The contribution of root respiration to soil CO2 efflux in Puccinellia tenuiflora dominated community in a semi-arid meadow steppe

Rising atmospheric CO2 and temperature are altering ecosystem carbon cycling. Grasslands play an important role in regional climate change and global carbon cycle. Below-ground processes play a key role in the grassland carbon cycle because they regulate …     

An explanation to the high efficiency ofm-THPC (temporfin) used in photodynamic therapy

Meso-tetrahydroxylphenyl chlorin (m-THPC) is one of the most efficient prospective sensitizers used in photodynamic therapy (PDT). ESR spectroscopy, fluorescence quenching experiments and cyclic voltammogram measurement were used to study its redox properties. The results showed that the ability of m-THPC generating superoxide radical anions was very strong, and the rate constant of m-THPC fluorescence quenching by oxygen k_q (O₂)=1.46×10¹⁰ mol^-1·s^-1. The values of fluorescence quen- ching rate constant of m-THPC by some other electron acceptors, such as methyl viologen (MV²⁺) and anthraquinone (An), were also measured. And they were k_q (MV²⁺)=5.51×10⁹ mol^-1·s^-1, k_q (An)=7.81×10⁹ mol^-1·s^-1. The oxidation potential of m-THPC was examined to be +0.62 V (vs. NHE) in acetonitrile. All these suggested that m-THPC should be a much stronger electron donor than photofrin, the currently used in clinical photodrug, and may react easily through electron transfer with biological matter to yield various radicals. So it seemed reasonable that the type Ⅰ reaction may play an important role in the high activity of m-THPC-PDT.     

Fluorescence Determination of Artemisinin Using Hemoglobin as Catalyst and Pyronine B as Substrate

0 IntroductionMaalnadria siusb atr ompajicosr .he aAltrthe pmrisoibnlienmi (n qtihneghtraoopsiucs,QHS,Fig.1) is a sesquiterpene endoperoxide isola-ted fromArtemisia annuaL., an ancient Chineseherbal medicine usedfor treatment of fever and ma-laria.Studies of the structure and activity relation-ship have shownthat endoperoxide groupis essentialfor anti malarial activity of QHS and absence of thismoiety lead to completely loss in activity of thedrug. Many techniques have been developed to de…     

Selective interfacial bonding and thermal conductivity of diamond/Cu-alloy composites prepared by HPHT technique

Cu-based and Cu-alloy-based diamond composites were made by high-pressure-high-temperature (HPHT) sintering with the aim of maximizing the thermal conductivity of the composites. Improvements in interfacial bonding strength and thermo-physical properties of the composites were achieved using an atomized copper alloy with minor additions of Co, Cr, B, and Ti. The thermal conductivity (TC) obtained exhibited as high as 688 W·m-1·K-1, but also as low as 325 W·m-1·K-1. A large variation in TC can be rationalized by the discrepancy of diamond-matrix interfacial bonding. It was found from fractography that preferential bonding between diamond and the Cu-alloy matrix occurred only on the diamond {100} faces. EDS analysis and Raman spectra suggested that selective interfacial bonding may be attributed to amorphous carbon increasing the wettability between diamond and the Cu-alloy matrix. Amorphous carbon was found to significantly affect the TC of the composite by interface modification.     

A novel Pd/silicalite-1 composite membrane for hydrogen separation

A novel Pd/silicalite-1 composite membrane supported on the macroporous tubular stainless steel substrate was successfully fabricated by electroless plating at 303 K. The structure, morphology and gaseous permeability of the membrane were detected by X-ray diffractiometry （XRD）, scanning electron microscopy （SEM） and single-gas permeation test, respectively. Results confirm the formation of a thin, smooth, and continuous Pd/silicalite-1 composite membrane. The obtained composite membrane shows a high H2 permeance of 1.15×10^-6 mol. m^-2. s^-1. Pa^-1 with moderate H2 selectivity of 250 for H2/N2 at 773 K, at 0.1 MPa pressure drop, suggesting the potential application for H2 separation.     

Preparation and properties of C/C-SiC brake composites fabricated by warm compacted-<Emphasis Type="Italic">in situ</Emphasis> reaction

Carbon fibre reinforced carbon and silicon carbide dual matrix composites (C/C-SiC) were fabricated by the warm compacted-in situ reaction. The microstructure, mechanical properties, tribological properties, and wear mechanism of C/C-SiC composites at different brake speeds were investigated. The results indicate that the composites are composed of 58wt% C, 37wt% SiC, and 5wt% Si. The density and open porosity are 2.0 g·cm⁻³ and 10%, respectively. The C/C-SiC brake composites exhibit good mechanical properties. The flexural strength can reach up to 160 MPa, and the impact strength can reach 2.5 kJ·m⁻². The C/C-SiC brake composites show excellent tribological performances. The friction coefficient is between 0.57 and 0.67 at the brake speeds from 8 to 24 m·s⁻¹. The brake is stable, and the wear rate is less than 2.02×10⁻⁶ cm³·J⁻¹. These results show that the C/C-SiC brake composites are the promising candidates for advanced brake and clutch systems.     

