Kyonggi University

Oxide nanofluids were produced and their thermal conductivities were measured by a transient hot-wire method. The experimental results show that these nanofluids, containing a small amount of nanoparticles, have substantially higher thermal conductivities than the same liquids without nanoparticles. Comparisons between experiments and the Hamilton and Crosser model show that the model can predict the thermal conductivity of nanofluids containing large agglomerated Al2O3 particles. However, the model appears to be inadequate for nanofluids containing CuO particles. This suggests that not only particle shape but size is considered to be dominant in enhancing the thermal conductivity of nanofluids.

In this letter, we report an experimental correlation [Eqs. (1a) and (1b) or (1c)] for the thermal conductivity of Al2O3 nanofluids as a function of nanoparticle size (ranging from 11nmto150nm nominal diameters) over a wide range of temperature (from 21to71°C). Following the previously proposed conjecture from the theoretical point-of-view (Jang and Choi, 2004), it is experimentally validated that the Brownian motion of nanoparticles constitutes a key mechanism of the thermal conductivity enhancement with increasing temperature and decreasing nanoparticle sizes.

The primary research objective of this study rests on presenting and validating a model for the antecedents and consequences of consumer trust in the context of online purchase decision-making by means of simulation and survey methods. For this purpose, the study seeks to validate the correlation and causal relationships among the model's elements involving antecedents to trust (transactional security, web-site properties, search functionality, and personal variables), consequences (purchase intention), and mediating variable (web-site awareness). Based on the findings of a controlled simulation study involving 122 college students, are the following major results: (1) web-site trust showed a significant response to site properties including the image-related variables such as company awareness and company reputation, while satisfaction significantly responded to navigation functionality; (2) personal variables such as familiarity with e-commerce and prior satisfaction with e-commerce were found to have high correlation with web-site satisfaction as well as trust; (3) web-site trust, web-site satisfaction, and web-site awareness all influenced the online-purchase intention, and (4) web-site trust and web-site satisfaction had a high correlation. The findings of this study suggest a new approach to understanding and identifying the antecedents and consequences of web-site trust whose importance is increasing in the study of Internet commerce. Also, the study findings provide the Internet marketers with the managerial implications to establish effective online marketing strategy.

The rates for up-conversion intersystem crossing (UISC) from the T1 state to the S1 state are calculated for a series of organic emitters with an emphasis on thermally activated delayed fluorescence (TADF) materials. Both the spin–orbit coupling and the energy difference between the S1 and T1 states (ΔEST) are evaluated, at the density functional theory (DFT) and time-dependent DFT levels. The calculated UISC rates and ΔEST values are found to be in good agreement with available experimental data. Our results underline that small ΔEST values and sizable spin–orbit coupling matrix elements have to be simultaneously realized in order to facilitate UISC and ultimately TADF. Importantly, the spatial separation of the highest occupied and lowest unoccupied molecular orbitals of the emitter, a widely accepted strategy for the design of TADF molecules, does not necessarily lead to a sufficient reduction in ΔEST; in fact, either a significant charge-transfer (CT) contribution to the T1 state or a minimal energy difference between the local-excitation and charge-transfer triplet states is required to achieve a small ΔEST. Also, having S1 and T1 states of a different nature is found to strongly enhance spin–orbit coupling, which is consistent with the El-Sayed rule for ISC rates. Overall, our results indicate that having either similar energies for the local-excitation and charge-transfer triplet states or the right balance between a substantial CT contribution to T1 and somewhat different natures of the S1 and T1 states, paves the way toward UISC enhancement and thus TADF efficiency improvement.

