Heriot-Watt University
  • Scotland, United Kingdom
Recent publications
The Antipodal Vivaldi Antenna (APVA) has been identified as a promising technology for use in 5G systems due to its high frequency, wide bandwidth, and high gain. In this study, we evaluated the performance of the APVA using Ferro A6s substrate at 60 GHz and compared it with other substrates. Our findings demonstrate that the Ferro A6s substrate exhibits superior performance in terms of return loss, gain, and bandwidth when compared with other substrates. Our research contributes to the field of high-frequency wireless communication and can pave the way for the development of better 5G systems. The results of this study have the potential to revolutionize 5G backbone communication.
In this study, we used 3D printing technology to develop and create a quad-ridged horn antenna for use in GSM mid-band and 5G networks. This antenna can function on two different frequencies, 1.8 and 3.5 GHz. Polylactic acid (PLA), a thermoplastic polymer recognised for its outstanding strength and adaptability for 3D printing, was used to create the prototype. The effect of various dimension adjustments on the antenna's performance was studied through a series of parametric experiments. Ridge heights of 3, 4, and 6.25 mm were thoroughly tested. The investigation found that the antenna had a reflection of −16.89 dB at 1.8 GHz and −28.60 dB at 3.5 GHz, proving that it could function at both frequencies with great efficiency. This study proves that 3D printing may be used to create functional prototypes of antennas for use in GSM mid-band and 5G networks. As an added bonus, it stresses the significance of parametric studies in antenna design for peak efficiency.
In human-altered environments, wildlife is impacted by a range of factors; therefore, understanding on responsible factors can aid in developing conservation strategies. Irrawaddy Dolphins (IRD: Oracella brevirostris) are a group of cetaceans listed as highly endangered species under - threatened species red list of IUCN. A subpopulation of IRD is found in Chilika lagoon, a brackish-water ecosystem in the eastern seaboard of India, which is also the single largest habitat of IRD in the world. They are survived by only a few hundred individuals in small pockets in Chilika and are therefore given maximum protection under the Indian Wildlife Protection Act (1972), but much remains to be done for their conservation as they have not drawn enough investigation. This article comprehensively synthesizes existing literature on IRD, has established linkages between their behavior and physiology with threats (both climate-driven and anthropogenic), and has finally laid down a conservation and management roadmap to safeguard their future in Chilika. Damming and diversion of rivers opening in Chilika, unsustainable dolphin watching tourism, pollution, and net entanglement are some of the prominent threats faced by IRD in Chilika. Predicted climate change scenarios such as potential warming of the lagoon, increased littoral drift, sea level rise, and increased frequency of cyclones would exacerbate their survival crisis. It is also emphasized that the conservation strategy of IRD must be moved from species-centric to ecosystem-based for their long-term sustenance.
Identifying the factors that influence the citation of articles helps authors improve the impact and reach of their research. Analysis of publications in the Journal of Fish Biology between 2008‐2021 revealed that variables such as the number of keywords, abstract length, number of authors and page length were associated with higher impact papers. These trends applied to both review and regular papers. These findings suggest that papers that are more informative, have higher numbers of authors, and more keywords are more likely to be cited. Adoption of some simple ‘best‐practice’ behaviours can improve the likelihood that a paper is cited. This article is protected by copyright. All rights reserved.
