Geodesy by radio interferometry: Effects of atmospheric modeling errors on estimates of baseline length

Analysis of very long baseline interferometry data indicates that systematic errors in prior estimates of baseline length, of order 5 cm for ~8000-km baselines, were due primarily to mismodeling of the electrical path length of the troposphere and mesosphere ("atmospheric delay"). Here we discuss observational evidence for the existence of such errors in the previously used models for the atmospheric delay and develop a new "mapping" function for the elevation angle dependence of this delay. The delay predicted by this new mapping function differs from ray trace results by less than ~5 mm, at all elevations down to 5° elevation, and introduces errors into the estimates of baseline length of •< 1 cm, for the multistation intercontinental experiment analyzed here

Empiric Models of the Earth's Free Core Nutation

Free core nutation (FCN) is the main factor that limits the accuracy of the modeling of the motion of Earth's rotational axis in the celestial coordinate system. Several FCN models have been proposed. A comparative analysis is made of the known models including the model proposed by the author. The use of the FCN model is shown to substantially increase the accuracy of the modeling of Earth's rotation. Furthermore, the FCN component extracted from the observed motion of Earth's rotational axis is an important source for the study of the shape and rotation of the Earth's core. A comparison of different FCN models has shown that the proposed model is better than other models if used to extract the geophysical signal (the amplitude and phase of FCN) from observational data.Comment: 8 pages, 3 figures; minor update of the journal published versio

Density-functional embedding using a plane-wave basis

The constrained electron density method of embedding a Kohn-Sham system in a substrate system (first described by P. Cortona, Phys. Rev. B {\bf 44}, 8454 (1991) and T.A. Wesolowski and A. Warshel, J. Phys. Chem {\bf 97}, 8050 (1993)) is applied with a plane-wave basis and both local and non-local pseudopotentials. This method divides the electron density of the system into substrate and embedded electron densities, the sum of which is the electron density of the system of interest. Coupling between the substrate and embedded systems is achieved via approximate kinetic energy functionals. Bulk aluminium is examined as a test case for which there is a strong interaction between the substrate and embedded systems. A number of approximations to the kinetic-energy functional, both semi-local and non-local, are investigated. It is found that Kohn-Sham results can be well reproduced using a non-local kinetic energy functional, with the total energy accurate to better than 0.1 eV per atom and good agreement between the electron densities.Comment: 11 pages, 4 figure

Lipoprotein particle concentration measured by nuclear magnetic resonance spectroscopy is associated with gestational age at delivery: a prospective cohort study

Objective: To estimate the association between lipoprotein particle concentrations in pregnancy and gestational age at delivery. Design: Prospective cohort study. Setting: The study was conducted in the USA at the University of North Carolina. Population: We assessed 715 women enrolled in the Pregnancy, Infection, and Nutrition study from 2001 to 2005. Methods: Fasting blood was collected at two time points (&lt;20 and 24–29 weeks of gestation). Nuclear magnetic resonance (NMR) quantified lipoprotein particle concentrations [low-density lipoprotein (LDL), high-density lipoprotein (HDL), very-low density lipoprotein (VLDL)] and 10 subclasses of lipoproteins. Concentrations were assessed as continuous measures, with the exception of medium HDL which was classified as any or no detectable level, given its distribution. Cox proportional hazards models estimated hazard ratios (HR) for gestational age at delivery adjusting for covariates. Main outcome measures: Gestational age at delivery, preterm birth (&lt;37 weeks of gestation), and spontaneous preterm birth. Results: At &lt;20 weeks of gestation, three lipoproteins were associated with later gestational ages at delivery [large LDL NMR (HR 0.78, 95% CI 0.64–0.96), total VLDL NMR (HR 0.77, 95% CI 0.61–0.98), and small VLDL NMR (HR 0.78, 95% CI 0.62–0.98], whereas large VLDL NMR (HR 1.19, 95% CI 1.01–1.41) was associated with a greater hazard of earlier delivery. At 24–28 weeks of gestation, average VLDL NMR (HR 1.25, 95% CI 1.03–1.51) and a detectable level of medium HDL NMR (HR 1.90, 95% CI 1.19–3.02) were associated with earlier gestational ages at delivery. Conclusion: In this sample of pregnant women, particle concentrations of VLDL NMR , LDL NMR , IDL NMR , and HDL NMR were each independently associated with gestational age at delivery for all deliveries or spontaneous deliveries &lt;37 weeks of gestation. These findings may help formulate hypotheses for future studies of the complex relationship between maternal lipoproteins and preterm birth. Tweetable abstract: Nuclear magnetic resonance spectroscopy may identify lipoprotein particles associated with preterm delivery

