Evaluation of race distance, track surface and season of the year on exercise-induced pulmonary haemorrhage in flat racing Thoroughbreds in Brazil

Reasons for performing study: To our knowledge no studies evaluating risk factors to EIPH have been undertaken with such a population of horses in Brazil, which is one of the few countries in the racing community to accept the use of frusemide (FUR) as a prerace medication for bleeders. We also compared national results with those already in the literature. Objectives: To verify the influence of variables such as distance of the race, racetrack surface, going and season of the year in the recurrence and severity of EIPH and its effect on the finishing position of flat racing Thoroughbreds in Brazil. Methods: 2118 post race respiratory endoscopies were recorded, in a total of 1003 individual horses. All horses in the study were certified bleeders (deemed positive by registered veterinarians following one or more endoscopies) and were administered FUR prior to each race. Data was analysed using both ordinary logistic regression and multiple logistic regression. Results: The results suggest that race distance, season of the year and racetrack surface affect the recurrence of EIPH. Also, despite the use of FUR, the majority (62%) of horses continued to display some degree of haemorrhage. Conclusions: There was a tendency for horses that remained positive despite the use of FUR to finish unplaced in a race. Horses which had a significant reduction in bleeding and became HPIE negative after the use of FUR, tended to finish in top positions. It was not possible to determine a pattern of severity of EIPH in horses with more than one endoscopy. Further studies are required to improve our understanding of this syndrome and its correlations to performance in the racing Thoroughbred, together with the role of FUR and its possible enhancing performance effects and efficacy in consistently diminishing EIPH. Potential relevance: This study enabled a better understanding of the use of FUR in Brazilian Thoroughbred racehorses and showed there was a tendency towards improvement in performance after administrion of FUR in bleeders. The fact that a large number of horses remained positive for EIPH despite the use of FUR should encourage the scientific community to search for better ways of reducing, or preventing, this syndrome. © 2006 EVJ Ltd.

Search for the standard model Higgs boson produced in association with a top-quark pair in pp collisions at the LHC

A search for the standard model Higgs boson produced in association with a top-quark pair is presented using data samples corresponding to an integrated luminosity of 5.0 fb-1 (5.1 fb-1) collected in pp collisions at the center-of-mass energy of 7 TeV (8 TeV). Events are considered where the top-quark pair decays to either one lepton+jets (tt̄ → ℓvqq̄bb̄) or dileptons (tt̄ → ℓ+vl- rfvn1̄bb̄), ℓ being an electron or a muon. The search is optimized for the decay mode H → bb̄. The largest background to the tt̄H signal is top-quark pair production with additional jets. Artificial neural networks are used to discriminate between signal and background events. Combining the results from the 7 TeV and 8 TeV samples, the observed (expected) limit on the cross section for Higgs boson production in association with top-quark pairs for a Higgs boson mass of 125 GeV is 5.8 (5.2) times the standard model expectation. [Figure not available: see fulltext.] © 2013 Cern for the benefit of the CMS collaboration.

Lamb mode diversity imaging for non-destructive testing of plate-like structures

Several Lamb wave modes can be coupled to a particular structure, depending on its geometry and transducer used to generate the guided waves. Each Lamb mode interacts in a particular form with different types of defects, like notches, delamination, surface defects, resulting in different information which can be used to improve damage detection and characterization. An image compounding technique that uses the information obtained from different propagation modes of Lamb waves for non-destructive testing of plate-like structures is proposed. A linear array consisting of 16 piezoelectric elements is attached to a 1 mm thickness aluminum plate, coupling the fundamental A0 and S0 modes at the frequencies of 100 kHz and 360 kHz, respectively. For each mode two images are obtained from amplitude and phase information: one image using the Total Focusing Method (TFM) and one phase image obtained from the Sign Coherence Factor (SCF). Each TFM image is multiplied by the SCF image of the respective mode to improve contrast and reduce side and grating lobes effects. The high dispersive characteristic of the A0 mode is compensated for adequate defect detection. The information in the SCF images is used to select one of the TFM mode images, at each pixel, to obtain the compounded image. As a result, dead zone is reduced, resolution and contrast are improved, enhancing damage detection when compared to the use of only one mode. © 2013 Elsevier Ltd.

