366 research outputs found
JaxoDraw: A graphical user interface for drawing Feynman diagrams. Version 2.0 release notes
A new version of the Feynman graph plotting tool JaxoDraw is presented.
Version 2.0 is a fundamental re-write of most of the JaxoDraw core and some
functionalities, in particular importing graphs, are not backward-compatible
with the 1.x branch. The most prominent new features include: drawing of Bezier
curves for all particle modes, on-the-fly update of edited objects, multiple
undo/redo functionality, the addition of a plugin infrastructure, and a general
improved memory performance. A new LaTeX style file is presented that has been
written specifically on top of the original axodraw.sty to meet the needs of
this this new version.Comment: 17 pages, 1 figur
Isotropic-Nematic Transition in Liquid-Crystalline Elastomers
In liquid-crystalline elastomers, the nematic order parameter and the induced
strain vary smoothly across the isotropic-nematic transition, without the
expected first-order discontinuity. To investigate this smooth variation, we
measure the strain as a function of temperature over a range of applied stress,
for elastomers crosslinked in the nematic and isotropic phases, and analyze the
results using a variation on Landau theory. This analysis shows that the smooth
variation arises from quenched disorder in the elastomer, combined with the
effects of applied stress and internal stress.Comment: 4 pages, including 4 postscript figures, uses REVTeX
Flexibility defines structure in crystals of amphiphilic DNA nanostars.
DNA nanostructures with programmable shape and interactions can be used as building blocks for the self-assembly of crystalline materials with prescribed nanoscale features, holding a vast technological potential. Structural rigidity and bond directionality have been recognised as key design features for DNA motifs to sustain long-range order in 3D, but the practical challenges associated with prescribing building-block geometry with sufficient accuracy have limited the variety of available designs. We have recently introduced a novel platform for the one-pot preparation of crystalline DNA frameworks supported by a combination of Watson-Crick base pairing and hydrophobic forces (Brady et al 2017 Nano Lett. 17 3276-81). Here we use small angle x-ray scattering and coarse-grained molecular simulations to demonstrate that, as opposed to available all-DNA approaches, amphiphilic motifs do not rely on structural rigidity to support long-range order. Instead, the flexibility of amphiphilic DNA building-blocks is a crucial feature for successful crystallisation
Chimpanzees behave prosocially in a group-specific manner
Chimpanzees act cooperatively in the wild, but whether they afford benefits to others, and whether their tendency to act prosocially varies across communities, is unclear. Here, we show that chimpanzees from neighboring communities provide valuable resources to group members at personal cost, and that the magnitude of their prosocial behavior is group specific. Provided with a resource-donation experiment allowing free (partner) choice, we observed an increase in prosocial acts across the study period in most of the chimpanzees. When group members could profit (test condition), chimpanzees provided resources more frequently and for longer durations than when their acts produced inaccessible resources (control condition). Strikingly, chimpanzees’ prosocial behavior was group specific, with more socially tolerant groups acting more prosocially. We conclude that chimpanzees may purposely behave prosocially toward group members, and that the notion of group-specific sociality in nonhuman animals should crucially inform discussions on the evolution of prosocial behavior
Chimpanzees behave prosocially in a group-specific manner
Funding: EJCvL was funded by a Postdoctoral Fellowship awarded by the Research Foundation Flanders (FWO) and an ERC-Synergy Grant (no. 609819) awarded to JC.Chimpanzees act cooperatively in the wild, but whether they afford benefits to others, and whether their tendency to act prosocially varies across communities, is unclear. Here, we show that chimpanzees from neighboring communities provide valuable resources to group members at personal cost, and that the magnitude of their prosocial behavior is group specific. Provided with a resource-donation experiment allowing free (partner) choice, we observed an increase in prosocial acts across the study period in most of the chimpanzees. When group members could profit (test condition), chimpanzees provided resources more frequently and for longer durations than when their acts produced inaccessible resources (control condition). Strikingly, chimpanzees’ prosocial behavior was group specific, with more socially tolerant groups acting more prosocially. We conclude that chimpanzees may purposely behave prosocially toward group members, and that the notion of group-specific sociality in nonhuman animals should crucially inform discussions on the evolution of prosocial behavior.Publisher PDFPeer reviewe
Entwicklung von Strukturmodellen für Hydroxy-Interkalierte Tonminerale zur quantitativen Rietveld-basierten Phasenanalyse von Böden
