• Journal of the Korean Society for Precision Engineering
• /
• v.9 no.4
• /
• pp.44-57
• /
• 1992

Ball screw systems have been used for positioning elements of machine tools and precision tables. In order to maintain the high rigidity and accuracy, a certain amount of preload is applied between the nut and the screw of ball screw systems. However, large amount of the preload oncreases the frictional heat. The temperature rises remarkably at the high speed motion, and the thermal expansion degrades the positioning accuracy. In this paper, a finite difference method is applied to analyse temperature distributions and thermal expansions of the ball screw system according to preload conditions and rotational speeds. Some simulation results show that the developed methodology is appropriate to study the thermal expansion characteristics of ball screw systems.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1996.05a
• /
• pp.131-136
• /
• 1996

An analytic nodal expansion method has been derived for the multigroup neutron diffusion equation in 2-D cylindrical(R-Z) coordinate. In this method we used the second order Legendre polynomials for source, and transverse leakage, and then the diffusion eqaution was solved analytically. This formalism has been applied to 2-D LWR model. $textsc{k}$$_{eff}$, power distribution, and computing time have been compared with those of ADEP code(finite difference method). The benchmark showed that the analytic nodal expansion method in R-Z coordinate has good accuracy and quite faster than the finite difference method. This is another merit of using R-Z coordinate in that the transverse integration over surfaces is better than the linear integration over length. This makes the discontinuity factor useless.s.

• Health Policy and Management
• /
• v.30 no.3
• /
• pp.326-334
• /
• 2020

Background: Korea has gradually expanded the coverage of medical care services in its national health insurance system. On April 1, 2018, it implemented a policy that expanded the coverage for an ultrasonography in the upper abdomen. In this study, we aimed to investigate the effect of the policy on the utilization of the ultrasonography in the upper abdomen in tertiary care hospitals. Methods: Using the dataset of the Health Insurance Review and Assessment Service, we explored changes in the utilization of the ultrasonography in the upper abdomen in tertiary care hospitals from July 1, 2017 to November 30, 2018 through the difference-in-difference (DID) mixed-effects-model method. Facility factor, equipment factor and personnel factors, type of hospital, the total amount of medical care expenses, and geographic region were considered as control variables. Results: On average, the utilization of the ultrasonography in the upper abdomen increased by 228% after the coverage expansion policy. However, the results of DID mixed-effects-model method analysis showed that the utilization increased by 73%. As for the number of beds, the utilization was higher with a group of 844-930, 931-1,217, and 1,218 or greater compared with a group of 843 or fewer, while the utilization of the number of ultrasonic devices was lower with a group of 45-49 compared with a group of 44 or fewer. The utilization decreased with the number of interns and the number of nurse assistants. Besides, relative to Seoul, the utilization was lower in the other metro-cities and provinces. Conclusion: The coverage expansion policy in the national health insurance system increased service utilization among people. Future research needs to investigate the degree to which such coverage expansion policy reduces the unmet medical care needs among the deprived in Korea.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.12 no.10
• /
• pp.932-940
• /
• 2000

An experimental study on evaporative heat transfer characteristics in micro-fin tubes before and after expansion process has been performed with R-22. Single-grooved micro-fin tubes with outer diameter of 9.52 mm were used as test sections, and it was uniformly heated by applying direct current to the test tubes. Experiments were conducted at mass flow rates of 20 and 30 kg/hr. For each mass flow rate condition, evaporation temperature was set at 5 and $15^{\circ}C$and heat flux was changed from 6 to 11 kW/$m^2$ The evaporative heat transfer coefficient of micro-fin tubes after expansion is decreased because of the crush of fins and enlargement of inner diameter compared to that before expansion. Convective boiling effect decreased remarkably at higher quality range in the micro-fin tube after expansion, and the difference of the heat transfer coefficient in micro-fin tubes before and after expansion was greater for higher quality region. The evaporative heat transfer coefficient of the micro-fin tube after expansion was 19.9% smaller on the average than that before expansion.

• Transactions of Materials Processing
• /
• v.18 no.1
• /
• pp.20-25
• /
• 2009

A finite element analysis was carried out for a 4:1 planar contraction die for polymer melts using the viscoelastic constitutive equation of Leonov. Viscoelastic fluids showed significant differences in pressure drop and birefringence in contraction and expansion flows. The pressure drop was higher and the birefringence smaller in expansion than in contraction flow. The difference increased with increasing flow rate. The nonlinear Leonov model was shown to describe the viscoelastic effects observed in experiments.