Estratégias didáticas de leitura utilizadas pelos professores e a competência leitora de alunos na 4. série do ensino fundamental

Pós-graduação em Educação - IBRC

Ensino e aprendizagem de avaliação funcional descritiva na atuação profissional de professores de ciências no ensino fundamental

Pós-graduação em Educação para a Ciência - FC

Ensinar-aprender frações em um curso de formação continuada para professores dos anos iniciais do ensino fundamental: conhecimentos e dificuldades evidenciadas

Este estudo apresenta os dados de uma pesquisa realizada na Universidade Federal do Pará - UFPA, no ano de 2009, em uma turma do Curso de Especialização em Educação em Ciências e Matemáticas para as Séries Iniciais. Durante o período em que se estudou o tema frações, nesse curso de formação continuada, foram investigados os conhecimentos e dificuldades que emergem no fazer ensinar-aprender das professoras que ensinam matemática nos anos iniciais do ensino fundamental. A fundamentação teórica usada para dar suporte a este estudo está apoiada em trabalhos dos autores: Brousseau (2009, 2008, 1996), D’Amore (2007), Pais (2006, 2005), Almouloud (2007), Igliori (2008), Bittencourt (1998). A pesquisa é qualitativa na modalidade descritiva. De uma turma composta de 29 (vinte e nove) professoras que frequentavam o curso de formação, 5 (cinco) foram selecionadas, dentre as que possuíam maior tempo de experiência em sala de aula, para serem os sujeitos investigados na pesquisa. Outras 10 (dez) professoras estão citadas, por terem dado valiosas contribuições para fundamentar as análises. Os instrumentos de investigação usados foram o caderno de campo, questionário, teste e registro produzido pelas professoras pesquisadas. Estes dados foram organizados e apresentados em forma de episódios. Os resultados apontam conhecimentos e dificuldades no fazer ensinar-aprender das professoras em relação ao tema frações. Algumas dificuldades identificadas: 1) fazer comparações entre frações; 2) fazer a representação esquemática de frações. O conhecimento identificado: 1) a construção de equação linear como resultado da leitura e interpretação de problemas com aplicação de frações; 2) a resolução algébrica de problemas envolvendo frações. Entretanto, essas professoras, conscientes de possuírem tais dificuldades, mostraram-se motivadas a superá-las. Essa motivação ficou evidenciada pelo comprometimento que apresentaram ao desenvolver as tarefas que foram propostas no referido curso.

Estratigrafia da sucessão sedimentar Pós-Barreiras (Zona Bragantina, Pará) com base em radar de penetração no solo

Investigação pioneira aplicando Radar de Penetração no Solo (GPR) na área da Praia do Atalaia, norte do Brasil, nos permitiu caracterizar, pela primeira vez, fácies e estratigrafia dos depósitos conhecidos informalmente como Sedimentos Pós-Barreiras (Plioceno e mais recente). Esta sucessão sedimentar recobre discordantemente o embasamento miocênico, representado pelas formações Pirabas/Barreiras. Três unidades estratigráficas foram reconhecidas. A Unidade 1, inferior, consiste em um intervalo com 6 m de espessura média dominado por reflexões pobremente definidas e de baixa amplitude, e que intergradam com reflexões de média escala dos tipos tangencial, obliquo e hummocky. A Unidade 2, intermediária, possui cerca de 9 m de espessura e inclui, principalmente, reflexões oblíquas de larga escala, cujas configurações variam de paralela, tangencial, sigmoidal a sigmoidal-complexa. A Unidade 3, superior, corresponde a um intervalo entre 3,5 e 9 m de espessura, sendo dominada por reflexões hummocky, seguidas por reflexões de média escala dos tipos oblíquo, paralelo a sub-paralelo, e em corte-e-preenchimento. A análise da configuração das reflexões internas e geometria das reflexões nos leva a propor que a unidade correspondente aos Sedimentos Pós-Barreiras é mais variável faciologicamente que inicialmente imaginado, incluindo depósitos eólicos (dunas costeiras), bem como depósitos de cordão litorâneo, planície de maré, canal e mangue. Além disto, o mapeamento das três unidades descritas acima é importante para desvendar a complexidade de sedimentação versus erosão durante o Neógeno tardio no norte do Brasil.

