261 research outputs found
An experimental and numerical investigation of the hydrodynamics of the ducted system of a "Van Rompay Turbine": with the goal to capture energy from the current of an ocean, river, estuary or similar
No full textHydrokinetic energy is an environmentally friendly source of electricity and it has the advantage to be more predictable compared to other renewables. According to IRENA (2020), the capacity of converting hydrokinetic energy into electricity is expected to increase in the coming decades as many concepts are in the pipeline. One of these hydrokinetic energy concepts is the patented Van Rompay Turbine. The Van Rompay Turbine consists of a duct, an air chamber and a paddlewheel. The duct, which is based on a Venturi working principle, consists of a converging inlet, a throat and a diverging outlet. Above the throat, an air chamber is present to provide an air environment to reduce resistance for the paddlewheel. The goal of this research was to experimentally and numerically test a prototype (L:4.05m x W:1.17m x H:1.17m) of the ducted system.Three inclination angles: 21°, 26° & 31°, for the converging inflow and diverging outflow segment were tested, referred to as the small, medium and large ramp size, respectively, to determine which size represents the lowest energy losses in the system. The small in -and outflow ramp represents the lowest energy losses compared to the medium and large ramp. Subsequently, on the small inflow ramp, five designs were tested, referred to as the straight, curved and the high, mid & low frequency waved designs; to again determine which design represents the lowest energy losses. Roughed waved wall designs are streamwise wavy walls with each a different wavelength and amplitude. The small ramp with a high, mid & low frequency waved design results in the lowest energy losses in comparison to the straight and curved designs for inlet velocities between 0 m/s and 0.4 m/s. For inlet velocities between 0.4 m/s and 0.5 m/s, the small ramp with a curved design represents the lowest energy losses in comparison to the straight and high, mid & low frequency waved designs.The data points acquired during the experiments were scattered due to external factors increasing the uncertainty of the measurements. Besides this, the experimental investigations were tested over an inlet velocity between 0 m/s and 0.5 m/s, limiting the data analysis. For this reason, several CFD simulations were carried out to acquire data with no influence of external factors and to investigate the system for higher velocities. The CFD simulations were executed for the five different inflow ramp designs with an in -and outflow inclination angle of 21°. The CFD model solves the Reynolds-averaged Navier–Stokes (RANS) equations with a k-epsilon turbulence closure model. Based on these CFD simulations, the best performing design for the inflow ramp in terms of the lowest energy losses for an inlet flow velocity between 0 m/s and 0.75 m/s is the high frequency waved design. Regarding velocities between 0.75 m/s and 3 m/s, the curved design represents thelowest energy losses compared to the straight and high, mid & low frequency waved designs. After scaling up the ducted system in CFD simulations with a factor 2 and 10, the flow velocity reduces as there are more energy losses in the system. However, as larger systems have a marginal lower specific surface of contact between the water and the duct, an increase in available flow power could be found. The extent to which the ducted system can be scaled up depends on the space restrictions at the specific location. Besides, the minimal required inflow area of the free water flow should be met. It can therefore be concluded that the potentially available energy for generation also depends the location where the Van Rompay will be deployed.Experiments need to be performed to study the hydrodynamic impact and the hydrodynamic efficiency of the paddlewheel to determine the power performance output and thus its potential value for the hydrokinetic energy market. It is recommended for future research to test the prototype at higher velocities and to test the prototype in a laboratory facility as these offer the benefits of controlled testing.Civil Engineering | Hydraulic Engineerin
Simian immunodeficiency virus (SIV) envelope quasispecies transmission and evolution in infant rhesus macaques after oral challenge with uncloned SIVmac251: increased diversity is associated with neutralizing antibodies and improved survival in previously immunized animals
No full textAbstract Background Oral infection of infant macaques with simian immunodeficiency virus (SIV) is a useful animal model to test interventions to reduce postnatal HIV transmission via breast-feeding. We previously demonstrated that immunization of infant rhesus macaques with either modified vaccinia virus Ankara (MVA) expressing SIV Gag, Pol and Env, or live-attenuated SIVmac1A11 resulted in lower viremia and longer survival compared to unimmunized controls after oral challenge with virulent SIVmac251 (Van Rompay et al., J. Virology 77:179–190, 2003). Here we evaluate the impact of these vaccines on oral transmission and evolution of SIV envelope variants. Results Limiting dilution analysis of SIV RNA followed by heteroduplex mobility assays of the V1–V2 envelope (env) region revealed two major env variants in the uncloned SIVmac251 inoculum. Plasma sampled from all infants 1 week after challenge contained heterogeneous SIV env populations including one or both of the most common env variants in the virus inoculum; no consistent differences in patterns of env variants were found between vaccinated and unvaccinated infants. However, SIV env variant populations diverged in most vaccinated monkeys 3 to 5 months after challenge, in association with the development of neutralizing antibodies. Conclusions These patterns of viral envelope diversity, immune responses and disease course in SIV-infected infant macaques are similar to observations in HIV-infected children, and underscore the relevance of this pediatric animal model. The results also support the concept that neonatal immunization with HIV vaccines might modulate disease progression in infants infected with HIV by breast-feeding.</p
