Single Slab Research Articles

Mantle Dynamics of the Eastern Mediterranean and Middle East: Constraints From P‐Wave Anisotropic Tomography

AbstractHigh‐resolution images of P‐wave anisotropic tomography beneath the Eastern Mediterranean and Middle East are determined by inverting a large number of high‐quality P‐wave arrival times. Our results clearly show along‐strike variations of subducting slabs in the Hellenic subduction zone. At least three high‐velocity anomalies are imaged beneath and behind the north Hellenides, which are associated with the subducting Hellenic slab at different stages, while in regions further south, a single slab is revealed that has subducted down to a depth of ~1,100 km. The slab feature is not prominent in the Cyprus subduction zone, but a fine‐scale high‐velocity structure is revealed beneath the central Anatolia, which may reflect the detached Cyprus slab. Trench‐parallel fast‐velocity directions occur in the forearc mantle wedge of the Hellenic subduction zone, which may reflect mantle flow induced by slab curvature. In the backarc north Aegean and westernmost Anatolia, dominant NNE‐SSW to N‐S fast‐velocity directions exist in the shallow mantle, which accord well with the extensional direction of present deformation at the surface, suggesting a vertically coherent deformation in the lithosphere. Our results reveal a large‐scale mantle flow beneath western Arabia, which is possibly related to the Zagros and Caucasus orogens and westward motion of the Anatolia lithosphere. The Arabian lithospheric plate is thinner beneath the Zagros than that under the Mesopotamian Foredeep, suggesting that a large portion of the crust was scrapped off from the subducted Arabian lithosphere during the Zagros orogen.

Depth-of-interaction study of a dual-readout detector based on TOFPET2 application-specific integrated circuit

Depth-of-interaction (DOI) capability is important for achieving high spatial resolution and sensitivity in dedicated organ and small animal positron emission tomography (PET) scanners. The dual-ended readout is one of the common methods that can achieve good DOI resolution. The aim of this study is to evaluate a dual-ended readout detector based on silicon photomultiplier (SiPM) and TOFPET2 application-specific integrated circuit (ASIC). The detector is based on 4 4 lutetium–yttrium oxyorthosilicate (LYSO) units, each unit contained 6 6 LYSO crystals, and the crystal size was 1 1 20 mm3. The four lateral surfaces of LYSO crystals were mechanically ground to W14 (surface roughness 10–14 m), and the two ended surfaces were polished (surface roughness <0.5 m). The reflector was Toray Lumirror E60, and the packing fraction of the LYSO block was 86.5%. Each LYSO unit was read out from both ends with two Hamamatsu S13361-3050AE-08 SiPM arrays. The analog output signals of SiPM were digitized by PETsys TOFPET2 ASIC and acquired by PETsys SiPM Readout System. The ASIC and SiPM were cooled by a fan and a Peltier element. To investigate the crystal resolvability, different light guide thicknesses including 0.8, 1, 1.2 and 2 mm were tested. The light guide was made of optical glass (H-K9L-Foctek Photoincs), and the size and refractive index were 6.45 6.45 mm2 and 1.53 (at 420 nm), respectively. To characterize the detector performance at different depths, another 1 25.8 20 mm3 single LYSO slab was used. Data were acquired at 10 depths (1, 3, …, 19 mm), and each depth had a 10 min acquisition time and about 40 thousand coincidence events. During the experiment, the SiPM temperature was controlled as 27.6 0.4 °C. The results showed that the 1.2 mm light guide offered the best crystal resolvability. The energy, coincidence time, and DOI resolution full-width at half-maximum of the detector were characterized as 15.66% 0.66%, 602.98 10.58 ps, and 2.33 0.07 mm, respectively. The good DOI resolution indicates the potential of utilizing the detector for high-resolution PET applications.

