• Journal of Korean Neurosurgical Society
• /
• 제37권3호
• /
• pp.207-212
• /
• 2005

Objective: Classically, single photon emission tomography is known to be the reference standard for evaluating the hemodynamic status of patients with moyamoya disease. Recently, T2-weighted perfusion magnetic resonance(MR) imaging has been found to be effective in estimating cerebral hemodynamics in moyamoya disease. We aim to assess the utility of perfusion-weighted MR imaging for evaluating hemodynamic status of moyamoya disease. Methods: The subjects were fourteen moyamoya patients(mean age: 7.21 yrs) who were admitted at our hospital between Sep. 2001 to Sep 2003. Four normal children were used for control group. Perfusion MR imaging was performed before any treatment by using a T2-weighted contrast material-enhanced technique. Relative cerebral blood volume(rCBV) and time to peak enhancement(TTP) maps were calculated. Relative ratios of rCBV and TTP in the anterior cerebral artery(ACA), middle cerebral artery(MCA) and basal ganglia were measured and compared with those of the posterior cerebral artery(PCA) in each cerebral hemispheres. Using this data, we analysed the hemodynamic aspect of pediatric moyamoya disease patients in regarding to the age, Suzuki stage, signal change in FLAIR MR imaging, and hemispheres inducing symptoms. Results: The mean rCBV ratio of ACA, MCA did not differ between normal children and moyamoya patients. However the significant TTP delay was observed at ACA, MCA territories (mean = 2.3071 sec, 1.2089 see, respectively, p < 0.0001). As the Suzuki stage of patients is advanced, rCBV ratio is decreased and TTP differences increased. Conclusion: Perfusion MR can be applied for evaluating preoperative cerebral hemodynamic status of moyamoya patients. Furthermore, perfusion MR imaging can be used for determine which hemisphere should be treated, first.

• Journal of Korean Neurosurgical Society
• /
• 제29권7호
• /
• pp.929-934
• /
• 2000

Objective : The results of secondary transsphenoidal surgery(TSS) for either residual or recurring pituitary adenomas have been reported to be unfavorable. To evaluate the effectiveness of secondary TSS, we analyzed the surgical results of residual or recurred pituitary adenomas in patients who underwent secondary TSS from 1992 to 1998. Material and Methods : Among the 95 patients who underwent TSS during this period, 14(15%) received repeated TSS. Two of the 14 patients underwent three TSS. Among the 11 patients with pituitary adenomas, three had nonfunctioning tumors ; six prolachnomas ; two GH-secreting adenomas. The remaining three patieats had craniopharyngioma, pituitary abscess and hemangioendothelioma respectively. The interval between the two surgical procedures ranged from one week to 33 months(mean ; 12 months). Causes of the secondary TSS were tumor recurrence in 11 patients, intentional staged operation in three, persistent disease despite medical therapy and CSF leak after initial operation in one respectively. Treatments prior to secondary TSS were medical treatment only in eight patients. Results : During the repeated operationtss some adhesion was noted in septal mucous membrane. The sphenoid cavity was filled with fibrous tissue which correlated with the methods of reconstruction of the sellar floor at the previous operation. There was no statistically significant difference in success rate of surgery between the initial and the second TSS(86% vs 81%). The complication rate was similar between the two procedures. There was no statistically significant factors affecting the results of second TSS. Conclusion : Transsphenoidal reoperation was regarded as a suitable approach for treating recurrent pituitary adenomas in spite of some degree of operative difficulties. In patients with transsphenoidally resectable tumor residuals or recurrences confirmed by magnetic resonance imaging, remissions can be obtained with high probability, especially in secondary surgery after an staged decompression.

• Advances in materials Research
• /
• 제5권4호
• /
• pp.279-298
• /
• 2016

Present disquisition proposes an analytical solution method for exploring the buckling characteristics of porous magneto-electro-elastic functionally graded (MEE-FG) plates with various boundary conditions for the first time. Magneto electro mechanical properties of FGM plate are supposed to change through the thickness direction of plate. The rule of power-law is modified to consider influence of porosity according to two types of distribution namely even and uneven. Pores possibly occur inside FGMs due the result of technical problems that lead to creation of micro-voids in these materials. The variation of pores along the thickness direction influences the mechanical and physical properties. Four-variable tangential-exponential refined theory is employed to derive the governing equations and boundary conditions of porous FGM plate under magneto-electrical field via Hamilton's principle. An analytical solution procedure is exploited to achieve the non-dimensional buckling load of porous FG plate exposed to magneto-electrical field with various boundary condition. A parametric study is led to assess the efficacy of material graduation exponent, coefficient of porosity, porosity distribution, magnetic potential, electric voltage, boundary conditions, aspect ratio and side-to-thickness ratio on the non-dimensional buckling load of the plate made of magneto electro elastic FG materials with porosities. It is concluded that these parameters play remarkable roles on the dynamic behavior of porous MEE-FG plates. The results for simpler states are confirmed with known data in the literature. Presented numerical results can serve as benchmarks for future analyses of MEE-FG plates with porosity phases.

