Elastic Constants And Structural Parameters Of Selected Polycrystalline Ceramics By Ultrasonic Technique

The present work is an attempt to probe the elastic properties in some dielectric ceramics, by using ultrasonic pulse echo overlap technique. The base Ba6-xSm8+2xTi18O54 and Ca5Nb2TiO12 are very important dielectrics ceramics used for microwave communication as well as for substrate materials. Ultrasonic is one of the most widely used and powerful techniques to measure elastic properties of solids. The ultrasonic technique is nondestructive in nature and the measurements are relatively straightforward to perform. One unique advantantage of the ultrasonic technique is that both static and dynamic properties can be measured simultaneously. The velocity and attenuation coefficients of the ultrasonic waves propagating through a medium are related to the microscopic structure of the material and they provide valuable information about the structural changes in the system. Among the various ultrasonic techniques, the pulse echo overlap method is the most accurate and precise one. In the present case the decreased elastic properties of Cas-XMg,Nb2TiO12 and Cas-,ZnNb2TiO12 ceramics can be attributed to their mixture phases beyond x = 1. Moreover, the abrupt change in elastic properties observed for x >1 can also be correlated to the structural transformation of the materials from their phase pure form to mixture phases for higher extent of substitution of the concerned material . Ca4(ANb2Ti)012 (A = Mg, Zn) is the strongest compound with the maximum values for elastic properties . This could be due to the possible substitution of Mg/Zn ions with lesser radius [25] than Ca2+ in perovskite B-site of Ca(Cali4Nb2i4Tili4) O3 material to contribute more ordering and symmetry to the system [20]. All other compositions (x > 1) contain mixed-phases and for such mixed-phase samples, the mechanical properties are difficult to explain.

Modification of Polypropylene and Polystyrene Using Nanosilica

The present work focuses on the modification of the commonly used thermoplastics, polypropylene and polystyrene using nanosilica preparcd from a cheap source of sodium silicate. Melt compounding technique has been used for nanocomposite preparation as it is simple and suited to injection moulding. Nanosilica in a polymer matrix provide significant enhancement in strength, stiffness and impact strength. Incorporation of silica particles in a polymer also improves its thennal stability. To achieve better dispersion of fillers in polymer matrices the mixing was done at different shear rates. The enhancement in material properties indicates that at higher shear rates there is greater interaction between particles and the matrix and it depends on filler concentration and type of polymer used. N anosilica is a useful filler in thennoplastic polymers and has been applied in automotive applications, electronic appliances and consumer goods.This thesis is divided into six chapters. General introduction to the topic is described in chapter 1. Salient features of polymer nanocomposites, their synthesis, properties and applications are presented. A review of relevant literature and the scope and objectives are also mentioned in this chapter.The materials used and the vanous experimental method and techniques employed in the study are described in chapter 2. Preparation of nanocomposites by melt blending using Thenno Haake Rheocord, preparation of samples, evaluation of mechanical and thennal properties using UTM, Impact testing and characterization using DMA, TGA and DSC and morphology by SEM are described.The preparation of nanosilica from a laboratory scale to a pilot plant scale is described in chapter 3. Generation of surface modified silica, evaluation of kinetic parameters of the synthesis reaction, scale up of the reactor and modeling of the reactor are also dealt with in this chapter.The modification of the commodity thennoplastic, Polypropylene using nanosilica is described in chapter 4. Preparation of PP/silica nanocomposites, evaluation of mechanical properties, thermal and crystallization characteristics, water absorption and ageing resistance studies are also presented.The modification of Polystyrene using synthesized nanosilica IS described in chapter 5. The method of preparation of PS/silica nanocomposites, evaluation of mechanical properties (static and dynamic), thermal properties melt flow characteristics using Haake Rheocord, water absorption and ageing resistance of these nanocomposites are studied.

