Band Spacing Research Articles

A single layer and very close band spacing frequency selective surface with enhanced isolation

An ultrathin and very closely located dual-band frequency selective surface (FSS) with enhanced isolation is proposed in this letter. The unit cell consists of two typical concentric hexagon rings, with several stubs loaded on each side of the inner ring. Through the stub-loaded configuration, the mutual coupling of adjacent resonators is highly decoupled and a very close band spacing FSS with better isolation can be achieved, and the ratio of the two operating bands can be as low as 1.06. Additionally, due to the independent resonant frequencies, the band ratio can be set over a wide range, from 1.06–2.43. Furthermore, the corresponding equivalent circuit model (ECM) is developed and analyzed for better comprehension of the underlying mechanisms of the proposed FSS. The validity of the design is then checked with a prototype, and the measured results show good agreement with the simulated ones.

Numerical studies of self-organization of shear bands in one and two dimensions

In the present manuscript we perform a numerical analysis of the self-organization processes of adiabatic shear bands formation in depleted uranium, aluminum alloy, and high-strength steel in one- and two-dimensional cases. Since the processes of shear bands formation are strongly nonlinear, three materials with significantly different parameters considered allow us to generalize obtained dependencies. For all materials, we investigate the evolution of stress, temperature and velocity fields from initial to final stage of localization. It is well known that localization processes occur during the high shear rate loads in the presence of initial microstructural defects in metallic materials. Starting with a random distribution of initial stress, which models microstructural defects, we obtained new dependencies for such significant parameters of the problem considered such as localization time and spacing between shear bands. The influence of initial plastic strain rate on these parameters was also studied. We obtain the linear dependence of localization time on initial strain rate and show that spatial dimension significantly influences on its value. Also, we introduce the method of shear bands selection during computations and present new statistical distributions for band spacing. We show that the interaction between shear bands significant influences on the spacing between them.

Prediction of inter-granular crack initiation susceptibility in post irradiated grade 300 steels

Grade 300 austenitic steel components are subjected to irradiation-assisted stress corrosion cracking hazard, in the context of nuclear pressurized water reactor operation. In this paper, it is assumed that inter-granular cracking susceptibility primarily depends on sub grain plasticity mechanisms, controlling the slip band thickness and spacing achieved for a plastic strain level imposed. A computational model evaluating the related grain-boundary stress evolutions is developed and evaluated, using actual post-irradiation observations. In practice, we calculate a quantitative damage susceptibility factor R depending on the characteristic local slip band arrangements and the grain to grain misorientation. The statistical R evolutions obtained are consistent with the strain localization and related intergranular crack susceptibility trends, under corresponding irradiation and deformation conditions.

A Pulsed-Precipitation Model of Dryland Vegetation Pattern Formation

We develop a model for investigating the impact of rainstorm variability on the formation of banded vegetation patterns in dryland ecosystems. Water input, during rare rainstorms, is modeled as an instantaneous kick to the soil water. The redistribution, from surface water to soil moisture, accounts for the impact of vegetation on infiltration rate and downslope overland flow speed. These two positive feedbacks between water and biomass distributions act on the fast timescales of rain storms. During dry periods, a classic reaction-diffusion framework is used for the slow processes associated with soil water and biomass. This pulsed precipitation model predicts that the preferred spacing of the vegetation bands is determined by the characteristic distance that a storm pulse of water travels overland before infiltrating into the soil. In this way, the vegetation pattern is determined by the fast ecohydrological processes and may be attuned with its dryland precipitation pattern. We demonstrate how this modeling framework, suited for stochastic rain inputs, can be used to investigate possible collapse of a dryland pattern-forming ecosystem under different precipitation patterns with identical low annual mean. Model simulations suggest, for instance, that shorter rainy seasons and greater variability in storm depth may both hasten ecosystem collapse.

