The occurrence of the nonzero leftmost digit, i.e., 1, 2, …, 9, of numbers from many real world sources is not uniformly distributed as one might naively expect, but instead, the nature favors smaller ones according to a logarithmic distribution, named Benford's law. This paper discusses systematically the first digit distributions of physical quantities in the fields of particle physics and astrophysics, and it is found that the full widths of hadrons and various quantities of pulsars conform to Benford's law very well. The first and second digit distributions of derivatives of period and frequency of pulsars are also found to obey the n-digit Benford's law. It is further pointed out that the pulsar data can serve as an ideal assemblage to study the first digit distributions of the real world data. Furthermore, three kinds of widely used physical statistics, i.e., the Boltzmann-Gibbs distribution, the Fermi-Dirac distribution, and the Bose-Einstein distribution, are found to conform to this law in an analytical manner. Thus, a new physical prospective is used to look into the underlying reason of this law. Moreover, various elegant mathematical properties of Benford's law are discussed in detail.

Shale gas is a kind of unconventional natural gas resources that comes from hydrocarbon rich shale formations. In recent years, the advances in horizontal drilling and in hydraulic fracturing, and the fast rising of natural gas price as a result of significant demand pressures, have made the shale gas production economically viable. The US Marcellus shale, which covers an area of about 95000 square miles, is the largest unconventional natural gas reserve in the world. Its recent estimates give 42.47 trillion cubic meters of reserves and 14 trillion cubic meters of recoverable reserves, which can meet the natural gas demand of the USA for more than 20 years. However, the water availability, water management and environmental impacts pose challenges during the Marcellus shale gas drilling and development, triggering national discussions on the sustainable development for energy and environment. According to a Temple University Summit, "Marcellus Shale Natural Gas Stewardship: Understanding the Environmental Impact", it is estimated that each well drilled using hydraulic fracturing (a process which pumps highly pressurized water to break or fracture the shale to extract the gas) will require 1-8 million gallons of water, with much of that water coming back 10-times saltier than seawater. This paper reviews the status of Marcellus shale gas development along with its environmental impacts, such as the effect of the water withdrawal on the water quantity in headwaters and the need for a cumulative impact assessment study on the areas surrounding the drilling sites. The review would provide some insights into the emerging development of shale gas in China. It is suggested that a combined multi-resource assessment should be conducted before the shale gas drilling, especially for the sustainable availability of freshwater in a regional scale. The shale gas development should ensure that the water demands of communities and regional ecosystems are not affected and that water quality and surrounding environments are protected. In addition, infrastructure, laws and regulations along with the drilling technologies and facilities should be combined to reduce water resource risks and environmental impacts of the shale gas development.

The applications of Fiber Reinforced Plastic(FRP) materials in the structure rehabilitation is discussed and compared with steel-bonded reinforcement. The related studies are systematically reviewed and analyzed. Some suggestions for the further researches in the future are put forward. First, the innovation should be emphasized for modification technology of high performance FRP and matching materials. Second, the conventional theory is not applicable to FRP, so the theoretical study should be carried out for structure rehabilitation by FRP. Third, the construction technology for the rehabilitation structure should be further developed. Fourth, because a widely accepted standard of the FRP detection technique is not available, studies in that direction are desirable. It is shown that the FRP structure rehabilitation can reduce the time and cost for maintenance, and the disturbance for traffic, and improve durability. It will play an important role in the structure rehabilitation field.

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Science & Technology Review. 2010, 28 (18): 118-118. ; doi:
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The Luodong complex is one of the typical mafic-ultramafic intrusions along Beishan Fault in Beishan area of Xinjiang and its generation shows a temporal consistency with the mafic-ultramafic complex belt in Eastern Tianshan, another typical mafic-ultramafic complex belt in Xinjiang well known for its rich deposits. Both the belts may share a similar tectonic background, related to intrusions of mantle melts during stretching after collision and the origion is affected by diving plates. Luodong intrusion consists of peridotite, lherzolite and gabbro. Olivines mainly consist of forsterites, with Fo from 81 to 88. Halo rings are characteristic of olivines, showing increasing trend of Mg moving from the marginal to central parts, which represents a reaction between the crystalized olivines and silicate melts. Based on calculations, the main composition of the primitive magma is simulated to obtain w(MgO)=8%, w(FeO)=6%, with a tholeiitic basalt composition. Quantitative simulated calculation implies that olivines are the products of magmatic evolution, without markable evidence of massive sulfide segregation.

