Parenting Influences on Depression: A Moderated Mediated Model

Little is known about the developmental processes through which parenting factors may influence clinical depression among youth. This study investigated whether parenting influences the onset of clinical depression through the mediating mechanism of negative attributional style, particularly under conditions of high stress, in a community sample of children and adolescents (N = 289). Results supported a moderated mediation model in which low levels of observed parent positive regard and sensitivity to distress during a youth stressor task were indirectly associated with an increased likelihood of experiencing an episode of depression over an 18 month period, through the mediating influence of youth negative attributional style, but only for youth who also experienced a high number of peer stressors. These findings elucidate mechanisms through which parenting may contribute to risk for depression during the transition into and across adolescence

On the Limitations of the Theory of the Positron

In a recent paper Dirac has suggested a further development of his theory of the positron. Dirac here considers the operators corresponding to charge and current density for a system of electrons in which nearly all the negative energy states are full, and shows that in the presence of an arbitrary external electromagnetic field these operators may be divided into two terms: one of these is infinite, and depends on the field but not on the state of the electrons; the other is finite and determinate, and depends on the field and on the electron state. Dirac makes the suggestion that these second terms be regarded as giving the charge and current density of the electron-positron distribution (epd): i.e., that the formalism of his theory of the electron be modified by the subtraction from the operators for charge and current density of the infinite and field-dependent terms. This modification leaves unaltered the Lorentz and gauge invariance of the theory and the validity of the conservation law for charge and current. Because, however, the way in which the operators are to be modified depends upon the value of the electromagnetic field, the method is not readily extended to take account of the field produced by the epd; on the other hand, it gives for the charge and current induced in the epd by an external field finite and definite results, and thus constitutes in this respect a true theoretical advance

Quasireversibility Methods for Non-Well-Posed Problems

The nal value problem, ae u t + Au = 0 ; 0 ! t ! T u(T ) = f with positive self-adjoint unbounded A is known to be ill-posed. One approach to dealing with this has been the method of quasireversibility, where the operator is perturbed to obtain a well-posed problem which approximates the original problem. In this work, we will use a quasi-boundary-value method, where we perturb the nal condition to form an approximate non-local problem depending on a small parameter. We show that the approximate problems are well posed and that their solutions u converge on 0; T] if and only if the original problem has a classical solution. We obtain several other results, including some explicit convergence rates

Correlated dynamics of inclusions in a supported membrane

The hydrodynamic theory of heterogeneous fluid membranes is extended to the case of a membrane adjacent to a solid substrate. We derive the coupling diffusion coefficients of pairs of membrane inclusions in the limit of large separation compared to the inclusion size. Two-dimensional compressive stresses in the membrane make the coupling coefficients decay asymptotically as $1/r^2$ with interparticle distance $r$. For the common case, where the distance to the substrate is of sub-micron scale, we present expressions for the coupling between distant disklike inclusions, which are valid for arbitrary inclusion size. We calculate the effect of inclusions on the response of the membrane and the associated corrections to the coupling diffusion coefficients to leading order in the concentration of inclusions. While at short distances the response is modified as if the membrane were a two-dimensional suspension, the large-distance response is not renormalized by the inclusions.Comment: 15 page

Eigenvalues of the 2p3pP3 and 2p3dD1,3 bound states of the helium isoelectronic sequence

The 1Z expansion method is used to calculate the eigenvalues of the 2p3pP3 and 2p3dD1,3 states of the helium isoelectronic sequence. The results are compared to variational calculations for neutral helium. Wavelengths are predicted for a number of transitions originating in doubly excited states of the heliumlike ions up to Fe xxv. The results for neutral helium are compared to recent beam-foil experiments and alternative line identifications are made. The predicted wavelength for the 2p3dD3-2p2P3 transition is 3014, in close agreement with the line observed by Berry et al. at 3012 ± 2. © 1972 The American Physical Society

