Organism abundance is a critical parameter in ecology, but its estimation is often challenging. Approaches utilizing eDNA to indirectly estimate abundance have recently generated substantial ...interest. However, preliminary correlations observed between eDNA concentration and abundance in nature are typically moderate in strength with significant unexplained variation. Here, we apply a novel approach to integrate allometric scaling coefficients into models of eDNA concentration and organism abundance. We hypothesize that eDNA particle production scales nonlinearly with mass, with scaling coefficients < 1. Wild populations often exhibit substantial variation in individual body size distributions; we therefore predict that the distribution of mass across individuals within a population will influence population‐level eDNA production rates. To test our hypothesis, we collected standardized body size distribution and mark–recapture abundance data using whole‐lake experiments involving nine populations of brook trout. We correlated eDNA concentration with three metrics of abundance: density (individuals/ha), biomass (kg/ha) and allometrically scaled mass (ASM) (∑(individual mass0.73)/ha). Density and biomass were both significantly positively correlated with eDNA concentration (adj. r2 = 0.59 and 0.63, respectively), but ASM exhibited improved model fit (adj. r2 = 0.78). We also demonstrate how estimates of ASM derived from eDNA samples in "unknown" systems can be converted to biomass or density estimates with additional size‐structure data. Future experiments should empirically validate allometric scaling coefficients for eDNA production, particularly where substantial intraspecific size distribution variation exists. Incorporating allometric scaling may improve predictive models to the extent that eDNA concentration may become a reliable indicator of abundance in nature.
The field of neuroaesthetics attempts to identify the brain processes underlying aesthetic experience, including but not limited to beauty. Previous neuroaesthetic studies have focussed largely on ...paintings and music, while performing arts such as dance have been less studied. Nevertheless, increasing knowledge of the neural mechanisms that represent the bodies and actions of others, and which contribute to empathy, make a neuroaesthetics of dance timely. Here, we present the first neuroscientific study of aesthetic perception in the context of the performing arts. We investigated brain areas whose activity during passive viewing of dance stimuli was related to later, independent aesthetic evaluation of the same stimuli. Brain activity of six naïve male subjects was measured using fMRI, while they watched 24 dance movements, and performed an irrelevant task. In a later session, participants rated each movement along a set of established aesthetic dimensions. The ratings were used to identify brain regions that were more active when viewing moves that received high average ratings than moves that received low average ratings. This contrast revealed bilateral activity in the occipital cortices and in right premotor cortex. Our results suggest a possible role of visual and sensorimotor brain areas in an automatic aesthetic response to dance. This sensorimotor response may explain why dance is widely appreciated in so many human cultures.
When we observe someone performing an action, do our brains simulate making that action? Acquired motor skills offer a unique way to test this question, since people differ widely in the actions they ...have learned to perform. We used functional magnetic resonance imaging to study differences in brain activity between watching an action that one has learned to do and an action that one has not, in order to assess whether the brain processes of action observation are modulated by the expertise and motor repertoire of the observer. Experts in classical ballet, experts in capoeira and inexpert control subjects viewed videos of ballet or capoeira actions. Comparing the brain activity when dancers watched their own dance style versus the other style therefore reveals the influence of motor expertise on action observation. We found greater bilateral activations in premotor cortex and intraparietal sulcus, right superior parietal lobe and left posterior superior temporal sulcus when expert dancers viewed movements that they had been trained to perform compared to movements they had not. Our results show that this ‘mirror system’ integrates observed actions of others with an individual's personal motor repertoire, and suggest that the human brain understands actions by motor simulation.