Energy-Efficient Cluster based Routing Schemes for Static and Mobile Sensor Networks

The theme of the thesis is centred around one important aspect of wireless sensor networks; the energy-efficiency.The limited energy source of the sensor nodes calls for design of energy-efficient routing protocols. The schemes for protocol design should try to minimize the number of communications among the nodes to save energy. Cluster based techniques were found energy-efficient. In this method clusters are formed and data from different nodes are collected under a cluster head belonging to each clusters and then forwarded it to the base station.Appropriate cluster head selection process and generation of desirable distribution of the clusters can reduce energy consumption of the network and prolong the network lifetime. In this work two such schemes were developed for static wireless sensor networks.In the first scheme, the energy wastage due to cluster rebuilding incorporating all the nodes were addressed. A tree based scheme is presented to alleviate this problem by rebuilding only sub clusters of the network. An analytical model of energy consumption of proposed scheme is developed and the scheme is compared with existing cluster based scheme. The simulation study proved the energy savings observed.The second scheme concentrated to build load-balanced energy efficient clusters to prolong the lifetime of the network. A voting based approach to utilise the neighbor node information in the cluster head selection process is proposed. The number of nodes joining a cluster is restricted to have equal sized optimum clusters. Multi-hop communication among the cluster heads is also introduced to reduce the energy consumption. The simulation study has shown that the scheme results in balanced clusters and the network achieves reduction in energy consumption.The main conclusion from the study was the routing scheme should pay attention on successful data delivery from node to base station in addition to the energy-efficiency. The cluster based protocols are extended from static scenario to mobile scenario by various authors. None of the proposals addresses cluster head election appropriately in view of mobility. An elegant scheme for electing cluster heads is presented to meet the challenge of handling cluster durability when all the nodes in the network are moving. The scheme has been simulated and compared with a similar approach.The proliferation of sensor networks enables users with large set of sensor information to utilise them in various applications. The sensor network programming is inherently difficult due to various reasons. There must be an elegant way to collect the data gathered by sensor networks with out worrying about the underlying structure of the network. The final work presented addresses a way to collect data from a sensor network and present it to the users in a flexible way.A service oriented architecture based application is built and data collection task is presented as a web service. This will enable composition of sensor data from different sensor networks to build interesting applications. The main objective of the thesis was to design energy-efficient routing schemes for both static as well as mobile sensor networks. A progressive approach was followed to achieve this goal.

Competitive strategy revisited: contested concepts and dynamic capabilities

Strategy is a contested concept. The generic literature is characterized by a diverse range of competing theories and alternative perspectives. Traditional models of the competitive strategy of construction firms have tended to focus on exogenous factors. In contrast, the resource-based view of strategic management emphasizes the importance of endogenous factors. The more recently espoused concept of dynamic capabilities extends consideration beyond static resources to focus on the ability of firms to reconfigure their operating routines to enable responses to changing environments. The relevance of the dynamics capabilities framework to the construction sector is investigated through an exploratory case study of a regional contractor. The focus on how firms continuously adapt to changing environments provides new insights into competitive strategy in the construction sector. Strong support is found for the importance of path dependency in shaping strategic choice. The case study further suggests that strategy is a collective endeavour enacted by a loosely defined group of individual actors. Dynamic capabilities are characterized by an empirical elusiveness and as such are best construed as situated practices embedded within a social and physical context.

On the localization of water-soluble porphyrins in micellar systems evaluated by static and time-resolved frequency-domain fluorescence techniques

