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Search Results: 1 - 10 of 83775 matches for " Y. Q. Ma "
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Comparative study of the effect of water on the heterogeneous reactions of carbonyl sulfide on the surface of α-Al2O3 and MgO
Y. Liu, Q. Ma,H. He
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: Here we compared the heterogeneous reactions of carbonyl sulfide (OCS) on the surface of α-Al2O3 and MgO and the effect of water on the reactions at 300 K using Knudsen cell–mass spectrometry, diffuse reflectance infrared Fourier transform spectroscopy, and temperature programmed reactions. H2S and CO2 were found to be hydrolysis products of OCS on both α–Al2O3 and MgO at ambient temperature. At low water vapor pressure (<6.8×10 6 Torr), when water vapor pressure in the Knudsen cell reactor increased from 2.3×10 6 to 6.8×10 6 Torr, the initial true uptake coefficient of OCS on α-Al2O3 decreased from 4.70±0.45×10 7 to 3.59±0.34×10 7; while it increased from 5.19±0.49×10 7 to 6.48±0.62×10 7 on MgO under the same conditions. At high relative humidity (0.07–0.67), the observed uptake coefficients of OCS on α-Al2O3 and MgO, which were measured using an in situ DRIFTS, decreased from 4.63±0.22×10 6 to 1.00±0.47×10 6 and from 9.72±0.46×10 5 to 7.68±0.36×10 5, respectively, when RH increased from 0.07 to 0.67 corresponding to 1.7–15.9 Torr of water vapor pressure. In the RH region of 0.17–0.67, the average observed uptake coefficient of OCS on α-Al2O3 and MgO was equal to 8.34±2.19×10 7 and 8.19±0.48×10 5, respectively. The restrictive effect of water on the heterogeneous reaction of OCS on the surface of α-Al2O3 and MgO was found to be related to competitive adsorption between water and OCS molecules; while the promotive effect of water on the heterogeneous reaction of OCS on the surface of MgO at low coverage was ascribed to the formation of surface hydroxyl groups. When the environmental RH was greater than the RH of the monolayer, which occurred readily at the atmospherically relevant humidity in the troposphere, thick water layer formed on the mineral dusts, especially, the basic thick water layer formed on the basic component of mineral dusts may be the primary contributor to the heterogeneous hydrolysis of OCS in the troposphere.
Comparative study of the effect of water on the heterogeneous reactions of carbonyl sulfide on the surface of α-Al2O3 and MgO
Y. Liu,Q. Ma,H. He
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: The heterogeneous reaction on mineral dust was considered as a new sink of OCS in the troposphere. Here we compared the heterogeneous reactions of carbonyl sulfide (OCS) on the surface of α-Al2O3 and MgO and the effect of water on the reactions at 300 K using Knudsen cell – mass spectrometry, diffuse reflectance infrared Fourier transform spectroscopy, and temperature programmed reactions. H2S and CO2 were found to be hydrolysis products of OCS on both α-Al2O3 and MgO at ambient temperature. At low water vapor pressure, when water vapor pressure in the Knudsen cell reactor increased from 2.3×10 6 to 6.8×10 6 Torr, the initial true uptake coefficient of OCS on α-Al2O3 decreased from 4.70×10 7 to 3.59×10 7; while it increased from 5.19×10 7 to 6.48×10 7 on MgO under the same conditions. At high relative humidity, the observed uptake coefficients of OCS on α-Al2O3 and MgO decreased from 4.63×10 6 to 1.00×10 6 and from 9.72×10 5 to 7.68×10 5, respectively, when RH increased from 0.07 to 0.67 which corresponding to 1.7–15.9 Torr of water vapor pressure. In the RH region of 0.17–0.67, the average observed uptake coefficient of OCS on α-Al2O3 and MgO was equal to 8.34±2.19×10 7 and 8.19±0.48×10 5, respectively. The restrictive effect of water on the heterogeneous reaction of OCS on the surface of α-Al2O3 and MgO was found to be related to competitive adsorption between water and OCS molecules; while the promotive effect of water on the heterogeneous reaction of OCS on the surface of MgO at low coverage was ascribed to the formation of surface hydroxyl groups. When the environmental RH was greater than the RH of the monolayer, which occurred readily at the typical relative humidity of the troposphere, liquid membrane formed on the mineral dusts, especially, the basic liquid membrane formed on the basic component of mineral dusts may be the primary contributor to the heterogeneous hydrolysis of OCS in the troposphere.
