Shield Areas Research Articles

Multiplexing Integration Meta‐Absorber in an Ultrathin Planar Board

A meta‐absorber is a type of metamaterial capable of absorbing incident electromagnetic waves, primarily used for isolating and attenuating these waves. Due to their unique properties, meta‐absorbers are widely used in areas of electronic shielding, radar cross‐section reduction, as well as military camouflage. To enhance the working bandwidth, conventional meta‐absorbers integrate multiresonance modes in different layers, resulting in increased thickness and limiting their applications. Herein, a multiplexing integration meta‐absorber is proposed in a one‐layer planar board, achieving an ultrathin thickness of 0.053 λ and an ultrawide absorption band covering the whole X and Ku bands (8.0–18.0 GHz) by harnessing the coupling of four resonant modes. Moreover, the designed meta‐absorber is insensitive to the polarization of incident waves and exhibits good angle stability within ±45°. The experimental results agree well with the simulations. These findings may inspire the development of ultrathin metadevices with multifunctionalities operating across different frequency domains.

Adjuvant Radiotherapy in Bladder Cancers: A Dosimetric Study Focusing on Ileal Conduit Sparing

PurposeTo compare ileal conduit (IC) and other organ at risk (OAR) dosimetry between treatment techniques in a prospective cohort of patients planned for adjuvant radiotherapy (RT) after radical cystectomy and IC reconstruction. Methods and materialsComputed tomography (CT datasets of twenty patients who underwent adjuvant RT were obtained and used prospectively for delineation of target volumes (primary and nodal) and OARs, including IC, uretero-ileal anastomosis and ileal stoma using a specified protocol for simulation including a delayed CT to identify IC. Three RT plans were generated for each patient for a dose of 54 gray (Gy) in 27 fractions (PTV V95% >95%): 3-dimensional conformal radiotherapy (3DCRT) with (3DCRT_S) and without (3DCRT_N) stoma shielding, and volumetric modulated arc therapy (VMAT), with OAR constraints specified for VMAT plans (IC: Dmax<54Gy, V50Gy < 20 cc). Constraints were given for other pelvic OARs (bowel, rectum, femur heads) as per published literature. Plans were evaluated for target coverage as well as OAR doses; in particular, IC and ileal stoma). ANOVA test was used to compare medians of achieved doses, and a p-value <0.05 was statistically significant. ResultsThe median IC volume was 63.34 (55.29–82.93) cc. The cranial end of IC was at L5 or L4 vertebral level in 95% of patients and caudal level at S2 or S3 in 80% of patients. In contrast, the ileal stoma spanned from L4 or L5 vertebral level cranially (100%) to L5 level caudally (80%). PTV V95% was similar for 3DCRT_N and VMAT plans while it was significantly lower for 3DCRT_S in areas of ileal stoma shielding (99.95% vs 99.01% vs 96.29%, p < 0.01). Median IC V50Gy was comparable in 3DCRT_N (38.81 cc) and 3DCRT_S (35.62 cc) while it was significantly lower in the VMAT plan (17.05 cc, p < 0.01). IC Dmax did not differ significantly between the three plans. On the other hand, when 3DCRT_N, 3DCRT_S, and VMAT plans were compared for ileal stoma doses, Dmean was comparable (11.93 Gy vs 7.41 Gy vs 9.54 Gy, p = 0.06) while Dmax was significantly higher for 3DCRT_N plan and least for VMAT plan (35.32 Gy vs 27.57 Gy vs 24.22 Gy, p < 0.01). VMAT plans fared significantly better than both 3DCRT plans for uretero-ileal anastomosis, bowel, and rectal dosimetry. ConclusionsIleal stoma shielding in 3DCRT compromises PTV coverage but does not spare IC effectively. Sparing IC with VMAT is feasible without compromising PTV coverage. Dosimetric gains with VMAT are expected to benefit patients needing higher pelvic RT doses and nodal RT by reducing the risk of anastomotic and mucosal complications. Clinical benefits should be evaluated in a prospective protocol.

