Junghoon Kim

Monolithic Encapsulation of Implantable Neuroprosthetic Devices Using Liquid Crystal Polymers

Flexible polymers have gained much attention in the development of low cost, magnetic resonance compatible, and nonfragile implantable medical devices. However, efficacy of the conventional polymer encapsulations containing hybrid interfaces is limited due to their relatively high moisture absorption and unstable interfacial adhesion in aqueous environments. As an alternative, we report on a monolithic encapsulation platform for neuroprosthetic devices using liquid crystal polymers (LCPs), which have a very low degree of moisture absorption (<;0.04%) and a fusion bondable interface. This platform offers monolithic encapsulation by fusion bonding of the hemispherical LCP package lids and LCP-based microelectrode arrays. The package lids were fabricated by thermoforming of the LCP films to provide the desired shape and size for encasing the electronic components and wireless telemetry coils. Fusion-bonded LCP encapsulations were evaluated using electrical leakage current measurements during in vitro soak tests. The measurements were done in both 37°C and 75°C phosphate-buffered saline (PBS) solution and showed that LCP encapsulation was superior and more reliable in PBS than polyimide and parylene-C encapsulations. In addition, LCP-based monolithic encapsulation provided reliable electrical insulation for more than 300 days in both 37°C and 75°C PBS solution.

Small Magnetic Bipoles Emerging in a Filament Channel

Observations have shown that quiescent prominences or filaments have a hemispheric magnetic pattern of chirality. Motivated by the question of whether the filament chirality is of subsurface origin or not, we have studied small magnetic bipoles that emerged in a quiescent filament channel at latitude N45°. During our 5 day observing run, performed in 1999 October, a huge filament erupted and reformed shortly in the same filament channel. Using high-cadence, long-integration line-of-sight magnetograms taken at Big Bear Solar Observatory, we identified a total of 102 bipoles that showed an average total flux of 2.8 × 1019 Mx, an average separation of 7400 km at the time of full development, and an emergence rate of 430 hr-1 per the entire solar surface area. These properties indicate that most of the bipoles are ephemeral regions. The most important finding in the present study is that the magnetic axes of the bipoles emerging in the filament channel are systematically oriented; a negative (trailing) pole is observed to be located preferentially to the south-east of its companion positive (leading) pole. This preferred orientation does not match either the Hale law of active region orientation or a theory that attributes the axial field of a filament to emerging bipoles. We propose two possible subsurface field configurations of bipoles consistent with the observed preferential orientation and discuss physical implications of our results for understanding filament magnetic fields.

A Rapid Change in Magnetic Connectivity Observed Before Filament Eruption and Its Associated Flare

To gain insight to the cause of filament eruptions and flares on the Sun, we observed a filament that erupted in active region NOAA 8597. The observations consisted of Hα filtergrams at three wavelengths (line center and ±0.5 A) and line-of-sight magnetograms. All were taken on 1999 June 24 at Big Bear Solar Observatory. We found from the time sequence of Hα images that the filament eruption was preceded by a rapid change in connectivity in a bundle of filament threads. The thread bundle was initially sharply curved near its one end of the filament and suddenly flipped and then became straight in the new orientation. The flipped segment of the thread bundle swept over a 100 × 50 area on the solar surface in about half an hour. At the latter stage of the connectivity change, we observed a downward draining of material along the thread bundle that had a transverse component of 50 km s-1. After that, the filament body split into two parallel parts, one part erupted while the other part remained, and the two-ribbon flare occurred. We also found canceling magnetic features in the vicinity of the initial location of the thread end, which displayed a flux decrease during the Hα connectivity change. Our results show clear and direct evidence that magnetic reconnection takes place in the low atmosphere prior to eruption. This preeruption reconnection seems to be very different from a posteruption coronal reconnection, which is believed to lead to a two-ribbon flare.

Optical measurement of neural activity using surface plasmon resonance.

We demonstrate that surface plasmon resonance (SPR) is applicable to the optical detection of neural signals. A low-noise SPR sensor was developed as a label- and artifact-free method for the extracellular recording of neural activity. The optical responses obtained from a rat sciatic nerve were highly correlated with simultaneously recorded electrical responses. Additional studies with stimulation intensity and lidocaine further confirmed that the optically measured signals originated from neural activities.

