Flat Features Research Articles

Anisotropic model for dark matter halo with Hernquist density profile

Using the observed flat galactic rotation curve feature and taking into account the presence of anisotropic dark matter with a Hernquist density profile, the space-time geometry of the halo region in galaxies is derived. The gravitational field inside the halo is attractive in nature, and the resultant space-time is flat. We find that our solution affirms the existence of stable circular orbits in the dark halo region. The expression for the equation of state parameter indicates that the matter within the dark halo is non-exotic in nature. An analysis is also conducted on several other aspects of the solution.

Two-dimensional tetragonal carbon nitride semiconductors with fascinating electronic/optical properties and low thermal conductivity

Abstract Exploring two-dimensional (2D) tetragonal carbon nitride materials is significant for unlocking new physical properties beyond those offered by traditional hexagonal lattices. In this work, we propose three theoretically stable 2D carbon nitride monolayers with tetragonal lattices, namely T-C3N, P-C3N, and PH-C5N4. Electronic structure calculations indicate that all three monolayers exhibit semiconducting characteristics, with T-C3N showing interesting flat band features. Additionally, these three carbon nitrides exhibit anisotropic and high carrier mobilities and excellent light absorption capabilities in the visible-light and near-infrared regions. Meanwhile, the calculated thermal conductivity (κp) of PH-C5N4 is 63.9 Wm−1K−1 at room temperature, significantly outperforming T-C3N (12.2 Wm−1K−1) and P-C3N (18.9 Wm−1K−1). Phonon scattering rates and Grüneisen parameters confirm the origin for the relatively high κp in PH-C5N4. Our study proposes three tetragonal carbon nitride structures with novel physical properties, which lays a theoretical foundation for the multifunctional applications of 2D carbon nitride materials.

Experimental investigation on the surface topographical improvement of selective laser melted SS316L using abrasive flow finishing

Selective laser melting (SLM) offers a precise fabrication of intricate geometries that are not achievable with conventional manufacturing processes. However, surface imperfections like adhered powder particles, waviness, and other anomalies impede the intended functional application and demand additional post-processing steps. Abrasive flow finishing (AFF) process is extensively used for enhancing the surface topography of SLM-built parts by reciprocating a viscoelastic polymer abrasive medium. The cost of commercial abrasive media is expensive, needs costlier and heavy equipment, has little tolerability, and releases hazardous gases during its preparation. In this work, a biopolymer-based abrasive media is developed in-house and employed to examine the surface topographical changes of SLM-built SS316L flat features. Compared to commercial abrasive media, the cost of the developed abrasive media is much lower, does not require expensive equipment, and is eco-friendly. The effect of extrusion pressure, number of finishing cycles, and size of the abrasive particles on the percentage change in areal surface roughness (%ΔSa) and waviness (%ΔWa) was studied. From the analysis of variance, irrespective of %ΔSa and %ΔWa, it was found that the number of cycles was the most contributing process parameter, followed by extrusion pressure and abrasive particle size. The optimised process parameters resulted in a maximum %ΔSa and %ΔWa of about 90.1 % and 66.25 %, respectively, from the initial as-built areal surface roughness of 6.6 ± 0.2 μm and areal surface waviness of 7.7 ± 0.4 μm.

Uniqueness of Landau levels and their analogs with higher Chern numbers

Landau levels are the eigenstates of a charged particle in two dimensions under a magnetic field and are at the heart of the integer and fractional quantum Hall effects, which are two prototypical phenomena showing topological features. Following recent discoveries of fractional quantum Hall phases in van der Waals materials, there is a rapid progress in understanding of the precise condition under which the fractional quantum Hall phases can be stabilized. It is now understood that the key to obtaining the fractional quantum Hall phases is the energy band whose eigenstates are holomorphic functions in both real and momentum space coordinates. Landau levels are indeed examples of such energy bands with an additional special property of having flat geometrical features. In this paper, we prove that, in fact, the only energy eigenstates having holomorphic wave functions with a flat geometry are the Landau levels and their higher Chern number analogs. Since it has been known that any holomorphic eigenstates can be constructed from the ones with a flat geometry such as the Landau levels, our uniqueness proof of the Landau levels allows one to construct any possible holomorphic eigenstate with which the fractional quantum Hall phases can be stabilized. Published by the American Physical Society 2024

