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      • KCI등재후보

        경추 추간판 전치환술과 단독 Cage를 이용한 경추 전방고정술의 임상적, 방사선학적 비교 분석

        김범준,서중근,조태형,태현석 대한척추신경외과학회 2009 대한척추신경외과학회지 Vol.6 No.1

        Objective: Total intervertebral disc replacement is designed to preserve motion and avoid limitations of fusion after removing local pathology. The authors report the results of a signle-center study to determine functional and radiologic outcomes associated with cervical total disc replacement versus those of cervical fusion. Methods: We retrospectively reviewed the charts and radiographs of patients who underwent a total intervertebral disc replacement (TDR) or a single-level anterior cervical fusion (ACDF) between January 1, 2004, and September 31, 2007. Clinical symptom was assessed using the Visual Analog Scale (VAS) of the neck and of the arm pain. Range of motion was determined by radiologic assessment of flexion-extension radiographs. Data were collected before surgery and at 6 weeks, 3, 6, 12, and 24 months after surgery. Result: A total of 125 patients were identified with 63 having TDR (43 males and 20 females) and 62 having fusion (42 males and 20 females). The average age was 49.1 years (TDR) and 51.7 years (ACDF) (p=0.229). The mean neck pain VAS before surgery was 6.52 (TDR) and 6.61 (ACDF)(p=0.732). At 2-year follow-up, the average neck pain VAS for the TDR group was 1.59 and ACDF 1.85(p=0.168). The mean arm pain VAS before surgery was 6.37 (TDR) and 6.60 (ACDF)(p=0.335). At 2 years: 1.41 (TDR) and 1.65 (ACDF)(P = 0.148). More motion (an average of 9.00° at 24 months) was retained after surgery in the TDR group than the fusion group at the treatment level. There was no significant difference in motion at adjacent levels. Conclusion: Total disc replacement maintained physiological segmental motion at the 2-year follow-up. The finding that there was no statistically significant difference between the groups in motion at adjacent levels must be verified on further studies. Objective: Total intervertebral disc replacement is designed to preserve motion and avoid limitations of fusion after removing local pathology. The authors report the results of a signle-center study to determine functional and radiologic outcomes associated with cervical total disc replacement versus those of cervical fusion. Methods: We retrospectively reviewed the charts and radiographs of patients who underwent a total intervertebral disc replacement (TDR) or a single-level anterior cervical fusion (ACDF) between January 1, 2004, and September 31, 2007. Clinical symptom was assessed using the Visual Analog Scale (VAS) of the neck and of the arm pain. Range of motion was determined by radiologic assessment of flexion-extension radiographs. Data were collected before surgery and at 6 weeks, 3, 6, 12, and 24 months after surgery. Result: A total of 125 patients were identified with 63 having TDR (43 males and 20 females) and 62 having fusion (42 males and 20 females). The average age was 49.1 years (TDR) and 51.7 years (ACDF) (p=0.229). The mean neck pain VAS before surgery was 6.52 (TDR) and 6.61 (ACDF)(p=0.732). At 2-year follow-up, the average neck pain VAS for the TDR group was 1.59 and ACDF 1.85(p=0.168). The mean arm pain VAS before surgery was 6.37 (TDR) and 6.60 (ACDF)(p=0.335). At 2 years: 1.41 (TDR) and 1.65 (ACDF)(P = 0.148). More motion (an average of 9.00° at 24 months) was retained after surgery in the TDR group than the fusion group at the treatment level. There was no significant difference in motion at adjacent levels. Conclusion: Total disc replacement maintained physiological segmental motion at the 2-year follow-up. The finding that there was no statistically significant difference between the groups in motion at adjacent levels must be verified on further studies.

      • 1P-73 : Water-gel for gating graphene transistors

        김범준,강문성,조정호 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

        Water, the primary electrolyte in biology, attracts significant interest as an electrolyte-type dielectric material for transistors compatible with biological systems. Unfortunately, the fluidic nature and low ionic conductivity of water prevents its practical usage in such applications. Here, we describe the development of a solid state, megahertzoperating, water-based gate dielectric system for operating graphene transistors. The new electrolyte systems were prepared by dissolving metal-substituted substituted DNA polyelectrolytes into water. The addition of these biocompatible polyelectrolytes induced hydrogelation to provide solid-state integrity to the system. They also enhanced the ionic conductivities of the electrolytes, which in turn led to the quick formation of an electric double layer at the graphene/electrolyte interface that is beneficial for modulating currents in graphene transistors at high frequencies. At the optimized conditions, the Na-DNA watergel- gated flexible transistors and inverters were operated at frequencies above 1 MHz and 100 kHz, respectively.

