A minimum hypothesis explanation for an IMF with a lognormal body and power law tail

We present a minimum hypothesis model for an IMF that resembles a lognormal distribution at low masses but has a distinct power-law tail. Even if the central limit theorem ensures a lognormal distribution of condensation masses at birth, a power-law tail in the distribution arises due to accretion from the ambient cloud, coupled with a non-uniform (exponential) distribution of accretion times.Comment: 2 pages, 1 figure, to appear in IMF@50, eds. E. Corbelli, F. Palla, and H. Zinnecker, Kluwer, Astrophysics and Space Science Librar

New Technologies for the Utilization of Biologically Based Raw Materials for Feed and Food Production

Within the activities undertaken by IIASA's Food and Agriculture Program one part has been directed to assessing the role which new technologies for protein production could play in the future in covering the global demand. This report contains the main papers submitted to the Task Force Meeting on "New Technologies for the Utilization of Biologically Based Raw Materials for Feed and Food Production" held at Tbilisi, Georgia, USSR in August 1981. The meeting was the second in a series of meetings dealing with the problems of new technologies for the utilization of agricultural wastes. The main topics for discussion at the Tbilisi meeting were defined during the first meeting held at IIASA in September 1980. Furthermore the network of collaborating institutions and teams, established after this first meeting, produced interesting background material in the form of answers to the questionnaires distributed by IIASA. (See Table 6 of this report) . The meeting was seen as a further step towards the assessment of the new technologies on protein production and the basis for future collaboration was outlined and the proposal for holding the next meeting was submitted

The spatial distribution of substellar objects in IC348 and the Orion Trapezium Cluster

Aims: Some theoretical scenarios suggest the formation of brown dwarfs as ejected stellar embryos in star-forming clusters. Such a formation mechanism can result in different spatial distributions of stars and substellar objects. We aim to investigate the spatial structure of stellar and substellar objects in two well sampled and nearby embedded clusters, namely IC348 and the Orion Trapezium Cluster (OTC) to test this hypothesis. Methods:Deep near-infrared K-band data complete enough to sample the substellar population in IC348 and OTC are obtained from the literature. The spatial distribution of the K-band point sources is analysed using the Minimum Spanning Tree (MST) method. The Q parameter and the spanning trees are evaluated for stellar and substellar objects as a function of cluster core radius R$_c$. Results: The stellar population in both IC348 and OTC display a clustered distribution whereas the substellar population is distributed homogeneously in space within twice the cluster core radius. Although the substellar objects do not appear to be bound by the cluster potential well, they are still within the limits of the cluster and not significantly displaced from their birth sites. Conclusions: The spatially homogeneous distribution of substellar objects is best explained by assuming higher initial velocities, distributed in a random manner and going through multiple interactions. The overall spatial coincidence of these objects with the cluster locations can be understood if these objects are nevertheless travelling slowly enough so as to feel the gravitational effect of the cluster. The observations support the formation of substellar objects as ``ejected stellar embryos''. Higher ejection velocities are necessary but net spatial displacements may not be necessary to explain the observational data.Comment: 4 pages. Accepted by A&A Letter

Expectations in Micro Data: Rationality Revisited

An increasing number of longitudinal data sets collect expectations information regarding a variety of future individual level events and decisions, providing researchers with the opportunity to explore expectations over micro variables in detail. We provide a theoretical framework and an econometric methodology to use that type of information to test the Rational Expectations hypothesis in models of individual behavior, and present tests using two different panel data sets.

Expectations in Micro Data: Rationality Revisited

An increasing number of longitudinal data sets collect expectations information regarding a variety of future individual level events and decisions, providing researchers with the opportunity to explore expectations over micro variables in detail. We present a theoretical framework and an econometric methodology to use that type of information to test the Rational Expectations (RE) hypothesis in models of individual behavior. This RE assumption at the micro level underlies a majority of the research in applied fields in economics, and it is the common foundation of most work in dynamic models of individual behavior. We present tests of three different types of expectations using two different panel data sets that represent two very different populations. In all three cases we cannot reject the RE hypothesis. Our results support a wide variety of models in economics, and other disciplines, that assume rational behavior.Rational Expectations, Retirement, Longevity, and Education Expectations, Instrumental Variables, Sample Selection.

