74 resultados para Échangeur à contact direct


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Yandex is the dominant search engine in Russia, followed by the world leader Google. This study focuses on the performance differences between the two in search advertising in the context of tourism, by running two identical campaigns and measuring the KPI’s, such as CPA (cost-per-action), on both campaigns. Search engine advertising is a new and fast changing form of advertising, which should be studied frequently in order to keep up with the changes. Research was done as an experimental study in cooperation with a Finnish tourism company and the data is gathered from the clickstream and not from questionnaires, which is recommended method by the literature. The results of the study suggests that Yandex.Direct performed better in the selected niche and that the individual campaign planning for Yandex.Direct and Google AdWords is an important part of the optimization of search advertising in Russia.

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Today’s electrical machine technology allows increasing the wind turbine output power by an order of magnitude from the technology that existed only ten years ago. However, it is sometimes argued that high-power direct-drive wind turbine generators will prove to be of limited practical importance because of their relatively large size and weight. The limited space for the generator in a wind turbine application together with the growing use of wind energy pose a challenge for the design engineers who are trying to increase torque without making the generator larger. When it comes to high torque density, the limiting factor in every electrical machine is heat, and if the electrical machine parts exceed their maximum allowable continuous operating temperature, even for a short time, they can suffer permanent damage. Therefore, highly efficient thermal design or cooling methods is needed. One of the promising solutions to enhance heat transfer performances of high-power, low-speed electrical machines is the direct cooling of the windings. This doctoral dissertation proposes a rotor-surface-magnet synchronous generator with a fractional slot nonoverlapping stator winding made of hollow conductors, through which liquid coolant can be passed directly during the application of current in order to increase the convective heat transfer capabilities and reduce the generator mass. This doctoral dissertation focuses on the electromagnetic design of a liquid-cooled direct-drive permanent-magnet synchronous generator (LC DD-PMSG) for a directdrive wind turbine application. The analytical calculation of the magnetic field distribution is carried out with the ambition of fast and accurate predicting of the main dimensions of the machine and especially the thickness of the permanent magnets; the generator electromagnetic parameters as well as the design optimization. The focus is on the generator design with a fractional slot non-overlapping winding placed into open stator slots. This is an a priori selection to guarantee easy manufacturing of the LC winding. A thermal analysis of the LC DD-PMSG based on a lumped parameter thermal model takes place with the ambition of evaluating the generator thermal performance. The thermal model was adapted to take into account the uneven copper loss distribution resulting from the skin effect as well as the effect of temperature on the copper winding resistance and the thermophysical properties of the coolant. The developed lumpedparameter thermal model and the analytical calculation of the magnetic field distribution can both be integrated with the presented algorithm to optimize an LC DD-PMSG design. Based on an instrumented small prototype with liquid-cooled tooth-coils, the following targets have been achieved: experimental determination of the performance of the direct liquid cooling of the stator winding and validating the temperatures predicted by an analytical thermal model; proving the feasibility of manufacturing the liquid-cooled tooth-coil winding; moreover, demonstration of the objectives of the project to potential customers.

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In this thesis, the contact resistance of graphene devices was investigated because high contact resistance is detrimental to the performance of graphene field-effect transistors (GFET). Method for increasing so-called edge-contact area was applied in device fabrication process, as few nanometers thick Ni layer was used as a catalytic etchant during the annealing process. Finally, Ni was also used as a metal for contact. GFETs were fabricated using electron beam lithography using graphene fabricated by chemical vapor deposition (CVD). Critical part of the fabrication process was to preserve the high quality of the graphene channel while etching the graphene at contact areas with Ni during the annealing. This was achieved by optimizing the combination of temperature and gas flows. The structural properties of graphene were studied using scanning electron microscopy, scanning confocal μ-Raman spectroscopy and optical microscopy. Evaluation of electric transport properties including contact resistance was carried out by transmission line method and four-probe method. The lowest contact resistance found was about at 350 Ωμm. In addition, different methods to transfer CVD graphene synthesized on copper were studied. Typical method using PMMA as a supporting layer leaves some residues after its removal, thus effecting on the performance of a graphene devices. In a metal assisted transfer method, metal is used as an interfacial layer between PMMA and graphene. This allows more effective removal of PMMA. However, Raman spectra of graphene transferred by metal assisted method showed somewhat lower quality than the PMMA assisted method

