Assessment of FEMA356 nonlinear static procedure and modal pushover analysis for seismic evaluation of buildings

Nonlinear static analysis as an essential part of performance based design is now widely used especially at design offices because of its simplicity and ability to predict seismic demands on inelastic response of buildings. Since the accuracy of nonlinear static procedures (NSP) to predict seismic demands of buildings affects directly on the entire performance based design procedure, therefore lots of research has been performed on the area of evaluation of these procedures. In this paper, one of the popular NSP, FEMA356, is evaluated and compared with modal pushover analysis. The ability of these procedures to simulate seismic demands in a set of reinforced concrete (RC) buildings is explored with two level of base acceleration through a comparison with benchmark results determined from a set of nonlinear time history analyses. According to the results of this study, the modal pushover analysis procedure estimates seismic demands of buildings like inter story drifts and hinges plastic rotations more accurate than FEMA356 procedure

A Novel Modal Analysis Method Based on Fuzzy Sets

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.A novel method of vibration modelling is proposed in this thesis. This method involves estimating the mode shapes of a general structure and describing these shapes in terms of fuzzy membership functions. These estimations or initial guesses are based on engineerâ s experience or physical insight into natural mode shapes assisted by end and boundary conditions and some rules. The guessed mode shapes were referred to as Mode Shape Forms (MSFs). MSFs are approximate mode shapes, therefore there are uncertainties involve with their values where this uncertainty is expressed by fuzzy sets. The deflection or displacement magnitude of the mode shape forms are described with Zero, Medium, and Large fuzzy linguistic terms and constructed using fuzzy membership functions and rules. Fuzzy rules are introduced for each MSF. In that respect fuzzy membership functions provides a means of dealing with uncertainty in measured data, it gives access to a large repertoire of tools available in fuzzy reasoning field. The second stage of the process addresses the issues of updating these curves by experimental data. This involves performing experimental modal analysis. The mode shapes derived from experimental FRFs collect a limited number of sampling points. When the fuzzy data is updated by experimental data, the method proposes that the points of the fuzzy data correspond to the sampling points of FRF are to be replaced by the experimental data. Doing this creates a new fuzzy curve which is the same as the previous one, except at those points. In another word a â spikedâ version of the original fuzzy curve is obtained. In the last stage of this process, neural network is used to â learnâ the spiked curve. By controlling the learning process (by preventing it from overtraining), an updated fuzzy curve is generated that is the final version of the mode shape. Examples are presented to demonstrate the application of the proposed method in modelling of beams, a plate and a structure (a three beams frame). The method is extended to evaluate the error where a wrong MSF is assumed for the mode shape. In this case the method finds the correct MSF among available guessed MSFs. A further extension of the method is proposed for cases where there is no guess available for the mode shape. In this situation the â closestâ MSF is selected among available MSFs. This MSF is modified by correcting the fuzzy rules that is used in constructing of the fuzzy MSF. Using engineering experience, heuristic knowledge and the developed MSF rules in this method are the capabilities that cannot be provided with any artificial intelligent system. This provides additional advantage relative to vibration modelling approaches that have been developed until now. Therefore this method includes all aspects of an effective analysis such as mixed artificial intelligence and experimental validation, plus human interface/intelligence. Another advantage is, MSF rules provide a novel approach in vibration modelling where enables the method to start and operate with unknown input parameters such as unknown material properties and imprecise structure dimensions. Hence the classical computational procedures of obtaining the vibration behaviour of the system, from these inputs, are not used in this approach. As a result, this method avoids the time consuming computational procedure that exhibit in existing vibration modelling methods. However, the validation procedure, using experimental tests (modal testing) is the same acceptable procedure that is used in any other available methods which proves the accuracy of the method. (This thesis was published in Dec 2005

Polymer Foam /Fly Ash Composites: Evaluation of Mechanical, Interfacial, Thermal, Viscoelastic and Microstructural Properties

