热带、亚热带近海设施生物污损特点与研究展望

生物污损现象会严重影响海洋设施的安全与使用寿命,对涉海经济活动产生极大危害。在热带和亚热带海区,引发生物污损的种类主要为牡蛎和藤壶,其次是珊瑚和水螅。今后的研究应着重于弄清大型污损生物对腐蚀的影响,建立污损生物数学生态模型,开展海洋恢复生态学研究工作。     

Linear Hygrothermal Viscoelastic Characterization of Nafion NRE 211 Proton Exchange Membrane

The tensile relaxation modulus of a commercially available proton exchange membrane, Nafion® NRE 211, was obtained over a range of humidity levels and temperatures using a commercial dynamic mechanical analyzer (DMA). Hygral stress relaxation master curves were first constructed, followed by a hygrothermal master curve using the time temperature moisture superposition principle. The hygrothermal master curve was fitted using a 10‐term Prony series and validated using longer term stress relaxation tests. To validate the results from the stress relaxation experiments, short and long‐term creep compliance was converted into stress relaxation modulus using a well‐known viscoelastic conversion formula, and compared with the relaxation modulus obtained under identical conditions. Good agreement was found between the two datasets. It was evident that relaxation data at 2% RH at the test temperatures was not superposable with the master curves obtained at higher relative humidity (10% < RH < 90%) at the temperature range 70 °C < T < 90 °C. It was observed that the longer term relaxation modulus under humid conditions matched well with the hygrothermal master curve; however, the longer term relaxation modulus under dry conditions was significantly higher than the relaxation master curve obtained under dry conditions, raising the possibility of a physical aging process in the ionomer and/or irreversible morphological changes in the membrane under dry conditions.     

Zinc corrosion runoff process induced by humid tropical climate

Zinc and hot dip galvanized steel are frecuently used metals in building application. They have relatively good atmospheric resistance to corrosion, due to its oxidation in air and formation of protective rust on its surface, which acts as barrier between the metal and environment. However, some part of the rust can be dissolved by pluvial precipitations and water condensed on the metal surface. This process, called metal runoff, contributes for zinc dispersion in soils and waters. In order to make accurate estimation of zinc runoff induced by atmosphere in humid tropical climate, samples of pure Zn and hot dip galvanized steel have been exposed in the Gulf of Mexico. The data reveal that this process is strongly influenced by factors which determine the aggressivity of the environment (pluvial precipitations, cycles of dry and rainy periods, atmospheric pollutants, air humidity). High annual rates of zinc runoff (6.5 – 8.5 ± 0.30 g Zn m^?2yr^?1) were released, being the runoff 63 – 87% of the zinc corrosion rust. The zinc mass loss has been related to several independent parameters, presenting linear equation, which indicates the air contaminant SO₂ as the major factor controlling the runoff of zinc. The reported results show higher runoff of zinc samples, compared to that of hot dip galvanized steel     

Yield and leaf composition of sunflower in relation to N,P, K,and lime treatments

Sunflower (Helianthus annus L), a drought resistant crop, is cultivated widely throughout the world. Still, few studies on the fertility requirements of the crop have been published, particularly in relation to cultivation on highly weathered soils and in terms of using foliar analysis as a tool in diagnosing nutritional needs.Two 3⁴ (N, P, K, lime) factorial experiments (high and low fertility levels) with trace elements as split plots were conducted on Farningham clay loam, a Typic Haplorthox. No significant yield response to added N or micronutrients was found on either experiment. Liming and P fertilization increased seed yields in the low fertility experiment. Increased K application gave significant yield increases in both experiments.Preliminary foliar diagnostic norms were developed using the Diagnosis and Reccommendation Integrated System (DRIS). The prognostic value of these norms was tested using the low fertility experiment. In 32 of the 37 cases where the DRIS analysis could be checked against actual experimental yield results, application of the nutrient diagnosed as the most yield limiting resulted in a positive yield response. These data suggest that sunflowers can be a successful crop on Oxisols provided fertility is adequate.     

Plant species characteristics and vegetation dynamics in the tropics

This paper attempts a differentiation of forest and savanna and an assessment of changes in these vegetation types based on their characteristic plant species. Farming activities are recognised as a main factor influencing the dynamics of the vegetations. The occurrences of plant species on selected fallow communities at various stages of development, along the regional boundary between forest and savanna, were therefore analysed. The analyses show that plant species not only differentiate between the two, but also suggest changing trends in their character. They show that forest and savanna are to a large extent, species specific, and that over a short term period, farming activities are capable of extending the present limit of savanna towards the forest areas.     

