• Journal of the Korean Society of Marine Environment & Safety
• /
• v.24 no.4
• /
• pp.467-474
• /
• 2018

The purpose of this study is related to automatic hull-form design for ships operating at two speeds. Research was conducted using a series 60 ($C_B=0.6$) ship as a target, which has the most basic ship hull-form. Hull-form development was pursued from the viewpoint of improving resistance performance. In particular, automatic hull-form design for a ship was performed to improve wave resistance, which is closely related to hull-forms. For this purpose, we developed automatic hull-form design software for ships by combining an optimization technique, resistance prediction technique and hull-form modification technique, appling the software developed to a target ship. A sequential quadratic programming method was used for optimization, and a potential-based panel method was used to predict resistance performance. A Gaussian-type modification function was developed and applied to change the ship hull-form. The software developed was used to design a target ship operating at two different speeds, and the performance of the resulting optimized hull was compared with the results of the original hull. In order to verify the validity of the program developed, experimental results obtained in model tests were compared with calculated values by numerical analysis.

• Applied Chemistry for Engineering
• /
• v.21 no.5
• /
• pp.495-499
• /
• 2010

To develop chemical and biosensors, this paper studies sensing characteristics of bulk carbon nanotube (CNT) electrodes by means of their electrical impedance properties due to their large surface area and excellence chemical absorptivity. The sensors were fabricated in the form of film and nano web style by using composite process for mass production. The bulk composite electrodes were fabricated with singlewall and multi-wall carbon nanotubes based on host polymers such as Nafion and PAN, using a solution-casting and an electrospinning technique. The resistance and the capacitance of electrodes were measured with LCR meter under the various amounts of buffer solution to study the electrical impedance change properties of them. On the experimental of sensor electrode, impedance characteristics of the composite electrode are affected by its host polymer and nanofiller and its sensing response showed saturated result after applying some amounts of buffer solution for test chemical. Especially, the capacitance values showed drastic changes while the resistance values only changed within few percent range. It is deduced that the ions in the solution penetrated and diffused into the electrodes surface changed the electrical properties of the electrodes much like a doping effect.

• Journal of the Korean Magnetics Society
• /
• v.12 no.4
• /
• pp.143-148
• /
• 2002

We report an experimental evidence of coexistence of the strong and weak exchange couplings in unidirectional NiO/NiFe (antiferromagneticlferromagnetic) bilayer thin films. The exchange bias was measured by VSM and AMR techniques and then, analyzed into the strong and weak exchange couplings by means of a regression method. In NiO(60nm)/NiFe(10nm) film, the ratio of the weak exchange coupling field over the average exchange coupling field was found to be almost unchanged within it range from 0.2 to 0.4 irrespective to the strength of an applied field. However, the ratio increased among the samples with decreasing the average exchange coupling field due to the increment of the weak exchange coupling area.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.8
• /
• pp.893-898
• /
• 2014

A direct pulsed laser process for welding and networking silver nanowires was developed. The welded nanowire network demonstrated modified electrical properties in a transparent substance. In particular, the welding points on the nanowires were investigated to measure the resistance at the connections. The level of networking in nanowires was explored with respect to various laser pulse widths and average power densities. In particular, the influence of laser beam density was investigated in detail. Selective laser treatment can be advantageous in imparting customized local property changes in transparent conducting materials. Various applications of the process are also discussed in this paper.

• Journal of the Society of Naval Architects of Korea
• /
• v.33 no.1
• /
• pp.1-8
• /
• 1996

A potential-based panel method has been developed for numerical computation of wave resistance on a hybrid hydrofoil. Hybrid hydrofoil is composed of a main body, two struts and two hydrofoils. The main body, which is assumed to be an axisymmetric body for the present analysis, is normally used to support displacement of a body with its buoyancy. Normal dipoles and the sources are distributed on the body(main body, struts, hydrofoils) and the sources are distributed on the free surface. Linearized free surface and the radiation conditions are satisfied using the fourth order finite difference operator and the semi-linear pressure Kutta condition is used for the numerical computation of the hydrofoils. Poisson type free surface condition has been used for the numerical computation and hyperboloidal panel method has been used for better numerical accuracy. To verify this numeric method, model tests are performed in circulation water channel. From the comparison of experimental results with numeric ones, the present method can be used as a useful tool for the design of high speed vessels.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.47 no.8
• /
• pp.1-6
• /
• 2010

