• Journal of electromagnetic engineering and science
• /
• 제1권1호
• /
• pp.73-77
• /
• 2001

We studied the fabrication of GaAs-based pseudomorphic high electron mobility transistors(PHEMT`s) for the purpose of millimeter- wave applications. To fabricate the high performance GaAs-based PHEMT`s, we performed the simulation to analyze the designed epitaxial-structures. Each unit processes, such as 0.1 m$\mu$$\Gamma$-gate lithography, silicon nitride passivation and air-bridge process were developed to achieve high performance device characteristics. The DC characteristics of the PHEMT`s were measured at a 70 $\mu$m unit gate width of 2 gate fingers, and showed a good pinch-off property ($V_p$= -1.75 V) and a drain-source saturation current density ($I_{dss}$) of 450 mA/mm. Maximum extrinsic transconductance $(g_m)$ was 363.6 mS/mm at $V_{gs}$ = -0.7 V, $V_{ds}$ = 1.5 V, and $I_{ds}$ =0.5 $I_{dss}$. The RF measurements were performed in the frequency range of 1.0~50 GHz. For this measurement, the drain and gate voltage were 1.5 V and -0.7 V, respectively. At 50 GHz, 9.2 dB of maximum stable gain (MSG) and 3.2 dB of $S_{21}$ gain were obtained, respectively. A current gain cut-off frequency $(f_T)$ of 106 GHz and a maximum frequency of oscillation $(f_{max})$ of 160 GHz were achieved from the fabricated PHEMT\\`s of 0.1 m$\mu$ gate length.h.

• The Journal of Advanced Prosthodontics
• /
• 제1권2호
• /
• pp.85-90
• /
• 2009

STATEMENT OF PROBLEM. Over the years, resin-bonded fixed partial dentures (RBFPDs) have gone through substantial development and refinement. Several studies examined the biomechanics of tooth preparation and framework design in relation to the success rate of RBFPDs and considered retention and resistance form essential for increase of clinical retention. However, these criteria required preparations to be more invasive, which violates not only the original intentions of the RBFPD, but may also have an adverse effect on retention due to loss of enamel, an important factor in bonding. PURPOSE. The object of this in vitro study was to compare the dislodgement resistance of the new types of RBFPDs, the conventional three-unit fixed partial denture, and conventional design of RBFPD (Maryland bridge). MATERIAL AND METHODS. Fifty resin mandibular left second premolars and second molars were prepared on dentiforms, according to the RBFPD design. After model fabrication (five group, n = 10), prostheses were fabricated and cemented with zinc phosphate cement. After cementation, the specimens were subjected to tensile loading at a cross head speed of 4 mm/min in a universal testing machine. The separation load was recorded and analyzed statistically using one-way analysis of variance followed by Duncan's multiple range test. RESULTS. Group V, the pin-retained RBFPDs, had the highest mean dislodgement resistance, whereas specimens of group II, the conventional RBFPDs, exhibited a significantly lower mean dislodgement resistance compared to the other 4 groups (P <.05). There were no significant differences between group I, III, and IV in terms of dislodgement resistance (P>.05). Group V had the highest mean MPa (N/$mm^2$) (P <.05). There was no significant difference between groups I, II, III and IV (P > .05). CONCLUSION. Within the limits of the design of this in vitro study, it was concluded that: 1. The modified RBFPDs which utilizes the original tooth undercuts and requires no tooth preparation, compared with the conventional design of RBFPDs, has significantly high dislodgement resistance (P < .05). 2. The modified RBFPDs which utilizes the original tooth undercuts and requires minimal tooth preparation, compared with the conventional FPDs, has significantly no difference in retention and dislodgement resistance)(P>.05). 3. The pin-retained FPDs showed a high dislodgement resistance compared to the conventional three-unit FPDs (P<.05).

