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In this study, the effects of salinity on the equilibrium and kinetics of sulfur hexafluoride (SF6), 1,1,1,2-tetrafluoroethane (HFC134a), and their mixture were evaluated to analyze their potential...

Gas hydrates are nonstoichiometric nano-structured crystalline compounds which are stabilized by gas molecules incorporated in the cages made of hydrogen bonding of water molecules at suitable thermodynamic conditions. The gas hydrate as a technology has been successful for several potential applications in various engineering fields, such as, gas separation, carbon dioxide sequestration, gas storage and transportation, desalination of salt water and wastewater treatment. Recently, metal-based nanofluids are considered as interesting kinetic promoter candidates for accelerating formation of gas hydrates. Although organic-based kinetic promoters are widely studied for the rapid formation of gas hydrates, research of a new material system is still a challenge. In this study, Silver (Ag) nanofluids as kinetic promoter of sulfur hexafluoride (SF6) hydrate were prepared by electrical explosion of pure metal wire in deionized water. The kinetics of SF6 gas hydrates were evaluated with different concentration of Ag nanofluids at condition of 276 K and 0.7 MPa, respectively. The Ag nanofluids, as kinetic nano-prompter, showed excellent effect on the formation of SF6 hydrates.

The PMMA (poly methyl methacrylate)/clay nanocomposite powders were synthesized by In-Situ suspension polymerizations using microwave heating. The PMMA/clay nanocomposites were also sampled using injection moulding to make specimens for material characterization. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) indicated the formation of a highly intercalated clay layer in the nanocomposites. It was found that the microstructure of PMMA/clay nanocomposites was strongly dependent of content of clay. Thermo gravimetric analysis (TGA) indicated an improvement in the thermal stability of nanocomposites compared to that of the pure PMMA. Differential scanning calorimetry (DSC) showed that the nanocomposites had a higher glass transition (Tg) temperature than the PMMA. Fourier-transform infrared (FT-IR) spectroscopy indicated an interaction between the carbonyl group of PMMA and hydroxyl group of the clay. Therefore, a possible reason in enhanced material properties of nanocomposites is that the chemical interaction and nanostructure of PMMA polymer and intercalated inorganic silicate layer has increased the thermal stability of the PMMA/clay nanocomposites.

In this study, the kinetics of methane and methane/propane hydrate formation/dissociation were investigated. Simultaneously, micro-level studies, including hydrate structure, preferential cage occu...

In this study, a low complexity tabu search (TS) algorithm for multiple-input multiple-output (MIMO) systems is proposed. To reduce the computational complexity of the TS algorithm, early neighbor rejection (ENR) and layer ordering schemes are employed. In the proposed ENR-aided TS (ENR-TS) algorithm, the least promising k neighbors are excluded from the neighbor set in each layer, which reduces the computational complexity of neighbor examination in each TS iteration. For efficient computation of the neighbors’ metrics, the ENR scheme can be incorporated into QR decomposition-aided TS (ENR-QR-TS). To further reduce the complexity and improve the performance of the ENR-QR-TS scheme, a layer ordering scheme is employed. The layer ordering scheme determines the order in which layers are detected based on their expected metrics, which reduces the risk of excluding likely neighbors in early layers. The simulation results show that the ENR-TS achieves nearly the same performance as the conventional TS while providing up to 82% complexity reduction.

The shortage of fresh water is among the most serious issues in the world. A representative technology to overcome the problem is desalination, but most conventional methods (RO membrane or thermal distillation) have been focused on the treatment of relatively low salinity water, such as seawater or brackish water. To strengthen water security, in this study, we introduce a possibly economic technology for desalination of high salinity water (over-saturated concentration, in this study, a 30 wt% NaCl system) via gas hydrate formation by coupling LNG waste cold energy. First, the thermodynamic effects of NaCl on CH4 (methane), SF6 (sulfur hexafluoride), and HFC-134a hydrates were investigated. Based on the phase equilibrium of each hydrate, experimental pressures for kinetic experiments were selected under vapor pressure boundaries as follows: 4.5 MPa for CH4, 0.75 MPa for SF6, and 0.16 MPa for HFC-134a at 258.15 K (assuming the use of LNG waste cold energy). The results of the formation kinetics on the basis of gas moles consumed for hydrates showed the order CH4 > HFC-134a > SF6; however, after considering the hydration numbers and structures for each hydrate, surprisingly, the conversion rate of water to gas hydrates showed the order HFC-134a > CH4 > SF6, even though the experimental pressure condition for HFC-134a was very mild (0.16 MPa) compared to CH4 (4.5 MPa). For this interesting phenomenon, we suggest a possible mechanism through visual observations during hydrate formation. We believe these thermodynamic, kinetic, and morphological results show potential as an alternative desalination technology, especially for saturated salinity water, with lower energy consumption.

