开展“静水”水上救生教学的探究与实践——以公安海警学院为例

游泳课程作为军事体育课程主要项目之一,学院在落实强军目标和实践课程要求方面做出进一步拓展,将实战环节与教学紧密联系,由此开展水上救生课程;重点介绍了"静水"水上救生基本技术,主要以"静水"水上救生技能训练的组织为出发点,对参训人员,考核的方式进行分析研究,指出了训练的重点,为更好地开展水上救生教育提出了建议。

Dynamic characteristics of coal specimens with varying static preloading levels under low-frequency disturbance load

The mechanical properties of residual coal pillars under the influence of upward mining disturbances significantly affect the safety of residual mining activities on working faces.This study conducted low-frequency disturbance dynamic uniaxial compression tests on coal specimens using a self-developed dynamic-static load coupling electro-hydraulic servo system,and studied the strength evolutions,surface deformations,acoustic emission(AE)characteristic parameters,and the failure modes of coal specimens with different static preloading levels were studied.The disturbance damage is positively correlated with the coal specimen static preload level.Specifically,the cumulative AE count rates of the initial accelerated damage stage for the coal specimens with static preloading level of 60%and 70%of the uniaxial compressive strength(UCS)were 2.66 and 3.19 times that of the 50%UCS specimens,respectively.Macroscopically,this behaviour manifested as a decrease in the compressive strength,and the mean strengths of the disturbance-damaged coal specimens with 60%and 70%of UCS static preloading decreased by 8.53%and 9.32%,respectively,compared to those of the specimens under pure static loading.The crack sources,such as the primary fissures,strongly control the dynamic response of the coal specimen.The difference between the dynamic responses of the coal specimens and that of dense rocks is significant.

如何求小船在静水中的速度

如图1所示，一条小船位于d=200m宽的河正中点处，从这里向下游s=100√3m处有一危险区， 当时水流速度为4m／s.

Determination of undrained shear strength using piezocone penetration test in clayey soil for bridge foundation

In order to obtain the reasonable undrained shear strength Su for geotechnical analyses of bridge foundations in Yangtze River floodplain clayey soils, a site-specific study is conducted using the imported piezocone penetration test （CPTu） with dissipation phases at the Fourth Nanjing Yangtze River Bridge construction sites. Taking the values of Su from laboratory tests as references, several existing Su-predicted methods based on CPTu are compared and evaluated. To verify the presented cone factor Nk, additional test sites are selected and examined. The results show that the values of cone factors such as Nkt, Nke, and Nau, depend on the shear test mode and disturbance. Generally, the values of Nke show more scattering than those of Nkt and N△u. For the stratified and layered sediments of the Yangtze River floodplain, it is recommended using the net cone resistance qT to estimate Su and the preliminary cone factor values Nkt are from 7 to 16, with an average of 11. It is also confirmed that the CPTu test, as a new technique in site characterization, can present reasonable parameters for bridge foundations.

Numerical Study of Viscous Wave-Making Resistance of Ship Navigation in Still Water

The prediction of a ship＇s resistance especially the viscous wave-making resistance is an important issue in CFD applications. In this paper, the resistances of six ships from hull 1 to hull 6 with different hull forms advancing in still water are numerically studied using the solver naoe-FOAM-SJTU, which was developed based on the open source code package OpenFOAM. Different components of the resistances are computed and compared while considering two speed conditions （12 kn and 16 kn）. The resistance of hull 3 is the smallest while that of hull 5 is the largest at the same speed. The results show hull 3 is a good reference for the design of similar ships, which can provide some valuable guidelines for hull form optimization.

Ductility improvement methods for commercial AZ31B magnesium alloy in cold forging

In order to realize cold forging of magnesium alloys in practical application,some methods for ductility improvement of a commercial wrought AZ31B magnesium alloy(Mg-3%Al-1%Zn,mass fraction) at room temperature were suggested.The effects of heat treatment before forging and hydrostatic pressure during forging on the ductility were investigated in cold upsetting and cup forging.High-temperature annealing was effective to reduce the degree of the texture anisotropy of the specimen,and it was found that the forging limit of the annealed specimen was improved in cold forging.On the other hand,cold cup forging of the annealed specimen was carried out with applying counter pressure.By applying counter pressures of 100-200 MPa during forging,the critical punch stroke for forging limit of the specimen without crack was improved by 25%in punch stroke.

The Effect of Hydrostatic Pressure Fields on the Dispersion Characteristics of Fluid-shell Coupled System

The effect of hydrostatic pressure on the vibration dispersion characteristics of fluid-shell coupled structures was studied.Both fluid-loaded cylindrical shells and fluid-filled cylindrical shells were considered.Numerical analysis was applied to solve the dispersion equations for shells filled with or loaded with fluid at various hydrostatic pressures.The results for external pressure showed that non-dimensional axial wave numbers are nearly independent when the pressure is below the critical level.The influence of internal pressure on wave numbers was found significant for the real branch s=1 and the complex branches of dispersion curves.The presence of internal pressure increased the cut on frequencies for the branch s=1 for high order wave modes.

