Optimizing the third-and-a-half post-Newtonian gravitational radiation-reaction force for numerical simulations

The gravitational radiation-reaction force acting on perfect fluids at 3.5 post-Newtonian order is cast into a form which is directly applicable to numerical simulations. Extensive use is made of metric-coefficient changes induced by functional coordinate transformations, of the continuity equation, as well as of the equations of motion. We also present an expression appropriate for numerical simulations of the radiation field causing the worked out reaction force.Comment: 22 pages to appear in Physical Review

The Kohn-Luttinger Effect in Gauge Theories

Kohn and Luttinger showed that a many body system of fermions interacting via short range forces becomes superfluid even if the interaction is repulsive in all partial waves. In gauge theories such as QCD the interaction between fermions is long range and the assumptions of Kohn and Luttinger are not satisfied. We show that in a U(1) gauge theory the Kohn-Luttinger phenomenon does not take place. In QCD attractive channels always exist, but there are cases in which the primary pairing channel leaves some fermions ungapped. As an example we consider the unpaired fermion in the 2SC phase of QCD with two flavors. We show that it acquires a very small gap via a mechanism analogous to the Kohn-Luttinger effect. The gap is too small to be phenomenologically relevant.Comment: 5 pages, 2 figure, minor revisions, to appear in PR

Rheology of human blood plasma: Viscoelastic versus Newtonian behavior

We investigate the rheological characteristics of human blood plasma in shear and elongational flows. While we can confirm a Newtonian behavior in shear flow within experimental resolution, we find a viscoelastic behavior of blood plasma in the pure extensional flow of a capillary break-up rheometer. The influence of the viscoelasticity of blood plasma on capillary blood flow is tested in a microfluidic device with a contraction-expansion geometry. Differential pressure measurements revealed that the plasma has a pronounced flow resistance compared to that of pure water. Supplementary measurements indicate that the viscoelasticity of the plasma might even lead to viscoelastic instabilities under certain conditions. Our findings show that the viscoelastic properties of plasma should not be ignored in future studies on blood flow.Comment: 4 figures, 1 supplementary material Highlighted in http://physics.aps.org/articles/v6/1

Biogas from manure – a new technology to close the nutrient and energy circuit on-farm

The Biodynamic Research Institute in Järna developed a two-phase on-farm biogas plant. The plant digests manure of dairy cattle and organic residues originating from the farm and the surrounding food processing units containing 17.7-19.6 % total solids. A new technology for continuously filling and discharging the hydrolysis reactor was developed and implemented. The output of the hydrolysis reactor is separated into a solid and liquid fraction. The solid fraction is composted. The liquid fraction is further digested in a methane reactor and the effluent used as liquid fertiliser. Initial results show that anaerobic digestion followed by aerobic composting of the solid fraction improves the nutrient balance of the farm compared to mere aerobic composting. Composted solid fraction and effluent together contain about 70.8 % of total input nitrogen and 93.3 % of input NH4. The manure that was merely aerobic digested contained about 51.3 % of total input nitrogen and 3.9 % of input NH4. Additionally anaerobic digestion improves the energy balance of the farm producing up to 269 l biogas kg-1 volatile solids or 1.7 kWh heat kg-1 volatile solids

Trocar and Veress needle injuries during laparoscopy

Background: Inadvertent lesions of the intraabdominal organs and vessels caused by trocars and Veress needles are rare but serious complications of laparoscopic surgery. Establishing the pneumoperitoneum is believed to be the most dangerous step. Methods: The Swiss Association for Laparoscopic and Thoracoscopic Surgery (SALTS) prospectively collected the data on 14,243 patients undergoing various standard laparoscopic procedures between 1995 and 1997. This database was investigated with special regard to intraabdominal complications caused by trocars and Veress needles. Results: There were 22 trocar and four needle injuries (incidence, 0.18%). Nineteen lesions involved visceral organs; the remaining seven were vessel injuries. The small bowel was the single most affected organ (six cases), followed by the large bowel and the liver (three cases each). All vascular lesions, except for one laceration of the right iliac artery, occurred as venous bleeding of either the greater omentum or the mesentery. Fourteen trocars were inserted under direct vision. Nineteen trocar injuries were recognized intra-operatively; diagnoses of two small bowel and one bladder injuries were made postoperatively. Needle injuries were all diagnosed intraoperatively. Only five injuries could be repaired laparoscopically; the remaining lesions were repaired openly. Four patients underwent an open reoperation, and another patient needed five reoperations. There was one death (4.0%). Conclusions: Trocar and needle injuries are rare complications of laparoscopy. However, if not recognized intraoperatively and repaired immediately, they induce increased morbidity and mortality. Both open and closed establishment of the pneumoperitoneum are related to a potential danger of perforating lesions, but inserting the first trocar under direct vision allows early recognition and immediate repai

Eingeladener Kommentar zu: "Der Einsatz von Einmal- und wiederverwendbaren Instrumenten bei der laparoskopischen Cholezystektomie in Österreich — Ergebnisse einer landesweiten Umfrage"

Schlußfolgerungen: Die LC ist der am besten etablierte und auch am häufigsten durchgeführte minimal invasive Eingriff. Der erreichte hohe Standardisierungsgrad erlaubt die Durchführung der Operation mit einer limitierten Anzahl von Instrumenten und Trokaren, welche heute in technisch ausgereifter Form zur Verfügung stehen. Wiederverwendbare Instrumente und Trokare weisen dabei relevante ökonomische und ökologische Vorteile auf bei gleicher apparativer Sicherheit wie Einmalinstrumente. Bei der großen Anzahl LC, welche jährlich durchgeführt werden, lassen sich so erhebliche Kosteneinsparungen erzielen. Einzig Optiktrokar, semi-disposible Clipzange und Bergebeutel weisen aus unserer Sicht Vorteile auf, welche die Verwendung als Einmalinstrumente rechtfertigen. Insofern schließen wir uns auchKriwanek et al. und deren Kernaussage an, welche die Kombination von Einmal- und wiederverwendbaren Instrumenten als derzeit geltender Standard propagiere

Polymer chain stiffness versus excluded volume: A Monte Carlo study of the crossover towards the wormlike chain model

When the local intrinsic stiffness of a polymer chain varies over a wide range, one can observe both a crossover from rigid-rod-like behavior to (almost) Gaussian random coils and a further crossover towards self-avoiding walks in good solvents. Using the pruned-enriched Rosenbluth method (PERM) to study self-avoiding walks of up to $N_b=50000$ steps and variable flexibility, the applicability of the Kratky-Porod model is tested. Evidence for non-exponential decay of the bond-orientational correlations $<\cos \theta (s) >$ for large distances $s$ along the chain contour is presented, irrespective of chain stiffness. For bottle-brush polymers on the other hand, where experimentally stiffness is varied via the length of side-chains, it is shown that these cylindrical brushes (with flexible backbones) are not described by the Kratky-Porod wormlike chain model, since their persistence length is (roughly) proportional to their cross-sectional radius, for all conditions of practical interest.Comment: 6 pages, 5 figures, to be published in Europhys. Lett. (2010