Bounds on Portfolio Quality

The signal-noise ratio of a portfolio of p assets, its expected return divided by its risk, is couched as an estimation problem on the sphere. When the portfolio is built using noisy data, the expected value of the signal-noise ratio is bounded from above via a Cramer-Rao bound, for the case of Gaussian returns. The bound holds for `biased' estimators, thus there appears to be no bias-variance tradeoff for the problem of maximizing the signal-noise ratio. An approximate distribution of the signal-noise ratio for the Markowitz portfolio is given, and shown to be fairly accurate via Monte Carlo simulations, for Gaussian returns as well as more exotic returns distributions. These findings imply that if the maximal population signal-noise ratio grows slower than the universe size to the 1/4 power, there may be no diversification benefit, rather expected signal-noise ratio can decrease with additional assets. As a practical matter, this may explain why the Markowitz portfolio is typically applied to small asset universes. Finally, the theorem is expanded to cover more general models of returns and trading schemes, including the conditional expectation case where mean returns are linear in some observable features, subspace constraints (i.e., dimensionality reduction), and hedging constraints

Randomized crossover comparison of proportional assist ventilation and patient-triggered ventilation in extremely low birth weight infants with evolving chronic lung disease

Background: Refinement of ventilatory techniques remains a challenge given the persistence of chronic lung disease of preterm infants. Objective: To test the hypothesis that proportional assist ventilation ( PAV) will allow to lower the ventilator pressure at equivalent fractions of inspiratory oxygen (FiO(2)) and arterial hemoglobin oxygen saturation in ventilator-dependent extremely low birth weight infants in comparison with standard patient-triggered ventilation ( PTV). Methods: Design: Randomized crossover design. Setting: Two level-3 university perinatal centers. Patients: 22 infants ( mean (SD): birth weight, 705 g ( 215); gestational age, 25.6 weeks ( 2.0); age at study, 22.9 days ( 15.6)). Interventions: One 4- hour period of PAV was applied on each of 2 consecutive days and compared with epochs of standard PTV. Results: Mean airway pressure was 5.64 ( SD, 0.81) cm H2O during PAV and 6.59 ( SD, 1.26) cm H2O during PTV ( p < 0.0001), the mean peak inspiratory pressure was 10.3 ( SD, 2.48) cm H2O and 15.1 ( SD, 3.64) cm H2O ( p < 0.001), respectively. The FiO(2) ( 0.34 (0.13) vs. 0.34 ( 0.14)) and pulse oximetry readings were not significantly different. The incidence of arterial oxygen desaturations was not different ( 3.48 ( 3.2) vs. 3.34 ( 3.0) episodes/ h) but desaturations lasted longer during PAV ( 2.60 ( 2.8) vs. 1.85 ( 2.2) min of desaturation/ h, p = 0.049). PaCO2 measured transcutaneously in a subgroup of 12 infants was similar. One infant met prespecified PAV failure criteria. No adverse events occurred during the 164 cumulative hours of PAV application. Conclusions: PAV safely maintains gas exchange at lower mean airway pressures compared with PTV without adverse effects in this population. Backup conventional ventilation breaths must be provided to prevent apnea-related desaturations. Copyright (c) 2007 S. Karger AG, Base

PAV ontology: provenance, authoring and versioning

Provenance is a critical ingredient for establishing trust of published scientific content. This is true whether we are considering a data set, a computational workflow, a peer-reviewed publication or a simple scientific claim with supportive evidence. Existing vocabularies such as DC Terms and the W3C PROV-O are domain-independent and general-purpose and they allow and encourage for extensions to cover more specific needs. We identify the specific need for identifying or distinguishing between the various roles assumed by agents manipulating digital artifacts, such as author, contributor and curator. We present the Provenance, Authoring and Versioning ontology (PAV): a lightweight ontology for capturing just enough descriptions essential for tracking the provenance, authoring and versioning of web resources. We argue that such descriptions are essential for digital scientific content. PAV distinguishes between contributors, authors and curators of content and creators of representations in addition to the provenance of originating resources that have been accessed, transformed and consumed. We explore five projects (and communities) that have adopted PAV illustrating their usage through concrete examples. Moreover, we present mappings that show how PAV extends the PROV-O ontology to support broader interoperability. The authors strived to keep PAV lightweight and compact by including only those terms that have demonstrated to be pragmatically useful in existing applications, and by recommending terms from existing ontologies when plausible. We analyze and compare PAV with related approaches, namely Provenance Vocabulary, DC Terms and BIBFRAME. We identify similarities and analyze their differences with PAV, outlining strengths and weaknesses of our proposed model. We specify SKOS mappings that align PAV with DC Terms.Comment: 22 pages (incl 5 tables and 19 figures). Submitted to Journal of Biomedical Semantics 2013-04-26 (#1858276535979415). Revised article submitted 2013-08-30. Second revised article submitted 2013-10-06. Accepted 2013-10-07. Author proofs sent 2013-10-09 and 2013-10-16. Published 2013-11-22. Final version 2013-12-06. http://www.jbiomedsem.com/content/4/1/3

