• Journal of Korean Neurosurgical Society
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• v.50 no.2
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• pp.134-138
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• 2011

The authors report a case of epidural and extraforaminal calcification caused by repetitive triamcinolone acetonide injections. A 66-year-old woman was admitted presenting with lower extremity weakness and radiating pain in her left leg. Ten months before admission, the patient was diagnosed as having an L4-5 spinal stenosis and underwent anterior lumbar interbody fusion followed by posterior fixation. Her symptoms had been sustained and she did not respond to transforaminal steroid injections. Repetitive injections (10 times) had been performed on the L4-5 level for six months. She had been taking bisphosphonate as an antiresorptive agent for ten months after surgery. Calcification in the ventral epidural and extraforaminal space was detected. The gritty particles were removed during decompressive surgery and these were proven to be a dystrophic calcification. The patient recovered from weakness and radiating leg pain. Repetitive triamcinolone acetonide injections after discectomy may be the cause of dystrophic calcification not only in the degenerated residual disc, but also in the posterior longitudinal ligament. Possible mechanisms may include the toxicity of preservatives and the insolubility of triamcinolone acetonide. We should consider that repetitive triamcinolone injections in the postdisectomy state may cause intraspinal ossification and calcification.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.106-113
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• 2008

The goal of crashworthiness is an optimized vehicle structure that can absorb the crash energy by controlled vehicle deformations while maintaining adequate space so that the residual crash energy can be managed by the restraint systems to minimize crash loads transfer to the vehicle occupants. Front side assembly is one of the most important energy absorbing components in relating to the crashworthiness design of vehicle. The structure and shape of the front side assemblies are different depending on auto-makers and size of vehicles. Thus, it is not easy to grab an insight on designer's intention when you glance at a new front side member without experiences. In this paper, we have performed the explicit nonlinear dynamic finite element analysis on the front side assembly of a passenger car to investigate the effect of thickness distribution of the front side assembly on the collapse shape, which is important in the aspect of controlling deformation to maintain adequate space, from the viewpoint of reverse engineering. To do this, we have performed crash FE analysis for the assembly by varying the thickness distribution of the assembly.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.118-128
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• 2017

In this study, we propose a real time inertial navigation system/global positioning system (INS/GPS) integrated smoothing algorithm based on an extended Kalman filter (EKF) and a position damping loop (PDL) for synthetic aperture radar (SAR). Integrated navigation algorithms usually induce discontinuities due to error correction update by the Kalman filter, which are as detrimental to the performance of SAR as the relative position error. The proposed smoothing algorithm suppresses these discontinuities and also reduces the relative position error in real time. An EKF estimates the navigation errors and sensor biases, and all the errors except for the position error are corrected directly and instantly. A PDL activated during SAR operation period imposes damping effects on the position error estimates, where the estimated position error is corrected smoothly and gradually, which contributes to the real time smoothing and small relative position errors. The residual errors are re-estimated by the EKF to maintain the estimation performance and the stability of the overall loop. The performance improvements were confirmed by Monte Carlo simulations. The simulation results showed that the discontinuities were reduced by 99.8% and the relative position error by 48% compared with a conventional EKF without a smoothing loop, thereby satisfying the basic performance requirements for SAR operation. The proposed algorithm may be applicable to low cost SAR systems which use a conventional INS/GPS without changing their hardware configurations.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.4
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• pp.601-613
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• 2017

An adjoint-based error estimation and mesh adaptation study is conducted for two-dimensional viscous flows on unstructured hybrid meshes. The error in an integral output functional of interest is estimated by a dot product of the residual vector and adjoint variable vector. Regions for the mesh to be adapted are selected based on the amount of local error at each nodal point. Triangular cells in the adaptive regions are refined by regular refinement, and quadrangular cells near viscous walls are bisected accordingly. The present procedure is applied to single-element airfoils such as the RAE2822 at a transonic regime and a diamond-shaped airfoil at a supersonic regime. Then the 30P30N multi-element airfoil at a low subsonic regime with a high incidence angle (${\alpha}=21deg.$) is analyzed. The same level of prediction accuracy for lift and drag is achieved with much less mesh points than the uniform mesh refinement approach. The detailed procedure of the adjoint-based mesh refinement for the multi-element airfoil case show that the basic flow features around the airfoil should be resolved so that the adjoint method can accurately estimate an output error.

