Search

Background: To investigate the impact of nutritional iodine deficiency on thyroid dysfunction (TD) in very low birth weight (VLBW) infants, we analyzed the association between iodine-deficient parenteral nutrition (PN) and TD requiring L-thyroxine (TD-LT4). Methods: Data of VLBW infants were obtained from the Korean Neonatal Network registry. Factors including duration of PN were analyzed according to TD-LT4. Results: TD-LT4 occurred in 490 (8.7%) of 5635 infants, and more frequently occurred in infants requiring PN for ≥4 weeks (10.2%). PN ≥ 4 weeks was one of the risk factors for TD-LT4, with an odds ratio (OR) of 1.346, p = 0.002. However, multivariate analysis showed that TD-LT4 was more of a risk for infants that were small for gestational age (OR 2.987, p < 0.001) and for other neonatal morbidities such as seizures (OR 1.787, p = 0.002) and persistent pulmonary hypertension (OR 1.501, p = 0.039) than PN ≥ 4 weeks (OR 0.791, p = 0.080). Conclusions: Prolonged iodine-deficient PN might affect TD-LT4 in VLBW infants. However, the effect of nutritional iodine deficiency on TD-LT4 risk was less than that of SGA or severe neonatal morbidities in Korean VLBW infants.

Environmental degradation in recent years has been threatening not only environmental sustainability but also human viability. To counter these threats, this study focuses on whether civic morality is associated with taxation for environmental protection (green taxation) and with higher pricing for environmental protection (green pricing) and whether the relationship between civic morality and green taxation, as well as that between civic morality and green pricing, is moderated by individuals’ perceptions of their own political participation. Employing the 2014 Korean General Social Survey and an ordered probit model, the study finds that civic morality is positively associated with green pricing and green taxation. Moreover, the positive relationship between civic morality and green pricing, as well as between civic morality and green taxation, is further strengthened when individuals’ perceptions of their own political participation are strong.

Since early 2020, the rapid expansion of COVID-19 has raised concerns about vaccine safety and the government’s handling of it. Particularly notable and concerning has been a growing number of people who oppose vaccines, as this opposition poses a threat to public health. Those for and against vaccination have become polarized along a political divide. Within this context, this study focuses on the role of political trust, exploring whether political ideology is associated with the perception that the government can ensure the safety of vaccines and whether there is a moderator that can alleviate the concerns of those who oppose the government’s handling of vaccine safety on ideological grounds. This study relies on the 2021 U.S. General Social Survey (GSS) and employs an ordered probit method because the dependent variable is an ordered category. The ordered probit model includes a weight provided by the U.S. GSS to account for the population. The sample size was 473 because of the inclusion of all the variables relevant to this study. The results obtained are as follows: First, conservatives associate negatively with support for the government’s handling of vaccine safety. Second, more importantly, conservatives exhibit a higher trust level toward the government to ensure vaccine safety if their level of political trust increases. The results point to important implications. Political ideology matters in how individuals view the government’s handling of vaccine safety. Political trust plays a key role in helping individuals alter their views toward the government’s handling of vaccine safety. This points to a need for the government to take political trust seriously and work hard to improve the public’s trust in the government.

Synthesizing the conservation of resource theory, proximal withdrawal state theory, and job demands-resources theory, the present study examined the relationships between two dimensions of emotional labor (i.e., surface and deep acting) and turnover intention, as well as the moderating role of perceived organizational support in these relationships, such as the context of Korean firefighters. Using survey data drawn from fire organizations in Gyeonggi-do, the largest province of South Korea, we found that both surface and deep acting are positively related to firefighter turnover intentions. Further analysis indicates that the perceived organizational support of firefighters, vital for public health and safety, attenuates the positive relationship between surface acting and turnover intention but has no significant moderating effect on the relationship between deep acting and turnover intention. Our results suggest that perceived organizational support acts through essential psychological resources to recover the loss of emotional resources and contributes to the retention of firefighter personnel who primarily perform challenging and stressful work, including firefighting and offering emergency medical services. Thus, this study examines a crucial tool to ensure firefighters’ public mental health.

