• Proceedings of the Korean Fiber Society Conference
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• 2002.04a
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• pp.466-469
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• 2002

Polyurethane(PU)은 segmented 블록공중합체로써 상온보다 높은 유리전이온도(glass transition temperature, Tg)를 갖는 hard segment(H.S)와 상온보다 낮은 Tg를 갖는 soft segment (S.S)로 구성되어 있다. 이들 두 segment간의 열역학적 불친화성으로 인해 미세 상분리 구조를 갖는다$^1$. 그 결과 hard segment-rich hard domain과 soft segment-rich soft matrix의 구조를 이룬다. 이중 hard domain(HD)은 상온에서 glassy한 성격을 띄므로 물리적 가교점과 충진제의 역할을 하며 soft domain(SD)은 rubbery한 성질을 가지므로 polurethane에 탄성을 부여하는 역할을 한다. (중략)

• Phonetics and Speech Sciences
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• v.2 no.4
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• pp.59-65
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• 2010

In this paper, we investigate acoustic characteristics of Korean /s/ when it is followed by both a high front and a round segment regardless of their order to one another. We show that Korean /s/ in this environment has characteristics of a labio-palatalized segment, being affected by both a high front and a round segment if they occur within the domain of a syllable. In the experiment, we show that Korean /s/ before a high front and a round segment shows a spectral shape different from that in other environments. Specifically, it is different from /s/ before a high front segment only, showing peaks around 2.5 kHz. Furthermore, it shows a rapid decrease of amplitude in 4-5 kHz, and sometimes another plateau of high peaks in 5-6 kHz. We also examined center of gravity frequency and band energy difference. Based on the results of this experiment, we argue that Korean /s/ is affected by the following segments within the domain of coarticulation, a syllable and that the degree of coarticulation is different from language to language.

• Journal of Korean Neurosurgical Society
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• v.45 no.2
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• pp.81-84
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• 2009

Objective : Many biomechanical and clinical studies on adjacent segment degeneration (ASD) have addressed cranial segment. No study has been conducted on caudal segment degeneration after upper segment multiple lumbar fusions. This is a retrospective investigation of the L5-S1 segment after spinal fusion at and above L4-5, which was undertaken to analyze the rate of caudal ASD at L5-S1 after spinal fusion on and above L4-5 and to determine that factors that might have influenced it. Methods : The authors included 67 patients with L4-5, L3-5, or L2-5 posterior fusions. Among these patients, 28 underwent L4-5 fusion, 23 L3-5, and 16 L2-5 fusions. Pre- and postoperative radiographs were analyzed to assess degenerative changes at L5-S1. Also, clinical results after fusion surgery were analyzed. Results : Among the 67 patients, 3 had pseudoarthrosis, and 35 had no evidence of ASD, cranially and caudally. Thirteen patients (19.4%) showed caudal ASD, 23 (34.3%) cranial ASD, and 4 (6.0%) both cranial and caudal ASD. Correlation analysis for caudal ASD at L5-S1 showed that pre-existing L5-S1 degeneration was most strongly correlated. In addition, numbers of fusion segments and age were also found to be correlated. Clinical outcome was not correlated with caudal ASD at L5-S1. Conclusion : If caudal and cranial ASD are considered, the overall occurrence rate of ASD increases to 50%. The incidence rate of caudal ASD at L5-S1 was significantly lower than that of cranial ASD. Furthermore, the occurrence of caudal ASD was found to be significantly correlated with pre-existing disc degeneration.

• Phonetics and Speech Sciences
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• v.4 no.3
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• pp.13-23
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• 2012

The sound /w/ has been traditionally regarded as an independent segment in Korean regardless of the phonological contexts in which it occurs. There have been, however, some questions regarding whether it is an independent phoneme in /CwV/ context (cf. Kang 2006). The present pilot study examined how Korean /w/ is realized in $/S^*wV/$ context by performing some perception tests. Our assumption was that if Korean /w/ is a part of the preceding complex consonant like $/C^w/$, it should be more or less uniformly articulated and perceived as such. If /w/ is an independent segment, it will be realized with speaker variability. Experiments I and II examined the identification rates as "labialized" of the spliced original stimuli of $/S^*-V/$ and $/S^{w*}-^wV/$, and the cross-spliced stimuli $/S^{w*}-V/$ and $/S^*-^wV/$. The results showed that round qualities of /w/ are perceived at significantly different temporal point with speaker and context variability. We therefore conclude that /w/ in $/S^*wV/$ context is an independent segment, not a part of the preceding segment. Full-scale examination of the production test in the future should be performed to verify the conclusion we suggested in this paper.

• Elastomers and Composites
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• v.54 no.4
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• pp.271-278
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• 2019

Polyurethane elastomers (PUEs) were synthesized using trans-1,4-bis(isocyanatomethyl) cyclohexane (1,4-H₆XDI), poly(oxytetramethylene) glycol, 1,4-butanediol (BD), and 1,1,1-trimethylol propane (TMP). To control the molecular aggregation state and mechanical properties of these PUEs, hard segment contents of 20 and 30 wt% and BD/TMP ratios of 10/0 and 8/2 were chosen. Differential scanning calorimetry and small-angle X-ray scattering measurements revealed that the degree of microphase separation increased with an increase in both hard segment content and BD ratio. The Young's modulus and strain at break of the 1,4-H₆XDI-based PUE were 6-20 MPa and 5-15, respectively. Incorporation of 20% TMP as a cross-linking agent into BD increased the melting temperature of the hard segment chains, that is, heat resistance, and decreased the Young's modulus. This could be due to the low density of the physical cross-linking network and the dispersion of hard segment chains in the soft segment matrix in the PUE in the presence of 20% TMP.

