Specific Geometry Research Articles

Determination of optimal solar-viewing geometry for in-flight polarization calibration using sun glint over ocean

The sun glint has been proven to be a valuable natural polarization calibration target because it is strongly polarized, and its polarization characteristics can be accurately simulated with models. It is convenient to calibrate the satellite’s in-flight polarimetry by comparing the polarization simulations with actual measurements. Meanwhile, the accuracy of polarization simulation at the top of the atmosphere (TOA) over sun glint is affected by several atmospheric and oceanic surface factors and depends on the specific solar-viewing geometry. In this paper, the sensitivity of the degree of linear polarization (DOLP) at the TOA to the uncertainties of the aerosol optical depth, aerosol model, absorption gas content (CWV, O3), sea surface instantaneous wind speed (WS), and chlorophyll concentration (Chl) under different solar-viewing geometries is analyzed via radiative transfer simulation. The error budgets indicate that aerosols and WS are the main error factors for polarization calibration, while the uncertainties of Chl and absorbing gases can be disregarded. The total DOLP error increases with the solar zenith angle and viewing zenith angle (i.e., the increase of atmospheric optical path) and the sun glint angle (SGA, the angle between the viewing and the specular directions of the sun) (i.e., the decrease of sun glint brightness). The dependence of the total DOLP error on SGA decreases with the WS (i.e., the increase of sun glint spot area and the decrease of the sun glint intensity) and increases with the wavelength (i.e., the decrease of atmospheric scattering contribution). Based on the error budgets, an optimized solar-viewing geometry screening strategy is proposed to ensure that the simulated DOLP error is limited to 0.02. The in-flight DOLP calibration result of POLDER/PARASOL shows that the proposed screening strategy obtained more calibration samples and covered a wider range of DOLP, especially for the samples with DOLP of less than 0.2, compared with the screening strategies of Toubbe et al. [IEEE Trans. Geosci. Remote Sens. 37, 513 (1999)IGRSD20196-289210.1109/36.739104]and Hagolle et al. [IEEE Trans. Geosci. Remote Sens. 42, 1472 (2004)IGRSD20196-289210.1109/TGRS.2004.826805] in previous work. The smaller standard error (SE) of the samples indicates more stable calibration results obtained for the optimized strategy. This research presents an optimized strategy for screening the solar-viewing geometry of the samples to calibrate satellite in-flight polarization measurements using the sun glint.

Superconducting Boride Nb2IrB2 with Variable and Tunable Stacking Behaviors of Two-Dimensional [Nb-Ir-Nb] Triangular Lattices.

In structures with special geometry lattices, variations in stacking sequences are ubiquitous, yielding many novel structures and functionalities. Despite a wealth of intriguing properties and wide-ranging applications, there remains a considerable gap in understanding the correlation between special geometry lattices and functionalities in borides. Here, we design and synthesize a new superconducting boride Nb2IrB2, with a body-centered orthorhombic structure, consisting of alternating two-dimensional [Nb-Ir-Nb] triple-triangular-lattice-layers and B fragment layers. Advanced aberration-corrected scanning transmission electron microscopy observations show variable stacking configurations between [Nb-Ir-Nb] triple-triangular-lattice layers that can be tuned through synthesis conditions. Density functional theory calculations reveal that the coherent low-energy boundary interface plane of {101} between [11̅1] and [010] domains is responsible for the variable stacking behaviors. Energetically favorable structures are thereby reasonably proposed, based on nanoscale imperfect structure units. These findings provide valuable insights for designing and exploring new structures and functionalities within boride systems involving special geometry lattices.

Corner and edge states in topological Sierpinski Carpet systems

Fractal lattices, with their self-similar and intricate structures, offer potential platforms for engineering physical properties on the nanoscale and also for realizing and manipulating high order topological insulator states in novel ways. Here we present a theoretical study on localized corner and edge states, emerging from topological phases in Sierpinski Carpet within a $\pi$-flux regime. A topological phase diagram is presented correlating the quadrupole moment with different hopping parameters. Particular localized states are identified following spatial signatures in distinct fractal generations. The specific geometry and scaling properties of the fractal systems can guide the supported topological states types and their associated functionalities. A conductive device is proposed by coupling identical Sierpinski Carpet units providing transport response through projected edge states which carry on the details of the system's topology. Our findings suggest that fractal lattices may also work as alternative routes to tune energy channels in different devices.