Goods and Services Tax: Is it in Accordance with the Federal Structure or Unitary Feature of the Constitution

This paper aims to analyse the multi-faceted indirect form of comprehensive tax structure which was enacted with the view to subsume all those taxes that were previously levied on the sale of goods or provision of services by either Central or State Government. Having faced 17 years of political setbacks, heavy debates, discussions and missing several deadlines, India’s biggest tax structure reform in India - the Goods and Services Tax was launched on July 1, 2017. Many number of countries around the globe have already implemented Goods and Services Tax in their government structure. For instance, the government of Canada saw the introduction of the tax in the year 1991, replacing the Manufacture’s Sales Tax. Change of Federal Wholesome Tax with GST in 2000 was witnessed by Australia. Singapore saw the implementation of the reform in 1994, while New Zealand did so in 1986. GST in Malaysia was introduced in 2015, and subsequently, India jumped on the bandwagon to provide benefits to the consumers, the industries, and the government. Having enforced, this paper tries to analyse whether the Goods and Services Tax’s introduction is in accordance with the Federal structure or the Unitary feature of the Constitution. Several digging up have been taken on the Government by the opposition, demonstrating the multiple slabs on which the tax is imposed in accordance with the nature of goods and type of services, and also the opposition promised for a single slab GST as a mark of proposition if elected in power. Having enforced, this paper tries to analyse whether the Goods and Services Tax’s introduction is in accordance with the Federal structure or the Unitary feature of the Constitution.

Magnetohydrodynamic Waves in Multi-Layered Asymmetric Waveguides: Solar Magneto-Seismology Theory and Application

Diagnosing the solar atmospheric plasma is one of the major challenges in solar physics. Magnetohydrodynamic (MHD) waves, by means of applying the powerful concept of solar magneto-seismology (SMS), provide a tool to obtain diagnostic insight into the magnetised solar plasma in MHD waveguides. This paper provides a road-map of simple but applicable models of solar atmospheric waveguides in the framework of Cartesian geometry. We focus on exploiting the diagnostic potential of waveguide asymmetry and consider the effects of steady flow. In particular, the dispersion relation describing linear MHD wave propagation along a multi-layered MHD waveguide is derived. Aiming at lower solar atmospheric applications of SMS, the special case of a single magnetic slab embedded in an asymmetric magnetised plasma environment is revisited. As a proof of concept, the Amplitude Ratio Method is used to make a seismological estimate of the local Alfvén speed in several chromospheric fibrils that exhibit asymmetric oscillations. Absolute ratios of boundary oscillations between 1.29 and 3.42 are detected and, despite the significant errors expected, the local Alfvén speed estimates agree with previously derived estimates from magnetic field extrapolations. Finally, the effects of asymmetric shear flows present in these slab MHD waveguides are considered as a suitable model of Kelvin-Helmholtz instability initiation that is applicable, for example, to coronal mass ejection flanks.

Three Dimensional Positive Contrast Susceptibility Fast Spin Echo MR Imaging with Variable Excitation Pulses and PD Algorithm.

A susceptibility-based positive contrast MR technique is applied to image the MR compatible metallic devices by solving a regularized ℓ1 minimization problem. However, the previous SE/FSE sequence is used for the data acquisition which can result in high SAR and low sampling efficiency in 3D imaging. Therefore, a 3D single slab 3D FSE sequence with slab selective and variable excitation pulse is proposed to implement 3D positive contrast MR imaging for low SAR and acquiring high-resolution 3D images within a shorter timeframe. Furthermore, in order to achieve faster reconstruction and better imaging quality of the 3D positive contrast MRI, the primal-dual iteration algorithm is also used to solve the regularized ℓ1 minimization problem. The visualization of the positive contrast and convergence behaviour of the proposed reconstruction framework base on the first-order PD algorithm were tested and validated on phantom experiments, compared with the previous nonlinear conjugate gradient (NLCG), fast iterative soft thresholding (FISTA) and alternating direction method of multipliers (ADMM) algorithms.

