Trolling for Nile perch (Lates niloticus) in Lake Kyoga

Nile perch were introduced into Lake Kyoga in the mid·1950s from Lake Albert. Murchison Falls on the River Nile, between the two lakes, prevented Nile Perch and other elements of the typical nilotic fish population from naturally reaching Lake Kyoga. The introduction has been successful and considerable stocks of Nile Perch now exist in Lake Kyoga. In 1967, 13,000 tons of Nile Perch were estimated to have been landed by the commercial fishermen, fish of 200 lb. being now caught and specimens of 100 lb. being fairly common. Large Nile perch are caught commercially on long lines baited with live Protopterus' spp. or Clarias spp. Large mesh gillnets uccasionally take Nile Perch of up to 30 lb., but the high cost of the nets does not, at the moment, appear to justify this method of fishing; a 10 in. net, stretched 100 yards long (unmounted). 15 meshes deep and 60-ply nylon. costs approximately U. Shs. 300. The long·lines used are extremely simple and cheap to make, but considerable labour is needed to catch bait. Small Protopterus are normally caught by turning over floating rafts of grasses and papyrus, and extracting the fish from the root mass; this is hard and dirty work. Other small fish, more readily available, do not, according to fishermen, work as well, possibly because they are not as durable as the Protopterus or Clarias. Dead bait is never used.

A discussion of possible management methods to revive the Labeo victorianus fishery of Lake Victoria, with special reference to the Nzoia river, Kenya

Labeo victorianus Boulenger, the "ningu", is commercially the most important migratory fish of Lake Victoria, as well as being one of the most abundant of all species landed. Annual catch records of the Fisheries Departments of Uganda, Kenya and Tanzania show that a high yielding seasonal, floating gill net fishery is based on the concentration of sexually mature fish at the river mouths at the time of migration during the bi-annual floods. Migrating fish used also to be caught in high numbers at "kek" barrier traps across the river, as at Hainga on the Nzoia river. Since the heavy exploitation at the river mouth which occurred with the introduction of nylon gill nets in 1956.

Fishery resource assessment and monitoring in the development and control of fisheries in the Lake Volta

Gill-netting and rotenoning have been used for assessing and monitoring fish stock abundance in Volta Lake. The lake and the main gear types used on it have been described. Before a gill-net sampling plan was set up, a preliminary survey was undertaken which largely determined the final form of the plan. An investigation as to whether or not the lake was being overfished concluded that it was being underfished. Commercial and experimental catch data analyses disclosed that the adults of the small species were being little utilized. Commercial sized species were also not being harvested according to their apparent proportion in the population. Production is presently fluctuating between approximately 37,000 and 40,000 tonnes. A high correlation between commercial and experimental catch was realized. Developments which have followed in the wake of stock assessment and monitoring studies include: introduction of monofilament nylon net, development of a special scoop net to permit mass harvest of clupeids after they have been attracted to light, and the design of a larger canoe which would help to extend the fishery into open water. New regulation and management policies will have to be formulated in the light of new findings before a rational exploitation of all the species can be achieved.

Lakes Wamala and Kijanebalola: evaluation of the fisheries resources during July 1975

This report presents the results of the second (in 1975) fisheries resource survey for Lake Wamala conducted from 10th to 16th July 1975. The first similar survey covered the period 14th to 20th May 1975. The areas sampled consisted of the river-month areas, the papyrus-fringed inshore waters and the open dee offshore waters. In an effort to find the possible major causes of the decline in catch and seasonal disappearance of fish-hence a solution to the problem(s)-a second fisheries resource survey using multifilament nylon gillnets was conducted on Lake Kijanebalola during the period 17th to 21st July 1975. The first survey was similar and covered the period 21st to 27th May 1975.

