Studies on the synthesis of block copolymers of acrylonitrile and ethylene oxide

The synthesis of polyacrylonitrile–poly(ethylene oxide) block copolymers was carried out with the use of modified initiator containing azo groups, being a product of reaction between poly(ethylene oxide) (mol wt 6000) with azobisisobutyronitrile. Effects of initiator concentration, temperature, and synthesis time on the yield, composition, and intrinsic viscosity of the copolymers were examined. To confirm the segmental structure of the obtained products, precipitation, fractionation, gel permeation chromatography, infrared, and ¹H nuclear magnetic resonance methods were used. © 1993 John Wiley & Sons, Inc.     

Synthesis of new anionic HTPB‐based polyurethane elastomers: Aqueous dispersion and physical properties

New segmented polyurethane (PU) anionomers based on hydroxytelechelic polybutadiene (HTPB) were synthesized via an environment‐friendly chemical route. Incorporation of carboxylated functions on the PU soft segment was carried out using a thiol‐ene reaction on HTPB vinyl double bonds with thioglycolic acid. PU water dispersions were obtained by addition of a water dispersible polyisocyanate, i.e., Bayhydur® 3100, to the modified ionic HTPB water dispersions. The key factor of this formulation is the control of ionic concentration apart from the hard segment content, oppositely to all other PU anionomer formulations. The influence of ionic content was studied through all steps of the PU material synthesis, from aqueous dispersions upto crosslinked materials' physical properties. For fully neutralized precursors, the stability of the ionic aqueous dispersions was higher than that was in six months. In all cases, particles were smaller than 200 nm. PU glass transition temperature, surface hydrophily and swelling increased with ionic content. But, however, PUs exhibit hydrophobic surface properties with a maximum surface tension of 45 mN m^?1 and a limited water uptake. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3312–3322, 2006     

林麝保护的现状及研究进展

就林麝保护的现状及相关研究的进展,从其分类、种群分布,及人工繁殖等方面进行介绍,并结合相关研究成果对林麝的保护和可持续利用提出自己的观点,以期对进一步深入研究林麝的保护和永久合理利用提供参考。     

Biotribological properties of dentures lubricated with artificial saliva

This paper presents the results of tests on the effect of adsorbed films of saliva substitutes on the tribological characteristics of metal alloys based on the example of stainless steel 316LVM and two alloys, Co–Cr–Mo and Ti?6Al–4V. Saliva substitutes were prepared based on animal mucin and xanthan gum dissolved in phosphate buffered saline (PBS). The adsorbed salivary films significantly reduced the coefficient of friction of the tested biomaterials. Low values of coefficient of friction have been achieved during the tests using PBS + mucin. The analysis of wear of tested materials showed lowest values in the process of friction using PBS + mucin + xanthan gum. An IR analysis of the studied surfaces confirmed the presence of wear marks on the adsorbed salivary films.     

Fertilizer management effects on oil palm yield and nutrient use efficiency on sandy soils with limited water supply in Central Kalimantan

Identifying optimal fertilizer management to ensure high nutrient use efficiency is important to reduce negative environmental impacts in oil palm (Elaeis guineensis) cultivation. A 4-year fertilizer trial was established in an oil palm plantation, located at a sandy area with occasional monthly water deficit in Central Kalimantan. We examined the responses of oil palm yield and nutrient use efficiency to fertilizer application frequency (standard frequency of 1–2 times yr^?1 versus 4 times yr^?1) and rate (standard rate of 136, 12, and 200 kg ha^?1 yr^?1 of N, P and K, respectively versus 80% of standard rate). There were no treatment effects on annual yield in fresh fruit bunch, bunch number, or individual bunch weight. Increasing fertilizer frequency did not increase nutrient use efficiency at the last 2 years of the trial. In contrast, reducing fertilizer rate resulted in higher nutrient use efficiency in K, compared to the standard treatment and increasing fertilizer frequency. Average concentrations of N, P, K, Mg, Ca, and Cl in leaflet under all treatments were above critical levels both in the beginning and at the end of the trial. Monthly yield in fresh fruit bunch correlated positively with soil water balance with correlation coefficients of 0.24–0.29, during the developmental period of inflorescence sex differentiation at 28–30 months before fruit maturity. Our study provides useful information for fertilizer management optimization in sandy areas with occasional water deficit, corresponding to most of the new expansion areas of oil palm in Southeast Asia.     

