DECENTRALIZED SOCIAL NETWORK SERVICE USING THE WEB HOSTING SERVER FOR PRIVACY PRESERVATION

In recent years, the number of subscribers of the social network services such as Facebook and Twitter has increased rapidly. In accordance with the increasing popularity of social network services, concerns about user privacy are also growing. Existing social network services have a centralized structure that a service provider collects all the user’s profile and logs until the end of the connection. The information collected typically useful for commercial purposes, but may lead to a serious user privacy violation. The user’s profile can be compromised for malicious purposes, and even may be a tool of surveillance extremely. In this paper, we remove a centralized structure to prevent the service provider from collecting all users’ information indiscriminately, and present a decentralized structure using the web hosting server. The service provider provides only the service applications to web hosting companies, and the user should select a web hosting company that he trusts. Thus, the user’s information is distributed, and the user’s privacy is guaranteed from the service provider

Cryptanalysis and improvement of a biometrics-based multi-server authentication with key agreement scheme

In 2010, Yoon et al. proposed a robust biometrics- based multi-server authentication with key agreement scheme for smart cards on elliptic curve cryptosystem. In this letter, however, we show that Yoon et al.’s scheme is vulnerable to off-line password guessing attack and propose an improved scheme to prevent the attack

Gypsum-Dependent Effect of NaCl on Strength Enhancement of CaO-Activated Slag Binders

This study explores the combined effect of NaCl and gypsum on the strength of the CaO-activated ground-granulated blast furnace slag (GGBFS) binder system. In the CaO-activated GGBFS system, the incorporation of NaCl without gypsum did not improve the strength of the system. However, with the presence of gypsum, the use of NaCl yielded significantly greater strength than the use of either gypsum or NaCl alone. The presence of NaCl largely increases the solubility of gypsum in a solution, leading to a higher concentration of sulfate ions, which is essential for generating more and faster formations of ettringite in a fresh mixture of paste. The significant strength enhancement of gypsum was likely due to the accelerated and increased formation of ettringite, accompanied by more efficient filling of pores in the system

Synergetic Influence of Microcrystalline Quartz and Alkali Content in Aggregate on Deterioration of Concrete Railroad Ties Used for 15 Years in High-Speed Railways

This study investigated the deteriorations of precast prestressed concrete (PSC) ties that were used for 15 years in high-speed railways in Korea and its damaging mechanism. The collected PSC ties with longitudinal cracks on sides and map cracks on surfaces exhibited strength degradation. The deteriorations were likely related to alkali-silica reaction (ASR) and delayed ettringite formation (DEF) together, given that the presence of massive ettringite crystals and the decomposition of ASR gel were found from microstructural analyses. Although there were no typical reactive siliceous aggregates for ASR in this study, ASR cracks were generated in the PSC ties. This is because the aggregates in the PSC ties with cracks were potentially reactive, and its high alkali-silica reactivity was likely attributable to the presence of microcrystalline quartz, supplying reactive SiO2 to trigger ASR. Furthermore, the alkali content in aggregates was associated with the deterioration of the PSC ties. The alkali-bearing minerals in aggregates (i.e., alkali feldspars) likely supplied enough alkalis for ASR. Besides, micas in aggregates could promote ASR due to their porous structure, which helps easy water ingress

Use of Coal Bottom Ash and CaO-CaCl2-Activated GGBFS Binder in the Manufacturing of Artificial Fine Aggregates through Cold-Bonded Pelletization