Fluorescence quenching of meso-tetrakis-4-sulfonatophenyl (TPPS4) and meso-tetrakis-4-N-methylpyridil (TMPyP) porphyrins is studied in aqueous solution and upon addition of micelles of sodium dodecylsulfate (SDS), cetyltrimethylammonium chloride (CTAC), N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and t-octylphenoxypolyethoxyethanol (Triton X-100). Potassium iodide (KI) was used as quencher. Steady-state Stern-Volmer plots were best fitted by a quadratic equation, including dynamic (K-D) and static (K-s) quenching. Ks was significantly smaller than K-D. Frequency-domain fluorescence lifetimes allowed estimating bimolecular quenching constants, k(q). At 25 degrees C, in aqueous solution, TMPyP shows k(q), values a factor of 2-3 higher than the diffusional limit. TPPS4 shows collisional quenching with pH dependent k(q) values. For TMPyP quenching results are consistent with reported binding constants: a significant reduction of quenching takes place for SDS, a moderate reduction is observed for H PS and almost no change is seen for Triton X-100. Similar data were obtained at 50 C. For CTAC-TPPS4 system an enhancement of quenching was observed as compared to pure buffer. This is probably associated to accumulation of iodide at the cationic micellar interface. The attraction between CTAC headgroups and 1(-), and repulsion between SDS and 1(-), enhances and reduces the fluorescence quenching, respectively, of porphyrins located at the micellar interface. The small quenching of TPPS4 in Triton X-100 is consistent with strong binding as reported in the literature. (C) 2008 Elsevier B.V. All rights reserved.

Evaluation of stitched fabric composite processed by RTM in quasi-static test

Stitched fabrics have been widely studied for potential application in aircraft structures since stitch yarns offer improvements in the out-of-plane mechanical properties and also can save time in the lay up process. The down side of stitch yarns came up in the manufacturing process of fabric in which defects introduced by the needle movement creating fiber-free-zones, fiber breakage and misalignment of fibers. The dry stitched carbon fabric preform has mainly been used in the Resin Transfer Molding (RTM) process which high fiber content is aimed, those defects influence negatively the injection behavior reducing the mechanical properties of final material. The purpose of this research work focused on testing in quasi-static mechanical mode (in-plane tension) of a monocomponent resin CYCOM (R) 890 RTM/carbon fiber anti-symmetric quadriaxial fabric stitched by PE 80Dtex yarn processed by RTM. The evaluation consisted in comparing the scatter of the quasi-static test with the attenuation of ultrasonic maps, which show the path of the resin and possible dry spots considering that interference of yarn in resin flow is detectable in ultrasonic measurement. Microscopic analysis was also considered for further evaluation in case of premature failure. (C) 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11

Preparation and thermal study of Mg-diclofenac compound in solid state

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Total secondary-electron yield of metals measured by a dynamic method

The secondary electron emission of dielectrics usually is measured by the pulse method, in which the dielectric is irradiated with short pulses of electrons. Attempts to use a dynamic method, in which the dielectric is irradiated continuously, have failed because the dielectric becomes charged and this charge interferes with the emission process. The dynamic method can, however, be applied to metals where volume charges are prevented. This article reports dynamic measurements of the total secondary emission yield from stainless steel, platinum, and aluminum and compares them with results from the current pulse method. In order to apply the dynamic method to metals a simple but important change in the setup was introduced: a dielectric slab was placed between the electrode and the metallic sample, which permitted the sample surface potential and therefore the energy of the incident electrons to change continuously. Unlike for dielectrics, the emission curves for metals are identical when obtained by the two methods. However, for a sample with deliberately oxidized surfaces the total secondary emission yield is smaller when measured with the dynamic method as compared with the pulse method, just as happens for dielectrics. (C) 2000 American Institute of Physics. [S0021-8979(00)03413-7].

Maize germ recovery and quality using the intermittent milling and dynamic steeping process

The intermittent milling and dynamic steeping (IMDS) process is an alternative method developed for wet milling of maize. In this process, the steeping stage can be reduced to 5 h by soaking maize in water at 60°C for 2 h and cracking the kernels to remove solution components diffusional barriers with minimum germ damage. Maize was dynamically steeped in solutions with 0.0, 0.1, and 0.2% sulphur dioxide (SO2) and 0.00, 0.55% lactic acid. Germ recovery, germ damage, fibre in germ, oil content and uncracked kernels were determined. A conventional steeping procedure was also performed. Germ recovery was higher for all tests using both SO2 and lactic acid than for the others with best germ yield for concentrations of 0.2% SO2 and 0.55% lactic acid. Germ damage ranged from 7.4 to 18.2% for all tests. The presence of lactic acid in the steeping solution decreased the amount of fibre in germ fraction. Germ oil content ranged from 39.3% (0-0% SO2, 0.55% lactic acid) to 44.0% (0.2% SO2, 0.55% lactic acid) for all treatments using IMDS. The smallest difference was 5.5% between IMDS (0.2% SO2, 0.55% lactic acid) and the conventional 36 h steeping process. An average of 1.3% of kernels remained uncracked after IMDS process. © 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved.

