Dynamic magnetic resonance spectroscopy of phosphate energetics during muscle exercise and recovery

Entailing of phosphorus exchanges in most bio-chemicals as a key factor in disease, increases researcher’s interest to develop the technologies capable of detecting this metabolite. Phosphorus magnetic resonance spectroscopy is able to detect key metabolites in a non-invasive manner. Particularly, it offers the ability to measure the dynamic rate of phosphocreatine(PCr) degeneration through the exercise and recovery. This metric as a valid indication of mitochondrial oxidative metabolism in muscle, differentiate between normal and pathological state. To do magnetic resonance imaging and spectroscopy, clinical research tools provide a wide variety of anatomical and functional contrasts, however they are typically restricted to the tissues containing water or hydrogen atoms and they are still blind to the biochemicals of other atoms of interests. Through this project we intended to obtain the phosphorus spectrum in human body – specificadenerativelly in muscle – using 31P spectroscopy. To do so a double loop RF surface coil, tuned to phosphorus frequency, is designed and fabricated using bench work facilities and then validated through in vitro spectroscopy using 3 Tesla Siemens scanner. We acquired in vitro as well as in vivo phosphorus spectrum in a 100 mM potassium phosphate phantom and human calf muscle in rest-exercise-recovery phase in a 3T MR scanner. The spectrum demonstrates the main constituent in high-energy phosphate metabolism. We also observed the dynamic variation of PCr for five young healthy subjects who performed planter flexions using resistance band during exercise and recovery. The took steps in this project pave the way for future application of spectroscopic quantification of phosphate metabolism in patients affected by carotid artery disease as well as in age-matched control subjects.

Advanced numerical study of impact forces on railway sleepers under wheel flat

Wheel-rail interaction is one of the most important research topics in railway engineering. It includes track vibration, track impact response and safety of the track. Track structure failures caused by impact forces can lead to significant economic loss for track owners through damage to rails and to the sleepers beneath. The wheel-rail impact forces occur because of imperfections on the wheels or rails such as wheel flats, irregular wheel profile, rail corrugation and differences in the height of rails connected at a welded joint. In this paper, a finite element model for the wheel flat study is developed by use of the FEA software package ANSYS. The effect of the wheel flat to impact force on sleepers is investigated. It has found that the wheel flat significantly increases impact forces and maximum Von Mises stress, and also delays the peak position of dynamic variation for impact forces on both rail and sleeper.

A Diffusion-Based Processor Reallocation Strategy for Tracking Multiple Dynamically Varying Weather Phenomena

Many meteorological phenomena occur at different locations simultaneously. These phenomena vary temporally and spatially. It is essential to track these multiple phenomena for accurate weather prediction. Efficient analysis require high-resolution simulations which can be conducted by introducing finer resolution nested simulations, nests at the locations of these phenomena. Simultaneous tracking of these multiple weather phenomena requires simultaneous execution of the nests on different subsets of the maximum number of processors for the main weather simulation. Dynamic variation in the number of these nests require efficient processor reallocation strategies. In this paper, we have developed strategies for efficient partitioning and repartitioning of the nests among the processors. As a case study, we consider an application of tracking multiple organized cloud clusters in tropical weather systems. We first present a parallel data analysis algorithm to detect such clouds. We have developed a tree-based hierarchical diffusion method which reallocates processors for the nests such that the redistribution cost is less. We achieve this by a novel tree reorganization approach. We show that our approach exhibits up to 25% lower redistribution cost and 53% lesser hop-bytes than the processor reallocation strategy that does not consider the existing processor allocation.

黄土丘陵植被恢复过程中土壤种子库萌发数量特征及动态变化

采用野外定点采样与室内土壤种子萌发试验相结合的研究方法,选取黄土丘陵区典型草原带宁夏固原地区不同植被恢复年限(2,5,12,24,35,55,75 a)及当年农地(对照)的8个样地,研究该区土壤种子库萌发数量特征及动态变化。结果表明,8个不同植被恢复年限样地土壤中可萌发的种子的平均数量为3542.5粒/m2,可萌发种子以双子叶植物为主,约占萌发总数的90%。0~5 cm土层可萌发种子数量变化于166.7~9100.0粒/m2;5~10 cm土层变化于133.38~2120.02粒/m2。土壤中可萌发种子数量随着恢复年限的增加表现先增加后下降的趋势。土壤中可萌发的种子数量随时间的变化近似单峰型,双子叶植物峰值主要出现在第4~6周,而单子叶植物萌发高峰在5~6周。表明在环境,气候等条件适宜时,黄土丘陵区典型草原带可萌发的土壤中的种子可形成萌发高峰。

