Tilt of the ring current during the main phases of intense geomagnetic storms

Based on the data from the SuperMAG collaboration in 2000–2014, the magnetic latitude(MLAT) location of the ring current(RC) denoted by the MLAT of the maximum horizontal magnetic disturbance during the main phase of 67 intense geomagnetic storms(Dst ≤-100 nT) are derived. The results show that the maximum horizontal magnetic disturbance does not always occur in the magnetic equator, indicating that the RC might be tilted in the latitudinal direction during these storms. Specifically, the tilt of the RC near the day-night line is affected by the direction of solar wind. When the solar wind flows southward against the magnetic equatorial plane, the RC is more likely to show a dayside-lifted tilt. When the solar wind flows northward, the pattern is opposite. Tilts of the RC near the dawn-dusk line are also found in most of these storms. The location of the RC is mainly lifted in the dusk side and declined in the dawn side for positive IMF BY, while the tilt is reversed for negative IMF BY. A possible interpretation might be the IMF BY-related twisting of the geomagnetic field. Besides, the monthly averaged MLAT of the fitted RC also varies with seasons. It is shifted to the southern hemisphere in the northern summer and to the northern hemisphere in the northern winter, which might indicate that the RC is not centered on a single plane. Such a seasonal variation might be related to the angle between the solar wind and the magnetic equatorial plane.     

Analysis of the ionospheric variability based on wavelet decomposition

In this work,the ionospheric variability is analyzed by applying the wavelet decomposition technique to the noontime fo F2,F10.7,interplanetary magnetic field(IMF)Bz,Ap,and lower thermospheric temperature at pressure of 10?4 h Pa in 2002.Results show that the variance of periodic oscillations in the ionosphere is largest in the 2–4-day period and declines with the increase of the period.The maximum variance of the periodic oscillations in solar irradiation is in the 16–32-day period.For geomagnetic activities,most of the variance is about equally distributed on intervals of periods shorter than 32 days.Variance distributions of IMF Bz and lower thermospheric temperature are similar to those of the ionosphere.They show the maximum in the 2–4-day period and decline with the increase of the period.By analyzing the distributions of the variances,the potential connections between the ionosphere and the external sources are discussed.     

Numerical modeling of permeability evolution based on degradation approach during progressive failure of brittle rocks

The permeability evolution of rock during the progressive failure process is described.In combination with the strength degradation index,the degradation formulas of s and a,which are dependent on the plastic confining strain component,the material constants of Hoek–Brown failure criterion are presented,and a modified elemental scale elastic–brittle–plastic constitutive model of rock is established.The relationship between volumetric strain and permeability through tri-axial compression is investigated.Based on the above,a permeability evolution model is established.The model incorporates confining pressuredependent degradation of strength,dilatancy and corresponding permeability evolution.The model is implemented in FLAC by the FISH function method.The permeability evolution behavior of rock is investigated during the progressive failure process in a numerical case.The results show that the model is capable of reproducing,and allowing visualization of a range of hydro-mechanical responses of rock.The effects of confining pressure on degradation of strength,dilatancy and permeability evolution are also reflected.     

An analysis of the correlation between the fluxes of high-energy electrons and low-middle-energy electrons in the magnetosphere

The variation of the flux of energetic electrons in the magnetosphere has been proven to be strongly related to the solar wind speed. Observations of GEO orbit show that the flux of low-energy electrons is not only modulated by the solar wind speed, but, if a time delay is added, is also positively correlated to the flux of high-energy electrons. This feature provides a possible method to forecast the flux of high-energy electrons in GEO orbit. In this study, the correlations of the fluxes between the high-energy electrons and low-middle-energy electrons obtained at different L values and in different orbits are investigated to develop the application of this feature. Based on the analysis of long–term data observed by NOAA POES and GOES, the correlations between the fluxes of high-energy electrons and low–middle–energy electrons are good enough at different L values and in different orbits in quiet time, but this correlation is strongly affected by CME–driven geomagnetic storms.     

Application and reliability analysis of DPM system in site investigation of HK weathered granite

A drilling process monitor （DPM） for ground characterization of weathered granite is presented. The monitor is portable and can be mounted on a hydraulic rotary drilling rig to record various drilling parameters in real time during normal subsurface investigation. The identification method for dominative and subsidiary interfaces has been established. The study reveals that the monitored drilling parameters are dependent on geotechnical materials and can be further applied to characterize ground interfaces. The t-test between manual logging and DPM logging has been carried out. The results show that the DPM has high accuracy in interfaces detection and well agreement with the manual logging. The findings show that the device and data analysis method are of potential application in subsurface drilling exploration in weathered granites. It also seems to have prospective uses in the determination of orebody boundary as well as in the detection of geohazards.     

