Ability, Parental Valuation of Education and the High School Dropout Decision

We use a large, rich Canadian micro-level dataset to examine the channels through which family socio-economic status and unobservable characteristics affect children's decisions to drop out of high school. First, we document the strength of observable socio-economic factors: our data suggest that teenage boys with two parents who are themselves high school dropouts have a 16% chance of dropping out, compared to a dropout rate of less than 1% for boys whose parents both have a university degree. We examine the channels through which this socio-economic gradient arises using an extended version of the factor model set out in Carneiro, Hansen, and Heckman (2003). Specifically, we consider the impact of cognitive and non-cognitive ability and the value that parents place on education. Our results support three main conclusions. First, cognitive ability at age 15 has a substantial impact on dropping out. Second, parental valuation of education has an impact of approximately the same size as cognitive ability effects for medium and low ability teenagers. A low ability teenager has a probability of dropping out of approximately .03 if his parents place a high value on education but .36 if their education valuation is low. Third, parental education has no direct effect on dropping out once we control for ability and parental valuation of education. Our results point to the importance of whatever determines ability at age 15 (including, potentially, early childhood interventions) and of parental valuation of education during the teenage years. We also make a small methodological contribution by extending the standard factor based estimator to allow a non-linear relationship between the factors and a covariate of interest. We show that allowing for non-linearities has a substantial impact on estimated effects.Idiosyncratic Shocks, Disability, Insurance, Marriage

Ability, parental valuation of education and the high school dropout decision

We use a large, rich Canadian micro-level dataset to examine the channels through which family socio-economic status and unobservable characteristics affect children's decisions to drop out of high school. First, we document the strength of observable socio-economic factors: our data suggest that teenage boys with two parents who are themselves high school dropouts have a 16 per cent chance of dropping out, compared to a dropout rate of less than 1 per cent for boys whose parents both have a university degree. We examine the channels through which this socio-economic gradient arises using an extended version of the factor model set out in Carneiro, Hansen, and Heckman (2003). Specifically, we consider the impact of cognitive and non-cognitive ability and the value that parents place on education. Our results support three main conclusions. First, cognitive ability at age 15 has a substantial impact on dropping out. The highest ability individuals are predicted never to drop out regardless of parental education or parental valuation of education. In contrast, the lowest ability teenagers have a probability of dropping out of approximately .36 if their parents have a low valuation of education. Second, parental valuation of education has a substantial impact on medium and low ability teenagers. A low ability teenager has a probability of dropping out of approximately .03 if his parents place a high value on education but .36 if their educational valuation is low. These effects are estimated while conditioning on ability at age 15. Thus, under some assumptions, they reflect parental influences during the upper teenage years and are in addition to any impact they might have in the early childhood years leading up to age 15. Third, parental education has no direct effect on dropping out once we control for ability and parental valuation of education. Overall, our results point to the importance of whatever determines ability at age 15 (including, potentially, early childhood interventions) and of parental valuation of education during the teenage years. Our work also provides a small methodological contribution by extending the standard factor based estimator to allow a more non-linear relationship between the factors and a co-variate of interest. We show that allowing for non-linearities has a substantial impact on estimated effects.

A coupled hydromechanical bounding surface model predicting the hysteretic behaviour of unsaturated soils

This paper presents a bounding surface model to predict the hydromechanical behaviour of unsaturated soils under isotropic stress states. The model combines the hydraulic law of Gallipoli et al. [8] with the mechanical law of Gallipoli and Bruno [9]. The hydraulic law relates the degree of saturation to the single variable scaled suction, which accounts for the effect of both suction and void ratio on the water retention behaviour of soils. The hydraulic law is made up of two closed-form equations, one for drying paths and one for wetting paths. Similarly, the mechanical law relates the void ratio to the single variable scaled stress, which accounts for the effect of both stress state and degree of saturation on the deformation of soils. The mechanical law is made up of two closed-form equations, one for loading paths and one for unloading paths. The proposed hydromechanical model is expressed in a finite form and has therefore the advantage of not requiring any approximate numerical integration. The model has been validated against four sets of laboratory data showing a good ability to predict the coupled behaviour of unsaturated soils (e.g. collapse-compression upon wetting) by means of a relatively small number of material parameters

Potential of high-frequency ultrasounds to improve sludge anaerobic conversion and surfactants removal at different food/inoculum ratio

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HIGH-FREQUENCY ULTRASOUNDS FOR THE DECONTAMINATION AND INTENSIVE STABILIZATION OF SEWAGE SLUDGE