Modeling CSF circulation and the glymphatic system during infusion using subject specific intracranial pressures and brain geometries

BackgroundInfusion testing is an established method for assessing CSF resistance in patients with idiopathic normal pressure hydrocephalus (iNPH). To what extent the increased resistance is related to the glymphatic system is an open question. Here we introduce a computational model that includes the glymphatic system and enables us to determine the importance of (1) brain geometry, (2) intracranial pressure, and (3) physiological parameters on the outcome of and response to an infusion test.MethodsWe implemented a seven-compartment multiple network porous medium model with subject specific geometries from MR images using the finite element library FEniCS. The model consists of the arterial, capillary and venous blood vessels, their corresponding perivascular spaces, and the extracellular space (ECS). Both subject specific brain geometries and subject specific infusion tests were used in the modeling of both healthy adults and iNPH patients. Furthermore, we performed a systematic study of the effect of variations in model parameters.ResultsBoth the iNPH group and the control group reached a similar steady state solution when subject specific geometries under identical boundary conditions was used in simulation. The difference in terms of average fluid pressure and velocity between the iNPH and control groups, was found to be less than 6% during all stages of infusion in all compartments. With subject specific boundary conditions, the largest computed difference was a 75% greater fluid speed in the arterial perivascular space (PVS) in the iNPH group compared to the control group. Changes to material parameters changed fluid speeds by several orders of magnitude in some scenarios. A considerable amount of the CSF pass through the glymphatic pathway in our models during infusion, i.e., 28% and 38% in the healthy and iNPH patients, respectively.ConclusionsUsing computational models, we have found the relative importance of subject specific geometries to be less important than individual differences in resistance as measured with infusion tests and model parameters such as permeability, in determining the computed pressure and flow during infusion. Model parameters are uncertain, but certain variations have large impact on the simulation results. The computations resulted in a considerable amount of the infused volume passing through the brain either through the perivascular spaces or the extracellular space.

Dynamics of converting skyrmion bags with different topological degrees into skyrmions in synthetic antiferromagnetic nanotracks

Skyrmion bags are spin textures with any integer topological degree, which can be driven by spin-polarized currents and generate multiple skyrmions when passing through racetracks with special geometries. We have proposed three nanotrack configurations with different narrow channels on synthetic antiferromagnetic racetracks and investigated the dynamic process of current-induced conversion of skyrmion bags into skyrmions. We have found that when skyrmion bags enter narrow channels, they can be converted into magnetic domains, while when the driving force from spin-transfer torque is strong enough, the magnetic domains can break free from the pinning at the ends of channels and form skyrmions. Both the number of channels and driving current density affect the number of generated skyrmions. As the number of channels rises, magnetic domains split at the junctions of channels, forming more magnetic domains and producing more skyrmions. Furthermore, the number of generated skyrmions is also related to the quantity, arrangement, and interaction forces of inner antiskyrmions. When the number of channels remains constant, the number of antiskyrmions only affects the transition of skyrmion bags to magnetic domains and does not affect the movement of magnetic domains or the transition of magnetic domains to skyrmions. The maximum of generated skyrmions in nanotracks with triple channels reaches 9. Dzyaloshinskii–Moriya interaction and anisotropy may play an important role in the structural stability of skyrmion bags, which can affect the splitting behavior of skyrmion bags. This work is beneficial for the design of artificial synapses and the application of neuromorphic computing based on skyrmion bags.

PUMA: Deep Metric Imitation Learning for Stable Motion Primitives

Imitation learning (IL) facilitates intuitive robotic programming. However, ensuring the reliability of learned behaviors remains a challenge. In the context of reaching motions, a robot should consistently reach its goal, regardless of its initial conditions. To meet this requirement, IL methods often employ specialized function approximators that guarantee this property by construction. Although effective, these approaches come with some limitations: 1) they are typically restricted in the range of motions they can model, resulting in suboptimal IL capabilities, and 2) they require explicit extensions to account for the geometry of motions that consider orientations. To address these challenges, we introduce a novel stability loss function that does not constrain the function approximator's architecture and enables learning policies that yield accurate results. Furthermore, it is not restricted to a specific state space geometry; therefore, it can easily incorporate the geometry of the robot's state space. Proof of the stability properties induced by this loss is provided and the method is empirically validated in various settings. These settings include Euclidean and non‐Euclidean state spaces, as well as first‐order and second‐order motions, both in simulation and with real robots. More details about the experimental results can be found at https://youtu.be/ZWKLGntCI6w.