A Dual-Band Planar Antenna Array With High-Frequency Ratio for Both Sub-6 Band and mm-Waveband

In the 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> Generation Partnership Project (3GPP), the major carrier frequency bands of the 5G communication are assigned in the Sub-6 band and the millimeter wave (MMW) band. The frequency ratio between the two bands is more than 4. Due to the contradiction between large element size in Sub-6 band and narrow element spacing in the MMW band, it is hard to design one antenna array to be used in both of the two carrier frequency bands especially for a miniaturized communication system. In this article, a novel dual-band planar antenna array is proposed to solve the contradiction by using recombining technology. The measured results show that the antenna array is able to satisfy the requirements of the two carrier bands. In the Sub-6 band, the antenna array scale is 4×4. The antenna array has an operating band of 4.5-6GHz with the array gain more than 12.9dBi. In ±40° beam scanning angle, the sidelobe level (SLL) is lower than -12dB and the gain variation is less than ±0.9dBi. The isolation between the adjacent elements is more than 20 dB. In the MMW band, the array scale is 4×8. The antenna array has an operating band of 24.5-26GHz with the array gain more than 20dBi. In ±40° beam scanning angle, the SLL is lower than -10dB and the gain variation is less than ±1.9dBi. The isolation between the adjacent elements is more than 20dB. The antenna array has also shown good performance in an actual over air communication test in the two carrier bands by using 16-QAM modulation.

Dislocation mediated dynamic tension-compression asymmetry of a Ni2CoFeV0.5Mo0.2 medium entropy alloy

Although tension-compression (T-C) asymmetry in yield strength was rarely documented in coarse-grained face centered cubic (FCC) metals as critical resolved shear stress (CRSS) for dislocation slip differs little between tension and compression, the T-C asymmetry in strength, i.e., higher strength when loaded in compression than in tension, was reported in some FCC high entropy alloys (HEAs) due to twinning and phase transitions activated at high strain regimes in compression. In this paper, we demonstrate a reversed and atypical tension-compression asymmetry (tensile strength markedly exceeds compressive strength) in a non-equiatomic FCC Ni2CoFeV0.5Mo0.2 medium entropy alloy (MEA) under dynamic loading, wherein dislocation slip governs dynamic deformation without twins or phase transitions. The asymmetry can be primarily interpreted as higher CRSS and more hard slip modes (lower average Schmid factor) activated in grains under dynamic tension than compression. Besides, larger strain rate sensitivity in dynamic tension overwhelmingly contributes to the higher flow stress, thanks to the occurrence of more immobile Lomer-locks, narrower spacing of planar slip bands and higher dislocation density. This finding may provide some insights into designing MEAs/HEAs with desired properties under extreme conditions such as blast, impact and crash.

Microstructural evolution and twins formation under tensile test of Ni-free Mn-N austenitic stainless steel using laser powder bed fusion method

At the initial uniaxial tensile stage, predominant planar dislocation slip occurs to generate dislocation pile-ups and dipole bundles. Low-energy Taylor lattice structure is then formed by co-planar slip bands along the primary slip system along [001]γ and [111]γ directions to form primary twins. Increasing the straining and generation of numerous micro-bands and crystallographic defects led to the strong restriction for dislocation motion, enhancing the formation of secondary twins with stacking fault near the deformation twin's energy. Decreasing the mean slip band and micoband spacing and configuration of complex dislocation arrangement would cause the dislocation slip, generating an extensive number of dislocation walls and cell blocks, resulting in forming a noncrystalline structure with multi-orientation. Molecular dynamics (MD) analyses revealed that deformation began by nucleation of Shockley partial dislocations with a burger vector of 1/6 〈112〉 from none-periodic boundaries. Afterwards, dislocations junctions created Hirth dislocations with a Burger vector of 1/3 〈100〉, which causes strain hardening in the system. At this point, Shockley dislocations nucleated from Hirth dislocations and strain hardening increases.

