Hyock Ju Kwon - Academia.edu (original) (raw)

Papers by Hyock Ju Kwon

The British Journal of Radiology, 2013

To propose a new and practical MRI grading method for cervical neural foraminal stenosis and to e... more To propose a new and practical MRI grading method for cervical neural foraminal stenosis and to evaluate its reproducibility.

$Research paper thumbnail of On the measurement of fracture toughness of soft biogel$

Polymer Engineering & Science, 2011

In this study, the rate dependent energy dissipation process and the fracture toughness of physic... more In this study, the rate dependent energy dissipation process and the fracture toughness of physical gels were investigated using agarose as a sample material. Both the J-integral and Essential work of Fracture (EWF) methods were examined. To assess the quasistatic fracture toughness of gels, linear regression was performed on critical J (J c) values at different loading rates resulting in a quasi-static J c value of 6.5 J/m 2. This is close to the quasi-static EWF value of 5.3 J/m 2 obtained by performing EWF tests at a quasi-static loading rate (crosshead speed of less than 2 mm/min). Nearly constant crack propagation rates at low loading rates, regardless of crack length, suggest viscoplastic chain pull-out is the fracture mechanism. At high loading rates failure was highly brittle, which is attributed to sufficient elastic energy accumulation to precipitate failure by chain scission. We conclude that in physical gels quasi-static fracture toughness can be evaluated by both the J-integral and EWF methods provided the effects of loading rate are investigated and accounted for.

Journal of Fluids and Structures, 2020

Micro and nanotubes have found major application in fluidic systems as channels for conveying flu... more Micro and nanotubes have found major application in fluidic systems as channels for conveying fluid. In some micro and nanofluidic applications such as drug delivery, a transverse magnetic field can be used to guide the fluid flow by generating an axial force in the flow direction. An important issue in the design of micro and nanofluidic systems is the structural vibration caused by the fluid flow. In the current study, we investigate the effect of transverse magnetic field on the vibration of cantilever micro and nanotubes conveying fluid by considering the small size effects. We couple the nonlocal Euler-Bernoulli beam model with Navier-Stokes theory to determine a fluid structure interaction (FSI) model for the vibration analysis of the system. We modify the FSI governing equation by driving a velocity correction factor to consider the effect of transverse magnetic field on the fluid flow's pattern through the tube. Then, we use the Galerkin's method to obtain the frequency diagrams for the instability analysis of the system. We show that the transverse magnetic field can have a substantial effect on the dynamics of tube conveying fluid by increasing the system's natural frequencies and critical flow velocity which contributes to the flutter instability. We also discover that although the transverse magnetic field plays a crucial role on dynamics of microstructures, its effect on the dynamics of nanotubes is not significant and can be ignored.

$Research paper thumbnail of Toughness of high-density polyethylene in shear fracture$

International Journal of Fracture, 2007

This paper evaluates the validity of a new test methodology for measuring shear fracture toughnes... more This paper evaluates the validity of a new test methodology for measuring shear fracture toughness (mode II) of high density polyethylene (HDPE). The methodology adopts Iosipescu test for the shear loading, and determines the toughness based on the essential work of fracture (EWF) concept. The results show that even under the Iosipescu loading, tensile deformation (mode I) is still involved in the fracture process, possibly due to the significant work hardening that HDPE develops during the plastic deformation. The study found that the mode II fracture toughness can be determined through data analysis using double linear regression, i.e., by extrapolating specific work of fracture to zero ligament length and zero ligament thickness. The paper demonstrates that the new test methodology can be used to evaluate mode II fracture toughness of ductile polymers like HDPE in which significant work-hardening may be involved in the fracture process. The paper also provides quantitative comparison of the fracture toughness for HDPE in mode II with its mode I counterpart.

Ultrasonic Imaging, 2015

Eshelby's solution is the analytical method that can derive the elastic field within and ... more Eshelby's solution is the analytical method that can derive the elastic field within and around an ellipsoidal inclusion embedded in a matrix. Since breast tumor can be regarded as an elastic inclusion with different elastic properties from those of surrounding matrix when the deformation is small, we applied Eshelby's solution to predict the stress and strain fields in the breast containing a suspicious lesion. The results were used to investigate the effectiveness of strain ratio (SR) from elastography in representing modulus ratio (MR) that may be the meaningful indicator of the malignancy of the lesion. This study showed that SR significantly underestimates MR and is varied with the shape and the modulus of the lesion. Based on the results from Eshelby's solution and finite element analysis (FEA), we proposed a surface regression model as a polynomial function that can predict the MR of the lesion to the matrix. The model has been applied to gelatin-based phantoms and clinical ultrasound images of human breasts containing different types of lesions. The results suggest the potential of the proposed method to improve the diagnostic performance of breast cancer using elastography.