Contribution of Saharan dust to chemical weathering fluxes and associated phosphate release in West Africa

Huge amounts of mineral dust are produced in northern Africa, representing the largest source of aerosols worldwide. Transatlantic dust transport is known to fertilize soils as far as in the Amazon Basin. Yet, the influence of Saharan dust on chemical weathering fluxes and associated nutrient release in West Africa remains largely overlooked. To address this issue, we analysed clay fractions (<2 µm) of river sediments (n = 37) from across the Niger River basin - the largest river system in West Africa - using neodymium and hafnium isotope compositions as proxies for provenance (εNd) and chemical weathering (ΔεHf CLAY).Compared to previously published data for corresponding sand fractions, measured εNd values indicate significant size-dependent decoupling for Nd isotopes in most samples, with εNd differences between clay and sand fractions yielding values as great as ∼26 ε-units. Using mixing models, we show that this discrepancy reflects the overwhelming presence in the studied clay fractions of Harmattan dust blown from the Bodélé Depression in Chad, which we estimate to account for about 40 % of the fine-grained sediment load exported to the Gulf of Guinea. Additionally, significant ΔεHf CLAY variability occurs across the Niger catchment, partly explained by the presence of zircon in clay-size fractions, but also by preferential alteration of dust-borne accessory phosphate minerals in the subtropical regions of the watershed.Based on these results, we propose that Saharan dust plays a major role in controlling regional patterns of chemical weathering in West Africa, suggesting that enhanced wet deposition of mineral dust in shield areas dominated by transport-limited weathering regime can result in a large increase in weatherability and associated release of phosphorus. These findings have general implications for the importance of mineral aerosols in controlling sediment yield and the supply of weathering-derived nutrients to continental areas bordering large subtropical deserts worldwide.

Proterozoic crustal evolution of the granitoids from the northern margin of the Chotanagpur Gneissic Complex (CGC), Bihar

Since the Proterozoic, considerable expansion of the continental crust has taken place. A significant amount of granitic plutons were deposited on the earth’s crust during this time. The dynamic structure of the earth plays a close role in the genesis of granites and related rocks. Information about the formation and development of the continental crust can be understood from the study of these rocks. The emplacement of large scale anorthosite massif in shield areas was another process that contributed to the Proterozoic expansion of the continental (Mukherjee, et al.,, 2005). One of the primary sources of information regarding the formation and evolution of the continents over geological time is the genesis of granite. Enclaves of supracrustal meta-sediments intrude the Chotanagpur Gneissic Complex (CGC), which is primarily composed of granites, granitoid gneisses, and migmatites exhibiting a wide range of structure, texture, and mineralogy variations.The granitic plutons exposed in the northern fringe of the Chotanagpur Gneissic Complex, CGC, and the associated anorthosites of the Barabar Anorthosite Complex along the northen margin of Bihar holds information about the various magmatic episodes that have taken place in that area millions of years ago.

Teleseismic P-Wave Attenuation Beneath the Arabian Plate

In order to prove that the Arabian Plate is a tectonically active region even in its shield areas, we obtained the attenuation structure tp* of the upper mantle beneath the Arabian Plate by applying the spectral inversion method to the newly established seismic network in Saudi Arabia operated by the Saudi Geological Survey (SGS). The data sets consisted of good quality vertical components of the teleseismic events for more than 4400 spectral ratios. The result showed significant and diverse tp* structures between the eastern and western regions of the Arabian Plate. High tp* was the predominant feature underneath the Arabian Shield (western Arabia) and low tp* within the Arabian Platform (eastern Arabia). The obtained tP* values range from −1.0 s to 1.0 s. The observed high tp* patterns followed a line from north to south through the Arabian Shield along the Red Sea margin. The high tp* distribution closely followed the volcanic region, in particular the Makka–Madina–Nafud Volcanic (MMNV) line. The maximum tp* values were observed in the southern region of the Arabian Shield, at the southern part of the Red Sea, where the African and Arabian Plates diverge. The observed high tp* will be attributed to the previously revealed low-velocity anomaly and thermal activities beneath the Arabian Shield, and it is also correlated with the topography (high elevation) in the region.