Prophylactic and Therapeutic Effects of 9-(2-Phosphonymethoxy-Propyl) Adenine (PMPA) in Newborn Macaques Infected Orally with SIVmac
No full textThe Use of Nonhuman Primate Models of HIV Infection for the Evaluation of Antiviral Strategies
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Aphrahat's Christology. A Contextual Reading
No full textThe present study represents an attempt at reading the views on Christ of fourth-century Syriac writer Aphrahat, author of 23 Demonstrations, within the context of coeval developments in Christian thought, especially in Syria. Given the breadth of the set of questions posed by the topic, these pages are not conceived as an exhaustive treatment, but rather as a series of incursions into a complicated terrain. The first chapter shows how scholars studying Aphrahat's Christology have often worked, more or less outspokenly, on the basis of confessional and dogmatic assumptions. I will argue for a change in this regard. The second chapter discusses the Syriac version of the so-called "Eunomian interpolation" found in Pseudoclementine Recognitions 3.2-11, and attested in Latin and Syriac. Through a work of contrasting and comparing the two versions of the text, I will examine the strategies of which the Syriac translator availed himself to moderate the anti-Nicene peaks of the Greek original. The peculiar characteristics of this translation need to be understood, I will suggest, as a token of the livelihood and conflictiveness of Syriac Christianity around the half of the fourth century. Against the same backdrop, presenting competing models for understanding the figure of Christ, I will propose that we read the complex Christological speculation developed by Aphrahat in his Dem. 17. The third chapter of the study interprets the seventh paragraph of this Demonstration, recounting the story of the creation of Adam in a highly unusual manner, as a coherent Christological discourse, rather than a mere digression. In that section we witness, I will argue, a synthetic integration of Adamitic Christology with the scheme of the prolatio of the Logos, and a dynamic engagement, on the part of the Persian Sage, with contemporary theological debates. The study does not reach overall conclusions about the tenets of Aphrahat's Christology, rather presenting itself as an invitation to take this author out of the intellectual isolation in which he has long been kept by scholars.</p
Expressions: Embodiment in the experience of design
No full textEXPRESSIONS: EMBODIMENT IN THE EXPERIENCE OF DESIGN Products are not just objects by means of which we get things done. Apart from bringing aesthetic pleasures, for instance, they may also embody values we hold dear, communicate our fine taste to others, and help us define who we are. These widely varying functionalities are rooted in our capacity to perceive essentially lifeless forms as dynamic objects expressive of basic human experiences. This expressiveness forms the starting point for this thesis. Perceiving products as expressive in most cases comes most natural. One may readily perceive one object as distant, another as involved, and yet another as humble or proud, for instance, and at the same have an intuitive sense of what it is in a products appearance that contributes to a particular expression. However, the moment one questions why specific product features connote the expressive or figurative meanings they do, one often finds that accounting for a products expression is not always that easy or straightforward. In this thesis, we therefore seek to account for the relations between a products appearance and its expressiveness. In the first chapter different perspectives on expression are presented. This discussion revolves around the tendency, common among researchers studying product expression, to focus primarily on either the object perceived or its perceiver. In the former approach figurative or expressive characteristics are considered authentic and objective qualities, conveyed by perceptual features such as shape and size. In the latter approach these characteristics do not belong to the object but rather to the perceiver. In this line of reasoning, the objects expressiveness is primarily seen as a mental construction. Although studies originating in these approaches in one way or the other acknowledge the importance of both constituents, American philosopher John Dewey, as early as 1934, pointed out the necessity of simultaneously taking into account the contributions of both object and perceiver in studying the objects expressiveness. His notions lie at the basis of a relatively new approach that seeks to account for figurative or expressive meanings in terms of spatial-relational structures characterizing interactions between people and their environment. Since these interactions are constrained by the peculiarities