The Luminosity Function of Omega Centauri

Deep HST-WFPC2 observations of the stellar population in the globular cluster Omega Cen (NGC 5139) have been used to measure the luminosity function of main sequence stars at the low-mass end. Two fields have been investigated, located respectively ~4.6' and ~7' away from the cluster center, or near the half-light radius of this cluster (~4.8'). The color-magnitude diagrams derived from these data show the cluster main sequence extending to the detection limit at I ~ 24. Information on both color and magnitude is used to build the luminosity functions of main sequence stars in these fields and the two independent determinations are found to agree very well with each other within the observational uncertainty. Both functions show a peak in the stellar distribution around M_I ~ 9 followed by a drop at fainter magnitudes well before photometric incompleteness becomes significant, as is typical of other globular clusters observed with the HST. This result is at variance with previous claims that the luminosity function of Omega Cen stays flat at low masses, but is in excellent agreement with recent near-IR NICMOS observations of the same cluster.Comment: To appear in The Astronomical Journal. Contains 7 pages, 4 figures, prepared with the AAS LaTeX macr

Ethics of modifying the mitochondrial genome

Recent preclinical studies have shown the feasibility of specific variants of nuclear transfer to prevent mitochondrial DNA disorders. Nuclear transfer could be a valuable reproductive option for carriers of mitochondrial mutations. A clinical application of nuclear transfer, however, would entail germ-line modification, more specifically a germ-line modification of the mitochondrial genome. One of the most prominent objections against germ-line modification is the fear that it would become possible to alter 'essential characteristics' of a future person, thereby possibly violating the child's right to an open future. As only the nuclear DNA would contain the ingredients for individual characteristics, modification of the mtDNA is often considered less controversial than modification of the nuclear DNA. This paper discusses the tenability of this dichotomy. After having clarified the concept of germ-line modification, it argues that modification of the mtDNA is not substantively different from modification of the nuclear DNA in terms of its effects on the identity of the future person. Subsequently the paper assesses how this conclusion affects the moral evaluation of nuclear transfer to prevent mtDNA disorders. It concludes that the moral acceptability of germ-line modification does not depend on whether it alters the identity of the future child-all germ-line modifications do-but on whether it safeguards the child's right to an open future. If nuclear transfer to prevent mtDNA disorders becomes safe and effective, then dismissing it because it involves germ-line modification is unjustified

Smale flows on S2×S1\mathbb{S}^2\times\mathbb{S}^1

In this paper, we use abstract Lyapunov graphs as a combinatorial tool to obtain a complete classification of Smale flows on $\mathbb{S}^2\times\mathbb{S}^1$. This classification gives necessary and sufficient conditions that must be satisfied by an abstract Lyapunov graph in order for it to be associated to a Smale flow on $\mathbb{S}^2\times\mathbb{S}^1$

ESHRE task force on ethics and law 15: Cross-border reproductive care

This paper analyses the ethical aspects of cross-border reproductive care. Ethical questions are raised by some of the main reasons of cross-border travelling, i.e. law evasion and unequal access to treatment. The phenomenon also generates possible conflicts linked to the responsibility of the professionals. Three points are discussed: the moral obligation of the physician to refer the patient, his/her duty to provide information and counselling and the acceptability of fee-splitting. The recommendations focus on measures to reduce or limit the number of patients that have to travel abroad and on steps to guarantee the safety and quality of the treatment wherever it is provided

The Mass Function of Main Sequence Stars in NGC6397 from Near IR and Optical High Resolution HST Observations

We have investigated the properties of the stellar mass function in the globular cluster NGC6397 using a large set of HST observations that include WFPC2 images in V and I, obtained at ~4' and 10' radial distances, and a series of deep images in the J and H bands obtained with the NIC2 and NIC3 cameras of NICMOS pointed to regions located ~4.5' and ~3.2' from the center. These observations span the region from ~1 to ~3 times the cluster's half-light radius. All luminosity functions, derived from color magniutde diagrams, increase with decreasing luminosity up to a peak at M_I~8.5 or M_H~7 and then precipitously drop well before photometric incompleteness becomes significant. Within the observational uncertainties, at M_I~12 or M_H~10.5 (~0.09 Msun) the luminosity functions are compatible with zero. By applying the best available mass- luminosity relation appropriate to the metallicity of NGC6397 to both the optical and IR data, we obtain a mass function that shows a break in slope at \~0.3 Msun. No single exponent power-law distribution is compatible with these data, regardless of the value of the exponent. We find that a dynamical model of the cluster can simultaneously reproduce all the luminosity functions observed throughout the cluster only if the IMF rises as m**-1.6 in the range 0.8-0.3 Msun and then drops as m**0.2 below ~0.3 Msun. Adopting a more physical log-normal distribution for the IMF, all these data taken together imply a best fit distribution with characteristic mass m_c~0.3 and sigma~1.8.Comment: 18 pages, 6 figures (ps). Accepted for publication in Ap

