Thermomechanical Description of Moving Discontinuities, Application to Fracture and Wear

The propagation of moving surface inside a body is analysed within the framework of thermomechanical couplings, when the moving surface is associated with an irreversible change of mechanical properties. The moving surface is a surface of heat sources and of entropy production, intensities of which are related to particular energy release rates defined in terms of Hamiltonian gradients. As emamples, we analyse the evolution of partial damage in a composite sphere and a model for study the contact wear phenomena between two bodies

Simultaneous influence of thermodynamics and aerosols on deep convection and lightning, The

2016 Spring.Includes bibliographical references.The dissertation consists of a multi-scale investigation of the relative contributions of thermodynamics and aerosols to the observed variability of deep convective clouds in the Tropics. First, estimates of thermodynamic quantities and cloud-condensation nuclei (CCN) in the environment are attributed to convective features (CFs) observed by the Tropical Rainfall Measuring Mission (TRMM) satellite for eight years (2004-2011) between 36⁰S-36⁰N across all longitudes. The collection of simultaneous observations was analyzed in order to assess the relevance of thermodynamic and aerosol hypotheses for explaining the spatial and temporal variability of the characteristics of deep convective clouds. Specifically, the impacts of normalized convective available potential energy (NCAPE) and warm cloud depth (WCD) as well as CCN concentrations (D ≥ 40 nm) on total lightning density (TLD), average height of 30 dBZ echoes (AVGHT30), and vertical profiles of radar reflectivity (VPRR) within individual CFs are the subject of initial curiosity. The results show that TLD increased by up to 600% and AVGHT30 increased by up to 2-3 km with increasing NCAPE and CCN for fixed WCD on the global scale. The partial sensitivity of TLD/AVGHT30 to NCAPE and CCN individually are found to be comparable in magnitude, but each independent variable accounts for a fraction of the total range of variability observed in the response (i.e., when the influences of NCAPE and CCN are considered simultaneously). Both TLD and AVGHT30 vary inversely with WCD such that maxima of TLD and AVGHT30 are found for the combination of high NCAPE, high CCN, and shallower WCD. The relationship between lightning and radar reflectivity is shown to vary as a function of CCN for a fixed thermodynamic environment. Analysis of VPRRs shows that reflectivity in the mixed phase region (altitudes where temperatures are between 0⁰C and -40⁰C) is up to 5.0-5.6 dB greater for CFs in polluted environments compared to CFs in pristine environments (holding thermodynamics fixed). A statistical decomposition of the relative contributions of NCAPE, CCN, and WCD to the variability of convective intensity proxies is undertaken. Simple linear models of TLD/AVGHT30 based on the predictor set composed of NCAPE, CCN, and WCD account for appreciable portions of the variability in convective intensity (R2 ≈ 0.3-0.8) over the global domain, continents, oceans, and select regions. Furthermore, the results from the statistical analysis suggest that the simultaneous contributions from NCAPE, CCN, and WCD to the variability of convective intensity are often comparable in magnitude. There was evidence for similar relationships over even finer-scale regions [O(106 km2)], but differences in the relative prognostic ability and stability of individual regression parameters between regions/seasons were apparent. These results highlight the need to investigate the connection between statistical behavior and local meteorological variability within individual regions. Following the global and regional analyses, data from Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign (2011-2012; central equatorial Indian Ocean (CIO)) and other sources was used to assess the relative impact of aerosols on deep convective clouds within a fine-scale environment with spatially homogeneous thermodynamics and variable aerosols in a pristine background over the CIO (CCN ~50-100 cm-3, on average; NCAPE and WCD are hypothesized to be approximately constant, spatially). The experiment was designed to compare differences in the convective cloud population developing in more-polluted and pristine regions, north and south of the equator, respectively. Analysis of the covariability of rainfall, cold cloud frequency, CCN, NCAPE, and lightning/radar reflectivity in deep convective clouds over multiple (> 20) episodes of the Madden-Julian Oscillation (MJO) leads to a hypothesis for a potential bi-directional interaction between aerosols and convective clouds that develop in association with the MJO. Close scrutiny of the results from climatology leads to the conclusion that thermodynamics and aerosols both influence deep convective cloud behavior over the CIO in a manner similar to that observed on the global scale, but the possibility that other factors are required to reproduce the full range of variability of deep convective clouds on fine-scales is acknowledged. The research presented in this dissertation constitutes one of the first efforts to link the documented variability of radar reflectivity and lightning within convective features observed by the TRMM satellite to their environment using novel representations of thermodynamic and aerosol quantities from reanalysis and a chemical transport model, respectively. The independent variables studied here (i.e., NCAPE, CCN, and WCD) were chosen specifically to address preeminent hypotheses in the literature and the results from this investigation suggest that NCAPE, CCN, and WCD each contribute significantly to the variability of deep convective clouds throughout the Tropics and Subtropics (and perhaps seasonally). Implications of the findings from the current investigations and the relevance of these results to future studies are discussed