Fly ash, a byproduct of coal combustion process in power plants, consists of fine, powdery particles that are predominantly spherical in shape, either solid or hollow, and mostly glassy (amorphous) in nature. It is capable of being recovered and used as a low-cost reinforcing filler. Adding fly ash particles to a thermoplastic foam poses many challenges to understanding the physical, mechanical, viscoelastic, thermal, and morphological changes to the composite. The effects of fly ash particles on the foaming process; e.g. nucleating and growth steps, cell types and size, and microstructure need to be evaluated in order to develop a commercial composite material. The main goal of this work is to evaluate the use of fly ash as a cost-effective and reinforcing filler in polymer foam composites. PVC foam is selected as the base polymer and it is expected that the research findings can be generalized to other polymer foam systems. Initially, two classes of fly ash, class-C and class-F (two different particle sizes) are well characterized and studied. Their elemental, chemical, structural, thermal and morphological properties are evaluated. Although both classes of fly ash have almost the same surface area, Class-C contains more quartz and lime content than class-F; whereas class-F is highly concentrated with iron oxides. In addition, 25 micron sized class-F fly ash possesses different chemical composition compared with 50 micron class-F fly ash. Structural analysis showed the presence of hydroxyl functional groups in both types of fly ash particles. In the second phase, PVC foam/fly ash composites containing various levels of fly ash are prepared using extrusion as a processing method. To understand all performance aspects of fly ash, a wide range of characterizing methods was used to evaluate the physical, mechanical, thermal, and morphological properties of the composites. The experimental results showed that the density increases with increasing the amount of fly ash, while the cell size decreases. Tensile and flexural properties increased by adding fly ash, which indicates that fly ash particles are properly incorporated into the polymer. However, the elongation and impact strength of the composites decreased with increasing fly ash due to the higher rigidity of the polymer composites. Thermal analysis shows that the glass transition temperature of the composites is not significantly affected by the addition of fly ash. Thermal decomposition studies show that the dehydrochlorination of PVC is accelerated in the presence of fly ash, while the main backbone crack is enhanced. Kinetic studies were carried out on the loaded and unloaded fly ash composites and the activation energies of both decomposition steps were estimated using Flynn-Wall model. A higher activation energy in the first step of decomposition of the pure PVC foam is noticed compared with that of fly ash loaded, while the estimated activation energy of the second step in the composites is significantly higher. Dynamic mechanical analysis confirmed the increase in stiffness as fly ash content increased in the composites due to good interfacial adhesion between the filler and the matrix. Dimensional stability of the composites improved considerably with the addition of fly ash at high loadings and morphological studies confirmed good dispersion, distribution, and interaction between fly ash and PVC matrix. The effect of the chemical composition of fly ash on the final properties of the foam composites are studied using both classes of fly ash, C and F. The experimental results show that class-C fly ash interacts better with the polymer matrix and improves the mechanical and thermal properties significantly when compared to class-F. This is attributed to a higher SiO2 and CaO content in class-C fly ash. Interfacial interaction of the composites reinforced with both classes of fly ash was estimated using Pukanszky model to confirm. Structural analysis confirmed the presence of hydroxyl (–OH) functional groups on the surface of SiO2, which plays a significant role in the formation of physical bonding and therefore interfacial interactions between fly ash particles and the polymer matrix. Morphological studies of the fracture surfaces using SEM/EDS line-scan also confirmed the effectiveness of silicon and calcium elements in the properties improvement due to their high concentration in the well-bonded particles. The effect of the particle size of fly ash on the composites structure and performance was also evaluated. Two pre-sieved fly ash particles in the size range of 25 micron and 50 micron were used to prepare rigid PVC/fly ash composites and examine the dependency of the composites performance on the filler size and composition. It was found that at the same fly ash loadings (10wt%), 25 micron sized loaded composites show better mechanical properties due to their higher surface area and the amount of hydroxyl groups. The interfacial interaction between the two different fly ash particle sizes with rigid PVC was evaluated experimentally, using nanoindentor, and quantitatively, using models developed by Pukanszky and Kubat. Recyclability and reprocess-ability of the fly ash filled composites were also investigated. The experimental results achieved by processing measurements showed that the maximum and minimum torque values increase by adding more regrind. Whereas, increasing fly ash content decreases the melt viscosity and improves processability. It was also observed that the mechanical properties of the reprocessed composites improve by adding more regrind, which indicates a good gelation in the composites containing both virgin and regrind of PVC/fly ash foam. SEM images confirmed a good level of mixing and gelation between virgin and regrind foam matrix up to 40wt% regrind content