Due to climate change, heatwaves are likely to become more frequent, prolonged and characterized by higher peak values, compared with climatological averages. However, the thermal tolerance of ...organisms depends on the actual exposure, which can be modulated by environmental context and microhabitat characteristics. This study investigated the frequency of occurrence of mass mortality events in the next decades for two species of farmed bivalves, the mussel Mytilus galloprovincialis and the clam Ruditapes philippinarum, in a shallow coastal lagoon, characterised by marked diurnal oscillations of water temperature. The effect of heatwaves was estimated by means of tolerance landscape models, which predict the occurrence of 50% mortality based on the exposure intensity and duration. Scenarios of water temperature up to the year 2100 were modelled by combining two mechanistic components, namely: 1) monthly mean water temperatures, simulated using a hydrodynamic model including the heat budget; 2) daily oscillations, estimated from the harmonic analysis of a twenty year-long site-specific time series of water temperature. Scenarios of mean daily sediment temperature were estimated by means of a cross-correlation model, using as input the water temperature one: the model parameters were estimated based on a comprehensive set of site-specific water and sediment temperature observations. The results indicate that for both species the risk of mass mortality rapidly increases starting from the 2060s. Furthermore, the daily patterns of water temperature seemed to be relevant, as overnight it falls below the predicted mortality thresholds for a few hours. These findings suggest that further studies should address: 1) the improvement of tolerance landscape models, in order to take into account the integrated effect of repeated non-lethal stress events on mortality rate; 2) the prediction of environmental temperature in specific habitat, by means of both process-based and data driven models.
•The risk of mass-mortality of two species of bivalves was investigated.•The tolerance landscape approach was used in combination with temperature scenarios.•Temperature scenarios were made habitat-specific (water column and sediment).•The combined scenarios predicted high mortality risk from 2060s for both species.
Engineering of component surfaces using Laser Shock Peening (LSP) requires optimisation of key process parameters to enhance performance through the generation of beneficial compressive residual ...stresses. Quantification of residual stress fields typically requires considerable experimental resources involving multiple complementary techniques to obtain reliable measurements through the depth of the target material. LSP induced plastic strains lead to the formation of residual stresses and cause deformation of thin components. This effect is routinely used in the assessment of mechanical Shot Peening (SP) where distortion coupons, called Almen strips, correlate the peening intensity to process parameters. This study explores the extension of this Almen strip concept to facilitate the quick assessment of LSP parameters for aluminium alloy 6056-T4 aeronautical structural applications. Direct measurements of the resulting LSP residual stresses have been performed using Synchrotron X-Ray Diffraction, Neutron Diffraction, and Incremental Hole Drilling, complemented by analyses of surface integrity and sub-surface modifications. It has been found that the attained near-surface compressive residual stress values and depths are strongly dependent on laser power intensity and spot coverage, whilst surface roughness and microhardness are mostly independent of the LSP parameters. Optimal parameter selection should therefore be primarily focused on the required residual stress field. A direct correlation has been observed between the magnitudes of LSP Almen distortions and the residual stresses. This qualifies extending the deflection based approach to be used as a quick, simple and effective qualitative screening technique of LSP process parameters, such as the laser power intensity saturation.
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•Laser Shock Peening parameter sets were identified for Aluminium Alloy 6056-T4•LSP residual stress profiles were characterised using complementary techniques•A strain energy and energy conversion efficiency methodology was developed•Distortions of LSP Almen coupons correlated well to measured residual stresses•A distortion approach was validated for initial LSP process parameters screening
Laser shock peening (LSP) technology is a laser-induced shock process implemented as a surface enhancement technique to introduce beneficial compressive residual stresses into metallic components. ...The process employs water to confine and enhance the pressure pulse delivered to the target. For thick water layers, or fully water immersed LSP, a cavitation bubble is generated by the surface vaporization of the LSP laser pulse. This research shows that the first bubble oscillation period of the cavitation bubble can be used to characterize effective and repeatable energy delivery to the target. High-speed shadowgraphy is implemented to show that variations in the bubble period occur before visual observations of dielectric breakdown in water. The diagnostic potential of the first bubble oscillation period is used to identify the dielectric breakdown threshold of water, which shows an increase with increasing water quality measured by water conductivity.
