Shield Region Research Articles

APPLICATION OF SUPERMC3.2 TO PRELIMINARY NEUTRONICS ANALYSIS FOR EUROPEAN HCPB DEMO

In the D-T fueled tokamak, the neutrons not only carry the approximately 80% energy released in the per fusion reaction, but also are the source of radioactivity in the fusion system. Therefore, high-fidelity neutronics simulation is required to support such reactor design and safety analysis. In the present work, taking European HCPB DEMO (Helium Cooled Pebble Bed demonstration fusion plant) developed by KIT (Karlsruhe Institute of Technology) as an example, the preliminary neutronics analysis covering the assessments of NWL (neutron wall loading), TBR (tritium breeding ratio), nuclear power generation, radiation loads on PFCs (plasma-facing components) and TFCs (toroidal field coils) has been carried out by using SuperMC in the case of both unbiased and biased simulations. The preliminary results indicate that the blanket scheme could satisfy the design requirements in terms of TBR and shielding of inboard blankets. Specially, a speed-up by ~164 times in the calculation for thick shielding region (TFC region) is achieved by using global weight windows generated via GWWG in SuperMC. In addition, compared to MCNP, SuperMC shows advantages in accurate and efficient modeling of complex system, efficient calculation and 3D interactive visualization.

High resolution measurements with miniature neutron scintillators in the SUR-100 zero power reactor

Three 1-mm3 miniature fiber-coupled scintillators have been used to perform cm-wise resolution measurements of the thermal neutron flux within experimental channels of the SUR-100 facility, a zero power thermal reactor operated by the Institute of Nuclear Technology and Energy Systems at the University of Stuttgart. The detection system is developed at the École Polytechnique Fédérale de Lausanne in collaboration with the Paul Scherrer Institut. Thermal neutrons count rates were measured along the experimental channels I and II, which cross the reactor at the center and tangentially to the core, respectively. The reactor was modelled with the Monte Carlo neutron transport code Serpent-2.1.31. The comparison of experimental and computed reaction rate distributions showed a good agreement within the core region, with discrepancies within 2σ. An unexpected discrepancy, probably caused by a geometric inconsistency in the computational model of the reactor, was observed in the reflector region of the experimental channel I, where a 20% difference (i.e. 8σ) was found between experimental and simulated results. Significant discrepancies, respectively worth 10σ and 15σ, were noticed at distance, in the lead shielding region, for both experimental channels I and II. In addition, reaction rate gradients across the 2.6 cm and 5.4 cm diameters of both channels were measured. A horizontal reaction rate gradient of (9.09 ± 0.20) % was measured within 2.4 cm across the diameter of the experimental channel II, with a difference from computed results of 2%. The absence of a vertical reaction rate gradient inside the experimental channel I was confirmed by measurements.

Improved 4H-SiC UMOSFET with super-junction shield region* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61774052 and 61904045), the Youth Foundation of the Education Department of Jiangxi Province, China (Grant No. GJJ191154), and the Youth Foundation of Ping Xiang University, China (Grant No. 2018D0230).

This article investigates an improved 4H-SiC trench gate metal–oxide–semiconductor field-effect transistor (MOSFET) (UMOSFET) fitted with a super-junction (SJ) shielded region. The modified structure is composed of two n-type conductive pillars, three p-type conductive pillars, an oxide trench under the gate, and a light n-type current spreading layer (NCSL) under the p-body. The n-type conductive pillars and the light n-type current spreading layer provide two paths to and promote the diffusion of a transverse current in the epitaxial layer, thus improving the specific on-resistance (R on,sp). There are three p-type pillars in the modified structure, with the p-type pillars on both sides playing the same role. The p-type conductive pillars relieve the electric field (E-field) in the corner of the trench bottom. Two-dimensional simulation (silvaco TCAD) indicates that R on,sp of the modified structure, and breakdown voltage (V BR) are improved by 22.2% and 21.1% respectively, while the maximum figure of merit () is improved by 79.0%. Furthermore, the improved structure achieves a light smaller low gate-to-drain charge (Q gd) and when compared with the conventional UMOSFET (conventional-UMOS), it displays great advantages for reducing the switching energy loss. These advantages are due to the fact that the p-type conductive pillars and n-type conductive pillars configured under the gate provide a substantial charge balance, which also enables the charge carriers to be extracted quickly. In the end, under the condition of the same total charge quantity, the simulation comparison of gate charge and OFF-state characteristics between Gauss-doped structure and uniform-doped structure shows that Gauss-doped structure increases the V BR of the device without degradation of dynamic performance.