Comparative study of the effect of water on the heterogeneous reactions of carbonyl sulfide on the surface of α-Al2O3 and MgO
Y. Liu,Q. Ma,H. He
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: Here we compared the heterogeneous reactions of carbonyl sulfide (OCS) on the surface of α-Al2O3 and MgO and the effect of water on the reactions at 300 K using Knudsen cell–mass spectrometry, diffuse reflectance infrared Fourier transform spectroscopy, and temperature programmed reactions. H2S and CO2 were found to be hydrolysis products of OCS on both α–Al2O3 and MgO at ambient temperature. At low water vapor pressure (<6.8×10 6 Torr), when water vapor pressure in the Knudsen cell reactor increased from 2.3×10 6 to 6.8×10 6 Torr, the initial true uptake coefficient of OCS on α-Al2O3 decreased from 4.70±0.45×10 7 to 3.59±0.34×10 7; while it increased from 5.19±0.49×10 7 to 6.48±0.62×10 7 on MgO under the same conditions. At high relative humidity (0.07–0.67), the observed uptake coefficients of OCS on α-Al2O3 and MgO, which were measured using an in situ DRIFTS, decreased from 4.63±0.22×10 6 to 1.00±0.47×10 6 and from 9.72±0.46×10 5 to 7.68±0.36×10 5, respectively, when RH increased from 0.07 to 0.67 corresponding to 1.7–15.9 Torr of water vapor pressure. In the RH region of 0.17–0.67, the average observed uptake coefficient of OCS on α-Al2O3 and MgO was equal to 8.34±2.19×10 7 and 8.19±0.48×10 5, respectively. The restrictive effect of water on the heterogeneous reaction of OCS on the surface of α-Al2O3 and MgO was found to be related to competitive adsorption between water and OCS molecules; while the promotive effect of water on the heterogeneous reaction of OCS on the surface of MgO at low coverage was ascribed to the formation of surface hydroxyl groups. When the environmental RH was greater than the RH of the monolayer, which occurred readily at the atmospherically relevant humidity in the troposphere, thick water layer formed on the mineral dusts, especially, the basic thick water layer formed on the basic component of mineral dusts may be the primary contributor to the heterogeneous hydrolysis of OCS in the troposphere.
A comprehensive characterisation of Asian dust storm particles: chemical composition, reactivity to SO2, and hygroscopic property
Q. Ma,Y. Liu,C. Liu,J. Ma
Atmospheric Chemistry and Physics Discussions , 2010, DOI: 10.5194/acpd-10-8899-2010
Abstract: Mineral dust comprises of a significant fraction of the globe's aerosol loading. Yet it remains the largest uncertainty in future climate predictions due to the complexity in its components and physico-chemical properties. Multi-analysis methods, including SEM-EDX, FTIR, BET, TPD/mass, and Knudsen cell/mass, were used in the present study to characterise Asian dust storm particles. The morphology, element fraction, source distribution, true uptake coefficient of SO2 and hygroscopic behaviour were studied. The major components of Asian dust storm particles were found to consist of aluminosilicate, SiO2, and CaCO3, which were coated with organic compounds and inorganic nitrate. The dust storm particles have a low reactivity to SO2 (true uptake coefficient of 5.767×10 6) which limits the conversion of SO2 to sulfate during a dust storm period. The low reactivity also demonstrated that the heterogeneous reaction of SO2, in both dry and humid air conditions, had little effect on the hygroscopic behaviour of the dust particles. These results indicate that the impact of dust storms on atmospheric SO2 removal should not be overestimated.
Accelerated drug release and clearance of PEGylated epirubicin liposomes following repeated injections: a new challenge for sequential low-dose chemotherapy
Yang Q,Ma Y,Zhao Y,She Z
International Journal of Nanomedicine , 2013,
Abstract: Qiang Yang,1 Yanling Ma,2 Yongxue Zhao,1 Zhennan She,1 Long Wang,1 Jie Li,1 Chunling Wang,1 Yihui Deng1 1College of Pharmacy, Shenyang Pharmaceutical University, Shenyang, People’s Republic of China; 2Sichuan Kelun Pharmaceutical Co, Ltd, Chengdu, People’s Republic of China Background: Sequential low-dose chemotherapy has received great attention for its unique advantages in attenuating multidrug resistance of tumor cells. Nevertheless, it runs the risk of producing new problems associated with the accelerated blood clearance phenomenon, especially with multiple injections of PEGylated liposomes. Methods: Liposomes were labeled with fluorescent phospholipids of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) and epirubicin (EPI). The pharmacokinetics profile and biodistribution of the drug and liposome carrier following multiple injections were determined. Meanwhile, the antitumor effect of sequential low-dose chemotherapy was tested. To clarify this unexpected phenomenon, the production of polyethylene glycol (PEG)-specific immunoglobulin M (IgM), drug release, and residual complement activity experiments were conducted in serum. Results: The first or sequential injections of PEGylated liposomes within a certain dose range induced the rapid clearance of subsequently injected PEGylated liposomal EPI. Of note, the clearance of EPI was two- to three-fold faster than the liposome itself, and a large amount of EPI was released from liposomes in the first 30 minutes in a complement-activation, direct-dependent manner. The therapeutic efficacy of liposomal EPI following 10 days of sequential injections in S180 tumor-bearing mice of 0.75 mg EPI/kg body weight was almost completely abolished between the sixth and tenth day of the sequential injections, even although the subsequently injected doses were doubled. The level of PEG-specific IgM in the blood increased rapidly, with a larger amount of complement being activated while the concentration of EPI in blood and tumor tissue was significantly reduced. Conclusion: Our investigation implied that the accelerated blood clearance phenomenon and its accompanying rapid leakage and clearance of drug following sequential low-dose injections may reverse the unique pharmacokinetic–toxicity profile of liposomes which deserved our attention. Therefore, a more reasonable treatment regime should be selected to lessen or even eliminate this phenomenon. Keywords: accelerated blood clearance (ABC) phenomenon, PEGylated liposomes, epirubicin, sequential low-dose injections, complement
Structural Phase Transition at High Temperatures in Solid Molecular Hydrogen and Deuterium
T. Cui,Y. Takada,Q. Cui,Y. Ma,G. Zou
Physics , 2001, DOI: 10.1103/PhysRevB.64.024108
Abstract: We study the effect of temperature up to 1000K on the structure of dense molecular para-hydrogen and ortho-deuterium, using the path-integral Monte Carlo method. We find a structural phase transition from orientationally disordered hexagonal close packed (hcp) to an orthorhombic structure of Cmca symmetry before melting. The transition is basically induced by thermal fluctuations, but quantum fluctuations of protons (deuterons) are important in determining the transition temperature through effectively hardening the intermolecular interaction. We estimate the phase line between hcp and Cmca phases as well as the melting line of the Cmca solid.