2019 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM), 2019

This paper presents an efficient global path planning method for a mobile robot using a new skele... more This paper presents an efficient global path planning method for a mobile robot using a new skeleton representation of a map. For practical consideration of both safety and agility of the robot in narrow corridors, we introduce the concept of allowable speed at each point of free space of the map based on the distance to the closest obstacle. We define a new cost-to-go function corresponding to the allowable speed in a time-relevant way that eventually results in a safe time-minimized path. To realize the main idea, we built a hierarchical graph representation of a map using the skeleton that has the topology of undirected multigraph at the higher level and corresponding metric points at the lower level. The cost-to-go of the metric points are added up to construct the weight values of the edges of the graph. Then, the safe time-minimized path can be efficiently computed by obtaining optimal topological path from the higher level representation and identifying the corresponding metric points from the lower level. Using this approach, a safe and agile path can be found, which provides a good trade-off between the shortest path criterion and the admissible navigation speed based on lateral safety margins. The proposed method offers enhanced performance and less computational cost. We demonstrate the advantages of the proposed method through simulation results using a real map, where we also compared its performance with that of the conventional shortest path strategy.

Nano Futures, 2021

High intensity focused ultrasound (HIFU) is emerging as a novel therapeutic technique for cancer ... more High intensity focused ultrasound (HIFU) is emerging as a novel therapeutic technique for cancer treatment through a hyperthermal mechanism using ultrasound. However, collateral thermal damages to healthy tissue and skin burns due to the use of high levels of ultrasonic energy during HIFU treatment remain major challenges to clinical application. The main objective of the current study is to evaluate the potential of carbon nanotubes (CNTs) as effective absorption-enhancing agents for HIFU to mediate the heating process at low ultrasonic power levels, and consequently upgrade hyperthermal therapeutic effects of HIFU. An experimental study using in vitro tissue phantoms was conducted to assess the effects of CNTs on HIFU’s heating mechanism. Detailed information was extracted from the experiments for thermal analysis, including rate of absorbed energy density and temperature rise profile at the focal region. Parametric studies were carried out, revealing the effects of ultrasound par...

Encyclopedia of Biomedical Engineering, 2019

The authors have requested that this preprint be removed from Research Square.

International Journal of Precision Engineering and Manufacturing, 2021

In nondestructive testing (NDT), geometrical features of a flaw embedded in the material such as ... more In nondestructive testing (NDT), geometrical features of a flaw embedded in the material such as its location, length, and orientation are critical factors to assess the severity of the flaw and make post-manufacturing decisions to improve the design. In this study, artificial intelligence (AI) based NDT approach was applied to the ultrasonic oscillograms obtained from virtual ultrasonic NDT to estimate geometrical features of a flaw. First, a numerical model of NDT specimen was constructed using acoustic finite element analysis (FEA) to produce the ultrasonic signals. The model was validated by comparing the simulated signals produced from the numerical model with the experimental data from actual NDT tests. Then, 750 numerical models containing flaws with different locations, lengths, and orientation angles were generated by FEA. Next, the oscillograms produced by the models were divided into 3 datasets: 525 for training, 113 for validation, and 112 for testing. Training inputs of...

2021 IEEE Canadian Conference on Electrical and Computer Engineering (CCECE), 2021

This paper presents a case study to apply artificial intelligence (AI) to the assembly of automot... more This paper presents a case study to apply artificial intelligence (AI) to the assembly of automotive parts. The sliding load of a car steering shaft assembly is controlled by selecting an appropriate size of the ball slider corresponding to the shaft and the tube. The manual assembly currently conducted by skilled workers has a low selection accuracy and long process time, which is the bottleneck of the whole manufacturing process. To increase the selection accuracy, an expert system based on a hybrid AI model was developed by combining Gaussian process regression and artificial neural network. The AI-based system could recommend suitable ball size corresponding to the over ball diameters measured on the tube and shaft. The system achieved 91.32% prediction accuracy in the test cases.

