The Fractal Dimension of Projected Clouds

The interstellar medium seems to have an underlying fractal structure which can be characterized through its fractal dimension. However, interstellar clouds are observed as projected two-dimensional images, and the projection of a tri-dimensional fractal distorts its measured properties. Here we use simulated fractal clouds to study the relationship between the tri-dimensional fractal dimension (D_f) of modeled clouds and the dimension resulting from their projected images. We analyze different fractal dimension estimators: the correlation and mass dimensions of the clouds, and the perimeter-based dimension of their boundaries (D_per). We find the functional forms relating D_f with the projected fractal dimensions, as well as the dependence on the image resolution, which allow to estimatethe "real" D_f value of a cloud from its projection. The application of these results to Orion A indicates in a self-consistent way that 2.5 < D_f < 2.7 for this molecular cloud, a value higher than the result D_per+1 = 2.3 some times assumed in literature for interstellar clouds.Comment: 27 pages, 13 figures, 1 table. Accepted for publication in ApJ. Minor change

Promoting best practice in COPD management

In primary care, a gap between current and evidence based care for COPD exists. This paper describes an educational intervention that helped to close this gap. Involving clinical teams, local speakers and patients and project work was crucial. Positive changes occurred at clinician and organisation level

Assessment and treatment of distorted schemas in sexual offenders

The aim of this review is to examine the literature related to the assessment and treatment of sex offenders’ distorted schemas. Where appropriate, the review draws upon current insights from the field of social cognition to aid in the critical evaluation of the findings. First, the review considers the various different methodologies for assessing distorted schemas, discussing their strengths and limitations. Second, the review examines the work related to the treatment of sex offenders’ schemas. Suggestions for future research, and the implications for clinical practice, are highlighted in the article

On the properties of fractal cloud complexes

We study the physical properties derived from interstellar cloud complexes having a fractal structure. We first generate fractal clouds with a given fractal dimension and associate each clump with a maximum in the resulting density field. Then, we discuss the effect that different criteria for clump selection has on the derived global properties. We calculate the masses, sizes and average densities of the clumps as a function of the fractal dimension (D_f) and the fraction of the total mass in the form of clumps (epsilon). In general, clump mass does not fulfill a simple power law with size of the type M_cl ~ (R_cl)**(gamma), instead the power changes, from gamma ~ 3 at small sizes to gamma<3 at larger sizes. The number of clumps per logarithmic mass interval can be fitted to a power law N_cl ~ (M_cl)**(-alpha_M) in the range of relatively large masses, and the corresponding size distribution is N_cl ~ (R_cl)**(-alpha_R) at large sizes. When all the mass is forming clumps (epsilon=1) we obtain that as D_f increases from 2 to 3 alpha_M increases from ~0.3 to ~0.6 and alpha_R increases from ~1.0 to ~2.1. Comparison with observations suggests that D_f ~ 2.6 is roughly consistent with the average properties of the ISM. On the other hand, as the fraction of mass in clumps decreases (epsilon<1) alpha_M increases and alpha_R decreases. When only ~10% of the complex mass is in the form of dense clumps we obtain alpha_M ~ 1.2 for D_f=2.6 (not very different from the Salpeter value 1.35), suggesting this a likely link between the stellar initial mass function and the internal structure of molecular cloud complexes.Comment: 32 pages, 13 figures, 1 table. Accepted for publication in Ap

A systematic review of the literature comparing male non-serial sexual killers and sexual aggressors: examining homogeneous and heterogeneous characteristics of these groups

This systematic review considers what is known about the characteristics of sexual killers and sexual aggressors. The aim was to identify which characteristics have consistently been shown to be similar (homogeneous) and which are different (heterogeneous) across these two groups. Ten studies, including approximately 300 sexual killers, were analysed. Only studies where the samples were directly compared and where sexual killers were male, predominantly non-serial and perpetrated against adult female victims were included. Results indicate that levels of loneliness and anger appear to be more prevalent in the sexual killer sample while mental health disorders, criminal history, family structure and history of sexual abuse as well as some crime scene behaviours seem to be similar across the two groups. The results of this review have also highlighted some methodological problems inherent to these types of studies and these issues are discussed from the perspective of improving research on these crimes

Modeling a high mass turn down in the stellar initial mass function

Statistical sampling from the stellar initial mass function (IMF) for all star-forming regions in the Galaxy would lead to the prediction of ~1000 Msun stars unless there is a rapid turn-down in the IMF beyond several hundred solar masses. Such a turndown is not necessary for dense clusters because the number of stars sampled is always too small. Here we explore several mechanisms for an upper mass cutoff, including an exponential decline of the star formation probability after a turbulent crossing time. The results are in good agreement with the observed IMF over the entire stellar mass range, and they give a gradual turn down compared to the Salpeter function above ~100 Msun for normal thermal Jeans mass, M_J. The upper mass turn down should scale with M_J in different environments. A problem with the models is that they cannot give both the observed power-law IMF out to the high-mass sampling limit in dense clusters, as well as the observed lack of supermassive stars in whole galaxy disks. Either there is a sharper upper-mass cutoff in the IMF, perhaps from self-limitation, or the IMF is different for dense clusters than for the majority of star formation that occurs at lower density. Dense clusters seem to have an overabundance of massive stars relative to the average IMF in a galaxy.Comment: 19 pages, 2 figures, Astrophysical Journal, Vol 539, August 10, 200

The initial stellar mass function from random sampling in hierarchical clouds II: statistical fluctuations and a mass dependence for starbirth positions and times

Observed variations in the slope of the initial stellar mass function are shown to be consistent with a model in which the protostellar gas is randomly sampled from hierarchical clouds at a rate proportional to the square root of the local density. RMS variations in the IMF slope around the Salpeter value are +/- 0.4 when only 100 stars are observed, and +/- 0.1 when 1000 stars are observed. The hierarchical-sampling model also reproduces the tendency for massive stars to form closer to the center of a cloud, at a time somewhat later than the formation time of the lower mass stars. The assumed density dependence for the star formation rate is shown to be appropriate for turbulence compression, magnetic diffusion, gravitational collapse, and clump or wavepacket coalescence. The low mass flattening in the IMF comes from the inability of gas to form stars below the thermal Jeans mass at typical temperatures and pressures. Consideration of heating and cooling processes indicate why the thermal Jeans mass should be nearly constant in normal environments, and why it might increase in some starburst regions. The steep IMF in the extreme field is not explained by the model, but other origins are suggested.Comment: 21 pages, 8 figures, scheduled for ApJ vol. 515, April 10, 199

Online child sexual exploitation:prevalence, process, and offender characteristics

This review provides an overview of current knowledge and understanding of the process of sexual grooming and exploitation of children via the Internet. Specifically, the prevalence of online sexual grooming and exploitation is explored as well as associated challenges relating to the identification of its occurrence. This is complemented by a detailed outline and discussion of the process, both online and in the physical world, and legal responses to this phenomenon. A number of factors are examined to provide an explanation of the facilitating and contributing role they may play in offense processes online. Finally, current typologies are discussed in relation to characteristics of Internet offenders in general and “groomers”/chat room offenders specifically. This review concludes by offering suggestions for future research. </jats:p