The infrared fundamental intensities of some cyanopolyynes

Some cyanopolyynes, HCnN (n = 1, 3, ... , 17), are investigated by means of calculations at the MP2/cc-pVTZ and CCSD/cc-pVDZ levels. Although the MP2/cc-pVTZ results for geometries and molecular dipole moments are encouraging, the CCSD/cc-pVDZ level was superior for the study of infrared fundamental intensities. The main bands are also analyzed with a charge-charge flux-dipole flux (CCFDF) partition model based on quantities given by the Quantum Theory of Atoms in Molecules (QTAIM). The intensity of vibrations corresponding to the stretching of CH bonds (3471-3473 cm(-1)) increases in line with the number of carbon atoms (from 61 to 146 km mol(-1) between HCN and HC13N). This increase is due to the charge flux contribution while the other contributions remain roughly unaltered except for HCN. Moreover, the hydrogen atom loses an almost constant amount of electronic charge during the CH bond enlargement and a small fraction of this charge spreads to atoms farther and farther away from hydrogen as the molecule size increases. The band associated with the doubly degenerate CH bending vibrations (643-732 cm(-1)) presents approximately the same intensity in all the studied cyanopolyynes (from 67 to 76 km mol(-1)). The CCFDF/QTAIM contributions are also nearly the same for these bending modes in HC5N and larger systems. The intensity of the mode mostly identified as CN stretching (around 2378-2399 cm(-1) except for HCN) increases from HCN up to HC7N (from 0.3 to 83 km mol(-1)) and nearly stabilizes around 80-90 km mol(-1) for larger systems. The CCFDF/QTAIM contributions for this mode also change significantly up to HC7N and remain almost constant in larger systems. We also observed the appearing of a very relevant band between 2283 and 2342 cm(-1). This mode is mainly associated with the symmetric stretching of CC triple bonds near the molecule center and exhibits large charge fluxes while the other contributions are almost negligible in the largest cyanopolyynes. The two vibrational bands associated with the smallest frequencies are also studied and extrapolation equations are suggested to predict their positions in larger cyanopolyynes. (C) 2012 Elsevier B.V. All rights reserved.

Self-potential signals from an analog biogeobattery mode

A tank experiment was conducted to check if self-potential (SP) signals can be generated when buried organic matter is wire-connected to a near-surface, oxygen-rich, sediment layer. This experiment demonstrated that once wired, there was a flux of electrons (hence an electric current) between the lower and upper layers of the sandbox with the system responding as a large-scale microbial fuel cell (a type of bioelectrochemical system). An electric current was generated by this process in the wire and the SP method was used to monitor the associated electric potential distribution at the top of the tank.. The electric field was controlled by the flux of electrons through the wire, the oxidation of the organic matter, the reduction of oxygen used as a terminal electron acceptor, and the distribution of the DC resistivity in the tank. The current density through the wire was limited by the availability of oxygen and not by the oxidation of the organic matter. This laboratory experiment incorporated key elements of the biogeobattery observed in some organic-rich contaminant plumes. This analogy includes the generation of SP signals associated with a flux of electrons, the capacity of buried organic matter in sustaining anodic reactions, network resistance connecting terminal redox reactions spatially separated in space, and the existence of anodic secondary coupled reactions. A resistivity tomogram of the tank, after almost a year in operation, suggests that oxidative processes triggered by this geobattery can be imaged with this method to determine the radius of influence of the bioelectrochemical system.