陕北黄土区陡坡地人工植被的土壤水分生态环境

通过定点土壤水分测定与对比分析,研究了陕北黄土区35~45°陡坡地人工植被的土壤水分亏缺状况、年际、年内动态变化规律、干燥化特征及其补偿恢复特征。结果表明:陡坡地多年生人工植被的土壤水分亏缺极为严重,贫水年0~10m土层贮水量仅相当于田间持水量的26.2%~42.0%,丰水年贮水量也仅占田间持水量的27.0%~43.3%;亏缺次序为:柠条>刺槐>苜蓿>侧柏>杨树>油松>荒坡>杏>枣>农地。年际间同一植被土壤水分含量的变化主要发生在200 cm以上土层内,变异程度随土壤深度的增加而减弱。同一生长季,各种植被0~120 cm土层含水量的变异系数都较大,但植被间差异较小;120 cm以下土层,变异系数较小,但植被间差异较大。陡坡地多年生植被均有永久干层存在,但深层土壤干燥化强度因植物种类和生长年限而存在明显的差异。雨季土壤水分的补偿和恢复深度为1.0~1.4m,但不同植被的土壤贮水增量和补偿度有较大差异。同一植被丰水年的雨水补偿深度比干旱年可增加60 cm以上,5m土层贮水增量增加3倍以上。在自然降雨条件下,陡坡地多年生人工植被的土壤贮水亏缺状况不能得到改善,土壤干化现象也不可能有所缓解。