HIGH-FREQUENCY ULTRASOUNDS FOR THE DECONTAMINATION AND INTENSIVE STABILIZATION OF SEWAGE SLUDGE Sewage treatment plants generate quite a large amount of sludge. Because of increased environmental awareness and stringent environmental standards governing the disposal of sewage sludge, its utilization in agricultural production has been gaining increasing interest and attention in recent years. Although rich in nutrients, organic substance and microelements, in some countries sewage sludge is not accepted as agricultural fertilizer due to the awareness regarding potential health risks derived from the accumulation of heavy metals, organic compounds, and pathogens,. To be used as agricultural fertilizer, secondary sludge must be decontaminated by organic micropollutants and stabilized, aerobically or anaerobically. The use of a unique ultrasonic treatment, at 200 kHz, was studied in order to obtain both decontamination and stabilization of sewage sludge. Sonolysis experiments directly on sludge samples were carried out to degrade the linear alkylbenzene sulphonates (LAS), which is one of the most abundant classes of organic micropollutants in sludge. LAS degradation of about 40% was obtained in less than 1 hour. However, in a complex matrix like sludge, surfactants degradation is affected by different parameters: the specific energy delivered to the samples and the sludge total solids seemed the most important. On the other hand, the effects of the ultrasound irradiation at 200 kHz on sludge floc structure was investigated and compared with the \u201cclassical\u201d sludge pretreatment at 20 kHz. Although the ultrasound treatment at 20 kHz was found to be more effective in sludge disintegration, in terms of solubilization of organic matter and flocs destruction, the treatment with 200 kHz gave also satisfactory and encouraging disintegration result. Afterwards, batch anaerobic digestion tests were performed with 20 and 200 kHz pretreated sludge to evaluate the efficacy of these two types of sludge pretreatment on the anaerobic digestion performances. Also the effect of food/inoculum ratio on the digestion performances was assessed. The treatment at higher frequency permitted to obtain satisfactory anaerobic digestion performances, as regards solubilisation and removal of organic substances and biogas production

A bounding surface hysteretic water retention model for deformable soils

The paper presents a soil water retention model that takes into account the effects of void ratio and hydraulic hysteresis on the variation of degree of saturation. Based on a modified form of the van Genuchten equation, the model defines two bounding surfaces, namely a main drying surface and a main wetting surface, which delimit the region of admissible soil states in the space of degree of saturation, suction and void ratio. Suction and void ratio are then combined into a single auxiliary variable, termed scaled suction, and the main surfaces are recast as main curves in the plane of degree of saturation and scaled suction. The effects of both suction and void ratio on the drying/wetting behaviour of the soil are simply incorporated by relating degree of saturation to scaled suction. The soil is dried when the scaled suction is increased and is wetted when the scaled suction is decreased. The model assumes that, inside the region of admissible soil states, the derivative of degree of saturation with respect to the scaled suction depends on the distance of the soil state from the main curves. This assumption ensures a smooth transition of the drying and wetting paths towards their respective main curves. Interestingly, the derivative of degree of saturation with respect to scaled suction can be integrated in a closed form and all wetting and drying paths can therefore be described by two explicit equations (one for drying paths and one for wetting paths), where different wetting or drying paths are characterised by different values of the integration constant. The integration of the model in a closed form facilitates its implementation into numerical codes. The model requires seven parameters, whose values can be obtained from a single drying\u2013wetting test. Predictions are validated against two different data sets published in the literature, which shows the capability of the model to capture the behaviour observed during laboratory tests on fine-grained soils

A microstructural insight into the hygro-mechanical behaviour of a stabilised hypercompacted earth

The use of raw earth as construction material can save embodied and operational energy because of low processing costs and passive regulation of indoor ambient conditions. Raw earth must however be mechanically and/or chemically stabilised to enhance stiffness, strength and water durability. In this work, stiffness and strength are enhanced by compacting raw earth to very high pressures up to 100 MPa while water durability is improved by using alkaline solutions and silicon based admixtures. The effect of these stabilisation methods on hygro-mechanical behaviour is explored and interpreted in terms of the microstructural features of the material. Stiffness and strength are defined at different humidity levels by unconfined compression tests while the moisture buffering capacity is measured by humidification/desiccation cycles as prescribed by the norm ISO 24353 (Hygrothermal performance of building materials and products determination of moisture adsorption/desorption properties in response to humidity variation. International Organization for Standardization, Geneva, 2008). As for the microstructural characterisation, different tests (i.e. X-ray diffractometry, Infrared Spectroscopy, Mercury Intrusion Porosimetry, Nitrogen Adsorption) are performed to analyse the effect of stabilisation on material fabric and mineralogy. Results indicate that the use of alkaline activators and silicon based admixtures significantly improves water durability while preserving good mechanical and moisture buffering properties. Similarly, the compaction to very high pressures results in high levels of stiffness and strength, which are comparable to those of standard masonry bricks. This macroscopic behaviour is then linked to the microscopic observations to clarify the mechanisms through which stabilisation affects the properties of raw earth at different scales