Graded damage in quasi-brittle solids

A novel approach to damage modeling for quasi-brittle solids is presented relying upon a differential inclusion that is closely related to the one of implicit gradient models. The proposed formulation naturally fits in the so-called nonlocal standard approach, whereby the framework of generalized standard materials is extended to include gradients of internal variables to account for the physics of the fracture phenomenon in a regularized sense, that is, via extended constitutive equations in which a length scale parameter brings to the macro level information about material microstructure. This concept is fully embodied into the present approach to quasi-brittle fracture, whereby progressive damage occurs in layers of finite thickness where the gradient of damage is bounded and a fully damaged region is understood as a fracture with no ambiguity. Key to the effective implementation of the model are the choice of two constitutive functions and the implicit tracking of regions in a state of progressive damage via Lagrange multipliers acting on internal constraints. The ideas are developed for a general Cauchy continuum and representative numerical simulations are included that demonstrate the model capabilities

A quantitative central limit theorem for linear statistics of random matrix eigenvalues

It is known that the fluctuations of suitable linear statistics of Haar distributed elements of the compact classical groups satisfy a central limit theorem. We show that if the corresponding test functions are sufficiently smooth, a rate of convergence of order almost $1/n$ can be obtained using a quantitative multivariate CLT for traces of powers that was recently proven using Stein's method of exchangeable pairs.Comment: Title modified; main result stated under slightly weaker conditions; accepted for publication in the Journal of Theoretical Probabilit

Real time polarization imaging of weld pool surfaces

The search for an efficient on-line monitoring system focused on the real-time analysis of arc welding quality is an active area of research. The topography and the superficial temperature field of the weld pool can provide important information which can be used to regulate the welding parameters for depositing consistent welds. One difficulty relies on accessing this information despite the bright dazzling welding arc. In the present work, Stokes polarimetry and associated shape-from-polarization methods are applied for the analysis of the weld pool through its 810 nm-wavelength infrared emissions. The obtained information can provide a better understanding of the process, such as the usage of the topography to seek Marangoni flows direction, or to have a denser 3D map to improve numerical simulation models

Hard rock seismic exploration of ore deposits in Australia

We present an overview of the developments and achievements, over the past four years in the application of seismic reflection methods for mineral exploration in Australia. We show that seismic methods can be successfully used to delineate exceptionally complex hard rock environment in Australia providing that the acquisition parameters and data processing strategy are adequate for the task. Moreover methodologies for the direct targeting of specific ore reserves as well as rock identification from seismic data are discussed

Nesting attempts and success of Arctic-breeding geese can be derived with high precision from accelerometry and GPS-tracking