Analysis of estrogens in environmental waters using polymer monolith in-polyether ether ketone tube solid-phase microextraction combined with high-performance liquid chromatography

A simple, rapid and sensitive on-line method for simultaneous determination of four endocrine disruptors (17 beta-estradiol, estriol, bisphenol A and 17 alpha-ethinylestradiol) in environmental waters was developed by coupling in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography (HPLC) with fluorescence detection (FLD). A poly(acrylamide-vinylpyridine-NAP-methylene bisacrylamide) monolith, synthesized inside a polyether ether ketone (PEEK) tube, was selected as the extraction medium. To achieve optimum extraction performance, several parameters were investigated, including extraction flow-rate, extraction time, and pH value, inorganic salt and organic solvent content of the sample matrix. By simply filtered with nylon membrane filter and adjusting the pH of samples to 6.0 with phosphoric acid, the sample solution then could be directly injected into the device for extraction. Low detection limits (S/N = 3) and quantification limits (S/N = 10) of the proposed method were achieved in the range of 0.006-0.10 ng/mL and 0.02-0.35 ng/mL from spiked lake waters, respectively. The calibration curves of four endocrine disruptors showed good linearity ranging from quantification limits to 50 ng/mL with a linear coefficient R-2 value above 0.9913. Good method reproducibility was also found by intra- and inter-day precisions, yielding the RSDs less than 12 and 9.8%, respectively. Finally, the proposed method was successfully applied to the determination of these compounds in several environmental waters. (c) 2006 Elsevier B.V. All rights reserved.

尺寸诱导的聚合物亚稳结晶

亚稳定性是凝聚态物质的一个重要特征。常温常压下，热力学上不稳定的、而实际上存在的相，都可称之为亚稳相。通常，影响物质亚稳态存在的外界因素有温度、压力、电场、磁场等等，而相态本身的大小也是决定它稳性的一个重要因素，这就是所谓的尺寸效应。随着纳米技术和微处理器技术的飞速发展，材料的应用尺寸日趋于小型化和微型化。研究聚合物相行为和相变中的尺寸效应，对于充分理解高分子凝聚态物理学的基本问题具有极度其重要的科学意义，它还为纳米科技中材料特殊的结构和性能提供新的认识途径和理论基础，这必将极度大地促进纳米材料的实用化进程。本文正是基于这样一种相变中的尺寸效应，选用了三种具有多晶型结构的结晶聚合物，聚偏氟乙烯（PVDF），聚反式1,4-丁二烯（TPBD）和尼龙1010（nylon 1010），对它们的晶体结构及其相转变过程和转变条件作了较详细的研究，着重探讨了各种晶型稳态和亚稳态的存在条件。在这三种聚合物当中，发现小尺寸晶体趋向于形成二维高有序的六方或拟六方堆积结构，成功地证明了晶体结构对尺寸的依赖性。在上述研究中，首次成功地为PVDF营造了不同程度的空间受限结晶环境，得到了尺寸小于100纳米受限结晶的亚稳态β晶；通过结合使用常温和低温的电子衍射术，并利用计算机模拟技术，提出了尺寸影响的TPBD相转变的具体实现过程；发现了培养尼龙1010单晶的另一理想溶剂二甲基甲酰胺（DMF），并首次用它培养出十分完善的单晶体；引入尺寸效应的观点来解释尼龙1010的Brill转变现象，定量地确定了基转变温度对尺寸的依赖关系，为解释这一古老但至仿仍存在极大争议的尼龙中特有的转变现象开辟了创造性的思维方式；首次用极度稀溶液喷雾法获得了尼龙1010的纳米和微米级微纤维晶，并解释了它的形成原因。

