Properties Of Slab Research Articles

Optical properties of photonic crystal slabs with an asymmetrical unit cell

Using the unitarity and reciprocity properties of the scattering matrix, we analyse the symmetry and resonant optical properties of the photonic crystal slabs (PCS) with complicated unit cell. We show that the reflectivity is not changed upon the 180deg-rotation of the sample around the normal axis, even in PCS with asymmetrical unit cell. Whereas the transmissivity becomes asymmetrical if the diffraction or absorption are present. The PCS reflectivity peaks to unity near the quasiguided mode resonance for normal light incidence in the absence of diffraction, depolarisation, and absorptive losses. For the oblique incidence the full reflectivity is reached only in symmetrical PCS.

Highly oriented molecular aggregates in 1-D photonic crystal slabs: toward the control of molecular arrangement from submicron to nanometer region

We have investigated the optical properties of one-dimensional photonic crystal slabs (PCSs) of molecular aggregates, and reported the vacuum Rabi splitting of 50 meV in pseudoisocyanine (PIC) J-aggregates in the strong coupling regime. The mode splitting should increase with the increase of the molecular density. Then, we fabricated PIC J-aggregates without any polymer matrix. As a result, we can observed Rabi splitting over 200 meV. Moreover, the strong J-band is observed only with the light polarization along the grooves. The observed strong anisotropy around the J-band indicates that almost all of the molecules are oriented along the grooves. It means the grooves with the several hundred nanometers period arrange the direction of molecules, nevertheless, the size of a molecule is less than 1 nm. This is one of the attractive features of molecular PCs, because we will be able to arrange nanometer structures with the use of the submicron structures.

The dynamics of subduction and trench migration for viscosity stratification

SUMMARY Although subduction plays a dominant role in plate tectonics, related processes such as trench migration are not well understood. We investigate the influence of viscosity stratification and different flow boundary conditions on the trench migration dynamics of a subducting lithosphere in a 2-D model using a finite-difference code. Subduction and mantle flow are driven by a compositionally prescribed density contrast between the high-viscosity slab and the ambient mantle; no overriding plate is assumed. The model rheology is viscoplastic at shallow, and viscous at greater depth; the mantle is stratified with a higher viscosity in the lower part of the computational domain. The plastic rheology allows the plate to decouple from the top of the box and is described by a simplified friction law to mimic the brittle deformation of the shallow lithosphere. The flow patterns and slab morphologies differ as a function of the velocity boundary conditions (BCs). For reflective BCs, we model either a plate which is fixed on the box side or a plate that can freely move. A slab with periodic BCs is always laterally free. We find that, when the slabs interact with the highly viscous lower mantle, the slab with reflective BCs is more folded than the periodic one, due to the confinement of mantle flow around the slab. In general, the trench is observed to roll back toward the oceanic plate. For free slabs with reflective BCs the trench retreat velocity deceases after the interaction with the lower mantle. In contrast, for the free slab with periodic BCs it is nearly constant or even increases with time if described in a reference frame fixed to the lower mantle. The free slab with periodic BCs exerts a force on the lower mantle, which causes a net differential flow between the upper and lower mantle. We also carried out additional experiments with different mechanical slab properties and thicknesses. Stiffer, free slabs subduct more steeply and are able to penetrate straight into the lower mantle. After penetration into the lower mantle the trench moves toward the continent. Thinner slabs deform more easily and are folded for all boundary conditions. We can generalize the rollback systematics for free slabs by normalizing trench velocities by the plate speed. Free slabs, being more representative of the West Pacific subduction zones, show large temporal variations of normalized trench velocities ranging between a retreat value of 1.0 to an advancing value of −0.3.

