Stick boundary conditions and rotational velocity auto-correlation functions for colloidal particles in a coarse-grained representation of the solvent

We show how to implement stick boundary conditions for a spherical colloid in a solvent that is coarse-grained by the method of stochastic rotation dynamics. This allows us to measure colloidal rotational velocity auto-correlation functions by direct computer simulation. We find quantitative agreement with Enskog theory for short times and with hydrodynamic mode-coupling theory for longer times. For aqueous colloidal suspensions, the Enskog contribution to the rotational friction is larger than the hydrodynamic one when the colloidal radius drops below 35nm.Comment: new version with some minor change

Dynamics of lane formation in driven binary complex plasmas

The dynamical onset of lane formation is studied in experiments with binary complex plasmas under microgravity conditions. Small microparticles are driven and penetrate into a cloud of big particles, revealing a strong tendency towards lane formation. The observed time-resolved lane formation process is in good agreement with computer simulations of a binary Yukawa model with Langevin dynamics. The laning is quantified in terms of the anisotropic scaling index, leading to a universal order parameter for driven systems.Comment: 4 pages, 3 figures, movies available at http://www.mpe.mpg.de/pke/lane-formation

Gravitational wave source populations: Disentangling an AGN component

The astrophysical origin of the over 90 compact binary mergers discovered by the LIGO and Virgo gravitational wave observatories is an open question. While the unusual mass and spin of some of the discovered objects constrain progenitor scenarios, the observed mergers are consistent with multiple interpretations. A promising approach to solve this question is to consider the observed distributions of binary properties and compare them to expectations from different origin scenarios. Here we describe a new hierarchical population analysis framework to assess the relative contribution of different formation channels simultaneously. For this study we considered binary formation in AGN disks along with phenomenological models, but the same framework can be extended to other models. We find that high-mass and high-mass-ratio binaries appear more likely to have an AGN origin compared to the same origin as lower-mass events. Future observations of high-mass black hole mergers could further disentangle the AGN component from other channels.Comment: 7 pages, 4 figures, and 1 tabl

Unwinding of a cholesteric liquid crystal and bidirectional surface anchoring

We examine the influence of bidirectional anchoring on the unwinding of a planar cholesteric liquid crystal induced by the application of a magnetic field. We consider a liquid crystal layer confined between two plates with the helical axis perpendicular to the substrates. We fixed the director twist on one boundary and allow for bidirectional anchoring on the other by introducing a high-order surface potential. By minimizing the total free energy for the system, we investigate the untwisting of the cholesteric helix as the liquid crystal attempts to align with the magnetic field. The transitions between metastable states occur as a series of pitchjumps as the helix expels quarter or half-turn twists, depending on the relative sizes of the strength of the surface potential and the bidirectional anchoring. We show that secondary easy axis directions can play a significant role in the unwinding of the cholesteric in its transition towards a nematic, especially when the surface anchoring strength is large

Thermodynamics of itinerant magnets in a classical spin fluctuation model

Thermodynamics of itinerant magnets is studied using a classical model with one parameter characterizing the degree of itinerancy. Monte Carlo simulations for bcc and fcc lattices are compared with the mean-field approximation and with the Onsager cavity field approximation extended to itinerant systems. The qualitative features of thermodynamics are similar to the known results of the functional integral method. It is found that magnetic short-range order is weak and almost independent on the degree of itinerancy, and the mean-field approximation describes the thermodynamics reasonably well. Ambiguity of the phase space measure for classical models is emphasized. The Onsager cavity field method is extended to itinerant systems, which involves the renormalization of both the Weiss field and the on-site exchange interaction. The predictions of this approximation are in excellent agreement with Monte Carlo results.Comment: 7 pages, 2 figure

The use of mesh in acute hernia: frequency and outcome in 99 cases

Background: Incarceration of inguinal, umbilical and cicatricial hernias is a frequent problem. However, little is known about the relationship between the use of mesh and outcome after surgery. The goal of this study was to describe the relationship between the use of mesh in incarcerated hernia and the clinical outcome. Patients and methods: Correspondence, operation reports and patient files between January 1995 and December 2005 of patients presented at one academic and one teaching hospital in Rotterdam were searched for the following keywords: incarceration, strangulation and hernia. The patient characteristics, clinical presentation, pre-operative findings and clinical course were scored and analysed. Results: A total of 203 patients could be identified: 76 inguinal, 52 umbilical, 39 incisional, 14 epigastric, 14 femoral, five trocar and three spigelian hernias. In the statistical analysis, epigastric, femoral, trocar and spigelian hernias were pooled, due to their small group sizes. One patient was excluded from the analysis because the hernia was not corrected during operation. In total, 99 hernias were repaired using mesh versus 103 primary suture repairs. Twenty-five wound infections were registered (12.3%). One mesh was removed during a reintervention for anastomotic leakage, although no signs of wound infection were present. Nine patients died, none of them due to wound-related problems [one cardiovascular, one ruptured aneurysm, two anastomotic leakage, two sepsis e causa incognita (e.c.i.), three pulmonary complications]. Univariate analysis showed that female patients (P = 0.007), adipose patients (P = 0.016), patients with an umbilical hernia (P = 0.01) and patients who underwent a bowel resection (P = 0.015) had a significantly higher rate of wound infections. The type of repair (e.g. primary suture or mesh), use of antibiotic prophylaxis, gender, ASA class and age showed no significant relation with post-operative wound infection. After logistic regression analysis, only bowel resection (P = 0.020) showed a significant relation with post-operative wound infection. Conclusions: Wound infection rates are high after the correction of acute hernia, but clinical consequences are relatively low. Mesh correction of an acute hernia seems to be safe and should be considered in every incarcerated hernia