Effect of Bridge Deck Pavement Stiffness on Vertical Fundamental Frequency of Simply Supported Hollow Slab Bridges

The influence of concrete deck pavement on the vertical fundamental frequency of simply supported hollow slab bridges mainly includes the quality and stiffness contributions of the pavement, and this stiffness is divided into longitudinal and transverse stiffness components. The traditional analysis model only considered the quality contribution of the pavement, but the stiffness and vertical fundamental frequency of the structure increased with the same mass. In order to investigate the effects of pavement stiffness on the vertical fundamental frequencies of simply supported hollow slab bridges, three finite element dynamic calculation models were proposed. Through a large number of statistical analyses, the influence of different pavement thicknesses on the vertical fundamental frequencies of simply supported hollow slab bridges with different calculated spans were systematically studied. The results demonstrate that the pavement stiffness has a significant effect on the vertical fundamental frequency of a simply supported hollow slab bridge. The variation rate of the fundamental frequency is between 14% and 29%. It is suggested that the contribution of pavement stiffness should be taken into account when evaluating the fundamental frequency of the hollow slab bridge; otherwise, the mechanical performance of the structure will be overestimated. The influence law and degree of pavement stiffness on the vertical fundamental frequency of the orthogonal and skew hollow slab bridges are different. When building the dynamic calculation model, an orthogonal hollow slab bridge can help establish either the single slab model or the grillage model, and the skew hollow slab bridge should help establish the grillage model.

Numerical single-particle analysis of Cherenkov free-electron laser

The behavior of a single electron is investigated in the single slab Cherenkov free-electron laser, for which the electron motion near the surface of a dielectric is the basis of its operation. Electron motion is studied to make certain that it stays in the interaction zone and does not hit the dielectric. The Lorentz force equation is used to derive a set of coupled differential equations that are solved numerically by the Runge–Kutta method to simulate the electron motion in the desired structure. The effects of an axial magnetic field and the radiation on the electron motion are studied in order to have an efficient interaction between the electron and the radiation.

Directivity enhancement of wire monopole antenna using magnetic metamaterials

This article proposes the use of a magnetic metamaterial (MTM) slab over the ground plane of a wire monopole antenna to improve its directivity. In this regard, mu very large (MVL) behavior of the metamaterial is utilized for enhancing the directivity of the monopole. Despite the directivity enhancement of about 5 dB, an improved bandwidth of 35% is obtained for the proposed configuration. Initially, a 2 × 3 array of a single MTM slab has been placed over the ground plane of the monopole. It is shown that, over the whole working band, a significant directivity improvement is maintained compared to the unloaded monopole. Further, the directivity performance has been investigated with different combination of MTM slab.

Single-Dielectric Wideband Partially Reflecting Surface With Variable Reflection Components for Realization of a Compact High-Gain Resonant Cavity Antenna

This communication presents a design methodology for a compact low-cost partially reflecting surface (PRS) for a wideband high-gain resonant cavity antenna (RCA) which requires only a single commercial dielectric slab. The PRS has one nonuniform double-sided printed dielectric, which exhibits a negative transverse-reflection magnitude gradient and, at the same time, a progressive reflection phase gradient over frequency. In addition, a partially shielded cavity is proposed as a method to optimize the directivity bandwidth and the peak directivity of RCAs. A prototype of the PRS was fabricated and tested with a partially shielded cavity, showing good agreement between the predicted and measured results. The measured peak directivity of the antenna is 16.2 dBi at 11.4 GHz with a 3 dB bandwidth of 22%. The measured peak gain and 3 dB gain bandwidth are 15.75 dBi and 21.5%, respectively. The PRS has a radius of 29.25 mm ( $1.1\lambda _{0}$ ) with a thickness of 1.52 mm ( $0.12\lambda _{g}$ ), and the overall height of the antenna is $0.6\lambda _{0} $ , where $\lambda _{0}$ and $\lambda _{g}$ are the free-space and guided wavelengths at the center frequency of 11.4 GHz.

