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Acoustic parameters of bat echolocation calls in Zambia : a collaborative effort to develop a call library for non-invasive research and monitoring
(Museum and Institute of Zoology, Polish Academy of Sciences, 2025-08) Taylor-Boyd, Helen; Fuentes-Montemayor, Elisa; Monadjem, Ara; Cooper-Bohannon, Rachael; Montaubans, Cecilia; Mata, Vanessa A.; Rebelo, Hugo; Kangwa, Bernard; Mateke, Clare; Park, Kirsty
Passive acoustic monitoring (PAM) of bats enables non-invasive research that improves monitoring efficiency, and can be used for species identification, documenting occurrence and measuring activity levels. However, equipment costs and a dearth of experienced personnel, as well as a lack of local open access reference datasets (call libraries), have limited the study of African bat communities using PAM. This study compiles the first publicly available call library of this scale from Zambia. Echolocation calls were recorded upon release of captured bats during various projects from 2015 to 2023, using full spectrum ultrasound detectors. Acoustic calls from 238 individuals of 22 species were collated. We aimed to determine whether Zambian bat species could be accurately distinguished using acoustic measures. We predicted that some species (or species groups) would be easily identifiable, while other species would have substantial similarities in their calls, which would hinder identification. After considering multicollinearity, we selected five acoustic parameters to analyse the recordings: ‘Frequency of Maximum Power’, ‘Preceding Interval’, ‘Start Slope’, ‘End Slope’ and ‘Ledge Duration’. Principal Component Analysis was conducted to identify parameters that were best able to separate the calls of different functional groups (identified by sonotype) or species. Discriminant Function Analysis was then used to determine the accuracy with which the parameters may be used to acoustically distinguish species or sonotypes. The parameters ‘Start Slope’ and ‘Frequency of Maximum Power’ were the most useful for separating the species considered. It was possible to separate some sonotypes and species with relatively high accuracy. Many species, however, could not be identified with certainty, underscoring the importance of other identification techniques, such as morphological measures or genetic sampling.
Applying Alex Broadbent's reverse counterfactual theory to the outbreak of World War I : a novel causal analysis
(Springer, 2025) Hanssen, John; u18021205@tuks.co.za
This article applies Alex Broadbent’s reverse counterfactual theory of causation to the causes of World War I (WWI), providing a novel framework for historical causal analysis. According to Broadbent’s theory, which differs radically from the more familiar account of David Lewis, an event Q is a cause of event R only if, without R, Q would not have occurred. The hypothesis posited here is that understanding the causes of WWI lies in identifying them based on a well-motivated causal philosophical framework. After showing that Broadbent’s theory is prima facie plausible, this study employs it to re-evaluate the extensively debated causes of WWI. Through doing so, it becomes evident that the Russian mobilization, rather than other frequently cited events, was the pivotal cause of Germany’s declaration of war and, consequently, the broader conflict. This analysis not only simplifies the complex causal reasoning process but also offers fresh insights into the historical narrative of WWI as well as reveals how a philosophical account of causation can have a weighty bearing on debates in social science. The implications of this approach extend beyond historical inquiry, suggesting broader applications for reverse counterfactual theory in understanding causation in complex events.
Usage of silica xerogel from African sugarcane leaves as a catalyst in biodiesel production through transesterification
(American Chemical Society, 2025-06) Maseko, Ncamisile Nondumiso; Enke, Dirk; Owolawi, Pius Adewale; Iwarere, Samuel Ayodele; Oluwafemi, Oluwatobi Samuel; Pocock, Jonathan
Biodiesel was produced through transesterification from canola oil and methanol in the presence of silica xerogel derived from sugar cane leaves as a solid catalyst. The transesterification reaction was carried out at 65 °C in a batch-type reactor where a three-neck round-bottom flask was used as a reaction vessel with a reflux setup. Reaction time, methanol to oil ratio, and weight percentage of the catalyst were varied to optimize the biodiesel yield. The xerogel catalyst was characterized by inductively coupled plasma-optical emission spectroscopy (ICP-OES), nitrogen physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The produced biodiesel was characterized using gas chromatography-mass spectroscopy (GC-MS), Fourier transform infrared spectroscopy (FTIR), and a viscometer. The synthesized catalyst was found to operate as a true heterogeneous catalyst, since it preserved its solid nature and did not leach into the reaction medium. A biodiesel yield of 96.9% was achieved under optimal reaction conditions of 60 min reaction time, 6:1 methanol to oil ratio, and 3 wt % catalyst loading. The produced biodiesel was found to have a mixture of both saturated and unsaturated fatty acid methyl esters and had physical properties that met the ASTM and EN standards. The investigated catalyst was found to have a potential of being recycled up to 3 times, which positively affects the biodiesel production costs.
