伦敦安大略西部大学

This study proposes an advanced theoretical model to accurately simulate the dynamic interaction of the inclined pile in layered soil by coupling the finite element method (FEM) and thin layer method (TLM). The one-dimensional (1D) elastic rod and Euler-Bernoulli beam theories are applied simultaneously to establish the dynamic equation of the inclined pile. The TLM describes the wave response of layered soil and the perfectly matched layers (PMLs) are adopted to represent energy dissipation of the underlying semi-infinite elastic space. The dynamic Green’s function of the surrounding soil is then obtained based on the TLM-PMLs. The dynamic impedance solution of the inclined pile is derived by applying the interaction conditions at the pile-soil interfaces. The developed model is validated by comparing its predictions with results of existing theoretical methods and 3D numerical simulation. Parameter analysis is then conducted to reveal the influence of key parameters on the dynamic impedances of the inclined pile. The proposed theoretical model can accurately predict the dynamic impedance of an inclined pile while achieving satisfactory computational efficiency.

We present a timing-based framework for interpreting braking-index measurements in young pulsars within a four-channel spin-down model that includes particle-wind, magnetic-dipole, mass-quadrupole, and current-quadrupole torques. In this formulation, the observed braking index is a torque-weighted average of the channel exponents, allowing equation-of-state-independent constraints on the torque fraction of a possible r-mode-like current-quadrupole component from timing data alone. For a positive, slowly varying secular model, the physically allowed range is 1 ≤ nobs ≤ 7. Within this domain, the lower and capped physical upper bounds on the k=7 torque fraction are f7,min=max[0,(nobs−5)/2] and f7,maxphys=min{1,max[0,(nobs−1)/6]}, respectively. These bounds are conditional on the non-negativity and slow secular evolution of the effective torque coefficients; if these assumptions are relaxed, a large braking index need not uniquely imply a current-quadrupole torque. Applying this bracket analysis to young pulsars with measured braking indices, we find that most sources do not require a gravitational-wave torque and can be explained by wind-plus-dipole electromagnetic spin-down. Sources with 3 < nobs < 5 require some higher-order contribution beyond the wind and dipole terms, but timing alone cannot uniquely identify this contribution as an r-mode torque. PSR J0537 - 6910 remains the most suggestive case: its large inter-glitch braking index approaches the n ≃ 7 limit, where the timing bounds are consistent, within the restricted positive secular model, with a strong current-quadrupole-like contribution. This interpretation is not unique, however, because vortex-creep and superfluid-recovery effects can generate similar effective inter-glitch braking behaviour without invoking gravitational-wave emission. We also translate the timing constraints into stellar-model-dependent r-mode amplitude bounds, braking-index-corrected characteristic ages, and gravitational-wave ranking metrics for continuous-wave searches with current and future detectors, including the reduction in sensitivity expected for glitch-limited semi-coherent searches.

