Search

Lysergic acid (LA) is the key precursor of ergot alkaloids, and its derivatives have been used extensively for the treatment of neurological disorders. However, the poor fermentation efficiency limited its industrial application. At the same time, the hardship of genetic manipulation has hindered the metabolic engineering of Claviceps strains to improve the LA titer further. In this study, an efficient genetic manipulation system based on the protoplast-mediated transformation was established in the industrial strain Claviceps paspali. On this basis, the gene lpsB located in the ergot alkaloids biosynthetic gene cluster was deleted to construct the LA-producing cell factory. Plackett-Burman and Box-Behnken designs were used in shaking flasks, achieving an optimal fermentation medium composition. The final titer of LA and iso-lysergic acid (ILA) reached 3.7 g·L−1, which was 4.6 times higher than that in the initial medium. Our work provides an efficient strategy for the biosynthesis of LA and ILA and lays the groundwork for its industrial production.

Nobel metallic Pt/ZSM-22 and Pt/ZSM-23 catalysts were prepared for hydroisomerization of normal dodecane and hydrodewaxing of heavy waxy lube base oil. The hydroisomerization performance of n-dodecane indicated that the Pt/ZSM-23 catalyst preferred to crack the C–C bond near the middle of n-dodecane chain, while the Pt/ZSM-22 catalyst was favorable for breaking the carbon chain near the end of n-dodecane. As a result, more than 2% of light products (gas plus naphtha) and 3% more of heavy lube base oil with low-pour point and high viscosity index were produced on Pt/ZSM-22 than those on Pt/ZSM-23 while using the heavy waxy vacuum distillate oil as feedstock.

The purpose of this study is to investigate the effective way of laying up basalt-fiber grilles in concrete to improve mechanical properties, involving how the evolution of cracks is hindered and how the strength of concrete is increased by basalt filaments. In this research, three layers of basalt fiber grilles were placed in different positions of concrete composites. The compressive, splitting tensile, and beam flexural properties of the concrete composites were studied after 28 days of as-made sample curing. The reason for reduced cracks growing from basalt fiber grilles was analyzed to reveal the mechanism of increased strength and toughening of concrete composites. The results showed that a reasonable lay-up method has the highest value of utilization rate and can improve the compressive and split tensile strength of concrete specimens, especially for the flexural specimens. The reason was found to be the energy absorption, stress transfer, and bridging load-bearing effect of the basalt-fiber grilles on the hindering of the expansion of loading-induced cracks effectively. A theoretical model was thereafter developed to predict the flexural strength of concrete beam composites based on grille lay-up architecture. According to the analytical model, the corresponding predicted values compared with experimental results indicate a good coincidence and a reasonable accuracy, which is less than 12% of their discrepancy.

In this study, we investigated the characteristics of and changes in the sources of carbonaceous aerosols in northern Chinese cities after the implementation of the Action Plan for Air Pollution Prevention and Control in 2013. We collected PM2.5 samples from three representative inland cities, viz. Beijing (BJ), Xi’an (XA), and Linfen (LF) from January 2018 to April 2019. Elemental carbon (EC), organic carbon (OC), levoglucosan, stable carbon, and radiocarbon were measured in PM2.5 to quantify the sources of carbonaceous aerosol employing Latin hypercube sampling. The best estimate of source apportionment showed that the emissions from liquid fossil fuels contributed 33.6 ± 12.9 %, 26.6 ± 16.4 %, and 24.6 ± 13.4 % of the total carbon (TC) in BJ, XA, and LF, whereas coal combustion contributed 11.2 ± 9.1 %, 19.2 ± 12.3 %, and 39.2 ± 20.5 %, respectively. Non-fossil sources accounted for 55 ± 11 %, 54 ± 10 %, and 36 ± 14 % of the TC in BJ, XA, and LF, respectively. In XA, 48.34 ± 32.01 % of non-fossil sources was attributed to biomass burning. The highest contributors to OC in LF and XA were fossil sources (65.4 ± 14.9 % and 44.9 ± 9.5 %, respectively), whereas that in BJ was non-fossil sources in BJ (56.1 ± 16.7 %). The main contributors to EC were fossil sources, accounting for 92.9 ± 6.13 %, 69.9 ± 20.9 %, and 90.8 ± 9.9 % of the total EC in BJ, XA, and LF, respectively. The decline (6–17 %) in fossil source contributions in BJ and XA since the implementation of the Action Plan indicates the effectiveness of air quality management. We suggest that measures targeted to each city should be strengthened in the future.

