Sensation Seeking and Perceived Need for Structure Moderate Soldiers’ Well-Being Before and After Operational Deployment

This study examined associations between sensation seeking and perceived need for structure, and changes in reported well-being among deployed soldiers. Participants (n = 167) were assessed before and after a six-month deployment to south Afghanistan. Results indicated that although well-being declined in the soldier sample as a whole following deployment, the degree of decrease was significantly different among soldiers with different personality profiles. Differences were moderated by soldiers’ level of sensation seeking and perceived need for structure. Results are discussed in terms of a person-environment fit theory in the context of preparation and rehabilitation of deployed military personnel

A deep photometric survey of the eta Chamaeleontis cluster down to the brown dwarf - planet boundary

We report the outcome of the deep optical/infrared photometric survey of the central region (33 X 33 arcmin or 0.9 pc^2) of the eta Chamaeleontis pre-main sequence star cluster. The completeness limits of the photometry are I = 19.1, J = 18.2 and H = 17.6; faint enough to reveal low mass members down to the brown dwarf and planet boundary of ~ 13 M_Jup. We found no such low mass members in this region. Our result combined with a previous shallower (I = 17) but larger area survey indicates that low mass objects (0.013 < M/M(solar mass) < 0.075) either were not created in the eta Cha cluster or were lost due to the early dynamical history of the cluster and ejected to outside the surveyed areas.Comment: 5 pages with 4 figures, accepted by MNRA

Simple estimation of absolute free energies for biomolecules

One reason that free energy difference calculations are notoriously difficult in molecular systems is due to insufficient conformational overlap, or similarity, between the two states or systems of interest. The degree of overlap is irrelevant, however, if the absolute free energy of each state can be computed. We present a method for calculating the absolute free energy that employs a simple construction of an exactly computable reference system which possesses high overlap with the state of interest. The approach requires only a physical ensemble of conformations generated via simulation, and an auxiliary calculation of approximately equal central-processing-unit (CPU) cost. Moreover, the calculations can converge to the correct free energy value even when the physical ensemble is incomplete or improperly distributed. As a "proof of principle," we use the approach to correctly predict free energies for test systems where the absolute values can be calculated exactly, and also to predict the conformational equilibrium for leucine dipeptide in implicit solvent.Comment: To appear in J. Chem. Phys., 10 pages, 6 figure

Astrometric Monitoring of the HR 8799 Planets: Orbit Constraints from Self-Consistent Measurements

We present new astrometric measurements from our ongoing monitoring campaign of the HR 8799 directly imaged planetary system. These new data points were obtained with NIRC2 on the W.M. Keck II 10 meter telescope between 2009 and 2014. In addition, we present updated astrometry from previously published observations in 2007 and 2008. All data were reduced using the SOSIE algorithm, which accounts for systematic biases present in previously published observations. This allows us to construct a self-consistent data set derived entirely from NIRC2 data alone. From this dataset, we detect acceleration for two of the planets (HR 8799b and e) at $>$3$\sigma$. We also assess possible orbital parameters for each of the four planets independently. We find no statistically significant difference in the allowed inclinations of the planets. Fitting the astrometry while forcing coplanarity also returns $\chi^2$ consistent to within 1$\sigma$ of the best fit values, suggesting that if inclination offsets of $\lesssim$20$^{o}$ are present, they are not detectable with current data. Our orbital fits also favor low eccentricities, consistent with predictions from dynamical modeling. We also find period distributions consistent to within 1$\sigma$ with a 1:2:4:8 resonance between all planets. This analysis demonstrates the importance of minimizing astrometric systematics when fitting for solutions to highly undersampled orbits.Comment: 18 pages, 11 figures. Accepted for publication in A

Lithium Depletion Boundary in a Pre-Main Sequence Binary System

A lithium depletion boundary is detected in HIP 112312 (GJ 871.1 A and B), a \~12 Myr old pre-main sequence binary system. A strong (EW 300 mA) Li 6708 A absorption feature is seen at the secondary (~M4.5) while no Li 6708 A feature is detected from the primary (~M4). The physical companionship of the two stars is confirmed from common proper motions. Current theoretical pre-main sequence evolutionary models cannot simultaneously match the observed colors, brightnesses, and Li depletion patterns of this binary system. At the age upper limit of 20 Myr, contemporary theoretical evolutionary models predict too slow Li depletion. If true Li depletion is a faster process than predicted by theoretical models, ages of open clusters (Pleiades, alpha Persei, and IC 2391) estimated from the Li depletion boundary method are all overestimated. Because of the importance of the open cluster age scale, development of self-consistent theoretical models to match the HIP 112312 data is desirable.Comment: Accepted in ApJL. 5 pages total (3 tables, 3 figures

VLT/X-shooter observations and the chemical composition of cool white dwarfs

We present a model atmosphere analysis of cool hydrogen-rich white dwarfs observed at the Very Large Telescope (VLT) with the X-shooter spectrograph. The intermediate-dispersion and high signal-to-noise ratio of the spectra allowed us to conduct a detailed analysis of hydrogen and heavy element line profiles. In particular, we tested various prescriptions for hydrogen Balmer line broadening parameters and determined the effective temperature and surface gravity of each star. Three objects (NLTT 1675, 6390 and 11393) show the presence of heavy elements (Mg, Al, Ca, or Fe). Our abundance analysis revealed a relatively high iron to calcium ratio in NLTT 1675 and NLTT 6390. We also present an analysis of spectropolarimetric data obtained at the VLT using the focal reducer and low dispersion spectrograph (FORS) and we established strict upper limits on the magnetic field strengths in three of the DAZ white dwarfs and determined the longitudinal magnetic field strength in the DAZ NLTT 10480. The class of DAZ white dwarfs comprises objects that are possibly accreting material from their immediate circumstellar environment and the present study contributes in establishing class properties.Comment: Accepted for publication in Astronomy and Astrophysic

The heavily polluted atmosphere of the DAZ white dwarf GALEX J193156.8+011745

We report on the discovery of a new heavily polluted white dwarf. The DAZ white dwarf GALEX J193156.8+011745 was identified in a joint GALEX/GSC survey of ultraviolet-excess objects. Optical spectra obtained at ESO NTT show strong absorption lines of magnesium and silicon and a detailed abundance analysis based on VLT-Kueyen UVES spectra reveal super-solar abundances of silicon and magnesium, and near-solar abundances of oxygen, calcium, and iron. The overall abundance pattern bears the signature of ongoing accretion onto the white dwarf atmosphere. The infrared spectral energy distribution shows an excess in the H and K bands likely associated with the accretion source.Comment: Accepted for publication in MNRAS Letter

Presymplectic current and the inverse problem of the calculus of variations

The inverse problem of the calculus of variations asks whether a given system of partial differential equations (PDEs) admits a variational formulation. We show that the existence of a presymplectic form in the variational bicomplex, when horizontally closed on solutions, allows us to construct a variational formulation for a subsystem of the given PDE. No constraints on the differential order or number of dependent or independent variables are assumed. The proof follows a recent observation of Bridges, Hydon and Lawson and generalizes an older result of Henneaux from ordinary differential equations (ODEs) to PDEs. Uniqueness of the variational formulation is also discussed.Comment: v2: 17 pages, no figures, BibTeX; minor corrections, close to published versio