Context. The number of meteor observation networks has expanded rapidly due to declining hardware costs, enabling professional and amateur groups to contribute substantial datasets. An accurate data reduction remains challenging, however, because variations in processing methods can significantly affect the trajectory reconstructions and orbital interpretations. Aims. Our goal is to thoroughly compare four professionally produced meteor data-reduction pipelines (FRIPON, DFN, WMPL, and AMOS) by reprocessing FRIPON Geminid observations. This analysis can be used for a comparison with other data-reduction methods. Methods. We processed a dataset of 5 84 Geminid fireballs observed by FRIPON between 2016 and 2023. The single-station astrometric data were converted into the global fireball exchange (GFE) standard format for uniform processing. We assessed variations in trajectory, velocity, and radiant and orbital element calculations in the pipelines and compared them to previously published Geminid measurements. Results. The radiant and velocity solutions provided by the four data-reduction pipelines are all within the range of previously published values, with some nuances. Particularly, the radiants estimated by WMPL, DFN, and AMOS are nearly identical, but FRIPON reports a systematic shift in right ascension (−0.3°) that is caused by an improper handling of the precession. Additionally, the FRIPON data-reduction pipeline also tends to overestimate the initial velocity (+0.3 km s−1), which is due to the deceleration model used as the velocity solver. The FRIPON velocity method relies on a well-constrained deceleration profile, but for the Geminids, many are low-deceleration events, which leads to an overestimation of the initial velocity. At the other end of the spectrum, the DFN tends to predict lower velocities, in particular, for poorly observed events. This velocity shift vanishes for the DFN when we considered Geminids alone with at least three observations or more, however. The primary difference identified in the analysis concerns the velocity uncertainties. Although all four pipelines achieved similar residuals between their trajectories and observations, their velocity uncertainties varied systematically. WMPL outputs the lowest values, followed by AMOS, FRIPON, and DFN. Conclusions. From this Geminid case study, we find that the default FRIPON data-reduction methods, while adequate for meteoritedropping events, are not optimal for all cases. Specifically, FRIPON tends to overestimate velocities for low-deceleration events because the fit is less strongly constrained, and the nominal radiants are not correctly output in J2000. On the other hand, the other data-reduction pipelines (DFN, WMPL, and AMOS) produce consistent results, provided that the observational data are sufficiently robust, that is, more than ∼50 data points from at least three observers. A key takeaway is that we need to reevaluate how the velocity uncertainties are estimated. Our results show that the uncertainty estimates vary systematically in different pipelines, even though the goodness-of-fit statistics is generally similar. The increasing availability of impact observations from varying sources (radar, video, photo, seismic, infrasound, satellite, telescopic, etc.) calls for greater collaboration and transparency in data-reduction practices.

Animal diets are shaped both by the availability of resources and preferences for certain food items over others. Environmental conditions can affect the availability of arthropod prey, and animals that rely on arthropods for food may need to shift their diet across years with different climatic conditions. Here, we tested for differences in Poecile gambeli (Mountain Chickadee) nestling diet between two elevational sites and across two years with extreme climatic differences. We present the first study characterizing P. gambeli nestling diet using fecal DNA metabarcoding. Fecal samples were obtained from nestlings at high- and low-elevation sites in the northern Sierra Nevada mountains, USA in 2022 and 2023. We also sampled arthropods on conifer trees during the fecal sampling period. The first year was characterized by low-to-average snow accumulation, while the second year was a heavy snow year. We used these naturally occurring climatic extremes to test for differences in diet and food availability between years and elevations. There were significant differences in the family-level community composition of available arthropods between elevations and years, except at low elevation, where community composition was not significantly different between years. There were also significant differences in the community composition of nestling diet between elevations and years. Differences in diet were associated with differences in food availability for commonly sampled arthropod families, but chickadees exhibited both selection for and avoidance of some prey families. Overall, chickadees utilized prey resources from a diverse suite of taxa and showed flexibility in provisioned diet both across small spatial scales and between years, potentially making them highly resilient to climate-related changes in prey availability. We studied Poecile gambeli (Mountain Chickadee) nestling diet and prey preference at 2 elevational sites in the Sierra Nevada mountains across 2 years with extreme differences in overwinter snow accumulation.Fecal DNA metabarcoding was used to document arthropod prey in nestling diets, and beat sheet sampling was used to measure the availability of arthropod prey in the environment.Family-level composition of arthropod communities in the environment differed between years and elevations, except at the lower elevation site, where the comparison between years was not significant.Nestling diet composition was significantly different between years and elevations, reflecting differences in the availability of certain prey taxa.Chickadees showed preferences for certain arthropod prey and avoided others, but overall, parents were more likely to feed their young items that were more available based on arthropod sampling. Las dietas animales est & aacute;n determinadas tanto por la disponibilidad de recursos como por la preferencia por ciertos & iacute;tems alimenticios sobre otros. Las condiciones ambientales pueden afectar la disponibilidad de presas artr & oacute;podas, y los animales que dependen de artr & oacute;podos como alimento pueden necesitar modificar su dieta entre a & ntilde;os con diferentes condiciones clim & aacute;ticas. Aqu & iacute; evaluamos diferencias en la dieta de polluelos de Poecile gambeli entre dos sitios a distinta elevaci & oacute;n y entre a & ntilde;os con diferencias clim & aacute;ticas extremas. Presentamos el primer estudio que caracteriza la dieta de polluelos de P. gambeli mediante metabarcoding de ADN fecal. Se obtuvieron muestras fecales de polluelos durante dos a & ntilde;os en sitios de alta y baja elevaci & oacute;n en el norte de las monta & ntilde;as de Sierra Nevada, EUA. Tambi & eacute;n muestreamos artr & oacute;podos en & aacute;rboles de con & iacute;feras durante el per & iacute;odo de muestreo fecal. El primer a & ntilde;o se caracteriz & oacute; por una acumulaci & oacute;n de nieve entre baja a promedio, mientras que el segundo fue un a & ntilde;o de intensa acumulaci & oacute;n de nieve. Utilizamos estos extremos clim & aacute;ticos naturales para evaluar diferencias en la dieta y en la disponibilidad de alimento entre a & ntilde;os y elevaciones. Hubo diferencias significativas en la composici & oacute;n comunitaria a nivel de familia de los artr & oacute;podos disponibles entre elevaciones y a & ntilde;os, excepto en la elevaci & oacute;n baja, donde la composici & oacute;n comunitaria no difiri & oacute; significativamente entre a & ntilde;os. Tambi & eacute;n hubo diferencias significativas en la composici & oacute;n comunitaria de la dieta de los polluelos entre elevaciones y a & ntilde;os. Las diferencias en la dieta se asociaron con diferencias en la disponibilidad de alimento para las familias de artr & oacute;podos com & uacute;nmente muestreadas, pero los carboneros mostraron tanto selecci & oacute;n como evitaci & oacute;n de algunas familias de presas. En conjunto, los carboneros utilizaron recursos presa provenientes de un conjunto diverso de taxones y mostraron flexibilidad en la dieta suministrada tanto a peque & ntilde;as escalas espaciales como entre a & ntilde;os, lo que potencialmente los hace altamente resilientes a cambios en la disponibilidad de presas asociados al clima.