Since the seminal work of Tang and Vanslyke in 1987 on small-molecule emitters and that of Friend and co-workers in 1990 on conjugated-polymer emitters, organic light-emitting diodes (OLEDs) have attracted much attention from academia as well as industry, as the OLED market is estimated to reach the $30 billion mark by the end of 2018. In these first-generation organic emitters, on the basis of simple spin statistics, electrical excitation resulted in the formation of ∼25% singlet excitons and ∼75% triplet excitons. Radiative decay of the singlet excitons to the singlet ground state leads to a prompt fluorescence emission, while the triplet excitons only lead to weak phosphorescence due to the very small spin-orbit couplings present in purely organic molecules. The consequence is a ca. 75% energy loss, which triggered wide-ranging efforts to try and harvest as many of the triplet excitons as possible. In 1998, Thompson, Forrest, and their co-workers reported second-generation OLED emitters based on coordination complexes with heavy transition metals (e.g., iridium or platinum). Here, the triplet excitons stimulate efficient and fast phosphorescence due to the strong spin-orbit couplings enabled by the heavy-metal atoms. Internal quantum efficiencies (IQE) up to 100% have been reported, which means that for every electron injected into the device, a photon is emitted. While these second-generation emitters are those mainly exploited in current OLED applications, there is strong impetus from both cost and environmental standpoints to find new ways of exploiting purely organic emitters, which in addition can offer greater flexibility to fine-tune the electronic and optical properties by exploiting the synthetic organic chemistry toolbox. In 2012, Adachi and co-workers introduced a promising strategy, based on thermally activated delayed fluorescence (TADF), to harvest the triplet excitons in purely organic molecular materials. These materials now represent the third generation of OLED emitters. Impressive photophysical properties and device performances have been reported, with internal quantum efficiencies also reaching nearly 100%. Our objectives in this Account are threefold: (i) to lay out a comprehensive description, at the molecular level, of the fundamental photophysical processes behind TADF emitters; (ii) to discuss some of the challenges facing the design of TADF emitters, such as the need to balance the efficiency of thermal activation of triplet excitons into the singlet manifold with the efficiency of radiative transition to the ground state; and (iii) to highlight briefly some of the recent molecular-design strategies that pave the way to new classes of TADF materials.

A coumarin-based fluorescent chemodosimeter with a salicylaldehyde functionality as a binding site has been developed for selective detection of cyanide anions over other anions in water at biological pH.

BACKGROUND: Studies suggest that vitamin D supplementation may reduce cancer and fracture risks. PURPOSE: To examine the benefits and harms of vitamin D with or without calcium supplementation on clinical outcomes of cancer and fractures in adults. DATA SOURCES: English-language studies identified from MEDLINE and the Cochrane Central Register of Controlled Trials through July 2011. STUDY SELECTION: Randomized, controlled trials (RCTs), prospective cohort studies, and nested case-control studies reporting incidence of or death from cancer and fracture outcomes. DATA EXTRACTION: Multiple reviewers extracted details about participant characteristics, including baseline vitamin D status and use of supplements; details of statistical analyses, including adjustments for confounding; and methodological quality. Differences were resolved by consensus. DATA SYNTHESIS: 19 RCTs (3 for cancer and 16 for fracture outcomes) and 28 observational studies (for cancer outcomes) were analyzed. Limited data from RCTs suggested that high-dose (1000 IU/d) vitamin D supplementation can reduce the risk for total cancer, and data from observational studies suggested that higher blood 25-hydroxyvitamin D (25-[OH]D) concentrations might be associated with increased risk for cancer. Mixed-effects dose-response meta-analyses showed that each 10-nmol/L increase in blood 25-(OH)D concentration was associated with a 6% (95% CI, 3% to 9%) reduced risk for colorectal cancer but no statistically significant dose-response relationships for prostate and breast cancer. Random-effects model meta-analysis showed that combined vitamin D and calcium supplementation reduced fracture risk (pooled relative risk, 0.88 [CI, 0.78 to 0.99]) in older adults, but the effects differed according to study setting: institution (relative risk, 0.71 [CI, 0.57 to 0.89]) versus community-dwelling (relative risk, 0.89 [CI, 0.76 to 1.04]). One RCT showed adverse outcomes associated with supplementation, including increased risk for renal and urinary tract stones. LIMITATIONS: Most trial participants were older (aged≥65 years) postmenopausal women. Observational studies were heterogeneous and were limited by potential confounders. CONCLUSION: Combined vitamin D and calcium supplementation can reduce fracture risk, but the effects may be smaller among community-dwelling older adults than among institutionalized elderly persons. Appropriate dose and dosing regimens, however, require further study. Evidence is not sufficiently robust to draw conclusions regarding the benefits or harms of vitamin D supplementation for the prevention of cancer. PRIMARY FUNDING SOURCE: Agency for Healthcare Research and Quality.