Anomalous continuum scattering and higher-order van Hove singularity in the strongly anisotropic S = 1/2 triangular lattice antiferromagnet

The S = 1/2 triangular lattice antiferromagnet (TLAF) is a paradigmatic example of frustrated quantum magnetism. An ongoing challenge involves understanding the influence of exchange anisotropy on the collective behavior within such systems. Using inelastic neutron scattering (INS) and advanced calculation techniques, we have studied the low and high-temperature spin dynamics of Ba2La2CoTe2O12 (BLCTO): a Co2+-based Jeff = 1/2 TLAF that exhibits 120° order below TN = 3.26 K. We determined the spin Hamiltonian by fitting the energy-resolved paramagnetic excitations measured at T > TN, revealing exceptionally strong easy-plane XXZ anisotropy. Below TN, the excitation spectrum exhibits a high energy continuum having a larger spectral weight than the single-magnon modes, suggesting a scenario characterized by a spinon confinement length that markedly exceeds the lattice spacing. We conjecture that this phenomenon arises from the proximity to a quantum melting point, even under strong easy-plane XXZ anisotropy. Finally, we highlight characteristic flat features in the excitation spectrum, which are connected to higher-order van Hove singularities in the magnon dispersion directly induced by easy-plane XXZ anisotropy. Our results provide a rare experimental insight into the nature of highly anisotropic S = 1/2 TLAFs between the Heisenberg and XY limits.

Atomically Thin Kagome-Structured Co9Te16 Achieved through Self-Intercalation and Its Flat Band Visualization.

Kagome materials have recently garnered substantial attention due to the intrinsic flat band feature and the stimulated magnetic and spin-related many-body physics. In contrast to their bulk counterparts, two-dimensional (2D) kagome materials feature more distinct kagome bands, beneficial for exploring novel quantum phenomena. Herein, we report the direct synthesis of an ultrathin kagome-structured Co-telluride (Co9Te16) via a molecular beam epitaxy (MBE) route and clarify its formation mechanism from the Co-intercalation in the 1T-CoTe2 layers. More significantly, we unveil the flat band states in the ultrathin Co9Te16 and identify the real-space localization of the flat band states by in situ scanning tunneling microscopy/spectroscopy (STM/STS) combined with first-principles calculations. A ferrimagnetic order is also predicted in kagome-Co9Te16. This work should provide a novel route for the direct synthesis of ultrathin kagome materials via a metal self-intercalation route, which should shed light on the exploration of the intriguing flat band physics in the related systems.

Biomechanical comparison of a new undercut thread design vs the V-shape thread design for pedicle screws

BACKGROUND CONTEXTThread shape is regarded as an important factor influencing the fixation strength and osseointegration of bone screws. However, commercial pedicle screws with a V-shaped thread are prone to generating stress concentration at the bone-screw interface, thereby increasing the risk of screw loosening. Thus, modification of the pedicle-screw thread is imperative. PURPOSEThis study aimed to investigate the fixation stability of pedicle screws with the new undercut thread design in comparison to pedicle screws with a V-shaped thread. STUDY DESIGNIn vitro cadaveric biomechanical test and finite element analysis (FEA). METHODSPedicle screws with the undercut thread (characterized by a flat crest feature and a tip-facing undercut feature) were custom-manufactured, whereas those with the V-shaped thread were procured from a commercial supplier. Fixation stability was assessed by the cyclic nonpullout compressive biomechanical testing on cadaveric female osteoporotic vertebrae. The vertical displacement and rotation angle of the 2 types of pedicle screws were calculated every 100 cycles to evaluate their resistance to migration and rotation. FEA was conducted to investigate the stress distribution and bone damage at the bone-screw interface for both types of pedicle screws. RESULTSBiomechanical testing revealed that the pedicle screws with the undercut thread exhibited significantly lower vertical displacement and rotation angles than the pedicle screws with the V-shape thread (p<0.05). FEA results demonstrated a more uniform stress distribution in the bone surrounding the thread in the undercut design than in the V-shape design. Additionally, bone damage resulting from the pedicle screw was lower in the undercut design than in the V-shape design. CONCLUSIONSPedicle screws with an undercut thread are less prone to migration and rotation and thus more stable in the bone than those with a V-shape thread. CLINICAL SIGNIFICANCEThe undercut thread design may reduce the incidence of pedicle-screw loosening.

