• Nuclear Engineering and Technology
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• v.54 no.5
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• pp.1726-1746
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• 2022

This paper presents fracture mechanics analysis results for various cracks located at pressurized water reactor pressure vessel nozzle crotch corners taking into consideration constraint effect. Technical documents such as the ASME B&PV Code, Sec.XI were reviewed and then a fracture mechanics analysis procedure was proposed for structural integrity assessment of various nozzle crotch corner cracks under normal operation conditions considering the constraint effect. Linear elastic fracture mechanics analysis was performed by conducting finite element analysis with the proposed analysis procedure. Based on the evaluation results, elastic-plastic fracture mechanics analysis taking into account the constraint effect was performed only for the axial surface crack of the reactor pressure vessel outlet nozzle with cladding. The fracture mechanics analysis result shows that only the axial surface crack in the reactor pressure vessel outlet nozzle has the stress intensity factor exceeding the low bound of upper-shelf fracture toughness irrespectively of considering the constraint effect. It is confirmed that the J-integral for the axial crack of the outlet nozzle does not exceed the ductile crack initiation toughness. Hence, it can be ensured that the structural integrity of all the cracks is maintained during the normal operation.

• Journal of Medicine and Life Science
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• v.19 no.3
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• pp.79-89
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• 2022

Whereas systolic blood pressure (SBP) continuously rises with age, diastolic blood pressure (DBP) gradually decreases after the age of 55 years. Therefore, hypertension in the elderly shows the pattern of isolated systolic hypertension. There is evidence on the benefits of controlling blood pressure (BP) in elderly patients with hypertension. The BP lowering effect has also been demonstrated in patients over 80 years of age with hypertension. The BP threshold for the initiation of antihypertensive drug treatment for older adults with hypertension is gradually decreasing. The antihypertensive treatment is recommended if, despite therapeutic lifestyle modifications, SBP ≥140 mmHg or DBP ≥90 mmHg in those aged 65-79 years old, and SBP ≥140-160 mmHg or DBP ≥90 mmHg in those aged ≥80 years old. Although there is no consensus on the target BP for older adults with hypertension, a target SBP of <130-140 mmHg and DBP of <80-90 mmHg are recommended. In older adults over 80 years of age with hypertension, the target SBP is <140-150 mmHg. When the dose of antihypertensive drugs is increased to reach the target SBP, DBP may decrease to less than 70 mmHg, but it should not be <60 mmHg. Thiazide diuretics, calcium channel blockers, angiotensin-converting enzyme inhibitors, or angiotensin receptor blockers can be selected as the first-line drug for older adults with hypertension. Beta-blockers may be selected in case of compelling indications.

• Atmosphere
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• v.25 no.3
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• pp.559-568
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• 2015

As is evident from its definition, Southern Oscillation Index variability conformed to a combination of the variations of Darwin and Tahiti pressure. Over the El-$Ni{\tilde{n}}o$ Southern Oscillation spectra, the Darwin pressure shared variations associated with the SSN tendency while the Tahiti had a connection with the stratospheric quasi-biennial oscillation modulating annual cycle. The power peak near the 3.5-year period comprised the third harmonic of the sun and the second of the modulated annual cycle. The derived harmonics came from both sources, so the initiation of El-$Ni{\tilde{n}}o$ could be predicted more successfully when including the effects of the sun and QBO.

• Journal of Welding and Joining
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• v.19 no.3
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• pp.298-304
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• 2001

Turbine blade is subject to force of three types ; the torsional force by torsional mount, the centrifugal force by the rotation of rotor and the cyclic bending force by steam pressure. The cyclic bending force was a main factor on fatigue strength. SEM fractography in root of turbine blade showed micro-clack width was not dependent on stress intensity factor range. Especially, fatigue did not exist on SEM photograph in root of turbine blade. To clear out the fracture mechanism of turbine blade, nanofractography was needed on 3-dimensional crack initiation and crack growth with high magnification. Fatigue striation partially existed on AFM photograph in root of turbine blade. Therefore, to find a fracture mechanism of the torsion-mounted blade in nuclear power plant, the relation between stress intensity factor range and surface roughness measured by AFM was estimated, and then the load amplitude ΔP applied to turbine blade was predicted exactly by root mean square roughness.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.5
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• pp.111-121
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• 1995

The initiation and propagation of detonation waves in the air/fuel spray mixture has been numerically analyzed. An improved pressure-based method has been applied to predict the transient heterogeneous reacting flows at all speeds. Numerical results indicate that variations in the temperature gradient, the droplet size, and the fuel vapor concentration have the significant effects on the development of detonation wave in the multi-phase reactive media. The interaction mechanism between the flame-generated pressure wave and the combustion wave is discussed in detail.