In this work, carbon fiber needle-punching preforms were designed into two structure according to the density change along the thickness direction. One structure is designed to two layers with low-density layer and high-density layer, and the other is to three layers with low-density exterior layer and high-density interior layer. Then the effect of the preform with different structure on the densification rate and compressive properties of C/C composites was investigated. The results show that both two designed preforms can effectively avoid surface blocking, and lead to the faster densification rate of C/C composites during the chemical vapor infiltration processes. These results are attributable to the change of pore size distribution and pyrocarbon thickness, which was caused by fiber architecture designs. Meanwhile, these structural changes can improve the compressive strength of C/C composites, especially for the three-layer preforms. When the density of preforms is 0.45 g/cm3, C/C composites with three-layer preform has the highest compressive strength. The damage of most C/C composites with two and three-layer preforms is caused by shear or delamination failure, while that of C/C composites with common preforms usually caused by matrix collapse. Cracks in C/C composites with two and three-layer preforms always happened on the low-density layer, and consequently ceased or changed propagation direction in the interface between two layers.

Ali CMB Polarization Telescope (AliCPT-1) is the first CMB degree-scale polarimeter to be deployed on the Tibetan plateau at 5,250m above sea level. AliCPT-1 is a 90/150 GHz 72 cm aperture, two-lens refracting telescope cooled down to 4 K. Alumina lenses, 800mm in diameter, image the CMB in a 33.4{\deg} field of view on a 636mm wide focal plane. The modularized focal plane consists of dichroic polarization-sensitive Transition-Edge Sensors (TESes). Each module includes 1,704 optically active TESes fabricated on a 150mm diameter silicon wafer. Each TES array is read out with a microwave multiplexing readout system capable of a multiplexing factor up to 2,048. Such a large multiplexing factor has allowed the practical deployment of tens of thousands of detectors, enabling the design of a receiver that can operate up to 19 TES arrays for a total of 32,376 TESes. AliCPT-1 leverages the technological advancements in the detector design from multiple generations of previously successful feedhorn-coupled polarimeters, and in the instrument design from BICEP-3, but applied on a larger scale. The cryostat receiver is currently under integration and testing. During the first deployment year, the focal plane will be populated with up to 4 TES arrays. Further TES arrays will be deployed in the following years, fully populating the focal plane with 19 arrays on the fourth deployment year. Here we present the AliCPT-1 receiver design, and how the design has been optimized to meet the experimental requirements., Comment: Proc. SPIE, 11453, 114532A (2020)

Green processing technology has been examined extensively in the area of textile coloring, because it is usually highly efficient, environmentally friendly, and energy conserving. Herein, a novel pigment coloring technology by electrochemical modification of wool fabric surfaces is reported. This technology exhibits superior color properties with higher efficiency and lower energy and chemical consumption than the conventional cationic pretreatment coloring method. The pigment-colored wool fabric was characterized to investigate its surface morphology and roughness, K/S value, and rubbing fastness (dry and wet) under a variety of experimental conditions. The mechanism of electrochemical pigment coloring technology has been revealed, and the color properties of the fabrics have been fully investigated. Optimized technological parameters, including voltage, coloring time, and electrolyte concentration, have been determined for further application of this promising technology. Electrochemical pigment coloring has great potential for commercialization as it results in superior color performance with less pollution, higher efficiency, and lower input consumption compared with other methods.

