Issues and Methods Concerning the Evaluation of Hypersingular and Near-Hypersingular Integrals in BEM Formulations

It is known that higher order modeling of the sources and the geometry in Boundary Element Modeling (BEM) formulations is essential to highly efficient computational electromagnetics. However, in order to achieve the benefits of hIgher order basis and geometry modeling, the singular and near-singular terms arising in BEM formulations must be integrated accurately. In particular, the accurate integration of near-singular terms, which occur when observation points are near but not on source regions of the scattering object, has been considered one of the remaining limitations on the computational efficiency of integral equation methods. The method of singularity subtraction has been used extensively for the evaluation of singular and near-singular terms. Piecewise integration of the source terms in this manner, while manageable for bases of constant and linear orders, becomes unwieldy and prone to error for bases of higher order. Furthermore, we find that the singularity subtraction method is not conducive to object-oriented programming practices, particularly in the context of multiple operators. To extend the capabilities, accuracy, and maintainability of general-purpose codes, the subtraction method is being replaced in favor of the purely numerical quadrature schemes. These schemes employ singularity cancellation methods in which a change of variables is chosen such that the Jacobian of the transformation cancels the singularity. An example of the sin,oularity cancellation approach is the Duffy method, which has two major drawbacks: 1) In the resulting integrand, it produces an angular variation about the singular point that becomes nearly-singular for observation points close to an edge of the parent element, and 2) it appears not to work well when applied to nearly-singular integrals. Recently, the authors have introduced the transformation u(x(prime))= sinh (exp -1) x(prime)/Square root of ((y prime (exp 2))+ z(exp 2) for integrating functions of the form I = Integral of (lambda(r(prime))((e(exp -jkR))/(4 pi R) d D where A (r (prime)) is a vector or scalar basis function and R = Square root of( (x(prime)(exp2) + (y(prime)(exp2) + z(exp 2)) is the distance between source and observation points. This scheme has all of the advantages of the Duffy method while avoiding the disadvantages listed above. In this presentation we will survey similar approaches for handling singular and near-singular terms for kernels with 1/R(exp 2) type behavior, addressing potential pitfalls and offering techniques to efficiently handle special cases

Experimental study of formwork tightness as a function of rheological properties of SCC

Several studies relating formwork pressure to rheology exist, however the relationship between rheology and leakage through formwork joints remains to be investigated. In practice, standard documents are used to define formwork tightness requirements, typically using a qualitative approach. To try bridge this gap in knowledge, we developed a test set-up to study tightness of formwork joints under pressure as a function of varying rheological properties. Coupled with standard rheology tests, this new test set-up provides means of linking flow rate, formwork pressure, flow area, and the rheological properties. The study seeks to provide insight on measurable governing parameters and thus inform formwork tightness requirements in a more quantifiable manner. This paper presents a test set-up designed to study the flow of fresh paste through small openings. It highlights a preliminary study on the pressure-driven flow of limestone paste through a bottom orifice in a cylindrical container. While this new device may not be directly representative of the actual conditions in formwork, it provides a good base for a fundamental study that can then be extrapolated to a more representative test operation. Preliminary results show a linear relationship between the flow rate and the applied pressure. The results also show that increasing the flow area by a factor of 2.33 had a higher impact than an increase in yield stress and viscosity by a factor of 2.54 and 3.80 respectively. However, more tests need to be carried out to obtain clear trends

Cement-Based Materials With Solid-Gel Phase Change Materials For Improving Energy Efficiency Of Building Envelope

This paper evaluated the cement-based materials incorporated with novel solid-gel phase change materials (PCMs) for improving the energy efficiency of building envelopes. This novel PCM is form-stable, which will not leak as solid-liquid PCMs do and not need encapsulation, and it features high energy-storage capacity. Experimental results showed that the thermal properties of cement-based materials were improved as the increase of PCM content. A 30% replacement of sand by volume with PCM can increase the latent heat of the mixture from around 0 to 7 J/g and decrease the thermal conductivity of PCM mortar based on the generalized self-consistent (GSC) model by about 20%. However, the workability and mechanical properties were compromised. The simulation results indicated that 30% PCM-incorporated walls can contribute to 5% energy saving for cooling in a whole year and 12% reduction in peak cooling load compared with the reference without PCM. The proposed PCM composite offers a promising avenue to achieve energy-efficient building envelopes

Molluscan diversity influenced by mangrove habitat in the khors of Qatar

The Exclusive Economic Zone (EEZ) of Qatar is a rapidly developing region within the Arabian Gulf, where monitoring of changes in benthic biodiversity and its functioning is needed. The influence of mangroves and seasonality on the nearshore subtidal molluscan diversity at three distinct khors (nearshore tidal bays) – natural mangroves (Al Dhakhira), planted mangroves (Al Mafyar) and no-mangroves (Dawhat Zekreet) – are investigated in this study. This study concludes that even the sub-tidal area is influenced by mangroves, and mangroves increase the diversity of molluscs compared to the site that lacks mangroves. The maximum salinity (59.8 psu) was observed at Dawhat Zekreet during summer, and the minimum (41.44 psu) at Al Dhakhira in winter. Chlorophyll a level was low for all the khors, and rarely exceeded 1 μg/L, depicting oligotrophic waters. Al Dhakhira demonstrated the highest molluscan species richness (32), and shared 28 species in common with Al Mafyar. Dawhat Zekreet had the fewest mollusc species number and no mangroves. When cumulative diversity over all seasons was considered, Dawhat Zekreet exhibited the lowest species richness; Al Dhakhira, the highest. Some mangrove regions have been already utilized for developmental activities, and Qatar needs to continue the program of mangrove conservation as a vital habitat for molluscs.Open access funding provided by the Qatar National Library. Part of this work has been supported by the QU-NIO joint IRCC project (No. IRCC-2019-002)

