Single Slab Research Articles

Complex subduction

Eastern Indonesia hosts one of the most complex and fascinating tectonic systems on the planet. Palaeogeographical reconstructions indicate that subduction and deformation of a single slab of oceanic crust created the complicated configuration.

Surface deformation and slab–mantle interaction during Banda arc subduction rollback

The reason for the spectacular curvature of the Banda subduction zone is debated. Tomographic images and plate reconstructions reveal subduction of a single slab. The ancient geometry of the Australian plate, as well as the interaction between the slab and the mantle, caused the deformation of the slab. The spectacularly curved Banda arc comprises young oceanic crust1,2 enclosed by a volcanic inner arc, outer arc islands and a trough parallel to the Australian continental margin3,4,5. Strong seismic activity in the upper mantle defines a folded surface6,7, for which there are two contrasting explanations: deformation of a single slab5,8 or two separate slabs subducting from the north and south6,9. Here we combine seismic tomography with the plate tectonic evolution of the region to infer that the Banda arc results from subduction of a single slab. Our palaeogeographic reconstruction shows that a Jurassic embayment, which consisted of dense oceanic lithosphere enclosed by continental crust, once existed within the Australian plate. Banda subduction began about 15 million years ago when active Java subduction tore eastwards into the embayment. The present morphology of the subducting slab is only partially controlled by the shape of the embayment. As the Australian plate moved northward at a high speed of about 7 cm yr−1, the Banda oceanic slab rolled back towards the south–southeast accompanied by active delamination separating the crust from the denser mantle. Increasing resistance of the mantle to plate motion progressively folded the slab and caused strong deformation of the crust. The Banda arc represents an outstanding example of large-scale deformation of the Earth’s crust in response to coupling between the crust, slab and surrounding mantle.

Casimir-type effects for scalar fields interacting with material slabs

We study the field theoretical model of a scalar field in the presence of spacial inhomogeneities in the form of one and two finite-width mirrors (material slabs). The interaction of the scalar field with the defect is described with a position-dependent mass term. For a single-layer system we develop a rigorous calculation method and derive explicitly the propagator of the theory, the S-matrix elements and the Casimir self-energy of the slab. Detailed investigation of particular limits of self-energy is presented, and the connection to known cases is discussed. The calculation method is also found applicable to the two-mirror case. With its help we derive the corresponding Casimir energy and analyze it. For particular values of parameters of the model an obtained result recovers the Lifshitz formula. We also propose a procedure to unambiguously obtain the finite Casimir self-energy of a single slab without reference to any renormalization conditions. We hope that our approach can be applied to the calculation of Casimir self-energies in other demanded cases (such as a dielectric ball, etc).

Chandra X-ray observations of two unusual BAL quasars

We report sensitive Chandra X-ray non-detections of two unusual, luminous Iron Low-Ionization Broad Absorption Line Quasars (FeLoBALs). The observations do detect a non-BAL, wide-binary companion quasar to one of the FeLoBAL quasars. We combine X-ray-derived column density lower limits (assuming solar metallicity) with column densities measured from ultraviolet spectra and CLOUDY photoionization simulations to explore whether constant-density slabs at broad-line region densities can match the physical parameters of these two BAL outflows, and find that they cannot. In the “overlapping-trough” object SDSS J0300+0048, we measure the column density of the X-ray absorbing gas to be N H ⩾ 1.8 × 10 24 cm −2. From the presence of Fe ii UV78 absorption but lack of Fe ii UV195/UV196 absorption, we infer the density in that part of the absorbing region to be n e ≃ 10 6 cm −3. We do find that a slab of gas at that density might be able to explain this object’s absorption. In the Fe iii-dominant object SDSS J2215–0045, the X-ray absorbing column density of N H ⩾ 3.4 × 10 24 cm −2 is consistent with the Fe iii-derived N H ⩾ 2 × 10 22 cm −2 provided the ionization parameter is log U > 1.0 for both the n e = 10 11 cm −3 and n e = 10 12 cm −3 scenarios considered (such densities are required to produce Fe iii absorption without Fe iiabsorption). However, the velocity width of the absorption rules out its being concentrated in a single slab at these densities. Instead, this object’s spectrum can be explained by a low density, high ionization and high temperature disk wind that encounters and ablates higher density, lower ionization Fe iii-emitting clumps.

