Some aspects of near-surface vortices

An experimental investigation of the dynamics of near surface vortices is presented. Using digital particle image velocimetry, the velocity and vorticity fields of a vortex ring and a pair of undulated vortices were mapped as they rise toward a free surface. Circulation measurements indicate that vortex disconnection and appearance of the surface-normal vortices are simultaneous. Vortex disconnection due to the vorticity flux through the surface is shown to be related to the free-surface deceleration

Experimental studies of vortex disconnection and connection at a free surface

An experimental study is presented that examines the interaction of a vortex ring with a free surface. The main objective of this study is to identify the physical mechanisms that are responsible for the self-disconnection of vortex filaments in the near-surface region and the subsequent connection of disconnected vortex elements to the free surface. The understanding of those mechanisms is essential for the identification and estimation of the appropriate spatial and temporal scales of the disconnection and connection process. In this regard, the velocity and vorticity fields of an obliquely approaching laminar vortex ring with a Reynolds number of 1150 were mapped by using Digital Particle Image Velocimetry (DPIV). The evolution of the near-surface vorticity field indicates that the connection process starts in the side regions of the approaching vortex ring where surface-normal vorticity already exists in the bulk. A local strain rate analysis was conducted to support this conclusion. Disconnection in the near-surface tip region of the vortex ring occurs because of the removal of surfaceparallel vorticity by the viscous flux of vorticity through the surface. Temporal and spatial mapping of the vorticity field at the surface and in the perpendicular plane of symmetry shows that the viscous flux is balanced by a local deceleration of the flow at the surface. It is found that the observed timescales of the disconnection and connection process scale with the near-surface vorticity gradient rather than with the core diameter of the vortex ring

Drifting Apart? European Journalists and Their Audiences

How do the current technological changes and socio-political developments impact on the relationship between European journalists and their audiences? This article draws on selected findings from a larger research project conducted in eleven European countries. Focusing on European journalists’ understanding of their audiences, the paper suggests that in many European countries digital technologies and increased competition play a significant role in the changing relationship between journalists and their audiences. The literature reviews undertaken in the eleven European countries indicate that the relationship between journalists/media professionals and their audiences has undergone significant changes. While the interviewed journalists are alert to a shift towards journalistic practices and formats which permit certain forms of audience participation, many of them sense an increasing disconnection from the public and severe mistrust by citizens; which crucially impacts on their relationship with audiences

The Internet of Things Connectivity Binge: What are the Implications?

Despite wide concern about cyberattacks, outages and privacy violations, most experts believe the Internet of Things will continue to expand successfully the next few years, tying machines to machines and linking people to valuable resources, services and opportunities

Robust H8 design for resonant control in a CVCF inverter application over load uncertainties

CVCF (constant voltage, constant frequency) inverters are electronic devices used to supply AC loads from DC storage elements such as batteries or photovoltaic cells. These devices are used to feed different kinds of loads; this uncertainty requires that the controller fulfills robust stability conditions while keeping required performance. To address this, a robust H8 design is proposed based on resonant control to track a pure sinusoidal voltage signal and to reject the most common harmonic signals in a wide range of loads. The design is based on the definition of performance bounds in error signal and weighting functions for covering most uncertainty ranges in loads. Experimentally, the H8 controller achieves high-quality output voltage signal with a total harmonic distortion less than 2%Peer ReviewedPostprint (published version

Beyond Power over Ethernet : the development of Digital Energy Networks for buildings

Alternating current power distribution using analogue control and safety devices has been the dominant process of power distribution within our buildings since the electricity industry began in the late 19th century. However, with advances in digital technology, the seeds of change have been growing over the last decade. Now, with the simultaneous dramatic fall in power requirements of digital devices and corresponding rise in capability of Power over Ethernet, an entire desktop environment can be powered by a single direct current (dc) Ethernet cable. Going beyond this, it will soon be possible to power entire office buildings using dc networks. This means the logic of “one-size fits all” from the existing ac system is no longer relevant and instead there is an opportunity to redesign the power topology to be appropriate for different applications, devices and end-users throughout the building. This paper proposes a 3-tier classification system for the topology of direct current microgrids in commercial buildings – called a Digital Energy Network or DEN. The first tier is power distribution at a full building level (otherwise known as the microgrid); the second tier is power distribution at a room level (the nanogrid); and the third tier is power distribution at a desktop or appliance level (the picogrid). An important aspect of this classification system is how the design focus changes for each grid. For example; a key driver of the picogrid is the usability of the network – high data rates, and low power requirements; however, in the microgrid, the main driver is high power and efficiency at low cost

Surveillance and the Self: Understanding Privacy and Identity in Digital Environments

The widespread use of internet enabled devices among contemporary US adults has given rise to a series of questions about issues of identity, privacy and group behaviors. The increasing use of algorithmic systems in social media and the attendant privacy concerns among users may also contribute to increased levels of strategic management of identity among users. In order to contribute to this discussion, this project examines perceptions and practices of privacy and self-representation in digital spaces among college age adults 18-24. This project utilizes semi-structured interview data collected with college students in the Eastern United States and focuses on both behavioral and attitudinal patterns. I specifically consider the impact of strategic interventions of corporate media platforms to collect, distribute, manage and utilize individual level data on participants\u27 information consumption, individual identity representation and group affiliation. Preliminary data suggests that participants engage partial and strategic representations of self across diverse media platforms. Patterns of self-representation are shaped by a wide variety of factors including in-group online community norms, perceptions of visibility and privacy, algorithmic distributions of information and individual perceptions of technology. Furthermore, online identity, while partial and strategically created, has the potential to impact self-identity and group affiliation in a diverse set of offline and online contexts

Metadata Augmentation for Semantic- and Context- Based Retrieval of Digital Cultural Objects

Cultural objects are increasingly stored and generated in digital form, yet effective methods for their indexing and retrieval still remain an open area of research. The main problem arises from the disconnection between the content-based indexing approach used by computer scientists and the description-based approach used by information scientists. There is also a lack of representational schemes that allow the alignment of the semantics and context with keywords and low-level features that can be automatically extracted from the content of these cultural objects. This paper presents an integrated approach to address these problems, taking advantage of both computer science and information science approaches. The focus is on the rationale and conceptual design of the system and its various components. In particular, we discuss techniques for augmenting commonly used metadata with visual features and domain knowledge to generate high-level abstract metadata which in turn can be used for semantic and context-based indexing and retrieval. We use a sample collection of Vietnamese traditional woodcuts to demonstrate the usefulness of this approach