Minimum Radius Research Articles

Screw-Tip Soft Magnetically Steerable Needles

We present a new paradigm in steerable needles comprising flexible tubing with a screw tip and a permanent magnet near the tip. The needle is rotated at its proximal end as the primary mechanism of insertion, rather than being pushed, enabling the screw tip to pull itself through the tissue as it is steered via magnetic torque. Our design enables turns with tighter curvature than previous designs, and it circumvents a well-known problem with existing steerable needles: it is challenging to turn more than 90 degrees without inducing damage. We evaluate our needle via human-in-the-loop robot-assisted magnetic steering in a brain-simulating gel tissue phantom, wherein we achieve a radius of curvature of 29 mm with 210 degrees of turning for a needle with a functional lumen. In a needle without the lumen we achieve a minimum radius of curvature of 10.1 mm. We further evaluate the needle in ex-vivo ovine brain via open-loop steering. We characterize the steerability of the needles as a function of independent parameters. The results demonstrate a needle that promises significantly improved steerability and safety, particularly for use in delicate tissues that create the greatest challenges for existing designs.

Effect of cutting conditions on tool wear and wear mechanism in micro-milling of additively manufactured titanium alloy

This study investigated the effects of different cutting conditions, including dry, flooded, chilled air, and the minimum quantity lubrication (MQL), on cutting forces, burr width, tool wear, and surface roughness using constant cutting parameters. The results showed that the minimum cutting forces were obtained with MQL, while the cutting forces obtained with dry and chilled air were 97% and 80% higher, respectively. During dry cutting, the tool diameter decreased by 3.4%, whereas in MQL and flood cutting, the tool diameter reduction was 2.2%. The minimum corner and edge radius change were achieved in MQL-assisted cutting. At the beginning of the cutting process, the difference between the Sa values obtained for dry and flood cutting was more than 200%, while at the end of the cutting process, this difference was about 140%. It was observed that chilled air has a positive effect on surface roughness. There is an average difference of 21% in burr widths between up and down milling.

The Minimal Spectral Radius with Given Independence Number

The Minimal Spectral Radius with Given Independence Number

Analysis of Lateral Forces for Assessment of Safety against Derailment of the Specialized Train Composition for the Transportation of Long Rails

This study proposes a theoretical method for evaluating the “safety against derailment” indicator of a specialized train composition for the transportation of very long rails. A composition of nine wagons, suitable for the transportation of rails with a length of 120 m in three layers, is considered. For the remaining recommended rail lengths, the number of wagons is reduced or increased, with the calculation model being modified depending on the required configuration. When the composition is in a curve with the minimum radius (R = 150 m), the rails bend, and some of them come into contact with the vertical stanchions of the wagon and cause additional lateral forces. These forces are then transferred through the wagon body, central pivot, bogie frame, and wheels and act on the wheel–rail contact points. They could potentially lead to derailment of the train composition. The goal of this study is to determine the additional lateral forces that arise because of the bent rails. For the purposes of this study, the finite element method was used. Based on the displacements of the support points of the rails (caused by the geometry of the curve), the bending line of the elastic load is determined and the forces in the supports are calculated. The resulting forces are considered when determining the derailment safety criterion. The analysis of the results shows that the wagon with fixing blocks is the most at risk of derailment. The front and intermediate wagons have criterion values very close to that of the empty wagon. This shows that the emerging horizontal elastic forces do not significantly influence the derailment process. The obtained results show that the transportation of long rails with specialized train composition can be realized on four layers. This will significantly increase the efficiency of delivering new long rails.

Dynamic gas liberation from water-immersed anthracite coal with varying wetting states under heating conditions: Unveiling the gas breakthrough phenomena

During coalbed methane recovery, the effective extraction of gas trapped in narrow pore throats encounters challenges due to the water blocking effect. To shed light on this phenomenon during thermal recovery of coalbed methane, this study investigated the breakthrough behaviors of CO2 traversing through a 0.2 mm diameter hole in water-immersed anthracite coal at varying temperatures (23 °C, 40 °C, and 60 °C). The measurements of breakthrough pressure (defined as the pressure at which the bubble achieves a semi-spherical shape with a minimum curvature radius), growth characteristics of CO2 bubbles, and coal wettability were conducted under varying thermal conditions and water immersion durations. The results showed that the breakthrough pressure initially increased continuously as water immersed into the coal and then gradually stabilized. During this process, the coal's water wettability increased, leading to a decrease in the diameter of the bubble's three-phase contact line, which in turn affected the breakthrough pressure. Moreover, higher temperatures accelerated the rate of water immersion, augmenting the coal's hydrophilicity. The elevated temperature also resulted in a decrease in water surface tension, consequently contributing to a lower breakthrough pressure. Interestingly, compared to CO2, He exhibited a faster increase in breakthrough pressure during water immersion. This disparity can be attributed to He's superior diffusion capacity and lower viscosity, enabling a swifter transformation of the coal's wetting state during water imbibition. This study revealed the dual mechanism of heating to reduce gas breakthrough pressure, as well as the effects of surface water content and gas properties. These findings highlight potential benefits of thermal treatment on coalbed methane recovery and provide valuable insights for its exploitation under different geological conditions.

