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Zhang W.,Desert Research Institute | Wang T.,Desert Research Institute | Wang W.,The Conservation Institute of Dunhuang Academy | Liu B.,Desert Research Institute
Environmental Earth Sciences

Wind tunnel experiments were carried out with respect to the vertical distributions of wind-blown sand flux and the processes of aeolian erosion and deposition under different wind velocities and sand supplies above beds with different gravel coverage. Preliminary results revealed that the vertical distribution of wind-blown sand flux was a way to determine whether the gobi sand stream was the saturated one or not. It had different significances to indicate characteristics of transport and deposition above gobi beds. Whether bed processes are of aeolian erosion or deposition was determined by the sand stream near the surface, especially within 0-6 cm height, while the sand transport was mainly influenced by the sand stream in the saltating layer above the height of 6 cm. The degree of the abundance of sand supply was one of the important factors to determine the saturation level of sand stream, which influenced the characteristic of aeolian erosion and deposition on gravel beds. Given the similar wind condition, the sand transport rates controlled by the saturated flow were between 2 and 8 times of the unsaturated one. Those bed processes controlled by the saturated flow were mainly of deposition, and the amount of sand accumulation increased largely as the wind speed increased. In contrast, the bed processes controlled by the unsaturated flow were mainly of aeolian erosion. Meanwhile, there was an obvious blocking sand ability within the height of 0-2 cm, and the maximal value of sand transport occurred within the surface of 2-5 cm height. © 2011 Springer-Verlag. Source

Li Q.,CAS Shanghai Institute of Optics and fine Mechanics | Liu S.,CAS Shanghai Institute of Optics and fine Mechanics | Su B.,The Conservation Institute of Dunhuang Academy | Zhao H.,CAS Shanghai Institute of Optics and fine Mechanics | And 2 more authors.
Microscopy Research and Technique

A total of nine tin-contained ancient glass beads were characterized by a combination of scanning electron microscopy coupled with energy-dispersive X-ray spectrometry and Raman spectroscopy. These glass beads dated from 1st century BC to 10th century AD were excavated from the Xinjiang and Guangxi provinces of China. Two kinds of tin-based opacifiers/colorants included crystalline cassiterite (SnO2) and lead-tin yellow types II were first found in these soda lime glass beads. The tentative chronology of the tin-based opacifiers/colorants used in ancient glasses from China and the West was compared. In addition, several transition metal ions colorants were also found in these beads. The detailed study of the glassy matrices, crystalline inclusions, and the microstructural heterogeneities for these glass beads has revealed some valuable information to trace the possible making technology and provenances. © 2012 Wiley Periodicals, Inc. Source

Li G.S.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Li G.S.,Gansu Center for Sand Hazard Reduction Engineering and Technology | Wang W.F.,The Conservation Institute of Dunhuang Academy | Qu J.J.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | And 2 more authors.
International Journal of Climatology

This article presents research on destructive environmental mechanisms affecting the murals in the Mogao Grottoes, specifically Grotto 72, from a meteorological perspective. Analysis of outside monitoring data during 1999-2008 shows that condensation of moisture and/or salt deliquescence on the mural affects a high percentage of the internal grotto, whereas the interchange of moisture between the interior grotto and the surrounding air accounts for a relatively small effect. But high humidity was the threat to the mural, so the planting of the shelterbelts was a new threat to the mural due to irrigation of shelterbelts. The higher relative humidity (RH) produced by shelterbelts in front of the grottoes is only weakly related to local precipitation but is highly correlated with the times of water irrigation of those shelterbelts. The intra-seasonal variability of temperature and RH on the mural surface is relatively stable because temperature inversion frequently occurs in the internal grotto and is favourable for maintenance of stable air stratification that is beneficial to the preservation of the wall paintings. Using ridge regression estimation of the period data, coupling equations of the change of temperature and humidity on the mural surface, the internal grotto air and the external environment are obtained. The real-time dynamics of temperature and humidity are thus analysed and reported here, offering a scientific basis for establishing a long-term monitoring network in the Mogao Grottoes. © 2012 Royal Meteorological Society. Source

Li H.,The Conservation Institute of Dunhuang Academy | Li H.,Key Scientific Research Base of Conservation for Ancient Mural | Wang W.,The Conservation Institute of Dunhuang Academy | Wang W.,Key Scientific Research Base of Conservation for Ancient Mural | Liu B.,Chinese Academy of Sciences
Journal of Hydrology

