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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
411

Whispering-Gallery Modes in Quantum Dot Embedded Microspheres for Sensing Applications

Beier, Hope T. 2009 December 1900 (has links)
New methods of biological analyte sensing are needed for development of miniature biosensors that are highly sensitive and require minimal sample preparation. One novel technique employs optical resonances known as Whispering Gallery Modes (WGMs). These modes arise from total internal reflection of light at the internal surface of a high index microsphere within a low index medium and produce an evanescent field that extends into the surrounding medium. The WGMs produce multiple narrow spectral peaks that shift position with variations in the local index of refraction sampled by the evanescent tail of the WGMs. To excite these WGMs, we embed quantum dots (QDs) in the periphery of polystyrene microspheres to serve as local light sources. By coupling emission from the QDs to the WGMs, the sensors can be excited and interrogated remotely and, by monitoring the shift of multiple resonance modes, may provide higher sensitivity and accuracy compared with similar techniques. The high refractometric sensitivity of the WGMs offers potential for trace detection of molecules adsorbed onto or bound to the microsphere sensor elements. The sensitivity of these sensors is demonstrated by monitoring the wavelength shift of multiple resonant modes as bulk index of refraction is changed. The potential for targeted biosensing is explored through addition of a protein that adsorbs to the microsphere surface, thrombin. Microsensor response in all cases demonstrated increased sensitivity over theoretical predictions. Models based on Mie theory and continuity of the radial functions across the sphere-media interface were used to model the location, Q-factor, and sensitivity of the WGMs in microspheres by considering the embedded QDs as a high index outer layer. This model was used, along with estimates of the QD-layer index and penetration depth, to relate the locations and sensitivities of the modes to our experimental results with strong agreement between the two. In all, these microspheres demonstrate feasibility for use as remote microsensors with sensitivities rivaling current techniques.
412

An Empirical Study on the Relationships among International Human Capital, Global Initiatives, and Financial Performance

Ling, Ya-Hui 18 June 2004 (has links)
The major aim of this study is to develop an integrative framework of the determinants and consequence of international human capital, the human capital which enables a firm to compete globally. The open systems view is introduced to develop a comprehensive measurement of international human capital, which includes input-based, transformational, output-based, and managerial international human capital. Human capital accumulation modes (the documentation mode and the socialization mode) are identified as the potential determinant, and global initiatives (global learning and global marketing) and financial performance as the potential outcome. The Structural Equation Modeling technique is employed to investigate the determinants and outcome of the human capital system. The results support our expectation that human capital accumulation modes foster the development of international human capital, which in turn enhances a firm¡¦s global initiatives and financial performance. Important role of output-based and managerial international human capital are also identified. Output-based international human capital not only enhances a firm¡¦s financial performance, but also facilitates its global initiatives. Managerial international human capital, on the other hand, indirectly fosters a firm¡¦s financial performance and global initiatives through its direct positive influences on the other international human capital components.
413

Modeling scattered intensity from microspheres in evanescent field

Shah, Suhani Kiran 10 October 2008 (has links)
The technique of single particle Total Internal Reflection Microscopy (TIRM) has been used to study the scattering intensity from levitated microspheres. TIRM can be used to monitor the separation between microscopic spheres immersed in liquid (water in our case) and a surface with nm resolution. In the technique, microspheres scatter light when the evanescent waves are incident upon them. The intensity of the scattered light is directly related to the height above the surface and allows determination of the height. From the separation distance histograms, the interaction between the microsphere and interface may be characterized with a force resolution in the range of 0.01 picoNewtons. Such a system can be applied to the measurement of biomolecular interactions biomolecules attached to the microsphere and the surface. The intensity and scattering pattern of this light has been modeled using a modified Mie theory which accounts for the evanescent nature of the incident light. Diffusing Colloidal Probe Microscopy (DCPM) is an extension of the TIRM technique that simultaneously monitors multiple microsphere probes. The use of multiple probes introduces the issue of probe polydispersity. When measured at the surface, a variation in scattered light intensity of nearly one order of magnitude has been observed from a purchased microsphere sample. Thus the polydisperse collection of microspheres adds significant complexity to the scattered light signal. It is hypothesized that the dependence of the total scattered light intensity on microsphere size accounts for the scattered intensity distribution in a polydisperse microsphere sample. Understanding this variation in the scattered light with microsphere size will allow improved characterization of the microsphere/surface separation. Additionally, larger microspheres have the ability to resonantly confine light and produce spectrally narrow Whispering Gallery Modes (WGMs). It is hypothesized that WGMs may be excited in microspheres with the DCPM system. These modes may be used as a refractometric biosensor with high sensitivity to local refractive index changes on the surface of the microsphere. This research involves modeling scattered intensity distributions for polydispersed collections of microspheres based on modified Mie theory. The theoretical results are compared to experimentally obtained results and found to qualitatively explain the scattered light intensity distribution in a multiple probe DCPM system. This is an important result suggesting that microsphere size variation plays a major role in determining the distribution of scattered intensity in multiple microsphere probe systems. This work also suggests that it may be possible to excite such WGMs in a DCPM system. The introduction of WGMs would enable refractometric biosensing in such evanescent mode systems.
414

