnetic resonance spectrum of the CH radical

Transitions between the spin-rotational levels of the ¹³CH radical in the v=0 level of the ground state have been detected by the technique of laser magnetic resonance at far-infrared wavelengths. These measurements have been combined with the previous measurements of the lambda-doubling intervals of the molecule [J. Chem. Phys. 85 (1986) 1276 ] to determine an improved set of molecular parameters for ¹³CH. The analysis provides accurate predictions of the transition frequencies between the low-lying spin-rotational levels of the radical at zero magnetic field. A comparison is made with the values of the corresponding parameters of ¹²CH which reveals small effects due to the breakdown of the Born-Oppenheimer approximation.     

A theory of order-disorder transition during crystallization of binary systems2

A theory is presented describing the order-disorder transition in binary crystals growing on the condition of supersaturation from nonsolid phases. The theory applies to systems that crystallize with an almost perfectly ordered structure if exposed to conditions close to thermodynamic equilibrium. Based on a model that assumes incorporation and detachment of single atoms to occur at the kink sites of mono-atomic steps existing at an otherwise smooth crystal surface a kinetic master equation for the time dependence of configuration probabilities has been formulated. Several simplifying assumptions have been employed. Any solution for the steady-state conditions depends on a roughness parameter λ, the far-order parameter η, the incorporation frequency ω₊ and a parameter q, related to the atomic interaction energies. The solutions are discussed for conditions prevailing near equilibrium with η 1 and within the range of order-disorder transition with η 0. The analysis reveals that for different incorporation frequencies different critical values of the parameter q exist for which a transition from an ordered to a disordered phase is predicted to occur. Each of these critical values of q corresponds to a critical transition temperature T_t.     

Polarization properties of rectangular lattice photonic crystal fiber

In this paper, polarization properties and propagation characteristics of rectangular lattice photonic crystal fibers with elliptical air-holes are investigated by using the full-vector finite element method with anisotropic perfectly matched layers. Numerical results show that the birefringence of the fiber is induced by asymmetries of the cladding. Moreover, by adjusting its structure parameters, such as the hole pitch Λ, and the air-hole elliptical rate η, we find the optimized design parameters of the fiber with high birefringence (the order of 10⁻²) and limited polarization mode dispersion, operating in a single mode region at an appropriate wavelength range.     

Absorption and fluorescence spectra of methyl salicylate in the vapor phase

Methylsalicylate (MSA) in vapor state shows two fluorescences originating from two different ground state species. The short wavelength emission is ascribed to free MSA molecules with open hydrogen bonds, whereas the blue fluorescence is due to closed MSA. From a study of the temperature dependence of the short-to-long wavelength fluorescence intensity ratio, the energy required for ring opening is found to be 15 kJ mol^-1.     

Energy levels and level ordering in the WKB approximation

Energy levels and level orderings for a particle in a non-relativistic potential are examined in the WKB approximation. In particular, power-law potentials (V(r) = ar^γ, ?2 < γ < ∞) are discussed in some detail. The energy levels are shown to be determined in terms of a single function G(η, γ) of a variable η. Expansions of this function, valid for small (large) angular momentum quantum numbers (l) and large (small) radial quantum numbers (n), approximate the energy levels well. The ordering of the levels follows from the monotonic behavior of (?/?η)G(η, γ). The values γ = 2 (harmonic oscillator potential) and γ = ?1 (Coulomb potential) for which the WKB approximation gives the exact (i.e. Schrödinger) results lead to degenerate levels. It is about these values of γ that the monotonic behavior of (?/?η)G(η, γ) changes sign (as a function of γ). We also find an ordering theorem for arbitrary central potentials which is valid for large l and small n and is possibly correct for smaller l. The ordering depends on various sums of derivatives of the potential. Similar theorems, which follow from the Schrödinger equation, have been obtained recently for low-lying levels and are compared to our results.     

New approach for analyzing time evolution of density operator in a dissipative channel by the entangled state representation

We analyze the time evolution of mixed state ρ₀ in a dissipative channel, characteristic of a decay constant κ, by virtue of the elegant properties of entangled state representation 〈η|. We find that the matrix element of the mixed state ρ(t) at time t in 〈η| representation is proportional to that of the initial ρ₀ in the decayed entangled state 〈ηe^-κt| representation, accompanying with a Gaussian damping factor . Thus we have a new insight about the nature of the dissipative process.     

Enhanced photovoltaic properties of polymer-fullerene bulk heterojunction solar cells by thermal annealing

The effect of a thermal annealing treatment on the performance of bulk heterojunction photovoltaic cells based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) and fullerene (C₆₀) composites is investigated. Upon thermal annealing at 120 ^°C, short-circuit current and power conversion efficiency (η) are more than tripled, while a sharp rise by eight times in and η is found for the device annealed at 200 ^°C. It is concluded that the improved phase separation between MEH-PPV and C₆₀ leads to the enhancement of and η at 120 ^°C, while thermodynamic molecule arrangement at the higher temperature of ∼200 ^°C induces a significant increase in all photovoltaic parameters of composite devices except the open-circuit voltage .     

Determination of the scattering coefficient of biological tissue considering the wavelength and absorption dependence of the anisotropy factor

The anisotropy factor g, one of the optical properties of biological tissues, has a strong influence on the calculation of the scattering coefficient μ _s in inverse Monte Carlo (iMC) simulations. It has been reported that g has the wavelength and absorption dependence; however, few attempts have been made to calculate μ _s using g values by taking the wavelength and absorption dependence into account. In this study, the angular distributions of scattered light for biological tissue phantoms containing hemoglobin as a light absorber were measured by a goniometric optical setup at strongly (405 nm) and weakly (664 nm) absorbing wavelengths to obtain g. Subsequently, the optical properties were calculated with the measured values of g by integrating sphere measurements and an iMC simulation, and compared with the results obtained with a conventional g value of 0.9. The μ _s values with measured g were overestimated at the strongly absorbing wavelength, but underestimated at the weakly absorbing wavelength if 0.9 was used in the iMC simulation.