Gene conversion in human rearranged immunoglobulin genes

Over the past 20 years, many DNA sequences have been published suggesting that all or part of the V<sub>H</sub> segment of a rearranged immunoglobulin gene may be replaced in vivo. Two different mechanisms appear to be operating. One of these is very similar to primary V(D)J recombination, involving the RAG proteins acting upon recombination signal sequences, and this has recently been proven to occur. Other sequences, many of which show partial V<sub>H</sub> replacements with no addition of untemplated nucleotides at the V<sub>H</sub>–V<sub>H</sub> joint, have been proposed to occur by an unusual RAG-mediated recombination with the formation of hybrid (coding-to-signal) joints. These appear to occur in cells already undergoing somatic hypermutation in which, some authors are convinced, RAG genes are silenced. We recently proposed that the latter type of V<sub>H</sub> replacement might occur by homologous recombination initiated by the activity of AID (activation-induced cytidine deaminase), which is essential for somatic hypermutation and gene conversion. The latter has been observed in other species, but not in human Ig genes, so far. In this paper, we present a new analysis of sequences published as examples of the second type of rearrangement. This not only shows that AID recognition motifs occur in recombination regions but also that some sequences show replacement of central sections by a sequence from another gene, similar to gene conversion in the immunoglobulin genes of other species. These observations support the proposal that this type of rearrangement is likely to be AID-mediated rather than RAG-mediated and is consistent with gene conversion

Consistent model of magnetism in ferropnictides

The discovery of superconductivity in LaFeAsO introduced the ferropnictides as a major new class of superconducting compounds with critical temperatures second only to cuprates. The presence of magnetic iron makes ferropnictides radically different from cuprates. Antiferromagnetism of the parent compounds strongly suggests that superconductivity and magnetism are closely related. However, the character of magnetic interactions and spin fluctuations in ferropnictides, in spite of vigorous efforts, has until now resisted understanding within any conventional model of magnetism. Here we show that the most puzzling features can be naturally reconciled within a rather simple effective spin model with biquadratic interactions, which is consistent with electronic structure calculations. By going beyond the Heisenberg model, this description explains numerous experimentally observed properties, including the peculiarities of the spin wave spectrum, thin domain walls, crossover from first to second order phase transition under doping in some compounds, and offers new insight in the occurrence of the nematic phase above the antiferromagnetic phase transition.Comment: 5 pages, 3 figures, revtex

Transverse-energy distributions at midrapidity in pp++pp, dd++Au, and Au++Au collisions at sNN=62.4\sqrt{s_{_{NN}}}=62.4--200~GeV and implications for particle-production models

Measurements of the midrapidity transverse energy distribution, d\Et/d\eta, are presented for $p$$+$$p$, $d$$+$Au, and Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV and additionally for Au$+$Au collisions at $\sqrt{s_{_{NN}}}=62.4$ and 130 GeV. The d\Et/d\eta distributions are first compared with the number of nucleon participants $N_{\rm part}$, number of binary collisions $N_{\rm coll}$, and number of constituent-quark participants $N_{qp}$ calculated from a Glauber model based on the nuclear geometry. For Au$+$Au, \mean{d\Et/d\eta}/N_{\rm part} increases with $N_{\rm part}$, while \mean{d\Et/d\eta}/N_{qp} is approximately constant for all three energies. This indicates that the two component ansatz, $dE_{T}/d\eta \propto (1-x) N_{\rm part}/2 + x N_{\rm coll}$, which has been used to represent $E_T$ distributions, is simply a proxy for $N_{qp}$, and that the $N_{\rm coll}$ term does not represent a hard-scattering component in $E_T$ distributions. The $dE_{T}/d\eta$ distributions of Au$+$Au and $d$$+$Au are then calculated from the measured $p$$+$$p$ $E_T$ distribution using two models that both reproduce the Au$+$Au data. However, while the number-of-constituent-quark-participant model agrees well with the $d$$+$Au data, the additive-quark model does not.Comment: 391 authors, 24 pages, 19 figures, and 15 Tables. Submitted to Phys. Rev. C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are publicly available at http://www.phenix.bnl.gov/papers.htm