the factors of entry strategies influence international AD companies- the study of Taiwan market

Tsao, Yung-chieh 30 July 2008 (has links)
Researchers have been addressing on entry strategies, most of them are foreign researchers conducted researches on multinational firms, especially firms entering developed European countries or USA. Domestic researches mainly focused on firms entering PRC market, literally few studies have been found served Taiwan as the market being entered. Since Taiwan released the limit on foreigner share holding proportions in 1984, international advertisement firms gradually entered Taiwan. In the score years, Taiwan¡¦s advertisement market have been totally owned by foreign firms, thus Taiwanese advertisement firms need a method to break through. Given southeastern Asia markets are emerging, for Taiwanese advertisement firms, they pose as a market to be invested. Thus this thesis analyzed the entry mode of international advertising firms in order to serve as a reference to Taiwanese advertisement firms. This research served the period between establishment and entering Taiwan, cultural differences, five years average growth rate of GDP per capita, five years average growth rate of FDI in origin country, year 1984 and the changes in the number of competitors as the independent variables, and ownership or not as the dependent variable, applied logistic regression models in testing the relation between the selected variables. Outcomes indicate that cultural differences factor and five years average growth rate of GDP per capita factor bear significant factor loading while the other yielded insignificant results. Emerging countries in Asia ¡V e.g. Vietnam and Thailand ¡V possess close culture characteristics with Taiwan. Thus if advertisement firms are willing to invest in these markets, it is suggested to enter with ownership ¡V especially when the underlying countries¡¦ GDP growth rates are high.
415

Dynamic Dealy Compensation and Synchronisation Services for Continuous Media Streams

Shivaprasad, Mala A 10 1900 (has links)
Multimedia' nature of an application refers to the presence of several media streams in parallel. Whether it is receiving real-time data or retrieving stored data, there exists an end-to-end delay in data transfer from source to destination over the network. This delay experienced can be split into a fixed part and a variable part. Data processing time like coding and decoding at the source and destination are the fixed delays experienced. The variable delay occurs mainly due to queuing at the intermediate nodes during its flow through the network. The variable or unequal delays introduce gaps or discontinuities within a stream. In multi-stream applications where each stream may flow on different routes based on the bandwidth availability experiencing different delays, mismatch between them can also occur. These discontinuities and skews result in poor quality of playout. Clock drift and variations in drift rates between the source/s and destination/s, clock also lead to poor quality of play out. To eliminate these skews and discontinuities, there must be mechanisms, viz., and synchronisation services to convey, reintroduce and maintain the temporal relationship between the media streams for presentation throughout the playout, at the destination. The reintroduction of this lost temporal relationship within a stream and between various media streams for presentation at the destination is the object of multimedia synchronisation and is the subject matter of this thesis. In the presence of synchronised clocks, the main cause of asynchronies between media streams is the difference in delays experienced and the jitter. In this work, to convey the temporal relationship between streams of an application to the playout site, each stream is assigned a priority л, based on its importance to the user. The media streams are then divided into synchronisation units called 'Groups' based on that stream's characteristics which has the highest priority л. A group may therefore consist of one video frame and other data which were generated in that interval. Or may consist of silence and talk-spurt periods of the voice stream with data units of other streams generated in the same interval. Since the quality of playout of temporally related delay-sensitive streams depends upon the delay-experienced, the concept of QoS can be extended to describe the presentation requirements of uch data. Depending on the user perception and the delay experienced, an application can have a range of playout times, giving the best performance. The presentation of many real-time applications can be considered satisfactory even when the delay bound is exceeded by a small amount for a short period of time under varying network conditions. This property can be exploited by defining two sets of QoS parameters, namely QoS optimum and QoSlimit for each real-time application. As the delay and its variations increase, the optimum playout time range decreases. QoS optimum specifies the performance parameters required to perceive 'realtime'. Multimedia data can be played out at its QoSlimit with a deterioration in quality under poor network conditions still maintaining the synchronisation between streams. To control the playout at two levels of QoS, and maintain intra-media and inter-media synchronisation, stream controllers and super stream controllers have been used. The dynamic delay compensation algorithm and synchronisation services were simulated using network delay models and performances studied. It is shown that the proposed algorithm not only synchronised media streams and smoothened jitter but also optimised buffer space and buffer occupancy time while meeting the desired quality of service requirements
416