Lamb mode diversity imaging fornon-destructivetesting of plate-likestructures

Several Lamb wave modes can be coupled to a particular structure, depending on its geometry and transducer used to generate the guided waves. Each Lamb mode interacts in a particular form with different types of defects, like notches, delamination, surface defects, resulting in different information which can be used to improve damage detection and characterization. An image compounding technique that uses the information obtained from different propagation modes of Lamb waves for non-destructive testing of plate-like structures is proposed. A linear array consisting of 16 piezoelectric elements is attached to a 1 mm thickness aluminum plate, coupling the fundamental A0 and SO modes at the frequencies of 100 kHz and 360 kHz, respectively. For each mode two images are obtained from amplitude and phase information: one image using the Total Focusing Method (TFM) and one phase image obtained from the Sign Coherence Factor (SCF). Each TFM image is multiplied by the SCF image of the respective mode to improve contrast and reduce side and grating lobes effects. The high dispersive characteristic of the A0 mode is compensated for adequate defect detection. The information in the SCF images is used to select one of the TFM mode images, at each pixel, to obtain the compounded image. As a result, dead zone is reduced, resolution and contrast are improved, enhancing damage detection when compared to the use of only one mode. (C) 2013 Elsevier Ltd. All rights reserved. (AU)

Mixed Mode Fracture Behaviour of Piezoelectric Materials

Piezoelectrics present an interactive electromechanical behaviour that, especially in recent years, has generated much interest since it renders these materials adapt for use in a variety of electronic and industrial applications like sensors, actuators, transducers, smart structures. Both mechanical and electric loads are generally applied on these devices and can cause high concentrations of stress, particularly in proximity of defects or inhomogeneities, such as flaws, cavities or included particles. A thorough understanding of their fracture behaviour is crucial in order to improve their performances and avoid unexpected failures. Therefore, a considerable number of research works have addressed this topic in the last decades. Most of the theoretical studies on this subject find their analytical background in the complex variable formulation of plane anisotropic elasticity. This theoretical approach bases its main origins in the pioneering works of Muskelishvili and Lekhnitskii who obtained the solution of the elastic problem in terms of independent analytic functions of complex variables. In the present work, the expressions of stresses and elastic and electric displacements are obtained as functions of complex potentials through an analytical formulation which is the application to the piezoelectric static case of an approach introduced for orthotropic materials to solve elastodynamics problems. This method can be considered an alternative to other formalisms currently used, like the Stroh’s formalism. The equilibrium equations are reduced to a first order system involving a six-dimensional vector field. After that, a similarity transformation is induced to reach three independent Cauchy-Riemann systems, so justifying the introduction of the complex variable notation. Closed form expressions of near tip stress and displacement fields are therefore obtained. In the theoretical study of cracked piezoelectric bodies, the issue of assigning consistent electric boundary conditions on the crack faces is of central importance and has been addressed by many researchers. Three different boundary conditions are commonly accepted in literature: the permeable, the impermeable and the semipermeable (“exact”) crack model. This thesis takes into considerations all the three models, comparing the results obtained and analysing the effects of the boundary condition choice on the solution. The influence of load biaxiality and of the application of a remote electric field has been studied, pointing out that both can affect to a various extent the stress fields and the angle of initial crack extension, especially when non-singular terms are retained in the expressions of the electro-elastic solution. Furthermore, two different fracture criteria are applied to the piezoelectric case, and their outcomes are compared and discussed. The work is organized as follows: Chapter 1 briefly introduces the fundamental concepts of Fracture Mechanics. Chapter 2 describes plane elasticity formalisms for an anisotropic continuum (Eshelby-Read-Shockley and Stroh) and introduces for the simplified orthotropic case the alternative formalism we want to propose. Chapter 3 outlines the Linear Theory of Piezoelectricity, its basic relations and electro-elastic equations. Chapter 4 introduces the proposed method for obtaining the expressions of stresses and elastic and electric displacements, given as functions of complex potentials. The solution is obtained in close form and non-singular terms are retained as well. Chapter 5 presents several numerical applications aimed at estimating the effect of load biaxiality, electric field, considered permittivity of the crack. Through the application of fracture criteria the influence of the above listed conditions on the response of the system and in particular on the direction of crack branching is thoroughly discussed.