The distribution of strata and reservoirs in the lower Paleozoic buried hill in Zhuanghai area is different in different well fields. The additional explorations of the buried hill are very important to identify the contributing factors of the complex reservoir space. The previous explanations of the reservoir formation, such as by the weathering crust, or those for fresh water of air, can not be applied here properly. The evidences of uniform temperature of inclusions and that of isotopes indicate that there are buried modifications in the studied area, and the main cause of the formation is the press-released water from the Tertiary. Modes of buried modifications are analyzed, and the three kinds of developmental modes of buried modifications are identified: the mode of supplying open-flow in the downward side; the mode of supplying contra-flow in the upward side; and the mode of directed influent supplying contra-flow in the bilateral bulge of anticline. The distribution of favorable reservoirs in the lower Paleozoic buried hill is controlled by the developmental modes of buried modifications. The stratum of the buried hill where the press-released water enters first of all usually is a favorable reservoir. On the other hand, the stratum of the buried hill where the press-released water passes out finally usually becomes a non-reservoir or a plugged zone. The results show that buried modifications can explain the formation of the complex reservoir space and the lower Paleozoic reservoirs and oil distribution models.

Among numerous tertiary technologies, Alkaline-Surfactant-Polymer(ASP) flooding is one of the most important enhanced oil recovery methods. In this method, the ASP solution system exhibits the characteristics of a non-Newtonian power-law fluid. A homogeneous well test model based on non-Newtonian power-law fluid is nonlinear and it is very difficult to obtain explicit exact analytical solutions. Generally, one can only obtain approximate solutions with numerical methods. Recently, an advanced method of separating variables with additions was proposed by the authors, which can be used to obtain exact analytical solutions . This method in this paper is used to solve the unsteady nonlinear well test equation. A series of exact analytical solutions(without using special functions or infinite series) are derived based on the theory of non-Newtonian power-law fluid. They can be used as the benchmark solutions to check the accuracy, convergence and stability of the numerical solutions and to develop the numerical computational approaches.

Electromagnetic wave propagation is one of the most important method of logging while drilling. The formation medium information is obtained through the amplitude ratio and phase difference of the electromagnetic wave. Different logging response characteristics can be generated by different frequency, different source spacing. Detection efficiency can be improved by selecting proper sensor parameters. Finite Element Method(FEM) is used to analyze the forward problem for inhomogeneous formation. Vertical resolution and radial exploration depth are calculated. The optimized design is achieved by using the neural network. The functions of vertical resolution and radial exploration depth against formation resistivity, frequency and source spacing are calculated by using FEM and neural network to obtain the optimized parameters of sensor. It is shown that the forward simulation results agree well with the results calculated by the neural network, with errors in an acceptable range. The neural network is an effective auxiliary method for optimized designing, which can reduce the forward simulation calculation time. Formation resistivity can be effectively reflected through the use of the new design parameters.

The aim of this study is to provide some basic research data for magnetic stent hyperthermia for restenosis prevention and treatment after PTCA induced heat of the 316L stainless steel stent with the Alternating Magnetic Field (AMF). The effects of heating on the proliferation, migration, apoptosis and cell cycle of rabbit vascular smooth muscle cells are also studied. VSMCs were incubated at 43℃, 47℃ or 37℃ (control) in temperature-controlled water baths. The cell viability, apoptosis rate, cell cycle rate, cell migration and expression of PCNA protein were measured by MTT assay, flow cytometry, scratch assay and immunocytochemistry, respectively, after the therapy. Results show that heating of coronary stent could be induced by the alternating magnetic field. The proliferation of VSMCs was significantly inhibited by hyperthermia. The cell viability of the 43℃ group was (83.23±2.87)%, while that of the 47℃ group was only (37.58±0.78)%. The apoptosis rate of the 47℃ group(87.37±2.95)% was significantly higher than that of the control group, while that of the 43℃ group saw no statistically significant difference compared with that of the control group. The cell cycle was arrested in S phase. After hyperthermia, the cell migration of the 47℃ group was significantly suppressed, but it had no influence on the cells of the 43℃ group. The expression of PCNA was decreased with the temperature of the bath. All above results suggest that the coronary stents can be heated by the alternating magnetic field. Hyperthermia can depress cell viability and induce VSMCs cell apoptosis. Also it can arrest the cell cycle in S phase and suppress the VSMCs cell migration. The expression of PCNA was reduced by hyperthermia, which may serve as the mechanism of the inhibition of hyperthermia on the proliferation and migration of VSMCs, and the promotion of VSMCs apoptosis.