Supplying the Latino Way : A study of the Mexican automotive industry

Törnlöf, Sofia, Ryttberg, Kajsa January 2006 (has links)
<p>Problem- Sweden is for the moment one of the countries in the world that is most dependent on the automotive industry. Significant companies within this industry at a global level move parts of, or entire operations abroad which increase the competition for Swedish companies. This fact conveys problem for the Swedish SMEs suppliers, as if a supplier only focus on the national market will not match the requirements from the OEMs such as integrated product development and delivery of complete systems on a JIT- basis. Considering these fact, SME suppliers in Sweden need to look for new opportunities on new markets, and create an understanding for how to act accordingly to the new market’s particular business conditions.</p><p>Purpose- The main purpose of this thesis is to examine business conditions and prerequisites that applies for the buyers and the suppliers in the supply chain in the Mexican auto-motive industry, and further to develop an understanding of the logic of the interaction and integration between them. Derived from the obtained knowledge, a sub-purpose of this thesis is to present recommendations for how Swedish suppliers should enter and act accordingly on the new market.</p><p>Method- In this thesis we have applied a case study method. We have conducted semi-structured interviews with four of the largest OEMs and five suppliers, all of whom have production in Mexico. We have in addition to the interviews with OEMs and suppliers supported the collected information with one interview with a representative of a trade association within the Mexican automotive industry and one representative from a governmental institution.</p><p>Results- Our analysis indicates that the conditions for Swedish automotive suppliers to enter the Mexican market are favorable. Factors such as Free Trade Agreements, the positive attitude towards Foreign Direct Investments and skilled but low labor costs all imply for opportunities for Swedish suppliers. Secondly, our analysis indicates that the OEMs are today doing supply base rationalizations. We consider that this is based on the fact that the OEMs are changing their ordering basis from purchasing single parts to complete systems in order to reduce costs and increase the efficiency. Thirdly, our analysis indicates that it is the buyer, no matter on what level in the supply chain it is acting, who forms the strategy of its suppliers. If the buyer has a lean approach, its suppliers are forced to use the same thinking and apply it to their suppliers in order to meet the pressures on costs reductions, product development and JIT delivery. This we entitle as a continues correlation, which permeate in the complete supply chain.</p>
417

Feedback control of resistive wall modes in the reversed field pinch

Yadikin, Dimitry January 2004 (has links)
<p>A wide range of unstable current driven MHD modes is present in the re- versed τeld pinch (RFP) conτguration. An ideally conducting wall facing the plasma can stabilize the ideal MHD modes. In the presence of a resistive wall characterized by the wall time τw, fast mode rotation with the frequency exceeding the inverse wall time gives stabilization for resistive MHD modes. The ideal MHD modes in the RFP are non-rotating modes and can not be stabilized by the resistive wall. Instead they are converted into resistive wall modes (RWM) growing with a growth rate proportional to the inverse of the wall time τw. EXTRAP T2R is an RFP device equipped with a thin resistive wall having the wall time shorter than the plasma pulse duration τw < τp. This feature allows the study of non-resonant non-rotating resistive wall modes. Resistive wall modes dynamics has been studied in EXTRAP T2R . RWM growth rates has been measured and compared with linear MHD stability calculations. Quantitative agreement is observed. In the case τw < τp the RWM can cause discharge degradation and should be stabilized. Active feedback is the way to stabilize the RWM in the RFP. An intelligent shell scheme is one possible feedback scenario. An active feed- back system including a set of sensors and discrete active coils is installed in EXTRAP T2R. The intelligent shell tries to keep the magnetic flux zero at the positions of the sensor. The analog PID controller for the intelligent shell feedback scheme has been studied. A model of the active control system was developed and comparison with the experimental results showed good agree- ment. Encouraging experimental results on the active feedback stabilization of multiple RWMs in the RFP plasmas were obtained.</p>
418