Graphene nanoplates (GNPs) and graphene oxide (GO) were used to investigate the effects of surface free energy (SFE) of nanoparticles on the cellular structure and mechanical properties of phenolic nanocomposite foams. The results showed that the SFE of nanoparticles is a key parameter in determining the interfacial action between fillers and matrix before foaming, which in turn determines the energy barrier of bubble nucleation during foaming process. It indicated that the higher interfacial energy of GO brought out the lower Gibbs free energy and smaller driving force for heterogeneous nucleation, leading to smaller cell size with more uniform distribution. According to the effect of SFE in foaming process, different mass fractions of GNPs and GO were used in phenolic foams to investigate the effects of heterogeneous nucleating agent on cell nucleation. As a result, phenolic foam with 0.6 wt% graphene oxide (GO-0.6/PF) exhibited the optimized mechanical properties and cell microstructure.

We present here an 11,000-year palaeomonsoonal record from a sediment core (SS-1) from Shantisagara (SS) Lake in Peninsular India, which is the longest published so far from the region. This is also a region with limited palaeoclimate records. Environmental magnetic, organic geochemical, sedimentological and carbon isotopic studies were carried out on the SS-1 sediments to reconstruct the Indian summer monsoon (ISM) variability during the Holocene. The chronology of the sediments is constrained by three AMS 14C dates. Environmental magnetic data reveal that there is no contribution from bacterial magnetite, greigite and anthropogenic magnetite/lithogenic grains and that the magnetic signal is contributed mainly by the pedogenic component. The environmental magnetic data also depict variations in pedogenic magnetite production in the catchment and detrital influx to the lake, which in turn is related to monsoonal rainfall amount. The sedimentological data reveal variations in sediment size related to monsoon. The Corg/N ratio and δ13C indicate palaeovegetational variations in the SS catchment. Periods of strong monsoon are characterized by high values of concentration-dependent magnetic parameters like χlf, χfd, χARM and SIRM, high sand content, low Corg/N ratio (fully aquatic-deep water conditions), relatively depleted δ13C values (more C3 but less C4 land plants) and vice versa. The prominent palaeomonsoon events documented in this study are: (i) 11,100–10,700 cal yr BP with a weak ISM, (ii) 10,700 to 8600 cal yr BP characterized by intensified ISM, corresponding to the Early Holocene Optimum, (iii) 8600 to 4500 cal yr BP with a weakened ISM, (iv) 4500 to 3300 cal yr BP characterized by fluctuating monsoonal conditions, (v) 3300 cal yr BP to the Present with a slight increasing trend in ISM. A similar pattern is also documented in many palaeomonsoon records from the region, which indicate that Shantisagara sediments were able to record regional climatic variations as well.

In this study, meta-aramid fibres were pretreated with 2-phenoxyethanol under different conditions to investigate the effect of 2-phenoxyethanol on the dyeing of aramid at low temperature (95 °C). Structural alteration of the pretreated fibres was reflected by thermogravimetry and Fourier transform infrared spectroscopy, indicating more H-bonds, lower crystallinity, and slightly lower thermal stability. The change in structure showed that 2-phenoxyethanol combined with the fibre macromolecules and resulted in swelling of the fibre. Creation of a biphasic system through the addition of 2-phenoxyethanol to the dyeing solution resulted in the cationic dye being partitioned more towards the 2-phenoxyethanol-rich phase than the aqueous phase. The cross-sections of the dyed fibre suggested that the meta-aramid fibre could be dyed more thoroughly with an appropriate concentration of 2-phenoxyethanol. The colour value of aramid fabric was tested by varying the concentration of 2-phenoxyethanol and the temperature of pretreatment, indicating a dramatic improvement in dyeing performance to aramid after 2-phenoxyethanol pretreatment. 2-Phenoxyethanol pretreatment and low-temperature dyeing can overcome the problems of chemical and energy waste while producing a satisfying colour.

