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Item Laser surface alloying of a novel Nb11.2Cr22.2 Co22.2Ni22.2Cu22.2/TiN/VC composite coating: A preliminary parametric study(2024-12) Alabi, A; Popoola, A; Popoola, O; Mathe, Ntombizodwa RA preliminary investigation was conducted to choose process parameters for laser surface alloying of a novel high-entropy alloy-based composite coating on a steel substrate. The chosen ranges for laser power, scanning speed and powder feed rate are 1500 to 2500 W, 0.4 to 0.8 m/min ute and 0.14 to 0.24 g/minute, respectively. The study examined the effect of powder feed rate and scanning speed on the properties of single beads. B eads' geometrical properties were measured, from which dilution percentage and aspect ratio were calculated. The correlation between microstructure and hardness value was also investigated. The highest combination of desired properties was achieved at 1500 W, 0.4 m/minute and 0.14 g/minute parameter settings. The bead deposited at the optimal condition resulted in dilution percentage, aspect ratio, and hardness value of 80.16%, 14.47, and 447.47 ± 6.60 HV0.3, respectively. It hardness profile across deposited layer interface revealed that hardness values decreased across bead-heat affected zone-substrate interface in the order: 447.47 ± 6.60 HV0.3 > 339 ± 36.93 HV0.3 >155.3 ± 1.01 HV0.3. Scanning electron microscopy revealed excellent bead-substrate melt pool mixing, resulting in good interfacial bonding, cracking, and pore-free microstructure.Item Material selection and optimisation of a 3D-printed indoor aerial robotics platform(2024-12) De Ronde, Willis; Botha, Natasha; Van Eden, Beatrice; Tshabalala, Lerato CBoth aerial robotic platforms and additive manufacturing (AM) have become more affordable to consumers. Indoor aerial robotic platforms are typically small and lightweight, while AM is renowned for creating small, high-strength prototypes and components. This paper discusses the material selection and structural optimisation of a 3D-printed indoor aerial robotic platform. Three commonly used AM materials were compared using finite element analysis (FEA): acrylonitrile butadiene styrene (ABS), polyethylene terephthalate glycol (PETG), and Nylon. It was found that Nylon offered the best performance in terms of the strength-to-weight ratio. The aerial robotic frame was optimised using an iterative design approach and previous knowledge with regards to the breaks observed during flight crashes. A dynamic FEA was performed to simulate a drop test from a height of one meter to compare the optimised design with the previous frame design. It was found that the improvements in the redesign have led to a 13.67 % decrease in weight and a 11.78 % decrease stress of the aerial robotic frame. This not only demonstrates the effectiveness of design optimisation, but also highlights the commitment to producing more efficient, reliable and sustainable designs.Item Developments in localized surface plasmon resonance(2024-12) Mcoyi, Michael P; Mpofu, Kelvin T; Sekhwama, Masindi; Mthunzi-Kufa, PatienceLocalized surface plasmon resonance (LSPR) is a nanoscale phenomenon associated with noble metal nanostructures that has long been studied and has gained considerable interest in recent years. These resonances produce sharp spectral absorption and scattering peaks, along with strong electromagnetic near-field enhancements. Over the past decade, advancements in the fabrication of noble metal nanostructures have propelled significant developments in various scientific and technological aspects of LSPR. One notable application is the detection of molecular interactions near the nanoparticle surface, observable through shifts in the LSPR spectral peak. This document provides an overview of this sensing strategy. Given the broad and expanding scope of this topic, it is impossible to cover every aspect comprehensively in this review. However, we aim to outline major research efforts within the field and review a diverse array of relevant literature. We will provide a detailed summary of the physical principles underlying LSPR sensing and address some existing inconsistencies in the nomenclature used. Our discussion will primarily focus on LSPR sensors that employ metal nanoparticles, rather than on those utilizing extended, fabricated structures. We will concentrate on sensors where LSPR acts as the primary mode of signal transduction, excluding hybrid strategies like those combining LSPR with fluorescence. Additionally, our examination of biological LSPR sensors will largely pertain to label-free detection methods, rather than those that use metal nanoparticles as labels or as means to enhance the efficacy of a label. In the subsequent section of this review, we delve into the analytical theory underpinning