50 research outputs found
The Relationships of SNS Use, Social Achievement Goals, and Life Satisfaction: A Study of Korean College Students
Social networking sites (SNS) provide efficient communication. However, SNS use sometimes risks a user’s life satisfaction. Based on the prior findings that one’s social orientation influences the impact of SNS use on life satisfaction, this study examined the pathways to explain how SNS use affects individuals’ life satisfaction through social achievement goals. A main path model and two gender-specified path models were tested using 438 Korean college student samples. The results showed that social development goals mediated the relationships between active SNS use and life satisfaction across all three path models. The social demonstration approach goal was positively predicted by active SNS use in the main model and the male model, but it did not predict life satisfaction in both models. The social demonstration-avoidance goal was positively predicted by active SNS use in the main and female models. Still, it negatively predicted life satisfaction in both models. Implications and directions for future study are discussed
A Meta-Analysis of Construct Reliability Indices and Measurement Model Fit Metrics???
The present research examined the distributional properties of construct reliability indices and model fit metrics, explored relationships between and among the indices and metrics, and investigated variables influencing the relative magnitudes of the indices and metrics in structural equation measurement models. A broad-based meta-analysis of reported construct reliability indices and selected model fit metrics revealed modest relationships among reliability indices, minimal relationships among model fit metrics, and a virtual absence of relationships between reliability indices and model fit metrics. Differences in magnitudes of selected reliability indices and model fit metrics were found to primarily be a function of the (total) number of items employed in a measurement model. The implications of the findings suggest that the current practice of indiscriminately computing and reporting of reliability indices and model fit metrics based only on arbitrary heuristics should be abolished and replaced by theoretically justified indices and metrics. ?? This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License, CC BY 4.0, which permits unrestricted use, distribution, and reproduction, provided the original work is properly cited
When Bigger Is Not Greener: Ensuring the Sustainability of Power- to-Gas Hydrogen on a National Scale
As the prices of photovoltaics and wind turbines continue to decrease, more renewable electricity-generating capacity is installed globally. While this is considered an integral part of a sustainable energy future by many nations, it also poses a significant strain on current electricity grids due to the inherent output variability of renewable electricity. This work addresses the challenge of renewable electricity surplus (RES) utilization with target-scaling of centralized power-to-gas (PtG) hydrogen production. Using the Republic of Korea as a case study, due to its ambitious plan of 2030 green hydrogen production capacity of 0.97 million tons year-1, we combine predictions of future, season-averaged RES with a detailed conceptual process simulation for green H2 production via polymer electrolyte membrane (PEM) electrolysis combined with a desalination plant in six distinct scale cases (0.5-8.5 GW). It is demonstrated that at scales of 0.5 to 1.75 GW the RES is optimally utilized, and PtG hydrogen can therefore outperform conventional hydrogen production both environmentally (650-2210 Mton CO2 not emitted per year) and economically (16-30% levelized cost reduction). Beyond these scales, the PtG benefits sharply drop, and thus it is answered how much of the planned green hydrogen target can realistically be if on an industrial scale
Melatonin Synergizes with Sorafenib to Suppress Pancreatic Cancer via Melatonin Receptor and PDGFR-β/STAT3 Pathway
Background/Aims: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignant tumors with poor prognosis. Conventional chemotherapies including gemcitabine have failed owing to weak response and side effects. Hence novel treatment regimens are urgently needed to improve the therapeutic efficacy. In this study, we aimed to assess the anticancer activity of melatonin and sorafenib as a novel therapy against PDAC. Methods: We used various apoptosis assay and PDAC xenograft model to assess anticancer effect in vitro and in vivo. We applied phospho-receptor tyrosine kinase (RTK) array and phospho-tyrosine kinase array to explore the mechanism of the combined therapy. Western blotting, proximity ligation assay, and immunoprecipitation assay were also performed for validation. Results: Melatonin synergized with sorafenib to suppress the growth of PDAC both in vitro and in vivo. The effect was due to increased apoptosis rate of PDAC cells that was accompanied by mitochondria dysfunction. The enhanced anticancer efficacy by the co-treatment could be explained by blockade of PDGFR-β/STAT3 signaling pathway and melatonin receptor (MT)-mediated STAT3. Conclusions: Melatonin reinforces the anticancer activity of sorafenib by downregulation of PDGFR-β/STAT3 signaling pathway and melatonin receptor (MT)-mediated STAT3. The combination of the two agents might be a potential therapeutic strategy for treating PDAC
Individual Differences in Online Privacy Concern
We examined the effects of socio-demographics and personality traits on online privacy concern. We investigated this relationship in general and across different Internet functions. Using a large, diverse, population-representative sample (N = 5,242), we found that females, educated, and wealthier individuals tend to be concerned with online privacy to a greater extent. Among personality traits, agreeableness and conscientiousness were generally associated with an increased probability of being concerned with online privacy. These results imply that socio-demographics and personality traits provide explanatory insights into online privacy concern
Comparative Economic Optimization for an Overseas Hydrogen Supply Chain Using Mixed-Integer Linear Programming