The evaluation of the stress field distribution of warp-reinforced 2.5D woven composites using meso-scale voxel-based model is described. The idealized geometry model is established by using measured parameters from the CT image. Comparison between voxel-based finite element method and experimental measurements is included. The results show that the proposed meso-scale voxel-based method is capable of accurately predicting the mechanical properties of warp-reinforced 2.5D woven composites, validated by the comparison of the initial modulus, max stress as well as the failure modes. Also, the numbers of representative volume element have an important effect on mechanical behaviors of warp-reinforced 2.5D woven composites.

In this present contribution, tensile mechanical properties of Ni–Co alloy nanowires with Co content from 0 to 20% were studied by molecular dynamics. The simulation results show the alloy nanowire with the Co content of 5% has the highest yield value of 9.72 GPa. In addition, more Frank dislocations were generated during the loading process to improve the performance of the alloy nanowire. The Young's modulus increases little by little from 105.68 to 179.78 GPa with the increase of Co content. Secondly, with the increase of temperature, the yield strength gradually decreases to 2.13 GPa. Young's modulus tends to decrease linearly from 170.7 GPa to 48.21 GPa. At the temperatures of 500 K and 700 K, it is easier to form Frank dislocation and Hirth dislocation, respectively, in the loading process. The peak value of the radial distribution function decreases and the number of peaks decreases, indicating the disappearance of the ordered structure. Finally, after the introduction of the surface and inner void, the yield strength of the nanowire drops about to 8.97 and 6.6 GPa, respectively, and the yield strains drop to 0.056 and 0.043. In the case of the existence of internal void, perfect dislocation and Hirth dislocation can be observed in the structure.

High energy X-ray telescope (HE) is one of the three instruments of Insight-HXMT(Hard X-ray Modulation Telescope) payload. The HE detector (HED) array is composed of 18 actively NaI(Tl)/CsI(Na) phoswich scintillators with a total geometric area of ~ 5100cm^2 and cover the energy range 20-250 keV. In this paper we describe the on-ground detector-level calibration campaigns and present the principal instrument properties of HEDs., Comment: 10 pages, 15 Figures

Based on the situ preparation of silica nanoparticles (SiO2) on the surface of Graphene nanoplatelets (GNPs) in the previous work, these unique three dimensional (3D) materials were introduced into epoxy resin to study the reinforcing and toughening synergy effect on the composites. Firstly, the tensile tests showed that Graphene/SiO2 hybrid materials attached with different size of SiO2 particles exhibited different reinforcing and toughening effect on the composites. With the increasing of the diameter of SiO2 particles, the toughness and strength properties of the composites firstly improved and then decreased, and when the average diameter was 0.14 μm, the elongation reached the max.. Meanwhile, the fractured surfaces presented on SEM images were consistent with the results of the tensile tests, which further explained the hybrid materials increased the interfacial adhesion between the fillers and matrix, leading to significant improvement in mechanical properties. Moreover, the DSC curves demonstrated that Graphene/SiO2 hybrid materials accelerated the curing process of epoxy resin due to the cross-link structure between fillers and matrix. Lastly, the crack propagation modes were built to clarify the synergy effect mechanism of reinforcing and toughening on nanoparticles/epoxy resin composites.