LSPR, exploring its physical origins and its dependency on the material properties of noble metals and the surrounding refractive index. We will discuss the behavior of both spherical and spheroidal particles and elaborate on how the LSPR response varies with particle aspect ratio. Further, we detail the fundamentals of nanoparticle-based LSPR sensing. This includes an exploration of single-particle and ensemble measurements and a comparative analysis of scattering, absorption, and extinction phenomena. The discussion will extend to how these principles are applied in practical sensing scenarios, highlighting the key experimental approaches and measurement techniques.Item Insights on formation of oxide layers, corrosion, and hydrogen embrittlement on the Ti2AlNb (1 1 0) surface: Density functional theory study(2024-11) Tshwane, David M; Maleka, Prettier M; Dima, Ratshilumela S; Mogakane, Lethabo; Ngcobo, Thabani; Maphanga, Rapela RTi2AlNb alloys offer good mechanical qualities and promise for use in various applications, such as aero-engines and other industries. However, corrosion and hydrogen embrittlement remain important concerns and limitations for their use. In this work, first-principle density functional theory is used to investigate the adsorption of hydrogen, fluorine and oxygen on the surface of Ti2AlNb (1 1 0). The effects of the considered adsorbates on the surface were compared by analysing the adsorption energy, charge density differences, density of states, and work function. The current findings revealed that the adsorption behaviour of all the adsorbates is exothermic and spontaneous due to the negative adsorption energy. More importantly, the effect of Van der Waals forces and dispersion correction was considered, it was found that for all adsorbates the dispersion correction approach exhibited the most stable adsorption energies than the standard density functional theory. Thus, the standard DFT underestimates the adsorption energy. Furthermore, it was shown that the adsorption energy strength is dependent on the surface adsorption site, with the Ti-Nb and Al-Nb bridge sites being the most preferred sites for hydrogen, fluorine and oxygen adsorption. Subsequently, it was discovered that oxygen adsorption on the surface of Ti2AlNb (1 1 0) was more thermodynamically stable than hydrogen and fluorine. This suggests that the Ti2AlNb surface will likely suffer from oxidation rather than corrosion and hydrogen embrittlement. In addition, surface atoms showed electron-charge depletion, while adsorbates showed charge accumulation. The adsorption caused charge density redistribution and altered the surface work function.Item Aerodynamic design of an electronics pod to maximise its carriage envelope on a fast-jet aircraft(2024-12) Du Rand, R; Jamison, Kevin K; Huyssen, BarbaraThe purpose of this paper is to reshape a fast-jet electronics pod’s external geometry to ensure compliance with aircraft pylon load limits across its carriage envelope while adhering to onboard system constraints and fitment specifications. Initial geometric layout determination used empirical methods. Performance approximation on the aircraft with added fairings and stabilising fin configurations was conducted using a panel code. Verification of loads was done using a full steady Reynolds-averaged Navier–Stokes solver, validated against published wind tunnel test data. Acceptable load envelope for the aircraft pylon was defined using two already-certified stores with known flight envelopes. Re-lofting the pod’s geometry enabled meeting all geometric and pylon load constraints. However, due to the pod's large size, re-lofting alone was not adequate to respect aircraft/pylon load limitations. A flight restriction was imposed on the aircraft’s roll rate to reduce yaw and roll moments within allowable limits. The geometry of an electronics pod was redesigned to maximise the permissible flight envelope on its carriage aircraft while respecting the safe carriage load limits determined for its store pylon. Aircraft carriage load constraints must be determined upfront when considering the design of fast-jet electronic pods. A process for determining the unknown load constraints of a carriage aircraft by analogy is presented, along with the process of tailoring the geometry of an electronics pod to respect aerodynamic load and geometric constraints.Item Design of a 3D-printed test rig for micro aerial robotics platforms(2024-12) Botha, Natasha; De Ronde, Willis; Van Eden, BeatriceDuring the development of an aerial robotic platform, it is necessary to characterise the flight controller to ensure flight stability. Even though this can be done through open-source software like Betaflight, flight testing can result in potential crashes. To prevent this, this paper aims to design