Two Essays on Investors\u27 Attention to Economically Linked Firms

My first essay examines the degree to which the market prices of publicly traded firms reflect and respond to new information regarding the economic viability and vitality of organizations to which they are strategically linked. More specifically, I exploit the uniquely transparent nature of the lessor-lessee relationship across commercial real estate markets to evaluate whether future returns to real estate investment trusts (REITs) are systematically affected by the financial return performance and/or operational opacity of the tenants who lease their investment properties. Using a hand collected data set identifying the principal tenants of 96 publicly traded REITs, I find those firms with the best performing tenants generate annualized abnormal returns which are approximately six percent higher than those realized by REITs with the worst performing tenants. These results are robust to a variety of model specifications, and a closer inspection of the results reveals these performance differentials are consistent with emerging evidence across the literature suggesting investors\u27 limited attention materially influences the return predictability of assets. With respect to the current investigation, I thus conclude investors\u27 limited attention leads to the failure of REIT prices to fully reflect the valuation implications of their tenants\u27 return performance. My second essay investigates how sophisticated investors, such as short sellers, trade on information along the supply chain. Short sellers are known to be generally better informed than common investors. Given the economic linkages that exist between the suppliers and customers, one would expect short sellers to trade on such information. My results indicate that short interest predicts unexpected earnings news, consistent with short sellers extracting information from economic relationships. When I evaluate stock return and short interests in regression analysis, I find strong negative relation between short interest in supplier firm and the future stock returns for the customer firm for the return in the next month. The negative relation persists for twelve months. I find similar results from portfolio approach. I argue that one plausible channel that explains the information content of supplier (customer) firm\u27s short interest for the customer (supplier) firms is short sale constraints on the customer (supplier) firms. My results are consistent with this explanation. Overall, my findings suggest that short sellers play an important role in the price discovery of related firms on supply chain, beyond their direct effects documented previously

Adjuvant tamoxifen in breast cancer : clinical and preclinical studies on the prediction value of estrogen receptor

Breast cancer (BC) exhibits great heterogeneity at histophatological, clinical and molecular levels. However, the different clinical outcomes in patients with seemingly similar breast cancer have led scientists to search for subgroups or for factors and characteristics related to the tumor or the patient that could anticipate clinical course (prognosis) of disease and/or response to given therapy (prediction). Estrogen receptor (ER) is the first molecule identified that has had great influence on the management of breast cancer. This thesis focuses on the role of ER and its significance in breast cancer. In one study, we compared the potential of ER-positive tamoxifen sensitive cells (MCF-7) versus ER- negative cells (MDA-231) to handle DNA repair, transmit signals from DNA damage, initiate apoptosis, control transmitted signals from the cell cycle and synthesize growth factors and receptors. Genes related to these processes were studied by cDNA microarray. We found that the ER-negative cells were characterized by a higher expression of growth factors and cell cycle regulation components, and improved DNA repair. We explored the long-term pattern of disease recurrence among pre-and post-menopausal patients with primary BC according to ER status. The patients were randomly given tamoxifen versus no systemic therapy. The results showed a reduction of locoregional, distant metastases and breast cancer death in ER-positive patients who received tamoxifen. The pattern of metastases was not different in these two groups. The conclusion was that the differences in term of gene expression appeared mainly to be related to endocrine sensitivity and not metastatic potential. Some more events in the first 5 years in ER-negative patients suggested that ER negativity in some cases is correlated with an increased tumour growth rate. ER had been measured by cytosol assays prior to around 1990 when these assays substituted of immunohistochemical (IHC) assay. However, ER predictive ability of response to tamoxifen has been assessed based on ER measurement by cytosol assays. We compared these two assays in a clinical trial and found a high concordance between the assays and concluded that IHC is as accurate as cytosol assays to predict long term response to adjuvant tamoxifen. The introduction of microarray technique a decade ago already has changed our knowledge of BC but it has some pitfalls that question its potential. In two methodical studies we showed the importance of tissue handling, the effect of heterogeneity of BC and standardization on the result from cDNA microarray. This thesis confirms the importance of ER in BC but also indicates a more complex phenotypic beyond that which can be explained purely by ER content or endocrine sensitivity. Microarray technique can provide useful information besides the traditional one but requires standardization of sample collection, storage, processing, normalization, interpretation of data and requires validation by large studies

The Effect of Interaction through Social Networks Sites on Learning English in Iranian EFL Context