An improved probabilistic seismic hazard mapping of peninsular shield region of India

This paper attempts to present improved probabilistic seismic hazard maps of the peninsular shield of India based on data driven seismicity and ground motion models. Combination of nine conventional area sources described by Gutenberg and Richter's (G-R) recurrence relationship and a vast tectonic province of southern peninsular shield described by a zone-free kernel smoothing approach has been used independently. Similar to that for the conventional area sources, the expected occurrence rates of earthquakes in different magnitude bins are estimated from the G-R relationships, but distributed non-uniformly among a grid of square cells in accordance with the smoothed epicentral density of the observed past seismicity. On the other hand, the occurrence rates for the tectonic province source are obtained directly by kernel smoothing of the gridded past seismicity. Other distinguishing features of the present study are (a) the use of a very comprehensive and thoroughly scrutinized earthquake catalogue, (b) data driven selection of ground motion prediction equations (GMPEs) using the limited accelerogram records available, (c) estimation of the source-to-site distances by accounting for the effects of the regional strike and dip angles of the fault rupture planes for a perfect compatibility with the distances involved in the selected GMPEs, and (d) permitting the rupture length to extend beyond the zone boundaries in the estimation of the source-to-site distances, which along with the non-uniform distribution of seismicity is able to normalize to some extent the effect of any uncertainty in deciding the zone boundaries. As the geometries of the area sources are decided mainly on the basis of the major tectonic features in the region, the hazard maps obtained are seen to depict the desired conformity with them fairly well. Also, due to the use of the data-driven selection of the highest ranking GMPEs, the hazard maps obtained are expected to be representative of the peninsular region. The rock site uniform hazard spectra for 14 important sites in different parts of the peninsular India as obtained from the presented hazard maps are compared with the corresponding design spectra based on the ASCE/SEI 7–10 and BIS codal provisions, and necessary modifications are proposed in the ASCE provisions in order to get the design spectra specific to the peninsular India. The paper also proposes empirical amplification factors to obtain uniform hazard spectra for a given VS30 value from the computed rock site uniform hazard spectra.

Using a digital relief model for searching for primary sources of gold in metamorphic complexes of the Evota region (Aldan-Stanovoy shield, North-Asian craton)

Placers of precious metals and other mineral resources are associated with the uplifted basement of the North-Asian craton and metamorphic terrains near its borders. The complex geological structure of these territories does not allow to make obvious conclusions about the sources of the placers. One of the areas of the southern outcrop of the craton basement, the Evota gold-bearing region of the Aldan-Stanovoy shield was studied. Analysis of the morphology of native gold selected from creeks of the region and eluvium from one of the primary deposits show that grains with similar morphological features occur. Probably, not far from the points of sampling, primary sources are located. Possible erosion and sediment removal should occur in positive forms of relief. Therefore, an attempt to determine the location of primary sources by modeling positive forms of relief, where erosion occurs and removal could be manifested, was made. The methodology for modeling these forms using modern geoinformation systems was considered as an attempt to analyze the obtained results. Digitized relief maps (topographic base) of the area and sample points with discovered gold were a basis for the calculations. Further steps were: building a surface of relief as a regular network of highs, calculating directions and slope angle of the surface, building a map of removal vectors, constructing a path with a maximum slope upward from the point with gold particles discover. Lines of positive forms of relief confined to gold discover points were constructed as a result. Field works for identifying signs of gold content in these lines and point sampling of rock debris were carried out. Microprobe analyses of rock debris were performed. Minerals of gold and silver were discovered in the debris. The obtained data shows that this method of analysis can be useful for deciphering ore-bearing structures and searching for primary sources.

