• Tribology and Lubricants
• /
• 제22권2호
• /
• pp.59-65
• /
• 2006

In hard disk drives as the head to disk spacing continues to decrease to facilitate recording densities, slider disk interactions have become much more severe due to direct contact of head and disk surfaces in both start/stop and flying cases. The slider disk interaction in CSS (contact-start-stop) mode is an important source of particle generation and tribocharge build-up. The tribocharge build-up in the slider disk interface can cause ESD (electrostatic discharge) damage. In turn, ESD can cause severe melting damage to MR or GMR heads. The spindle speed of typical hard disk drives has increased in recent years from 5400 rpm to 15000 rpm and even higher speeds are anticipated in the near future. And the increasing disk velocity leads to increasing disk acceleration and this might affect the tribocharging phenomena of the slider/disk interface. We investigated the tribocurrent/voltage build-up generated in HDD, operating at increasing disk accelerations. In addition, we examined the effects with relative humidity conditions and rest time. We found that the tribocurrent/voltage was generated during pico-slider/disk interaction and its level was about $3\sim16pA$ and $0.1\sim0.3V$, respectively. Tribocurrent/voltage build-up was reduced with increasing disk acceleration. Higher humidity conditions $(75\sim80%)$ produced lower levels tribovoltage/current. Therefore, a higher tribocharge is expected at a lower disk acceleration and lower relative humidity condition. Rest time affected the charge build-up at the slider-disk interface. The degree of tribocharge build-up increased with increasing rest time.

• 실천공학교육논문지
• /
• 제13권2호
• /
• pp.327-332
• /
• 2021

교육용으로 사용되는 피삭재(소재)는 SM20C, Al6061, 아크릴 등의 소재를 사용한다. SM20C 소재는 탄소강으로서 자격증 시험 및 기능경기대회에서 많이 사용되지만 산업현장에서도 많이 사용된다. Al6061 소재는 탄소강에 비하여 경도가 낮아지고 전성(연성)이 강한 소재이기에 공구의 구성인선이 많이 발생하는 소재 라고 한다. 아크릴 소재를 이용하여 학생들에게 실습지도 하면 어느 부분에서 과다 절삭으로 인하여 진동이 발생하고 공구의 파손이 발생하는 소재이다. 이러한 과정에서 5축장비인 2NC헤드에게 가해지는 충격이 정밀도 제어에는 어느정도 영향을 줄 수 있는지 알아본다. 5축장비의 가장 취약한 부분은 AC축을 제어하는 헤드가 가장 약한 부분이라 할 수 있다. 이 부분의 정밀도 및 누적 공차가 발생할 경우 모든 제품의 정밀도가 떨어지는 현상이 발생한다. 따라서 2NC헤드의 핵심적인 부분, 스핀들 하우징은 Al7075 T6(미국 알코아사) 소재를 사용하고 전체 바디는 FCD450 (구상흑연주철) 사용하여 진행하였다. 이 두가지 소재에서 작용되는 진동 및 절삭 과정에서 힘을 극한조건에서 유한요소 해석으로 적용되는 값을 밝혀 내고자 해석을 진행하였다. 이러한 해석 데이터를 활용하여 학생들이 5축절삭 보다 5축 가공기의 구조를 보고 이해하는데 도움이 되기를 기대한다.

• 한국정밀공학회지
• /
• 제31권7호
• /
• pp.627-634
• /
• 2014

Machine tool vibration is well known for reducing machining accuracy. Because vibration response of a linear structure generally depends on its transfer function if the magnitude of excitation were kept constant, this study introduces a RET(Random Excitation Test) based on FRF method to evaluate stiffness of a prototype HDMTL(Heavy-Duty Multi-Tasking Lathe) for large crankshaft of marine engine. Firstly, two force loops of the lathe and corresponding structural loops were identified:1) workpiece - spindle - head stock - main bed, 2) workpiece - tool post - carriage bed. Secondly, compliances of each structural loop were measured respectively using RET with a hydraulic exciter and then converted into stiffness. Finally, the measured stiffness was compared with that obtained previously by FEM analysis. As the result, both measured and computed stiffness were closely in agreement with each other. And the prototype HDMTL has evidently sufficient rigidity above ordinary heavy-duty lathes.

• 대한세포병리학회지
• /
• 제9권2호
• /
• pp.241-244
• /
• 1998

Lipoblastoma is a rare benign neoplasm occurring exclusively in children below the age of three years. It affects chiefly the upper and lower extremities, and less commonly head and neck area, trunk, mediastinum, mesentery, and retroperitoneum. We present two cases of lipoblastoma occurring in the mediastinum of a 21-month-old boy and in the back of a 15-month-old boy. The characteristic features of Fine needle aspiration cytology smears were the presence of immature fat cells in the form of spindle-shaped cells, stellate cells and vacuolated lipoblasts along with lipocytes against a myxomatous background. Two tumors were histologically confirmed to be lipoblastomas. Lipoblastoma can be cytologically diagnosed by considering the cytologic findings and the age of the patient.