ObjectiveTo investigate the efficacy of entecavir combined with alprostadil in the treatment of hepatitis B-related cirrhotic ascites. MethodsA total of 100 patients with hepatitis B-related cirrhotic ascites who were admitted to Dezhou Hospital of Traditional Chinese Medicine from May 2012 to February 2014 were selected and randomly divided into treatment group and control group, with 50 patients in each group. The patients in both groups received the liver-protecting treatment, diuretic treatment, and intermittent supplementation of albumin(Alb). Additionally, the patients in the treatment group received oral entecavir 0.5 mg once a day, combined with intravenous infusion of alprostadil 20 μg+5% glucose injection 100 ml once a day, and those in the observation group only received oral entecavir 0.5 mg once a day. The patients were hospitalized and treated for 4 weeks. Ascites regression, changes in the levels of alanine aminotransferase (ALT), total bilirubin (TBil), Alb, blood urea nitrogen (BUN), creatinine (Cr), and hepatitis B virus (HBV) DNA, and prothrombin activity (PTA) were observed in both groups. After discharge, the patients in both groups continued to take oral entecavir 0.5 mg once a day, and the long-term therapeutic effect was observed through follow-up for 3 months. The t-test was applied for comparison of continuous data between groups, and the chi-square test was applied for comparison of categorical data between groups. ResultsThe patients in both groups had varying degrees of reduction in the amount of ascites after treatment, and the treatment group had a significantly higher overall response rate than the control group (χ2=6.018, P＜0.05). The patients in both groups had varying degrees of improvement in each index of liver and renal function (ALT, TBil, Alb, BUN, and Cr) and PTA after treatment; the treatment group had a better treatment outcome than the control group, and there were significant differences in each index after treatment between the treatment group and the control group (t=7.567, 6.875, -4.782, 6.786, 8.542, and 8.976, all P＜0.01). The patients in both groups had varying degrees of reduction in HBV DNA level after treatment (t=8.976 and 5.758, both P＜0.01), but HBV DNA level showed no significant difference between the two groups after treatment (P＞0.05). The patients were followed up for 3 months after discharge, and the treatment group had a better treatment outcome than the control group in terms of stabilization of liver and renal function and recurrence of ascites. ConclusionEntecavir combined with alprostadil has a good therapeutic effect in hepatitis B-related cirrhotic ascites, as well as a good long-term effect, and is worthy of clinical application. Entecavir monotherapy does not improve renal function significantly, but can improve liver function significantly.

Vegetational history vis a vis climate change during the past 3100 cal. years BP was deciphered from pollen data supplemented with magnetic susceptibility and particle size data for a 2.5 m long sediment core from Pookot Lake, Kerala, southern India. Pollen data suggest a mixed assemblage of upland tropical elements and wetland mangrove taxa. The presence of trace amounts of pollen grains of montane taxa like Betula, Pinus and Alnus points to their long distance dispersal. Pollen grains of Ixora, Syzygium, Symplocos, Moraceae and Arecaceae that represent tropical vegetation were also recovered, indicating modern vegetation in and around Pookot Lake. Mangrove elements are mostly represented by species of Rhizophora and Ceriops decandra along with other taxa. High-rainfall periods are characterised by high sand % and low clay % and vice versa. The pollen data correspond well with magnetic susceptibility and particle size data. The data obtained suggest three broad phases of climate, with minor oscillations, during the past 3100 cal. years BP: (1) wet climate during 3100–2500 cal. years BP; (2) dry climate spanning a long period that ended around 1000 cal. years BP; (3) amelioration in climate after 1000 cal. years BP, reflected in the presence of luxuriant vegetation and high magnetic susceptibility values.

Graphene nanoplatelets (GNPs)/SiO2 hybrid materials had been prepared successfully via chemical grafting in one step. Herein, SiO2 particles and GNPs were connected by poly acryloyl chloride (PACl). The results from Fourier transform infrared spectroscopy showed that functionalized GNPs and SiO2 particles had been successfully bridged with chemical bonds like OCO and SiOC. And the nanostructure of hybrid materials was characterized by scanning electron microscopy and transmission electron microscopy. All the images indicated that SiO2 particles were grafted on the surface of GNPs successfully. Moreover, the result of Raman spectroscopy showed that carbon atoms of GNPs became much more disorder, due to destroying the carbon domains during the process of chemical drafting. Meaningfully, the results from tensile tests indicated that Graphene/SiO2 hybrid materials had better toughening effect on epoxy composites than graphene oxide and SiO2 particles. POLYM. COMPOS., 36:907–912, 2015. © 2014 Society of Plastics Engineers

This article first examines the reasons behind the initial emergence of the securities market in post-Mao China. It then provides a narrative of the rapid development of the market, which is follow...

