Water and heat transport in boreal soils: implications for soil response to climate change

Soil water content strongly affects permafrost dynamics by changing the soil thermal properties. However, the movement of liquid water, which plays an important role in the heat transport of temperate soils, has been under-represented in boreal studies. Two different heat transport models with and without convective heat transport were compared to measurements of soil temperatures in four boreal sites with different stand ages and drainage classes. Overall, soil temperatures during the growing season tended to be over-estimated by 2-4 °C when movement of liquid water and water vapor was not represented in the model. The role of heat transport in water has broad implications for site responses to warming and suggests reduced vulnerability of permafrost to thaw at drier sites. This result is consistent with field observations of faster thaw in response to warming in wet sites compared to drier sites over the past 30 years in Canadian boreal forests. These results highlight that representation of water flow in heat transport models is important to simulate future soil thermal or permafrost dynamics under a changing climate.     

拆建物料循环再造的发展

由于公众对社会的持续及长久发展日趋关注，循环再造已被香港建造业认同为一项有价值的工序，能把无用的物料转化成有用的制品。本文探讨了拆建物料循环再造的初步构想、引用循环再造的拆建物料的预备工作、推广使用这些产品，以及如何筹建首间试验性循环再造设施。最后提出有关循环再造拆建物料的策略。     

Equal opportunity tactic: Redesigning and applying competition games in classrooms

Competition, despite its potential drawbacks, is an easily adopted and frequently used motivator in classrooms. Individual abilities, in the years of schooling, are inevitably different, and performance in competition is heavily ability dependent, resulting that more-able students always win while less-able students always lose. Students easily perceive how well they perform through the result of competition, which is termed as perceived performance in this paper. Consistently demonstrating lower perceived performance than their peers, the less-able students feel discouraged and frustrated, hardly having the same opportunity for owning the sense of achievement as the more-able students. In this study, the authors designed a computerized mechanism, equal opportunity tactic, to lessen the difference in perceived performance between more-able and less-able students. Equal opportunity tactic is incorporated into a version of a competitive learning game called AnswerMatching, in which every student is assigned an opponent with similar ability. An experiment was also conducted to preliminarily investigate the effectiveness and effects of the tactic. Results showed that equal opportunity tactic could reduce the effect of individual ability difference on the perceived performance as well as the belief about how well students could achieve. In other words, less-able students could have similar opportunity of success and build confidence similar to more-able students in a competition.     

Beta carotene and its oxidation products have different effects on microsome mediated binding of benzo[a]pyrene to DNA

The effects of beta-carotene (betaC) and its oxidation products on the binding of benzo[a]pyrene (BaP) metabolites to calf thymus DNA was investigated in the presence of rat liver microsomes. Mixtures of betaC oxidation products (betaCOP) as well as separated, individual betaC oxidation products were studied. One set of experiments, for example, involved the use of the mixture of betaCOP obtained after a 2-h radical-initiated oxidation. For this data set, the incorporation of unoxidized betaC into microsomal membranes caused the level of binding of BaP metabolites to DNA to decrease by 29% over that observed in the absence of betaC; however, the incorporation of the mixture of betaCOP caused the binding of BaP metabolites to DNA to increase 1.7-fold relative to controls without betaC. Two variations of this experiment were studied: (1) When no NADPH was added, betaC decreased the binding of BaP metabolites to DNA by 19%, but the mixture of betaCOP increased binding by 3.3-fold relative to that observed in the absence of betaC. (2) When NADPH was added under near-anaerobic conditions, betaC caused an almost total (94%) decrease in binding whereas betaCOP had no effect on the amount of binding relative to that observed in the absence of betaC. Both betaCOP and cumene hydroperoxide caused BaP metabolites to bind to DNA even when NADPH was omitted from the incubation mixture. Separation of the mixture of betaC oxidation products into fractions by HPLC allowed preliminary testing of individual betaC oxidation products separately; of the various fractions tested, the products tentatively identified as 11,15'-cyclo-12,15-epoxy-11,12,15,15'-tetrahydro-beta-carotene and beta-carotene-5,6-epoxide appeared to cause the largest increase in BaP-DNA binding. Microsomes from rats induced with 3-methylcholanthrene (3MC) or Aroclor 1254 produced different levels of binding in some experimental conditions. We hypothesize that, under some conditions, the incorporation of betaC into microsomal membranes can be protective against P450-catalyzed BaP binding to DNA; however, the incorporation of betaCOP facilitates the formation of BaP metabolites that bind DNA, although only certain P450 isoforms catalyze the binding process.     