西藏齿突蟾蝌蚪冷适应策略研究

本文通过对高海拔两栖类西藏齿突蟾(Scutiger boulengeri)蝌蚪在实验室特定低温条件下的冷适应微空间行为分布的动态变化分析、温度耐受性实验及在不同适应温度的乳酸脱氢酶(LDH)同工酶的酶量与活性比较分析, 探讨了高海拔两栖类蝌蚪的部分冷适应策略。 西藏齿突蟾蝌蚪在不同温度的行为分布是一连续、动态过程，需用多种检验方法综合利用才能进行判断；在15℃, 除低海拔分布的西藏齿突蟾种群外所有实验物种蝌蚪均符合负二项分布、NeymanⅡ型分布；在10℃, 高海拔两栖类蝌蚪均符合负二项分布、NeymanⅡ型分布；在5℃、0℃低温时，高海拔两栖类不同分组的西藏齿突蟾蝌蚪的负二项分布、NeymanⅡ型分布均呈现明显差异, 这可能与高海拔两栖类蝌蚪在低温条件下通过不断地改变其行为分布方式来避免自身被冻伤有关。野外观察表明：高海拔两栖类蝌蚪常选择与流动河水相连的静水水体这种微生境中生存, 蝌蚪应对环境温度极端变化会不断改变其行为分布方式来选择最佳生存温度以避免极端高、低温对自身身体的伤害, 这种对微生境的利用能力对高海拔两栖类蝌蚪耐受极端环境温度的变化极其重要。 两栖类蝌蚪的温度耐受性实验表明不同的驯化温度可以改变西藏齿突蟾蝌蚪、两栖类仙琴水蛙蝌蚪的最适温度、逃避温度，并具有显著影响。 随着驯化温度5℃、10℃逐渐升高, 其最适温度、逃避温度也在一定范围内升高，但驯化温度对低海拔的仙琴水蛙蝌蚪的最适温度、逃避温度的改变效应大于高海拔的西藏齿突蟾蝌蚪的改变效应, 仙琴水蛙蝌蚪对温度的耐受范围、最适温度和逃避温度的ARRS值都大于西藏齿突蟾蝌蚪, 这说明仙琴水蛙蝌蚪对环境温度变化的适应能力大于西藏齿突蟾蝌蚪。 高海拔地区不同分组的两栖类蝌蚪, 在0℃适应温度时, LDH5条带的酶相对含量最高，而在5℃、10℃、15℃适应温度时，LDH5条带的酶相对含量明显都降低, 这表明酵解作用是高海拔两栖类蝌蚪的一些组织在低温﹑缺氧环境中的重要供能方式。高海拔两栖类蝌蚪同一分组的LDH总酶活性总是表现为10℃适应温度的总酶活性最高，而对低海拔的两栖类蝌蚪则是0℃适应温度的总酶活性最高, 这说明高海拔两栖类蝌蚪的LDH同工酶A、B两亚基基因活性在10℃时最高, 而低海拔两栖类蝌蚪的LDH同工酶A、B两亚基基因活性在0℃时最高。同时发现在15℃适应温度组的高海拔两栖类蝌蚪的LDH电泳图谱都有第6条带,有可能由LDH - C亚基组成, 对高海拔两栖类蝌蚪的LDH - C亚基只在15℃适应温度下才表达的机理还有待进一步的研究。 高海拔两栖类西藏齿突蟾蝌蚪通过行为分布方式的改变来选择最佳的生存温度, 这种温度选择过程与野外特定的微生境的存在密切相关, 现在由于人类对河道的不合理利用正在导致高海拔两栖类蝌蚪赖以生存的这种微生境逐渐消失, 这种微生境的消失将加速高海拔的两栖类种群数量衰退的进程。高海拔两栖类物种蝌蚪在低温（0℃）上表现出的同工酶多谱带说明，其A、B两亚基都有所表达，及其参与代谢的方式也是正常的，而低海拔两栖类物种蝌蚪只有A亚基表达的LDH5存在，因此其主要参与酵解过程，这种通过动物自身生理代谢方式的改变来适应极端环境温度条件的变化是高海拔两栖类蝌蚪能适应低温环境的重要策略。但高海拔物种的适应温度变化范围显著小于低海拔物种，对环境温度的变化适应能力有限，特别是对高温区域，因此全球气候变化可能对高海拔物种影响更为显著。 The partly cold-adaptation stratagem of the high altitude amphibian tadpole were researched in the laboratory by analyzing the high altitude amphibian tadpole of Scutiger boulengeri mainly on endpoints related to the dynamic variation of the micro-spatial behavior distribution patterns, the experiment of the temperature tolerance, and the enzyme content and activity of the lactic acid dehydrogenase(LDH) isozyme in special temperature condition. The behavior distribution of the Scutiger boulengeri tadpole is continuous and variable, but it can be figured out by multple testing ways. At 15℃, all of the experiment amphibian tadpoles behavior distribution fit both for the negative binomial distribution and NeymanⅡtype distribution except for the low altitude Scutiger boulengeri tadpoles. At 10℃, all of the high altitude amphibian tadpoles behavior distribution fit both for the negative binomial distribution and NeymanⅡtype distribution. At lower temperature, 5℃ and 0℃, the high altitude amphibian tadpoles of the Scutiger boulengeri at different groups behavior distribution fit for or don’t fit for behavior distribution respectively. It is denoted that the high altitude amphibian tadpoles probably avoid frostbiting by varying the behavior distribution patterns at low temperature condition. The high altitude amphibian tadpoles often actively select the special microhabitat which has the connected still water body and the flowing water body in the wild. It is important that tadpoles can endure the extreme temperature variety in this kind of microhabitat, because tadpoles can be better survival through select temperature condition through migrating in these kinds of microhabitats by varying their own behavior distribution patterns. Different acclimation temperature causes the significant change of preferred temperature(PT)、 avoiding temperature(AT) both in high altitude amphibian Scutiger boulengeri tadpoles and in low altitude amphibian Rana daunchina tadpoles in the temperature endurance experiment. With the acclimation temperature growing from 5℃ to 10℃. the PT and the AT of them would be uprise to some extent, but the effect of acclimation temperature on the PT and the AT of the tadpoles of Rana daunchina is more significant than the ones on the tadpoles of Scutiger boulengeri, at the same, the effects on the temperature endurance range, the ARRs of the tadpoles of Rana daunchina would be stronger than the ones on the tadpoles of Scutiger boulengeri. It is implied that the adaptation ability of tadpoles of Rana daunchina to the surroundings temperature alternation preferred to tadpoles of Scutiger boulengeri. At 0℃ acclimation temperature, the LDH5 enzyme comparative content of the high altitude amphibian tadpoles at different groups was highest, but it becomes lower at 5℃、10℃、15℃ acclimation temperature. It indicated that the alcoholysis role was the important ways of applying energy for special tissue of the high altitude amphibian tadpoles in low-temperature and low-oxygen condition. The total enzyme activity of the LDH of the high altitude amphibian tadpoles in the same group always keeps the highest at 10℃ acclimation temperature, but the low altitude amphibian tadpoles’ was maximum at 0℃. It was denoted that the gene activity of LDH -A and LDH – B submit was highest at 10℃ acclimation temperature for the high altitude amphibian tadpoles, but the low altitude amphibian tadpoles’ was maximum at 0℃. Meanwhile, the LDH electrophoretogram of the high altitude amphibian tadpoles always composed of 6 stripes at 15℃ acclimation temperature，the extra stripe probably was composed by LDH-C submit。It is unknown why LDH-C expresses only under high temperature。. The high altitude amphibian tadpoles can select the most optimal temperature by changing their behavior distribution patterns ceaselessly, but this course of selecting the most suitable temperature correlated with the special microhabitat in the wild closely. Nowadays, this kind of microhabitat which the high altitude amphibian tadpoles rely on are lossing gradually for human being exploit the riverway unreasonably. The disappearing of the microhabitat would accelerate the decline of the high altitude amphibian population. Compare to one band of LDH5, which only composed by the LDH-A submit, presents in the low altitude amphibian at 0℃, the five bands which composed by the LDH-A and LDH-B are checked out, this means the species which occurred in the highland is more adaptable to the low temperature. It is an important stratagem for the high altitude amphibian tadpoles adapt to the limited low temperature depends on the animal energy metabolism change.However, this kind of adaption is restricted, the adaption range to the temperature is much norrow in the high altitude amphibian than in the low one, especially for the high temperature side. The global climate change will be more serious for the high altitude species.