• Journal of Astronomy and Space Sciences
• /
• 제29권1호
• /
• pp.23-31
• /
• 2012

Thermal analysis and control design are prerequisite essential to design the satellite. In the space environment, it makes satellite survive from extreme hot and cold conditions. In recent years CubeSat mission is developed for many kinds of purpose. Triplet Ionospheric Observatory (TRIO)-CubeSat for Ion, Neutral, Electron, MAgnetic fields (CINEMA) is required to weigh less than 3 kg and operate on minimal 3 W power. In this paper we describe the thermal analysis and control design for TRIO-CINEMA mission. For this thermal analysis, we made a thermal model of the CubeSat with finite element method and NX6.0 TMG software is used to simulate this analysis model. Based on this result, passive thermal control method has been applied to thermal design of CINEMA. In order to get the better conduction between solar panel and chassis, we choose aluminum 6061-T6 for the material property of standoff. We can increase the average temperature of top and bottom solar panels from $-70^{\circ}C$ to $-40^{\circ}C $ and decrease the average temperature of the magnetometer from $+93^{\circ}C$ to $-4^{\circ}C$ using black paint on the surface of the chassis, inside of top & bottom solar panels, and magnetometer.

• Journal of Korean Neurosurgical Society
• /
• 제30권3호
• /
• pp.366-370
• /
• 2001

Objective : The authors present three cases of brain tumors in which epidural hematomas(EDHs) were developed postoperatively in the remote areas from craniotomy sites. The preventive tactics as well as possible mechanisms of development of remote EDH are discussed. Material and Methods : The magnetic resonance imagings of three patients revealed a left lateral ventricular mass located just aside of foramen Monro in a 27-year-old male, a large cystic mass in the temporal lobe in a 35-year-old male, and a partially calcified pineal mass in a 27-year-old male patient. The surgical removals of these tumors were performed without any noticeable events during surgery via left frontal transcortical transventricular approach for lateral ventricular tumor, left temporal craniotomy for cystic temporal tumor, and right occipital transtentorial approach for pineal tumor. Results : Postoperative EDHs remote from the sites of craniotomy were detected by the immediate postoperative computerized tomographic scans. We obtained good outcomes without any morbidity in all three patients with emergent evacuation of the hematoma. The pathologic diagnoses were lateral ventricular ependymoastrocytoma, temporal craniopharyngioma and mixed germinoma of the pineal region. Conclusion : It is postulated that a sudden reduction of intracranial pressure(ICP) at the time of tumor removal may strip the dura from the inner table of the skull to cause EDH from the remote site of craniotomy. Gradual reduction of ICP with slow drainage of cerebrospinal fluid before tumor removal as well as lowering the head position of patient during surgery might be helpful for preventing this unusual complication.

• 자원리싸이클링
• /
• 제12권6호
• /
• pp.8-12
• /
• 2003

본 논문에서는 최근 고품위 TV 및 고정세도 디스플레이용으로 화상의 정세도를 향상시키기 위해 수평주파수를 높이려는 움직임이 있어, 편향 요크용 페라이트 코아에는 고주파수 영역에 있어서도 코아로스가 낮은 재료가 요구되고 있는 실정이다. Mg-Zn 페라이트에 있어서 화학조성 및 프로세스가 미세구조에 미치는 영향에 착안하여 저온 소결화를 하였다. 저손실인 Mg-Zn계 Ferrite에 Cu를 첨가하였다. MgO, ZnO, $Fe_2$$O_3$, CuO를 선택한 후 조성비의 변화를 두며 CuO를 MgO로 치환하였다. 이 시료를 $980∼1350^{\circ}C$까지 3시간 소결하였다. 측정은 투자율, 전력손실, 수축율, 코아로스를 측정하였다. 시료의 수축율을 개시하는 온도는 $900^{\circ}C$부근이며 Cu치환에 따라 수축율이 증가하였으며, Cu 치환에 따라 소성온도가 약 $-50∼-75^{\circ}C$ 낮아졌다.