苏北凹陷北汉庄油田出砂机理研究及防砂工艺优选

苏北溱潼凹陷北汉庄油田主要出砂原因为油层胶结疏松、地层压力下降、强水敏、原油粘度高、含水上升等。该油田油井出砂指数都小于2×104MPa,声波时差均大于295μs/m,平均孔隙度为37%,这三个方面的预测结果均表明出砂不可避免,因此,必须采取相应的防砂措施。针对该油田特点优选了封隔高压一次充填防砂工艺作为主要的防砂工艺,在三口油井中实施后含砂量大幅下降,而产量和含水率变化极小,取得了明显的效果。     

Investigation of Thermal Shock in a High-Temperature Refractory Ceramic: A Fracture Mechanics Approach

The results of a study on the thermal shock behavior of a high-temperature refractory ceramic that is used as a furnace liner in the melting of steels are presented in this paper. The experimental studies show that thermal shock damage initiates by edge cracking after the first shock cycle. Subsequent subcritical crack growth occurs by the incremental extension of dominant cracks until catastrophic failure occurs. The observations of the crack profiles also reveal the formation of viscoelastic bridges that promote crack-tip shielding/toughening via crack bridging. Following a brief discussion of the respective mechanisms of fracture and thermal shock damage at different temperatures and temperature ranges, the implications of the results are discussed for refractory ceramics that are toughened by viscoelastic crack bridging.     

Formation of high aspect ratio GaAs nanostructures with metal-assisted chemical etching

Periodic high aspect ratio GaAs nanopillars with widths in the range of 500-1000 nm are produced by metal-assisted chemical etching (MacEtch) using n-type (100) GaAs substrates and Au catalyst films patterned with soft lithography. Depending on the etchant concentration and etching temperature, GaAs nanowires with either vertical or undulating sidewalls are formed with an etch rate of 1-2 μm/min. The realization of high aspect ratio III-V nanostructure arrays by wet etching can potentially transform the fabrication of a variety of optoelectronic device structures including distributed Bragg reflector (DBR) and distributed feedback (DFB) semiconductor lasers, where the surface grating is currently fabricated by dry etching.     

Conformal Coating of Co/N‐Doped Carbon Layers into Mesoporous Silica for Highly Efficient Catalytic Dehydrogenation–Hydrogenation Tandem Reactions

To maximize the utilizing efficiency of cobalt (Co) and optimize its catalytic activity and stability, engineering of size and interfacial chemical properties, as well as controllable support are of ultimate importance. Here, the concept of coating uniform thin Co/N‐doped carbon layers into the mesopore surfaces of mesoporous silica is proposed for heterogeneous aqueous catalysis. To approach the target, a one‐step solvent‐free melting‐assisted coating process, i.e., heating a mixture of a cobalt salt, an amino acid (AA), and a mesoporous silica, is developed for the synthesis of mesoporous composites with thin Co/N‐doped carbon layers uniformly coated within mesoporous silica, high surface areas (250–630 m² g⁻¹), ordered mesopores (7.0–8.4 nm), and high water dispersibility. The strong silica/AA adhesive interactions and AA cohesive interactions direct the uniform coating process. The metal/N coordinating, carbon anchoring, and mesopore confining lead to the formation of tiny Co nanoclusters. The carbon intercalation and N coordination optimize the interfacial properties of Co for catalysis. The optimized catalyst exhibits excellent catalytic performance for tandem hydrogenation of nitrobenzene and dehydrogenation of NaBH₄ with well‐matched reaction kinetics, 100% conversion and selectivity, high turnover frequencies, up to ≈6.06 mol_nitrobenzene mol_Co⁻¹ min⁻¹, the highest over transition‐metal catalysts, and excellent stability and magnetic separability.     

A Scalable Priority-Based Multi-Path Routing Protocol for Wireless Sensor Networks

In this paper, a scalable priority-based multi-path routing protocol (PRIMP) is proposed for wireless sensor networks to offer extended network lifetime and robust network fault tolerance, under the context of stringent energy constraint and vulnerability of sensors to dynamic environmental conditions. A novel interest dissemination strategy which invokes an on-demand virtual source technique is designed in PRIMP to minimize communication overheads and energy wastage. In routing, data traffic is distributed over multiple braided data paths simultaneously by a priority-based probabilistic approach at each hop to achieve the robustness against the unreliable transmission due to frequent node failures. Extensive simulations validate that PRIMP exhibits significantly better performance in energy conservation, load-balancing and data delivery than comparable schemes, while at the same time PRIMP achieves a nice scalability feature in terms of energy dissipation with various network sizes and network densities. Last but not least, PRIMP addresses the slow startup problem that is prevalent in data-centric routing schemes.     

The Goodman-Kruskal coefficient and its applications in genetic diagnosis of cancer

Increasing interest in new pattern recognition methods has been motivated by bioinformatics research. The analysis of gene expression data originated from microarrays constitutes an important application area for classification algorithms and illustrates the need for identifying important predictors. We show that the Goodman-Kruskal coefficient can be used for constructing minimal classifiers for tabular data, and we give an algorithm that can construct such classifiers.