As environmental problems become serious, many countries have been striving to change fossil-based energy to renewable and sustainable hydrogen energy. However, there are large capacity differences for each country's hydrogen production, making hydrogen trading necessary. Although extensive research has investigated hydrogen technologies and economics, to the best of our knowledge, no study has examined the optimization of the overall hydrogen supply chain, from overseas supply to domestic consumption, considering various feasibility scenarios. This is a case study on the hydrogen supply chain for South Korea, which is expected to be one of the major hydrogen-importing countries, considering the decarbonized hydrogen requirements of the importing country and the production capacities of exporting countries over two decades. This study's optimized results for a hydrogen supply chain via mixed-integer linear programming reveal that it is most feasible for South Korea to import blue hydrogen from Qatar and Russia and green hydrogen from UAE and India, using liquefied hydrogen in the near term. This is because of the significantly lesser resource prices compared to other countries. The share of blue hydrogen supply dominates in the near term, while the green hydrogen supply is expected to gradually prevail over blue hydrogen due to an exponential drop in the renewable electricity price. With the price drop of green hydrogen, green hydrogen purchases from other countries in tandem with the UAE are predicted, rather than the blue hydrogen supply, considering that long-term demand will exceed the UAE's predicted capacity
Carbon-neutral methanol synthesis as carbon dioxide utilization at different scales: Economic and environmental perspectives
Methanol is emerging as the carbon dioxide utilization technology and hydrogen carrier that can produce methanol using captured carbon dioxide and hydrogen. In this study, four cases were classified as methanol production according to which pathway was used to produce hydrogen: case 1 (steam methane reforming), case 2 (coal gasification), case 3 (water electrolysis), and case 4 (direct methanol production by carbon dioxide electrolysis). To figure out the best pathway in terms of economic and environmental perspectives, itemized cost estimation, sensitivity analysis, uncertainty analysis, and carbon footprint analysis were performed for four cases of methanol production with methanol production capacities of 1, 10, 20, and 50 ton d-1. From itemized cost estimation reflecting carbon footprint analysis results, respective unit methanol production costs of 3.66, 2.99, 3.69, and 0.55 kg- 1) from fossil fuel-based production, direct methanol production has become feasible than other cases. And, from sensitivity and uncertainty analysis, the cost of reactant and electricity were major economic parameters for cases 1-3 and case 4, respectively, and the possible unit methanol production cost ranges due to the cost fluctuations in future were investigated
Techno-economic analysis of a biological desulfurization process for a landfill gas (LFG) in Korea
We report techno-economic analysis of a biological desulfurization process to remove H2S and to produce sulfur from a landfill gas (2000 m3 h−1) produced in Korea. With a process simulation model developed using Aspen Plus??, parametric assessment to determine the effect of various operating parameters such as a NaOH flow rate, a NaOH concentration, and a recycle ratio has been carried out. Based on results from process simulation, economic analysis was conducted to evaluate feasibility of this technology in Korea through a cash flow diagram, net present value (NPV), and discounted payback period (DPBP). It was demonstrated that DPBP of 6.9 years and NPV of 0.39 MM$ were obtained with a 10% discount rate
Comparative numerical analysis for an efficient hydrogen production via a steam methane reforming with a packed-bed reactor, a membrane reactor, and a sorption-enhanced membrane reactor
Following the adoption of the Paris Agreement, H-2 has come to be considered a promising alternative energy carrier owing to its eco-friendly characteristics. However, H-2 is mostly obtained via carbon-based production methods, which account for approximately 96% of the global H-2 yield and emit CO2 as a by-product. A membrane reactor (MR) was introduced to produce H-2 more efficiently via a positive chemical equilibrium shift, according to Le Chatelier's principle. CaO was employed as a CO2 adsorbent in an MR to form a sorption-enhanced membrane reactor (SEMR), in which the additional CO2 removal enhanced the equilibrium shift. Additionally, the direction of sweep gas through the membrane with respect to that of the reactants, i.e., co-current or counter-current flow, was found to affect the performance of the reactors. In this study, numerical simulations based on chemical reaction kinetics were carried out to investigate the effects of the employment of H-2 separation membrane and/or CO2 adsorbent as well as those of co-current and counter-current flows. Based on the numerical simulation results, H-2 yield rates of 0.00143, 0.00145, 0.00127, 0.00121, and 0.00852 mol s(-1) were achieved using the SEMR with counter-current flow, SEMR with co-current flow, MR with counter-current flow, MR with co-current flow, and a packed-bed reactor, respectively. This showed that an SEMR can be used to not only enhance H-2 production but also achieve this in an environment-friendly manner
What is the best green propylene production pathway?: technical, economic, and environmental assessment
Owing to the increasing demand for propylene, many propylene production pathways have been developed, such as naphtha catalytic cracking, olefin metathesis, propane dehydrogenation, and methanol to propylene (MTP) conversion. As environmental regulations become more stringent, green propylene should be explored to enhance sustainable production and reduce CO2 emissions. MTP conversion through CO2 hydrogenation (indirect MeOH synthesis) and CO2 electrolysis (direct MeOH synthesis) has been explored as a green propylene production pathway. To evaluate the possibility of green propylene production from technical, economic, and environmental perspectives, process simulation, economic analysis, and environmental assessment were performed for MTP conversion via indirect and direct methanol synthesis. Furthermore, the best alternative for green propylene production was determined via an analytic hierarchy process, considering technical, economic, and environmental aspects, at the same time, with different weighted values of each criterion, under uncertainty. Our results indicated that MTP via direct MeOH synthesis was superior in cases where the environmental impact is the most important, while MTP via indirect MeOH synthesis was the most appropriate alternative for green propylene production, with the technical and economic impacts being more critical than the environmental impacts