Copper(II) complexes derived from halogen-substituted Schiff base ligands : synthesis, crystal structures, antibacterial activity, and molecular docking studies
(American Chemical Society, 2025) Yusuf, Tunde Lewis; Waziri, Ibrahim; Oladipo, Segun D.; Abd El-Maksoud, Mostafa S.; Muller, Alfred J.; Vatsha, Banele; yusuf.tl@up.ac.za
In the face of escalating bacterial resistance to conventional antibiotics, the quest for novel antimicrobial strategies is urgenter than ever. Metal complexes, particularly those with biological activity, stand out as a promising alternative due to their unique mechanisms of action and potential for fewer side effects in comparison to standard organic antibiotics. This investigation focuses on the synthesis and characterization of six Cu(II) complexes, each formulated from halogen-substituted bidentate Schiff base ligands. Employing a suite of analytical methods, Fourier transform infrared, UV–vis, elemental analysis, and single-crystal X-ray diffraction, the structures of the complexes were fully established. All of the complexes were assigned to have square planar geometry, with the ligand acting as a bidentate and coordinate to the Cu(II) ion via nitrogen and oxygen atoms. The antibacterial efficacy of these complexes was rigorously tested against both Gram-positive bacteria Staphylococcus aureus and Streptococcus pyogenes and Gram-negative bacteria Escherichia coli and Klebsiella pneumoniae, utilizing the broth microdilution technique. The results revealed a spectrum of activity, with minimum inhibitory concentrations (MICs) spanning from less than 15.63 to 125 μg/mL. Notably, Complex 2 demonstrated remarkable potency against S. aureus and S. pyogenes, registering an MIC of less than 15.63 μg/mL. To elucidate the underlying mechanism of action, molecular docking studies were performed targeting the topoisomerase IV receptor. The docking outcomes corroborated the empirical data, underscoring the strong affinity of the complexes for the bacterial targets.
Enhanced gram-negative membrane disruption and in vivo efficacy via lysine-arginine enrichment of Opis16a
(American Chemical Society, 2025-05) Van der Walt, Mandelie; Oosthuizen, Carel B.; Serian, Miruna; Lorenz, Christian D.; Mason, A. James; Bester, Megan Jean; Gaspar, Anabella Regina Marques; anabella.gaspar@up.ac.za
Infections complicate burn wound care, especially with the rise of antimicrobial resistance. Antimicrobial peptides (AMPs) offer the potential for advancing wound care by combating persistent infections. Opis16a, a scorpion venom-derived AMP, exhibits potent antibacterial activity by targeting Gram-negative membranes, causing rapid membrane disruption and bacterial cell death. Here, four novel Opis16a analogues were developed with improved membrane targeting and antibacterial efficacy. One analogue shows particular promise for topical application in Gram-negative burn wound infections. Enhanced peptide–lipid hydrogen bonding increases conformational stability, membrane insertion, and permeabilization rates. Substituting lysine residues in the C-terminal with arginine leads to the most consistent improvement in activity, selectivity for pathogen over HaCat cells, and stability in serum. In an in vivo Galleria mellonella burn wound model, a 5 mg/kg topical dose provides better protection than Opis16a against Enterobacter cloacae NICD 16103. These findings highlight the potential of optimized bactericidal AMPs to improve burn wound care.