Investigation of reflection and transmission properties of dielectric slabs randomly doped with conducting objects

Using a finite-element method, the likelihood of producing useful frequency-dependent reflection/transmission characteristics of randomly doped dielectric slabs is investigated. The responses of short conducting wires randomly embedded throughout the slab and conducting triangular patches and wires limited to the dielectric surface are investigated using a computationally efficient algorithm. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 83–86, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21268

Motion of diffusional transformation fronts in multi-component systems

The material properties of a steel slab produced during continuous casting are significantly influenced by the kinetics of the austenite(γ)-to-ferrite(α) phase transformation. Former theoretical models either have used a semi-empirical approach (such as the Johnson-Mehl-Avrami equation) or simplified the situation by assuming an infinite mobility of the phase interface and/or zero mobility of substitutionally dissolved components. In general the transformation kinetics in a multi-component system depends on the interface mobility and on the diffusion of the components. A finite mobility model for the phase transformation has been developed that takes into account the diffusion of substitutionally dissolved components. As an example the kinetics of the γ/α-phase transformation is simulated in the Fe-Cr-Ni system.

Optical properties of an ideal homogeneous causal left-handed material slab

The optical properties of a homogeneous slab of material characterized by causal permittivity epsilon (f) , and permeability mu (f) are investigated through finite difference time domain simulations. Lorentzian epsilon (f) and mu (f) are used to produce values of interest in the resulting index n (f) , namely, n<0 , 0<n<1 , and n approximately 0 . Negative refraction of both cw and pulsed waves is observed when operated in the left-handed medium (LHM) regime. In particular, we examined materials having both an impedance matched to free space and an impedance not matched to free space, as is the case of a split-ring resonator structure, and find it to exhibit LHM behavior, in agreement with previously published claims. Spherical aberration and channeling are observed as the magnitude of the negative index is increased beyond -1 . Critical angle phenomena are seen for indices in the range 0<n<1 , and a spatial filter effect is identified in the n approximately 0 region. A transmission bandpass in the vicinity of n approximately 0 is identified as a "ferromagnetic antiresonance," where the material acts as both a frequency and a spatial filter.

Ab initio calculations of the LaMnO3 surface properties

We present the results of ab initio Hartree–Fock calculations of the LaMnO3 (001) and (110) polar surfaces. Using 7- and 8-plane slabs periodic in 2D along the x, y-axes, we compare the properties of a stoichiometric slabs with structural oxygen vacancies, and non-stoichiometric, defect-free slabs, analyze the dispersion of the effective charges near the surface, and calculate the surface energy, for both ferromagnetic and antiferromagnetic spin orderings in a slab.

Transmission study of prisms and slabs of lossy negative index media

Within an effective medium theory, we numerically study by means of a finite element method the transmission properties of prisms and slabs of media with negative refractive index. The constitutive parameters employed are similar to those of recent experiments that confirmed the existence of negative refraction as well as the focusing property of flat slabs. In this way, we further analyze in detail the influence of diffraction and scattering due to the large wavelength of the radiation in use, and its suppression by employing waveguide configurations with absorbing walls. Also, we address the effects of different amounts of absorption on both the angle of refraction, (for which we derive a new refraction law in prisms), and on the position, resolution and isoplantism of the focus produced by flat slabs.

カプセル型中空材を用いた中空スラブ工法の開発 : 構造実験及び設計手法(構造)

This is a technical report for the structural properties of capsule-shaped void slab, which has been developed and introduced to actual buildings in order to eliminate beams at slab ceiling. This void slab has two characteristics. One is high void ratio to provide one of the lightest void slab in Japan. Two is its isotropy nature which enables to design variously outlined slab. Both are verified by the isotopic round shape voids around which concrete is easily cast against their narrow gaps contributing its high void ratio.

On the fracture toughness of snow

AbstractThe release of a dry-snow slab avalanche involves brittle fracture. It is therefore essentially a non-linear fracture mechanics problem. Traditional snow-stability evaluation has mainly focused on snow strength measurements. Fracture toughness describes how well a material can withstand failure. The fracture toughness of snow is therefore a key parameter to assess fracture propagation propensity, and hence snows lope stability. Fracture toughness in tension KIc and shear KIIc was determined with notched cantilever-beam experiments in a cold laboratory. Measurements were performed at different temperatures and with different snow types of density ρ = 100–300 kgm–3, corresponding to typical dry-snow slab properties. The fracture toughness in tension KIc was found to be larger (by about a factor of 1.4) than in shear KIIc. Typical values of the fracture toughness were 500–1000 Pam1/2 for the snow types tested. This suggests that snow is one of the most brittle materials known to man. A power-law relation of toughness KIc on relative density was found with an exponent of about 2. The fracture toughness in tension KIc decreased with increasing temperature following an Arrhenius relation below about –8°C with an apparent activation energy of about 0.16 eV. Above –6°C the fracture toughness increased with increasing temperature towards the melting point, i.e. the Arrhenius relation broke down. The key property in dry-snow slab avalanche release, the critical crack size under shear at failure, was estimated to be about 1 m.

