The structure and stability of molecular cloud cores in external radiation fields

We have considered the thermal equilibrium in pre-protostellar cores in the approximation where the dust temperature is independent of interactions with the gas and where the gas is heated both by collisions with dust grains and ionization by cosmic rays. We have then used these results to study the stability of cores in the limit where thermal pressure dominates over magnetic field and turbulence. We find that for cores with characteristics similar to those observed, the gas and dust temperatures are coupled in the core interior. As a consequence, the gas temperature like the dust temperature decreases towards the center of these objects. The density structure computed taking into account such deviations from isothermality are not greatly different from that expected for an isothermal Bonnor-Ebert sphere. It is impossible in the framework of these models to have a stable equilibrium core with mass above about 5 solar masses and column density compatible with observed values. We conclude from this that observed high mass cores are either supported by magnetic field or turbulence or are already in a state of collapse. Lower mass cores on the other hand have stable states and we conclude that the much studied object B68 may be in a state of stable equilibrium if the internal gas temperature is computed in self-consistent fashion. Finally we note that in molecular clouds such as Ophiuchus and Orion with high radiation fields and pressures, gas and dust temperatures are expected to be well coupled and hence one expects temperatures to be relatively high as compared to low pressure clouds like Taurus.Comment: 11 pages, 6 figures. Astronomy & Astrophysics, in pres

Optimal experiment design revisited: fair, precise and minimal tomography

Given an experimental set-up and a fixed number of measurements, how should one take data in order to optimally reconstruct the state of a quantum system? The problem of optimal experiment design (OED) for quantum state tomography was first broached by Kosut et al. [arXiv:quant-ph/0411093v1]. Here we provide efficient numerical algorithms for finding the optimal design, and analytic results for the case of 'minimal tomography'. We also introduce the average OED, which is independent of the state to be reconstructed, and the optimal design for tomography (ODT), which minimizes tomographic bias. We find that these two designs are generally similar. Monte-Carlo simulations confirm the utility of our results for qubits. Finally, we adapt our approach to deal with constrained techniques such as maximum likelihood estimation. We find that these are less amenable to optimization than cruder reconstruction methods, such as linear inversion.Comment: 16 pages, 7 figure

Kinematics of a hot massive accretion disk candidate

Characterizing rotation, infall and accretion disks around high-mass protostars is an important topic in massive star formation research. With the Australia Telescope Compact Array and the Very Large Array we studied a massive disk candidate at high angular resolution in ammonia (NH3(4,4) & (5,5)) tracing the warm disk but not the envelope. The observations resolved at ~0.4'' resolution (corresponding to ~1400AU) a velocity gradient indicative of rotation perpendicular to the molecular outflow. Assuming a Keplerian accretion disk, the estimated protostar-disk mass would be high, similar to the protostellar mass. Furthermore, the position-velocity diagram exhibits additional deviation from a Keplerian rotation profile which may be caused by infalling gas and/or a self-gravitating disk. Moreover, a large fraction of the rotating gas is at temperatures >100K, markedly different to typical low-mass accretion disks. In addition, we resolve a central double-lobe cm continuum structure perpendicular to the rotation. We identify this with an ionized, optically thick jet.Comment: 5 pages, 3 figures, accepted for Astrophysical Journal Letters, a high-resolution version of the draft can be found at http://www.mpia.de/homes/beuther/papers.htm

The ‘2-in-1’ stage : indications, technique & results

Prosthetic joint infections remain an ongoing challenge for orthopaedic surgeons with an interest in knee arthroplasty, which relates to their often difficult diagnoses, need for multiple surgeries, increased technical and financial requirements. Peri-prosthetic joint infection is devastating complication for the patient and with the current literature unable to either demonstrate superiority of one or two stage revision then we should continue to assess on a case by case basis. The use of a ‘2 in 1’ single-stage approach has been recently been promoted as a form of single stage revision for infection on account of the potential for reduction in risks, costs, and complications. Where it is safe to do so, a single stage procedure can avoid several of the drawbacks which may occur with a formal two stage approach. Particularly, it can reduce the risk of post-operative stiffness and arthrofibrosis which can be associated with two stage surgery. Use of a single stage may be more cost effective, by saving the patient having to undergo a second major procedure. This article reviews the indications for its use, technique and results. The use of ‘2-in-1’ single-stage revision can be considered as an effective option for treating infection following TKR and cases with associated bone loss.Publisher PDFPeer reviewe

Proteomic analysis of the effect of metabolic acidosis on the apical membrane of the renal proximal convoluted tubule

2011 Spring.Includes bibliographical references.Metabolic acidosis is a physiological disturbance which results in a decrease in blood and extracellular pH and HCO3-. The renal response to this disturbance is initiated in the proximal convoluted tubule (PCT) of the kidney. At the PCT, the brush border membrane facilitates solute reabsorbtion and excretion of acid during acidosis. However, the extent of the global remodeling of proteins at the brush border remains mostly unknown. Therefore a proteomic investigation of the remodeling of theseproteins during metabolic acidosis at the brush border was completed. First, using LTQ mass spectrometry and spectral counting, an enrichment method was tested that analyzed brush border membrane vesicles (BBMV) from cortex versus those which were derived from purified proximal convoluted tubules. From these results we detected and hypothesized that enzymes of glucose metabolism localized at the brush border would be altered in abundance during acidosis at the PCT brush border. Next, we performed a quantitative analysis of the temporal response to metabolic acidosis during 1-d, 3-d and 7-d acidosis using Q-TOF mass spectrometry and spectral counting. As expected, the results indicated a decrease of enzymes of glucose metabolism including Fructose-1,6-bisphosphatase 1 and Enolase A. Aldolase A was found to be transiently decreased during 1-d and 3-d acidosis. In addition, the Na+-glucose transporter 2 was found to be transiently increased during 1-d and 3-d acidosis. Finally, to confirm these abundance changes detected using spectral counting, an accurate mass and time tag method was developed. Using this method, we successfully developed an AMT database of the previously identified spectra. This database was used to match peptides detected using QTOF-LC-MS to the previously identified peptides. Peptide abundance by spectral counting was validated using the more accurate peak intensities and were generally in concordance with those abundance measurements using spectral counting. The developed model suggested a mechanism for internalization of these enzymes of glucose metabolism in support of glutamine metabolism, which is central to the cellular response to acidosis by the PCT