• The Korean Journal of Pharmacology
• /
• 제7권1호
• /
• pp.53-65
• /
• 1971

It is well known that diabetes mellitus is associated with metabolic derangements, such as hyper-glycemia, ketosis, glycosuria, and also widespread alterations in the blood vessels, kidneys, eyes, peripheral nerves and heart. It is also recognized that healing of skin wound is delayed in diabetics. In bone, according to Aegerter, osteopenia develops in diabetes mellitus and it is chiefly ascribed to overutilization of protein. Shim claims that total blood flow to the entire skeletal system is approximately 4 to 8 percent of resting cardiac output and blood supply to the skeletal system would be decreased on account of secondary arteriosclerotic changes in the diabetics. An adequate blood supply is an essential factor in the healing process of fracture, and disturbed blood flow, either local or systemic, will invariably delay union of the fragments or the fragments from being fused. As the author has encountered several cases of diabetics in whom healing of fracture was delayed or incomplete, this experimental study was undertaken to elucidate the effects of hyperglycemia and diabetes mellitus on the healing process of fracture. In this experiment adult albino rabbits, weighing about 2 kg. were used and divided into 6 groups. The femur of each animal was fractured surgically, and then the healing process of fracture was periodically checked by radiography at an interval of one week for a period of 6 weeks. Thereafter, all the rabbits were killed to obtain tissue preparation of the femur. The experimental groups were as follows; 1) Control group: Six rabbits sustained a surgical fracture to the femur, without being given any other treatment or drug. 2) Alloxan-treated group: For inducing diabetes, alloxan was given intravenously to 17 rabbits in various dose as follows; to 7 of them 40 mg/kg, to 6 rabbits 80 mg/kg and to 4 rabbits 120 mg/kg of body weight, respectively. 3) Insulin-treated group: Protamine-zinc insulin was injected subcutaneously to each of 6 rabbits in a daily dose of 1 unit per kilogram of body weight. 4) Group treated with insulin after alloxan: Four rabbits were given 80 mg of alloxan once and than 1 unit of insulin per kilogram of body weight daily. Another 5 rabbits were injected 1 unit of insulin per kg of body weight daily following administration of alloxan in a dose of 120 mg/kg. 5) Homotransplantation group: Following intravenous injection of alloxan in a dose of 120 mg/kg, 10 rabbits underwent homotransplantation of a short bone segment to the femur. Five of them were subsequently given 1 unit/kg of insulin daily. 6) Sugar-treated group: six rabbits were fed $15{\sim}20$ gm of sugar daily throughout the period of experiment. The results obtained are summarized as follows; 1. Blood sugar level and damage to the pancreatic islet increased proportionately when alloxan was given to the rabbits in various doses. No appreciable change could be observed in the islets when the blood sugar level was altered by either oral administration of sugar or subcutaneous injection of insulin. 2. Comparing with the control group, healing of fracture was delayed in the alloxan-treated group, while callus formation and periosteal reaction were shown to be more prominent in this group and subsequently, the ultimate osseous tissue formed at the fracture site was significantly smaller in amount and less compact. These findings were more marked as the amount of alloxan increased. 3. Administration of insulin prevented the delay in healing process of fracture in the rabbits with alloxan-induced hyperglycemia. In this case, the course and progression of fracture healing were almost similar to those of control group. 4. Union between the host bone and the fragment transplanted from other rabbit of the same species was more delayed in the group treated with alloxan alone than in the group to which insulin was administered after development of alloxan-induced diabetes. In both groups periosteal new bone developed from the ends of the host bone, above and below the transplanted fragment, and directly fused with failure of periosteal callus to bridge the adjacent ends of the host bone and the transplanted fragment. 5. The healing process of fracture was not inhibited by alteration in blood sugar level when the blood sugar was abnormally increased by excessive sugar intake or lowered by administration of insulin alone. The healing of fracture in these groups progressed similarly as in the control group. In brief summary, it appears that the healing process of fracture would be definitely disturbed in diabetic state brought about by damage to the pancreatic islet. As such an inhibition could be overcome with insulin, it seems that insulin plays an important role in healing of fracture, but alteration in blood sugar level alone does not modify healing process of fracture to significant degree.

• Journal of Dental Rehabilitation and Applied Science
• /
• 제26권1호
• /
• pp.21-32
• /
• 2010

The convergence angle of a prepared tooth is a very important factor in the retention and resistance of a crown restoration. But various intraoral environments and clinician's techniques make it difficult to obtain the ideal inclination. Therefore, in this study, clinical convergence angle of a prepared tooth was investigated. The data was collected from the patient models of prosthodontic residents and the patient models of general practitioners. The images of mesiodistal and buccolingual surfaces were taken with a digital camera to evaluate the convergence angle on 'ImageJ' program. The images were classified according to the criteria (1. Clinician group, 2. Position in the dental arch, 3. The purpose of abutment preparation)and then analyzed. The mean convergence angle of a prepared tooth for Korean clinicians was $15.02^{\circ}$ (${\pm}10.13^{\circ}$). 1. It was significant in the convergence angle between the general practitioner group and the prosthodontic resident group(p<0.05). 2. It was significant between the mesiodistal and buccolingual surface in the the prosthodontic resident group(p<0.05). 3. For the general practitioner group, it was significant when anteriors and premolars were compared with molars(p<0.05). For the prosthodontic resident group, it was significant when anteriors and premolars were compared with molars (p<0.05). 4. When divided into upper and lower arches, for the general practitioner group, it showed significant difference in the buccolingual aspect(p<0.05). Also in the prosthodontic resident group, it showed significant difference in the buccolingual aspect(p<0.05). 5. Dividing left and right sides of the arches, there was no significant difference in the general practitioner group and the prosthodontic resident group(p>0.05). 6. In the general practitioner group, it was significant in the mesiodistal axial convergence angle of single crown abutment and 3 unit bridge abutment(p<0.05). In the prosthodontic resident group, it was significant in the mesiodistal and overall axial convergence angle of single crown abutment and 3 unit bridge abutment(p<0.05). Clinical convergence angle of prepared tooth in Korea was included in agreement with other studies investigating convergence angle that ranged from 10 to 22 degrees, achieved in clinical practice.