AIMS To succeed in clinical trials for glioblastoma we need in vitro models capable of more faithfully replicating dis- ease biology and more accurately predicting patient drug responses. To this end, new bioprinting technologies have the potential to biofabricate clinically relevant biomimetic tissues which can accelerate drug discovery and additionally serve as a platform for personalized medicine. METHOD We evaluated the effect of individual biomaterials and combinations of biomaterials, including decellularised pig brain extracellular matrix (dECM), fibrin, gelatin-methacryloyl (GelMA), hyaluronic acid-methacrylate (HAMA), Matrigel and alginate, on the proliferation and invasion of aggressive brain cancer cells (U87) in vitro. Cell viability was assessed using propidium iodide. Invasiveness was studied employing confocal microscopy. Data generated from Z-stacks was analysed using ImageJ to determine the size and circularity of cells. RESULTS Although Matrigel supports rapid cell proliferation and invasion, it has mechanical properties unsuited to bio- printing. In contrast, HAMA displays a pronounced shear-thinning behaviour and rapid controllable photo- crosslinking. Combinations of HAMA-fibrin provided results comparable to those seen with Matrigel or HAMA- Matrigel. However, high levels of crosslinking affected these biomaterial mixtures, resulting in a decreased ability of cells to grow and spread. CONCLUSIONS Initial results indicate that the addition of fibrin to HAMA promoted the growth and spreading of U87 cells. In further work, we aim to improve our printed constructs by including porcine brain dECM, microglia and recently established cell lines from paediatric patients. The project will test whether these bioprinted models can provide drug testing data with closer results to human disease than current, simpler alternatives.
The rapid development of seafood trade networks alongside the decline in biomass of many marine populations raises important questions about the role of global trade in fisheries sustainability. Mounting empirical and theoretical evidence shows the importance of trade development on commercially exploited species. However, there is limited understanding of how the development of trade networks, such as differences in connectivity and duration, affect fisheries sustainability. In a global analysis of over 400,000 bilateral trade flows and stock status estimates for 876 exploited fish and marine invertebrates from 223 territories, we reveal patterns between seafood trade network indicators and fisheries sustainability using a dynamic panel regression analysis. We found that fragmented networks with strong connectivity within a group of countries and weaker links between those groups (modularity) are associated with higher relative biomass. From 1995 to 2015, modularity fluctuated, and the number of trade connections (degree) increased. Unlike previous studies, we found no relationship between the number or duration of trade connections and fisheries sustainability. Our results highlight the need to jointly investigate fisheries and trade. Improved coordination and partnerships between fisheries authorities and trade organizations present opportunities to foster more sustainable fisheries.
A novel dual-input DC-DC boost converter that can perform the integration of harvested energy from solar and vibrational input energy sources is proposed. Firstly, the background of a hybrid energy system that relates to multi-input DC-DC converters is discussed, and the limitations of the current designs of power converter ICs are highlighted. A detailed design analysis of the proposed converter was done to justify its performance. A current and voltage stress analysis has been performed to ensure suitable switching devices are selected for the converter. Two different power control strategies are proposed for the DIDCB converter to manage output voltage during source and load-side disturbances. Performance analysis of the circuit is carried out using MATLAB Simulink software. Different duty ratios for power switches in the converter were tested to determine the maximum boost ratio and the highest efficiency that can be achieved by the converter. To demonstrate the feasibility of the proposed converter, the performance of the converter is compared with existing converter topologies. The proposed converter achieved a high efficiency of 99.4%, had less fluctuation in the output voltage, and had reduced overshoot. In addition, the proposed converter demonstrated a simpler configuration and required fewer component counts, which helped reduce the cost and size of the system.
While concepts of connectivity are increasingly used in determining locations for marine protected areas, they are much less applied in the management of fish stocks, which are assumed to be well-mixed populations. However, due to seascape structure and often asymmetrical dispersal, the stocks of many species are unlikely to be well mixed and there is potential to enhance management by utilising emerging ecological modelling approaches that incorporate functional connectivity. Here, we apply a new model, MerMADE, that couples biophysical modelling of dispersal with spatial population demography, to predict within-stock patterns of connectivity of sandeels in the North Sea. By deriving origin- and destination-centrality measures, we highlight a set of key origin sites within the area occupied by the stock that contribute immigrants to many other sites and also identify patches that are particularly isolated, unlikely to receive immigrants from elsewhere. We show that the connectivity characteristics of the stock have a strong impact on how rapidly it recovers following a major harvesting event that leads to a patch depletion. Furthermore, the recovery of a local population will depend on the demographic status of the sites from which it can obtain immigrants. Thus, sites that provide strong out-centrality (especially if they themselves have weak in-centrality) and sites that are especially isolated should be harvested less heavily. To reduce the potential for local or regional stock collapse, models incorporating both biophysical dispersal and local demography are needed to support spatially explicit management of commercial marine species.
