What Explains Fertility? Evidence from Italian Pension Reforms

Why do people have kids in developed societies? We propose an empirical test of two alternative theories — children as “consumption” vs. “investment” good. We use as a natural experiment the Italian pension reforms of the 90s that introduced a clear discontinuity in the treatment across workers. This policy experiment is particularly well suited, since the “consumption” motive predicts lower future pensions to reduce fertility, while the “old-age security” to increase it. Our empirical analysis identifies a clear and robust positive effect of less generous future pensions on post-reform fertility. These findings are consistent with “old-age security” even for contemporary fertility.old-age security, public pension systems, fertility, altruism

Processing eutectics in space

The investigations of directional solidification have indicated the necessity of establishing a secure foundation in earth-based laboratory processing in order to properly assess low-gravity processing. Emphasis was placed on evaluating the regularity of microstructure of the rod-like eutectic Al-Al3Ni obtained under different conditions of growth involving the parameters of thermal gradient, solidification rate, and interfacial curvature. In the case of Al-Al3Ni, where the Al3Ni phase appears as facets rods, solidification rate was determined to be a controlling parameter. Zone melting of thin eutectic films showed that for films of the order of 10 to 20 micrometers thick, the extra surface energy appears to act to stabilize a regular microstructure. The results suggest that the role of low-gravity as provided in space-laboratory processing of materials is to be sought in the possibility of generating a higher thermal gradient in the solidifying ingot for a given power input-output arrangement than can be obtained under normal one-g processes

Processing eutectics in space

Experimental work is reported which was directed toward obtaining interface shape control while a numerical thermal analysis program was being made operational. An experimental system was developed in which the solid-liquid interface in a directionally solidified aluminum-nickel eutectic could be made either concave to the melt or convex to the melt. This experimental system provides control over the solid-liquid interface shape and can be used to study the effect of such control on the microstructure. The SINDA thermal analysis program, obtained from Marshall Space Flight Center, was used to evaluate experimental directional solidification systems for the aluminum-nickel and the aluminum-copper eutectics. This program was applied to a three-dimensional ingot, and was used to calculate the thermal profiles in axisymmetric heat flow. The results show that solid-liquid interface shape control can be attained with physically realizable thermal configurations and the magnitudes of the required thermal inputs were indicated

Processing eutectics in space

Studies which have been done in an earth-based laboratory environment have generally not yielded specimens with the degree of perfection required of the eutectic microstructure to provide test data to evaluate their nonstructural applications. It has been recognized that the low-g environment of an orbiting space laboratory provides a unique environment to re-examine the process of solidification with the goal of producing better microstructures. The objective of this program is to evaluate the feasibility of using the space environment for producing eutectics with microstructures which can be of value on earth. In carrying out this objective, evaluative investigations were carried out on the technology of solidification in a 1-g environment to provide sound baseline data for planning space laboratory experiments

Ground-motion intensity measure correlations observed in Italian strong-motion records

Ground-motion models (GMMs) are widely used in probabilistic seismic hazard analysis (PSHA) to estimate the probability distributions of earthquake-induced ground-motion intensity measures (IMs) at a site, given an earthquake of a certain magnitude occurring at a nearby location. Accounting for spatial and cross-IM correlations in earthquake-induced ground motions has important implications on probabilistic seismic hazard and loss estimates. This study first develops a new Italian GMM with spatial correlation for 31 amplitude-related IMs, including peak ground acceleration (PGA), peak ground velocity (PGV) and 5% damped elastic pseudospectral accelerations (PSAs) at 29 periods ranging from 0.01 s to 4 s. The model estimation is performed through a recently-developed one-stage non-linear regression algorithm proposed by the authors, known as the Scoring estimation approach. In fact, current state-of-practice approaches estimate spatial correlation separately from the GMM estimation, resulting in inconsistent and statistically inefficient estimators of inter- and intraevent variances and parameters in the spatial correlation model. We test whether this affects the subsequent cross-IM correlation analysis. To this aim, based on the newly-developed GMM, the empirical correlation coefficients from inter- and intraevent residuals are investigated. Finally, a set of analytical correlation models between the selected IMs are proposed. This is of special interest as several correlation models between different IMs have been calibrated and validated based on advanced GMMs and global datasets, lacking earthquakes in extensional regions; however, modeling the correlation between different IM types has not been adequately addressed by current, state-of-the-art GMMs and recent ground-motion records for Italy

Engineering Analysis of Strong Motion Data from Recent Earthquakes in Sichuan, China

Recent earthquakes in the Sichuan Province have contributed to significantly expand the existing ground-motion database for China with new, high-quality ground-motion records. This study investigated the compatibility of ground-motion prediction equations (GMPEs) established by the NGA-West2 project in the US and local GMPEs for China, with respect to magnitude scaling, distance scaling, and site scaling implied by recent Chinese strong-motion data. The NGA-West2 GMPEs for shallow crustal earthquakes in tectonically active regions are considerably more sophisticated than widely used previous models, particularly in China. Using a mixed-effects procedure, the study evaluated event terms (inter-event residuals) and intra-event residuals of Chinese data relative to the NGA-West2 GMPEs. Distance scaling was investigated by examining trends of intra-event residuals with source-to-site distance. Scaling with respect to site conditions was investigated by examining trends of intra-event residuals with soil type. The study also investigated other engineering characteristics of Chinese strong ground motions. In particular, the records were analyzed for evidence of pulse-like forward-directivity effects. The elastic median response spectra of the selected stations were compared to code-mandated design spectra for various mean return periods. Results showed that international and local GMPEs can be applied for seismic hazard analysis in Sichuan with minor modification of the regression coefficients related to the source-to-site distance and soil scaling. Specifically, the Chinese data attenuated faster than implied by the considered GMPEs and the differences were statistically significant in some cases. Near-source, pulse-like ground motions were identified at two recording stations for the 2008 Wenchuan earthquake, possibly implying rupture directivity. The median recorded spectra were consistent with the code-based spectra in terms of amplitude and shape. The new ground-motion data can be used to develop advanced ground-motion models for China and worldwide and, ultimately, for advancing probabilistic seismic hazard assessment (PSHA)