Investigation of the cross-reaction mechanism of C<Subscript>6</Subscript>H<Subscript>5</Subscript>F-HNO<Subscript>2</Subscript> aqueous solution irradiated at 355 nm by transient absorbance spectrum technique

The transient absorption spectrum technique was employed to investigate the cross-reaction mechanism of C6H5F-HNO2 aqueous solution irradiated at 355 nm. The characteristic and the kinetic parameters of transient species were also detected. Hydroxyl radical derived from the photolysis of HNO2 was added to monofluorobenzene with a second-order rate constant of （5.83±0.17）×10^9 L·mol^-1·s^-1 to form an adduct, C6H5F…OH, which was able to react with HNO2 as the main reaction pathway with a rate constant of （8.3±0.1）×10^7 L·mol^-1·s^-1. The C6F6…OH adduct can also be decayed by elimination of H2O to yield monofluorophenyl radical C6H4F-. By GC-MS technique, the final products were identified to be monofluorophenol, nitro-monofluorobenzene, nitro-monofluorophenol and para-fluorobiphenyl.     

Third-order optical nonlinearities for lanthanum (III) complexes with 1, 10-phenanthroline components

The nonlinear refractive indexesn ₂ for the ethanol solutions of 1, 10-phenanthroline (2.0 × 10⁻³ mol · L⁻¹), [bis(l, 10-phenanthroline) lanthanum (III)] nitrate (1.0 × 10⁻³ mol · L⁻¹), and [nitrato-fluoracil-bis (1, 10_{-phenanthroline}) lanthanum (III) ] nitrate (1.0 × 10⁻³ mol · L⁻¹) are first measured, the third-order nonlinear optical susceptibilities χ(³) and 〈γ〉 are calculated, and the mechanisms of the third-order optical nonlinearities enhanced by lanthanum (III) are discussed preliminarily.     

Electrochemical determination of trace amounts of lead (II) and cadmium (II) at a calix[6]arene modified carbon paste electrode

An electrochemical method for the simultaneous determination of lead(II) and Cadmium(II) with a calix[6]arene modified carbon paste electrode (CPE) has been developed. Pb²⁺ and Cd²⁺ were accumulated at the surface of the modified electrode via formation of chemical complexes with calix[6]arene, and reduced at 1.40 V. During the following anodic potential sweep, reduced lead and cadmium were oxidized, and two well-defined striping peaks appeared at about −0.60 V and −0.84 V. Compared with a bare carbon paste electrode, the calix[6]arene modified CPE greatly improves the sensitivity of determining lead and cadmium. The stripping peak currents change linearly with the concentration of Pb²⁺ 3.0×10⁻⁸–8.0×10⁻⁶ mol·L⁻¹ and with that of Cd²⁺ 6.0×10⁻⁸–1.0×10⁻⁵ mol ·L⁻¹. The detection limits of Pb²⁺ and Cd²⁺ are found to be 8.0×10⁻⁹ mol·L⁻¹ and 2.0×10⁻⁸ mol·L⁻¹, respectively. The modified carbon paste electrode was applied to determine trace levels of lead and cadmium in water samples. Comparing with that of atomic absorption spectrometry, the results suggests that the calix[6]arene modified CPE has great potential for the practical sample analysis. Foundation item: Supported by the National Natural Science Foundation of China (60171023) Biography: JI Xiao-bo (1980-), male, Master, research direction: electroanalytical chemistry.     

Methane emissions from wetlands on the Qinghai-Tibet Plateau

The areal extent of cold freshwater wetlands on the Qinghai-Tibet Plateau (QTP) is estimated at 0.133 × 10⁶ km², suggesting a significant methane potential. Methane fluxes from wet alpine meadows, peatlands,Hippuris vulgaris mires and secondary marshes were 43.18, 12.96, −0.28 and 45.90 mg · m⁻² · d⁻¹, respectively based on the transect flux studies at the Huashixia Permafrost Station (HPS) from July to August 1996. Average CH₄ fluxes in the thaw season were extrapolated at 5.68 g · m⁻² according to the areal percentage of wetland areas in the Huashixia region. The CH₄ fluxes at four fixed sites, representative of similar ecosystems, ranged from −19.384–347.15 mg · m⁻² · d⁻¹, and the average CH₄ fluxes varied from 6.54 to 71.97 mg · m⁻² · d⁻¹ at each site during the observation period from April to September 1997. The CH₄ emissions at each site during the entire thaw season was estimated from 1.21 to 10.65 g · m⁻², displaying strong spatial variations. Seasonal variations of CH₄ fluxes also were observed at four sites: CH₄ outbursts occurred upon the spring thaw in May and June, CH₄ fluxes increased afterwards with rising soil temperatures. Episodic fluxes were observed in summer, which influenced the average CH₄ fluxes considerably. Annual CH₄ emissions from cold wetlands on the QTP were estimated at about 0.7–0.9 Tg based on the distribution of wetlands, representative CH₄ fluxes, and number of thaw days. The centers of CH₄ releasing were located in the sources of the Yangtze and Yellow rivers, and Zoigê Peatlands.     