For the past decade, circular economy (CE) has gained widespread recognition as an umbrella of strategies that can help society better manage resources in the pursuit of sustainability. A CE favors Circular Business Models (CBMs) that cycle existing materials, extend the life of products, intensify the use of fewer resources, or dematerialize the economy. However, whilst many businesses and supply chains have tried to become more circular in recent years, not all have been successful. The limited application of circularity potentially indicates the existence of trade-offs at the business or supply chain levels; however, there is limited empirical evidence to draw upon to theorize about such tensions and trade-offs, particularly evidence from units of analysis broader than single focal companies. This study therefore aimed to address this knowledge gap by investigating the positive and negative implications of cycling, extending, intensifying, and dematerializing business models for the business and for the supply chain. The phenomenon was explored through eight qualitative case studies in different industries. Data were collected from semi-structured interviews and triangulated with secondary publicly available sources. As a result, we present our findings on the positive and negative implications of CBMs, contributing to the theory with propositions on the trade-offs of the CE. This study also has implications for practitioners by helping them understand and contrast different circular possibilities in their businesses and supply chains.
We recently identified CaCuP as a potential low cost, low density thermoelectric material, achieving zT = 0.5 at 792 K. Its performance is limited by a large lattice thermal conductivity, κL, and by intrinsically large p-type doping levels. In this paper, we address the thermal and electronic tunability of CaCuP. Isovalent alloying with As is possible over the full solid solution range in the CaCuP1–xAsx series. This leads to a reduction in κL due to mass fluctuations but also to a detrimental increase in p-type doping due to increasing Cu vacancies, which prevents zT improvement. Phase boundary mapping, exploiting small deviations from 1:1:1 stoichiometry, was used to explore doping tunability, finding increasing p-type doping to be much easier than decreasing the doping level. Calculation of the Lorenz number within the single parabolic band approximation leads to an unrealistic low κL for highly doped samples consistent with the multiband behavior in these materials. Overall, CaCuP and slightly Cu-enriched CaCu1.02P yield the best performance, with zT approaching 0.6 at 873 K.
Estuaries are among the highly productive coastal ecosystems and are considered biogeochemical hotspots. In estuaries, phytoplankton are the important primary producers that support dynamic food web. This study reviews the variability of phytoplankton primary production (PPP) in Indian estuaries by comprehensively analyzing available literature to understand the patterns of productivity and its environmental control. Only two methods have been deployed to measure PPP in Indian estuaries; among them, the oxygen evolution method (19 out of 30 studies) was way more popular than the 14C incubation method (11 out of 30 studies). PPP of west coast estuaries registered a wider range of values (4–11,934 mg C m−3 day−1) compared to east coast estuaries (24–4272 mg C m−3 day−1). Among the riverine estuaries (RE), lagoons, and backwater, the highest PPP values were recorded from Hooghly RE (4272 mg C m−3 day−1), Muthupet lagoon (3656 mg C m−3 day−1), and Cochin backwater (11,934 mg C m−3 day−1), respectively. A striking seasonality in PPP can be seen in Indian estuaries in relation to monsoon – the water column productivity driven by phytoplankton reaches its maximum during the post-monsoon season (October–December) when residence time of water parcel, light penetration, and nutrient levels reach their optimum. This is the time window when dominantly heterotrophic Indian estuaries turn autotrophic. Alternatively, in the months of monsoon (July - September), high surface runoff of refractile terrestrial detritus fuels extremely high bacterial respiration and decomposition, resulting in high CO2 partial pressure and air-water exchange in Indian estuaries. The PPP in Indian estuaries is controlled by the complex interplay of inorganic macronutrient stoichiometry at spatial-seasonal scale. However, a general lack of interest among the scientific communities can be seen when it comes to PPP-related investigation in Indian estuaries, as the SCOPUS database retrieved only 58 research paper records during 1965 to 2021. In the context of climate change, increased anthropogenetic pressure, and coastal developments, more intensive and regular study on estimating and understanding PPP in Indian estuaries is needed.