Enhanced high-harmonic generation in a polarization-insensitive all-dielectric metasurface exploiting dual-Fano resonance

Nonlinear optics demands efficacious techniques for nonlinear properties engineering. Metasurfaces, as a flat technology with easy fabrication in various arrangements and without the need for phase-matching conditions, are suitable platforms for nonlinear optics. This study proposes a silicon metasurface with special geometry that provides high conversion efficiency by exploiting Fano resonances and the excitation of magnetic and toroidal dipoles. The results indicate the high efficiencies of third harmonic generation of 5.17×10−3 W−2 and fifth harmonic generation of 7.92×10−9 W−4 under 1 GW/cm2 pump intensity in the near-infrared regime. More specifically, linear and nonlinear optical responses of the structure are completely polarization-independent.

Poly(l-lactic acid) Janus Shape Memory Membranes with Uniform Vertically Penetrative Channels and Slit Pores for Enhanced Fog Collection: Synergistic Effect of Transport through Membranes and Sequential Sliding Behaviors of Water Droplets.

In this work, poly(l-lactic acid) (PLLA) Janus shape memory membranes with uniform vertically penetrative channels (SMEUVs) with slit pores have been fabricated with the help of template-assisting spray-coating and uniaxial tension at high temperature. During fog collection, superhydrophobic and hydrophilic surfaces act as the front (fog-facing) side and back side, respectively, in which the structural characteristics play essential roles. On one hand, the vertically penetrative channels in SMEUVs and the special pore geometry contribute to lower resistance, accelerating the transport of captured water through membranes (from the superhydrophobic side to the hydrophilic side). On the other hand, the movement of water droplets along the back side has been guided by the oriented structures of slit pores, promoting the detachment of droplets from the hydrophilic surface. Their synergistic effect removes captured water in a timely manner and provides fresh sites for the subsequent nucleation of water, enhancing fog collection performance. As a result, the optimal specimen (Janus SMEUVs with a draw ratio of 2.5, placed in the parallel direction) exhibits a much higher water collection rate (∼6×) relative to references (superhydrophobic and hydrophilic membranes). Our results are significant for sustainable development in view of both fog collection in arid regions and the biodegradability of PLLA.

Effect of food hydrocolloids on 3D meat-analog printing and deep-fat-frying

Three-dimensional (3D) printing of food product is an emerging technology. This study investigated the effects of hydrocolloid addition on 3D printing of plant-protein based meat-analogs. Meat-analog inks were formulated with soy protein isolate, gluten, canola oil, and water. Hydrocolloids (xanthan gum, pectin, hydroxypropyl methylcellulose, guar gum, locust bean gum) were added to meat-analogs formulation. The influence of hydrocolloid addition and deep-fat-frying on 3D printing process parameters, thermal, structural, and physicochemical properties of meat-analogs, were investigated. Formulated inks were used to create a specific 3D cylindrical model geometry and the printed structure were subjected to deep-fat-frying (at 180 °C, 90sec) in canola oil. Results showed that the meat-analog ink's viscosity (3871–5482 Pa s), 3D printing rate (0.34–0.39 g s−1), printing error (2.51–10.37%), printing precision (81.97–97.27%), dimensional stability (91.22–98.61%), and cooking loss (5.69–14.23%) were significantly (p < 0.05) impacted by the incorporation of hydrocolloid. Moisture-fat profile of uncooked 3D printed meat-analogs were identical, however, differences in color attributes (L∗, a∗, b∗) among the hydrocolloids added samples were observed. Moisture, fat, and color traits of 3D printed meat-analogs were substantially impacted by deep-fat-frying. During deep-fat-frying, the loss of moisture, absorption of fat, and changes in color attributes were associated with the types of hydrocolloids incorporated in formulating the meat-analog's ink. Overall, surface's structure, chemical profile, and glass-transition-temperature of 3D printed deep-fat-fried meat-analogs were extremely impacted by the addition of hydrocolloids as well as by the types of used hydrocolloids in meat-analog ink.

