2,160 research outputs found
Simulation of multilevel cell spin transfer switching in a full-Heusler alloy spin-valve nanopillar
No full textAuthor name used in this publication: Shi, S. Q.2012-2013 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishedVoR allowe
KENAF BAST FOR FIBER REINFORCED POLYMER COMPOSITES
No full textCellulosic fibers sized from the macro-scale to the nano-scale were prepared hierarchically from kenaf bast fibers using chemicals. The process began with a hermetical alkaline retting followed by a bleaching treatment. The bleached fibers were hydrolyzed using inorganic acid, from which microfibers and cellulose nanowhiskers (CNWs) were fabricated. Inorganic nanoparticle impregnation (INI) was used to treat the retted fibers for the improvement of the interfacial compatibility between the fiber and polypropylene (PP) matrix. The retted fibers and INI-treated fibers were used as reinforcement for the PP polymer composites. Film casting process was used to make CNW/PVA composites. The hermetical retting process used in this study produced fibers with high cellulose contents (81-92%) by removing the lignin and hemicelluloses. Higher retting temperature resulted in higher fiber surface hardness and elastic moduli. The tensile strengths and tensile moduli of the fibers decreased as the temperature increased. The SEM images showed the micropores in the cell wall structure for the fibers retted at over 130°C, providing the possibility to anchor nanoparticles into the cell wall. Surface morphology of the INI-treated fibers was examined with SEM, and showed that the CaCO3 nanoparticle crystals grew onto the fiber surface. Energy-dispersive X-ray spectroscopy (EDS) was used to verify the CaCO3 particle deposits on the fiber surface. As the size scale of the fibers decreased, the fiber crystallinity increased from 49.9% (retted fibers) to 83.9% (CNWs). About 23% á-cellulose in the raw kenaf bast fibers had been converted into CNWs. The retted fibers without INI treatment had poor compatibility with the polypropylene matrix. The INI treatment improved the compatibility between the fibers and the PP matrix, resulting in an improvement in kenaf fiber/PP composite tensile moduli and tensile strengths. The CNWs prepared from kenaf bast fiber gave excellent reinforcement for PVA composites. A nine percent increase of CNWs in the CNW/PVA composites yielded significant improvements in tensile strength and modulus of about 46% and 152%, respectively, compared with pure PVA
The Shi arrangement and the Ish arrangement
No full textThis paper is about two arrangements of hyperplanes. The first — the Shi arrangement — was introduced by Jian-Yi Shi to describe the Kazhdan-Lusztig cells in the affine Weyl group of type A. The second — the Ish arrangement — was recently defined by the first author who used the two arrangements together to give a new interpretation of the q,t-Catalan numbers of Garsia and Haiman. In the present paper we will define a mysterious "combinatorial symmetry'' between the two arrangements and show that this symmetry preserves a great deal of information. For example, the Shi and Ish arrangements share the same characteristic polynomial, the same numbers of regions, bounded regions, dominant regions, regions with c "ceilings'' and d "degrees of freedom'', etc. Moreover, all of these results hold in the greater generality of "deleted'' Shi and Ish arrangements corresponding to an arbitrary subgraph of the complete graph. Our proofs are based on nice combinatorial labellings of Shi and Ish regions and a new set partition-valued statistic on these regions.Cet article traite de deux arrangements d'hyperplans. Le premier — arrangement Shi — a été introduit par Jian-Yi Shi pour décrire les cellules de Kazhdan-Lusztig du groupe de Weyl affine de type A. Le deuxième — arrangement Ish — a été récemment défini par le premier auteur pour donner une nouvelle interprétation des nombres q,t-Catalan de Garsia et Haiman. Ici nous définissons une mystérieuse "symétrie combinatoire" entre les deux arrangements et nous montrons que cette symétrie conserve un grand nombre d'informations. Par exemple, les arrangements Shi et Ish ont le même polynôme caractéristique, le même nombre de régions, de régions bornées, de régions dominantes, de régions avec c "plafonds'' et d "degrés de liberté'', etc. En outre, ces résultats se généralisent aux arrangements Shi et Ish "deleted'' correspondant à un sous-graphe arbitraire du graphe complet. Nos preuves reposent sur des étiquetages combinatoires des régions Shi et Ish, et sur une nouvelle statistique associée