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Even though e-commerce systems are expected to have many advantages compared to the traditional ways of doing business, it is not always the reality. Lack of trust is still said to be one of the most important barriers to online shopping. In traditional stores, trust has usually been established in a direct contact between the customer and the company or its personnel. In online stores, there is no direct interaction. The purpose of this thesis is to identify the key antecedents to online trust and to distinguish between effective and ineffective practices. A model on how consumers establish initial trust towards an unknown online vendor was proposed based on previous theories. The model was tested empirically by targeting an online survey at higher degree students in Finland and in Germany. The data confirmed the proposed view that trusting intentions are affected by individual characteristics, characteristics of the company as well as characteristics of the website. Additionally national differences were found between Finnish and German respondents. The data suggested that online vendors can convey a message of trustworthiness by improving information quality and overall usefulness of the website. Perceived risk of online shopping was found to depend especially on general trust in the Internet, service quality and ease of use. A trustworthy online store should include several payment methods as well as means to access and modify given data. The vendors should also make sure that inquiries are addressed quickly, transactions are confirmed automatically and that customers have a possibility to track their order. A model that includes three different sources of trust should contribute to the theoretical understanding of trust formation in online stores. The resulting list of trust antecedents can also be used as a checklist when e-commerce practitioners wish to optimize the trust building.

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The direct synthesis from hydrogen and oxygen is a green alternative for production of hydrogen peroxide. However, this process suffers from two challenges. Firstly, mixtures of hydrogen and oxygen are explosive over a wide range of concentrations (4-94% H2 in O2). Secondly, the catalytic reaction of hydrogen and oxygen involves several reaction pathways, many of them resulting in water production and therfore decreasing selectivity. The present work deals with these two challenges. The safety problem was dealed by employing a novel microstructured reactor. Selectivity of the reaction was highly improved by development a set of new catalysts. The final goal was to develop an effective and safe continuous process for direct synthesis of hydrogen peroxide from H2 and O2. Activated carbon cloth and Sibunit were examined as the catalysts’ supports. Palladium and gold monometallic and palladium-gold bimetallic catalysts were thoroughly investigated by numerous kinetic experiments performed in a tailored batch reactor and several catalyst charachterization methods. A complete set of data for direct synthesis of H2O2 and its catalytic decomposition and hydrogenation was obtained. These data were used to assess factors influencing selectivity and activity of the catalysts in direct synthesis of H2O2 as well as its decomposition and hydrogenation. A novel microstructured reactor was developed based on hydrodynamics and mass transfer studies in prototype microstractural plates. The shape and the size of the structural elements in the microreactor plate were optimized in a way to get high gas-liquid interfacial area and gas-liquid mass transfer. Finally, empirical correlations for the volumetric mass transfer coefficient were derived. A bench-scale continuous process was developed by using the novel microstructral plate reactor. A series of kinetic experiments were performed to investigate the effects of the gas and the liquid feed rates and their ratio, the amount of the catalyst, the gas feed composition and pressure on the final rate of H2O2 production and selectivity.