Abstract This paper investigates the way in which environmental responsibility impacts on corporate financial performance, measured by return on equity (ROE) and return on assets (ROA). Using a sample of Korean firms covering the period 2011–2012, and employing two different test methods, namely the OLS and 2SLS methods, we show that the relationships between environmental responsibility performance and firms’ ROE and ROA are positive and statistically significant. However, we show that research and development (R&D) intensity (expenditure) does not affect either environmental responsibility or corporate financial performance. The results of this analysis encourage further empirical analysis of the industries, as well as the use of more than one estimation method to determine environmental responsibility and corporate financial performance within firms. Copyright © 2014 John Wiley & Sons, Ltd and ERP Environment

Designing a highly efficient catalyst is essential to improve the electrochemical performance of Li-O2 batteries for long-term cycling. Furthermore, these batteries often show significant capacity fading due to the irreversible reaction characteristics of the Li2O2 product. To overcome these limitations, we propose a bifunctional composite catalyst composed of electrospun one-dimensional (1D) Co3O4 nanofibers (NFs) immobilized on both sides of the 2D nonoxidized graphene nanoflakes (GNFs) for an oxygen electrode in Li-O2 batteries. Highly conductive GNFs with noncovalent functionalization can facilitate a homogeneous dispersion in solution, thereby enabling simple and uniform attachment of 1D Co3O4 NFs on GNFs without restacking. High first discharge capacity of 10 500 mAh/g and superior cyclability for 80 cycles with a limited capacity of 1000 mAh/g were achieved by (i) improved catalytic activity of 1D Co3O4 NFs with large surface area, (ii) facile electron transport via interconnected GNFs functionalized by Co3O4 NFs, and (iii) fast O2 diffusion through the ultrathin GNF layer and porous Co3O4 NF networks.

There are currently a large variety of wireless access networks, including the emerging vehicular ad hoc networks (VANETs). A large variety of applications utilizing these networks will demand features such as real-time, high-availability, and even instantaneous high-bandwidth in some cases. Therefore, it is imperative for network service providers to make the best possible use of the combined resources of available heterogeneous networks (wireless area networks (WLANs), Universal Mobile Telecommunications Systems, VANETs, Worldwide Interoperability for Microwave Access (WiMAX), etc.) for connection support. When connections need to migrate between heterogeneous networks for performance and high-availability reasons, seamless vertical handoff (VHO) is a necessary first step. In the near future, vehicular and other mobile applications will be expected to have seamless VHO between heterogeneous access networks. With regard to VHO performance, there is a critical need to develop algorithms for connection management and optimal resource allocation for seamless mobility. In this paper, we develop a VHO decision algorithm that enables a wireless access network to not only balance the overall load among all attachment points (e.g., base stations and access points) but also maximize the collective battery lifetime of mobile nodes (MNs). In addition, when ad hoc mode is applied to 3/4G wireless data networks, VANETs, and IEEE 802.11 WLANs for a more seamless integration of heterogeneous wireless networks, we devise a route-selection algorithm for forwarding data packets to the most appropriate attachment point to maximize collective battery lifetime and maintain load balancing. Results based on a detailed performance evaluation study are also presented here to demonstrate the efficacy of the proposed algorithms.

Purpose The purpose of this paper is to explore structural relationships between quality, destination image, perceived value, tourist satisfaction and destination loyalty with emphasis on the mediating effect of tourist satisfaction on relations between destination image and destination loyalty, and between perceived value and destination loyalty in the context of small-scale sporting events. Design/methodology/approach Construct validity of the measurement scale was verified by confirmatory factor analysis, factor loadings, average variance extracted, construct reliability and correlation analysis. Reliability of the measurement scale was verified by Cronbach’s α analysis. A structural equation modeling test with maximum likelihood estimation was used to test structural relationships between variables in the proposed model using the responses of 311 participants. Findings Results showed significant and powerful impacts of: event quality, destination image and perceived value on tourist satisfaction; destination image, perceived value, and tourist satisfaction on destination loyalty and demonstrated; and tourist satisfaction fully mediates relationships between destination image and destination loyalty, and between perceived value and destination loyalty. Originality/value The study shows: it is meaningful to include quality and value in tourism destination image-satisfaction-loyalty models; provides empirical evidence that tourist satisfaction fully mediates the relation between perceived value and destination loyalty; and confirms small-scale as well as large-scale sporting events should be viewed as important aspects of marketing strategies aimed at improving quality, image, value, satisfaction and loyalty.