紫色土丘陵区农用地土壤水分动态变化规律研究

依据定位观测数据，对紫色土丘陵区农用地土壤水分的动态变化规律进行了初步研究。结果表明，该区农用地土壤水分的季节变化主要受降水、蒸发和土地利用状况的影响，呈现出明显的三峰三谷型；垂直梯度变化由于受降雨入渗分布与土壤水分向上蒸发的综合作用，基本表现为增长型。并利用标准差和变异系数对土壤水分的垂直梯度变化进行了具体描述和层次划分。最后，通过分析该地区典型农作物及其不同栽培方式对农用地土壤水分的影响，认为优化农作物栽培方式是提高紫色土丘陵区农用地土壤水分利用效率和减少水土流失的有效途径。

降雨条件下碎石土滑坡稳定性研究

Debris Landslide is one of the types of landslides with the widest distribution, largest quantity, and the closest relationship with engineering construction. It is also one of the most important types of landslides that can cause disaster. This kind of landslide often occurs in the loose slopes which are made up of loose congeries formed by earth filling, residual soil, slope wash, dilapidation, landslide or full weathered material of hard rock. Rainfall is always the chief inducing factor of debris Landslide. Therefore, to research stability of debris Landslide during rainfall not only has important theoretical significance for understanding developing law and deformation and failure mechanism of debris landslide, but also has important practical significance for investigating, appraising, forecasting, preventing and controlling debris landslides. This thesis systematically summarized the relationships between rainfall and landslide, the method to survey water table in the landslides, the deformation and failure mechanism of debris landslide, and the progress in the stability analysis of landslides based on the analyses of data collected widely at home and abroad. The problems in the study of the stability of debris landslide during rainfall was reviewed and discussed. Due to the complicated geological conditions and the random rainfall conditions, the research on the landslides' stability must be based on engineering geological qualitative analysis. Through the collection of the data about the Panxi region and the Three Gorges Reservoir region, the author systematically summarized the engineering geological conditions, hydro-geological condition, distribution characteristics of stress field in the slope, physical and mechanical properties and hydro-mechanical properties of debris. In the viewpoint of dynamics of soil water and hydromechanics, physical process of rainfall to supply groundwater of debris landslides can be divided into two phases, i.e. non-saturated steady infiltrating phase and saturated unsteady supplying phase. The former can be described by mathematical model of surface water infiltration while the latter can be described by equivalent continuous medium model of groundwater seepage. With regard to specific hydrological geology system, we can obtain the dynamic variation law of water content, water table, landslide stability of rock and soil mass, along with quantity and duration of rainfall after the boundary condition on hydrological geology has been ascertained. This is a new way to study the response law of groundwater in the landslides during rainfall. After wet face of rock and soil mass connects with ground water table, the raising of water table will occur due to the supply of rainfall. Then interaction between ground water and rock and soil mass will occur, such as the action of physics, water, chemistry and mechanics, which caused the decrease of shearing strength of sliding zone. According to the action of groundwater on rock and soil mass, a concise mechanical model of debris landslide’s deformation was established during rainfall. The static equilibrium condition of landslide mass system was achieved according to the concise mechanical model, and then the typical deformation and failure process and failure mode of debris landslide during rainfall were discussed. In this thesis, the former limiting equilibrium slice method was modified and improved based on shearing strength theory of , a stability analysis program of debris landslide was established and developed taking account of the saturated-unsaturated seepage, by introducing the shearing strength theory of unsaturated soil mass made by (1978). The program has reasonable data storage and simple interface and is easy to operate, and can be perfectly used to carry out sensitivity analysis of influencing factors of landslides' stability, integrated with the program of Office Excel. The design of drainage engineering are always bases on empirical methods and is short of effective quantitative analysis and appraise, therefore, the conception of critical water table of debris landslide was put forward. For debris landslides with different kinds of slide face in the engineering practice, a program to search the critical water table of debris landslide was developed based on native groundwater table. And groundwater table in the slope should be declined below the critical water table in the drainage works, so the program can be directly used to guide drainage works in the debris landslide. Taking the slope deformation body in the back of former factory building of Muli Shawan hydroelectric power station as an example, a systematic and detailed research on debris landslides' stability during rainfall was researched systematically, the relationship among quantity of rainfall, water table and stability of slope was established, the debris landslides' stability in process of rainfall from dynamic viewpoint was analyzed and researched.