• International Journal of Automotive Technology
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• v.8 no.2
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• pp.219-224
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• 2007

Recently, atmospheric contaminations has become worse due to the increased number of automobile. The PCV (Positive Crankcase Ventilation) valve acts as a flow control to allow re-combustion of blow-by gas by having it flow from a crankcase to an inlet manifold suction tube. Also, during the fabrication of the PCV valve, micro cracks may occur in the valve body and be extended under operation. The excessive stress distribution and crack initiation on the PCV valve body would bring an unstable blow-by gas flow rate control and would cause valve failure. The purpose of this study is to examine the crack affects on the stress and strain variations on the PCV valve according to the inlet and outlet manifold under differential pressures. From the results, we can explain the behavior of the crack extension for a safe condition of PCV valve.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.112-118
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• 1990

Catastrophic fracture cannot be avoided after cracks(initiated from pre-existing defects) propagate rapidly with speeds comparable to a sound wave velocity of the materials. Preventing catastropic failure, crack arrest fracture toughness defined from dynamic(or kinetic) fracture mechanics point of view has been introduced in determining accurate and/or proper crack arrest fracture toughness of a material. For the past decades, many studies have been carried out to render proper theoretical and experimental backgrounds on the use of the static plain strain crack arrest fracture toughness, $K_{1a}$ (which seems to be a material property). $K_{1a}$ has been used to predict the performance of thick walled structures and has been considered as a measure of the ability of a material to stop a fast running crack. Determination of such a material property is of prime importance to the nuclear reactor pressure vessel and bridge materials industries. However, standards procedures for measuring toughness associated with fast running cracks are yet to exist. This study intends to give insight on the determination of the crack arrest fracture toughness of materials such as polymethylmethacrylate(PMMA), SM45C-steel, and A1 7075-T6. The effects of crack jump lengths and fast crack initiation stress intensity factor on the determination of $K_{1a}$ have been experimentally observed.erved.

• Fire Science and Engineering
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• v.13 no.2
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• pp.26-32
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• 1999

We had investigated combustion pro야$\pi$ies of rice bran dusts. Decomposition of rice bran d dusts with temperature were investigated using DSC and the weight loss according to t temperature using TGA in order to find the thermal hazard of rice bran dusts, and the p properties of dust explosion in variation of their dust with the same particle size. Using H Hartman's dust explosion apparatus which estimate dust explosion by electric ignition after m making dust disperse by compressed air, dust explosion experiments have been conducted by v varying concen$\sigma$ation and size of rice br뻐 dust. According to the results for thermodynamic stability of rice bran dust, there are little change of initiation temperature of heat generation 때d heating value for used particle size. But i initiation temperature of heat generation decreased with high heating rate whereas d decomposition heat increased with particle size. Also, the explosion pressure was increased as t the ignition energy increased and average maximum explosion pressure was 13.5 kgv'cnt for 5 BJ/60 mesh and 1.5 뼈Ie미 dust concentration.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.53-62
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• 1992

Material can be degraded by using it for a long service under the high temperature and pressure circumstances, Therefore, material degradation can affect the strength of mechanical structures. At present, the life prediction of the degraded structures is considered as an important technical problem. In this paper, the degraded 21/4Cr-lMo steel is the material used for about 10 years around 400.deg. C in an oil refinery plant. The recovered one was prepared out of the above degraded steel by heat treatment for one hour at 650.deg. C. The degradation effect was investigated through the tension test, Hardness test and Charpy impact test. On the smooth surface material, the fatigue crack initiation, growth and coalescence stages of the distributed small cracks were investigated with photographs, and the crack length and density were measured. The measuring results were analyzed by quantative and statistical methods.

• Asian Pacific Journal of Cancer Prevention
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• v.17 no.7
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• pp.3533-3540
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• 2016

Background: Cigarette smoking is one of the leading global causes of premature and preventable death. In Brunei Darussalam, smoking-related diseases have been a primary cause of mortality for the past three decades. Despite the increasing efforts that have been made in recent years to reduce the consumption of tobacco products in Brunei, the prevalence of adolescent smoking cigarette, however has risen alarmingly, from 8.9% in 2013 to 11.4% in 2014, with a higher prevalence found in males (17.8%) than in females (4.8%). In response to the need for more effective smoking prevention programmes in Brunei, this study sought to explore factors that influence Bruneian male adolescents to start and continue smoking. Materials and Methods: A qualitative study using focus group discussions (FGDs) as the data collection method was conducted from October to November 2015. A total of 43 studentss, comprising 31 smokers and 12 non-smokers, aged 13-17 years, from two government secondary schools in Bandar Seri Begawan, participated in six FGDs. Discussions were recorded and translated. Transcripts were entered into NVivo10, before thematic analysis was conducted. Results: We identified three themes under the core construct of 'factors influencing smoking initiation' ('family as teachers', 'overt pressure from peers' and 'perceived smoking has many advantages') and three themes under the core construct of 'factors influencing smoking continuation' ('craving and addiction', 'smoking as a 'social activity' and 'easy accessibility of cigarettes'). Conclusions: Based on the findings, it is recommended that future prevention activities should be embedded in a comprehensive approach, involving all stakeholders within a community, and should be focused towards bringing a change in smoking and parenting behavior of parents, social norms within the culture towards all population levels, and at strengthening the existing non-smoking policies in schools and other public places where young people congregate.