10,752 research outputs found
Estimación de edades arqueológicas usando la hidratación de obsidianas: dos fuentes de los andes meridionales
Obsidian is abundant in archaeological sites throughout Mendoza Province, Argentina but no obsidian hydration rates exist to date these assemblages. Direct dating of obsidian artifacts is particularly important in west-central Argentina because the surface record is extensive but well-defined time marker artifacts are lacking. The costs of non-optical hydration dating techniques currently preclude their regular use in the region, however. We present and evaluate 12 models for age estimation based on optical hydration rim measurements for the two most commonly used obsidian types in the region (Las Cargas and Laguna del Maule). Age estimation equations are derived for each source using observed hydration rim-radiocarbon date pairs, and parameterized by variables known to influence obsidian hydration in experimental settings. The equations advanced here are currently best at predicting the known ages of artifacts independently dated by radiocarbon, and can be cautiously used to estimate the ages of obsidian artifacts.Las obsidianas son abundantes en los sitios arqueológicos de la provincia de Mendoza (Argentina). Sin embargo, hasta el momento no existen estimaciones para las tasas de hidratación de estas rocas que puedan utilizarse para fechar esos conjuntos líticos. La realización de fechados directos sobre artefactos de obsidiana resulta particularmente importante para esta región, dado que existe un vasto registro arqueológico de superficie –compuesto principalmente por artefactos líticos– y solo se cuenta con tipos morfológicos cronológicamente sensibles para el Holoceno Tardío. Aquí se presentan y evalúan 12 modelos para estimar las edades de los artefactos de obsidiana basados en la medición óptica de los anillos de hidratación. Específicamente estos modelos fueron desarrollados para las dos obsidianas más comunes en los contextos arqueológicos de la región, procedentes de las fuentes de Las Cargas y Laguna del Maule. Las edades estimadas son derivadas para cada fuente a partir de pares de medición del espesor de la corteza de hidratación-fechado radiocarbono, y calibradas con variables cuya influencia sobre la hidratación ha sido establecida experimentalmente. Las ecuaciones que presentamos son actualmente las que mejor predicen las edades conocidas de artefactos que han sido fechados independientemente por radiocarbono y, por lo tanto, pueden utilizarse con cautela para estimar la antigüedad de los artefactos de obsidiana procedentes de la región.Fil: Garvey, Raven. University of Michigan; Estados UnidosFil: Carpenter, Tim. Archaeometrics; Estados UnidosFil: Gil, Adolfo Fabian. Universidad Nacional de Cuyo. Facultad de Filosofía y Letras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; ArgentinaFil: Neme, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; ArgentinaFil: Bettinger, Robert. University of California at Davis; Estados Unido
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Twin-tunnelling-induced changes to clay stiffness
With urban tunnel construction growing worldwide, the ability to accurately predict the ground and structural response to tunnelling and the associated risks is now more important than ever before. Engineers are expected to consider all aspects of tunnel engineering in order to safeguard existing infrastructure, by employing field monitoring, physical modelling and numerical analysis in developing a detailed knowledge of multiple soil-structure interactions. The Geotechnique Symposium in Print took place at the Institution of Civil Engineers on 14th September 2017 to discuss the wider aspects of tunnelling in urban locales. The papers included here bring together important international research presented at the symposium and featured in Geotechnique . Topics of discussion, amongst others, included - case studies from Crossrail, CTRL and Barcelona metro projects - open-face tunnelling effects on non-displacement piles in clay - influence of building characteristics on tunnelling-induced ground movements - impact of new tunnel construction on structural performance of existing tunnels. Tunnelling in the Urban Environment offers practitioners and researchers alike with important coverage of the increasingly complex and varied challenges engineers have to face when constructing tunnels in urban centres
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Explanation for twin tunnelling-induced surface settlements by changes in soil stiffness on account of stress history
