Longitudinal Heating Gradient: Another Possible Factor Influencing the Intensity of the Asian Summer Monsoon Circulation

The largest longitudinal heating gradients in the tropics exist between the African desert and Asian convective regions during summer once the South Asian monsoon is established. The heating gradients are anchored by the latent heat release and net radiative flux convergence over the monsoon region, and by the dominant net radiative flux divergence over the desert.An apparent relationship is found between the intensity of the Asian summer monsoon circulation and the longitudinal heating gradients mentioned, in addition to the latitudinal heating gradients cross the monsoon region. The monsoon circulation measured in terms of the zonal wind component is stronger when the longitudinal heating gradients are large, and vice versa. Thus, we claim that the longitudinal heating gradient may be another important factor which influences the intensity of the Asian summer monsoon circulation. There is little evidence that the interannual variability of the longitudinal heating gradients between Africa and Asia and, thus, the intensity of the Asian summer monsoon circulation, is a strong function of the El Nino / Southern Oscillation cycle.

A new preparation technology of structural- gradient materials without a brittle transition zone in a Mn-Si-Cr-B bainitic cast steel

In the present work, a unique gradient cooling heat treatment process(GCHT) for a Mn-Si-Cr-B bainitic cast steel was developed, and microstructure and mechanical properties were examined by OM, SEM, EBSD and a uniaxial tensile test. The results showed that the structural-gradient-material(SGM) with a gradient microstructure from granular bainite to martensite was successfully produced, and it exhibited a good ductility(~13.8%) at one end and an excellent ultimate strength(~1,720 MPa) at the other end. In between the bainite and martensite, a transition region with a superior combination of tensile strength and ductility(1,700 MPa and 11.1%) was obtained, which is different from the normal knowledge of a brittle transition region. Moreover, through changing the gradient of cooling rate, the optimized SGM with a new gradient microstructure from pearlite to martensite showed a more stable structural gradient and an improved ductility(22.8%) at one end. The microstructure variation in the sample was mainly related to the carbon diffusion rate during heat treatment, and the diffusion rate could be controlled by regulating the cooling velocity. Therefore, the SGMs with different gradient microstructures could be designed to meet the needs of different properties. As a result, this work provides a new approach for preparation of the gradient structured steel, which has potential for practical application for dual-property automobile parts.

Tailoring thermal conductivity by engineering com- positional gradients in Sil-xGex superlattices

The transport properties of artificially engineered superlattices （SLs） can be tailored by incorporating a high density of interfaces in them. Specifically, SiGe SLs with low thermal conductivity values have great potential for thermoelectric generation and nano-cooling of Si-based devices. Here, we present a novel approach for customizing thermal transport across nanostructures by fabricating Si/Sil-xGex SLs with well-defined compositional gradients across the SiGe layer from x = 0 to 0.60. We demonstrate that the spatial inhomogeneity of the structure has a remarkable effect on the heat-flow propagation, reducing the thermal conductivity to -2.2 W.m-1.K-1, which is significantly less than the values achieved previously with non-optimized long-period SLs. This approach offers further possibilities for future applications in thermoelectricity.

An optimization of harmonic structure nickel-saving cryogenic steel via combinatorial high-throughput experiment

A combinatorial high-throughput experiment(HTE)was used to optimize composition and process of nickel-saving cryogenic steel.A gradient temperature heat treatment method with a high linear distribution of heat treatment temperature using customized graphite sleeve direct current heating was used in the combinatorial HTE,which enhanced the richness of the sample library for the single preparation of the 10^(2) level component process variables.Cryogenic steel with excellent mechanical properties was optimized using this combinatorial HTE,and the Ni content was reduced from the traditional 9 to 5.6 wt.%by using Mn instead of Ni.The heterogeneous structure architecture strategy and strengthening and toughening mechanism of the harmonic structure induced by intrinsic heat treatment of additive manufacturing were revealed.Taking the composition process optimization of Ni-saving cryogenic steel as an example,the boosting ability of combinatorial HTE in the research and development of new metal materials was proposed.

Geological Conditions Favourable for High-Wax Oil Enrichment in Damintun Depression,Bohai Bay Basin

ABSTRACT： The Damintun （大民屯） depression, a small （about 800km^2 in area） subunit in the Bohai （渤海） Bay basin, hosts nearly 2×10^8 t of high-wax oils with wax contents up to 60%. The high-wax oils have high consolidation temperatures and viscosities. The high-wax oils were generated from the fourth member of the Shahejie Formation （Es4）, which is also important source rocks for oils in other subunits of the Bohai Bay basin. Yet high-wax oils have not been found in significant volumes elsewhere in the Bohai Bay basin. Geological conditions favourable for high-wax oil enrichment were studied. This study shows that the unusual concentrations of high-wax oils in the depression seem to result from at least three different factors： （1） the presence of organic-matter rich source rocks which were prone to generate wax-rich hydrocarbons; （2） the formation of early overpressures which increased the expul- sion efficiency of waxy hydrocarbons; and （3） reductions in subsidence rate and basal heat flows, which minimized the thermal cracking of high molecular-weight （waxy） hydrocarbons, and therefore prevented the high-wax oils from being transformed into less waxy equivalents.