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기업 간 시장지배력의 양극화 확대와 이에 따른 통화정책 효과의 이질성 분석
조윤구,김보경,김현태 한국경제학회 2022 經濟學硏究 Vol.70 No.3
본고는 한국의 선도기업과 후발기업 간 시장지배력의 격차가 2000년대 중반 이후 지속적으로 확대되어 왔는지를 검증하고, 이러한 시장지배력 격차 확대로 인해 기업에 대한 통화정책 효과의 이질성이 심화 되었다는 실증 증거를 제시한다. 분석 결과는 다음과 같다. 첫째, 2000년대 중반 이후 기업 간 시장지배력의 격차는 지속적으로 확대된 것으로 나타났다. 산업별로 살펴보면 비제조업 부문에서이러한 격차 확대가 두드러진 것으로 나타났으며, 제조업의 경우에는 비교적 안정적인 흐름을 보였다. 둘째, 이러한 시장지배력 격차는 기업 간 통화정책 효과의이질성과 연관이 있는 것으로 나타났다. 본 결과는 지속적으로 확대된 기업 간 시장지배력 격차에 의해 기업에 대한 통화정책 효과의 이질성이 더욱 심화되어 왔을 가능성을 시사한다.
조윤구 대한영상의학회 1997 대한영상의학회지 Vol.37 No.3
Purpose:The purpose of this study was to evaluate the characteristics MR findings of intramedullary spinal cord tumors according to histologic diagnosis. Materials and Methods:MR images of 34 patients with surgically-proven intramedullary spinal cord tumor were retrospectively reviewed. Histologic diagnosis revealed 15 ependymomas, ten astrocytomas, three hemangioblastomas, two oligidendrogliomas, one malignant schwannoma, one glioblastoma multiforme, one neuroblastoma and one ganglioglioma. MR images were analyzed for location, size, shape, signal intensity, and degree and pattern of contrast enhancement of the tumors. Results:All tumors showed cord expansion and a varying extent of involvement ranging from 1.5 to 30cm. Variable degrees of contrast enhancement were seen in all cases. Cervical, cervico-thoracic, thoracic, and thoraco-lumbar spinal ependymomas accounted for three, two, six, and four cases, respectively, while four, two cases of cervical, cervico-thoracic, and thoracic spinal astrocytomas respectively, were seen. Other tumors were located most commonly in the thoracic spinal cord. A sharply-defined tumor margin was seen in 13 of 15 ependymomas, in all three gemangioblastomas, one neuroblastoma and one ganglioglioma. Tumors usually showed slightly low- or iso- signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Peritumoral cysts were seen in nine ependymomas, one hemangioblastoma, and one astrocytoma, while peritumoral hemorrhage was seen only in three ependymomas. Relatively homogeneous enhancement was seen in nine of 13 ependymomas, all hemangioblastomas and one neuroblastoma. All ten astrocytomas showed a poorly defined tumor margin and heterogeneous enhancement. Conclusion:On the basis of characteristics MR findings, intramedullary cord tumors may be histopathiologically diagnosed.
조윤구 대한영상의학회 1997 대한영상의학회지 Vol.37 No.5
Purpose : To compare the usefulness of echo-planar imaging(EPI) and fast spin-echo(FSE) in routine brain MRimaging. Materials and Methods : Twenty-five patients with various intracranial diseases were prospectivelyexamined with T2-weighted MR imaging on a 1.5T unit using FSE, spin echo singl-shot EPI(SS-EPI) and multi-shotEPI(MS-EPI) techniques. For qualitative assessment, overall image quality, discrimination between corticalgray-white matter and between basal ganglia-white matter, lesion conspicuity, image distortion andartifacts(motion, ghost, flow, and susceptibility) were all evaluated using a subjective scoring system rangingfrom 1 to 4 (1 for the worst and 4 for the best). For quantitative assessment, contrast and contrast-to-noiseratio(CNR) were calculated for cortical gray-white matter, basal ganglia-white matter, and lesion-white matter.Results : Overall image quality, discrimination between cortical gray-white matter, basal ganglia-white matter,and lesion-white matter, lesion conspicuity, image distortion and susceptibility artifacts showed the highestvalue in FSE and the lowest in SS-EPI. Motion artifacts were seen only in FSE, while flow and ghost artifacts weremost commonly seen in SS-EPI. Contrast and CNR of anatomical and pathologic structures showed the highest value inFSE, especially for cortical gray-white matter and basal ganglia-white matter . Conclusion : With regard tooverall image quality, image distortion, susceptibility artifacts, contrast and CNR, EPI is far inferior to FSE.In routine brain MR imaging., the usefulness of EPI techniques would therefore be very limited.