Spontaneous thought is often considered an unconstrained, internally generated mode of thinking that is independent of the present perceptual environment, making it difficult to study empirically. However, recent accounts have raised the possibility that the generation and content of spontaneous thought can be shaped by even weak perceptual constraints. We leveraged this new perspective to develop a novel approach using music, a ubiquitous stimulus that permeates our everyday environments, as a window into the mechanisms supporting spontaneous thought content. Adults spanning four age groups listened to music from ten different genres and completed the open-ended task of writing descriptions of any thoughts that arose. By applying natural language processing analysis to the spontaneous thought descriptions, we found that thoughts sustained while hearing music from the same genre shared greater semantic similarity than those sustained while hearing music from different genres, and participants from the same age group experienced more similar thoughts than those from different age groups. Properties that varied naturally with genre, including the music’s auditory features, expressed emotions, and contextual associations, all contributed significantly to explaining the greater semantic similarity of thoughts within genres. These results demonstrate that spontaneous thought is jointly shaped by perceptual and experiential constraints, opening new avenues for understanding when and why particular thoughts come to mind, with implications for creativity and mental health.
Ammonia-fuelled engines have primarily targeted light-duty automotive internal combustion engines. However, ammonia can be a potential carbon-free fuel for large-bore marine engines to decarbonise the maritime sector. In this study, a CFD model was developed and validated to assess direct ammonia injection in a large-bore marine engine. The impacts of liquid ammonia energy ratios up to 77% and injection timings on combustion, engine performance, and emissions were examined. The results showed that the highest indicated thermal efficiency of 48.3% was achieved at SOINH3 - 40 CAD, where the main combustion occurred at TDC and overlapped with diesel ignition, leading to a shorter combustion duration. Varying ammonia injection timing revealed that the minimum NH3 slip of 4.1 g/kWh was at SOI - 40 CAD and increased for both earlier and later ammonia injection timings. Liquid ammonia significantly reduced NOX emissions from 7.7 g/kWh in the diesel case to just 1.3 g/ kWh due to lower combustion temperature. Moreover, advancing ammonia SOINH3 from - 15 to - 50 CAD significantly reduced CO emissions from 9.1 to 2.7 g/kWh. The results also showed that N2O primarily forms in thin mid-temperature NH3-rich layers ahead of the flame front, and earlier ammonia injection expands these zones, increasing N2O emissions.
The mid-Holocene decline in elm (Ulmus) pollen frequencies is perhaps the most debated and researched pollen-analytical feature of vegetation history in northwest Europe, with various causes or combination of causes proposed to explain it. It has a significant radiocarbon age range in Britain, but its timing in the early stages of Neolithic settlement suggests that subsistence farming activities probably played a role as well as factors such as disease and climate change. With these variables unproven, we have investigated ascospores of the wood-rot fungus Ustulina deusta as an independent proxy indicator of elm tree mortality, as the distinctive spores are often stratified in Elm Decline levels. Inspection of 20 sites in north Britain shows the distinct association of U. deusta with the Elm Decline, although with considerable variation between sites in the amplitude and shape of the U. deusta curve across the Elm Decline levels. U. deusta relies for successful infection on physically damaged trees, and we contend that girdling of elms by early Neolithic farmers to provide clearings for cereal cultivation and cattle grazing provided the conditions for U. deusta infection. Curves for Plantago lanceolata and Sporormiella, other indicators of herbivore presence, mirror the U. deusta curve, supporting this hypothesis. We conclude that the behaviour of the U. deusta curve at the Elm Decline supports early Neolithic animal husbandry and woodland manipulation as a primary cause of the mid-Holocene fall in elm populations.
The vegetation history of Cumbria, in north-west England, has been intensively studied for many years by pollen analysis, particularly in the upland area of the Lake District but also the lowlands of the river Eden valley to the east and the coastal lowlands to the south and north. However, the Shap Fells, an eastern outlier of the upland massif, has so far not been the subject of palynological research despite it being an archaeologically rich area. This study presents a radiocarbon dated pollen diagram from a valley mire, covering all the Holocene except for the first and last millennia, with modelled ages throughout. Fine resolution pollen and non-pollen palynomorph (NPP) analyses are applied through the mid-Holocene Elm Decline. Results show that the site was heavily wooded in the early and mid-Holocene with tree successions similar to the rest of the Cumbrian upland, but with considerable variation in woodland composition. The site experienced only a gradual reduction in woodland cover until expansion of bog and heathland from Roman times onwards, with little human disturbance except briefly in the Bronze Age. Fine-resolution pollen analysis at the Elm Decline showed very low-scale pastoral activity at the Elm Decline and in a ‘landnam’-type phase soon afterwards, while the NPP data provided a detailed local environmental record of a wide range of wetland environments, as well as a fungal spore record that reflected a pastoral Neolithic economy. This study confirms the value of adding NPP analyses to pollen studies as they greatly improve local environmental interpretations, particularly at the fine-resolution level.
Partially crystalline nodules are occasionally discovered within breccias linked to large ignimbrite-forming eruptions, providing evidence of the fragmentation of the plutonic reservoir and conduit system during such eruptions. These nodules offer valuable insights into the magmatic systems fuelling these highly explosive volcanoes. On Tenerife, crystal-rich samples containing interstitial melt are preserved in several Plinian eruption deposits spanning over 1.8 million years, but the crustal architecture and interactions between magma reservoirs beneath the island remain poorly understood. This study focuses on explosively fragmented juvenile nodules from Tenerife’s pyroclastic deposits, which provide snapshots of the mush reservoir preceding caldera-forming events. Petrological, major element and trace element analyses were conducted on juvenile nodules from five major caldera-forming eruptions: Caleta (221 ka), Fasnia (312 ka), San Juan (1.50 Ma), Morteros ( 1.70 Ma), and Gaviotas (1.84 Ma). These nodules preserve a range of crystallisation stages within Tenerife’s alkaline magmatic system, uniquely containing interstitial groundmass that existed in a supra-solidus state at the time of eruption, with an average melt content of 25 vol
