16,516 research outputs found
Multiplicity distribution and source deformation in full-overlap U+U collisions
We present a full Monte Carlo simulation of the multiplicity and eccentricity
distributions in U+U collisions at sqrt(s) = 200 A GeV. While unavoidable
trigger inefficiencies in selecting full-overlap U+U collisions cause
significant modifications of the multiplicity distribution shown in PRL94,
132301 (2005), a selection of source eccentricities by cutting the multiplicity
distribution is still possible.Comment: 4 pages. Corrected error in Eq. (4), recalculated Figs. 2-4 and added
Fig. 5 and more discussion. As a result of correcting this error, the
spectator cut for a useful definition of "full-overlap" collisions had to be
tightened by a factor 10, to the 0.5% of events with the lowest number of
spectator
Structure and Phase Transitions of Alkyl Chains on Mica
We use molecular dynamics as a tool to understand the structure and phase
transitions [Osman et. al. J. Phys. Chem. B 2000, 104, 4433; 2002, 106, 653] in
alkylammonium micas. The consistent force field 91 is extended for accurate
simulation of mica and related minerals. We investigate mica sheets with 12
octadecyltrimethylammonium (C18) ions or 12 dioctadecyldimethylammonium (2C18)
ions, respectively, as single and layered structures at different temperatures
with periodicity in the xy plane by NVT dynamics. The alkylammonium ions reside
preferably above the cavities in the mica surface with an aluminum-rich
boundary. The nitrogen atoms are 380 to 390 pm distant to the superficial
silicon-aluminum plane. With increasing temperature, rearrangements of C18 ions
on the mica surface are found, while 2C18 ions remain tethered due to geometric
restraints. We present basal-plane spacings in the duplicate structures, tilt
angles of the alkyl chains, and gauche-trans ratios to analyze the chain
conformation. Also, the individual phase transitions of the two systems on
heating are explained. Where experimental data are available, the agreement is
very good. We propose a geometric parameter lamba for the saturation of the
surface with alkyl chains, which determines the preferred self-assembly
pattern, i.e., islands, intermediate, or continuous. Lambda also determines the
tilt angles in continuous layers on mica or other surfaces. The thermal
decomposition appears to be a Hofmann elimination with mica as a base-template.Comment: 45 pages with 6 tables and 5 figure
Viscosity from elliptic flow: the path to precision
Using viscous relativistic hydrodynamics we show that systematic studies of
the impact parameter dependence of the eccentricity scaled elliptic flow can
distinguish between different models for the calculation of the initial source
eccentricity. This removes the largest present uncertainty in the extraction of
the specific viscosity of the matter created in relativistic heavy-ion
collisions from precise elliptic flow measurements.Comment: 4 pages, incl. 4 figure
The biomechanical function of periodontal ligament fibres in orthodontic tooth movement
Orthodontic tooth movement occurs as a result of resorption and formation of the alveolar bone due to an applied load, but the stimulus responsible for triggering orthodontic tooth movement remains the subject of debate. It has been suggested that the periodontal ligament (PDL) plays a key role. However, the mechanical function of the PDL in orthodontic tooth movement is not well understood as most mechanical models of the PDL to date have ignored the fibrous structure of the PDL. In this study we use finite element (FE) analysis to investigate the strains in the alveolar bone due to occlusal and orthodontic loads when PDL is modelled as a fibrous structure as compared to modelling PDL as a layer of solid material. The results show that the tension-only nature of the fibres essentially suspends the tooth in the tooth socket and their inclusion in FE models makes a significant difference to both the magnitude and distribution of strains produced in the surrounding bone. The results indicate that the PDL fibres have a very important role in load transfer between the teeth and alveolar bone and should be considered in FE studies investigating the biomechanics of orthodontic tooth movement. © 2014 McCormack et al
Critical systems heuristics
Critical systems heuristics (CSH) is a framework for reflective professional practice organised around the central tool of boundary critique. This paper, written jointly by the original developer, Werner Ulrich, and Martin Reynolds, an experienced practitioner of CSH, offers a systematic introduction to the idea and use of boundary critique. Its core concepts are explained in detail and their use is illustrated by means of two case studies from the domain of environmental planning and management. A particular focus is on working constructively with tensions between opposing perspectives as they arise in many situations of professional intervention. These include tensions such as âsituationâ versus âsystemâ, âisâ versus âoughtâ judgements, concerns of âthose involvedâ versus âthose affected but not involvedâ, stakeholdersâ âstakesâ versus âstakeholding issuesâ, and others. Accordingly, boundary critique is presented as a participatory process of unfolding and questioning boundary judgements rather than as an expert-driven process of boundary setting. The paper concludes with a discussion of some essential skills and considerations regarding the practice of boundary critique.
Parts of the account of the NRUA-Botswana study in Section 6.2 of the present paper are reproduced from an earlier publication by one of the authors (Reynolds 2007); we are grateful to the publishers of Edge Press, Point Reyes, CA, for granting us permission to reproduce this material. We do not need the systems concept at all if we are not interested in handling systems boundaries critically
Rescue of myeloid lineage-committed preprogenitor cells from cytomegalovirus-infected bone marrow stroma
The effect of murine cytomegalovirus on myelopoiesis was studied in long-term bone marrow culture to find an in vitro correlate for the lethal virus interference with bone marrow reconstitution (W. Mutter, M. J. Reddehase, F. W. Busch, H.-J. BĂŒhring, and U. H. Koszinowski, J. Exp. Med. 167:1645-1658, 1988). The in vitro generation of granulocyte-monocyte progenitors (CFU-GM) discontinued after infection of the stromal cell layer, whereas the proliferation and differentiation of CFU-GM to granulocyte-monocyte colonies remained unaffected. A protocol was established to probe the functional integrity of earlier hematopoietic cells. Pre-CFU-GM (the progenitors of the CFU-GM) could be recovered from an infected bone marrow donor culture by transfer onto an inductive recipient stromal cell layer. Thus, at least in vitro, infection of bone marrow stroma appears to be the only cause of the defect in myelopoiesis
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