A Jitter-Robust 40 Gb/s ADC-Based Multicarrier Receiver Front-End With 4-GS/s Baseband Pipeline-SAR ADCs in 22-nm FinFET

Demand for increased data rates in serial link transceivers calls for innovative architectures capable of overcoming impairments such as limited channel bandwidth (BW) and stringent jitter specifications. This article presents a receiver front-end (RXFE) architecture that supports multicarrier signaling to provide a ~3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> relaxation in clock jitter requirements. A total of 40 Gb/s data rate is supported by three 4-GS/s bands with baseband (BB) four-level pulse amplitude modulation (PAM4) and mid-band (MB) and high-band (HB) 16-state quadrature amplitude modulation (QAM16) on 4- and 8-GHz orthogonal carriers, respectively. The RXFE uses three per-band optimized continuous-time linear equalizers (CTLEs) to partially equalize the in-band channel loss and four-way time-interleaved 7-b pipelined-successive approximation register (SAR) analog-to-digital converters (ADCs). Tight band spacing is achieved with tolerable inter-channel interference (ICI) using resettable integrators in the receiver segments. Fabricated in a 22-nm fin field-effect transistor (FinFET), the proposed 40-Gb/s multicarrier RXFE can tolerate up to 1.6-psrms jitter and achieve a bit error rate (BER) < 10−5 operating over a channel with 20-dB loss at 10 GHz when combined with an off-chip one-tap digital ICI canceller. The ADC-based front-end achieves 3.05-pJ/bit power efficiency, including all the front-ends, ADC, and clocking power.

Dynamic programming-based band selection method for hyperspectral unmixing

ABSTRACT Band selection (BS) is a method for optimizing feature selection, which aims to of reduce the computational complexity of processing hyperspectral image (HSI). However, there are many BS methods applied to image classification, target detection, and anomaly detection. Furthermore, the existing BS methods ignore the spatial structure of HSI. To solve the above problems, we proposed a dynamic programming-based BS method for hyperspectral unmixing. In this paper, we use the convex geometric structure of HSI in band space to project it into the subspace to obtain depth spectral features, then construct a dynamic programming model to select representative bands. To verify the effectiveness of the proposed method, experiments are conducted on three widely used datasets, and compared with three popular BS methods. The experimental results show that the proposed method has satisfactory performance in different evaluation indexes (including signal to reconstruction error (SRE), root mean square error (RMSE)) and three quantitative evaluations (average information entropy (AIE), average correlation coefficient (ACC) and average relative entropy (ARE)).

Effect of prior-austenite grain size on the microstructure and mechanical properties of ultrafine-grained dual-phase layer-structured steel produced by hot rolling of intercritical annealed bainite

In this study, ultrafine-grained (UFG) ferrite/martensite (F/M) layer-structured (LS) steels were fabricated by hot rolling of intercritical annealed bainite steels with a rolling reduction of 75% to ease the strength-toughness trade-off dilemma, and the effect of prior-austenite grain (PAG) size of the bainitic steels on the microstructure and mechanical properties were systematically studied. The results showed that the layer thickness of martensite and ferrite was not affected by the PAG size, but the spacing of parallel lamellae bands (PLS), which evolved from the packet of bainite, decreased with the decrease of PAG size. The PLS had negligible influence on strength and ductility, but the decrease of the PLS led to the increase of delamination and both room temperature (RT) and cryogenic toughness enhancement. By reducing the PLS to introduce more delamination in this steel, the RT and cryogenic impact energy were increased 5.7 times (301 J) and 21 times (102 J at −196 °C), but without the sacrifice of strength (over 1.5 GPa) and ductility (total elongation of about 14%), compared with the initial bainite steel with the same composition respectively. The significantly improved toughness, especially the cryogenic toughness, was considered to result from the special UFG dual-phase layered structure as strain localization could be restrained and ductile fracture could be promoted by this special microstructure even at −196 °C. The cryogenic toughness improvement with the decrease of the spacing of PLS was confirmed to originate from the ductile crack path increase induced by delamination.

