Kangwon Shin

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Effects of Transportation Accessibility on Residential Property Values

Transportation Research Record, 2007

A number of studies have focused on estimating the effects of accessibility on housing values by ... more A number of studies have focused on estimating the effects of accessibility on housing values by using the hedonic price model. In the majority of studies, estimation results have revealed that housing values increase as accessibility improves, although the magnitude of estimates has varied across studies. Adequately estimating the relationship between transportation accessibility and housing values is challenging for at least two reasons. First, the monocentric city assumption applied in location theory is no longer valid for many large or growing cities. Second, rather than being randomly distributed in space, housing values are clustered in space-often exhibiting spatial dependence. Recognizing these challenges, a study was undertaken to develop a spatial lag hedonic price model in the Seoul, South Korea, metropolitan region, which includes a measure of local accessibility as well as systemwide accessibility, in addition to other model covariates. Although the accessibility measures can be improved, the modeling results suggest that the spatial interactions of apartment sales prices occur across and within traffic analysis zones, and the sales prices for apartment communities are devalued as accessibility deteriorates. Consistent with findings in other cities, this study revealed that the distance to the central business district is still a significant determinant of sales price.

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How automated speed enforcement may reduce travel time variability and result in travel time savings: The case study of the loop 101 speed enforcement program in Scottsdale, Arizona

How automated speed enforcement may reduce travel time variability and result in travel time savi... more

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Estimating Path Travel Time by Aggregating Link Travel Times Obtained through Dedicated Short Range Communication Probe Data

18th ITS World CongressTransCoreITS AmericaERTICO - ITS EuropeITS Asia-Pacific, 2011

Korea Expressway Corporation (KEC) began utilizing vehicles equipped with the dedicated short ran... more Korea Expressway Corporation (KEC) began utilizing vehicles equipped with the dedicated short range communication (DSRC) based electronic toll collection system as traffic probes for collecting path travel times, thereby reducing traffic congestion on highway. Since it is not always possible to obtain sufficient sample size for calculating certain path travel time in the DSRC system, KEC attempts to estimate the path travel time by the simple and progressive addition of link travel times on its component links as in past studies—often referred to as link based model (LBM). However, an assessment is lacking on how accurately the LBM estimates the path travel time. Hence, this study examines whether the LBM can be used for obtaining reliable path travel times. The analysis results reveal that the differences between the LBM estimates and the path travel times obtained from the probe vehicles traveling whole links on the path are less than 63 seconds. Thus, when the number of probe vehicles traveling whole links on its path is small, the aggregated link travel times proposed in this study can be used as a substitute for path travel times. Although it is anticipated that the analysis results are sufficient to provide the feasibility of the LBM in estimating path travel times, the results should be treated with caution because this study was based on relatively small samples due to data limitation.

Porous gelatin-siloxane hybrid scaffolds with biomimetic structure and properties for bone tissue regeneration

Journal of Biomedical Materials Research Part B, Mar 5, 2014

We produced highly porous gelatin-siloxane (GLA-S) hybrid scaffolds with biomimetic anisotropic p... more We produced highly porous gelatin-siloxane (GLA-S) hybrid scaffolds with biomimetic anisotropic porous structure, physiochemical properties, mechanical behaviors and biological functions by treating gelatin-siloxane hybrid gels in an ammonium hydroxide solution. The siloxane used as an inorganic phase could effectively crosslink the gelatin polymer, which allowed for the unidirectional enlargement of ammonia vacuoles during ammonium hydroxide treatment. This created aligned pores in an axial direction when the siloxane contents (10 and 20 wt %) were high. In addition, the gelatin polymer could be uniformly hybridized with the siloxane phase at the molecular level, while intense interaction between these two phases could be achieved. This resulted in a significant increase in mechanical properties. The GLA-S hybrid scaffold with a siloxane content of 10 wt % showed reasonably high compressive yield strength of 4.2 6 0.1 MPa and compressive modulus of 84 6 5 MPa at a porosity of 86 vol %, which would be comparable to those of natural cancellous bone. In addition, the GLA-S hybrid scaffold had good biocompatibility assessed by in vitro cell tests using pre-osteoblast MC3T3-E1 cells. V

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False Congestion Detection Rate: Loop Detector Speed vs. Progressive DSRC Link Travel Speed

19th ITS World CongressERTICO - ITS EuropeEuropean CommissionITS AmericaITS Asia-Pacific, 2012