MULTIFRACTAL q RÉNYI DIMENSIONS OF POLISH SPACES FOR q < 1
No full text In earlier work the second author investigated the multifractal q Rényi dimensions of Polish spaces for q ≥ 1. In this paper we complement those results by investigating the multifractal q Rényi dimensions of Polish spaces for q < 1. </jats:p
THE EFFECT OF LAYUP AND PRESSURE ON MECHANICAL PROPERTIES OF FIBERGLASS AND KENAF FIBER COMPOSITES
No full textIn an effort to present more ‘green’ material for massive manufacturing that are both competitive in their properties and can be more environmental friendly, natural fibers are being considered for possible applications in the automotive industry. This paper shows an exploratory study of the effects of pressure and layup on a hybrid composite of randomly oriented woven kenaf fibers and fiberglass/polyester sheet molding compound (SMC). In addition to initial testing performed on their water absorption and other important properties, these hybrid composites were tested to determine the bending modulus of elasticity (MOE) and the bending modulus of rupture (MOR) as well as the tensile modulus of elasticity (MOE), ultimate tensile strength. Pictures are taken from a Spectral Electron Microscope to determine if the fiber mats were properly penetrated by the resin and if the structural integrity of the fibers was maintained during manufacture
Zhi mi xing ti zhong de I-Love-Q guan xi shi
No full textM.Phil.The objective of this thesis is to study I-Love-Q relations of compact stars through the post-Minkowskian expansion. The properties of compact stars, such as the moment of inertia (I) , the tidal deformability (λ) and the spininduced quadrupole moment (Q) are calculated analytically and expressed in terms of a series in compactness (C).In the first part, we follow the post-Minkowskian expansion of compact stars proposed by Chan et al. [Physical Review D, 91, 04417, (2015)] to calculate the spin-induced quadrupole moment (Q) for incompressible stars. The formalism of calculating the equilibrium configurations of slowly rotating stars is proposed by Hartle [The Astrophysical Journal, 150, 1005, (1967)]. With the help of the Pade approximation, the quantity Q is related to I and λ, forming the I-Love-Q relations. Furthermore, the procedure of calculating Q is repeated for other equation of state (EOS) models. Hence the stationarity of the I-Love-Q relations about the incompressible limit is shown.In the second part, we study the change of the I-Love relation taking the effect of elasticity into consideration. Quark matter in the crystalline color superconducting phase could provide a shear modulus much larger than that of normal neutron star crusts. A compact star made of quark matter in such a phase can be considered as a solid star. With the introduction of elasticity, the problem of tidal deformation is once again solved by using the post-Minkowskian expansion. The breaking of the universal I-Love relation is shown. Furthermore, by enclosing a thin layer of fluid on top of a solid core, the effect of elasticity is screened out. Such a novel phenomenon is also studied analytically.本論文的目的在於透過以微擾的方法去計算和學習緻密星體中的I-Love-Q關係式，當中I、Love 和Q分別代表為星體的轉動慣量、用以量化星體受潮汐影響以致變形的潮汐樂甫數(tidal Love number)和因星體自旋而引起自身的四極矩(spin-induced quadrupole moment)。在本文的第一部分，我們首先以不能壓縮的物態方程(equation of state)去代表將被計算的星體，透過微擾的方法拆解有關物理量Q的微分方程，並且組成以該物態方程組成的星體的I-Love-Q關係式和成功地展示出該關係式對於由不同物態方程而組成的星體有著不敏感的特性。其後我們把計算拓展至一個更複雜和有廣泛性的物態方程，利用相同的手法去取得該星體的物理量Q和組成I-Love-Q關係式。當中更展示出不同的I-Love-Q關係式對不能壓縮的物態方程有著平穩性和嘗試以數學的角度去解釋I-Love-Q關係式對於由不同物態方程而組成的星體的不敏感特性。在本文的第二部分，我們嘗試利用相同的微擾方法去解決星體加入彈性(elasticity)後受到潮汐影響以致變形的問題。在加入彈性的考慮下，從計算中顯示星體中的I-Love關係式會隨著剪切模量(shear modulus)的增加而打破之前所提及的不敏感特性。最後，儘管系統的複雜程度提升，但我們也順利地透過微擾的方法去解決以及將計算推廣至其他星體的模型，藉此顯示該方法之可行性。Shek, Hiu Fung = 緻密星體中的I-Love-Q關係式 / 石曉楓.Thesis M.Phil. Chinese University of Hong Kong 2018.Includes bibliographical references (leaves 108-112).Abstracts also in Chinese.Title from PDF title page (viewed on …).Shek, Hiu Fung = Zhi mi xing ti zhong de I-Love-Q guan xi shi / Shi Xiaofeng
Development and application of a three-dimensional water quality model in a partially-mixed estuary, Southampton Water, UK
