绿洲农田土壤优先流特征及其对灌溉量的响应

优先流是土壤养分和水分快速通过土壤剖面的普遍物理现象.研究农田土壤优先流特征及其影响因素,对量化绿洲灌溉深层渗漏量、提高水肥利用效率以及降低浅层地下水质污染的风险具有重要意义.在绿洲农田利用亮蓝溶液进行原位染色示踪试验,结果表明：沟与垄位置处的染色路径数目在土壤深度7.3～16.7 cm差异显著,而优先流最大入渗深度差异不显著.优先流最大入渗深度主要受蚂蚁洞穴和灌溉量的影响,平均灌溉量120 mm下优先流的最大入渗深度为(43.1±5.9) cm;受到蚂蚁洞的影响,灌溉量55 mm的样方优先流最大入渗深度达(68.3±7.6) cm.细根(Φ≤2 mm)与优先流显著相关,粗根与优先流相关性不显著,表明植物根系中的细根对优先流的产生有重要作用.绿洲农田土壤优先流特征受到灌溉量、垄沟耕作、蚂蚁洞穴和根系等因素的影响,而蚂蚁洞穴是影响优先流最大入渗深度的不确定因素.     

Puncturing ability of idealized canine teeth: edged and non-edged shanks

Idealized edged and non-edged indenters, mimicking canine teeth, were used to puncture thin materials and thick materials. Less force was needed for the edged (triangular in cross section) indenter to penetrate thin Mylar, paper, leather, beetle elytra and turkey skin than the non-edged (circular in cross-section) indenter. Oak, grass and magnolia leaves responded equally to both indenters. In thick materials, the edged indenter punctured beetles, shrimp, bananas, and chicken flesh more easily than the non-edged indenter. Apple, tomato and avocado were punctured equally well. The edged indenter directs cracks at the corners so that the material can fold away in the direction of puncture, whereas cracks form unpredictably with the non-edged indenter. Edged indenters have the advantage in many of the materials tested.     

The Constructional Properties of the Exoskeleton of Homarid, Palinurid, and Scyllarid Lobsters

Lobsters, as members of the Arthropoda, are already endowed with a laminated exoskeleton due to the mineralization of their cuticle. Mineralized laminate structures are found throughout animal phyla and convey, through their multiple surfaces, matrix planes that act as crack-blunting mechanisms. In addition, spiny and slipper lobsters, but not clawed lobsters, add a surface tubercle system that reflects a ventral surface pit system in the carapace. The architecture of these systems coincides with known strategies for crack blunting in composite materials. The division of vertical and horizontal crack blunting systems corresponding to laminate and tubercular systems and pit systems, respectively, may not be so easily separable in a functional sense. Although there is overlap in crack-blunting ability in both systems, separation into horizontal and vertical crack-blunting systems is a convenient way to discuss how skeletons of lobsters resist failure. While laminate structures dissipate forces horizontally in each layer, tubercle and pit systems serve to increase the surface area available to dissipate forces. These systems may represent evolutionary solutions to predation, particularly by predators that strike, crush or bite holes, rather than those that engulf.     

Temperature‐induced unfolding behavior of proteins studied by tensorial elastic network model

Motivated by single molecule experiments and recent molecular dynamics (MD) studies, we propose a simple and computationally efficient method based on a tensorial elastic network model to investigate the unfolding pathways of proteins under temperature variation. The tensorial elastic network model, which relies on the native state topology of a protein, combines the anisotropic network model, the bond bending elasticity, and the backbone twist elasticity to successfully predicts both the isotropic and anisotropic fluctuations in a manner similar to the Gaussian network model and anisotropic network model. The unfolding process is modeled by breaking the native contacts between residues one by one, and by assuming a threshold value for strain fluctuation. Using this method, we simulated the unfolding processes of four well‐characterized proteins: chymotrypsin inhibitor, barnase, ubiquitein, and adenalyate kinase. We found that this step‐wise process leads to two or more cooperative, first‐order‐like transitions between partial denaturation states. The sequence of unfolding events obtained using this method is consistent with experimental and MD studies. The results also imply that the native topology of proteins “encrypts” information regarding their unfolding process. Proteins 2016; 84:1767–1775. © 2016 Wiley Periodicals, Inc.     

Detection of cracks in dried spaghetti using transmission images

Cracks are formed during the drying process of spaghetti production, which reduces its commercial value and quality; hence, it is very important to detect the cracks during the manufacturing process of dried spaghetti. However, the presence of mottles, originating from wheat bran, hinders automatic identification of cracks. In this study, we developed a simple method to detect the cracks induced in spaghetti using a digital camera. The cracks and mottles were distinguished by pixelating the transmission light image of the spaghetti and analyzing the image based on the geometric characteristics in the histogram consisting of all the pixels. The method was able to detect the cracks induced in the spaghetti with a rough surface, which was prepared via a bronze die using vacuum extrusion molding, as well as those induced in the spaghetti with a smooth surface, which was prepared using a Teflon die.     