Measurement of the oscillation frequency of B s mesons in the hadronic decay mode B s pi D s (phi pi) X with the D0 detector at the Fermilab Tevatron collider

The standard model (SM) of particle physics is a theory, describing three out of four fundamental forces. In this model the Cabibbo-Kobayashi-Maskawa (CKM) matrix describes the transformation between the mass and weak eigenstates of quarks. The matrix properties can be visualized as triangles in the complex plane. A precise measurement of all triangle parameters can be used to verify the validity of the SM. The least precisely measured parameter of the triangle is related to the CKM element |Vtd|, accessible through the mixing frequency (oscillation) of neutral B mesons, where mixing is the transition of a neutral meson into its anti-particle and vice versa. It is possible to calculate the CKM element |Vtd| and a related element |Vts| by measuring the mass differences Dmd (Dms ) between neutral Bd and bar{Bd} (Bs and bar{Bs}) meson mass eigenstates. This measurement is accomplished by tagging the initial and final state of decaying B mesons and determining their lifetime. Currently the Fermilab Tevatron Collider (providing pbar{p} collisions at sqrt{s}=1.96 TeV) is the only place, where Bs oscillations can be studied. The first selection of the "golden", fully hadronic decay mode Bs->Ds pi(phi pi)X at DØ is presented in this thesis. All data, taken between April 2002 and August 2007 with the DØ detector, corresponding to an integrated luminosity of int{L}dt=2.8/fb is used. The oscillation frequency Dms and the ratio |Vtd|/|Vts| are determined as Dms = (16.6 +0.5-0.4(stat) +0.4-0.3(sys)) 1/ps, |Vtd|/|Vts| = 0.213 +0.004-0.003(exp)pm 0.008(theor). These results are consistent with the standard model expectations and no evidence for new physics is observable.

Nanoscale surface properties and interaction with fundamental biomolecules of chlorite and phlogopite

The surface properties of minerals have important implications in geology, environment, industry and biotechnology and for certain aspects in the research on the origin of life. This research project aims to widen the knowledge on the nanoscale surface properties of chlorite and phlogopite by means of advanced methodologies, and also to investigate the interaction of fundamental biomolecules, such as nucleotides, RNA, DNA and amino acid glycine with the surface of the selected phyllosilicates. Multiple advanced and complex experimental approaches based on scanning probe microscopy and spatially resolved spectroscopy were used and in some cases specifically developed. The results demonstrate that chlorite exposes at the surface atomically flat terraces with 0.5 nm steps typically generated by the fragmentation of the octahedral sheet of the interlayer (brucitic-type). This fragmentation at the nanoscale generates a high anisotropy and inhomogeneity with surface type and isomorphous cationic substitutions determining variations of the effective surface potential difference, ranging between 50-100 mV and 400-500 mV, when measured in air, between the TOT surface and the interlayer brucitic sheet. The surface potential was ascribed to be the driving force of the observed high affinity of the surface with the fundamental biomolecules, like single molecules of nucleotides, DNA, RNA and amino acids. Phlogopite was also observed to present an extended atomically flat surface, featuring negative surface potential values of some hundreds of millivolts and no significant local variations. Phlogopite surface was sometimes observed to present curvature features that may be ascribed to local substitutions of the interlayer cations or the presence of a crystal lattice mismatch or structural defects, such as stacking faults or dislocation loops. Surface chemistry was found similar to the bulk. The study of the interaction with nucleotides and glycine revealed a lower affinity with respect to the brucite-like surface of chlorite.

