Uniform Geometry Research Articles

Direct Visualization of Nearly Free Electron States Formed by Superatom Molecular Orbitals in a Li@C60 Monolayer.

Using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we directly determine the spatial and energetic distributions of superatom molecular orbitals (SAMOs) of an Li@C60 monolayer adsorbed on a Cu(111) surface. Utilizing a weakly bonded [Li+@C60] NTf2- (NTf2-: bis(trifluoromethanesulfonyl)imide) salt makes it possible to produce a Li@C60 monolayer with high concentration of Li@C60 molecules. Because of the very uniform adsorption geometry of Li@C60 on Cu(111), the pz-SAMO, populated above the upper hemisphere of the molecule, exhibits an isotropic and delocalized nature, with an energy that is significantly lower compared to that of C60. The isotropic overlapping of pz-SAMOs in the condensed monolayer of Li@C60 results in a laterally homogeneous STM image contributing to the formation of a free-electron-like states. These findings make an important step toward further basic research and applicative utilization of Li@C60 SAMOs.

Ground states of elliptic problems over cones

Given a reflexive Banach space X, we consider a class of functionals \(\Phi \in C^1(X,{\mathbb {R}})\) that do not behave in a uniform way, in the sense that the map \(t \mapsto \Phi (tu)\), \(t>0\), does not have a uniform geometry with respect to \(u\in X\). Assuming instead such a uniform behavior within an open cone \(Y \subset X \setminus \{0\}\), we show that \(\Phi \) has a ground state relative to Y. Some further conditions ensure that this relative ground state is the (absolute) ground state of \(\Phi \). Several applications to elliptic equations and systems are given.

Low Noise Hybrid Nanopore with Engineered OmpG and Bilayer MoS2

Hybrid nanopores combine the durability of a solid-state nanopore with the precise structure of a biological nanopore. When a DNA strand is pulled electrophoretically through a solid-state nanopore it can be sensed using the ionic blockade current produced by each translocating molecule. However, owing to the lack of chemical specificity and pore size reproducibility, solid-state nanopore sensing suffers from poor repeatability. Biological nanopores which have a constant geometry ensure sensitive and repeatable sensing. In this study, hybrid nanopores were formed by insertion of a engineered outer membrane porin G (eOmpG) in a bilayer (BL) molybdenum disulfide (MoS2) solid-state nanopore. Engineered outer membrane porin G (eOmpG) is used as the biological counterpart of the hybrid nanopore due to its uniform cylindrical geometry and controlled gating useful for specific detection of label-free analytes. BL MoS2 is used as the solid-state support for the hybrid construct owing to its surface charge and 2D layered properties, which ensures a stable support with low capacitive noise, favorable for precise sensing. To realize the hybried nanopore a single eOmpG was electrophoretically pulled through a 3.4 nm BL MoS2 solid-state nanopore at neutral pH and +80 mV trans bias. A hybrid BL MoS2-eOmpG nanopore was found to demonstrate 32% lower noise levels with nearly 1.9 times improved in the signal-to-noise ratio (SNR) and 6.5 times longer dwell times for dA30 molecular sensing compared to the BL MoS2 solid-state nanopore. Thus, the low-noise biocompatible platform of the hybrid BL MoS2-eOmpG nanopore can be used for highly resolved biomolecular sensing.

Calibration of neutron detectors at ASDEX Upgrade, measurement and model

The neutron production in ASDEX Upgrade (AUG) neutral beam injection (NBI) heated discharges is dominated by beam-target fusion reactions. Hence, the neutron rate (NR) and energy distributions are footprints of the fast ion distribution. This motivates to establish a reliable neutron rate calibration. Comparisons at AUG between the experimental NR and the one predicted by the TRANSP code show systematic variations from campaign to campaign. Potential reason for this is the delicate absolute calibration of the neutron detectors. Therefore, a different calibration technique was performed, enabling longer acquisition time, uniform geometry, better statistics and thus less uncertainty. A toy train carrying a radioactive source (238Pu/B) over two radial positions on the equatorial plane shows a periodical NR on the epithermal 3He neutron detector. The calibration results are compared to a neutron transport simulation using the Monte Carlo (MC) code Serpent. Preliminary comparisons for one source position on the outer railway track show a discrepancy factor of about 130 in the position of least material inside the simulation, in the direct line of sight to the detector. For a better understanding of these results, two additional measurements were performed. The results were again compared to a detailed Serpent simulation. This paper describes the calibration set-up for the neutron measurements in AUG, provides a brief simulation background on reaction rate estimations and a survey on the comparison between the measured and calculated neutron rates.

