Tyndall National Institute - Journal Articles
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- ItemWater-soluble binders that improve electrochemical sodium-ion storage properties in a NaTi2(PO4)3 anode(IOP Publishing, 2023-05-22) Zhang, Yan; Grant, Alex; Carroll, Aoife; Gulzar, Umair; Ferguson, Matthew; Roy, Ahin; Nicolosi, Valeria; O'Dwyer, Colm; Horizon 2020; Irish Research Council; Science Foundation IrelandWater-soluble binders are demonstrated to provide significantly better capacity, cycle life stability and rate response for NASICON-type NaTi2(PO4)3 Na-ion battery anodes during reversible sodiation compared to electrodes made using polyvinylidene difluoride-containing slurries. The role of carboxymethyl cellulose (CMC) binders on the physical structure and chemical interfacial reactions with sodium-poor NaTi2(PO4)3 are uncovered using electron microscopy and spectroscopy data and we show that a more stable NASICON NaTi2(PO4)3 structure is found from the desodiation process from compensation of sodium deficiencies in the NaTi2(PO4)3 by extra sodium from the CMC binder. When the binder comprises CMC and a styrene butadiene rubber (SBR) additive, the electrode delivers significantly better voltammetric and galvanostatic electrochemical response with a specific capacity of ∼120 mAh g−1 with capacity retention of 90.5% for 500 cycles at 0.2 C (1 C = 133 mAh g−1), and ∼54 mAh g−1 at 20 C. The durability of the electrode during cycling and the stability of the redox processes ensures a higher capacity, longer cycle life electrode which is important for sustainable materials development for Na-ion technologies.
- ItemSIW-DGS bandpass filter design for C band satellite communications(Springer Nature Switzerland AG, 2023-03-29) Nasser, Mohammed; Celik, Ali Recai; Helhel, Selcuk; Akdeniz ÜniversitesiIn this paper, a bandpass filter is designed and fabricated for C-band satellite communication applications. The substrate integrated waveguide and defected ground structures are used in the design process. CST Microwave Studio software is used to analyze and design the proposed filter. It is built over DiClad 880 laminate having a thickness of 0.508 mm, and formed by etching three cascaded DGS cells on the SIW’s top plane. There is a good agreement between the simulated and measured results. The filter is centered at 6.175 GHz with 500 MHz bandwidth (8.1% fractional bandwidth) in line with applicable US Federal Communications Committee Rules. The simulated insertion loss at the center frequency is around 0.80 dB and the return loss in the passband is better than 30 dB. The measured minimum insertion loss is 1.4 dB, and the measured return loss in the passband is better than 14.5 dB. The obtained results are presented, discussed, and compared with other studies. It can be said that the features of the proposed filter such as size, order, return loss, insertion loss, upper band rejection, etc. are better than those of many other filters given in the literature.
- ItemFactors Influencing Continued Wearable Device Use in Older Adult Populations: Quantitative Study.(JMIR Publications, 2023-01-19) Muñoz Esquivel, Karla; Gillespie, James; Kelly, Daniel; Condell, Joan,; Davies, Richard; McHugh, Catherine; Duffy, William; Nevala, Elina; Alamäki, Antti; Jalovaara, Juha; Tedesco, Salvatore; Barton, John; Timmons, Suzanne; Nordström, Anna; InterregThe increased use of wearable sensor technology has highlighted the potential for remote telehealth services such as rehabilitation. Telehealth services incorporating wearable sensors are most likely to appeal to the older adult population in remote and rural areas, who may struggle with long commutes to clinics. However, the usability of such systems often discourages patients from adopting these services. This study aimed to understand the usability factors that most influence whether an older adult will decide to continue using a wearable device. Older adults across 4 different regions (Northern Ireland, Ireland, Sweden, and Finland) wore an activity tracker for 7 days under a free-living environment protocol. In total, 4 surveys were administered, and biometrics were measured by the researchers before the trial began. At the end of the trial period, the researchers administered 2 further surveys to gain insights into the perceived usability of the wearable device. These were the standardized System Usability Scale (SUS) and a custom usability questionnaire designed by the research team. Statistical analyses were performed to identify the key factors that affect participants' intention to continue using the wearable device in the future. Machine learning classifiers were used to provide an early prediction of the intention to continue using the wearable device. The study was conducted with older adult volunteers (N=65; mean age 70.52, SD 5.65 years) wearing a Xiaomi Mi Band 3 activity tracker for 7 days in a free-living environment. The results from the SUS survey showed no notable difference in perceived system usability regardless of region, sex, or age, eliminating the notion that usability perception differs based on geographical location, sex, or deviation in participants' age. There was also no statistically significant difference in SUS score between participants who had previously owned a wearable device and those who wore 1 or 2 devices during the trial. The bespoke usability questionnaire determined that the 2 most important factors that influenced an intention to continue device use in an older adult cohort were device comfort (t=0.34) and whether the device was fit for purpose (t=0.34). A computational model providing an early identifier of intention to continue device use was developed using these 2 features. Random forest classifiers were shown to provide the highest predictive performance (80% accuracy). After including the top 8 ranked questions from the bespoke questionnaire as features of our model, the accuracy increased to 88%. This study concludes that comfort and accuracy are the 2 main influencing factors in sustaining wearable device use. This study suggests that the reported factors influencing usability are transferable to other wearable sensor systems. Future work will aim to test this hypothesis using the same methodology on a cohort using other wearable technologies.