Microstructures and Dielectric Properties Of pb (Al,Vl-,)Ohs Systems

The microstructures and electrical properties of Pb(AlxV1-x)03*cse ramic have been investigated. The samples were prepared using solid-state technique and were sintered at 800 OC, 850 OC and 900 OC. Surface morphology studies show that small grains with submicron size - 0.25 pm coexist with the bigger grains in micron size. As the sintering temperature increased, the grains size increase and thus become more compact. From )(RD analysis, the sample structure obtained is an orthorhombic system with space group PMMA and unit cell volume is 469.595 A3. The dielectric constant, e' for sample PAV 71800, PAV 71850 and PAV 71900 increased as the sintering temperature increased where the values of E' for sample sintered at 900 O C is - 6000 at 10'~H z and - 90 at 1 kHz. However, the loss factor, E" for sample sintered at 900 O C is higher than that of other samples. The loss tangent, E"/E' for sample PAV 71800, PAV 71850 and PAV 71900 at 1 kHz are 0.1, 0.12 and 0.16 respectively. The PAV 0.9 shows the highest E' -4000 at Hz but the E" for this sample is also high. This is followed by sample PAV 0.7 and PAV 0.3. Between frequencies higher than 1 kHz, the magnitudes of the E' data dispersion (- 80) are similar for samples PAV 0.3, PAV 0.7 and PAV 0.9. At 1 0-2 Hz to 1 kHz, the dispersion of E' is strongly dependent on frequency. However, the E' dispersion is independent with frequency at 1 kHz to lo5 Hz. The mechanisms that are observed from all samples are quasi dc, dipolar and barrier layer. A peak observed at lo2 Hz is due to the ionic relaxation processes. The activation energy that is obtained from sample PAV 71800 is 0.416. It indicates that the electrons hopping are weak. An equivalent circuit model has been proposed to represent the mechanism observed. The conductivity, ,o is increased from 3.0x10-~to 8.0x10-~r nholm for sample PAV 71800 and PAV 71900 respectively. For other samples with different Al composition, o, increased from 1.0x10-~ to 1.0x10-~ mholm for sample PAV 0.3 and PAV 0.9 respectively. The o, curve exhibits two distinct regions where the low frequency region is weakly dependent on frequency due to free charge carriers while the high frequency region is strongly dependent with frequency due to bound charge carriers in this sample. The IS, is increased from to lo4 mholm for 50 O C and 290 "C respectively. The activation energy of sample PAV 71800 and PAV 0.1 is -0.65 eV and may be due to the ac conduction in terms of hopping transport of charge carrier in a narrow band of localization states as the Fermi level. In complex impedance plots, only one semicircle is observed at low frequency and does not started fiom the origin due to the high frequency resistance effect. For sample PAV 71800, the resistance obtained from the plot is 8 . 9 9 ~ 1 0oh~m /m and the value of the capacitance is 1.5x10-'~F . The capacitance value obtained is in the range of bulk ferroelectric mechanism. In direct current measurement, the curve obtained obeyed the Ohm's law and the activation energy increased from 0.85 eV to 1.15 eV was the sintering temperature increases from 800 O C to 900 O C and 0.71 eV to 1.62 eV when A1 compositions increase from PAV 0.1 to PAV 0.9

The eclipsing Cataclysmic Variable GS Pavonis: Evidence for disk radius changes

We have obtained differential time series photometry of the cataclysmic variable GS Pavonis over a timespan of 2 years. These show that this system is deeply eclipsing (~2-3.5 mag) with an orbital period of 3.72 hr. The eclipse depth and out-of-eclipse light levels are correlated. From this correlation we deduce that the disk radius is changing and that the eclipses in the low state are total. The derived distance to GS Pav is 790+/-90 pc, with a height above the galactic plane of 420+/-60 pc. We classify GS Pav as a novalike system.Comment: 4 pages, including 2 figures, accepted for publication in A&A Letter

Нобелівська лекція як віддзеркалення світогляду лауреата

Статтю присвячено дослідженню змістової складової такого специфічного мовленнєвого жанру як Нобелівська лекція. Увагу зосереджено на проблемно-тематичних характеристиках англомовних лекцій, які були прочитані лауреатами в галузі літератури. Проаналізовано чинники, що впливають на зміст лекції. Встановлено взаємозв’язок між темою доповіді та офіційним обґрунтуванням нагороди членами Шведської академії