Cryogenic Pits and Quaternary Glacial Evidence in Central Iran

Quaternary glaciation studies in Central Iran reveal that it is not implausible to anticipate glaciation traces in this region. It is feasible to provide conclusive evidence about the behavior of ice sheets by referring to geomorphological factors and climatic statistical analyses. Factors such as flatness and accidental geographical features contribute to the existence of ice sheets in the Namdan Fars region. The digital reconstruction of past climatic conditions، using the Wright method، along with the absence of lake terraces around Kaftar Lake، signifies the presence of ice instead of water in the lake. The multi-axial morphology of the Namdan Plain، the shape and form of main valleys and passes، and the existence of numerous glacial cirque traces in the surrounding heights are also indicators of this phenomenon. The lack of evidence of ancient settlements in the plain، despite the availability of water and fertile soil، can be attributed to the region's historical thermal conditions. Investigating ancient glaciers helps us understand the natural history of the land. This knowledge can aid planners in devising macro strategies for regional development and water resource management، as glacial performance has always been associated with optimal water levels. Although glacial activities can create aquifers، the movement of ice sheets or ice surfaces does not support the accumulation of sediments required for creating aquifers with sufficient water storage. Instead، their performance leads to the creation of suitable agricultural soil layers. In summary، regional glaciers play a positive role in transforming and creating favorable agricultural soils and can be beneficial in adapting to climatic changes and extending statistical periods.

Nonsymmorphic symmetry protected nodal lines in layered topological semimetal Ta3GeTe6

Topological semimetals have garnered significant attention due to their distinctive physical properties. However, the ideal material platforms for studying these phenomena remain limited. Here, we report the synthesis and nontrivial topological properties of high-quality van der Waals material Ta3GeTe6. Angle-resolved photoemission spectroscopy studies performed systematically on the as-grown Ta3GeTe6 single crystal along different high-symmetry directions reveal the formation of two nodal lines located near 0.07 and 0.55 eV below EF along the loop X-U-R-S, which arises from band crossings protected by nonsymmorphic symmetry. Furthermore, the nodal lines near the Fermi level along the S-R and S-X directions exhibit a flat feature. The discovery of this material enriches the family of topological nodal line semimetals and provides a promising platform for future investigations into exotic electronic correlation phenomena and potential device applications.

Rainfall-Runoff Response of A Suburban Area

Batu Pahat experiences flash floods whenever intense rainfall coincides with high tide. Among the factors which cause flash floods are due to Batu Pahat river catchment's flat and low-lying geographical features as well as high-intensity rainfall. The goals of the study are to analyse the frequency of rainfall events for SMK Munshi Sulaiman station and to investigate runoff due to severe rainfall events within the study area. The observed daily rainfall depth record between 2010 and 2021 was obtained from the Department of Irrigation and Drainage (DID) Malaysia. The frequency of rainfall events within the 11-year period is examined using empirical rainfall intensity formulation. Rainfall-runoff of the five most heavy rainfall events in 2021 within the study area are simulated using HEC-HMS. It has been found that most daily rainfall events have a frequency of a 1-year return period. Only three events were found to have a return period of up to 2-year ARI, with a maximum rainfall depth of 110.67 mm. Five heaviest rainfall events in 2021 were obtained from DID's real-time online platform for rainfall-runoff simulations. One of the events, which occurred in June 2021 has a frequency larger than a 100-year return period while other events have return periods ranging from 1-year to 5-year. Simulations produced by HEC-HMS for these events in January, April, May, June, and September 2021 have resulted in peak flow of 6.7 m3/s, 26.8 m3/s, 24.7 m3/s, 39.9 m3/s, and 39.9 m3/s, respectively. Based on frequency analysis, rainfall-runoff simulations, and field observations, it can be concluded that flash floods are highly possible due to high-intensity rainfall as well as lowland topographical features of the study area. Therefore, flood mitigation measures need to be carried out to improve the drainage system for the suburban area.