Performance Characterization of a Silicon Drift Detector for Gamma Ray Imaging

This study examined the intrinsic performance of silicon drift detector (SDD)-based gamma detectors under a variety of conditions. The prototype detector consisted of an array of seven hexagon-shaped SDDs optically coupled to a single slab of a scintillator. The active area of the SDD sensor was 15.2 mm in diameter, as measured from one vertex to another. The detector unit (SDD array, scintillator and preamplifier circuits) was operated in a cooling chamber with a typical operating temperature of -20°C. Nitrogen gas was supplied to the detector unit to prevent condensation. The drift time was measured using a LED pulse generation device and the longest drift time was measured to be 4.6 μsec from the edge of the sensor. The intrinsic energy resolution with a BBFe source for direct X-ray conversion was 3% at the 5.9 keV peak. For indirect conversion, i.e. photon detection, the energy resolution for CsI(Tl) and Nal(Tl) was 7.9% and 8.2% with a 13 μsec and 2.71 μsec shaping time, respectively. For this indirect conversion measurement, the temperature was set to -20°C and a 1 × 1 × 1 cm3 cube scintillator was coupled directly to the sensor. For the intrinsic spatial resolution measurement with a hole-phantom (3 × 2 mm diameter holes), the x and y directional profiles at a center hole were 2.2 and 2.1 mm in FWHM, respectively. Overall, the intrinsic performance of the SDD prototype is quite promising and advantages of this technology makes it highly feasible for use as a gamma ray detector.

Integrated 2D photonic crystal stack filter fabricated using nanoreplica molding

The design, fabrication, and characterization of an integrated 2D photonic crystal stack are described for application as optical filters with improved optical density and angle tolerance compared to single photonic crystal slabs. The 2D photonic crystals are designed as polarization independent reflectance filters with a narrow spectral bandwidth centered at lambda=532 nm by utilizing the guided mode resonance effect. Up to three photonic crystal layers are vertically stacked upon a single plastic substrate by using repeated nanoreplica molding process steps, with no alignment required between stacked layers. The photonic crystal stack filters achieve optical density of 2.24 with an angular tolerance of 14.8 degrees.

Optofluidic dye laser in a foil

First order distributed feedback optofluidic dye lasers embedded in a 350 microm thick TOPAS((R)) foil are demonstrated. They are designed in order to give high output pulse energies. Microfluidic channels and first order distributed feedback gratings are fabricated in parallel by thermal nanoimprint into a 100 microm foil. The channels are closed by thermal bonding with a 250 microm thick foil and filled with 5.10(-3) mol/l Pyrromethene 597 in benzyl alcohol. The fluid forms a liquid core single mode slab waveguide of 1.6 microm height on a nanostructured grating area of 0.5 x 0.5 mm(2). This results in a large gain volume. Two grating periods of 185 nm and 190 nm yield single mode laser light emission at 566 nm and 581 nm respectively. High emitted pulse energies of more than 1 microJ are reported. Stable operation for more than 25 min at 10 Hz pulse repetition rate is achieved.

Pipe damper, Part II: Application to bridges

Theoretical and experimental verification of the pipe damper was investigated in Part I of the two companion papers. In this paper, the application of the pipe damper to structures is examined. In particular, single span slab–girder bridges are considered for analytical investigations. A practical detail for the installation of the pipe damper is introduced. Nonlinear dynamic time history analyses are conducted on bridges equipped with the pipe damper and the results are compared with ordinary bridges. Bridge span, ground motion and the pipe length are varied in the analyses. Results show that the pipe damper is a reliable and economical metallic-yielding device that can easily be installed and replaced. A step-by-step method using inelastic response spectra is also introduced for optimum selection of such devices.

The Advocate ophiolite mantle, Baie Verte, Newfoundland: regional correlations and evidence for metasomatismGeological Survey of Canada, Earth Sciences Sector, Contribution 20090211.