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Online sexual solicitation (solicitation) of youth has received widespread media and research attention during the last decade. The prevalence rates of youth who have experienced solicitation or solicitation attempts vary between studies depending on the methodology used (e.g., whether youth or adults are the target study group). In studies focusing on youth victims, the prevalence of solicitation attempts made by adults during the past year is typically reported to be between 5 and 9%. Adults who solicit youth online have been found to use deception and other manipulative behaviors to gain access to sexual activities with youth. However, previous studies have lacked a control group of adults who solicit other adults online. Without this comparison, one could argue that deceiving others online about one’s identity, and engaging in manipulative behaviors, is an inherent part of most online sexual interactions with strangers. Additionally, little is known about the associations between manipulative behaviors and the solicitation outcomes. In research concerning offline sexual behaviors, it has been noted that situational factors, such as sexual arousal, may alter both sexual interest and behavior. The effects of situational factors on online sexual behaviors have been less extensively studied (especially so with a quantitative approach); no studies have to date focused on adults’ solicitation of youth. Investigating the role of a lowered sexual age preference and the role of situational factors in the soliciting adults could be an important step in order to receive deeper knowledge of the role of traits and states in the context of solicitation. Additionally, there is a lack of knowledge of the effect of the age of the youth. Although previous studies on solicitation has found that older youth, compared with younger youth and children, are more often solicited, the possible reasons for this have not been investigated. Are adults who solicit youth affected by legal deterrence (through the legal age of consent), is it because older youth are more available online, or are the adults’ age preferences merely a product of a normally distributed age preference in the population? The purpose of the present thesis was fivefold: 1) to obtain an estimate of the frequency of adults’ solicitation of youth as self-reported and observed in actual behavior; 2) to explore whether the legal age of consent (LAC) affects solicitation frequency, or whether a normally distributed sexual age preference more accurately describe the proportion of solicited youth of different ages; 3) to investigate the associations of both traits (e.g., lower sexual age preference) and states (immediate situational factors, such as alcohol intoxication), and the solicitation target; 4) to explore whether adults who solicit youth and adults who solicit adults are equally deceitful and manipulative online, and whether the different solicitation outcomes are as common in both groups; and 5) to investigate whether the deceitful and manipulative behaviors engaged in had different associations with the solicitation outcomes depending on the age of the solicited. In the survey study, a convenience sample of 1393 adult participants (aged 18 years or older) self-reported any online communication with strangers during the past year. Of these, 56% (776 respondents) reported that they had solicited or attempted to solicit at least one stranger. Of the respondents, 453 (58.4%) were men, and 323 (41.6%) were women. Participants with only adult contacts (18 years or older) constituted the majority (640 respondents). In contrast, 136 individuals reported a youth contact (a 13 year old or younger, or a 14 to 17-year old). Approximately half of the participants were men in the adult contact group, while 75% of the participants were men in the youth contact group. Approximately 60% of the participants with youth contacts were recruited from two websites associated with a pedophilic sexual interest. In an online quasi-experimental study, with researchers impersonating youth of different ages (10–18 year olds) in chat rooms, 251 online conversations with chat room visitors made up the entire sample. All chat room visitors alleged to be men. The self-reported frequency of having solicited youth (0–17-year olds) during the past year was approximately 10% in our sample of adults who reported communicating with any strangers online. When we observed this behavior in chat rooms, we found that approximately 30% of the chat room visitors who believed they interacted with a 10 to 14 year old attempted to solicit the youth. We found that solicitation attempts increased equally much when increasing the age of the impersonated youth from 14 to 16, as from 16 to 18. Thus, we concluded that a normally distributed age preference in the population was a more plausible explanation to the effect of the age of the solicited, rather than the LAC (here; 15 and 16). If the chat room visitors would have been deterred only by the LAC, we would have expected that the change in amount of solicitation attempts from an illegal age group to a legal age group would have been significantly stronger than changes between age groups within illegal-illegal and legal-legal groups. Our subsample of survey participants from the pedophilia-related websites expectedly reported that they had solicited youth more often in comparison to the sample gathered through general (i.e., not associated with any particular sexual preference) websites. We also found that participants with a youth contact reported higher levels of sexual arousal and shame before the sexual interaction with their online contact, compared with participants with an adult contact. Additionally, the participants with youth contacts who reported consumption of child- and adolescent pornography also reported being more sexually aroused before the interaction, compared to the participants with youth contacts who did not report consumption of these kinds of pornography. We also found clear indications that the online sexual interaction had an alleviatory effect on reported levels of sadness, boredom and stress, independent of the age of the contact. Generally, the participants with youth and adult contacts reported deceiving their contacts as often and suggesting keeping the communication a secret from someone as often. Participants with a youth contact, however, reported using more persuasion techniques for online sexual purposes or for the purpose of an offline meeting, compared to those with an adult contact. In the chat rooms, we found that more indirect ways of future sexual communication (e.g., continuing chatting) was suggested by the chat room visitors that were under the assumption of interacting with youth aged 10 to 14, compared with more direct means (e.g., meeting offline). Survey participants with youth contacts who had used deception, suggested keeping the interactions a secret, and/or persuaded their contact by appealing to the contacts feelings of love and attachment for the participant had also more often engaged in cybersex with the contact. No other manipulative behaviors were associated with the other investigated solicitation outcomes (receiving a sexual picture, meeting offline, and engaging in sexual contact offline) within this group of participants. However, using deception, suggesting secrecy and using persuasion was also positively associated with certain solicitation outcomes within participants with an adult contact. In summary, adults’ solicitation of youth is much more frequent when observed in chat rooms than self-reported. Additionally, an underlying lowered sexual age preference seems to be a motivating factor on a group level in adults who solicit youth. We concluded that directed prevention efforts should be made on pedophiliarelated websites. Additionally, the role of situational factors, especially sexual arousal in persons with a pedo- or hebephilic sexual interest should be investigated further in the context of online sexual solicitation.