In this article, a group of representative centrifuge tests were selected for numerical modelling to explain the surface settlements induced by sequential twin tunnelling. Both Modified Cam Clay model (MCC) and Three-Surface Kinematic Hardening model (3-SKH) were adopted in the simulation, which indicated the use of 3-SKH model conduced to mimicking more closely centrifuge model response. Via performing more contrastive numerical analyses with 3-SKH model, the influence of the first tunnel event on the stiffness of the soil around the second tunnel was quantitatively investigated, whereby the mechanism behind the observed surface settlements was finally made clear
Learning and Reacting with Inaccurate Prediction: Applications to Autonomous Excavation
Motivated by autonomous excavation, this work investigates solutions to a class of problem where disturbance prediction is critical to overcoming poor performance of a feedback controller, but where the disturbance prediction is intrinsically inaccurate. Poor feedback controller performance is related to a fundamental control problem: there is only a limited amount of disturbance rejection that feedback compensation can provide. It is known, however, that predictive action can improve the disturbance rejection of a control system beyond the limitations of feedback. While prediction is desirable, the problem in excavation is that disturbance predictions are prone to error due to the variability and complexity of soil-tool interaction forces. This work proposes the use of iterative learning control to map the repetitive components of excavation forces into feedforward commands. Although feedforward action shows useful to improve excavation performance, the non-repetitive nature of soil-tool interaction forces is a source of inaccurate predictions. To explicitly address the use of imperfect predictive compensation, a disturbance observer is used to estimate the prediction error. To quantify inaccuracy in prediction, a feedforward model of excavation disturbances is interpreted as a communication channel that transmits corrupted disturbance previews, for which metrics based on the sensitivity function exist. During field trials the proposed method demonstrated the ability to iteratively achieve a desired dig geometry, independent of the initial feasibility of the excavation passes in relation to actuator saturation. Predictive commands adapted to different soil conditions and passes were repeated autonomously until a pre-specified finish quality of the trench was achieved. Evidence of improvement in disturbance rejection is presented as a comparison of sensitivity functions of systems with and without the use of predictive disturbance compensation
Diverse perceptions of smart spaces
This is the era of smart technology and of ‘smart’ as a meme, so we have run three workshops to examine the ‘smart’ meme and the exploitation of smart environments. The literature relating to smart spaces focuses primarily on technologies and their capabilities. Our three workshops demonstrated that we require a stronger user focus if we are advantageously to exploit spaces ascribed as smart: we examined the concept of smartness from a variety of perspectives, in collaboration with a broad range of contributors. We have prepared this monograph mainly to report on the third workshop, held at Bournemouth University in April 2012, but do also consider the lessons learned from all three. We conclude with a roadmap for a fourth (and final) workshop, which is intended to emphasise the overarching importance of the humans using the spac
Dynamic Modeling of Bucket-Soil Interactions Using Koopman-DFL Lifting Linearization for Model Predictive Contouring Control of Autonomous Excavators
A lifting-linearization method based on the Koopman operator and Dual Faceted
Linearization is applied to the control of a robotic excavator. In excavation,
a bucket interacts with the surrounding soil in a highly nonlinear and complex
manner. Here, we propose to represent the nonlinear bucket-soil dynamics with a
set of linear state equations in a higher-dimensional space. The space of
independent state variables is augmented by adding variables associated with
nonlinear elements involved in the bucket-soil dynamics. These include
nonlinear resistive forces and moment acting on the bucket from the soil, and
the effective inertia of the bucket that varies as the soil is captured into
the bucket. Variables associated with these nonlinear resistive and inertia
elements are treated as additional state variables, and their time evolution is
represented as another set of linear differential equations. The lifted linear
dynamic model is then applied to Model Predictive Contouring Control, where a
cost functional is minimized as a convex optimization problem thanks to the
linear dynamics in the lifted space. The lifted linear model is tuned based on
a data-driven method by using a soil dynamics simulator. Simulation experiments
verify the effectiveness of the proposed lifting linearization compared to its
counterpart
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Interleukin-17A upregulates receptor activator of NF-kappaB on osteoclast precursors.