A composite B-pillar was designed and manufactured by design optimization combined with an impact analysis. A carbon-fiber-reinforced plastic (CFRP) was used for the reinforcement part of the B-pillar assembly to substitute the conventional steel materials for reducing the weight of vehicle. To maximize the impact performance by finite element method, the equivalent static loads method was used. The shape, stacking sequence, and thickness of the CFRP reinforcement were optimized to minimize the deflection profile for improving the crashworthiness while reducing the weight. The designed CFRP B-pillar was manufactured and its performance was evaluated by a drop weight test. As a result, the CFRP B-pillar exhibited an improved impact performance and reduced weight compared to those of the conventional steel B-pillar.

In this study, a combined forming-structural analysis of composite structures was performed. Fiber orientation and shear angle changes of the composite materials during its thermo-compression molding processes were predicted with commercial software PAM-FORM. In addition, the material properties, such as elastic modulus and strength, from the shearing of woven fabrics, were measured. The predicted shear angle changes were transformed and reflected to the structural analysis by a self-developed vector-mapping program. The load-displacement curves of the composite structures from the combined forming and structural simulation were compared with the experimental compression and bending test results of hemispherical and U-shaped components, respectively. Finally, it was found that the mechanical behaviors of composite structures can be accurately predicted by the developed combined thermo-forming structural analysis method.

This paper is concerned with the improvement of a tensile test method and the material properties of carbon fiber reinforced polymer manufactured by resin transfer molding considering stacking sequences at various strain rates for auto-body. Auto-body structure experiences the strain rates up to several hundreds per second during car crash. In order to apply the carbon fiber reinforced polymer panel into auto-body structures, it is critical to acquire the material properties of carbon fiber reinforced polymer at various strain rates considering stacking sequences. The tensile test method is improved for acceptable test results. Test specimens are modified for high-speed tensile tests of carbon fiber reinforced polymer in order to achieve designated strain rates and eliminate the effect from unfavorable conditions of inhomogeneity of deformation. Various types of grip tab materials are employed for acceptable failure modes. Tensile tests have been carried out with non-crimp fabric made by 50K high strength carbon fiber (NCF) and woven fabric made by a 2/2 twill pattern of 3K high strength carbon fiber (TWILL) with different stacking sequences of 0° and 90° unidirectional cases as well as [0°/90°] and [45°/−45°] symmetric cases. Digital image correlation method and force equilibrium grid method are adopted for strain and stress measurement of a carbon fiber reinforced polymer specimen during a tensile test. The material properties acquired indicate that the carbon fiber has little rate dependency, while the epoxy matrix has remarkable rate hardening at strain rates from 0.001 s−1to 100 s−1.

In this study, design optimization of a composite hood for automobiles was carried out to mitigate the impact of pedestrian head injuries based on finite element analysis. Reduced vehicle, headform impactor and single hood models were established to obtain optimal composite hood designs. The carbon fiber reinforced composite (CFRP) and the hybrid Glass fiber reinforced composite (CFRP/GFRP) laminates were selected as composite material candidates. Both stacking angle sequence and topometry of the composite hood were optimized based on the equivalent static load method. After the optimization, the head injury criterion (HIC), deflection and weight were measured to evaluate the performance of the composite hood. The developed CFRP and hybrid CFRP/GFRP type hoods with optimized final design exhibited the improved impact performance and significant weight reduction while satisfying bending and torsion deflection requirements compared to those of conventional steel and aluminum hoods.

Car accidents involving pedestrians have become an issue of great concern owing to the high fatality and injury rates. To reduce the loss of life during car accidents, the safety of automobiles is evaluated on the basis of standards such as the Federal Motor Vehicle Safety Standards and the European New Car Assessment Program, which provide information about automobile safety to drivers and require manufacturers to produce safe automobiles. Regarding car accidents involving pedestrians, the head injury criterion is used to evaluate pedestrian injury when the head of the pedestrian hits the windshield. In this study, the windshield impact tests were numerically simulated using the Tuler–Butcher criterion as the failure criterion, and considering simulation conditions such as the types of element, the sizes of elements and the parameters of the failure criterion. A parametric study was conducted to investigate the effect of the simulation conditions on the key results such as the head injury criterion, the initial acceleration peak, the displacement and the cracking modes of the windshield, with the purpose of improving the accuracy of the simulation results. The results of the simulations were also compared with those of tests to determine the accuracy of the former.