An investigation on the wear resistance of high strength concretes

In this study, a relationship was determined between the mechanical properties (compressive and splitting tensile strengths) and wear resistance of high strength concretes (HSC) having compressive strength between 65 and 85 MPa. For this purpose, 108 test specimens were produced from six different mixtures. After 28 days standard curing, compressive strength, splitting tensile strength, and wear resistance tests were performed on the specimens. From the test results, mathematical expressions were developed to estimate the wear resistance of concrete regarding their compressive strength and splitting tensile strength. As result a reliable relationship was produced from this properties.     

The Influence of Alkali Metal Chloride Treatments on the Wear Resistance of Silicon Surfaces for Possible Use in MEMS

The wear of contacting silicon surfaces in microelectromechanical systems (MEMS) has been a longstanding concern. To address this issue, the effects of immersing silicon surfaces into alkali metal chloride solutions (LiCl, NaCl, CsCl) on their sliding friction and wear were investigated. A custom-built reciprocating tribometer was used with a sapphire ball as the counterbody. Results indicated that the friction coefficient between the silicon surface (p-doped, orientation (100)) and a sapphire ball can be reduced by up to 30% by treating the silicon surfaces in aqueous salt solutions (concentration 1 mol/L, exposure for 24 h). These modified surfaces also have higher wear resistance and a significant change in wettability. After immersion, the contact angle between the silicon surface and water was reduced by approximately 50%. These results may lead to new, simple, and inexpensive methods to increase the wear resistance of silicon surfaces for use in MEMs devices.     

Effectiveness and challenges of participatory governance: the case of agricultural and rural management councils in the Western Democratic Republic of the Congo

Local management councils and multi-stakeholder forums are institutional arrangements used for policy dialogue, priority-setting and program monitoring but are rarely evaluated. This paper evaluates the effectiveness of 55 local-level Agricultural and Rural Management Councils (CARGs) in 23 randomly-selected territories in the western Democratic Republic of the Congo. These CARGs are similar to the farmers’ forums in Uganda and research-extension linkages committees in Ghana and Nigeria in terms of their multi-level structures that aggregate inputs from villages up to the provincial and national levels, and are similar to Uganda’s barazas at the sub-county level on participatory monitoring of programs and public service delivery. CARGs also play a major role in sharing innovations and providing advice to farmers by brokering knowledge and linking various experts and stakeholders, such as forming innovation platforms in various countries. However, CARGs are wider in the breadth of activities and are more generic in the thematic scope and coverage than other platforms. This paper identifies several problems and challenges in CARG implementation and the overall weaknesses in CARG formation. Our review suggests that only half of the surveyed CARGs achieved results consistent with at least one of their main goals, while the rest have not achieved any tangible outputs consistent with their objectives. Although the majority of stakeholders interviewed were aware of CARGs, only 33 % attended CARG meetings and perceived CARGs to be useful; and only 11 % reported having benefitted or knowing someone who had benefitted from CARGs. However, CARGs differ in performance and exhibit different financial capacity, coordination capacity, coordination commitment of its leaders, and representation of government officials, which are all significantly correlated to how well CARGs fulfill their objectives, link to other actors, and are perceived by stakeholders.     

Rock mass movements around development workings in various density of standing-and-roof-bolting support

Presented measurement results of roof rocks and wall rock movements of underground development workings after their drifting. The research was carried out in the coal mine workings with standing-and-roof bolting support. There were various density of the support, so the aim of the special monitoring programme was to determine movement intensity of rock mass in the premises of the heading area. There were four types of research did by the authors. They measured convergence, roof layers separation using telltales and sonic probes and load bearing of the headings’ roofs by hydraulic dynamometers. Evaluation of fracture zone around the heading and investigation the load zone caused by failed roof rocks may become a basement for the determination of support parameters of the workings. The combined system of standing support and roof bolting seems to be an essential for underground headings protection. Supported by the Ministry of Science and Higher Education Nr of Projects (4T12A00229)