马尾松种子园郁闭度对采种母树结实层效率的影响分析

采用方差分析法,研究了马尾松种子园郁闭度对母树结实层效率的影响。结果表明:随着种子园郁闭度逐渐加大,结实层效率逐渐降低。当种子园郁闭度为0.6时,采种母树平均结实层效率为77.64%;当种子园郁闭度为0.9时,采种母树平均结实层效率为56.22%;当种子园郁闭度在0.6～0.9这个区段时,郁闭度每上升0.1,采种母树平均结实层效率就下降7.14%。而且种子园的郁闭度在0.9时,采种母树结实层效率显著地小于郁闭度在0.6时。因此,可以认为:种子园的郁闭度对采种母树结实层效率有显著的影响。

整形技术对马尾松种子园结实层的影响

本实验研究表明:截除马尾松高生长主梢和各级侧枝的主梢能有效地控制马尾松的树高生长和树冠增长,缩小树冠内膛空间,提高树冠有效采光面,从而可提高种子园采种母树密度;控制结实层上移,可有效降低种子园采种难度;增大采种母树结实层厚度,可提高采种母树的单株产量。

促进云南松母树林开花结实研究

云南松(Pinus yunnanensis)木材质量下降,其主要原因是用遗传品质低劣的种子造林。为保证云南松材质优良,提高林分经济价值,必须选用优质种子造林。优质种源基地建立以后,如何使母树早结实、多结实,作者在云南省永仁县白马河林场云南松母树林中进行了试验研究。经过四年的实施、观察、分析得出下列结论:对云南母树施氮肥,种子产量增加265％;施硼砂,种子产量增加175.32％;在树干上注射赤霉素和高锰酸钾,种子产量增加43.76％和87.66％;对云南松母树树冠适当修剪能改变树冠的形状,增加结实层和树冠表面积,这些措施既不会改变云南松的遗传特性,又能提高种子产量,在生产上简单易行,建议在林木种子生产部门试用。

Experimental study on convection heat transfer and air drag in sinter layer

Convection heat transfer coefficient and air pressure drop in sinter layer are important factors for the design of sinter cooling craft. Due to the lack of necessary data, the two parameters are studied by experimental method. The experimental results show that heat conduction of sinter impacts the measurement of convection heat transfer coefficient. Convection heat transfer increases with the increase of air volumetric flow rate. Sinter layer without small particles(sample I) gives higher convection heat transfer coefficient than that with small particles(sample II). Under the considered conditions, volumetric convection heat transfer coefficient is in the range of 400-1800 W/(m3·°C). Air pressure drop in sinter layer increases with the increase of normal superficial velocity, as well as with the rise of air temperature. Additionally, air pressure drop also depends on sinter particle size distribution. In considered experimental conditions, pressure drop in sinter sample II is 2-3 times that in sinter sample I, which resulted from 17% small scale particles in sinter sample II.

Experimental investigation on rainfall infiltration and solute transport in layered porous and fractured media

Layered structures with upper porous and lower fractured media are widely distributed in the world. An experimen- tal investigation on rainfall infiltration and solute transport in such layered structures can provide the necessary foundation for effectively preventing and forecasting water bursting in mines, controlling contamination of mine water, and accomplishing ecological restoration of mining areas. A typical physical model of the layered structures with porous and fractured media was created in this study. Then rainfall infiltration experiments were conducted after salt solution was sprayed on the surface of the layered structure. The volumetric water content and concentration of chlorine ions at different specified positions along the profile of the experiment system were measured in real-time. The experimental results showed that the lower fractured media, with a considerably higher permeability than that of the upper porous media, had significant effects on preventing water infil- tration. Moreover, although the porous media were homogeneous statistically in the whole domain, spatial variations in the features of effluent concentrations with regards to time, or so called breakthrough curves, at various sampling points located at the horizontal plane in the porous media near the porous-fractured interface were observed, indicating the diversity of solute transport at small scales. Furthermore, the breakthrough curves of the outflow at the bottom, located beneath the underlying fractured rock, were able to capture and integrate features of the breakthrough curves of both the upper porous and fractured media, which exhibited multiple peaks, while the peak values were reduced one by one with time.

A new diamond bit for extra-hard, compact and nonabrasive rock formation

A new impregnated diamond bit was designed to solve the slipping problem when impregnated diamond bit was used for extra-hard, compact, and nonabrasive rock formation. Adding Si C grits into matrix, Si C grits can easily be exfoliated from the surface of the matrix due to weak holding-force with matrix, which made the surface non-smooth. Three Ф36/24 mm laboratorial bits were manufactured to conduct a laboratory drilling test on zirconiacorundum refractory brick. The laboratory drilling test indicates that the abrasive resistance of the bit work layer is proportional to the Si C concentation. The higher the concentration, the weaker the abrasive resistance of matrix. The new impregnated diamond bit was applied to a mining area drilling construction in Jiangxi province, China. Field drilling application indicates that the ROP(rate of penetration) of the new bit is approximately two to three times that of the common bits. Compared with the common bits, the surface of the new bit has typical abrasive wear characteristics,and the metabolic rate of the diamond can be well matched to the wear rate of the matrix.