Simultaneous Effects of Hydrostatic Pressure and Conduction Band Non-parabolicity on Binding Energies and Diamagnetic Susceptibility of a Hydrogenic Impurity in Spherical Quantum Dots

Simultaneous effects of conduction band non-parabolicity and hydrostatic pressure on the binding energies of 1S, 2S, and 2P states along with diamagnetic susceptibility of an on-center hydrogenic impurity confined in typical GaAs/Alx- Ga1-x As spherical quantum dots are theoretically investigated using the matrix diagonalization method. In this regard, the effect of band non-parabolieity has been performed using the Luttinger-Kohn effective mass equation. The binding energies and the diamagnetic susceptibility of the hydrogenic impurity are computed as a function of the dot radius and different values of the pressure in the presence of conduction band non-parabolicity effect. The results we arrived at are as follows： the incorporation of the band edge non-parabolicity increases the binding energies and decreases the absolute value of the diamagnetic susceptibility for a given pressure and radius; the binding energies increase and the magnitude of the diamagnetic susceptibility reduces with increasing pressure.

Changing spectrum of Budd-Chiari syndrome in India with special reference to non-surgical treatment

AIM： To evaluate patterns of obstruction, etiological spectrum and non-surgical treatment in patients with Budd-Chiari syndrome in India. METHODS： Forty-nine consecutive cases of Budd- Chiari syndrome （BCS） were prospectively evaluated. All patients with refractory ascites or deteriorating liver function were, depending on morphology of inferior vena cava （IVC） and/or hepatic vein （HV） obstruction, triaged for radiological intervention, in addition to anticoagulation therapy. Asymptomatic patients, patients with diuretic-responsive ascites and stable liver function, and patients unwilling for surgical intervention were treated symptomatically with anticoagulation. RESULTS： Mean duration of symptoms was 41.5 ± 11.2 （range = 1-240） too. HV thrombosis （HVT） was present in 29 （59.1%）, IVC thrombosis in eight （16.3%）, membranous obstruction of IVC in two （4%） and both IVC-HV thrombosis in 10 （20.4%） cases. Of 35 cases tested for hypercoagulability, 27 （77.1%） were positive for one or more hypercoagulable states. Radiological intervention was technically successful in 37/38 （97.3%）： IVC stenting in seven （18.9%）, IVC balloon angioplasty in two （5.4%）, combined IVC-HV stenting in two （5.4%）, HV stenting in 11 （29.7%）, transjugular intrahepatic portosystemic shunt （TIPS） in 13 （35.1%） and combined TIPS-IVC stenting in two （5.4%）. Complications encountered in follow-up： death in five, re-stenosis of the stent in five （17.1%）, hepatic encephalopathy in two and hepatocellular carcinoma in one patient. Of nine patients treated medically, two showed complete resolution of HVT. CONCLUSION： IN our series, HVT was the predominant cause of BCS. In the last five years with the availability of sophisticated tests for hypercoagulability, etiologies were defined in 85.7% of cases. Non-surgical management was successful in most cases.

Prediction of plastic zone size around circular tunnels in non-hydrostatic stress field

This paper discusses the calculation of plastic zone properties around circular tunnels to rock-masses that satisfy the Hoek–Brown failure criterion in non-hydrostatic condition,and reviews the calculation of plastic zone and displacement,and the basis of the convergence–confinement method in hydrostatic condition.A two-dimensional numerical simulation model was developed to gain understanding of the plastic zone shape.Plastic zone radius in any angles around the tunnel is analyzed and measured,using different values of overburden(four states)and stress ratio(nine states).Plastic zone radius equations were obtained from fitting curve to data which are dependent on the values of stress ratio,angle and plastic zone radius in hydrostatic condition.Finally validation of this equation indicate that results predict the real plastic zone radius appropriately.

EFFECTS OF ROCK BEHAVIOR AND STRESS CONDITION ON FIELD STRESS DETERMINATION

Non-consistency of stress results is of ten observed during field measurements. In some cases, even the rneasurernents are made at the same location in a massive rockrnass, the results can vary widely. In order to solve the problem, extensive research has been carried out to study the major factors wh1ch rnay affect stress deterrnlnation. They include the rock behaviour and the stress state. For rocks showing non-isotropic behaviour, the values of Young’s modulus and Poisson ratio vary with the orientation of loading and measurement. Stress condition in the rock affects the rock behaviour. Furtherrnore, the loading condition on rock samples durlng laboratory tests is different from in the field and therefore the determined e1astic constants may not represent the field condi tion. In general , the Young’s modulus may depend on the orientation, the loading path, the stress magnitude and the stress ratio. This paper examines in detail the effects of those factors, especially for rocks showing transversely isotropic behaviour. It is found that the discrepancy of stress results from field measurernents in this type of rock is mainly due to over simplification of the rock behavior and inadequate use of elastic constants of the rock during stress calculation. A case study is given,which indicates the significance of these factors and demonstrates the proper procedure for stress calculation from measurements.