This study aims to investigate the effect of interaction in social network websites on enhancing acquisition of English language in students studying in language institutes. Since the emergence of Social Network Sites (SNS) in 2005, they have been potentially affective in area of education in general and foreign language learning in particular. Language learners may use social networks sites (SNS) as a mean to get engaged and motivated in meaningful communicative situations. This study was conducted among 40 active and regular EFL intermediate level EFL learners in Qalame Bartar Language institute joining a Facebook group who are familiar with using computer and internet as participants of the study. The data were collected from the learners’ interactional exchanges in the weekly posts, from social interaction and discussion in SNSs; research conducted in related subject and the tests given to these participants after using SNS for 60 days. Based on data analysis, the EFL learners’ language learning skills in the treatment group highly increased during this period in comparison to the control group. The findings indicate interaction through SNS putting learner in real communicative situations plays an important role in enhancing the development of foreign language learning

Effect of Cenosphere Fly Ash on the Thermal, Mechanical, and Morphological Properties of Rigid PVC Foam Composites

Cenosphere fly ash is a byproduct of coal combustion processes of power plants. It is composed of hollow, hard shelled, minute spheres, which are made up of silica, iron, and alumina. In this study, cenosphere fly ash is incorporated into rigid PVC foam to improve thermal and mechanical properties of their composites. Microstructural, physical, mechanical, and thermal properties of rigid PVC foam extruded with different loadings of cenosphere fly ash (6, 12, 18phr) are characterized. The measured density of the extruded PVC foam composites increased with cenosphere content, indicating a hindrance to the foaming process. Tensile and flexural mechanical properties improved at higher cenosphere content, while the impact strength decreased at initial loading of 6 phr of cenosphere particles and remained steady at higher loadings. Thermal characterization of the extruded samples showed that glass transition temperature remained almost unaffected, while TGA analysis revealed no change in the initial degradation temperature and significant improvement in the final degradation temperature. Thermo-mechanical properties measured by DMA revealed a remarkable improvement in the viscoelastic properties of the composites reinforced with cenosphere particles. SEM analysis of the composites microstructure confirmed that the cenosphere particles were mechanically interlocked with good interfacial interaction in the PVC matrix

The Effect of Computer Assisted Language Learning (CALL) Program on Learning Vocabulary among EFL Left and Right Hemispheric Dominant Learners

Vocabulary is a core component of language proficiency, and provides much of the basis for how well learners speak, listen, read, and write. Without  an extensive vocabulary and strategies  for acquiring new vocabulary, learners often achieve less than their potential and may be discouraged from making use  of  language learning  opportunities around them  such  as  listening  to  the radio, listening to native  speakers,  using  the  language  in  different  contexts,  reading  or  watching  television. CALL refers to the use of computer in the teaching and learning of a second or foreign language. The field of CALL includes the use of a computer in the language process. CALL programs aims to teach students in aspects of the language learning process via the medium of computers. Unfortunately, in Iran, textbook writers and syllabus designers have paid less attention to the role played by the CALL in classrooms. Teaching is not supplemented with modern technologies, specially CALL in teaching English. The use of Computer Assisted Language Learning (CALL) in the field of education has increased remarkably in recent years due to the modern changes in language software. However, CALL is not widely employed in the field of second/foreign (L2) language learning in Iran.  Interested in the application of CALL,  this  study  examines  two  methods  of  vocabulary  teaching/learning  (CALL-based  versus  non-CALL based). For this purpose, 38 male and 48 female elementary Iranian EFL learners participate in the study. They are randomly assigned into CALL-users   and non-CALL users and posttest control group design is employed.  To  collect data,  a proficiency  test will be used to homogenize the participants and  a multiple-choice vocabulary test  will be  used  as  posttests  to  find  out  the  effectiveness  of  the  methods. Finally, The results of  t-tests and the  pedagogical implications  of  this  study  for  L2  teachers  and learners will be presented

Modeling and Design of a Highly Efficient Switch-Mode RF/Microwave Power Amplifier Based-on Microstrip Bandpass Filter

This paper presents a broadband Switch-Mode Power Amplifier (SMPA) using a Band-Pass Filter (BPF) at the Output Matching Network (OMN). The proposed SMPA integrates a microstrip BPF as an output impedance matching network to significantly reduce the final circuit size. The microstrip lines of the filter simultaneously play the role of filtering and impedance matching. This proposed method reduces the size of the PA and reduces the power dissipation as much as possible. The BPF is placed at the output of the circuit using microstrip lines and the RT Duroid 6006 substrate. This BPF covers a wide bandwidth ranging from 3.0 GHz to 4.4 GHz. Simulation results show 9 – 14 dB gain with 44 – 56.6 % drain efficiency (DE %), and the output power of 39 – 41.3 dBm would be achieved across the frequency band from 3.0 GHz to 4.4 GHz