Korea Expressway Corporation (KEC) has collected the travel times of each section (expressway sec... more Korea Expressway Corporation (KEC) has collected the travel times of each section (expressway section between two consecutive interchanges) on expressway using the dedicated short range communication (DSRC) probe data. Specifically, KEC estimates the section travel time by the progressive addition of link travel times on its component links. Despite the extensive collected dataset of the DSRC travel speeds, the loop detector-based vehicle detection system (VDS) travel speeds are still used to identify the traffic congestion conditions of expressway sections in Korea. Hence, this study evaluates how accurately the DSRC travel speeds detect the traffic congestion conditions. The empirical data analysis results show that the two travel speeds are significantly different at α=0.05. In addition, the analysis results present that the average false congestion detection rate of DSRC (1.90%) is significantly less than that of VDS (12.05%) regardless of traffic conditions. Thus, when the DSRC data can be obtained on the consecutive links the given section, the progressive DSRC link travel times can be used to identify the traffic congestion condition properly.

The impact of red light cameras on safety in Arizona

Accident Analysis & Prevention, Nov 1, 2007

Red light cameras (RLCs) have been used in a number of US cities to yield a demonstrable reductio... more Red light cameras (RLCs) have been used in a number of US cities to yield a demonstrable reduction in red light violations; however, evaluating their impact on safety (crashes) has been relatively more difficult. Accurately estimating the safety impacts of RLCs is challenging for several reasons. First, many safety related factors are uncontrolled and/or confounded during the periods of observation. Second, "spillover" effects caused by drivers reacting to non-RLC equipped intersections and approaches can make the selection of comparison sites difficult. Third, sites selected for RLC installation may not be selected randomly, and as a result may suffer from the regression to the mean bias. Finally, crash severity and resulting costs need to be considered in order to fully understand the safety impacts of RLCs. Recognizing these challenges, a study was conducted to estimate the safety impacts of RLCs on traffic crashes at signalized intersections in the cities of Phoenix and Scottsdale, Arizona. Twenty-four RLC equipped intersections in both cities are examined in detail and conclusions are drawn. Four different evaluation methodologies were employed to cope with the technical challenges described in this paper and to assess the sensitivity of results based on analytical assumptions. The evaluation results indicated that both Phoenix and Scottsdale are operating cost-effective installations of RLCs: however, the variability in RLC effectiveness within jurisdictions is larger in Phoenix. Consistent with findings in other regions, angle and left-turn crashes are reduced in general, while rear-end crashes tend to increase as a result of RLCs.

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An Optimal Layout of Hi-Pass Lane in Expressway Toll Plaza Considering Traffic Flow

17th ITS World CongressITS JapanITS AmericaERTICO, 2010

The Electronic Toll Collection system of KEC (Korea Expressway Corporation), so called Hi-pass, c... more The Electronic Toll Collection system of KEC (Korea Expressway Corporation), so called Hi-pass, collects toll from vehicles equipped with Hi-pass OBU (On Board Unit) by wireless communication. Introduced in 2000, now over 400 million vehicles are equipped with Hi-pass OBU and 45% of vehicles on expressways use Hi-pass as of May 2010. In spite of the growth, there is still doubt as to where the Hi-pass lane should be located in the toll plaza. The design handbook of KEC mandated the number of the Hi-pass lane as one leftmost lane, except special cases like high volume, separated toll plaza, and/or multi-connected ramps. This paper deals with the location issue of the Hi-pass lane. In this paper, the TransModeler simulation package has been utilized to identify the best Hi-pass lane layout based on the proportion of Hi-pass usage and traffic volume. The simulation results show that the current Hi-pass lane layout is quite appropriate because this layout minimizes the system-wide total travel time and weaving actions thereby reducing the accident risks in the toll plaza.

Bus Stop Design Guide by Identifying the Relationship between Bus Stopping Behaviors and Bus Stop Conditions

KSCE Journal of Civil and Environmental Engineering Research, Feb 1, 2019

To improve bus service quality and passengers' safety at bus stops, it is necessary to analyze th... more To improve bus service quality and passengers' safety at bus stops, it is necessary to analyze the relationship between bus stopping behaviors and bus stop conditions. Thus, this study investigated the proper stopping rate at 31 bus stops on Central Boulevard in Busan metropolitan city and analyzed the relationship between the proper stopping rate and bus stop operating conditions such as the length of berth, the distance from the front line of berth to bus shelter and so on. The analysis results show that the proper stopping rate is 45.82 % and the rates are closely related to each bus stop operating condition. Therefore, it is highly recommended that the front line of berth should be located parallel to bus shelter for improving the safety of bus passengers. In addition, it is suggested that the length of berth should be longer than 15m and the pavement marking of berth be redesigned with dash lines to take account of buses' entering and leaving the berth.