New Damage Detection Index Based on Mid-span Displacement and Its Application to Simply Supported Beam

This study presents a new idea of using only mid-span displacement measurement for damage detection of simply supported beams. Equivalent element concept is introduced at the beginning. In order to relate the damage detectability by means of mid-span dlsplacement measurement with the damage-eaused local stiffness change, a novel index termed as symmetrical mid-span displacement difference index （SMDDI） is proposed. The proposed method based on SMDDI is sensitive to tiny damage and comparatively small quantities of measurements are required during the application process. Another significant attraction of this method is putting aside the knowledge a-priori of the intact state. An example using simulated data has been conducted to examine the suitability of this method and assess its comparative advantages over the previous modal method.

CdS/ZnS/ZnO ternary heterostructure nanofibers fabricated by electrospinning for excellent photocatalytic hydrogen evolution without co-catalyst

In recent years,ternary heterostructures(HSs)composed of three semiconductors have attracted significant attention because of the effective separation and transfer of photogenerated electrons and holes in these materials.In this work,new ternary Cd S/Zn S/Zn O(CZZ)HSs with one-dimensional(1D)nanofiber morphology have been successfully fabricated for the first time by a series of processes:electrospinning Zn O nanofibers,sulfurizing Zn O in situ to form Zn S/Zn O binary HSs,and depositing Cd S quantum dots in situ on the Zn S/Zn O HSs.Benefiting from the efficient separation and transfer of photoinduced charge carriers,the optimized CZZ ternary HSs exhibit a hydrogen evolution rate of 51.45 mmol h^-1 g^-1(quantum efficiency:26.88%at 420 nm)without any co-catalyst,which is 93.54 and 2.28 times higher than those exhibited by pristine Zn O and Zn S/Zn O binary HSs,respectively,under the same conditions.Furthermore,the rate of hydrogen evolution over the 1D CZZ nanofibers is significantly higher than that over 2D CZZ nanosheets(27.25 mmol h^-1 g^-1,in the presence of a Pt co-catalyst)prepared by the same sulfurization and deposition procedures.This can be ascribed to the significantly smaller geometric sizes of 1D nanofibers compared to those of 2D nanosheets,resulting in effectively suppressed recombination of photogenerated charge carriers and promotion of photocatalytic H2 evolution performance.

Classification of underwater still objects based on multi-field features and SVM

A Support Vector Machine is used as a classifier to the automatic detection and recognition of underwater still objects. Discrimination between the objects can be transferred into different projection spaces by the process of multi-field feature extraction. The multi-field feature vector includes time-domain, spectral, time-frequency distribution and bi-spectral features. Underwater target recognition can be considered as a problem of small sample recognition. SVM algorithm is appropriate to this kind of problems because of its outstanding generalizability. The SVM is contrasted with a Gaussian classifier and a k-nearest classifier in some experiments using real data of lake or sea trial. The experimental results indicate that SVM is better than the others two.

Succession and biodiversity indices in eutrophication process of static landscaping water body in northern China

Many biodiversity indices were used to indicate the biological contamination degree in studies of lake water or seawater. Some were studied on biodiversity comparison for different areas at the same time, or initial structure succession of some aerial lake water systems. The phytoplankton changed with the development of various dominant species. In this study, the dominant species at these stages were Chlorophyta in the beginning stage, Cyanophyta in the second stage, and Xanthophyta in the last stage. Seven of nine biodiversity indices (Margalef's, IE, Shannon-Wiener, Simpson's, McNaughton's, Species and Odds Measure of Diversity) showed their failure to represent the eutrophication trend, and the other two indices (Menhinick's and Monk) exhibited good efficiency to indicate the eutrophication trend for the static landscaping water body.