Design and performance optimization of a lattice-based radial flow field in proton exchange membrane fuel cells.

The design of the flow field structure in Proton Exchange Membrane Fuel Cells (PEMFCs) plays a pivotal role in determining their electrochemical performance. This study presents a lattice-based radial flow field configuration designed to improve PEMFC efficiency. The difference between the flow field and the traditional flow field is that the flow field is segmented by a small cylindrical rib instead of a longer rib. The research employs COMSOL Multiphysics simulation software to establish the model of the operating conditions of PEMFCs, focusing on analyzing how the number of rib branches and the minimum rib radius influence the oxygen distribution, water distribution, and pressure drop in the system. The results demonstrate that varying the number of rib branches and the minimum radius of the cylindrical ribs has a pronounced impact on the PEMFC's performance. Furthermore, a comparative analysis of multiple design configurations reveals the optimal operating parameters. Specifically, within a quarter of the computational domain, the configuration featuring a minimum rib radius of 0.135 cm and six rib branches delivers the best electrochemical performance.

Anti-tumor effect of pH-sensitive drug-loaded nanoparticles optimized via an integrated computational/experimental approach.

The acidic pH of tumor tissue has been used to trigger drug release from nanoparticles. However, dynamic interactions between tumor pH and vascularity present challenges to optimize therapy to particular microenvironment conditions. Despite recent development of pH-sensitive nanomaterials that can accurately quantify drug release from nanoparticles, tailoring release to maximize tumor response remains elusive. This study hypothesizes that a computational modeling-based platform that simulates the heterogeneously vascularized tumor microenvironment can enable evaluation of the complex intra-tumoral dynamics involving nanoparticle transport and pH-dependent drug release, and predict optimal nanoparticle parameters to maximize the response. To this end, SPNCD nanoparticles comprising superparamagnetic cores of iron oxide (Fe3O4) and a poly(lactide-co-glycolide acid) shell loaded with doxorubicin (DOX) were fabricated. Drug release was measured in vitro as a function of pH. A 2D model of vascularized tumor growth was calibrated to experimental data and used to evaluate SPNCD effect as a function of drug release rate and tissue vascular heterogeneity. Simulations show that pH-dependent drug release from SPNCD delays tumor regrowth more than DOX alone across all levels of vascular heterogeneity, and that SPNCD significantly inhibit tumor radius over time compared to systemic DOX. The minimum tumor radius forecast by the model was comparable to previous in vivo SPNCD inhibition data. Sensitivity analyses of the SPNCD pH-dependent drug release rate indicate that slower rates are more inhibitory than faster rates. We conclude that an integrated computational and experimental approach enables tailoring drug release by pH-responsive nanomaterials to maximize the tumor response.

On the minimum spectral radius of connected graphs of given order and size

On the minimum spectral radius of connected graphs of given order and size

О корректности размера позитрония

It is noted that initially the minimum size of the hydrogen atom was determined by the semiclassical method, which is still widely used today. When calculating the minimum size of a positronium atom, the method tested on the hydrogen atom was not used. Instead, in the formula for the radius, the mass was replaced by the reduced mass of positronium. There would be nothing wrong with this if the above “hydrogen” method gave the same result. However, it is not. The difference between the formula for positronium and the “hydrogen” formula is the coefficient “2”, due to the fact that the positive charge is not in the center of mass. In the literature, the minimum size of a positronium atom (Bohr radius of positronium) was determined in accordance with the two-body problem method. In the particular case under consideration, the method of the two-body problem is redundant and can be successfully replaced by solving the problem of the motion of one of the bodies. This allows you to obtain more visual and obvious solutions without excessive formalism with the reduced mass and displacement vector. The doubly refined value of the positronium radius was determined using the semiclassical method. However, positronium is a quantum object. Therefore, a quantum mechanical consideration is also presented. The textbook solutions are taken as a basis. The solution to the problem of two particles is found in the form of an equivalent solution for one of the particles moving relative to a stationary center of mass, especially since there is a reliable quantum mechanical solution for the case of a spherically symmetric force field, which assumes a stationary center of force. The latter is especially important, since the mobility of the force center (electric charge) can lead to radiation and, consequently, a change in the energy balance. It has been established that the calculated minimum radius of positronium (the distance from its center of mass at which the probability of finding an electron/positron is maximum) is equal to four, and not two Bohr radii of hydrogen, as indicated in the literature. In this case, the semiclassical and quantum solutions do not contradict each other.