Axicon imaging by scalar diffraction theory

Burvall, Anna January 2004 (has links)
<p>Axicons are optical elements that produce Bessel beams,i.e., long and narrow focal lines along the optical axis. Thenarrow focus makes them useful ine.g. alignment, harmonicgeneration, and atom trapping, and they are also used toincrease the longitudinal range of applications such astriangulation, light sectioning, and optical coherencetomography. In this thesis, axicons are designed andcharacterized for different kinds of illumination, using thestationary-phase and the communication-modes methods.</p><p>The inverse problem of axicon design for partially coherentlight is addressed. A design relation, applicable toSchell-model sources, is derived from the Fresnel diffractionintegral, simplified by the method of stationary phase. Thisapproach both clarifies the old design method for coherentlight, which was derived using energy conservation in raybundles, and extends it to the domain of partial coherence. Thedesign rule applies to light from such multimode emitters aslight-emitting diodes, excimer lasers and some laser diodes,which can be represented as Gaussian Schell-model sources.</p><p>Characterization of axicons in coherent, obliqueillumination is performed using the method of stationary phase.It is shown that in inclined illumination the focal shapechanges from the narrow Bessel distribution to a broadasteroid-shaped focus. It is proven that an axicon ofelliptical shape will compensate for this deformation. Theseresults, which are all confirmed both numerically andexperimentally, open possibilities for using axicons inscanning optical systems to increase resolution and depthrange.</p><p>Axicons are normally manufactured as refractive cones or ascircular diffractive gratings. They can also be constructedfrom ordinary spherical surfaces, using the sphericalaberration to create the long focal line. In this dissertation,a simple lens axicon consisting of a cemented doublet isdesigned, manufactured, and tested. The advantage of the lensaxicon is that it is easily manufactured.</p><p>The longitudinal resolution of the axicon varies. The methodof communication modes, earlier used for analysis ofinformation content for e.g. line or square apertures, isapplied to the axicon geometry and yields an expression for thelongitudinal resolution. The method, which is based on abi-orthogonal expansion of the Green function in the Fresneldiffraction integral, also gives the number of degrees offreedom, or the number of information channels available, forthe axicon geometry.</p><p><b>Keywords:</b>axicons, diffractive optics, coherence,asymptotic methods, communication modes, information content,inverse problems</p>
419

Stability analysis and control design of spatially developing flows

Bagheri, Shervin January 2008 (has links)
<p>Methods in hydrodynamic stability, systems and control theory are applied to spatially developing flows, where the flow is not required to vary slowly in the streamwise direction. A substantial part of the thesis presents a theoretical framework for the stability analysis, input-output behavior, model reduction and control design for fluid dynamical systems using examples on the linear complex Ginzburg-Landau equation. The framework is then applied to high dimensional systems arising from the discretized Navier–Stokes equations. In particular, global stability analysis of the three-dimensional jet in cross flow and control design of two-dimensional disturbances in the flat-plate boundary layer are performed. Finally, a parametric study of the passive control of two-dimensional disturbances in a flat-plate boundary layer using streamwise streaks is presented.</p>
420

Contribution à la commande non linéaire d'un système électropneumatique pour une utilisation aéronautique: application sur un benchmark dédié

Girin, Alexis 04 December 2007 (has links) (PDF)
L'objectif de ce travail de thèse est d'évaluer la pertinence et les performances des techniques avancées de commande et d'observation des systèmes non linéaires et de voir si elles rendent possible l'utilisation d'un système électropneumatique haute performance pour le positionnement de gouvernes d'engin aérodynamique. Pour cela un banc d'essai et un benchmark associé ont été réalisés, en collaboration par les laboratoires AMPERE / IRCCyN, par le Laboratoire de Recherche en Balistique et Aérodynamique de la DGA et par MBDA (Groupe EADS). <br />L'étude montre que l'utilisation de commandes non linéaires permet d'obtenir les performances souhaitées. Des commandes non linéaires par modes glissants d'ordre supérieur mono et multi variables sont appliquées sur le système électropneumatique lui assurant une convergence en temps fini et la robustesse face aux incertitudes paramétriques et aux perturbations, ce qui constitue une des principales contributions de ce travail. Par ailleurs, dans le but de minimiser le nombre de capteurs et/ou pallier à leur défaillance, la synthèse d'observateurs pour cette plateforme expérimentale a été étudiée. Ainsi, une étude de l'observabilité, une synthèse d'observateurs à grands gains et par modes glissants a été effectuée.<br />La conclusion de ce travail permet de déterminer qu'il est possible d'utiliser des actionneurs électropneumatiques pour le positionnement d'une gouverne de missile, sous réserve de concevoir des composants intégrables. Cette thèse permet de déterminer les caractéristiques que devront avoir ces composants pour permettre d'obtenir l'ensemble des performances souhaitées.

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