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1.
In this study a field‐sampling technique for dissolved hydrogen (H2) in groundwater will be presented which allows the transport of gaseous samples into the laboratory for further analysis. The method consists of transferring the headspace trapped in a gas‐sampling bulb which is continuously purged by groundwater into previously evacuated vials using a gas‐tight syringe. Three transfer steps with preceding evacuation of the vial led to a H2‐recovery of 100 % in laboratory experiments. The method has been applied to determine H2 concentrations in an aquifer contaminated with chlorinated solvents. Tests concerning the effect of different pumping techniques on H2 concentrations revealed that most reliable values were obtained with a bladder pump, while an electrically driven submersible pump generated considerable amounts of hydrogen due to electrochemical interactions with the sampled water. Concentrations of dissolved hydrogen in field and laboratory samples were about two orders of magnitude higher when sampling was performed with the electrically driven submersible pump compared to sampling with the bladder pump and a peristaltic pump. Lab experiments with a Plexiglas reservoir to produce H2‐enriched water were used to study the effect of two tubing materials (PVC, polyamide) on H2 losses. PVC tubing turned out to allow transfer of H2‐enriched water over 25 m without significant losses, while PA‐tubing was not suitable for sampling of H2. 相似文献
2.
High speed liquid jet and shockwave can be produced when a bubble collapses near a rigid wall, which may cause severe damage to solid structures. A hybrid algorithm was adopted to simulate bubble motion and associated pressures near a wall combining Level Set-Modified Ghost Fluid-Discontinuous Galerkin (LS-MGF-DG) method and boundary element method (BEM). Numerical results were compared with experimental data to validate the presented algorithm. Jet formation was simulated by BEM and the induced pressure on the wall was calculated with auxiliary function. The pressure at the point on the wall where the jet points to reaches its peak value after the jet penetrates the bubble. Bubble collapse and rebounding were simulated by the LS-MGF-DG method. Shock-wave is induced when the bubble collapse toroidally to a minimum volume and the pressure at wall center reaches the maximum due to shockwave superposition. A third pressure peak is found associated with the bubble rebounds and bubble splitting. In the case studied, a higher pressure was found due to collapse shockwave than bubble jet and affects a larger area of the wall. In addition, the three pressure peaks due to jet impact, collapse impact as well as bubble rebounding and splitting decrease with the increase of the standoff distance. 相似文献
3.
伊宁地块早石炭世球泡流纹岩的发现及地球化学特征 总被引：3，自引：2，他引：1
伊宁地块西段中部阿腾套山一带发现的球泡流纹岩,多数产于早石炭世海相无球泡流纹岩夹层中,整体呈层状、互层状,球泡通气孔顺层平行于流纹构造定向分布,推断是海相极浅水环境下的产物,因而具有精细指相意义。该球泡流纹岩与同期A型花岗岩类共生,属碱性岩类,SiO_2含量为69.18%~77.69%,K_2O大于4%,Al_2O_3为11.32%~16.24%,Ga/Al×10~4=2.1~7.8,∑REE=85.22×10~(-6)~348.8×10~(-6),(La/Yb)_N=6.7~14.8,相对富集轻稀土,δEu具明显负异常,稀土配分及大离子元素蛛网图均与A型花岗岩类地球化学特征总体相同。ε_(Hf)(t)均大于0(+12.5~+15.5),两阶段锆石Hf模式年龄大于锆石U-Pb年龄,表明源区可能为早古生代新生地壳物质部分熔融演化而来。A型球泡流纹岩与同期A型花岗岩类均形成于拉张构造环境,是区内早石炭世大哈拉军山组中迄今唯一发现的显示拉张构造环境的珍贵实例。为揭示和探讨伊宁地块总体处于汇聚大背景下的局部拉张环境,以及东窄西宽之楔形构造形态提供了可能。 相似文献
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5.