This study investigated the use of coal bottom ash (bottom ash) and CaO-CaCl2-activated ground granulated blast furnace slag (GGBFS) binder in the manufacturing of artificial fine aggregates using cold-bonded pelletization. Mixture samples were prepared with varying added contents of bottom ash of varying added contents of bottom ash relative to the weight of the cementless binder (= GGBFS + quicklime (CaO) + calcium chloride (CaCl2)). In the system, the added bottom ash was not simply an inert filler but was dissolved at an early stage. As the ionic concentrations of Ca and Si increased due to dissolved bottom ash, calcium silicate hydrate (C-S-H) formed both earlier and at higher levels, which increased the strength of the earlier stages. However, the added bottom ash did not affect the total quantities of main reaction products, C-S-H and hydrocalumite, in later phases (e.g., 28 days), but simply accelerated the binder reaction until it had occurred for 14 days. After considering both the mechanical strength and the pelletizing formability of all the mixtures, the proportion with 40 relative weight of bottom ash was selected for the manufacturing of pilot samples of aggregates. The produced fine aggregates had a water absorption rate of 9.83% and demonstrated a much smaller amount of heavy metal leaching than the raw bottom ash

MICROSTRUCTURE ANALYSIS OF CHEMICALLY-ACTIVATED FLY ASH BINDERS, BOTTOM ASH AGGREGATE, AND DETERIORATED CONCRETE

Department of Urban and Environmental Engineering (Urban Infrastructure Engineering)Microstructural characterization including identification of reaction products and pore structure of the new developed chemically-activated fly ash binder, cold-bonded pelletized bottom ash aggregate, and deteriorated concrete ties using X-ray fluorescence spectroscopy, laser diffraction particle size analyzer, compressive strength test, thermogravimetric analysis, mercury intrusion porosimetry, pH meter, petrographic analysis, and scanning electron microscopy with energy dispersive spectroscopy analysis. The existing cementless fly ash binder has low mechanical performance that cannot replace the use of Portland cement. Thus, a new CaO-activated fly ash binder with the use of CaCl2 was developed and the significant enhancing effect of CaCl2 on the strength development of the CaO-activated Class F fly ash system was reported. The strength enhancement was mainly achieved because the presence of CaCl2 promoted (1) a higher degree of fly ash dissolution, (2) increasing C-S-H formation, and (3) an overall reduction of pore size and volume. However, although a higher content of CaCl2 induced more C-S-H formation, leading to strength improvement, an excessive dosage of CaCl2 was disadvantageous for the strength development because the strength was significantly reduced by the formation of calcium oxychloride, which generally causes expansive cracking and depends on w/b; thus, the best quantity of CaCl2 for the greatest strength was determined differently by the w/b ratio. In XRD, when CaCl2 was present, Ca(OH)2 was mostly rapidly consumed mainly due to the new formation of hydrocalumite, and more C-S-H formation from the enhanced pozzolanic reaction between Ca(OH)2 and the amorphous phase of fly ash. When CaCl2 was used more than a certain limit, calcium oxychloride formed. In TG, as the CaCl2 content increased, although the quantities of hydrocalumite did not significantly change, the quantity of C-S-H increased. The ICP-OES results showed that the fly ash was significantly more dissolved at an early age with more CaCl2 content which differs from the accelerating effect of CaCl2 on the cement hydration. Last, through the MIP and phase diagram analysis, the samples with the synthesis of calcium oxychloride had relatively large pores near 1???10 ??m. These pores were likely the results of expansive cracking due to the formation of calcium oxychloride. The CaO-CaCl2-activated fly ash binder can be used as a high strength structural binder for the production of construction products (e.g., cementless high strength bricks and blocks). Sugar is used as a chemical admixture to delay the hydration reaction of Portland cement. However, in Ca(OH)2-Na2CO3-activated Class F fly ash system, sugar acts not only (1) delaying setting time, but also (2) enhancing compressive strength with high temperature curing which has never been reported in previous studies. This was attributed to the (1) higher degree of dissolution of fly ash and Ca(OH)2, (2) more C-S-H formation, and (3) reduction in pore size and volume. Although false set of Portland cement mostly occurs owing to secondary gypsum crystallization, the false set of the system was likely ascribed to calcite formation, which is possibly produced from the initial reaction of Ca(OH)2 and Na2CO3. However, in the presence of sugar, the false set did not occur because the calcite formation was obstructed, possibly due to the formation of a calcium-sugar complex acting as a retardation barrier at room temperature. At room temperature, the samples with sugar did not gain any strength until 24 h. However, the use of sugar at elevated curing temperature significantly increased the compressive strength. The ICP-OES results provided that