Dust storms come to central and southwestern China, too: implications from a major dust event in Chongqing
Q. Zhao,K. He,K. A. Rahn,Y. Ma
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: Dust storms from major Asian sources are usually carried by northwesterly or westerly winds over northern and southeastern China to the Pacific Ocean. These pathways leave central and southwestern China nearly free of incursions. But a strong dust event on 5–6 May 2005 was captured in a 15-month series of weekly filter samples of PM2.5 at three sites in Chongqing. It illustrated that desert dust can be transported to this region, and sometimes strongly. Annual PM2.5 and dust were similar at the three sites, but higher than in simultaneous samples in Beijing. High correlations of dust concentration were found between the cites during spring, indicating that Asian dust affects a broader swath of China than is often realized. During the event, the concentrations of mineral dust were high at all sites (20–30 μg m 3; 15%–20% of PM2.5 in Chongqing, and 15 μg m 3; 20%–30% of PM2.5 in Beijing), and were part of a broader spring maximum. The proportions of crustal elements and pollution-derived components such as Pb, SO42 , and organic carbon indicated that the sources for this dust differed from Beijing. The dust was considerably enriched in Ca and Mg, characteristic of western deserts, whereas Beijing's dust had the lower Ca and Mg of eastern deserts. This observation agrees with synoptic patterns and back-trajectories. Driven by a cold air outbreak from the northwest, dust from the western Gobi Desert was transported at lower altitudes (<2 km above ground level), while dust from the Takla Makan Desert was transported to Chongqing at higher altitudes. Desert dust can also be important to wide areas of China during the cold season, since almost all the weekly dust peaks in the two cities coincided with extensive dust emissions in source regions. These findings collectively suggest that the amount of Asian-dust in China has been underestimated both spatially and temporally, and that transported alkaline dust can even be mitigating the effects of acidic deposition in southern China.
Pituitary adenoma and vestibular schwannoma: Case report and review of the literature
Niu Y,Ma L,Mao Q,Wu L
Journal of Postgraduate Medicine , 2010,
Abstract: The concurrence of the intracranial multiple primary tumors (MPTs) consisting of acoustic neuroma (AN) and pituitary adenoma is very rare. Here, we report a 42-year-old female who presented with left AN associated with pituitary adenoma. A total of three such cases have been reported before and which also presented with left AN with pituitary adenoma. Recently, a new "field cancerization" model has been proposed, which could explain MPTs and is consistent with the pathogenesis of such cases. The model also indicates that when a pituitary tumor or AN is detected separately, we might consider the development of "expanding field" after oncological treatment especially after radiotherapy in order to prevent the second field tumor occurring.
Neutron rich nuclei in density dependent relativistic Hartree-Fock theory with isovector mesons
B. Q. Chen,Z. Y. Ma,F. Gruemmer,S. Krewald
Physics , 1999, DOI: 10.1016/S0370-2693(99)00428-1
Abstract: Density dependent relativistic Hartree-Fock theory has been extended to describe properties of exotic nuclei. The effects of Fock exchange terms and of pi - and rho - meson contributions are discussed. These effects are found to be more important for neutron rich nuclei than for nuclei near the valley of stability.
Bulk properties of light deformed nuclei derived from a medium-modified meson-exchange interaction
F. Gruemmer,B. Q. Chen,Z. Y. Ma,S. Krewald
Physics , 1996, DOI: 10.1016/0370-2693(96)01126-4
Abstract: Deformed Hartree-Fock-Bogoliubov calculations for finite nuclei are carried out. As residual interaction, a Brueckner G-matrix derived from a meson-exchange potential is taken. Phenomenological medium modifications of the meson masses are introduced. The binding energies, radii, and deformation parameters of the Carbon, Oxygen, Neon, and Magnesium isotope chains are found to be in good agreement with the experimental data.
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