Highlights • Thermodynamic and kinetic influences of NaCl on HFC-125a hydrate were investigated. • NaCl enrichment in the unconverted solution resulted in a lower conversion. • The presence of NaCl had little effect on the ΔH of HFC-125a hydrate. • The hydrate dissociation was retarded due to the formation of NaCl⋅2H2O. In this study, HFC-125a was selected as a hydrate-forming guest for gas hydrate-based desalination. The thermodynamic and kinetic effects of NaCl on HFC-125a hydrates were investigated with a primary focus on phase equilibria, gas uptake, dissociation enthalpy, and dissociation behavior. The equilibrium curve of HFC-125a hydrate shifted to higher pressure regions at any given temperature depending on the concentration of NaCl. The presence of NaCl also reduced the gas uptake and conversion to hydrates, because of the enrichment of NaCl in the solution during gas-hydrate formation. Even though NaCl did not affect the dissociation enthalpy of the HFC-125a hydrate, the thermograms obtained using a high-pressure micro-differential scanning calorimeter (HP μ-DSC) demonstrated that HFC-125a + NaCl hydrates started to dissociate at lower temperatures due to NaCl in unconverted solutions. Rietveld refinement of powder X-ray diffraction (PXRD) patterns indicated that the HFC-125a hydrate (sII) was transformed into Ih as it dissociated. The dissociation of HFC-125a + NaCl hydrates was retarded and completely ended at higher temperatures compared to the pure HFC-125a hydrate by the sodium chloride dihydrate (NaCl⋅2H2O). Overall, these results could facilitate a better understanding of HFC-125a hydrates in the presence of NaCl; further, they might also be useful in the design and operation of hydrate-based desalination plants using HFC-125a.

Experiments of CH4 hydrate formation and decomposition were carried out in a semi-batch stirred reactor under constant temperature and pressure. In this study, we report microscopic observations such as the preferential enclathration of guest molecules by coupling an in-situ Raman spectroscopy at agitating condition in the stirred reactor. Simultaneously, the macroscopic observations (gas uptake or releasing measurements) were also reported under the same conditions. It was observed that at the beginning of hydrate growth phase, the Raman peak intensity of methane occupying the large cage (51262) and small cage (512) gradually increased after abrupt decline of dissolved methane. The encapsulation rate of large cages was faster than that of small cage throughout the hydrate formation process. In the decomposition step, the large and small cage dissociated gradually, but the dissociate rates (the ratio of Raman peak intensities of large and small cages with respect to time) were similar at the initial stage of decomposition, then large cages were dissociated more rapidly. In all experiments, we found that the Raman intensity at 3200 cm-1 is more increased along with the higher content of free water, which might will provide valuable information for further hydrogen-bonded researches including hydrate study. With the aid of in-situ Raman spectroscopy, this study successfully observed the process of hydrate formation/decomposition and further behavior of host and guest molecules under the agitated systems.

Natural gas hydrate plugging is one of the costly and challenging problems for the oil and gas industry, especially for subsea fields. One way to prevent gas hydrate formation at low cost is the use of low-dosage hydrate inhibitors (LDHI). Poly(N-isopropylmethacrylamide) (PNIPAM) with amide group have previously been shown to be an outstanding low-dosage hydrate inhibitor (LDHI). PNIPAMs are usually polymerized via radical polymerization, which can allow control over the molecular weight. We have synthesized PNIPAMs using control radical polymerization giving a fairly high degree of polymerization control. Additionally various Kinetic Hydrate Inhibitors (KHIs) were tested as CH4 hydrate inhibitors with polymeric hydrate inhibitor, PNIPAM. Furthermore, to check the synergetic effects of tetra butyl phosphonium bromide (TBPB), PNIPAM and their mixture TBPB-PNIPAM were tested as KHIs for methane gas hydrate formation. In this paper we present results on the performance of various polymeric inhibitors in KHI tests on methane gas in stirred autoclaves and on structure I hydrate formation. When PNIPAM alone was used as a single KHI, PNIPAM exhibited worst performance among the KHIs tested in this study. However the mixing of TBPB with PNIPAM further extended the induction time and reduced the CH4 hydrate growth rate. TBPB was an excellent synergist in blends with PNIPAM for kinetic hydrate inhibition of structure I forming CH4 hydrate. In summary, the mixture TBPB-PNIPAM was proven that great synergist for prevent the CH4 hydrate and good potential in achieving the industrial application of Oil & Gas production technology and therefore was a significantly meaningful discovery in the field of energy production.

