An Empirical Analysis of 'Acting White'

There is a debate among social scientists regarding the existence of a peer externality commonly referred to as 'acting white.' Using a newly available data set (the National Longitudinal Study of Adolescent Health), which allows one to construct an objective measure of a student's popularity, we demonstrate that there are large racial differences in the relationship between popularity and academic achievement; our (albeit narrow) definition of 'acting white.' The effect is intensified among high achievers and in schools with more interracial contact, but non-existent among students in predominantly black schools or private schools. The patterns in the data appear most consistent with a two-audience signaling model in which investments in education are thought to be indicative of an individual's opportunity costs of peer group loyalty. Other models we consider, such as self-sabotage among black youth or the presence of an oppositional culture, all contradict the data in important ways.

A Plasticity Theory Approach for the Stability Analysis of Vertical Layers of Concrete in the Fresh State

The industrial production of cement is currently responsible for around 5% of global CO2 emissions. Hence, the development of technologies aimed at minimizing the use of cement in concrete structures, while preserving their strength and durability properties, plays a vital role in the reduction of carbon emissions. The use of cement in concrete structures can be minimized through the manufacture of functionally layered structural elements where concrete with high cement content is used rationally only when it contributes significantly to the performance of the structure. In functionally layered concrete, horizontal variation in material composition can be achieved by casting adjacent vertical layers of different materials. Removable vertical panels can be used to demarcate the mixes during casting. A good bond between the layers can be achieved by removing the panels prior to concrete hardening. However, a major problem with this application is the control of the fresh-state deformations of the adjacent vertical layers. This study investigates the fundamental problem of fresh state stability of concrete prisms that consist of two vertical layers of different mixes. A novel limit-state approach based on plasticity theory is formulated to assess the stability of the system as a function of material properties and geometry. The relationship between material parameters, system stability and geometry is determined and the formulated limit-state approach is validated against experimental results.The authors would like to acknowledge the financial support of EPSRC - the Engineering and Physical Sciences Research Council (UK) [Project reference number: EP/N017668/1]

Fresh state stability of vertical layers of concrete

The production of cement is currently associated with around 5% of global carbon emissions. The manufacture of functionally graded structural elements, where the material composition is varied over the volume, allows the use of cement to be optimized and minimized. Horizontal gradation of material properties can be achieved by casting vertical layers having homogeneous composition. However, a key problem in this application is the control of the fresh state deformations of the layers. This study investigates for the first time the fundamental problem of the fresh state stability of concrete prisms that consist of two vertical layers of different mixes. Original experiments are designed to invoke stable and unstable behaviour. Two novel limit-state models are formulated to assess the stability of the system as a function of material properties and geometry. The results show that a relationship between system stability, geometry and material parameters exists, and that it is captured by the presented models

Functionally graded concrete elements composed of vertical layers of different mixes

The industrial production of cement is currently responsible for 5-7% of global CO2 emissions. The manufacture of functionally graded concrete structures, where the use of material is optimized by varying the material composition over the volume, opens up vast opportunities to reduce the use of cement. In functionally graded concrete, horizontal gradation can be achieved by casting vertical layers having homogeneous properties. However, a major problem with this kind of application is the control of the fresh state deformations. This study investigates the fresh state stability of concrete prisms that consist of two vertical layers of different mixes. Experiments are performed to invoke stable or unstable behaviour. The results show that, for a given geometry, a relationship between the material parameters and system stability exists.EPSRC - the Engineering and Physical Sciences Research Council (UK) [Project reference number: EP/N017668/1

Interface bond strength of lightweight low-cement functionally layered concrete elements

Production of cement accounts for around 5% of human-made carbon emissions. When the selection of a cement-intensive mix with low porosity is driven by durability requirements, the resulting low permeability of the material is only fully exploited in peripheral regions of the element where the material acts as a physical barrier against the penetration of aggressive substances. This paper explores the potential of casting layered prismatic elements composed of an external durability layer and a lightweight core section as a means to achieve cement and weight savings. Layered elements are traditionally obtained by casting new concrete layers onto already hardened older concrete layers. A major problem with this technique is that planes of weakness are obtained at the interfaces between the layers. The bond between the layers can be improved by casting the materials at approximately the same time. However, research to date has not yet demonstrated the viability of producing elements with wet cast external layers and the effects of delays between successive pours on the mechanical tensile performance of the interfaces in layered elements have not been quantified. An original method is presented to form prismatic elements composed of an external durability layer and a lightweight core section by casting two concrete mixes at approximately the same time. The approach is validated by realising a proof-of-concept prototype layered element. A set of additional layered elements are cast with various pour delays and cored across the interface between their layers to characterize the interlayer bond strength by direct tension. To interpret the mechanisms affecting the bond, the variation of tensile bond strength with the location of the sample and the impact of roughness are also investigated. When the pour delay was minimal, failure did not occur at the interlayer but the relationship between pour delay and bond strength is markedly nonlinear, with bond strength reductions of more than 30% for pour delays of only three hours. It was also found that the bond strength of the interface varies significantly with the considered location and that up to 40% of the bond strength reduction due to a delay between the castings can be recovered by roughening the surface of the older concrete prior to casting of the newer mix. The successful realisation of wet cast prismatic elements with an external durability layer is an important step towards the realisation of light-weight layered concrete elements with low embodied energy

