24,410 research outputs found
Fermionic characters for graded parafermions
Fermionic-type character formulae are presented for charged
irreduciblemodules of the graded parafermionic conformal field theory
associated to the coset . This is obtained by counting the
weakly ordered `partitions' subject to the graded exclusion principle.
The bosonic form of the characters is also presented.Comment: 24 p. This corrects typos (present even in the published version) in
eqs (4.4), (5.23), (5.24) and (C.4
Simulations of the angular dependence of the dipole-dipole interaction among Rydberg atoms
The dipole-dipole interaction between two Rydberg atoms depends on the
relative orientation of the atoms and on the change in the magnetic quantum
number. We simulate the effect of this anisotropy on the energy transport in an
amorphous many atom system subject to a homogeneous applied electric field. We
consider two experimentally feasible geometries and find that the effects
should be measurable in current generation imaging experiments. In both
geometries atoms of character are localized to a small region of space
which is immersed in a larger region that is filled with atoms of
character. Energy transfer due to the dipole-dipole interaction can lead to a
spread of character into the region initially occupied by atoms. Over
long timescales the energy transport is confined to the volume near the border
of the region which is suggestive of Anderson localization. We calculate a
correlation length of 6.3~m for one particular geometry.Comment: 6 pages, 5 figures, revised draf
Energetic Extremes in Aquatic Locomotion by Coral Reef Fishes
Underwater locomotion is challenging due to the high friction and resistance imposed on a body moving through water and energy lost in the wake during undulatory propulsion. While aquatic organisms have evolved streamlined shapes to overcome such resistance, underwater locomotion has long been considered a costly exercise. Recent evidence for a range of swimming vertebrates, however, has suggested that flapping paired appendages around a rigid body may be an extremely efficient means of aquatic locomotion. Using intermittent flow-through respirometry, we found exceptional energetic performance in the Bluelined wrasse Stethojulis bandanensis, which maintains tuna-like optimum cruising speeds (up to 1 metre s(-1)) while using 40% less energy than expected for their body size. Displaying an exceptional aerobic scope (22-fold above resting), streamlined rigid-body posture, and wing-like fins that generate lift-based thrust, S. bandanensis literally flies underwater to efficiently maintain high optimum swimming speeds. Extreme energetic performance may be key to the colonization of highly variable environments, such as the wave-swept habitats where S. bandanensis and other wing-finned species tend to occur. Challenging preconceived notions of how best to power aquatic locomotion, biomimicry of such lift-based fin movements could yield dramatic reductions in the power needed to propel underwater vehicles at high speed.Funding was provided by the Australian Research Council (to CJF) and the Danish Agency for Science, Technology and Innovation (to JFS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Spectrum of injuries associated with paediatric ACL tears: an MRI pictorial review
OBJECTIVE: Magnetic resonance imaging (MRI) findings in anterior cruciate ligament (ACL) injury are well known, but most published reviews show obvious examples of associated injuries and give little focus to paediatric patients. Here, we demonstrate the spectrum of MRI appearances at common sites of associated injury in adolescents with ACL tears, emphasising age-specific issues. METHODS: Pictorial review using images from children with surgically confirmed ACL tears after athletic injury. RESULTS: ACL injury usually occurs with axial rotation in the valgus near full extension. The MRI findings can be obvious and important to management (ACL rupture), subtle but clinically important (lateral meniscus posterior attachment avulsion), obvious and unimportant to management (femoral condyle impaction injury), or subtle and possibly important (medial meniscocapsular junction tear). Paediatric-specific issues of note include tibial spine avulsion, normal difficulty visualising a thin ACL and posterolateral corner structures, and differentiation between incompletely closed physis and impaction fracture. CONCLUSION: ACL tear is only the most obvious sign of a complex injury involving multiple structures. Awareness of the spectrum of secondary findings illustrated here and the features distinguishing them from normal variation can aid in accurate assessment of ACL tears and related injuries, enabling effective treatment planning and assessment of prognosis. TEACHING POINTS: • The ACL in children normally appears thin or attenuated, while thickening and oedema suggest tear. • Displaced medial meniscal tears are significantly more common later post-injury than immediately. • The meniscofemoral ligaments merge with the posterior lateral meniscus, complicating tear assessment. • Tibial plateau impaction fractures can be difficult to distinguish from a partially closed physis. • Axial MR sequences are more sensitive/specific than coronal for diagnosis of medial collateral ligament (MCL) injury
A (Bounded) Bestiary of Feynman Integral Calabi-Yau Geometries
We define the rigidity of a Feynman integral to be the smallest dimension
over which it is non-polylogarithmic. We argue that massless Feynman integrals
in four dimensions have a rigidity bounded by 2(L-1) at L loops, and we show
that this bound may be saturated for integrals that we call marginal: those
with (L+1)D/2 propagators in (even) D dimensions. We show that marginal Feynman
integrals in D dimensions generically involve Calabi-Yau geometries, and we
give examples of finite four-dimensional Feynman integrals in massless
theory that saturate our predicted bound in rigidity at all loop orders.Comment: 5+2 pages, 11 figures, infinite zoo of Calabi-Yau manifolds. v2
reflects minor changes made for publication. This version is authoritativ
Gypsum-DL: an open-source program for preparing small-molecule libraries for structure-based virtual screening