Numerical Simulation Analysis of Switching Characteristics in the Source-Trench MOSFET’s

In this paper, we compare the static and switching characteristics of the 4H-SiC conventional UMOSFET (C-UMOSFET), double trench MOSFET (DT-MOSFET) and source trench MOSFET (ST-MOSFET) through TCAD simulation. In particular, the effect of the trenched source region and the gate trench bottom P+ shielding region on the capacitance is analyzed, and the dynamic characteristics of the three structures are compared. The input capacitance is almost identical in all three structures. On the other hand, the reverse transfer capacitance of DT-MOSFET and ST-MOSFET is reduced by 44% and 24%, respectively, compared to C-UMOSFET. Since the reverse transfer capacitance of DT-MOSFET and ST-MOSFET is superior to that of C-UMOSFET, it improves high frequency figure of merit (HF-FOM: RON-SP × QGD). The HF-FOM of DT-MOSFET and ST-MOSFET is 289 mΩ∙nC, 224 mΩ∙nC, respectively, which is improved by 26% and 42% compared to C-UMOSFET. The switching speed of DT-MOSFET and ST-MOSFET are maintained at the same level as the C-UMOSFET. The switching energy loss and power loss of the DT-MOSFET and ST-MOSFET are slightly improved compared to C-UMOSFET.

Visualizing NMR‐shielding effect in fullerene‐ZnPc aggregates: Characteristic patterns of ZnP‐based hosts and encapsulation nature from DFT calculations

AbstractThe formation of supramolecular aggregates incorporating C60 fullerenes can be followed and characterized by nuclear magnetic resonance (NMR) measurements. Here, we unravel the particular patterns provided by zinc‐porphyrin (ZnP)‐bridged dimers, where the aromatic character of each ZnP unit leads to an enhanced shielding region for the closest fullerene atoms, denoting a slight shielding effect for the equatorial atoms. The nature of the stabilization is discussed and compared to a single ZnPC60 aggregate and a ZnP‐dimer (ZnP2C60) model, with a significant contribution from noncovalent ππ interactions, allowing us to address the role of bridging chains. The experimental 13C‐NMR spectrum of C60 in a bridged ZnP dimer shows a single peak owing to the constant tumbling inside the host, which averages the different groups of carbon atoms. The calculations in a static scenario reveal information concerning the local chemical environment underlying the observed shift in relation to isolated C60. We expect that the current approach can be useful to rationalize and predict the origin of the NMR shift upon the formation of host‐guest aggregates involving small and large host species.

4H-SiC trench MOSFET with an integrated Schottky barrier diode and L-shaped P+ shielding region

A novel 4H-SiC trench MOSFET is presented and investigated by simulation in this paper. The device features an integrated Schottky barrier diode and an L-shaped P+ shielding region beneath the gate trench and aside one wall of the gate trench (S-TMOS). The integrated Schottky barrier diode works as a free-wheeling diode in reverse recovery and reverse conduction, which significantly reduces reverse recovery charge (Qrr) and reverse turn-on voltage (VF). The L-shaped P+ region effectively shields the coupling of gate and drain, resulting in a lower gate–drain capacitance (Cgd) and date–drain charge (Qgd). Compared with that of conventional SiC trench MOSFET (C-TMOS), the VF and Qrr of S-TMOS has reduced by 44% and 75%, respectively, with almost the same forward output current and reverse breakdown voltage. Moreover, the S-TMOS reduces Qgd and Cgd by 32% and 22%, respectively, in comparison with C-TMOS.