Mapping density, diversity and species-richness of the Amazon tree flora

Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution.

Research on Improving the Shielding Effect of Stacked Superconducting Bulks Based on Increasing the Gap Reluctance

Superconducting bulk has great advantages in shielding magnetic fields owing to its high critical current density. Since the shielded area is usually larger than the size of a single bulk, superconducting bulks need to be stacked together to form a shielding layer. However, bulks stacked together can cause the magnetic flux to concentrate at the gaps between bulks. In order to increase the shielding effect, multiple shielding layers are usually required. This increases the shielding cost. In this paper, a shielding structure that makes an angle between gap and external field non-parallel is explored. This structure can increase the gap reluctance and reduce the magnetic flux leakage, which provides a method to get a uniform shielding area in a relatively economical way. The shielding effects are studied by experiment and finite element calculation. The established simulation model can be used to further explore and optimize new shielding structures.

Environmental governance of transnational regions based on ecological security: The China-Mongolia-Russia Economic Corridor

Ecological security patterns (ESPs) can alleviate the conflict between economic development and ecological protection to ensure regional ecological security. The present study considered the use of the China-Mongolia-Russia Economic Corridor (CMREC) for building an interregional ESP by integrating ecological vulnerability with the supply and demand of ecosystem services using the circuit theory. The results revealed that the supply and demand of ecosystem services in the CMREC were not consistently spatially distributed. High supply areas decreased from east to west and north to south, whereas high demand mainly occurred in highly urbanized areas. The supply and demand imbalance of ecosystem services affected the determination of ecological sources. Fifty-five ecological sources (529,635.56 km2), mainly distributed east of the Northeast Plain, Far East, and around Lake Baikal, were identified. There were no ecological sources in the southwest. Ecological vulnerability decreased from south to north. Mongolia (0.60) had the highest average ecological resistance, followed by China (0.42) and Russia (0.38). According to the circuit theory, 87 ecological corridors (13,306.42 km) and 13 main ecological corridors (3302.50 km) can effectively connect the ecological resources of the CMREC. These sources and corridors are dominated by forests and grasslands. The results also suggest that the connectivity of ecological corridors among the three countries should be improved, ecological restoration in the southern part of the Mongolian Plateau should be emphasized, and the functional stability of the ecological shield areas should be ensured. We propose some management guidelines for optimizing regional ESPs and collaborative environmental governance of the CMREC.

Synergistic electrostatic shielding manipulation of Na+ and desolvation effect of Zn2+ enabled by glycerol for long-lifespan and dendrite-free Zn anodes

The development of aqueous Zn-based energy storage devices is severely restricted by uncontrollable Zn dendrite growth, serious parasitic side-reactions, and poor low-temperature performance. In this work, we introduce glycerol (Gl) with an appropriate concentration of 2.1 M (mol L−1) as a synergistic manipulator and desolvater in the 1 M Zn(ClO4)2 and 0.5 M Na2SO4 electrolyte for zinc batteries. Theoretical calculations and experimental analysis confirm that the Gl-Na+ structure adsorbs onto the Zn anode during the plating process, which increases the electrostatic shielding area of negative charge on Zn dendrites and thus inhibit their growth. Meanwhile, the desolvation effect of Zn2+ enabled by Gl promotes the optimization of solvated structure, resulting in uniform deposition of Zn2+. Additionally, Gl suppresses parasitic side-reactions and coagulation of the electrolyte to ensure a homogeneous electrode surface and improve low-temperature performance. In the modified electrolyte, stable Zn plating-stripping has been achieved for 2930 h at 2 mA cm−2 and 1 mA h cm−2, which is about 7.5 times longer than that in the Gl-free electrolyte. Moreover, even at −10 ℃, the hybrid capacitor with activated carbon and V2O5//Zn full battery realizes 95.37% and 62.84% capacity retention after 30,000 and 3000 cycles, respectively. This work presents an effective strategy for the synergism of double additives to promote the stability of the Zn electrode for high-performance aqueous batteries.