Interactions of rhizobia with rice and wheat

Recently, evidence has been obtained that naturally occurring rhizobia, isolated from the nodules of non-legume Parasponia species and from some tropical legumes, are able to enter the roots of rice, wheat and maize at emerging lateral roots by crack entry. We have now investigated whether Azorhizobium caulinodans strain ORS571, which induces root and stem nodules on the tropical legume Sesbania rostrata as a result of crack entry invasion of emerging lateral roots, might also enter rice and wheat by a similar route. Following inoculation with ORS571 carrying a lacZ reporter gene, azorhizobia were observed microscopically within the cracks associated with emerging lateral roots of rice and wheat. A high proportion of inoculated rice and wheat plants had colonized lateral root cracks. The flavanone naringenin at 10 and 10 M stimulated significantly the colonization of lateral root cracks and also intercellular colonization of wheat roots. Naringenin does not appear to be acting as a carbon source and may act as a signal molecule for intercellular colonization of rice and wheat by ORS571 by a mechanism which is nod gene-independent, unlike nodule formation in Sesbania rostrata. The opportunity now arises to compare and to contrast the ability of Azorhizobium caulinodans with that of other rhizobia, such as Parasponia rhizobia, to intercellularly colonize the roots of non-legume crops.     

Cracks in the palisade cuticle of soybean seed coats correlate with their permeability to water

BACKGROUND AND AIMS: Soybean (Glycine max) is among the many legumes that are well known for 'hardseededness'. This feature can be beneficial for long-term seed survival, but is undesirable for the food processing industry. There is substantial disagreement concerning the mechanisms and related structures that control the permeability properties of soybean seed coats. In this work, the structural component that controls water entry into the seed is identified. METHODS: Six soybean cultivars were tested for their seed coat permeabilities to water. To identify the structural feature(s) that may contribute to the determination of these permeabilities, fluorescent tracer dyes, and light and electron microscopic techniques were used. KEY RESULTS: The cultivar 'Tachanagaha' has the most permeable seed coat, 'OX 951' the least permeable seed coat, and the permeabilities of the rest ('Harovinton', 'Williams', 'Clark L 67-3469', and 'Harosoy 63') are intermediate. All seeds have surface deposits, depressions, a light line, and a cuticle about 0.2 microm thick overlaying the palisade layer. In permeable cultivars the cuticle tends to break, whereas in impermeable seeds of 'OX 951' it remains intact. In the case of permeable seed coats, the majority of the cracks are from 1 to 5 micro m wide and from 20 to 200 micro m long, and occur more frequently on the dorsal side than in other regions of the seed coat, a position that correlates with the site of initial water uptake. CONCLUSIONS: The cuticle of the palisade layer is the key factor that determines the permeability property of a soybean seed coat. The cuticle of a permeable seed coat is mechanically weak and develops small cracks through which water can pass. The cuticle of an impermeable seed coat is mechanically strong and does not crack under normal circumstances.     

Numerical Simulation of Bone Plate with Fatigue Crack and Investigation of Attraction Hole for Retarding Crack Growth

Premature fracture of the bone plate caused by fatigue crack is the main failure mode in treating femoral shaft fracture. In order to improve the durability of the plate, this study proposed a crack attraction hole (CAH) to retard the crack propagation based on the fracture mechanics. In this paper, a numerical model of the femoral fracture internal fixation system was constructed, in which the femur was developed using a validated simplified model. First, the fatigue crack initiation location was defined at the stress concentration through static analysis. Next, with the joint simulation method of Franc3D and ABAQUS, the fatigue crack path in the bone plate was predicted. Meanwhile, the Paris parameters of Ti-6Al-4V obtained through experiments were encoded into Franc3D to calculate the crack propagation life. Finally, we considered the influence of CAH designs with different relative vertical distances (2.0, 3.0, and 4.0 mm) and diameters (1.5, 2.0, and 2.5 mm) on the crack propagation path and life of the bone plate. Additionally, the effects of all CAH configurations on the biomechanical performance of the bone plate fixation system were evaluated. The results indicated that the fatigue crack growth path in the bone plate is comparable to a straight line, and the crack growth rate significantly increases when the crack tip reaches the outer boundary of the plate. The findings suggest that the addition of CAH in the bone plate will lead to the deflection of the crack path and increase the fatigue life. Equally important, the improvement of the fatigue life was positively correlated with the diameter of CAH and negatively correlated with the relative vertical distance. In addition, the biomechanical properties of the bone plate system were slightly affected by CAH, substantiating the feasibility of this method. Finally, the comparative analysis verified that a CAH with a relative vertical distance of 3 mm and a diameter of 2 mm exhibited superior improvement in the comprehensive performance on the bone plate.     

Childhood sexual abuse and HIV risk among crack-using commercial sex workers in San Salvador, El Salvador: a qualitative analysis

This article explores the relationship between childhood sexual abuse (CSA) and later HIV risk. It draws on qualitative, in-depth interviews with 40 women who either used crack or engaged in commercial sex work in the greater metropolitan area of San Salvador, El Salvador, 28 of whom experienced CSA. Although the relationship between CSA and later HIV risk has been clearly demonstrated, the processes that lead women who have experienced CSA to experience HIV risk are unclear. The theoretical model presented here incorporates the psychological effects of CSA, particularly stigmatization, as well as its social consequences and the larger context of poverty in which these women live. The meanings women draw from past abuse experiences and their rationale for choices made help explain the association between CSA and later risk as mediated through sex work and crack addiction. Self-report data gathered in this study indicate that HIV prevalence may be considerably higher in this high-risk population than Salvadoran national rates.