Emerging evidence indicates that associations between landscape contexts and population change may vary with prevailing weather conditions. Agricultural landscapes are often more homogeneous, receive greater agrochemical inputs, and support altered or reduced insect prey communities, influencing buffering capacity during challenging conditions. Because weather can constrain avian thermoregulation, alter foraging patterns, and insect availability, associations between agricultural intensity and aerial insectivore fitness may vary in magnitude and direction under different weather conditions. We therefore evaluate whether the relationship between row-crop cover and fitness varies with weather across breeding attempts. We paired a 13-yr dataset of Hirundo rustica (Barn Swallow) clutch size, hatching ratio, and fledging success, gathered across a gradient of agricultural intensity in southwestern Ontario, Canada, with historical weather conditions collected during periods relevant to each parameter of reproductive success. We used this dataset to test the hypothesis that the relationship between agricultural intensity and the outcome of a breeding attempt may be modulated by the experienced weather conditions. Our analyses treated first and second breeding attempts separately. For first attempts, temperature modified the association between agricultural intensity and both hatching and fledging success, and precipitation modified the association for fledging success only. Interactions were not supported for clutch size in either attempt or for hatching in second attempts. Together, these results indicate that the effects of agricultural intensity on reproduction likely depends on prevailing weather conditions, and the stage of the breeding season. Considering projected increases in heat extremes and heavy rainfall, this context dependence suggests that climate change may alter, and in some cases intensify, the demographic consequences of intensive agriculture. Declines of aerial insectivores are often attributed to agricultural intensification and climate change, yet their combined effects on breeding performance are rarely evaluated. We monitored Hirundo rustica (Barn Swallow) reproduction for 13 yr (2006-2018) at 32 barn-based colonies in southern Ontario, Canada. We evaluated the extent to which row crop cover (a proxy for agricultural intensity) was associated with clutch size, hatching ratio, and fledging success, and whether these relationships varied with temperature and precipitation measured during biologically relevant windows. Clutch size showed little evidence of weather-by-row crop interactions, although clutch size tended to decline under warmer and wetter conditions. In contrast, hatching ratio and especially fledging success provided strong evidence that weather conditions modified the relationship between row crop cover and breeding outcomes. This implies that climate variability can amplify or dampen land-use effects, and that models incorporating weather may improve predictions of reproductive performance.