No full textThe aim of this research was to develop a 'transportable' water quality model for the Solent and Southampton Water estuarine system, as a part of an effort to examine the effects of human activity and natural processes on estuarine water quality. Dissolved oxygen (DO), as a main indicator of water quality, is influenced by physical, chemical and biological processes, and has been chosen as the core parameter to link the different processes to be modelled. Monthly surveys of DO, planktonic community respiration rates and other water quality parameters (temperature, salinity, chlorophyll, suspended particulate matter, inorganic nutrients etc.) in the Itchen Estuary and Southampton Water were conducted from January 1998 to April 1999. DO data shows that Southampton Water is a relatively healthy estuary, despite receiving considerable loads of oxygen demanding organic sewage effluent discharged from a number of points. A persistent moderate DO sag (DO saturation > 80%) was observed in the upper Itchen Estuary throughout the year. In the lower Itchen Estuary and Southampton Water, the waters were DO saturated during the non-phytoplankton growth season. Surface DO supersaturation was observed during the phytoplankton growth season especially during algal blooms, but no severe DO depletion was detected following the bloom collapse. Community respiration rates maintained a substantial level in the upper Itchen estuary, while in the lower estuary respiration rates were low during the non-phytoplankton season and increased during the phytoplankton growth season. It is suggested that the high winter respiration rate in the upper Itchen Estuary are sustained by inputs from external sources (rivers, sewage and industrial effluents) and that the summer increase in the lower estuary is a consequence of phytoplankton photosynthesis. Nutrients in the Itchen Estuary and Southampton Water show mainly conservative behaviour in a plot of nutrient concentration against salinity. The removal of the nutrients by phytoplankton activity occurred at high salinities during the spring to summer period.A 3-D finite element baroclinic hydrodynamic model with two-equation q2-q2l turbulence closure has been developed including a mass conservation scheme. The model successfully simulated the tides, tidal currents, and estuarine circulation in the Southampton Water and Solent estuarine system. The modelled tidal induced residual currents and water mass transportation in Southampton Water and the Solent have been examined. Model results show the existence of a predominant westward tidal induced residual current in the Solent. The tidal induced residual water mass transport is extremely limited in Southampton Water, except near the entrance to Southampton Water, where it joins the Solent. The estuarine circulation with surface, seaward flowing fresher water and bottom, landward flowing saltier water provides the main mechanism for water mass transport in the model. The short residence time of waters in the estuary estimated from the survey salinity data confirmed how effective the estuarine circulation is for sea water from the Solent to replace the water within Southampton Water. The trapping effect of estuarine circulation is also crucial for the water quality in the estuary. A water quality model has been developed and coupled with the 3-D hydrodynamic model. The water quality model consists of an external (dissolved oxygen-biochemical oxygen demand) model, which models the direct impact of external inputs (riverine discharge, domestic and industrial effluents) to the water quality, and an internal model, which simulates the impact of local estuarine phytoplankton growth on the water quality. DO and dissolved inorganic nutrients are the 'link substances' between the external model and internal model. The integrated water quality model output has been compared against the survey data for 1998, and has been shown to reproduce the spatial and temporal change in oxygen, nutrients, chlorophyll and planktonic respiration in Southampton Water
NOVEL TYPE ENGINEERED STRUCTURAL BEAMS FROM PINE LUMBER
