Time Dependent Models of Magnetospheric Accretion onto Young Stars

Accretion onto Classical T Tauri stars is thought to take place through the action of magnetospheric processes, with gas in the inner disk being channeled onto the star's surface by the stellar magnetic field lines. Young stars are known to accrete material in a time-variable manner and the source of this variability remains an open problem, particularly on the shortest (~ day) timescales. Using one-dimensional time-dependent numerical simulations that follow the field line geometry, we find that for plausibly realistic young stars, steady-state transonic accretion occurs naturally in the absence of any other source of variability. However, we show that if the density in the inner disk varies smoothly in time with ~ day long time-scales (e.g., due to turbulence) this complication can lead to the development of shocks in the accretion column. These shocks propagate along the accretion column and ultimately hit the star, leading to rapid, large amplitude changes in the accretion rate. We argue that when these shocks hit the star the observed time-dependence will be a rapid increase in accretion luminosity followed by a slower decline and could be an explanation for some of the short period variability observed in accreting young stars. Our one-dimensional approach bridges previous analytic work to more complicated, multi-dimensional simulations, and observations.Comment: 16 Pages, 12 figure

Assessment of motivation to control alcohol use: The motivational thought frequency and state motivation scales for alcohol control

publisher: Elsevier articletitle: Assessment of motivation to control alcohol use: The motivational thought frequency and state motivation scales for alcohol control journaltitle: Addictive Behaviors articlelink: http://dx.doi.org/10.1016/j.addbeh.2016.02.038 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved

A transitional disk around an intermediate mass star in the sparse population of the Orion OB1 Association

We present a detailed study of the disk around the intermediate mass star SO 411, aiming to explain the spectral energy distribution of this star. We show that this is a transitional disk truncated at $\sim$11 au, with $\sim$0.03 lunar masses of optically thin dust inside the cavity. Gas also flows through the cavity, since we find that the disk is still accreting mass onto the star, at a rate of $\sim 5x10^{-9}$ Msun/yr. Until now, SO 411 has been thought to belong to the $\sim$3 Myr old {$\sigma$} Orionis cluster. However, we analyzed the second Gaia Data Release in combination with kinematic data previously reported, and found that SO 411 can be associated with an sparse stellar population located in front of the {$\sigma$} Orionis cluster. If this is the case, then SO 411 is older and even more peculiar, since primordial disks in this stellar mass range are scarce for ages $>$5 Myr. Analysis of the silicate 10$\mu$m feature of SO 411 indicates that the observed feature arises at the edge of the outer disk, and displays a very high crystallinity ratio of $\sim$0.5, with forsterite the most abundant silicate crystal. The high forsterite abundance points to crystal formation in non-equilibrium conditions. The PAH spectrum of SO 411 is consistent with this intermediate state between the hot and luminous Herbig Ae and the less massive and cooler T Tauri stars. Analysis of the 7.7$\mu$m PAH feature indicates that small PAHs still remain in the SO 411 disk.Comment: Accepted in the Astrophysical Journal (17 pages, 9 Figures

The Mini Alcohol Craving Experience Questionnaire: Development and Clinical Application

Background - Standardised alcohol craving scales are rarely used outside of research environments despite recognised clinical utility. Scale length is a key barrier to more widespread application. A brief measure of alcohol craving is needed to improve research and treatment of Alcohol Use Disorders (AUDs). Grounded in the Elaborated Intrusion Theory of Desire, the Alcohol Craving Experience (ACE) questionnaire comprises two 11 - item self-report scales which assess past-week frequency and maximum strength of alcohol craving . This study aimed to create a brief version of the ACE while maintaining psychometric integrity and clinical utility. Methods - Patients attending a university hospital alcohol and drug out-patient service for treatment of AUD completed the ACE as part of a questionnaire battery. Three patient samples were utilised: 519 patients with pre-treatmen t and outcome data; 228 patients with pre-treatment data; and 66 patients who completed the ACE at treatment sessions one and two. Results - The Frequency scale of the ACE possessed greater clinical utility and predictive validity than the Strength scale. Revision of the Frequency measure produced a 5-item ‘Mini Alcohol Craving Experience’ (MACE) questionnaire. Satisfactory validity (construct, predictive, concurrent, convergent, and incremental ) and reliability ( internal and test-retest ) was maintained. A one standard deviation increase in pre-treatment MACE score was associated with a 54 percent increase in the odds of patient lapse or dropout. Conclusions - The MACE provides a brief, theoretically and psychometrically robust measure of alcohol craving suitable for use with AUD populations in time-limited clinical and research settings

Broadband Measurement of Absorption Cross-Section of the Human Body in a Reverberation Chamber

