43 research outputs found
Meer zoogdieren bij minder vaak maaien van slootkanten
Meer natuur langs perceelranden hoeft dus niet altijd te leiden tot een verminderde agrarische productie op de percelen
Human eye inspired log-polar pre-processing for neural networks
In this paper we draw inspiration from the human visual system, and present a
bio-inspired pre-processing stage for neural networks. We implement this by
applying a log-polar transformation as a pre-processing step, and to
demonstrate, we have used a naive convolutional neural network (CNN). We
demonstrate that a bio-inspired pre-processing stage can achieve rotation and
scale robustness in CNNs. A key point in this paper is that the CNN does not
need to be trained to identify rotation or scaling permutations; rather it is
the log-polar pre-processing step that converts the image into a format that
allows the CNN to handle rotation and scaling permutations. In addition we
demonstrate how adding a log-polar transformation as a pre-processing step can
reduce the image size to ~20\% of the Euclidean image size, without
significantly compromising classification accuracy of the CNN. The
pre-processing stage presented in this paper is modelled after the retina and
therefore is only tested against an image dataset. Note: This paper has been
submitted for SAUPEC/RobMech/PRASA 2020
Hydrological and associated biogeochemical consequences of rapid global warming during the Paleocene-Eocene Thermal Maximum
The Paleocene-Eocene Thermal Maximum (PETM) hyperthermal, ~ 56 million years ago (Ma), is the most dramatic example of abrupt Cenozoic global warming. During the PETM surface temperatures increased between 5 and 9 °C and the onset likely took < 20 kyr. The PETM provides a case study of the impacts of rapid global warming on the Earth system, including both hydrological and associated biogeochemical feedbacks, and proxy data from the PETM can provide constraints on changes in warm climate hydrology simulated by general circulation models (GCMs). In this paper, we provide a critical review of biological and geochemical signatures interpreted as direct or indirect indicators of hydrological change at the PETM, explore the importance of adopting multi-proxy approaches, and present a preliminary model-data comparison. Hydrological records complement those of temperature and indicate that the climatic response at the PETM was complex, with significant regional and temporal variability. This is further illustrated by the biogeochemical consequences of inferred changes in hydrology and, in fact, changes in precipitation and the biogeochemical consequences are often conflated in geochemical signatures. There is also strong evidence in many regions for changes in the episodic and/or intra-annual distribution of precipitation that has not widely been considered when comparing proxy data to GCM output. Crucially, GCM simulations indicate that the response of the hydrological cycle to the PETM was heterogeneous â some regions are associated with increased precipitation â evaporation (P â E), whilst others are characterised by a decrease. Interestingly, the majority of proxy data come from the regions where GCMs predict an increase in PETM precipitation. We propose that comparison of hydrological proxies to GCM output can be an important test of model skill, but this will be enhanced by further data from regions of model-simulated aridity and simulation of extreme precipitation events
A reâevaluation of the Plenus Cold Event, and the links between CO2, temperature, and seawater chemistry during OAE 2
International audienceThe greenhouse world of the midâCretaceous (~94 Ma) was punctuated by an episode of abrupt climatic upheaval: Oceanic Anoxic Event 2 (OAE 2). Highâresolution climate records reveal considerable changes in temperature, carbon cycling, and ocean chemistry during this climatic perturbation. In particular, an interval of cooling has been detected in the English Chalk on the basis of an invasive boreal fauna and bulk oxygenâisotope excursions registered during the early stages of OAE 2âa phenomenon known as the Plenus Cold Event (PCE), which has tentatively been correlated with climatic shifts worldwide.Here we present new highâresolution neodymiumâ, carbonâ, and oxygenâisotope data, as well as elemental chromium concentrations and cerium anomalies, from the English Chalk exposed at Dover, UK, which we evaluate in the context of >400 records from across the globe. A negative carbonâisotope excursion that correlates with the original âPCEâ is consistently expressed worldwide, and CO2 proxy records, where available, indicate a rise and subsequent fall in CO2 over the Plenus interval. However, variability in the timing and expression of cooling at different sites suggests that, although seaâsurface paleoâtemperatures may reflect a response to global CO2 change, local processes likely played a dominant role at many sites. Variability in the timing and expression of changes in waterâmass character, and problems in determining the driver of observed proxy changes, suggest that no single simple mechanism can link the carbon cycle to oceanography during the Plenus interval and other factors including upwelling and circulation patterns were locally important. As such, it is proposed that the Plenus carbonâisotope event is a more reliable stratigraphic marker to identify the Plenus interval, rather than any climatic shifts that may have been overprinted by local effects
Investigating ocean deoxygenation during the PETM through the Cr isotopic signature of foraminifera
Over the past several decades, oxygen minimum zones have rapidly expanded due to rising temperatures raising concerns about the impacts of future climate change. One way to better understand the drivers behind this expansion is to evaluate the links between climate and seawater deoxygenation in the past especially in times of geologically abrupt climate change such as the Palaeocene-Eocene Thermal Maximum (PETM), a well characterised period of rapid warming ~56 million years ago. We have developed and applied the novel redox proxies of foraminiferal Cr isotopes(ÎŽ53Cr) and Ce anomalies (Ce/Ce*) to assess changes in paleo-redox conditions arising from changes in oxygen availability. Both ÎŽ53Cr and Cr concentrations decrease notably over the PETM at intermediate to upper abyssal water depths,indicative of widespread reductions in dissolved oxygen concentrations. An apparent correlation between the sizes of ÎŽ53Cr and benthic ÎŽ18O excursions during the PETM suggests temperature is one of the main controlling factors of deoxygenation in the open ocean. ODP Sites 1210 in the Pacific and 1263 in the Southeast Atlantic suggest that deoxygenation is associated with warming and circulation changes, as supported by Ce/Ce* data. Our geochemical data are supported by simulations from an intermediate complexity climate model (cGENIE), which show that during the PETM anoxia was mostly restricted to the Tethys Sea, while hypoxia was more widespread as a result of increasing atmospheric CO2 (from 1 to 6 times pre-industrial values)
Factors affecting consistency and accuracy in identifying modern macroperforate planktonic foraminifera
Planktonic foraminifera are widely used in biostratigraphic, palaeoceanographic and evolutionary studies, but the strength of many study conclusions could be weakened if taxonomic identifications are not reproducible by different workers. In this study, to assess the relative importance of a range of possible reasons for among-worker disagreement in identification, 100 specimens of 26 species of macroperforate planktonic foraminifera were selected from a core-top site in the subtropical Pacific Ocean. Twenty-three scientists at different career stages â including some with only a few days experience of planktonic foraminifera â were asked to identify each specimen to species level, and to indicate their confidence in each identification. The participants were provided with a species list and had access to additional reference materials. We use generalised linear mixed-effects models to test the relevance of three sets of factors in identification accuracy: participant-level characteristics (including experience), species-level characteristics (including a participantâs knowledge of the species) and specimen-level characteristics (size, confidence in identification). The 19 less experienced scientists achieve a median accuracy of 57 %, which rises to 75 % for specimens they are confident in. For the 4 most experienced participants, overall accuracy is 79 %, rising to 93 % when they are confident. To obtain maximum comparability and ease of analysis, everyone used a standard microscope with only 35Ă magnification, and each specimen was studied in isolation. Consequently, these data provide a lower limit for an estimate of consistency. Importantly, participants could largely predict whether their identifications were correct or incorrect: their own assessments of specimen-level confidence and of their previous knowledge of species concepts were the strongest predictors of accuracy