Total external reflection from metamaterials with ultralow refractive index

Metamaterials composed of metal-dielectric nanostructures are engineered to have an effective refractive index less than unity at optical wavelengths. The effect of total external reflection is demonstrated when light from vacuum is incident onto these materials at an angle exceeding the critical angle defined by Snell’s law. Novel approaches are discussed to derive the effective index of refraction from the reflection and refraction properties of finite slabs. The effect of losses and dispersion are analyzed in the visible range of frequencies by consideration of the measured properties of silver. The differences among ultralow refractive-index metamaterials, photonic bandgap materials, and metals are discussed. Remarkably, a bandgap is not required to obtain total external reflection.

Molecular dynamics study of melting of the bcc metal vanadium. II. Thermodynamic melting

We present molecular dynamics simulations of the thermodynamic melting transition of a bcc metal, vanadium using the Finnis-Sinclair potential. We studied the structural, transport and energetic properties of slabs made of 27 atomic layers with a free surface. We investigated premelting phenomena at the low-index surfaces of vanadium; V(111), V(001), and V(011), finding that as the temperature increases, the V(111) surface disorders first, then the V(100) surface, while the V(110) surface remains stable up to the melting temperature. Also, as the temperature increases, the disorder spreads from the surface layer into the bulk, establishing a thin quasiliquid film in the surface region. We conclude that the hierarchy of premelting phenomena is inversely proportional to the surface atomic density, being most pronounced for the V(111) surface which has the lowest surface density.

Water solubility in majoritic garnet in subducting oceanic crust

Water in majoritic garnet synthesized in the mid‐oceanic ridge basalt (MORB) + H2O composition at 20 GPa and 1400–1500°C was measured by secondary ion mass spectrometry (SIMS) and infrared spectroscopy. We found that the majorite contains 1130 to 1250 ppm OH by weight. The infrared absorption band showed that incorporation of the hydroxyl in majorite is most likely due to the hydrogarnet substitution. Our results indicate that water can be transported into the mantle transition zone by nominally anhydrous minerals such as omphacite and majorite in the subducting basaltic crust. Such water may have great influences on the physical properties of slab in the transition zone.

Fundamental optical properties of photonic crystal slabs in the strong coupling regime

We report on the transmission and photoluminescence (PL) properties of semiconductor-imbedded photonic crystal slabs where the photon mode is strongly mixed with the exciton mode. The samples are prepared by incorporating PbI-based inorganic–organic layered perovskites with the large oscillator strength of excitons into periodically arranged square holes on a quartz substrate. In transmission spectra, well-pronounced dips due to the excitation of quasi-guided modes are observed, when a polystyrene layer is overcoated with an appropriate thickness on the substrate. The quasi-guided and exciton modes exhibit an anticrossing with large Rabi splitting of over 100 meV, which demonstrates the formation of polaritons via the strong coupling between these two modes. In PL spectra, we found that the polariton PL is significantly enhanced where the polariton has the largest population. Thus, the optical properties of excitons can be controlled by the electromagnetic periodic boundary condition via strong coupling with a quasi-guided mode in a photonic crystal slab.

Meander line polarizer on a chiral slab (transverse electric case)

In this contribution, we present a theoretical investigation of power reflection and transmission coefficients for a meander line polarizer placed periodically on a chiral slab. A meander line polarizer converts the wave polarization from linear to circular as the wave propagates through the polarizer at normal incidence. The design parameters are the dimensions of meander line and the material properties of dielectric slab. We introduce a new independent parameter, chirality admittance, which controls the wave polarization, replacing the dielectric slab with the chiral slab. The results demonstrate that the resonant frequency and the bandwidth of the meander line polarizer depend strongly on the value of chirality admittance.