Topological and geometric hyperbolicity criteria for polynomial automorphisms of

AbstractWe prove that uniform hyperbolicity is invariant under topological conjugacy for dissipative polynomial automorphisms of $\mathbb {C}^2$ . Along the way we also show that a sufficient condition for hyperbolicity is that local stable and unstable manifolds of saddle points have uniform geometry.

An Efficient Approach for Sidelobe Level Reduction Based on Recursive Sequential Damping

Recently, antenna array radiation pattern synthesis and adaptation has become an essential requirement for most wireless communication systems. Therefore, this paper proposes a new recursive sidelobe level (SLL) reduction algorithm using a sidelobe sequential damping (SSD) approach based on pattern subtraction, where the sidelobes are sequentially reduced to the optimum required levels with near-symmetrical distribution. The proposed SSD algorithm is demonstrated, and its performance is analyzed, including SLL reduction and convergence behavior, mainlobe scanning, processing speed, and performance under mutual coupling effects for uniform linear and planar arrays. In addition, the SSD performance is compared with both conventional tapering windows and optimization techniques, where the simulation results show that the proposed SSD approach has superior maximum and average SLL performances and lower processing speeds. In addition, the SSD is found to have a constant SLL convergence profile that is independent on the array size, working effectively on any uniform array geometry with interelement spacing less than one wavelength, and deep SLL levels of less than −70 dB can be achieved relative to the mainlobe level, especially for symmetrical arrays.

A NEW RING STENT WITH GRADED GEOMETRY FOR TREATING COARCTATION OF CURVED AORTA ARTERIES

Ring stent implantation has been widely used to treat coarctation of the aorta (CoA) as an alternative to surgery. Currently adopted stents with uniform geometry may cause uneven stress distribution and high stress concentration in curved vessels, leading to in-stent restenosis (ISR). Inspired by functional graded material, here we propose a new ring-and-link stent, which has graded geometry in order to achieve a reduced peak stress when deployed in curved arteries. Numerical simulation of a single ring of the graded stent indicated that by varying the circumferential spacing of wave crest, the maximum stress exerted on the artery was reduced by as much as 27.86% in comparison with the uniform one. The effects of stent geometric parameters and artery curvature were also obtained through a parametric study. Finally, a whole stent was studied to verify the design, and a maximum stress reduction by 31.96% was achieved. In summary, the proposed graded ring stent shows great potential in clinical applications to reduce the risk of ISR.

Simulating Drillstring Dynamics Motion and Post-Buckling State with Advanced Transient Dynamics Model

SummaryAs drilling sections become deeper and longer, transferring more weight downhole to improve rate of penetration is the primary concern for the operator. Drillstring dynamics and buckling are some primary limiters for drilling efficiency. Aggressive drilling parameters may lead to severe downhole dynamics, which leads to cutter breakage and tool damage. When axial compression exceeds a certain threshold, the drillstring buckles sinusoidally inside the wellbore first, followed by helical buckling. Buckling leads to accelerated joint wear, tool fatigue failures, and lower drilling efficiency. To better manage drillstring dynamics and buckling, we propose a method of simulating drillstring dynamics motion and postbuckling state using an advanced transient dynamics model.An analysis methodology was developed on the basis of the finite element transient dynamics model. The model captures the enriched physics of drillstring dynamics and loading: the large deformation of buckled drillstring, the strong nonlinearity of contact and friction forces, and the dynamically triggered instability caused by drilling rotation. Transient dynamics simulations are conducted for drillstring with the actual well trajectory and rotation speed. The weight on bit (WOB) is ramped up gradually, and the drillstring deformation is monitored to detect the onset of buckling or dynamics instability.To conduct the model validation, the buckling inception loads predicted by the model are compared against the analytical equation of critical buckling loads. A field extended reach drilling (ERD) job was simulated by the model. The downhole weight and torque data from the measurement-while-drilling (MWD) tool was used to validate the weight transfer prediction by the model. Most existing buckling theories use the analytical equations of critical buckling load, which were normally derived on the basis of the idealized assumptions, such as perfect wellbore shape and uniform tubular geometry. The proposed method simulates the drillstring behaviors in the field drilling conditions and aims to capture effects of wellbore friction and string rotation. The transient dynamics model is capable of simulating drillstring dynamics movement (whirling and snaking) and weight lockup under severe helical buckling. An automatic method is proposed to interpret the drillstring behaviors from the simulation results. Using the transient dynamics model, the procedure presented in this article can simulate the dynamics and buckling behaviors of drillstring and help mitigate associated risks in well-planning and execution phases.

