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      • 三次元 切削에서 切削力의 解析的 硏究

        鄭準基 弘益大學校 1982 弘大論叢 Vol.14 No.2

        The cutting forces on obique cutting with single cutting edge are investigated analytically, based on the thin shear zone model. To predict the three components of oblique cutting forces analytically, an experimental data of orthogonal cutting and cutting energy method are used. And the predicted results are in good agreement with the experimental results under the equivalent cutting conditions. The results obtained in this study are summerized as follows, 1.The cutting forces of the oblique cutting can be predicted analytically by applying energy method even if only orthogonal cutting data are in hand. 2.The analytical prediction of cutting forces on oblique cutting with single cutting edge is applicable to the double cutting edge model.

      • 小麥의 根毛에 關한 考察

        鄭濬 慶北大學校 1963 論文集 Vol.7 No.2

        It has been known by experiment that the root hair of a higher plants absorbs inorganic nutrient and water, and the importance of it also is recognized. But there are a few nucertain viewpoint about the living condition of root hair. In the course of studying root hair, especially the relation between the origin of root hair and nucleus, it is learned that when root hair growns 50μlong nucleus moves into root hair, but they are not correlative. And above the growth of root hair and the movement of nucleus, though it is said that there is any relation between them, the observation during the time between the origin of root hair and the full growth of it is rare, and so there seems not to be any unified point of view. The clear up there, I examined root hair by means of Triticum aestium L. and I. wiil report the outline of the experiments as following. The experiment shows that the origin of root hair can be recognized from the position of an average 2650μ. of the root including root cap. and in the result of comparing epidermal cell generating root hair with that not producing root hair, the length of the former is 176μ. and that of the latter 262μ. but a few epidermal cells producing root hair is comparatively longer than that not generating root hair. In eqidermal cell which produces root hair the position of producing root hair is located at the end of the root of the cell and shows polarity. That is, the length of epidermal cell producing root hair is average 176μ. while root hair is produced at the position of average 37μ. from the end of the cell. Though nucleus of epidermal cell, before root hair is produced, is locted in the enter of the cell, as root hair is begin to produced it gradually moves toward the base of toot hair. Until root hair grows to 50μ. of length nucleus moves on almost into the inside of root hair, then its movement completed at the length of 100μ. There seemed no regular relation between the position of which completed its movement into the insides of root hair and the length of root hair, and there are many differences of the position of each nucleus in the root hair of the same length.

      • KCI등재

        퇴적물 토양의 영양염류가 호소 수질에 미치는 잠재 요인 분석

        정준오,김영우,Jung,,Joon-Oh,Kim,,Young-Woo 한국환경보건학회 2009 한국환경보건학회지 Vol.35 No.5

        '스콜라' 이용 시 소속기관이 구독 중이 아닌 경우, 오후 4시부터 익일 오전 7시까지 원문보기가 가능합니다.

        The characteristics of Lake Cheonhoji water and sediment were investigated in oder to utilize these as fundamental materials for the management of lake water quality. The hydrographic properties of Lake Cheonhoji which are relatively low chance of nutrients loading from the watershed and a long retention time of lake water, lead to the probability of high lake productivity. It was also observed that lake water showed stratification during summer and complete mixing during fall, even though water depth was relatively shallow. The trophic state was eutrophic to hypertrophic from summer to late fall. The overall properties of the sediment were oligohumic, high ignition loss and high composition of NAIP and Resid.-P, which might serve as potential pollution sources of lake water quality. In laboratory scale experiments, it was observed that leaching potential of nutrients in the sediment was greatly dependant upon water temperature and dissolved oxygen. Finally, water pollution in Lake Cheonhoji was considered to be largely due to the adverse cycle of uncontrollable eutrophication, which resulted in the subsequent occurrence of dead algae and animal plankton, organic sedimentation, reduction of dissolved oxygen and nutrients leaching, which again reinforced the cycle of eutrophication in the lake.