IntroductionThe interaction between the immune and skeletal systems is evidenced by the bone loss observed in autoimmune diseases such as rheumatoid arthritis. In this paper we describe a new mechanism by which the immune cytokine IL-17A directly affects osteoclastogenesis.MethodsHuman CD14+ cells were isolated from healthy donors, cultured on dentine slices and coverslips and stimulated with IL-17A and/or receptor activator of NF-kappaB ligand (RANKL). Osteoclast differentiation was evaluated by gene expression, flow cytometry, tartrate-resistant acid phosphatase staining, fluorescence and electron microscopy. Physiologic bone remodelling was studied in wild-type (Wt) and IL-17A-/- mice using micro-computer tomography and serum RANKL/osteoprotegerin concentration. Functional osteoclastogenesis assays were performed using bone marrow macrophages isolated from IL-17A-/- and Wt mice.ResultsIL-17A upregulates the receptor activator for NF-kappaB receptor on human osteoclast precursors in vitro, leading to increased sensitivity to RANKL signalling, osteoclast differentiation and bone loss. IL-17A-/- mice have physiological bone homeostasis indistinguishable from Wt mice, and bone marrow macrophages isolated from these mice develop fully functional normal osteoclasts.ConclusionsCollectively our data demonstrate anti-IL-17A treatment as a selective therapeutic target for bone loss associated with autoimmune diseases
Coupling of morphology to surface transport in ion-beam irradiated surfaces. I. Oblique incidence
We propose and study a continuum model for the dynamics of amorphizable
surfaces undergoing ion-beam sputtering (IBS) at intermediate energies and
oblique incidence. After considering the current limitations of more standard
descriptions in which a single evolution equation is posed for the surface
height, we overcome (some of) them by explicitly formulating the dynamics of
the species that transport along the surface, and by coupling it to that of the
surface height proper. In this we follow recent proposals inspired by
``hydrodynamic'' descriptions of pattern formation in aeolian sand dunes and
ion-sputtered systems. From this enlarged model, and by exploiting the
time-scale separation among various dynamical processes in the system, we
derive a single height equation in which coefficients can be related to
experimental parameters. This equation generalizes those obtained by previous
continuum models and is able to account for many experimental features of
pattern formation by IBS at oblique incidence, such as the evolution of the
irradiation-induced amorphous layer, transverse ripple motion with non-uniform
velocity, ripple coarsening, onset of kinetic roughening and other.
Additionally, the dynamics of the full two-field model is compared with that of
the effective interface equation.Comment: 23 pages, 14 figures. Movies of figures 6, 7, and 8 available at
http://gisc.uc3m.es/~javier/Movies
Ancient Urban Ecology Reconstructed from Archaeozoological Remains of Small Mammals in the Near East
Acknowledgments We especially thank the many archaeologists who collaborated closely with our project and invested pioneering efforts in intensive fine-scale retrieval of the archaeozoological samples that provided the basis for this study: Shai Bar, Amnon Ben-Tor, Amit Dagan, Yosef Garfinkel, Ayelet Gilboa, Zvi Greenhut, Amihai Mazar, Stefan Munger, Ronny Reich, Itzhaq Shai, Ilan Sharon, Joe Uziel, Sharon Zuckerman, and additional key excavation personnel who were instrumental in collection of the samples or in assisting the work including: Shimrit Bechar, Jacob Dunn, Norma Franklin, Egon Lass and Yiftah Shalev. Funding:The research was funded by a post-doctoral grant awarded to L.W. from the European Research Council under the European Community’s Seventh Framework Program (FP7/2007e2013)/ERC grant agreement number 229418. The laboratory work was also supported by funding by the Israel Science Foundation (Grant 52/10). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD
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