Effect of mainstream forced entrainment on the combustion performance of a gas turbine combustor

In trapped vortex combustors, a radial strut is designed to improve the combustion efficiency and achieve uniform temperature distribution. However, under the action of the strut, a mainstream forced entrainment phenomenon may take place in the cavity, which would extinguish the local flame there. In this study, to achieve high combustion efficiency with robust stability, a strategy to optimize the radial strut was proposed to control the mainstream forced entrainment phenomenon. Then, an experimental study was conducted to investigate the effects of mainstream forced entrainment on the combustion efficiency, ignition, and lean blowout performance in a workable trapped vortex combustor. Additionally, numerical simulations on the flow field were performed to obtain insights into the experimental results. It was found that the mainstream entrained into the cavity is helpful for improving the combustion efficiency and inner-cavity ignition performance. This occurs because the entrained mainstream changes the flow field behind the strut, which provides many more shield regions for fuel combustion and flame propagation. However, the mainstream entrained into the cavity is harmful to the ignition of the outer cavity and lean blowout performance, because the entrained mainstream can not only decrease the size of the main vortex of the cavity, but also reduce the local fuel to air ratio inside the cavity. Additionally, it was found that a change in the strut dimensionless parameter L/D can effectively control the flow fields, and thus the combustion performance. Furthermore, a critical value of 0.50 was obtained for the strut dimensionless parameter L/D.

New records of Platynectes (s. str.) diving beetles from South America with description of two new species (Coleoptera: Dytiscidae: Agabinae)

Diving beetles in the genus Platynectes (s. str.) in South America are relatively large and charismatically colored, yet relatively rare in museum collections. Recent fieldwork in northern and central South America has resulted in the collection of hundreds of new specimens that substantially expand our distributional knowledge of the genus. Here, we provide new distributional records for Platynectes decemnotatus (Aubé, 1838), P. garciai Gustafson, Short & Miller, 2016, P. submaculatus (Laporte, 1835), and P. tafelbergensis Gustafson, Short & Miller, 2016. In addition, two new species were identified and described herein: Platynectes bicolor sp. nov. of the P. ornatifrons species group from Brazil (Goiás and Mato Grosso do Sul), and P. colombicus sp. nov. of the P. submaculatus species group from the Guiana Shield region of eastern Colombia. These new records suggest that Platynectes (s. str.) is likely widespread across the Brazilian and Guiana Shield regions of the continent, and that some individual species have substantial range sizes of nearly 2000 km. An updated key to the species groups of Neotropical Platynectes (s. str.) and to the species of P. submaculatus species group are provided.

Interplay Between Planar and Spherical Aromaticity: Shielding Cone Behavior in Dual Planar-Planar, Planar-Spherical and Spherical-Spherical Aromatics.

The shielding cone concept is one of the most characteristic aspects of planar aromatic species. Herein, we explored how two neighbor aromatic moieties behave as dual planar-planar, planar-spherical, and spherical-spherical species given by biphenyl, [PhCB11 H11 ]- , and [CB11 H11 ]2 2- , respectively. Our results show two separate aromatic regimes given by Clar's sextet and spherical aromatic states, with independent shielding cones sharing shielding regions of moderate strength, which can be extended for networks involving multiple independent aromatic states.

A New Hyphessobrycon (Characiformes: Characidae) from the Guiana Shield in Northern Brazil

A new species of Hyphessobrycon from a tributary of the Rio Paru do Oeste (Rio Trombetas basin), at the lower Amazon basin draining the Guiana Shield region in Para State, Brazil, is described. The new species presents a unique combination of an irregularly-shaped humeral blotch, a broad diffuse midlateral stripe, and a roughly triangular caudal peduncle blotch. The new species is herein included in the Hyphessobrycon agulha species-group, and comparisons with species belonging to this group and to a similar-looking non-congener, Hemigrammus bellottii, are presented.

A Novel 4H-SiC Super Junction UMOSFET with Hetero-Junction Diode for Enhanced Reverse Recovery Characteristics and Low Switching Loss

In this paper, a novel silicon carbide (SiC) super-junction U-shape metal-oxide semiconductor field-effect transistor (UMOSFET) with an integrated hetero-junction diode (HJD) is proposed and investigated using numerical simulations. The integrated HJD substantially improves body diode characteristics and reduces switching losses without degrading the static characteristics of the device. In this structure, a p+ shielding region between the p-poly region and p-pillar protects not only the bottom gate oxide but also the p-poly region from high electric fields. Compared with conventional SJ UMOSFETs, the proposed structure reduces the peak reverse recovery current (IRR) by a factor of 2.58 and the reverse recovery charge (QRR) by a factor of 4.94. Moreover, the total switching energy loss is decreased by 50.2%.