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Effects of Chemical Composition of Titanium Material Surface on SAMs Formation by Functional Groups of Alkanethiol and Alkanesilanes

Annals of Transplantation, Jan 15, 2004

Self-assembled monolayers (SAMs) have become an essential technique for biochemical modification ... more Self-assembled monolayers (SAMs) have become an essential technique for biochemical modification of a biomaterial surface using specific peptides. Previous studies reported effects of their terminal functionalities including organic molecules on apatite formation in a simulated body fluid. Biological responses are influenced by the surface chemical characteristics of SAMs as well. This study investigated the adsorption behavior of alkanethiol and two alkanesilanes on modified titanium surfaces using an electrochemical quartz crystal nanobalance (EQCN). The formation of SAMs on three working electrode surfaces: Au coated Ti, commercialized pure Ti (c.pTi) and TiO2 were also examined. The resolution limit obtained for the constructed EQCN was about 0.1 ng. The mass change ratio on the surfaces versus immersion time was investigated using EQCN. The quantity of Thiol-I SAM adsorbed on c.pTi is about 67% compared with the quantity formed on Au coated titanium substrate. Contrarily, there was no SAM formation on the TiO2 surface with a thick titanium oxide layer obtained by the electrochemical oxidation method. The SAM amounts (for organosilanes) adsorbed on TiO2 surfaces of Silane-I[ (CH3O)3Si(SH2)3NHCH2CH2NH2)] and Silane-II[H2N(CHS)3Si(OCH3)3] were approximately 19% and 14% more than that of c.pTi. The results obtained in this study show that by altering titanium surface chemistry and introducing functional groups, titanium surfaces may be modified into functional bioactive surfaces and can be used in the same way as the Au substrate.

An Empirical Model for Estimating Bus Boarding and Alighting Time

Daehan gyotong haghoeji, Apr 30, 2014

The total boarding and alighting time models have been developed by applying the multiple regress... more The total boarding and alighting time models have been developed by applying the multiple regression analysis with three variables; numbers of boarding or alighting passengers, non-sitting passengers, and the step-height from the ground. Such variables have influenced to the total boarding time model with the most influential in the numbers of boarding or alighting passengers and the least in the step-height. On the total alighting time model, the numbers of alighting passengers are the most strongest while the step-heights the least. The total boarding and alighting time models can be used in practices for the prediction of current and future bus stops' capacities in TOD-based towns.

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Fabrication of highly porous titanium (Ti) scaffolds with two interlaced periodic pores

Materials Letters, Jun 1, 2009

This paper reports a novel type of porous titanium (Ti) scaffolds with two interlaced periodic po... more This paper reports a novel type of porous titanium (Ti) scaffolds with two interlaced periodic pores that were produced by coating the surfaces of a dual-channeled hydroxyapatite (HA) scaffold, as a supporting framework, with a titanium hydride (TiH 2) slurry followed by heat-treatment at 1200°C for 3 h in a vacuum to convert TiH 2 to Ti metal. This method allowed the porous Ti scaffolds to mimic the original pore structure of the dual-channeled HA scaffold in a tightly controlled manner. It was observed that the Ti layer was strongly adhered to the HA layer, owing to the diffusion of P ions into the Ti layer. The fabricated sample showed a high compressive strength of 6.0 ± 0.77 MPa and a porosity of 78 vol.% due to its unique pore structure, as well as perfect interconnections between the pores.

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Analyzing the Relationship Between Precipitation and Transit Ridership Through a Seemingly Unrelated Regression Model

Daehan gyotong haghoeji, Apr 30, 2014

Weather condition is one of the crucial factors affecting travelers' mode choice. Nevertheless, t... more Weather condition is one of the crucial factors affecting travelers' mode choice. Nevertheless, there are numerous indefinite traffic phenomena under various weather conditions. This study was conducted to verify the hypothesis that transit riderships decrease as precipitation increases. To clarify the relationship between precipitation and transit ridership, a seemingly unrelated regression model was employed with data such as daily precipitation and daily transit riderships of 3 transit modes (bus, metro, and shuttle bus) collected in Busan for recent 24 months. The estimation results show that transit riderships decreased as the daily precipitation increased when the daily precipitation is greater or equal to 10mm/day (0.169%, 0.101%, and 0.172% reduction in bus, metro, and shuttle bus riderships, respectively, when the daily precipitation increased by 1mm). When comparing the impact of precipitation on transit riderships by modes using a cross-equation parameter restriction test, the decrease in metro ridership is relatively insensitive to the change in precipitation. However, the negative coefficient of precipitation in the metro ridership estimation model indicates that the transit users in Busan may alter their mode to taxi or automobile and/or may give up the trip itself in bad weather condition.