Faults strengthen or heal with time in stationary contact, and this healing may be an essential ingredient for the generation of earthquakes. In the laboratory, healing is thought to be the result of ...thermally activated mechanisms that weld together micrometre-sized asperity contacts on the fault surface, but the relationship between laboratory measures of fault healing and the seismically observable properties of earthquakes is at present not well defined. Here we report on laboratory experiments and seismological observations that show how the spectral properties of earthquakes vary as a function of fault healing time. In the laboratory, we find that increased healing causes a disproportionately large amount of high-frequency seismic radiation to be produced during fault rupture. We observe a similar connection between earthquake spectra and recurrence time for repeating earthquake sequences on natural faults. Healing rates depend on pressure, temperature and mineralogy, so the connection between seismicity and healing may help to explain recent observations of large megathrust earthquakes which indicate that energetic, high-frequency seismic radiation originates from locations that are distinct from the geodetically inferred locations of large-amplitude fault slip.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We compare thermally and seismically induced sliding mechanisms of blocks that are separated from the rock mass by a tension crack and slide along a frictional interface. The rock slopes of Masada ...Mountain, Israel, are used to demonstrate our approach. Crack displacement coupled with thermal fluctuations is measured in the West slope of the mountain during two years (2009–11). Physical and mechanical lab tests provide the assumed depth of penetration of the heating front during seasonal cycles of exposure as well as the thermal expansion coefficient of the rock mass. These, along with the shear stiffness of the sliding interface, allow us to quantify the expected thermally induced displacement rate of blocks in Masada, through a proposed wedging–ratcheting failure mechanism. A distinct block in the East slope of the mountain exhibiting a tension crack opening of 200mm was monitored for displacement and temperature during a single seasonal cycle in 1998. Based on the assumed seismicity of the region and the known topographic site effect, along with the laboratory measured frictional resistance and shear stiffness of the sliding interface, we subject the mapped geometry of the block in the East face to simulated cycles of earthquake vibrations utilizing the numerical, discrete element, discontinuous deformation analysis (DDA) method. We find that for a time window of 5000 years, the observed 200mm displacement of the East slope block is more likely to have been thermally, rather than seismically, controlled. This result implies that in climatic regions where the temperature amplitude over a seasonal cycle is sufficiently high, thermally induced displacements play an important role in rock slope erosion.
• Thermally induced wedging mechanism for rock blocks with filled tension cracks is proposed.• Seasonal temperature amplitude is sufficient to induce permanent plastic displacement.• For Masada slopes the wedging mechanism may lead to greater displacements than seismic loading over time.• Wedging mechanism should be considered when quantitatively assessing surface erosion of rock slopes.
•Laser shock peening performed on AA7075-T651 to improve fatigue performance.•XRD and incremental hole drilling show deep compressive residual stresses.•4-point bend testing and fractography show a ...change in fatigue regime and large increase in fatigue life.•Modelling highlights sensitive balance between surface roughness, residual stress and micro-mechanisms of crack initiation.
A laser shock peening (LSP) treatment was performed on AA7075-T651 for maximum fatigue improvement. Surface and microstructural characterisation techniques (micro-hardness, SEM-EBSD, contact-profilometry) showed LSP surface modification was limited, and LSP generated deep compressive residual stresses above −300 MPa. Fatigue testing showed a two-order magnitude increase in overall life, due to the mechanism of crack initiation changing from surface second-phase particles to subsurface crack initiation dependent on the local stress field. Modelling highlights the sensitive balance between surface roughness (including LSP-induced pits) and residual stress on the micro-mechanism of crack initiation, and how this can be used to maximise fatigue life extension.
There are a variety of approaches to seismic sensing, which range from collecting sparse measurements with high-fidelity seismic stations to non-quantitative, post-earthquake surveys. The sparse ...nature of the high-fidelity stations and the inaccuracy of the surveys create the need for a high-density, semi-quantitative approach to seismic sensing. To fill this void, the UC Berkeley iShake project designed a mobile client-backend server architecture that uses sensor-equipped mobile devices to measure earthquake ground shaking. iShake provides the general public with a service to more easily contribute more quantitatively significant data to earthquake research by automating the data collection and reporting mechanisms via the iShake mobile application. The devices act as distributed sensors that enable measurements to be taken and transmitted with a cellular network connection. Shaking table testing was used to assess the quality of the measurements obtained from the iPhones and iPods on a benchmark of 150 ground motions. Once triggered by a shaking event, the devices transmit sensor data to a backend server for further processing. After a seismic event is verified by high-fidelity stations, filtering algorithms are used to detect falling phones, as well as device-specific responses to the event. A method was developed to determine the absolute orientation of a device to estimate the direction of first motion of a seismic event. A "virtual earthquake" pilot test was conducted on the UC Berkeley campus to verify the operation of the iShake system. By designing and fully implementing a system architecture, developing signal processing techniques unique to mobile sensing, and conducting shaking table tests to confirm the validity of the sensing platform, the iShake project serves as foundational work for further studies in seismic sensing on mobile devices.
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