Passive Control of Transonic Flow over a Blunt Body Using Aerospikes

Blunt nose cones used in launch vehicles can excite buffet due to shock oscillations over the payload fairing on the leeward side at transonic Mach numbers and small angles of attack. Wind-tunnel tests show that the overall aerodynamic characteristics, such as the pitching moment and location of the center of pressure, experience sudden jumps at these conditions. Thus, the longitudinal stability and controllability of a launch vehicle, as well as unsteady loading on the payload fairing, can be affected. The cause of these oscillations is found to be interactions between the streamwise flow and reverse flow induced by a pair of counter-rotating vortices over the payload fairing. An aerospike was found to prevent the formation of counter-rotating vortices, shock oscillations, as well as jumps in overall aerodynamic characteristics, with no significant changes in the drag coefficient. The observations are supported by high-speed shadowgraphs and surface-flow visualizations. Computational fluid dynamics studies suggest that the shear layer from the tip of the aerospike envelops a significant region of the heat shield in a reverse flow due to the formation of a separation bubble. Mean-flow models of the topologies of the flowfield for the model without and with aerospike are proposed.

Earthquake source dynamics and kinematics of the Eastern Indian Shield and adjoining regions

The Eastern Indian Shield (EIS) consists of two cratonic nuclei, namely Singhbhum craton and Chhotanagpur Granitic Gneissic terrain. This area contains several crisscross faults, lineaments, shear zones, numerous hot springs and three major rivers (e.g., Ganga, Brahmaputra and Damodar). The area is regionally covered by 7 seismic stations and jointly recorded 16 events from the study area, and less noisy waveforms of 4 events were used for focal mechanism analysis using the Cut and Paste method. The focal parameters of these 4 events were compiled with results of 8 events computed by different workers for the study area. To understand the detailed tectonics, focal mechanisms of 21 events for the Himalayan segment were taken from CMT Harvard catalog of duration 1976–2017. Spatial variations of operative stress fields for major tectonic domains were analyzed in the present study based on stress inversion of focal mechanism parameters. We observed strike-slip-dominated movements in the EIS, which changes partially into extension in the northeast part between the Ganga and Brahmaputra Rivers. Thrust-dominated movements evidenced by focal mechanisms and the pure compression in the western segment of the Himalaya in the north might be promoting shear movements in the EIS and adjoining regions. The pure strike-slip in the eastern segment of the Himalaya and its deeper level account for lateral shearing and eastward movements of different tectonic blocks. The normal faulting earthquakes in the northeast part might be indicating stretching in the basement because of convergence of Indian lithosphere beneath the Myanmar plate.

Gravity Anomalies, Isostasy and Density Structure of the Indian Continental Lithosphere

Gravity anomalies across the Indian region depict most of the geological and tectonic domains of the Indian continental lithosphere, which evolved through Archean cratonic nucleation, Proterozoic accretion, Phanerozoic India-Eurasia plate convergence, and modification through many thermal perturbations and rifting. Integrated analysis of gravity and geoid anomalies together with topographic and heat flow data led to deciphering the mechanism of isostatic compensation of topographic and geological loads, lithospheric structure, and composition. This study discusses the nature of gravity (free-air, Bouguer and Isostatic) and geoid anomalies in relation to the topography, geology, and tectonics, and presents a lithospheric density model across the peninsular India and Himalaya. Southern peninsular Indian region shows relatively low Bouguer gravity anomalies compared to the northern region. The mobile belts are generally observed to have relatively higher Bouguer gravity anomalies, e.g., Eastern Ghats Mobile Belt compared to the shield regions. The gravity lows are observed over topographic features like the Western Ghats and Himalaya, while some of the topographic highs like Aravalli show positive gravity anomaly. The Indian Ocean Geoid Low varies from -82 m over Dharwar Craton to -98 m over the Southern Granulite Terrain and finally reaches a significant low of -106 m in the Indian Ocean. Flexural isostatic compensation with variable Effective Elastic Thickness (EET) ~10 km to 50 km prevails over the stable continental region. The lithospheric thickness varies from 80 km along the coastal region to 120-130 km beneath the Saurashtra Plateau, the Southern Granulite Terrain, and the Eastern Indian Shield, and reaches to more than 200 km under the Himalayan orogenic belt in the north. From Dharwar Craton to Bundelkhand Craton in central India, the lithospheric thickness varies between 160 and 180 km.