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Nonsolvent induced phase separation (NIPS)-based 3D plotting for 3-dimensionally macrochanneled poly(ε-caprolactone) scaffolds with highly porous frameworks

Materials Letters, May 1, 2014

This study demonstrates the utility of nonsolvent induced phase separation (NIPS)-based 3D plotti... more This study demonstrates the utility of nonsolvent induced phase separation (NIPS)-based 3D plotting as a novel SFF technique for the production of 3-dimensionally macrochanneled poly(ε-caprolactone) (PCL) scaffolds with highly porous PCL frameworks. In particular, a PCL/tetrahydrofuran (THF) solution was deposited in an EtOH bath to rapidly solidify PCL filaments with a highly porous structure through exchange of THF solvent and EtOH nonsolvent. All the scaffolds produced with various PCL concentrations (14 wt%, 18 wt%, and 22 wt%) showed well-constructed 3-D macrochannels with highly porous PCL frameworks. However, the mechanical properties of the scaffolds, measured by compressive and tensile strength tests, increased with an increase in PCL concentration owing to a decrease in the overall porosity.

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Clinical study on screw loosening in dental implant prostheses: a 6-year retrospective study

Journal of The Korean Association of Oral and Maxillofacial Surgeons, Apr 30, 2020

Objectives: In this study, we determined the incidence and pattern of screw loosening in patients... more Objectives: In this study, we determined the incidence and pattern of screw loosening in patients who received dental implants. Materials and Methods: Patients who received implants between January 2008 and October 2013 and completed their prosthetic rehabilitation were evaluated for the incidence, frequency, and onset of screw loosening using dental charts and radiographs. The association between each factor and screw loosening was analyzed using the chi-square test and a multivariate analysis with binary logistic regression models (P<0.05). Results: Total 1,928 implants were placed in 837 patients (448 males, 389 females), whose follow-up period after loading varied from 0.25 to 70 months (mean period, 31.5 months). Screw loosening occurred in 7.2% of implants. Most cases occurred less than six months after loading. Among those, 22.3% experienced recurrent screw loosening. Screw loosening was most common in the molar region (8.5%) and frequently associated with an implant diameter of ≥5 mm (14.2%). External implant-abutment connections (8.9%) and screw-retained implant prostheses (10.1%) showed higher incidence of problems than internal implant-abutment connections and cement-retained implants, respectively. Screw loosening was most common in implant prostheses with single crowns (14.0%). Conclusion: Within the limits of the current study, we conclude that the incidence of screw loosening differs significantly according to the position of implant placement, the type of implant and manufacturer, implant diameter, the type of implant-abutment connection, the type of retention in the implant prosthesis, and the type of implant prosthesis.

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Highly Porous Biphasic Calcium Phosphate (BCP) Ceramics with Large Interconnected Pores by Freezing Vigorously Foamed BCP Suspensions under Reduced Pressure

Journal of the American Ceramic Society, Oct 20, 2011

This article proposes a new way of producing highly porous biphasic calcium phosphate (BCP) ceram... more This article proposes a new way of producing highly porous biphasic calcium phosphate (BCP) ceramics with large interconnected pores by freezing a vigorously foamed BCP suspension under reduced pressure, which allows the air bubbles incorporated into the BCP suspension to expand extensively. All the fabricated samples produced with various degrees of expansion of the BCP suspension (0, 150, 200, and 250 vol%) showed a highly uniform porous structure with their unique microporous BCP walls. The sizes of the pores and interconnections between the pores increased remarkably from 74 ± 21 μm to 295 ± 93 μm and 22 ± 8 μm to 123 ± 60 μm, respectively, with increasing degree of expansion from 0 to 250 vol%. However, the compressive strength decreased from 1.2 ± 0.29 MPa to 0.4 ± 0.07 MPa with increasing degree of expansion from 150 to 250 vol%.

Improving the strength and biocompatibility of porous titanium scaffolds by creating elongated pores coated with a bioactive, nanoporous TiO2 layer

Materials Letters, Nov 1, 2010

This paper reports a novel way of improving the mechanical properties and biocompatibility of por... more This paper reports a novel way of improving the mechanical properties and biocompatibility of porous Ti scaffolds using a combination of the modified sponge replication method and anodization process. The use of a stretched polymeric sponge as a novel template allowed the creation of elongated pores in a porous Ti scaffold, which, accordingly, led to a high compressive strength of

Production of porous calcium phosphate (CaP) ceramics with highly elongated pores using carbon-coated polymeric templates