Computational techniques such as structure-based virtual screening require carefully prepared 3D models of potential small-molecule ligands. Though powerful, existing commercial programs for virtual-library preparation have restrictive and/or expensive licenses. Freely available alternatives, though often effective, do not fully account for all possible ionization, tautomeric, and ring-conformational variants. We here present Gypsum-DL, a free, robust open-source program that addresses these challenges. As input, Gypsum-DL accepts virtual compound libraries in SMILES or flat SDF formats. For each molecule in the virtual library, it enumerates appropriate ionization, tautomeric, chiral, cis/trans isomeric, and ring-conformational forms. As output, Gypsum-DL produces an SDF file containing each molecular form, with 3D coordinates assigned. To demonstrate its utility, we processed 1558 molecules taken from the NCI Diversity Set VI and 56,608 molecules taken from a Distributed Drug Discovery (D3) combinatorial virtual library. We also used 4463 high-quality protein-ligand complexes from the PDBBind database to show that Gypsum-DL processing can improve virtual-screening pose prediction. Gypsum-DL is available free of charge under the terms of the Apache License, Version 2.0
Global modeling of secondary organic aerosol formation from aromatic hydrocarbons: high- vs low-yield pathways
Formation of SOA from the aromatic species toluene, xylene, and, for the first time, benzene, is added to a global chemical transport model. A simple mechanism is presented that accounts for competition between low and high-yield pathways of SOA formation, wherein secondary gas-phase products react further with either nitrogen oxide (NO) or hydroperoxy radical (HO2) to yield semi- or non-volatile products, respectively. Aromatic species yield more SOA when they react with OH in regions where the [NO]/[HO2] ratios are lower. The SOA yield thus depends upon the distribution of aromatic emissions, with biomass burning emissions being in areas with lower [NO]/[HO2] ratios, and the reactivity of the aromatic with respect to OH, as a lower initial reactivity allows transport away from industrial source regions, where [NO]/[HO2] ratios are higher, to more remote regions, where this ratio is lower and, hence, the ultimate yield of SOA is higher. As a result, benzene is estimated to be the most important aromatic species with regards to formation of SOA, with a total production nearly equal that of toluene and xylene combined. In total, while only 39% percent of the aromatic species react via the low-NOx pathway, 72% of the aromatic SOA is formed via this mechanism. Predicted SOA concentrations from aromatics in the Eastern United States and Eastern Europe are actually largest during the summer, when the [NO]/[HO2] ratio is lower. Global production of SOA from aromatic sources is estimated at 3.5 Tg/yr, resulting in a global burden of 0.08 Tg, twice as large as previous estimates. The contribution of these largely anthropogenic sources to global SOA is still small relative to biogenic sources, which are estimated to comprise 90% of the global SOA burden, about half of which comes from isoprene. Compared to recent observations, it would appear there are additional pathways beyond those accounted for here for production of anthropogenic SOA. However, owing to differences in spatial distributions of sources and seasons of peak production, there are still regions in which aromatic SOA produced via the mechanisms identified here are predicted to contribute substantially to, and even dominate, the local SOA concentrations, such as outflow regions from North America and South East Asia during the wintertime, though total SOA concentrations there are small (~0.1 μg/m^³)
The Elliptic Double-Box Integral: Massless Amplitudes Beyond Polylogarithms
We derive an analytic representation of the ten-particle, two-loop double-box
integral as an elliptic integral over weight-three polylogarithms. To obtain
this form, we first derive a four-fold, rational (Feynman-)parametric
representation for the integral, expressed directly in terms of
dual-conformally invariant cross-ratios; from this, the desired form is easily
obtained. The essential features of this integral are illustrated by means of a
simplified toy model, and we attach the relevant expressions for both integrals
in ancillary files. We propose a normalization for such integrals that renders
all of their polylogarithmic degenerations pure, and we discuss the need for a
new 'symbology' of iterated elliptic/polylogarithmic integrals in order to
bring them to a more canonical form.Comment: 4+2 pages, 2 figures. Explicit results are included as ancillary
files. v2: minor changes made for clarification; references adde
Manifesting Color-Kinematics Duality in the Scattering Equation Formalism
We prove that the scattering equation formalism for Yang-Mills amplitudes can
be used to make manifest the theory's color-kinematics duality. This is
achieved through a concrete reduction algorithm which renders this duality
manifest term-by-term. The reduction follows from the recently derived set of
identities for amplitudes expressed in the scattering equation formalism that
are analogous to monodromy relations in string theory. A byproduct of our
algorithm is a generalization of the identities among gravity and Yang-Mills
amplitudes.Comment: 20 pages, 20 figure
Analytic Representations of Yang-Mills Amplitudes
Scattering amplitudes in Yang-Mills theory can be represented in the
formalism of Cachazo, He and Yuan (CHY) as integrals over an auxiliary
projective space---fully localized on the support of the scattering equations.
Because solving the scattering equations is difficult and summing over the
solutions algebraically complex, a method of directly integrating the terms
that appear in this representation has long been sought. We solve this
important open problem by first rewriting the terms in a manifestly
Mobius-invariant form and then using monodromy relations (inspired by analogy
to string theory) to decompose terms into those for which combinatorial rules
of integration are known. The result is a systematic procedure to obtain
analytic, covariant forms of Yang-Mills tree-amplitudes for any number of
external legs and in any number of dimensions. As examples, we provide compact
analytic expressions for amplitudes involving up to six gluons of arbitrary
helicities.Comment: 29 pages, 43 figures; also included is a Mathematica notebook with
explicit formulae. v2: citations added, and several (important) typos fixe
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