A method for predicting launch vehicle vibration levels in the region of the spacecraft adaptor

Prediction curves for launch vehicle vibration levels in region of spacecraft adapto

The Effect of Institutional and Cultural Factors on the Perceptions of Earnings Management

In this study we examine the effect of stakeholder orientation versus shareholder orientation, and the level of cultural secrecy on individuals’ perceptions of earnings management practices. Examining perceptions from 1,260 participants from 13 countries indicates that individuals from stakeholder-oriented institutional back- grounds were less accepting of earnings management, including both accounting earn- ings management and operating earnings management activities, than participants from shareholder-oriented institutional backgrounds, and that individuals from secretive cultures were more accepting of both types of earnings management activities. Our findings provide evidence of the anticipated perceptual differences across countries with respect to earnings management and suggest the need for further research linking perceptions to reported earnings management measures

Inferring Rn-222 soil fluxes from ambient Rn-222 activity and eddy covariance measurements of CO2

We present a new methodology, which we call Single Pair of Observations Technique with Eddy Covariance (SPOT-EC), to estimate regional-scale surface fluxes of 222Rn from tower-based observations of 222Rn activity concentration, CO2 mole fractions and direct CO2 flux measurements from eddy covariance. For specific events, the regional (222Rn) surface flux is calculated from short-term changes in ambient (222Rn) activity concentration scaled by the ratio of the mean CO2 surface flux for the specific event to the change in its observed mole fraction. The resulting 222Rn surface emissions are integrated in time (between the moment of observation and the last prior background levels) and space (i.e. over the footprint of the observations). The measurement uncertainty obtained is about ±15 % for diurnal events and about ±10 % for longer-term (e.g. seasonal or annual) means. The method does not provide continuous observations, but reliable daily averages can be obtained. We applied our method to in situ observations from two sites in the Netherlands: Cabauw station (CBW) and Lutjewad station (LUT). For LUT, which is an intensive agricultural site, we estimated a mean 222Rn surface flux of (0.29 ± 0.02) atoms cm−2 s−1 with values  > 0.5 atoms cm−2 s−1 to the south and south-east. For CBW we estimated a mean 222Rn surface flux of (0.63 ± 0.04) atoms cm−2 s−1. The highest values were observed to the south-west, where the soil type is mainly river clay. For both stations good agreement was found between our results and those from measurements with soil chambers and two recently published 222Rn soil flux maps for Europe. At both sites, large spatial and temporal variability of 222Rn surface fluxes were observed which would be impractical to measure with a soil chamber. SPOT-EC, therefore, offers an important new tool for estimating regional-scale 222Rn surface fluxes. Practical applications furthermore include calibration of process-based 222Rn soil flux models, validation of atmospheric transport models and performing regional-scale inversions, e.g. of greenhouse gases via the SPOT 222Rn-tracer method

The radio source B 1834+620: A double-double radio galaxy with interesting properties

We present a study of the peculiar radio galaxy B 1834+620. It is characterised by the presence of a 420-kpc large edge-brightened radio source which is situated within, and well aligned with, a larger (1.66 Mpc) radio source. Both sources apparently originate in the same host galaxy, which has a R_s-magnitude of 19.7 and a redshift of 0.5194, as determined from the strong emission-lines in the spectrum. We have determined the rotation measures towards this source, as well as the radio spectral energy distribution of its components. The radio spectrum of the large outer source is steeper than that of the smaller inner source. The radio core has a spectrum that peaks at a frequency of a few GHz. The rotation measures towards the four main components are quite similar, within $\sim\!2$ rad m$^{-2}$ of 58 rad m$^{-2}$. They are probably largely galactic in origin. We have used the presence of a bright hotspot in the northern outer lobe to constrain the advance velocity of the inner radio lobes to the range between 0.19c and 0.29c, depending on the orientation of the source. This corresponds to an age of this structure in the range between 2.6 and 5.8 Myr. We estimate a density of the ambient medium of the inner lobes of \la 1.6 \times 10^{-30} gr\,cm$^{-3}$ (particle density \la 8 \times 10^{-7} cm$^{-3}$). A low ambient density is further supported by the discrepancy between the large optical emission-line luminosity of the host galaxy and the relatively low radio power of the inner lobes.Comment: Accepted for publication in MNRA

Spanning tussen thuiswerken en carrière

Hoewel loopbanen steeds persoonlijker worden, en het gezin en het sociale leven bij velen een steeds hogere prioriteit lijken te krijgen, blijft ook carrière maken een ambitie van velen. Indien wij gaan thuiswerken, worden we dan gedwongen om te kiezen of kan dit goed gecombineerd worden met carrière maken

Semiparametric theory and empirical processes in causal inference

In this paper we review important aspects of semiparametric theory and empirical processes that arise in causal inference problems. We begin with a brief introduction to the general problem of causal inference, and go on to discuss estimation and inference for causal effects under semiparametric models, which allow parts of the data-generating process to be unrestricted if they are not of particular interest (i.e., nuisance functions). These models are very useful in causal problems because the outcome process is often complex and difficult to model, and there may only be information available about the treatment process (at best). Semiparametric theory gives a framework for benchmarking efficiency and constructing estimators in such settings. In the second part of the paper we discuss empirical process theory, which provides powerful tools for understanding the asymptotic behavior of semiparametric estimators that depend on flexible nonparametric estimators of nuisance functions. These tools are crucial for incorporating machine learning and other modern methods into causal inference analyses. We conclude by examining related extensions and future directions for work in semiparametric causal inference