and manufacture a test rig to test and characterise the flight controller reliably. A 4-degree-of-freedom (DOF) test rig was developed to allow for vertical motion and characterise the yaw, pitch, and roll angles. It was also entirely constructed utilising additive manufacturing (AM). An iterative design approach was considered to improve the design after practical testing with a micro aerial robotic platform. This approach significantly enhanced the design of the ball joint and linear shaft to assist in better performance of the micro aerial robotic platform when using the test rig.Item Modelling the power consumption of a commercial unmanned aerial vehicle using machine learning(2024-12) Setati, Tiro; Nkomo, Brighton VAs popular as Unmanned Aerial Vehicles (UAVs) have become, one of their major drawbacks is their operational time. Specifications are provided about the possible length of their flights, but a detailed analysis of the operating time is needed when planning flights that utilise energy- consuming custom payloads without their own power supply. This paper makes use of flight data and various machine-learning algorithms to determine a power consumption model for a commercial UAV with a custom payload drawing power from the main power source to assist with flight planning, flight operations and battery management.Item 3D printed microfluidic chip design for diagnostic studies(2024-12) Sekhwama, Masindi; Mpofu, Kelvin T; Mcoyi, Michael P; Sivarasu, SIn this study, additive manufacturing (3D printing) is utilised to fabricate lateral flow microfluidic chips (LFMC). Our chips were designed using Autodesk design software and printed using a Formlabs 3D printer. They are printed using Formlabs V4 resin polymer. In this work, the design process is highlighted in detail and shows an LFMC design that is made for potential applications in diagnostics studies. Our study also tested the performance of one of the chip designs in actual diagnostics experiment on an optical transmittance setup with a peristaltic pump. The LFMC was integrated onto a custom-built transmittance optical biosensor to measure the transmission intensity. A real-time kinetic study was conducted using an HIV-1 oligonucleotide probe. The study involved performing real-time transmittance analysis by pumping the HIV-1 oligonucleotide probe at different flow rates, ranging from 9. 5 μm/min to 13 μm/min with intervals of 0.5 μm/min. During the experiment, transmission intensity or transmitted light was measured in real time as the oligonucleotide HIV probe bound to neutravidin immobilised on the Au metal surface. These measurements were recorded using a USB400 spectrometer, with a broad- band UV light source that emits wavelengths ranging from 400 to 800 nm. The study underscored the significance of microfluidic chips as devices capable of enhancing the performance of biosensors as well as the use of 3D printing in the design and manufacture of these microfluidic chips.Item The generation of human induced pluripotent stem cell lines from individuals of Black African ancestry in South Africa(2024-12) Naidoo, Jerolen; Hurrell, Tracey; Scholefield, JanineThe lack of equitable representation of African diversity in scientific resources, such as genome-wide association studies and human induced pluripotent stem cell (hiPSC) repositories, has perpetuated inequalities in the advancement of health research. HiPSCs could be transformative in regenerative and precision medicine, therefore, the generation of diverse lines is critical in the establishment of African-relevant preclinical cellular models. HiPSC lines were derived from two healthy donors of Black African ancestry using Sendai virus reprogramming of dermal fibroblasts, and characterised to confirm stemness markers, trilineage differentiation, and genetic integrity. These hiPSCs represent a valuable resource for modelling African relevant disease biology.Item The economic impacts of marine plastic debris in South Africa: A preliminary estimate(2024-12) Nahman, Anton; Oelofse, Suzanna H; Haywood, Lorren KMarine plastic debris can affect the delivery of ecosystem services and cause direct damage to affected industries; with resulting impacts on the economy. This paper applies a version of the benefits transfer method to provide a preliminary estimate of the economic impacts of marine plastic in South Africa, in terms of impacts on ecosystem services, direct damage to industry, and clean-up costs. The total economic impact associated with the plastic reaching South Africa's marine environment each year ranges between R3.5 billion and R34.9 billion per year (0.05 to 0.5 % of annual GDP), with a mid-range estimate of R14.1 billion per year (0.2 % of GDP). The cost per tonne of plastic (per year) ranges between R70 635 and R698 186 (mid-range estimate of R282 028 per tonne). The lifetime cost per tonne of marine plastic, in terms of its impacts on ecosystem services over its lifetime, ranges between R3.4 million and R33.8 million per tonne (mid-range estimate = R13.5 million per tonne). The plastic entering South Africa's marine environment each year imposes a total cost of between R169 billion and R1.69 trillion (mid-range estimate = R677 billion) in terms of impacts on ecosystem services over its lifetime. However, there is a need for further research to assess the full set of environmental, social and economic costs and benefits of plastics, of alternatives to plastic, and of various types of intervention strategies; to inform the most suitable strategies for reducing the leakage of plastic waste to the environment.Item Comparative investigation and optimization of cutting tools performance during milling machining of titanium alloy (Ti6Al4V) using response surface methodology(2024-02) Phokobye, SN; Desai, DA; Tlhabadira, I; Sadiku, ER; Mutombo, KalendaThe purpose of this paper is to study the optimization of the cutting performance of three different cutting inserts, during the machining operation of titanium alloy (Ti6Al4V) by making use of the response surface methodology (RSM) on a computer numerical control (CNC) milling. The cutting tools employed for the optimisation of the cutting performance during machining operation are silicon, aluminium, oxygen, nitrogen (SiAlON), cubic-boron nitride and carbide cutting inserts. Scanning electron microscope (SEM) was used for the determination of the tool wear for the cutting inserts being compared during machining of Ti6Al4V, and the cutting parameters, which are cutting speed (Vc), feed per tooth (fz) and depth-of-cut that were evaluated from the cutting tools as per the manufacturer’s design specifications. The determination of the tool wear on the cutting inserts was achieved by using the SEM, while the machining operation for the experimental trails was performed from the CNC milling machine, where face milling operation was executed. The optimization process showed that carbide cutting inserts yielded the best performing results and were considered the most significant choice of cutting insert in machining Ti6Al4V when compared to SiAlON and CBN cutting inserts. This choice was from the cutting tool life obtained where a cutting tool life of 29 min was obtained from a use of carbide cutting inserts; 28 min resulted from a use SiAlON cutting inserts and 26 min from a use of CBN cutting inserts. This work finds appropriate value in assisting the machinists in the selection of the best most performing and cost-effective cutting tool.Item Photoresponse properties of green-assisted Fe3O4 nanoparticles supported activated carbon(2024-11) Idisi, DO; Aigbe, UO; Chilukusha, D; Mwakikunga, Bonex W; Asante, JKOThe photoresponse properties of green synthesized Fe3O4 (gFe3O4) supported-activated carbon (AC/g-Fe3O4) were studied using a photocurrent characterization approach. Preliminary UV–Vis analysis suggested a reduction in the band gap energy when activated carbon is incorporated into gFe3O4 nanoparticles (2.61 → 1.57 eV). The current-voltage characteristics indicate semiconductor features for both gFe3O4 and AC/gFe3O4 nanoparticles. The photodetector measurements indicate a significantly enhanced response for AC/gFe3O4 and can be attributed to increased rectification and photogenerated carriers emanating from the activated carbon incorporation. The study proposes AC/gFe3O4 nanocomposite as a novel material that can be used for the fabrication of photodetectors and other related optoelectronic devices.Item Nature positive engineering in West Indian Ocean Ports: Perspectives on marine and estuarine ecology(2024-11) Weerts, Steven PThis presentation on nature-positive engineering in West Indian Ocean Ports includes the following discussions: Ecological processes in marine and estuarine systems lend resilience; They can be “created” (not necessarily restored); They can be “designed” (for function, but not predicted with certainty and multidisciplinary approaches increase degree of confidence.Item Assessing potential drug-drug interactions between clofazimine and other frequently used agents to treat drug-resistant tuberculosis(2024-04) Kengo, A; Nabeemeeah, F; Denti, P; Sabet, R; Okyere-Manu, G; Abraham, P; Weisner, L; Mosala, MH; Tshabalala, Sibongile; Scholefield, JanineClofazimine is included in drug regimens to treat rifampicin/drug-resistant tuberculosis (DR-TB), but there is little information about its interaction with other drugs in DR-TB regimens. We evaluated the pharmacokinetic interaction between clofazimine and isoniazid, linezolid, levofloxacin, and cycloserine, dosed as terizidone. Newly diagnosed adults with DR-TB at