• Journal of Astronomy and Space Sciences
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• v.29 no.1
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• pp.79-84
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• 2012

After a visit by Peter Waddell from the University of Strathclyde, Glasgow, UK in 1991, Robert H. Koch launched a program at the University of Pennsylvania to build lightweight pneumatic membrane mirrors, initially for balloon flight observations where weight is at a premium. Mirror cells were fabricated from sizes 0.18 m to 1.77 m, and experiments conducted to characterize the mirror figure and stability. Most of the work stopped after Prof. Koch's retirement in 1996 until 2006 when the authors expressed an interest in building an array of medium-aperture portable telescopes. The program restarted in earnest at Gravic, Inc. in Malvern, PA in 2008 with Koch using his extensive observational astronomy experience to guide the fabrication of a fully operational 1.07 m membrane mirror telescope with an optical tube assembly weighing under 45 Kg. Residual wavefront aberrations remediation resulted in Koch and the authors investigating membrane tensioning techniques with different cell designs, active secondary wavefront correction, photometric algorithms for aberrated images, and the use of additional lightweight mirror substrates from the Alt-Az Initiative Group, such as foamed glass. The best result for the lightweight mirrors was a point spread function spot size of several arc seconds. A lightweight 1.6 m cast aluminum cell alt-az telescope was subsequently designed by Koch and the authors for prime focus use.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1079-1086
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• 2008

During transfer alignment navigation information transferred MINS(master inertial navigation system) to SINS(slave inertial navigation system) has a changed time delay. The changed time delay degrades the performance of transfer alignment. This paper proposes an adaptive filter that estimates covariance of a time delay in real-time using residual of measurements. The performance of the adaptive filter is compared with that of the EKF(extended Kalman filter) in case of transfer alignment for vertical launcher in the ship. The results show that proposed method is more effective than EKF in estimating attitude errors.

• Smart Structures and Systems
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• v.26 no.1
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• pp.23-33
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• 2020

Majority of the damage in engineering structures is nonlinear. Damage sensitive features (DSFs) extracted by traditional methods from linear time series models cannot effectively handle nonlinearity induced by structural damage. A new DSF is proposed based on vector space cosine similarity (VSCS), which combines K-means cluster analysis and Bayesian discrimination to detect nonlinear structural damage. A reference autoregressive moving average (ARMA) model is built based on measured acceleration data. This study first considers an existing DSF, residual standard deviation (RSD). The DSF is further advanced using the VSCS, and then the advanced VSCS is classified using K-means cluster analysis and Bayes discriminant analysis, respectively. The performance of the proposed approach is then verified using experimental data from a three-story shear building structure, and compared with the results of existing RSD. It is demonstrated that combining the linear ARMA model and the advanced VSCS, with cluster analysis and Bayes discriminant analysis, respectively, is an effective approach for detection of nonlinear damage. This approach improves the reliability and accuracy of the nonlinear damage detection using the linear model and significantly reduces the computational cost. The results indicate that the proposed approach is potential to be a promising damage detection technique.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.10a
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• pp.15-20
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• 2000

In this paper. Thermally Stimulated Current spectra have been measured in the Polypy - romellitimide (polyimide). As a result of the investigation. three peaks have been observed: $A(50^{\circ}C)$, $B(120^{\circ}C)$, $C(200^{\circ}C)$. Among three peaks, C peak has been observed in detail. The C peak is shown to be created due to the polarization of ionic space charge from the experimental results which were measured as a function of forming time, forming temperature. forming voltage and collecting voltage. As a result, we have measured the TSC in ion ($Na^+$) implanted - Polyimide, also found the peak at $215^{\circ}C$. Therefore, TSC characteristics in the C peak is probably caused by residual impurity. And The activation energy caculated by means of initial rising method 1.8eV, hopping distance. $90{\AA}$. and the mobility. $2.88{\times}10^{-11}cm^2/v.s$

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.1
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• pp.52-57
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• 2007

One of the hot issues in composite patching is to reduce the thermal residual stresses between composite patch and aluminum surface which occurs after bonding of composite patch. In this study, the edge crack patching is adopted for different curing cycles. For the analysis, three layer Mindlin plate elements are used, and Paris' law is adopted to predict the fatigue life of composite patch plate. The analysis results show a good agreement with the experimental fatigue life and this technique can be applied for the prediction of fatigue life of aircraft structures.

• Journal of Astronomy and Space Sciences
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• v.20 no.1
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• pp.1-10
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• 2003

A precise kinematic orbit determination (P-KOD) procedure for Low Earth Orbiter(LEO) using the GPS ion-free triple differenced carrier phases is presented. Because the triple differenced observables provide only relative information, the first epoch's positions of the orbit should be held fixed. Then, both forward and backward filtering was executed to mitigate the effect of biases of the first epoch's position. p-KOD utilizes the precise GPS orbits and ground stations data from International GPS Service (IGS) so that the only unknown parameters to be solved are positions of the satellite at each epoch. Currently, the 3-D accuracy off-KOD applied to CHAMP (CHAllenging Min-isatellite Payload) shows better than 35 cm compared to the published rapid scientific orbit (RSO) solution from GFZ (GeoForschungsZentrum Potsdam). The data screening for cycle slips is a particularly challenging procedure for LEO, which moves very fast in the middle of the ionospheric layer. It was found that data screening using SNR (signal to noise ratio) generates best results based on the residual analysis using RSO. It is expected that much better accuracy are achievable with refined prescreening procedure and optimized geometry of the satellites and ground stations.