Atmospheric, Evolutionary, and Spectral Models of the Brown Dwarf Gliese 229 B

Theoretical spectra and evolutionary models that span the giant planet--brown dwarf continuum have been computed based on the recent discovery of the brown dwarf, Gliese 229 B. A flux enhancement in the 4--5 micron window is a universal feature from Jovian planets to brown dwarfs. We confirm the existence of methane and water in Gl 229 B's spectrum and find its mass to be 30 to 55 Jovian masses. Although these calculations focus on Gliese 229 B, they are also meant to guide future searches for extra-solar giant planets and brown dwarfs.Comment: 8 pages, plain TeX, plus four postscript figures, gzipped and uuencoded, accepted for Scienc

Gravitational Collapse with a Cosmological Constant

We consider the effect of a positive cosmological constant on spherical gravitational collapse to a black hole for a few simple, analytic cases. We construct the complete Oppenheimer-Snyder-deSitter (OSdS) spacetime, the generalization of the Oppenheimer-Snyder solution for collapse from rest of a homogeneous dust ball in an exterior vacuum. In OSdS collapse, the cosmological constant may affect the onset of collapse and decelerate the implosion initially, but it plays a diminishing role as the collapse proceeds. We also construct spacetimes in which a collapsing dust ball can bounce, or hover in unstable equilibrium, due to the repulsive force of the cosmological constant. We explore the causal structure of the different spacetimes and identify any cosmological and black hole event horizons which may be present.Comment: 7 pages, 10 figures; To appear in Phys. Rev.

The Ultraviolet Detection of Diffuse Gas in Galaxy Groups

A small survey of the UV-absorbing gas in 12 low-$z$ galaxy groups has been conducted using the Cosmic Origins Spectrograph (COS) on-board the Hubble Space Telescope (HST). Targets were selected from a large, homogeneously-selected sample of groups found in the Sloan Digital Sky Survey (SDSS). A critical selection criterion excluded sight lines that pass close ($<1.5$ virial radii) to a group galaxy, to ensure absorber association with the group as a whole. Deeper galaxy redshift observations are used both to search for closer galaxies and also to characterize these $10^{13.5}$ to $10^{14.5} M_{\odot}$ groups, the most massive of which are highly-virialized with numerous early-type galaxies (ETGs). This sample also includes two spiral-rich groups, not yet fully-virialized. At group-centric impact parameters of 0.3-2 Mpc, these $\mathrm{S/N}=15$-30 spectra detected HI absorption in 7 of 12 groups; high (OVI) and low (SiIII) ion metal lines are present in 2/3 of the absorption components. None of the three most highly-virialized, ETG-dominated groups are detected in absorption. Covering fractions $\gtrsim50$% are seen at all impact parameters probed, but do not require large filling factors despite an enormous extent. Unlike halo clouds in individual galaxies, group absorbers have radial velocities which are too low to escape the group potential well without doubt. This suggests that these groups are "closed boxes" for galactic evolution in the current epoch. Evidence is presented that the cool and warm group absorbers are not a pervasive intra-group medium (IGrM), requiring a hotter ($T\sim10^6$ to $10^7$ K) IGrM to be present to close the baryon accounting.Comment: Resubmitted to ApJS after first review; 82 pages (27 for main text, rest are Appendices and supplemental figures and tables), 47 figures, 21 table

Black hole formation in perfect fluid collapse

We construct here a special class of perfect fluid collapse models which generalizes the homogeneous dust collapse solution in order to include non-zero pressures and inhomogeneities into evolution. It is shown that a black hole is necessarily generated as end product of continued gravitational collapse, rather than a naked singularity. We examine the nature of the central singularity forming as a result of endless collapse and it is shown that no non-spacelike trajectories can escape from the central singularity. Our results provide some insights into how the dynamical collapse works, and into the possible formulations of the cosmic censorship hypothesis, which is as yet a major unsolved problem in black hole physics.Comment: Revtex4, To appear in Physical Review