Ceramics International, 2012

This study reports a new way of enhancing the compressive strength of porous calcium phosphate (C... more This study reports a new way of enhancing the compressive strength of porous calcium phosphate (CaP) ceramics by creating highly elongated pores. These elongated pores were produced by casting a CaP/camphene slurry into stretched polymeric sponges with a thick carbon coating layer used as a template. The sample produced after sintering at 1250 8C for 3 h showed a highly elongated porous structure with a porosity of 38 AE 1.2 vol%, where elongated pores with a size of 512 AE 96 mm were formed as a replica of the template. In addition, CaP walls with a thickness of 841 AE 239 mm were fully densified without any noticeable defects due to the high CaP content of 40 vol% in the CaP/camphene slurry. The compressive strength of the sample was as high as 21 AE 4.9 MPa when tested parallel to the direction of pore elongation, which is much higher than that (12 AE 2.4 MPa) of the sample tested normal to the direction of pore elongation. The sample also showed good biocompatibility, as assessed by the in vitro cell test using a pre-osteoblast cell line.

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Direct coating of bioactive sol–gel derived silica on poly(ε-caprolactone) nanofibrous scaffold using co-electrospinning

Materials Letters, Jul 1, 2010

This study reports a novel way of directly coating a poly(ε-caprolactone) (PCL) nanofibrous scaff... more This study reports a novel way of directly coating a poly(ε-caprolactone) (PCL) nanofibrous scaffold with bioactive sol-gel derived silica by directly co-electrospinning (Co-ES) a PCL solution and silica sol, used as the core and shell materials, respectively. In particular, the silica sols prepared using a sol-gel process at room temperature were heat-treated at 60°C for various times, ranging from 0 to 9 h, in order to improve their spinability. The surface of the individual PCL nanofibers could be covered completely with a bioactive silica layer using a silica sol heat-treated at 60°C for more than 6 h, whilst preserving the nanofibrous structure. Fourier-transform infrared spectroscopy (FT-IR) revealed only the characteristic bands associated with the PCL and sol-gel derived silica materials without any noticeable band shift.

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Bioactive glass microspheres as reinforcement for improving the mechanical properties and biological performance of poly(ε-caprolactone) polymer for bone tissue regeneration

Journal of Biomedical Materials Research Part B, Jan 25, 2012

This study examined the utility of sol-gel-derived bioactive glass microspheres (BGMs) as a reinf... more This study examined the utility of sol-gel-derived bioactive glass microspheres (BGMs) as a reinforcement to improve the mechanical properties and biological performance of poly(e-caprolactone) (PCL) polymer. All of the PCL-BGMs composites produced, with a variety of BGMs contents (10, 20, and 30 wt %), showed a uniform distribution of the BGMs in the PCL matrix, particularly owing to their spherical shape and small size. This led to a considerable increase in the elastic modulus from 93 6 12 MPa to 635 6 179 MPa with increasing BGMs content from 0 to 30 wt %. Furthermore, the addition of the BGMs to the PCL polymer significantly increased the hydrophilicity of the PCL-BGMs composites, which led to a higher water absorption and degradation rate. The PCL-BGMs composite with a BGMs content of 30 wt % showed vigorous growth of apatite crystals with a high aspect ratio on its surface after soaking in the simulated body fluid for 7 days, resulting in the creation of a porous carbonate hydroxyapatite layer. V

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Sol–gel derived nanoscale bioactive glass (NBG) particles reinforced poly(ε-caprolactone) composites for bone tissue engineering

Materials Science and Engineering: C, Apr 1, 2013

This study investigated the effect of the addition of sol-gel derived nanoscale bioactive glass (... more This study investigated the effect of the addition of sol-gel derived nanoscale bioactive glass (NBG) particles on the mechanical properties and biological performances of PCL polymer, in order to evaluate the potential applications of PCL/NBG composites for bone tissue regeneration. Regardless of the NBG contents (10, 20, and 30 wt.%), the NBG particles, which were synthesized through the sol-gel process using polyethylene glycol (PEG) polymer as a template, could be uniformly dispersed in the PCL matrix, while generating pores in the PCL/NBG composites. The elastic modulus of the PCL/NBG composites increased remarkably from 89 ± 11 MPa to 383 ± 50 MPa with increasing NBG content from 0 to 30 wt.%, while still showing good ultimate tensile strength in the range of 15-19 MPa. The hydrophilicity, water absorption and degradation behavior of the PCL/NBG composites were also enhanced by the addition of the NBG particles. Furthermore, the PCL/ NBG composite with a NBG content of 30 wt.% showed significantly enhanced in vitro bioactivity and cellular response compared to those of the pure PCL.

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