The robust stabilization method via the dynamic surface control (DSC) is proposed for uncertain nonlinear systems with unknown time delays in parametric strict-feedback form. That is, the DSC technique is extended to state time delay nonlinear systems with linear parametric uncertainties. The proposed control system can overcome not only the problem of ldquoexplosion of complexityrdquo inherent in the backstepping design method but also the uncertainties of the unknown time delays by choosing appropriate Lyapunov-Krasovskii functionals. In addition, we prove that all the signals in the closed-loop system are semiglobally uniformly bounded. Finally, an example is provided to illustrate the effectiveness of the proposed control system.

Scalar and vector Kalman filters are implemented for filtering speech contaminated by additive white noise or colored noise, and an iterative signal and parameter estimator which can be used for both noise types is presented. Particular emphasis is placed on the removal of colored noise, such as helicopter noise, by using state-of-the-art colored-noise-assumption Kalman filters. The results indicate that the colored noise Kalman filters provide a significant gain in signal-to-noise ratio (SNR), a visible improvement in the sound spectrogram, and an audible improvement in output speech quality, none of which are available with white-noise-assumption Kalman and Wiener filters. When the filter is used as a prefilter for linear predictive coding, the coded output speech quality and intelligibility are enhanced in comparison to direct coding of the noisy speech.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Abstract Proton‐exchange‐membrane water electrolysis (PEMWE) requires an efficient and durable bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, Ir‐based electrocatalyst is designed using the high entropy alloy (HEA) platform of ZnNiCoIrX with two elements (X: Fe and Mn). A facile dealloying in the vacuum system enables the construction of a nanoporous structure with high crystallinity using Zn as a sacrificial element. Especially, Mn incorporation into HEAs tailors the electronic structure of the Ir site, resulting in the d‐band center being far away from the Fermi level. Downshifting of the d‐band center weakens the adsorption energy with reaction intermediates, which is beneficial for catalytic reactions. Despite low Ir content, ZnNiCoIrMn delivers only 50 mV overpotential for HER at −50 mA cm −2 and 237 mV overpotential for the OER at 10 mA cm −2 . Furthermore, ZnNiCoIrMn shows almost constant voltage for the HER and OER for 100 h and a high stability number of 3.4 × 10 5 n hydrogen n Ir −1 and 2.4 × 10 5 n oxygen n Ir −1 , demonstrating the exceptional durability of the HEA platform. The compositional engineering of ZnNiCoIrMn limits the diffusion of elements by high entropy effects and simultaneously tailors the electronic structure of active Ir sites, resulting in the modified cohesive and adsorption energies, all of which can suppress the dissolution of elements.

This brief proposes an adaptive neural sliding mode control method for trajectory tracking of nonholonomic wheeled mobile robots with model uncertainties and external disturbances. The dynamic model with model uncertainties and the kinematic model represented by polar coordinates are considered to design a robust control system. Self recurrent wavelet neural networks (SRWNNs) are used for approximating arbitrary model uncertainties and external disturbances in dynamics of the mobile robot. From the Lyapunov stability theory, we derive online tuning algorithms for all weights of SRWNNs and prove that all signals of a closed-loop system are uniformly ultimately bounded. Finally, we perform computer simulations to demonstrate the robustness and performance of the proposed control system.

