The Angular Separation of the Components of the Cepheid AW Per

The 6.4 day classical Cepheid AW Per is a spectroscopic binary with a period of 40 years. Analyzing the centroids of HST/STIS spectra obtained in November 2001, we have determined the angular separation of the binary system. Although we currently have spatially resolved data for a single epoch in the orbit, the success of our approach opens the possibility of determining the inclination, sini, for the system if the measurements are repeated at additional epochs. Since the system is potentially a double lined spectroscopic binary, the combination of spectroscopic orbits for both components and the visual orbit would give the distance to the system and the masses of its components, thereby providing a direct measurement of a Cepheid mass.Comment: 12 pages, accepted version -- minor change

Index Funds and Stock Market Growth

In the present paper we analyze the relationship between index funds and asset prices. In particular, our analysis of daily index fund flows indicates a strong contemporaneous correlation between fund inflows and S&P market returns. We also document a strong negative correlation between fund out flows and S&P market returns with the exception of outflows from a fund with very high initial investment requirement. These effects may be interpreted in two ways. Either investor supply and demand affects S&P market prices, or investors condition their demand and supply on intra-day market fluctuations. To sort out these effects, we examine trailing investor reaction to market moves. Our results suggest the market reacts to daily demand. However, only negative reactions appear due to past returns. We investigate whether index investor demand shocks are permanent or temporary by examining the related behavior of the S&P futures index. Clear evidence supports the hypothesis that they are permanent. This result may help explain the unusual recent relative performance of the S&P 500 index. Using the average market-timing newsletter recommendation over the period, we find that investors appear to react to expert' advice about the market. Bullish newsletter sentiment is associated with greater inflows, although outflows are not well explained by newsletter advice. Dispersion in advice is associated with lower inflows. We find a high correlation among a number of variables used as a proxy for investor disagreement.

Disposition Matters: Volume, Volatility and Price Impact of a Behavioral Bias

In this paper, we estimate the behavioral component of the Grinblatt and Han (2002) model and derive several testable implications about the expected relationship between the preponderance of disposition-prone investors in a market and volume, volatility and stock returns. To do this, we use a large sample of individual accounts over a six-year period in the 1990's in order to identify investors who are subject to the disposition effect. We then use their trading behavior to construct behavioral factors. We show that when the fraction of irrational' investor purchases in a stock increases, the unexplained portion of the market price of the stock decreases. We further show that statistical exposure to a disposition factor explains cross-sectional differences in daily returns, controlling for a host of other factors and characteristics. The evidence is consistent with the hypothesis that trade between disposition-prone investors and their counter-parties impacts relative prices.

Portfolio Diversification and City Agglomeration

We relate the degree of investor portfolio focus to the broader urban economic context of the household. Using a detailed panel of investors in Sweden over the period 1995 to 2000, we find that the level of investor diversification, as measured by number of stocks in the portfolio and by the average correlation among holdings, is partially explained by city industrial characteristics. We find that rural portfolios are more diversified than urban portfolios and that portfolio diversification is characterized by factors associated with urban growth. We consider a number of theories to explain investor focus, including behavioral biases, real and perceived informational advantage, local social competition and hedging of non-tradable risk. We find little evidence to support social and hedging motives to explain the lack of portfolio diversification, and some evidence in favor of perceived informational advantage in an urban setting. We attribute this evidence as support for the broader 'knowledge spillover' processes documented in the recent urban economics literature. Portfolio effects may be added to the list of factors that define and differentiate urbanism.

An Instrument for Describing Mathematical Curves

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Do interactions between plant roots and the rhizosphere affect parasitoid behaviour?

Multitrophic interactions are powerful forces shaping the structure of living communities. Plants encounter a great diversity of organisms in their environment: some of these interactions are beneficial (e.g. symbiotic fungi and insect pollinators) while some are detrimental (e.g. herbivorous insects and pathogenic micro-organisms). Multitrophic interactions between below-ground and above-ground organisms are receiving increasing attention because they may influence plant defences against biotic and abiotic stresses. In this study we show that an arbuscular mycorrhizal symbiosis makes tomato plants significantly more resistant towards aphids, by enhancing both direct defences, both attractivity towards aphid parasitoids

Extracellular nanovesicles secreted by human osteosarcoma cells promote angiogenesis

Angiogenesis involves a number of different players among which extracellular nanovesicles (EVs) have recently been proposed as an efficient cargo of pro-angiogenic mediators. Angiogenesis plays a key role in osteosarcoma (OS) development and progression. Acidity is a hallmark of malignancy in a variety of cancers, including sarcomas, as a result of an increased energetic metabolism. The aim of this study was to investigate the role of EVs derived from osteosarcoma cells on angiogenesis and whether extracellular acidity, generated by tumor metabolism, could influence EVs activity. For this purpose, we purified and characterized EVs from OS cells maintained at either acidic or neutral pH. The ability of EVs to induce angiogenesis was assessed in vitro by endothelial cell tube formation and in vivo using chicken chorioallantoic membrane. Our findings demonstrated that EVs derived from osteosarcoma cells maintained either in acidic or neutral conditions induced angiogenesis. The results showed that miRNA and protein content of EVs cargo are correlated with pro-angiogenic activity and this activity is increased by the acidity of tumor microenvironment. This study provides evidence that EVs released by human osteosarcoma cells act as carriers of active angiogenic stimuli that are able to promote endothelial cell functions relevant to angiogenesis

The Influence of Stellar Wind Variability on Measurements of Interstellar O VI Along Sightlines to Early-Type Stars

A primary goal of the FUSE mission is to understand the origin of the O VI ion in the interstellar medium of the Galaxy and the Magellanic Clouds. Along sightlines to OB-type stars, these interstellar components are usually blended with O VI stellar wind profiles, which frequently vary in shape. In order to assess the effects of this time-dependent blending on measurements of the interstellar O VI lines, we have undertaken a mini-survey of repeated observations toward OB-type stars in the Galaxy and the Large Magellanic Cloud. These sparse time series, which consist of 2-3 observations separated by intervals ranging from a few days to several months, show that wind variability occurs commonly in O VI (about 60% of a sample of 50 stars), as indeed it does in other resonance lines. However, in the interstellar O VI $\lambda$1032 region, the O VI $\lambda$1038 wind varies only in $\sim$30% of the cases. By examining cases exhibiting large amplitude variations, we conclude that stellar-wind variability {\em generally} introduces negligible uncertainty for single interstellar O VI components along Galactic lines of sight, but can result in substantial errors in measurements of broader components or blends of components like those typically observed toward stars in the Large Magellanic Cloud. Due to possible contamination by discrete absorption components in the stellar O VI line, stars with terminal velocities greater than or equal to the doublet separation (1654 km/s) should be treated with care.Comment: Accepted for publication in the Astrophysical Journal Lette