Assemblage of encrusting organisms on floating marine debris along the west coast of Qatar

The floating marine debris (FMD) and the associated rafting communities are one of the major stressors to ecosystem services, global biodiversity, economy, and human health. In this study, assemblages of encrusting organisms on different types of stranded FMD along the west coast of Qatar, Arabian Gulf (hereafter referred to as 'Gulf') were examined. The analysis showed 18 fouling species belonging to 5 phyla (Annelida, Anthropoda, Bryozoa, Mollusca and Porifera) on the FMD. The most abundant fouling species were the encrusting Amphibalanus amphitrite, polychaete Spirobranchus kraussii, Bryozoan species and Megabalanus coccopoma. More number of taxa were found on larger size FMD than on smaller FMD. Some of the barnacle rafting types were found to be non-indigenous species. The central and northwestern parts of Qatar had more FMD and fouled species than in other locations. The present study confirmed that huge amount of bio-fouled FMD items, causing great damage to biodiversity, drift in the surface layer of ocean under the influence of coastal dynamics, and eventually strand onto the beaches. We propose a simple, but an effective management plan for FMD and associated organisms at regional scale to restore the biodiversity, sustainability and health of the marine ecosystem in the Gulf

Older adults experiences of rehabilitation in acute health care

Rehabilitation is a key component of nursing and allied healthcare professionals’ roles in most health and social care settings. This paper reports on stage 2 of an action research project to ascertain older adult's experience of rehabilitation. Twenty postdischarge interviews were conducted and the interview transcripts were analysed using thematic content analysis. All older adults discharged from an acute older acute rehabilitation ward to their own homes in the community were eligible to participate. The only exclusion criterion was older adults who were thought to be unable to give consent to participate by the nurse in charge and the researcher. Whilst 92 older adults were eligible to participate in this research study, only 20 were interviewed. The findings from this study suggest that older adults valued communication with health professionals but were aware of their time constraints that hindered communication. This study suggests that both nurses and allied health professionals are not actively providing rehabilitative services to promote health and well-being, which contradicts the focus of active ageing. Furthermore, there was evidence of unmet needs on discharge, and older adults unable to recall the professions that were involved in their interventions and the rationale for therapy input. It is suggested that further research is needed to explore the effectiveness of allied health rehabilitation in the acute setting. This study highlights the need for further research into older adults’ perceptions of the rehabilitation process in the acute setting

Sources, spatial distribution and characteristics of marine litter along the west coast of Qatar

The spatial distribution, sources and characteristics of marine litter (ML) from 36 locations spread over 12 beaches along the west coast of Qatar have been assessed. A total of 2376 ML items with varying sizes were found with an average abundance of 1.98 items/m2. The order of abundance of ML along the coast was as follows: plastics (71.4%) > metal (9.3%) > glass (5.1%) > paper (4.4%) > fabric (4.0%) > rubber (3.9%) > processed wood (2.0%). Locations in the south and northwest coasts of Qatar had significantly higher concentrations of ML. Surprisingly, nearly 47% of the beached polyethylene terephthalate (PET) bottles were derived from the countries bordering the Arabian/Persian Gulf (Gulf), and most of them were produced in the last 2 years. The plastic materials were drifted by winds and currents to the Qatar coast. Gulf circulation provides evidence to the pathways of ML beached on the Qatar coast.We acknowledge ORS, QU for awarding the Project (QUEX-ESC-QP-TM-18/19), funded by the Qatar Petroleum

Microplastics in the beach sediments around the Ras Rakan Island, Qatar

The ubiquitous microplastic (MP) pollution is an emerging environmental issue in the marine environment. In this study, historical accumulation trends of MPs in the beach sediments around the Ras Rakan Island of Qatar have been established. The vertical distribution of MPs ranged from 0 to 665 particles/kg with maximum abundance at the surface layer (0-5 cm). Pellets were the dominant type of MPs in the surface sediments, whereas fibers were dominant in the bottom sediments. The polymer composition of MPs was identified using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy. Polyethylene (PE), polypropylene (PP), polyamide (PA), polyethylene terephthalate (PET), polyvinyl chloride (PVC) and Polystyrene (EPS) were the abundant polymers present in the sediments. High MP concentrations were found in the western and northern parts of the island. The prevailing winds, waves, tides and currents are the forces responsible for the distribution and transport of MPs from the offshore to the island and further to vertical re-distribution as time progresses. The level of MP pollution along the Coast of Ras Rakan Island was higher than that found on the coast of mainland Qatar. This informs that remote islands should also be considered for MP pollution monitoring to assess the risk associated with MP on the biota