Gas hydrate formation experiments were performed using methane in the presence of tetrahydrofuran (THF) in aqueous solution in a transparent bubble column in which a single pipe or a sintered plate ...was used to produce bubbles. The mole fraction of THF in aqueous solution was fixed at 6%. The hydrate formation kinetic behaviors on the surface of the rising bubble, the mechanical stability of hydrate shell formed on the surface of the bubble, the interactions among the bubbles with hydrate shell were observed and investigated morphologically. The rise velocities of individual bubbles with hydrate shells of different thickness and the consumption rates of methane gas were measured. A kinetic model was developed to correlate the experimentally measured gas consumption rate data. It was found that the hydrate formation rate on the surface of the moving bubble was high, but the formed hydrate shell was not very easy to be broken up. The bubbles with hydrate shells tended to agglomerate rather than merge into bigger bubble. This kind of characteristic of hydrate shell hindered the further formation of hydrate and led to the lower consumption rate of methane. The consumption rate of methane was found to increase with the decrease of temperature or increase of pressure. The increase of gas flux led to a linear increase in consumption rate of methane. It was demonstrated that the developed kinetic model could be used to correlate the consumption rate satisfyingly.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Wide bandgap semiconductors materials (WBGSMs) are of great interest for their applications in transparent electronics and power electronics. Recent studies have shown that BaS is a potential ...transparent conducting material but the knowledge of it is deficient. Herein, we systemically investigate its electronic structure and evaluate the effects of its intrinsic defects and extrinsic dopants by utilizing the hybrid density functional method. The obtained results show that BaS is an indirect bandgap semiconductor with a bandgap of 3.88 eV. Its electron-effective mass is very small (0.33
m
0
). We find that the intrinsic n-type conductivity of BaS is connected with the shallow donor defect sulfur vacancy (
V
S
). Regarding extrinsic dopants (group IA atoms), we find that Li and Na are favorable n-type dopants, while K and Rb are p-type dopants. Among these impurities, the Li interstitial (Li
int
) configuration possesses the lowest formation energy of 0.114 eV. Based on thermodynamic simulations, we find that the electron density can reach 2.39 × 10
20
cm
−3
in Li-doped BaS at room temperature, which is comparable to those of typical WBGSMs In
2
O
3
, BaSnO
3
, and β-Ga
2
O
3
. We expect BaS could replace typical WBGSMs in some applications. Moreover, its component elements Ba and S are non-toxic, cheap, and earth-abundant, making it a very competitive candidate for WBGSMs. Based on these results, we deem BaS a promising candidate for optoelectronic applications.
In WBGSM BaS, the high density of electrons can be obtained by means of the Li
int
defects.
Perioperative use of dexmedetomidine is associated with reduction in postoperative analgesic requirements. This study examined whether dexmedetomidine added to i.v. patient-controlled analgesia (PCA) ...morphine could improve analgesia while reducing opioid-related side-effects.
In this double-blinded, randomized, controlled study, 100 women undergoing abdominal total hysterectomy were allocated to receive either morphine 1 mg ml−1 alone (Group M) or morphine 1 mg ml−1 plus dexmedetomidine 5 μg ml−1 (Group D) for postoperative i.v. PCA, which was programmed to deliver 1 ml per demand with a 5 min lockout interval and no background infusion. Cumulative PCA requirements, pain intensities, cardiovascular and respiratory variables, and PCA-related adverse events were recorded for 24 h after operation.
Compared with Group M, patients in Group D required 29% less morphine during the 0–24 h postoperative period and reported significantly lower pain levels from the second postoperative hour onwards and throughout the study. Whereas levels of sedation were similar between the groups at each observational time point, decreases in heart rate and mean blood pressure from presurgery baseline at 1, 2, and 4 h after operation were significantly greater in Group D (by a range of 5–7 beats min−1 and 10–13%, respectively). The 4–24 h incidence of nausea was significantly lower in Group D (34% vs 56.3%, P<0.05). There was no bradycardia, hypotension, oversedation, or respiratory depression.
The addition of dexmedetomidine to i.v. PCA morphine resulted in superior analgesia, significant morphine sparing, less morphine-induced nausea, and was devoid of additional sedation and untoward haemodynamic changes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The structure of the atmospheric boundary layer (ABL) and its influence on regional air quality over the Pearl River Delta (PRD) were examined through two intensive observations in October 2004 and ...July 2006. Analytical results show the presence of two types of typical weather conditions associated with poor air quality over the PRD. The first is the warm period before a cold front (WPBCF) and the second is the subsidence period controlled by a tropical cyclone (SPCTC). Two typical low air quality situations, which are affected by WPBCF and SPCTC, and one high air quality situation were analysed in detail. Results showed that continuously low or calm ground winds resulted in the accumulation of pollutants, and sea-land breezes had an important role during low air quality conditions. Data on recirculation factors showed that recirculation was significant during low air quality conditions, and steady transportation occurred during high air quality conditions. The ventilation index and the 24 h average ventilation index during high air quality conditions were significantly higher than those during low air quality conditions. Deep and stable inversion layers inside the ABL remarkably affected low air quality. Surface and low-altitude inversions were usually observed during WPBCF, contrary to during SPCTC, during which only the low-altitude inversion appeared frequently.
