The DCU laser ion source

Laser ion sources are used to generate and deliver highly charged ions of various masses and energies. We present details on the design and basic parameters of the DCU laser ion source (LIS). The theoretical aspects of a high voltage (HV) linear LIS are presented and the main issues surrounding laser-plasma formation, ion extraction and modeling of beam transport in relation to the operation of a LIS are detailed. A range of laser power densities (I ∼ 108–1011 W cm−2) and fluences (F = 0.1–3.9 kJ cm−2) from a Q-switched ruby laser (full-width half-maximum pulse duration ∼ 35 ns, λ = 694 nm) were used to generate a copper plasma. In “basic operating mode,” laser generated plasma ions are electrostatically accelerated using a dc HV bias (5–18 kV). A traditional einzel electrostatic lens system is utilized to transport and collimate the extracted ion beam for detection via a Faraday cup. Peak currents of up to I ∼ 600 μA for Cu+ to Cu3+ ions were recorded. The maximum collected charge reached 94 pC (Cu2+). Hydrodynamic simulations and ion probe diagnostics were used to study the plasma plume within the extraction gap. The system measured performance and electrodynamic simulations indicated that the use of a short field-free (L = 48 mm) region results in rapid expansion of the injected ion beam in the drift tube. This severely limits the efficiency of the electrostatic lens system and consequently the sources performance. Simulations of ion beam dynamics in a “continuous einzel array” were performed and experimentally verified to counter the strong space-charge force present in the ion beam which results from plasma extraction close to the target surface. Ion beam acceleration and injection thus occur at “high pressure.” In “enhanced operating mode,” peak currents of 3.26 mA (Cu2+) were recorded. The collected currents of more highly charged ions (Cu4+–Cu6+) increased considerably in this mode of operation

Functional Morphology and Fluid Interactions During Early Development of the Scyphomedusa Aurelia aurita

Scyphomedusae undergo a predictable ontogenetic transition from a conserved, universal larval form to a diverse array of adult morphologies. This transition entails a change in bell morphology from a highly discontinuous ephyral form, with deep clefts separating eight discrete lappets, to a continuous solid umbrella-like adult form. We used a combination of kinematic, modeling, and flow visualization techniques to examine the function of the medusan bell throughout the developmental changes of the scyphomedusa Aurelia aurita. We found that flow around swimming ephyrae and their lappets was relatively viscous (1 < Re < 10) and, as a result, ephyral lappets were surrounded by thick, overlapping boundary layers that occluded flow through the gaps between lappets. As medusae grew, their fluid environment became increasingly influenced by inertial forces (10 < Re < 10,000) and, simultaneously, clefts between the lappets were replaced by organic tissue. Hence, although the bell undergoes a structural transition from discontinuous (lappets with gaps) to continuous (solid bell) surfaces during development, all developmental stages maintain functionally continuous paddling surfaces. This developmental pattern enables ephyrae to efficiently allocate tissue to bell diameter increase via lappet growth, while minimizing tissue allocation to inter-lappet spaces that maintain paddle function due to boundary layer overlap

Absolute photoionization cross section measurements of the Kr I-isoelectronic sequence

Photoionization spectra have been recorded in the 4s, 4p and 3d resonance regions for the Kr Iisoelectronic sequence using both the dual laser produced plasma technique (at DCU) to produce photoabsorption spectra, and the merged ion beam and synchrotron radiation technique (at ASTRID) to measure absolute photoionization cross sections. Profile parameters are compared for the 4s − np resonances of Rb+ and Sr2+. Many new 4p " ns, md transitions are identified with the aid of Hartree-Fock calculations, and consistent quantum defects are observed for the various ns and md Rydberg series. Absolute single and double photoionization cross sections recorded in the 3d region for Rb+ and Sr2+ ions show preferential decay via double photoionization. This is only the second report where both the DLP technique and the merged beam technique have been used simultaneously to record photoionization spectra, and the advantages of both techniques (i.e. better resolution in the case of DLP and values for absolute photoionization cross sections in the case of the merged beam technique) are highlighted

Techno-economic WEC system optimisation – Methodology applied to Wavebob system definition

The overall system optimisation of wave energy converters remains a challenging task. Firstly, this is associated with the large number of system parameters and their related constraints, secondly, the complexity of numerical system representations capturing overall system behaviour and, thirdly, the uncertainties in the prediction and formulation of appropriate overall economic system performance objectives. The parameterisation and the modelling challenges require a staged approach for an overall system optimisation. This ranges from simplified system representations exposed to variations within a large parameter space to more sophisticated system models subject to evaluation for a reduced and focused parameter zone. The description of the system dynamics, operation and performance needs to capture the key characteristics of the WEC concept functionality, the technical implementation and the economic application from the beginning and throughout the optimisation and development process. The paper describes the problems that are associated with the widely employed sequential development of wave energy converter (WEC) systems from concept through technology to economic application and presents the methodology applied to the overall techno-economic system optimisation and development process of Wavebob WECs