Control of Robot Motion in Radial Mass Density Field

T In this article, a new approach to control of robot motion in the radial mass density field is presented. This field is between the maximal and the minimal radial mass density values. Between these two limited values, one can use n points (n = 1, 2, . . . nmax) that can be included in the related algorithm for control of the robot motion. The number of the points nstep can be calculated by using the relation nstep = nmax / nvar , where nvar is the control parameter. The radial mass density is maximal at the minimal gravitational radius and minimal at the maximal gravitational radius. This is valid for Planck scale and for the scales that are less or higher of that one. Using the ratio of Planck mass and Planck radius it is generated the energy conservation constant κ = 0.99993392118.

ВСТАНОВЛЕННЯ ВПЛИВУ ПАРАМЕТРІВ ПРЕСУВАННЯ НА ПРОЦЕС ГНУТТЯ БУКОВИХ МЕБЛЕВИХ ЗАГОТОВОК

It is substantiated that the technology of cold bending of pre-pressed blanks has a perspective. It was established that the minimum bending radius depends on the direction of pressing and the degree of pressing. It was determined that pressing in the radial and tangential directions does not give the desired effect during bending, which is evidenced by a large number of defects (respectively 47-67% and 34-61%) associated with the specific structure of the wood. In particular, during pressing, the wood cells are deformed along the pressing line, and during subsequent bending, the elongation of the wood in the peripheral part passes across the pressing line and is only partially compensated by the pressed cell walls. It was experimentally established that the results are significantly different when the workpieces are axially pressed. When the degree of pressing is increased from 15 to 25%, the number of high-quality blanks increases and amounts to 83-97%, respectively. This can be explained by the fact that during axial pressing, wood cells are deformed along the line of pressing. During subsequent bending, the elongation of the wood in the peripheral part also takes place along the line of pressing and is compensated to a much greater extent by the pressed cell walls. It was found that when the workpieces are pressed along the axis, uneven pressing along the length occurs, that is, only approximately half of the length of the workpiece is pressed. This is probably the main reason for the defect. Additional research and possibly new technological solutions are needed to solve the problem of uneven pressing during axial pressing. Prospective directions of research into bending processes of beech furniture blanks have been formed, in particular from the development of new bending technologies; optimization of pressing parameters; modeling of bending processes; study of the influence of humidity and temperature; study of the strength and durability of bent blanks.

The Q-minimizer graph with given independence number

Let Gn,α be the set of all connected graphs of order n with independence number α. A graph is called the Q-minimizer graph (A-minimizer graph) if it attains the minimum signless Laplacian spectral radius (adjacency spectral radius) over all graphs in Gn,α. In this paper, we first show that the Q-minimizer graph must be a tree for α≥⌈n2⌉, and then we derive seven propositions about the Q-minimizer graph. Moreover, when n−α is a constant, the structure of the Q-minimizer graph is characterized. The method of getting Q-minimizer graph in this paper is different from that of getting A-minimizer graph. As applications, we determine the Q-minimizer graphs for α=n−1,n−2,n−3 and n−4, respectively. The results of α=n−1,n−2,n−3 are consistent with that in Li and Shu (2010) [15] and the result of α=n−4 is new. Interestingly, the Q-minimizer graph in Gn,n−4 is unique, which is exactly one of the A-minimizer graphs in Gn,n−4.

A tunable high-Q flexible ferroelectric film capacitor for GHz RF applications

With the development of flexible electronics, flexible tunable capacitors with high dielectric constant, high tunability, and low loss become important components in modern communication. A tunable Ba0.6Sr0.4TiO3 capacitor for radio frequency devices is prepared on a flexible substrate. The capacitor has a dielectric constant greater than 1000, capacitance tunability n exceeding 70%, and minimum loss tangent lower than 0.03 at 500 kHz. The Q factor can be above 103 at the GHz frequency range. These parameter values (especially the Q factor) have been comparable to the rigid substrate tunable capacitor. Meanwhile, the minimum radius of curvature of the flexible tunable capacitor can be 3 mm with stable electrical performances. The flexible tunable capacitor retains its mechanical and electrical stability after 24 000 high-frequency bending cycles, which provides potential uses in bendable, collapsible tunable capacitors at the radio frequency range.