Corrosion-enhanced dislocation emission and motion resulting in initiation of stress corrosion cracking

A special constant deflection device for TEM has been designed, and then change of dislocation configuration ahead of a crack tip during stress corrosion cracking (SCC) of brass in water and of Ti-24Al-11Nb alloy in methanol and initiation of SCC can he observed in TEM In situ tensile test in TEM for brass was carried out for comparison The results show that anodic dissolution during SCC can facilitate dislocation emission, multiplication and motion, and a dislocation free zone (DFZ) is formed The stress at a particular site in the DFZ, which is an elastic zone and is thinned gradually through corrosion-enhanced dislocation emission and motion, is possibly up to the cohesive strength, resulting in initiating of a nanocrack of SCC in the DFZ or sometimes at the crack tip. Because of the action of the corrosion solution the nanocrack of SCC propagates into a cleavage or intergranular microcrack rather than blunts into a void like in situ tension in TEM     

Deformation of freezing water droplets on a cold copper surface

Freezing processes of water and peanut oil droplets on a cold surface are investigated in this paper. We observed during our experiments that the base surface of a water droplet that is in direct contact with the cold surface keeps its original shape, but the other part of the droplet shows an obvious growth along the direction normal to the base surface. One small protrusion appears on the top of the water droplet at the end of the freezing process. The experimental observations also show that no obvious shape change happens during the freezing of peanut oil droplets. It is postulated that the effects of sur- face tension and volume dilatation resulted from liquid-to-solid phase change cause the shape change and protrusions formation. Based on this postulation, a physical and mathematical model is developed. The results of the model of a water droplet’s freezing process correspond with our experimental observations. The observed phenomenon that frost-growth speed on the protrusion is higher than that on the other part of the water droplet is also analyzed.     

Adaptive Robust Control of Multi-Machine Power Systems with Control Time Delay

The adaptive H_∞ control problem of multi-machine power system in the case of disturbances and uncertain parameters is discussed,based on a Hamiltonian model.Considered the effect of time delay during control and transmission,a Hamilton model with control time delay is established.Lyapunov-Krasovskii function is selected,and a controller which makes the system asymptotically stable is got.The controller not only achieves the stability control for nonlinear systems with time delay,but also has the ability to suppress the external disturbances and adaptive ability to system parameter perturbation.The simulation results show the effect of the controller.     

Fluid Flow in Tundish Due to Different Type Arrangement of Weir and Dam

Tundish is an important metallurgical reactor in the continuous casting process,In order to control the fluid flow in tundish and thus take full advantage of the residence time available for the removal of inclusions from molten steel,the effect of weir and dam on the fluid flow has been studied in a water model based on the characteristic number Froude and Reynold number similarity criteria.The residence time distribution curves of the flow were measured by SG800,The optimum arrangement of dam and weir and the nonstationary flow in tundish were discussed.The results show that the comnbination of weir and dam is benefit for the flow pattern in tundish,weir can prevent the upper recirculating flow.dam can cut off the bottom flow and turn to upwards,it is advantageous to separate the nometallic inclusions.Furthermore,it is importnat to exceed the critical depth of bath during exchange ladles,not only for the inclusion floatation but also for avoiding tundish slag drainage earlier.     

Experimental Study of Seepage Properties of Non-Darcy Flow in Granular Coal Gangues

By using the steady-state seepage method, a patent seepage device together with the MTS815.02 Rock Mechanics Test System is used to test the seepage properties of non-Darcy flow in a granular gangue with five different grain sizes during the compaction. The experimental results show that the seepage properties are not only related to the stress or displacement level, but also to the grain size, the pore structure of the granular gangue, and the current porosity The permeability and the non-Darcy flow coefficient can be fitted respectively by the cubic polynomials and the power functions of the porosity, Formally, the flow in granular gangue satisfies the Forchheimer＇s binomial flow, but under the great axial and confining pressure and owing to the grain＇s crushing, the flow in granular gangues is different from that in rock-fills which are naturallv oiled un. As a result, the non-Darer flow coefficient may be negative.     