Mantle rocks of the Advocate ophiolite near Flatwater Pond (Baie Verte, Newfoundland) are dominated by harzburgite tectonites, which are extensively converted to listvenite along the Baie Verte Road fault and represent a potential gold exploration target. Most Advocate harzburgites have forsteritic olivine (Fo90.5 to Fo93) and Cr-spinels, with Cr# (= 100Cr/(Cr + Al)) between 52 and 64 and Mg# (= 100Mg/(Mg + Fe2+)) between 56 and 68. These mineral chemical signatures, together with high whole-rock MgO (46%–48%), low Al2O3 (<1%), and TiO2 (<0.003%), imply the Advocate harzburgites are refractory residues after ca. 25%–35% melting. Cr-spinel compositions of Advocate mantle rocks overlap with Cr-spinels from the mantle rocks of the Point Rousse and Betts Cove ophiolites, with Mg# higher than those of Bay of Islands or Thetford Mines mantle Cr-spinels. Although refractory in terms of major elements and mineral chemistry, Advocate harzburgites contain high La–Ce–Pr–Pb–Nd–Sm–Zr contents suggestive of pervasive metasomatism. Similar geochemical signatures occur in all ophiolitic mantle rocks from the Baie Verte Peninsula examined so far. The enrichments are not consistent with supra-subduction zone syn-melting metasomatism as observed in other Appalachian ophiolites. The apparent absence of visible metasomatic channels in most outcrops suggests that metasomatism occurred before obduction by diffuse percolation, but the nature and origin of the metasomatic agent remain speculative. The similarities of mineral and whole-rock geochemistry imply that all mantle rocks from Baie Verte ophiolites are correlative and may represent remnants of a single obducted slab.

The characteristic of the stero-coupling high-Q photonic crystal slab cavity

Inspired by the idea of the stero-coupling, we propose a new sandwich-like photonic crystal microcavity which is composed of double layer photonic crystal slabs H1 (DLPCS-H1) cavity with an air layer in between. We calculate the electromagnetic field distribution and the quality factor of the dipole mode by the three-dimensional finite-difference time-domain method and the Padé approximation method. Through carefully analyzing the effect of the air layer height on the quality factor of the dipole mode, we obtain an optimized DLPCS-H1 cavity in which the height of intermediate air layer is about 0.5a (a is the lattice constant, a=420 nm). In this cavity, the quality factor of the dipole mode is 4 times as large as that of the conventional single layer photonic crystal slab H1 cavity. Furthermore, we study the three-layer photonic crystal slabs H1 cavity, and the quality factor of its dipole mode is increased over 7 times.

Design and Simulation of Photonic Crystal Based Polarization Converter

A periodic asymmetrically loaded photonic-crystal (PC) based polarization converter has been designed and fabricated. The polarization converter structure consists of a single defect line square hole PC slab waveguide with asymmetrically loaded top layer. The design methodology consists of finding the birefringence induced by geometrical asymmetry through full-wave modal analysis. The proposed design methodology can be extended to arbitrary air hole shape photonic-crystal-based polarization converter. The length and total number of top loaded layers are determined upon full-wave modal analysis. The thickness of the loaded top layer has been optimized to provide wideband and low loss polarization conversion. The optimized thickness of the top loaded layer is 0.2 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> for which polarization conversion takes place over the propagation distance of 13lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . For this distance, the coupling efficiency higher than 90% is achieved within the normalized frequency band of 0.258-0.267 corresponding to 584-604.5 GHz for the design example presented in III.

Extraordinary optical transmission through multi-layered systems of corrugated metallic thin films

Optical transmission through multi-layered systems of corrugated metallic thin films is investigated by rigorous electromagnetic simulations based on an exact Green tensor method. Compared to a single metal slab of equivalent thickness and volume, it was found that the multi-layered system can significantly impede the field decay, often leading to transmission greater than that expected from the Fabry-Perot resonance-like behavior exhibited by subwavelength slits in a single slab. Extraordinary optical transmission is also observable for systems of layers whose combined thicknesses are much greater than the skin depth of the metal. Structures consisting of up to five layers with a net thickness of 500 nm for the metal films were considered in our study. These findings demonstrate that an appreciable fraction of the optical power that is incident on the thin metal films can be transmitted over distances greater than their skin depth using plasmonic resonances.