Feasibility study of the bio-barrier with biologically-active tire rubbers for treating chlorinated hydrocarbons

The leachate from landfill released into the subsurface environment can result in serious environmental problems such as soil and groundwater contaminations because there is no landfill liner system in the unsanitary landfill. The authors developed the multi-permeable reactive barriers (M-PRBs) to treat mixed contaminants in leachate and to get over the limitation of a single reactive barrier. The M-PRBs consist of two reactive barriers using the abandoned materials such as waste steel ccrap mixed with converter slag acting as an iron-based barrier and biologically active tire acting as a bio-barrier. In this study, the efficiency of tire rubbers as a sorption media and a biologically active media were evaluated. Tire rubbers extensively adsorbed amounts of chlorinated compounds and the biologically active tire media removed chlorinated organic compounds (93% of TCE and 77% of PCE) as well as organic matters (80%) for 10 days. Overall, this work suggests that biologically active tire media followed by an iron-based barrier in the M-PRBs can effectively treat mixed contaminants in landfill leachates through bioaugmentation.

An Analysis of User Dynamics in P2P Live Streaming Services

Peer-to-peer (P2P) live streaming services are getting more popular as the average link capacity in the Internet becomes greater for end hosts. In order to provide a high quality P2P live streaming service, it is essential to handle user dynamics effectively to mitigate streaming disruptions caused by user churn. We collect massive user traces from the largest P2P live streaming site in Korea, namely, Afreeca. Based on the trace results obtained, we analyze user dynamics in the service. In particular, we analyze the user behaviors in terms of three criteria: long-stay users, short-stay users, and user churn. (1) The results show that a certain amount of long-stay users exist in a live streaming session, and it is challenging to recognize the long-stay users online, which will help to provide more resilient live streaming service. (2) Around 20% of the users stay in a session shorter than 1% of the session length. Short-stay users incur high control overhead and we discuss how to efficiently handle the short-stay users. (3) By intentionally disrupting a video streaming, we closely observe the users leaving behavior and suggest the acceptable recovery time to keep the users remaining the session. We believe our findings can be useful not only to P2P live streaming systems, but also to every live streaming systems.

Long-term results of new deproteinized bovine bone material in a maxillary sinus graft procedure.

Purpose The aim of this case report is to present the longitudinal results of sinus grafting using a new demineralized bovine bone material (DBBM) in human cases. Methods A patient with a resorbed maxilla was treated by maxillary sinus grafting using a new deproteinized bovine bone material. After a healing period of 6.5 months, three implants were placed and restored. The patient was periodically recalled and followed up for 5 years after restoration. Results Twelve partially edentulous patients (average age, 55.7 years) were followed up. All patients had insufficient residual height in their maxillary posterior area and underwent maxillary sinus graft surgery to increase the height of their maxilla. In all, 27 fixtures were placed in the augmented bone area. On average, 8.6 months later, implants were loaded using provisional or final restorations. The observation period ranged from 27 to 75 months (average, 43.3 months), and the patients did not show any severe resorption of the graft material or any infection during this time. Conclusions Our results show that the new DBBM is useful for a maxillary sinus graft procedure. Good healing responses as well as reliable results were obtained for an average follow-up period of 43.3 months. Graphical Abstract

Effect of microthreads on removal torque and bone-to-implant contact: an experimental study in miniature pigs

PURPOSEnThe objective of this study was to evaluate the effect of microthreads on removal torque and bone-to-implant contact (BIC).nnnMETHODSnTwelve miniature pigs for each experiment, a total of 24 animals, were used. In the removal torque analysis, each animal received 2 types of implants in each tibia, which were treated with sandblasting and acid etching but with or without microthreads at the marginal portion. The animals were sacrificed after 4, 8, or 12 weeks of healing. Each subgroup consisted of 4 animals, and the tibias were extracted and removal torque was measured. In the BIC analysis, each animal received 3 types of implants. Two types of implants were used for the removal torque test and another type of implant served as the control. The BIC experiment was conducted in the mandible of the animals. The P1-M1 teeth were extracted, and after a 4-month healing period, 3 each of the 2 types of implants were placed, with one type on each side of the mandible, for a total of 6 implants per animal. The animals were sacrificed after a 2-, 4-, or 8-week healing period. Each subgroup consisted of 4 animals. The mandibles were extracted, specimens were processed, and BIC was analyzed.nnnRESULTSnNo significant difference in removal torque value or BIC was found between implants with and without microthreads. The removal torque value increased between 4 and 8 weeks of healing for both types of implants, but there was no significant difference between 8 and 12 weeks. The percentage of BIC increased between 2 and 4 weeks for all types of implants, but there was no significant difference between 4 and 8 weeks.nnnCONCLUSIONSnThe existence of microthreads was not a significant factor in mechanical and histological stability.