聚合物结晶过程及形态结构的研究

聚合物结晶过程是高分子科学中的一个重要研究方向。本论文在系统研究几种聚合物结晶过程及形态结构的基础上，通过寻求合适的解析聚合物结晶动力学参数的方法，为聚合物结晶动力学的表征和加工工艺设计提供科学依据。采用偏光显微镜（POM）研究了尼龙1212（Nylon 1212）、聚丁二酸丁二醇酷（PBS）及其与己二酸的共聚物（PBS／A）的等温结晶过程。发现碰撞前后球晶的生长速率不变，而在结晶后期球晶生长速率逐渐减慢。PBS／A环带球晶生长过程中球晶半径和结晶时间并非完全的线性关系，而是在直线两侧周期性地摆动。首次非常清晰地观察到PBS结晶后期弱区中新球晶的成核和生长。采用非等温方法在较低的降温速率下获得的聚合物球晶生长速率与等温方法得到的结果有可比性。在计算Nyton1212平衡热力学参数的基础上，采用L-H二次成核理论对N贝on1212的结晶行为进行分析，发现区域I→II和II-III转变分别发生在179Oc和159OC。随着结晶温度的降低，Nylon1212的结晶形态分别为轴状结构晶体、环带球晶和非环带球晶。广角X射线衍射（WAXD）研究表明，PBS和PBS／A具有相同的晶体结构。与PBS相比，PBS／A的结晶度和结晶速率下降。PBS和PBS／A均出现了区域n一Hl的转变，分别发生在％。C和75OC。随着结晶温度的降低，PBS和PBS／A的结晶形态分别为轴状结构晶体、非环带球晶和环带球晶。与PBS相比，PBS／A形成的环带球晶更规整。采用示差扫描量热法（DSC）研究了Nylon 1212、PBS、PBS／A和间规1，2聚丁二烯（st-1，2PB）的本体结晶动力学。发现采用序列一并列Avrami方程能较好地描述Nylon1212的等温结晶全过程。采用不同方法对st-1，2PB的非等温结晶动力学进行研究，发现由Jeziony方法和ozawa方法分析很难得到可靠的动力学参数，而根据莫志深等提出的新方法可较好地进行描述。采用Vyazovkin方法计算了Nylon 1212、st-1，2PB、PBS和PBS／A的非等温结晶活化能，均发现结晶活化能随相对结晶度的升高而升高。初步研究了结晶条件和扫描速率对Nylon 1212、st-1，2PB、PBs和PBs／A熔融行为的影响，并根据Hoffinan-Weeks方法求得了几种聚合物的平衡熔融温度。

The investigation of exfoliation process of organic modified montmorillonite in thermoplastic polyurethane with different molecular weights

Cloisite 30B (30B) was melt-mixed with two kinds of thermoplastic polyurethane (TPU) with different molecular weights to discern the roles of molecular diffusion and shear in the exfoliation process. The higher level of exfoliation was achieved in TPU matrix with higher molecular weight due to the appropriate viscosity. In order to have an insight into the mechanism of exfoliation, the degree of dispersion and exfoliation of 30B was characterized by wide angle X-ray diffraction and transmission electron microscopy. The layers of 30B were exfoliated via a slippage process, which was also observed in polyamide 12 nanocomposites recently.

Critical behavior of brittle-ductile transition of polymers

We report that the brittle-ductile transition of polymers induced by temperature exhibits critical behavior. When t close to 0, the critical surface to surface interparticle distance (IDc) follows the scaling law: IDc proportional to t(-v) where t = 1 - T/T-BD(m) (T and T-BD(m) are the test temperature and brittle-ductile transition temperature of matrix polymer, respectively) and v = 2/D. It is clear that the scaling exponent v only depends on dimension (D). For 2, 3, and 4 dimension, v = 1, 2/3, and 1/2 respectively. The result indicates that the ID, follows the same scaling law as that of the correlation length (xi), when t approach to zero.

A strategy of fabricating exfoliated thermoplastic polyurethane/clay nanocomposites via introducing maleated polypropylene

By reducing the attraction between the platelets of octaclecylammonium chloride modified montmorillonite (OMMT-C18) via pre-intercalation of maleated polypropylene (MAPP), OMMT-C18 was exfoliated in thermoplastic polyurethane (TPU) matrix during melt-mixing. Wide angle X-ray diffraction, transmission electron microscopy and thermogravimetric analysis were used to investigate the microstructure of TPU nanocomposites. Three factors (including introducing sequence, the kind and the content of MAPP) showed important effects on the dispersion degree of OMMT-C18 in TPU matrix. The results confirmed that the pre-intercalation of MAPP was necessary for the exfoliation of OMMT-C18; however, the role of MAPP in TPU nanocomposites was different from that in polypropylene nanocomposites.