Simulation of Water Adsorption on Kaolinite under Atmospheric Conditions

Grand canonical Monte Carlo calculations are employed to investigate water adsorption on kaolinite at 298 and 235 K. Both basal planes (the Al and Si surfaces) as well as two edge-like surfaces are considered. The general force field CLAYFF is used together with the SPC/E and TIP5P-E models for water. Problems that occur in single slab simulations due to arbitrary truncation of the point charge lattice are identified, and a working remedy is discussed. The edges and the Al surface adsorb water at subsaturation in the atmospherically relevant pressure range. The Si surface remains dry up to saturation. Both edges have a very strong affinity for water and adsorb continuously up to monolayer coverage. The Al surface has a weaker affinity for water but forms a subsaturation monolayer. On the Al surface, the monolayer is formed in an essentially sharp transition, and strong hysteresis is observed upon desorption. This indicates collective behavior among the water molecules which is not present for the edges. Binding energies of singly adsorbed water molecules at 10 K were determined to understand the differences in water uptake by the four kaolinite surfaces. Binding energies (SPC/E) of -21.6, -46.4, -73.5, and -94.1 kJ/mol, were determined for the Si surface, Al surface, unprotonated edge, and protonated edge, respectively. The water monolayer on the Al surface, particularly at 235 K, exhibits hexagonal patterns. However, the associated lattice parameters are not compatible with ice Ih. Water density and hydrogen bonding in the monolayers at both 298 and 235 K were also determined to better understand the structure of the adsorbed water.

TH-D-210A-03: Thick Monolithic Pixelated Scintillator Array for Megavoltage Imaging

We describe the fabrication and evaluation of a thick pixelated scintillator for megavoltage (MV) imaging composed of a ceramic containing over 99.9% gadolium oxysulfide. This sintered material offers a 59% increase in density over the Lanex Fast B (LFB) phosphor screens most commonly employed in MV imaging. The sintered pixelated array (SPA) is fabricated from a single slab of ceramic. This obviates the need to assemble over a million separate crystals in order to cover a 40.96cm × 40.96cm detector area. As a consequence, the design is amenable to fabrication using methods of mass production. Method and Materials: A 1.8mm‐thick 274 × 250 pixel SPA with 0.4mm pixel pitch is attached to the light‐sensitive surface of an amorphous silicon flat panel detector (Perkin Elmer XRD1640AN). Image quality is characterized using 1MU exposures of the 6MV beam of a Siemens Primus Linac. A QC‐3V phantom is employed to calculate the modulation transfer function(MTF) and contrast‐to‐noise ratio (CNR). The detective quantum efficiency (DQE) is computed. A LFB screen is then evaluated under identical conditions for comparative purposes. Cone beam CT(CBCT)imaging is performed with four arrays tiled side‐by‐side on the detector surface. Results: The half‐maximum value of MTF occurs at 0.32 and 0.34lp/mm for the SPA and LFB, respectively. The DQE(0.1lp/mm) of SPA is 5.8%, versus 1.0% for LFB. The SPA offers a 235% improvement in CNR over LFB. Previously undetectable low‐contrast phantom inserts are clearly visible in SPA MV‐CBCT images.Conclusions: The SPA appears to offer a practical and cost‐effective means of attaining major improvements in MV image quality. The measured MTF and DQE values underestimate the achievable performance, since the SPA and detector photodiode arrays were imperfectly aligned during these evaluations. A DQE(0) value closer to the maximum attainable 7.8% is expected. Conflict of Interest: Sponsored by Siemens.

ABCD matrix formalism for propagation of Gaussian beam through left-handed material slab system

We apply a simple ABCD matrix formalism to investigate beam propagation in left-handed material (LHM) slab systems. Firstly, we derive the expressions for the matrix elements for a single LHM slab. Based on the ABCD matrix, we obtain the field distributions both inside and outside the LHM slab, and the conditions for focusing and phase compensation of the Gaussian beam. Secondly, the derived ABCD law is applied to analyze the propagation properties of Gaussian beams through various cascaded LHM slab systems. The corresponding focusing and phase compensation conditions of the Gaussian beam are also obtained. Our theoretic formalism may be applied as a compact and effective tool for the research of light beam propagation in complex LHM slab systems, since it avoids the complicated integral operation.

