A retrospective segmentation analysis of placental volume by magnetic resonance imaging from first trimester to term gestation

Background Abnormalities of the placenta affect 5–7% of pregnancies. Because disturbances in fetal growth are often preceded by dysfunction of the placenta or attenuation of its normal expansion, placental health warrants careful surveillance. There are limited normative data available for placental volume by MRI. Objective To determine normative ranges of placental volume by MRI throughout gestation. Materials and methods In this cross-sectional retrospective analysis, we reviewed MRI examinations of pregnant females obtained between 2002 and 2017 at a single institution. We performed semi-automated segmentation of the placenta in images obtained in patients with no radiologic evidence of maternal or fetal pathology, using the Philips Intellispace Tumor Tracking Tool. Results Placental segmentation was performed in 112 women and had a high degree of interrater reliability (single-measure intraclass correlation coefficient =0.978 with 95% confidence interval [CI] 0.956, 0.989; P<0.001). Normative data on placental volume by MRI increased nonlinearly from 6 weeks to 39 weeks of gestation, with wider variability of placental volume at higher gestational age (GA). We fit placental volumetric data to a polynomial curve of third order described as placental volume = –0.02*GA3 + 1.6*GA2 – 13.3*GA + 8.3. Placental volume showed positive correlation with estimated fetal weight (P=0.03) and birth weight (P=0.05). Conclusion This study provides normative placental volume by MRI from early first trimester to term gestation. Deviations in placental volume from normal might prove to be an imaging biomarker of adverse fetal health and neonatal outcome, and further studies are needed to more fully understand this metric. Assessment of placental volume should be considered in all routine fetal MRI examinations

The transformed Gram Charlier distribution: Parametric properties and financial risk applications

In this paper we study an extension of the Gram-Charlier (GC) density in Jondeau and Rockinger (2001) which consists of a Gallant and Nychka (1987) transformation to ensure positivity without parameter restrictions. We derive its parametric properties such as unimodality, cumulative distribution, higher-order moments, truncated moments, and the closed-form expressions for the expected shortfall (ES) and lower partial moments. We obtain the analytic k-th order stationarity conditions for the unconditional moments of the TGARCH model under the transformed GC (TGC) density. In an empirical application to asset return series, we estimate the tail index; backtest the density, VaR and ES; and implement a comparative analysis based on Hansen's skewed-t distribution. Finally, we present extensions to time-varying conditional skewness and kurtosis, and a new class of mixture densities based on this TGC distribution

Atom chips with two-dimensional electron gases: theory of near surface trapping and ultracold-atom microscopy of quantum electronic systems

We show that current in a two-dimensional electron gas (2DEG) can trap ultracold atoms $<1 \mu$m away with orders of magnitude less spatial noise than a metal trapping wire. This enables the creation of hybrid systems, which integrate ultracold atoms with quantum electronic devices to give extreme sensitivity and control: for example, activating a single quantized conductance channel in the 2DEG can split a Bose-Einstein condensate (BEC) for atom interferometry. In turn, the BEC offers unique structural and functional imaging of quantum devices and transport in heterostructures and graphene.Comment: 5 pages, 4 figures, minor change

Copula methods for evaluating relative tail forecasting performance

We apply our method to analyze which portfolios are capable of providing superior performance to those based on the Sharpe ratio. In this paper we illustrate the use of conditional copulas for identifying differences in alternative portfolio performance strategies. We analyze which portfolios are capable of providing superior performance to those based on the Sharpe ratio. Our results show that under the Gaussian copula, both expected tail ratio and skewness-kurtosis ratio portfolios exhibit remarkably low correlations respecting the Sharpe ratio (SR) portfolio. This means that these two portfolios are different respecting the SR one. We also find that copulas which focus on either the upper tail (Gumbel) or the lower tail (Clayton) render significant differences. In short, our copula analysis is useful to understand what kind of equity-screening strategy based on its corresponding performance measure performs better in relation to the SR portfolio. Our copula methods to evaluate models' performance differences is significant because when models’ performance is rather similar, conclusions on statistical differences, can be defective as they may hinge on the subsample type or size used, leading to inefficient investment decisions. Our method contributes to address this issue

Hall effect in strongly correlated low dimensional systems

We investigate the Hall effect in a quasi one-dimensional system made of weakly coupled Luttinger Liquids at half filling. Using a memory function approach, we compute the Hall coefficient as a function of temperature and frequency in the presence of umklapp scattering. We find a power-law correction to the free-fermion value (band value), with an exponent depending on the Luttinger parameter $K_{\rho}$. At high enough temperature or frequency the Hall coefficient approaches the band value.Comment: 7 pages, 3 figure

Estrategias para la capacitación y control del servicio dirigidas a los restaurantes tradicionales del cantón nobol

The reality we live today shows that the quality of food is the main concern for consumers and customers, as they require more detailed information about the food they purchase; and therefore, its nature, systems and production processes, culinary traditions, and everything that highlight their characteristics and origins, achieve greater relevance among them. Situation that drives us to a non too distant future, in which all countries will establish certificates in order to commercialize food products and beverages according to recognized standards of quality control. In our territory, there are zones that can be developed as new tourism niches by embracing its touristic resources which differentiates them from each other, as in the case of Nobol canton from Guayas province, where Santa Narcisa Jesus’ remains are resting and revered by thousands of believers and devotees since her beatification in 1992. And being the cuisine of great importance to the new trends in travel and leisure, strategies are being designed to integrate the Nobol’s restoration service providers into the development of their business environment. For this reason, it is proposed a system of certification, among other strategies, which ensure food security of the final product along with what consumers today are demanding while choosing a food and beverage place; and when assurances that fit into the demanding requirements and characteristics are provided, they choose these sites

Hall effect in quasi one-dimensional organic conductors

We study the Hall effect in a system of weakly coupled Luttinger Liquid chains, using a Memory function approach to compute the Hall constant in the presence of umklapp scattering along the chains. In this approximation, the Hall constant decomposes into two terms: a high-frequency term and a Memory function term. For the case of zero umklapp scattering, where the Memory function vanishes, the Hall constant is simply the band value, in agreement with former results in a similar model with no dissipation along the chains. With umklapp scattering along the chains, we find a power-law temperature dependance of the Hall constant. We discuss the applications to quasi 1D organic conductors at high temperatures.Comment: Proceedings of the ISCOM conference "Sixth International Symposium on Crystalline Organic Metals, Superconductors, and Ferromagnets", Key West, Florida, USA (Sept. 2005), to be plublished in the Journal of Low Temperature Physic