Studies on reduced extent method for inhibited thermokinetics of enzyme-catalyzed reaction

The thermokinetic reduced extent equations of reversible inhibitions for Michaiels-Menten enzymatic reaction were deduced, and then the criteria for distinguishing inhibition type was given and the methods for calculating kinetic parameters,K _M,K _i andv _m were suggested. This theory was applied to inverstigate the inhibited thermokinetics of laccase-catalyzed oxidation ofo-dihydroxybenzene bym-dihydroxybenzene. The experimental results show the inhibition belongs to reversible competitive type,K _M=6.224×10⁻³ mol·L⁻¹,K _i=2.363×10⁻² mol·L⁻¹. Xiong Ya: born Sep. 1961, Ph. D. graduate student. Curent research interest is in biothermochemistry research Supported by the National Natural Science Foundation of China     

Fluxes of carbon dioxide and methane from swamp and impact factors in Sanjiang Plain,China

Incomplete decomposition of organic matter results in the accumulation of the carbon and other nutriments in wetlands. The wetland ecosystem gains a large amount of carbon from atmosphere CO2 by photosynthesis, and it loses much of which back into the atmosphere as CO2 and CH4 emission through the decomposition and respiration. Climate change, such as global warming and reduction of precipitation could drive the wetlands from carbon sink to source[1,2]. Wetland plays an important role in car…     

Investigation of Ru （ phen ）3^2＋-Hydrazine-Ce（Ⅳ） Chemiluminescence System and Its Analytical Application

0 IntroductionThbiep ycroidmipnlee)xru ctahteinoinu mof(Ⅱ r)u t(he Rniuu(mbip,y m)3ai2n +ly) atrnids- t(r2is -,(21’ -,10-phenanthroline)ruthenium(Ⅱ) (Ru(phen)32 +) ,is a kindof sensitive analytical reagent for electrogenerated chemilumi-nescence(ECL) and chemiluminescence(CL) ,on which a par-ticular review has been presented[1]. The earliest publicationon the synthesis of Ru(bipy)32 +appeared in 1936[2], andduringthefollowing30 years ,theinvestigations relatedtothissubstance were only in…     

Synthesis and surface activity of biquaternary ammonium salt gemini surfactants with ester bond

The synthesis and surface activity of gemini surfactants with ester bond as spacer are described. Their critical micelle concentrations （CMC） are much lower than that of conventional surfactants, i.e., 1.62×10^-5, 1.38×10^-5, 1.28×10^-5 mol·L^-1 for gemini Ⅰ, Ⅱ and Ⅲ respectively. Surface tension at the CMC of gemini Ⅰ, Ⅱ and Ⅲ were 36.4, 38.5, 41.2 mN · m^-1. The physico-chemical properties such as Krafft points, foaming abilities and emulsifying power were also investigated. It is found that the title compounds have low Krafft points and show good solubility in water. The gemini surfactants synthesized also exhibit good foaming properties and excellent emulsifying power toward toluene. The foaming abilities and emulsifying power increase with the increase in carbon number of hydrophobic chain, and this might be caused by the sheer viscosity of different gemini surfactant solution.     

Rate constants for the reaction of ozone with <Emphasis Type="Italic">n</Emphasis>-butyl, <Emphasis Type="Italic">s</Emphasis>-butyl and <Emphasis Type="Italic">t</Emphasis>-butyl methyl sulfides

The rate constants for the ozone reactions with n-butyl methyl sulfide （n-BMS, CHaCH2CH2CH2SCH3）, sec-butyl methyl sulfide （s-BMS, CH3CH2（CH3）CHSCHa） and tert-butyl methyl sulfide （t-BMS, （CH3）3CSCH3） were measured using our smog chamber under supposedly pseudo-first-order conditions at 30002 K and 760 Torr. The experimental determined rate constants for n-butyl, s-butyl and t-butyl methyl sulfide are （1.23 ± 0.06）×10-19, （5.08 ± 0.19）×10-20 and （2.26 ± 0.14）×10-20 cm3 molecule-1· s-1, respectively. The reactivity-structure relationship of the reactions was discussed and used to illustrate the mechanism of the ozone reaction with thioethers. The results enrich the kinetics data of atmospheric chemistry.     