Manufacturing Concept and Prototype for Train Component Using the FSW Process

Friction stir welding (FSW) is a process originally developed for joining light materials, such as aluminum and magnesium, as an answer to their poor weldability by conventional fusion processes. In Colombia, the technique has been studied but its industrial implementation is uncommon, due to the high cost of specialized machinery and the unfamiliarity with the technique of local industries. This article presents an implementation case study of FSW on a 6082-aluminum alloy train component from Metro de Medellín (MdM), aiming to establish the component design changes required to accommodate the FSW process, and conventional machines available in the local area which may be available for welding. Additionally, a simple comparison was made between the cost of this approach versus the manufacturing strategy currently used for the selected component. Initially, welding forces were measured when performing the seam on the selected component using an FSW machine. This data was then used to downselect the local milling machines with these capabilities. A simple but specific tool was designed for the geometry of one of the component features. Finally, a prototype was fabricated, and weld samples were obtained, polished, etched, and examined using a microhardness machine and an optical microscope. Results show a good opportunity for the execution of simple components with uniform geometries, which can be carried out using locally available machinery because they do not surpass their maximum loading capacity, the welds do not present visible discontinuities, and an average hardness of 69.5 HV and mechanical efficiency of 95% can be achieved. Additionally, the manufacturing process is around 30% cheaper compared to traditional methods, making the application viable, economically speaking.

Investigation of Specific FDM Process Parameters to Optimize the Polymer Discharge of Carbon Fiber Reinforced PEEK

AbstractFused deposition modeling (FDM) is a widely used manufacturing process and the materials market is growing due to the increased requirements on materials. In particular, processing of high‐temperature materials such as PEEK is challenging. The aim of these studies is to investigate and improve the processability of a carbon fiber reinforced polyether ether ketone (PEEK) material in the FDM process. The first step is to define the relevant process parameters, which remain constant over the entire investigation. In particular, the material‐specific temperatures must be defined. Based on previous investigations regarding the weld seam strength and the warpage of the selected PEEK materials, a method to determine and adjust essential process parameters should be developed. One approach is the consideration of the volumetric polymer discharge at a stationary filament feed rate. The optimized adjustment of the feed rate ensures increased component densities and an improved process reliability. In this context, the component areas with non‐stationary extruder movement, such as in corner areas, have got a huge influence on the component quality. The acceleration and deceleration processes do not result in a desired uniform strand geometry due to the pressure changes within the nozzle. The acceleration can result in thinner strands while the deceleration can lead to a thickening of the polymer discharge. The aim is to adjust the pressure inside the nozzle depending on the acceleration profile to enable a homogenous strand geometry. The method should therefore allow the improvement of the processability of PEEK materials.

Development of a 3D dual pore‒system leaching model: Application on metal extraction from oxide copper ore

Leaching from packed ore beds in hydrometallurgical operations involves various sub-processes, including flow of solution, transport of leaching agent and leached product, liquid-solid reactions at the mineral surface and transfer of reaction heat, in heterogeneous multi-scale porous media. A 3D dual pore‒system leaching model based on heterogeneous ore pack geometry reconstructed from X-ray computed tomography (CT) images was developed to account for the coupled flow–transport–reaction–heat transfer processes across the pore scales of inter-particle macro-pore and intra-particle micro-pore. The model was deployed to investigate the leaching kinetics of an oxide copper ore by sulphuric acid. Ultimately, the velocity field, mineral leaching rate, concentration of leached ions, concentration of leaching agent and temperature were solved numerically by finite element method. The influence of leaching agent concentration, irrigation rate and environment temperature on the competitive leaching of malachite and gangue minerals was revealed. The dual pore‒system model is able to provide insights into the heterogeneous leaching behaviours that otherwise cannot be revealed by models built on basis of uniform geometries.