NPK-fertilizer efficiency — a situation analysis for the tropics

This paper examines the efficiency of applied N, P, and K fertilizers under tropical conditions. To meet their food demands, tropical countries are importing large quantities of fertilizers at an enormous cost. There is a need for improving crop yields at a reduced cost and a better understanding of the factors that contribute to the overall efficiency of applied fertilizers. It is estimated that under tropical condition, the efficiency of applied N is less than 50%, less than 10% for P and for K it is somewhere around 40%. Losses of N are mainly due to leaching, runoff and volatile losses of ammonia. Under flooding and in alternate wetting and drying conditions of rice lands and low lands, dentrification and volatile ammonia losses are considerable. The N losses from these soil could be minimized by proper management such as rate, methods and time of application. The coating of urea with S has shown some improvement in increasing efficiency. Nitrification and urea hydrolysis inhibitors can improve fertilizer efficiency in certain situations provided they are properly used. The efficiencies of these inhibitors depend on the nature of the chemical compounds, soil properties, and method of application. Low efficiency of applied P fertilizer is mainly due to retention of P by soil clay fractions and iron and aluminum hydroxides. Even though retained P is not available to the first crop, it is made available to a certain extent to the succeeding crops. The rate and methods of P applications and forms of P determine the efficiency of applied P fertilizers. The use of native rock phosphate along with P fertilizers on acid soils appears to be an attractive alternative in reducing the fertilizer cost. The loss of K in tropical soils is largely attributed to leaching and runoff. To reduce K loss by leaching, it is more advisible to apply K in split doses than a single dose. Liming has a beneficial effect in retention of K and reducing P fixation in acid soils.Senior author formerly was a Research Advisor to EMBRAPA/IICA/World Bank program at National Corn and Sorghum Research Center, Sete Lagos, MG, Brazil.     

Efficient fertilizer use for increased crop production: The humid Nigeria experience

Fertilizer use in Nigeria, though growing, is still very low especially if considered in relation to the growing food needs of the country. Efforts have been made through scientific investigations to find ways of increasing fertilizer use efficiency in the humid zone of the country. Investigations have been carried out mainly on nitrogen, phosphorus, potassium, mixed and compound fertilizers. The secondary nutrients sulphur, calcium and magnesium as well as the micronutrients have received comparatively little attention. In the Southeastern humid zone, a considerable effort has been made to solve the problem of soil acidity through liming. Interaction of the primary nutrients under field conditions has not been investigated sufficiently.Results of experiments carried out on comparisons of P sources, urea placement methods and interaction of N, P, K, S fertilizers in the Ultisols of Southeastern Nigeria show that single superphosphate was superior to Togo phosphate rock, partially acidulated Togo phosphate rock, and diammonium phosphate for the production of maize. Methods of application of urea did not significantly affect maize grain yield. There was no significant interaction of N, P, K, S in the Ultisol but S was limiting. An application of a minimum of 45 kg/N/ha appears to be threshold for positive response to P by maize stover. More effort is needed to understand nutrient interaction in the Ultisols which are dominant in the humid Southern zone of Nigeria.     

Quantifying adsorbed water monolayers on silicon MEMS resonators exposed to humid environments

This study investigated the influence of temperature and humidity on the adsorbed water layer on micron-scale monocrystalline silicon (Si) films in air, using a Si-MEMS kHz-frequency resonator. Both temperature and relative humidity induced a reversible change in resonant frequency, attributed to the temperature-dependent properties of Si and to a change in adsorbed water layer. The excellent precision in resonant frequency measurement (0.02 Hz, or 0.5 ppm) allowed precise calculation of the changes in adsorbed water layer thickness over the specimen surface. The increase in water thickness with relative humidity was a function of temperature and could not be described with simple multimolecular adsorption theories such as the BET theory. A likely explanation is the presence of hydrocarbon contaminants on the Si surface. Guidelines are provided to accurately measure the influence of temperature and relative humidity on the adsorbed water layer thickness on micron-scale Si surfaces, using this technique.     

A new thermal performance index for dwelling roofs in the warm humid tropics

This research aims to find a scientific rating scheme for roof system for the warm humid tropics. The overall air-to-air thermal transmittance (U-value) or thermal resistance (R-value) of roof are most widely used properties, but these are based on steady-state heat conduction and do not respond to changing conditions of climate, design and comfort needs. The paper presents a new thermal performance index, which is based on thermal comfort and actual thermal performance of a roof design option. It provides a basis for identifying the optimum roof design for unconditioned and acclimatised regimes. A review of the acceptable limits of ceiling surface temperature is presented. The mathematical modelling for predicting performance of roof based on admittance procedure and derivation of thermal performance index is described. In the proposed scheme the galvanized iron roof is given 0% rating and the roof satisfying the comfort needs for the given climate is rated as 100%. Illustrative examples of built roofs or design options are taken from India and Australia. It clearly shows that the roofs with the highest thermal resistance are not necessarily optimum solutions.