Klerksdorp/Tshepong Hospital, South Africa, were started on the then-standard treatment with clofazimine temporarily excluded for the initial 2 weeks. Pharmacokinetic sampling was done immediately before and 3 weeks after starting clofazimine, and drug concentrations were determined using validated liquid chromatography-tandem mass spectrometry assays. The data were interpreted with population pharmacokinetics in NONMEM v7.5.1 to explore the impact of clofazimine co-administration and other relevant covariates on the pharmacokinetics of isoniazid, linezolid, levofloxacin, and cycloserine. Clofazimine, isoniazid, linezolid, levofloxacin, and cycloserine data were available for 16, 27, 21, 21, and 6 participants, respectively. The median age and weight for the full cohort were 39 years and 52 kg, respectively. Clofazimine exposures were in the expected range, and its addition to the regimen did not significantly affect the pharmacokinetics of the other drugs except levofloxacin, for which it caused a 15% reduction in clearance. A posteriori power size calculations predicted that our sample sizes had 97%, 90%, and 87% power at P < 0.05 to detect a 30% change in clearance of isoniazid, linezolid, and cycloserine, respectively. Although clofazimine increased the area under the curve of levofloxacin by 19%, this is unlikely to be of great clinical significance, and the lack of interaction with other drugs tested is reassuring.Item Dry sliding wear behavior of experimental lowcost titanium alloys(2024-06) Rundora, NR; Klenam, DEP; Polat, S; Mathabathe, Maria N; Van der Merwe, J; Bodunrin, MOThe high cost and potential toxicity associated with the common commercial Ti-6Al-4V alloy are major concerns against its continued use in the biomedical industry. Low-cost, less toxic titanium alloys have been developed as a possible alternative to Ti-6Al-4V. Because of the various wear processes that take place in the human body, it is imperative to have a good understanding of the wear properties and wear resistance of these alloys. This study, therefore, investigated the resistance to wear of the low-cost Ti-3Fe, Ti-4.5Al-1V-3Fe, and Ti-4.5Al-1V-3Fe alloys under dry sliding conditions in contrast to the common commercial alloy, Ti-6Al-4V. The findings revealed that among the tested alloys, Ti-3Fe exhibited the lowest resistance to wear as it displayed the highest coefficient of friction (0.55) and wear rate (5.55E-06mm3/Nm). The Ti-4.5Al-1V-3Fe alloy demonstrated superior wear resistance compared to the rest of the alloys, including Ti-6Al-4V, as it had the lowest wear rate (4.27E-06mm3/Nm) and wear volume (0.0026mm3). Overall, the experimental alloys displayed very similar wear resistance to Ti-6Al-4V, making them promising commercial alloys that can replace Ti-6Al-4V in bioimplant applications.Item NASA Bioreach field campaign for assessing the capabilities of remote sensing blue Africa(2024-10) Van Deventer, Heidi; Campbell, A; Naidoo, Laven; Stovall, A; Smith, K; Thakali, P; Adam, E; Jensen, D; Barenblitt, A; Fatoyinbo, LEstuaries, together with inland wetlands, are considered the most threatened ecosystem in South Africa (Skowno et al., 2019). Less than 43% of habitat maps out of the 290 estuarine functional zones (EFZs) and less than 10 of the 42 microestuaries have been digitised by various ecologists in the country to date (Van Deventer et al., in review). The images of several space-borne, remote sensing instruments, including RapidEye, Sentinel-1 and -2, and WorldView has proven useful to distinguish some wetland vegetation communities in the country, however, the use of different Light Detection and Radar (LiDAR) and hyperspectral images at higher spatial resolutions, remains to be assessed.Item Performance of laser deposited Inconel 625 coating during heat treatment and carbonisation(2024-02) Tlotleng, Monnamme; Lekoadi, Paul M; Kgoahla, Reneilwe M; Kgomo, Matshela TH; Mokomele, Kgothatso; Skhosane, Besabakhe S; Masina, Bathusile N; Pityana, Sisa LLaser cladding system available at the CSIR South Africa was used to laser clad Inconel 625 on 304L SS substrate. The produced clad was studied for effects of heat treatment and carbonisation on the microstructural and hardness properties. The microstructural changes were summarized as: Laves/Eutectic-rich to primary dendritic to MC carbide rich to anisotropic Laves-rich to isotropic grain then finally precipitated and large MC carbides microstructure. The As-built sample had higher hardness value followed by the water quenched and carbonized samples which had similar hardness value. Aging and stress relieve conditions softened the sample. The obtained hardness values support the observed microstructures.Item A review on thermally induced phase separation technology in the fabrication of microporous polymer membrane