Assessment of predicting temperature distribution of friction stir welded AA6061 induced by pin profiles for developing sustainable industry

Nowadays, the aspects of energy and environmental pollution have been becoming a big challenge in developing sustainable industries. Using green technology is considered as priority solution for any manufacturing process. Friction stir welding (FSW) is invented as green technology applied widely in many field industries. To evaluate its applicability, this study focused on the prediction of temperature distribution of FSWed AA6061 induced by various pin profiles. Research efforts are being made to gain a better understanding of FSW process, to explore different tool configurations, and their influence on the heat generation. The numerical model was developed in Abaqus software, utilizing the coupled Eulerian Lagrangian method, the Johnson-Cook material model, and the mass scaling technique. The model’s accuracy is verified by comparing its simulated temperature values with experimental data in Stir zone (SZ) and Heat-affected zone (HAZ). The numerical results show the high correlation with the experimental study, with the deviation around 10%. It is shown that tool pin profiles with the combination of thread and flat features generated the highest temperature.

Technical, economical, and socio-environmental analysis of forest road maintenance using the HDM-4 software

As they do not have a sealant coating, forest roads are more susceptible to degradation and traffic obstruction, requiring better construction and maintenance attention. This study aimed to assess the performance of maintenance carried out on unpaved roads in technical, economic, and socio-environmental scopes by application of the Highway Development &amp; Management Model (HDM-4) and to show the best project proposals. The analyses consisted of inputting the HDM-4 with the characteristic data of roads, of and the maintenance to be adopted and the type of used vehicle. The association of this information made it possible to envision scenarios that consider either the replacement or non-replacement of gravel materials on the roads as a methodology. For management without gravel replacement, the most effective scenario was that of roads with gravel under the bed, located in a tropical climate, with flat features and 90 kilometers in length, initial thickness of 175 mm of gravel, high volume of traffic, and subject high-level maintenance at 30-day intervals. For the management with gravel replacement, the ideal scenario was that of roads with gravel under the bed, located in a temperate climate, on rolling terrain and 30 kilometers long, initial thickness of 175 mm of gravel, high traffic intensity, and subjected to high-level maintenance every 30 days. High-level maintenance was the best option for maximizing the quality of the roads and providing the best total net benefit, lowest gas emission rates, least fuel, and tire consumption, and adequate pavement condition by the end of the project.

Flat bread baking: Single to double layer transition

Double-layered flat bread features an impressive oven rise and delamination during baking, leading to the formation of an internal pocket capable of holding various solid foods – a key quality criterion for consumers. These breads are unique in their baking method, which requires specialized ovens and high temperatures between 350 and 550 °C. Use of high baking temperatures to achieve the double layering development (called delamination) during baking has raised concerns over excessive energy consumption. In this study, whether or not the application of fermentation (affecting the accumulation of dissolved CO2) and baking temperature (which affects gas generation) were varied and the impacts on delamination were evaluated. To complement this evaluation, dough water content and temperature were monitored during baking. In a novel manner, this study characterized water distribution in flat bread, explaining the surprising decrease of water loss with increasing baking temperature. Our study has clearly shown water vapor to be the prime cause of delamination. The role of water pressure in dough inflation and in causing the edges to detach from the deck and the heterogeneity of flat bread water content were highlighted and a concept map proposed.