A semi-analytical model for predicting the shear buckling of laminated composite honeycomb cores in sandwich panels

Laminated composite honeycomb cellular core sandwich panels are widely utilized in various industries due to their exceptional stiffness-to-weight ratio and strength characteristics. Current analytical models often simplify honeycomb cores as homogenized continua, effectively predicting stiffness but falling short in capturing crucial failure modes, particularly shear buckling of honeycomb core walls. Existing theoretical studies on shear buckling are limited to isotropic materials and specific honeycomb geometries. While numerical models can simulate cell wall buckling, their computational demands render them impractical for large structures employing sandwich panels. This paper introduces a novel, simplified semi-analytical approach that accurately predicts the shear buckling load of laminated composite honeycomb cellular cores. The model accounts for bend-twist coupling effects and rotational restraints at laminate wall boundaries. To validate the proposed approach, predictions are compared with finite element analysis results for hexagonal honeycomb cores and cores of varying shapes, incorporating diverse fibre lay-up configurations. The findings demonstrate excellent agreement between the proposed approach and finite element analysis, indicating its reliability in predicting shear buckling. This research addresses the gap in existing methodologies by offering a practical and efficient tool for predicting shear buckling in laminated composite honeycomb cores, extending applicability beyond isotropic materials and specific honeycomb geometries. The proposed approach holds promise for optimizing the design and structural integrity of sandwich panels, impacting industries relying on these lightweight and high-performance structures.

A general method to synthesize planar overconstrained mechanism

Traditionally, planar overconstrained mechanisms has been explained through special geometry, which often lacks clarity and specificity. This paper addresses this challenge by introducing two explicit criteria for analyzing and synthesizing planar overconstrained mechanisms. With the criteria, one may synthesize new planar overconstrained systematically and confidently. To create new planar overconstrained mechanisms, three approaches are employed: the parallelogram-aided approach, the stretch-rotation approach, and an optimization-based method. Given that the mobility of mechanisms is independent of the choice of the ground link and that the mathematical treatment of function generation is straightforward, this paper proposes a systematic approach for synthesizing novel function cognates. By combining these approaches, new types of overconstrained mechanisms are discovered. Leveraging advanced computational tools, a special geometric condition for function cognates of inverted slider cranks is found for the first time. Through inversion, the coupler cognates for slider cranks are also identified. The success of these results indicates that the proposed criteria are explicit and crucial for discovering new mechanisms, and the concept may be extended to spherical or spatial cases.

Autonomous Inflow Control Devices Help Maximize Life of Wells in Deepwater West Africa

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 35418, “Design Execution and Evaluation of Advanced Completions in Deepwater West Africa,” by Piyush Pankaj, SPE, Matthew S. Jackson, and Lokesh, ExxonMobil, et al. The paper has not been peer reviewed. Copyright 2024 Offshore Technology Conference. _ Deepwater wells offshore West Africa traverse a complicated faulted block with sand bodies that can feature thicknesses of tens of meters. The study described in the complete paper provides insight into designing advanced well completions under various challenging reservoir conditions with autonomous inflow control devices (AICDs) that enable maximizing the producing life of the wells. Introduction The study area for this paper has been a challenging brownfield. Wells have been drilled in difficult deepwater conditions, and the target reservoirs have been lenticular sands with interbedded shale layers. To further complicate production, the sand bodies are poorly consolidated. Openhole wells with standalone screen and gravel packs have become a common approach to address sand control. Water- and gas-injection programs have been used actively in the field during the past 25 years, which further augments production and reservoir management challenges. Water and gas breakthrough in the infill wells has been a major concern for reservoir management. To address the gas buildup in the near-wellbore region and early water production, AICDs have become a popular feature in the lower well-completion designs in high-angled wells that intersect multiple sand bodies along the lateral completion interval. Two case studies are provided in the complete paper; one is included in this synopsis. Flow-Control Technology Although technology that empowers the ability to control the flow of unwanted fluids from zones in the well has been in use since the 1990s, flow-control technology has rapidly evolved, with advancement fueled by the need for long, complex well designs. The two broad categories of these approaches include active and passive flow control. The decision to use inflow-control technologies can be driven by the following economic values: - Balance drawdown along the wellbore - Increase recovery factor and reserves - Improve well cleanup - Reduces risk of erosion or hot-spotting of sandface completion Choice of Inflow Control for West Africa Field of Study Fluidic-diode AICDs were chosen because of their applicability to encountered fluid properties and reservoir conditions and their robustness of design in providing reliable long-term solutions. The reliability is prolonged in such AICDs because they work without any moving parts. Upon changes in viscosity, density, and rate, the fluid flow path will vary to gain the required control of flow rates. This AICD design, with its special geometry, alters the flow path or pattern for preferential fluid restriction. Operational Execution Ultimately, the AICDs were deployed on an inner string. This allowed the standard wire-wrapped screens and gravel pack to function as the traditional sand-control mechanism, while the inner string, deployed inside the lower completion, provides resistance to flow from unwanted gas production.