Angle Estimation and Mutual Coupling Self‐Calibration in Bistatic MIMO System with Arbitrary Geometry

Ideal array responses are often desirable to a multiple‐input multiple‐output (MIMO) system. Unfortunately, it may not be guaranteed in practice as the mutual coupling (MC) effects always exist. Current works concerning MC in the MIMO system only account for the uniform array geometry scenario. In this paper, we generalize the issue of angle estimation and MC self‐calibration in a bistatic MIMO system in the case of arbitrary sensor geometry. The MC effects corresponding to the transmit array and the receive array are modeled by two MC matrices with several distinct entities. Angle estimation is then recast to a linear constrained quadratic problem. Inspired by the MC transformation property, a multiple signal classification‐ (MUSIC‐) like strategy is proposed, which can estimate the direction‐of‐departure (DOD) and direction‐of‐arrival (DOA) via two individual spectrum searches. Thereafter, the MC coefficients are obtained by exploiting the orthogonality between the signal subspace and the noise subspace. The proposed method is suitable for arbitrary sensor geometry. Detailed analyses with respect to computational complexity, identifiability, and Cramer‐Rao bounds (CRBs) are provided. Simulation results validate the effectiveness of the proposed method.

Nanocatalytic Medicine of Iron-Based Nanocatalysts

Iron can be found in all mammalian cells and is of critical significance to diverse cellular activities within human bodies. Widespread applications and the underlying chemical and biological funda...

Fabrication and characterization of forcespun polycaprolactone microfiber scaffolds

Forcespinning technique was used to fabricate sub-micron size polycaprolactone (PCL) fibers. Forcespinning method uses centrifugal forces for the generation of fibers unlike the electrospinning method which uses electrostatic force. PCL has been extensively used as scaffolds for cell regeneration, substrates for tissue engineering and in drug delivery systems. The aim of this study is to qualitatively analyze the force spun fiber mats and investigate the effect of the spinneret rotational speed on the fiber morphology, thermal and mechanical properties. The extracted fibers were characterized by scanning electron microscopy differential scanning calorimetry, tensile testing and dynamic mechanical analysis. The results showed that higher rotational speeds produced uniform fibers with less number of beads. The crystallinity of the fibers decreased with increase in rotational speeds. The Young’s modulus of the forcespun fibers was found to be in the range of 3.5 to 6 MPa. Storage and loss moduli decreased with the increase in the fiber diameter. The fibers collected at farther distance from spinneret exhibited optimal mechanical properties compared to the fibers collected at shorter distances. This study will aid in extracting fibers with uniform geometries and lower beads to achieve the desired nanofiber drug release properties.

Signal Feature Extraction and Combination to Enhance the Detection and Localization of Railroad Track Irregularities

Tracks are critical and expensive railroad asset, requiring frequent maintenance. The stress from heavy car axle loads increases the risk of deviations from uniform track geometry. Irregularities in track geometry, such as track warping, can cause an excessive harmonic rocking condition that can lead to derailments, traffic delays, and associated financial losses. This article presents an approach to enhance the location identification accuracy of track geometry irregularities by combining measurements from sensors aboard Hi-Rail vehicles. However, speed variations, position recording errors, low GPS update rates, and the non-uniform sampling rates of inertial sensors pose significant challenges for signal processing, feature extraction, and signal combination. This study introduces a method of extracting features from the fused data of inertial sensors and GPS receivers with multiple traversals to locate and characterize irregularities of track geometry. The proposed method provides robust detection and enhanced accuracy in the localization of irregularities within spatial windows along the track segment. Tradeoff analysis found that the optimal spatial window size is 5-meter.

Vortex shedding modes around oscillating non-uniform double heave plates

Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total theoretical added mass of a general non-uniform double disk is proposed when it is in the zone which vortex interaction take places. The results show that a non-uniform double disk has better hydrodynamic performance as compared to the uniform double configuration for a given spacing. It is also observed that the mode and direction of the vortex shedding are different for uniform and non-uniform arrangements in a given spacing and KC value.