In the era of ubiquitous sensors and smart devices, detecting malware is becoming an endless battle between ever-evolving malware and antivirus programs that need to process ever-increasing security related data. For malware detection, various approaches have been proposed. Among them, dynamic analysis is known to be effective in terms of providing behavioral information. As malware authors increasingly use obfuscation techniques, it becomes more important to monitor how malware behaves for its detection. In this paper, we propose a novel approach for dynamic analysis of malware. We adopt DNA sequence alignment algorithms and extract common API call sequence patterns of malicious function from malware in different categories. We find that certain malicious functions are commonly included in malware even in different categories. From checking the existence of certain functions or API call sequence patterns matched, we can even detect new unknown malware. The result of our experiment shows high enough F-measure and accuracy. API call sequence can be extracted from most of the modern devices; therefore, we believe that our method can detect the malware for all types of the ubiquitous devices.

The effective management of water resources is essential to environmental stewardship and sustainable development. Traditional approaches to water resource management (WRM) struggle with real-time data acquisition, effective data analysis, and intelligent decision-making. To address these challenges, innovative solutions are required. Artificial Intelligence (AI) and Big Data Analytics (BDA) are at the forefront and have the potential to revolutionize the way water resources are managed. This paper reviews the current applications of AI and BDA in WRM, highlighting their capacity to overcome existing limitations. It includes the investigation of AI technologies, such as machine learning and deep learning, and their diverse applications to water quality monitoring, water allocation, and water demand forecasting. In addition, the review explores the role of BDA in the management of water resources, elaborating on the various data sources that can be used, such as remote sensing, IoT devices, and social media. In conclusion, the study synthesizes key insights and outlines prospective directions for leveraging AI and BDA for optimal water resource allocation.

Enzyme inhibitors are ubiquitous in all living systems, and their biological inhibitory activity is strongly dependent on their molecular shape. Here, we show that small zinc oxide nanoparticles (ZnO NPs)-pyramids, plates, and spheres-possess the ability to inhibit activity of a typical enzyme β-galactosidase (GAL) in a biomimetic fashion. Enzyme inhibition by ZnO NPs is reversible and follows classical Michaelis-Menten kinetics with parameters strongly dependent on their geometry. Diverse spectroscopic, biochemical, and computational experimental data indicate that association of GAL with specific ZnO NP geometries interferes with conformational reorganization of the enzyme necessary for its catalytic activity. The strongest inhibition was observed for ZnO nanopyramids and compares favorably to that of the best natural GAL inhibitors while being resistant to proteases. Besides the fundamental significance of this biomimetic function of anisotropic NPs, their capacity to serve as degradation-resistant enzyme inhibitors is technologically attractive and is substantiated by strong shape-specific antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), endemic for most hospitals in the world.

Factor VIII (fVIII) is a serum protein in the coagulation cascade that nucleates the assembly of a membrane-bound protease complex on the surface of activated platelets at the site of a vascular injury. Hemophilia A is caused by a variety of mutations in the factor VIII gene and typically requires replacement therapy with purified protein. We have determined the structure of a fully active, recombinant form of factor VIII (r-fVIII), which consists of a heterodimer of peptides, respectively containing the A1-A2 and A3-C1-C2 domains. The structure permits unambiguous modeling of the relative orientations of the 5 domains of r-fVIII. Comparison of the structures of fVIII, fV, and ceruloplasmin indicates that the location of bound metal ions and of glycosylation, both of which are critical for domain stabilization and association, overlap at some positions but have diverged at others.

With the present climate change and increasing world population, there is an urgent need to discover creative, efficient, and cost-effective natural products for the benefit of humanity. Biosurfactants are produced by various microorganisms that have several distinct properties compared to other synthetic surfactants, including mild production conditions, multifunctionality, higher biodegradability, and lower toxicity of living cells synthesis of active compounds. Due to their surface tension reducing, emulsion stabilizing, and biodegrading properties of these in place of chemical surfactants, they are generating huge demand in terms of research and usage. Biosurfactants are widely used in the food industry as food-formulation ingredients and antiadhesive agents as emulsifiers, de-emulsifiers, spreading agents, foaming agents, and detergents that find application in various fields such as agriculture, industrial sectors, and environmental recreation. Recent research focused more on heavy metal bioremediation from compost was achieved using biosurfactants-producing bacteria, which resulted in an improvement in compost quality. Although a number of studies on biosurfactants synthesis have been reported, very limited information on its cinematics and the consumption of renewable substrates are available. In this review paper, we made an attempt to critically review biosurfactants, their usage, research related to them, and challenges faced.