Enhanced regeneration of rabbit mandibular defects through a combined treatment of electrical stimulation and rhBMP-2 application

We evaluated the new bone regeneration of a rabbit mandibular defect using hBMSCs under electrical stimulation combined with rhBMP-2 in this study. An inner scaffold prepared by setting a collagen sponge with hBMSCs and hydrogel was placed into a polycaprolactone (PCL) outer box, and an electrical stimulation device was installed between the inner scaffold and the outer box. There were three experimental groups depending on electrical stimulation and application of rhBMP-2. The experimental group was divided into the following three groups. Group 1, in which rhBMP-2 (5xa0μg/defect) was added to hydrogel and electrical stimulation was not applied; Group 2, in which rhBMP-2 (5xa0μg/defect) was added as in Group 1 and electrical stimulation was applied; and Group 3, in which electrical stimulation was applied and rhBMP-2 (5 μg/defect) was injected directly into defect site. The delivered electrical stimulation was charge-balanced bi-phasic electric current pulses, and electrical stimulation was conducted for 7xa0days. The stimulation parameters of the bi-phasic electrical current set at an amplitude of 20xa0μA, a duration of 100xa0μs and a frequency of 100xa0Hz. Four weeks after surgery, new bone formation in each group was evaluated using radiography, histology, and micro-computed tomographyxa0(μCT). Groups 2 and 3 exhibited a significant increase in new bone formation compared to Group 1, while Group 3 showed the highest level of new bone regeneration. In a comparison between two groups, Group 2 showed a higher bone volume (BV) by 260xa0% (pxa0<xa00.01) compared with Group 1, and Group 3 showed a higher BV by 442xa0% (pxa0<xa00.01) compared with Group 1. The trend of the bone surface density (ratio of new bone to the real defect volume, BS/TV), trabecular number, and connectivity was identical to that of the BV. The total bone mineral density (BMD) of Groups 2 and 3 showed values higher by the ratios of 103xa0% (pxa0<xa00.01) and 107.5xa0% (pxa0<xa00.01) compared with Group 1, respectively. Part BMD for Groups 2 and 3 showed higher values by the ratios of 104.9xa0% (pxa0<xa00.01) and 122.4xa0% (pxa0<xa00.01) compared with Group 1, respectively. These results suggest that the combined treatment of electrical stimulation, hBMSCs, a collagen sponge, hydrogel, and rhBMP-2 was effective for bone regeneration of large-size mandibular defects. The application of rhBMP-2 with an injection following electrical stimulation demonstrated better efficiency as regards bone regeneration.

Waterfall: Video Distribution by Cascading Multiple Swarms

Video on demand services have been increasingly proliferated in the Internet. One popular way to disseminate video files among numerous users is to leverage peer-to-peer (P2P) systems (e.g., BitTorrent). However, BitTorrent is not designed with video streaming requirements and hence suffers from long setup delay. In this paper, the drawbacks of existing P2P-based streaming solutions are analyzed in terms of sequential delivery. Then we propose Waterfall that splits the whole swarm into multiple swarms, which are then cascaded by the scene sequence. In this way, peers in a swarm download the chunks of the same video scene from the peers in the same swarm as well as the ones in the preceding swarm that already moved on to the next scene. The average setup delay and maximum playback rate of Waterfall are analyzed. Experiments from a wide area network testbed reveal that Waterfall achieves two to three times higher playback rate and significantly low setup delay than the prior BitTorrent-based streaming solutions.