DFT Insights into the Hydrodenitrogenation and Ring-Opening of Indole on an M (M = Ni, Pt, Ni–Pt) Slab Model

Density functional theory (DFT) calculation has been used to study the hydrodenitrogenation (HDN) and ring-opening of indole on an M (M = Ni, Pt, Ni–Pt) slab surface. The possible reaction pathway of indole hydrogenation has been investigated in order to reveal the bimetallic synergistic effects of an M slab surface. Compared to the mechanism of indole hydrogenation on an M slab surface, it was found that a PtNi(111) surface favors indole hydrogenation. According to the results of DFT calculation, it suggests that the bimetallic effect of the M surface plays an important role in indole hydrogenation.

Tracking slab surface temperatures with electrical conductivity of glaucophane

Slab surface temperature is one of the key parameters that incur first-order changes in subduction dynamics. However, the current thermal models are based on empirical thermal parameters and do not accurately capture the complex pressure–temperature paths of the subducting slab, prompting significant uncertainties on slab temperature estimations. In this study, we investigate whether the dehydration-melting of glaucophane can be used to benchmark the temperature in the slab. We observe that dehydration and melting of glaucophane occur at relatively low temperatures compared to the principal hydrous phases in the slab and produce highly conductive Na-rich melt. The electrical properties of glaucophane and its dehydration products are notably different from the hydrous minerals and silicate melts. Hence, we conclude that the thermodynamic instability of glaucophane in the slab provides a unique petrological criterion for tracking temperature in the present-day subduction systems through magnetotelluric profiles.

Sediment-Peridotite Reaction Controls Fore-Arc Metasomatism and Arc Magma Geochemical Signatures

Subduction of oceanic crust buries an average thickness of 300–500 m of sediment that eventually dehydrates or partially melts. Progressive release of fluid/melt metasomatizes the fore-arc mantle, forming serpentinite at low temperatures and phlogopite-bearing pyroxenite where slab surface reaches 700–900 °C. This is sufficiently high to partially melt subducted sediments before they approach the depths where arc magmas are formed. Here, we present experiments on reactions between melts of subducted sediments and peridotite at 2–6 GPa/750–1100 °C, which correspond to the surface of a subducting slab. The reaction of volatile-bearing partial melts derived from sediments with depleted peridotite leads to separation of elements and a layered arrangement of metasomatic phases, with layers consisting of orthopyroxene, mica-pyroxenite, and clinopyroxenite. The selective incorporation of elements in these metasomatic layers closely resembles chemical patterns found in K-rich magmas. Trace elements were imaged using LA-ICP-TOFMS, which is applied here to investigate the distribution of trace elements within the metasomatic layers. Experiments of different duration enabled estimates of the growth of the metasomatic front, which ranges from 1–5 m/ky. These experiments explain the low contents of high-field strength elements in arc magmas as being due to their loss during melting of sedimentary materials in the fore-arc.

Differentiating induced versus spontaneous subduction initiation using thermomechanical models and metamorphic soles

Despite the critical role of subduction in plate tectonics, the dynamics of its initiation remains unclear. High-temperature low-pressure metamorphic soles are vestiges of subduction initiation, providing records of the pressure and temperature conditions along the subducting slab surface during subduction initiation that can possibly differentiate the two end-member subduction initiation modes: spontaneous and induced. Here, using numerical models, we show that the slab surface temperature reaches 800–900 °C at ~1 GPa over a wide range of parameter values for spontaneous subduction initiation whereas for induced subduction initiation, such conditions can be reached only if the age of the overriding plate is <5 Ma. These modeling results indicate that spontaneous subduction initiation would be more favorable for creating high-temperature conditions. However, the synthesis of our modeling results and geological observations indicate that the majority of the metamorphic soles likely formed during induced subduction initiation that involved a young overriding plate.

Review of Punching Shear Strengthening Methods [Case Study: Application of Post Installed Shear Bolt Papers]

Flats slabs became a common solution for buildings because they are easy and fast to build. In the last few years, some building that constructed using flat slab system required strengthening for column to slab junction due to either some imperfections during design, construction or due to increase of the design load in case of change of the building function. The common strengthen methods against punching shear (column heads, drop panels) leave an obvious trace which in most cases conflicts with some extensions parts and may reduce the height of the story considered, thus it can’t be applied in such cases. A relatively new technique was studied, it consists of high tensile steel bolts installed vertically through the slabs by drilling and bonding with high-performance epoxy adhesive and mechanically anchored to the slab surface. Many studies validated the efficiency of the technique in strengthen against punching shear and also in enhancing the ductility of the slab-column connection and the results shows that the method can be applied in practice. In this paper, the post-installed bolts technique is presented and applied in a practical case study. The capacity of the slab enhanced by 53% and it was easy to design and construct. Also, it took not more than few hours for its application. In addition, the building extension utilities (Heating ventilation and air conditioning, communications...etc.) was not harmed because the slab surface remains clear. Those advantages make the technique a favorable option for owners and engineers when strengthening against punching shear.