Ground-motion intensity measure correlations observed in Italian data

Ground-motion models (GMMs) are used in probabilistic seismic hazard analysis (PSHA) to estimate the probability distribution of earthquake-induced ground-motion intensity measures (IMs). Accounting for spatial correlation and cross-IM correlation in ground-motion data has important implications on seismic hazard and risk assessment outputs. The current practice estimates the spatial correlation separately from the GMM estimation process, which may result in inconsistent and inefficient estimators of parameters in the spatial correlation models and GMMs. Moreover, several correlation models between different IMs have been calibrated and validated based on the NGA-West and NGA-West2 databases and advanced GMMs. However, modeling the correlation between different IM types has not been adequately addressed by current, state-of-the-art GMMs for Italy. To address those issues, this study first develops a series of new Italian GMMs with spatial correlation for 31 amplitude-related IMs, including peak ground acceleration (PGA) and peak ground velocity (PGV) and 5% damped elastic pseudo-spectral accelerations (PSA) at 29 periods ranging from 0.01 s to 4 s. The model estimation is performed through a recently-developed one-stage non-linear regression algorithm proposed by the authors, known as the Scoring estimation approach. Based on the newly-developed GMMs, this study finally proposes a set of analytical correlation models between the selected IMs for the considered Italian dataset

Information theory measures for the engineering validation of ground-motion simulations

This short communication introduces a quantitative approach for the engineering validation of ground-motion simulations based on information theory concepts and statistical hypothesis testing. Specifically, we use the Kullback-Leibler divergence to measure the similarity of the probability distributions of recorded and simulated ground-motion intensity measures (IMs). We demonstrate the application of the proposed validation approach to ground-motion simulations computed by using a variety of methods, including Graves and Pitarka hybrid broadband, the deterministic composite source model, and a stochastic white noise finite-fault model. Ground-motion IMs, acting as proxies for the (nonlinear) seismic response of more complex engineered systems, are considered herein to validate the considered ground-motion simulation methods. The list of considered IMs includes both spectral-shape and duration-related proxies, shown to be the optimal IMs in several probabilistic seismic demand models of different structural types, within the framework of performance-based earthquake engineering. The proposed validation exercise (1) can highlight the similarities and differences between simulated and recorded ground motions for a given simulation method and/or (2) allow the ranking of the performance of alternative simulation methods. The similarities between records and simulations should provide confidence in using the simulation method for engineering applications, while the discrepancies should help in improving the tested method for the generation of synthetic records

Ultimate Limit State Fragility of Offshore Wind Turbines on Monopile Foundations

Assessing the risk posed by extreme natural events to the failure of offshore wind turbines (OWTs) is a challenging task. Highly stochastic environmental conditions represent the main source of variable loading; consequently, a high level of uncertainty is associated with assessing the structural demand on OWT structures. However, failure of any of the primary structural components implies both complete loss of the OWT and loss of earnings associated with production stoppage (i.e., business interruption). In this paper, we propose the use of the Catastrophe (CAT) Risk Modelling approach to assess the structural risk posed by extreme weather conditions to OWTs. To help achieving this, we develop fragility curves – a crucial element of any CAT models – for OWTs on monopile foundations. Fragility functions express the likelihood of different levels of damage (or damage states) sustained by a given asset over a range of hazard intensities. We compare the effect of modelling and analysis decisions on the fragility curves, highlighting how different procedures could affect the estimated probability of failure. We apply the proposed framework to two case-study locations, one in the Baltic Sea and one in the North Sea

Gaussian process regression for fatigue reliability analysis of offshore wind turbines

The fatigue limit state (FLS) often drives the design of offshore wind turbine (OWT) substructures in European waters. Assessing fatigue damage over the intended design life of an OWT is computationally expensive, primarily as dynamic structural analyses have to be run for a large number of stochastic wind and wave loading conditions. This makes structural reliability assessment for the FLS a challenging task. In addition to evaluating load-induced fatigue damage, simulation-based structural reliability analysis also requires sampling of random variables that model uncertainties in the capacity of OWT structural components. To this aim, we develop and validate a computational framework for OWT fatigue reliability analysis that relies on Gaussian process (GP) regression to build surrogate models of load-induced fatigue damage. We demonstrate that the proposed approach can reduce the computational effort required to evaluate FLS reliability with high accuracy through application to three plausible offshore wind farm sites in Europe. The sensitivity of various goodness-of-fit metrics to different model assumptions is investigated to further reduce the computational effort required to perform GP regression/predictions. The results from this study can provide guidance for practical applications of the proposed framework in OWT projects