Axially symmetric exponential metric

We present a new family of vacuum axially symmetric static solutions to Einstein’s field equations. This solution is a geometrically modified version of the Yilmaz exponential metric (YEM) which has recently been shown to represent a traversable wormhole. This vacuum solution is a one-parameter static singular solution with its singularity located at r=0. Furthermore, it is shown that both the YEM and its geometrically modified version, introduced in this work i.e., the Axially Symmetric Exponential metric (ASEM) belong to a general 2-parameter class of solutions supported by an anisotropic fluid. Depending on the parameters the generic energy–momentum tensor represents either an exotic or a normal fluid. Concerning the ASEM, the circular stable orbit does not exist for a null particle, however, for a massive particle such orbit exists provided its radius is larger than a minimum radius. This is in analogy with the Schwarzschild black hole as well as the YEM.

Morphometric analysis of airways in pre-COPD and mild COPD lungs using continuous surface representations of the bronchial lumen.

Introduction: Chronic Obstructive Pulmonary Disease (COPD) is a prevalent respiratory disease that presents a high rate of underdiagnosis during onset and early stages. Studies have shown that in mild COPD patients, remodeling of the small airways occurs concurrently with morphological changes in the proximal airways. Despite this evidence, the geometrical study of the airway tree from computed tomography (CT) lung images remains underexplored due to poor representations and limited tools to characterize the airway structure. Methods: We perform a comprehensive morphometric study of the proximal airways based on geometrical measures associated with the different airway generations. To this end, we leverage the geometric flexibility of the Snakes IsoGeometric Analysis method to accurately represent and characterize the airway luminal surface and volume informed by CT images of the respiratory tree. Based on this framework, we study the airway geometry of smoking pre-COPD and mild COPD individuals. Results: Our results show a significant difference between groups in airway volume, length, luminal eccentricity, minimum radius, and surface-area-to-volume ratio in the most distal airways. Discussion: Our findings suggest a higher degree of airway narrowing and collapse in COPD patients when compared to pre-COPD patients. We envision that our work has the potential to deliver a comprehensive tool for assessing morphological changes in airway geometry that take place in the early stages of COPD.

Single droplet formation by controlling the viscoelasticity of polymer solutions during inkjet printing

Inkjet printing has emerged as a potential solution processing method for large-area patterned films. During inkjet printing, a single droplet without satellite droplet is required for high-quality film. Herein, we propose a strategy for obtaining a single droplet by adjusting the reduced concentration (c/c*, where c* is the critical overlap concentration) in the range of 1.0–1.5. Droplet formation can be categorized into three distinct regimes: (1) c/c* < 1.0, satellite droplet; (2) c/c* = 1.0–1.5, single droplet; (3) c/c* > 2.0, no droplet. Furthermore, an inertial-capillary balance led to the 2/3-power scaling of the minimum radius with time for the solutions of c/c* < 1.0. However, for the solutions of c/c* = 1.0–1.5, the ligament radius decreased exponentially with time. Moreover, the Weissenberg number was higher than the critical value of 0.5, indicating that the polymer chains underwent coil-stretch transition. The viscoelastic-capillary balance dominated instead of the inertial-capillary balance. The resulting viscoelastic resistance reduced the length of the ligament and increased the velocity difference between the satellite and main droplets. Consequently, a single droplet was formed. In addition, the law can be successfully generalized to various molecular weights, molecular structures and solvents.

Влияние формы тороидальной задней поверхности на углы режущего клина и механические напряжения вдоль режущей кромки сверла

Introduction. Drilling holes with standard tolerance varying from IT8 to IT12 is widely used in industrial production. However, at present time, there are neither comprehensive studies, nor scientifically justified recommendations for the rational choice of the geometry of the cutting part of drills with a toroidal flank surface. Therefore, the computer-aided design (CAD) of new drill designs with a toroidal flank surface and finite element modeling (FEM) of the stressed state of its cutting part are important tasks. The purpose of the work is reducing both the range of change in the rake angle and the wedge angle of the cutting wedge along the cutting edge from the periphery to the center and the equivalent stresses in the cutting wedge. In this paper we investigate changes in the rake and wedge angles of the cutting wedge depending on the radius of the generatrix line of the toroidal flank surface as well as changes in equivalent stresses in the cutting wedge, which depend on changes in the radius of the generatrix line of the toroidal flank surface. The research methods include the fundamentals of the theory of cutting, CAD methods, and the FEM, which was applied in this work to new drill designs. Results and discussion. It is found that the range of changes in the rake angle and the wedge angle of the cutting wedge of the drill decreases compared to the standard design with decreasing radius of the generatrix line of the flank surface. A CAD system for drills with a toroidal flank surface is developed. As a result, the range of changes in the rake angle along the cutting edge decreased by 86 % for a drill with a minimum radius of the generatrix line of the toroidal surface compared to that with the conical flank surface, the range of the wedge angle of the cutting wedge decreased by 56 %, and the maximum equivalent stresses decreased by 2.13 times. It is also important to note that in this case, the wedge angle is close to constant for half of the drill tooth. These indicators exceed those for existing designs of the twist drills that indicate the key achievement of this paper.