important indication of calcium complexation of sugar, which increases dissolution of calcium compound by forming sugar-calcium complex, causing greater dissolution of fly ash. However, unlike at the room temperature, the retardation barrier was either removed or weakened at elevated temperatures, thus facilitating a pozzolanic reaction and C-S-H formation and resulting in a significant improvement in the compressive strength of the system. The pH values of Ca(OH)2-Na2CO3-activated fly ash diluted solution samples were above 14, which indicates that NaOH was likely produced from the mixture of Ca(OH)2 and Na2CO3. Regardless of the presence of sugar, high curing temperatures increased the dissolution of fly ash and the strength of the system. Microstructural characterizing techniques were used to investigate the concrete deteriorations (i.e., map cracking and longitudinal cracking) of the 15-year used high-speed railroad PSC ties in Korea. However, the main causes of the deterioration in this study were slightly different from the typical major causes for ASR; the deterioration was primarily due to (1) the presence of micro-sized quartz grains, (2) the alkali release from the alkali-bearing minerals such as feldspar in aggregates, and (3) the presence of fragile porous mica which promote concrete deterioration. Static flexural loading test shows that strength of the damaged PSC ties significantly decreased, indicating that generation of significant damages inside the concrete. In particular, the strength of the damaged PSC ties with mapping cracks showed only ~53% to the design fracture load, which must be rejected for use. XRD analysis for the coarse aggregate shows that no aggregates contained reactive amorphous phase which is well-known cause of ASR. The aggregates of the damaged PSC ties contained various types of alkali-bearing minerals (i.e., microcline, sanidine, and orthoclase). These feldspars were known to release alkali content and then causing ASR cracking even in low alkali cement concretes. TG results show that ASR gel and ettringite only existed in the damaged PSC ties, indicating that the concrete deterioration might be evidently associated with ASR and DEF. Polarized light microscope analysis confirmed that the coarse aggregate of the damaged PSC ties was mainly composed of micro-sized quartz grains, which is potentially deleterious reactive, while that of the undamaged PSC ties consisted of large quartz grains, which is non-reactive. ICP-OES results show that the more severely damaged PSC ties, the more reactive aggregates existed in it. The dissolution of aggregate might be strongly linked with size of the quartz grains in the aggregate. In particular, the aggregates released large quantities of alkalis (Na+K) as well as Si and Al ions under alkaline environment. The aggregates of the damaged PSC ties released more alkalis than in those of the undamaged PSC ties. The alkali release was more accelerated in higher pH environment. From the results of pH test and dissolution of Si, the aggregates in the damaged PSC ties were potentially reactive while those of the undamaged PSC ties were innocuous aggregates. SEM analysis displays that micro-cracks were found in the damaged PSC ties while the dense ITZ existed in the undamaged PSC ties. In particular, in the damaged PSC ties, (1) ettringite-filled air voids, (2) ettringite-covered fractured surface, and (3) penetrating cracks from aggregate into matrix were found, which are typical microstructural features of DEF and ASR. Finally, material characterizations was also used to manufacture disk-pelletized aggregate involving bottom ash and GGBFS. The adding bottom ash in this study increased early compressive strength before 14 days, although it was not beneficial in improving the 28-day strength. However, when the additional bottom ash was over a certain limit (80 relative weight in this study), the early strength improvement vanished. The results of the XRD, TG, ICP-OES, and IC tests indicate that the bottom ash was not entirely inert in the binder reaction but was selectively soluble depending on the type of element; that is, Ca, Si, and Mg were likely present in a dissolvable state while Al was not. Additionally, the presence of the bottom ash in the mixture likely suppressed the dissolution of sulfur in the GGBFS. The main reaction products were C-S-H and hydrocalumite although the bottom ash was dissolved to some extent, this did not affect. However, when a proper amount (up to 60 relative weight) of bottom ash was added, it appears to have increased formation of C-S-H before 14 days, as the concentrations of Ca and Si were increased at the early age. After considering mechanical strength and pelletizing formability, the mixture proportion B/S0.4 was selected for manufacturing artificial fine aggregates. The bottom ash particles seem to have acted as nucleating seeds during the pelletization due to their wet surfaces after water spraying. The water absorption of the artificial fine aggregates was 9.83 wt%. In addition, all target heavy metals were leached far less in the produced aggregates (B/S0.4) than in the bottom ash, and no concentration was detected for Ni, Cu, Pb, Cr, Cd, and As in the produced aggregates.clos