Young Brown Dwarfs in the Core of the W3 Main Star-Forming Region

We present the results of deep and high-resolution (FWHM ~ 0".35) JHK NIR observations with the Subaru telescope, to search for very low mass young stellar objects (YSOs) in the W3 Main star-forming region. The NIR survey covers an area of ~ 2.6 arcmin^2 with 10-sigma limiting magnitude exceeding 20 mag in the JHK bands. The survey is sensitive enough to provide unprecedented details in W3 IRS 5 region and reveals a census of the stellar population down to objects below the hydrogen-burning limit. We construct JHK color-color (CC) and J-H/J and H-K/K color-magnitude (CM) diagrams to identify very low luminosity YSOs and to estimate their masses. Based on these CC and CM diagrams, we identified a rich population of embedded YSO candidates with infrared excesses (Class I and Class II), associated with the W3 Main region. A large number of red sources (H-K > 2) have also been detected around W3 Main. We argue that these red stars are most probably pre-main-sequence (PMS) stars with intrinsic color excesses. Based on the comparison between theoretical evolutionary models of very low-mass PMS objects with the observed CM diagram, we find there exists a substantial substellar population in the observed region. The mass function (MF) does not show the presence of cutoff and sharp turnover around the substellar limit, at least at the hydrogen-burning limit. Furthermore, the MF slope indicates that the number ratio of young brown dwarfs and hydrogen-burning stars in the W3 Main is probably higher than those in Trapezium and IC 348. The presence of mass segregation, in the sense that relatively massive YSOs lie near the cluster center, is seen. The estimated dynamical evolution time indicates that the observed mass segregation in the W3 Main may be the imprint of the star formation process.Comment: 39 pages, 15 figures. Accepted for publication in the Astrophysical Journa

Objective User Engagement With Mental Health Apps: Systematic Search and Panel-Based Usage Analysis.

BACKGROUND: Understanding patterns of real-world usage of mental health apps is key to maximizing their potential to increase public self-management of care. Although developer-led studies have published results on the use of mental health apps in real-world settings, no study yet has systematically examined usage patterns of a large sample of mental health apps relying on independently collected data. OBJECTIVE: Our aim is to present real-world objective data on user engagement with popular mental health apps. METHODS: A systematic engine search was conducted using Google Play to identify Android apps with 10,000 installs or more targeting anxiety, depression, or emotional well-being. Coding of apps included primary incorporated techniques and mental health focus. Behavioral data on real-world usage were obtained from a panel that provides aggregated nonpersonal information on user engagement with mobile apps. RESULTS: In total, 93 apps met the inclusion criteria (installs: median 100,000, IQR 90,000). The median percentage of daily active users (open rate) was 4.0% (IQR 4.7%) with a difference between trackers (median 6.3%, IQR 10.2%) and peer-support apps (median 17.0%) versus breathing exercise apps (median 1.6%, IQR 1.6%; all z≥3.42, all P CONCLUSIONS: Although the number of app installs and daily active minutes of use may seem high, only a small portion of users actually used the apps for a long period of time. More studies using different datasets are needed to understand this phenomenon and the ways in which users self-manage their condition in real-world settings

The Star Formation Region NGC 6530: distance, ages and Initial Mass Function

We present astrometry and $BVI$ photometry, down to $V\simeq22$, of the very young open cluster NGC6530, obtained from observations taken with the Wide Field Imager camera at the MPG/ESO 2.2 m Telescope. Both the $V$ vs. $B-V$ and the $V$ vs. $V-I$ color-magnitude diagrams (CMD) show the upper main sequence dominated by very bright cluster stars, while, due to the high obscuration of the giant molecular cloud surrounding the cluster, the blue envelopes of the diagrams at $V\gtrsim 14$ are limited to the main sequence stars at the distance of NGC6530. This particular structure of the NGC6530 CMD allows us to conclude that its distance is about $d \simeq 1250$ pc, significantly lower than the previous determination of d=1800 pc. We have positionally matched our optical catalog with the list of X-ray sources found in a Chandra-ACIS observation, finding a total of 828 common stars, 90% of which are pre-main sequence stars in NGC6530. Using evolutionary tracks of Siess et al. (2000)}, mass and age values are inferred for these stars. The median age of the cluster is about 2.3 Myr; in the mass range (0.6--4.0)$M_\odot$, the Initial Mass Function (IMF) shows a power law index $x=1.22\pm0.17$, consistent with both the Salpeter index (1.35), and with the index derived for other young clusters ; towards smaller masses the IMF shows a peak and then it starts to decrease.Comment: 32 pages, 13 ps figures, in press in Astronomy and Astrophysic

A Constraint on brown dwarf formation via ejection: radial variation of the stellar and substellar mass function of the young open cluster IC2391

Using the Wide Field Imager (WFI) at the ESO 2.2m telescope at La Silla and the CPAPIR camera at the CTIO 1.5m telescope at Cerro Tololo, we have performed an extensive, multiband photometric survey of the open cluster IC2391 (D~146pc, age~50Myr, solar metallicity). Here we present the results from our photometric survey and from a spectroscopic follow-up of the central part of the survey.Comment: 4 pages, 3 figures, to appear in the proceedings of the Cool Stars 15 conferenc