The study of flow and temperature fields in conducting droplets suspended in a DC/AC combination field

Electromagnetic Levitation (EML) is a valuable method for measuring the thermo-physical properties of metals - surface tensions, viscosity, thermal/electrical conductivity, specific heat, hemispherical emissivity, etc. – beyond their melting temperature. In EML, a small amount of the test specimen is melted by Joule heating in a suspended AC coil. Once in liquid state, a small perturbation causes the liquid envelope to oscillate and the frequency of oscillation is then used to compute its surface tension by the well know Rayleigh formula. Similarly, the rate at which the oscillation is dampened relates to the viscosity. To measure thermal conductivity, a sinusoidally varying laser source may be used to heat the polar axis of the droplet and the temperature response measured at the polar opposite – the resulting phase shift yields thermal conductivity. All these theoretical methods assume that convective effects due to flow within the droplet are negligible compared to conduction, and similarly that the flow conditions are laminar; a situation that can only be realised under microgravity conditions. Hence the EML experiment is the method favoured for Spacelab experiments (viz. TEMPUS). Under terrestrial conditions, the full gravity force has to be countered by a much larger induced magnetic field. The magnetic field generates strong flow within the droplet, which for droplets of practical size becomes irrotational and turbulent. At the same time the droplet oscillation envelope is no longer ellipsoidal. Both these conditions invalidate simple theoretical models and prevent widespread EML use in terrestrial laboratories. The authors have shown in earlier publications that it is possible to suppress most of the turbulent convection generated in the droplet skin layer, through use of a static magnetic field. Using a pseudo-spectral discretisation method it is possible compute very accurately the dynamic variation in the suspended fluid envelope and simultaneously compute the time-varying electromagnetic, flow and thermal fields. The use of a DC field as a dampening agent was also demonstrated in cold crucible melting, where suppression of turbulence was achieved in a much larger liquid metal volume and led to increased superheat in the melt and reduction of heat losses to the water-cooled walls. In this paper, the authors describe the pseudo-spectral technique as applied to EML to compute the combined effects of AC and DC fields, accounting for all the flow-induced forces acting on the liquid volume (Lorentz, Maragoni, surface tension, gravity) and show example simulations.

Avaliação da compressibilidade de um Nitossolo Vermelho distroférrico sob sistema plantio direto, preparo convencional e mata nativa