耐电压；N-异丙基丙烯酰胺；甲基丙烯酸N,N-二甲氨基乙酯；水凝胶The electric-field sensitive hydrogel, composed of macromolecule's three-dimensional network and water, could bend and deswell under the action of an electric field. A series of electric field sensitive gels were prepared by free-radical polymerization with N-isopropylacrylamide(PNIPAAm) and N-(2-(dimethylamino)ethyl)-methacrylamide(DMAEMA) as the monomers, N,N′-methylene bisacrylamide as the crosslinking agent, ammounium persulfate and sodium bisulfite as the redox initiator. The influences of the concentration of aqueous NaCl solutions, temperature and contacting DC electric field on the swelling ratios of the hydrogels were studied in detail. It is shown that the equilibrium swelling ratios decrease as the NIPAAm and the concentration of NaCl increase. Even in a normal saline with concentration of 0.9%, the equilibrium swelling ratio can be around 89g/g, that is to say, the retention is around 44%. The obtained hydrogels, with LCST around 43℃, could be a kind of temperature sensitive materials. Under the action of a contacting DC electric field, the Rm of hydrogels decreases as DMAEMA increases. Traditionally, the hydrogel prepared by anion or cation monomer, could deswell in an electric field. But in this paper, the hydrogel was prepared by copolymerization with anion monomer and non-ionic, the relationship between Rm and time could be described with fitting formulas, which indicate that the water retention could reach 53%. Due to the excellent voltage tolerance, the gels can be applied in the artificial muscle and bionic technology, and can substitute conventional metal fuses in the future.

The different damage levels of targets can be expressed by different P-I diagrams. P-I diagrams, which are very important in the estimation of the blasting effect on targets, also provide a basis for the design of protective structures. Targets can be represented by metal plates with a certain thickness, and with the reflected parameters, the reflected pressure-impulse criterion can be used to assess the damage caused by the blast. This paper combines the analytical and numerical methods to obtain the P-I diagrams of a certain metal plate. Using the finite element analysis software ANSYS/LS-DYNA, the numerical model is built, where the process of TNT column blasting above the metal plate is simulated. The variations of pressure and impulse are studied, for different mass of TNT and the blast distance. With the obtained P-I diagrams, the coefficients affected by the boundary condition of the experiments are studied. The results of the experiments and simulations are found in good agreement, which validates the numerical model.

In the building of a horizontal tunnel of 10000m long in Xiaoqinling, Yuling town, with a buried depth of over 800m, when it goes through the gray marble or limestone, rock burst accidents often occur. In order to control the rock burst, based on the tunnel ground pressure distribution, the blasting vibration is used to shift the peak stress at the front end and sides to the deep rock mass, to release some concentrated stress, and, therefore to increase the carrying capacity of the decompression zone. The field burst tests are carried out with the largest number of times of crossing over the excavation depth, the minimum ratio of over cycle excavation depth, the maximum number of super-deep hole and the minimum number of ultra-deep hole in an orthogonal manner, and it is shown that the rock burst of the front end can be successfully controlled in the 3400mm×3000mm tunnel when three secondary blasting boreholes of 1.2 to 2 times of crossing over the excavation depth are triangularly distributed. In addition, the field burst tests are carried out at places of 1.8~2.0m high and 1.0, 1.5 and 2.0m in distance along the strike in the tunnel waist wall. The results show that the side rock burst can also be successfully controlled when the distance of the vibration blasting borehole of 2.0m deep is not more than 2.0m. If the spacing of the vibration borehole is too small, the blasting vibration may lead to cracking of the wall.