UV LED Assisted Printing Platform for Fabrication of Micro-Scale Polymer Pillars

Ultraviolet (UV) assisted printing has emerged as a promising additive manufacturing (AM) technology, which puts UV light sources with focused emission in high demand. Unfortunately, current ultraviolet light-emitting diodes (UV LEDs) are not able to provide adequately focused UV emission required for printing. Thus, a UV LED package with focused UV emission was proposed and fabricated using microelectromechanical system (MEMS) technology in this study. An optical model of the UV LED package with focused UV emission was developed. Based on the designed model, a silicon reflector stacked on another was achieved. By assembling the stacked silicon reflector and hemispherical quartz lenses, the UV LED package with focused UV emission was successfully achieved. A narrow beam with a beam angle of 16° between half maximum intensity was achieved, while the intensity at 0° was greater than 1000 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the focal point. The UV LED curing system using two focused UV LED packages was successfully developed based on the optical simulation results. Polymer pillars were fabricated by instantaneous UV curing process with synchronized UV curable polymer jetting process in one shot, and micro-scale polymer pillars with a diameter of 20 μm were achieved. Thanks to the high intensity and focused UV emission, polymer pillars can be formed in as little as 100 ms. 13600 polymer pillars were printed on a silicon wafer with uniform diameter and geometry in a single dispensing cycle. The UV LED assisted printing platform was successfully demonstrated for fabrication of micro-scale 3D structures in a fast speed with smooth printing process.

Spatially Organized Differentiation of Mouse Pluripotent Stem Cells on Micropatterned Surfaces.

Pluripotent stem cells (PSCs) are the in vitro counterpart of the pluripotent epiblast of the mammalian embryo with the capacity to generate all cell types of the adult organism. During development, the three definitive germ layers are specified and simultaneously spatially organized. In contrast, differentiating PSCs tend to generate cell fates in a spatially disorganized manner. This has limited the in vitro study of specific cell-cell interactions and patterning mechanisms that occur in vivo. Here we describe a protocol to differentiate mouse PSCs in a spatially organized manner on micropatterned surfaces. Micropatterned chips comprise many colonies of uniform size and geometry facilitating a robust quantitative analysis of patterned fate specification. Furthermore, multiple factors may be simultaneously manipulated with temporal accuracy to probe the dynamic interactions regulating these processes. The micropattern system is scalable, providing a valuable tool to generate material for large-scale analysis and biochemical experiments that require substantial amounts of starting material, difficult to obtain from early embryos.

Aqueous adsorption of sulfamethoxazole on an N-doped zeolite beta-templated carbon

A zeolite beta-templated carbon (BTC) and its N-doped form (nBTC) were prepared and used for the adsorptive removal of sulfamethoxazole (SMX) antibiotic from water. Both demonstrated excellent adsorption properties, and the maximum adsorption capacity of nBTC (1367 mg/g) was exceptionally high, and surpassed those of other adsorbents reported to date. Adsorption kinetic studies indicated that the adsorption was efficient, and adsorption equilibrium was reached within 10 min. The excellent adsorption performance of nBTC was attributed to the high-surface-area hydrophobic carbons with strong π–π interactions and H-bonding in the uniform microporous geometry of the material. The effect of the solution pH and thermodynamics of the adsorption process were subsequently investigated. nBTC was easily regenerated by washing with acetone, and a recyclability test confirmed that ~88% of the initial SMX adsorption capacity of nBTC was retained after the fifth adsorption–desorption cycle. Moreover, nBTC presented excellent capacity for the adsorptive removal of bisphenol A from water.

CENTIMETRE-ACCURACY IN FORESTS AND URBAN CANYONS – COMBINING A HIGH-PERFORMANCE IMAGE-BASED MOBILE MAPPING BACKPACK WITH NEW GEOREFERENCING METHODS

Abstract. Advances in digitalization technologies lead to rapid and massive changes in infrastructure management. New collaborative processes and workflows require detailed, accurate and up-to-date 3D geodata. Image-based web services with 3D measurement functionality, for example, transfer dangerous and costly inspection and measurement tasks from the field to the office workplace. In this contribution, we introduced an image-based backpack mobile mapping system and new georeferencing methods for capture previously inaccessible outdoor locations. We carried out large-scale performance investigations at two different test sites located in a city centre and in a forest area. We compared the performance of direct, SLAM-based and image-based georeferencing under demanding real-world conditions. Both test sites include areas with restricted GNSS reception, poor illumination, and uniform or ambiguous geometry, which create major challenges for reliable and accurate georeferencing. In our comparison of georeferencing methods, image-based georeferencing improved the median precision of coordinate measurement over direct georeferencing by a factor of 10–15 to 3 mm. Image-based georeferencing also showed a superior performance in terms of absolute accuracies with results in the range from 4.3 cm to 13.2 cm. Our investigations showed a great potential for complementing 3D image-based geospatial web-services of cities as well as for creating such web services for forest applications. In addition, such accurately georeferenced 3D imagery has an enormous potential for future visual localization and augmented reality applications.