Vacancy-mediated anomalous phononic and electronic transport in defective half-Heusler ZrNiBi

Studies of vacancy-mediated anomalous transport properties have flourished in diverse fields since these properties endow solid materials with fascinating photoelectric, ferroelectric, and spin-electric behaviors. Although phononic and electronic transport underpin the physical origin of thermoelectrics, vacancy has only played a stereotyped role as a scattering center. Here we reveal the multifunctionality of vacancy in tailoring the transport properties of an emerging thermoelectric material, defective n-type ZrNiBi. The phonon kinetic process is mediated in both propagating velocity and relaxation time: vacancy-induced local soft bonds lower the phonon velocity while acoustic-optical phonon coupling, anisotropic vibrations, and point-defect scattering induced by vacancy shorten the relaxation time. Consequently, defective ZrNiBi exhibits the lowest lattice thermal conductivity among the half-Heusler family. In addition, a vacancy-induced flat band features prominently in its electronic band structure, which is not only desirable for electron-sufficient thermoelectric materials but also interesting for driving other novel physical phenomena. Finally, better thermoelectric performance is established in a ZrNiBi-based compound. Our findings not only demonstrate a promising thermoelectric material but also promote the fascinating vacancy-mediated anomalous transport properties for multidisciplinary explorations.

Lake Atotonilco: A First Approach to Determining the Minimum Lake Level Necessary to Sustain Its Biodiversity

Lake Atotonilco is a shallow saline water body located in the central-west portion of Mexico. The lake is in the low plain of an endorheic watershed. It is shallow, with a large area of surrounding wetlands and serves as a refuge for dozens of native and migratory waterfowl. Its extremely flat morphometric features coupled with the precipitation and runoff regime from the watershed cause significant changes in the lake surface area and storage volume throughout the year. In recent years, the lake has behaved as an intermittent lake, remaining practically dry in June, and reaching its highest storage volume in October. An ecological water volume that the lake must maintain to support its biodiversity was estimated. This minimum lake storage volume can only be achieved if public policies are implemented to rationalize the use of water resources in the basin and to protect the few forest areas that remain in the watershed. Key Words: ecological minimum volume, endorheic watershed, lake bathymetry, playa lake.

Mechanism of pin thread and flat features affecting material thermal flow behaviors and mixing in Al-Cu dissimilar friction stir welding

Three different features of pin models in Al-Cu dissimilar friction stir welding processes are established to analyse the effects of threads and flats on the two-phase material thermal flow behaviors. Based on computational fluid dynamics (CFD), a simulation methodology that calculates pins with complex morphologies through an adaptive force boundary is proposed. The pin characteristics are gradually optimized from “conical contour” to “conical-thread” and then to “thread-flats”. For dissimilar Al-Cu materials, the physical properties are weighted by the volume fractions of two-phase materials in the mixing zone. To build a dynamic adaptive contact model that varies with the material flow state, the interfacial friction shear stress is calculated by using the relative slip between the tool and material. The linkage effects between the “thread + flats” on the dissimilar Al/Cu welding mechanisms are systematically analysed. The enhancing mechanisms of the thread and flats on the material flow are different. The thread mainly reinforces the longitudinal migration of the Al/Cu materials, which is perpendicular to the horizontal plane. The flats effectively expand the plastic flow range and material mixing zone on the horizontal plane. These flow expanding effects are observed on the Z = 1 mm plane since the radial range of material flow enlarges from 2 mm to 3 mm under the action of the flats, while the horizontal flow range undergoes little change with the thread. The coupled mechanism of the “thread + flats” shows 0.06 s periodic strengthening, and the fluctuation threshold of the material flow velocity is wider, significantly improving the upwards stirring of the bottom material. The enhanced horizontal flow and vertical migration are beneficial to the uniform dispersion of the second-phase material (Cu) and local material softening for the formation of Al-Cu heterogeneous joints. Moreover, the accuracy of the model is verified by comparing the simulated and experimental TMAZ boundaries.