Accelerated bridge construction using precast bridge substructures can enable reduction of traffic disruption, increased worker safety, and increased quality through controlled conditions a...

The PMMA (poly methyl methacrylate)/clay nanocomposite powders were synthesized by

Precast bent caps offer the opportunity to reduce onsite labor and materials and to accelerate the speed of construction. For many bridges, the weight is manageable for shipping and placeme...

The current knowledge of guest–guest interactions and co-occupation in clathrate hydrates is exclusive for the same guests (H2 or N2) at moderate pressure. Here, we introduce the unusual co-occupation of distinct guests in the metastable state of hydrates. With controlled hydrate fraction, particle size, and intensification of the sintering of SF6 hydrate particles formed from water and SF6 gas as a help gas, we observed an abnormal but unique synchronous behavior in Raman intensities of two guest molecules (SF6 and N2/H2) in hydrates consistently and repeatedly; over time, the scattering intensity for the guests (i) increases, (ii) decreases, and (iii) finally reaches the stable level. Without a concentration change of SF6, this abnormal behavior must arise from the possible changes in the scattering cross section of the molecules, suggesting that N2/H2 strongly interacts with SF6 in the large cages, resulting in a possible co-occupation during the metastable transition. These observations on the metasta...

Fluorinated gases (F-gases), such as 1,1,1,2-tetrafluoroethane (HFC-134a) and sulfur hexafluoride (SF6), are used widely in a variety of industrial processes but they are some of the most potent gr...

We present pure CH4 and CH4/C3H8 mixed hydrate phase equilibria formed from a mixture of NaCl (10 wt %) and monoethylene glycol (MEG, 10 and 30 wt %) solutions. As expected for thermodynamic inhibitors, the mixture of salt and glycol causes the hydrate phase equilibrium boundary to shift to lower temperatures and higher pressures, and on increasing the MEG concentration, the hydrate stable region shifted more. The measured experimental data are also compared with a thermodynamic model recently developed, named the Hu–Lee–Sum correlation, showing that the data match well with the predictions. The experimental data were used to calculate the enthalpy of hydrate dissociation. The enthalpies of CH4 hydrates in the mixture of 10 wt % NaCl brine and 10 or 30 wt % MEG were found to be ∼58.7 and 54.63 kJ/mol, respectively, corresponding to structure I hydrates, whereas for the CH4/C3H8 (91.98:8.02 mol %) mixed gas system, the enthalpies of dissociation were found to be ∼101.10 kJ/mol (10 wt % NaCl + 10 wt % MEG) ...

Natural gas (NG), the cleanest burning fossil fuel, plays a crucial role in meeting the global energy demand, contributing to 24% and is projected to grow at a rate of about 2% until 2040. Natural gas is also considered as the bridging fuel to transition into a carbon-constrained world with reduced carbon dioxide emissions whilst catering to the huge energy demand. Efficient and effective modes of NG storage/transport are dire need in the current golden era of natural gas. A plethora of advantages offered by storing NG in the form of hydrates carve a niche for this novel technology. Termed as solidified natural gas (SNG) technology, it has remarkable potential to store multi-fold volumes of natural gas in compact hydrate crystals offering the safest and the most environmental friendly mode of NG storage. This review provides an account on the research efforts put forth in this technology. Hydrate formation and storage aspects have been examined thoroughly with a subtle account on the gas recovery. The review encompasses studies conducted using different promoters (thermodynamic, kinetic or a combination of both) in different reactor configurations, novel/innovative approaches and hybrid processes adopted to improve the kinetics of hydrate formation and to increase the gas storage capacity. Detailed sections on the ‘self-preservation’ and ‘tuning’ effect in hydrates have been included due to their significance in SNG technology. Process chain of the SNG technology, underlying challenges and measures adopted to deploy the SNG technology for large-scale NG storage applications are included in this review.