Quantification of Slip Band Distribution in Polycrystals: An Automated Fast Fourier Transform Decomposition Approach.

Plastic deformation is accumulated in slip bands in a wide variety of engineering alloys. Multiple material and loading conditions impact their distribution and degree of slip localization, but these effects are rarely quantified. To tackle this, the current work introduces a fast Fourier transform (FFT) decomposition method and applies it to a tensile-loaded polycrystalline nickel-based superalloy imaged via high-resolution digital image correlation and electron backscatter diffraction. This approach identifies active slip planes over the FFT images of individual grains and performs inverse transforms such that slip band traces with shared orientations are isolated. This technique enabled the largest quantification of slip band spacings and in-plane strains to date, with a total of 6,557 slip bands detected. The results show that the slip band spacings increase with grain size, with no evident dependence on grain orientation and Schmid factor. Slip bands are found to develop similar spacings along different octahedral planes and continue to spread over larger regions of the grain as the resolved shear stress of the active slip system increases. The FFT decomposition technique, which could be employed with multiple microscopy techniques, will allow for much-needed large-scale quantitative studies of slip localization.

Microstructural Pattern Formation during Far-from-Equilibrium Alloy Solidification.

We introduce a new phase-field formulation of rapid alloy solidification that quantitatively incorporates nonequilibrium effects at the solid-liquid interface over a very wide range of interface velocities. Simulations identify a new dynamical instability of dendrite tip growth driven by solute trapping at velocities approaching the absolute stability limit. They also reproduce the formation of the widely observed banded microstructures, revealing how this instability triggers transitions between dendritic and microsegregation-free solidification. Predicted band spacings agree quantitatively with observations in rapidly solidified Al-Cu thin films.

Shear Bond Strength of Different Types of Cement Used for Bonding Band and Loop Space Maintainer

Shear Bond Strength of Different Types of Cement Used for Bonding Band and Loop Space Maintainer

Thermodynamic, Spectroscopic, and Structural Study on a Sodium Uranyl Tri-2-Methoxybenzoate Dodecahydrate Coordination Compound with Considerably Low Solubility in Acidic Conditions.

A spontaneous crystallization of an uranium(VI)-organic coordination compound with sodium and 2-methoxybenzoate (2-mba) was observed in acidic solutions, and the solubility product, molecular vibrations, crystal structure, thermal stability, and emission properties of the atypically low-soluble U(VI) complex (Na[UO2(2-mba)3]·12H2O(s)) were fully investigated for the first time. A long-term solubility experiment and speciation modeling gave a solubility product of log Ks,0 = -12.18 ± 0.02 (T = 25 °C and I = 0.1 M NaClO4), and vibrational analyses confirmed the overall molecular structure of complex and the frequencies of characteristic stretching motions of uranyl moiety as well. The crystal quality of Na[UO2(2-mba)3]·12H2O(s) was improved by a digestion method, and X-ray diffraction analysis of the single crystalline specimen verified that the newly studied uranyl-organic compound contains one-dimensional channels with a diameter of 20 Å along the [001] direction; the sodium and water molecules are arranged in the channel structures. In the coordination environment around uranyl, three aromatic carboxylates are symmetrically bound in the equatorial plane of uranyl coplanarily, and the unit [UO2(2-mba)3]- complexes are further extended along the plane to form the layered-morphologies. The three-dimensional packing of [UO2(2-mba)3]- anions is driven by the parallel-displaced π-stacking of aromatic rings with a centroid-centroid distance of 3.7 Å. Additional thermogravimetric analysis confirmed that the Na[UO2(2-mba)3]·12H2O(s) is stable up to 250 °C, and dehydration and release of the organic ligand were subsequently observed beyond that temperature. Photoluminescence spectrum of the Na[UO2(2-mba)3]·12H2O(s) clearly displayed the characteristic U(VI) emission, and a band spacing between the ground electronic states of U(VI) uranyl was evaluated to be 831 ± 14 cm-1. Such detailed characterization of the unique Na[UO2(2-mba)3]·12H2O(s) is advancing upon a systematic understanding of the structural effects of the aromatic model ligands on U(VI) complexation, with relevance to the environmental chemistry of U(VI) and crystal engineering for development of diverse uranyl-organic frameworks.