Techno-economic WEC system optimisation – Methodology applied to Wavebob system definition

The overall system optimisation of wave energy converters remains a challenging task. Firstly, this is associated with the large number of system parameters and their related constraints, secondly, the complexity of numerical system representations capturing overall system behaviour and, thirdly, the uncertainties in the prediction and formulation of appropriate overall economic system performance objectives. The parameterisation and the modelling challenges require a staged approach for an overall system optimisation. This ranges from simplified system representations exposed to variations within a large parameter space to more sophisticated system models subject to evaluation for a reduced and focused parameter zone. The description of the system dynamics, operation and performance needs to capture the key characteristics of the WEC concept functionality, the technical implementation and the economic application from the beginning and throughout the optimisation and development process. The paper describes the problems that are associated with the widely employed sequential development of wave energy converter (WEC) systems from concept through technology to economic application and presents the methodology applied to the overall techno-economic system optimisation and development process of Wavebob WECs

Understanding the Doctoral Capstone Coordinator Position: A Unique Faculty Role in Occupational Therapy Education

The doctoral capstone coordinator (DCC) position is a required faculty position in U.S. entry-level OTD programs, but there is limited information about this role. This descriptive study aimed to explore the demographics of DCCs; their required workload, tasks, and responsibilities; and the supports available to DCCs. The researchers administered an online survey and analyzed the data using descriptive statistics and content analysis. The results revealed much variability in DCCs’ experiences, workloads, and responsibilities across OTD programs. Of the DCCs survey, 74.0% previously held leadership positions in academia or clinical practice before taking the role, and 60.5% of the DCCs worked overtime for at least half of the previous year. Approximately half of the DCCs spent different percentages of time on teaching, research, service, and clinical responsibilities than expected by their universities. Common capstone tasks completed only by the DCC involved educating others about the capstone process, developing and evaluating the capstone processes, and teaching capstone courses. Tasks commonly completed with support include ensuring student completion of preparatory requirements, securing placements and affiliation agreements, and advising students. The responses varied regarding the individuals involved with mentoring and student assessment responsibilities. Overall, 67.7% of the DCCs were slightly to extremely satisfied with their existing workload

An efficient system for reliably transmitting image and video data over low bit rate noisy channels

This research project is intended to develop an efficient system for reliably transmitting image and video data over low bit rate noisy channels. The basic ideas behind the proposed approach are the following: employ statistical-based image modeling to facilitate pre- and post-processing and error detection, use spare redundancy that the source compression did not remove to add robustness, and implement coded modulation to improve bandwidth efficiency and noise rejection. Over the last six months, progress has been made on various aspects of the project. Through our studies of the integrated system, a list-based iterative Trellis decoder has been developed. The decoder accepts feedback from a post-processor which can detect channel errors in the reconstructed image. The error detection is based on the Huber Markov random field image model for the compressed image. The compression scheme used here is that of JPEG (Joint Photographic Experts Group). Experiments were performed and the results are quite encouraging. The principal ideas here are extendable to other compression techniques. In addition, research was also performed on unequal error protection channel coding, subband vector quantization as a means of source coding, and post processing for reducing coding artifacts. Our studies on unequal error protection (UEP) coding for image transmission focused on examining the properties of the UEP capabilities of convolutional codes. The investigation of subband vector quantization employed a wavelet transform with special emphasis on exploiting interband redundancy. The outcome of this investigation included the development of three algorithms for subband vector quantization. The reduction of transform coding artifacts was studied with the aid of a non-Gaussian Markov random field model. This results in improved image decompression. These studies are summarized and the technical papers included in the appendices

The TREC2001 video track: information retrieval on digital video information

The development of techniques to support content-based access to archives of digital video information has recently started to receive much attention from the research community. During 2001, the annual TREC activity, which has been benchmarking the performance of information retrieval techniques on a range of media for 10 years, included a ”track“ or activity which allowed investigation into approaches to support searching through a video library. This paper is not intended to provide a comprehensive picture of the different approaches taken by the TREC2001 video track participants but instead we give an overview of the TREC video search task and a thumbnail sketch of the approaches taken by different groups. The reason for writing this paper is to highlight the message from the TREC video track that there are now a variety of approaches available for searching and browsing through digital video archives, that these approaches do work, are scalable to larger archives and can yield useful retrieval performance for users. This has important implications in making digital libraries of video information attainable