We report on the electrical properties of Ti/Al/Ni/Au (20 nm/ 150 nm/ 30 nm/ 100 nm) Ohmic contacts and the anisotropic conductivity of n-type ${\alpha}$-plane ([11-20]) GaN grown on $\gamma$-plane ([1-102]) sapphire substrates. The Ti/Al/Ni/Au Ohmic contacts and their sheet resistances are characterized by using the transfer length method (TLM) as a function of azimuthal angles. It is found that the specific contact resistance does not depend on the axis orientation and there are significant electrical anisotropy in ${\alpha}$-plane GaN films on $\gamma$-plane sapphire substrates, and the sheet resistance varies with azimuthal angles. The sheet resistance values in the direction parallel to m-axis [1-100] are 25% ~ 75% lower than those parallel to c-axis [0001] directions. Thus, Basal stacking faults (BSFs) are offered as a feasible source of the anisotropic mobility in defected m-axis direction because the band-edge discontinuities owing to the differential band gap structure.

• Geotechnical Engineering
• /
• v.6 no.1
• /
• pp.43-58
• /
• 1990

In order to get ultimate pullout resistance of ground anchor, the position of failure surface, normal stress and friction angle on the failure surface should be known. In this study, the position of failure surface is obtained by observing deformation of ground around anchor, and stresses on the anchor surface are analyzed by measuring normal and shear stresses on the anchor surface through model anchor test in plane strain. In addition, the relationship between lateral earth pressure and the position of failure surface is analyzed and the formula for calculating ultimate pullout resistance of anchor is proposed by using non-dimensional coefficient of ultimate pullout resistance.

• Journal of the Society of Naval Architects of Korea
• /
• v.33 no.3
• /
• pp.35-47
• /
• 1996

A surface panel method treating a boundary-value problem of the Dirichlet type is presented to design a three dimensional body with free surface corresponding to a prescribed pressure distribution. An integral equation is derived from Green's theorem, giving a relation between total potential of known strength and the unknown local flux. Upon discretization, a system of linear simultaneous equations is formed including free surface boundary condition and is solved for an assumed geometry. The pseudo local flux, present due to the incorrect positioning of the assumed geometry, plays a role f the geometry corrector, with which the new geometry is computed for the next iteration. Sample designs for submerged spheroids and Wigley hull and carried out to demonstrate the stable convergence, the effectiveness and the robustness of the method. For the calculation of the wave resistance, normal dipoles and Rankine sources are distributed on the body surface and Rankine sources on the free surface. The free surface boundary condition is linearized with respect to the oncoming flow. Four-points upwind finite difference scheme is used to compute the free surface boundary condition. A hyperboloidal panel is adopted to represent the hull surface, which can compensate the defects of the low-order panel method. The design of a 5500TEU container carrier is performed with respect to reduction of the wave resistance. To reduce the wave resistance, calculated pressure on the hull surface is modified to have the lower fluctuation, and is applied as a Dirichlet type dynamic boundary condition on the hull surface. The designed hull form is verified to have the lower wave resistance than the initial one not only by computation but by experiment.