• Journal of the Korean Geotechnical Society
• /
• 제35권11호
• /
• pp.111-119
• /
• 2019

The high-speed railway system is mainly composed of tunnel, bridge, and viaduct to meet the straightness needed for keeping the high speed up to 400 km/s. Seismic fragility for the high-speed railway infrastructure can be assessed as two ways: one way is studying each element of infrastructure analytically or numerically, but it requires lots of research efforts due to wide range of railway system. On the other hand, empirical method can be used to access the fragility of an entire system efficiently, which requires case history data. In this study, we collect the 2004 M_W 6.6 Niigata earthquake case history data to develop empirical seismic fragility function for a railway system. Five types of intensity measures (IMs) and damage levels are assigned to all segments of target system for which the unit length is 200 m. From statistical analysis, probability of exceedance for a certain damage level (DL) is calculated as a function of IM. For those probability data points, log-normal CDF is fitted using MLE method, which forms fragility function for each damage level of exceedance. Evaluating fragility functions calculated, we observe that T=3.0 spectral acceleration (SA_T3.0) is superior to other IMs, which has lower standard deviation of log-normal CDF and low error of the fit. This indicates that long-period ground motion has more impacts on railway infrastructure system such as tunnel and bridge. It is observed that when SA_T3.0 = 0.1 g, P(DL>1) = 2%, and SA_T3.0 = 0.2 g, P(DL>1) = 23.9%.

• The Journal of Korean Academy of Prosthodontics
• /
• 제45권6호
• /
• pp.753-759
• /
• 2007

Statement of problem. In distal extension removable partial denture, the preservation of health of abutment teeth is very important, but abutment teeth are subjected to unfavorable stress under unilateral loading specially. Purpose. The purpose of this study was to investigate the biomechanical effects of mandibular removable partial dentures with various prosthetic designs under unilateral loading, using strain gauge analysis. Material and methods. Artificial teeth of both canines were anchored bilaterally in a mandibular edentulous model made of resin. Bilateral distal extension removable partial dentures with splinted and unsplinted abutments were fabricated. Group 1: Clasp-retained mandibular removable partial denture with unsplinted abutments Group 2: Clasp-retained mandibular removable partial denture with splinted abutments by 6-unit bridge. Group 3: Bar-retained mandibular removable partial denture Strain gauges were bonded on the labial plate of the mandibular resin model, approximately 2 mm dose to the abutments. Two unilateral vertical experimental loadings (30N and 100N) were applied subsequently via miniature load cell that were placed at mandibular left first molar region. Strain measurements were performed and simultaneously monitored from a computer connected to data acquisition system. For within-group evaluations, t-test was used to compare the strain values and for between-group comparisons, a one-way analysis of variance (ANOVA) was used and Tukey test was used as post hoc comparisons. Results. The strain values of group 1 and 2 were tensile under loadings. In contrast, strain values of group 3 were compressive in nature. Strain values increased as the applied load in increased from 30N to 100N (p<.05) except for right side in group 1. Under 30N loading, in left side, group 1 showed higher strain values than groups 2 and 3 in absolute quantity (p<.05). And group 2 showed higher strain values than group 1 (p<.05). In right side, group 1 and 2 showed higher strain values than group 3 in absolute quantity (p<.05). Under 100N loading in left side, group 1 showed higher strain values than groups 2 and 3 in absolute quantity (p<.05). And group 2 showed higher strain values than group 1 (p<.05). In right side, group 1 and 2 showed higher strain values than group 3 in absolute quantity (p<.05). Under 30N loading, group 2 and 3 showed higher strain values in right side than in left side. Under 100N loading, right side strain values were higher than left side ones for all groups. Conclusion. Splinting of two isolated abutments by bridge reduced the peri-abutment strain in comparison with unsplinted abutments under unilateral loading. Bar-retained removable partial denture showed the lowest strain of three groups, and compressive nature.