• Journal of Korean Neurosurgical Society
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• v.46 no.4
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• pp.340-345
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• 2009

Objective : We investigated the locations of compressing vessels in hemifacial spasm. To approach compression sites, we described and evaluated the efficacy of the infranuchal infrafloccular (INIF) approach. Methods : A retrospective review of 31 consecutive patients who underwent microvascular decompression (MVD) through INIF with a minimum follow-up of 1 year was performed. Along the intracranial facial nerve, we classified the compression sites into the transitional zone (TRZ), the central nervous system (CNS) segment and the peripheral nervous system (PNS) segment. The INIF approach was used to inspect the CNS segment and the TRZ. Subdural patch graft technique was used in order to achieve watertight dural closure. The cranioplasty was performed using polymethylmethacrylate. The outcome and procedure-related morbidities were evaluated. Results : Twenty-nine patients (93%) showed complete disappearance of spasm. In two patients, the spasm was resolved gradually in 2 and 4 weeks, respectively. Late recurrence was noted in one patient (3%). The TRZ has been identified as the only compression site in 19 cases (61.3%), both the TRZ and CNS segment in 11 (35.5%) and the CNS segment only in 1 (3.2%). There was no patient having a compressing vessel in the PNS segment. Infection as a result of cerebrospinal fluid leak occurred in one patient (3%). Delayed transient facial weakness occurred in one patient. Conclusion : The TRZ and the CNS segment were more vulnerable area to the compression of vessels. We suggest that surgical avenue with the INIF approach provides early identification of this area.

• Journal of Korean Neurosurgical Society
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• v.42 no.3
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• pp.184-190
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• 2007

Objective : The authors retrospectively analyzed clinical and radiographic features of patients who developed symptomatic adjacent segment degeneration (ASD) that required re-operation. Methods : From 1995 to 2004, among 412 patients who underwent posterior lumbar fusion surgery, the authors experienced twenty-six patients who presented symptomatic ASD. Records of these patients were reviewed to collect clinical data at the first and second operations. Results : The patients were 9 males and 17 females whose mean age was $63.5{\pm}8.7$ years. Among 319 one segment and 102 multi-segment fusions, 16 and 10 patients presented ASD, respectively. Seventeen ASDs were noticed at the cephalad to fusion (65%), eight at the caudad (31%), and one at the cephalad and caudad, simultaneously (4%). All patients underwent decompression surgery. Nine patients underwent additional fusion surgeries to adjacent degenerated segments. In 17 patients who underwent only decompression surgery without fusion, the success rate was 82.4%. In fusion cases. the success rate was observed as 55.5%. There were no statistically significant factors to be related to development of ASD. However, in cases of multi-level fusion surgery, there was a tendency toward increasing ASD. Conclusion : Multi-segment fusion surgery could be associated with a development of ASD. In surgical treatment of symptomatic ASD, selective decompression without fusion may need to be considered as a primary procedure, which could reduce the potential risk of later occurrence of the other adjacent segment disease.

• Proceedings of the Korean Fiber Society Conference
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• 1998.04a
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• pp.5-8
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• 1998

Polyurethane elastomers are segmented cocoplymer with an [HS]n-type structure. Typically, these materials are two-phase systems, prepared from relatively polar and stiff component called the hard segment(H) and relatively flexible component known as the soft segment(S). Diisocyanate and chain extender together form the hard segment, which is dispersed within a matrix of the soft segment, composed of the macrodiolos.(omitted)

• Journal of Korean Neurosurgical Society
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• v.58 no.1
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• pp.54-59
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• 2015

Objective : The aim of this prospective study was to evaluate the efficacy of bone cement-augmented percutaneous short segment fixation for treating Kummell's disease accompanied by severe osteoporosis. Methods : From 2009 to 2013, ten patients with single-level Kummell's disease accompanied by severe osteoporosis were enrolled in this study. After postural reduction for 1-2 days, bone cement-augmented percutaneous short segment fixation was performed at one level above, one level below, and at the collapsed vertebra. Clinical results, radiological parameters, and related complications were assessed preoperatively and at 1 month and 12 months after surgery. Results : Prior to surgery, the mean pain score on the visual analogue scale was $8.5{\pm}1.5$. One month after the procedure, this score improved to $2.2{\pm}2.0$ and the improvement was maintained at 12 months after surgery. The mean preoperative vertebral height loss was $48.2{\pm}10.5%$, and the surgical procedure reduced this loss to $22.5{\pm}12.4%$. In spite of some recurrent height loss, significant improvement was achieved at 12 months after surgery compared to preoperative values. The kyphotic angle improved significantly from $22.4{\pm}4.9^{\circ}$ before the procedure to $10.1{\pm}3.8^{\circ}$ after surgery and the improved angle was maintained at 12 months after surgery despite a slight correction loss. No patient sustained adjacent fractures after bone cement-augmented percutaneous short segment fixation during the follow-up period. Asymptomatic cement leakage into the paravertebral area was observed in one patient, but no major complications were seen. Conclusion : Bone cement-augmented percutaneous short segment fixation can be an effective and safe procedure for Kummell's disease.

• Journal of Korean Ophthalmic Optics Society
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• v.6 no.1
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• pp.119-124
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• 2001

Dimethyl terephthalate (DMT). 1.4-butanediol (1.4-BD) and poly (tetramethylene ether) glycol (PTMG) in the molecular weight of 2000 (g/mol) were used to synthesize poly(ether-b-ester) thermoplastic elastomers (TPEEs). The final copolymers were annealed to improve thermal stability at elevated temperatures and mechanical properties. This study showed that as the proportion of soft segment increases melting temperature and degree of crystallinity of TPEEs decrease constantly. In case of mechanical properties like flexural strength and flexural elastic modulus. $35-PTMG^{2000}$ indicates the highest values due to more efficient physical interlock.