Hyuk-Min Harry Kwon, Violin

Violin Sonata No. 3, Op. 108 / Johannes Brahms; Violin Sonata No. 3, Op. 45 / Edvard Grie

Hyuk-Min Harry Kwon, Violin

Partita for Solo Violin No. 2 in D minor, BWV 1004 / J.S. Bach; Violin Concerto in E minor, Op. 64 / F. Mendelssoh

Tailoring hydrodynamics of non-wetting droplets with nano-engineered surfaces

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 47-53).Considering that contacts between liquid and solid are ubiquitous in almost all energy processes, including steam turbines, oil pumping, condensers and boilers, the efficiency of energy transportation can be maximized such that the liquid-solid interaction is optimized. Texture based super-hydrophobicity, also known as the Lotus effect, has been one of the most extensively studied topics in the last decade. Many of the recent studies have focused on how textures induce more water repellency, and how these textures can be manufactured with different methods and materials. However, few studies have shown how these surfaces benefit the real energy processes in which the interaction between liquid droplets and solid surfaces is vigorous and influences the energy transfer performances. This work focuses on altering the hydrodynamics of droplets with nano-engineered surfaces such that it enables a variety of energy transport processes to achieve better efficiency. Firstly, the wetting transition on textured super-hydrophobic surfaces is explored. The careful investigation of Cassie-Baxter to Wenzel transition of a pendant drop during the deposition explains that the rapid deceleration-induced water hammer pressure causes the transition. This new transition mechanism for large droplets enables a new wetting transition phase diagram with a previously known Laplace mechanism that explains the small drop transition. Another class of non-wetting droplet, the Leidenfrost drop, is studied with textured super-wetting surfaces. The liquid drop loses its contact to the solid by its own vapor, created by a large superheat from the solid. The Leidenfrost effect is undesirable in cooling applications as the vapor layer acts as a barrier for heat transfer. Here, it has been studied that how textured super-hydrophilic surfaces induce droplets to wet at higher superheat via capillary wicking compare to smooth surfaces. A physical model based on scaling is developed to predict the Leidenfrost drop on single length scale textures, and validated by the experiments. Additionally, the physical mechanism suggests that hierarchical textures have a higher Leidenfrost temperature compared to single-length-scale textures, confirmed experimentally. Lastly, the recently discovered rare-earth oxide ceramics are studied, which ensures the benefits of water repellency under harsh conditions such as high temperature and abrasive wear. Texturing of the rare-earth oxide ceramic is explored by the laser ablation technique. Unique micro- and nano-scale hierarchical textures are created, enhancing the water repellency, resulting in the super-hydrophobic rare-earth ceramic.by Hyuk-Min Kwon.Ph. D

Fluid-driven mechanical responses of deformable porous media during two-phase flows: Hele-Shaw experiments and hydro-mechanically coupled pore network modeling

Injecting fluid into a porous material can cause deformation of the pore structure. THis hydromechaniically coupled (i.e. poromechanical) phenomenon plays an essential role in many geological and biological operations across a wide range of scale, from geologic carbon storage, enhanced oil recovery and hydraulic fracturing to the transport of fluids through living cells and tissues, and to fuel cells. In this study, we conducted an experimental and numerical investigation of the hydro-mechanical coupling during fluid flows in porous media at the fundamental pore-scale. First, experimental undertaken to ascertain the effect of the hydro-mechanical coupling for two-phase fluid flows in either deformable or non-deformable porous media. Next, a hydro-mechanically coupled pore network model (HM-PNM) was employed to test a various range of influential parameters. The HM-PNM results were consistent with the experimental observations, including the advancing patterns of fluids and the development of the poroelastic deformation, when the vicious drop was incorporated. The hydromechanical coupling was observed to reduce the inlet pressure required to maintain a constant flow rate, whereas its effects on the pattern of fluid flow was minimal. The interfacial tension alteration also changed the pressure and deformation. The viscosity invading fluid showed significant effects on both the patterns of fluid displacement and mechanical deformations

Sex Differences in Spatial Accuracy Relate to the Neural Activation of Antagonistic Muscles in Young Adults

Sex is an important physiological variable of behavior, but its effect on motor control remains poorly understood. Some evidence suggests that women exhibit greater variability during constant contractions and poorer accuracy during goal-directed tasks. However, it remains unclear whether motor output variability or altered muscle activation impairs accuracy in women. Here, we examine sex differences in endpoint accuracy during ankle goal-directed movements and the activity of the antagonistic muscles. Ten women (23.1 ± 5.1 years) and 10 men (23 ± 3.7 years) aimed to match a target (9° in 180 ms) with ankle dorsiflexion. Participants performed 50 trials and we recorded the endpoint accuracy and the electromyographic (EMG) activity of the primary agonist (Tibialis Anterior; TA) and antagonist (Soleus; SOL) muscles. Women exhibited greater spatial inaccuracy (Position error: t = −2.65, P = 0.016) but not temporal inaccuracy relative to men. The motor output variability was similar for the two sexes (P \u3e 0.2). The spatial inaccuracy in women was related to greater variability in the coordination of the antagonistic muscles (R 2 0.19, P = 0.03). These findings suggest that women are spatially less accurate than men during fast goal-directed movements likely due to an altered activation of the antagonistic muscles