• PNF and Movement
• /
• v.19 no.2
• /
• pp.205-213
• /
• 2021

Purpose: This study investigated the immediate effects of a figure-8 shoulder brace and taping intervention on round shoulder posture, thoracic kyphosis, and chest expansion mobility in forward head posture. Methods: Thirty patients with forward head posture were assigned randomly to the figure-8 shoulder brace group (n = 15) or the taping intervention group (n = 15). Patients were assessed for forward head posture, shoulder posture, thoracic kyphosis, and chest expansion. Results: The figure-8 shoulder brace and taping intervention groups showed a significant difference for forward head posture, shoulder posture, and thoracic kyphosis after the experiment (p < 0.05). There was no significant difference between the groups (p > 0.05). Conclusion: These results suggest that a figure-8 shoulder brace and taping intervention has a positive effect on rounded shoulder posture, thoracic kyphosis, and chest expansion in patients with forward head posture.

• 한국연소학회:학술대회논문집
• /
• 1999.10a
• /
• pp.47-54
• /
• 1999

A method is developed to include the effect of volume expansion in the description of the flame dynamics using G-equation. Line volume-source is used to represent the effect of the exothermic process of combustion with source strength assigned by the density difference between the burned and the unburned region. The present model provides good agreement with the experimental results by using realistic volume expansion ratio which was not reached in the previous researches. Including volume expansion, the flow predicts the same behavior of measured velocity field qualitatively. The flame propagation in varying flow field due to volume expansion provides a promising way to represent the wrinkled turbulent premixed flames in a numerically efficient manner.

• 한국전산유체공학회:학술대회논문집
• /
• 1998.11a
• /
• pp.204-210
• /
• 1998

A method is developed to include the effect of volume expansion in the description of the flame dynamics using G-equation. Line volume-source is used to represent the effect of the exothermic process of combustion with source strength determined by the density difference between the burned and the unburned region. Volume expansion adjusts the flow field to accommodate the increased volume flow rate crossing the flame front. Test result predicted the measured velocity field qualitatively. The method was applied to study the interaction of vortex and premixed flame. Increased volume expansion did not change the initial growth rate of flame area. However, the residence time and flame surface area increased with higher expansion ratios.

• Journal of the Korean Society of Physical Medicine
• /
• v.19 no.3
• /
• pp.73-80
• /
• 2024

PURPOSE: This study examined the immediate effects of thoracic mobility exercises on the thoracic range of motion and chest expansion to provide data on thoracic mobility exercises in adults. METHODS: Adults were assigned randomly to two groups: the group that performed thoracic mobility exercises (TME group; n=10) or the group that performed thoracic mobility exercises using balance tools (TMEB group; n=10). The exercises were performed for 10 min in three different positions. The range of motion and chest expansion were measured before and after the exercise. RESULTS: The within-group comparisons before and after the intervention showed significant differences in the range of motion measurements for lateral flexion and rotation in the TME and TMEB groups (p < .05); difference in measurements of chest expansion was observed only in the TMEB group (p < .05). No significant differences in the range of motion for flexion and extension were observed in either group or during chest expansion in the TME group (p > .05). The between-group comparisons showed a significant difference in left lateral flexion (p < .05), whereas no other measures differed significantly (p > .05). CONCLUSION: The TME and TMEB groups showed significant increases in the thoracic range of motion; the TMEB group showed a significant increase in chest expansion.

• Nuclear Engineering and Technology
• /
• v.16 no.2
• /
• pp.70-79
• /
• 1984

With the help of the nuclear computational system for a large LMFBR (KAERI-26 group cross section library/1DX/2DB), the reactivity coefficients for the diagrid expansion and the pad expansion at the beginning of cycle of the equilibrium core of SUPER-PHENIX I are calculated and reviewed. the core is described using R-Z geometry model, and a two-dimensional multigroup diffusion theory is used. For reference cases, reactivity calculations for radial and axial uniform expansion are performed, and also calculated are reactivity variations due to changes in material density and core volume. The reactivity coefficient for the diagrid expansion is calculated to be -0.553pcm/mil. The temperature coefficient corresponding to the above value is -1.0766pcm/$^{\circ}C$ and is well in accord with the French datum of -1.09pcm/$^{\circ}C$ within 1.2% difference. With the use of 4he calculational method for the diagrid expansion effect, reactivity calculations for the pad expansion bringing about nonuniform expansion are performed, which show that the calculational method is very useful in the analysis of the pad expansion effect. The reactivity coefficients for the pad expansion are calculated to be -0.2743 pcm/mil and -0.2786pcm1mi1 for the averaged expansion model and for the integrated pancake model, respectively. Under the assumption of the free expanding core the temperature reactivity coefficients for each model are obtained to be -0.5766pcm/$^{\circ}C$ and -0.5858pcm/$^{\circ}C$, both of which agree with the French datum of -0.574pcm/$^{\circ}C$ within 2% difference.