On-Chip Photonic Crystal Surface-Emitting Membrane Lasers

Photonic crystal lasers can be realized either based on photonic bandgap defect mode or defect-free bandedge mode, while the bandgap is not essential for the latter. We review here defect-free bandedge mode based photonic crystal surface-emitting lasers (PCSELs) for on-chip integration. We first discuss ultra-thin membrane reflector vertical-cavity surface-emitting lasers (MR-VCSELs), where single layer photonic crystal slabs can be designed as a broadband membrane reflector. Later, we discuss another type of defect-free PCSELs where the lasing cavity is formed based on evanescent coupling of gain medium with the photonic crystal bandedge mode near bandedge. Cavity designs were carried out for the optimal modal overlap and high confinement factors. Lateral cavity size scaling was also investigated both theoretically and experimentally in PCSELs. Buried tunnel junction based InGaAsP quantum well heterostructures were also designed and incorporated into electrically injected PCSELs. Finally, discussions are given toward energy efficient lasers.

PRINCIPAL AND INDEPENDENT COMPONENT ANALYSIS OF HYBRID COMBUSTION FLAME

Hybrid rocket engines are a promising technology for a variety of applications, due to their advantages with respect to solid and liquid propulsion systems. However, their use has been hindered in the past due to the low regression rate performance associated with classical polymeric hybrid fuels. The discovery of high regression rate hybrid fuels has renewed the interest in hybrid rocket propulsion. The increase in regression rate is caused by a different combustion mechanism, which still needs to be fully understood. Since 2013, many optical investigations on the so-called liquefying hybrid fuels have been done at the German Aerospace Center, Institute of Space Propulsion in Lampoldshausen, Germany, in order to better understand the mechanism responsible for droplet entrainment. The liquid layer combustion process of paraffin-based fuels in combination with gaseous oxygen has been visualized with different optical techniques in a two-dimensional single slab burner. Tests have been performed under both sub- and supercritical pressure conditions. The fuel slab configuration and composition and oxidizer mass flow rate have also been varied to understand their influence on the phenomenon. The latest results of this research are presented and discussed in this work. In all of the tests, the flame is characterized by a wave-like structure, whose frequencies and wavelengths are determined by using decomposition algorithms. Droplet formation is observed mainly during the transients. At elevated operating pressures, the flame becomes unsteady and highly turbulent. Many flame bursting and blowing events are also visualized.

Spacing effects on downward flame spread over thin PMMA slabs

To explore the flame spread mechanism over non-charring materials, the downward flame spread over polymethyl methacrylate (PMMA) samples is studied experimentally under the spacing scenarios of 2 mm, 7 mm, 13 mm, 19 mm and 25 mm. The experimental results show that: (1) As the spacing increases, the flame height, the length of the preheating zone and mass loss rate all increase first and then decrease. When the spacing is 13 mm, each value reaches the maximum. (2) As the spacing increases, the flame spread speed increases first and then decreases, approaching the single burning PMMA slab finally. In this study, a heat transfer model is proposed to examine the spacing effect over PMMA slabs. According to experimental results, a correlation between the flame spread rate and spacing is derived. Besides, experimental data agree well with the theoretical model.

Machine Learning Approach for Data Analysis of Magnetic Orbital Moments and Magnetocrystalline Anisotropy in Transition-Metal Thin Films on MgO(001)

Using the Least Absolute Shrinkage and Selection Operator (LASSO) technique, we analyze a long-standing issue in the field of magnetism: the relationship between orbital magnetic moments and magnetocrystalline anisotropy (MCA) energy in transition-metal thin films. Our LASSO regression utilizes the data obtained from first principles calculations for single slabs with six atomic-layers of binary Au-Fe, Au-Co, and Fe-Co films on MgO(001). In the case of Fe-Co thin films, we have successfully regressed the MCA energy against the anisotropy of orbital moments along the in-plane and the perpendicular plane directions, giving a linear behavior. For the Au-Fe and Au-Co thin films, however, our data-driven analysis shows no relation between the MCA energy and the anisotropy of orbital moments.