Measurements of the daily evaporation characteristics of deeply buried phreatic water in an extremely arid area are reported. The results are used to analyze the mechanism responsible for water movement in the groundwater-soil-plant-atmosphere continuum. A closed PVC greenhouse was set up on Gobi land at the top of the Mogao Grottoes where phreatic water is more than 200. m deep. An air-conditioning unit and an automatic weighing scale were placed inside the greenhouse to condense and monitor phreatic evaporation and soil water changes in this extremely arid region. Soil temperature and humidity at various depths (0-40. cm) and other meteorological factors were also recorded on a sub-hourly basis. The relationship between evaporated water and soil water movement was analyzed by observing changes in soil weight, the condensate from the air-conditioning unit, and air moisture. The results show that phreatic water evaporation occurs from this deeply buried source in this extremely arid zone. The daily characteristics are consistent with the variation in the Sun's radiation intensity (i.e. both show a sinusoidal behavior). In the daytime, most of the soil water does not evaporate but moves to cooler sub-layers. In the afternoon, the shallow soil layer absorbs moisture as the temperature decreases. At night, an abundance of water vapor moves upwards from the sub-layers and supplements the evaporated and downward-moving moisture of the superstratum in the daytime, but there is no evaporation. The stable, upwardly migrating vapor and film water is supported by geothermy and comes from phreatic water, the daily evaporation characteristics of which changes according to soil temperature when it reaches the ground. © 2014 Elsevier B.V. Source

Li H.,The Conservation Institute of Dunhuang Academy | Li H.,Key Scientific Research Base of Conservation for Ancient Mural Dunhuang Academy | Wang W.,The Conservation Institute of Dunhuang Academy | Wang W.,Key Scientific Research Base of Conservation for Ancient Mural Dunhuang Academy | And 5 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica

In the extremely arid area with little rainfall, a closed plastic canopy was constructed in the gobi land on the top of Mogao Grottoes in Dunhuang, northwestern China. An air-conditioner was put into the canopy to restrain the greenhouse effect. The refrigeration function was used to restrain the raising temperature effect and reduce the humidity. In this way, by making the temperature and humidity inside the canopy the same as those outside, we could evaluate the evaporation intensity of phreatic water in the field by measuring the weight of air-conditioning refrigeration water. The temperature, relative humidity, and absolute humidity at five different heights (+50,-10,-20,-30,-40cm) inside the canopy are higher than those outside. At the corresponding heights, differences of temperature are 3. 85, 1. 90, 1. 18, 0. 70 and 0. 51°C, for relative humidity they are 11. 3%, 1. 00%, 1. 03%, 2. 07% and 6. 45% and for absolute humility they are 3. 84, 1.05, 1. 15, 1.22, 1.92 g/m 3. Even values of the key parameter inside the canopy are higher than those outside, soil temperature and humidity profiles showed little difference, and soil conditions were suitable to the upward migration of water both inside and outside the canopy, so we can eliminate the possibility that the evaporation inside was caused by the greenhouse effect. During the 45-day-long observation period, 29572g refrigeration water was collected in total, and the average daily evaporation quantity in the later 20 days was 703. 6g and higher than that of 612. 7g in the former 25 days. The result is 8 times larger than the data gained in 2008 under a similar condition but without air-conditioner, still it is expected smaller than real values since the inside temperature and humidity were higher than outside due to the low-capacity of the air-conditioner. This demonstrates that the soil water content inside the canopy did not decline but increase slightly even evaporated constantly, and the evaporated and discharged water from soil was not resident rainfall water; phreatic water evaporation is an universal phenomenon in arid areas, and the evaporative capacity is no less than 0. 0219 mm/d in this field experiment in which the ground water table is deeper than 200m. Solar radiation intensity, temperature, and relative humidity have close relations with phreatic water evaporation, among which relative humidity shows the highest correlation with the values of evaporation. The corresponding correlation coefficient are 0. 474 (P =0. 01), 0. 376 (P = 0.05) and-0.610 (P =0. 01), respectively. Apart from climate factors, soil characteristics of the unsaturated zone including water content, void ratio and salinity also contribute a lot. Preliminary measurement result shows the evaporation of phreatic water, which is the primary water for plants in extremely arid area, is considerable and has great ecological and utility value. This work could be a basis for the assessment of ecological reconstruction with phreatic water in desert area, and is significant to the research of deep buried Groundwater-Soil-Plant-Atmosphere Continuum (GSPAC) hydrology system as well as the exploitation of deep ground water. Since evaporation intensity of phreatic water can be used to ascertain the vapor flux in the adjacent rock around Caverns, this work is also important to the protection of Mogao Grottoes. Source

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