Acid gas removal from natural gas by water washing

Projections in the future energy scenario outline an important role played by fossil fuels to meet the increasing global energy demand. A “golden age” has been recently outlined for natural gas, in particular, as the fastest growing and the cleanest of all fossil fuels. Although natural gas is mostly considered to be a “clean” fuel with respect to the emission of pollutants from its combustion, the raw natural gas found in reservoir deposits is not free of contaminants. Among the others, hydrogen sulphide and carbon dioxide are two undesired compounds, which are responsible for the sour or acidic nature of natural gas and must be removed for operational and safety reasons. Acid gas treating is typically performed in facilities built at surface locations, mainly by means of chemical absorption into aqueous amine solutions. However, subsurface technologies may allow to possibly separate the gas undesired compounds directly downhole. The high pressure encountered in this environment makes the use of water as liquid absorbent worth considering. This work investigates the possibility of acid gas removal from natural gas by downhole water washing and presents a preliminary evaluation of the performances of the process, which is assumed to be carried out in the gas production casing that can be represented as a bubble column. A previously proposed correlation for the gas holdup in this type of contacting device operated counter-currently has been used to determine the volumetric mass transfer coefficient for design purposes, considering different raw gas flow rates and inlet acid gas concentrations. By solving a simplified model of a bubble column and by using water flow rates compatible with reinjection into the reservoir, it has been found that it is possible to reduce the H2S content from the inlet concentration to the commonly accepted value to meet pipeline specifications and, depending on the inlet CO2 concentration, to perform a bulk removal of it

Why haven't loose globular clusters collapsed yet?

We report on the discovery of a surprising observed correlation between the slope of the low-mass stellar global mass function (GMF) of globular clusters (GCs) and their central concentration parameter c=log(r_t/r_c), i.e. the logarithmic ratio of tidal and core radii. This result is based on the analysis of a sample of twenty Galactic GCs with solid GMF measurements from deep HST or VLT data. All the high-concentration clusters in the sample have a steep GMF, most likely reflecting their initial mass function. Conversely, low-concentration clusters tend to have a flatter GMF implying that they have lost many stars via evaporation or tidal stripping. No GCs are found with a flat GMF and high central concentration. This finding appears counter-intuitive, since the same two-body relaxation mechanism that causes stars to evaporate and the cluster to eventually dissolve should also lead to higher central density and possibly core-collapse. Therefore, more concentrated clusters should have lost proportionately more stars and have a shallower GMF than low concentration clusters, contrary to what is observed. It is possible that severely depleted GCs have also undergone core collapse and have already recovered a normal radial density profile. It is, however, more likely that GCs with a flat GMF have a much denser and smaller core than suggested by their surface brightness profile and may well be undergoing collapse at present. In either case, we may have so far seriously underestimated the number of post core-collapse clusters and many may be lurking in the Milky Way.Comment: Four pages, one figure, accepted for publication in ApJ Letter

Uncovering the topology of configuration space networks

The configuration space network (CSN) of a dynamical system is an effective approach to represent the ensemble of configurations sampled during a simulation and their dynamic connectivity. To elucidate the connection between the CSN topology and the underlying free-energy landscape governing the system dynamics and thermodynamics, an analytical soluti on is provided to explain the heavy tail of the degree distribution, neighbor co nnectivity and clustering coefficient. This derivation allows to understand the universal CSN network topology observed in systems ranging from a simple quadratic well to the native state of the beta3s peptide and a 2D lattice heteropolymer. Moreover CSN are shown to fall in the general class of complex networks describe d by the fitness model.Comment: 6 figure

Food Restriction and Atherosclerotic Plaque Stabilization

Food restriction is a promising therapy for many age-associated pathologies as it stimulates the health-supportive mechanism autophagy. Because atherosclerosis is an inflammatory, age-related disease, dietary modification can be an important strategy in preventing atherosclerotic plaque development. A cholesterol-supplemented diet, used to induce plaque formation in rabbits, induces a pronounced hypercholesterolemia, which can be reversed after 4 weeks of normal diet. However, food restriction induces a further increase in circulating LDL cholesterol. These elevated cholesterol levels are associated with the induction of autophagy. Although neither a short-term normal diet nor food restriction alters plaque size, rabbits fed a normal diet show signs of increased plaque stability such as elevated collagen content and decreased expression of vascular cell adhesion molecule (VCAM)-1. Surprisingly, these favorable effects are not present after 4 weeks of food restriction. On the contrary, atherosclerotic plaques of food-restricted rabbits displayed enhanced apoptosis, a process known to further undermine plaque stability. In conclusion, severe short-term food restriction in rabbits prevents stabilization of atherosclerotic plaques as observed after regular cholesterol withdrawal via a normal diet

VLA observations of candidate high-mass protostellar objects at 7 mm

We present radio continuum observations at 7 mm made using the Very Large Array towards three massive star forming regions thought to be in very early stages of evolution selected from the sample of Sridharan et al. (2002). Emission was detected towards all three sources (IRAS 18470-0044, IRAS 19217+1651 and IRAS 23151+5912). We find that in all cases the 7 mm emission corresponds to thermal emission from ionized gas. The regions of ionized gas associated with IRAS 19217+1651 and IRAS 23151+5912 are hypercompact with diameters of 0.009 and 0.0006 pc, and emission measures of 7.0 x 10^8 and 2.3 x 10^9 pc cm^(-6), respectively.Comment: 17 pages, 5 figures, accepted by The Astronomical Journa