• 대한세포병리학회지
• /
• 제14권2호
• /
• pp.96-101
• /
• 2003

Synovial sarcoma is a rare soft tissue tumor accounting for 5-10% of soft tissue sarcomas. Most arise in the extremities and trunk, and a small proportion occur in the abdominal wall, head and neck legion, and mediastinum. It manifests different phenotypic subtypes that render their cytologic evaluation challenging. Moreover, cytomorphologic description of the epithelial component of synovial sarcoma is rare in Korea. We report a case of biphasic synovial sarcoma on the right lower extremity in a 49-year-old woman diagnosed by fine needle aspiration cytology. The aspirate was moderately cellular and composed of a mixture of tissue fragments and dissociated cells with bland chromatin, inconspicuous nucleoli, and oval to spindle-shaped cytoplasm. Mitosis was rare. A monolayer sheet of epithelial component was seen. The cells in this monolayer sheet had more abundant distinct cytoplasm, round nuclei, and prominent micronucleoli. Histologic examination showed a biphasic pattern consisting of mostly sarcomatous stroma and a few small glandular areas at the periphery of the tumor.

• 한국생산제조학회지
• /
• 제7권4호
• /
• pp.96-103
• /
• 1998

With the advance of processing technology , so as to spare fuel, piston heads used in automobile reciprocating engine have complex 3-dimension, with respect to shape such as ovality, profile, eccentricity, offset, recess. Therefore, coming out of the existing process work used master cam. the process work is performed using a CNC lathe. For a precision processing, the processing work is need to make study of high speed feed gear synchronized with the rotative speed of main spindle. And then the high speed feeding system must maintain high dynamic stiffness, high speed and high positioning accuracy . In this paper, in order to achieve high speed cutting tool feeding. The linear brushless DC motor is used for satisfying this process work. The ball bush and turicite is used as the guidance of the feed gear system. Also linear encoders, digital servo amplifiers and controller are used for controlling driving motor. This paper presents the design and simulation of the new tool feed system for noncircular machining.

• Archives of Plastic Surgery
• /
• 제36권4호
• /
• pp.500-502
• /
• 2009

Purpose: Cutaneous lipomatous neurofibroma is a rare variant of neurofibroma. Histologically, it includes adipose tissue. As far as we aware, only 11 cases of this variant were reported which was predominantly on head, neck and trunk, so we present a case of left pretibial area with literature review. Method: A 17 - year old female who showed a non - tender, protruding $4{\times}4{\times}2cm$ sized mass on the left pretibial area for several months. We totally excised the mass including skin and the subcutaneous fat layer. Results: Pathologic report showed cutaneous lipomatous neurofibroma which was well circumscribed and noncapsulated neoplasm present with focal fatty change. Adipose cells were entrapped in the whirls of spindle cells. There were no lipoblasts or atypical adipocytes. Conclusion: A cutaneous lipomatous neurofibroma on the lower extremity is very rare. In our patient, there were no trauma - related histopathologic changes. Therefore, focal fatty change can be a consequence of metaplasia from multipotential neural cells after migration.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• 제28권6호
• /
• pp.484-487
• /
• 2002

Leiomyoma is a benign smooth muscle tumor that usually arise in the uterus, skin and gastrointestinal system. Only 2 percent are located in the head and neck. Leiomyomas of oral cavity are uncommon as only two cases have been reported in the Korean literature. The common location of oral cavity has been tongue, but other sites include buccal mucosa, lips, palate. mouth floor, and gingiva. Our patient was 30 years old female who complained of swelling and discomfort in the mouth floor. Microscopically this tumor showed bundles of intertwining spindle cells within fibrous connective tissue stroma. The nuclei were generally pale staining and blunt ended. Masson's trichrome stain was positive for muscle, and immunohistochemical study for ${\alpha}$-smooth muscle actin revealed strong positivity. It was treated by surgical excision. We experienced a case of leiomyoma of oral cavity, so we report with literature reviews

• 대한두개안면성형외과학회지
• /
• 제15권1호
• /
• pp.43-46
• /
• 2014

Nodular fasciitis is a reactive, non-neoplastic lesion that is most commonly found in the subcutaneous or superficial fascia of the extremities and trunk. Head and neck lesions are relatively uncommon and reports vary from 7% to 15% depending on the authors. Nodular fasciitis grows quickly, and shows a pleomorphic spindle cell pattern with increased mitotic activity. Such factors lead to cases where the lesion is mistaken for a malignancy such as fibrosarcoma and the case may end up with unnecessarily aggressive treatments. The intent of this paper is to report a relatively rare case of nodular fasciitis occurring in the periorbital area and also to highlight the importance of accurate diagnosis and non-aggressive management of this benign lesion.

• 한국수정란이식학회지
• /
• 제33권4호
• /
• pp.229-235
• /
• 2018

Polo-like kinase 1 (Plk1) has been known to be a critical element in cell division including centrosome maturation, cytokinesis and spindle formation in somatic, cancer, and mammalian embryonic cells. In particular, Plk1 is highly expressed in cancer cells. Plk1 inhibitors, such as BI2536, have been widely used to prevent cell division as an anticancer drug. In this study, the fertilized murine oocytes were treated with BI2536 for 30 min after recovery from the oviduct to investigate the effect of down-regulation of Plk1 in the in vivo-fertilized murine embryos. Then, the localization and expression of Plk1 was observed by immunofluorescence staining. The sperm which had entered into the oocyte cytoplasm did not form male pronuclei in BI2536-treated oocytes. The BI2536-treated oocytes showed significantly lower expression of Plk1 than non-treated control group. In addition, alpha-tubulin and Plk1 gathered around sperm head in non-treated oocytes, while BI2536-treated oocytes did not show this phenomenon. The present study demonstrates that the Plk1 inhibitor, BI2536, hinders fertilization by inhibiting the formation of murine male pronucleus.