• Journal of the Mineralogical Society of Korea
• /
• 제6권2호
• /
• pp.116-121
• /
• 1993

A single crystla of zeolite $Na_{78}Rb_{28}-X$ (approximate composition) was prepared by exposing $Na_{92}-X$ at $350^{\circ}C$ to 0.1 Torr of rubidium vapor, and its structure was determined by single-crystal x-ray diffraction methods in the cubic space group, Fd3, ${\alpha}=25.045(4){\AA}$. The structure was refined to the final error indices $R_1=0.082$ and $R_2=0.084$ with 353 for which I>$3{\sigma}(I)$. Only about 28 of the 92 $Na^+$ ions per unit cell were reduced and only about 14 of the 28 $Na^0$ atoms produced were retained within the zeolite. A $Na_5{^{4+}}$ cluster is present within each sodalite cavity. It is a centered tetrahedron (like $CH_4$) with bond $length=2.80(2){\AA}$ and angle tetrahedral by symmetry, and shows the full symmetry of its site. $T_d$, at the center of the sodalite cavity. Each of the four terminal atoms of the $Na_5{^{4+}}$ cluster bond to three framework oxygens at $2.36(2){\AA}$. At the centers of some double 6-rings are sodium atoms which bridge linearly between $Na_5{^{4+}}$ clusters to form agglomerations such as short zig-zag chains $Na_5{^{4+}}$ clusters. Delocalized electrons, located primarily on the sodiums at centers of the sodalite and (likely) double-six-ring cavities, contribute to the stability of the clusters.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• 제19권3호
• /
• pp.179-184
• /
• 2019

In many countries, such as developing countries where electricity is scarce, small wind turbines in the form of Off Grid are an effective solution to solve power supply problems. In some countries, the expansion of power systems and the decline of electricity-intensive areas have led to the use of small wind power in urban road lighting, mobile communications base stations, aquaculture and seawater desalination. With this change, the size of the small wind power industry is expected to have greater potential than large-scale wind power. In the case of small wind power generators, the generator is controlled at a variable speed, and the voltage and current generated by the generator have many harmonic components. To solve this problem, the AC to DC converter to be studied in this paper is a three-phase step-up type converter with a single switch. The inductor current is controlled in discontinuous mode, and has a characteristic of having a unit power factor by eliminating the harmonic of the input current. The proposed converter is composed of LCL filter and three phase rectification boost converter at the input stage and a single phase full bridge for grid connection. It is a control system with energy storage system(ESS) that the system stabilization can be pursued against the electric power.

• Corrosion Science and Technology
• /
• 제8권2호
• /
• pp.53-61
• /
• 2009

In this study, both evaluations by visual imaging for exterior view of coating and by EIS were executed for epoxy primer coated specimens deteriorated by accelerated test, and comparison and analysis were carried out for 2 evaluation methods. In the comparison between total damaged area ratio acquired by image processing method and deterioration point, higher deterioration points were appeared for rusted specimens than for non-rusted specimens. It is attributed that deterioration point per unit area ratio given for rust is higher than for peeling. In the comparison between total damaged area ratio and EIS result, impedance of coating was largely decreased as about TEX>$10^4{\Omega}{\cdot}cm^2$ or less when rust area ratio is more than about 0.1%, and blistering area ratio is more than about 3%. Charge transfer resistance ($R_{ct}$) and double layer capacitance ($C_{dl}$) values were appeared for all specimens except 2 ones, which shows that water is accumulated and steel substrate is corroded at coated film-steel interface. In the comparison between deterioration point and EIS result, more than 10 points as deterioration point were given for specimens of below $10^6{\Omega}{\cdot}cm^2$ of impedance at low frequency. For specimens deteriorated by NORSOK cyclic test, impedance was lowest of all, though deterioration point was not high. It is thought to be attributed that coating system and accelerated deterioration condition of cyclic tested specimens were different from those of main specimens. From the result, it is thought that coating resistance can be relatively more decreased than deterioration degree estimated from exterior view under more severe corrosion environment or in the present of more complex deterioration factors.

• Journal of Korean Society of Steel Construction
• /
• 제20권2호
• /
• pp.227-236
• /
• 2008

The kind of concrete generally used in steel concrete composite bridges is normal-weight concrete whose unit weight is ${2,300kg/m^{3}}$. However, using lightweight concrete in composite bridges diminishes the sectional forces due to the self-weight of concrete decks. As a result, this will make the bridge design more economical. The type of concrete deck that could be adopted in composite bridges using lightweight con crete may be classified into Cast-In-Place (C.I.P.) concrete deck and precast concrete deck. These two types of decks have some differences with respect to structural behavior and constructional method, and hence,structural behavior of stud shear connectors that connect a concrete deck to a steel girder is changed with the type of deck used. In this study, push-out tests were conducted to evaluate the characteristics of static behavior of the stud shear connectors with a precast deck using lightweight concrete. Also, additional precast deck specimens with bedding layer that had shear keys and devices for transverse confinement of the bedding layer for the prevention of cracks occurring in the bedding layer were tested. These cracks The efficiency of these devices was then evaluated.