Effect of edge distance-diameter ratio on pin-bearing strength of TC18 by laser melting deposition

Abstract This paper presents an experimental study on the pin-bearing characteristics of TC18 titanium alloy produced by laser melting deposition. Two types of specimens with edge distance-to-diameter ratios (e/D) were manufactured for pin-bearing tests. The S-Basis values of bearing strength are calculated based on statistical analysis of experimental data. The results indicate that the S-Basis value of bearing ultimate stress with e/D =1.5 specimens is 1648.12 MPa, and the S-Basis value of bearing ultimate stress is 1967.89 MPa for e/D =2.0 specimens. The S-Basis value of bearing ultimate stress for e/D=2.0 specimens is higher by 19.4% than that of e/D=1.5. The test result showed three different failure modes: shear-out, cleavage, and bearing. Each failure mode depends on the specific hole edge geometry adopted. The proportion of shear-out failure for e/D=1.5 samples is more than for e/D=2.0 specimens.

Application of computational fluid dynamics to investigate pathophysiological mechanisms in exercise-induced laryngeal obstruction.

The underlying pathophysiological mechanisms of exercise-induced laryngeal obstruction (EILO) remain to be fully established. It is hypothesized that high inspiratory flow rates can exert a force on laryngeal airway walls that contribute to its inward collapse causing obstruction. Computational fluid dynamics (CFD) presents an opportunity to explore the distribution of forces in a patient-specific upper airway geometry. The current study combined exercise physiological data and CFD simulation to explore differences in airflow and force distribution between a patient with EILO and a healthy matched control. Participants underwent incremental exercise testing with continuous recording of respiratory airflow and laryngoscopic video, followed by an MRI scan. The respiratory and MRI data were used to generate a subject-specific CFD model of upper respiratory airflow. In patient with EILO, the posterior supraglottis experiences an inwardly directed net force, whose magnitude increases nonlinearly with larger flow rates, with slight changes in the direction toward the center of the airway. The control demonstrated an outwardly directed force at all regions of the wall, with a magnitude that increases linearly with larger flow rates. A comparison is made between the CFD results and endoscopic visualization of supraglottic collapse, and a very good agreement is found. The current study presents the first hybrid physiological and computational approach to investigate the pathophysiological mechanisms of EILO, with preliminary findings showing great potential, but should be used in larger sample sizes to confirm findings.NEW & NOTEWORTHY The current study is the first to use a hybrid combined computational fluid dynamics (CFD) and exercise physiology approach to investigate pathophysiology in exercise-induced laryngeal obstruction (EILO). The hybrid methodology is a promising approach to explore the pathophysiological mechanisms underlying the condition. Notable differences occur in the distribution of airflow and wall forces between the EILO and control participants, which align with symptoms and visual observations.

Impact of hydrocolloids on 3D meat analog printing and cooking

This study investigated the effects of hydrocolloid addition on three-dimensional (3D) printing and cooking of plant ingredients-based meat analog (MA). The MA inks were formulated with soy protein isolate, wheat gluten, canola oil, water, and hydrocolloids (xanthan gum, pectin, hydroxypropyl methylcellulose, guar gum, locust bean gum) at a ratio of 22:12:15:88:2. Formulated inks were used to create a specific 3D cylindrical model geometry and the printed structure were subjected to air frying (AF:180°C, 15 min) and infrared heating (IR:180°C, 15 min). Results showed that the MA ink’s viscosity (3871–5482 Pa. s), 3D printing rate (0.34–0.39 g.sec−1), printing error (2.51–10.37 %), and printing precision (81.97–97.27 %) were significantly (p<0.05) impacted by the incorporation of hydrocolloids. The dimensional stability (63.17–98.58 %), and cooking loss (6.70–17.41 %) were greatly impacted by both the hydrocolloids and post-printing cooking methods. Moisture (1.71 db) and fat (0.28 db) content of uncooked 3D printed MA were identical, whereas, differences in color attributes (L value:80.21–98.88, a value:0.01–0.13, b value:0.11–2.11) among the studied hydrocolloid added samples were observed. Moisture, fat, and color traits of 3D printed meat-analogs were significantly (p<0.05) impacted by post-printing cooking methods (AF, IR). During post-printing cooking, the loss of mass (moisture, fat) and changes in color tones were associated with the types of hydrocolloids incorporated in formulating the 3D printing ink. Surfaces and internal structure, mass loss, chemical profile, and glass-transition-temperature of 3D printed meat-analogs were significantly (p<0.05) impacted by both the type of incorporated hydrocolloids and post-printing cooking methods.