HFC-134a gas was investigated as a potential guest molecule to improve the thermodynamic conditions and formation rate for CO2 hydrate. In the phase equilibrium study, the equilibrium pressure of CO2 + HFC-134a was lower than that of pure CO2 gas, and the equilibrium pressure decreased gradually with increasing HFC-134a concentration. The dissociation enthalpy (ΔHd) was calculated using the Clausius–Clapeyron equation, and the ΔHd value also changed with increasing HFC-134a concentration. In particular, the ΔHd of 8 mol % HFC-134a-added CO2 hydrate was 143.2 kJ/mol, which was similar to that of pure HFC-134a (structure-II). In the kinetic study, the reactor was initially filled with CO2 + HFC-134a gas only and pure CO2 gas was then supplied as a source when the hydrate reaction proceeded. As a result, the formation rate of the HFC-134a mixture in the initial 2 min was faster than that of pure CO2. This was consistent with the gas chromatography results, which showed that HFC-134a occupies the cage at the ...

Poly(N-vinylcaprolactam) (PVCap) has previously been shown to be an outstanding low-dosage hydrate inhibitor (LDHI). The inhibition performance of LDHI is known to be influenced by molecular weight (Mw) and molecular weight distribution. In this study, PVCaps were synthesized by two different methods. The first method, reversible addition–fragmentation chain transfer (RAFT) polymerization, was used to prepare PVCap with a narrow molecular weight distribution (about Mw/Mn 1.5). In a semi-batch stirrer reactor, hydrate inhibition performance of PVCap was evaluated. It was found that the inhibition performance was increased when the PVCap molecular weight decreased. PVCap with the narrower molecular weight distribution also showed the better inhibition performance.

Both CO 2 and SF 6 are potent greenhouse gases responsible for global warming and associated environmental issues. Hydrate-based separation and capture of these gases from gas mixtures produced by industry have been proposed, and improving the commercial viability of these processes is crucial. Here, we report the phase equilibria and characterization of binary hydrates containing CO 2 and SF 6 . The introduction of SF 6 considerably lowered the formation pressure of CO 2 hydrates by readily occupying the structure II hydrate cages and hence altering the crystal structure. Hydrate phases with different crystalline structures were found to coexist as a result of competition in occupying different hydrate cages. The structural instability caused by the coexistence of structure I and II hydrates was observed, and this feature would be important to understand the mixed gas hydrate systems. The ability of SF 6 to significantly reduce the formation pressure of hydrates suggests that it has a potential to serve as a hydrate promoter. This feature of SF 6 combined with its non-toxic and non-flammable properties would be efficient for practical applications such as CO 2 sequestration using hydrates.

The phase change from germ nuclei to growth nuclei and subsequent volume transformation in a crystallization process was modeled by Avrami equations. The phase change during the hydrate formation was fitted with the classical Avrami model by utilizing gas uptake data. The idea is to understand the difference in growth behavior of hydrate crystals when in small pores compared to a stirred tank reactor which does not pose any physical restrictions to hydrate growth. The parameters n and k of the Avrami equation were determined explicitly for CO2 hydrate formation.

It is known that the prestressed half PC (precast) slab system has many advantages such as a reduced construction period and use of long-span one-way slab systems over reinforced concrete and half PC slab systems without prestressing. For this reason, prestressed half slabs are commonly used for both residential and basement parking structures in Korea and other countries. The prestressed half PC slab systems currently being used only have the pre-tensioning system only for PC slabs. To ensure better performance of the half PC slab system with larger span-to-depth ratio, a new system using both pre-tensioning and post-tensioning methods is suggested for basement parking structures in this paper. The main purpose of this paper was to analyse the suggested model and verify its safety and serviceability for a given span and a given load. The second purpose is to suggest a preliminary calculation process for the suggested system that satisfies the ACI 318 requirements. A parametric study is conducted ...

The inclusion of tert -butyl alcohol (tBA) as a co-guest of clathrate hydrates in the presence of CH 4 , CO 2 , and N 2 was investigated for its potential role in gas storage and CO 2 sequestration. The 13 C NMR, Raman spectroscopy, and powder X-ray diffraction revealed that the guest gas (CH 4 , CO 2 , and N 2 ) + tBA + water systems form sII hydrates. The enclathration of tBA molecules in the sII large (5 12 6 4 ) cages resulted in significant thermodynamic stabilization of the CH 4 + tBA and N 2 + tBA hydrates. However, the hydrate phase equilibrium curves of the CO 2 + tBA hydrates were shifted to inhibited regions despite the participation of tBA molecules as a co-guest in the sII hydrate lattices. tBA was found to function as a thermodynamic promoter for both CH 4 and N 2 hydrates, whereas it functioned as a thermodynamic inhibitor for CO 2 hydrate. The overall experimental results provide a better understanding of the thermodynamic behaviors, structural transitions, and guest distributions of the guest gas (CH 4 , CO 2 , and N 2 ) + tBA hydrates for the potential use of tBA in gas storage and CO 2 sequestration.