A new species of the feather mite genus Allodectes (Acariformes: Proctophyllodidae) from the ruby-throated hummingbird, Archilochus colubris (Apodiformes: Trochilidae), in Canada

A new feather mite species, Allodectes archilochus sp. n. (Pterodectinae: Rhamphocaulini) is described from the ruby-throated hummingbird, Archilochus colubris (Apodiformes: Trochilidae), in Manitoba, Canada. This is the first record of the genus Allodectes on hummingbirds in the northern part of North America. The new species is close to A. thaluraniae Hernandes, 2017, and distinguished from the latter in the following features: in both sexes, the anterior margin of the hysteronotal shield is deeply concave; in males, setae d2 are situated at the midlevel of metapodosomal sclerites, and tarsus IV is without extension on the inner margin; in females, the anterolateral extensions of the prodorsal shield do not extend to the lateral margins of propodosoma, and the anteromedian area of the hysteronotal shield is covered with dense striation. A checklist of the 15 currently known Allodectes species is provided.

Tuning the giant magnetoimpedance response of a glass-coated microwire reinforced polymer by in-situ laser annealing

The ability to modify the giant magnetoimpedance (GMI) effect in amorphous glass-coated ferromagnetic Co-based microwire reinforced polymer via laser irradiation is presented. Through in-situ laser annealing of microwires embedded into a polymer matrix, a 25 % improvement in the GMI response is demonstrated after only 4.9 min of annealing. This improvement is compared to a conventional oven anneal technique, requiring an hour of oven annealing, subsequent sample cooling and polymer casting. This unique in-situ technique offers a novel and expedient path toward tailorable multi-functional composites in the areas of tunable electromagnetic shielding, structurally integrated antennas and magnetic sensors.

Smart Wood Dual‐Action Off/On Versatile Switches Based On Highly Sensitive Electrical And Electromagnetic Mechanosensing Performances

AbstractSmart electromagnetic (EM) functional materials that can arbitrarily utilize EM energy and reduce EM pollution are attractive for future EM devices in an information society; however, studies on precise EM interference (EMI) shielding and sensing are rare. In this work, dual‐action electrical and EM‐responsive mechanoreceptors are prepared from electrically conductive polypyrrole (PPy) nanoparticle (NP)‐infiltrated anisotropic wood (PW) aerogels. The prepared PW aerogels are composed of curved stacked layers of aligned cellulose nanofibers, and can be reversibly condensed and reconstructed for conductive network control during cyclic compression. These PW aerogels can withstand up to 74% compressive strain in a tangential direction and exhibit pressing‐enhanced electrical conductivity and polarization loss. The piezoresistive gauge factor (GF) and linearity of the PW aerogels can be adjusted by varying the PPy deposition time, leading to varying GF values in the range of 1.87–4.62. During mechanosensing based on EMI shielding effectiveness (SE), rapid off/on switching between the EM wave transmission and shielding is achieved when the SE varies above and below the effective EMI shielding area (&gt;20 dB) through continuous compression. Such dual‐action electrical/EM off/on wood aerogel switches provide opportunities for the development of advanced smart devices from biomass resources.

Greisen and pseudo-greisen in the Tamanrasset area (Central Hoggar, Algeria): Petrography, geochemistry and insight on the fluids origin from mica chemistry

In the Tamanrasset area of the Pan-African Tuareg Shield, some of the late Pan-African intrusions collectively known as the Taourirt granites are associated with tin and tungsten prospects of both the quartz-vein and greisen types, with a variety of greisen styles. The mineralized intrusions are albite-topaz-protolithionite granites and microgranites. In the present work, we combine new observations and mica analyses with a reinterpretation of existing wall-rock geochemical data in order to assess the possible role of both magmatic-hydrothermal and external fluids in the greisenizing process at Tamanrasset.Greisens at Tamanrasset appear to result from two process: the first is acid leaching forming quartz-topaz and quartz-rich greisens, followed by an episyenitization which is characterized by quartz dissolution and replacements by Li-rich micas, leading to mica-rich greisens (that could better be named “pseudo-greisens”). Distinct trends recorded by the mica compositions in the granitic rocks and the greisens allow to disentangle the involvement of magmatic-hydrothermal fluids, on the one hand, and of mainly metamorphic external fluids, on the other hand, in the greisenizing process. The latter fluids were CO2-rich, and could have contributed to the source of the acidity.