Organic Thin-Film Transistor Memory With Nanoparticle Floating Gate

Organic thin-film transistor memory devices were realized by inserting a layer of nanoparticles (such as Ag or CaF2) between two Nylon 6 gate dielectrics as the floating gate. The transistor memories were fabricated on glass substrates by full thermal deposition. The transistors exhibit significant hysteresis behavior in current-voltage characteristics, due to the separated Ag or CaF2 nanoparticle islands that act as charge trap centers. The mechanism of the transistor memory operation was discussed.

Thermal stability, crystallization, structure and morphology of syndiotactic 1,2-polybutadiene/organoclay nanocomposite

Syndiotactic 1,2-polybutadiene/organoclay nanocomposites were prepared and characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC), respectively. The XRD shows that exfoliated nanocomposites are formed dominantly at lower clay concentrations (less than 2%), at higher clay contents intercalated nanocomposites dominate. At the same time, the XRD indicates that the crystal structures of sPB formed in the sPB/organoclay nanocomposites do not vary, only the relative intensity of the peaks corresponding to (0 1 0) and (2 0 0)/(1 1 0) crystal planes, respectively, varies. The DSC and POM indicate that organoclay layers can improve cooling crystallization temperature, crystallization rate and reducing the spherulite sizes of sPB. TGA shows that under argon flow the nanocomposites exhibit slight decrease of thermal stability, while under oxygen flow the resistance of oxidation and thermal stability of sPB/organoclay nanocomposites were significantly improved relative to pristine sPB. The primary and secondary crystallization for pristine sPB and sPB/organoclay (2%) nanocomposites were analyzed and compared based on different approaches.

The effect of multiwall carbon nanotube on the crystallization, morphology, and rheological properties of nylon1010 nanocomposites

Nanocomposites based on poly(iminosebacoyl imino-decamethylene) (PA1010) and multiwall carbon nanotubes (MWNTs) were successfully prepared by melt blending technique. environmental scanning electron microscope micrographs of the fracture surfaces showed that not only is there an evenly dispersion of MWNTs throughout the PA1010 matrix but also a strongly interfacial adhesion with the matrix. The combined effect of more defects on MWNTs and low temperature buckling fracture is mainly responsible for the broken tubes. Differential scanning calorimeter results showed that the MWNTs acted as a nucleation agent and increased the crystallization rate and decreased crystallite size. In the linear region, rheological measurements showed a distinct change in the frequency dependence of storage modulus, loss modulus, and complex viscosity particularly at low frequencies. We conclude that the rheological percolation threshold might occur when the content of MWNTs is over 2 wt% in the composites.

Morphology evolutions of organically modified montmorillonite/polyamide 12 nanocomposites

Organically modified montmorillonites (OMMTs) by octadecylammonium chloride with two adsorption levels were dispersed in polyamide 12 (PA12) matrices with two molecular weights for different melt mixing times in order to investigate morphology evolutions and factors influencing fabrication of PA12 nanocomposites. Different adsorption levels of the modifier in the OMMTs provide different environments for diffusion of polymer chains and different attractions between MMT layers. Wide-angle X-ray diffraction (WAXD), transmission electron microscope (TEM) and gas permeability were used to characterize morphologies of the nanocomposites. Both OMMTs can be exfoliated in the PA12 matrix with higher molecular weight, but only OMMT with lower adsorption level can be exfoliated in the PA12 matrix with lower molecular weight. It was attributed to the differences in the levels of shear stress and molecular diffusion in the nanocomposites. The exfoliation of OMMT platelets results from a combination of molecular diffusion and shear. After intercalation of PA12 into interlayer of OMMT in the initial period of mixing, further dispersion of OMMTs in PA12 matrices is controlled by a slippage process of MMT layers during fabricating PA12 nanocomposites with exfoliated structure.