13,749 research outputs found
Quark-gluon vertex dressing and meson masses beyond ladder-rainbow truncation
We include a generalized infinite class of quark-gluon vertex dressing
diagrams in a study of how dynamics beyond the ladder-rainbow truncation
influences the Bethe-Salpeter description of light quark pseudoscalar and
vector mesons. The diagrammatic specification of the vertex is mapped into a
corresponding specification of the Bethe-Salpeter kernel, which preserves
chiral symmetry. This study adopts the algebraic format afforded by the simple
interaction kernel used in previous work on this topic. The new feature of the
present work is that in every diagram summed for the vertex and the
corresponding Bethe-Salpeter kernel, each quark-gluon vertex is required to be
the self-consistent vertex solution. We also adopt from previous work the
effective accounting for the role of the explicitly non-Abelian three gluon
coupling in a global manner through one parameter determined from recent
lattice-QCD data for the vertex. With the more consistent vertex used here, the
error in ladder-rainbow truncation for vector mesons is never more than 10% as
the current quark mass is varied from the u/d region to the b region.Comment: 15 pages, 12 figure
Quasi-hermitian Quantum Mechanics in Phase Space
We investigate quasi-hermitian quantum mechanics in phase space using
standard deformation quantization methods: Groenewold star products and Wigner
transforms. We focus on imaginary Liouville theory as a representative example
where exact results are easily obtained. We emphasize spatially periodic
solutions, compute various distribution functions and phase-space metrics, and
explore the relationships between them.Comment: Accepted by Journal of Mathematical Physic
Skistodiaptomus pallidus (Copepoda: Diaptomidae) establishment in New Zealand natural lakes, and its effects on zooplankton community composition
The North American calanoid copepod Skistodiaptomus pallidus is an emerging invader globally, with non-indigenous populations recorded from constructed waters in New Zealand, Germany and Mexico since 2000. We examined the effects of S. pallidus establishment on the zooplankton community of a natural lake, Lake Kereta, where it was first recorded in late-2008, coincident with releases of domestically cultured grass carp (Ctenopharyngodon idella). Although not present in any of our samples prior to August 2008, S. pallidus was found in all samples collected in the subsequent five years. ANOSIM indicated zooplankton community composition significantly differed between samples collected before and after S. pallidus invasion, whether the invader was included in the analysis or not. Zooplankton species affected most greatly were the copepods Calamoecia lucasi and Mesocyclops sp., which decreased in their relative importance, and the cladocerans Bosmina meridionalis and Daphnia galeata, which increased. Rotifer species were relatively unaffected. As the length of grass carp released were >6.5 cm, direct predatory effects by this species on the zooplankton community are unlikely. Associated reductions in macrophyte biomass could explain increases in the relative abundances of planktonic cladocerans (B. meridionalis and D. galeata). However, the effect of macrophyte reduction by grass carp on zooplankton communities is considered to be limited elsewhere, while the reduced macrophyte biomass cannot explain the decrease in relative abundance of the native planktonic calanoid copepod C. lucasi. Competition between C. lucasi and S. pallidus is the most compelling explanation for the reduction in importance of the native calanoid copepod species. Skistodiaptomus pallidus appears to have undergone a “boom-and-bust” cycle in Lake Kereta, increasing in relative abundance in the first three years following establishment, before declining in importance
A controlled experiment for the empirical evaluation of safety analysis techniques for safety-critical software
Context: Today's safety critical systems are increasingly reliant on
software. Software becomes responsible for most of the critical functions of
systems. Many different safety analysis techniques have been developed to
identify hazards of systems. FTA and FMEA are most commonly used by safety
analysts. Recently, STPA has been proposed with the goal to better cope with
complex systems including software. Objective: This research aimed at comparing
quantitatively these three safety analysis techniques with regard to their
effectiveness, applicability, understandability, ease of use and efficiency in
identifying software safety requirements at the system level. Method: We
conducted a controlled experiment with 21 master and bachelor students applying
these three techniques to three safety-critical systems: train door control,
anti-lock braking and traffic collision and avoidance. Results: The results
showed that there is no statistically significant difference between these
techniques in terms of applicability, understandability and ease of use, but a
significant difference in terms of effectiveness and efficiency is obtained.
Conclusion: We conclude that STPA seems to be an effective method to identify
software safety requirements at the system level. In particular, STPA addresses
more different software safety requirements than the traditional techniques FTA
and FMEA, but STPA needs more time to carry out by safety analysts with little
or no prior experience.Comment: 10 pages, 1 figure in Proceedings of the 19th International
Conference on Evaluation and Assessment in Software Engineering (EASE '15).