Concatenated silicon etalon tunable filter for hyperspectral imaging in the near infrared

A critical limitation imposed on all imaging systems is to achieve an optimal balance between optical resolution and bandwidth. The optical system determines and affects the relations between temporal information, spatial bandwidth, and resolution, so the resulting signal may differ for each wavelength. This is of significant importance for hyperspectral imaging in particular, because it extracts both spatial and temporal wavelength information. We present a dispersive device that can be used for hyperspectral imaging hypercube image measurements. We utilize the Vernier effect by integrating two silicon slabs that act together as a modified Fabry–Perot filter. The transition between wavelength bands is achieved by heating, utilizing the thermo-optic effect. Importantly, we show that red-shifting with concatenated slabs requires less heating than with a single slab. With the presented technique, a wide effective free spectral range of up to 90 nm around a central wavelength of 1550 nm was achieved along with 20-nm full-width-at-half-maximum resolution. With the same configuration, observing a narrower 0.7-nm free spectral range bandwidth, a fine spectrum resolution of 0.07 nm was obtained. Such variety covers most of the spatial and temporal standard limitations of current hyperspectral imaging requirements.

Non-linear reflection engineered enhanced broadband SHG in a hyperbolic profiled GaAs slab using TIR-QPM

A highly enhanced broadband conversion scheme of Second Harmonic Generation is analytically described in a hyperbolic profiled single crystal GaAs slab using Total Internal Reflection Quasi Phase Matching. The inclusion of the effect arising from the basic law of Non Linear Reflection has interestingly boosted up the conversion efficiency, which otherwise trims down the same as revealed in the conversion schemes comprising parallel, tapered and reverse tapered structures of isotropic semiconductors. Here, the simulated result indicates an enhancement both in terms of efficiency and bandwidth due to higher compensation of the spatial walk-off between the generated Second Harmonic waves along the slab length owing to the hyperbolic profiled upper surface configuration. Consequently, an extremely broad 3 dB bandwidth of 800 nm is obtained in a 32 mm GaAs slab and the conversion efficiency rises to a value of 2.151% which is as high as 1.7 times compared to that without considering the effect of the Non-linear Reflection phenomenon.

Perfect absorption in cascaded asymmetric hyperbolic metamaterial slabs

The absorption of single asymmetric hyperbolic metamaterial (AHM) slab and cascaded AHM slabs has been theoretically studied in this paper. The proposed AHM consists of Polymethyl methacrylate (PMMA) and silver sheet. The numerical results show that the absorption of the single AHM slab is very sensitive to the azimuth angle, and the average absorption over the azimuth angle is only 0.2. However, the absorption of the cascaded AHM slabs can reach 0.7 in all the azimuth angles, and the average absorption over the azimuth angle can reach 0.88. Compared with the average absorption of the single AHM slab, the average absorption of the cascaded AHM slabs increases threefold.

Subduction Zones Interaction Around the Adria Microplate and the Origin of the Apenninic Arc

AbstractThe study of slab‐slab interactions has come to the front of geodynamics researches to explain geological and geophysical observations from tectonically complex areas. Here we aim to better understand the geodynamics of the Central Mediterranean, where the Adria plate subducts on its two opposite sides. Additionally, the slab below the Central South Apennines has been progressively breaking off during the last 3 Myr. The role of a slab window in a single slab or in an outward dipping double‐sided subduction system is addressed by analog models at the scale of the upper mantle, realized using glucose syrup and silicone putty, to model the interaction between the Earth's mantle and the lithosphere. Our results show that the presence of a slab window modifies the pattern of mantle circulation, as well as the trench geometry and kinematics. In particular, the opening of the slab window induces the formation of two arcs flanking the window, while the mantle flows through it and turns toward the arcs, creating a small‐scale toroidal flow. The effect of a slab window is more pronounced on double subduction systems, as the outflow through the window is amplified, while internal deformation is induced in the plate by the opposite slab pull force. These experimental results suggest that the origin of the Apenninic and the Calabrian arcs is the result of the formation of a slab window, providing a new interpretation of the surface deformation and the SKS shear wave splitting pattern of the Adria microplate.