A novel approach to prevent bubble coalescence during measurement of bubble size in flotation简

Effect of frothers in preventing bubble coalescence during flotation of minerals has long been investigated. To evaluate the performance of a frother, an apparatus to measure the bubble size is a basic necessity. McGill Bubble Size Analyzer （MBSA） or bubble viewer that has been developed and completed by McGill University＇s Mineral Processing Group during the last decade is a unique instrument to serve this purpose. Two parameters which are thought to influence the bubble size measurements by McGill bubble viewer include water quality and frother concentration in the chamber. Results show that there is no difference in Sauter mean （D32） when tap or de-ionized water was used instead of process water. However, the frother concentration, in this research DowFroth 250 （DF250）, inside the chamber exhibited a pronounced effect on bubble size. Frother concentration below a certain point can not prevent coalescence inside the chamber and therefore caution must be taken in plant applications. It was also noted that the frother concentration which has been so far practiced in plant measurements （CCC75-CCC95） is high enough to prevent coalescence with the bubble viewer.     

Influence of welding parameters on nitrogen content in welding metal of 32Mn-7Cr-1Mo-0.3N austenitic steel

The transfer behavior of nitrogen into the welding metal during gas tungsten arc welding process of 32Mn-TCr-1Mo-0.3N steel was investigated. The effects of gas tungsten arc welding process variables, such as the volume fraction of nitrogen in shielding gas, arc holding time and arc current on the nitrogen content in the welding metal were also evaluated. The results show that the volume fraction of nitrogen in gas mixture plays a major role in controlling the nitrogen content in the welding metal. It seems that there exhibits a maximum nitrogen content depending on the arc current and arc holding time. The optimum volume fraction of nitrogen in shielding gas is 4% or so. The role of gas tungsten arc welding processing parameters in controlling the transfer of nitrogen is further confirmed by the experimental results of gas tungsten arc welding orocess with feeding metal.     

Anodic passivation of Pb-Ag-Nd anode in fluoride-containing H_2SO_4 solution

An attempt was made to build up a thick and compact oxide layer rapidly by pre-treating the Pb-Ag-Nd anode in fluoride-containing H2SO4 solution. The passivation reaction of Pb-Ag-Nd anode during pre-treatment process was investigated using cyclic voltammetry, linear scanning voltammetry, environmental scanning electron microscopy and X-ray diffraction analysis. The results show that Pb F2 and PbSO4 are formed near the potential of Pb/PbSO4 couple. The pre-treatment in fluoride-containing H2SO4 solution contributes to the formation of a thick, compact and adherent passive film. Furthermore, pre-treatment in fluoride-containing H2SO4 solution also facilitates the formation of PbO2 on the anodic layer, and the reason could be attributed to the formation of more PbF2 and PbSO4 during the pre-treatment which tend to transform to PbO2 during the following electrowinning process. In addition, the anodic layer on anode with pre-treatment in fluoride-containing H2SO4 solution is thick and compact, and its predominant composition is β-PbO2. In summary, the pre-treatment in fluoride-containing H2SO4 solution benefits the formation of a desirable protective layer in a short time.     

Theoretical study on boiling heat transfer in the Xi’an pulsed reactor

Boiling heat transfer condition has significance for pool-type research reactors cooled by natural circulation.It has important effect on the fuel element safety of reactor.On the basis of heat transfer characteristics of the Xi’an pulsed reactor(XAPR),fuel conduction,single-phase convection and boiling heat transfer,and void fraction models of the core are constructed.To validate the correctness of the physical models presented in the paper,numerical calculation based on a subchannel analysis method of XAPR is carried out,and the temperature fields are measured in some reactor coolant channels.The comparison between the calculated and experimental results verifies the effectiveness of the models.These physical models are used to calculate the thermal-hydraulic parameters of XAPR at the rated power(for XAPR the rated power is 2.0 MW in steady-state operation).The results indicate that subcooled boiling occurs in the XAPR core but it exhibits a subcooling degree which is considerably higher than that of saturation boiling.Subcooled boiling improves the efficiency of heat transfer between the fuel element surface and coolant,as well as effectively protects fuel elements.This research is also a beneficial reference in thermal-hydraulic analysis for other natural circulation reactors.     