In this paper, the non-linear mechanical behavior of shear deformed woven composite was predicted using a representative volume element (RVE) model based on multi-scale progressive failure analysis. The micro-scale RVE model, consisting of single fiber and a matrix, was employed to determine the stress amplification factor and distinguish the failure of each fiber and the matrix constituent. Then, a meso-scale RVE model of shear deformed twill woven composite was developed to predict non-linear behavior using micro-stress transferring with finite element simulation. Fiber yarn shapes were observed with respect to the shear angle of the twill fabric. Based on the observed yarn geometry, shear deformed twill composite was modeled by using the open source software TexGen. To prove validity of the proposed model, shear deformed twill woven composite was fabricated using a picture frame, followed by a vacuum assisted resin transfer molding process. Mechanical tests were conducted and the failure progress during the tests was observed to determine their failure analysis. As a result, a good correlation between the multi-scale progressive damage model and experimental results such as mechanical properties, the non-linear stress-strain curve, and failure modes were achieved.

Axial tension and transverse compression experiments on single fibers were performed to investigate the mechanical behavior of three high-performance fibers (Kevlar, Kevlar 129, and Twaron) with diameters in the order of 9e12 mm. The single fibers were manufactured from 1998 through 2008. A miniaturized tensile Kolsky bar was used to determine the tensile response of PPTA single fibers at a high strain rate. Gage length and strain rate were found to have minimum effects on the tensile strength of PPTA single fibers. Manufacturing time over a decade was found to have negligible effects on the tensile strength of the fibers. Initial transverse compression on the fibers reduces their ultimate tensile strengths. A high resolution scanning electron microscope (SEM) was also used to examine the fracture modes of transversely deformed fibers. Different types of fracture morphology were observed. 2010 Elsevier Ltd. All rights reserved.

Uniaxial tensile experiments were performed on pig skin to investigate the tensile stress–strain response at both quasi-static and dynamic rates of deformation. A Kolsky tension bar, also called a split Hopkinson tension bar (SHTB), was modified to conduct the dynamic experiments. Semiconductor strain gages were used to measure the low levels of the transmitted signal from pig skin. A pulse shaper technique was used for generating a suitable incident pulse to ensure stress equilibrium and approximate constant strain rate in the specimen of a thin skin sheet wrapped around the ends of the bars for minimizing radial inertia. In order to investigate the strain-rate effect over a wide range of strain rates, quasi-static tests were also performed. The experimental results show that pig skin exhibits rate-sensitive, orthotropic, and non-linear behavior. The response along the spine direction is stiffer at lower rate but is less rate sensitive than the perpendicular direction. An Ogden model with two material constants is adopted to describe the rate-sensitive tensile behavior of the pig skin.

We adopted a non-contact laser technique to measure axial small strain (

The mechanical behavior of A265 high-performance fibers was experimentally investigated at both low and high strain rates. Axial, transverse, and torsional experiments were performed to measure the five material constants on a single fiber assumed as a linear, transversely isotropic material. In order to determine the tensile response of the fiber at high rates, a modified Kolsky tensile bar, also known as a split Hopkinson tension bar (SHTB) for single-fiber tests, was used. The diameter of each fiber was measured individually using a high-resolution scanning electron microscope for accurate stress calculation. A pulse shaper technique was adopted to generate a smooth and constant-amplitude incident pulse to produce deformation in the fiber specimen at a nearly constant strain rate. The tensile strength of the fiber exhibits both rate and gage-length effects.

Studies of fracture and friction under dynamic loading conditions have benefited enormously from the use of optical methods of diagnosfis. Specifically, photoelasticity and high-speed photography have provided methods of detailed characterisation of these phenomena. In this paper, we present the results from experiments aimed at investigating fracture and frictional sliding under shear loading conditions.

Multi-layers of woven fabric, characterized by high strength, high flexibility and low density, have been widely used for protective systems, from bulletproof vests to turbine engine fragment barriers. Under ballistic impact, the kinetic energy of the projectile is absorbed by the fabrics deforming largely in out-of- plane direction, which retards the motion of the projectile. Interfacial friction between yarns is known as one of the factors that affect the energy absorption by the fabric. In this study, we experimentally investigated the mechanical response during the pulling out of a single yarn from a single layer of Kevlar® or Twaron® fabric at high rates. In order to perform the dynamic experiments, a pendulum impact was generated to pull out the yarn. Displacement was measured from a noncontact laser system and pull-out force signal was received by a quartz transducer connected to the yarn being pulled out. Quasi-static experiment was also performed to study the effects of loading rates on the mechanical response when a yarn is pulled out perpendicular to the fabric plane.