针对波浪破碎试验中气泡区速度与水体速度无法同时测量的难题,基于实验室条件,搭建了粒子图像测速（PIV）和气泡图像测速（BIV）系统,采用声学多普勒测速仪（ADV）对PIV测量精度和不同场景下BIV测量精度进行了细致的验证,并设计多种试验方案以期实现BIV与PIV的同步耦合测量。试验结果表明,7W激光+后置灯的优化照明方案,其耦合测量的气泡区速度代表参数与标准BIV照明方案的结果误差小于5%,且耦合测量的气泡区下方水质点的速度曲线与标准PIV测量结果吻合,表明该改进方案满足PIV与BIV耦合测量的条件。本文实现的PIV与BIV耦合测量有利于优化测量和分析工作,减小破碎波浪重复生成的影响,有利于提高测量精度,为大范围波浪破碎速度场的快速测量提供了新的方案。 相似文献
6.
本文通过MHD理论研究了细磁流通管在二维静止平衡介质中的运动.用地球磁尾中的一维细丝来表示流通管,通过数值模拟可以得到细丝随时间变化的一些性质.重联产生的细丝磁场比周围磁场偶极性更强,运动时表现出了很强的地向流.结果还显示了阿尔芬波、慢激波等MHD波从磁层的赤道面传播到地球电离层上并部分地反射回来.细丝在电离层上的足点的赤道向运动滞后于赤道面上的地向运动.虽然在模拟中细丝的初始等离子体压强低于周围压强,但是当它开始迅速向地球方向运动时,它的等离子体压强很快上升到与周围压强相当,甚至有时候大于周围压强的值. 相似文献
7.
Analytical models for decompressional bubble growth in a viscous magma are developed to establish the influence of high magma viscosity on vesiculation and to assess the time-scales on which bubbles respond to decompression. Instantaneous decompression of individual bubbles, analogous to a sudden release of pressure (e.g. sector collapse), is considered for two end-member cases. The infinite melt model considers the growth of an isolated bubble before significant bubble interaction occurs. The shell model considers the growth of a bubble surrounded by a thin shell and is analogous to bubble growth in a highly vesicular magmatic foam. Results from the shell model show that magmas less viscous than 109 Pa s can freely expand without developing strong overpressures. The timescales for pressure re-equilibration are shortened by increased ratios of bubble radius to shell thickness and by larger decompression. Time-scales for isolated bubbles in rhyolitic melts (infinite melt model) are significantly longer, implying that such bubbles could experience internal pressures greater than the ambient pressure for at least a few hours following a sudden release of pressure. The shell model is developed to assess bubble growth during the linear decompression of a magma body of constant viscosity. For the range of decompression rates and viscosities associated with actual volcanic eruptions, bubble growth continues at approximately the equilibrium rate, with no attendant excess of internal pressure. The results imply that viscosity does not have any significant role in preventing the explosive expansion of high viscosity foams. However, for viscosities of >109 Pa s there is the potential for a viscosity quench under the extreme decompression rates of an explosive eruption. It is proposed that the typical vesicularities of pumice of 0.7–0.8 are a consequence of the viscosity of the degassing magmas becoming sufficiently high to inhibit bubble expansion over the characteristic time-scale of eruption. For fully degassed silicic lavas with viscosities in the range 1010 to 1012 Pa s time-scales for decompression of isolated bubbles can be hours to many months. 相似文献
8.