Characteristics of microstructural evolution during deformation-enhanced ferrite transformation in Nb-microalloyed HSLA steel

Microstructure evolution during deformation of undercooled austenite at 760℃ was investigated in Nb-microalloyed steel by using SEM （scanning electron microscope）, TEM （transmission electron microscope）, and EBSD （electron backscattered diffraction）. It is indicated that during deformation-enhanced ferrite transformation （DEFT） in Nb-microalloyed steel, the incubation period is prolonged, and the higher strain is needed to accomplish ferrite transformation. Therefore, the transformation kinetics curves move to high strain parallelly; and the transformation kinetics curves of Nb-microalloyed steel can be divided into three stages. At the fast stage, the solute drag effect of Nb and the consumption of strain energy for the dynamic precipitation of Nb（CN） led to a long incubation period, and at the second stage, ferrite transformation was accelerated significantly and fine Nb（CN） precipitates restrict the grain growth of ferrite effectively. The results also showed that DEFT in Nb-microalloyed steel is still a nucleation dominated process, and during the microstructure evolution the interchange of 〈001〉 and 〈111〉 texture was obtained.     

Pollution and Prevention of Pb during Cement Calcination

Emission pollution and prevention measures of Pb during cement calcination were discussed. The content of Pb and the variation of composition were explored by means of atomic absorption spectroscopy （AAS） and X-ray diffraction. The results show that a number of Pb emits during cement calcination, F and Cl promote the emission of Pb, and Pb is enriched in kiln dust. The smaller the particle of kiln dust, the higher the content of Pb. When utilizing the raw materials with a high content ofPb, a more efficient dust collector should be used and the kiln dust should be used as the addition of cement. Pb in clinker is enriched in the intermediate phase. The reduction of silica modulus is useful to increase the solidification content of Pb in clinker. The solidification content of Pb in calcium sulphoaluminate mineral is higher than that in calcium aluminate mineral.     

Filling ability of semi-solid A356 aluminum alloy slurry in rheo-diecasting

The effects of slurry temperature, injection pressure, and piston velocity on the rheo-filling ability of semisolid A356 alloys were studied by the reho-diecasting methods. The results show that the slurry temperature of the semi-solid A356 aluminum alloy has an important effect on the filling ability; the higher the slurry temperature, the better is the filling ability, and the appropriate slurry temperature for rheo-filling is in the range of 585-595℃. The injection pressure also has a great effect on the filling ability, and it is appropriate to the rheo-filling when the injection pressure is in the range of 15-25 MPa. The piston velocity also has a great effect on the filling ability, and it is appropriate to the rheo-filling when the piston velocity is in the range of 0.072-0.12 m/s. The filling ability of the slurry prepared by low superheat pouring with weak electromagnetic stirring is very good and the microstructural distribution in the rheo-formed die castings is homogeneous, which is advantageous to the high quality die casting. 2008 University of Science and Technology Beijing. All rights reserved.     

Numerical Simulation of Transient Thermal Stress Field for Laser Metal Deposition Shaping

To decrease thermal stress during laser metal deposition shaping(LMDS)process,it is of great importance to learn the transient thermal stress distribution regularities.Based on the“element life and death”technique of finite element analy- sis(FEA),a three-dimensional multi-track and multi-layer numerical simulation model for LMDS is developed with ANSYS parametric design language(APDL)for the first time,in which long-edge parallel reciprocating scanning paths is introduced. Through the model,detailed simulations of thermal stress during whole metal cladding process are conducted,the generation and distribution regularities of thermal stress are also discussed in detail.Using the same process parameters,the simulation results show good agreement with the features of samples which fabricated by LMDS.     

Non-classical diffusion model for heat and mass transfer in laser drying

A numerical analysis of the laser drying process by employing a generalized, Maxwell-Cattaneo equation to treat both heat and mass transfer was presented. Calculations were performed to illustrate the non-classical transport of heat and moisture. The effect of the heat flux density and the initial moisture content on water removal was also investigated. The results indicate that the nonequilibrium mass diffusion plays an important role during the very early stages of moisture removal, especially at the surface of the medium. Away from the surface, the non-Fickian model shows a delay in the reduction of the moisture content. The calculation resuits also show that the initial moisture content of the medium has a considerable effect on water removal.     

Isotope techniques for the research of groundwater in the potential site of China's high-level waste repository

Using the isotope techniques, the groundwater origin, evolution and circulation in the potential site of China's high-level waste repository are studied. The results indicate that both shallow groundwaters and deep groundwaters in the site area are of meteoric origin. The shallow groundwaters are mainly recharged by modern and local precipitation, and the deep groundwaters are originated from regional precipitation at higher elevation, or may be from the precipitation during the geological history period with lower temperature. Through the study we can also understand that the deep underground is a very low-permeability system where the groundwater flow-rates are very low.