The complexation of boric acid (B(OH)3), the primary form of aqueous boron at moderate pH, with polyols is proposed and mechanistically studied as an efficient way to improve membrane processes such as reverse osmosis (RO) for removing boron in seawater by increasing the size of aqueous boron compounds. Computational chemistry based on the density functional theory (DFT) was used to manifest the reaction pathways of the complexation of B(OH)3 with various polyols such as glycerol, xylitol, and mannitol. The reaction energies were calculated as −80.6, −98.1, and −87.2 kcal/mol for glycerol, xylitol, and mannitol, respectively, indicating that xylitol is the most thermodynamically favorable for the complexation with B(OH)3. Moreover, the 1: 2 molar ratio of B(OH)3 to polyol was found to be more favorable than the ratio of 1: 1 for the complexation. Meanwhile, latest lab-scale actual RO experiments successfully supported our computational prediction that 2 moles of xylitol are the most effective as the complexing agent for 1 mole of B(OH)3 in aqueous solution.

Gas hydrate (GH) desalination process is based on a liquid (salty water) to solid (GH) phase change coupled with a physical process to separate the GHs from the remaining salty water. However, GH process exhibits less than 90% of salt rejection, so reverse osmosis (RO) process is needed to finally meet the desalinated product water quality. In order to increase the total recovery of the GH and RO hybrid system, the concentrate of the RO process should return to the feed stream of the GH process. In this work, RO simulation was carried out to find an optimal RO recovery with which the energy consumption of RO was minimized. The optimal RO recovery values for GH processes with salt rejection of 78, 84, and 90% were 0.6, 0.8, and 0.8, respectively. The minimal total energy consumption appears at higher RO recovery rates than the optimal values to minimize the RO energy consumption because the portion of the GH energy consumption is inversely proportional to the RO recovery. The simulation also reveal...

In this study, the influences of large molecular alcohols (LMAs) including pinacolyl alcohol (PCA) and tert-amyl alcohol (tAA) on thermodynamic phase behaviors and structural characteristics of CH 4 and CO 2 hydrates were investigated for their potential use in gas storage and CO 2 sequestration. The experimentally measured hydrate phase equilibria demonstrated that CH 4 hydrates were stabilized in the presence of PCA and tAA. 13 C NMR and Raman spectroscopy confirmed sH hydrate formation from both CH 4 + PCA + water and CH 4 + tAA + water systems, resulting from the enclathration of LMAs in the large 5 12 6 8 cages. The sH hydrate formation of the CH 4 + PCA + water system was also confirmed by an endothermic dissociation thermogram from a differential scanning calorimeter (DSC). In contrast with CH 4 hydrates, the addition of both PCA and tAA to CO 2 hydrates resulted in thermodynamic inhibition. Through Raman and powder X-ray diffraction (PXRD) analyses, both CO 2 + PCA and CO 2 + tAA hydrates were characterized as sI hydrates, indicating that LMAs simply inhibit the formation of CO 2 hydrates without being captured in the hydrate lattices. Therefore, PCA and tAA are expected to function as thermodynamic promoters which reduce the hydrate forming pressure in natural gas storage applications, while they can serve as thermodynamic inhibitors which prevent CO 2 hydrate formation in pipelines for CO 2 transportation to sequestration sites.

In order to evaluate hydrate-based desalination (HBD), experiments with seawater samples were carried out at various conditions (i.e. hydraulic pressure, washing step, and hydrate-forming gas). Before and after the hydrate process, cations (Na+, K+, Mg2 +, Ca2 +, and B3 +) and anions (Cl− and SO42 −) were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and ion chromatography (IC). In a single stage of CO2 hydrate process without any pretreatment, 71%–94% of each cation was removed in the following order: K+ > Na+ ≈ Mg2 + ≈ Ca2 + > B3 + and 73%–83% of each anion was removed. When the brines on the surface of hydrate pellets were removed, the ion removal efficiency increased above 4%. It was also found that the desalting efficiency depended on the hydrate-forming gas (CO2 > CH4) and the hydraulic pressure (6–10 MPa) to produce hydrate pellets. In this study, the removal efficiency of cations and anions in a real seawater sample using HBD processes were reported for the first time.