      • 1LA-1 : Design of electroactive materials for improving mechanical and thermal stabilities in efficient polymer solar cells

        김범준 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

        The long-term stabilities of polymer solar cells (PSCs) are key requirements for commercialization, but progress has been limited in this area. Most PSCs are not stable as subsequent exposure to heat which drives further macrophase separation at the micrometer scale and environmental stress that causes the mechanical failure at the weak interfaces of the PSCs. Here, we present various molecular designs of electroactive polymers to improve the thermal stability of PSCs. For example, we developed a series of well-defined poly(3-hexylthiophene)-graft-poly (2-vinylpyridine) (P3HT-g-P2VP) copolymers, in which the P2VP chains had different molecular weights. P3HT-g-P2VP polymers can be used as efficient compatibilizers in the active layer of PSCs and can modify the sharp interface between polymer donors and fullerenes, resulting in a dramatic enhancement of thermal stabilities and the mechanical properties of PSCs. In the second part of talk, a template approach is presented for the fabrication of semiconducting polymer blend thin films that combine the properties of electrical conductivity and enhanced stability. Nanometer-sized monodisperse polystyrene nanospheres (PS NSs) were designed as an opal template for the formation of three-dimensionally continuous PEDOT:PSS films. The resultant films were successfully applied as an anode buffer layer to produce highly-efficient PSCs with improved ambient stability. Furthermore, the PS NSs can be used as interfacial modifiers and binders in the PEDOT:PSS film, which resulted in the enhancement of mechanical durability of the PSCs.

      • 1P-74 : Understanding the impact of device geometry on operation of coplanar gated graphene transistors

        김범준,강문성,조정호 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

        In this manuscript, our intension is to analysis delay of phase angle and change of charge density by different geometry factor; namely, the switching speed of the coplanar-gated graphene FETs should be changed by the different geometry factor even when device mobility of the semiconductor is almost same value; it is the geometry factor that would determine the frequency limits for these type of devices.

      • KCI등재

        Reducible oxide (CeO2, ZrO2, and CeO2-ZrO2) promoted Ni-MgO catalysts for carbon dioxide reforming of methane reaction

        김범준,전경원,나현석,이열림,안선용,김경진,장원준,심재오,노현석 한국화학공학회 2020 Korean Journal of Chemical Engineering Vol.37 No.7

        Ni-MgO catalysts have been widely applied for carbon dioxide reforming (CDR) reaction due to their ability of anti-carbon formation. However, activation of Ni-MgO catalyst consumes considerable energy because of its very low reducibility. In this study, ZrO2, CeO2, and CeO2-ZrO2 promoted Ni-MgO catalysts were prepared via a facile coprecipitation method and applied to the CDR reaction. Among the prepared catalysts, the ZrO2-promoted Ni-MgO catalyst showed the highest methane conversion. The high catalytic performance of the ZrO2-promoted Ni-MgO catalyst is mainly due to easier reducibility, high Ni dispersion, and high specific surface area.

      • SCOPUSKCI등재

        Spin-coating법에 의한 $TiO_2$의 광촉매 효율

        김범준,변동진,이중기,박달근,Kim, Beom-Jun,Byeon, Dong-Jin,Lee, Jung-Gi,Park, Dal-Geun 한국재료학회 2000 한국재료학회지 Vol.10 No.4

        TiO$_2$thin films were prepared on the glass by a conventional spin coating method with $TiO_2$ sol(30wt%, anatase). The thickness of the thin films were controlled by the number of coating cycles: one cycle is composed of spin coating, drying, and heating process. The reaction rate of the film was obtained by the photodecomposition of gaseous benzene under 0.44 and 2.0mW/$\textrm{cm}^2$ UV light on the film surface. For an incident UV light intensity of 0.44mW/$\textrm{cm}^2$, the reaction rate was increased with the thickness of the film, caused by extent of surface area, but there was no change over the thickness of about 4$\mu\textrm{m}$. The porous $TiO_2$ thin film has comparatively vast effective surface area, which under relatively high-intensity UV illumination causes the reaction rate to be controlled by the film thickness. $TiO_2$sol(30wt%, anatase)을 이용하여 스핀코팅으로 유리기판에 $TiO_2$박막을 제조하였다. 박막의 두께는 코팅주기의 횟수가 조절하였다. 한 코팅주기는 스핀코팅, 건조, 열처리를 포함한다. 박막의 반응성은 막 위에서의 자외선강도가 0.44와 2.mW/$\textrm{cm}^2$인 조건에서 벤젠기체의 광분해 속도를 통해 조사하였다. 박막의 두께가 증가할수록 표면적으로 증가로 인해 반응성은 증가하였으며, 0.44mW/$\textrm{cm}^2$일 때 4$\mu\textrm{m}$정도 이상의 두께에서 반응성은 더 이상 증가되지 않았다. porous한 $TiO_2$박막은 비교적 넓은 유효표면적을 가지고 있으며, 그것은 비교적 높은 자외선 강도하에서 박막두께에 따라 반응속도를 증가시키는 결과를 낳았다.