Contemporary Youth Subcultures： The CDA Approach

In recent years, the cultural studies began to take a linguistic turn. This paper employed the three-dimensioned model of Fairclough, a critical discourse analysis （CDA） approach to explore youth subcultures. The cultural discourse of youth in different periods was examined in terms of discursive strategies, discursive practices, and social practices. The analysis shows that the subcultural groups adopt various discursive strategies to resist mainstream ideologies and construct the subcultural ideology and their collective identity. Meanwhile, their discursive practices build effective interaction mode within the subcultural groups. The examples of subcultures reveal that subcultures often emerge in the time of the social and cultural change and reshape the mainstream ideologies and unreasonable social structure.

SEE Laboratory： Single-Story, Single-Bay Portal Frame

This research paper describes an SEE （Structural Engineering Encounter） Lab project. The paper reports on the development of a single-story, single-bay portal frame model as part of the AIMS2 （attract, inspire, mentor and support students） grant supported through the US DOE （Department of Education） summer research program at California State University, Northridge. This research effort is part of a comprehensive program to develop laboratory models of structures commonly encountered in civil engineering practice, which can serve the dual purpose of accomplishing engineering education and research in the areas of structural and earthquake engineering. The objective of the present study was to construct a physical model of the aforementioned frame to experimentally collect data due to the application of vertical and lateral loadings through instrumentation such as strain gages and an LVDT （linear variable differential transformer） displacement transducer, and also to make comparisons with theoretical and numerical predictions.

Experimental investigation on coherent structures at early stage of boundary layer bypass transition induced by wake impingement

The early stage of a boundary layer bypass transition induced by the direct impingement of a circular cylinder wake is experimentally investigated in water tunnel,with the primary interest in both the evolution of coherent structures and their effects on the disturbance growth inside the boundary layer.It is found that spanwise vortices with small scale first form in the near-wall region around the leading-edge,which are either the residual of the wake rollers cut by the leading-edge or the high-order structures induced by the wake rollers.The formation of these spanwise vortices leads to the first rapid disturbance growth inside the boundary layer.On the other hand,streamwise vortices,which result from the impingement of longitudinal braids onto the leading-edge,are also observed inside the boundary layer.They lead to the three dimensional destabilization and the subsequent dispersion of spanwise vortices,and soon become the most dominant coherent structures inside the transitional boundary layer.It is suggested that the formation and evolution of these streamwise vortices contribute to the secondary disturbance growth stage and thus promote the completion of the transition process.The difference between the present transition scenario triggered by direct wake impingement and that by indirect wake-vortex inducement is further discussed.

Large-eddy simulation of the generation and propagation of internal solitary waves

A modified large-eddy simulation model,the dynamic coherent eddy model(DCEM)is employed to simulate the generation and propagation of internal solitary waves(ISWs)of both depression and elevation type,with wave amplitudes ranging from small,medium to large scales.The simulation results agree well with the existing experimental data.The generation process of ISWs is successfully captured by the DCEM method.Shear instabilities and diapycnal mixing in the initial wave generation phase are observed.The dissipation rate is not equal at different locations of an ISW.ISW-induced velocity field is analyzed in the present study.The structure of the bottom boundary layer(BBL)of internal wave packets is found to be different from that of a single ISW.A reverse boundary jet instead of a separation bubble exists behind the leading internal wave while separation bubbles appear in other parts of the wave-induced velocity field.The boundary jet flow resulting from the adverse pressure gradients has distinctive dynamics compared with free shear jets.

In situ investigation of SiC powder's microwave sintering by SR-CT technique

Microwave sintering is being developed as a novel technique for the preparation of dense structural ceramics,but the mature theory has not been established due to the technical difficulties.The synchrotron radiation X-ray computed tomography(SR-CT) technique was introduced for the first time into the study of microwave sintering to in-situ observe the microstructure evolution of silicon carbide(SiC) material in this paper.By applying the SR-CT technique,the reconstructed 2D and 3D images of the specimen were obtained and the double logarithm curve of mean neck size and time(Ln(x)-Ln(t)) were obtained from these reconstructed images.Various sintering phenomena including sintering neck growth during microwave treatment were observed from the reconstructed images.Furthermore,the differences in microstructure evolution and sintering kinetics between microwave and conventional sintering were analyzed based on the reconstructed images and the Ln(x)-Ln(t) curve.1) The sharp surface of grains near the contact region distinctly grew blunt and the sintering neck growth between these grains were obviously observed at the early stage.Besides,the larger particles grew faster than smaller ones.The main reason for these phenomena may be the micro-focusing effect of electric fields.2) During each of the three sintering stages,the sintering kinetics curve of double logarithm relationship between mean neck size and time shows a good linear relationship,but at the middle stage the slope of the curve increases dramatically,which is quite larger than conventional sintering.The preliminary interpretation for these extraordinary phenomena has been discussed in details.