ACM, 201
Inflatonless Inflation
We consider a 4+N dimensional Einstein gravity coupled to a non-linear sigma
model. This theory admits a solution in which the N extra dimensions contract
exponentially while the ordinary space expand exponentially. Physically, the
non-linear sigma fields induce the dynamical compactification of the extra
dimensions, which in turn drives inflation. No inflatons are required.Comment: 12 pages, version to appear in IJMP
Transmission of Predictable Sensory Signals to the Cerebellum via Climbing Fiber Pathways Is Gated during Exploratory Behavior
International audiencePathways arising from the periphery that target the inferior olive [spino-olivocerebellar pathways (SOCPs)] are a vital source of information to the cerebellum and are modulated (gated) during active movements. This limits their ability to forward signals to climbing fibers in the cerebellar cortex. We tested the hypothesis that the temporal pattern of gating is related to the predictability of a sensory signal. Low-intensity electrical stimulation of the ipsilateral hindlimb in awake rats evoked field potentials in the C1 zone in the copula pyramidis of the cerebellar cortex. Responses had an onset latency of 12.5 +/- 0.3 ms and were either short or long duration (8.7 +/- 0.1 vs 31.2 +/- 0.3 ms, respectively). Both types of response were shown to be mainly climbing fiber in origin and therefore evoked by transmission in hindlimb SOCPs. Changes in response size (area of field, millivolts per millisecond) were used to monitor differences in transmission during rest and three phases of rearing: phase 1, rearing up; phase 2, upright; and phase 3, rearing down. Responses evoked during phase 2 were similar in size to rest but were smaller during phases 1 and 3, i.e., transmission was reduced during active movement when self-generated (predictable) sensory signals from the hindlimbs are likely to occur. To test whether the pattern of gating was related to the predictability of the sensory signal, some animals received the hindlimb stimulation only during phase 2. Over similar to 10 d, the responses became progressively smaller in size, consistent with gating-out transmission of predictable sensory signals relayed via SOCPs
Electrophysiological Mapping of Novel Prefrontal – Cerebellar Pathways
Whilst the cerebellum is predominantly considered a sensorimotor control structure, accumulating evidence suggests that it may also subserve non-motor functions during cognition. However, this possibility is not universally accepted, not least because the nature and pattern of links between higher cortical structures and the cerebellum are poorly characterized. We have therefore used in vivo electrophysiological methods in anaesthetized rats to directly investigate connectivity between the medial prefrontal cortex (prelimbic subdivision, PrL) and the cerebellum. Stimulation of deep layers of PrL evoked distinct field potentials in the cerebellar cortex with a mean latency to peak of approximately 35 ms. These responses showed a well-defined topography, and were maximal in lobule VII of the contralateral vermis (a known oculomotor centre); they were not attenuated by local anaesthesia of the overlying M2 motor cortex, though M2 stimulation did evoke field potentials in lobule VII with a shorter latency (approximately 30 ms). Single unit recordings showed that prelimbic cortical stimulation elicits complex spikes in lobule VII Purkinje cells, indicating transmission via a previously undescribed cerebro-olivocerebellar pathway. Our results therefore establish a physiological basis for communication between PrL and the cerebellum. The role(s) of this pathway remain to be resolved, but presumably relate to control of eye movements and/or distributed networks associated with integrated prefrontal cortical functions
Spectral Functions of the Uniform Electron Gas via Coupled-Cluster Theory and Comparison to the and Related Approximations
We use, for the first time, ab initio coupled-cluster theory to compute the
spectral function of the uniform electron gas at a Wigner-Seitz radius of
. The coupled-cluster approximations we employ go significantly
beyond the diagrammatic content of state-of-the-art theory. We compare our
calculations extensively to and -plus-cumulant theory, illustrating
the strengths and weaknesses of these methods in capturing the quasiparticle
and satellite features of the electron gas. Our accurate calculations further
allow us to address the long-standing debate over the occupied bandwidth of
metallic sodium. Our findings indicate that the future application of
coupled-cluster theory to condensed phase material spectra is highly promising.Comment: 6 pages, 2 figure
Rapid assembly of highly-functionalised difluorinated cyclooctenones via ring-closing metathesis
Building block methodology from trifluoroethanol and ringclosing metathesis using a Fürstner modification of Grubbs’ conditions allows the rapid synthesis of novel difluorinated cyclooctenones
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