Tuning electronic phase of monolayer [formula omitted]-borophene via adsorbed gas molecules: Generation of van Hove singularity

We consider manifolds of the tunable electronic density of states in single-layer β12-borophene, parameterized by a manifold electron hopping amplitude. We study the hybridization properties of orbitals in the presence of gas molecules (GM) with a tight-binding model and Green’s function approach. Independent of how we dope the layer by GM, van Hove singularities are significantly generated and associated with various broadness and flatness features of bands. We demonstrate that β12-borophene with GM-doped {a,e}, {a,c}, {b,d}, and {b,c} atoms is described by a semimetallic phase, where the metallic phase is washed out in the vicinity of Fermi level. We also find a gapless semiconducting phase at the Fermi energy for GM-doped c atoms; however, the most inherent character of the system remains unchanged once all atoms are simultaneously doped with GM. These findings can apply to tuning field-effect transistor-based gas sensors.

Photonic Realization of a Generic Type of Graphene Edge States Exhibiting Topological Flat Band.

Cutting a honeycomb lattice (HCL) ends up with three types of edges (zigzag, bearded, and armchair), as is well known in the study of graphene edge states. Here, we propose and demonstrate a distinctive twig-shaped edge, thereby observing new edge states using a photonic platform. Our main findings are (i)the twig edge is a generic type of HCL edge complementary to the armchair edge, formed by choosing the right primitive cell rather than simple lattice cutting or Klein edge modification; (ii)the twig edge states form a complete flat band across the Brillouin zone with zero-energy degeneracy, characterized by nontrivial topological winding of the lattice Hamiltonian; (iii)the twig edge states can be elongated or compactly localized at the boundary, manifesting both flat band and topological features. Although realized here in a photonic graphene, such twig edge states should exist in other synthetic HCL structures. Moreover, our results may broaden the understanding of graphene edge states, as well as new avenues for realization of robust edge localization and nontrivial topological phases based on Dirac-like materials.

Test of conformal theory of gravity as an alternative paradigm to dark matter hypothesis from gravitationallensing studies

Weyl's conformal gravity theory, which is considered as a compelling alternative to general relativity theory, has been claimed to describe the observed flat rotation curve feature of spiral galaxies without the need of invoking dark matter. However, it is important to examine whether the Weyl theory can also explain the relevant gravitational lensing observations correctly without considering any dark matter. In this regard, the gravitational bending angle in static spherically space-time (Mannheim-Kazanas metric) in Weyl theory has been calculated by several authors over the last two decades, but the results are found largely divergent. In this work, we have revisited the problem and obtain the correct and consistent expression of the deflection angle in conformal gravity. Subsequently we perform the gravitational lensing analysis. We compare the prediction of Weyl gravity with the gravitational lensing observations of the rich galaxy clusters Abell 370 and Abell 2390 and is found that Weyl theory cannot describe the stated lensing observations without considering dark matter.

Prediction of tandem cold-rolled strip flatness based on Attention-LSTM model

Flatness is a key quality indicator of tandem cold-rolled strip. Tandem cold-rolled production is a multi-stand simultaneous rolling process. The prediction of flatness is a typical spatial sequence data prediction problem by considering not only the complex generation mechanism but also the spatial dimension dependence. However, the currently available mechanistic and machine learning models for flatness prediction only focus on its highly nonlinear characteristics and ignore its complex spatial correlation. In addition, the over-parameterized “black box” nature of machine learning models has often been questioned. Based on this, a long-short-term memory model with an attention mechanism (Attention-LSTM) is proposed in this paper. The model is structured as a two-layer LSTM network to fully learn the highly nonlinear and complex spatial data correlation of tandem cold-rolled strip flatness. Furthermore, attention mechanisms are also added to the spatial dimension and flatness feature vector dimension, respectively, to enhance the interpretability of the model. The superiority of the proposed model is verified by comparing the error back propagation neural network model (BPNN), the extreme gradient boosting algorithm model (XGBoost), the deep neural network model (DNN), the LSTM model without the attention mechanism, and the Attention-LSTM model with the same dataset and the same optimum training method. The interpretation of the attention mechanism weights is consistent with the mechanistic model, which enhances the credibility of the model. The results of the ablative experiments also validate the effectiveness of incorporating the attention mechanism in the model.