Seismological evidence of a dehydration reaction in the subducting oceanic crust beneath western Shikoku in southwest Japan

SUMMARY The Philippine Sea plate (PHS) is subducting beneath southwest Japan from the Nankai Trough. In this region, deep low-frequency earthquakes/tremors (LFEs) are active and their epicentres are distributed along the downdip of the source region of M8-class earthquakes that have occurred every 100–150 yr. The LFE activity may potentially be strongly related to the occurrence of great earthquakes between tectonic plates. To investigate the structural features around the LFEs, we applied teleseismic receiver function (RF) analysis to the seismograms observed at permanent and temporal seismograph stations in western Shikoku and we detected seismological evidence of a slab dehydration reaction linked to LFE activity. Based on the first-order harmonic decomposition of RFs, we first estimated the average plunge azimuth of the PHS beneath western Shikoku. Considering the backazimuth dependence of converted phase amplitude, we constructed the cross-section of the radial component RFs, excluding the incoming waveform data from the updip directions of the dipping slab. In this profile, the parallel negative and positive P-to-S converted phase alignment within a distance of 10 km were imaged. These phase alignments corresponded to the top of the slab and the slab Moho discontinuity, respectively. At the northern side of the profile, the landward (continental) Moho was also detected. In the region where LFEs were actively distributed, both the landward Moho and slab surface were unclear. The second-order harmonic decomposition of RFs for several kilometres above the slab Moho indicated that the anisotropic symmetry axes suddenly changed at the southern limit of the LFE active region; the fast axes in the region were normal to the trench though axes in the southern area were parallel. According to the thermal and pressure condition, a phase transition with a dehydration reaction can occur in the oceanic crust near the southern edge of the LFE active region. Once the dehydration process advances, released water causes the serpentinization of the mantle material near the slab surface and the corresponding seismic velocity decreases. The impedance contrast decreases at the boundary between the lower crust and the mantle wedge, as well as that between the mantle wedge and oceanic crust; therefore, the amplitudes of the converted phases at these boundaries also become small. Considering that serpentinite ordinarily has strong anisotropy with a seismic fast axis direct to the shear direction, all features observed are evidence of the dehydration process in the flat slab.

A closer look at the relationship between slab (un)bending and double seismic zone seismicity

&lt;p&gt;The origin of double seismic zones (DSZs), parallel planes of intraslab seismicity observed in many subduction zones around the globe, is still highly debated. While most researchers assume that fluid release from prograde metamorphic reactions in the slab is an important control on DSZ occurrence, the role of slab unbending is currently unclear.&lt;br&gt;Slab bending at the outer rise is instrumental in hydrating the downgoing oceanic plate through bend faulting, and is evident from earthquake focal mechanisms (prevalence of shallow normal faulting events). Observations from NE Japan show that focal mechanisms of DSZ earthquakes are downdip compressive in the upper and downdip extensive in the lower plane of the DSZ, which strongly hints at slab unbending. This coincidence of slab unbending and DSZ seismicity in NE Japan has given rise to several models in which unbending forces are a prerequisite for DSZ occurrence.&lt;/p&gt;&lt;p&gt;To globally test a potential correlation of slab unbending with DSZ seismicity, we derived downdip slab surface curvatures on trench-perpendicular profiles every 50 km along all major oceanic slabs using the slab2 grids of slab surface depth. We here make a steady-state assumption, i.e. we assume that the slab geometry is relatively constant with time, so that the downdip gradient of slab curvature corresponds to slab (un)bending. We compiled the loci and depth extent of all DSZ observations avalable in literature, and compare these to the slab bending or unbending estimates.&lt;/p&gt;&lt;p&gt;Preliminary results indicate that while there is a clear correspondence between the depth of slab unbending to DSZ seismicity in the Japan-Kurile slab, most other slabs do not show this correlation. Moreover, some DSZs deviate from the above-mentioned focal mechanism pattern and exhibit downdip extension in both planes (e.g. Northern Chile, New Zealand). It appears that the global variability of slab geometries in the depth range 50-200 km is larger than anticipated, and DSZ seismicity is not limited to slabs where unbending is prevalent at these depths. The Northern Chile case is especially interesting because focal mechanisms there not only do not fit the pattern observed in NE Japan, but also can not be explained with the current slab geometry alone. This could indicate a direct influence of ongoing metamorphic reactions on focal mechanisms (e.g. via volume reduction and densification), or it may be a hint that our steady-state assumption is invalid for the Nazca slab here (i.e. that it is in the process of changing its geometry).&lt;/p&gt;

Computational study of reverse water gas shift reaction on Cu38 cluster model and Cu slab model

Density functional theory (DFT) calculation has been applied to investigate the adsorption behaviors of reactive adsorbate and the reaction pathway of reverse water gas shift (RWGS) reaction on Cu[Formula: see text] cluster and Cu slab surface. The possible adsorption configuration, sites and energies of reactive intermediates on Cu[Formula: see text] cluster and Cu slab surface have been calculated to reveal the effects between Cu[Formula: see text] cluster and Cu slab surface. In addition, transition states, reaction energies and activation barriers were calculated to RWGS mechanism on Cu[Formula: see text] cluster and Cu slab model. Compared to the mechanism of RWGS on different surfaces, it was found the Cu[Formula: see text] cluster facilitates the RWGS reaction. The intrinsic differences between Cu cluster and Cu slab model suggest that surface defects play a pivotal role in RWGS reaction.

Cherenkov Emission Generated by a Modulated Source in 2D Dispersive Photonic Crystal Slabs

This work presents a systematic numerical study of Cherenkov optical radiation generated by a modulated source that moves with uniform velocity on a two-dimensional (2D) photonic crystal (PCr) slab surface. We apply the FDTD technique with emphasis on the dispersion properties of the periodic medium to perform our numerical analysis. The field oscillations generated at the passage of a modulated source in the PCr produce a series of spectral resonances corresponding to the eigenmodes in the spatial frequency domain for the photonic slab. The amplitudes of the field oscillations have maximal values in the group cone closely to the path of the moving charge.