Viscous growth and rebound of a bubble near a rigid surface

Motivated by the dynamics of microbubbles near catalytic surfaces in bubble-powered microrockets, we consider theoretically the growth of a free spherical bubble near a flat no-slip surface in a Stokes flow. The flow at the bubble surface is characterised by a constant slip length allowing us to tune the hydrodynamic mobility of its surface and tackle in one formulation both clean and contaminated bubbles as well as rigid shells. Starting with a bubble of infinitesimal size, the fluid flow and hydrodynamic forces on the growing bubble are obtained analytically. We demonstrate that, depending on the value of the bubble slip length relative to the initial distance to the wall, the bubble will either monotonically drain the fluid separating it from the wall, which will exponentially thin, or it will bounce off the surface once before eventually draining the thin film. Clean bubbles are shown to be a singular limit which always monotonically get repelled from the surface. The bouncing events for bubbles with finite slip lengths are further analysed in detail in the lubrication limit. In particular, we identify the origin of the reversal of the hydrodynamic force direction as due to the change in the flow pattern in the film between the bubble and the surface and to the associated lubrication pressure. Last, the final drainage dynamics of the film is observed to follow a universal algebraic scaling for all finite slip lengths.ER

Stellar neutron capture cross sections of ²⁰ ²¹ ²²Ne

The stellar (n,γ) cross sections of the Ne isotopes are important for a number of astrophysical quests, i.e., for the interpretation of abundance patterns in presolar material or with respect to the s-process neutron balance in red giant stars. This paper presents resonance studies of experimental data in the keV range, which had not been fully analyzed before. The analyses were carried out with the R-matrix code sammy. With these results for the resonant part and by adding the components due to direct radiative capture, improved Maxwellian-averaged cross sections (MACS) could be determined. At kT=30keV thermal energy we obtain MACS values of 240±29,1263±160, and 53.2±2.7 μbarn for ²⁰Ne,²¹Ne, and ²²Ne, respectively. In earlier work the stellar rates of ²⁰Ne and ²¹Ne had been grossly overestimated. ²²Ne and ²⁰Ne are significant neutron poisons for the s process in stars because their very small MACS values are compensated by their large abundances

Pretransplant malignancy in candidates and posttransplant malignancy in recipients of cardiac transplantation

Background: Malignancy is generally considered a contraindication for cardiac transplantation, whereas secondary malignancy has been described under chronic immunosuppression. Patients and methods: We report here the frequency of malignancy encountered among the 495 patients evaluated at our cardiac transplant centre as well as the incidence and the course of post-transplant malignancy among 129 consecutive patients who underwent cardiac transplantation, with a subsequent minimum follow-up of 6 months. Results: A total of 10 out of 495 patients (2%) evaluated for heart transplantation presented with a history of previous malignancy: 3 of them underwent transplantation (2 survive, 1 died) whereas in the remaining 7 patients neoplasia was considered a contraindication for cardiac transplantation, and all 7 died (4 cardiac, 3 tumor-related deaths). Post-transplant malignancy was diagnosed in 10 of 129 patients (9%) 35 ± 15 months after transplantation (6 skin cancers, 1 lymphoproliferative disease, 3 solid tumors). No significant association was found between post-transplant malignancy and primary prophylaxis with antithymocyte globulin (ATG) or murine antihuman T-cell monoclonal antibodies (OKT3). Conclusions: These results confirm that pre-transplant malignancy is not an absolute contraindication for cardiac transplantation and that post-transplant follow-up must include careful monitoring of post-transplant malignanc

Does exercise-induced myocardial ischaemia cause enhanced platelet activation and fibrin formation in patients with stable angina and severe coronary artery disease?

In this study, betathromboglobulin (BTG) and fibrinopeptide A (FPA) in peripheral venous blood were measured in 20 patients with stable angina pectoris before and immediately after exercise-induced myocardial ischaemia; in 5 of the 20 patients stable angina was associated with typical peripheral artery disease. A total of 10 patients with angiographically documented peripheral artery disease without angina and 10 normal volunteers were taken as control groups. BTG and FPA in the 15 patients with stable angina before exercise were 41±14 ng ml-1 and 2.3±09 ng ml-1 and were not statistically different from the values in normal controls; after exercise-induced myocardial ischaemia no significant increase occurred in these patients. Conversely, in the 5 patients with stable angina associated with peripheral artery disease BTG and FPA before exercise were 6l±10 ng ml-1 and 3.5±0.8 ng ml-1 and increased to 114±14 ng ml-1 (P<0.001) and 4.l±0.5 ng ml-1 (P<0.01): These results were similar to those found in the 10 patients with isolated peripheral artery disease. We conclude that BTG and FPA in peripheral venous blood in patients with stable angina are not elevated either at rest or after exercise-induced myocardial ischaemia. Elevated values of BTG and FPA in patients with stable angina may reflect a major interaction between blood and atherosclerotic vessel wall, suggesting the presence of associated atherosclerotic lesions in peripheral artery diseas

The s-process branching at 185W

The neutron capture cross section of the unstable nucleus 185W has been derived from experimental photoactivation data of the inverse reaction 186W(gamma,n)185W. The new result of sigma = (687 +- 110) mbarn confirms the theoretically predicted neutron capture cross section of 185W of sigma = 700 mbarn at kT = 30 keV. A neutron density in the classical s-process of n_n = (3.8 +0.9 -0.8} * 1e8 cm-3 is derived from the new data for the 185W branching. In a stellar s-process model one finds a significant overproduction of the residual s-only nucleus 186Os.Comment: ApJ, in pres