      • KCI등재

        Potential Biomarkers to Improve the Prediction of Osteoporotic Fractures

        김범준,이승헌,고정민 대한내분비학회 2020 Endocrinology and metabolism Vol.35 No.1

        Osteoporotic fracture (OF) is associated with high disability and morbidity rates. The burden of OF may be reduced by early identification of subjects who are vulnerable to fracture. Although the current fracture risk assessment model includes clinical risk factors(CRFs) and bone mineral density (BMD), its overall ability to identify individuals at high risk for fracture remains suboptimal. Efforts have therefore been made to identify potential biomarkers that can predict the risk of OF, independent of or combined withCRFs and BMD. This review highlights the emerging biomarkers of bone metabolism, including sphongosine-1-phosphate, leucinerich repeat-containing 17, macrophage migration inhibitory factor, sclerostin, receptor activator of nuclear factor-κB ligand, andperiostin, and the importance of biomarker risk score, generated by combining these markers, in enhancing the accuracy of fractureprediction.

      • KCI등재

        재전송 타임아웃이 TCP 성능에 미치는 영향과 완화 방안들의 모델링을 통한 성능 분석

        김범준,김석규,이재용 한국통신학회 2004 韓國通信學會論文誌 Vol.29 No.7B

        TCP 처리율(throughput) 저하의 가장 큰 원인인 재전송 타임아웃(retransmission timeout)을 사전에 방지하기 위한 많은 노력들이 진행되어 왔다. TCP 손실 복구 알고리듬 자체의 오 동작으로 발생하는 타임아웃의 원인은 크게 세 가지로 분류될 수 있다. 현재 가장 널리 사용되고 있는 TCP Reno의 동일한 윈도우께서 발생한 여러 개의 패킷 손실로 인한 타임아웃은 TCP NewReno 혹은 선택 승인(selective acknowledgement) 옵션을 통해서 방지할 수 있고, 윈도우의 크기가 작은 상황에서 중복 승인 패킷(duplicate acknowledgement)의 부족으로 인해서 발생하는 패킷 손실은 제한 전송(Limited Transmit) 기법에 의해서 방지할 수 있다. 본 논문에서는 TCP 타임아웃이 발생하는 상황과 이를 완화하기 위한 방안들로 인한 개선 정도를 정확한 모델링을 통한 수학적 분석과 시뮬레이션을 통해서 비교 분석한다. 본 논문의 결과를 토대로 앞으로 사용할 TCP의 패킷 손실 정도에 따른 손실 복구(loss recovery)성능을 정량적으로 분석하고 예측하는 것이 가능하다. TCP의 성능은 손실 복구 과정의 성능에 크게 좌우된다는 점을 고려할 때 이는 매우 큰 중요성을 가진다. There have been several efforts to avoid unnecessary retransmission timeouts (RTOs), which is the main cause for TCP throughput degradation. Unnecessary RTOs can be classified into three groups according to their cause. RTOs due to multiple packet losses in the same window for TCP Reno, the most prevalent TCP version, can be avoided by TCP NewReno or using selective acknowledgement (SACK) option. RTOs occurring when a packet is lost in a window that is not large enough to trigger fast retransmit can be avoided by using the Limited Transmit algorithm. In this Paper, we comparatively analyze these schemes to cope with unnecessary RTOs by numerical analysis and simulations. On the basis of the results in this paper, TCP performance can be quantitatively predicted from the aspect of loss recovery probability. Considering that overall performance of TCP is largely dependent upon the loss recovery performance, the results shown in this paper are of great importance.

      • 2SD-2 : Architectural engineering of rod-coil compatibilizers for producing mechanically and thermally stable polymer solar cells

        김범준 한국공업화학회 2014 한국공업화학회 연구논문 초록집 Vol.2014 No.1

        While most of high-efficiency polymer solar cells (PSCs) are made of bulk hetrojunction (BHJ) blends of conjugated polymers and fullerene derivatives, they inhere a significant morphological instability issue against the mechanical and thermal stress. Herein, we developed an architecturally new type of compatibilizer, poly(3-hexylthiophene)-graft-poly(2-vinylpyridine) (P3HT-g-P2VP) that effectively modifies the sharp interface of a BHJ layer comprised of a P3HT donor and various fullerene acceptors, resulting in a dramatic enhancement of mechanical and thermal stabilities. We directly measured the mechanical properties of active layer thin films without a supporting substrate for the first time by floating a thin film on water, and the enhancement of mechanical stability without loss of the electronic functions of PSCs were successfully demonstrated. Supramolecular interactions between the P2VP of the P3HT-g-P2VP polymers and the fullerenes generated their universal use as compatibilizers regardless of the type of fullerene acceptors, including mono- and bis-adduct fullerenes, while maintaining their high device efficiency. Most importantly, the P3HT-g-P2VP copolymer had better compatibilizing efficiency than linear type P3HT-b-P2VP with much enhanced mechanical and thermal stabilities. The graft architecture promotes preferential segregation at the interface, resulting in broader interfacial width and lower interfacial tension as simulated by molecular dynamics model. Both the experiments and computational simulations consistently supported that the graft architecture is beneficial for the design of compatiblizers for enhancing the stabilities of highly efficient PSCs.

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