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Thesis: A liquid-cooled, direct-drive, permanent-magnet, synchronous generator with helical, double-layer, non-overlapping windings formed from a copper conductor with a coaxial internal coolant conduit offers an excellent combination of attributes to reliably provide economic wind power for the coming generation of wind turbines with power ratings between 5 and 20MW. A generator based on the liquid-cooled architecture proposed here will be reliable and cost effective. Its smaller size and mass will reduce build, transport, and installation costs. Summary: Converting wind energy into electricity and transmitting it to an electrical power grid to supply consumers is a relatively new and rapidly developing method of electricity generation. In the most recent decade, the increase in wind energy’s share of overall energy production has been remarkable. Thousands of land-based and offshore wind turbines have been commissioned around the globe, and thousands more are being planned. The technologies have evolved rapidly and are continuing to evolve, and wind turbine sizes and power ratings are continually increasing. Many of the newer wind turbine designs feature drivetrains based on Direct-Drive, Permanent-Magnet, Synchronous Generators (DD-PMSGs). Being low-speed high-torque machines, the diameters of air-cooled DD-PMSGs become very large to generate higher levels of power. The largest direct-drive wind turbine generator in operation today, rated just below 8MW, is 12m in diameter and approximately 220 tonne. To generate higher powers, traditional DD-PMSGs would need to become extraordinarily large. A 15MW air-cooled direct-drive generator would be of colossal size and tremendous mass and no longer economically viable. One alternative to increasing diameter is instead to increase torque density. In a permanent magnet machine, this is best done by increasing the linear current density of the stator windings. However, greater linear current density results in more Joule heating, and the additional heat cannot be removed practically using a traditional air-cooling approach. Direct liquid cooling is more effective, and when applied directly to the stator windings, higher linear current densities can be sustained leading to substantial increases in torque density. The higher torque density, in turn, makes possible significant reductions in DD-PMSG size. Over the past five years, a multidisciplinary team of researchers has applied a holistic approach to explore the application of liquid cooling to permanent-magnet wind turbine generator design. The approach has considered wind energy markets and the economics of wind power, system reliability, electromagnetic behaviors and design, thermal design and performance, mechanical architecture and behaviors, and the performance modeling of installed wind turbines. This dissertation is based on seven publications that chronicle the work. The primary outcomes are the proposal of a novel generator architecture, a multidisciplinary set of analyses to predict the behaviors, and experimentation to demonstrate some of the key principles and validate the analyses. The proposed generator concept is a direct-drive, surface-magnet, synchronous generator with fractional-slot, duplex-helical, double-layer, non-overlapping windings formed from a copper conductor with a coaxial internal coolant conduit to accommodate liquid coolant flow. The novel liquid-cooling architecture is referred to as LC DD-PMSG. The first of the seven publications summarized in this dissertation discusses the technological and economic benefits and limitations of DD-PMSGs as applied to wind energy. The second publication addresses the long-term reliability of the proposed LC DD-PMSG design. Publication 3 examines the machine’s electromagnetic design, and Publication 4 introduces an optimization tool developed to quickly define basic machine parameters. The static and harmonic behaviors of the stator and rotor wheel structures are the subject of Publication 5. And finally, Publications 6 and 7 examine steady-state and transient thermal behaviors. There have been a number of ancillary concrete outcomes associated with the work including the following. X Intellectual Property (IP) for direct liquid cooling of stator windings via an embedded coaxial coolant conduit, IP for a lightweight wheel structure for lowspeed, high-torque electrical machinery, and IP for numerous other details of the LC DD-PMSG design X Analytical demonstrations of the equivalent reliability of the LC DD-PMSG; validated electromagnetic, thermal, structural, and dynamic prediction models; and an analytical demonstration of the superior partial load efficiency and annual energy output of an LC DD-PMSG design X A set of LC DD-PMSG design guidelines and an analytical tool to establish optimal geometries quickly and early on X Proposed 8 MW LC DD-PMSG concepts for both inner and outer rotor configurations Furthermore, three technologies introduced could be relevant across a broader spectrum of applications. 1) The cost optimization methodology developed as part of this work could be further improved to produce a simple tool to establish base geometries for various electromagnetic machine types. 2) The layered sheet-steel element construction technology used for the LC DD-PMSG stator and rotor wheel structures has potential for a wide range of applications. And finally, 3) the direct liquid-cooling technology could be beneficial in higher speed electromotive applications such as vehicular electric drives.