ROSE: a Package for Binary Imbalanced Learning

The ROSE package provides functions to deal with binary classification problems in the presence of imbalanced classes. Artificial balanced samples are generated according to a smoothed bootstrap approach and allow for aiding both the phases of estimation and accuracy evaluation of a binary classifier in the presence of a rare class. Functions that implement more traditional remedies for the class imbalance and different metrics to evaluate accuracy are also provided. These are estimated by holdout, bootstrap or cross-validation methods

Small area estimation: An application of a flexible fay-herriot method

The importance of small area estimation in survey sampling is increasing, due to the growing demand for reliable small area estimation from both public and private sectors. In this paper, we address the important issue of using statistical modeling techniques to compute more reliable small area estimates. The main aim is to assess the use of a flexible methodology for small area estimation. We formulate a new flexible small area model by incorporating a tuning (index) parameter into the standard area-level (Fay-Herriot) model. We achieve this using a combination of two methods namely, empirical Bayes (EB) approach and hierarchical Bayes (HB) approach. Our results suggest that the proposed model can be seen as advancement over the standard Fay-Herriot model. The novelty here isthat we have developed a flexible way to handle random effects in small area estimation. The Implementation of the proposed model is only mildly more difficult than the Fay-Herriot model. We have obtained results for both EB approach and the HB approach. Compared with the corresponding HB procedure, the EB approach saves a tremendous computing time and is very simple to implement.Key words: Area-level, empirical Bayes, Fay-Herriot model, hierarchical Bayes, small are

Functionally graded concrete: Design objectives, production techniques and analysis methods for layered and continuously graded elements

The pressing need to reduce global carbon emissions together with recent advances in automated manufacturing have driven a growing interest in functionally graded concrete. In functionally graded concrete, the material composition is spatially varied to meet performance demands that differ within regions of a structural element. This offers significant potential to reduce cement consumption. Step-wise layered and continuously graded concrete systems are introduced and investigations of concrete mix combinations to achieve durability, fracture resistance, strength, ductility, cost saving, weight reduction or lower embodied energy improvements are discussed. Production techniques for horizontally layered and vertically layered structural elements in the context of fresh-on-hardened and fresh-on-fresh casting as well as emerging continuously graded processes are presented. Challenges associated with fresh-state deformations, layer interfaces and the need for appropriate fresh and hardened-state modelling tools are critically assessed.EPSRC - EP/N017668/

Analytical and numerical seismic assessment of heritage masonry towers

Abstract The new Italian building code, published in 2018 [MIT in NTC 2018: D.M. del Ministero delle Infrastrutture e dei trasporti del 17/01/2018. Aggiornamento delle Norme Tecniche per le Costruzioni (in Italian), 2018], explicitly refers to the Italian “Guidelines for the assessment and mitigation of the seismic risk of the cultural heritage” [PCM in DPCM 2011: Direttiva del Presidente del Consiglio dei Ministri per valutazione e riduzione del rischio sismico del patrimonio culturale con riferimento alle norme tecniche per le costruzioni, G.U. n. 47 (in Italian), 2011] as a reliable source of guidance that can be employed for the vulnerability assessment of heritage buildings under seismic loads. According to these guidelines, three evaluation levels are introduced to analyse and assess the seismic capacity of historic masonry structures, namely: (1) simplified global static analyses; (2) kinematic analyses based on local collapse mechanisms, (3) detailed global analyses. Because of the complexity and the large variety of existing masonry typologies, which makes it particularly problematic to adopt a unique procedure for all existing structures, the guidelines provide different simplified analysis approaches for different structural configurations, e.g. churches, palaces, towers. Among the existing typologies of masonry structures there considered, this work aims to deepen validity, effectiveness and scope of application of the Italian guidelines with respect to heritage masonry towers. The three evaluation levels proposed by the guidelines are here compared by discussing the seismic risk assessment of a representative masonry tower: the Cugnanesi tower located in San Gimignano (Italy). The results show that global failure modes due to local stress concentrations cannot be identified if only simplified static and kinematic analyses are performed. Detailed global analyses are in fact generally needed for a reliable prediction of the seismic performance of such structures.</jats:p