- ItemDesign, theoretical, and experimental investigation of tensile-strained germanium quantum-well laser structure(ACS Publications, 2021-10-14) Hudait, Mantu K.; Murphy-Armando, Felipe; Saladukha, Dzianis; Clavel, Michael B.; Goley, Patrick S.; Maurya, Deepam; Bhattacharya, Shuvodip; Ochalski, Tomasz J.; National Science Foundation; Science Foundation IrelandStrain and band gap engineered epitaxial germanium (ε-Ge) quantum-well (QW) laser structures were investigated on GaAs substrates theoretically and experimentally for the first time. In this design, we exploit the ability of an InGaAs layer to simultaneously provide tensile strain in Ge (0.7–1.96%) and sufficient optical and carrier confinement. The direct band-to-band gain, threshold current density (Jth), and loss mechanisms that dominate in the ε-Ge QW laser structure were calculated using first-principles-based 30-band k·p electronic structure theory, at injected carrier concentrations from 3 × 1018 to 9 × 1019 cm–3. The higher strain in the ε-Ge QW increases the gain at higher wavelengths; however, a decreasing thickness is required by higher strain due to critical layer thickness for avoiding strain relaxation. In addition, we predict that a Jth of 300 A/cm2 can be reduced to <10 A/cm2 by increasing strain from 0.2% to 1.96% in ε-Ge lasing media. The measured room-temperature photoluminescence spectroscopy demonstrated direct band gap optical emission, from the conduction band at the Γ-valley to heavy-hole (0.6609 eV) from 1.6% tensile-strained Ge/In0.24Ga0.76As heterostructure grown by molecular beam epitaxy, is in agreement with the value calculated using 30-band k·p theory. The detailed plan-view transmission electron microscopic (TEM) analysis of 0.7% and 1.2% tensile-strained ε-Ge/InGaAs structures exhibited well-controlled dislocations within each ε-Ge layer. The measured dislocation density is below 4 × 106 cm–2 for the 1.2% ε-Ge layer, which is an upper bound, suggesting the superior ε-Ge material quality. Structural analysis of the experimentally realistic 1.95% biaxially strained In0.28Ga0.72As/13 nm ε-Ge/In0.28Ga0.72As QW structure demonstrated a strained Ge/In0.28Ga0.72As heterointerface with minimal relaxation using X-ray and cross-sectional TEM analysis. Therefore, our monolithic integration of a strained Ge QW laser structure on GaAs and ultimately the transfer of the process to the Si substrate via an InGa(Al)As/III–V buffer architecture would provide a significant step toward photonic technology based on strained Ge on a Si platform.
- ItemMicrofluidic-based bacterial molecular computing on a chip(Institute of Electrical and Electronics Engineers (IEEE), 2022-07-25) Martins, Daniel P.; Taynnan Barros, Michael; O’Sullivan, Benjamin J.; Seymour, Ian; O’Riordan, Alan; Coffey, Lee; Sweeney, Joseph B.; Balasubramaniam, Sasitharan; Science Foundation Ireland; Department of Agriculture, Food, and Marine; Science Foundation IrelandBiocomputing systems based on engineered bacteria can lead to novel tools for environmental monitoring and detection of metabolic diseases. In this paper, we propose a Bacterial Molecular Computing on a Chip (BMCoC) using microfluidic and electrochemical sensing technologies. The computing can be flexibly integrated into the chip, but we focus on engineered bacterial AND Boolean logic gate and ON-OFF switch sensors that produces secondary signals to change the pH and dissolved oxygen concentrations. We present a prototype with experimental results that shows the electrochemical sensors can detect small pH and dissolved oxygen concentration changes created by the engineered bacterial populations’ molecular signals. Additionally, we present a theoretical model analysis of the BMCoC computation reliability when subjected to unwanted effects, i.e., molecular signal delays and noise, and electrochemical sensors threshold settings that are based on either standard or blind detectors. Our numerical analysis found that the variations in the production delay and the molecular output signal concentration can impact on the computation reliability for the AND logic gate and ON-OFF switch. The molecular communications of synthetic engineered cells for logic gates integrated with sensing systems can lead to a new breed of biochips that can be used for numerous diagnostic applications.