This paper aims to develop a load forecasting method for short-term load forecasting, based on an adaptive two-stage hybrid network with self-organized map (SOM) and support vector machine (SVM). In ...the first stage, a SOM network is applied to cluster the input data set into several subsets in an unsupervised manner. Then, groups of 24 SVMs for the next day's load profile are used to fit the training data of each subset in the second stage in a supervised way. The proposed structure is robust with different data types and can deal well with the nonstationarity of load series. In particular, our method has the ability to adapt to different models automatically for the regular days and anomalous days at the same time. With the trained network, we can straightforwardly predict the next-day hourly electricity load. To confirm the effectiveness, the proposed model has been trained and tested on the data of the historical energy load from New York Independent System Operator.
This study is focused on improving the reactivity of a CaO sorbent for its use in a reaction-based process for the separation of carbon dioxide (CO2) from flue gas. The separation process consists of ...cyclical carbonation (of a metal oxide) and calcination (of the metal carbonate formed) reactions to yield concentrated CO2 from flue gas. CaO sorbents synthesized from naturally occurring limestone and dolomite were microporous in nature. Pore filling and pore pluggage of these micropores limited the conversion of CaO in the carbonation reaction to about 45−50% of the stoichiometric limit. A wet precipitation process was tailored to synthesize high-surface-area precipitated calcium carbonate (PCC). The pores of PCC predominantly lie in the mesoporous range (5−20 nm). The CaO sorbent obtained from PCC (PCC-CaO) was less susceptible to pore pluggage and attained over 90% conversion. PCC-CaO was also capable of maintaining its high reactivity (>90%) over two carbonation−calcination cycles.
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IJS, KILJ, NUK, PNG, UL, UM
Abstract
We identify a strong Ly
α
damping wing profile in the spectrum of the quasar P183+05 at
z
= 6.4386. Given the detection of several narrow metal absorption lines at
z
= 6.40392, the most ...likely explanation for the absorption profile is that it is due to a damped Ly
α
system. However, in order to match the data a contribution of an intergalactic medium 5%–38% neutral or additional weaker absorbers near the quasar is also required. The absorption system presented here is the most distant damped Ly
α
system currently known. We estimate an H
i
column density of 10
20.68±0.25
cm
−2
, metallicity O/H = −2.92 ± 0.32, and relative chemical abundances of a system consistent with a low-mass galaxy during the first Gyr of the universe. This object is among the most metal-poor damped Ly
α
systems known and, even though it is observed only ∼850 Myr after the big bang, its relative abundances do not show signatures of chemical enrichment by Population III stars.
Loop Current warming by Hurricane Wilma Oey, L.-Y.; Ezer, T.; Wang, D.-P. ...
Geophysical research letters,
April 2006, Volume:
33, Issue:
8
Journal Article
Peer reviewed
Open access
Hurricanes mix and cool the upper ocean, as shown here in observations and modeling of the Caribbean Sea and the Gulf of Mexico during the passage of hurricane Wilma. Curiously, the upper ocean ...around the Loop Current warmed prior to Wilma's entrance into the Gulf. The major cause was increased volume and heat transports through the Yucatan Channel produced by storm‐induced convergences in the northwestern Caribbean Sea. Such oceanic variability may have important impacts on hurricane predictions.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The syngas chemical looping (SCL) process coproduces hydrogen and electricity. The process involves reducing metal oxides with syngas followed by regeneration of reduced metal oxides with steam and ...air in a cyclic manner. Iron oxide is determined to be a desired oxygen carrier for hydrogen production considering overall properties including oxygen carrying capacity, thermodynamic properties, reaction kinetics, physical strength, melting points, and environmental effects. An iron oxide based particle can maintain good reactivity for more than 100 reduction−oxidation (redox) cycles in a thermogravimetric analyzer (TGA). The particle exhibits a good crushing strength (>20 MPa) and low attrition rate. Fixed bed experiments are carried out which reaffirm its reactivity. More than 99.75% of syngas is converted during the reduction stage. During the regeneration stage, hydrogen with an average purity of 99.8% is produced.
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IJS, KILJ, NUK, PNG, UL, UM
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