Electric field tunable 60 GHz ferromagnetic resonance response in barium ferrite-barium strontium titanate multiferroic heterostructures

A magnetic-ferroelectric film heterostructure with a large electric field tuning of the ferromagnetic resonance (FMR) mode was fabricated. Pulse laser deposited 30 nm thick Pt electrodes and 3 μm thick barium strontium titanate films on Nb-doped strontium titanate substrates were capped with an unbonded 200 μm thick single crystal in-plane c-axis barium hexaferrite slab. The structure gives a 60 GHz FMR frequency shift of 16 MHz at a bias of 29 V, for an average response of 0.55 MHz/V. The maximum incremental tuning response at 29 V was 1.3 MHz/V. This is a hundredfold improvement over previous results.

On vehicle/track impact at connection between a floating slab and ballasted track and floating slab track's effectiveness of force isolation

When a vehicle runs over the connection between a floating slab track (FST) and ballasted track, wheel/rail impact may occur because of the stiffness difference in the two kinds of track, and thus a transition sector is usually included at the connection to smoothen the stiffness change. This phenomenon is studied by numerical simulation using a time-domain model for an idealised case without such a transition to determine whether it is actually necessary. Calculation results show that the wheel/rail impact load is moderate for a light FST and increases with the vehicle speed or decreasing the natural frequency of the FST. From simulation the wheel/rail parametric excitation is observed, as a result of variation in the stiffness of the FST with the period of the single slab length. The wheel/rail load due to the parametric excitation also increases with the vehicle speed. In addition, good performance of vibration isolation can be seen for the FST in terms of the force transmitted to the infrastructure.

Ultra-compact photonic crystal based polarization rotator

An asymmetrically loaded photonic crystal based polarization rotator has been introduced, designed and simulated. The polarization rotator structure consists of a single defect line photonic crystal slab waveguide with asymmetrically etched upper layer. To continue the rotation from a given input polarization to the desired output polarization the upper layer is alternated on either side of the defect line, periodically. Coupled mode theory based on semi-vectorial modes and plane wave expansion methods are employed to design the polarization rotator structure around a particular frequency band of interest. The 3D-FDTD simulation results agree with the coupled mode analysis around the region of interest specified during the design. Complete polarization rotation is achieved over the propagation length of 12lambda. For this length, the coupling efficiency higher than 90% is achieved within the normalized frequency band of 0.258-0.262.

An exact theory of interfacial debonding in layered elastic composites

An exact theory of interfacial debonding is developed for a layered composite system consisting of distinct linear elastic slabs separated by nonlinear, nonuniform decohesive interfaces. Loading of the top and bottom external surfaces is defined pointwise while loading of the side surfaces is prescribed in the form of resultants. The work is motivated by the desire to develop a general tool to analyze the detailed features of debonding along uniform and nonuniform straight interfaces in slab systems subject to general loading. The methodology allows for the investigation of both solitary defect as well as multiple defect interaction problems. Interfacial integral equations, governing the normal and tangential displacement jump components at an interface of a slab system are developed from the Fourier series solution for the single slab subject to arbitrary loading on its surfaces. Interfaces are characterized by distinct interface force–displacement jump relations with crack-like defects modeled by an interface strength which varies with interface coordinate. Infinitesimal strain equilibrium solutions, which account for rigid body translation and rotation, are sought by eigenfunction expansion of the solution of the governing interfacial integral equations. Applications of the theory to the bilayer problem with a solitary defect or a defect pair, in both peeling and mixed load configurations are presented.

Optical manipulation of a particle placed within a planar dielectric cavity

We study theoretically the electromagnetic force exerted on a small dielectric particle lying within a planar, dielectric cavity, under plane-wave illumination. We find, in particular, that due to the confinement of an incident wavefield within the cavity, the force exerted on the particle is several orders of magnitude stronger than the corresponding force when the particle is placed next to a single planar slab. We also observed when the particle is placed in the middle of the cavity, it can be trapped at frequencies corresponding to the transmission maxima. We have also found that, for any given position within the cavity, there exist several frequencies for which the particle can be trapped. For the case of a Bragg-stack cavity, there exist more trapping frequencies in a given spectral region allowing for easier optical manipulation of the particle.