The automatic gain control system (AGC) is designed to continuously monitor and automatically control the gain of the phoswich detectors of the Hard X-ray Modulation Telescope (HXMT). It consists of a Am-241 radioactive source distributed within a plastic scintillator (BC408) viewed by Multi-Pixel Photon Counter (MPPC). To verify the feasibility of application in space experiments, four MPPCs (S10362-33-050C) from Hamamatsu were irradiated using a beam of 23 MeV protons with flux 1.0×10(exp8)pcm(exp-2), 2.0×10(exp8)pcm(exp-2), 4.0× 10(exp8)pcm(exp-2) and 1.0×10(exp10)pcm(exp-2). The leakage current of irradiated MPPC samples is found to increase linearly with total dose due to radiation damage. The device has completely lost its photon-counting capability when irradiated up to 13.6Gy. The pulse-height resolution has deteriorated hardly after irradiation and couldn’t work with more than 450Gy, where the measured sample has been illuminated with a few hundred photons by the Am-241 radioactive source., 形態: カラー図版あり, 著者人数: 11名, Physical characteristics: Original contains color illustrations, Number of authors: 11, 資料番号: AA0061889039, レポート番号: JAXA-SP-12-008E

A 3MV multi-element accelerator mass spectrometer (AMS) has been installed in Xi'an, China, and preliminary tests have been completed. The results of both background and precision tests for 4 nuclides are 3.1 × 10–16, 0.2% (14C); 1.8 × 10–14, 1.4% (10Be); 2.3 × 10–15, 1.14% (26Al); and 2.0 × 10–14, 1.75% (129I). The unique features of this facility are the newly developed ion source accepting solid and CO2 samples; the specially designed low-energy injector, including a “beam blanking unit” and “Q-snout”; the acceleration tube structure with the combined magnetic and electrostatic suppression; and the function of the slit stabilization in the post-acceleration system. These features are discussed in terms of the end-user's point of view.

A method for situ preparing a hybrid material consisting of silica nanoparticles (SiO2) attached onto the surface of functionalized graphene nanoplatelets (f-GNPs) is proposed. Firstly, polyacrylic acid (PAA) was grafted to the surface of f-GNPs to increase reacting sites, and then 3-aminopropyltriethoxysilane (APTES) KH550 reacted with abovementioned product PAA-GNPs to obtain siloxane-GNPs, thus providing reaction sites for the growth of SiO2 on the surface of GNPs. Finally, the SiO2/graphene nanoplatelets (SiO2/GNPs) hybrid material is obtained through introducing siloxane-GNPs into a solution of tetraethyl orthosilicate, ammonia and ethanol for hours' reaction. The results from Fourier transform infrared spectroscopy (FTIR) showed that SiO2 particles have situ grown on the surface of GNPs through chemical bonds as Si-O-Si. And the nanostructure of hybrid materials was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). All the images indicated that SiO2 particles with similar sizes were grafted on the surface of graphene nanoplatelets successfully. And TEM images also showed the whole growth process of SiO2 particles on the surface of graphene as time grows. Moreover, TGA traces suggested the SiO2/GNPs hybrid material had stable thermal stability. And at 900°C, the residual weight fraction of polymer on siloxane-GNPs was about 94.2% and that of SiO2 particles on hybrid materials was about 75.0%. However, the result of Raman spectroscopy showed that carbon atoms of graphene nanoplatelets became much more disordered, due to the destroyed carbon domains during the process of chemical drafting. Through orthogonal experiments, hybrid materials with various sizes of SiO2 particles were prepared, thus achieving the particle sizes controllable. And the factors’ level of significance is as follows: the quantity of ammonia > the quantity of tetraethyl orthosilicate (TEOS) > the reaction time.