Patterns in and kinetics of phase separation in binary mixtures

This work focused mainly on two aspects of kinetics of phase separation in binary mixtures. In the first part, we studied the interplay of hydrodynamics and the phase separation of binary mixtures. A considerably flat container (a laterally extended geometry), at an aspect ratio of 14:1 (diameter: height) was chosen, so that any hydrodynamic instabilities, if they arise, could be tracked. Two binary mixtures were studied. One was a mixture of methanol and hexane, doped with 5% ethanol, which phase separated under cooling. The second was a mixture of butoxyethanol and water, doped with 2% decane, which phase separated under heating. The dopants were added to bring down the phase transition temperature around room temperature.rnrnAlthough much work has been done already on classical hydrodynamic instabilities, not much has been done in the understanding of the coupling between phase separation and hydrodynamic instabilities. This work aimed at understanding the influence of phase separation in initiating any hydrodynamic instability, and also vice versa. Another aim was to understand the influence of the applied temperature protocol on the emergence of patterns characteristic to hydrodynamic instabilities. rnrnOn slowly cooling the system continuously, at specific cooling rates, patterns were observed in the first mixture, at the start of phase separation. They resembled the patterns observed in classical Rayleigh-Bénard instability, which arises when a liquid continuously is heated from below. To suppress this classical convection, the cooling setup was tuned such that the lower side of the sample always remained cooler by a few millikelvins, relative to the top. We found that the nature of patterns changed with different cooling rates, with stable patterns appearing for a specific cooling rate (1K/h). On the basis of the cooling protocol, we estimated a modified Rayleigh number for our system. We found that the estimated modified Rayleigh number is near the critical value for instability, for cooling rates between 0.5K/h and 1K/h. This is consistent with our experimental findings. rnrnThe origin of the patterns, in spite of the lower side being relatively colder with respect to the top, points to two possible reasons. 1) During phase separation droplets of either phases are formed, which releases a latent heat. Our microcalorimetry measurements show that the rise in temperature during the first phase separation is in the order of 10-20millikelvins, which in some cases is enough to reverse the applied temperature bias. Thus phase separation in itself initiates a hydrodynamic instability. 2) The second reason comes from the cooling protocol itself. The sample was cooled from above and below. At sufficiently high cooling rates, there are situations where the interior of the sample is relatively hotter than both top and bottom of the sample. This is sufficient to create an instability within the cell. Our experiments at higher cooling rates (5K/h and above) show complex patterns, which hints that there is enough convection even before phase separation occurs. Infact, theoretical work done by Dr.Hayase show that patterns could arise in a system without latent heat, with symmetrical cooling from top and bottom. The simulations also show that the patterns do not span the entire height of the sample cell. This is again consistent with the cell sizes measured in our experiment.rnrnThe second mixture also showed patterns at specific heating rates, when it was continuously heated inducing phase separation. In this case though, the sample was turbid for a long time until patterns appeared. A meniscus was most probably formed before the patterns emerged. We attribute the reason of patterns in this case to Marangoni convection, which is present in systems with an interface, where local differences in surface tension give rise to an instability. Our estimates for the Rayleigh number also show a significantly lower number than that's required for RB-type instability.rnrnIn the first part of the work, therefore, we identify two different kinds of hydrodynamic instabilities in two different mixtures. Both are observed during, or after the first phase separation. Our patterns compare with the classical convection patterns, but here the origins are from phase separation and the cooling protocol.rnrnIn the second part of the work, we focused on the kinetics of phase separation in a polymer solution (polystyrene and methylcyclohexane), which is cooled continuously far down into the two phase region. Oscillations in turbidity, denoting material exchange between the phases are seen. Three processes contribute to the phase separation: Nucleation of droplets, their growth and coalescence, and their subsequent sedimentation. Experiments in low molecular binary mixtures had led to models of oscillation [43] which considered sedimentation time scales much faster than the time scales of nucleation and growth. The size and shape of the sample therefore did not matter in such situations. The oscillations in turbidity were volume-dominated. The present work aimed at understanding the influence of sedimentation time scales for polymer mixtures. Three heights of the sample with same composition were studied side by side. We found that periods increased with the sample height, thus showing that sedimentation time determines the period of oscillations in the polymer solutions. We experimented with different cooling rates and different compositions of the mixture, and we found that periods are still determined by the sample height, and therefore by sedimentation time. rnrnWe also see that turbidity emerges in two ways; either from the interface, or throughout the sample. We suggest that oscillations starting from the interface are due to satellite droplets that are formed on droplet coalescence at the interface. These satellite droplets are then advected to the top of the sample, and they grow, coalesce and sediment. This type of an oscillation wouldn't require the system to pass the energy barrier required for homogenous nucleation throughout the sample. This mechanism would work best in sample where the droplets could be effectively advected throughout the sample. In our experiments, we see more interface dominated oscillations in the smaller cells and lower cooling rates, where droplet advection is favourable. In larger samples and higher cooling rates, we mostly see that the whole sample becomes turbid homogenously, which requires the system to pass the energy barrier for homogenous nucleation.rnrnOscillations, in principle, occur since the system needs to pass an energy barrier for nucleation. The height of the barrier decreases with increasing supersaturation, which in turn is from the temperature ramp applied. This gives rise to a period where the system is clear, in between the turbid periods. At certain specific cooling rates, the system can follow a path such that the start of a turbid period coincides with the vanishing of the last turbid period, thus eliminating the clear periods. This means suppressions of oscillations altogether. In fact we experimentally present a case where, at a certain cooling rate, oscillations indeed vanish. rnrnThus we find through this work that the kinetics of phase separation in polymer solution is different from that of a low molecular system; sedimentation time scales become relevant, and therefore so does the shape and size of the sample. The role of interface in initiating turbid periods also become much more prominent in this system compared to that in low molecular mixtures.rnrnIn summary, some fundamental properties in the kinetics of phase separation in binary mixtures were studied. While the first part of the work described the close interplay of the first phase separation with hydrodynamic instabilities, the second part investigated the nature and determining factors of oscillations, when the system was cooled deep into the two phase region. Both cases show how the geometry of the cell can affect the kinetics of phase separation. This study leads to further fundamental understandings of the factors contributing to the kinetics of phase separation, and to the understandings of what can be controlled and tuned in practical cases. rn