We present broadband reverberation chamber measurements of the absorption cross section (ACS) of the hu- man body averaged over all directions of incidence and angles of polarization. This frequency-dependent parameter characterizes the interactions between the body and the enclosures of rever- berant environments such as aircraft cabins, and is therefore important for the determination of the overall Q-factor and hence the field strength illuminating equipment inside such en- closures. It also correlates directly with the electromagnetic expo- sure of occupants of reverberant environments. The average absorption cross section of nine subjects was measured at fre- quencies over the range 1-8.5 GHz. For a 75 kg male the ACS varied between 0.18 and 0.45 square meters over this range. ACS also correlated with body surface area for the subjects tested. The results agree well with computational electromagnetic simu- lations, but are obtained much more rapidly. We have used the obtained values of absorption cross section to estimate the effect of passengers on the Q-factor of a typical airliner cabin. Index Terms—reverberation chamber, absorption cross

Alcohol-related expectancies are associated with the D2 dopamine receptor and GABAa receptor B3 subunit genes

Molecular genetic research has identified promising markers of alcohol dependence, including alleles of the D2 dopamine receptor (DRD2) and the GABAA receptor ￢3 subunit (GABRB3) genes. Whether such genetic risk manifests itself in stronger alcohol-related outcome expectancies, or in difficulty resisting alcohol, is unknown. In the present study, A1+ (A1A1 and A1A2 genotypes) and A1- (A2A2 genotype) alleles of the DRD2 and G1+ (G1G1 and G1 non-G1 genotypes) and G1- (non-G1 non-G1 genotype) alleles of the GABRB3 were determined in a group of 56 medically-ill patients diagnosed with alcohol dependence. Mood-related Alcohol Expectancy (AE) and Drinking Refusal Self-Efficacy (DRSE) were assessed using the Drinking Expectancy Profile (Young and Oei, 1996). Patients with the DRD2 A1+ allele, compared to those with the DRD2 A1- allele, reported lower DRSE in situations of social pressure (p=. 009). Similarly, lower DRSE was reported under social pressure by patients with the GABRB3 G1+ allele when compared to those with the GABRB3 G1- allele (p=.027). Patients with the GABRB3 G1+ allele also revealed reduced DRSE in situations characterized by negative affect than patients with the GABRB3 G1- alleles (p=. 037). Patients carrying the GABRB3 G1+ allele showed stronger AE relating to negative affective change (for example, increased depression) than their GABRB3 G1- counterparts (p=. 006). Biological influence in the development of some classes of cognitions is hypothesized. The clinical implications, particularly with regard to patient-treatment matching and the development of an integrated psychological and pharmacogenetic approach are discussed

Probing CO and N_2 Snow Surfaces in Protoplanetary Disks with N_2H^+ Emission

Snowlines of major volatiles regulate the gas and solid C/N/O ratios in the planet-forming midplanes of protoplanetary disks. Snow surfaces are the 2D extensions of snowlines in the outer disk regions, where radiative heating results in an increasing temperature with disk height. CO and N_2 are two of the most abundant carriers of C, N, and O. N_2H^+ can be used to probe the snow surfaces of both molecules, because it is destroyed by CO and formed from N_2. Here we present Atacama Large Millimeter/submillimeter Array (ALMA) observations of N_2H^+ at ~0.”2–0.”4 resolution in the disks around LkCa 15, GM Aur, DM Tau, V4046 Sgr, AS 209, and IM Lup. We find two distinctive emission morphologies: N_2H^+ is either present in a bright, narrow ring surrounded by extended tenuous emission, or in a broad ring. These emission patterns can be explained by two different kinds of vertical temperature structures. Bright, narrow N_2H^+ rings are expected in disks with a thick Vertically Isothermal Region above the Midplane (VIRaM) layer (LkCa 15, GM Aur, DM Tau) where the N_2H^+ emission peaks between the CO and N_2 snowlines. Broad N_2H^+ rings come from disks with a thin VIRaM layer (V4046 Sgr, AS 209, IM Lup). We use a simple model to extract the first sets of CO and N_2 snowline pairs and corresponding freeze-out temperatures toward the disks with a thick VIRaM layer. The results reveal a range of N_2 and CO snowline radii toward stars of similar spectral type, demonstrating the need for empirically determined snowlines in disks

Miniature exoplanet radial velocity array I: design, commissioning, and early photometric results

The MINiature Exoplanet Radial Velocity Array (MINERVA) is a US-based observational facility dedicated to the discovery and characterization of exoplanets around a nearby sample of bright stars. MINERVA employs a robotic array of four 0.7 m telescopes outfitted for both high-resolution spec- troscopy and photometry, and is designed for completely autonomous operation. The primary science program is a dedicated radial velocity survey and the secondary science objective is to obtain high precision transit light curves. The modular design of the facility and the flexibility of our hardware allows for both science programs to be pursued simultaneously, while the robotic control software provides a robust and efficient means to carry out nightly observations. In this article, we describe the design of MINERVA including major hardware components, software, and science goals. The telescopes and photometry cameras are characterized at our test facility on the Caltech campus in Pasadena, CA, and their on-sky performance is validated. New observations from our test facility demonstrate sub-mmag photometric precision of one of our radial velocity survey targets, and we present new transit observations and fits of WASP-52b—a known hot-Jupiter with an inflated radius and misaligned orbit. The process of relocating the MINERVA hardware to its final destination at the Fred Lawrence Whipple Observatory in southern Arizona has begun, and science operations are expected to commence within 2015