Effects of torsional control on the optical and electronic properties of monolayer NbS2: A first-principles study

Based on the first principle calculation, the torsional deformation control of single-layer graphene transition metal disulfide NbS 2 at different angles is systematically studied in this paper. The electronic properties include the energy gap change of the electronic band structure, the composition of the density of States, the trends of the real and imaginary parts of the dielectric function, and the electronic and optical properties such as absorption and reflection spectra. Our analysis shows that distortion can change the bond length of NbS 2 . Under torsion, the initial key length is 2.492 A, the shortest is 2.240 A, and the longest extended key is 2.744 A. On the other hand, the study of electronic and optical properties shows that the band structure of NbS 2 will have a split band gap at the Fermi level. When the torsion angle is 12 °, we notice that the electronic and optical properties of NbS 2 will change significantly, the energy band spacing will increase, and the corresponding minimum particle number will decrease significantly. The optical properties show that the torsion system can improve the storage capacity and polarizability of the material, improve the local optical response, and strongly impact the properties of the ultraviolet region. At the same time, it can improve the optical response to visible light and photocatalytic activity and effectively improve the transmittance of the material itself.

Laser-Based Characterisation of the Copper Uranyl Sulphate, Johannite

Uranyl sulphate minerals are common alteration phases in uranium mines and uraniferous waste deposits where they occur in conjunction with other products of acidic drainage such as jarosite. Although not persistent in nature due to their high solubility, they may play an important role in governing uranium mobility during the operational and immediate post-closure environment of an engineered radioactive waste repository where oxidising conditions prevail. One such mineral, johannite (Cu(UO2)2(SO4)2(OH)2·8H2O), is of particular interest given the stated intention of several countries to use copper canisters in the disposal of spent nuclear fuel. A museum reference sample of johannite has been characterised by luminescence and multiple-laser Raman spectroscopy, resulting in the first reported luminescence excitation and emission spectra for this mineral. Well-defined Raman features were observed using 785, 633, and 532 nm lasers with the resolved peaks corresponding well to the published spectra. The Raman spectrum measured with the 457 nm laser was mostly masked by a series of repeating doublets attributed to the luminescence emission features, from which band spacing values of 831 and 823 cm−1 were extracted; the former corresponded to both the resolved 785 nm ν1(UO2)2+ peak position and the band spacing value obtained from the first reported luminescence emission spectrum for johannite. Four emission and nine excitation peaks were resolved from the luminescence spectra. The findings indicate that a suite of complementary laser-based techniques offer the potential for real-time characterisation of johannite formed in environments where intrusive sampling, transportation, and ‘off-site’ laboratory analysis are not feasible.

Characterisation of carnotite and tyuyamunite using Raman, luminescence and laser-induced breakdown spectroscopy

Among the wide range of natural uranium minerals, uranyl vanadates have attracted particular attention due to the economic viability of co-producing uranium and vanadium for industrial applications The typically remote locations of the ore deposits favour in situ analytical techniques offering rapid, minimally destructive characterisation wherever possible. This study reports on the use of luminescence, Raman and laser-induced breakdown spectroscopy to characterise the two most commonly found uranyl vanadates in nature, carnotite (K2(UO2)2V2O8·3H2O) and tyuyamunite (Ca(UO2)2V2O8·5–8H2O); the first attempt to use all three laser-based techniques in tandem for these phases. Significant differences in the luminescence emission signal intensity along with a noticeable shift in the resolved emission peak positions enable carnotite and tyuyamunite to be readily distinguished. Extraction of the band spacing from luminescence emission spectra provides confirmation of the position of the equivalent Raman uranyl symmetric stretch, ν1(UO2)2+, vibration for each mineral. Raman itself, was unable to differentiate carnotite and tyuyamunite owing to the weak signals obtained; however, the degree of splitting in the vanadate symmetric stretch, ν1(VO3)3-, feature and, to a lesser extent, the position of the ν1(UO2)2+ peak might be used to distinguish between tyuyamunite and metatyuyamunite, although further studies are required for confirmation. Compositional LIBS analysis was successful in identifying minor quartz, gypsum, Mg- and Fe-bearing inclusions, subsequently confirmed by optical and scanning electron microscopy. The findings indicate that multiple laser-based techniques offer the potential for real-time characterisation of uranyl vanadate phases where intrusive sampling, transportation and ‘off-site’ laboratory analysis is impracticable.