• Tuberculosis and Respiratory Diseases
• /
• v.46 no.5
• /
• pp.697-708
• /
• 1999

Background : Leukotriene (LT) $C_4$, $D_4$, and $E_4$, the main components of slow-reacting substance of anaphylaxis (SRS-A), have been suggested to play an important role in bronchial asthma such as antigen-induced bronchoconstriction, airway hyperreactivity, and pulmonary eosinophil accumulation. The purpose of this study was to evaluate the effects of treatment with the cysteinyl-LTs (cys-LTs) antagonist, pranlukast on allergen-induced guinea pig asthma model. Methods : Guinea pigs of treatment and placebo groups were sensitized by subcutaneous injection of ovalbumin(OVA) and challenged by inhalation of aerosolized OVA (1% weight/volume OVA). Normal control group did not sensitize with OVA. Oral ingestion of pranlukast and normal saline to the treatment and placebo groups was performed. In the treatment and placebo groups, airway resistance was measured before and after oral ingestion. Serum $LTC_4$ and eosinophilic infiltration of the bronchiolar and peribronchiolar tissues were measured after ingestion in the treatment and placebo groups. Results : Allergen-induced airway constriction developed in 20 (8 in treatment group, 12 in placebo group) among 35 guinea pigs. Airway resistance was significantly decreased at 3 and 6 minutes after OVA challenge in the pranlukast treatment group. In the placebo group, there was no difference of airway resistance between before and after saline ingestion. Serum $LTC_4$ levels showed 348.4 pg/ml in the treatment group, 373.9 pg/ml in the placebo group, and 364.4 pg/ml in the control group. There were no statistically significant difference between treatment and placebo group (p=0.232), and treatment and control group (p=0.501). Eosinophilic infiltrations in the peribronchiolar region per one-microscopic field ($\times$400 high power fields) demonstrated 7.06 in the treatment group, 19.2 in the placebo group, and 4.50 in the control group. There was significant decrement of eosinophilic infiltration in the treatment group which was compared with placebo group (p=0.001). Conclusion : These results demonstrate that pranlukast, a cys-LTs receptor antagonist, can attenuate allergen induced early-phase bronchoconstriction and eosinophilic infiltration in the bronchiolar tissues.

• Tuberculosis and Respiratory Diseases
• /
• v.42 no.1
• /
• pp.67-75
• /
• 1995

Background: Although we gain new knowledge, the problem of pneumonia will not be eliminated. We should understand who is at risk, why these people develop this problem, what causes the pneumonia, and how to manage and prevent respiratory infection. To clarify the alterations of the etiologies of bacterial pneumonia we analysed the recent causative organisms and evaluated the therapeutic implications. Methods: A retrospective four-year study of bacterial pneumonia was conducted in Soon Chun Hyang University Hospital. 190 episodes of bacterial pneumonia was investigated. Results: 1) The causative organisms were isolated in 173 cases on the sputum culture: 154 cases (89%) were gram negative bacilli and 19 cases(11%) were gram positive cocci. The major organisms were Pseudomonas species 49 cases(28%), Klebsiella pneumoniae 29 cases(17%), Enterobacter species 25 cases(14%), and Acinetobacter species 20 cases(12%) in decreasing order. Pseudomonas species(13 cases, 34%) were frequently found in nosocomial pneumonia. 2) The causative organisms were isolated in 16 cases on the blood culture: 7 cases(43%) were gram negative bacilli and 9 cases(57%) were gram positive cocci. The major organisms were Staphylococcus aureus(6 cases, 38%), Pseudomonas species(3 cases, 19%) in decreasing order. 3) In the susceptibility test of causative organisms to antimicrobial drugs, Pseudomonas was susceptible to amikacin, ciprofloxacin, aztreonam, ceftazidime(more than 50%) and resistant to piperacillin, gentamicin, carbenicillin(more than 60%). Klebsiella was susceptible to chloramphenicol, gentamicin, cefotetan(more than 70%) and resistant to carbenicillin, ampicillin(more than 70%). Staphylococcus was susceptible to methicillin(64%), and Streptococcus pneumoniae was susceptible to oxacillin(94%). 4) The response rate after antibiotics therapy was 81% and the mortality rate was 19%. Conclusion: As considering the changes of causative organisms and antibiotic resistance, it behooves us to exercise caution in dispending antibiotics in order to maximize their continued efficacy and to do appropiate antibiotics therapy based on cultures and susceptibility test.