Os efeitos do tráfego de máquinas nos atributos do solo de acordo com o tempo de adoção do sistema plantio direto são ainda pouco pesquisados em ambientes tropicais, e muitas dúvidas ainda persistem sobre a variação dinâmica da estrutura do solo e a sua interação com máquinas e equipamentos. Objetivou-se com este estudo avaliar o efeito do tempo de adoção do sistema plantio direto, comparativamente com área de mata nativa e de preparo convencional, usando os modelos de compressibilidade do solo. O estudo foi realizado em um Nitossolo Vermelho distroférrico, sob mata nativa (MN), preparo convencional (PC), plantio direto com um ano (PD1), plantio direto com quatro anos (PD4), plantio direto com cinco anos (PD5) e plantio direto com 12 anos (PD12). Amostras indeformadas e deformadas foram coletadas em duas profundidades (0-5 e 10-15 cm). O tempo de adoção do sistema plantio direto alterou o comportamento compressivo dos solos em ambas as profundidades, por meio das mudanças na pressão de preconsolidação. A profundidade de 0-5 cm apresentou menor capacidade de suporte de carga do que a profundidade de 10-15 cm. A profundidade de 0-5 cm, em todos os sistemas de manejo, mostrou-se mais susceptível à compactação em relação à profundidade de 10-15 cm. Os sistemas de plantio direto e convencional apresentaram a capacidade de suporte de carga crescente na seguinte ordem: PD5 < PD12 < PD1 < PD4 @ PC, para a profundidade de 0-5 cm e para a profundidade de 10-15 cm: MN @ PD12 < PC @ PD4 < PD5, enquanto o sistema PD1 apresentou comportamento diferenciado.

Avaliação dos atributos físicos e da compressibilidade de um nitossolo vermelho distroférrico sob sistemas de plantio direto, preparo convencional e mata nativa

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

The study and measurements of the behaviour and characteristics of electromagnetic relays

The thesis presents a theoretical and practical study of the dynamic behaviour of electromagnetic relays. After discussing the problem of solving the dynamicc equations analytically and presenting a historical survey of the earlier works in the relay and its dynamics, the simulation of a relay on the analogue computer is discussed. It is shown that the simulation may be used to obtain specific solutions to the dynamic equations. The computer analysis provides the dynamic characteristics for design purposes and may be used in the study of bouncing, rebound oscillations and stability of the armature motion. An approximate analytical solution to the two dynamic equations is given based on the assumption that the dynamic variation of the pull with the position of the armature is linear. The assumption is supported by the Computer-aided analysis and experimental results. The solution is intended to provide a basis for a rational design. A rigorous method of analysing the dynamic performance by using Ahlberg's theory is also presented. This method may be justified to be the extension of Ahlberg's theory by taking the mass and frictional damping forces into account. While calculating the armature motion mathematically, Ahlberg considers the equilibrium of two kinds of forces, namely pull and load, and disregards the mass and friction forces, whereas the present method deals with the equilibrium of all four kinds of forces. It is shown how this can be utilised to calculate the dynamic characteristics for a specific design. The utility of this method also extends to the study of stability, contact bounce and armature rebound. The magnetic circuit and other related topics which are essential to the study of relay dynamics are discussed and some necessary experimental results are given.

Damping Torque Analysis of Power Systems with DFIGs for Wind Power Generation

A grid-connected DFIG for wind power generation can affect power system small-signal angular stability in two ways: by changing the system load flow condition and dynamically interacting with synchronous generators (SGs). This paper presents the application of conventional method of damping torque analysis (DTA) to examine the effect of DFIG’s dynamic interactions with SGs on the small-signal angular stability. It shows that the effect is due to the dynamic variation of power exchange between the DFIG and power system and can be estimated approximately by the DTA. Consequently, if the DFIG is modelled as a constant power source when the effect of zero dynamic interactions is assumed, the impact of change of load flow brought about by the DFIG can be determined. Thus the total effect of DFIG can be estimated from the result of DTA added on that of constant power source model. Applications of the DTA method proposed in the paper are discussed. An example of multi-machine power systems with grid-connected DFIGs are presented to demonstrate and validate the DTA method proposed and conclusions obtained in the paper.

Variation in dynamic elastic shear modulus of sandstone upon fluid saturation and substitution

Experimental acoustic measurements on sandstone rocks at both sonic and ultrasonic frequencies show that fluid saturation can cause a noticeable change in both the dynamic bulk and shear elastic moduli of sandstones. We observed that the change in dynamic shear modulus upon fluid saturation is highly dependent on the type of saturant, its viscosity, rock microstructure, and applied pressures. Frequency dispersion has some influence on dynamic elastic moduli too, but its effect is limited to the ultrasonic frequency ranges and above. We propose that viscous coupling, reduction in free surface energy, and, to a limited extent, frequency dispersion due to both local and global flow are the main mechanisms responsible for the change in dynamic shear elastic modulus upon fluid saturation and substitution, and we quantify influences.