Neutron Capture Cross Sections for the Weak s Process

In past decades a lot of progress has been made towards understanding the main s-process component that takes place in thermally pulsing Asymptotic Giant Branch (AGB) stars. During this process about half of the heavy elements, mainly between 90<=A<=209 are synthesized. Improvements were made in stellar modeling as well as in measuring relevant nuclear data for a better description of the main s process. The weak s process, which contributes to the production of lighter nuclei in the mass range 56<=A<=90 operates in massive stars (M>=8Msolar) and is much less understood. A better characterization of the weak s component would help disentangle the various contributions to element production in this region. For this purpose, a series of measurements of neutron-capture cross sections have been performed on medium-mass nuclei at the 3.7-MV Van de Graaff accelerator at FZK using the activation method. Also, neutron captures on abundant light elements with A<56 play an important role for s-process nucleosynthesis, since they act as neutron poisons and affect the stellar neutron balance. New results are presented for the (n,g) cross sections of 41K and 45Sc, and revisions are reported for a number of cross sections based on improved spectroscopic information

The barium isotopic mixture for the metal-poor subgiant star HD140283

Current theory regarding heavy element nucleosynthesis in metal-poor environments states that the r-process would be dominant. The star HD140283 has been the subject of debate after it appeared in some studies to be dominated by the s-process. We provide an independent measure of the Ba isotope mixture in HD140283 using an extremely high quality spectrum and an extensive chi^2 analysis. We exploit hyperfine splitting of the BaII 4554 \AA\ and 4934 \AA\ resonance lines in an effort to constrain the isotope ratio in 1D LTE. Using the code ATLAS in conjunction with KURUCZ06 model atmospheres we analyse 93 Fe lines to determine the star's macroturbulence. With this information we construct a grid of Ba synthetic spectra and, using a \chi^2 code, fit these to our observed data to determine the isotopic ratio, fodd, which represents the ratio of odd to even isotopes. We also analyse the Eu lines. We set a new upper limit of the rotation of HD140283 at vsin{i}\leq3.9\kms, a new upper limit on [Eu/H] < -2.80 and abundances [Fe/H] = -2.59\pm0.09, [Ba/H] = -3.46\pm0.11. This leads to a new lower limit on [Ba/Eu] > -0.66. We find that, in the framework of a 1D LTE analysis, the isotopic ratios of Ba in HD140283 indicate fodd=0.02\pm0.06, a purely s-process signature. This implies that observations and analysis do not validate currently accepted theory. We speculate that a 1D code, due to simplifying assumptions, is not adequate when dealing with observations with high levels of resolution and S/N because of the turbulent motions associated with a 3D stellar atmosphere. New approaches to analysing isotopic ratios, in particular 3D hydrodynamics, need to be considered when dealing with the levels of detail required to properly determine them. However published 3D results exacerbate the disagreement between theory and observation.Comment: 16 pages, 10 figures, 7 tables, 1 online appendix Accepted by A&

TUNGSTEN NUCLEAR ANOMALIES IN PLANETESIMAL CORES

Use of the extinct 182 Hf- 182 W chronometer to constrain the timing of planetary accretion and differentiation rests ontheassumptionthatthesolarnebulahadhomogeneoustungstenisotopiccomposition.Here,wereportdeficiencies of � 0.1 part in 10,000 in the abundance of 184 Win group IVB iron meteorites relative to the silicate Earth. These are mostlikelyduetoincompletemixingattheplanetesimalscale(2Y4kmradiusbodies)oftheproductsof slow(s-)and rapid (r-) neutron-capture nucleosynthesis in the solar nebula. The correction that must be applied to the 182 Hf- 182 W model age of core formation in IVB irons due to the presence of these nuclear anomalies is � 0.5 Myr. Subject headingg minor planets, asteroids — nuclear reactions, nucleosynthesis, abundances — solar system: formation — stars: abundance

s-Processing in the Galactic Disk. I. Super-Solar Abundances of Y, Zr, La, Ce in Young Open Clusters

In a recent study, based on homogeneous barium abundance measurements in open clusters, a trend of increasing [Ba/Fe] ratios for decreasing cluster age was reported. We present here further abundance determinations, relative to four other elements hav- ing important s-process contributions, with the aim of investigating whether the growth found for [Ba/Fe] is or not indicative of a general property, shared also by the other heavy elements formed by slow neutron captures. In particular, we derived abundances for yttrium, zirconium, lanthanum and cerium, using equivalent widths measurements and the MOOG code. Our sample includes 19 open clusters of different ages, for which the spectra were obtained at the ESO VLT telescope, using the UVES spectrometer. The growth previously suggested for Ba is confirmed for all the elements analyzed in our study. This fact implies significant changes in our views of the Galactic chemical evolution for elements beyond iron. Our results necessarily require that very low-mass AGB stars (M < 1.5M\odot) produce larger amounts of s-process elements (hence acti- vate the 13 C-neutron source more effectively) than previously expected. Their role in producing neutron-rich elements in the Galactic disk has been so far underestimated and their evolution and neutron-capture nucleosynthesis should now be reconsidered.Comment: ApJ accepte