Abstract Sensors, such as accelerometers, in tracking devices allow for detailed bio-logging to understand animal behaviour, even in remote places where direct observation is difficult. To study breeding in birds remotely, one needs to understand how to recognise a breeding event from tracking data, and ideally validate this by direct observation. We tagged 49 adult female pink-footed geese (Anser brachyrhynchus) with transmitter neckbands in Finland in spring of 2018 and 2019, and in Svalbard in summer 2018, and validated inferences from tracking by field observations of nesting sites and family status in 2018–2020 (54 spring–summer tracks). We estimated nesting locations by taking the median coordinates of GPS-fixes at which the goose was motionless (overall dynamic body acceleration, ODBA    75% of time within 50 m of the nest, because nest site attendances steeply increased within one day to above this threshold. Nesting duration (number of consecutive days with  >  75% nest site attendance) ranged between 3 and 44 days (n  =  28), but was 30–34 days in confirmed successful nests (n = 9). The prolonged nesting of 39–44 days (n = 3) suggested incubation on unhatchable egg(s). Nest losses before hatching time occurred mostly in day 3–10 and 23–29 of nesting, periods with an increased frequency of nest site recesses. As alternative method, allowing for non-simultaneous GPS and accelerometer data, we show that nesting days were classified with 98.6% success by two general characteristics of breeding: low body motion (daily median ODBA) and low geographic mobility (daily SD of latitude). Median coordinates on nesting days approached real nest sites closely (within 0.8–3.6 m, n  =  6). When considering only geographic mobility (allowing for GPS data only) nesting locations were similarly accurate, but some short nesting attempts were undetected and non-breeding tracks misclassified. We show that nesting attempts, as short as 3 days, and nesting success can be detected remotely with good precision using GPS-tracking and accelerometry. Our method may be generalised to other (precocial) bird species with similar incubation behaviour

Differential modulation of cellular death and survival pathways by conjugated bile acids

BACKGROUND: The liver-derived McNtcp.24 cells transport bile acids and show distinctive responses to the two classes of conjugated bile acids. Whereas taurine-conjugated bile acids are non-toxic, glycine-conjugated bile acids efficiently induce apoptosis. The aim of this study was to determine if the differential sensitivity is limited to cells that normally transport bile acids and if bile acid binding proteins could reduce bile acid-mediated apoptosis. The apical sodium/bile acid co-transporter (asbt) was expressed in Chinese hamster ovary (CHO) cells to establish active bile acid transport in a non-liver-derived cell model (CHO.asbt). A high-affinity bile acid binder was expressed in McNtcp.24 cells. RESULTS: The tolerance of McNtcp.24 cells to taurine-conjugated bile acids was associated with the stimulation of phosphatidylinositol 3-kinase (PI3K) activity. Treatment of CHO.asbt cells with taurine- and glycine-conjugated bile acids resulted in apoptosis. Unlike in McNtcp.24 cells, PI3K activity was not increased in CHO.asbt cells treated with taurine-conjugated bile acids. High level expression of a bile acid binder did not attenuate bile acid-induced cytotoxicity in McNtcp.24 cells. CONCLUSION: The data suggest that McNtcp.24 cells possess a mechanism that can elaborate distinctive responses to the different classes of bile acids. Additionally, activation of a signaling pathway involving PI3K appears to be the dominant mechanism responsible for the tolerance of McNtcp.24 cells to taurine-conjugated bile acids

Numerical simulation of exciton dynamics in Cu2O at ultra low temperatures within a potential trap

We have studied theoretically the relaxation behaviour of excitons in cuprous oxide (Cu2O) at ultra low temperatures when excitons are confined within a potential trap by solving numerically the Boltzmann equation. As relaxation processes, we have included in this paper deformation potential phonon scattering, radiative and non-radiative decay and Auger decay. The relaxation kinetics has been analysed for temperatures in the range between 0.3K and 5K. Under the action of deformation potential phonon scattering only, we find for temperatures above 0.5K that the excitons reach local equilibrium with the lattice i.e. that the effective local temperature is coming down to bath temperature, while below 0.5K a non-thermal energy distribution remains. Interestingly, for all temperatures the global spatial distribution of excitons does not reach the equilibrium distribution, but stays at a much higher effective temperature. If we include further a finite lifetime of the excitons and the two-particle Auger decay, we find that both the local and the global effective temperature are not coming down to bath temperature. In the first case we find a Bose-Einstein condensation (BEC) to occur for all temperatures in the investigated range. Comparing our results with the thermal equilibrium case, we find that BEC occurs for a significantly higher number of excitons in the trap. This effect could be related to the higher global temperature, which requires an increased number of excitons within the trap to observe the BEC. In case of Auger decay, we do not find at any temperature a BEC due to the heating of the exciton gas