Transparent conducting oxides (TCOs) show unprecedented optical nonlinearities in the near infrared wavelength range, where the real part of their linear refractive index approaches zero. More specifically, the Kerr nonlinearities of these materials have sparked widespread attention due to their magnitude and speed. However, due to the absorptive nature of these nonlinear processes, it is of fundamental interest to further investigate the imaginary component of the nonlinear index. The present work studies the nonlinear optical absorption properties of aluminium‐doped zinc oxide (AZO) thin films in their near‐zero‐index (NZI) spectral window. It is found that the imaginary part of the refractive index is reduced under optical excitation such that the field penetration depth more than doubles. An optically induced shift of the NZI bandwidth of ≈120 nm for a pump intensity of 1.3 TW cm ⁻² is also demonstrated. Looking into the optically induced spectral redistribution of the probe signal, local net gain is recorded, which is ascribed to a nonlinear adiabatic energy transfer. The present study adds key information about the fundamental interplay between real and imaginary nonlinear indices in NZI media, while advancing parametric amplification as viable direction for loss compensation.
Microbes play a significant role in the degradation of petroleum hydrocarbons in the oceans, yet little is known about the native bacteria that metabolize hydrocarbons before an oil spill. The Faroe-Shetland Channel (FSC) is a deepwater subarctic region of the North Atlantic with prominent oil production and a diverse microbial community associated with the degradation of petroleum. Here, we combine DNA-based stable-isotope probing (DNA-SIP) with metagenomics to elucidate the metabolic underpinnings of native alkane-degrading bacteria from the FSC. From two ¹³ C n -hexadecane SIP experiments using seawater from 5 and 700 m depths in the FSC, we obtained 42 metagenome-assembled genomes (MAGs) belonging to 19 genera, including two previously overlooked hydrocarbon-degrading bacteria, Lentibacter (Alphaproteobacteria) and Dokdonia (Bacteroidetes). Diversity surveys indicated Lentibacter were dominant members of the FSC, constituting up to 17% of these communities. Many of the SIP-enriched MAGs (20/42) encoded a complete alkane oxidation pathway, including alkane monooxygenase (AlkB), rubredoxin reductase (AlkT), and rubredoxin-2 (AlkG). Fourteen Aphaproteobacteria MAGs lacked AlkG for electron transfer. Instead, they encoded novel disulfide isomerases with iron-binding cysteine motifs conserved across rubredoxins. Dokdonia lacked AlkT and AlkG, however, their central alkane-degradation catabolic pathways were complete. We describe previously unrecognized bacteria capable of hydrocarbon degradation, including the dominant genera Lentibacter , which may continuously purge hydrocarbons released from oil exploration activities in the FSC. This advances the understanding of the diversity and physiologies of alkane degradation in the North Atlantic and provides evidence of new mechanisms used to metabolize alkanes. IMPORTANCE Petroleum pollution in the ocean has increased because of rapid population growth and modernization, requiring urgent remediation. Our understanding of the metabolic response of native microbial communities to oil spills is not well understood. Here, we explored the baseline hydrocarbon-degrading communities of a subarctic Atlantic region to uncover the metabolic potential of the bacteria that inhabit the surface and subsurface water. We conducted enrichments with a ¹³ C-labeled hydrocarbon to capture the fraction of the community actively using the hydrocarbon. We then combined this approach with metagenomics to identify the metabolic potential of this hydrocarbon-degrading community. This revealed previously undescribed uncultured bacteria with unique metabolic mechanisms involved in aerobic hydrocarbon degradation, indicating that temperature may be pivotal in structuring hydrocarbon-degrading baseline communities. Our findings highlight gaps in our understanding of the metabolic complexity of hydrocarbon degradation by native marine microbial communities.