Based on the features of quasi-pentadiagonal matrix and the idea of forward elimination and backward substitution algorithm, an algorithm for solving the quasi-pentadiagonal linear equations is proposed in this paper. This algorithm consists of the following two steps. First, the quasi-pentadiagonal matrix A, as the coefficient matrix of the linear equations, is decomposed into three simple matrices L, U, D with A=LUD, where L is the lower triangular matrix, U is the upper triangular matrix, D is the unit quasi-diagonal matrix. Then, the quasi-pentadiagonal linear equations are decomposed into the following three simpler linear equations: Lz=f, Uy=z, Dx=y. Two equations are solved in the traditional LU decomposition algorithm, while three linear equations are solved in this algorithm, but without increasing the complexity. The total computational cost is only O(39n), less than that of the traditional algorithm. The main idea of this algorithm is the same as that of the forward elimination and backward substitution algorithm, consequently, the algorithm proposed in this paper is stable if the coefficient matrix is a strictly diagonally dominant matrix. The stability analysis and the corresponding results are also presented in this paper. Numerical experiments indicate that a linear relation is preserved between the computational time and the order n of equations.

The least squares estimation is widely used in linear models. However, in the least squares estimation, the square error may be great, when there are a multiple collinearity between variables. To solve this problem, it is suggested that, instead of an unbiased estimate, a biased estimate is used. As a biased estimate, the generalized ridge estimate is an estimate in a wide use. In many practical problems, aggregated data can be observed. For a linear model with aggregated data, the definition of aggregated Liu estimates is given in this paper. The Liu estimates with respect to two relative efficiencies of the least squares estimation are proposed and the upper bounds for the two relative efficiencies are obtained. This paper also gives the aggregated Liu estimates relative to Peter-Karsten estimates for two relative efficiencies and their upper bounds. The aggregation of generalized ridge estimates was often said to reduce the mean square error, and the stability of estimated parameters was emphasized, ignoring the non-bias effect of the estimated parameters. Aggregated Liu estimates, presented in this paper, with the introduction of new parameters, can not only guarantee the stability of estimated parameters, but also ensure the approximate unbiasedness of the estimated parameters. In this sense, they are better than the aggregated generalized ridge estimates.

The Steel Staggered-Truss Framing System(SSTFS) is a new type of structural system, which is developed on the basis of the Steel Frame Structure (SFS). Though there are already a large number of examples of engineering applications of SSTFS in the world, in China, its application is still in an initial stage. In order to study its fire resistance performance and to provide a possible theoretical foundation for related codes of fire protection, the structure design strategy and the fire protection strategy of SSTFS and SFS are studied in this paper based on the structure design and traditional fire protection design theories. The amounts of steel and fireproof coatings used are compared and the potential domino collapse effects of two kinds of structures exposed to fire are studied. Results show that with the same ultimate bearing capacity and fire resistance, SSTFS could greatly reduce the amount of steel, as compared to SFS. However, it would need larger amount of fireproof coatings, and the domino collapse is more likely to occur during a fire, which reduces the economic advantages of SSTFS. As the traditional fire protection design can not be directly extended for the fire protection of SSTFS, the corresponding fire protection strategy must be established and a new fire protection design method, suitable for the structure of SSTFS, should be found.

The dynamics of the tyre-ground system is important for vehicle's performance. A dynamics model of the tyre-ground system is the key in its simulation and should be as close to the real working conditions as possible. Based on the Discrete Element Method (DEM), a model of granule tyre and granule ground is built, and the complicated dynamic problems of vehicle driving are solved. The accuracy of the model is verified through calculating a number of parameters in the vehicle-ground system. So far, there is no effective method to simulate the earth sinkage caused by the tyre slip. With the above mentioned model, the sandy soil sinkage caused by the slip of the resilient tyre on it is calculated, and the results agree well with experimental data. The model can be effectively used in the study and calculation of the slip rate, the earth sinkage property and the relationships between vehicle and ground.

To meet the needs of information warfare for the Revolution in Military Affairs(RMA), networked weapon system platforms become a development trend of Network Centric Warfare (NCW). The battlefield wireless sensor networks have attracted much attention of the world's military powers. Time Division Multiple Access (TDMA) technology allows several users to share the same frequency channel by dividing the signal into different time slots, and it is widely used in the wireless communication for its reliability and stability. Considering the lightweight and low-power requirements of the communication protocol for battlefield wireless sensor networks, the principles and difficulties in the applications of TDMA communication protocol are analyzed in the aspects of hardware and software separately. A low-power TDMA communication protocol for battlefield environments is designed and implemented with MSP430F449 mixed signal microcontroller and CC2500 low-cost 2.4GHz RF transceiver. The battlefield wireless sensor network nodes platform and the implementation of the low-power communication protocol are discussed in detail. The experimental results have verified the reliability, scalability and flexibility of the protocol. Also, it is shown to require a small amount of codes and to stay in a low-power state when there is no wireless communication data. Thus, it is suitable for various low-power wireless sensor network applications.