Arctic-North Pacific Coupled Impacts on the Late Autumn Cold in North America

The Pacific Decadal Oscillation (PDO) is known to bring an anomalously cold (warm) period to southeastern (northwestern) North America during the cold season of its positive phase through a Rossby wave linkage. This study provides evidence that the remote connection between the North Pacific and the downstream temperature over central North America is strengthened by the warm arctic conditions over the Chukchi and East Siberian Sea, especially in the late autumn season. The modulation effect of the Arctic manifests itself as an altered Rossby wave response to a transient vorticity forcing that results from an equatorward storm track shift, which is induced collaboratively by the PDO and the warm Arctic. This observational finding is supported by two independent modeling experiments: 1) an idealized coupled GCM experiment being nudged toward the warm arctic surface condition and 2) a simple stationary wave model (SWM) experiment forced by transient eddy forcing

Capric Acid Inhibits NO Production and STAT3 Activation during LPS-Induced Osteoclastogenesis

Capric acid is a second medium-chain fatty acid, and recent studies have shown that fatty acids are associated with bone density and reduce bone turnover. In this study, we investigated the effects of capric acid on lipopolysaccharide (LPS)-induced osteoclastogenesis in RAW264.7 cells. After treatment with capric acid (1 mM), the number of tartrate resistant acid phosphatase (TRAP)-positive cells decreased significantly. Capric acid reduced LPS-induced TRAP expression, an osteoclast differentiation marker, without inhibiting cell viability. LPS strongly upregulated inducible nitric oxide synthase (iNOS) mRNA levels and nitric oxide (NO) production, whereas capric acid inhibited them. Furthermore, capric acid also inhibited monocyte chemoattractant protein-1 (MCP-1) mRNA expression. Subsequently, we investigated various intracellular signaling proteins, including nuclear factor-κB (NF-κB), c-Jun-N-terminal kinase (JNK), extracellular signal regulated kinase 1/2 (ERK1/2), and signal transducer and activator of transcription 1 (STAT1) and STAT3 associated with osteoclastogenesis. Capric acid had no effects on LPS-induced activation of the NF-κB, JNK, ERK1/2, and STAT1 pathways. However, capric acid inhibited LPS-induced phosphorylation of Ser727 in STAT3. Additionally, stattic (a STAT3 inhibitor) inhibited LPS-induced iNOS and MCP-1 gene expression. In conclusion, we demonstrated that capric acid inhibited LPS-induced osteoclastogenesis by suppressing NO production via the STAT3 pathway. These results suggest that capric acid has important therapeutic implications for treating bone diseases associated with excessive osteoclastogenesis

Patient Perception of Natural Orifice Transluminal Endoscopic Surgery in an Endoscopy Screening Program in Korea

Purpose Natural orifice transluminal endoscopic surgery (NOTES) is a new method of accessing intracavitary organs in order to minimize pain by avoiding incisions in the body wall. The aim of this study is to determine patients' acceptance of NOTES in Korea and to compare their views about laparoscopic surgery and NOTES for benign and malignant diseases. Materials and Methods The target number of total subjects was calculated to be 540. The subjects were classified into 18 sub-groups based on age groups, gender, and history of prior surgery. The questionnaire elicited information about demographic characteristics, medical check-ups, diseases, endoscopic and surgical histories, marital status and childbirth, the acceptance of NOTES, and the preferred routes for NOTES. In addition, the subjects chose laparoscopic surgery or NOTES for a hypothetical cholecystectomy and rectal cancer surgery, and responded to questions regarding the acceptable complication rate of NOTES, the appropriate cost of NOTES, and the reason(s) why they did not select NOTES. Results: 486 of 540 patients (90.0%) who agreed to participate in this study completed the questionnaire. NOTES was preferred by the following patients: elderly; a history of treatment due to a disease; having regular check-ups; and a history of an endoscopic procedure (p<0.05). The most preferred route for NOTES was the stomach (67.1%). Eighty-four percent of the patients choosing NOTES responded that the complication rate of the new surgical method should be the same or lower than laparoscopic surgery. Vague anxiety over a new surgical method was the most common reason why NOTES was not selected in benign and malignant diseases (64% and 73%), respectively. Conclusion: Patients appear to be interested in the potential benefits of NOTES and would embrace it if their concerns about safety are met. We believe that qualified surgical endoscopists can meet these safety concerns, and that NOTES development has the potential to flourish

The Singer's Formant and Speaker's Ring Resonance: A Long-Term Average Spectrum Analysis

ObjectivesWe previously showed that a trained tenor's voice has the conventional singer's formant at the region of 3 kHz and another energy peak at 8-9 kHz. Singers in other operatic voice ranges are assumed to have the same peak in their singing and speaking voice. However, to date, no specific measurement of this has been made.MethodsTenors, baritones, sopranos and mezzo sopranos were chosen to participate in this study of the singer's formant and the speaker's ring resonance. Untrained males (n=15) and females (n=15) were included in the control group. Each subject was asked to produce successive /a/ vowel sounds in their singing and speaking voice. For singing, the low pitch was produced in the chest register and the high notes in the head register. We collected the data on the long-term average spectra of the speaking and singing voices of the trained singers and the control groups.ResultsFor the sounds produced from the head register, a significant energy concentration was seen in both 2.2-3.4 kHz and 7.5-8.4 kHz regions (except for the voices of the mezzo sopranos) in the trained singer group when compared to the control groups. Also, the chest register had a significant energy concentration in the 4 trained singer groups at the 2.2-3.1 kHz and 7.8-8.4 kHz. For speaking sound, all trained singers had a significant energy concentration at 2.2-5.3 kHz and sopranos had another energy concentration at 9-10 kHz.ConclusionThe results of this study suggest that opera singers have more energy concentration in the singer's formant/speaker's ring region, in both singing and speaking voices. Furthermore, another region of energy concentration was identified in opera singer's singing sound and in sopranos' speaking sound at 8-9 kHz. The authors believe that these energy concentrations may contribute to the rich voice of trained singers