Effects of High Hydrostatic Pressure Treatment on Physicochemical Characteristics of Sea Cucumber

The effects of high hydrostatic pressure （HHP） treatment on sea cucumber qualities, such as shelf-life, autoenzyme, total volatile basic nitrogen （TVB-N）, mucopolysaccha ride and protein, were investigated experimentally. The shelf-life of sea cucumber was greatly prolonged by HHP treatment. High pressure treatment of sea cucumber significantly reduced the activity of autoenzyme at 550 MPa. The TVB-N content was 8.4 mg/100 g in the HHP-treated samples after 38 days＇ storage at 4 ~C, while it had already reached 11.2 mg/100 g in the untreated ones after 5 days＇ storage under the same condition. The relative mucopolysaccharide content of the HHP-treated samples was 94.3%, while that of the heat-treated ones was only 35.5%. The sodium dodecyl sulfate polyacrylamide gel electrophoresis （SDS-PAGE）, Differential scanning calorimetric （DSC）, ANS fluorescence probe method and fourier-transform infrared （FTIR） spectroscopy results indicated some changes in protein subunits, denaturation, surface hydrophobicity and secondary structure of sea cucumber protein. This study has provided complementary information of pressure-induced structural changes on both the molecular and the sub-molecular level of sea cucumber protein.

Structure and Properties of Hydrotalcite Using Electrostatic Potential Energy Model

The electrostatic potential energy model of hydrotalcites was based on the theory of crystallography. The anionic potential energy of MgAl-hydrotalcites, with 20 layers and 2107 anions per layer, was calculated, and the anionic stability of the hydrotalcites was investigated. The charge density of the layer and the distance between the adjacent anions varied with the molar ratio of Al^3＋/（Mg^2＋ ＋ Al^3＋）. Anionic potential energy depended on the charge and size of the anions. Calculation results remained consistent with thermal stability and the ion exchange ability reported. This model is able to predict anionic stability of the hydrotalcites.

Three-dimensional consolidation deformation analysis of porous layered soft soils considering asymmetric effects

Long-term settlements for underground structures, such as tunnels and pipelines, are generally observed after the completion of construction in soft clay. The soil consolidation characteristic has great influences on the long-term deformation for underground structures. A three-dimensional consolidation analysis method under the asymmetric loads is developed for porous layered soil based on Biot's classical theory. Time-displacement effects can be fully considered in this work and the analytical solutions are obtained by the state space approach in the Cartesian coordinate. The Laplace and double Fourier integral transform are applied to the state variables in order to reduce the partial differential equations into algebraic differential equations and easily obtain the state space solution. Starting from the governing equations of saturated porous soil, the basic relationship of state space variables is established between the ground surface and the arbitrary depth in the integral transform domain. Based on the continuity conditions and boundary conditions of the multi-layered pore soil model, the multi-layered pore half-space solutions are obtained by means of the transfer matrix method and the inverse integral transforms. The accuracy of proposed method is demonstrated with existing classical solutions. The results indicate that the porous homogenous soils as well as the porous non-homogenous layered soils can be considered in this proposed method. When the consolidation time factor is 0.01, the value of immediate consolidation settlement coefficient calculated by the weighted homogenous solution is 27.4% bigger than the one calculated by the non-homogeneity solution. When the consolidation time factor is 0.05, the value of excess pore water pressure for the weighted homogenous solution is 27.2% bigger than the one for the non-homogeneity solution. It is shown that the material non-homogeneity has a great influence on the long-term settlements and the dissipation process of excess pore water pressure.

RADIOACTIVE OR NATURAL TRACER TECHNIQUES FOR LEAK DETERMINING OF DAM ABUTMENT

Infiltration and localization of preferential infiltration zones at the dam abutment are measured using radioactive tracer tests of flow in boreholes, meanwhile interconnection between boreholes and the energing water points is analysed. The theory and practice of radioactive tracer synthetic detective method are described to give methods and calculation formulae used under the condition of stable flow in single well to measure permeability coefficient and hydrostatic heads. Major single hole techniques including measurement for seepage line, velocity, rate of seepage flow and relationship of recharge of groundwater in aquifers are introduced briefly.The possibilities offered by natural tracers are analysed, including electric-conduct,pH-value and temperature of water as well as stable isotopes (D, 18O) and tritium.Furthermore, the sensibilities of this theory and methods were confirmed by detecting seepage flow field of Xinanjiang Dam.

Hydrostatic settling velocity of sediments

The settling of sediments is an accelerative process in which the concentration of the main sediments zone will heavily influence settling velocity,but the explicit relationship between the concentration and settling velocity has not been reported in literature. Here a theoretical function was built for the time dependent concentration and time dependent settling velocity of sediments;then the entire settling process reflecting concentration was shown on the basis of sediments instant\|settlement theory and mathematical method. Agreement of computed results and experimental data was found. Several governing parameters,including particle size,particle density,initial suspended sediments concentration and suspension height,were discussed with a series of calculated velocity curves. The research indicated that ⑴ the presented concentration\|velocity time relationship is rational,⑵ settling process of the sediments group with variation of concentration consists of acceleration stage,uniform motion stage and deceleration stage,and ⑶ particle size,particle density and initial suspended sediments concentration have more influence on the settling velocity than the suspension height and water temperature.