Pilot study of high‐performance air filtration for classroom applications

A study was conducted to investigate the effectiveness of three air purification systems in reducing the exposure of children to air contaminants inside nine classrooms of three Southern California schools. Continuous and integrated measurements were conducted to monitor the indoor and outdoor concentrations of ultrafine particles (UFPs), fine and coarse particulate matter (PM_2.5 and PM₁₀, respectively), black carbon (BC), and volatile organic compounds. An heating, ventilating, and air conditioning (HVAC)‐based high‐performance panel filter (HP‐PF), a register‐based air purifier (RS), and a stand‐alone air cleaning system (SA) were tested alone and in different combinations for their ability to remove the monitored pollutants. The combination of a RS and a HP‐PF was the most effective solution for lowering the indoor concentrations of BC, UFPs, and PM_2.5, with study average reductions between 87% and 96%. When using the HP‐PF alone, reductions close to 90% were also achieved. In all cases, air quality conditions were improved substantially with respect to the corresponding baseline (preexisting) conditions. Data on the performance of the gas‐absorbing media included in the RS and SA unit were inconclusive, and their effectiveness, lifetime, costs, and benefits must be further assessed before conclusions and recommendations can be made.     

Concept development of an underground research tunnel for validating the Korean reference HLW disposal system

In order to dispose of high-level radioactive waste (HLW) safely in geological formations, it is necessary to assess the feasibility, safety, appropriateness, and stability of the disposal concept at an underground research laboratory (URL) constructed in the same geological formation as the host rock. In this study, minimum requirements and the conceptual design for an efficient construction of a small scale URL were derived based on a literature review. To confirm the validity of the conceptual design for construction at KAERI, a geological survey including a seismic refraction survey, electronic resistivity survey, borehole drilling, and in situ and laboratory tests were carried out. The mechanical stability of the URL was investigated with a consideration of the surface topography, tunnel geometry, tunnel slope, sequential excavation, in situ stress ratio, erosion effect, and rock property variation along the tunnel using the three-dimensional code, FLAC3D. From the study, it was possible to conclude that the small scale URL will be effectively constructed in a granite mass at KAERI and will satisfy the minimum requirements.     

Analysis of total harmonic distortion in microspeakers considering coupling effect

With the advent of the mobile phone, Digital Multimedia Broadcasting (DMB) service for multimedia data communication will soon be realized. With regard to the acoustic aspects of this service, a smaller and lighter microspeaker also soon will be implemented in MP3 song players and speakerphones. The sound quality of such microspeakers, as evaluated with reference to total harmonic distortion (THD) is becoming more important. THD is the proportion of the higher-order frequency output response to a sinusoidal input signal. It is affected by uneven magnetic distribution and nonlinear responses of diaphragms. In this work, THD was analyzed in consideration of the coupling effects between mechanical vibration and electromagnetic exciting forces. Simulated THD results were compared with the experimental data. The THD in the lower frequency range increased due to the increased displacement of the voice coil and the elevated high-order component response of the sound pressure.     

Characteristic analysis of the isokinetic strength in lower limbs of the elderly on training for postural control

The principal objective of this study was to assess the characteristic of muscular strength in the lower limbs of elderly subjects after 8 weeks of postural control training with a postural control training system designed specifically for the elderly. In order to verify the characteristic of muscular strength in the lower limbs, 15 elderly volunteers (training group, TG) took part in a balance training regimen using the postural control training system. An additional 15 elderly volunteers (control group, CG), who were employed as the control group, were also tested for comparison with the training group. To evaluate the effects of the training and the characteristic of the muscular strength, we measured the relevant parameters, such as the sway path and the sway area of center of pressure under different visual conditions and the concentric isokinetic strength of the joints in the lower limbs prior to, during, and after training. In this study, we hypothesized that the participants would evidence better balance control, i.e. smaller postural sway and greater concentric isokinetic strength of the ankle and knee joints, than those who did not participate in the training program. We also assessed the relationship of the COP sway area and the concentric isokinetic strength of the ankle, knee, and hip joints of the elderly subjects. The results demonstrated that the correlation between isokinetic strength of the ankle and knee joints and the postural stability dropped significantly in a negative-linear fashion. However, no significant difference was noted between the concentric isokinetic strength of the hip joint and the postural stability of the subjects. The concentric isokinetic strength of the ankle and knee joints was found to be more relevant to the movement of the lower limbs, which is important in terms of the postural strategy. Via these results, we confirmed the characteristics of muscular strength in the lower limbs of the elderly and the relationship between muscular strength and postural stability. Therefore, the elderly that is reinforced muscular strength of the joints of lower limbs can perform increased postural training capability.     

Real-time quality monitoring and control system using an integrated cost effective support vector machine

The quality monitoring and control (QMC) has been an essential process in the manufacturing industries. With the advancements in data analytics, machine-learning based QMC has become popular in various manufacturing industries. At the same time, the cost effectiveness (CE) of the QMC is perceived as a main decision criterion that explicitly accounts for inspection efforts and has a direct relationship with the QMC capability. In this paper, the cost-effective support vector machine (CESVM)-based automated QMC system (QMCS) is proposed. Unlike existing models, the proposed CESVM explicitly incorporates inspection-related expenses and error types in the SVM algorithm. The proposed automated QMCS is verified and validated using an automotive door-trim manufacturing process. Next, we perform a design of experiment to assess the sensitivity analysis of the proposed framework. The proposed model is found to be effective and could be viewed as an alternative or complementary tool for the traditional quality inspection system.

     

Loosening mechanism of threaded fastener for complex structures

Journal of Mechanical Science and Technology - Threaded fasteners are widely used in mechanical structures primarily owing to their easy disassembly for maintenance and low cost. However, the...     

Hot working characteristics of S32760 super duplex stainless steel

Journal of Mechanical Science and Technology - Hot deformation behavior of S32760 super austenitic stainless steel was studied in the temperature range of 950 ∼ 1250 °C and strain rate...     

A study on 65 % potential efficiency of the gas turbine combined cycle

Journal of Mechanical Science and Technology - This study investigates the possibility of achieving 65 % efficiency in a gas turbine combined cycle. Several options to realize it were compared. A...     

Permeability characteristics of carbonated concrete considering capillary pore structure

During carbonation process, the calcium phases present in cement are attacked by CO₂ and converted into CaCO₃ and the permeability of concrete is changing due to the change in porosity. The rate of carbonation depends upon porosity and moisture content of the concrete. Especially in underground reinforced concrete structures, the interior portion of concrete surface may be exposed to carbonation and the exterior portion of concrete surface exposed to wet soil or underground water. As carbonation proceeds from outer surface into internal portion of concrete, microstructure is also changed continuously from outer surface into internal portion of concrete. Even the deteriorations in the structures due to the carbonation have been reported more, research on permeability characteristics of concrete considering carbonation and micro-structural information is very scarce.In this study, the permeability coefficient in carbonated concrete is derived by applying a capillary pore structure formation model in carbonated cement mortar and assuming that aggregates do not affect carbonation process in early-aged concrete as a function of porosity. The permeability obtained from the micro-level modeling for carbonated concrete is verified with the results of accelerated carbonation test and water penetration test in cement mortar.