Pressure–Temperature History of the &gt;3 Ga Tartoq Greenstone Belt in Southwest Greenland and Its Implications for Archaean Tectonics

The Tartoq greenstone belt of southwest Greenland represents a well-preserved section through &gt;3 Ga old oceanic crust and has the potential to provide important constraints on the composition and geodynamics of the Archaean crust. Based on a detailed structural examination, it has been proposed that the belt records an early style of horizontal convergent plate tectonics where elevated temperatures, compared to the modern-day, led to repeated aborted subduction and tonalite–trondhjemite–granodiorite (TTG) type melt formation. This interpretation hinges on pressure–temperature (P–T) constraints for the belt, for which only preliminary estimates are currently available. Here, we present a detailed study of the pressure–temperature conditions and metamorphic histories for rocks from all fragments of the Tartoq belt using pseudosection modelling and geothermobarometry. We show that peak conditions are predominantly amphibolite facies, but range from 450 to 800 °C at up to 7.5 kbar; reaching anatexis with formation of TTG-type partial melts in the Bikuben segment. Emplacement of the Tartoq segments into the host TTG gneisses took place at approximately 3 Ga at 450–500 °C and 4 kbar as constrained from actinolite–chlorite–epidote–titanite–quartz parageneses, and was followed by extensive hydrothermal retrogression related to formation of shear zone-hosted gold mineralisation. Tourmaline thermometry and retrograde assemblages in mafic and ultramafic lithologies constrain this event to 380 ± 50 °C at a pressure below 1 kbar. Our results show that the convergent tectonics recorded by the Tartoq belt took place at a P–T gradient markedly shallower than that of modern-day subduction, resulting in a hot, weak and buoyant slab unable to generate and transfer ‘slab pull’, nor sustain a single continuous downgoing slab. The Tartoq belt suggests that convergence was instead accomplished by under-stacking of slabs from repeated aborted subduction. The shallow P–T path combined with thermal relaxation following subduction stalling subsequently resulted in partial melting and formation of TTG melts.

Isotropic wavevector domain image filters by a photonic crystal slab device.

We show that several types of isotropic image filters in the wavevector domain can be implemented with a single photonic crystal slab device. Such a slab is designed so that the guided resonance near the Γ point exhibits an isotropic band structure. Depending on the light frequency and the choice of transmission or reflection mode, the device realizes isotropic high-pass, low-pass, band-reject, and band-pass filtering in wavevector space. These filter functions are important for various image processing tasks, including edge detection, smoothing, white noise suppression, and suppression or extraction of periodic noises. We numerically demonstrate these filter functionalities by simulations of a slab structure that is designed to operate in the visible wavelength range. Our work expands the application of nanophotonics-based optical analog computing for image processing.

High extinction ratio hexagonal boron nitride polarizer

In this paper, we theoretically studied that the high extinction ratio polarizers can be designed with hexagonal boron nitride (hBN). We demonstrated that the transverse electric wave can pass the single hBN slab with high transmissivity in the range of 6.25–7.4 μm, while the transverse magnetic wave cannot pass through. The extinction ratio is always over 14 dB in that range. Besides, we also proposed a photonic crystal polarizer made of hBN and silicon, which can work in the visible band. The numerical results show that the polarizer allows the transverse magnetic wave to pass and block the transverse electric wave in the range of 0.45–0.53 μm. The minimum extinction ratio is 30 dB in this range. Therefore, we believe the low loss hBN is a promising anisotropic material for realizing polarizers and it may have applications in photography and liquid-crystal display (LCD) technology.