Plane wave diffraction by the junction of a thick impedance half-plane and a thick dielectric slab

Plane wave diffraction at the junction of a thick impedance half-plane and a thick dielectric slab is investigated by using the Fourier transform technique. Relying upon the image bisection principle, the original problem is split into two simpler ones and each individual boundary-value problem is formulated as a modified Wiener-Hopf equation whose solution requires the determination of a set of infinitely many expansion coefficients which satisfy an infinite linear system of algebraic equations which can be solved easily by numerical tools. The effects of the material properties of the dielectric slab, the thickness of the junction and the characteristic impedances on different faces of the thick half-plane are presented graphically.

Simulation of quasi-two-dimensional dipolar systems

A brief survey is given of recent simulation work of quasi-two-dimensional (Q2D)systems, monolayers and systems of finite thickness, involving dipolarinteractions. Representative examples include colloidal particles at an interface,electrorheological fluids, magnetic thin films, nanocrystals deposited on asubstrate etc. Methodological aspects related to the long range of the dipolarinteraction and its directional nature (energy calculation, cluster moves) aresummarized. Taking as an example a bilayer of dipolar hard spheres, wedemonstrate that the energy and structural properties of a thin slab of dipolarparticles periodic in two dimensions and finite in the third can be accuratelycalculated by means of the usual three-dimensional Ewald sum. Some newsimulation results for the structural properties of Q2D dipolar hard spheres withadditional attraction, in an external field or in bilayers, are presented.

Resonance and Bound States in Photonic Crystal Slabs

Using boundary-integral projections for time-harmonic electromagnetic (EM) fields, and their numerical implementation, we analyze EM resonance in slabs of two-phase dielectric photonic crystal materials. We characterize resonant frequencies by a complex Floquet--Bloch dispersion relation $\omega = W(\beta)$ defined by the existence of a nontrivial nullspace of a pair of boundary-integral projections parameterized by the wave number $\beta$ and the time-frequency $\omega$. At resonant frequencies, the crystal slab supports a source-free EM field. We link complex resonant frequencies, where the imaginary part is small, to resonant scattering behavior of incident source fields at nearby real frequencies and anomalous transmission of energy through the slab. At a real resonant frequency, the source-free field supported by the slab is a bound state. We present numerical examples which demonstrate the effects of structural defects on the resonant properties of a crystal slab and surface waves supported by a die...

Experiments and modeling of head cut migration in stratified soils

A two‐dimensional model is developed to predict head cut migration rate for the specific case of a relatively erosion‐resistant soil layer overlying a deep, relatively erosive base soil. For this geometry, head cut migration can occur as a series of discrete mass failures of the surface layer caused by undercutting in a plunge pool formed immediately downstream. The length scale of one failure episode is modeled as a cantilevered slab failing in bending. The timescale for each failure episode is controlled by the rate and geometry of base layer scour, which is modeled independently of cantilevered slab properties. An integration of the two model components for the case of steady flow and uniform soil properties predicts linear upstream head cut migration with time, occurring in discrete steps bounded by successive mass failure events. The model is calibrated and tested in a series of flume experiments representing ideal conditions of different initial geometries and flow conditions. Head cut migration occurred by the proposed mechanism in a nearly linear rate. Average error between the observed and predicted retreat rate is 40%, most of this error is attributable to prediction of the scour hole shape.

Self-collimation in planar photonic crystals

We analyze, in three dimensions, the dispersion properties of dielectric slabs perforated with two-dimensional photonic crystals (PCs) of square symmetry. The band diagrams are calculated for all k-vectors in the first Brillouin zone, and not only along the characteristic high-symmetry directions. We have analyzed the equal-frequency contours of the first two bands, and we found that the square lattice planar photonic crystal is a good candidate for the self-collimation of light beams. We map out the group velocities for the second band of a square lattice planar PC and show that the group velocity is the highest in the region of maximum self-collimation. Such a self-collimated beam is predicted to show beating patterns due to the specific shape of the equal-frequency contours. A geometrical transformation maps the region of the first and second photonic bands where self-collimation takes place one onto the other and gives additional insights on the structural similarities of self-collimation in those two bands.