Use of Coal Bottom Ash and CaO-CaCl2-Activated GGBFS Binder in the Manufacturing of Artificial Fine Aggregates through Cold-Bonded Pelletization

This study investigated the use of coal bottom ash (bottom ash) and CaO-CaCl2-activated ground granulated blast furnace slag (GGBFS) binder in the manufacturing of artificial fine aggregates using cold-bonded pelletization. Mixture samples were prepared with varying added contents of bottom ash of varying added contents of bottom ash relative to the weight of the cementless binder (= GGBFS + quicklime (CaO) + calcium chloride (CaCl2)). In the system, the added bottom ash was not simply an inert filler but was dissolved at an early stage. As the ionic concentrations of Ca and Si increased due to dissolved bottom ash, calcium silicate hydrate (C-S-H) formed both earlier and at higher levels, which increased the strength of the earlier stages. However, the added bottom ash did not affect the total quantities of main reaction products, C-S-H and hydrocalumite, in later phases (e.g., 28 days), but simply accelerated the binder reaction until it had occurred for 14 days. After considering both the mechanical strength and the pelletizing formability of all the mixtures, the proportion with 40 relative weight of bottom ash was selected for the manufacturing of pilot samples of aggregates. The produced fine aggregates had a water absorption rate of 9.83% and demonstrated a much smaller amount of heavy metal leaching than the raw bottom ash

Novel cell balancing applied near-field coupling and Serial–Parallel Circuit configuration

This paper proposes a near-field cell balancing method to be applied to batteries of higher capacity and power. This method involves a wireless power transfer to balance battery cells, which produces higher efficiency than conventional passive approaches, and faster equalization than active approaches. Cell balancing is a crucial function of the battery management system (BMS) that maintains the balance of charge and discharge between cells of individual batteries. Furthermore, this method is designed to meet the increasing demand for faster cell balancing associated with high-capacity and high-power batteries. We selected a serial–parallel configuration to minimize the technical concern for isolation, or energy transfer to unselected cells. Experiments were conducted with two battery cells, and voltage equalization accelerated by 51% when the proposed cell balancing approach was applied

Microstructural and strength improvements through the use of Na2CO3 in a cementless Ca(OH)2-activated Class F fly ash system

This study explores the beneficial effects of Na2CO3 as an additive for microstructural and strength improvements in a Ca(OH)2-activated fly ash system. NaOH-activated fly ash samples were also tested to compare the effect of Na2CO3. Compressive strength testing, XRD, SEM/BSE/EDS, 29Si/27Al MAS-NMR, MIP and TGA were performed. The testing results indicate that the use of Na2CO3 for Ca(OH)2-activation led to a noticeable improvement in strength and microstructure, primarily due to (1) more dissolution of raw fly ash at an early age, (2) more formation of C-S-H [or C-S-H(I)], (3) porosity reduction, and (4) pore-size refinement. We also found that (1) an early high alkalinity from the NaOH formation was not a major cause of strength, (2) geopolymer was not formed despite the early NaOH formation, and (3) no visible pore-filling action of CaCO3 was observed. However, Na2CO3 did not produce any improvement in strength for NaOH-activated fly ash.close