No full textThe intersection of decreasing resource size and increasing population and its associated demand creates a pressing need to develop products that act as alternatives to solid sawn lumber. Engineered composite lumber is one such alternative. The product described herein utilizes a modified form of sawn lumber as the raw material. The objective of this research was to manufacture, mechanically test, and evaluate a novel type of engineered lumber. Non destructive evaluation of raw materials and finished beams, and final mechanical testing to determine mean strength and stiffness values as per ASTM 5456 were used. The mechanical property data was converted into design values for fiber stress in bending (Fb) and stiffness (MOE). These design values was compared to those published by the U.S. (NDS) for wood construction. Pine logs were reduced into cants and further processed into matched symmetrical trapezoids. Symmetrical trapezoids were then non-destructively evaluated via E-computer and Director, and sorted by results. Next, the sorted trapezoids were matched into pairs and assembled into bowtie beams. Polyvinyl acetate adhesive was used throughout. Stiffness of the manufactured beams was nondestructively evaluated too. Then the beams were mechanically tested. The information from the E-computer was correlated to the strength and stiffness for each beam. The design strength and stiffness was compared to the values of sections of equivalent depth and maximum width as shown in the NDS. Also, non destructive test values were compared and correlated to those from the destructive tests. Finally, the design strength and stiffness values were respectively multiplied by the sectional area or the moment of inertia. This produced a strength efficiency factor and a stiffness efficiency factor. These factors were compared to factors derived from multiplying the design strength or design stiffness values (from the NDS) times the area or the moment of inertia of a rectangular section of equivalent depth and maximum width. It is found that the mechanically efficient bowtie section produced an increased strength and stiffness efficiency as compared to that of solid sawn material
FRACTIONATION OF SOYBEAN MEAL, COTTONSEED MEAL AND WHEAT MIDDLINGS USING COMBINATION OF SIEVING AND AIR CLASSIFICATION.
No full textFiber separation from these animal feeds could increase the protein and hence increase the value of the animal feed. The objective of the study was to evaluate the combination of sieving and air classification for fiber separation from soybean meal (SBM), cottonseed meal (CSM) and wheat middlings (WM). The effect of yields of lighter fractions on fiber separation from size fractions was also investigated. At low yields of lighter fraction (5%), the quantity of fiber product separated was 3.7, 1.3 and 4.8% by weight of SBM, CSM and WM respectively. At high yields of lighter fractions (15%), the quantity of fiber product separated was 8.9, 3.5 and 11% by weight of SBM, CSM and WM respectively. For CSM and SBM, the enhanced product contained 0.6 to 2.0% higher protein content than unprocessed feed. For WM, the enhanced product contained 0.2 to 0.7% higher protein content than unprocessed feed
Effect of Density and Polymer Content on the Hygroscopic Thickness Swelling Rate of Compression Molded Wood Fiber/Polymer Composites
No full textThe effects of polymer content and board density on the hygroscopic thickness swelling rate of compression-molded wood fiber/polymer composites were investigated in this study. A swelling model developed by Shi and Gardner (2005) was used to study the thickness swelling process of wood fiber/polymer composites exposed to water vapor conditions in which a parameter, KSR, was used for the comparison of the swelling rates. The polymer materials used to process the wood fiber/polymer composites were from a reclaimed automobile plastic mixture, also called polymer fluff. Polymeric diphenylmethane diisocyanate (pMDI) resin was used as a binder. Six polymer contents (0, 15, 30, 45, 60, and 100%) and four target specific gravities (0.55, 0.75, 0.90, and 1.00) were evaluated in the experiments using the swelling model. It was shown that the swelling model successfully fit the empirical swelling rate data as impacted by different board densities and polymer contents. Board density has a significant effect on the swelling rate of the composites. The swelling rate increased linearly as board density decreased. The effect of polymer content on the swelling rate depends partially on board density. Polymer content did not show a significant effect on swelling rate at an oven-dry density of 900 kg/m3. It was also confirmed from this study that the accuracy of the swelling model prediction is a function of the magnitude of the swelling rate parameter. The lower the thickness swelling rate of the composites, the more accurate the prediction obtained from the swelling model
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