On Nonlinear Dynamics and Control of A Particular Portal Frame Foundation Model, Excited by a Non-Ideal Motor

The nonlinear dynamic response and a nonlinear control method of a particular portal frame foundation for an unbalanced rotating machine with limited power (non-ideal motor) are examined. Numerical simulations are performed for a set of control parameters (depending on the voltage of the motor) related to the static and dynamic characteristics of the motor. The interaction of the structure with the excitation source may lead to the occurrence of interesting phenomena during the forward passage through the several resonance states of the systems. A mathematical model having two degrees of freedom simplifies the non-ideal system. The study of controlling steady-state vibrations of the non-ideal system is based on the saturation phenomenon due to internal resonance.

Regional integration in Latin America and dynamic gains from macroeconomic cooperation

Includes bibliography

Uranium-lead dating method at the Pará-Iso isotope geology laboratory, UFPA, Belém – Brazil

ABSTRACT: Analytical procedures for U-Pb isotope dilution analyses at the Pará-Iso isotope geology laboratory of the Federal University of Pará (UFPA) are described in detail. The procedures are applied to zircon, titanite, rutile, apatite, columbite-tantalite and whole rock. Reagent preparation and chemical processing are done in clean-room conditions. Samples are dissolved using Teflon™ microcapsules in steel jacket Teflon™ Parr Instrument™ bomb or Teflon™ screw cap containers. U and Pb are separated using anion exchange AG 1x8 resin columns. Typical blanks for mineral sample amounts of 0.01 to 1.0 mg are less than 1 pg U and 20-30 pg Pb. Isotope analysis of the U and Pb from the same filament are carried out using a Finnigan MAT 262 mass-spectrometer in static and dynamic modes. The current analytical level is demonstrated on analyses of international standard zircon 91500 with three different ²³⁵U-²⁰⁵Pb and ²³⁵U-²⁰⁸Pb isotope tracers and whole rock standards. Results of analyses of two zircon samples are also presented.

ACUTE EFFECTS OF A WARM-UP INCLUDING ACTIVE, PASSIVE, AND DYNAMIC STRETCHING ON VERTICAL JUMP PERFORMANCE

Carvalho, FLP, Carvalho, MCGA, Simao, R, Gomes, TM, Costa, PB, Neto, LB, Carvalho, RLP, and Dantas, EHM. Acute effects of a warm-up including active, passive, and dynamic stretching on vertical jump performance. J Strength Cond Res 26(9): 2447-2452, 2012-The purpose of this study was to examine the acute effects of 3 different stretching methods combined with a warm-up protocol on vertical jump performance. Sixteen young tennis players (14.5 +/- 2.8 years; 175 +/- 5.6 cm; 64.0 +/- 11.1 kg) were randomly assigned to 4 different experimental conditions on 4 successive days. Each session consisted of a general and specific warm-up, with 5 minutes of running followed by 10 jumps, accompanied by one of the subsequent conditions: (a) Control Condition (CC)-5 minutes of passive rest; (b) Passive Stretching Condition (PSC)-5 minutes of passive static stretching; (c) Active Stretching Condition (ASC)-5 minutes of active static stretching; and (d) Dynamic Stretching Condition (DC)-5 minutes of dynamic stretching. After each intervention, the subjects performed 3 squat jumps (SJs) and 3 countermovement jumps (CMJs), which were measured electronically. For the SJ, 1-way repeated measures analysis of variance (CC x PSC x ASC x DC) revealed significant decreases for ASC (28.7 +/- 4.7 cm; p = 0.01) and PSC (28.7 +/- 4.3 cm; p = 0.02) conditions when compared with CC (29.9 +/- 5.0 cm). For CMJs, there were no significant decreases (p > 0.05) when all stretching conditions were compared with the CC. Significant increases in SJ performance were observed when comparing the DC (29.6 +/- 4.9 cm; p = 0.02) with PSC (28.7 +/- 4.3 cm). Significant increases in CMJ performance were observed when comparing the conditions ASC (34.0 +/- 6.0 cm; p = 0.04) and DC (33.7 +/- 5.5 cm; p = 0.03) with PSC (32.6 +/- 5.5 cm). A dynamic stretching intervention appears to be more suitable for use as part of a warm-up in young athletes.