Optimization of highly sensitive three-layer photonic crystal fiber sensor based on plasmonic

In this work, a photonic crystal fiber (PCF) refractive index (RI) sensor has been designed and optimized. The RIs range covered by the sensor is from 1.38 to 1.41. The proposed optical sensor has three layers of air holes with 24, 12 and 6 holes in each layer. The geometry parameters of the proposed sensor (the radius of the air holes and the thickness of the plasmonic layer) have been optimized using the Nelder-Mead algorithm and the FEM numerical with the objective of achieving the highest sensitivity. To achieve an optimized structure with minimal sensitivity to fabrication errors, the rotation angle of the hole layers has been analyzed. The results indicate that, due to the specific geometry of the proposed structure, variations in the rotation angle and displacement of the air holes have no significant impact on the outcomes. The results also indicate that the sensor’s maximum amplitude sensitivity (AS), maximum wavelength sensitivity (WS), and figure of merit (FOM) are 10000 (RIU−1), 23000 (nm/RIU) and 131 (RIU−1) respectively. The optimized design provides high sensitivity, a wide diagnostic range for the detection of the analytes’ RIs, and the advantages of a gold plasmonic layer, ensuring high stability in biological environments. This combination results in enhanced performance of the sensor for various applications particularly in biosensing and medical fields. The designed structural geometry also eliminates the effects of tolerances in manufacturing processes which makes the proposed PCF device a very efficient sensor.

Transducer module apodization to reduce bone heating during focused ultrasound uterine fibroid ablation with phased arrays: A numerical study.

During magnetic resonance-guided focused ultrasound (MRgFUS) surgery for uterine fibroids, ablation of fibrous tissues in proximity to the hips and spine is challenging due to heating within the bone that can cause patients to experience pain and potentially damage nerves. This far-field bone heating limits the volume of fibroid tissue that is treatable viaMRgFUS. To investigate transducer module apodization for improving the ratio of focal-to-bone heating ( ) when targeting fibroid tissue close to the hips and spine, to enable MRgFUS treatments closer to thebone. Acoustic and thermal simulations were performed using 3D magnetic resonance imaging (MRI)-derived anatomies of ten patients who underwent MRgFUS ablation for uterine fibroids using a low-frequency ( ) 6144-element flat fully-populated modular phased array system (Arrayus Technologies Inc., Burlington, Canada) at our institution as part of a larger clinical trial (NCT03323905). Transducer modules ( per module) whose beams intersected with no-pass zones delineated within the field were identified, their output power levels were reduced by varying blocking percentage levels, and the resulting temperature field distributions were evaluated across multiple sonications near the hip and spine bones in each patient. Acoustic and thermal simulations took approximately ( ) and ( ) to run for a single near-spine (near-hip) target,respectively. For all simulated sonications, transducer module blocking improved compared to the no blocking case. In just over half of sonications, full module blocking maximized (increase of 82% 38% in 50% of hip targets and 49% 30% in 62% of spine targets vs. no blocking; mean±SD), at the cost of more diffuse focusing (focal heating volumes increased by 13%±13% for hip targets and 39%±27% for spine targets) and thus requiring elevated total (hip: 6%±17%, spine: 37%±17%) and peak module-wise (hip: 65%±36%, spine: 101%±56%) acoustic power levels to achieve equivalent focal heating as the no blocking control case. In the remaining sonications, partial module blocking provided further improvements in both (increased by 29%±25% in the hip and 15%±12% in the spine) and focal heating volume (decrease of 20%±10% in the hip and 34%±17% in the spine) relative to the full blocking case. The optimal blocking percentage value was dependent on the specific patient geometry and target location of interest. Although not all individual target locations saw the benefit, element-wise phase aberration corrections improved the average compared to the no correction case (increase of 52%±47% in the hip, 35%±24% in the spine) and impacted the optimal blocking percentage value. Transducer module blocking enabled ablative treatments to be carried out closer to both hip and spine without overheating or damaging the bone (no blocking: / , full blocking: / , optimal partial blocking: / for hip/spine). The proposed transducer apodization scheme shows promise for improving MRgFUS treatments of uterine fibroids, and may ultimately increase the effective treatment envelope of MRgFUS surgery in the body by enabling tissue ablation closer to bonystructures.