        Preventive Effects of Zoledronic Acid on Bone Metastasis in Mice Injected with Human Breast Cancer Cells

        정준,이경선,최양규,오영주,이희대 대한의학회 2011 Journal of Korean medical science Vol.26 No.12

        Bisphosphonates are used routinely to reduce bone-related events in breast cancer patients with bone metastasis. We evaluated the effects of zoledronic acid, a third generation,nitrogen-containing bisphosphonate, to prevent bone metastasis in breast cancer. Zoledronic acid or vehicle alone was administered to nude mice either simultaneously or after intracardiac injection of human breast cancer MDA-MB-231 cells. Nude mice treated with zoledronic acid at early time points showed a lower incidence of bone metastases than did vehicle-treated nude mice, but these differences were not statistically significant. Only 37.5% of mice treated with zoledronic acid at the time of tumor cell inoculation developed bone metastases compared to over 51.8% of mice receiving vehicle alone (P = 0.304). Cell count of apoptosis confirmed by immunohistochemical staining in metastatic bone tissue significantly increased in the zoledronic acid-treated groups compared to non-treated group (1,018.3 vs 282.0; P = 0.046). However, metastatic tumor cells, which invade soft tissue around the bone, did not show extensive apoptosis;there were no differences between the zoledronic acid-treated and control groups. These results suggest that zoledronic acid increases apoptosis of metastatic breast tumor cells in the bone and could therefore reduce metastatic tumor burden. These results support the use of zoledronic acid to reduce the incidence of bone metastasis in breast cancer.

      • 채터의 검출에 관한 실험적 연구

        鄭準基 弘益大學校 1988 弘大論叢 Vol.20 No.2

        In this study, the method determining chatter threshold was investigated experimentally. For the exact discrimination of the chatter threshold, the variations of the tool acceleration, cutting force, horizontal deflection of the workpiece, vibration amplitude of the workpiece, and surface roughness of the finished workpiece surface at the chatter threshold were observed. Its critical value was determined by making a comparative study of abrupt changes of the above quantities. By the experimental study, the following results are obtained. The chatter threshold can be discriminated exactly by measuring the variation of the tool acceleration which reacts more sensitively than the above other methods. And the critical value of the tool acceleration was 0.4g at all the cutting condition used in this experiment.

      • 음향방출신호 감지에 의한 공구마모와 표면거칠기 사이의 관계 연구

        鄭準基 弘益大學校 科學技術硏究所 1993 科學技術硏究論文集 Vol.3 No.-

        AE signal contains the informations the information about what makes the machined surface roughness decrease and deviate from theoretical values. So, a properly designed AE sensing scheme should be used to investigate the surface finish at the on-line monitoring condition in precision machining On The other hand, any defect existing on the tools will deteriorate the surface finish and may cause the scrapping of the workpiece which waste the long cutting time and substantially reduce the efficiency. If the surface generation mechanisms can be related with the tool condition during the rough cutting stage of the start and the finishing stage, any malfunction of the tools or machines can be detected and also can be corrected before the final surface is generated by changing the tool or cutting conditions. In this reason, AE signals were sensed and analyzed using various signal processing technique to correlate the surface qualities with the tool wear conditions during the actual cutting condition.

      • 음향방출신호를 이용한 공구마모 감시에 관한 연구

        鄭準基,孟玟在 弘益大學校 科學技術硏究所 1994 科學技術硏究論文集 Vol.4 No.-

        Acoustic Emission signal can detect the state of tool wear and fracture in turning. In metal cutting process. AE signal is detected by AE sensor, then amplified and transmitted to analysing equipment. Experiments were performed in SM25C and STS304 steels at uniform feed-rate, cutting speed and depth of cut. The results of experimental data show apparently that the emission intensity is generated due to the growth of tool wear at the 165KHz, 200KHz in the SM25C and 140KHz, 165KHz, 200KHz in the STS304 respectively.

      • CNC 선반의 절삭력 제어를 위한 퍼지제어기의 적용

        鄭準基,徐永達 弘益大學校 科學技術硏究所 1998 科學技術硏究論文集 Vol.9 No.1

        Cutting conditions including depth of cut, feedrate, cutting speed, tool geometry, and setting angle are parameters that give significant effect to the cutting force in metal cutting operations. And the cutting force can be controlled to maintain constant value by combining and regulating these parameters. Generation of excessive cutting force and cutting heat can be restrained at the constant cutting force and then, we can achieve the progressive cutting stability and performance of machine-tool and tool itself. In this study, fuzzy control is introduced to determine proper feed-override. The application of fuzzy systems can simulate human experience, human intelligence, and experimental information for cutting processes, and can be used to control very complex and uncertain processes(including machining processes) such as multi input-multi output, and non-linearity, etc. Fuzzy algorithm of automatic feed-override regulation is also proposed to control cutting forces in CNC lathe turning. The experimental results reveal that the fuzzy controller is suitable to the regulating feed-override of AC servo-motor of CNC lathe.

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