Journal of Petroleum Science and Engineering, 2022

Robotics, 2021

The field of robotics has been rapidly developing in recent years, and the work related to traini... more The field of robotics has been rapidly developing in recent years, and the work related to training robotic agents with reinforcement learning has been a major focus of research. This survey reviews the application of reinforcement learning for pick-and-place operations, a task that a logistics robot can be trained to complete without support from a robotics engineer. To introduce this topic, we first review the fundamentals of reinforcement learning and various methods of policy optimization, such as value iteration and policy search. Next, factors which have an impact on the pick-and-place task, such as reward shaping, imitation learning, pose estimation, and simulation environment are examined. Following the review of the fundamentals and key factors for reinforcement learning, we present an extensive review of all methods implemented by researchers in the field to date. The strengths and weaknesses of each method from literature are discussed, and details about the contribution ...

Ultrasonics, 2020

This paper proposed a hybrid design approach of a vibro-concentrator, a vital component of an ult... more This paper proposed a hybrid design approach of a vibro-concentrator, a vital component of an ultrasonic tactile sensor, by using electro-mechanical analogy. Lab experiments on soft materials with elastic modulus from 14 kPa to 150 kPa were conducted using the tactile sensor installed with the vibro-concentrator to verify the performance of the design. Various mechanical and electrical parameters, such as resonance frequency shift and equivalent conductance, were discussed, focusing on their feasibility as new stiffness indicators. As a variant of tactile sensors, ultrasonic tactile sensors have the advantage of high sensitivity and minimal contact with the object over traditional tactile sensors based on force-displacement principle. They detect the changes in mechanical vibration characteristics, mostly resonance frequency shift of the sensor, as an indicator of the mechanical properties of the object. A vibro-concentrator has been frequently adopted to improve the performance an ultrasonic tactile sensor, but its design has yet been systematically considered. We propose a hybrid design approach based on electro-mechanical analogy for both mechanical and electrical analyses. Mechanically, impedance analogy was adopted to design an ultrasonic vibration concentrator for the sensor to localize the contact and reinforce the vibration behavior at ~40 kHz. Electrically, we used mobility analogy to derive electrical parameters from the tactile sensing tests in lab environment. The competence of the design was demonstrated by mechanical and electrical characteristic tests. By investigating various electrical parameters from tactile sensing tests, the equivalent conductance determined by the electro-mechanical analysis was found to have almost perfectly linear relationship (R2 = 0.9998) with the samples' elastic modulus ranging from 10 kPa to 70 kPa, and showed its potential as a new stiffness indicator for soft materials. Further analyses suggested that the electrically determined series resonance frequency shift, parallel resonance frequency shift, and maximum phase angle frequency shift also had excellent linearities (R2 = 0.9947, 0.9842, and 0.9935, respectively) with sample's modulus and can be considered as indicator candidates.

Progress in Canadian Mechanical Engineering, May 30, 2018

An ultrasonic tactile sensor that can measure the stiffness of the tissue was developed. By combi... more An ultrasonic tactile sensor that can measure the stiffness of the tissue was developed. By combining analytical and numerical approaches, efficient design methodology was presented. The electrical and mechanical performance of developed sensor was experimentally validated. Ultrasonics; Tactile sensing; Equivalent circuit I.

IEEE Transactions on Biomedical Engineering, 2020

Objective: High intensity focused ultrasound (HIFU) is a new noninvasive therapeutics that allows... more Objective: High intensity focused ultrasound (HIFU) is a new noninvasive therapeutics that allows local treatment of solid tumors through a hyperthermal mechanism using ultrasonic energy. One promising strategy to increase the thermal efficiency of HIFU is to employ nanoparticles (NPs) as ultrasound agents for the hyperthermia procedure. However, the interaction mechanism between NPs and ultrasonic waves has not been well understood. Methods: In an effort to investigate the heating process of NPs-enhanced HIFU, we derived a set of HIFU equations governing the temperature variation during the thermal ablation based on the principle of conservation of energy for heat transfer mechanism. A numerical model was developed to solve the HIFU equations to simulate the absorption mechanism of HIFU in the presence of NPs, the consequent heat transfer process, and the temperature rise profile during the sonication period. The accuracy of numerical model was verified by performing a series of experiments on tissue-mimicking phantoms embedded with magnetic NPs (MNPs). Results: The transport processes taking place at the boundaries between NPs and surrounding medium played the major role in the temperature rise during HIFU sonication. Besides, the effects of MNPs on rising temperature were improved by amplifying the ultrasonic power and frequency as well as by increasing the MNP concentration. Conclusion: A quantitative comparison with experimental results demonstrated the potential of the numerical model to accurately predict the heating mechanism of HIFU mediated by NPs. Significance: The proposed method can help with simulation of HIFU when NPs are employed as ultrasound agents.