Mechanical behavior of flat and curved laminates interleaved by electrospun nanofibers

A major weakness of composite materials is that low-velocity impact, introduced accidentally during manufacture, operation or maintenance of the aircraft, may result in delaminations between the plies. Therefore, the first part of this study is focused on mechanics of curved laminates under impact. For this aim, the effect of preloading on impact response of curved composite laminates is considered. By applying the preload, the stress through the thickness and curvature of the laminates increased. The results showed that all impact parameters are varied significantly. For understanding the contribution rate of preloading and pre-stress on the obtained results another test is designed. The interesting phenomenon is that the preloading can decrease the damaged area when the curvature of the both specimens is the same. Finally the effect of curvature type, concave and convex, is investigated under impact loading. In the second part, a new composition of nanofibrous mats are developed to improve the efficiency of curved laminates under impact loading. Therefore, at first some fracture tests are conducted to consider the effect of Nylon 6,6, PCL, and their mixture on mode I and mode II fracture toughness. For this goal, nanofibers are electrospun and interleaved between mid-plane of laminate composite to conduct mode I and mode II tests. The results shows that efficiency of Nylon 6,6 is better than PCL in mode II, while the effect of PCL on fracture toughness of mode I is more. By mixing these nanofibers the shortage of the individual nanofibers is compensated and so the Nylon 6,6/PCL nanofibers could increased mode I and II fracture toughness. Then all these nanofibers are used between all layers of composite layers to investigate their effect on damaged area. The results showed that PCL could decrease the damaged area about 25% and Nylon 6,6 and mixed nanofibers about 50%.