Rapid assessment of the ichthyofauna of the southern Guiana Shield tributaries of the Amazonas River in Pará, Brazil

ABSTRACT The Northern Pará Drainage System encompasses the left-bank tributaries of the Amazonas River in the southern Guiana Shield region of Pará state, Brazil. Five of the region’s state protected areas are considered strategic for the conservation of its biodiversity. In the present study, we assessed the ichthyofauna of the five state protected areas of the Northern Pará Drainage System. Seven expeditions were conducted between January 2008 and January 2009, which surveyed stretches of the Cuminá, Cuminapanema, Curuá, Jari, Mapuera, Nhamundá, and Paru rivers. These surveys yielded 286 species belonging to 38 families and eight orders, including seven new records of fish species for Brazil, six of which are also new records for the Amazon basin. Our results provide a valuable database for future research and conservation programs in the protected areas of the region.

And then there were three…

And then there were three…

Integrated geological and geophysical studies for delineation of laterite covered chromiferous ultramafic bodies around Bhuban, southwestern part of Sukinda ultramafic complex, Odisha

Chromite and Platinum Group of Elements (PGE) mineralization in the Eastern Indian Shield region is found in the ultramafic rocks distributed in the Baula-Nuasahi and Sukinda massifs intrusive into the Iron Ore Group (IOG) of rocks. In addition to this, recent geological studies have also reported the occurrences of chromiferous ultramafic bodies within the granulite tracts of Eastern Ghat Group around Asurabandha and Maulabhanja areas in the southwestern part of Sukinda Massif. In the present study, detailed gravity and magnetic surveys (1510 stations) were conducted over a laterite covered area of ~0.16 km2 at Bhuban-Asurabandha to locate the anomalous zones/sources, the geometry of the chromite bearing host rocks and its depth continuity in the subsurface. Four distinct coincident positive gravity anomalies (up to ~0.18 to 0.36 mGal) and residual magnetic anomalies (~−200 to 350 nT) with the NE-SW strike indicate the presence of high density mafic/ultramafic bodies under the laterite cover. The results of 3-D Euler deconvolution and two-dimensional compact gravity inversion models in this region further suggest the presence of high-density material (~3100–3600 kg/m3) at a depth of 20–40 m in the subsurface. Exploratory drill hole data in the area confirms the subsurface occurrence of thin chromiferous serpentinite as lensoidal and sandwiched bodies within the granulite rocks of Eastern Ghat Group. Petrological studies of the drill core samples reveal the occurrences of disseminated and thin banded chromite within the serpentinites which is identical to the Sukinda ultramafics in terms of its mineralogy and alteration. On the other hand, the surrounding mafic granulite rocks contain occasional magnetite and sulfides within the granulite rocks. Hence, the chromiferous ultramafic bodies within the granulite rocks can be considered as the tectonically detached portions of the Sukinda ultramafic rocks during the regional thrusting.

Finite-Element Modeling of Conductive Multilayer Shields by Artificial Material Single-Layer Method

The artificial material single-layer (AMSL) method, recently proposed to model solid conductive shields in finite-element solvers without using a fine discretization, is here extended to model multilayer shields. First, the admittance matrix of a multilayer shield is analytically derived by the transmission line (TL) theory. Then, considering that the field through conductive shields propagates normally to the shield surface, the TL admittance matrix is equated to that of a 1-D finite element to extract the physical constants of a homogenized artificial material. These constants are adopted to model the multilayer shield region in the finite-element method (FEM) calculations by using only one layer of finite elements in the direction of the field propagation. By the AMSL-FEM, the field propagation through the multilayer shield is accurately modeled taking into account the skin effect and avoiding the fine discretization of the shield.