Youxue Zhang 《Bulletin of Volcanology》1998,59(4):281-290
Simulated gas-driven eruptions using CO2–water-polymer systems are reported. Eruptions are initiated by rapidly decompressing CO2–saturated water containing up to 1.0 wt.% CO2. Both cylindrical test cells and a flask test cell were used to examine the effect of magma chamber/conduit geometry on eruption
dynamics. Bubble-growth kinetics are examined quantitatively in experiments using cylindrical test cells. Uninhibited bubble
growth can be roughly expressed as dr/dt≈λD(β-1)/(γt
1/3) for a CO2–water-polymer system at 0–22 °C and with viscosities up to 5 Pa·s, where r is the radius of bubbles, λ and D are the Ostwald solubility coefficient and diffusivity of the gas in the liquid, β is the degree of saturation (decompression
ratio), and γ characterizes how the boundary layer thickness increases with time and is roughly 1.0×10–5 m/s1/3 in this system. Unlike the radius of cylindrical test cells, which does not affect the eruption threshold and dynamics, the
shape of the test cells (flask vs cylindrical) affects the dynamics but not the threshold of eruptions. For cylindrical test
cells, the front motion is characterized by constant acceleration with both Δh (the height increase) and ΔV (the volume increase) being proportional to t
2; for the flask test cell, however, neither Δh nor ΔV is proportional to t
2 as the conduit radius varies. Test-cell geometry also affects foam stability. In the flask test cell, as it moves from the
wider base chamber into the narrower conduit, the bubbly flow becomes fragmented, affecting the eruption dynamics. The fragmentation
may be caused by a sudden increase in acceleration induced by conduit-shape change, or by the presence of obstacles to the
bubbly flow. This result may help explain the range in vesicularities of pumice and reticulite.
Received: 16 May 1997 / Accepted: 11 October 1997 相似文献
9.
优化偏最小二乘光度法同时测定铑铱钯的研究 总被引：6，自引：0，他引：6
采用局部加权、随机矩阵法等步骤,使建立的校准模型能充分反映未知样品的数字结构特征,达到优化的目的,从而改善偏最小二乘法在处理实际未知样品数据时的解析能力,以提高计算结果的精度。用该优化偏最小二乘法对模拟地质样品中痕量贵金属Ｒｈ、Ｉｒ、Ｐｄ进行多组分光度测定,其分析结果的相对误差均小于１０％;分别测定９．５μｇ／Ｌ、３５．０μｇ／Ｌ、６６．０μｇ／Ｌ含量的Ｒｈ、Ｉｒ和Ｐｄ７次,其标准偏差Ｒｈ为０．２;Ｉｒ为１．１;Ｐｄ为２．０。 相似文献
10.
Heiko Sahling Gerhard Bohrmann Yuriy G. Artemov André Bahr Markus Brüning Stephan A. Klapp Ingo Klaucke Elena Kozlova Aneta Nikolovska Thomas Pape Anja Reitz Klaus Wallmann 《Marine and Petroleum Geology》2009
Vodyanitskii mud volcano is located at a depth of about 2070 m in the Sorokin Trough, Black sea. It is a 500-m wide and 20-m high cone surrounded by a depression, which is typical of many mud volcanoes in the Black Sea. 75 kHz sidescan sonar show different generations of mud flows that include mud breccia, authigenic carbonates, and gas hydrates that were sampled by gravity coring. The fluids that flow through or erupt with the mud are enriched in chloride (up to ∼650 mmol L−1 at ∼150-cm sediment depth) suggesting a deep source, which is similar to the fluids of the close-by Dvurechenskii mud volcano. Direct observation with the remotely operated vehicle Quest revealed gas bubbles emanating at two distinct sites at the crest of the mud volcano, which confirms earlier observations of bubble-induced hydroacoustic anomalies in echosounder records. The sediments at the main bubble emission site show a thermal anomaly with temperatures at ∼60 cm sediment depth that were 0.9 °C warmer than the bottom water. Chemical and isotopic analyses of the emanated gas revealed that it consisted primarily of methane (99.8%) and was of microbial origin (δD-CH4 = −170.8‰ (SMOW), δ13C-CH4 = −61.0‰ (V-PDB), δ13C-C2H6 = −44.0‰ (V-PDB)). The gas flux was estimated using the video observations of the ROV. Assuming that the flux is constant with time, about 0.9 ± 0.5 × 106 mol of methane is released every year. This value is of the same order-of-magnitude as reported fluxes of dissolved methane released with pore water at other mud volcanoes. This suggests that bubble emanation is a significant pathway transporting methane from the sediments into the water column. 相似文献