Trace determination of zirconium using anodic adsorptive voltammetry at a carbon paste electrode modified with multi-walled carbon nanotubes

A carbon paste electrode modified with multi-walled carbon nanotubes （MWCNT） was prepared and the determination of ultra trace amount of zirconium based on the anodic adsorptive voltammetry of the zirconium-calcium-alizarin red S mix-polynuclear complex is described in this paper for the first time. The results showed that the sensitivity and the selectivity of the method are excellent. The second derivative linear scan voltammograms of the complex were recorded by polarographic analyzer from 200 to 1200 mV （vs. SCE） and it was found that the complex can be adsorbed on the surface of the electrode, yielding a peak at about 840 mV, corresponding to the oxidation of ARS in the complex. The peak current increases linearly with Zr （IV） concentration in the range of 6.0×10^-12--6.0×10^-11 mol. L^-1 （accumulation time 120 s）, 6.0×10^-11--2.0×10^-9 mol. L-1 （accumulation time 90 s） and 2.0×10^-9--1.0×10^-7 mol. L^-1 （accumulation time 60 s） and the detection limit （S/N = 3） is 2.0×10^-12 mol. L^-1 （accumulation time 180 s）. The procedure has been successfully applied to the determination of zirconium in the ore samples.     

Export and remineralization of POM in the Southern Ocean and the South China Sea estimated from 210Po/210Pb disequilibria

Disequilibria between ^210Po and ^210Pb in the upper water and their potential applications as a proxy of particle export and remineralization were examined in the Southern Ocean （station IV3） and the South China Sea （NS44）. ^210po was deficit in surface waters but excessive relative to ^210Pb in subsurface waters. Good positive correlation between ^210Po and particulate organic carbon （POC） indicated deficits and excess of ^210Po resulted from particulate organic matter （POM） export and remJneralization respectively, which was also supported by the decreased δ^13C and increased δ^15N downwards as a result of particle remineralization. On the basis of ^210Po/^210Pb box-model, POC export flux out of the surface waters were 1.2 mmol C. m^-2. d^-1 and 2.3 mmol C. m^-2. d^-1 for station NS44 and IV3, respectively. In the subsurface waters, remineralization fluxes of ^210Po were 0.062 Bq. m^-2.d^-1 and 0.566 Bq.m^-2.d^-1 for station NS44 and IV3 along with the recycle efficiency of 52±26% and 119±52%, respectively. Remineralized fluxes of POM derived from ^210Po and exported POC were 0.6 mmol C.m^-2.d^-1 and 2.7 mmol C. m^-2. d^-1 for NS44 and IV3. This study suggested that ^210Po was a powerful tracer of particle export and remineralization.     

The minimization of non-equilibrium plasma source at high pressure

The density of plasma produced by atmospheric non-equilibrium plasma source is the function of energy dissipation rate in ionization electric field and gas particles momentum. The experiment shows that the plasma density highly rises with the increasing of energy dissipation rate and gas particles momentum. When the energy dissipation rate of activation field is 2.18 Wh/m^3 and the average gas particles momentum is 109×10^-22 g· m/s, the air throughput of plasma source whose volume is only 2.5 cm^3 can be up to 12 m^3/h and the density of plasma can be up to 10^10 cm^-3. The research can develop a method of producing minitype plasma source which is low energy consumption but high ion concentration used for chemical industry, environmental engineering and military.     

Validating a dust production model by field experiment in Mu Us Desert, China

It is essential for validation and improvement of a dust production model to perform field observations on dust emissions. The dust production model (DPM model) consists of two physically explicit sub-models, namely saltation model [1, 2] (eq. (1)) and sandblasting model [3] (eqs. (2) and (3)). Fh is saltation flux, E is fraction of erodible surface, C is a dimensional constant, ρa is air density, g is gravitational acceleration, U* is the wind friction velocity, Ut*(Dp) is threshold frict…     

Description of mechanism function about dehydration of cobalt oxalate dihydrate by multiple rates isotemperature method

0　IntroductionThetechnologyofthermalanalysishasbeenwidelyusedinthestudyofthermalbehaviorandthermalcharacterofsolidstatereaction ,theprimaryintentionofthermalanalysiskineticsistoestablishseparatevaluesofapparentactivationenergyE ,themostprobablemechanism g(α)andthepre exponentialfactorA ,meanwhilethedeterminationofg(α)hasgraduallybeenthefocusofthisfield .Inthisfield ,therearemostlygeneralkineticsmethodsused presently ,suchasCoats Redfern’s[1 ] integralmethod ,Achar’s[2 \〗differentialmet…