A study using physical sphere-in-contact models to investigate the structure of close-packed nanoparticles supported on flat hexagonal, square and trigonal lattices

The tailored design of nanoparticles becomes more important with the advancement of heterogeneous catalysis and materials science. The formation of nanoparticles in catalysts with a specific geometry of the active site becomes necessary to improve activity and selectivity in catalysis. Here we have used physical sphere-in-contact models of various nanoparticles with hexagonal, square and trigonal geometries on flat close-packed surfaces to understand how the distribution of (100) and (111) sites changes as a function of nanoparticle (NP) size in a simplified model of nanoparticle supported metals. The results from this approach clearly show that in 2-layer NPs that have a hexagonal base have 2–3 times more (100) sites than the square and trigonal base NPs as a function of the number of atoms in the NP. In 3D isotropic NPs, this phenomenon is even more pronounced than the 2-layer NPs. We derive equations that estimate the number of (100), (111), the number of atoms and the aspect ratio as a function of n. These equations are important in tailoring the properties of NPs supported on close-packed metal surfaces, which may find applications in materials science, nanotechnology and catalysis.

A Thermal Model for a Hybrid Gas Bearing System in Oil-Free Turbochargers

Abstract With little drag friction, gas bearings operate at high rotor speed and high temperature and thus enable long operating life along with material damping for mechanical energy dissipation. However, most computational tools for modeling gas bearings are not accessible to bearing manufacturers or potential end-users, and the models are restricted to specific geometries and operating conditions or are missing important features, thus limiting their utility. This paper presents the thermal energy transport in a hybrid gas bearing for oil-free turbochargers with integrated heat and fluid flow models to produce a comprehensive thermo-hydrodynamic analysis predictive tool, and to design and evaluate air-lubricated gas bearings by predictions and experiments. An efficient algorithm couples the solution of the Reynolds equations and the thermal energy transport equations in the film between the rotor and a pad of the hybrid gas bearing, and updates the temperature-dependent viscosity and film thicknesses during the iterative process. The test repeats and averaged for each rotor speed from 2 krpm to 22 krpm at intervals of 2 krpm, for supply pressure varying along 25 psi to 100 psi and predicted film temperature matches well with the measured one. The parameters of interest in this analysis include the gas supply condition, bearing configuration, and the gas properties at high altitudes and high rotation speeds. The parametric study results show the density and kinematic viscosity are the most dominant properties of the gas lubrication for the film temperature.

Dendrite Growth in Single-Grain and Cyclic-Twinned Sn–3Ag–0.5Cu Solder Joints

The microstructure of electronic solder joints is generated by the solidification of a small volume of bulk undercooled liquid. Here, we study β-Sn dendrite growth in Sn–3Ag–0.5Cu in the specific geometry and nucleation conditions of ball grid array (BGA) solder joints by combining electron backscatter diffraction and imaging of microstructures. It is shown that, while ⟨110⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 110\\rangle$$\\end{document} is the preferred dendrite growth direction, out-of-plane branching and growth with ⟨11W⟩\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\langle 11W\\rangle$$\\end{document} directions are important for allowing dendrites to fan out into the spheroidal volume of BGA joints due to the low symmetry of β-Sn. We find that the crystallographic orientation of β-Sn at the nucleation point plays a strong role in subsequent dendrite growth. In single-grain joints, dendrites are often unfavorably oriented for growth, resulting in different types of zig-zag dendrite growth. In cyclic-twinned joints, it is shown how competitive out-of-plane trunk growth between three dendrite orientations produces {101} boundaries and the characteristic beachball microstructure.