of the human body, studies originating in this approach view such meanings as essentially embodied. Central to this interactional approach is the notion that specific types of interactions give rise to particular kinds of experiences. Interactions characterized by a sense of containment (e.g., seeking shelter from the storm inside a cabin, or taking refuge inside ones office to get some work done) may give rise to a sense of safety or security (for reasons of protection from threatening or disruptive influences), but at the same time to a sense of isolation from others (i.e., a container separates those inside from those outside) or constriction (i.e., a container limits ones freedom of movement). The spatial-relational structure these interactions have in common (in our example all interactions involve a bounded space in which one can be in or out) is referred to as an image schema. The central assumption of this thesis is that products can make reference to such spatial-relational structures through their visual-spatial appearance. This perceived congruence is expected to lie at the basis of the understanding of products as expressive. (Arguably, a product making reference to the containment schema is for that reason perceived as expressing degrees of security, isolation, and constriction.) In the second chapter we put this claim to a first test. Regardless of the manner in which products make reference to an image schema, ratings of products on experiences arising from the same type of interactions should be highly related. Products generally rated high on secure, for instance, should also receive high ratings on constricting (i.e., both experiences arise from interactions characterized by a sense of containment). The results of a study in which 10 chairs were rated on a wide variety of expressive characteristics were in line with this prediction. Following this confirmation, in the third chapter we explore the manner in which a product can make reference to spatial-relational (i.e., image schematic) structures through its form features. Based on a tentative discussion of the manner in which chairs and bus shelters can embody image schematic structures, in the third chapter form features of two everyday products (a jug and an alarm clock) are manipulated on the basis of the spatial-relational structure of three image schemas. Following our line of reasoning, we should be able to predict the effects of these manipulations on the objects figurative or expressive meanings. Secondly, the effects of these manipulations might be expected to show considerable consistency across cultures since interactions between people and their environment are highly similar, regardless of the region in which they take place. Our bodies, that is, show little variation, and the same applies, at least to some extent, to the environment we interact with. The results of the two experiments testing the first claim (one involving students of design, the other involving participants who had no background in design) were largely in line with our predictions. The findings from the same experiment conducted in Brazil, testing the second claim, were only partly as predicted. Having established a solid scientific basis for our project, in the fourth chapter we set out to make our approach actionable. That is, how can the insights be of practical relevance for designers intent on creating a particular expression? To provide an answer to that question we explored different ways to study the spatial-relational structures characterizing interactions giving rise to a particular experience. In one such study 11 designers were asked to design a public smoking object with a particular expression. Did these designers think of the guidelines as inspiring and useful? In order to answer these questions we discuss a questionnaire that revealed that the designers had thought of the guidelines as both inspiring and useful. However, comparison of the results of these designers to those of 11 designers receiving no special guidelines failed to confirm our prediction that the latter would be less successful in creating a particular product expression. In closing this chapter, possible explanations for this lack of differentiation are discussed. In the fifth and final chapter the most striking findings and implications of the studies discussed in previous chapters are reviewed. A large part of this chapter is devoted to a discussion of metaphor. The understanding of product expression discussed in previous chapters is metaphorical in so far as products are understood in terms of experiences that have their origin in embodied interactions in and with the environment. But not all metaphors are of this embodied type. Next to making a distinction between two types of metaphor (i.e., embodied metaphors and metaphors not, or to a lesser degree, grounded in embodied interactions), we elaborate on a fascinating aspect characterizing our understanding of the embodied metaphors discussed throughout this thesis. This understanding, we argue, presupposes an identification process by which we project our own embodied experiences onto the object via perspective taking. In closing this thesis, directions for further research are suggested. In addition, we speculate on the relevance of our findings for studies addressing facets of product experience not or sparsely discussed in this thesis, such as the expressiveness of product- materials or sounds, and the role of contextual factors.Industrial Design Engineerin
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