• 한국재료학회지
• /
• 제21권1호
• /
• pp.67-71
• /
• 2011

La doped CuO-ZnO-$Al_2O_3$ powders are prepared by sol-gel method with aluminum isopropoxide and primary distilled water as precursor and solvent. In this synthesized process, the obtained metal oxides caused the precursor such as copper (II) nitrate hydrate and zinc (II) nitrate hexahydrate were added. To improve the surface areas of La doped CuO-ZnO-$Al_2O_3$ powder, sorbitan (z)-mono-9-octadecenoate (Span 80) was added. The synthesized powder was calcined at various temperatures. The dopant was found to affect the surface area and particle size of the mixed oxide, in conjunction with the calcined temperature. The structural analysis and textual properties of the synthesized powder were measured with an X-ray Diffractometer (XRD), a Field-Emission Scanning Electron Microscope (FE-SEM), Bruner-Emmett-Teller surface analysis (BET), Thermogravimetry-Differential Thermal analysis (TG/DTA), $^{27}Al$ solid state Nuclear Magnetic Resonance (NMR) and transform infrared microspectroscopy (FT-IR). An increase of surface area with Span 80 was observed on La doped CuO-ZnO-$Al_2O_3$ powders from $25m^2$/g to $41m^2$/g.

• 한국자기학회지
• /
• 제21권1호
• /
• pp.15-22
• /
• 2011

강자성체를 정밀해석하기 위해서는 포화자화 현상과 히스테리시스 현상을 모두 고려해 주어야만 한다. Preisach 모델링은 변화율이 심한 히스테리시스 현상을 매우 잘 표현해 낼 수 있는 수치모사 방법이다. 하지만 정자기 유한요소법과 Preisach 모델링을 사용한 자화해석 반복 과정에서 수렴성이 떨어진다는 큰 문제점을 가지고 있다. 특히 자화율의 기울기가 급격히 변화할 경우 수렴에 많은 문제점을 가지고 있다. 이러한 문제점은 일반적인 M-H 변수를 사용하지 않고, M-B 변수를 사용하면 해결할 수 있다. 본 논문에서는 일반적인 M-H를 이용한 Preisach 모델링의 평면 분포로부터 M-H 변수를 M-B 변수화 시키는 방법을 제안하고 있고, 2차원 정자기 유한요소법과 M-H, M-B 변수를 이용한 Preisach 모델링을 비교 분석하여 Preisach 모델링의 수렴성 문제를 해결하는 방법에 대해 기술하였다.

• E2M - 전기 전자와 첨단 소재
• /
• 제10권3호
• /
• pp.226-232
• /
• 1997

Ternary semiconductor $Al_{x}$G $a_{1-x}$ Sb crystals which have energy gap of 0.7eV-1.6 eV at room temperature according to the composition ratios were grown by the vertical Bridgman method. The characteristics of the crystals were investigated by XRD, HRTEM and Hall effect. The lattice constants of $Al_{x}$G $a_{1-x}$ Sb crystals were varied from 6.096A over .deg. to 6.135A over .deg. with the composition ratio x. The Hall effect of the $Al_{x}$G $a_{1-x}$ Sb crystals were measured by van der Pauw method with the magnetic field of 3 kilogauss at room temperature. The resistivities of Te-doped $Al_{x}$G $a_{1-x}$ Sb crystals were increased from 0.071 to 5 .OMEGA.-cm at room temperature according to the increment of the composition ratio x. The mobilies of $Al_{x}$G $a_{1-x}$ Sb crystals varied with the composition ratio x resulted in the following three different regions of GaSb-like (0.leq.x.leq.0.3), intermediate (0.3.leq.x.leq.0.4) and AlSb-like (0.4.leq.x.leq.l).q.l).q.l).q.l).

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• 제36권4호
• /
• pp.270-274
• /
• 2010

Introduction: Limited mouth opening is a representative clinical symptom of temporomandibular disorders (TMD) with anterior disc displacement without reduction (ADDWOR). Various treatment methods have been proposed for patients with ADDWOR. This study examined the clinical effectiveness of template therapy for patients with mouth opening difficulty due to the ADDWOR. Material and Methods: A total of 14 patients (female 12, male 2, average age: $29.1{\pm}14.4$), who had been treated in the template clinic, Sooncheonhyang University Bucheon Hospital, from January of 2006 to December of 2008, were enrolled in this study. The subjects were selected according to the following criteria: more than 2 weeks after the onset of locking, mouth opening range <35 mm, and confirmed ADDWOR without a synovial pathology by magnetic resonance imaging (MRI). All patients were treated with the template appliance, instructed to wear it while sleeping and exercise for at least 10 hours per day. The maximum mouth opening (MMO) range and pain recognition scores before and after template therapy were recorded and compared. A paired t-test and Wilcoxon's signed rank test were used for statistical analysis. Results: After the periodical follow up, significant improvement in the opening range was observed in the template treatment group. The average MMO range before treatment was $30.2{\pm}3.5mm$ and the average MMO after treatment and follow up was $47.1{\pm}4.7mm$. The mean amount of mouth opening increment was $16.9{\pm}5.4mm$ (P<0.01) and the pain recognition scores before and after treatment was also improved.(P=0.001) Conclusion: The template appliance proved to be efficient for the treatment of TMD with a closed lock and painful joint due to ADDWOR.