Mesoscale Convective Systems in DYAMOND Global Convection‐Permitting Simulations

AbstractThis study examines the deep convection populations and mesoscale convective systems (MCSs) simulated in the DYAMOND (DYnamics of the atmospheric general circulation modeled on non‐hydrostatic domains) winter project. A storm tracking algorithm is applied to six DYAMOND simulations and a global high‐resolution satellite cloud and precipitation data set for comparison. The simulated frequencies of tropical deep convection and organized convective systems vary widely among models and regions, although robust MCSs are generally underestimated. The diurnal cycles of MCS initiation and mature stages are well simulated, but the amplitudes are exaggerated over land. Most models capture the observed MCS lifetime, cloud shield area, rainfall volume and movement speed. However, cloud‐top height and convective rainfall intensity are consistently overestimated, and stratiform rainfall area and amount are consistently underestimated. Possible causes for the model differences compared to observations and implications for future model developments are discussed.

Strong-Scattering Multiparameter Reconstruction Based on Elastic Direct Envelope Inversion and Full-Waveform Inversion with Anisotropic Total Variation Constraint

Strong-scattering medium can usually form a good sealing medium for oil and gas resources. However, conventional elastic full-waveform inversion (EFWI) methods are difficult to build reliable velocity models under the condition of lacking low-frequency information. The elastic direct envelope inversion (EDEI) method has been proven to be able to model large-scale Vp and Vs structures of strong-scattering media. The successive use of EDEI and EFWI can obtain fine structures of the strong scatterers and their shielding areas. However, the inversion effects of inner velocity and bottom boundaries of strong scatterers by the existing methods need to be improved. In this paper, we propose the elastic direct envelope inversion with anisotropic total variation constraint (EDEI-ATV). The anisotropic total variation (ATV) constraint has the advantage of making the velocity more uniform inside the layer and sharper on boundaries, which can be used to improve the inversion results of EDEI. During the iterations, the ATV constraint is directly applied to the update of Vp and Vs, and the alternately iterative algorithm can achieve good results. After obtaining reliable large-scale Vp and Vs structures, the EFWI with anisotropic total variation constraint (EFWI-ATV) is performed to obtain high-precision Vp and Vs structures. Numerical examples verify the effectiveness of the proposed method.

Multifunctional NiCo@RGO/SWNTs foam with oriented pore structure for excellent electromagnetic interference shielding

Constructing multifunctional material toward advanced electromagnetic interference (EMI) shielding has become a development trend. Carbon-based foams with excellent EMI shielding performance and structural stability for various environments are being widely studied. Here, an oriented pore structure was assembled with a carbon-based conductive skeleton, consisting of single-walled carbon nanotubes (SWNTs) and two-dimensional reduced graphene oxide (RGO), for facilitating the electromagnetic wave (EMW) to be multilevelly reflected in the confined space. In addition, magnetic NiCo nanoparticles were introduced to further improve the shielding performance by enhancing the magnetic loss. The as-prepared NiCo@RGO/SWNTs foam (NiCo@RSF) exhibited an exceptional EMI shielding effectiveness (SE) of 105 dB at the whole X band (8.2–12.4 GHz) with an ultralow density (0.0135 g cm−3). Moreover, the foam possessed extraordinary heat insulation and flame-retardant properties. Overall, the lightweight multifunctional foam with an oriented pore structure is thus promising for applications in advanced EMI shielding and other specific areas.

Design and Experimental Study of a Curved Contact Quadrupole Railgun

The railgun is a promising weapon, but suffers from poor contact and harsh magnetic field environment. We used the moment of inertia to measure the deformation resistance of the rail, studied the contact characteristics of the railgun by contact force, and compared the performances of different structures of the rail. The magnetic field environment in the bore and the thrust on the armature of different structure railguns were studied by FEM-BEM simulation, and the final structure of the hyperbolic augmented quadrupole railgun was determined. The new structure of the railgun possesses better deformation resistance and contact characteristics, and can provide an electromagnetic shielding area and greater thrust. The test results show that the proposed railgun exhibits less rail damage and less armature ablation after launch.