Chemische und physikalische Bodeneigenschaften werden entscheidend vom Tongehalt und der Zusammensetzung der Tonfraktion geprägt. Tonminerale pedogenen Ursprungs können dabei sehr komplex sein. Insbesondere unter sauren Bedingungen kann gelöstes Al in den Zwischenschichten quellfähiger 2:1 Tonminerale (Smectit, Vermiculit) durch die Bildung nicht austauschbarer Al-Polymere gebunden werden. So kann eine Reihe sogenannter Hydroxy-Interkalierter Minerale (HIM) entstehen. Gegenwärtig entziehen sich diese Phasen jedoch einer verlässlichen Quantifizierung mittels Röntgenbeugung und Rietveld-Analyse, da hierfür keine kristallografischen Strukturmodelle vorliegen. Ziel unseres Projektes ist daher die Entwicklung von Strukturmodellen für die quantitative Beschreibung pedogener HIM-Phasen, welche folgende Schritte umfasst: (1) Identifizierung wichtiger natürlich vorkommender HIM in Böden unterschiedlichen Verwitterungsgrades, (2) Abtrennung/Herstellung phasenreiner Proben zur Prüfung/Verbesserung des Strukturmodells, sowie (3) Überprüfung des Strukturmodells an natürlichen Proben (Phasengemischen). Die Identifizierung typischer HIM wurde anhand einer 120.000 Jahre alten Bodenchronosequenz (Franz-Josef Gletscher, Neuseeland) vorgenommen. Hierbei konnten diverse intermediäre Phasen wie z.B. Vermiculit, Chlorit und Chlorit-Hydroxy-Interkalierter Smectit identifiziert werden, weshalb Hydroxy-Interkalierter Smectit (HIS) als erstes zu erstellendes Strukturmodell ausgewählt wurde. Da sich HIM generell im gleichen Korngrößenbereich anderer Tonminerale befinden, bzw. mit diesen verwachsen sind, können sie nicht phasenrein abgetrennt werden, wie für den zweiten Schritt der Modellentwicklung notwendig. Aus diesem Grund wurde im Labor eine Probenserie von 7 HIS aus natürlichem Smectit (Bentonit von Milos, Griechenland) mit unterschiedlichem Grad der Al-Belegung (0-100%) hergestellt. Hierfür wurde zu 6 Teilproben 0,1 mol/L AlCl3 gegeben und mit 0,3 mol/L NaOH Lösung bis pH=5,5 titriert. Die Teilproben unterschieden sich anhand der Volumina 0,1 mol/L AlCl3 Lösung sowie den Reaktionszeiten. Eine siebte Teilprobe wurde nicht behandelt (0% Belegung). Alle Proben wurden mittels Multimethodeneinsatz charakterisiert. Der vorliegende Beitrag gibt einen Einblick in den Ablauf und die damit verbundenen Schwierigkeiten in der Entwicklung eines Strukturmodells für HIM, welche eine quantitative Beschreibung von Hydroxy-Interkalierten Tonmineralen in Böden zukünftig ermöglichen soll
Stationary solutions for the parity-even sector of the CPT-even and Lorentz-covariance-violating term of the standard model extension
In this work, we focus on some properties of the parity-even sector of the
CPT-even electrodynamics of the standard model extension. We analyze how the
six non-birefringent terms belonging to this sector modify the static and
stationary classical solutions of the usual Maxwell theory. We observe that the
parity-even terms do not couple the electric and magnetic sectors (at least in
the stationary regime). The Green's method is used to obtain solutions for the
field strengths E and B at first order in the Lorentz- covariance-violating
parameters. Explicit solutions are attained for point-like and spatially
extended sources, for which a dipolar expansion is achieved. Finally, it is
presented an Earth-based experiment that can lead (in principle) to an upper
bound on the anisotropic coefficients as stringent as
Comment: 8 pages, revtex style, revised published version, to appear in EPJC
(2009
Consistency analysis of a nonbirefringent Lorentz-violating planar model
In this work analyze the physical consistency of a nonbirefringent
Lorentz-violating planar model via the analysis of the pole structure of its
Feynman propagators. The nonbirefringent planar model, obtained from the
dimensional reduction of the CPT-even gauge sector of the standard model
extension, is composed of a gauge and a scalar fields, being affected by
Lorentz-violating (LIV) coefficients encoded in the symmetric tensor
. The propagator of the gauge field is explicitly evaluated
and expressed in terms of linear independent symmetric tensors, presenting only
one physical mode. The same holds for the scalar propagator. A consistency
analysis is performed based on the poles of the propagators. The isotropic
parity-even sector is stable, causal and unitary mode for .
On the other hand, the anisotropic sector is stable and unitary but in general
noncausal. Finally, it is shown that this planar model interacting with a
Higgs field supports compactlike vortex configurations.Comment: 11 pages, revtex style, final revised versio
On the influence of a Coulomb-like potential induced by the Lorentz symmetry breaking effects on the Harmonic Oscillator
In this work, we obtain bound states for a nonrelativistic spin-half neutral
particle under the influence of a Coulomb-like potential induced by the Lorentz
symmetry breaking effects. We present a new possible scenario of studying the
Lorentz symmetry breaking effects on a nonrelativistic quantum system defined
by a fixed space-like vector field parallel to the radial direction interacting
with a uniform magnetic field along the z-axis. Furthermore, we also discuss
the influence of a Coulomb-like potential induced by Lorentz symmetry violation
effects on the two-dimensional harmonic oscillator.Comment: 14 pages, no figure, this work has been accepted for publication in
The European Physical Journal Plu
- …