The characteristics of methane–propane hydrate crystal growth on the surface of gas bubble in pure water were investigated using optical microscope and compared with those in aqueous solutions of sodium dodecyl sulfate (SDS) or poly-N-vinylcaprolactam (PVCap). Most of morphology works in literature mainly focused on the hydrate crystal growth at the gas/water interface or surface of water droplets. However, this study monitors crystal growth at the bubble surface. In the case of pure water, smooth hydrate film was formed initially and the film surface on the bubble became rough as experiment proceeded. It was also observed that the hydrate crystals developed as the dendritic shape from the surface of hydrate film. In the presence of SDS, drastic changes in morphology were observed in that smoke-like crystals appeared from the top of the bubble. Besides, the gas bubble was not fully covered by hydrate film when the SDS concentration increased. In the PVCap solution, seed-like or small spot of hydrate crystals occurred sparsely on the bubble surface and spread out the whole surface as experiment progressed. The experimental results showed that the presence of SDS or PVCap affect morphological characteristics of methane–propane hydrate crystal on the surface of gas bubble.

Spherical biphasic calcium phosphate (BCP) micro-granules consisting of hydroxyapatite (HAp) and tricalcium phosphate (TCP) were prepared using a rotary spray drying and sintering process. A significant phase transformation of TCP in BCP granules occurred according to the relative content of HAp and TCP in the BCP granules depending on the sintering temperature. The crystal growth of HAp in BCP was suppressed by a phase transformation of TCP with a change in the electron density distribution in a crystal unit cell. In addition, these progressive changes in the hydroxyl and phosphate group of BCP granules might be due to the phase transformation of TCP. Consequently, such structural changes in the BCP granules led to an unexpected change in granule size and micro-cracks on their surface at high temperatures.

A new apparatus for seawater desalination, based on the principle of gas hydrates, is suggested. The equipment continuously produces and pelletizes gas hydrates by a squeezing operation in a dual cylinder unit, which is able to extract pure hydrate pellets from the seawater-containing reactor. Desalination efficiency for each dissolved ion from seawater samples was tested by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and ion chromatography (IC) analysis. This study demonstrates that the suggested method and the stated apparatus may solve the difficulty of separating hydrate crystals from concentrated brine solutions, and therefore may be applied to improve the efficiency of existing desalination processes.

Spherical tricalcium phosphate (TCP) micro-granules were prepared using a jet wheel impact atomization and calcination process. Spherical TCP granules were obtained which can exhibit phase transformation between the alpha and beta polymorphs as a function of the heating temperature. The progressive changes in the phosphate group of TCP granules were attributed to the phase transformation. Consequently, such structural changes in the TCP micro-granules can be used to control the dissolution and degradation of TCP through the controlled density and microporosity of the micro-granules.

In this study, experimental research was carried out to investigate the seismic and structural performance of precast concrete exterior beam-column joints using bolt type connection and prestressing method. A total of five full-scale exterior beam-column joints were constructed and tested under reversed cyclic loading, controlled by displacement. Results of the test are as follows: Energy dissipation capacity and pinching phenomenon of PC beam-column joints showed disadvantageous behavior compared to RC beam-column joints. However, drift capacity of the PC joint was excellent. Also, yield mechanism concentrated on embedded nuts was suitable as an exterior beam-column joint of lateral load resistance frame. Additional application of prestressing method was also very effective to control excessive pinching and cracking in the joint region, and thus improved an overall seismic performance of the PC joint.

In-depth understanding of the CH4 hydrate formation and decomposition processes is essential for energy recovery as well as related transportation/storage technologies. Raman spectroscopy is well suited for hydrate studies of aqueous-hydrate conditions, because it is not susceptible to interference from aqueous environments. In order to obtain more specific and ongoing information on the CH4 hydrate formation and dissociation, two different in-situ Raman spectroscopies with specially designed fiber-optic probes were used in a semi-batch stirred reactor (total volume 365 mL). With these arrangements, it was possible to obtain macroscopic (gas uptake, releasing, CH4 solubility) and microscopic (structural, cage occupancy, water structure) data simultaneously during CH4 hydrate formation and decomposition. Based on in-situ Raman observations, we are able to determine the time-dependent encapsulation of CH4 in large and small cage through hydrate formation and decomposition. In all experiments, the Raman intensity of the OH-stretching band (3000–3800 cm−1) was significantly reduced or increased at the point where hydrates were formed or dissociated, which is expected to provide valuable information for further hydrogen-bond research including hydrate study. In addition, in-situ Raman spectroscopy was used to determine the concentration of dissolved CH4 under hydrate formation/decomposition conditions and the results were in good agreement with experimental data in the literature.