devices for sustained-repellent delivery: Crystallization and morphological studies(2024-08) Tewo, RK; Mapossa, AB; Ray, Suprakas S; Mhike, W; Sundararaj, UThis article reports recent advances in thermally induced phase separation technology in fabricating microporous scaffold polymeric membranes as devices suitable for the controlled release of insect repellent. The key aspects, such as the crystallization behavior and morphological study of the polymeric membrane-based repellent, were reported and discussed. Studies demonstrated that trapping of such repellents into microporous polymeric materials can be achieved by spinodal decomposition of the polymer/liquid repellent system. Usually, solubility is enhanced at elevated temperatures. Rapid cooling of such solution below the UCST leads to the formation of cocontinuous phase structures by decomposition. The polymer then forms an open-cell structure with the repellent trapped inside. Approaches to forming such an open-cell polymer structure containing mosquito repellent were successfully performed and confirmed with the SEM and POM techniques. It showed the structure of a polymer and liquid repellent prepared by spinodal decomposition, providing proof that thermally induced spinodal decomposition is a route to trap liquid mosquito repellent into a microporous polymer matrix. Additionally, the effects of polymer type, repellent nature, cooling conditions, and fillers on the morphology and performance of TIPS membranes are also discussed. Finally, challenges in developing microporous polymeric membrane-based repellent using TIPS technology are addressed.Item Forecasting of standardized precipitation index using hybrid models: A case study of Cape Town, South Africa(2024-08) Sibiya, S; Mbatha, Nkanyiso B; Ramroop, S; Melesse, S; Silwimba, FDroughts have negative impacts on agricultural productivity and economic growth. Effective monitoring and accurate forecasting of drought occurrences and trends are crucial for minimizing drought losses and mitigating their spatial and temporal effects. In this study, trend dynamics in monthly total rainfall time series measured at Cape Town International Airport were analyzed using the Mann–Kendall (MK) test, Modified Mann–Kendall (MMK) test and innovative trend analysis (ITA). Additionally, we utilized a hybrid prediction method that combined the model with the complementary ensemble empirical mode decomposition with adaptive noise (CEEMDAN) technique, the autoregressive integrated moving average (ARIMA) model, and the long short-term memory (LSTM) network (i.e., CEEMDAN-ARIMA-LSTM) to forecast SPI values of 6-, 9-, and 12-months using rainfall data between 1995 and 2020 from Cape Town International Airport meteorological rainfall stations. In terms of trend analysis of the monthly total rainfall, the MK and MMK tests detected a significant decreasing trend with negative z-scores of −3.7541 and −4.0773, respectively. The ITA also indicated a significant downward trend of total monthly rainfall, especially for values between 10 and 110 mm/month. The SPI forecasting results show that the hybrid model (CEEMDAN-ARIMA-LSTM) had the highest prediction accuracy of the models at all SPI timescales. The Root Mean Square Error (RMSE) values of the CEEMDAN-ARIMA-LSTM hybrid model are 0.121, 0.044, and 0.042 for SPI-6, SPI-9, and SPI-12, respectively. The directional symmetry for this hybrid model is 0.950, 0.917, and 0.950, for SPI-6, SPI-9, and SPI-12, respectively. This indicates that this is the most suitable model for forecasting long-term drought conditions in Cape Town. Additionally, models that use a decomposition step and those that are built by combining independent models seem to produce improved SPI prediction accuracy.Item Evaluating the Enhanced Bathtub Model for Coastal Flood Risk Assessment in Table Bay, South Africa(2024-10) Lück-Vogel, Melanie; Van Coller, J; Williams, LLCoastal zones are susceptible to increasing pressures from urban development and natural hazards, such as storm events, climate change, and rising sea levels. The GIS-based enhanced bathtub model (eBTM) enables the identification of areas at risk of flooding as a baseline for disaster management and coastal adaptation. This study aims to establish the methodological robustness of the eBTM for coastal flood modeling, by analyzing eight sites flooded during a recent storm event in Table Bay, Cape Town by comparing eBTM outputs with observed flood extent data collected after the storm. The validation showed that for 74% of the 332 validation points the spatial modeling error was <6m and for 56% below 3m. The root mean square error for the model was 4.88m, indicating an acceptable level of accuracy of the eBTM outputs for coastal risk assessments where more sophisticated models are unavailable.