Cyanobacteria are ancient photosynthetic prokaryotes that have adapted successfully to adverse environments including high-light irradiation. Although it is known that the repair of photodamaged photosystem II (PSII) in the organisms is a highly regulated process, our knowledge of the molecular components that regulate each step of the process is limited. We have previously identified a hypothetical protein Slr0151 in the membrane fractions of cyanobacterium Synechocystis sp. PCC 6803. Here, we report that Slr0151 is involved in PSII repair of the organism. We generated a mutant strain (Δslr0151) lacking the protein Slr0151 and analyzed its characteristics under normal and high-light conditions. Targeted deletion of slr0151 resulted in decreased PSII activity in Synechocystis. Moreover, the mutant exhibited increased photoinhibition due to impairment of PSII repair under high-light condition. Further analysis using in vivo radioactive labeling and 2-D blue native/sodium dodecylsulfate polyacrylamide gel electrophoresis indicated that the PSII repair cycle was hindered at the levels of D1 synthesis and disassembly and/or assembly of PSII in the mutant. Protein interaction assays demonstrated that Slr0151 interacts with D1 and CP43 proteins. Taken together, these results indicate that Slr0151 plays an important role in regulating PSII repair in the organism under high-light stress condition. Published version

The mechanical properties of the hybrid materials and epoxy and carbon fiber (CF) composites were improved significantly as compared to the CF composites made from unmodified epoxy. The reasons could be attributed to the strong interfacial interaction between the CF and the epoxy composites for the existence of carbon nanomaterials. The microstructure and dispersion of carbon nanomaterials were characterized by transmission electron microscopy (TEM) and optical microscopy (OM). The results showed that the dispersion of the hybrid materials in the polymer was superior to other carbon nanomaterials. The high viscosity and shear stress characterized by a rheometer and the high interfacial friction and damping behavior characterized by dynamic mechanical analysis (DMA) indicated that the strong interfacial interaction was greatly improved between fibers and epoxy composites. Remarkably, the tensile tests presented that the CF composites with hybrid materials and epoxy composites have a better reinforcing and toughening effect on CF, which further verified the strong interfacial interaction between epoxy and CF for special structural hybrid materials.

The vegetation cover is an important parameter to characterize the canopy evapotranspiration of regional vegetation. For studying the ecological water requirement of vegetation, the vegetation cover was retrieved using the dimidiate pixel model and the Normalized Difference Vegetation Index (NDVI) from the image of Landsat TM in the groundwater-fluctuating belt in lower reaches of Heihe River, northwest China. And the precision validation of the retrieval results was conducted by the field survey data from 40 sample plots in the study area. The conclusions show that the vegetation cover is very low and maldistribution in the study area. The dimidiate pixel model based on NDVI can be used in the retrieval of vegetation cover in the study area and similar desert region. This study lays the foundation for estimating the regional water requirement of ecology, understanding the canopy properties of the natural vegetation and the environmental change in the groundwater-fluctuating belt in the lower reaches of Heihe River.

To meet the measurement demands on small-mass radiocarbon (carbon content at 10 �6 g level) which are becoming increasingly significant, Xi'an-AMS has made improvements to the existing method of sample loading and has upgraded the Cs sputter ion source from the original SO-110 model. In order to study the feasibility of small-mass samples in Xi'an-AMS and evaluate the radiocarbon sample preparation ability using existing routine systems of H2/Fe and Zn/Fe, the small-mass samples prepared by four different methods are tested. They are the mass division method, mass dilution method, H2/Fe reduction method and Zn/Fe reduction method. The results show that carbon mass above 25 µg can be prepared using the existing Zn/Fe system, but no less than 100 µ gi s required using the existing H2/Fe system, which can be improved. This indicates Xi'an-AMS are now able to analyze small-mass radiocarbon samples.