Assessment of γ-radiation shielding behavior of some mixed nature clays

Recently, clay materials have earned prominence as potential materials in the γ-radiation shielding and protection areas compared to other conventional materials. From this point, the present study is devoted to preparing a new composite of two types of clays, based on bentonite clay, as a natural, plentiful, and low-cost matrix. The chemical composition of prepared samples was indicated by Energy dispersive x-ray analysis (EDX). Morphology of clay samples was examined using scanning electron microscopy (SEM). The SEM images showed that the homogeneity and porosity of a cross section of samples. Measurements of the γ-ray shielding performance was analyzed and determined at numerous γ-ray photon energies emitted from five point sources of γ-rays using NaI(Tl) scintillation detector. Thus, the linear attenuation coefficient (LAC) was calculated by obtaining area under each peak of the energy spectrum observed from Genie 2000 software in the presence and absence of the clay sample. The experimental results obtained were compared theoretically with XCOM software. The comparison was examined the validity of experimental results. The other dependent radiation shielding parameters on the LAC such as a half attenuator layer (HAL), mean free path (MFP), Transmission factor (TF), and the radiation absorption ratio (RAR) were measured. It was confirmed that the γ-ray shielding properties were enhanced by mixing two types of clay comparing with the individual one. Clay materials would be good applicants for use in construction and civil engineering, as well as in the fabrication of building materials used in medical and nuclear establishments.

A Simple Model for Tropical Convective Cloud Shield Area Growth and Decay Rates Informed by Geostationary IR, GPM, and Aqua/AIRS Satellite Data

AbstractDeep convective system maximum areal extent is driven by the stratiform anvil area since convective area fractions are much less than unity when systems reach peak size. It is important to understand the processes that drive system size given the impact large systems have on rainfall and that of anvils on high cloud feedbacks. Using satellite diabatic heating and convective‐stratiform information mapped to convective systems, composite analyses suggest that system maximum sizes occur at the temporal mid‐point of system lifecycles with both maximum size and duration correlating with peak heating above the melting level. However, variations in system growth rates exist, with the overall smooth composites emerging as the average of highly variable system trajectories. Thus, this study focuses on understanding convective system growth rates on short (30‐min) timescales via development of a simple analytical source—sink model that predicts system area changes. Growth occurs when detrained convective mass (inferred from the vertical gradient of diabatic heating and temperature lapse rates) and/or generation of convective area exceeds a sink term whose magnitude is proportional to the current cloud shield size. The model works well for systems over land and ocean, and for systems characterized by varying degrees of convective organization and duration (1.5–35 hr, with correlations often &gt;0.8 across lifetime bins). The model may serve as a useful foundation for improved understanding of processes driving changes in tropics‐wide convective system cloud shields, and further supports conceptual development and evaluation of prognostic climate model stratiform anvil area parameterizations.

Radiation Protection and Shielding Analysis of the Versatile Test Reactor

The Versatile Test Reactor (VTR) is currently under development by the U.S. Department of Energy. It will provide very high fast neutron flux irradiation capabilities that are currently unavailable in the United States. Given the increasingly large number of advanced reactor concepts being pursued in recent years, this irradiation testing capability will be essential to support maturation of these designs. Radiation protection is an important part of the VTR design. High neutron fluxes can pose a challenge for radiation protection of the structures and equipment near the reactor core. This paper provides a summary on the status of the radiation protection considerations and shielding analysis performed for VTR under a nominal operating condition. The main radiation sources identified and examined in the study are applicable only under this operating condition. The paper focuses on three areas of radiation protection and shielding: secondary sodium activation in the intermediate heat exchanger, air activation in the reactor vessel auxiliary cooling system, and dose rate above the head access area due to primary sodium activation. VTR design and development are continuously progressing, and as such, the shielding considerations discussed in this paper will evolve alongside the overall VTR design.