The spread of the brown seaweed Sargassum muticum is one of the best documented invasions of a non-native marine species. Observation of a potentially established population of S. muticum in the Orkney Islands archipelago, located off the northern coast of Scotland, was reported by recreational snorkellers in 2019 and 2020. The present study summarises a focussed investigation to confirm its presence and current local distribution, using data from 46 survey sites monitored as a part of the Orkney Islands Council Harbour Authority monitoring programme. Findings in this study represent the most northerly record of an established population of S. muticum in the United Kingdom, extending the latitudinal range in this country by 1.44° (159 km) northwards, and indicate only localised presence of this species. Analysis of a partial cytochrome oxidase I gene sequence confirmed the visual species identification. Possible vectors of introduction, gaps in the geographic range, local ecological and economic impacts, and the potential ameliorating factor of deep rockpools on wave exposed shores for S. muticum are discussed.
This paper explores the influence of military directors in protecting shareholders’ wealth through CEO compensation and corporate dividend payout policies. Based on manually collected data on corporate boards of non-financial companies operating in Pakistan, the results indicate a significant negative association between the presence of military directors on corporate boards and CEO compensation, thus supporting the notion that such directors are effective in monitoring and curtailing excessive rent seeking behaviour by the agents. In other words, presence of military directors on Pakistani corporate boards reduces agency costs and in turn enhances shareholders’ wealth. Results also indicate significant positive relationship between presence of military directors on boards and dividend payout, hence signifying that such directors are effective in enhancing shareholders’ wealth by reducing free cash flow opportunities that would otherwise be deployed by agents for their private benefits. We further found military directors with business education and wider networks to have significant positive association with dividend payout but not the case with CEO compensation. We control for board attributes, agent heterogeneity and firm-specific attributes in all our models. Overall, the benefits of military directors’ inclusion on corporate boards in Pakistan have far broader strategic, economic and policy implications on the nation besides resolving the principal-agent problems in the boardroom.
A pair of simulated left and right circularly polarized ultra‐fast laser pulses of duration 20 femtoseconds that induce a mixture of excited states are applied to ethane. The response of the electron dynamics is investigated within the next generation quantum theory of atoms in molecules (NG‐QTAIM) using third‐generation eigenvector‐trajectories which are introduced in this work. This enables an analysis of the mechanical and chiral properties of the electron dynamics of ethane without needing to subject the C‐C bond to external torsions as was the case for second‐generation eigenvector‐trajectories. The mechanical properties, in particular, the bond‐flexing and bond‐torsion were found to increase depending on the plane of the applied laser pulses. The bond‐flexing and bond‐torsion, depending on the plane of polarization, increases or decreases after the laser pulses are switched off. This is explainable in terms of directionally‐dependent effects of the long‐lasting superpositions of excited states. The chiral properties correspond to the ethane molecule being classified as formally achiral consistent with previous NG‐QTAIM investigations. Future planned investigations using ultra‐fast circularly polarized lasers are briefly discussed.
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17,295 members
Yeaw Chu Lee
  • Department of Mechanical Engineering
Dhanan Sarwo Utomo
  • Edinburgh Business School
Mark G. J. Hartl
  • Centre for Marine Biodiversity and Biotechnology, School of Life Sciences
Eamon P. McErlean
  • Department of Electrical, Electronic and Computer Engineering
Debaditya Choudhury
  • Institute of Photonics and Quantum Sciences (IPaQS)
Heriot-Watt University, Scotland, United Kingdom