Continuity and Change in New Products

This doctoral dissertation is triggered by an emergent problem: how can firms reinvent themselves? Continuity- and change-oriented decisions fundamentally shape overtime the activities and potential revenues of organizations and other adaptive systems, but both types of actions draw upon limited resources and rely on different organizational routines and capabilities. Most organizations appear to have difficulties in making tradeoffs, so that it is easier to overinvest in one of them than to successfully achieve a mixture of both. Nevertheless, theory and empirical evidence suggest that too little of either may reduce performance, indicating a need to learn more about how organizations reconcile these tensions. In the first paper, I moved from the consideration that rapid changes in competitive environments increasingly require firms to be “ambidextrous” implementing organizational mechanisms and structures that allow continuity- and change-oriented activities to be engaged at the same time. More specifically, I show that continuity- and change-related decisions can’t be confined either inside or outside the firm, but span overtime across distinct decision domains located within and beyond the organizational boundaries. Reconciling static and dynamic perspectives of ambidexterity, I conceptualize a firm’s strategy as a bundle of decisions about product attributes and components of the production team, proposing a multidimensional and dynamic model of structural ambidexterity that explains why and how firms could manage conflicting pressures for continuity and change in the context of new products. In the second study I note how rigorous systematic evidence documenting the success of ambidextrous organizations is lacking, and there has been very little investigation of how firms deal with continuity and change in new products. How to manage the transition form a successful product to another? What to change and what to keep? Incumbents that deal with series of products over time need to update their offerings in order to have the most relevant attributes to prospect clients without disappoint the current customer base. They need to both match and anticipate consumers’ preferences, blending something old with something new to satisfy the current demand and enlarge the herd by appealing to newer audiences. This paper contributes to strategic renewal and ambidexterity-related research with the first empirically assessment of a positive consumer response to ambidexterity in new products. Also, this study provides a practical method to monitor overtime the degree to which a brand or a firm is continuity- or change- oriented and evaluate different strategy profiles across two decision domains that play a pivotal role in new products: product attributes and components of the production team.

Stochastic models and dynamic measures for the characterization of bistable circuits

During the last few years, a great deal of interest has risen concerning the applications of stochastic methods to several biochemical and biological phenomena. Phenomena like gene expression, cellular memory, bet-hedging strategy in bacterial growth and many others, cannot be described by continuous stochastic models due to their intrinsic discreteness and randomness. In this thesis I have used the Chemical Master Equation (CME) technique to modelize some feedback cycles and analyzing their properties, including experimental data. In the first part of this work, the effect of stochastic stability is discussed on a toy model of the genetic switch that triggers the cellular division, which malfunctioning is known to be one of the hallmarks of cancer. The second system I have worked on is the so-called futile cycle, a closed cycle of two enzymatic reactions that adds and removes a chemical compound, called phosphate group, to a specific substrate. I have thus investigated how adding noise to the enzyme (that is usually in the order of few hundred molecules) modifies the probability of observing a specific number of phosphorylated substrate molecules, and confirmed theoretical predictions with numerical simulations. In the third part the results of the study of a chain of multiple phosphorylation-dephosphorylation cycles will be presented. We will discuss an approximation method for the exact solution in the bidimensional case and the relationship that this method has with the thermodynamic properties of the system, which is an open system far from equilibrium.In the last section the agreement between the theoretical prediction of the total protein quantity in a mouse cells population and the observed quantity will be shown, measured via fluorescence microscopy.