IEEE Transactions on NanoBioscience, 2019

High intensity focused ultrasound (HIFU) has gained increasing attention as a noninvasive therape... more High intensity focused ultrasound (HIFU) has gained increasing attention as a noninvasive therapeutic method for wide range of biomedical applications from drug delivery to cancer treatment. However, high level of ultrasonic power required for efficient HIFU treatment can cause adverse effects such as damage to surrounding healthy tissues and skin burns. One of the strategies to improve the therapeutic mechanism of HIFU is to use ultrasound absorption agents during the treatment. The objectives of current study are to investigate the feasibility of adopting gold nanoparticles (AuNPs) as ultrasound absorption agents to enhance the HIFU thermal ablation when the NPs were injected locally to the focal region; and to examine the dose effects of AuNPs on both heating and cooling mechanisms of HIFU. To this end, we conducted an experimental study on tissue-mimicking phantoms where AuNPs were injected to the focal region under the guidance of ultrasound imaging. A set of thermal parameters including temperature, specific absorption rate of acoustic energy, and cooling rate were measured to monitor the mechanism of AuNPs-mediated HIFU. The results suggest that both heating and cooling rates of HIFU procedure could be greatly improved by injecting AuNPs, which demonstrates the feasibility of using AuNPs to reduce the level of ultrasonic power from extracorporeal source for HIFU treatment.

International Journal of Precision Engineering and Manufacturing, 2019

Vibro-tactile sensors have been utilized to measure the mechanical properties of soft materials b... more Vibro-tactile sensors have been utilized to measure the mechanical properties of soft materials based on the shift of resonant frequency. However, their low signal to noise ratio (SNR) has impeded them from critical applications where accurate measurements are required. One of the ways to improve the SNR is to add an ultrasonic concentrator as a mechanical filter to the vibro-tactile sensor. In order to maximize the SNR, the concentrator should be optimally designed; however, systematic design approach of the concentrator has rarely been considered so far. In this paper, a hybrid design approach employing both analytical analysis and numerical simulation is presented. For analytical analysis, impedance analogy was used to facilitate the designing process, and the numerical simulation using FEA was conducted to carry out the parametric refinement of the design. The performance of the final design was verified by mechanical and electrical characteristics tests. Tests results indicate that the longitudinal resonance mode of the sensor was significantly enhanced and the increase in its mechanical quality factor was achieved by the ultrasonic concentrator. The tactile sensing experiments on the silicone rubber samples showed the high potential of the vibro-tactile sensor in estimating the elastic moduli of soft materials in the range of 5–100 kPa, which is not readily available with conventional testing methods.

Physica E: Low-dimensional Systems and Nanostructures, 2018

Abstract CNT (Carbon nanotube)-based fluidic systems hold a great potential for emerging medical ... more Abstract CNT (Carbon nanotube)-based fluidic systems hold a great potential for emerging medical applications such as drug delivery for cancer therapy. CNTs can be used to deliver anticancer drugs into a target site under a magnetic field guidance. One of the critical issues in designing such systems is how to avoid the vibration induced by the fluid flow, which is undesirable and may even promote the structural instability. The main objective of the present research is to develop a fluid structure interaction (FSI) model to investigate the flutter instability of a cantilevered CNT induced by a magnetic fluid flow under a longitudinal magnetic field. The CNT is assumed to be embedded in a viscoelastic matrix to consider the effect of biological medium around it. To obtain a dynamical model for the system, the Navier–Stokes theory of magnetic-fluid flow is coupled to the Euler–Bernoulli beam model for CNT. The small size effects of the magnetic fluid and CNT are considered through the small scale parameters including Knudsen number (Kn) and the nonlocal parameter. Then, the extended Galerkin's method is applied to solve the FSI governing equations, and to derive the stability diagrams of the system. Results show how the magnetic properties of the fluid flow have an effect on improving the stability of the cantilevered CNT by increasing the flutter velocity.

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, Jul 1, 2017

Feasibility of applying compressive sensing (CS) to ultrasound radio-frequency (RF) data to produ... more Feasibility of applying compressive sensing (CS) to ultrasound radio-frequency (RF) data to produce elastography is investigated. The research also compares the performance of various CS frameworks associated with three common model bases (Fourier transform, discrete cosine transform (DCT), and wave atom (WA)) and two reconstruction algorithms (ℓ minimization and block sparse Bayesian learning (BSBL)) using the quality of B-mode images and elastograms from the RF data subsampled and reconstructed by each framework. Results suggest that CS reconstruction adopting BSBL algorithm with DCT model basis can yield the best results for all the measures tested, and the maximum data reduction rate for producing readily discernable elastograms is around 60%.