Разработка ультразвукового приемопередатчика для скважинной телеметрии

Hydrocarbons are the significant part of the Russian Federation's exports. Due the exploration of hard-to-recover reserves, it is necessary to design and improve technical tools and methods to increase the efficiency of the geophysical information transfer in the logging of wells. A new communication channel for the telemetry transfer is proposed and investigated. The main idea is to use an acoustic signal in the ultrasonic frequency band and inner tube space as a transmission media. The inner tube space contains a more homogeneous media than the rocks behind the casing string. The use of ultrasonic frequencies reduces the signal scattering into the annular space. It is assumed that it will improve the reliability of the transferred information. The designed ultrasonic receiver and digital signal transmitter in the “Manchester II” code are presented based on the ma40s4s ultrasonic radiating element and the ma40s4r ultrasonic sensor. A test bench has been designed to evaluate the effectiveness of the technical solution. During the experiments, a significant influence of interference was revealed. Despite significant attenuation in a conductive media, this phenomenon significantly increases the signal amplitude, but makes it difficult to identify it, because the pauses between symbols are filled with the reflected signal. Evaluation of the ultrasonic signal attenuation in the inner tube space was carried out, and a conclusion was carried out concern the prospects of ultrasonic communication channel.

Children’s satisfaction and survival rate of fiber-reinforced space maintainer versus band and loop space maintainer in children with premature loss of maxillary primary first molar

Background: Band and loop space maintainer (BLSM) are well tolerated and long-lasting appliances, but it comes with several drawbacks, including longer lab times, more frequent cement loss dislodgements, longer visits, and the inability to avoid the rotation or tilting of neighboring teeth. These limitations motivate the search for alternative appliance such as fiber-reinforced space maintainers. Aim of the study: Evaluation of children’s satisfaction and survival rate of fiber-reinforced space maintainer versus band and loop space maintainer in children with premature loss of maxillary primary 1st molar. Materials and Methods: Thirty patients, randomly divided into two groups (n=15). BLSM group: which included (15) patients who receive band and loop space maintainer. FRSM group: which included (15) patients who were received fiber-reinforced space maintainer. The patients were evaluated for satisfaction based on Likert -type scale and survival rate. Results: The FRSM group showed a higher satisfaction score than BLSM group. For survival rate the fiber-reinforced space maintainers showed a greater success rate than band and loop space maintainers. Conclusions: The FRSM can be used as an alternative to BLSM regarding clinical performance and patient’s satisfaction in children with premature loss of maxillary 1st primary molars.

Transitions in the thermal stability of pre-strained austenite – competing effects between defect density and slip band spacing

The transition from mechanical destabilization to stabilization in metastable austenite is an important issue affecting the design of structures used at lower temperatures. We have conducted in-situ magnetic measurement and detailed microscopy work to reveal the underlying mechanisms of such transition. Austenite destabilization is attributed to the increase of slip band and dislocation densities which provide extra nucleation sites. The decreased slip band spacing divides the austenite grains into small units, hindering the growth of martensite. It also inhibits the formation of multiple martensite variants and retards nucleation. The competition between defect density and spacing is the key to the transition.