Donor states in modulation-doped Si/SiGe heterostructures

We present a unified approach for calculating the properties of shallow donors inside or outside heterostructure quantum wells. The method allows us to obtain not only the binding energies of all localized states of any symmetry, but also the energy width of the resonant states which may appear when a localized state becomes degenerate with the continuous quantum well subbands. The approach is non-variational, and we are therefore also able to evaluate the wave functions. This is used to calculate the optical absorption spectrum, which is strongly non-isotropic due to the selection rules. The results obtained from calculations for Si/Si$_{1-x}$Ge$_x$ quantum wells allow us to present the general behavior of the impurity states, as the donor position is varied from the center of the well to deep inside the barrier. The influence on the donor ground state from both the central-cell effect and the strain arising from the lattice mismatch is carefully considered.Comment: 17 pages, 10 figure

Associations between PM2.5 and risk of preterm birth among liveborn infants

Purpose: Studies suggest exposure to ambient particulate matter less than 2.5 μg/m3 in aerodynamic diameter (PM2.5) may be associated with preterm birth (PTB), but few have evaluated how this is modified by ambient temperature. We investigated the relationship between PM2.5 exposure during pregnancy and PTB in infants without birth defects (1999–2006) and enrolled in the National Birth Defects Prevention Study and how it is modified by concurrent temperature. Methods: PTB was defined as spontaneous or iatrogenic delivery before 37 weeks. Exposure was assigned using inverse distance weighting with up to four monitors within 50 kilometers of maternal residence. To account for state-level variations, a Bayesian two-level hierarchal model was developed. Results: PTB was associated with PM2.5 during the third and fourth months of pregnancy (range: (odds ratio (95% confidence interval) = 1.00 (0.35, 2.15) to 1.49 (0.82, 2.68) and 1.31 (0.56, 2.91) to 1.62 (0.7, 3.32), respectively); no week of exposure conveyed greater risk. Temperature may modify this relationship; higher local average temperatures during pregnancy yielded stronger positive relationships between PM2.5 and PTB compared to nonstratified results. Conclusions: Results add to literature on associations between PM2.5 and PTB, underscoring the importance of considering co-exposures when estimating effects of PM2.5 exposure during pregnancy

Just a guy in pajamas? Framing the blogs in mainstream US newspaper coverage (1999—2005)

When new technologies are introduced to the public, their widespread adoption is dependent, in part, on news coverage (Rogers, 1995).Yet, as weblogs began to play major role in the public spheres of politics and journalism, journalists faced a paradox: how to cover a social phenomenon that was too large to ignore and posed a significant threat to their profession. This article examines how blogs were framed by US newspapers as the public became more aware of the blogging world. A content analysis of blog-related stories in major US newspapers from 1999 to 2005 was conducted. Findings suggest that newspaper coverage framed blogs as more beneficial to individuals and small cohorts than to larger social entities such as politics, business and journalism. Moreover, only in the realm of journalism were blogs framed as more of a threat than a benefit, and rarely were blogs considered an actual form of journalism.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Large-Eddy Simulations of Magnetohydrodynamic Turbulence in Heliophysics and Astrophysics

We live in an age in which high-performance computing is transforming the way we do science. Previously intractable problems are now becoming accessible by means of increasingly realistic numerical simulations. One of the most enduring and most challenging of these problems is turbulence. Yet, despite these advances, the extreme parameter regimes encountered in space physics and astrophysics (as in atmospheric and oceanic physics) still preclude direct numerical simulation. Numerical models must take a Large Eddy Simulation (LES) approach, explicitly computing only a fraction of the active dynamical scales. The success of such an approach hinges on how well the model can represent the subgrid-scales (SGS) that are not explicitly resolved. In addition to the parameter regime, heliophysical and astrophysical applications must also face an equally daunting challenge: magnetism. The presence of magnetic fields in a turbulent, electrically conducting fluid flow can dramatically alter the coupling between large and small scales, with potentially profound implications for LES/SGS modeling. In this review article, we summarize the state of the art in LES modeling of turbulent magnetohydrodynamic (MHD) ows. After discussing the nature of MHD turbulence and the small-scale processes that give rise to energy dissipation, plasma heating, and magnetic reconnection, we consider how these processes may best be captured within an LES/SGS framework. We then consider several special applications in heliophysics and astrophysics, assessing triumphs, challenges,and future directions