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In Finnish discourse, “The China Effect” refers to the surge of offshoring activities by Western companies to China during the past couple of decades. Inspired by event studies concerning announcements of foreign direct investment, this thesis investigates the market’s reaction to Finnish companies’ announcement of FDI targeting the People’s Republic of China. Standard event study methodology is applied to 135 announcements related to subsidiaries, joint ventures and acquisitions between 1997 and 2014. The data is checked for contamination by unrelated coinciding events and outliers. A positive average abnormal return is found to take place on the date of the announcement. Additionally, the abnormal returns are found to exist only for projects announced before 2008, and only when the investment project is new, as opposed to investments made to extend previously established projects. Ownership arrangement and the novelty of facilities do not influence the market’s reaction towards the investment announcement.

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The design process of direct-driven permanent magnet synchronous machines (PMSMs) for a full electric 4 ´ 4 sports car is presented. The rotor structure of the machine consists of two permanent magnet layers embedded inside the rotor laminations thus resulting in some inverse saliency, where the q-axis inductance is larger than the d-axis one. An integer slot stator winding was selected to fully take advantage of the additional reluctance torque. The performance characteristics of the designed PMSMs were calculated by applying a twodimensional finite element method. Cross-saturation between the d- and q-axes was taken into account in the calculation of the synchronous inductances. The calculation results are validated by measurements.

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A direct-driven permanent magnet synchronous machine for a small urban use electric vehicle is presented. The measured performance of the machine at the test bench as well as the performance over the modified New European Drive Cycle will be given. The effect of optimal current components, maximizing the efficiency and taking into account the iron loss, is compared with the simple id=0 – control. The machine currents and losses during the drive cycle are calculated and compared with each other.

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This doctoral dissertation explores the contribution of environmental management practices, the so-called clean development mechanism (CDM) projects, and foreign direct investment (FDI) in achieving sustainable development in developing countries, particularly in Sub- Saharan Africa. Because the climate change caused by greenhouse gas emissions is one of the most serious global environmental challenges, the main focus is on the causal links between carbon dioxide (CO2) emissions, energy consumption, and economic development in Sub-Saharan Africa. In addition, the dissertation investigates the factors that have affected the distribution of CDM projects in developing countries and the relationships between FDI and other macroeconomic variables of interest. The main contribution of the dissertation is empirical. One of the publications uses crosssectional data and Tobit and Poisson regressions. Three of the studies use time-series data and vector autoregressive and vector error correction models, while two publications use panel data and panel data estimation methods. One of the publications uses thus both timeseries and panel data. The concept of Granger causality is utilized in four of the publications. The results indicate that there are significant differences in the Granger causality relationships between CO2 emissions, energy consumption, economic growth, and FDI in different countries. It appears also that the causality relationships change over time. Furthermore, the results support the environmental Kuznets curve hypothesis but only for some of the countries. As to CDM activities, past emission levels, institutional quality, and the size of the host country appear to be among the significant determinants of the distribution of CDM projects. FDI and exports are also found to be significant determinants of economic growth.