Improved structural efficiency in composite manufacturing via hammered printing for large-curvature fiber paths

Maximizing the structural efficiency of composite materials is often limited by the minimum turning radius of fibers in composite manufacturing. Neglected defects, such as local fiber buckling, become more pronounced in regions with a large curvature, leading to reduced load-carrying capabilities and a deviation from the target design specifications. This study introduces “hammered printing” as a novel approach for achieving a large curvature of the fiber path in composite manufacturing. By utilizing the transition of the modulus with temperature of a thermoset epoxy pre-polymer, the proposed hammered printing technique generates a unique pressure effect that improves adhesion between the fiber tow and the substrate. This enables the production of accurate and uniform composite structures with a minimum curvature radius of 2 mm, while reducing the occurrence of wrinkling and bending deformations. A continuous fiber path with a small radius (2 mm) for open-hole plates was accurately printed using this printing pattern. Compared with conventional laminates and drilled composites, the obtained printed samples exhibit 75.3% and 28.8% increments in the tensile and bearing strengths, respectively, indicating that this continuous small-radius fiber path can effectively retain the strength and safety of fastened composite parts. Finally, comparisons indicate the great potential of the proposed technique as a large-curvature-path and high-performance manufacturing alternative for the cutout of composite assemblies in the aerospace and related engineering industries.

Degree reduction of ball Said‐Ball surfaces using an enhanced coot optimization algorithm

Degree reduction of ball Said‐Ball (BSB) surface is a complex and unsolved problem in computer‐aided design (CAD) and computer graphics (CG), which has potential application prospects in many engineering fields of geometric modeling. In this paper, the degree reduction of BSB surface is transformed into the optimization problems of center surface and radius function, and the improved coot optimization algorithm is used to solve it. An effective method to solve the degree reduction of BSB surface by intelligent optimization algorithm is proposed. Firstly, the degree reduction of BSB surface is decomposed into center surface reduction and radius function reduction, and the objective function and constraint conditions are determined according to the optimization idea, then the degree reduction optimization model of center surface and radius function is established. Secondly, an enhanced coot (ECOOT for short) algorithm is proposed, which combines chain strategy, dispersed foraging strategy, and quadratic interpolation strategy. Compared with the original algorithm, ECOOT algorithm has better convergence performance and higher calculation accuracy. Finally, the proposed ECOOT algorithm is used to solve the degree reduction optimization model, and the optimal center surface and minimum distance radius function of the BSB surface after degree reduction are obtained. The experimental results show that the ECOOT algorithm can effectively solve the problem of degree reduction for BSB surface, the degree reduction error is reduced by about 20% compared to the original COOT algorithm, and is superior to other intelligent optimization algorithms in accuracy, robustness, and convergence.

Optimization of bend stiffeners of a suspended inter-array power cable between two floating offshore wind turbines

The concept of a suspended inter-array power cable assumes that the cable floats within the water column instead of being laid on the seabed. This setup requires additional equipment, such as buoyancy modules or buoys, to achieve the desired cable configuration. The implementation of buoyancy modules introduces abrupt changes in stiffness between the cable sections with clamped-on buoyancy modules and bare cable sections. Large stiffness variations can negatively impact cable bending, causing excessive curvature and fatigue damage. In order to form a smooth transition in stiffness between the buoyancy sections and the bare cable, bend stiffeners can be equipped. The study aims to optimize the bend stiffener design for a representative suspended power cable between two floating offshore wind turbines (FOWTs). The inter-array power cable system is simulated in OrcaFlex. Two parameters, including the outer diameter and the length of the bend stiffener, are adjusted to generate different cases. Eight environmental conditions are applied to the dynamic analysis of the cases. The fitness factor approach is used as a criterion to assess the overall performance of different bend stiffener designs. Adjusting the outer diameter of bend stiffeners clearly influences the maximum effective tension and the minimum bending radius by changing the stiffness profile of the bend stiffener and its submerged weight. In the investigated range of parameters, increasing the overall length of bend stiffeners is found to be less effective than adjusting the outer diameter of the bend stiffener.