Packet filtering of the router is the first defense line for the network security and plays a crucial role. The current studies focus on the data packet detection and filtering, without due consideration of the packet filter device deployment. If the packet filter is deployed properly, the network performance and efficiency can be significantly improved. Packet filters are always placed on the border of the administrative network, the boundaries between trusted and non-trusted networks. Generally, the packet filters are placed on the router in the border of the network, and a tremendous amount of time and space would be consumed, that results in time-delay and congestion, and hampers the efficiency of the network. In this paper, a new disposition algorithm is proposed. To compare various kinds of risks in the border and to remove the edge with operation risks, the packet filters can be placed in an efficient way by generating a shortest border, to provide a perfect protection for trusted networks between the internal network nodes. Experiment results show that the number of packet filters is reduced by 20% to 50%. The network delay time is reduced and the network connectivity is improved.

In view of the difficulty of temperature measurement for drum brake, a drum brake temperature measurement system based on wireless data transmission was designed. It consists of two modules: the temperature data acquisition and transmission module and the temperature data receiving and storage module. The temperature data acquisition and transmission module is installed in the brake drum and rotates with the drum brake. The temperature data receiving and storage module is installed in the driver's cab. The temperature data acquisition and transmission module consists of temperature sensors, MAX6675, a singlechip and nRF2401. The temperature data receiving and storage module consists of a singlechip, nRF2401, MAX232 serial communication chip and the host computer. The singlechip treats the temperature data collected by MAX6675 and transmits the temperature data in the form of wireless communication packets using nRF2401. The temperature data receiving and storage module receives the wireless packets, checks their validity, and transmits them to the host computer, where they are displayed and saved. Its applications indicate that the system enjoys features of small size, light weight and strong anti-jamming ability, and can meet the requirement of temperature measurements for drum brake.

Two issues should be considered in designing a water-bath system, namely, the accuracy and sensitivity of temperature control. The sensor's accuracy directly determines the system's accuracy. The system's sensitivity is largely related with the heat source and the thermal medium. The low accuracy of traditional thermocouples leads to low accuracy of the system. The traditional heat source and thermal medium make the heat distribution uneven in the temporal and spatial domains, resulting in a low sensitivity of the system. In this paper, a system is designed with the hardware and the software combined. First of all, the single-bus temperature sensor DS18B20 is used to improve the system's accuracy. Secondly, the system's sensitivity is enhanced through utilizing the electrolyte solution heating technique. Some experiments are designed to test the system's accuracy. The results show that the system's accuracy is up to 0.05℃. Other experiments are used to test the system's sensitivity according to the electrochemical theory. The results show that the system can maintain the temperature synchronization in space and time. That is to say, the sensor can capture the system's temperature in real time.

The simulation model of PV module in this paper is based on Simulink software, PV module's physical equivalent circuit and its mathematical model. Its basic parameters are the same as those of Solarex MSX60 60W, and other parameters are calculated with basic parameters and the mathematical model. This Simulink model can be used to show the U-I output characteristics of the 60W PV module under various insulations and temperatures. Meanwhile, this model can be applied to cases of other powers neatly and used to study module's parallel and serial characteristics. According to the output U-I characteristics, the U-P curve of the PV module is a single peak curve, which means that the PV module has a Maximum Power Point (MPP). On the basis of this Simulink model, Maximum Power Point Tracking (MPPT) methods are discussed. Among various MPPT methods, the incremental conductance method(IncCond) has an excellent control effect, so it is mainly discussed in this paper, and its control effect is compared with two of its improvements, which are two step-sizes IncCond and gradient variable step size IncCond. The two improved methods have both relaxed the restriction of the fixed step in IncCond. Setting the environmental parameters of the simulation model with the approximate variation of insulation in a day, the MPPT control of PV module is simulated. The simulation results further verify the accuracy of the model and the improved MPPT algorithm.

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Science & Technology Review. 2010, 28 (18): 120-121. ; doi:
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